A PROCESS FOR PURIFYING CRUDE 4,4'-DICHLORODIPHENYL SULFONE

Abstract

The invention relates to a process for purifying crude 4,4′-dichlorodiphenyl sulfone comprising: (a) dissolving the crude 4,4′-dichlorodiphenyl sulfone which may contain water in an organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C. and optionally adding water to obtain a solution which comprises 4,4′-dichlorodiphenyl sulfone, the organic solvent and 1 to 30 wt % water based on the amount of 4,4′-dichlorodiphenyl sulfone and water; (b) cooling the solution to a temperature below the saturation point of 4,4′-dichlorodiphenyl sulfone to obtain a suspension comprising crystallized 4,4′-dichlorodiphenyl sulfone; (c) carrying out a solid-liquid separation to obtain residual moisture containing 4,4′-dichlorodiphenyl sulfone and a mother liquor; (d) washing the residual moisture containing 4,4′-dichlorodiphenyl sulfone with an organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C.; (e) optionally repeating steps (b) to (d); (f) drying the 4,4′-dichlorodiphenyl sulfone.

Claims

1.-16. (canceled)

17. A process for purifying crude 4,4′-dichlorodiphenyl sulfone comprising: (a) obtaining a solution which comprises 4,4′-dichlorodiphenyl sulfone, an organic solvent, in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C., and 1 to 30 wt % water based on the amount of 4,4′-dichlorodiphenyl sulfone and water by dissolving the crude 4,4′-dichlorodiphenyl sulfone which optionally contains water in the organic solvent and optionally adding water; (b) cooling the solution to a temperature below the saturation point of 4,4′-dichloro-diphenyl sulfone to obtain a suspension comprising crystallized 4,4′-dichlorodiphenyl sulfone; (c) carrying out a solid-liquid separation to obtain residual moisture containing 4,4′-di-chlorodiphenyl sulfone and a mother liquor; (d) washing the residual moisture containing 4,4′-dichlorodiphenyl sulfone with an organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C.; (e) optionally repeating steps (b) to (d); (f) drying the 4,4′-dichlorodiphenyl sulfone.

18. The process according to claim 17, wherein the solution in (b) is cooled with a cooling rate of from 10 to 40 K/h.

19. The process according to claim 17, wherein the solution in (b) is cooled to a temperature in the range from 0 to 25° C.

20. The process according to claim 17, wherein for dissolving the crude 4,4′-di-chlorodiphenyl sulfone in the organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C., a suspension is formed comprising the crude 4,4′-di-chlorodiphenyl sulfone and the organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C. and to heat the suspension to a temperature in the range from 90 to 120° C.

21. The process according to claim 17, wherein cooling (b) comprises: (i) reducing the pressure of the solution to a pressure at which the organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C. starts to evaporate; (ii) condensing the evaporated organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C. by cooling; (iii) mixing the condensed organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C. with the solution to obtain the suspension.

22. The process according to claim 21, wherein the pressure is reduced stepwise or continuously.

23. The process according to claim 21, wherein after completing cooling the pressure is set to ambient pressure.

24. The process according to claim 17, wherein the solid-liquid separation is a filtration.

25. The process according to claim 17, wherein the solid-liquid separation and the washing are carried out in the same apparatus.

26. The process according to claim 17, wherein at least a part of the mother liquor and optionally the organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C. used for washing are worked up by distillation.

27. The process according to claim 17, wherein 50 to 100 wt % of the mother liquor and optionally the organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C. used for washing are worked up by distillation.

28. The process according to claim 17, wherein the organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C. in which the 4,4′-dichlorodiphenyl sulfone is solved and the organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C. for washing are the same.

29. The process according to claim 17, wherein the organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C. is methanol, ethanol, isopropanol, acetone, methyl tert-butyl ether, acetic acid, toluene, ethyl acetate or monochlorobenzene.

30. The process according to claim 17, wherein the drying (f) is carried out in a contact dryer, wherein the contact dryer preferably is operated with a wall temperature in the range from 105° C. to 140° C.

