IMPROVED PROCESS FOR PRODUCTION OF ALKALI METAL METHOXIDES

Abstract

The present invention relates to a process for producing at least one alkali metal methoxide by reactive distillation in at least one reaction column. At the lower end of the reaction column(s), the respective alkali metal methoxide dissolved in methanol is withdrawn. The methanol/water mixture obtained at the top of the reaction column(s) is separated by distillation in a rectification column. The energy from the vapour obtained at the top of the rectification column is transferred to a liquid or gaseous heat transfer medium, and the gaseous heat transfer medium obtained as a result is compressed in at least two stages. The energy from the respectively compressed heat transfer medium is advantageously transferred to the bottom stream and sidestream from the rectification column. This enables particularly energy-efficient use of the energy from the vapour in the process of the invention. The energy from the compressed heat transfer medium may additionally be used for operation of the reaction column(s) or for operation of a reaction column in which a process for transalcoholization of alkali metal alkoxides is conducted.

Claims

1-15. (canceled)

16. A process for preparing at least one alkali metal methoxide of the formula M.sub.AOCH.sub.3 wherein M.sub.A is sodium, lithium, or potassium, said process comprising: (a1) a reactant stream S.sub.AE1 comprising methanol is reacted with a reactant stream S.sub.AE2 comprising M.sub.AOH in countercurrent in a reactive rectification column RR.sub.A to produce a crude product RP.sub.A comprising M.sub.AOCH.sub.3, water, methanol, M.sub.AOH; wherein a bottom product stream S.sub.AP comprising methanol and M.sub.AOCH.sub.3 is withdrawn at the lower end of RR.sub.A and a vapour stream S.sub.AB comprising water and methanol is withdrawn at the upper end of RR.sub.A; (a2) simultaneously with, and spatially separate from, step (a1), a reactant stream S.sub.BE1 comprising methanol is reacted with a reactant stream S.sub.BE2 comprising M.sub.BOH in countercurrent in a reactive rectification column RR.sub.B to give a crude product RP.sub.B comprising M.sub.BOCH.sub.3, water, methanol, and M.sub.BOH, wherein M.sub.B is selected from sodium, lithium, potassium; wherein a bottom product stream S.sub.BP comprising methanol and M.sub.BOCH.sub.3 is withdrawn at the lower end of RR.sub.B and a vapour stream S.sub.BB comprising water and methanol is withdrawn at the upper end of RR.sub.B; (a3) at least a portion of vapour stream S.sub.AB, and at least a portion of vapour stream S.sub.BB, mixed with S.sub.AB or separate from S.sub.AB, is directed into a rectification column RD.sub.A and separated in RD.sub.A into at least one vapour stream S.sub.OA comprising methanol, which is withdrawn at the upper end of RD.sub.A, and at least one stream S.sub.UA comprising water, which is withdrawn at the lower end of RD.sub.A; (b) at least one side stream S.sub.ZA is withdrawn from RD.sub.A and recycled back into RD.sub.A; (c) energy is transferred from at least a portion of S.sub.OA to a liquid or gaseous heat transfer medium W*.sub.1, to produce gaseous heat transfer medium W*.sub.2; (d) at least a portion of the gaseous heat transfer medium W*.sub.2 is compressed to obtain a gaseous heat transfer medium W*.sub.3 that has been compressed relative to W*.sub.2; (e) energy is transferred from a first portion W*.sub.31 of the gaseous heat transfer medium W*.sub.3 to S.sub.ZA before S.sub.ZA is recycled into RD.sub.A; (f) a portion of the gaseous heat transfer medium W*.sub.3 other than W*.sub.31, W*.sub.32, is compressed further to obtain a gaseous heat transfer medium W*.sub.4 that has been compressed relative to W*.sub.31; and (g) energy is transferred from at least a portion of W*.sub.4 to at least a portion S.sub.UA1 of S.sub.UA before S.sub.UA1 is recycled into RD.sub.A.

17. The process of claim 16, wherein, in step (e), energy is transferred from W*.sub.31 to S.sub.ZA in an intermediate evaporator V.sub.ZRD.

18. The process of claim 16, wherein, in step (g), energy is transferred from at least a portion of W*.sub.4 to the at least one portion S.sub.UA1 of S.sub.UA in a reboiler V.sub.SRD.

19. The process of claim 16, wherein, once energy has been transferred from W*.sub.31 to S.sub.ZA as per step (e), energy is transferred from at least a portion of W*.sub.31 to S.sub.OA, and/or once energy has been transferred from at least a portion of W*.sub.4 to S.sub.UA1 as per step (g), energy is transferred from at least a portion of W*.sub.4 to S.sub.OA.

20. The process of claim 16, wherein at least two of the columns selected from rectification column RD.sub.A, reaction column RR.sub.A and reaction column RR.sub.B are accommodated in one column shell, wherein the columns are at least partially separated from one another by a dividing wall extending to the bottom of the column.

21. The process of claim 16, wherein a portion of S.sub.OA is used as reactant stream S.sub.AE1 in step (a1), and alternatively or in addition, as reactant stream S.sub.BE1 in step (a2).

22. The process of claim 16, wherein energy is transferred from at least a portion of a stream selected from W*.sub.3, or W*.sub.4 to the crude product RP.sub.A and, alternatively or in addition to, crude product RP.sub.B.

23. The process of claim 16, wherein M.sub.A is sodium or potassium, and M.sub.B is sodium or potassium.

24. The process of claim 23, wherein M.sub.A is sodium, and M.sub.B is potassium.

25. The process of claim 16, wherein: in a reactive rectification column RR.sub.C, a reactant stream S.sub.CE1 comprising M.sub.cOR is reacted in countercurrent with a reactant stream S.sub.CE2 comprising ROH to produce a crude product RP.sub.C comprising M.sub.COR and ROH; wherein a bottom product stream S.sub.CP comprising M.sub.COR is withdrawn at the lower end of RR.sub.C and a vapour stream S.sub.CB comprising ROH is withdrawn at the upper end of RR.sub.C; R and R are two different C.sub.1 to C.sub.6 hydrocarbon radicals, and M.sub.c is a metal selected from lithium, sodium, potassium; and energy is transferred from at least a portion of a stream selected from W*.sub.3, or W*.sub.4 to the crude product RP.sub.C.

26. The process of claim 25, wherein R=methyl.

27. The process of claim 26, wherein at least a portion of S.sub.AP is used as S.sub.CE1.

28. The process of claim 26, wherein at least a portion of S.sub.BP is used as S.sub.CE1.

29. The process of claim 26 wherein R is selected from the group consisting of: ethyl, n-propyl, iso-propyl, sec-butyl, 2-methyl-2-butyl, tert-butyl, 2-methyl-2-pentyl, 3-methyl-3-pentyl, 3-ethyl-3-pentyl, 2-methyl-2-hexyl, and 3-methyl-3-hexyl.

30. The process of claim 29, wherein R=ethyl.

31. A process for preparing at least one alkali metal methoxide of the formula M.sub.AOCH.sub.3 wherein M.sub.A is selected sodium, lithium, or potassium, and wherein: (a1) a reactant stream S.sub.AE1 comprising methanol is reacted with a reactant stream S.sub.AE2 comprising M.sub.AOH in countercurrent in a reactive rectification column RR.sub.A to produce a crude product RP.sub.A comprising M.sub.AOCH.sub.3, water, methanol, and M.sub.AOH; wherein a bottom product stream S.sub.AP comprising methanol and M.sub.AOCH.sub.3 is withdrawn at the lower end of RR.sub.A and a vapour stream S.sub.AB comprising water and methanol is withdrawn at the upper end of RR.sub.A; (a3) at least a portion of the vapour stream S.sub.AB, and at least a portion of the vapour stream S.sub.BB, mixed with S.sub.AB or separate from S.sub.AB, is directed into a rectification column RD.sub.A and separated in RD.sub.A into at least one vapour stream S.sub.OA comprising methanol, which is withdrawn at the upper end of RD.sub.A, and at least one stream S.sub.UA comprising water, which is withdrawn at the lower end of RD.sub.A; (b) at least one side stream S.sub.ZA is withdrawn from RD.sub.A and recycled back into RD.sub.A; (c) energy is transferred from at least a portion of S.sub.OA to a liquid or gaseous heat transfer medium W*.sub.1, to produce a gaseous heat transfer medium W*.sub.2; (d) at least a portion of the gaseous heat transfer medium W*.sub.2 is compressed to obtain a gaseous heat transfer medium W*.sub.3 that has been compressed relative to W*.sub.2; (e) energy is transferred from a first portion W*.sub.31 of the gaseous heat transfer medium W*.sub.3 to S.sub.ZA before S.sub.ZA is recycled into RD.sub.A; (f) a portion of the gaseous heat transfer medium W*.sub.3 other than W*.sub.31, W*.sub.32, is compressed further to obtain a gaseous heat transfer medium W*.sub.4 that has been compressed relative to W*.sub.31; and (g) energy is transferred from at least a portion of W*.sub.4 to at least a portion S.sub.UA1 of S.sub.UA before S.sub.UA1 is recycled into RD.sub.A.

32. The process of claim 31, wherein M.sub.A is selected from sodium or potassium.

33. The process of claim 31, wherein: in a reactive rectification column RR.sub.C a reactant stream S.sub.CE1 comprising M.sub.cOR is reacted in countercurrent with a reactant stream S.sub.CE2 comprising ROH to produce a crude product RP.sub.C comprising M.sub.COR and ROH; wherein a bottom product stream S.sub.CP comprising M.sub.COR is withdrawn at the lower end of RR.sub.C and a vapour stream S.sub.CB comprising ROH is withdrawn at the upper end of RR.sub.C; R and R are two different C.sub.1 to C.sub.6 hydrocarbon radicals, and M.sub.C is a metal selected from lithium, sodium, potassium; and energy is transferred from at least a portion of a stream selected from W*.sub.3, W*.sub.4 to the crude product RP.sub.C.

34. The process of claim 31, wherein R=methyl.

35. The process of claim 34, wherein R is selected from the group consisting of: ethyl; n-propyl; iso-propyl; sec-butyl; 2-methyl-2-butyl; tert-butyl; 2-methyl-2-pentyl; 3-methyl-3-pentyl; 3-ethyl-3-pentyl; 2-methyl-2-hexyl; and 3-methyl-3-hexyl.

Description

3. FIGURES

3.1 FIG. 1

[0018] FIG. 1 shows a comparative process for preparing alkali metal methoxide, in which the distillative separation of the methanol-water mixture is not according to the invention.

[0019] This involves reacting aqueous NaOH S.sub.AE2 <102> in a reaction column RR.sub.A <100> with methanol S.sub.AE1 <103> to give methanolic sodium methoxide solution. At the top of the reaction column RR.sub.A <100> an aqueous NaOH solution is added as reactant stream S.sub.AE2 <102>. It is alternatively also possible to add a methanolic NaOH solution as reactant stream S.sub.AE2 <102>. The corresponding potassium methoxide is prepared by adding aqueous or methanolic KOH solution as reactant stream S.sub.AE2 <102>. Above the bottom of the reaction column RR.sub.A <100>, methanol is added in vapour form as reactant stream S.sub.AE1 <103>.

[0020] At the bottom of the reaction column RR.sub.A <100>, a solution of the corresponding methoxide in methanol S.sub.AP* <104> is withdrawn. The bottom evaporator V.sub.SA <105> and the optional evaporator V.sub.SA <106> at the bottom of the column RR.sub.A <100> are used to adjust the concentration of the sodium methoxide solution S.sub.AP* <104> to the desired value.

[0021] At the top of the reaction column RR.sub.A <100>, a vapour stream S.sub.AB <107> is withdrawn. A portion of the vapour stream S.sub.AB <107> is condensed in the condenser K.sub.RRA <108> and applied in liquid form to the top of the reaction column RR.sub.A <100> as reflux. However, condenser K.sub.RRA <108> and the establishment of the reflux are optional.

[0022] The vapour S.sub.AB <107> obtained is sent wholly or partly to a rectification column, the water/methanol column, RD.sub.A <300>. The rectification column RD.sub.A <300> contains internals <310>. The water/methanol mixture is distillatively separated therein, and methanol is recovered by distillation overhead as vapour S.sub.OA <302>.

[0023] A reflux is established in the rectification column RD.sub.A <300>. A portion of the vapour S.sub.OA <302> is condensed in a condenser K.sub.RD <407>. The condensation of the stream directed through K.sub.RD <407> may be completed in a further condenser beyond K.sub.RD <407> with another cooling medium (water, air). The portion of the vapour S.sub.OA <302> thus condensed is then recycled back to the rectification column RD.sub.A <300>. The remaining portion of S.sub.OA <302>, i.e. that not sent to the condenser K.sub.RD <407>, is compressed by means of compressor V.sub.DAB2 <303> and recycled to the reaction column RR.sub.A <100>, where it is used as reactant stream S.sub.AE1 <103>.

[0024] In the condenser K.sub.RD <407>, energy is transferred from a portion of S.sub.OA <302> to a liquid heat transfer medium W*.sub.1 <701>, which is preferably n-butane. W*.sub.1 <701> is evaporated thereby, and a gaseous heat transfer medium W*.sub.2 <702> is obtained. W*.sub.2 <702> is fed to the compressor VD.sub.1 <401>, and W*.sub.2 <702> is optionally additionally heated (not shown in FIG. 1) before being fed to the compressor VD.sub.1 <401>. In VD.sub.1 <401>, W*.sub.2 <702> is compressed further to give the gaseous heat transfer medium stream W*.sub.3 <703>, from which energy can be removed in the optional intermediate cooler WT.sub.X <402>.

[0025] W*.sub.3 <703> is compressed further by means of compressor VD.sub.X <405>, and the resultant gaseous heat transfer medium stream W*.sub.4 <704> is fed to the evaporator V.sub.SRD <406> at the bottom of the rectification column RD.sub.A <300> for heating. As a result of the release of energy, W*.sub.4 <704> becomes W*.sub.1 <701> again; in particular W*.sub.4 <704> is at least partly condensed, again affording W*.sub.1 <701>, which then undergoes a new cycle again as described above.

[0026] Fresh methanol <408> can be fed to the process via the reflux into the rectification column RD.sub.A <300>.

[0027] Obtained at the bottom of the rectification column RD.sub.A <300> is a water stream S.sub.UA <304> which is at least partly (stream S.sub.UA1 <320>) recycled back into the rectification column RD.sub.A <300>, in which case it is passed through the evaporator V.sub.SRD <406> and/or V.sub.SRD <410>.

3.2 FIG. 2

[0028] FIG. 2 shows a further comparative process for preparing alkali metal methoxide, in which the distillative separation of the methanol-water mixture is not according to the invention.

[0029] This embodiment corresponds to the one described in FIG. 1 with the following additional/different features: In addition to the evaporators V.sub.SRD <406> and V.sub.SRD <410> at the bottom, the rectification column RD.sub.A <300> comprises an intermediate evaporator V.sub.ZRD <409>. A side stream S.sub.ZA <305> is withdrawn from the rectification column RD.sub.A <300> and passed through V.sub.ZRD <409> before being returned to the rectification column RD.sub.A <300>. A portion of the vapour stream S.sub.OA <302> is compressed by means of compressor VD.sub.AB2 <303> and recycled as reactant stream S.sub.AE1 <103> to the reaction column RR.sub.A <100>.

[0030] The other portion of the vapour S.sub.OA <302> is condensed in a condenser K.sub.RD <407> and then recycled back to the rectification column RD.sub.A <300>. The condensation of the stream directed through K.sub.RD <407> may be completed in a further condenser beyond K.sub.RD <407> with another cooling medium (water, air).

[0031] In the condenser K.sub.RD <407>, energy is transferred from a portion of S.sub.OA <302> to a liquid heat transfer medium W*.sub.1 <701>, which is preferably n-butane. W*.sub.1 <701> is evaporated thereby, and a gaseous heat transfer medium W*.sub.2 <702> is obtained. W*.sub.2 <702> is fed to the compressor VD.sub.1 <401>, where it is compressed further to give the gaseous heat transfer medium stream W*.sub.3 <703>, from which energy can be removed in the optional intermediate cooler WT.sub.X <402>.

[0032] The gaseous heat transfer medium stream W*.sub.3 <703> is fed to the intermediate evaporator V.sub.ZRD <409> for heating. There is no heating in the evaporator V.sub.SRD <406> or in the evaporator V.sub.SRD <410> by W*.sub.3 <703>. As a result of the release of energy, W*.sub.3 <703> becomes W*.sub.1 <701> again; in particular W*.sub.3 <703> is at least partly condensed, again affording W*.sub.1 <701>, which then undergoes a new cycle again as described above.

3.3 FIG. 3

[0033] FIG. 3 shows one embodiment of the process according to the invention. The rectification column RD.sub.A <300> used therein comprises an intermediate evaporator V.sub.ZRD <409> and a reboiler V.sub.SRD <406>, and optionally the reboiler V.sub.SRD <410>.

