A PROCESS FOR OBTAINING 4,4'-DICHLORODIPHENYL SULFONE

Abstract

The invention relates to a process for obtaining 4,4′-dichlorodiphenyl sulfone from an organic mixture comprising 4,4′-dichlorodiphenyl sulfone and a linear C.sub.6 to C.sub.10 carboxylic acid as organic solvent, comprising: (a) cooling the organic mixture by (a1a) mixing the organic mixture with water in a crystallization vessel to obtain a liquid mixture; (a1b) cooling the liquid mixture obtained in (a1a) to a temperature below the saturation point of 4,4′-dichlorodiphenyl sulfone by (i) reducing the pressure in the crystallization vessel to a pressure at which the water starts to evaporate, (ii) condensing the evaporated water by cooling, (iii) mixing the condensed water into the liquid mixture in the crystallization vessel, to obtain a suspension comprising crystallized 4,4′-dichlorodiphenyl sulfone; or by (a2) bringing the organic mixture into contact with at least one coolable surface and thereby reducing the temperature in the organic mixture with a cooling rate in the range from 5 to 50 K/h until a temperature in the range from 10 to 30° C. is reached, wherein the organic mixture and the at least one coolable surface have a temperature difference which is kept during the whole cooling process in the range from 1 to 30 K to obtain a suspension comprising crystallized 4,4′-dichlorodiphenyl sulfone. (b) carrying out a solid-liquid-separation of the suspension obtained in (a1b) or in (a2) to obtain a residual moisture containing solid 4,4′-dichlorodiphenyl sulfone as product and mother liquor comprising the organic solvent and water.

Claims

1.-16. (canceled)

17. A process for obtaining 4,4′-dichlorodiphenyl sulfone from an organic mixture comprising 4,4′-dichlorodiphenyl sulfone and a linear C.sub.6 to C.sub.10 carboxylic acid as organic solvent, comprising: (a) cooling the organic mixture by (a1a) mixing the organic mixture with water in a crystallization vessel to obtain a liquid mixture; (a1b) cooling the liquid mixture obtained in (a1a) to a temperature below the saturation point of 4,4′-dichlorodiphenyl sulfone by (i) reducing the pressure in the crystallization vessel to a pressure at which the water starts to evaporate, (ii) condensing the evaporated water by cooling, (iii) mixing the condensed water into the liquid mixture in the crystallization vessel, to obtain a suspension comprising crystallized 4,4′-dichlorodiphenyl sulfone; or by (a2) bringing the organic mixture into contact with at least one coolable surface and thereby reducing the temperature in the organic mixture with a cooling rate in the range from 5 to 50 K/h until a temperature in the range from 0 to 30° C. is reached, wherein the organic mixture and the at least one coolable surface have a temperature difference which is kept during the whole cooling process in the range from 1 to 30 K to obtain a suspension comprising crystallized 4,4′-dichlorodiphenyl sulfone. (b) carrying out a solid-liquid-separation of the suspension obtained in (a1b) or in (a2) to obtain a residual moisture containing solid 4,4′-dichlorodiphenyl sulfone as product and mother liquor comprising the organic solvent and water.

18. The process according to claim 17, wherein the amount of water mixed to the organic mixture in (a1a) is such that the amount of water in the liquid mixture is in the range from 10 to 60 wt % based on the total amount of the liquid mixture.

19. The process according to claim 17, wherein the pressure is reduced in (i) until the suspension has cooled down to a temperature in the range from 10 to 30° C.

20. The process according to claim 17, wherein the pressure is reduced in (i) stepwise or continuously.

21. The process according to claim 17, wherein an additional cooling is started after the temperature of the liquid mixture is reduced to a temperature in the range from 50 to 20° C. in (a1b).

22. The process according to claim 21, wherein the crystallization vessel is provided with coolable surfaces for the additional cooling.

23. The process according to claim 17, wherein the coolable surfaces comprise a cooling jacket, cooling coils, half-pipe coils or cooled baffles.

24. The process according to claim 17, wherein after completing cooling in (a1b) the process is finished and the pressure is set to ambient pressure.

25. The process according to claim 17, wherein the organic mixture is mixed with water such that the obtained mixture contains 10 to 60 wt % water before bringing the organic mixture into contact with the at least one coolable surface in (a2).

26. The process according to claim 25, wherein the water has a temperature in the range from 40 to 100° C.

27. The process according to claim 17, wherein the mother liquor comprising the organic solvent is separated into an aqueous phase and an organic phase comprising the organic solvent.

28. The process according to claim 17, wherein the organic mixture is obtained by an oxidization reaction of 4,4′-dichlorodiphenyl sulfoxide and an oxidization agent.

29. The process according to claim 27, wherein the organic phase is recycled into the oxidization reaction.

30. The process according to claim 17, wherein the linear C6 to C.sub.10 carboxylic acid is n-hexanoic acid, n-heptanoic acid, or a mixture thereof.

31. The process according to claim 17, wherein for initializing crystallization of the 4,4′-dichlorodiphenyl sulfone following steps are carried out before reducing the pressure in step (i): reducing the pressure in the crystallization vessel such that the boiling point of the water in the liquid mixture is in the range between 80 and 100° C.; evaporating water until an initial formation of solids takes place; increasing the pressure in the vessel and heating the liquid mixture in the crystallization vessel to a temperature in the range from 1 to 10° C. below the saturation point of DCDPS.

