A PROCESS FOR PRODUCING 4,4'-DICHLORODIPHENYL SULFONE

Abstract

The invention relates to a process for producing 4,4′-dichlorodiphenyl sulfone, comprising: (a) reacting 4,4′-dichlorodiphenyl sulfoxide and an oxidizing agent in at least one carboxylic acid as solvent to obtain a reaction mixture comprising 4,4′-dichlorodiphenyl sulfone and carboxylic acid; (b) separating the reaction mixture into a first stream comprising 4,4′-dichlorodiphenyl sulfone and a second stream comprising carboxylic acid; (c) purifying the second stream comprising carboxylic acid by distilling a part of the second stream comprising carboxylic acid stripping low boilers from at least a part of the second stream comprising carboxylic acid (d) recycling the purified carboxylic acid into the reaction (a).

Claims

1.-18. (canceled)

19. A process for producing 4,4′-dichlorodiphenyl sulfone, comprising: (a) reacting 4,4′-dichlorodiphenyl sulfoxide and an oxidizing agent in at least one carboxylic acid as solvent to obtain a reaction mixture comprising 4,4′-dichlorodiphenyl sulfone and the at least one carboxylic acid; (b) separating the reaction mixture into a first stream comprising 4,4′-dichlorodiphenyl sulfone and a second stream comprising the at least one carboxylic acid; (c) purifying the second stream comprising the at least one carboxylic acid by distilling a part of the second stream comprising the at least one carboxylic acid; stripping low boilers from at least a part of the second stream comprising the at least one carboxylic acid; (d) recycling the purified at least one carboxylic acid into the reaction (a).

20. The process according to claim 19, wherein purifying the second stream comprising the at least one carboxylic acid comprises: (a1) stripping low boilers from the second stream comprising the at least one carboxylic acid in a stripping column using a stripping gas to obtain a crude carboxylic acid; (b1) separating the crude carboxylic acid into a first carboxylic acid stream and a second carboxylic acid stream; (c1) distilling the second carboxylic acid stream to obtain a bottom stream comprising high boiling impurities, a top stream comprising low boiling impurities and a side stream comprising the at least one carboxylic acid; and (d1) mixing the first carboxylic acid stream and the side stream to obtain the purified at least one carboxylic acid.

21. The process according to claim 19, wherein purifying the second stream comprising the at least one carboxylic acid comprises: (a2) separating the second stream comprising the at least one carboxylic acid into a first part and a second part; (b2) stripping low boilers from the first part comprising the at least one carboxylic acid in a stripping column using a stripping gas to obtain a crude carboxylic acid; (c2) distilling the second part to obtain a bottom stream comprising high boiling impurities, a top stream comprising low boiling impurities and a side stream comprising the at least one carboxylic acid; and (d2) mixing the crude carboxylic acid obtained in (b2) and the side stream comprising the at least one carboxylic acid obtained in (c2) to obtain the purified at least one carboxylic acid.

22. The process according to claim 19, wherein purifying the second stream comprising the at least one carboxylic acid comprises: (a3) separating the second stream comprising the at least one carboxylic acid into a first part and a second part; (b3) distilling the second part to obtain a bottom stream comprising high boiling impurities, a top stream comprising low boiling impurities and a side stream comprising the at least one carboxylic acid; and (c3) mixing the side stream comprising the at least one carboxylic acid obtained in (b3) and the first part of the second stream comprising the at least one carboxylic acid to obtain crude carboxylic acid; (d3) stripping low boilers from the crude carboxylic acid obtained in (c3) in a stripping column using a stripping gas to obtain the purified at least one carboxylic acid.

23. The process according to claim 19, wherein the oxidizing agent is a peroxide.

24. The process according to claim 19, wherein the low boilers stripped from the second stream comprising the at least one carboxylic acid and the low boiling impurities comprise at least one of water and monochlorobenzene.

25. The process according to claim 19, wherein the part of the second stream comprising the carboxylic acid which is distilled contains 2 to 25 vol % of the second stream comprising the carboxylic acid.

26. The process according to claim 19, wherein the high boiling impurities comprise at least one of lactone, linear or branched C.sub.4 to C.sub.7 alkanes.

27. The process according to claim 19, wherein stripping the low boilers from the second stream comprising the at least one carboxylic acid is performed at a temperature in the range from 80 to 100° C. and a pressure in the range from 0.1 to 0.7 bar(abs).