31. The process according to claim 17, wherein the crude 4,4′-dichlorodiphenyl sulfone comprises n-hexanoic acid, n-heptanoic acid or a mixture thereof which is removed by washing with the organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C.

32. Use of a gastight closed vessel for cooling a solution which comprises 4,4′-dichlorodiphenyl sulfone, organic solvent and 1 to 30 wt % water based on the amount of 4,4′-dichlorodiphenyl sulfone and water, by: (i) reducing the pressure of the solution to a pressure at which the organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C. starts to evaporate; (ii) condensing the evaporated organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C. by cooling; (iii) mixing the condensed organic solvent in which 4,4′-dichlorodiphenyl sulfone has a solubility of 0.5 to 20% at 20° C. with the solution to obtain the suspension.

Description

[0080] An illustrative embodiment of the invention is shown in the figure and explained in more detail in the following description.

[0081] FIG. 1 shows a flow diagram of an embodiment of the inventive process.

[0082] In FIG. 1 the process for purifying crude DCDPS is shown in a flow diagram.

[0083] To purify crude DCDPS, particulate crude DCDPS 1 which preferably contains 1 to 30 wt % water and an organic solvent 3, preferably methanol, are fed into a gastight closed vessel 5. In the gastight closed vessel 5 the particulate crude DCDPS 1 is solved in the organic solvent 3. To support solving the particulate crude DCDPS 1 in the organic solvent 3, the mixture of particulate crude DCDPS and organic solvent in the gastight closed vessel 5 is heated to a temperature in the range from 90 to 120° C. For heating the mixture, the gastight closed vessel 5 is equipped with a double jacket 7 which can be flown through by a heating medium, for example a thermal oil or steam. For supporting solving the crude DCDPS in the organic solvent, further an agitating means 9 is comprised for mixing the crude DCDPS and the organic solvent. The agitating means can be for example a stirrer. After completing solving the crude DCDPS in the organic solvent, the thus produced solution is cooled to recrystallize the DCDPS. If the particulate crude DCDPS 1 does not contain a sufficient amount of water, additionally water is fed into the gastight closed vessel 5 to achieve a solution which also contains 1 to 30 wt % water based on the amount of DCDPS and water.

[0084] For cooling the solution, the pressure in the gastight closed vessel 5 is reduced. Due to the pressure reduction, the organic solvent starts to evaporate. The evaporated organic solvent is withdrawn from the gastight closed vessel 5 and flows into a condenser 11. In the condenser 11, the vaporous organic solvent is cooled and condenses. The thus condensed and cooled organic solvent is returned into the gastight closed vessel 5. By the pressure reduction and the resulting evaporating and condensing the organic solvent, the solution in the gastight closed vessel 5 is cooled until a temperature in the range from 0 to 25° C. is achieved. Due to cooling the solution, the DCDPS crystallizes in the solution and a suspension is formed. To keep the crystallized DCDPS in the suspension and to avoid fouling on the surfaces of the gastight closed vessel 5, the suspension which forms in the gastight closed vessel 5 is mixed with the agitating means 9. To reduce the pressure in the gastight closed vessel, for example a vacuum pump 13 can be used which is arranged downstream the condenser 11. Evaporated organic solvent which is pumped out of the gastight closed vessel 5 can be condensed and collected or disposed.

[0085] After the desired temperature in the gastight closed vessel 5 is achieved, the suspension formed in the gastight closed vessel 5 is withdrawn via line 15 and fed into a buffer container 17. From the buffer container 17, the suspension is fed into a filtration apparatus 19. By using the buffer container 17 it is possible to carry out the crystallization in the gastight closed vessel 5 batchwise and the filtration in the filtration apparatus 19 continuously. However, also for the crystallization and the filtration being carried out batchwise it is preferred to use the buffer container 17, to allow use of a filtration apparatus 19 which has a different capacity than the gas-tight closed vessel 5. This allows to use a gastight closed vessel 5 and a filtration apparatus 19 which each are optimized regarding throughput and energy consumption. In the filtration apparatus 19 the crystallized DCDPS is separated from the mother liquor which contains the organic solvent, water, non-crystallized DCDPS and impurities. The mother liquor is withdrawn from the filtration apparatus 19 and collected in an organic solvent collecting tank 21. After being separated from the mother liquor, the residual moisture containing DCDPS is washed with organic solvent. In the embodiment shown in the figure, the washing also is carried out in the filtration apparatus. After being used for washing, the organic solvent also is collected in the organic solvent collecting tank 21. To collect the mother liquor and the organic solvent for washing in only one organic solvent collecting tank 21 as shown in the figure, it is necessary that the organic solvent used to dissolve the DCDPS and the organic solvent for washing are the same.