[0034] This embodiment of the invention has the following differences from the embodiments described in FIGS. 1 and 2: [0035] 1. After compression of the gaseous heat transfer medium W*.sub.2 <702> in the compressor VD.sub.1 <401>, the gaseous heat transfer medium stream W*.sub.3 <703> is divided into two portions W*.sub.31 <7031> and W*.sub.32 <7032>. [0036] 2. W*.sub.31 <7031> is fed to the intermediate evaporator V.sub.ZRD <409> for heating of stream S.sub.ZA <305>. [0037] 3. W*.sub.32 <7032> is compressed further in the compressor VD.sub.x <405> to give stream W*.sub.4 <704>. In an optional embodiment, energy is removed from W*.sub.32 <7032> in the optional intermediate cooler WT.sub.x <402> before W*.sub.32 <7032> is compressed. W*.sub.4 <704> is fed to the reboiler V.sub.SRD <406> for heating of stream S.sub.UA1 <320>. [0038] 4. Once W*.sub.31 <7031> and W*.sub.4 <704> have left the respective evaporator V.sub.ZRD <409> or V.sub.SRD <406>, and condense especially as a result of the release of energy to the respective stream, they are combined and can undergo a new cycle as W*.sub.1<701>.

[0039] On account of the differences in the inventive procedure and the division of the compressed gaseous heat transfer medium stream W*.sub.3 <703> into two portions W*.sub.31 <7031> and W*.sub.32 <7032>, of which only W*.sub.32 <7032> is additionally compressed, the energy from the once-compressed stream W*.sub.31 <7031> or twice-compressed stream W*.sub.4 <704>, by comparison with the embodiment according to FIGS. 1 and 2, can be utilized more efficiently for heating of the rectification column RD.sub.A <300> by means of the intermediate evaporator V.sub.ZRD <409> or the reboiler V.sub.SRD <406>.

3.4 FIG. 4

[0040] FIG. 4 shows one embodiment of the process according to the invention. This corresponds to the embodiments described in FIG. 3, with the difference that, in a second reaction column RR.sub.B<200>, an aqueous KOH solution S.sub.BE2 <202> is reacted with methanol S.sub.BE1 <203> to give potassium methoxide.

[0041] At the top of the reaction column RR.sub.B <200> an aqueous KOH solution is added as reactant stream S.sub.BE2 <202>. It is alternatively possible to add a methanolic KOH solution as reactant stream S.sub.BE2 <202>. Above the bottom of the reaction column RR.sub.B <200>, methanol is added in vapour form as reactant stream S.sub.BE1 <203>.

[0042] At the bottom of the reaction column RR.sub.B <200>, a mixture of the corresponding methoxide in methanol S.sub.BP <204> is withdrawn. The reboiler V.sub.SB <205> and the optional evaporator V.sub.SB <206> at the bottom of the column RR.sub.B <200> are used to adjust the concentration of the potassium methoxide solution S.sub.BP <204> to the desired value.

[0043] At the top of the reaction column RR.sub.B <200>, a vapour stream S.sub.BB <207> is withdrawn. A portion of the vapour stream S.sub.BB <207> is condensed in the condenser K.sub.RRB <208> and applied in liquid form as reflux to the top of the reaction column RR.sub.B <200>. However, condenser K.sub.RRB <208> and the establishment of the reflux are optional.

[0044] The obtained vapour S.sub.BB <207> is supplied to the rectification column RD.sub.A <300> in admixture with the portion of the vapour S.sub.AB <107> not condensed in the condenser K.sub.RRA <108>. Alternatively, the vapours S.sub.AB <107> and S.sub.BB <207> may also be fed to the rectification column RD.sub.A <300> separately, i.e. at two different feed points. These two feed points are preferably in the lower half of RD.sub.A <300>, preferably beneath the internals <310>.

[0045] A further difference from the embodiment according to FIG. 3 is that the portion of the vapour S.sub.OA <302> compressed by means of compressor V.sub.DAB2 <303> is partly recycled to the reaction column RR.sub.A <100> and RR.sub.B <200>, where it is used as reactant stream S.sub.AE1 <103>/S.sub.BE1 <203>.

3.5 FIG. 5

[0046] FIG. 5 shows a further embodiment of the process according to the invention. This corresponds to the embodiments described in FIG. 4, with the difference that a portion of W*.sub.4 <704> is also utilized for heating the evaporator V.sub.SA <106> at the bottom of the column RR.sub.A <100> and the evaporator V.sub.SB<206> at the bottom of the column RR.sub.B <200>.

3.6 FIG. 6

[0047] FIG. 6 shows a further embodiment of the process according to the invention. This corresponds to the embodiment described in FIG. 5 with the difference that the reaction columns RR.sub.A <100> and RR.sub.B <200> each comprise an intermediate evaporator V.sub.ZA <110> and V.sub.ZB <210>. A side stream S.sub.ZAA <111> is withdrawn from the reaction column RR.sub.A <100> and passed through V.sub.ZA <110> before being returned to the reaction column RR.sub.A <100>. A side stream S.sub.ZBA <211> is withdrawn from the reaction column RR.sub.B <200> and passed through V.sub.ZB <210> before being returned to the reaction column RR.sub.B <200>.

[0048] By contrast with FIG. 5, a portion of W*.sub.4 <704> is utilized solely for heating of the evaporator V.sub.SA <106> at the bottom of the column RR.sub.A <100>, but not for heating of the evaporator V.sub.SB <206> at the bottom of the column RR.sub.B <200>. By contrast, a portion of W*.sub.31 <7031> is utilized for heating of the evaporator V.sub.ZB <210>.

3.7 FIG. 7

[0049] FIG. 7 shows a further embodiment of the process according to the invention. This corresponds to the embodiments described in FIG. 5 with the difference that the reaction column RR.sub.A <100> comprises an intermediate evaporator V.sub.ZA <110>. A side stream S.sub.ZAA <111> is withdrawn from the reaction column RR.sub.A <100> and passed through V.sub.ZA <110> before being returned to the reaction column RR.sub.A <100>. By contrast with FIG. 5, a portion of W*.sub.4 <704> is utilized solely for heating of the evaporator V.sub.SB <206> at the bottom of the column RR.sub.B <200>, but not for heating of the evaporator V.sub.SA <106> at the bottom of the column RR.sub.A <100>. The intermediate evaporator V.sub.ZA <110> is heated via a heat transfer medium W* <502>, in particular water, which is transported by a pump <501> and which absorbs heat from W*.sub.32 <7032> in the intermediate cooler WT.sub.X <402> and releases it in the intermediate evaporator V.sub.ZA <110>.

3.8 FIG. 8

[0050] FIG. 8 shows a further embodiment of the process according to the invention. This corresponds to the embodiment described in FIG. 5 with the difference that the reaction columns RR.sub.A <100> and RR.sub.B <200> each comprise an intermediate evaporator V.sub.ZA <110> and V.sub.ZB <210>. A side stream S.sub.ZAA <111> is withdrawn from the reaction column RR.sub.A <100> and passed through V.sub.ZA <110> before being returned to the reaction column RR.sub.A <100>. A side stream S.sub.ZBA <211> is withdrawn from the reaction column RR.sub.B <200> and passed through V.sub.ZB <210> before being returned to the reaction column RR.sub.B <200>.

[0051] In addition, FIG. 8 shows a further preferred embodiment of the process according to the invention. It shows a reactive rectification column RR.sub.C <600> for transalcoholization of sodium methoxide to sodium ethoxide which is at least partially operated with energy from stream W*.sub.32 <7032>. The column RR.sub.C <600> comprises the reboilers V.sub.SC <605> and V.sub.SC <606>.

[0052] This involves reacting sodium methoxide solution S.sub.CE1 <602> in a reaction column RR.sub.C <600> in countercurrent with ethanol S.sub.CE2 <603> to give sodium ethoxide and this is withdrawn as ethanolic solution S.sub.CP <604>.

[0053] At the bottom of the reaction column RR.sub.C <600>, a bottom product stream S.sub.CP <604> comprising sodium ethoxide is accordingly withdrawn.

[0054] At the top of the reaction column RR.sub.C <600>, a vapour stream S.sub.CB <607> is withdrawn. Preferably, at least a portion of the vapour stream S.sub.CB <607> is condensed in the condenser K.sub.RRC <608>, and at least a portion thereof is applied in liquid form to the top of the reaction column RR.sub.C <600> as reflux. The vapour stream S.sub.CB <607> is partly withdrawn either in gaseous form upstream of the condenser K.sub.RRC <608> (marked by dashed line) and/or partly in liquid form downstream of the condenser K.sub.RRC <608> as stream <609>.

[0055] A side stream S.sub.ZC <610> is preferably withdrawn from the reaction column RR.sub.C <600>, with transfer of energy to said stream via an intermediate evaporator V.sub.ZC <611>, and S.sub.ZC <610> may then be recycled into RR.sub.C <600>.

[0056] As the sodium methoxide solution S.sub.CE1 <602> it is preferable to utilize at least a portion of the bottom streams S.sub.AP <104> and S.sub.BP <204> obtained in the reaction columns RR.sub.A <100> and RR.sub.B<200>.

[0057] The reboiler V.sub.SC<606> is heated via a heat transfer medium W* <502>, in particular water, which is transported by a pump <501> and which absorbs heat from W*.sub.32 <7032> in the intermediate cooler WT.sub.X <402> and releases it in the reboiler V.sub.SC <606>.

[0058] Alternatively, energy may also be appropriately transferred to the reboiler V.sub.SC <606> or the other reboiler V.sub.SC <605> from another stream selected from W*.sub.4 <704>, W*.sub.31 <7031>, W*.sub.3 <703> before the separation into W*.sub.31 <7031> and W*.sub.32 <7032>. Energy may likewise be transferred to the ethanol stream S.sub.CE1 <603>, the sodium methoxide solution S.sub.CE1 <602> or the side stream S.sub.ZC <610> from at least one of the streams W*.sub.3 <703>, W*.sub.31 <7031>, W*.sub.32 <7032>, W*.sub.4 <704>.

3.9 FIG. 9

[0059] FIG. 9 shows one embodiment of the process according to the invention. This corresponds to the embodiment described in FIG. 8, with the difference that the reboiler V.sub.SC <606> is heated directly with a portion of W*.sub.4 <704>.

3.10 FIG. 10

[0060] FIG. 10 illustrates the energy saving in the inventive process according to Example 3 compared to the noninventive process according to Examples 1 and 2. The x axis denotes the respective example, the y axis the power to be applied in MW.

[0061] The hatched portion of the bars indicates the sum total of the compressor outputs. The white portion of the bars shows the necessary heating output via low-pressure steam.

4. DETAILED DESCRIPTION OF THE INVENTION

[0062] The present invention relates to a process for preparing at least one alkali metal methoxide of the formula M.sub.AOCH.sub.3 where M.sub.A is selected from sodium, potassium, lithium, preferably sodium, potassium, and M.sub.A is most preferably sodium.

[0063] The process according to the invention is conducted in at least one reactive rectification column, and the vapour streams obtained in the at least one reactive rectification column that comprise methanol and water are then separated in a reaction column at least partly into water and methanol. In this distillative separation, there is efficient integration of the energy of the vapours obtained.

4.1 Step (a1)

[0064] In step (a1) of the process according to the invention, a reactant stream S.sub.AE1 comprising methanol is reacted with a reactant stream S.sub.AE2 comprising M.sub.AOH in countercurrent in a reactive rectification column RR.sub.A to afford a crude product RP.sub.A comprising M.sub.AOCH.sub.3, water, methanol, M.sub.AOH.

[0065] According to the invention a reactive rectification column is defined as a rectification column in which, at least in some parts, the reaction according to step (a1) or step (a2) of the process according to the invention proceeds. It may also be abbreviated to reaction column.

[0066] In step (a1), a bottom product stream S.sub.AP comprising methanol and M.sub.AOCH.sub.3 is withdrawn at the lower end of RR.sub.A. A vapour stream S.sub.AB comprising water and methanol is withdrawn at the upper end of RR.sub.A.

[0067] M.sub.A is selected from sodium, lithium, potassium. M.sub.A is especially selected from sodium, potassium. Preferably, M.sub.A=sodium.

[0068] The reactant stream S.sub.AE1 comprises methanol. In a preferred embodiment, the proportion by mass of methanol in S.sub.AE1 is 95% by weight, yet more preferably 99% by weight, and S.sub.AE1 otherwise comprises especially water.

[0069] The methanol used in step (a1) as reactant stream S.sub.AE1 may also be commercially available methanol having a proportion by mass of methanol of more than 99.8% by weight and a proportion by mass of water of up to 0.2% by weight.

[0070] The reactant stream S.sub.AE1 is preferably introduced in vapour form.

[0071] The reactant stream S.sub.AE2 comprises M.sub.AOH. In a preferred embodiment, S.sub.AE2 comprises not only M.sub.AOH but also at least one further compound selected from water, methanol. S.sub.AE2 more preferably comprises water in addition to M.sub.AOH, in which case S.sub.AE2 is an aqueous solution of M.sub.AOH.

[0072] When the reactant stream S.sub.AE2 comprises M.sub.AOH and water, the proportion by mass of M.sub.AOH, based on the total weight of the aqueous solution forming S.sub.AE2, is especially within a range from 10% to 75% by weight, preferably from 15% to 54% by weight, more preferably from 30% to 53% by weight and especially preferably from 40% to 52% by weight.

[0073] When the reactant stream S.sub.AE2 comprises M.sub.AOH and methanol, the proportion by mass of M.sub.AOH in methanol, based on the total weight of the solution forming S.sub.AE2, is especially within a range from 10% to 75% by weight, preferably from 15% to 54% by weight, more preferably from 30% to 53% by weight and especially preferably from 40% to 52% by weight.

[0074] In the particular case in which the reactant stream S.sub.AE2 comprises both water and methanol in addition to M.sub.AOH, it is particularly preferable that the proportion by mass of M.sub.AOH in methanol and water, based on the total weight of the solution forming S.sub.AE2, is especially within a range from 10% to 75% by weight, preferably from 15% to 54% by weight, more preferably from 30% to 53% by weight and particularly preferably from 40% to 52% by weight.

[0075] Step (a1) is performed in a reactive rectification column (or reaction column) RR.sub.A.

[0076] Step (a2), elucidated further down, is performed in a reactive rectification column (or reaction column) RR.sub.B.

[0077] The reaction column RR.sub.A/RR.sub.B preferably contains internals. Suitable internals are, for example, trays, structured packings or unstructured packings. When the reaction column RR.sub.A/RR.sub.B contains trays, then bubble cap trays, valve trays, tunnel-cap trays, Thormann trays, cross-slit bubble cap trays or sieve trays are suitable. When the reaction column RR.sub.A/RR.sub.B contains trays it is preferable to choose trays where not more than 5% by weight, more preferably less than 1% by weight, of the liquid trickles through the respective trays. The construction measures required to minimize trickle-through of the liquid are familiar to those skilled in the art. In the case of valve trays, for example, particularly tightly closing valve designs are selected. Reducing the number of valves also makes it possible to increase the vapour velocity in the tray openings to twice the value typically established. When sieve trays are used, it is particularly favourable to reduce the diameters of the tray openings and to maintain or even increase the number of openings.

[0078] When structured or unstructured packings are used, structured packings are preferred in terms of uniform distribution of the liquid.

[0079] For columns comprising unstructured packings, especially comprising random packings, and for columns comprising structured packings, the desired characteristics of the liquid distribution may be achieved when the liquid trickling density in the edge region of the column cross section adjacent to the column shell, corresponding to about 2% to 5% of the total column cross section, is reduced compared to the other cross-sectional regions by up to 100%, preferably by 5% to 15%. This can easily be achieved by, for example, targeted distributions of the drip points of the liquid distributors or the holes thereof.

[0080] The process according to the invention can be performed either continuously or batchwise. It is preferably performed continuously.

[0081] According to the invention, the reaction of a reactant stream S.sub.AE1 comprising methanol with a reactant stream S.sub.AE2 comprising M.sub.AOH in countercurrent is achieved more particularly by virtue of the feed point for at least a portion of the reactant stream S.sub.AE1 comprising methanol in step (a1) being below the feed point of the reactant stream S.sub.AE2 comprising M.sub.AOH in the reaction column RR.sub.A.

[0082] The reaction column RR.sub.A preferably comprises at least 2, in particular 15 to 40, theoretical plates between the feed point of the reactant stream S.sub.AE1 and the feed point of the reactant stream S.sub.AE2.

[0083] The reaction column RR.sub.A may be operated as a pure stripping column. In that case, the reactant stream S.sub.AE1 comprising methanol is introduced in vapour form in the lower region of the reaction column RR.sub.A.