28. The process according to claim 19, wherein the stripping gas is nitrogen, a noble gas, carbon dioxide, or a mixture thereof.

29. The process according to claim 19, wherein distilling of the part of the second stream comprising the at least one carboxylic acid is carried out at a bottom temperature in the range from 130 to 250° C., a top temperature in the range from 50 to 150° C. and a pressure in the range from 10 to 400 mbar (abs).

30. The process according to claim 19, wherein the purified at least one carboxylic acid is collected in a buffer vessel before being recycled into the reaction (a).

31. The process according to claim 19, wherein the purified at least one carboxylic acid is tempered to a temperature in the range between 80 and 100° C. before being recycled into the reaction (a).

32. The process according to claim 19, wherein for separating the reaction mixture into a first stream comprising 4,4′-dichlorodiphenyl sulfone and a second stream comprising the at least one carboxylic acid, the reaction mixture is cooled to a temperature where the 4,4′-dichlorodiphenyl sulfone crystallizes to obtain a suspension comprising the crystallized 4,4′-dichlorodiphenyl sulfone and a liquid phase and the suspension is separated by a solid-liquid separation into residual moisture comprising 4,4′-dichlorodiphenyl sulfone and mother liquor.

33. The process according to claim 32, wherein the residual moisture comprising 4,4′-dichlorodiphenyl sulfone is washed with an aqueous base and subsequently with water.

34. The process according to claim 33, wherein the aqueous base after being used for washing is mixed with a strong acid by which an aqueous phase comprising a water soluble salt and an organic phase comprising the at least one carboxylic acid is obtained.

35. The process according to claim 34, wherein the organic phase comprising the at least one carboxylic acid is mixed with the mother liquor to obtain the second stream comprising the at least one carboxylic acid or wherein the mother liquor and the aqueous base are mixed before carrying out a phase separation to obtain the aqueous phase comprising a salt and the organic phase comprising the at least one carboxylic acid, the organic phase comprising the at least one carboxylic acid being the second stream comprising the at least one carboxylic acid.

36. The process according to claim 19, wherein the at least one carboxylic acid is n-hexanoic acid, n-heptanoic acid or a mixture thereof.

Description

[0175] An illustrative embodiment of the invention is shown in the figure and explained in more detail in the following description.

[0176] FIG. 1 shows a flow diagram of an embodiment of the inventive process.

[0177] In a process for producing DCDPS, 4,4′-dichlorodiphenyl sulfoxide 1, carboxylic acid 3, particularly heptanoic acid, and an oxidant 5, for example hydrogen peroxide are fed into an oxidation reactor 7. The oxidation reaction preferably is carried out in an inert atmosphere. To obtain the inert atmosphere, an inert gas 9, for example nitrogen, is fed into the oxidation reactor 7. In the oxidation reactor, the 4,4′-dichlorodiphenyl sulfoxide is oxidized forming DCDPS. This reaction preferably is carried out in the presence of an acidic catalyst. The acidic catalyst for example is a strong inorganic acid like sulfuric acid or a strong organic acid like methane sulfonic acid, or a mixture of at least two strong acids. The acidic catalyst also is fed into the oxidation reactor 7. To feed the acidic catalyst into the oxidation reactor 7, it is for example possible to feed the acidic catalyst via a separate feed line or to mix the catalyst with any of the other components added to the oxidation reactor 7, for example the 4,4′-dichlorodiphenyl sulfoxide 1, the oxidant 5 or the carboxylic acid 3. If the acidic catalyst is mixed with one of the compounds fed into the oxidation reactor 7, it is most preferred to mix the acidic catalyst with the carboxylic acid 3 and add this mixture into the oxidation reactor 7 just before heating up to reaction temperature.

[0178] In the oxidation reactor 7 a reaction mixture 11 is formed comprising the DCDPS. This reaction mixture 11 is withdrawn from the oxidation reactor 7 and fed into a crystallization apparatus 13. In the crystallization apparatus 13 the reaction mixture 11 is cooled and the DCDPS starts to solidify and form crystals. By this process a suspension is formed comprising the solid DCDPS in a mother liquor, the mother liquor comprising carboxylic acid, non-crystallized DCDPS and further liquid by-products and non-reacted reactants of the oxidization reaction.

