Two-stage hydroformylation process with circulating gas and SILP technology

Abstract

The invention relates to processes for preparing aldehydes by hydroformylation of alkenes, in which an alkene-containing feed mixture is subjected to a primary hydroformylation with synthesis gas in the presence of a homogeneous catalyst system, the primary hydroformylation being effected in a primary reaction zone from which a cycle gas containing at least some of the products and unconverted reactants of the primary hydroformylation are drawn off continuously and partly condensed, with recycling of uncondensed components of the cycle gas into the primary reaction zone, and with distillative separation of condensed components of the cycle gas in an aldehyde removal stage to give an aldehyde-rich mixture and a low-aldehyde mixture. The problem that it addresses is that of developing the process such that it achieves high conversions and affords aldehyde in good product quality even in the case of a deteriorating raw material position. More particularly, a solution is to be found for making legacy oxo process plants capable of utilizing lower-value raw material sources. This problem is solved by separating the low-aldehyde mixture into a retentate and a permeate by means of a membrane separation unit in such a way that alkenes present in the low-aldehyde mixture become enriched in the permeate, while alkanes present in the low-aldehyde mixture become enriched in the retentate. The alkene-rich permeate is then transferred into a secondary reaction zone and subjected to a secondary hydroformylation therein with synthesis gas in the presence of an SILP catalyst system. The reaction product obtained from the secondary hydroformylation is recycled into the aldehyde removal stage.

Claims

1. Process for preparing aldehydes by hydroformylation of alkenes, in which an alkene-containing feed mixture is subjected to a primary hydroformylation with synthesis gas in the presence of a homogeneous catalyst system, the primary hydroformylation being effected in a primary reaction zone from which a cycle gas containing at least some of the products and unconverted reactants of the primary hydroformylation are drawn off continuously and partly condensed, with recycling of uncondensed components of the cycle gas into the primary reaction zone, and with distillative separation of condensed components of the cycle gas in an aldehyde removal stage to give an aldehyde-rich mixture and a low-aldehyde mixture, wherein the low-aldehyde mixture is separated into a retentate and a permeate by means of a membrane separation unit in such a way that alkenes present in the low-aldehyde mixture become enriched in the permeate, while alkanes present in the low-aldehyde mixture become enriched in the retentate, and in that the permeate is transferred into a secondary reaction zone and subjected to a secondary hydroformylation therein with synthesis gas in the presence of an SILP catalyst system, with supply of the reaction product obtained from the secondary hydroformylation to the aldehyde removal stage.

2. Process according to claim 1, wherein the feed mixture used is a C.sub.3 mixture containing between 10% and 90% by weight of alkenes having three carbon atoms, based on the total weight of the feed mixture.

3. Process according to claim 1, wherein the feed mixture used is a C.sub.4 mixture containing between 10% and 90% by weight of alkenes having four carbon atoms, based on the total weight of the feed mixture.

4. Process according to claim 1, mixture and a second feed mixture are used, whereby the first feed mixture used is a C.sub.3 mixture containing between 10% and 90% by weight of alkenes having three carbon atoms, based on the total weight of the first feed mixture, whereby the second feed mixture used is a C.sub.4 mixture containing between 10% and 90% by weight of alkenes having four carbon atoms, based on the total weight of the second feed mixture, whereby is parallel preparation of C.sub.4 aldehydes from the C.sub.3 mixture and C.sub.5 aldehydes from the C.sub.4 mixture, with the proviso that the C.sub.3 mixture is subjected to a primary C.sub.3 hydroformylation with synthesis gas in the presence of a homogeneous catalyst system, the primary C.sub.3 hydroformylation being effected in a primary C.sub.3 reaction zone from which a C.sub.3 cycle gas containing at least some of the products and unconverted reactants of the primary C.sub.3 hydroformylation are drawn off continuously and partly condensed, and uncondensed components of the C.sub.3 cycle gas being recycled into the primary C.sub.3 reaction zone, and the condensed components of the C.sub.3 cycle gas being separated by distillation in a C.sub.4 aldehyde removal stage to give a C.sub.4 aldehyde-rich mixture and a low-C.sub.4 aldehyde mixture, and in that the C.sub.4 mixture is subjected to a primary C.sub.4 hydroformylation with synthesis gas in the presence of a homogeneous catalyst system, the primary C.sub.4 hydroformylation being effected in a primary C.sub.4 reaction zone from which a C.sub.4 cycle gas containing at least some of the products and unconverted reactants of the primary C.sub.4 hydroformylation are drawn off continuously and partly condensed, and uncondensed components of the C.sub.4 cycle gas being recycled into the primary C.sub.4 reaction zone, and the condensed components of the C.sub.4 cycle gas being separated by distillation in a C.sub.5 aldehyde removal stage to give a C.sub.5 aldehyde-rich mixture and a low-C.sub.5 aldehyde mixture, wherein, optionally, the low-C.sub.4 aldehyde mixture or the low-C.sub.5 aldehyde mixture is fed to the membrane separation unit and the resultant permeate is subjected to the secondary hydroformylation in the presence of the SILP catalyst system, and wherein the reaction product obtained from the secondary hydroformylation is fed to the corresponding C.sub.4 or C.sub.5 aldehyde removal stage.

