A PROCESS FOR PURIFYING 4,4'-DICHLORODIPHENYL SULFONE

Abstract

The invention relates to a process for purifying 4,4′-dichlorodiphenyl sulfone comprising: (a) providing a suspension comprising particulate 4,4′-dichlorodiphenyl sulfone in carboxylic acid, (b) carrying out a solid-liquid separation of the suspension to obtain residual moisture containing 4,4′-dichlorodiphenyl sulfone and a carboxylic acid comprising filtrate, (c) washing the residual moisture containing 4,4′-dichlorodiphenyl sulfone with an aqueous base and then with water, (d) mixing the aqueous base after being used for washing with a strong acid, or mixing the aqueous base after being used for washing, the carboxylic acid comprising filtrate and a strong acid, (e) carrying out a phase separation in which an aqueous phase and an organic phase comprising the carboxylic acid are obtained.

Claims

1.-14. (canceled)

15. A process for purifying 4,4′-dichlorodiphenyl sulfone comprising: (a) providing a suspension comprising particulate 4,4′-dichlorodiphenyl sulfone in carboxylic acid, (b) carrying out a solid-liquid separation of the suspension to obtain residual moisture containing 4,4′-dichlorodiphenyl sulfone and a carboxylic acid comprising filtrate, (c) washing the residual moisture containing 4,4′-dichlorodiphenyl sulfone with an aqueous base and then with water, (d) mixing the aqueous base after being used for washing with a strong acid and then mixing at least a part of the carboxylic acid comprising filtrate with the aqueous base mixed with the strong acid, or mixing the aqueous base after being used for washing, at least a part of the carboxylic acid comprising filtrate and a strong acid, (e) carrying out a phase separation in which an aqueous phase and an organic phase comprising the carboxylic acid are obtained.

16. The process according to claim 15, wherein the carboxylic acid is a linear C.sub.6 to C.sub.10 carboxylic acid.

17. The process according to claim 15, wherein the carboxylic acid is selected from the group consisting of n-hexanoic acid, n-heptanoic acid.

18. The process according to claim 15, wherein the aqueous base is an aqueous alkali metal hydroxide.

19. The process according to claim 18, wherein the aqueous alkali metal hydroxide comprises from 1 to 50 wt % alkali metal hydroxide based on the total amount of aqueous alkali metal hydroxide.

20. The process according to claim 15, wherein the amount of the aqueous base used for washing is in the range from 0.5 to 10 kg per kg dry 4,4′-dichlorodiphenyl sulfone.

21. The process according to claim 15, wherein the amount of water used for washing after washing with the aqueous base is in the range from 0.5 to 10 kg per kg dry 4,4′-dichlorodiphenyl sulfone.

22. The process according to claim 15, wherein the solid-liquid separation (b) and the washing (c) are carried out in one apparatus.

23. The process according to claim 15, wherein the strong acid is sulfuric acid or alkane sulfonic acid.

24. The process according to claim 15, wherein the carboxylic acid comprising filtrate and the aqueous base after being used for washing are mixed before mixing with the strong acid.

25. The process according to claim 15, wherein at least a part of the aqueous phase obtained in the phase separation (e) is recirculated into the mixing (d) of the aqueous base with the strong acid.

26. The process according to claim 15, wherein at least a part of the water after being used for washing is used for producing the aqueous base.

27. The process according to claim 15, wherein at least a part of the carboxylic acid obtained in (e) is used in a process for producing 4,4′-dichlorodiphenyl sulfone by oxidation of 4,4′-dichlorodiphenyl sulfoxide in the presence of a carboxylic acid

28. The process according to claim 15, wherein the 4,4′-dichlorodiphenyl sulfone is used as starting material for producing sulfone polymers, particularly polyarylene(ether)sulfone.

Description

[0141] An illustrative embodiment of the invention is shown in the FIGURE and explained in more detail in the following description.

[0142] FIG. 1 shows a flow diagram of an embodiment of the inventive process.

[0143] In FIG. 1 the process for purifying a DCDPS comprising suspension is shown in a flow diagram.