[0179] Preferably, for cooling the reaction mixture to crystallize the DCDPS, water 15 is added to the crystallization apparatus 13. Then the pressure is reduced that water starts to evaporate. The evaporated water is cooled to condense, and the condensed water is returned into the crystallization apparatus 13. By this process, the reaction mixture is cooled without using cooled surfaces on which crystallized DCDPS can deposit and form solid deposits which have to be removed in a cleaning process.

[0180] The suspension 17 formed in the crystallization apparatus 13 then is fed into a solid-liquid separation apparatus 19. In the solid-liquid separation apparatus 19 first mother liquor is filtrated off the solid DCDPS whereby moist DCDPS is obtained. After the solid-liquid separation, in a first washing phase, an aqueous base 21 is added to the moist DCDPS. In this first washing phase the anion of the carboxylic acid reacts with the cation of the aqueous base forming an organic salt. The main portion of the organic salt formed by this reaction is removed from the filtration apparatus 19 with the aqueous base 23 which was used for washing. After washing with the aqueous base, in a second washing phase, the DCDPS is washed with water 25. Washing with water may be carried out in one or more steps. Washing with water thereby preferably is continued until the washed DCDPS is neutral which means a pH value in the range from 6.5 to 7.5. After being used for washing, the used water 27 is withdrawn from the process. It is particularly preferred as shown in the figure to carry out the solid-liquid separation and the washing in the same apparatus.

[0181] Washed DCDPS 29 is withdrawn from the solid-liquid separation apparatus 19 as product. The solid-liquid separation apparatus 19 can be any suitable filtration apparatus like an agitated pressure nutsche, a rotary pressure filter, a drum filter, a belt filter. Besides a filtration apparatus, the solid-liquid separation apparatus 19 also can be a centrifuge. Further, it is also possible to carry out the solid-liquid separation in one apparatus and the washing in a washing apparatus.

[0182] In the inventive process, after being withdrawn from the washing, the used aqueous base 23 is mixed with a strong acid 31. This mixture is fed into a phase separation 33 where an aqueous phase comprising a water-soluble salt and an organic phase comprising carboxylic acid is obtained. The aqueous phase 35 comprising salts which was obtained by the reaction of the aqueous base with the carboxylic acid and subsequently by the reaction with the strong acid 31 is withdrawn from the process.

[0183] The organic phase 37 which comprises the carboxylic acid in the following also is termed as “stream comprising carboxylic acid”. The stream 37 comprising the carboxylic acid is separated into a first part 39 and a second part 41.

[0184] The first part 39 is fed into a stripping apparatus 43, where low boilers are stripped from the first part of the stream comprising carboxylic acid. For stripping the low boilers, a stripping gas 45 is fed into the stripping apparatus 43. The stripping gas 45 preferably is nitrogen. By bringing the first part of the stream comprising carboxylic acid into contact with the inert gas, the low boilers, particularly water and solvent, for example monochlorobenzene, are at least partly separated from the carboxylic acid and mix with the nitrogen. The nitrogen with the low boilers then is withdrawn from the stripping apparatus 43 as flue gas 47. The carboxylic acid from which the low boilers are stripped is withdrawn from the stripping apparatus 43 as crude carboxylic acid 57.

[0185] The second part 41 of the stream comprising carboxylic acid is fed into a distillation 49. In the distillation, low boilers as well as high boilers are separated from the carboxylic acid. The low boilers are removed from the distillation 49 as top stream 51 and the high boilers as bottom stream 53. The carboxylic acid is removed from the distillation 49 as a side stream 55.

[0186] The side stream 55 comprising the carboxylic acid and the crude carboxylic acid 57 withdrawn from the stripping apparatus 43 are mixed and returned into the oxidation reactor 7 as carboxylic acid 3.

[0187] The process conditions for carrying out the process for producing DCDPSO correspond to those as described above.

EXAMPLES

Example 1

[0188] Distillation

[0189] 310 g of the mother liquor as second stream comprising carboxylic acid obtained in an oxidation/crystallization process for producing DCDPS were fed into a batch distillation column with 10 trays. The mother liquor had following composition:

[0190] 0.715 wt % monochlorobenzene, 0.02 wt % dodecane, 0.003 wt % heptanoic acid methyl ester, 0.026 wt % valeric acid, 0.315 wt % hexanoic acid, 95.02 wt % heptanoic acid and 3.5 wt % water. This mother liquor was distilled with a bottom temperature of 160° C., and a top temperature of 135° C. at a pressure of 52 mbar (abs) for about 4.5 h. The carboxylic acid obtained by this distillation had the following composition:

[0191] 0.014 wt % monochlorobenzene, 0.002 wt % dodecane, 0.0 wt % heptanoic acid methyl ester, 0.005 wt % valeric acid, 0.185 wt % hexanoic acid, and 99.52 wt % heptanoic acid.