5. Process according to claim 1, wherein the membrane separation unit comprises at least one membrane having a separation-active membrane material, whereby the membrane separation unit has been provided with a carrier medium capable of entering into compounds with alkenes for which the membrane material has a higher permeability than for the corresponding non-compounded alkenes.

6. Process according to claim 1, wherein the SILP catalyst system of the secondary hydroformylation comprises the following components: a) a solid porous carrier material; b) an ionic liquid; c) a metal selected from group 9 of the Periodic Table of the Elements; d) a phosphorus-containing organic ligand; e) optionally an organic amine.

7. Process according to any of claim 1, wherein the permeate enters the secondary reaction zone in gaseous form.

8. Process according to claim 7, wherein the permeate is obtained at least partly in liquid form in the membrane separation unit and, prior to entry into the secondary reaction stage, is evaporated by the action of heat by means of an evaporator.

9. Process according to claim 7, wherein the permeate is obtained in gaseous form in the membrane separation unit.

10. Process according to claim 1, wherein the homogeneous catalyst system of the primary hydroformylation comprises rhodium and at least one phosphine or phosphite or phosphoramidite ligand, the homogeneous catalyst system being fully dissolved in a liquid phase of the reaction mixture of the primary reaction zone.

11. Process for preparing aldehydes by hydroformylation of alkenes, in which an alkene-containing feed mixture is subjected to a primary hydroformylation with synthesis gas in the presence of a homogeneous catalyst system, the primary hydroformylation being effected in a primary reaction zone from which a cycle gas containing at least some of the products and unconverted reactants of the primary hydroformylation are drawn off continuously and partly condensed, with recycling of uncondensed components of the cycle gas into the primary reaction zone, and with distillative separation of condensed components of the cycle gas in an aldehyde removal stage to give an aldehyde-rich mixture and a low-aldehyde mixture, wherein the cycle gas, prior to the partial condensation thereof, is separated into a retentate and a permeate by means of a membrane separation unit in such a way that alkenes present in the cycle gas become enriched in the permeate, while alkanes present in the cycle gas become enriched in the retentate, and in that the permeate is transferred into a secondary reaction zone and subjected to a secondary hydroformylation therein with synthesis gas in the presence of an SILP catalyst system, with supply of the reaction product obtained from the secondary hydroformylation to the partial condensation stage.

12. Process according to claim 11, wherein the membrane separation unit comprises at least one membrane having a separation-active membrane material, wherein the membrane separation unit has been provided with a carrier medium capable of entering into compounds with alkenes for which the membrane material has a higher permeability than for the corresponding non-compounded alkenes.

13. Process according to claim 11, wherein the SILP catalyst system of the secondary hydroformylation comprises the following components: a) a solid porous carrier material; b) an ionic liquid; c) a metal selected from group 9 of the Periodic Table of the Elements; d) a phosphorus-containing organic ligand; e) optionally an organic amine.

14. Process according to claim 11, wherein the homogeneous catalyst system of the primary hydroformylation comprises rhodium and at least one phosphine or phosphite or phosphoramidite ligand, the homogeneous catalyst system being fully dissolved in a liquid phase of the reaction mixture of the primary reaction zone.

Description

(1) The invention is now to be elucidated by working examples. The figures show:

(2) FIG. 1: a simplified process flow diagram of a two-stage oxo process according to the invention, in which the SILP stage follows after the partial condensation of the cycle gas;

(3) FIG. 2: a simplified process flow diagram of a plant complex having two primary hydroformylations;

(4) FIG. 3: a simplified process flow diagram of a two-stage oxo process according to the invention, in which the SILP stage precedes the partial condensation of the cycle gas.