[0144] A suspension 1 comprising solid DCDPS in a carboxylic acid and optionally water is fed into a solid-liquid separation apparatus 3, for example a filtration apparatus. The filtration apparatus can be an agitated pressure nutsche, a rotary pressure filter, a drum filter or a belt filter. Besides a filtration apparatus, the solid-liquid separation apparatus also can be a centrifuge.

[0145] In the solid-liquid separation apparatus 3 the suspension is separated into moist DCDPS and a carboxylic acid and optionally water comprising filtrate 5 which is withdrawn from the solid-liquid separation apparatus.

[0146] After completion of the solid-liquid separation, the moist DCDPS is washed in two phases. In a first phase, the moist DCDPS is washed with an aqueous base 7 and after completing washing with the aqueous base, in a second phase the moist DCDPS is washed with water 9. The aqueous base for washing in the first phase preferably is aqueous alkali metal hydroxide, particularly sodium hydroxide. The moist DCDPS after washing with aqueous base and water is withdrawn from the solid-liquid separation apparatus 3 as product stream 10.

[0147] The solid-liquid separation and the two washing phases can be carried out in only one apparatus or in different apparatus for solid-liquid separation and washing. If a continuous belt filter is used for solid-liquid separation and washing, the moist DCDPS is transported on the belt from the solid-liquid separation to the position where the washing takes place. If a solid liquid apparatus is used in which the moist DCDPS cannot be transported on the filter, solid-liquid separation and washing can be carried out in the same apparatus in succession. In this case, the moist DCDPS forming a filter cake is removed from the filter after completion of the solid-liquid separation and the washing phases.

[0148] After being used for washing, the aqueous base 11 is fed into a vessel 13. The water after use is withdrawn from the process by drainage line 15. Further it is possible to use at least a part of the water after use for diluting the aqueous base 7. This is exemplary shown with dashed line 16.

[0149] By washing the moist DCDPS with the aqueous base, remainders of the carboxylic acid react with the base forming a carboxylate. To reduce the amount of waste and to increase the amount of carboxylic acid which can be reduced, after being used for washing, the aqueous base is mixed with a strong acid 17. The strong acid reacts with the carboxylate forming a salt and the carboxylic acid. The mixing of the aqueous base after being used and the strong acid can take place in a stirred tank, a tube or a static mixer. In the embodiment according to the FIGURE, the strong acid is added to the aqueous base in the line through which the aqueous base is fed into the vessel 13. The vessel 13 is a stirred tank in which the components fed into the vessel 13 are agitated, particularly stirred. Therefore, the reaction of the strong acid with the carboxylate in the aqueous base takes place in the vessel 13.

[0150] According to the embodiment shown in the FIGURE, also the filtrate 5 is fed into the vessel 13 and mixed with the strong acid and the aqueous base.

[0151] As an alternative, it is also possible to add the aqueous base 11, the strong acid 17 and the filtrate 5 via separate feed lines into the vessel 13. This allows for mixing the aqueous base 11 and the filtrate 5 in a first step and to add the strong acid 17 to this mixture.

[0152] Besides the embodiment shown in the FIGURE, it is also possible to complete the reaction of the strong acid and the carboxylate in the aqueous base before feeding into a buffer container into which also the filtrate is fed. Preferably, the buffer container is equipped with a mixing device for mixing the aqueous base and the filtrate.

[0153] To improve the phase separation, the filtrate 5 can be heated in a heat exchanger 29. Preferably, the filtrate 5 is heated to a temperature in the range from 30 to 50° C. A further advantage of heating the filtrate 5 to such a temperature is that precipitation of solids can be avoided.

[0154] From the vessel 13 or alternatively the buffer container, the mixture of the filtrate and the aqueous base is fed into a phase separation apparatus 19. In the phase separation apparatus 19, the mixture is separated into an organic phase 21 comprising the carboxylic acid and an aqueous phase 23 in which the salt formed from the anion of the strong base and the cation of the aqueous base is solved. The organic phase 21 is withdrawn from the phase separation apparatus 19 and the carboxylic acid can be reused. If necessary, it is possible to subject the organic phase to further purification steps before reusing the carboxylic acid.

[0155] Due to the small amount of aqueous phase compared to the amount of organic phase and to facilitate the phase separation, a part of the aqueous phase is recycled into the vessel 13 via recirculation line 25. Besides recycling into the vessel 13, alternatively it is also possible to recycle the aqueous phase directly into the phase separation apparatus 19. The part of the aqueous phase 23 which is not recycled is withdrawn from the process and disposed, optionally after being purified.

