METHOD FOR PROCESSING BENZENE POLYCARBOXYLIC ACID ESTERS AND USE OF SAME TO PRODUCE CYCLOHEXANE POLYCARBOXYLIC ACID ESTERS

Abstract

The present invention relates to a process for purifying benzenepolycarboxylic esters and for preparing cyclohexanepolycarboxylic esters by hydrogenating the purified benzenepolycarboxylic esters. The invention further relates to benzenepolycarboxylic esters and cyclohexanepolycarboxylic esters having a small proportion of by-products, especially of dialkyl ethers, and especially to diisononyl cyclohexane-1,2-dicarboxylate having a small proportion of diisononyl ether. The invention also relates to the use of the cyclohexanepolycarboxylic esters as plasticizers, especially in products intended for human contact, such as children's toys, food packaging and medical articles.

Claims

1.-15. (canceled)

16. A process for workup of a crude ester from the esterification of a benzenepolycarboxylic acid with at least one C.sub.4-C.sub.12 monoalkanol, wherein the crude ester additionally comprises at least one di-(C.sub.4-C.sub.12-alkyl) ether from the etherification of the at least one C.sub.4-C.sub.12 monoalkanol, optionally the at least one C.sub.4-C.sub.12 monoalkanol, and optionally water, in which the crude ester is subjected to a thermal purification in at least one mass transfer apparatus by introducing a steam-containing gas stream in the region of the bottom of the mass transfer apparatus to obtain a bottom product enriched in the at least one benzenepolycarboxylic ester and depleted of the at least one di-(C.sub.4-C.sub.12-alkyl) ether and a vapor enriched in the at least one di-(C.sub.4-C.sub.12-alkyl) ether; wherein the vapor is at least partly condensed, and the condensate is separated into an aqueous phase and an organic phase comprising di-(C.sub.4-C.sub.12-alkyl) ether and C.sub.4-C.sub.12 monoalkanol, a portion of the organic phase is recycled as reflux stream into the thermal purification of the crude ester, and another portion of the organic phase is discharged.

17. The process according to claim 16, wherein the crude ester used for workup comprises 91% to 99.8% by weight of at least one ester of a benzenepolycarboxylic acid with at least one C.sub.4-C.sub.12 monoalkanol, 0.05% to 1% by weight of at least one di-(C.sub.4-C.sub.12-alkyl) ether, 0.1% to 5% by weight of at least one C.sub.4-C.sub.12 monoalkanol, and 0.05% to 3% by weight of water.

18. The process according to claim 16, wherein thermal purification is accomplished using at least one column having a side feed for the crude ester, a rectifying section above the feed point for the crude ester, a reflux feed for at least a portion of the condensed vapor above the rectifying section, a feed for the steam-containing gas stream in the region of the bottom of the column.

19. The process according to claim 18, wherein the rectifying section above the feed point for the crude ester has 0 to 10 theoretical plates.

20. The process according to claim 16, wherein a third portion of the organic phase is recycled into the esterification of the benzenepolycarboxylic acid with the at least one C.sub.4-C.sub.12 monoalkanol.

21. The process according to claim 16, wherein the discharge of a portion of the organic phase is batchwise or continuous.

22. The process according to claim 16, wherein the content in the bottom product of di-(C.sub.4-C.sub.12-alkyl) ether is controlled by implementing control interventions on at least one of the following manipulated variables: the mass flow of the reflux stream of the organic phase, the mass flow of the organic phase recycled into the esterification, the mass flow of the organic phase discharged.

23. The process according to claim 22, in which a target value for the content in the bottom product of di-(C.sub.4-C.sub.12-alkyl) ether and an upper and lower limit for the variance of the actual value from the target value are fixed, the actual value of the content in the bottom product of di-(C.sub.4-C.sub.12-alkyl) ether is determined, on attainment of the upper limit for the variance of the actual value from the target value, control interventions are implemented until the content in the bottom product of di-(C.sub.4-C.sub.12-alkyl) ether has fallen to the lower limit for the variance of the actual value from the target value.

24. The process according to claim 23, wherein the target value for the content in the bottom product of di-(C.sub.4-C.sub.12-alkyl) ether is not more than 1000 ppm by weight.