(5) FIG. 1 shows a simplified process flow diagram for performance of a two-stage hydroformylation. The plant complex 0 necessary for the process is composed of a first complex component 1 and a second complex component 2. The first complex component 1 serves for conduction of a primary hydroformylation, for example of butenes, in the gas recycle method, while the second complex component 2 is intended for the conversion of the butenes unconverted in the first complex component 1 by way of a secondary SILP hydroformylation.

(6) The first complex component 1 corresponds to a conventional gas recycle plant for butene hydroformylation, as known, for example, from EP2280920B1.

(7) At the core of the gas recycle plant is a primary reaction zone 4, for example in the form of a bubble column reactor of a stirred tank, a loop reactor or a jet nozzle reactor. Within the primary reaction zone 4, a liquid reaction phase and a gaseous reaction phase are formed. The liquid phase is formed essentially from liquid reaction product (C.sub.5 aldehyde), dissolved synthesis gas and butenes, and also from dissolved homogeneous catalyst. In addition, liquid solvents, for example isononyl benzoate, may be present.

(8) A C.sub.4 mixture 5 which comprises butenes and is to be hydroformylated and synthesis gas 6 consisting of carbon monoxide and hydrogen are run into the primary reaction zone 4. If required, fresh catalyst 7 is likewise run into the primary reaction zone 4. The catalyst 7 is especially a conventional rhodium/phosphite system.

(9) In a manner known per se, within the primary reaction zone 4, the C.sub.4 mixture 5 is reacted with synthesis gas 6 in the presence of the homogeneously dissolved catalyst 7 to give corresponding C.sub.5 aldehydes. The C.sub.5 aldehydes are drawn off as cycle gas 8 from the gas phase of the primary reaction zone 4 together with excess synthesis gas. The cycle gas 8 is sucked out by means of a cycle gas compressor 9. A heat exchanger-condenser combination 10 partly condenses the cycle gas 8. This affords a condensate 11 comprising essentially the C.sub.5 aldehydes, and also unconverted butenes and inert constituents of the C.sub.4 mixture 5. The uncondensed constituents of the cycle gas 12 comprise essentially unconverted synthesis gas. They are returned to the primary reaction zone 4, i.e. the cycle gas reactor.

(10) Meanwhile, the condensate 11 is transferred to an aldehyde removal stage 13. The aldehyde removal stage 13 works essentially by distillation. Thus, the condensate 11 is separated into an aldehyde-rich mixture 14 and a low-aldehyde mixture 15.

(11) The aldehyde-rich mixture 14 is guided to an aldolization 16, in order to be subjected therein to an aldol condensation in a manner known per se. This process is described in DE102009001594A1.

(12) Meanwhile, the low-aldehyde mixture 15, preferably the uncondensed vapour from the distillation column utilized as aldehyde removal stage, is transferred into the second complex component 2. It is first fed therein to a membrane separation unit 17 and separated therein into a retentate 18 and a permeate 19. The membrane separation unit 17 may, in a manner known per se, comprise one or more membrane modules connected to one another in parallel or series. The exact configuration of the membrane separation unit is not what matters here. What is instead crucial is that the membrane separation unit 17 is suitable for enriching the olefins present in the low-aldehyde mixture 15 in its permeate 19, while the inert alkanes become enriched in the retentate 18. Suitable membranes are described in the prior art cited above.

(13) The butanes present in the low-aldehyde mixture 15 originally come from the C.sub.4 mixture 5 and are additionally formed in a hydrogenating side reaction within the primary reaction zone 4 from butenes and hydrogen. The butanes are no longer directly amenable to the hydroformylation, and so they are discharged via the retentate 18 of the membrane separation unit and sent to a butane utilization 20. The butane utilization 20 which is not described in detail here comprises essentially a hydrogenation of the unsaturated compounds remaining and a purification. The butane thus obtained can be utilized as motor fuel or as heating fuel.

(14) Should the membrane separation unit 17 be fed directly from the vapour of the aldehyde removal stage 13, a portion of the retentate is fed to the top condenser (not shown) of the distillation column utilized as the aldehyde removal stage. The portion of the retentate branched off then corresponds to the column return stream.

