PROCESS FOR ISOLATING PURE 2-ETHYLHEXYL ACRYLATE OR PURE 2-PROPYLHEPTYL ACRYLATE FROM THE CORRESPONDING CRUDE ALKYL ACRYLATE BY DISTILLATION

Abstract

Process for isolating pure 2-ethylhexyl acrylate or pure 2-propylheptyl acrylate from the corresponding crude alkyl acrylate by distillation, wherein the process is carried out in a dividing wall column (1) which has separation-active internals and vaporizer (7) and in which a dividing wall (8) is arranged in the longitudinal direction of the column to form an upper joint column region (9), a lower joint column region (14), an inflow section (10, 12) having a side feed point (2) and an offtake section (11, 13) having a side offtake point (3), the column has a number of theoretical plates in the range from 10 to 60, where the number of theoretical plates of the dividing wall column (1) relates to the sum of the theoretical plates in the joint upper column region (9), the joint lower column region (14) and the inflow section (10, 12), the side feed point (2) for the corresponding crude alkyl acrylate is arranged at a theoretical plate in the region commencing at least two theoretical plates above the bottommost theoretical plate and ending at least two theoretical plates below the uppermost theoretical plate, the side offtake point (3) for the pure 2-ethylhexyl acrylate or pure 2-propylheptyl acrylate is arranged at a theoretical plate in the region commencing at least two theoretical plates above the bottommost theoretical plate and ending at least two theoretical plates below the uppermost theoretical plate and the dividing wall (8) is arranged in the column in the region commencing at least one theoretical plate above the bottommost theoretical plate and ending at least one theoretical plate below the uppermost theoretical plate, where the ratio of amount of liquid at the upper end of the dividing wall (8) going to the enrichment section (10) and the stripping section (11) of the column is set in the range from 1:0.2 to 1:5.

Claims

1-24. (canceled)

25. A process for isolating pure 2-ethylhexyl acrylate or pure 2-propylheptyl acrylate from the corresponding crude alkyl acrylate by distillation, the process comprising carrying out the isolation in a dividing wall column which has separation-active internals and vaporizer and in which a dividing wall is arranged in the longitudinal direction of the column to form an upper joint column region, a lower joint column region, an inflow section having a side feed point and an offtake section having a side offtake point, the column has a number of theoretical plates in the range from 10 to 60, where the number of theoretical plates of the dividing wall column relates to the sum of the theoretical plates in the joint upper column region, the joint lower column region and the inflow section, the side feed point for the corresponding crude alkyl acrylate is arranged at a theoretical plate in the region commencing at least two theoretical plates above the bottommost theoretical plate and ending at least two theoretical plates below the uppermost theoretical plate, the side offtake point for the pure 2-ethylhexyl or pure 2-propylheptyl acrylate is arranged at a theoretical plate in the region commencing at least two theoretical plates above the bottommost theoretical plate and ending at least two theoretical plates below the uppermost theoretical plate and the dividing wall is arranged in the column in the region commencing at least one theoretical plate above the bottommost theoretical plate and ending at least one theoretical plate below the uppermost theoretical plate, where the ratio of amount of liquid at the upper end of the dividing wall going to the enrichment section and the stripping section of the column is set in the range from 1:0.2 to 1:5 and the ratio of amounts of the vapor streams at the lower end of the dividing wall going to the stripping section and the enrichment section of the column is set in the range from 1:0.5 to 1:2.0.

26. The process according to claim 25, wherein the side feed point for the corresponding crude alkyl acrylate is arranged at a theoretical plate in the region commencing at least four theoretical plates above the bottommost theoretical plate and ending at least four theoretical plates below the uppermost theoretical plate, the side offtake point for the pure 2-ethylhexyl acrylate or pure 2-propylheptyl acrylate is arranged at a theoretical plate in the region commencing at least four theoretical plates above the bottommost theoretical plate and ending at least four theoretical plates below the uppermost theoretical plate and the dividing wall in the column is arranged in the region commencing at least two theoretical plates above the bottommost theoretical plate and ending at least two theoretical plates below the uppermost theoretical plate.

27. The process according to claim 25, wherein the column has a number of theoretical plates in the range from 15 to 30, the side feed point for the corresponding crude alkyl acrylate is arranged at a theoretical plate in the region commencing at least eight theoretical plates above the bottommost theoretical plate and ending at least six theoretical plates below the uppermost theoretical plate, the side offtake point for the pure 2-ethylhexyl acrylate or pure 2-propylheptyl acrylate is arranged at a theoretical plate in the region commencing at least five theoretical plates above the lowermost theoretical plate and ending at least eight theoretical plates below the uppermost theoretical plate and the dividing wall in the column is arranged in the region commencing at least three theoretical plates above the bottommost theoretical plate and ending at least three theoretical plates below the uppermost theoretical plate.