25. The process according to claim 16, wherein the vapor is at least partly condensed, the condensate is separated into an aqueous phase and an organic phase comprising di-(C.sub.4-C.sub.12-alkyl) ether and C.sub.4-C.sub.12 monoalkanol, at least a portion of the organic phase is subjected to a separation into a di-(C.sub.4-C.sub.12-alkyl) ether-enriched fraction and a C.sub.4-C.sub.12 monoalkanol-enriched fraction, and the di-(C.sub.4-C.sub.12-alkyl) ether-enriched fraction is partly or fully discharged.

26. The process according to claim 25, wherein a portion of the organic phase is subjected to a separation into a di-(C.sub.4-C.sub.12-alkyl) ether-enriched fraction and a C.sub.4-C.sub.12 monoalkanol-enriched fraction, and another portion of the organic phase is recycled as reflux stream into the thermal purification of the crude ester.

27. The process according to claim 25, wherein the C.sub.4-C.sub.12 monoalkanol-enriched fraction is partly or fully recycled as a reflux stream into the thermal purification of the crude ester.

28. The process according to claim 25, wherein the C.sub.4-C.sub.12 monoalkanol-enriched fraction is partly or fully recycled into the esterification of the benzenepolycarboxylic acid with the at least one C.sub.4-C.sub.12 monoalkanol.

29. A process for preparing a cyclohexanepolycarboxylic ester, in which i) a crude ester from the esterification of a benzenepolycarboxylic acid with at least one C.sub.4-C.sub.12 monoalkanol is provided, ii) the crude ester provided in step i) is subjected to a workup as defined in claim 16 to obtain a benzenepolycarboxylic ester depleted of di-(C.sub.4-C.sub.12-alkyl) ethers compared to the crude ester, iii) the benzenepolycarboxylic ester depleted of di-(C.sub.4-C.sub.12-alkyl) ethers which is obtained in step ii) is subjected to a hydrogenation with a hydrogen-containing gas in the presence of a hydrogenation catalyst.

30. The process according to claim 29, wherein the hydrogenation catalyst used in step iii) is selected from catalysts comprising, as active metal, at least one metal from transition group VIII of the Periodic Table of the Elements applied to a support, where 5% to 50% of the pore volume of the support in each case is formed by macropores having a pore diameter in the range from 50 nm to 10 000 nm and 50% to 95% of the pore volume of the support by mesopores having a pore diameter in the range from 2 to less than 50 nm, wherein the sum total of the pore volumes adds up to 100%, and eggshell catalysts comprising an active metal selected from ruthenium, rhodium, palladium, platinum and mixtures thereof, applied to a support material comprising silicon dioxide, where the pore volume of the support material is 0.6 to 1.0 mL/g, determined by Hg porosimetry, the BET surface area is 280 to 500 m.sup.2/g, and at least 90% of the pores present have a diameter of 6 to 12 nm.

31. The process according to claim 18, wherein the rectifying section above the feed point for the crude ester has 0 to 5 theoretical plates.

32. The process according to claim 18, wherein the rectifying section above the feed point for the crude ester has 0 to 2 theoretical plates.

33. The process according to claim 23, wherein the target value for the content in the bottom product of di-(C.sub.4-C.sub.12-alkyl) ether is not more than 800 ppm by weight.

34. The process according to claim 23, wherein the target value for the content in the bottom product of di-(C.sub.4-C.sub.12-alkyl) ether is not more than 600 ppm by weight.

35. The process according to claim 23, wherein the target value for the content in the bottom product of di-(C.sub.4-C.sub.12-alkyl) ether is not more than 500 ppm by weight.

Description

DESCRIPTION OF FIGURES

[0295] The invention is elucidated in detail hereinafter with reference to FIGS. 1 to 3, but without restricting the invention to the embodiments shown therein.