[0084] Step (a1) also encompasses the case where a portion of the reactant stream S.sub.AE1 comprising methanol is added in vapour form below the feed point of the reactant stream S.sub.AE2 comprising M.sub.AOH but nevertheless at the upper end or in the region of the upper end of the reaction column RR.sub.A. This makes it possible to reduce the dimensions of the lower region of the reaction column RR.sub.A. When a portion of the reactant stream S.sub.AE1 comprising methanol is added, especially in vapour form, at the upper end or in the region of the upper end of the reaction column RR.sub.A, only a fraction of 10% to 70% by weight, preferably of 30% to 50% by weight, (based in each case on the total amount of methanol used in step (a1)) is introduced at the lower end of the reaction column RR.sub.A, and the remaining fraction is added in vapour form in a single stream or divided into a plurality of substreams, preferably 1 to 10 theoretical plates, more preferably 1 to 3 theoretical plates, below the feed point of the reactant stream S.sub.AE2 comprising M.sub.AOH.

[0085] In the reaction column RR.sub.A, the reactant stream S.sub.AE1 comprising methanol is then reacted with the reactant stream S.sub.AE2 comprising M.sub.AOH according to the above-described reaction <1> to give M.sub.AOCH.sub.3 and H.sub.2O, where these products are present in admixture with the methanol and M.sub.AOH reactants since the reaction is an equilibrium reaction. Accordingly, in step (a1), a crude product RP.sub.A comprising methanol and M.sub.AOH in addition to the M.sub.AOCH.sub.3 and water products is obtained in the reaction column RR.sub.A.

[0086] The bottom product stream S.sub.AP comprising methanol and M.sub.AOCH.sub.3 is then obtained and withdrawn at the lower end of RR.sub.A.

[0087] The stream of methanol that still contains water, referred to above as vapour stream S.sub.AB comprising water and methanol, is withdrawn at the upper end of RR.sub.A, preferably at the column top of RR.sub.A.

[0088] This vapour stream S.sub.AB comprising water and methanol is directed in step (a3) at least partly into a rectification column RD.sub.A, where it is separated by distillation at least partly into a vapour stream S.sub.OA comprising methanol, which is withdrawn at the upper end of RD.sub.A, and at least one stream S.sub.UA comprising water, which is withdrawn at the lower end of RD.sub.A. In the embodiments of the present invention in which step (a2) is conducted, at least a portion of vapour stream S.sub.BB, mixed with S.sub.AB or separately from S.sub.AB, is additionally directed into the rectification column RD.sub.A.

[0089] A portion of the methanol obtained in stream S.sub.OA in the distillation in step (a3) may be fed to the reaction column RR.sub.A as reactant stream S.sub.AE1.

[0090] In a preferred embodiment of the process according to the invention, a portion of S.sub.OA is used as reactant stream S.sub.AE1 in step (a1) and, if step (a2) is performed, alternatively or additionally as reactant stream S.sub.BE1 in step (a2).

[0091] In a more preferred embodiment of the process according to the invention, 5% to 95% by weight, preferably 10% to 90% by weight, more preferably 20% to 80% by weight, yet more preferably 30% to 70% by weight, yet more preferably 50% to 60% by weight, yet more preferably 56.7% by weight, of the vapour stream S.sub.OA is used as reactant stream S.sub.AE1 or, if step (a2) is performed, alternatively or additionally as reactant stream S.sub.BE1 in step (a2).

[0092] In this preferred embodiment, it is advantageous to compress the portion of the stream S.sub.OA used as reactant stream S.sub.AE1/as reactant stream S.sub.BE1.

[0093] The amount of methanol encompassed by the reactant stream S.sub.AE1 is preferably chosen such that it simultaneously serves as solvent for the alkali metal methoxide M.sub.AOCH.sub.3 obtained in the bottom product stream S.sub.AP. The amount of methanol in the reactant stream S.sub.AE1 is preferably chosen so as to achieve, in the bottom of the reaction column, the desired concentration of the alkali metal methoxide solution which is withdrawn as bottom product stream S.sub.AP comprising methanol and M.sub.AOCH.sub.3.

[0094] In a preferred embodiment of the process according to the invention, and especially in the cases in which S.sub.AE2 comprises not only M.sub.AOH but also water, the ratio of the total weight (mass; unit: kg) of methanol used as reactant stream S.sub.AE1 in step (a1) to the total weight (mass; unit: kg) of M.sub.AOH used as reactant stream S.sub.AE2 in step (a1) is 4:1 to 50:1, more preferably 8:1 to 48:1, even more preferably 10:1 to 45:1, yet more preferably 20:1 to 40:1, even more preferably 22:1.

[0095] The reaction column RR.sub.A is operated with or without, preferably with, reflux.

[0096] With reflux means that the vapour stream S.sub.AB/S.sub.BB comprising water and methanol withdrawn at the upper end of the respective column, in step (a1) from the reaction column RR.sub.A, in the optional step (a2) from the reaction column RR.sub.B, is not completely discharged. In that case, in step (a3), the respective vapour stream S.sub.AB/S.sub.BB is thus not directed in its entirety into a rectification column RD.sub.A, but rather at least partly, preferably partly, returned to the respective column as reflux, in step (a1) to the reaction column RR.sub.A, and in the optional step (a2) to the reaction column RR.sub.B. In the cases where such a reflux is established, the reflux ratio is preferably 0.01 to 1, more preferably 0.02 to 0.9, yet more preferably 0.03 to 0.34, yet more preferably 0.04 to 0.27, yet more preferably 0.05 to 0.24, yet more preferably 0.06 to 0.10, yet more preferably 0.07 to 0.08.

[0097] A reflux can be established by mounting a condenser at the top of the respective column. In step (a1) this is achieved in particular by attaching a condenser K.sub.RRA to the reaction column RR.sub.A. In step (a2) this is achieved in particular by attaching a condenser K.sub.RRB to the reaction column RR.sub.B. In the respective condenser, the respective vapour stream S.sub.AB/S.sub.BB is at least partly condensed and returned to the respective column, in step (a1) to the reaction column RR.sub.A, or in step (a2) to the reaction column RR.sub.B.

[0098] In the embodiment in which a reflux is established in the reaction column RR.sub.A, the M.sub.AOH used as reactant stream S.sub.AE2 in step (a1) may also be at least partly mixed with the reflux stream, and the resulting mixture may be supplied as such to step (a1).

[0099] Step (a1) is performed especially at a temperature within a range from 45 C. to 150 C., preferably 47 C. to 120 C., more preferably 60 C. to 110 C., and at a pressure of 0.5 bar abs. to 40 bar abs., preferably within a range from 0.7 bar abs. to 5 bar abs., more preferably within a range from 0.8 bar abs. to 4 bar abs., more preferably within a range from 0.9 bar abs. to 3.5 bar abs., yet more preferably at 1.0 bar abs. to 3 bar abs., yet more preferably 1.25 bar abs.

[0100] In a preferred embodiment, the reaction column RR.sub.A comprises at least one evaporator which is especially selected from intermediate evaporators V.sub.ZA and reboilers V.sub.SA. The reaction column RR.sub.A more preferably comprises at least one bottom evaporator V.sub.SA.

[0101] According to the invention, intermediate evaporators V.sub.Z refer to evaporators disposed above the bottom of the respective column, especially above the bottom of the reaction column RR.sub.A/RR.sub.B (in that case referred to as V.sub.ZA/V.sub.ZB) or above the bottom of the rectification column RD.sub.A (in that case referred to as V.sub.ZRD). In the case of RR.sub.A/RR.sub.B, what is evaporated therein is especially crude product RP.sub.A/RP.sub.B which is withdrawn from the column as side stream S.sub.ZAA/S.sub.ZBA.

[0102] According to the invention, reboilers V.sub.Z refer to evaporators which heat the bottom of the respective column, especially the bottom of the reaction column RR.sub.A/RR.sub.B, or RR.sub.C as used in the preferred embodiment and more particularly described hereinafter (in that case referred to as V.sub.SA or V.sub.SA/V.sub.SB or V.sub.SB/V.sub.SC or V.sub.SC) or the bottom of the rectification column RD.sub.A (in that case referred to as V.sub.SRD or V.sub.SRD). In the case of RR.sub.A/RR.sub.B, what is evaporated therein is especially at least a portion of the bottom product stream S.sub.AP/S.sub.BP. In the case of RR.sub.C, what is evaporated therein is especially bottom product stream S.sub.CP. In the case of RD.sub.A, what is evaporated therein is especially bottom product stream S.sub.UA or a portion of S.sub.UA, S.sub.UA1.

[0103] An evaporator is typically disposed outside the respective reaction column or rectification column. Since evaporators transfer energy, in particular heat, from one stream to another, they are heat transferrers WT. The mixture to be evaporated is withdrawn via a takeoff from the column and supplied to the at least one evaporator. In the case of the reaction column RR.sub.A/RR.sub.B, intermediate evaporation of the crude product RP.sub.A/RP.sub.B involves drawing it off and supplying it to the at least one intermediate evaporator V.sub.ZA/V.sub.ZB.

[0104] In the case of the rectification column RD.sub.A, intermediate evaporation involves withdrawing (drawing off) at least one side stream S.sub.ZA from RD.sub.A and supplying it to the at least one intermediate evaporator V.sub.ZRD.

[0105] In the case of the rectification column RD.sub.A, bottoms evaporation involves withdrawing (drawing off) at least one stream S.sub.UA from RD.sub.A and supplying at least a portion, preferably a portion, thereof to the at least one reboiler V.sub.SRD.

[0106] The evaporated mixture is recycled back into the respective column optionally with a residual proportion of liquid via at least one feed. When the evaporator is an intermediate evaporator, i.e. in particular an intermediate evaporator V.sub.ZA/V.sub.ZB/V.sub.ZRD, the takeoff via which the respective mixture is withdrawn and supplied to the evaporator is a side stream takeoff, and the feed via which the evaporated mixture is returned to the respective column is a side stream feed. When the evaporator is a reboiler, i.e. heats the column bottoms, i.e. is in particular a reboiler V.sub.SA/V.sub.SB/V.sub.SRD, at least a portion of the bottoms takeoff stream, in particular S.sub.AP/S.sub.BP, is supplied to the reboiler, evaporated and recycled back into the respective column in the region of the column bottom. However, it is alternatively also possible to form tubes, for example on a suitable tray when using an intermediate evaporator or in the bottom of the respective column, that are traversed by the heat transfer medium, for example the respective compressed heat transfer medium W*.sub.31/W*.sub.4 (when V.sub.S/V.sub.Z is present in the rectification column RD.sub.A) or a heat transfer medium W.sub.1. In this case, the evaporation occurs on the tray or in the bottom region of the column. However, it is preferable to arrange the evaporator outside the respective column.

[0107] Suitable evaporators that can be used as intermediate evaporators and bottom evaporators include, for example, natural circulation evaporators, forced circulation evaporators, forced circulation flash evaporators, kettle evaporators, falling-film evaporators or thin-film evaporators. Heat exchangers for the evaporator typically that are used in the case of natural circulation evaporators and forced circulation evaporators are a shell-and-tube or plate apparatus. When a shell-and-tube exchanger is used, the heat transfer medium, for example the compressed heat transfer medium W*.sub.31/W*.sub.4 in V.sub.ZRD or V.sub.SRD at the rectification column RD.sub.A, or the heat transfer medium W.sub.1 may either flow through the tubes and the mixture to be evaporated around the tubes, or else the heat transfer medium, for example the compressed heat transfer medium W*.sub.31/W*.sub.4 in V.sub.ZRD/V.sub.SRD at the rectification column RD.sub.A, or the heat transfer medium W.sub.1 flows around the tubes and the mixture to be evaporated through the tubes. In the case of a falling-film evaporator, the mixture to be evaporated is typically introduced as a thin film on the inside of a tube and the tube is heated externally. In contrast to a falling-film evaporator, a thin-film evaporator additionally comprises a rotor with wipers which distributes the liquid to be evaporated on the inner wall of the tube to form a thin film.

[0108] As well as those mentioned, it is also possible to use any desired further evaporator type which is known to those skilled in the art and is suitable for use in a rectification column.

[0109] When the evaporator operated, for example, with the compressed heat transfer medium W*.sub.31/the heat transfer medium W.sub.1 as heating steam is an intermediate evaporator, it is preferable when the intermediate evaporator is disposed in the stripping section of the rectification column RD.sub.A in the region between the feed point(s) of the vapour stream S.sub.AB/vapour stream S.sub.BB and above the column bottom or, in the case of reaction columns RR.sub.A/RR.sub.B, below the feed point of the reactant stream S.sub.AE2/S.sub.BE2. This makes it possible to introduce a predominant proportion of the heat energy via the intermediate evaporator. It is thus possible, for example, to introduce more than 80% of the energy via the intermediate evaporator. According to the invention, the intermediate evaporator is preferably arranged and/or configured such that it is used to introduce more than 10%, in particular more than 20%, of the total energy required for the distillation.

[0110] Where an intermediate evaporator is used, it is especially advantageous when the intermediate evaporator is arranged such that the respective rectification column/reaction column has 1 to 50 theoretical plates below the intermediate evaporator and 1 to 200 theoretical plates above the intermediate evaporator. In particular, it is preferable when the rectification column/reaction column has 2 to 10 theoretical plates below the intermediate evaporator and 20 to 80 theoretical plates above the intermediate evaporator.

[0111] The side stream takeoff via which the mixture from the rectification column/reaction column is supplied to the intermediate evaporator V.sub.Z and the side stream feed via which the evaporated mixture from the intermediate evaporator V.sub.Z is returned to the respective rectification column/reaction column may be positioned between the same trays of the column. However, it is also possible for the side stream takeoff and side stream feed to be at different heights.

[0112] Such an intermediate evaporator V.sub.ZA can convert liquid crude product RP.sub.A present in the reaction column RR.sub.A and comprising M.sub.AOCH.sub.3, water, methanol, M.sub.AOH to the gaseous state, thus improving the efficiency of the reaction in step (a1) of the process according to the invention.

[0113] Such an intermediate evaporator V.sub.ZB can convert liquid crude product RP.sub.B present in the reaction column RR.sub.B and comprising M.sub.BOCH.sub.3, water, methanol, M.sub.BOH to the gaseous state, thus improving the efficiency of the reaction in step (a2) of the process according to the invention.

[0114] By virtue of the arrangement of one or more intermediate evaporators V.sub.ZA in the upper region of the reaction column RR.sub.A, it is possible to reduce the dimensions in the lower region of the reaction column RR.sub.A. In the embodiment having at least one, preferably two or more, intermediate evaporators V.sub.ZA, it is also possible to introduce substreams of the methanol in liquid form in the upper region of the reaction column RR.sub.A.

[0115] In a further preferred embodiment, energy, preferably heat, is transferred from at least a portion of a heat transfer medium, where the heat transfer medium is selected from W*.sub.2, W*.sub.3, W*.sub.4, preferably from W*.sub.3, W*.sub.4, more preferably W*.sub.3, yet more preferably selected from W*.sub.31, W*.sub.32, yet more preferably W*.sub.32, to the crude product RP.sub.A and, if step (a2) is conducted, alternatively or additionally to the crude product RP.sub.B. The at least a portion of W*.sub.3 is selected here especially from W*.sub.31, W*.sub.32.

[0116] Transfer of energy, preferably heat, from at least a portion of a heat transfer medium, where the heat transfer medium is selected from W*.sub.2, W*.sub.3, W*.sub.4, to the crude product RP.sub.A and, if step (a2) is conducted, alternatively or additionally to the crude product RP.sub.B accordingly also encompasses the transfer of energy, preferably heat, from at least one heat transfer medium selected from W*.sub.31, W*.sub.32, or from the heat transfer medium W*.sub.3 before it is separated into W*.sub.31, W*.sub.32, to the crude product RP.sub.A and, if step (a2) is conducted, alternatively or additionally to the crude product RP.sub.B. It also encompasses the transfer of energy from a portion of W*.sub.31, W*.sub.32 to the crude product RP.sub.A and, if step (a2) is conducted, alternatively or additionally to the crude product RP.sub.B.

[0117] For this purpose, in particular, a portion of the respective heat transfer medium selected from W*.sub.2, W*.sub.3, W*.sub.4 is conducted at least partly via an intermediate evaporator V.sub.ZA/V.sub.ZB, and the energy is transferred from the respective heat transfer medium selected from W*.sub.2, W*.sub.3, W*.sub.4 to the crude product stream drawn off by side draw from RR.sub.A/RR.sub.B, especially in that the respective heat transfer medium selected from W*.sub.2, W*.sub.3, W*.sub.4 is utilized for heating of the evaporator V.sub.ZA/V.sub.ZB. Optionally, in this embodiment, a heat transfer medium other than W*.sub.2, W*.sub.3, W*.sub.4 is intermediately inserted. This means that, at first, energy, especially heat, is transferred from at least one heat transfer medium selected from W*.sub.2, W*.sub.3, W*.sub.4 to , and then the energy is transferred from to the crude product stream drawn off by side draw from RR.sub.A/RR.sub.B, especially in that is utilized for heating of the evaporator V.sub.ZA/V.sub.ZB.

