PROCESS FOR ISOLATING PURE TERT-BUTYL (METH)ACRYLATE FROM CRUDE TERT-BUTYL (METH)ACRYLATE BY DISTILLATION

Abstract

Process for isolating pure tert-butyl (meth)acrylate from crude tert-butyl (meth)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 20 to 80, 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 crude tert-butyl (meth)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 tert-butyl (meth)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. A process for isolating pure tert-butyl (meth)acrylate from crude tert-butyl (meth)acrylate by distillation, wherein the process is carried out in a dividing wall column which has separation-active internals and a vaporizer and in which a dividing wall is arranged in a longitudinal direction of the dividing wall 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 dividing wall column has a number of theoretical plates in a range of from 20 to 80, where the number of theoretical plates of the dividing wall column relates to a 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 crude tert-butyl (meth)acrylate is arranged at a theoretical plate in a region commencing at least two theoretical plates above a bottommost theoretical plate and ending at least two theoretical plates below an uppermost theoretical plate, the side offtake point for the pure tert-butyl (meth)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 dividing wall column in a 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 a ratio of amounts of liquid at an upper end of the dividing wall going to an enrichment section and a first stripping section of the dividing wall column is set in a range of from 1:0.2 to 1:5, and a ratio of amounts of vapor streams at a lower end of the dividing wall going to a second stripping section and an enrichment section of the dividing wall column is set in a range of from 1:0.5 to 1:2.0.

2. The process of claim 1, wherein the side feed point for the crude tert-butyl (meth)acrylate is arranged at a theoretical plate in a region commencing at least five theoretical plates above the bottommost theoretical plate and ending at least five theoretical plates below the uppermost theoretical plate, the side offtake point for the pure tert-butyl (meth)acrylate is arranged at a theoretical plate in the region commencing at least five theoretical plates above the bottommost theoretical plate and ending at least five theoretical plates below the uppermost theoretical plate and the dividing wall in the dividing wall column is arranged in a region commencing at least four theoretical plates above the bottommost theoretical plate and ending at least four theoretical plates below the uppermost theoretical plate.

3. The process of claim 1, wherein the dividing wall column has a number of theoretical plates in a range of from 30 to 40, the side feed point for the crude tert-butyl (meth)acrylate is arranged at a theoretical plate in a region commencing at least 12 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 tert-butyl (meth)acrylate is arranged at a theoretical plate in a region commencing at least 10 theoretical plates above the lowermost theoretical plate and ending at least 10 theoretical plates below the uppermost theoretical plate and the dividing wall in the dividing wall column is arranged in a region commencing at least five theoretical plates above the bottommost theoretical plate and ending at least five theoretical plates below the uppermost theoretical plate.

4. The process of claim 1, wherein the 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, a side having a greatest total number of theoretical plates in the region of the dividing wall is employed for counting the number of theoretical plates for determining a relative height position of feed point and offtake point.

5. The process of claim 1, wherein random packing elements, ordered packing and/or trays are provided as separation-active internals.

6. The process of claim 5, wherein dual-flow trays are used as trays.

7. The process of claim 6, wherein there are dual-flow trays on the inflow side and offtake side, and the dual-flow trays on the inflow side and offtake side have different opening ratios for setting an optimal gas distribution over the two sides of the dividing wall.

8. The process of claim 1, wherein a residence time in the vaporizer and an associated piping system is limited to from 1 to 60 minutes.

9. The process of claim 1, 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 dividing wall column is set in the range from 1:0.5 to 1:2.

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

11. The process of claim 1, wherein a pressure at a top of the dividing wall column is in a range of from 20 mbar to 5 bar.

12. The process of claim 1, wherein a temperature signal below the uppermost theoretical plate, which utilizes a distillate flow, a reflux ratio or an amount of reflux as a manipulated variable, is used to regulate temperature in the upper joint column region.

13. The process of claim 1, wherein a temperature signal above the bottommost theoretical plate, which utilizes an amount taken off at a bottom of the dividing wall column as a manipulated variable, is used to regulate temperature in the lower joint column region.

14. The process of claim 1, wherein there is level regulation at a bottom of the dividing wall column which utilizes an amount taken off at a side of the dividing wall column as a manipulated variable.