[0296] The following reference signs are used in the figures: [0297] A stripping section [0298] B vapor condenser [0299] D distillation column [0300] K condenser [0301] R rectification column [0302] S phase separation vessel [0303] V rectifying section [0304] 1 bottom product (ester) [0305] 2 steam-containing gas stream (steam) [0306] 3 feed (crude ester with alcohol, ether, water) [0307] 4 vapor [0308] 5 vapor condensate [0309] 6 aqueous phase [0310] 7 organic phase (ether, alcohol) [0311] 8 reflux of organic phase (ether, alcohol) [0312] 8′ reflux of alcohol condensate [0313] 9 discharge stream of organic phase (ether, alcohol) [0314] 9′ discharge stream of ether [0315] 10 substream of organic phase [0316] 11 alcohol-containing gas phase [0317] 12 alcohol condensate [0318] 13 condensate reflux [0319] 14 draw of alcohol condensate

[0320] FIG. 1 shows a preferred embodiment of the process of the invention with a vapor phase separation vessel.

[0321] FIG. 2 shows a further preferred embodiment of the process of the invention with an additional distillation column for removal of the vapor condensate.

[0322] FIG. 3 shows a likewise preferred embodiment of the process of the invention with an additional distillation column for separation of the vapor condensate in an alternative mode of connection to the embodiment shown in FIG. 2.

[0323] FIG. 4 shows the diisononyl ether content in the bottom product depending on the inlet temperature of the crude ester.

[0324] FIG. 5 shows an embodiment according to variant 2 of the process of the invention. Curve 2 shows that the organic phase obtained by phase separation from the condensed vapor is run at a constant rate (200 kg/h) as recycle stream to the top of the stripping column. Curve 3 shows the intervals in which the remaining amount of the organic phase is recycled into the ester synthesis or discharged. Curve 1 shows the diisononyl ether content in the bottom product.

[0325] FIG. 1 shows an embodiment of the process of the invention. In a rectification column R, a crude ester as feed 3 is fed in between stripping section A and rectifying section V. The crude ester consists essentially of one or more benzenepolycarboxylic ester(s), C.sub.4-C.sub.12monoalkanol(s), di-(C.sub.4-C.sub.12-alkyl) ether(s) and water. In the stripping section A, a steam-containing gas stream 2 (also referred to hereinafter as steam) is fed in in countercurrent from above the column bottom. Bottom product 1 is drawn off in the column bottom. The bottom product 1 consists essentially of benzenepolycarboxylic ester with a depleted proportion of di-(C.sub.4-C.sub.12-alkyl) ether, C.sub.4-C.sub.12 monoalkanol and water compared to the feed. The steam 2 flows through the stripping section A and then the rectifying section V, with passage of alcohol, ether and water from the feed 3 into the vapor phase 2. Vapor 4 is drawn off at the top of the column. The vapor 4 is a mixture comprising steam, di-(C.sub.4-C.sub.12-alkyl) ether and C.sub.4-C.sub.12 monoalkanol, and small amounts of benzenepolycarboxylic ester and further components may also be present. The vapor 4 is at least partly condensed in a vapor condenser B and fed as vapor condensate 5 to a phase separation vessel S. In the phase separation vessel S, an aqueous phase 6 comprising essentially water is drawn off in the lower region. Above that, an organic phase 7 comprising essentially di-(C.sub.4-C.sub.12-alkyl) ether and C.sub.4-C.sub.12 monoalkanol is drawn off. The organic phase 7 drawn off from the phase separation vessel S is divided into a discharge stream 9 and a condensate reflux stream 8. The condensate reflux stream 8 is fed to the top of the rectification column R above the rectifying section V, such that it is guided in countercurrent to the steam 2.

[0326] The aqueous phase 6 drawn off from the phase separation vessel S can suitably be disposed of or optionally recycled into the workup process. The discharge stream 9 may suitably be disposed of or sent to a suitable use.

[0327] FIG. 2 shows a further embodiment of the process of the invention. In the rectification column R, the crude ester as feed 3 is fed in between stripping section A and rectifying section V. In the stripping section A, steam 2 is fed in in countercurrent from above the column bottom. The bottom product 1 is drawn off in the column bottom. The steam 2 flows through the stripping section A and then the rectifying section V, with passage of alcohol, ether and water from the feed 3 into the vapor phase. The vapor 4 is drawn off at the top of the column. The vapor 4 is at least partly condensed in a vapor condenser B and fed as vapor condensate 5 to a phase separation vessel S. In the phase separation vessel S, the aqueous phase 6 is drawn off in the lower region. The aqueous phase 6 drawn off from the phase separation vessel S can suitably be disposed of or optionally recycled into the workup process.