[0118] Heat transfer media utilized may be any of the heat transfer media known to the person skilled in the art; preferably, is selected from the group consisting of air, water; alcohol-water solutions; salt-water solutions, also including ionic liquids, for example LiBr solutions, dialkylimidazolium salts such as, in particular, dialkylimidazolium dialkylphosphates; mineral oils, for example diesel oils; thermal oils, for example silicone oils; biological oils, for example limonene; aromatic hydrocarbons, for example dibenzyltoluene. Most preferably, the heat transfer medium used is water or air, more preferably water.

[0119] According to the invention, reboilers are disposed at the bottom of the respective rectification column RD.sub.A/reaction column RR.sub.A/RR.sub.B/RR.sub.c and are then referred to as V.sub.SRD or V.sub.SRD/V.sub.SA or V.sub.SA/V.sub.SB or V.sub.SB V.sub.SC or V.sub.SC. A bottom product stream (in particular S.sub.AP/S.sub.BP) present in the respective column (in particular reaction column RR.sub.A/RR.sub.B) may be directed into such a reboiler and, for example, methanol may be at least partly removed therefrom. In the case of S.sub.AP/S.sub.BP, this may afford a bottom product stream S.sub.AP* having an elevated proportion by mass of M.sub.AOCH.sub.3 compared to S.sub.AP or a bottom product stream S.sub.BP* having an elevated proportion by mass of M.sub.BOCH.sub.3 compared to S.sub.BP.

[0120] In step (a1) of the process according to the invention, a bottom product stream S.sub.AP comprising methanol and M.sub.AOCH.sub.3 is withdrawn at the lower end of the reaction column RR.sub.A.

[0121] It is preferable that the reaction column RR.sub.A comprises at least one reboiler V.sub.SA through which some of the bottom product stream S.sub.AP is then directed and methanol is partly removed therefrom, which affords a bottom product stream S.sub.AP* having an elevated proportion by mass of M.sub.AOCH.sub.3 compared to S.sub.AP.

[0122] In another preferred embodiment, therefore, the procedure for transferring energy, preferably heat, from at least a portion of a heat transfer medium, where the heat transfer medium is selected from W*.sub.2, W*.sub.3, W*.sub.4, preferably from W*.sub.3, W*.sub.4, and is more preferably W*.sub.4, to the crude product RP.sub.A and, if step (a2) is conducted, alternatively or additionally to the crude product RP.sub.B, is as follows:

[0123] In that case, in particular, a portion of the respective heat transfer medium selected from W*.sub.2, W*.sub.3, W*.sub.4 is directed at least partly through a reboiler V.sub.SA/V.sub.SB and the energy is transferred from the respective heat transfer medium selected from W*.sub.2, W*.sub.3, W*.sub.4 to the bottom product stream S.sub.AP/S.sub.BP, especially in that the respective heat transfer medium selected from W*.sub.2, W*.sub.3, W*.sub.4 is utilized for heating of the evaporator V.sub.SA/V.sub.SB.

[0124] The proportion by mass of M.sub.AOCH.sub.3 in the bottom product stream S.sub.AP* is elevated in particular compared to the proportion by mass of M.sub.AOCH.sub.3 in the bottom product stream S.sub.AP by at least 0.5%, preferably by 1%, more preferably by 2%, yet more preferably by 5%.

[0125] It is preferable when S.sub.AP or, if at least one reboiler V.sub.SA through which the bottom product stream S.sub.AP is at least partly directed and methanol is at least partly removed therefrom is used, S.sub.AP* has a proportion by mass of M.sub.AOCH.sub.3 in methanol within a range from 1% to 50% by weight, preferably 5% to 35% by weight, more preferably 15% to 35% by weight, most preferably 20% to 35% by weight, based in each case on the total mass of S.sub.AP/S.sub.AP*.

[0126] The proportion by mass of residual water in S.sub.AP/S.sub.AP*is preferably <1% by weight, preferably <0.8% by weight, more preferably <0.5% by weight, based on the total mass of S.sub.AP/S.sub.AP*.

[0127] The proportion by mass of reactant M.sub.AOH in S.sub.AP/S.sub.AP* is preferably <1% by weight, preferably <0.8% by weight, more preferably <0.5% by weight, based on the total mass of S.sub.AP/S.sub.AP*.

4.2 Step (a2) (Optional)

[0128] Step (a2) is an optional embodiment of the process according to the invention. This means that, in the context of the preferred embodiment of the process according to the invention, step (a2) is or is not performed.

[0129] In optional step (a2), simultaneously with and spatially separate from step (a1), a reactant stream S.sub.BE1 comprising methanol is reacted with a reactant stream S.sub.BE2 comprising M.sub.BOH in countercurrent in a reactive rectification column RR.sub.B to afford a crude product RP.sub.B comprising M.sub.BOCH.sub.3, water, methanol, M.sub.BOH.

[0130] In optional step (a2) of the process according to the invention, a bottom product stream S.sub.BP comprising methanol and M.sub.BOCH.sub.3 is withdrawn at the lower end of RR.sub.B. A vapour stream S.sub.BB comprising water and methanol is withdrawn at the upper end of RR.sub.B.

[0131] M.sub.B is selected from sodium, lithium, potassium. M.sub.B is especially selected from sodium, potassium. Preferably, M.sub.B=potassium.

[0132] The reactant stream S.sub.BE1 comprises methanol. In a preferred embodiment, the proportion by mass of methanol in S.sub.BE1 is 95% by weight, yet more preferably 99% by weight, and S.sub.BE1 otherwise comprises especially water.

[0133] The methanol used in the optional step (a2) of the process according to the invention as reactant stream S.sub.BE1 may also be commercially available methanol having a proportion by mass of methanol of more than 99.8% by weight and a proportion by mass of water of up to 0.2% by weight.

[0134] The reactant stream S.sub.BE1 is preferably introduced in vapour form.

[0135] The reactant stream S.sub.BE2 comprises M.sub.BOH. In a preferred embodiment, S.sub.BE2 comprises not only M.sub.BOH but also at least one further compound selected from water, methanol. It is yet more preferable when S.sub.BE2 also comprises water in addition to M.sub.BOH; in that case, S.sub.BE2 is an aqueous solution of M.sub.BOH.

[0136] When the reactant stream S.sub.BE2 comprises M.sub.BOH and water, the proportion by mass of M.sub.BOH, based on the total weight of the aqueous solution forming S.sub.BE2, is especially within a range from 10% to 75% by weight, preferably from 15% to 54% by weight, more preferably from 30% to 53% by weight and especially preferably from 40% to 52% by weight.

[0137] When the reactant stream S.sub.BE2 comprises M.sub.BOH and methanol, the proportion by mass of M.sub.BOH in methanol, based on the total weight of the solution forming S.sub.BE2, is especially within a range from 10% to 75% by weight, preferably from 15% to 54% by weight, more preferably from 30% to 53% by weight and especially preferably from 40% to 52% by weight.

[0138] In the particular case in which the reactant stream S.sub.BE2 comprises both water and methanol in addition to M.sub.BOH, it is particularly preferable that the proportion by mass of M.sub.BOH in methanol and water, based on the total weight of the solution forming S.sub.BE2, is especially within a range from 10% to 75% by weight, preferably from 15% to 54% by weight, more preferably from 30% to 53% by weight and particularly preferably from 40% to 52% by weight.

[0139] The optional step (a2) of the process according to the invention is performed in a reactive rectification column (or reaction column) RR.sub.B. Preferred embodiments of the reaction column RR.sub.B are described in section 4.1.

[0140] According to the invention, the reaction of a reactant stream S.sub.BE1 comprising methanol with a reactant stream S.sub.BE2 comprising M.sub.BOH in countercurrent is achieved more particularly by virtue of the feed point for at least a portion of the reactant stream S.sub.BE1 comprising methanol in the optional step (a2) being below the feed point of the reactant stream S.sub.BE2 comprising M.sub.BOH in the reaction column RR.sub.B.

[0141] The reaction column RR.sub.B preferably comprises at least 2, in particular 15 to 40, theoretical plates between the feed point of the reactant stream S.sub.BE1 and the feed point of the reactant stream S.sub.BE2.

[0142] The reaction column RR.sub.B may be operated as a pure stripping column. In that case, the reactant stream S.sub.BE1 comprising methanol is introduced in vapour form in the lower region of the reaction column RR.sub.B.

[0143] The optional step (a2) also encompasses the case where a portion of the reactant stream S.sub.BE1 comprising methanol is added in vapour form below the feed point of the reactant stream S.sub.BE2 comprising M.sub.BOH but nevertheless at the upper end or in the region of the upper end of the reaction column RR.sub.B. This makes it possible to reduce the dimensions of the lower region of the reaction column RR.sub.B. When a portion of the reactant stream S.sub.BE1 comprising methanol is added, especially in vapour form, at the upper end or in the region of the upper end of the reaction column RR.sub.B, only a fraction of 10% to 70% by weight, preferably of 30% to 50% by weight, (based in each case on the total amount of the methanol used in step (a2)) is fed in at the lower end of the reaction column RR.sub.B, and the remaining fraction is added in vapour form in a single stream or divided into a plurality of substreams, preferably 1 to 10 theoretical plates, more preferably 1 to 3 theoretical plates, below the feed point of the reactant stream S.sub.BE2 comprising M.sub.BOH.

[0144] In the reaction column RR.sub.B, the reactant stream S.sub.BE1 comprising methanol is then reacted with the reactant stream S.sub.BE2 comprising M.sub.BOH according to the above-described reaction <1> to give M.sub.BOCH.sub.3 and H.sub.2O, where these products are present in admixture with the methanol and M.sub.BOH reactants since the reaction is an equilibrium reaction. Accordingly, a crude product RP.sub.B which contains not only the M.sub.BOCH.sub.3 and water products but also methanol and M.sub.BOH is obtained in the reaction column RR.sub.B in the optional step (a2) of the process according to the invention.

[0145] The bottom product stream S.sub.BP comprising methanol and M.sub.BOCH.sub.3 is then obtained and withdrawn at the lower end of RR.sub.B.

[0146] The stream of methanol that still contains water, referred to above as vapour stream S.sub.BB comprising water and methanol, is withdrawn at the upper end of RR.sub.B, preferably at the column top of RR.sub.B.

[0147] This vapour stream S.sub.BB comprising water and methanol is directed in step (a3) at least partly into a rectification column RD.sub.A, where it is separated by distillation at least partly into a vapour stream S.sub.OA comprising methanol, which is withdrawn at the upper end of RD.sub.A, and at least one stream S.sub.UA comprising water, which is withdrawn at the lower end of RD.sub.A. A portion of the methanol obtained in stream S.sub.OA in the distillation in step (a3) may be fed to the reaction column RR.sub.B as reactant stream S.sub.BE1.

[0148] In this case, in step (a3) of the process according to the invention, when step (a2) is conducted, at least a portion of the vapour stream S.sub.BB, having or having not been mixed with S.sub.AB (i.e. in that case separately from S.sub.AB), is directed into the rectification column RD.sub.A. Preferably, in step (a3) of the process according to the invention, vapour streams S.sub.BB and S.sub.AB are mixed, and then the mixture is directed into the rectification column RD.sub.A.

[0149] The amount of methanol encompassed by the reactant stream S.sub.BE1 is preferably chosen such that it simultaneously serves as solvent for the alkali metal methoxide M.sub.BOCH.sub.3 obtained in the bottom product stream S.sub.BP. The amount of methanol in the reactant stream S.sub.BE1 is preferably chosen so as to achieve, in the bottom of the reaction column, the desired concentration of the alkali metal methoxide solution which is withdrawn as bottom product stream S.sub.BP comprising methanol and M.sub.BOCH.sub.3.

[0150] In a preferred embodiment of the process according to the invention, and especially in the cases in which S.sub.BE2 comprises not only M.sub.BOH but also water, the ratio of the total weight (mass; unit: kg) of methanol used as reactant stream S.sub.BE1 in the optional step (a2) to the total weight (mass; unit: kg) of M.sub.BOH used as reactant stream S.sub.BE2 in the optional step (a2) is 4:1 to 50:1, more preferably 8:1 to 48:1, even more preferably 10:1 to 45:1, yet more preferably 20:1 to 40:1, most preferably 22:1.

[0151] The reaction column RR.sub.B is operated with or without, preferably with, reflux.

[0152] In the embodiment in which a reflux is established in the reaction column RR.sub.B, the M.sub.BOH used as reactant stream S.sub.BE2 in the optional step (a2) can also be mixed at least partly with the reflux stream and the resulting mixture can thus be supplied to the optional step (a2).

[0153] The optional step (a2) is performed especially at a temperature within a range from 45 C. to 150 C., preferably 47 C. to 120 C., more preferably 60 C. to 110 C., and at a pressure of 0.5 bar abs. to 40 bar abs., preferably within a range from 0.7 bar abs. to 5 bar abs., more preferably within a range from 0.8 bar abs. to 4 bar abs., more preferably within a range from 0.9 bar abs. to 3.5 bar abs., yet more preferably at 1.0 bar abs. to 3 bar abs., most preferably at 1.25 bar abs.

[0154] In a preferred embodiment, the reaction column RR.sub.B comprises at least one evaporator which is in particular selected from intermediate evaporators V.sub.ZB and reboilers V.sub.SB. The reaction column RR.sub.B more preferably comprises at least one reboiler V.sub.SB.

[0155] Such an intermediate evaporator V.sub.ZB can convert liquid crude product RP.sub.B present in the reaction column RR.sub.B and comprising M.sub.BOCH.sub.3, water, methanol, M.sub.BOH to the gaseous state, thus improving the efficiency of the reaction in the optional step (a2) of the process according to the invention.

[0156] By virtue of the arrangement of one or more intermediate evaporators V.sub.ZB in the upper region of the reaction column RR.sub.B, it is possible to reduce the dimensions in the lower region of the reaction column RR.sub.B. In the embodiment having at least one, preferably two or more, intermediate evaporators V.sub.ZB, it is also possible to introduce substreams of the methanol in liquid form in the upper region of the reaction column RR.sub.B.

[0157] In the optional step (a2) of the process according to the invention, a bottom product stream S.sub.BP comprising methanol and M.sub.BOCH.sub.3 is withdrawn at the lower end of the reaction column RR.sub.B.

[0158] It is preferable that the reaction column RR.sub.B comprises at least one reboiler V.sub.SB through which the bottom product stream S.sub.BP is then directed at least partly and methanol is at least partly removed therefrom, thus affording a bottom product stream S.sub.BP* having an elevated proportion by mass of M.sub.BOCH.sub.3 compared to S.sub.BP.

[0159] The proportion by mass of M.sub.BOCH.sub.3 in the bottom product stream S.sub.BP* is elevated in particular compared to the proportion by mass of M.sub.BOCH.sub.3 in the bottom product stream S.sub.BP by at least 0.5%, preferably by 1%, more preferably by 2%, yet more preferably by 5%.

[0160] It is preferable when S.sub.BP or, if at least one reboiler V.sub.SB through which the bottom product stream S.sub.BP is at least partly directed and methanol is at least partly removed therefrom is used, S.sub.BP* has a proportion by mass of M.sub.BOCH.sub.3 in methanol within a range from 1% to 50% by weight, preferably 5% to 35% by weight, more preferably 15% to 35% by weight, most preferably 20% to 35% by weight, based in each case on the total mass of S.sub.BP/S.sub.BP*.

[0161] The proportion by mass of residual water in S.sub.BP/S.sub.BP* is preferably <1% by weight, preferably <0.8% by weight, more preferably <0.5% by weight, based on the total mass of S.sub.BP/S.sub.BP*.

[0162] The proportion by mass of reactant M.sub.BOH in S.sub.BP/S.sub.BP* is preferably <1% by weight, preferably <0.8% by weight, more preferably <0.5% by weight, based on the total mass of S.sub.BP/S.sub.BP*.

[0163] In the embodiments of the present process in which step (a2) is also performed, it is preferable when the bottom product stream S.sub.AP is at least partly directed through a reboiler V.sub.SA and methanol is at least partly removed from S.sub.AP to afford a bottom product stream S.sub.AP* having an elevated proportion by mass of M.sub.AOCH.sub.3 compared to S.sub.AP and/or, preferably and, the bottom product stream S.sub.BP is at least partly directed through a reboiler V.sub.SB and methanol is at least partly removed from S.sub.BP to afford a bottom product stream S.sub.BP* having an elevated proportion by mass of M.sub.BOCH.sub.3 compared to S.sub.BP.

[0164] In the embodiments of the present invention in which it is performed, step (a2) of the process according to the invention is performed simultaneously with and spatially separately from step (a1). Spatial separation is ensured by performing steps (a1) and (a2) in the two reaction columns RR.sub.A and RR.sub.B.