[0086] For purifying, the organic solvent collected in the organic solvent collecting tank 21 is fed into a distillation column 23. In the distillation column high boilers and low boilers are separated. The low boilers comprise essentially the organic solvent and the high boiler comprises non-crystallized DCDPS and high boiling impurities. The low boiling organic solvent then is fed into an organic solvent storage tank 25.

[0087] After washing, the washed DCDPS is withdrawn from the filtration apparatus 19 and fed into a dryer 27. In the dryer the organic solvent is removed from the DCDPS. The dried DCDPS preferably contains less than 400 ppm organic solvent. The dried DCDPS is withdrawn from the dryer 27 as product 29. The organic solvent which is separated from the DCDPS in the dryer by evaporation is withdrawn from the dryer 27 and fed into a condenser 31. To support evaporation and to avoid an oxidation, an inert gas 33, preferably nitrogen, is fed into the dryer 27. The inert gas is withdrawn from the dryer 27 together with the evaporated organic solvent. In the condenser 31, the organic solvent is separated from the inert gas. The condensed organic solvent is fed into the organic solvent storage tank 25 and the inert gas is vented via venting line 35.

[0088] To provide a sufficient amount of organic solvent and to replace organic solvent withdrawn from the process for example from the gastight closed vessel 5, the condenser 31 or the distillation column 23, fresh organic solvent 37 can be added into the organic solvent storage tank 25.

[0089] From the organic solvent storage tank 25, the organic solvent is supplied to the gastight closed vessel 5 for producing the solution and to the filtration apparatus 19 for washing the DCDPS.

EXAMPLES

[0090] 500.4 g crude DCDPS containing 115 g water and containing about 0.24% heptanoic acid and about 240 ppm isomers of 4,4′-DCDPS were suspended into 1385 g methanol. This mixture was heated to a temperature of 100° C. in a closed vessel. The temperature was kept at 100° C. for 2 h and 20 min. Then the pressure in the vessel was reduced and methanol started to evaporate. Evaporation of methanol resulted in crystallization of the DCDPS. The temperature in the vessel was reduced linearly with a rate of 10 Kelvin per hour until a temperature of 10° C. was reached. After this temperature was reached, the vessel was vented until ambient pressure was achieved. The thus obtained mixture of crystallized DCDPS and methanol was filtered in a filter nutsche. By this filtration a wet filter cake which weighted 613,5 g was obtained. The wet filter cake was washed with fresh 400 g methanol. Afterwards, the washed wet filter cake was dried for 5 hours in a Rotavapor® rotary evaporator with a wall temperature of 130° C. The thus obtained product had the following composition:

[0091] 99,987% 4,4′-DCDPS

[0092] 120 ppm methanol

[0093] 90 ppm DCDPS-isomers

[0094] 20 ppm remaining carboxylic acid.

LIST OF REFERENCE NUMERALS

[0095] 1 crude DCDPS

[0096] 3 organic solvent

[0097] 5 gastight closed vessel

[0098] 7 double jacket

[0099] 9 agitating means

[0100] 11 condenser

[0101] 13 vacuum pump

[0102] 15 line

[0103] 17 buffer container

[0104] 19 filtration apparatus

[0105] 21 organic solvent collecting tank

[0106] 23 distillation column

[0107] 25 organic solvent storage tank

[0108] 27 dryer

[0109] 29 product

[0110] 31 condenser

[0111] 33 inert gas

[0112] 35 venting line

[0113] 37 organic solvent