[0328] In the phase separation vessel S, the organic phase 7 is drawn off via the aqueous phase 6. The organic phase 7 is divided into a reflux stream 8 and a substream 10. The reflux stream 8 is fed to the top of the rectification column R above the rectifying section V, such that it is guided in countercurrent to the steam 2.

[0329] The substream 10 is sent to a distillation column D above the bottom. In the bottom of the distillation column D, a discharge stream 9′ comprising essentially di-(C.sub.4-C.sub.12-alkyl) ether, C.sub.4-C.sub.12 monoalcohol and/or benzenepolycarboxylic ester is drawn off. The discharge stream 9′ may suitably be disposed of or sent to a suitable use.

[0330] At the top of the distillation column D, an alcohol-containing gas phase is drawn off and at least partly condensed in a condenser K. The alcohol-containing gas phase may, as well as C.sub.4-C.sub.12 monoalkanol, comprise small amounts of water and di-(C.sub.4-C.sub.12-alkyl) ether. A portion of the alcohol condensate 12 obtained is recycled as condensate reflux stream 13 to the top of the distillation column D. The remaining alcohol condensate is discharged as condensate draw stream 14 and may be partly or fully recycled into the esterification of the benzenepolycarboxylic acid with the at least one C.sub.4-C.sub.12 monoalkanol.

[0331] FIG. 3 shows a further embodiment of the process of the invention. This is an alternative mode of connection to the variant shown in FIG. 2 with distillative separation of the organic phase. In the rectification column R, the crude ester as feed 3 is fed in between stripping section A and rectifying section V. In the stripping section A, steam 2 is fed in in countercurrent from above the column bottom. The bottom product 1 is drawn off in the column bottom. The steam 2 flows through the stripping section A and then the rectifying section V, with passage of alcohol, ether and water from the feed 3 into the vapor phase. The vapor 4 is drawn off at the top of the column. The vapor 4 is at least partly condensed in a vapor condenser B and fed as vapor condensate 5 to a phase separation vessel S. In the phase separation vessel S, the aqueous phase 6 is drawn off in the lower region. The aqueous phase 6 drawn off from the phase separation vessel S can suitably be disposed of or optionally recycled into the workup process.

[0332] In the phase separation vessel S, the organic phase 7 is drawn off via the aqueous phase 6. The organic phase 7 is sent to a distillation column D above the bottom. In the bottom of the distillation column D, a discharge stream 9′ comprising essentially di-(C.sub.4-C.sub.12-alkyl) ether and possibly additions of water, C.sub.4-C.sub.12 monoalcohol and/or benzenepolycarboxylic ester is drawn off. The discharge stream 9′ may suitably be disposed of or sent to a suitable use.

[0333] At the top of the distillation column D, an alcohol-containing gas phase 11 is drawn off and at least partly condensed in a condenser K. The alcohol-containing gas phase may, as well as C.sub.4-C.sub.12 monoalkanol, comprise small amounts of water and di-(C.sub.4-C.sub.12-alkyl) ether. A portion of the alcohol condensate 12 obtained is recycled as condensate reflux stream 13 to the top of the distillation column D. A further portion of the remaining alcohol condensate 12 is fed as reflux stream 8′ to the top of the rectification column R above the rectifying section V, such that it is guided in countercurrent to the steam 2. The remaining portion of the alcohol condensate 12 is discharged as condensate draw stream 14 and may be partly or fully recycled into the esterification of the benzenepolycarboxylic acid with the at least one C.sub.4-C.sub.12 monoalkanol.