[0165] In an advantageous embodiment of the invention, the reaction columns RR.sub.A and RR.sub.B are accommodated in one column shell, where the column is at least partially subdivided by at least one dividing wall. Such a column having at least one dividing wall will be referred to as TRD. Such dividing wall columns are known to the person skilled in the art and are described, for example, in U.S. Pat. No. 2,295,256, EP 0 122 367 A2, EP 0 126 288 A2, WO 2010/097318 A1 and by I. Dejanovi, Lj. Matijaevi, . Oluji, Chemical Engineering and Processing 2010, 49, 559-580. CN 105218315 A likewise describes dividing wall columns which are used in the rectification of methanol.

[0166] In the dividing wall columns suitable for the process according to the invention, the dividing walls preferably extend to the column floor and, in particular, preferably span at least a quarter, more preferably at least a third, yet more preferably at least half, yet more preferably at least two thirds, yet still more preferably at least three quarters, of the column by height. They divide the columns into at least two reaction spaces in which spatially separate reactions may be carried out. The reaction spaces provided by the at least one dividing wall may be of identical or different sizes.

[0167] In this embodiment, the bottom product streams S.sub.AP and S.sub.BP may be withdrawn separately in the respective regions separated by the dividing wall and preferably passed through the reboiler V.sub.SA/V.sub.SB provided for each reaction space formed by the at least one reaction wall, in which methanol is at least partly removed from S.sub.AP/S.sub.BP to afford S.sub.AP*/S.sub.BP*.

[0168] In a preferred embodiment of the process according to the invention, accordingly, at least two, more preferably exactly two, of the columns selected from rectification column RD.sub.A, reaction column RR.sub.A and, if step (a2) is performed, reaction column RR.sub.B are accommodated in one column shell, in which case the columns are at least partly separated from one another by a dividing wall extending to the bottom of the column.

[0169] In the integrated system composed of reaction column RR.sub.A [or, in the embodiments in which step (a2) is performed, reaction column RR.sub.A and reaction column RR.sub.B] together with rectification column RD.sub.A in the process according to the invention, the rectification column RD.sub.A is preferably operated at a pressure selected such that the pressure gradient between the columns is low.

[0170] The methanol is consumed in the process according to the invention, and especially in a continuous process regime this therefore has to be replaced by fresh methanol.

[0171] The fresh methanol is especially fed directly as reactant stream S.sub.AE1 comprising methanol into the reaction column RR.sub.A or, in the embodiments in which step (a2) is performed, into reaction columns RR.sub.A and RR.sub.B.

[0172] In the process according to the invention, it is further preferable to use the methanol-comprising vapour stream S.sub.OA partly as reactant stream S.sub.AE1 in step (a1) and, if step (a2) is conducted, alternatively or additionally as reactant stream S.sub.BE1 in step (a2). In this preferred embodiment, it is yet more preferable when the fresh methanol is added to the rectification column RD.sub.A.

[0173] When the fresh methanol is added to the rectification column RD.sub.A, it is preferably fed in either in the rectifying section of the rectification column RD.sub.A or directly at the top of the rectification column RD.sub.A. The optimal feed point depends on the water content of the fresh methanol used, and secondly on the desired residual water content in the vapour stream S.sub.OA. The higher the proportion of water in the methanol used, and the higher the purity requirement in the vapour stream S.sub.OA, the more advantageous it is to feed it in a few theoretical plates below the top of the rectification column RD.sub.A. Up to 20 theoretical plates below the top of the rectification column RD.sub.A and in particular 1 to 5 theoretical plates are preferred.

[0174] When the fresh methanol is added to the rectification column RD.sub.A, it is added at the top of the rectification column RD.sub.A at temperatures up to boiling point, preferably at room temperature. A dedicated feed may be provided here for the fresh methanol, or else fresh methanol after the condensation and recycling of a portion of the methanol withdrawn at the top of the rectification column RD.sub.A may be mixed therewith and be fed together to the rectification column RD.sub.A. In this case it is particularly preferable when the fresh methanol is added to a condensate vessel in which the methanol condensed out of the vapour stream S.sub.OA is collected.

[0175] As described above, in an advantageous embodiment of the invention, at least two of the columns selected from rectification column RD.sub.A, reaction column RR.sub.A and, if step (a2) is performed, the reaction column RR.sub.B are accommodated in one column shell, in which case the columns are each at least partly separated from one another by a dividing wall extending to the bottom of the column. In the above-described preferred embodiment in which step (a2) is performed, these are accordingly separated from one another by two dividing walls, where the two dividing walls extend to the bottom of the column.

[0176] In this preferred embodiment the reaction to afford the crude product RP.sub.A according to step (a1) or the crude products RP.sub.A and RP.sub.B according to steps (a1) and (a2) are in particular performed in one part of the TRD, wherein the reactant stream S.sub.AE2 and optionally the reactant stream S.sub.BE2 are added below but at approximately the height of the upper end of the dividing wall and the reactant stream S.sub.AE1 and optionally the reactant stream S.sub.BE1 are added in vapour form at the lower end. The methanol/water mixture formed above the feed point of the reactant stream is then distributed above the dividing wall over the entire column region which serves as rectifying section of the rectification column RD.sub.A. The second/third lower part of the column which has been separated off by the dividing wall is the stripping section of the rectification column RD.sub.A. The energy required for the distillation is then supplied via an evaporator at the lower end of the second portion of the column separated by the dividing wall, and this evaporator may be heated conventionally or heated with a portion of the compressed vapour stream S.sub.OA2. When the evaporator is heated conventionally, an intermediate evaporator heated with a portion of the compressed heat transfer medium, e.g. W*.sub.31 or W*.sub.4, may additionally be provided.

[0177] In the embodiments in which a portion of S.sub.OA is used as reactant stream S.sub.AE1 and/or reactant stream S.sub.BE1, S.sub.OA is especially compressed with a compressor V.sub.DAB2, and in this way the difference in the pressures inside the reaction columns RR.sub.A and RR.sub.B compared to the pressure in RD.sub.A may be taken into account.

[0178] Alternatively or additionally, in this preferred embodiment, it is also possible to use, rather than the compressor VD.sub.AB2 which is downstream of the rectification column RD.sub.A and in which S.sub.OA is compressed, a compressor VD.sub.AB1 which is upstream of the rectification column RD.sub.A and with which S.sub.AB, S.sub.BB, or the mixture of S.sub.AB and S.sub.BB before the respective stream is directed into RD.sub.A, is compressed.

4.3 Step (a3)

[0179] In step (a3) of the process according to the invention, at least a portion of the vapour stream S.sub.AB, and, if step (a2) is conducted, at least a portion of the vapour stream S.sub.BB, mixed with S.sub.AB or separately from S.sub.AB, is directed into a rectification column RD.sub.A and separated in RD.sub.A into at least one vapour stream S.sub.OA comprising methanol, which is withdrawn at the upper end of RD.sub.A, and at least one stream S.sub.UA comprising water, which is withdrawn at the lower end of RD.sub.A.

[0180] In the embodiments of the invention in which step (a2) is conducted, it is preferable when, in step (a3), the at least one portion of the vapour stream S.sub.AB and the at least one portion of the vapour stream S.sub.BB are mixed and then directed into a rectification column RD.sub.A. S.sub.AB and S.sub.BB may alternatively also be directed into the rectification column RD.sub.A at two different feed points.

[0181] In step (a3) of the process according to the invention, at least a portion of the vapour stream S.sub.AB, and, if step (a2) is conducted, at least a portion of the vapour stream S.sub.BB, mixed with S.sub.AB or separately from S.sub.AB, is directed into a rectification column RD.sub.A and separated in RD.sub.A into at least one vapour stream S.sub.OA comprising methanol, which is withdrawn at the upper end of RD.sub.A, and at least one stream S.sub.UA comprising water, which is withdrawn at the lower end of RD.sub.A.

[0182] At least one vapour stream S.sub.OA comprising methanol which is withdrawn at the upper end of RD.sub.A means that the vapour obtained at the upper end of RD.sub.A may be withdrawn there as one or more vapour streams. If said stream is withdrawn there in more than one vapour stream, the m vapour streams are referred to as vapour stream S.sub.OAI, vapour stream S.sub.OAII, [ . . . ], vapour stream S.sub.OAm, where m indicates the number of vapour streams withdrawn at the upper end of RD.sub.A (in Roman numerals).

[0183] At least one stream S.sub.UA comprising water which is withdrawn at the lower end of RD.sub.A means that water obtained at the lower end of RD.sub.A may be withdrawn there as one or more streams. If said stream is withdrawn there in more than one stream, the n streams are referred to as stream S.sub.UAI, stream S.sub.UAII, [ . . . ], stream S.sub.UAn, where n is the number of streams withdrawn at the lower end of RD.sub.A (in Roman numerals).

[0184] The at least one portion of vapour stream S.sub.AB and, when step (a2) is conducted, the at least one portion of vapour stream S.sub.BB may be directed into the rectification column RD.sub.A via one or more feed points. They are introduced via two or more feed points, for example, in the embodiments in which step (a2) is performed in the process according to the preferred aspect of the invention and, in step (a3), at least a portion of the vapour stream S.sub.BB is used separately from S.sub.AB. In this embodiment, the at least one portion of vapour stream S.sub.AB and the at least one portion of vapour stream S.sub.BB are accordingly directed into the rectification column RD.sub.A as two separate streams.

[0185] In the embodiments of the present invention in which the at least one portion of the vapour stream S.sub.AB and, when step (a2) is conducted, the at least one portion of the vapour stream S.sub.BB is/are directed into the rectification column RD.sub.A as two or more separate streams, it is advantageous when the feed points for the individual streams are at essentially the same height on the rectification column RD.sub.A.

[0186] In a preferred embodiment of step (a3) of the process according to the invention, the at least one portion of vapour stream S.sub.AB, and, when step (a2) is conducted, the at least one portion of vapour stream S.sub.BB are separated in the rectification column RD.sub.A into a vapour stream S.sub.OA comprising methanol, which is withdrawn at the upper end of RD.sub.A, and a stream S.sub.UA comprising water, which is withdrawn at the lower end of RD.sub.A.

[0187] Another term for upper end of a rectification column is top.

[0188] Another term for lower end of a rectification column is bottom or foot.

[0189] The pressure of the at least one vapour stream S.sub.OA is referred to as p.sub.OA and its temperature as T.sub.OA. This relates especially to the pressure and temperature of the at least one vapour stream S.sub.OA when it is withdrawn from the rectification column RD.sub.A in step (a3).

[0190] The pressure p.sub.OA is especially within a range from 0.5 bar abs. to 8 bar abs., more preferably within a range from 0.6 bar abs. to 7 bar abs., more preferably within a range from 0.7 bar abs. to 6 bar abs., yet more preferably within a range from 1 bar abs. to 5 bar abs., yet more preferably within a range from 1 bar abs. to 4 bar abs., yet more preferably within a range from 1.0 bar abs. to 2.0 bar abs., and is most preferably 1.1 bar abs.

[0191] The temperature T.sub.OA is especially in the range from 45 C. to 150 C., more preferably in the range from 48 C. to 140 C., more preferably in the range from 50 C. to 130 C., yet more preferably in the range from 60 C. to 120 C., yet more preferably in the range from 60 C. to 110 C., yet more preferably in the range from 65 C. to 80 C., most preferably 67 C.

[0192] Any desired rectification column known to those skilled in the art may be used as rectification column RD.sub.A in step (a3) of the process. The rectification column RD.sub.A preferably contains internals. Suitable internals are, for example, trays, unstructured packings or structured packings. Trays used are typically bubble-cap trays, sieve trays, valve trays, tunnel-cap trays or slotted trays. Unstructured packings are generally beds of random packing elements. Random packing elements used are typically Raschig rings, Pall rings, Berl saddles or Intalox saddles. Structured packings are sold, for example, under the Sulzer Mellapack trade name. Apart from the internals mentioned, further suitable internals are known to a person skilled in the art and can likewise be used.

[0193] Preferred internals have a low specific pressure drop per theoretical plate. Structured packings and random packing elements have, for example, a significantly lower pressure drop per theoretical plate than trays. This has the advantage that the pressure drop in the rectification column RD.sub.A remains as low as possible and the mechanical power of the compressor and the temperature of the methanol/water mixture to be evaporated therefore remain low.

[0194] When the rectification column RD.sub.A contains structured packings or unstructured packings, these may be divided or in the form of an uninterrupted packing. Typically, however, at least two packings are provided: [0195] 1) Preferably, [0196] when step (a2) is not performed: one packing above the feed point of S.sub.AB; [0197] when step (a2) is performed and S.sub.AB and S.sub.BB are mixed and then directed into RD.sub.A: one packing above the feed point of the mixture of S.sub.AB and S.sub.BB; [0198] when step (a2) is performed and S.sub.AB and S.sub.BB are directed separately into RD.sub.A: one packing above the feed points of S.sub.AB and S.sub.BB. [0199] 2) Preferably, moreover: [0200] when step (a2) is not performed: one packing below the feed point of S.sub.AB; [0201] when step (a2) is performed and S.sub.AB and S.sub.BB are mixed and then directed into RD.sub.A: one packing below the feed point of the mixture of S.sub.AB and S.sub.BB; [0202] when step (a2) is performed and S.sub.AB and S.sub.BB are directed separately into RD.sub.A: one packing below the feed points of S.sub.AB and S.sub.BB.

[0203] It is also possible to provide one packing above the feed point of S.sub.AB/S.sub.AB and S.sub.BB and multiple trays below the feed point of S.sub.AB/S.sub.AB and S.sub.BB. If an unstructured packing is used, for example a random packing, the random packing elements are typically disposed on a suitable support grid (for example sieve tray or mesh tray).

[0204] In the respective embodiment, it is preferable that the feed point of S.sub.AB/S.sub.AB and S.sub.BB is in the lower half of the column RD.sub.A, i.e. S.sub.AB/S.sub.AB and S.sub.BB are directed into the lower half of the column RD.sub.A.

[0205] In step (a3) of the process according to the invention, the at least one vapour stream S.sub.OA comprising methanol is then withdrawn at the upper end of the rectification column RD.sub.A. The preferred proportion by mass of methanol in this vapour stream S.sub.OA is 99% by weight, more preferably >99.6% by weight, yet more preferably >99.9% by weight, and the remainder is especially water.

[0206] Withdrawn at the lower end of RD.sub.A is at least one stream S.sub.UA comprising water which may preferably include <1% by weight, more preferably 5000 ppmw, yet more preferably 2000 ppmw of methanol.

[0207] The withdrawal of the at least one vapour stream S.sub.OA comprising methanol at the top of the rectification column RD.sub.A in the context of the present invention means more particularly that the at least one vapour stream S.sub.OA is withdrawn above the internals in the rectification column RD.sub.A as a top stream or as a side stream takeoff.

[0208] The withdrawal of the at least one stream S.sub.UA comprising water at the bottom of the rectification column RD.sub.A in the context of the present invention means more particularly that the at least one stream S.sub.UA is withdrawn as bottom stream or at the lower tray of the rectification column RD.sub.A.

[0209] The rectification column RD.sub.A is operated with or without, preferably with, reflux.

[0210] With reflux means that the vapour stream S.sub.OA withdrawn at the upper end of the rectification column RD.sub.A is not completely discharged but rather partly condensed and returned to the respective rectification column RD.sub.A. In the cases where such a reflux is established, the reflux ratio is preferably 0.0001 to 10, more preferably 0.1 to 5, yet more preferably 0.5 to 2, yet more preferably 0.7 to 1, yet more preferably 0.76.

[0211] A reflux may be established by mounting a condenser K.sub.RD at the top of the rectification column RD.sub.A. The vapour stream S.sub.OA is partly condensed in the condenser K.sub.RD and returned to the rectification column RD.sub.A. Generally and in the context of the present invention, a reflux ratio is understood to mean the ratio of the proportion of the mass flow withdrawn from the column (kg/h) that is recycled to the column in liquid form (reflux) to the proportion of this mass flow (kg/h) that is discharged from the respective column in liquid form or gaseous form.

4.4 Step (b) of the Process According to the Invention

[0212] In step (b) of the process according to the invention, at least one side stream S.sub.ZA is withdrawn from RD.sub.A and recycled to RD.sub.A.

[0213] In a preferred embodiment of step (b) of the process according to the invention, a side stream S.sub.ZA is withdrawn from RD.sub.A and recycled to RD.sub.A.

[0214] According to the invention, side stream S.sub.ZA from RD.sub.A means that the stream is withdrawn at a withdrawal point E.sub.ZA below the top and above the bottom of RD.sub.A and in particular additionally recycled to RD.sub.A at a feed point Z.sub.ZA (this is the point at which the respective side stream S.sub.ZA is recycled to the rectification column RD.sub.A) below the top and above the bottom of RD.sub.A.

[0215] This means more particularly that the withdrawal point E.sub.ZA and preferably also the feed point Z.sub.ZA of the respective side stream S.sub.ZA on the rectification column RD.sub.A are below the withdrawal points E.sub.OA for all vapour streams S.sub.OA withdrawn from RD.sub.A, preferably at least 1, more preferably at least 5, yet more preferably at least 10, theoretical plates below the withdrawal point E.sub.OA for the vapour stream S.sub.OA withdrawn from RD.sub.A that has the withdrawal point E.sub.OA furthest down the rectification column RD.sub.A.