28. The process according to claim 25, wherein the opposite side offtake point is located at least one theoretical plate below the side feed point, where in the case of different numbers of theoretical plates in the offtake section and the inflow section, the side having the greatest total number of theoretical plates in the region of the dividing wall is employed for counting the number of theoretical plates for determining the relative height position of feed point and offtake point.

29. The process according to claim 25, wherein random packing elements, ordered packing and/or trays are provided as separation-active internals.

30. The process according to claim 29, wherein dual-flow trays are used as trays.

31. The process according to claim 30, wherein the dual-flow trays on the inflow side and offtake side have different opening ratios for setting the optimal gas distribution over the two sides of the dividing wall.

32. The process according to claim 25, wherein the residence time in the vaporizer and the associated piping system is limited to from 1 to 60 minutes.

33. The process according to claim 25, wherein the ratio of amounts of liquid at the upper end of the dividing wall going to the enrichment section and the stripping section of the column is set in the range from 1:0.5 to 1:2.

34. The process according to claim 25, wherein the ratio of amounts of the vapor streams at the lower end of the dividing wall going to the stripping section and the enrichment section of the column is set in the range from 1:0.9 to 1:1.5.

35. The process according to claim 25, wherein the pressure at the top of the column is in the range from 10 mbar to 5 bar.

36. The process according to claim 25, wherein there is temperature regulation in the upper joint column region, by means of a temperature signal below the uppermost theoretical plate, which utilizes the distillate flow, the reflux ratio or the amount of reflux as manipulated variable.

37. The process according to claim 25, wherein there is temperature regulation in the lower joint column region, by means of a temperature signal above the bottommost theoretical plate, which utilizes the amount taken off at the bottom as manipulated variable.

38. The process according to claim 25, wherein there is level regulation at the bottom of the column which utilizes the amount taken off at the side as manipulated variable.

39. The process according to claim 25, wherein the ratio of the cross-sectional areas of the region of the offtake section to the region of the inflow section is from 4:1 to 1:4.

40. The process according to claim 25, wherein the ratio of the cross-sectional areas of the region of the offtake section to the region of the inflow section is from 1.5:1 to 1:1.5.

41. The process according to claim 25, for isolating pure 2-ethylhexyl acrylate from crude 2-ethylhexyl acrylate having a purity of 98.5% by weight by distillation.

42. The process according to claim 25, for isolating pure 2-propylheptyl acrylate from crude 2-propylheptyl acrylate having a purity of 98.5% by weight by distillation.

43. The process according to claim 41, wherein the crude 2-ethylhexyl acrylate has the following composition: from 40 to 99% by weight of 2-ethylhexyl acrylate, from 0.1 to 10% by weight of 2-ethylhexanol, from 0.1 to 10% by weight of relatively high boilers (relative to 2-ethylhexyl acrylate), from 0.1 to 10% by weight of further low boilers (relative to 2-ethylhexyl acrylate).

44. The process according to claim 42, wherein the crude 2-propylheptyl acrylate has the following composition: from 40 to 99% by weight of 2-propylheptyl acrylate, from 0.1 to 10% by weight of 2-propylheptanol, from 0.1 to 10% by weight of relatively high boilers (relative to 2-propylheptyl acrylate), from 0.1 to 10% by weight of further low boilers (relative to 2-propylheptyl acrylate).

45. The process according to claim 25, wherein a stabilizer 1 is introduced into the enrichment section of the inflow section.

46. The process according to claim 45, wherein the stabilizer 1 is phenothiazine (PTZ).

47. The process according to claim 25, wherein a stabilizer 2 is introduced into the container which collects the condensate and/or into the conduit of a quenching circuit, where this is a liquid return stream of part of the condensate into the condenser, and/or at the top of the condenser.

48. The process according to claim 47, wherein the stabilizer 2 is p-methoxyphenol (MeHQ).

Description

EXAMPLES

[0065] The modes of operation are presented with the aid of data from a thermodynamic simulation of an overall plant for preparing 2-ethylhexyl acrylate.