EXAMPLES

Example 1

[0334] Influence of Inlet Temperature of the Crude Ester into the Stripping Column

[0335] Into a rectification column (stripping column) according to FIG. 1 is fed, between the stripping section and rectifying section, a crude diisononyl phthalate as feed at a feed rate of 13 000 kg/h. The crude ester further comprises diisononanol, diisononyl ether and water. The stripping column is operated at a pressure of 50 mbar absolute. Above the column bottom, in countercurrent to the crude ester, steam is fed in at 4 bar and the crude ester is stripped with 3% by weight of steam, based on crude ester. The inlet temperature of the crude ester into the column is at first left constant at 185° C. and then increased in multiple steps to 195° C. At the top of the column, the vapor is drawn off, condensed and discharged. There is no recycling of condensed vapor to the top of the column. The diisononyl ether content in the bottom product is determined. FIG. 4 shows the diisononyl ether content in the bottom product depending on the inlet temperature of the crude ester. It shows that the diisononyl ether content in the bottom product can be distinctly reduced from about 600-800 ppm by weight to about 400 ppm by weight by increasing the inlet temperature of the crude ester into the column.

Example 2

Hydrogenation of Diisononyl Phthalate (DINP) to Diisononyl Cyclohexane-1,2-Dicarboxylate (DINCH)

[0336] The raw material used for the inventive hydrogenation 1 was diisononyl phthalate from a batch from example 1 in which the diisononyl ether content was 500 ppm by weight owing to the elevated stripping temperature. The hydrogenation V1 is a comparative experiment wherein the raw material used was diisononyl phthalate from a batch from example 1 wherein the ether concentration was 590 ppm by weight owing to the lower stripping temperature. The hydrogenation catalyst used in all experiments was a ruthenium catalyst on a macro/mesoporous alumina support prepared according to the catalyst preparation example on page 7 lines 36-47 of DE 19624485 A1. The ruthenium content of the catalyst was 0.5%.

[0337] The hydrogenations were conducted in a cascade of 3 reactors (internal diameter 1 m, length 20 m). The first reactor was operated as the main reactor with circulation, i.e. the discharge from the first reactor was partly recycled to the inlet of the first reactor. The last 2 reactors were operated as postreactors in straight pass. The reactors were each charged with 9000 kg of catalyst.

[0338] The hydrogenation was conducted with pure hydrogen. The feed was chosen such that the catalyst hourly space velocity in the main reactor (kg(diisononyl phthalate)/L(catalyst).Math.h) reaches the value specified in the table below. The recycle rate was chosen such that the superficial velocity in the main reactor has the values specified in table 1. The hydrogen was supplied in a pressure-regulated manner at the pressure specified in table 1. The reaction temperatures are likewise specified in table

TABLE-US-00002 TABLE 1 Hydrogenation experiments Pressure Main reactor Postreactor 1 Postreactor 2 Reactors No. A B C D A B C A B C [bar] V1 9.8 160 123 10 3.0 52 138 1.3 23 117 250 1 9.8 160 123 10 3.0 52 138 1.3 23 117 250 A) catalyst hourly space velocity: kg(diisononyl phthalate)/(L(catalyst) h) B) superficial velocity: m.sup.3(diisononyl phthalate)/(m.sup.2(reactor cross section) (h)) C) temperature [° C.] D) recycle rate: kg of hydrogenation product recycled/kg diisononyl phthalate

[0339] The analysis of the diisononyl phthalate used and of the diisononyl cyclohexane-1,2-dicarboxylate obtained was effected by the following GC method: [0340] Column: DB-1 30 m (100% dimethylpolysiloxane), ID 0.32 mm, FD 0.25 μm [0341] Detector: flame ionization detector (FID) [0342] Temperature program: starting temperature 80° C., hold time 1 min, heating at 5° C./min to 300° C., hold time 15 min [0343] Injection volume: 0.2 μL [0344] Inlet temperature: 300° C. [0345] Detector temperature: 320° C. [0346] Retention times: [0347] Isononanol: 4-9.5 min [0348] Diisononyl cyclohexane-1,2-dicarboxylate (DINCH): 32.5-43 min

Tables 2a and 2b: Results of the Hydrogenation Experiments

[0349]

TABLE-US-00003 Diisononyl phthalate (DINP) Diisononyl cyclohexane-1,2-dicarboxylate (DINCH) Diisononyl ether DINCH Diisononyl ether Total of others No. [% by wt.].sup.a) [% by wt.] [% by wt.] [% by wt.] V1 0.059 99.84 0.113 0.047 1 0.050 99.82 0.082 0.098 .sup.a)determined as GC area %