[0156] To facilitate the phase separation in the phase separation in a continuously operated phase separation apparatus 19 as shown in the FIGURE, a coalescing aid 27 is provided. The coalescing aid for example is a random packing, for example a layer of Pall® rings, Raschig® rings or saddles or a structured packing.

EXAMPLES

Example 1

[0157] 4902 g suspension comprising 1547 g crystallized DCDPS, 811 g water and 2544 g n-heptanoic acid were filled on a laboratory nutsche. A pressure of 500 mbar(abs) was set to the filtrate side of the nutsche for 60 seconds to carry out the filtration. After finishing the filtration the thus obtained filter cake was dried 30 seconds with dry air.

[0158] Afterwards the filter cake was washed with 2 kg of diluted NaOH 5%. For washing a pressure of 750 mbar(abs) were set to the filtrate side of the nutsche.

[0159] Washing with diluted NaOH was followed by washing with 1.5 kg water. For washing with water a pressure of 500 mbar(abs) were set to the filtrate side of the nutsche. Subsequently the filter cake was dried for 30 seconds drying with air.

[0160] After washing and drying, the content of carboxylic acid in the filter cake was 0.24 wt %. The final filter cake mass was 1369 g.

[0161] The mother liquor obtained in the filtration process was subjected to a phase separation. By phase separation, 482 g aqueous phase and 2712 g organic phase were obtained.

Example 2

[0162] 1000 g DCDPSO having an APHA-number of 100 were dissolved in 3000 g n-heptanoic acid. This solution was heated to 90° C. Then 1.3 g sulfuric acid and 197 g H.sub.2O.sub.2 were added over a period of 3 h and 40 min for oxidizing the DCDPSO to obtain DCDPS. To the solution obtained by the oxidation reaction, 794 g water were added.

[0163] After adding the water, the thus obtained solution was cooled to crystallize the DCDPS obtained in the oxidation reaction. For cooling, the pressure was continuously reduced over a period of 5 h. Due to the pressure reduction, the water started to evaporate. The evaporated water was condensed and returned into the solution. By this process the temperature was reduced by 83 K. By this cooling process the DCDPS crystallized and a suspension formed. This suspension was separated into a DCDPS containing filter cake and a mother liquor by solid-liquid separation.

[0164] The filter cake was washed with 1.3 kg diluted NaOH 5%. After washing with the diluted NaOH, the filter cake was washed two times with 1.3 kg water each. After washing the DCDPS was dried at 60° C. for 16 h. The thus obtained DCDPS had an APHA-number of 30 and contained 0.16 wt % n-heptanoic acid.

[0165] The pressures and the operation times at which the solid-liquid separation and washing steps were carried out were the same as described for example 1.

[0166] After being used for washing, the diluted NaOH was mixed with the mother liquor obtained by the solid-liquid separation. 175.2 g 50% sulfuric acid were added to the mixture of diluted NaOH and mother liquor. The thus obtained liquid mixture was subjected to a phase separation to obtain an aqueous phase and an organic phase. The aqueous phase and the waste water of the water washing steps were mixed. This resulted in 4.8 L cumulated waste water which had a TOC of 2700 mg/L which corresponds to 13 g organic compounds which were primarily the carboxylic acid. This shows that only 0.43% of the carboxylic acid which was used for dissolving the DCDPSO were withdrawn from the process by the waste water.

[0167] The organic phase which essentially comprised heptanoic acid was worked-up for purifying the heptanoic acid and the heptanoic acid was recycled into the production process of DCDPS.

LIST OF REFERENCE NUMERALS

[0168] 1 suspension [0169] 3 solid-liquid separation apparatus [0170] 5 filtrate [0171] 7 aqueous base [0172] 9 water [0173] 10 product stream [0174] 11 aqueous base after being used for washing [0175] 13 vessel [0176] 15 drainage line [0177] 17 strong acid [0178] 19 phase separation apparatus [0179] 21 organic phase [0180] 23 aqueous phase [0181] 25 recirculation line [0182] 27 coalescing aid