(15) The alkenes not hydroformylated within the primary reaction zone 4 in the first pass ultimately accumulate in the permeate 19 of the membrane separation unit 17. If the transmembrane pressure is high enough, the permeate virtually evaporates on exit from the membrane. Should the permeate 19 not yet have evaporated completely, it can be evaporated by means of an optional evaporator 21. The evaporator 21 is operated with heat from the heat exchanger 10 in order to save energy. Beyond the evaporator 21 or earlier, the permeate 19 is gaseous. In this state, it is transferred into a secondary reaction zone 22 and subjected to a secondary hydroformylation therein over an SILP catalyst system. The secondary hydroformylation also requires synthesis gas. If this is not present to a sufficient degree in the permeate 19, additional synthesis gas 23 is metered in. The secondary hydroformylation in the secondary reaction zone 22 is effected in the presence of an SILP catalyst system in a manner known per se as described in WO2012041846A1. The reaction output 24 from the secondary reaction zone 22 is likewise gaseous. It is cooled in a cooler 25, and is partly liquefied again. Synthesis gas 26 which outgases in the process can be recycled into the secondary reaction zone 22. The cooled reaction output 24 from the secondary hydroformylation is finally conducted back into the aldehyde removal stage 13. The C.sub.5 aldehydes formed in the SILP hydroformylation are therefore removed in the same aldehyde removal stage 13 as the pentanals which are formed in the primary hydroformylation in the first complex component 1. The second stage in the second complex component 2 thus does not need any dedicated aldehyde removal stage.

(16) In a preferred development of the invention, the second complex component 2 comprising essentially the membrane separation unit 17 and the secondary reaction zone 22 is an extension of an existing gas recycle plant 1.

(17) A particular advantage can be achieved by the invention when a C.sub.4 hydroformylation 1 is being operated alongside a C.sub.3 hydroformylation 3 within an integrated site. In a preferred development of the invention, it is possible to supplement the C.sub.3 oxo process plant 3 and the C.sub.4 oxo process plant 1 with an SILP hydroformylation 2 which can optionally be combined with the C4 oxo process plant 1 and the C3 oxo process plant 3. In this way, the plant complex 0 shown in FIG. 2 comprising three complex components 1, 2, 3 is obtained.

(18) Depending on the product quality of the C.sub.4 mixture 5 used for the first complex component and the C.sub.3 mixture 27 used for the third complex component 3, the SILP complex 2 is coupled either to the C.sub.4 oxo process plant 1 or to the C.sub.3 oxo process plant 3. In that case, the recycling from the SILP process is effected into the C.sub.5 aldehyde removal stage 13 or the C.sub.4 aldehyde removal stage 28.

(19) In this way, the three-part plant complex from FIG. 2 can be used to react to different product qualities of the mixtures 5, 27 provided or the particular demand for butanal or pentanal.

(20) FIG. 3 shows a further embodiment of the invention in which the second complex component 2 is arranged within the first complex component 1, namely upstream of the heat exchanger/condenser combination 10 in which the partial condensation of the cycle gas 8 is effected. The membrane separation unit 17 is charged directly with the cycle gas 8 drawn off fresh from the primary hydroformylation. Alkenes present in the cycle gas 8 become enriched in the permeate 19 of the membrane separation unit 17 and are fed to the SILP-based secondary reaction zone 22 in order to be converted therein. The non-hydroformylatable alkanes collect preferentially in the retentate 18 of the membrane separation unit 17 and are discharged from the cycle gas in the direction of the aldehyde removal stage 13. This reduces the burden on the cycle gas compressor 9.

(21) The reaction output 24 from the secondary hydroformylation 22 is fed to the heat exchanger/condenser combination 10, such that the workup of the output from the two hydroformylations 4, 22 is effected together in the aldehyde removal stage 13.

(22) The advantage of this configuration of the invention over the variant shown in FIG. 1 is that it is possible to dispense with up to two heat exchangers. The disadvantage is the greater volume flow rate through the SILP stage, such that the dimensions of the membrane separation unit 17 and the secondary reaction zone 22 have to be increased correspondingly. The ultimate decision is made via a consideration of economic viability in relation to the preferred process variant.

LIST OF REFERENCE SYMBOLS

(23) 0 plant complex 1 first complex component (C.sub.4 oxo process plant) 2 second complex component (SILP plant) 3 third complex component (C.sub.3 oxo process plant) 4 primary reaction zone 5 C.sub.4 mixture 6 synthesis gas 7 catalyst 8 cycle gas 9 cycle gas compressor 10 heat exchanger/condenser combination 11 condensate 12 uncondensed constituents of the cycle gas 13 (C.sub.5) aldehyde removal stage 14 aldehyde-rich mixture 15 low-aldehyde mixture 16 aldol condensation 17 membrane separation unit 18 retentate 19 permeate 20 butane utilization 21 evaporator 22 secondary reaction zone 23 additional synthesis gas 24 reaction output from the secondary hydroformylation 25 cooler 26 outgassing synthesis gas 27 C.sub.3 mixture 28 C.sub.4 aldehyde removal stage