[0192] Stripping

[0193] 2627 g of the mother liquor as second stream comprising carboxylic acid obtained in an oxidation/crystallization process with a temperature of 88° C. were provided in a buffer vessel and continuously fed into a stripping column with a feed rate of 66 ml/min.

[0194] The mother liquor had the following composition:

[0195] 0.715 wt % monochlorobenzene, 0.02 wt % dodecane, 0.003 wt % heptanoic acid methyl ester, 0.026 wt % valeric acid, 0.315 wt % hexanoic acid, 95.02 wt % heptanoic acid and 3.5 wt % water.

[0196] The stripping column had 10 trays and the mother liquor was fed on top into the stripping column and 150 NL per hour nitrogen were fed into the stripping column at the bottom as stripping gas. The pressure in the stripping column was set to 300 mbar.

[0197] After stripping, the carboxylic acid was continuously removed from the stripping column and had the following composition:

[0198] 0.456 wt % monochlorobenzene, 0.018 wt % dodecane, 0.003 wt % heptanoic acid methyl ester, 0.025 wt % valeric acid, 0.333 wt % hexanoic acid, 95.36 wt % heptanoic acid, and 0.42 wt % water.

[0199] The carboxylic acid obtained by distillation and the carboxylic acid obtained by stripping were mixed and the resulting purified carboxylic acid contained 0.41 wt % monochlorobenzene, 2.2 wt % 4,4′-DCDPS, 0.54% 2,4′-DCDPS, about 600 ppm lactones, 4000 ppm n-hexanoic acid, 240 ppm valerian acid, 100 ppm esters, and 160 ppm dodecane.

Example 2

[0200] Distillation

[0201] 311 g of the mother liquor as second stream comprising carboxylic acid obtained in an oxidation/crystallization process for producing DCDPS were fed into a batch distillation column with 10 trays. The mother liquor contained:

[0202] 0.696 wt % monochlorobenzene, 0.016 wt % dodecane, 0.024 wt % valeric acid, 0.292 wt % hexanoic acid, 2.6 wt % DCDPS, 95.006 wt % heptanoic acid. The remainders were further impurities, particularly water.

[0203] This mother liquor was distilled with a bottom temperature of 160° C., and a top temperature of 135° C. at a pressure of 52 mbar (abs) for about 4.5 h. The energy consumption for distillation was about 465 kJ steam per kg DCDPS produced.

[0204] The carboxylic acid obtained by this distillation had the following composition:

[0205] 210 ppm monochlorobenzene, 10 ppm dodecane, 30 ppm valeric acid, 1500 ppm hexanoic acid, and 99.67 wt % heptanoic acid.

[0206] The bottom stream of the distillation contained about 71 wt % heptanoic acid and about 20 wt % DCDPS. Due to the temperature in the bottom stream the DCDPS changed its color and therefore the bottom stream was disposed.

[0207] Stripping

[0208] 2608 g of the mother liquor with the same composition as described above for the mother liquor fed into the distillation were provided in a buffer vessel with a temperature which was kept in a range between 78° C. and 86° C. and continuously fed into a stripping column with a feed rate of 66 ml/min.

[0209] The stripping column had 10 trays and the mother liquor was fed on top into the stripping column and 150 NL per hour nitrogen were fed into the stripping column at the bottom as stripping gas. The pressure in the bottom of the stripping column was set to 300 mbar.

[0210] After stripping, the carboxylic acid was continuously removed from the stripping column and had the following composition:

[0211] 0.484 wt % monochlorobenzene, 0.015 wt % dodecane, 0.022 wt % valeric acid, 0.305 wt % hexanoic acid, 2.4 wt % DCPDS and 95.47 wt % heptanoic acid.

[0212] The combined carboxylic acid was recycled in the production of DCDPS.

[0213] As only the bottom stream of the distillation was disposed and the combined carboxylic acid obtained in the distillation and stripping processes was recycled into the production of DCDPS, the amount of DCDPS which was lost was 0.38 wt % of the DCDPS produced and the amount of heptanoic acid which was lost was 0.47 wt % of the heptanoic acid used in the process.