15. The process of claim 1, wherein a ratio of cross-sectional areas of a region of the offtake section and a region of the inflow section is from 4:1 to 1:4.

16. The process of claim 1, wherein a ratio of cross-sectional areas of a region of the offtake section and a region of the inflow section is from 1.5:1 to 1:1.5.

17. The process of claim 1, comprising isolating pure tert-butyl (meth)acrylate having a purity of 98.5% by weight by distillation.

18. The process of claim 1, wherein the tert-butyl (meth)acrylate is tert-butyl acrylate.

19. The process of claim 1, wherein the tert-butyl (meth)acrylate is tert-butyl methacrylate.

20. The process of claim 18, wherein the crude tert-butyl acrylate has the following composition: from 40 to 90% by weight of tert-butyl acrylate, from 0.1 to 50% by weight of acrylic acid, from 0.1 to 5% by weight of isobutene, from 0.1 to 5% by weight of diisobutene, from 0.1 to 5% by weight of relatively high boilers (relative to tert-butyl acrylate), from 0.1 to 5% by weight of further low boilers (relative to tert-butyl acrylate).

21. The process of claim 19, wherein the crude tert-butyl methacrylate has the following composition: from 40 to 90% by weight of tert-butyl methacrylate, from 0.1 to 50% by weight of methacrylic acid, from 0.1 to 5% by weight of isobutene, from 0.1 to 5% by weight of diisobutene, from 0.1 to 5% by weight of relatively high boilers (relative to tert-butyl methacrylate), from 0.1 to 5% by weight of further low boilers (relative to tert-butyl methacrylate).

22. The process of claim 1, wherein a stabilizer is introduced into the enrichment section of the inflow section.

23. The process of claim 22, wherein the stabilizer is phenothiazine (PTZ).

24. The process of claim 1, wherein a stabilizer is introduced into a container which collects a condensate and/or into a conduit of a quenching circuit, where this is a liquid return stream of part of the condensate into a condenser, and/or at a top of the condenser.

25. The process of claim 24, wherein the stabilizer is p-methoxyphenol (MeHQ).

Description

EXAMPLES

[0069] The modes of operation are presented with the aid of data from a thermodynamic simulation of an overall plant for preparing tert-butyl acrylate.

[0070] 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

[0071] (Ratio of amount of liquid at the upper end of the dividing wall (8), enrichment section (10):stripping section (11)=1:3.4 and

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

[0072] A crude tert-butyl acrylate stream of 2424 kg/h having a temperature of 24 C. was fed in in liquid form at the 20th theoretical plate of a dividing wall column (1) having a total of 38 theoretical plates. The crude tert-butyl acrylate had the following composition:

tert-Butyl acrylate: 68.3% by weight
Acrylic acid: 27.8% by weight
Isobutene: 1.0% by weight
Diisobutene: 1.4% by weight
tert-Butyl acetate: 0.1% by weight

[0073] Further relatively high boilers (relative to tert-butyl acrylate): balance

[0074] The dividing wall (8) extended from the 8th to the 28th theoretical plate. The side offtake (3) was located at the 17th theoretical plate. The column was operated at a pressure at the top of 75 mbar and a pressure at the bottom of 223 mbar.

[0075] At the top of the column condensation was carried out at a temperature of 21 C. A gaseous low boiler-comprising stream (19) of 42 kg/h was taken off from the condenser (6). A substream (4) of 17 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 724 kg/h and a temperature of 97 C. At the side offtake, the desired product pure tert-butyl acrylate was obtained in liquid form at a temperature of 64 C. in an amount of 1640 kg/h.

[0076] The side offtake stream (3) had the following composition:

tert-Butyl acrylate: 99.93% by weight
Acrylic acid: <0.01% by weight
Isobutene: <0.01% by weight
Diisobutene: 0.06% by weight
tert-Butyl acetate: 8 ppm by weight

[0077] Further relatively high boilers (relative to tert-butyl acrylate): balance

[0078] The minimum content of acrylate of >99.5% by weight and the commercial specifications for the secondary component tert-butyl acetate at 100 ppm are adhered to. The distillation yield for tert-butyl acrylate was more than 99%.