[0216] This also means more particularly that the withdrawal point E.sub.ZA, and preferably also the feed point Z.sub.ZA for the respective side stream S.sub.ZA on the rectification column RD.sub.A are above the withdrawal points E.sub.UA for all streams S.sub.UA withdrawn from RD.sub.A, preferably at least 1, yet more preferably at least 2, yet more preferably at least 4, theoretical plates above the withdrawal point E.sub.UA for the stream S.sub.UA that has the withdrawal point E.sub.UA furthest up the rectification column RD.sub.A.

[0217] In the cases in which at least one vapour stream S.sub.OA is at least partly recycled into the rectification column RD.sub.A (which is the case when a reflux is established at the rectification column RD.sub.A for example), the feed point Z.sub.OA (i.e. the point at which the at least one vapour stream S.sub.OA is at least partly recycled into the rectification column RD.sub.A) of the at least one vapour stream S.sub.OA is especially also above the withdrawal points E.sub.ZA and especially also above the feed points Z.sub.ZA for all side streams S.sub.ZA withdrawn from RD.sub.A, preferably at least 1, more preferably at least 5, yet more preferably at least 10, theoretical plates above the highest point of all withdrawal and feed points for all side streams S.sub.ZA withdrawn from RD.sub.A.

[0218] In the cases in which at least one stream S.sub.UA is at least partly recycled into the rectification column RD.sub.A, moreover, the feed point Z.sub.UA (i.e. the point at which the at least one stream S.sub.UA is at least partly recycled into the rectification column RD.sub.A) of the at least one stream S.sub.UA is below the withdrawal points E.sub.ZA and especially also below the feed points Z.sub.ZA of all side streams S.sub.ZA withdrawn from RD.sub.A, preferably at least 1, yet more preferably at least 2, yet more preferably at least 4, theoretical plates below the lowest point of all withdrawal and feed points for all side streams S.sub.ZA withdrawn from RD.sub.A.

[0219] The withdrawal point E.sub.ZA of the side stream S.sub.ZA and the feed point Z.sub.ZA of the side stream S.sub.ZA on the rectification column RD.sub.A may be positioned between the same trays of RD.sub.A. However, they may also be at different heights.

[0220] In a preferred embodiment of the process according to the invention, the withdrawal point E.sub.ZA and preferably also the feed point Z.sub.ZA of the at least one side stream S.sub.ZA on the rectification column RD.sub.A are below the feed point Z.sub.SAB, and above the bottom of RD.sub.A. It is yet more preferable when the withdrawal point E.sub.ZA and preferably also the feed point Z.sub.ZA of the at least one side stream S.sub.ZA on the rectification column RD.sub.A are also below the rectifying section of RD.sub.A.

[0221] The feed point Z.sub.SAB refers to the lowermost feed point of all feed points of S.sub.AB into RD.sub.A, of all feed points of S.sub.BB into RD.sub.A, and of all feed points of the mixture of S.sub.AB and S.sub.BB into RD.sub.A.

[0222] In a particularly preferred embodiment of the process according to the invention, the withdrawal point E.sub.ZA and more preferably also the feed point Z.sub.ZA of the at least one side stream S.sub.ZA on the rectification column RD.sub.A are in the upper , preferably upper , preferably upper 7/10, more preferably upper , more preferably upper , of the region on the rectification column RD.sub.A below the feed point Z.sub.SAB and above the uppermost of all withdrawal and feed points for all streams S.sub.UA withdrawn from RD.sub.A.

[0223] It is yet more preferable when the withdrawal point E.sub.ZA and preferably also the feed point Z.sub.ZA of the at least one side stream S.sub.ZA on the rectification column RD.sub.A are then also below the rectifying section of RD.sub.A.

[0224] In a further particularly preferred embodiment of the process according to the invention, rectification column RD.sub.A contains a rectifying section, and the withdrawal point E.sub.ZA and more preferably also the feed point Z.sub.ZA of the at least one side stream S.sub.ZA on the rectification column RD.sub.A are in the upper , preferably upper , preferably upper 7/10, more preferably upper , more preferably upper , of the region on the rectification column RD.sub.A below the rectifying section and above the uppermost of all withdrawal and feed points for all streams S.sub.UA withdrawn from RD.sub.A.

4.5 Step (c) of the Process According to the Invention

[0225] In step (c) of the process according to the invention, energy, preferably heat, is transferred from at least a portion of S.sub.OA to a liquid or gaseous, preferably liquid, heat transfer medium W*.sub.1, which affords a gaseous heat transfer medium W*.sub.2.

[0226] The heat transfer medium W*.sub.1 utilized may be any working medium familiar to the person skilled in the art. The heat transfer medium W*.sub.1 is especially selected from the group consisting of water, optionally fluorinated alkanes, ammonia, alcohols. Preferably, W*.sub.1 is selected from n-hexane, n-pentane, n-butane, n-propane, methanol, ethanol, propanol. Most preferably, W*.sub.1=n-butane.

[0227] Step (c) of the process according to the invention transfers energy, preferably heat, from at least a portion of S.sub.OA to the liquid or gaseous, preferably liquid, heat transfer medium W*.sub.1, and hence the gaseous heat transfer medium W*.sub.2 is obtained.

[0228] This means that, when the heat transfer medium W*.sub.1 is used in liquid form in step (c), energy, preferably heat, is supplied thereto in step (c), such that the liquid heat transfer medium W*.sub.1 at least partly evaporates, and hence a gaseous heat transfer medium W*.sub.2 is obtained.

[0229] What is meant more particularly by liquid heat transfer medium W*.sub.1 is that 10% by weight of the heat transfer medium W*.sub.1 used in step (c) is in the liquid state of matter, based on the total weight of the heat transfer medium W*.sub.1 used in step (c). It preferably means that 25% by weight, more preferably 50% by weight, more preferably 55% by weight, more preferably 75% by weight, more preferably >90% by weight, more preferably >99% by weight, of the heat transfer medium W*.sub.1 used in step (c) is in the liquid state of matter, based on the total weight of the heat transfer medium W*.sub.1 used in step (c).

[0230] If a liquid heat transfer medium W*.sub.1 is used in step (c) of the process according to the invention, in one preferred embodiment a sufficient amount of energy, preferably heat, is transferred in step (c) of the process according to the invention from at least a portion of S.sub.OA to the liquid heat transfer medium W*.sub.1 that, during step (c), 10% by weight, preferably 20% by weight, preferably 30% by weight, preferably 40% by weight, preferably 50% by weight, preferably 60% by weight, preferably 70% by weight, preferably 80% by weight, preferably 90% by weight, preferably 99% by weight, of the heat transfer medium W*.sub.1 used in the liquid state of matter is converted to the gaseous state, more preferably that, during step (c), the liquid heat transfer medium W*.sub.1 is converted completely to the gaseous state.

[0231] Alternatively, the heat transfer medium W*.sub.1 may be used in gaseous form in step (c). In that case, since it is supplied with energy, preferably heat, in step (c), a gaseous heat transfer medium W*.sub.2 is obtained after step (c).

[0232] What is meant more particularly by gaseous heat transfer medium W*.sub.1 is that the heat transfer medium W*.sub.1 used in step (c) is entirely in the gaseous state of matter.

[0233] According to the invention, transfer of energy especially means heating, i.e. transfer of energy in the form of heat.

[0234] Transfer of energy, preferably heat, from at least a portion of S.sub.OA to a liquid or gaseous, preferably liquid, heat transfer medium W*.sub.1 also encompasses the embodiments of step (c) in which S.sub.OA is first divided, for example into a portion S.sub.OA1 which, optionally after compression of this portion S.sub.OA1, is used as methanol stream S.sub.AE1 and/or S.sub.BE1, and a portion S.sub.OA2 which is recycled to the column RD.sub.A as return stream, in which case energy, especially heat, is transferred solely from S.sub.OA2 to W*.sub.1.

[0235] W*.sub.2 has an elevated energy content compared to W*.sub.1. By contrast, there is a drop in the energy content of S.sub.OA during step (c).

[0236] The transfer of energy, especially heat, from at least a portion of S.sub.OA to the liquid or gaseous, preferably liquid, heat transfer medium W*.sub.1 is preferably direct or indirect, more preferably direct. Another word for transfer of heat is heating.

[0237] What is meant more particularly by directly is that S.sub.OA is contacted with W*.sub.1 without mixing of S.sub.OA and W*.sub.1, such that energy, especially heat, is transferred from S.sub.OA to W*.sub.1.

[0238] This can be performed with the aid of methods known to the person skilled in the art.

[0239] In particular, S.sub.OA and W*.sub.1 can be directed through a heat transferrer in which energy, preferably heat, is transferred from S.sub.OA to W*.sub.1.

[0240] Heat transferrers used (another term for heat transferrer=heat exchanger) may be the heat transferrers that are familiar to the person skilled in the art, especially evaporators, especially kettle evaporators, as described above (in point 4.1). Preference is given here to using a kettle evaporator in which W*.sub.1 is expanded and, thereafter or at the same time, energy is absorbed from S.sub.OA.

[0241] As described above, in a preferred embodiment of the present invention, a return stream is established in the rectification column RD.sub.A, in which case the vapour stream S.sub.OA is partly condensed in a condenser K.sub.RD mounted at the top of the rectification column RD.sub.A in particular, and fed back to the rectification column RD.sub.A.

[0242] In this preferred embodiment, the direct transfer of energy, preferably heat, from S.sub.OA to W*.sub.1 is undertaken in the condenser K.sub.RD in particular. This has the advantage that the condenser K.sub.RD can be used simultaneously as heat transferrer, and there is no need to install any additional evaporator/condenser.

[0243] Indirectly means more particularly that S.sub.OA is contacted with a heat transfer medium W.sub.1 other than W*.sub.1, preferably via at least one heat transferrer WT.sub.x, where the heat transfer medium W.sub.1* is not W*.sub.1, and is thus distinct from W*.sub.1, and so energy, preferably heat, is transferred from S.sub.OA to W.sub.1 without mixing of the two streams, and the heat is then transferred from W.sub.1 to in that the heat transfer medium comes into contact with the heat transfer medium W*.sub.1, with or without mixing of W*.sub.1 and , but preferably without. If and W*.sub.1 do not mix, the energy, preferably heat, is transferred especially in a further heat transferrer WT.sub.Y.

[0244] In a further embodiment of the process according to the invention, in the case of indirect energy transfer from S.sub.OA to W*.sub.1, in particular heating of W*.sub.1 by S.sub.OA, it is also possible for energy, preferably heat, first to be transferred from S.sub.OA to , preferably by contacting via at least one heat exchanger WT.sub.x, and then transferred from to a further heat transfer medium distinct from W*.sub.1, preferably by contacting via at least one heat exchanger WT.sub.Y. The last step then transfers the heat from to W*.sub.1, with or without mixing of W*.sub.1 and , but preferably without. If and W*.sub.1 do not mix, the energy, preferably heat, is transferred especially in a further heat transferrer WT.sub.Z.

[0245] It will be apparent that still further heat transfer media , , etc. may accordingly be utilized in further embodiments of the present invention.

[0246] Utilizable heat transfer media and additionally further utilized heat transfer media , , , include any heat transfer media known to those skilled in the art, preferably selected from the group consisting of air; water; alcohol-water solutions; salt-water solutions, also including ionic liquids, for example LiBr solutions, dialkylimidazolium salts such as, in particular, dialkylimidazolium dialkylphosphates; mineral oils, for example diesel oils; thermal oils, for example silicone oils; biological oils, for example limonene; aromatic hydrocarbons, for example dibenzyltoluene. Most preferably, the heat transfer medium used is water or air, most preferably water.

[0247] As described above, in a preferred embodiment of the present invention, a return stream is established in the rectification column RD.sub.A, in which case the vapour stream S.sub.OA is partly condensed in a condenser K.sub.RD mounted at the top of the rectification column RD.sub.A in particular, and fed back to the rectification column RD.sub.A.

[0248] In this preferred embodiment, the direct or indirect transfer of energy, preferably heat, from S.sub.OA to W*.sub.1 or S.sub.OA to is undertaken in the condenser K.sub.RD in particular. This has the advantage that the condenser K.sub.RD can be used simultaneously as heat transferrer, and there is no need to install any additional evaporator/condenser.

[0249] After step (c) of the process according to the invention, a gaseous heat transfer medium W*.sub.2 is obtained.

[0250] The pressure of W*.sub.2 is referred to as p.sub.W*2 and its temperature as T.sub.W*2.

[0251] The pressure of W*.sub.1 is referred to as p.sub.W*1 and its temperature as T.sub.W*1.

[0252] In a preferred embodiment of the present invention, W*.sub.1 is at a temperature T.sub.W*1 in the range from 50 C. to 170 C., more preferably 90 C., and, especially when W*.sub.1 is gaseous, at a pressure p.sub.W*1 of 1 bar to 35 bar, more preferably 1.5 bar to 20 bar.

[0253] In a preferred embodiment of the present invention, W*.sub.2 is at a temperature T.sub.W*2 in the range from 25 C. to 150 C., more preferably 70 C., and at a pressure p.sub.W*2 of 1 bar to 35 bar, more preferably 5 bar to 8 bar, even more preferably 6.4 to 6.7 bar.

[0254] It will be apparent that the heat transfer medium W*.sub.2 is the same as the heat transfer medium W*.sub.1, and W*.sub.2 and W*.sub.1 differ only in their respective pressures p.sub.W*2 and p.sub.W*1 and/or their temperature T.sub.W*2 and T.sub.W*1, and, as the case may be, when W*.sub.1 has been used in liquid form, by their state of matter.

4.6 Step (d) of the Process According to the Invention

[0255] In step (d) of the process according to the invention, at least a portion of the gaseous heat transfer medium W*.sub.2 is compressed. This affords a compressed gaseous heat transfer medium W*.sub.3 relative to W*.sub.2.

[0256] The pressure of W*.sub.2 is referred to as p.sub.W*2 and its temperature as T.sub.W*2.

[0257] The pressure of W*.sub.3 is referred to as p.sub.W*3 and its temperature as T.sub.W*3.

[0258] The pressure p.sub.W*3 is higher than p.sub.W*2. The exact value of p.sub.W*3 can be adjusted by the person skilled in the art according to the requirements in step (d) provided that the condition p.sub.W*3>p.sub.W*2 is met. The quotient of p.sub.W*3/p.sub.W*2 (pressures each in bar abs.) is preferably in the range from 1.1 to 10, more preferably 1.2 to 8, more preferably 1.25 to 7, more preferably 1.3 to 6, yet more preferably 1.5 to 2, yet more preferably 1.6 to 1.8, most preferably 1.7.

[0259] The temperature T.sub.W*3 is especially higher than the temperature T.sub.W*2, and the quotient of T.sub.W*3/T.sub.W*2 (temperature in C. in each case) is preferably in the range from 1.03 to 10, more preferably 1.04 to 9, more preferably 1.05 to 8, more preferably 1.06 to 7, more preferably 1.07 to 6, most preferably 1.08 to 5.

[0260] The preferred values of p.sub.W*3 and T.sub.W*3 are also correspondingly applicable to the preferred pressure and the preferred temperature of W*.sub.31 and W*.sub.32.

[0261] The at least one portion of the gaseous heat transfer medium W*.sub.2 can be compressed in step (d) in any desired manner known to the person skilled in the art. For example, the compression can be performed mechanically and as a single-stage or multistage compression, preferably a multistage compression. In a multistage compression, it is possible to use two or more compressors of the same type or compressors of different types. A multistage compression can be effected with one or more compressors. The use of single-stage compression or multistage compression depends on the compression ratio and thus on the pressure to which the gaseous heat transfer medium W*.sub.2 is to be compressed.

[0262] The compressor used in the process according to the invention, especially for compression of the gaseous heat transfer medium W*.sub.2 to W*.sub.3 or W*.sub.32 to W*.sub.4, is any desired compressor, preferably mechanical compressor, which is known to the person skilled in the art and with which gas streams can be compressed. Suitable compressors are, for example, single-stage or multistage turbines, piston compressors, screw compressors, centrifugal compressors or axial compressors.

[0263] In a multistage compression, compressors suitable for the respective pressure stages to be overcome are used.

4.7 Step (e) of the Process According to the Invention

[0264] In step (e) of the process according to the invention, energy, especially heat, is transferred from a first portion W*.sub.31 of the gaseous heat transfer medium W*.sub.3 to S.sub.ZA before S.sub.ZA is recycled into RD.sub.A.

[0265] The gaseous heat transfer medium W*.sub.3 is first divided into at least two portions W*.sub.31 and W*.sub.32, especially in step (e). The ratio of the mass flows (in kg/h) of W*.sub.31 to W*.sub.32 is preferably in the range from 1:99 to 99:1, more preferably in the range from 1:50 to 50:1, yet more preferably in the range from 1:20 to 30:1, yet more preferably in the range from 5:20 to 15:1, more preferably 2:1 to 5:1, yet more preferably 4:1 to 4.5:1, most preferably 4.4:1.