TABLE-US-00004 Diisononyl cyclohexane-1,2-dicarboxylate (DINCH) Residual Pt/Co aromatics Water Acid number color (DINP) No. [% by wt.] [mg KOH/g] number [ppm] V1 0.019 0.03 3 4 1 0.013 0.01 4 2

[0350] The experiments show that, by the process of the invention, a diisononyl phthalate having a low content of diisononyl ether affords, through hydrogenation using a ruthenium catalyst on a macro/mesoporous alumina support, a diisononyl cyclohexane-1,2-dicarboxylate (DINCH) having a content of diisononyl ethers of not more than 0.1% by weight. The experiments likewise show that a diisononyl phthalate having an elevated content of diisononyl ethers, by means of the hydrogenation process of the invention, affords a diisononyl cyclohexane-1,2-dicarboxylate (DINCH) having an undesirably high content of diisononyl ethers of more than 0.1% by weight.

Example 3

[0351] Into the stripping column according to FIG. 1 is continuously fed a crude diisononyl phthalate as feed at a feed rate of 20 000 kg/h. The inlet temperature of the crude ester into the column is 185° C. The stripping column is operated at 50 mbar absolute. Above the column bottom, in countercurrent to the crude ester, steam is fed in at 4 bar and the crude ester is stripped with 3% by weight of steam, based on crude ester. The condensed vapors are separated in a phase separation vessel into an aqueous phase and an organic phase. The aqueous phase is disposed of in each case. Until day 8, the organic phase is also drawn off completely from the phase separation vessel as discharge stream. The continuous discharge of the condensed vapor reduces the concentration of diisononyl ether in the bottom product from 310 ppm by weight to 250 ppm by weight within 8 days. Correspondingly, there is also a decrease in the concentration of diisononyl ether in the organic phase. By contrast, the concentration of product of value (DINP) in the organic phase and the total amount of vapor (distillate) remain unchanged.

[0352] The implementation of a reflux stream of 200 kg/h of organic phase on days 28 and 46 and recycling of the remaining organic phase into the ester synthesis distinctly reduces the concentration of DINP in the organic phase. The total amount of vapor (distillate) also declines; there is simultaneously a slight increase in the amount of diisononyl ether in the organic phase and in the stripped bottom product. This behavior is reproducible.

TABLE-US-00005 TABLE 3 Results of the operating experiment Reflux rate Vapor to top of discharged or Distillate Low High Ether in column back to top and rate boilers.sup.a) Ethers boilers Isononanol DINP the product Day [kg/h] into synthesis [kg/h] % by wt. % by wt. % by wt. % by wt. % by wt. ppm by wt. 0 0 Disposal 171 1.4 3.3 0 71 23 310 1 0 Disposal 182 1.2 3 0 76 19 310 4 0 Disposal 183 0.9 2.56 0 77 19 280 5 0 Disposal 179 0.8 2.4 0 72 23 260 8 0 Disposal 179 0.9 2.24 0 77 20 250 28 200 Synthesis 165 1.1 4.3 0 87.5 5.8 350 42 0 Disposal 190 1 2.2 0 72.5 23.8 200 44 0 Disposal 188 1 2.2 0 72.4 23.8 300 46 200 Synthesis 150 1 3.6 0 89.5 4.8 320 49 0 Disposal 182 1.2 3.7 0 89.5 4.6 370 50 0 Disposal 200 0.9 2.5 0 73 22.6 280 .sup.a)primarily C.sub.9-alkene

Example 4

[0353] As described in example 3, a crude diisononyl phthalate is treated in a stripping column according to FIG. 1. A portion of the organic phase obtained by phase separation from the condensed vapor is run as recycle stream to the top of the stripping column (200 kg/h). The remaining amount of the organic phase is alternately recycled into the ester synthesis or discharged. By this method, the concentration of diisononyl ether in the bottom product can be controlled and kept at the desired content of 300 to 400 ppm by weight. It is thus possible to achieve low ether contents in the product and simultaneously to distinctly reduce the proportion of product of value (DINP) in the discharged vapor stream (see FIG. 5).