[0079] 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 1:3.4. 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 502 kW.

[0080] The process of the invention enabled the distillation of crude tert-butyl acrylate to give pure tert-butyl acrylate to be carried out, for example, at an annual capacity of 13 100 metric tons while adhering to the required specifications with a capital cost saving of 20% and an energy cost saving of 20% compared to a conventional two-stage distillation process.

Comparative Example 1

[0081] (Ratio of amount of liquid at the upper end of the dividing wall (8), enrichment section (10):stripping section (11)=1:7)

[0082] A crude tert-butyl acrylate stream of 2424 kg/h having a temperature of 24 C. was fed in in liquid form at the 20th theoretical plate of a dividing wall column (1) having a total of 38 theoretical plates. The crude tert-butyl acrylate had the following composition:

tert-Butyl acrylate: 68.3% by weight
Acrylic acid: 27.8% by weight
Isobutene: 1.0% by weight
Diisobutene: 1.4% by weight
tert-Butyl acetate: 0.1% by weight

[0083] Further relatively high boilers (relative to tert-butyl acrylate): balance

[0084] The dividing wall (8) extended from the 8th to the 28th theoretical plate. The side offtake (3) was located at the 17th theoretical plate. The column was operated at a pressure at the top of 75 mbar and a pressure at the bottom of 223 mbar.

[0085] At the top of the column, condensation was carried out at a temperature of 21 C. A gaseous low boiler-comprising stream (19) of 42 kg/h was taken off from the condenser (6). A substream (4) of 17 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 724 kg/h and a temperature of 96 C. At the side offtake, the desired product pure tert-butyl acrylate was obtained in liquid form at a temperature of 65 C. in an amount of 1640 kg/h.

[0086] The side offtake stream (3) had the following composition:

tert-Butyl acrylate: 98.25% by weight
Acrylic acid: 1.70% by weight
Isobutene: <0.01% by weight
Diisobutene: 0.04% by weight
tert-Butyl acetate: 7 ppm by weight

[0087] The minimum content of acrylate of >99.5% by weight is not adhered to.

[0088] The distillation yield for tert-butyl acrylate was more than 97%.

[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 500 kW.

Comparative Example 2

[0090] (Ratio of amounts of the vapor streams at the lower end of the dividing wall (8), stripping section (12):enrichment section (13)=3:1)

[0091] A crude tert-butyl acrylate stream of 2424 kg/h having a temperature of 24 C. was fed in in liquid form at the 20th theoretical plate of a dividing wall column (1) having a total of 38 theoretical plates. The crude tert-butyl acrylate had the following composition:

tert-Butyl acrylate: 68.3% by weight
Acrylic acid: 27.8% by weight
Isobutene: 1.0% by weight
Diisobutene: 1.4% by weight
tert-Butyl acetate: 0.1% by weight

[0092] Further relatively high boilers (relative to tert-butyl acrylate): balance

[0093] The dividing wall (8) extended from the 8th to the 28th theoretical plate. The side offtake (3) was located at the 17th theoretical plate. The column was operated at a pressure at the top of 75 mbar and a pressure at the bottom of 223 mbar.

[0094] At the top of the column, condensation was carried out at a temperature of 21 C. A gaseous low boiler-comprising stream (19) of 42 kg/h was taken off from the condenser (6). A substream (4) of 7 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 734 kg/h and a temperature of 96 C. At the side offtake, the desired product pure tert-butyl acrylate was obtained in liquid form at a temperature of 64 C. in an amount of 1640 kg/h.

[0095] The side offtake stream (3) had the following composition:

tert-Butyl acrylate: 98.11% by weight
Acrylic acid: 1.29% by weight
Isobutene: <0.01% by weight
Diisobutene: 0.58% by weight
tert-Butyl acetate: 158 ppm by weight

[0096] The minimum content of acrylate of >99.5% by weight and the commercial specification for the secondary component tert-butyl acetate are not adhered to.

[0097] The distillation yield for tert-butyl acrylate was more than 97%.

[0098] 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 1:3.5. 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 500 kW.