[0266] In step (e) of the process according to the invention, energy is transferred from the first portion W*.sub.31 to S.sub.ZA. Step (e) lowers the energy of W*.sub.31, such that W*.sub.31 in particular is at least partly condensed.

[0267] According to the invention, transfer of energy especially means heating, i.e. transfer of energy in the form of heat.

[0268] Transfer of energy from a first portion W*.sub.31 of the compressed vapour stream W*.sub.3 to S.sub.ZA also encompasses the cases in which a portion of W*.sub.31 is separated off and energy is transferred to S.sub.ZA solely from that portion. This is the case for example in embodiments of the invention in which energy is additionally transferred from W*.sub.31 to the crude product RP.sub.A and, if step (a2) is performed, alternatively or additionally to the crude product RP.sub.B (described in section 4.1).

[0269] The transfer of energy from W*.sub.31 to S.sub.ZA, preferably the heating of S.sub.ZA by W*.sub.31, is preferably direct or indirect.

[0270] Direct means that W*.sub.31 is contacted with S.sub.ZA without mixing of the two streams, and so energy, especially heat, is transferred from W*.sub.31 to S.sub.ZA.

[0271] This can be implemented in that W*.sub.31 and S.sub.ZA are directed through an intermediate evaporator V.sub.ZRD in the rectification column RD.sub.A, and W*.sub.31 heats S.sub.ZA.

[0272] Heat transferrers used (another term for heat transferrer=heat exchanger), especially the heat transferrers WT.sub.x, WT.sub.Y, WT.sub.Z mentioned hereinafter, may be the heat transferrers, especially evaporators, that are familiar to the person skilled in the art. In step (e) of the process according to the invention, energy, more preferably heat, is in particular transferred from W*.sub.31 to S.sub.ZA in an intermediate evaporator V.sub.ZRD.

[0273] Indirect means more particularly that W*.sub.31 is contacted with a heat transfer medium , preferably by means of at least one heat transferrer WT.sub.X, where the heat transfer medium is not S.sub.ZA, i.e. is different from S.sub.ZA, such that energy, preferably heat, is transferred from W*.sub.31 to without mixing of the two streams, and the heat is then transferred from to S.sub.ZA in that is contacted with stream S.sub.ZA, with or without mixing of S.sub.ZA and , but preferably without mixing. If and S.sub.ZA do not mix, energy, preferably heat, is transferred especially in a further heat transferrer WT.sub.Y.

[0274] In a further embodiment of the process according to the invention, in the case of indirect energy transfer from W*.sub.31 to S.sub.ZA, especially heating of S.sub.ZA by W*.sub.31, it is also possible for energy, preferably heat, first to be transferred from W*.sub.31 to , preferably by contacting via at least one heat exchanger WT.sub.x, and then transferred from to a further heat transfer medium distinct from S.sub.ZA, preferably by contacting via at least one heat exchanger WT.sub.Y. The last step then transfers the heat from to S.sub.ZA, with or without mixing of S.sub.ZA and , but preferably without mixing. If and S.sub.ZA do not mix, the energy, preferably heat, is transferred in a further heat transferrer WT.sub.z in particular.

[0275] It will be apparent that still further heat transfer media , , etc. may accordingly be utilized in further embodiments of the present invention.

[0276] Utilizable heat transfer media and additionally further utilized heat transfer media , , , include any heat transfer media known to those skilled in the art, preferably selected from the group consisting of air, water; alcohol-water solutions; salt-water solutions, also including ionic liquids, for example LiBr solutions, dialkylimidazolium salts such as, in particular, dialkylimidazolium dialkylphosphates; mineral oils, for example diesel oils; thermal oils, for example silicone oils; biological oils, for example limonene; aromatic hydrocarbons, for example dibenzyltoluene. Most preferably, the heat transfer medium used is water or air, yet more preferably water.

[0277] Salt-water solutions that may be used are also described for example in DE 10 2005 028 451 A1 and WO 2006/134015 A1.

[0278] In a preferred embodiment, energy transfer from W*.sub.31 continues, especially after the transfer of energy to S.sub.ZA.

[0279] In a preferred embodiment of the process according to the invention, energy, preferably heat, is transferred from W*.sub.31, after W*.sub.31 has transferred energy to S.sub.ZA as per step (e), to S.sub.OA or a portion of S.sub.OA, especially to the portion of S.sub.OA, S.sub.OA1 which is sent to a compression, and this may be a precompression of the portion of S.sub.OA. This makes it possible to use a portion of the residual energy or residual heat still stored by W*.sub.31 in the process, in this case for heating of S.sub.OA or of a portion of S.sub.OA, S.sub.OA1.

[0280] Precompression refers in particular to the first compression stage in the case of a multistage compression.

[0281] Other, preferred additional sinks for the energy, preferably heat, in W*.sub.31 are described further down (see paragraph 4.10).

[0282] Step (e) of the process according to the invention reflects one aspect of the unexpected effect of the present invention. This is that the surplus energy obtained in the compression of the gaseous heat transfer medium W*.sub.2 to give the compressed gaseous heat transfer medium W*.sub.3 does not dissipate without being utilized, but instead is used in the rectification. This is effected in such a way that W*.sub.2 is first compressed to give W*.sub.3, which enables adjustment to the value optimal for energy transfer from W*.sub.31 to S.sub.ZA, and then a portion W*.sub.32 that is distinct from W*.sub.31 may be compressed further to give W*.sub.4. The heat of condensation obtained in the further compression of W*.sub.32 further to give W*.sub.4 is introduced into the column in the reboiler. The required additional compressor power is less than the heating steam power saved thereby. The process according to the invention requires less energy than that of the prior art, as shown in examples 1 and 2. Compression to W*.sub.4 allows the pressure and temperature of W*.sub.4 to be adjusted such that optimal energy transfer from W*.sub.4 to S.sub.UA1 or S.sub.UA is possible.

4.8 Step (f) of the Process According to the Invention

[0283] In step (f) of the process of the invention, a portion of the gaseous heat transfer medium W*.sub.3 other than W*.sub.31, W*.sub.32, is compressed further to obtain a vapour stream W*.sub.4 that has been compressed relative to W*.sub.31.

[0284] It will be apparent that W*.sub.4, after performance of step (f), is also compressed relative to W*.sub.32 and W*.sub.3.

[0285] The pressure of the vapour stream W*.sub.4 is referred to as p.sub.W*4 and its temperature as T.sub.W*4.

[0286] The pressure p.sub.W*4 is higher than p.sub.W*3, and the quotient of p.sub.W*4/p.sub.W*3 (pressures each in bar abs.) is preferably in the range from 1.1 to 10, more preferably 1.2 to 8, more preferably 1.25 to 7, more preferably 1.3 to 6, more preferably 1.4 to 5, more preferably 1.5 to 2, more preferably 1.5 to 1.8, most preferably 1.61.

[0287] The temperature T.sub.W*4 is especially higher than the temperature T.sub.W*3, and the quotient of T.sub.W*4/T.sub.W*3 (temperature in C. in each case) is preferably in the range from 1.03 to 10, more preferably 1.04 to 9, more preferably 1.05 to 8, more preferably 1.06 to 7, more preferably 1.07 to 6, most preferably 1.08 to 5.

[0288] The compressing of W*.sub.32 in step (f) may be performed by processes familiar to those skilled in the art. For instance, the compression may be performed mechanically and as a single-stage or multistage compression, preferably a multistage compression. In a multistage compression, it is possible to use two or more compressors of the same type or compressors of different types. The use of single-stage compression or multi-stage compression depends on the pressure to which the vapour W*.sub.32 is to be compressed. The embodiments of the compression and also the preferred compressor types that have been described in the context of step (d) for W*.sub.2 may also be used for the compression of W*.sub.32 to give W*.sub.4, but compression in one stage is sufficient in step (f) in particular, i.e. using a compressor VD.sub.X.

4.9 Step (g) of the Process According to the Invention

[0289] In step (g) of the process according to the invention, energy is transferred from at least a portion of W*.sub.4 to at least a portion S.sub.UA1 of the at least one stream S.sub.UA before S.sub.UA1 is recycled into RD.sub.A.

[0290] Preferably, in step (g), energy is transferred from at least a portion of W*.sub.4 to a portion S.sub.UA1 of the at least one stream S.sub.UA before S.sub.UA1 is recycled into RD.sub.A.

[0291] Step (g) lowers the energy of W*.sub.4, such that W*.sub.4 in particular is at least partly condensed.

[0292] Step (g) of the process according to the invention is preferably performed according to the following embodiments (g1), (g2), (g3): [0293] (g1) energy is transferred from at least a portion of W*.sub.4 to a portion S.sub.UA1 of the at least one stream S.sub.UA, and S.sub.UA1 is then recycled into RD.sub.A; [0294] (g2) energy is transferred from at least a portion of W*.sub.4 to a portion S.sub.UA1* of the at least one stream S.sub.UA, and then a portion S.sub.UA1 of S.sub.UA1* is recycled into RD.sub.A; [0295] (g3) energy is transferred from at least a portion of W*.sub.4 to the whole of stream S.sub.UA and then the whole of stream S.sub.UA or only a portion S.sub.UA1 of stream S.sub.UA, preferably only a portion S.sub.UA1 of stream S.sub.UA, is recycled into RD.sub.A.

[0296] The transfer of energy from at least a portion of W*.sub.4 to the at least a portion S.sub.UA1 of the at least one stream S.sub.UA, preferably the heating of the at least a portion S.sub.UA1 of the at least one stream S.sub.UA by at least a portion of W*.sub.4, is preferably direct or indirect.

[0297] Direct means that at least a portion of W*.sub.4 is contacted with the at least a portion S.sub.UA1 of the at least one stream S.sub.UA without mixing of the two streams, and so energy, especially heat, is transferred from at least a portion W*.sub.4 to the at least a portion S.sub.UA1 of the at least one stream S.sub.UA.

[0298] This may be performed in that the at least a portion of W*.sub.4 and the at least a portion S.sub.UA1 of the at least one stream S.sub.UA are directed through a reboiler V.sub.SRD in the rectification column RD.sub.A, and W*.sub.4 heats the at least a portion S.sub.UA1 of the at least one stream S.sub.UA.

[0299] Heat transferrers used, in particular the heat transferrers WT.sub.X, WT.sub.Y, WT.sub.Z mentioned hereinafter, may be the heat exchangers familiar to the person skilled in the art, in particular evaporators. In step (g) of the process according to the invention, the energy, preferably heat, is in particular transferred from at least a portion of W*.sub.4 to the at least a portion S.sub.UA1 of the at least one stream S.sub.UA in a reboiler V.sub.SRD.

[0300] Indirect means more particularly that the at least a portion of W*.sub.4 is contacted with at least one heat transfer medium W.sup..sub.1, preferably by means of at least one heat exchanger WT.sub.X, where the heat transfer medium is not the at least a portion S.sub.UA1 of the at least one stream S.sub.UA, i.e. W.sup..sub.1 is distinct therefrom, such that energy, preferably heat, is transferred from the at least a portion of W*.sub.4 to the at least one heat transfer medium W.sup..sub.1 without mixing of the two streams, and the heat is then transferred from W.sup..sub.1 to the at least a portion S.sub.UA1 of the at least one stream S.sub.UA in that W.sup..sub.1 makes contact with stream S.sub.UA1 with or without mixing of the at least a portion S.sub.UA1 of the at least one stream S.sub.UA and W.sup..sub.1, but preferably without mixing.

[0301] In a further embodiment of the process according to the invention, in the case of indirect energy transfer from the at least a portion of W*.sub.4 to the at least a portion S.sub.UA1 of the at least one stream S.sub.UA, in particular heating of the at least a portion S.sub.UA1 of the at least one stream S.sub.UA by the at least a portion of W*.sub.4, it is also possible for energy, preferably heat, first to be transferred from W*.sub.4 to W.sup..sub.1, preferably by contacting via at least one heat exchanger WT.sub.X, and then transferred from to a further heat transfer medium W.sup..sub.2 distinct from the at least a portion S.sub.UA1 of the at least one stream S.sub.UA, preferably by contacting via at least one heat exchanger WT.sub.Y. The last step then transfers the heat from W.sup..sub.2 to the at least a portion S.sub.UA1 of the at least one stream S.sub.UA, with or without mixing of the at least a portion S.sub.UA1 of the at least one stream S.sub.UA and W.sub.2, but preferably without.

[0302] It will be apparent that still further heat transfer media W.sup..sub.3, W.sup..sub.4, W.sup..sub.5 etc. may accordingly be utilized in further embodiments of the present invention.

[0303] Utilizable heat transfer media W.sup..sub.1 and additionally further utilized heat transfer media W.sup..sub.2, W.sup..sub.3, W.sup..sub.4, W.sup..sub.5 include any heat transfer media known to those skilled in the art, preferably selected from the group consisting of air; water; alcohol-water solutions; salt-water solutions, also including ionic liquids, for example LiBr solutions, dialkylimidazolium salts such as, in particular, dialkylimidazolium dialkylphosphates; mineral oils, for example diesel oils; thermal oils, for example silicone oils; biological oils, for example limonene; aromatic hydrocarbons, for example dibenzyltoluene. Most preferably, the heat transfer medium W.sup..sub.1 used is water or air, yet more preferably water.

[0304] Salt-water solutions that may be used are also described for example in DE 10 2005 028 451 A1 and WO 2006/134015 A1.

[0305] In a preferred embodiment, after step (g), transfer of energy from at least a portion of W*.sub.4 is continued, especially after the transfer of the energy to the at least a portion S.sub.UA1 of S.sub.UA.

[0306] In a preferred embodiment of the process according to the invention, energy, more preferably heat, is transferred from at least a portion of W*.sub.4, after W*.sub.4 has transferred energy to the at least a portion S.sub.UA1 of S.sub.UA as per step (g), to S.sub.OA or a portion of S.sub.OA, especially to the portion of S.sub.OA, S.sub.OA1 which is sent to a compression, and this may be a precompression of the portion of S.sub.OA. This makes it possible to use a portion of the residual energy or residual heat still stored by the at least a portion W*.sub.4 in the process, in this case for heating of S.sub.OA or of a portion of S.sub.OA, S.sub.OA1.

[0307] After step (g), at least a portion of W*.sub.4 can then be combined again with the heat transfer medium W*.sub.3, W*.sub.31, W*.sub.32 obtained after performance of step (d) or (e) and sent as liquid or gaseous heat transfer medium W*.sub.1 to a new cycle of the process in step (c). Optionally, W*.sub.4 is expanded before being combined with one of streams W*.sub.3, W*.sub.31, W*.sub.32.

[0308] In a preferred embodiment of the invention, a portion of the heat transfer medium W*.sub.4 obtained after step (g) is also expanded to a lower pressure by means of a valve before being fed to a new cycle as W*.sub.1. This can lower the pressure from W*.sub.4 to the preferred range of W*.sub.1.

[0309] Alternatively or additionally to a valve, energy, especially heat, may be transferred from at least a portion of the heat transfer medium W*.sub.4 obtained after step (g) to W*.sub.2 before W*.sub.2 is compressed in step (d).

[0310] Alternatively or additionally, a portion of the heat transfer medium W*.sub.4 obtained after step (g) may also be expanded by a valve or into a condensate vessel, and the portion thus expanded may then be combined with W*.sub.3, especially one of the portions W*.sub.31 or W*.sub.32 of the gaseous heat transfer medium W*.sub.3.

[0311] Other, preferred additional sinks for the energy, preferably heat, in the at least a portion of W*.sub.4 are described further down (see paragraph 4.10).

[0312] In a further preferred embodiment, energy is transferred from the bottom product stream S.sub.AP and, if step (a2) is conducted, alternatively or additionally from the bottom product stream S.sub.BP to S.sub.OA or a portion of S.sub.OA, especially to the portion of S.sub.OA, S.sub.OA1 which is sent to a compression, and this may be a precompression of the portion of S.sub.OA.

[0313] In a further preferred embodiment, energy is transferred from the bottom product stream S.sub.AP and, if step (a2) is conducted, alternatively or additionally from the bottom product stream S.sub.BP to at least a portion of W*.sub.1 before W*.sub.1 is used in step (c).

4.10 Preferred Aspect: Process for Transalcoholization of an Alkali Metal Alkoxide

[0314] In an advantageous embodiment of the present invention, the energy encompassed in at least one of the streams W*.sub.3, W*.sub.31, W*.sub.32, W*.sub.4 is used for operation of other industrial processes. This is advantageous especially in sites hosting integrated systems (chemistry parks, technology parks) where there is always a need for heating. This energy may be advantageously utilized especially in the case of integrated systems comprising two or more plants for alkali metal alkoxide production. Such integrated systems typically also comprise processes for transalcoholization as described in DE 27 26 491 A1. U.S. Pat. No. 3,418,383 A, WO 2021/122702 A1 describe processes for transalcoholization from methoxides to propoxides.