[0066] The thermodynamic simulation of the process was carried out using the software Aspen Plus (Aspen for short). Aspen is comprehensive simulation software which is used for the modeling, simulation and optimization of chemical processes and plants in industry. Aspen has comprehensive modeling data banks for modeling the basic operations and also materials data banks for the materials properties of many different substances. The properties of mixtures are calculated by Aspen by means of various thermodynamic models from the materials data of the pure substances.

Example 1

[0067] (Ratio of amount of liquid at the upper end of the dividing wall (8), enrichment section (10): stripping section (11)=1:2 and

[0068] ratio of amount of the vapor streams at the lower end of the dividing wall (8), stripping section (12): enrichment section (13)=1:1)

[0069] A crude 2-ethylhexyl acrylate stream of 19 180 kg/h having a temperature of 145 C. was fed in in liquid form at the 14th theoretical plate of a dividing wall column (1) having a total of 22 theoretical plates. The crude 2-ethylhexyl acrylate had the following composition:

2-Ethylhexyl acrylate: 96.3% by weight
2-Ethylhexanol: 2.5% by weight
Di-2-ethylhexyl ether: 0.2% by weight
2-Ethylhexyl acetate: 0.3% by weight
2-Ethylhexyloxy ester: 0.5% by weight

[0070] Further relatively high boilers (relative to 2-ethylhexyl acrylate): balance

[0071] The dividing wall (8) extended from the 4th to the 17th theoretical plate. The side offtake (3) was located at the 6th theoretical plate. The column was operated at a pressure at the top of 22 mbar and a pressure at the bottom of 43 mbar.

[0072] At the top of the column condensation was carried out at a temperature of 26 C. A gaseous low boiler-comprising stream (19) of 5 kg/h was taken off from the condenser (6). A substream (4) of 566 kg/h was taken off from the condensed stream. The high-boiling impurities (5) were taken off at the bottom of the column at a flow rate of 1396 kg/h and a temperature of 122 C. At the side offtake, the desired product pure 2-ethylhexyl acrylate was obtained in liquid form at a temperature of 117 C. in an amount of 17 213 kg/h.

[0073] The side offtake stream (3) had the following composition:

2-Ethylhexyl acrylate: 99.98% by weight
2-Ethylhexanol: 0.05% by weight
Di-2-ethylhexyl ether: 62 ppm by weight
2-Ethylhexyl acetate: 855 ppm by weight
2-Ethylhexyloxy ester: <0.01% by weight

[0074] Further relatively high boilers (relative to 2-ethylhexyl acrylate): balance

[0075] The minimum content of acrylate of >99.5% by weight and the commercial specifications for the secondary components 2-ethylhexyl acetate at 1000 ppm and for di-2-ethylhexyl ether at 100 ppm are adhered to.

[0076] The distillation yield for 2-ethylhexyl acrylate was more than 93%.

[0077] The ratio of amounts of liquid for the liquid at the upper end of the dividing wall (8), enrichment section (10): stripping section (11), was 1:2. At the lower end of the dividing wall (8), the amounts of vapor stream, stripping section (12): enrichment section (13), were divided in the ratio 1:1. The heating power of the vaporizer was 2175 kW.

[0078] The process of the invention enabled the distillation of crude 2-ethylhexyl acrylate to give pure 2-ethylhexyl acrylate to be carried out, for example, at an annual capacity of 130 000 metric tons while adhering to the required specifications with a capital cost saving of 25% and an energy cost saving of 32% compared to a conventional two-stage distillation process.

Comparative Example 1

[0079] (Ratio of amount of liquid at the upper end of the dividing wall (8), enrichment section (10): stripping section (11)=1:7 and

[0080] ratio of amount of vapor streams at the lower end of the dividing wall (8), stripping section (12): enrichment section (13)=1:1)

[0081] A crude 2-ethylhexyl acrylate stream of 19 180 kg/h having a temperature of 145 C. was fed in in liquid form at the 14th theoretical plate of a dividing wall column (1) having a total of 22 theoretical plates. The crude 2-ethylhexyl acrylate had the following composition:

2-ethylhexyl acrylate: 96.3% by weight
2-ethylhexanol: 2.5% by weight
Di-2-ethylhexyl ether: 0.2% by weight
2-ethylhexyl acetate: 0.3% by weight
2-ethylhexyloxy ester: 0.5% by weight

[0082] Further relatively high boilers (relative to 2-ethylhexyl acrylate): balance

[0083] The dividing wall (8) extended from the 4th to the 17th theoretical plate. The side offtake (3) was located at the 6th theoretical plate. The column was operated at a pressure at the top of 22 mbar and a pressure at the bottom of 43 mbar.