Example 5

Separation of Ether and Alcohol on the Laboratory Scale

[0354] An oil-heated 2 L jacketed vessel with stirrer and with a distillation column on top (diameter 30 mm, length 3.05 m, filled with 1.75 m of Sulzer DX and 1.3 m of Montz A3-1000 structured packing) was used. The column has a tops condenser, by means of which a defined reflux can be established, and which enables distillation under reduced pressure.

[0355] 1.3 kg of a mixture that comprised 5.36% by weight of water, 1.15% by weight of low boilers (nonenes, phthalic anhydride, phthalide, benzoic acid, nonyl benzoate), 84.5% by weight of isononanol, 3.5% by weight of diisononyl ether, 1.04% by weight of further medium boilers and 4.4% by weight of DINP was initially charged in the pot.

[0356] The distillation was conducted under a reduced pressure of 100 mbar; the supply of heat to the vessel and hence the distillation temperature was controlled via the pressure drop across the column. The reflux ratio was set to a value of 2, and the pressure drop across the column to 2.5 mbar.

[0357] The components of the mixture were distilled off successively in accordance with their boiling temperature. Samples of the distillate, each of 20 to 30 g, were taken over the duration of the experiment. A total of 23 samples were taken and analyzed by means of gas chromatography. The composition of the samples is shown in table 4. On attainment of a bottom temperature of 180° C., the distillation was ended. The residue in the vessel was analyzed by means of gas chromatography. Through the distillation, it is possible to concentrate the DINP/ether mixture from about 7.9% to about 84%. Distillates isolated were isononanol/water mixtures having an alcohol concentration of more than 95%. Such an alcohol can be used for synthesis of DINP.

TABLE-US-00006 TABLE 4 Composition of the distillate samples and of the bottoms remaining at the end of the distillation Medium Diisononyl Medium Distillate Water Low boilers Isononanol boilers 1.sup.a) ether boilers 2.sup.b) DINP sample [% by wt.] [% by wt.] [% by wt.] [% by wt.] [% by wt.] [% by wt.] [% by wt.] 1 88.48 8.59 2.35 0.00 0.00 0.00 0.00 2 96.62 1.79 0.59 0.00 0.00 0.00 1.00 3 99.90 0.07 0.02 0.00 0.00 0.00 0.01 4 46.39 22.36 31.87 0.04 0.00 0.00 0.30 5 1.14 15.01 83.77 0.07 0.00 0.00 0.01 6 1.83 3.72 94.11 0.17 0.00 0.00 0.16 7 1.19 1.39 97.17 0.16 0.00 0.00 0.10 8 1.42 0.46 97.77 0.15 0.00 0.00 0.21 9 0.89 0.05 98.38 0.21 0.00 0.01 0.46 10 0.78 0.04 98.53 0.65 0.00 0.00 0.00 11 1.72 0.03 96.31 1.94 0.00 0.00 0.00 12 1.00 0.02 96.62 2.28 0.00 0.00 0.00 13 0.40 0.01 96.91 2.69 0.00 0.00 0.00 14 0.14 0.01 96.84 3.01 0.00 0.00 0.00 15 0.06 0.00 99.26 0.68 0.00 0.00 0.00 16 0.03 0.00 99.46 0.50 0.00 0.00 0.00 17 0.03 0.00 99.59 0.39 0.00 0.00 0.00 18 0.03 0.00 99.64 0.33 0.00 0.00 0.00 19 0.04 0.01 99.40 0.55 0.00 0.00 0.01 20 0.04 0.00 99.69 0.19 0.00 0.00 0.06 21 0.02 0.00 99.86 0.11 0.00 0.00 0.00 22 0.02 0.00 99.89 0.08 0.00 0.00 0.02 23 0.04 0.01 99.86 0.09 0.00 0.00 0.01 Bottoms 0.01 0 6.25 8.44 34.92 0.61 49.75 .sup.a)lower-boiling than diisononyl ether .sup.b)higher-boiling than diisononyl ether