[0315] In a preferred aspect of the present invention, in the process according to the present invention, in a reactive rectification column RR.sub.C a reactant stream S.sub.CE1 comprising M.sub.cOR, with or without ROH, is reacted in countercurrent with a reactant stream S.sub.CE2 comprising ROH to afford a crude product RP.sub.C comprising M.sub.cOR and ROH, [0316] wherein a bottom product stream S.sub.cp comprising M.sub.cOR is withdrawn at the lower end of RR.sub.c and a vapour stream S.sub.CB comprising ROH is withdrawn at the upper end of RR.sub.c, [0317] and wherein R and R are two different C.sub.1 to C.sub.6 hydrocarbon radicals, and M.sub.c is a metal selected from lithium, sodium, potassium, preferably sodium, potassium, more preferably sodium, [0318] and wherein energy is transferred from at least a portion of a stream selected from W*.sub.3, W*.sub.4 to the crude product RP.sub.C.

[0319] The process according to the invention in the preferred aspect of the invention is a process for transalcoholization of a given alkali metal alkoxide M.sub.cOR to afford another alkali metal alkoxide M.sub.cOR as described for example in DE 27 26 491 A1 or WO 2021/122702 A1.

[0320] R and R here are two different C.sub.1 to C.sub.6 hydrocarbon radicals, preferably two different C.sub.1 to C.sub.4 hydrocarbon radicals.

[0321] Yet more preferably, R is methyl and R is a C.sub.2 to C.sub.4 hydrocarbon radical.

[0322] Yet more preferably, R is methyl and R is selected from ethyl, n-propyl, iso-propyl, sec-butyl, 2-methyl-2-butyl, tert-butyl, 2-methyl-2-pentyl, 3-methyl-3-pentyl, 3-ethyl-3-pentyl, 2-methyl-2-hexyl, 3-methyl-3-hexyl, especially from ethyl, iso-propyl, 2-methyl-2-butyl, 3-methyl-3-pentyl, 3-ethyl-3-pentyl.

[0323] Even more preferably, R=methyl and R=ethyl.

[0324] The process according to the preferred aspect of the invention (also referred to hereinafter as transalcoholization) is performed in a reactive rectification column RR.sub.C. Suitable reactive rectification columns include columns described for RR.sub.A at point 4.1 in the context of step (a1).

[0325] The reaction column RR.sub.C is operated with or without, preferably with, reflux. If a reflux is established, the vapour S.sub.CB in particular is directed partly or completely through a condenser K.sub.RRC, and the condensed vapour may then be returned to the reaction column RR.sub.C or, when R=methyl, used as reactant stream S.sub.AE1 or S.sub.BE1. When R=methyl, it may also be used as fresh alcohol stream in RD.sub.A.

[0326] In the transalcoholization, a bottom product stream S.sub.CP comprising M.sub.COR is withdrawn at the lower end of RR.sub.C. A vapour stream S.sub.CB comprising ROH is withdrawn at the upper end of RR.sub.C.

[0327] In a preferred embodiment, when R=methyl, the reactant stream S.sub.CE1 used, comprising M.sub.cOR with or without ROH, is at least a portion of S.sub.AP, and, when step (a2) is conducted, alternatively (when M.sub.A and M.sub.B are different alkali metals or when M.sub.A and M.sub.B are the same alkali metal, especially when M.sub.A and M.sub.B are different alkali metals) or additionally (especially when M.sub.A and M.sub.B are the same alkali metal), at least a portion of S.sub.BP is used. More preferably, in that case, R=ethyl. What accordingly takes place is a transalcoholization of alkali metal methoxide to the corresponding alkali metal ethoxide.

[0328] When S.sub.BP and S.sub.AP comprise the same alkali metal methoxide, these two streams may also be used separately or in mixed form as S.sub.CE1, i.e. in particular first mixed and then fed to the column RR.sub.C as reactant stream S.sub.CE1 or fed to the column RR.sub.c separately as two reactant streams S.sub.CE1.

[0329] The reactant stream S.sub.CE2 comprises ROH. In a preferred embodiment, the proportion by mass of ROH in S.sub.CE2 is 85% by weight, yet more preferably 90% by weight, where S.sub.CE2 otherwise includes M.sub.COR in particular or another denaturing agent. The alcohol ROH used as reactant stream S.sub.CE2 may also be commercially available alcohol having a proportion by mass of alcohol of more than 99.8% by weight and a proportion by mass of water of up to 0.2% by weight.

[0330] According to the invention, reaction of a reactant stream S.sub.CE1 comprising M.sub.cOR, with or without ROH, with a reactant stream S.sub.CE2 comprising ROH in countercurrent is achieved more particularly by virtue of the feed point for at least a portion of the reactant stream S.sub.CE1 comprising M.sub.cOR being above the feed point of the reactant stream S.sub.CE2 comprising ROH in the reaction column RR.sub.C.

[0331] The reaction column RR.sub.C is operated with or without, preferably with, reflux.

[0332] In a preferred embodiment, the reaction column RR.sub.c comprises at least one evaporator which is in particular selected from intermediate evaporators V.sub.ZC and reboilers V.sub.SC. The reaction column RR.sub.C more preferably comprises at least one reboiler V.sub.SC.

[0333] In the case of the reaction column RR.sub.C, intermediate evaporation comprises withdrawal (takeoff) of at least one side stream S.sub.ZC from RR.sub.C and feeding thereof to the at least one intermediate evaporator V.sub.ZC.

[0334] In the case of the reaction column RR.sub.C, bottoms evaporation comprises withdrawal (takeoff) of at least one stream, for example S.sub.CP from RR.sub.C, and feeding of at least a portion, in the case of S.sub.CP preferably a portion, to the at least one reboiler V.sub.SC.

[0335] Suitable evaporators that can be used as intermediate evaporators and reboilers are described in section 4.1.

[0336] In the transalcoholization, energy, preferably heat, is transferred from at least a portion of a stream selected from W*.sub.3, W*.sub.4 to the crude product RP.sub.C. This is preferably effected by transfer of energy from at least a portion of a stream selected from W*.sub.3, W*.sub.4 to S.sub.CE1 or S.sub.CE2 before they are directed into RR.sub.C, followed by transfer of energy from S.sub.CE1/S.sub.CE2 to the crude product RP.sub.C present in RR.sub.C, with which they are mixed.

[0337] Accordingly, energy, preferably heat, is transferred from at least a portion of a heat transfer medium selected from W*.sub.3, W*.sub.4, especially from at least one heat transfer medium selected from W*.sub.31, W*.sub.32, W*.sub.4, preferably from at least one heat transfer medium selected from W*.sub.32, W*.sub.4, to the crude product RP.sub.C.

[0338] Transfer of energy, preferably heat, from at least a portion of W*.sub.3 to the crude product RP.sub.C also encompasses the transfer of energy, preferably heat, from at least one heat transfer medium selected from W*.sub.31, W*.sub.32, W*.sub.3, before separation thereof into W*.sub.31, W*.sub.32, to the crude product RP.sub.C.

[0339] In addition, it is also possible to direct crude product RP.sub.C through an intermediate evaporator V.sub.ZC or a reboiler V.sub.SC and, in V.sub.ZC or V.sub.SC, to transfer energy, preferably heat, from at least a portion of a heat transfer medium selected from W*.sub.3, W*.sub.4 to the crude product RP.sub.C.

[0340] In addition, it is also possible to direct the bottom product stream S.sub.cp partly through a reboiler V.sub.SC and then to recycle it partly back into RR.sub.C, in which case, in V.sub.SC, energy, preferably heat, is transferred from at least a portion of a heat transfer medium selected from W*.sub.3, W*.sub.4 to the recycled portion of S.sub.CP and then, in column RR.sub.C, from S.sub.CP to crude product RP.sub.C present in the column.

[0341] Energy is transferred here directly or indirectly from at least a portion of a heat transfer medium selected from W*.sub.3, W*.sub.4 to the streams mentioned, i.e. without or with heat transfer medium , as described correspondingly in section 4.7.

[0342] The preferred embodiment of the process according to the invention makes it possible to efficiently use the energy from W*.sub.3, W*.sub.4, especially from W*.sub.4, W*.sub.31, W*.sub.32. This reduces the total energy demand.

5. EXAMPLES

5.1 Example 1 (Noninventive), Corresponding to FIG. 1

[0343] The noninventive example corresponds to FIG. 1, except that the intermediate cooler WT.sub.X <402> shown in FIG. 1 (or FIG. 2 or FIG. 3) is not utilized. This also applies to the noninventive Example 2, and to the inventive Example 3.

[0344] A stream of aqueous NaOH (50% by weight) S.sub.AE2 <102> of 5000 kg/h is fed at 30 C. to the top of a reaction column RR.sub.A <100>. A vaporous methanol stream S.sub.AE1 <103> of 56700 kg/h is fed in countercurrent at the bottom of the reaction column RR.sub.A <100>. The reaction column RR.sub.A <100> is operated at a top pressure of 1.25 bar abs. At the bottom of the column RR.sub.A <100>, a virtually water-free product stream S.sub.AP* <104> of 11 000 kg/h is withdrawn (30% by weight sodium methoxide in methanol). The evaporator V.sub.SA <105> of the reaction column RR.sub.A <100> introduces about 1200 KW of heating power using low pressure steam. A vaporous methanol-water stream S.sub.AB <107> is withdrawn at the top of the reaction column RR.sub.A <100> and 4000 kg/h thereof are condensed in the condenser K.sub.RRA <108> and returned to the reaction column RR.sub.A <100> as reflux while the remaining stream of 50800 kg/h is supplied to a rectification column RD.sub.A <300>.

[0345] The rectification column RD.sub.A <300> is operated at a top pressure of 1.1 bar abs. At the bottom of the rectification column RD.sub.A <300>, a liquid water stream S.sub.UA <304> of 3500 kg/h is discharged (500 ppmw of methanol). The bottom temperature of RD.sub.A <300> is 105 C. at 1.2 bar abs. At the top of the rectification column RD.sub.A <300>, a vaporous methanol stream S.sub.OA <302> (1.1 bar, 67 C.; 200 ppmw of water) of 100 000 kg/h is withdrawn, of which 43 300 kg/h is used as reflux and directed through a condenser K.sub.RD <407> in which most of the heat of condensation (9.4 MW) is utilized in order to evaporate the working medium W*.sub.1 <701> n-butane at 61.8 C. and 6.7 bar abs. to give stream W*.sub.2 <702>. The remaining vapour stream from RD.sub.A <300> of 56 700 kg/h is fed to a compressor V.sub.DAB2 <303>, compressed to 1.7 bar abs. therein and recycled to the reaction column RR.sub.A <100>.

[0346] The gaseous n-butane stream W*.sub.2 <702> is fed to a compressor VD.sub.1 <401>, and preferably heated upstream of that through a superheater (T=20 K). Subsequently, the resultant stream W*.sub.3 <703> is fed to the compressor VD.sub.x <405>, such that there is multistage compression of stream W*.sub.2 <702> to give stream W*.sub.4 <704>. A total of 169 t/h of W*.sub.2 <702> is compressed to give stream W*.sub.4 <704> (18.6 bar abs.). This corresponds to a condensation temperature of 110.5 C. In the heat transferrer V.sub.SRD <406>, a temperature differential of 5 K is established, and the heat is transferred from W*.sub.4 <704> to a portion S.sub.UA1 <320> of the vapour stream S.sub.UA <304>, so as again to result in a stream W*.sub.1 <701> that can be fed again to the condenser K.sub.RD <407>.

[0347] Before stream W*.sub.1 <701> is fed again to the condenser K.sub.RD <407>, it is possible to utilize any residual heat present in the condensed stream W*.sub.1 <701> for superheating of the n-butane stream upstream of the compressor VD.sub.1 <401>.

[0348] A total electrical compressor output of 2.7 MW is required, while no external heating media (e.g. steam) were required.

5.2 Example 2 (Noninventive), Corresponding to FIG. 2

[0349] The arrangement in the noninventive Example 2 corresponds to that of Example 1 with the following differences:

[0350] The rectification column RD.sub.A <300> comprises an intermediate evaporator V.sub.ZRD <409>. A liquid stream S.sub.ZA <305> is withdrawn from the rectification column RD.sub.A <300> at 80 C. and about 10 500 KW of heat is transferred thereto in the intermediate evaporator V.sub.ZRD <409>, with partial evaporation of the stream, which is then returned to the rectification column RD.sub.A <300>. At the top of the rectification column RD.sub.A <300>, a vaporous methanol stream S.sub.OA <302> (1.1 bar, 67 C.; 200 ppm by weight of water) of 100 000 kg/h is withdrawn, of which 43 300 kg/h is used as reflux and directed through a condenser K.sub.RD <407> in which most of the heat of condensation (9.5 MW) is utilized in order to evaporate the working medium W*.sub.1 <701> n-butane at 61.8 C. and 6.7 bar abs. to give stream W*.sub.2 <702>. The remaining vapour stream of 56 700 kg/h is fed to a compressor V.sub.DAB2 <303>, where it is compressed to 1.7 bar abs., and returned to the reaction column RR.sub.A <100>.

[0351] The gaseous n-butane stream W*.sub.2 <702> is fed to a compressor VD.sub.1 <401>, and preferably heated upstream of that through a superheater (T=13 K). The stream W*.sub.3 <703> is obtained. A total of 127 t/h of W*.sub.2 <702> is compressed to give stream W*.sub.3 <703> (11.5 bar abs.).

[0352] By comparison with Example 1, the pressure level of the n-butane working fluid does not have to be selected at such a high level, since the temperature in the intermediate evaporator V.sub.ZRD <409> is 80 C. (and not 105 C. as in the bottom of RD.sub.A <300>). Accordingly, the electrical power of the compressor VD.sub.1 <401> is reduced compared to Example 1. Because of the smaller temperature jump, the power of the compressor is 1 MW. A thermal power for V.sub.ZRD <409> of 10.5 MW is provided. Nevertheless, the use of a heat pump in the form described cannot achieve complete electrification of the RD.sub.A <300>. The reboiler <406> is operated with low-pressure steam (alternatively: a different waste heat source), and it is necessary to use 2.04 MW. Accordingly, a total of 1.0 MW of electrical power and 2.04 MW of heating steam are used.

5.3 Example 3 (Inventive), Corresponding to FIG. 3

[0353] The arrangement in the inventive Example 3 corresponds to that of Examples 1 and 2 with the following differences:

[0354] A vaporous methanol stream S.sub.OA <302> (1.1 bar, 67 C.; 200 ppmw of water) of 100 000 kg/h is withdrawn at the top of the rectification column RD.sub.A <300>, of which 43 300 kg/h are used as reflux and directed through a condenser K.sub.RD <407>.

[0355] 11.14 MW of heat of condensation is used in the condenser K.sub.RD <407> in order to evaporate the working medium W*.sub.1 <701> n-butane at 61.8 C. and 6.7 bar abs. to give stream W*.sub.2 <702>. The remaining vapour stream from RD.sub.A <300> of 56 700 kg/h is fed to a compressor V.sub.DAB2 <303>, compressed therein to 1.7 bar abs. and recycled to the reaction column RR.sub.A <100>.

[0356] The gaseous n-butane stream W*.sub.2 <702> is fed to a compressor VD.sub.1 <401>, and preferably upstream of that through a superheater (T=20 K). Subsequently, the resultant stream W*.sub.3 <703> (11.5 bar, 110.5 C.) is divided.

[0357] 127 t/h of n-butane from stream W*.sub.3 <703> (=stream W*.sub.31 <7031>) are directed at 11.5 bar abs. to the side evaporator V.sub.ZRD <409> in order to transmit 10.5 MW there.

[0358] The remaining portion of stream W*.sub.3 <703>, i.e. W*.sub.32 <7032>, 29 t/h, is fed to the compressor VD.sub.x <405> and compressed from 11.5 bar abs. to 18.6 bar abs. to give stream W*.sub.4 <704>. Stream W*.sub.4 <704 > is then condensed in the reboiler V.sub.SRD <406> (2.04 MW).

[0359] A total of 1.4 MW of electrical power is required for the compressor stages VD.sub.1 <401> and VD.sub.2 <405>.

[0360] By comparison with Example 1 and Example 2, the total energy requirement is reduced with establishment of the same boundary conditions and the same power. Moreover, compared to Example 2, no additional heating medium is used. This column is thus fully electrified. In the case of use of green power, it is thus possible to assure CO.sub.2-free separation.

[0361] The total energy to be supplied is minimized by the process according to Example 3.

[0362] The proportion of heating power provided by low pressure steam and compressor power required in each case is shown in FIG. 10.

[0363] Result: The inventive procedure of staged compression of the heat transfer medium and therefore of operating the intermediate evaporator and reboiler with the heat transfer medium compressed to different extents can surprisingly achieve energy savings.