[0084] At the top of the column, condensation was carried out at a temperature of 26 C. A gaseous low boiler-comprising stream (19) of 5 kg/h was taken off from the condenser (6). A substream (4) of 123 kg/h was taken off from the condensed stream. The high-boiling impurities (5) were taken off at the bottom of the column at a flow rate of 1838 kg/h and a temperature of 122 C. At the side offtake, the desired product pure 2-ethylhexyl acrylate was obtained in liquid form at a temperature of 116 C. in an amount of 17 213 kg/h.

[0085] The side offtake stream (3) had the following composition:

2-Ethylhexyl acrylate: 97.61% by weight
2-Ethylhexanol: 2.06% by weight
Di-2-ethylhexyl ether: 26 ppm by weight
2-Ethylhexyl acetate: 3312 ppm by weight
2-Ethylhexyloxy ester: <0.01% by weight

[0086] Further relatively high boilers (relative to 2-ethylhexyl acrylate): balance

[0087] The minimum content of acrylate of >99.5% by weight and the commercial specification for the secondary component 2-ethylhexyl acrylate at 1000 ppm are not adhered to.

[0088] The distillation yield for 2-ethylhexyl acrylate was more than 90%.

[0089] The ratio of amounts of liquid for the liquid at the upper end of the dividing wall (8), enrichment section (10): stripping section (11), was 1:7. At the lower end of the dividing wall (8), the amounts of vapor stream, stripping section (12): enrichment section (13), were divided in the ratio 1:1. The heating power of the vaporizer was 2875 kW.

Comparative Example 2

[0090] (Ratio of amount of liquid at the upper end of the dividing wall (8), reinforcement section (10): stripping section (11)=1:2 and

[0091] ratio of amounts of the vapor streams at the lower end of the dividing wall (8), stripping section (12): enrichment section (13)=3:1)

[0092] A crude 2-ethylhexyl acrylate stream of 19 180 kg/h having a temperature of 145 C. was fed in in liquid form at the 14th theoretical plate of a dividing wall column (1) having a total of 22 theoretical plates. The crude 2-ethylhexyl acrylate had the following composition:

2-Ethylhexyl acrylate: 96.3% by weight
2-Ethylhexanol: 2.5% by weight
Di-2-ethylhexyl ether: 0.2% by weight
2-Ethylhexyl acetate: 0.3% by weight
2-Ethylhexyloxy ester: 0.5% by weight

[0093] Further relatively high boilers (relative to 2-ethylhexyl acrylate): balance

[0094] The dividing wall (8) extended from the 4th to the 17th theoretical plate. The side offtake (3) was located at the 6th theoretical plate. The column was operated at a pressure at the top of 22 mbar and a pressure at the bottom of 43 mbar.

[0095] At the top of the column, condensation was carried out at a temperature of 26 C. A gaseous low boiler-comprising stream (19) of 5 kg/h was taken off from the condenser (6). A substream (4) of 498 kg/h was taken off from the condensed stream. The high-boiling impurities (5) were taken off at the bottom of the column at a flow rate of 1463 kg/h and a temperature of 122 C. At the side offtake, the desired product pure 2-ethylhexyl acrylate was obtained in liquid form at a temperature of 117 C. in an amount of 17 213 kg/h.

[0096] The side offtake stream (3) had the following composition:

2-Ethylhexyl acrylate: 99.49% by weight
2-Ethylhexanol: 0.39% by weight
Di-2-ethylhexyl ether: 121 ppm by weight
2-Ethylhexyl acetate: 1039 ppm by weight
2-Ethylhexyloxy ester: <0.01 ppm by weight

[0097] Further relatively high boilers (relative to 2-ethylhexyl acrylate): balance

[0098] The minimum content of acrylate of >99.5% by weight and the commercial specifications for the secondary components 2-ethylhexyl acetate at 1000 ppm and for di-2-ethylhexyl ether at 100 ppm are not adhered to.

[0099] The distillation yield for 2-ethylhexyl acrylate was more than 92%.

[0100] The ratio of amounts of liquid for the liquid at the upper end of the dividing wall (8), enrichment section (10): stripping section (11), was 1:2. At the lower end of the dividing wall (8), the amounts of vapor stream, stripping section (12): enrichment section (13), were divided in the ratio 3:1. The heating power of the vaporizer was 2175 kW.