32. A method comprising utilizing a gastight closed vessel as crystallization vessel in a process for obtaining 4,4′-dichlorodiphenyl sulfone from an organic mixture comprising 4,4′-dichlorodiphenyl sulfone and an organic solvent which comprises cooling the organic mixture comprising 4,4′-dichlorodiphenyl sulfone and an organic solvent by mixing the organic mixture with water in the gastight closed vessel to obtain a liquid mixture; cooling the liquid mixture to a temperature below the saturation point of 4,4′-dichlorodiphenyl sulfone by (i) reducing the pressure in the crystallization vessel to a pressure at which the water starts to evaporate, (ii) condensing the evaporated water by cooling, (iii) mixing the condensed water into the liquid mixture in the crystallization vessel, to obtain a suspension comprising crystallized 4,4′-dichlorodiphenyl sulfone.

Description

[0112] An illustrative embodiment of the invention is shown in the FIGURE and explained in more detail in the following description.

[0113] FIG. 1 shows a crystallization vessel for crystallization of DCDPS by reducing the pressure to evaporate water, condensing the water by cooling and recycle the condensed water and mix it into the liquid mixture.

[0114] The only FIGURE shows a crystallization vessel for crystallization of DCDPS by reducing the pressure to evaporate water, condensing the water by cooling and recycle the condensed water and mix it into the liquid mixture.

[0115] In one embodiment, crystallization of DCDPS is carried out in a crystallization vessel 100, which is a gastight closed vessel. The cooling and thereby the crystallization of DCDPS is performed by pressure reduction and lowering the boiling point of water in the liquid mixture due to the reduced pressure.

[0116] Via feed line 101 an organic mixture comprising DCDPS and an organic solvent is fed into the crystallization vessel 100. By a second feed line 102, additionally water is fed into the crystallization vessel 100. The crystallization vessel 100 preferably is a stirred tank comprising at least one stirrer 103. By stirring, the water is mixed into the organic mixture in the form of fine droplets, forming a liquid mixture. Further, by stirring the liquid mixture in the vessel, crystallized DCDPS is kept in the forming suspension and precipitation of crystallized DCDPS and thus fouling is avoided.

[0117] Besides adding the water via a second feed line 102 as shown in the FIGURE, it is also possible to add the water into the feed line 101 and feed the organic mixture and the water together into the crystallization vessel 100. Further, the water and the organic mixture also can be fed into a mixing unit (not shown in FIG. 1) and from the mixing unit into the crystallization vessel 100.

[0118] For cooling the liquid mixture in the crystallization vessel 100 by dropping the boiling point of the water in the liquid mixture due to pressure reduction, an exhaust gas line 105 is provided which is connected to a vacuum pump 107. A suitable vacuum pump 107 for example is a liquid ring pump, vacuum steam jet pump or steam jet ejector. Between the crystallization vessel 100 and the vacuum pump 107, a condenser 109 is accommodated in the exhaust gas line 105. In the condenser 109 water which is evaporated from the boiling liquid mixture in the crystallization vessel 100 is condensed by cooling. The condensed water then is returned into the crystallization vessel 100 via line 111. Further, to remove low boilers from the crystallization a withdrawing line 113 is provided via which condensed water and low boilers if present, can be removed from the process.

[0119] By a drain line 115 a suspension comprising crystallized DCDPS is withdrawn from the crystallization vessel 100. The drain line 115 preferably is connected to a solid-liquid separation step, for example a filtration.

[0120] The crystallization vessel 100 for cooling and crystallization can be operated either batchwise or continuously. If the crystallization vessel 100 for cooling and crystallization is operated batchwise, in a first step the organic mixture and water are fed into the crystallization vessel 100, wherein the water and the organic mixture can be fed into the crystallization vessel 100 simultaneously or one after the other. After a predefined filling level is reached, feeding of the organic mixture and of the water is stopped. In a next step, the pressure in the crystallization vessel 100 is reduced using the vacuum pump 107 until a pressure in the crystallization vessel 100 is reached at which the boiling point of the water in the liquid mixture is in a range between 80 and 95° C. Due to pressure reduction the water in the liquid mixture starts boiling and water and low boilers evaporate. Once the saturation point of the DCDPS in the liquid mixture is reached, the pressure in the crystallization vessel 100 is increased and the liquid mixture is heated to a temperature between 85 and 100° C. to dissolve partially the DCDPS to achieve crystal nuclei of a homogeneous size. After this heating phase, the pressure in the crystallization vessel 100 is reduced again. By this pressure reduction the boiling point of the water in the liquid mixture drops, water evaporates and is withdrawn from the crystallization vessel 100 via exhaust gas line 105. In the condenser 109 the evaporated water is condensed by cooling and the condensed water is recycled into the crystallization vessel 100. This recycling of water results in cooling of the liquid mixture leading to crystallization of DCDPSO. The temperature reduction in the crystallization vessel by pressure reduction and evaporation of the liquid is continued until the temperature in the vessel is in the range between 10 and 30° C., preferably ambient temperature.

[0121] After this temperature is reached, the pressure in the crystallization vessel 100 is increased until ambient pressure is reached without heating the liquid mixture. Therefore, the suspension produced in the crystallization vessel 100 preferably has ambient temperature and ambient pressure before it is withdrawn from the crystallization vessel 100 via drain line 115.

[0122] By this process for cooling the liquid in the crystallization vessel 100 no cooled surfaces have to be provided on which DCDPS would crystallize. Therefore, during crystallization no solid deposits on walls are formed. However, it is possible to support cooling of the liquid mixture by additional cooling after the temperature of the liquid mixture is reduced to a temperature in the range from 20 to 60° C. For this additional cooling for example coolable surfaces can be provided. These coolable surfaces for example can be a cooling jacket 117 as shown in the FIGURE or alternatively or additionally cooling coils or cooling baffles.

[0123] If the crystallization vessel 100 is operated continuously, organic mixture and water are continuously fed into the crystallization vessel 100 via feed lines 101 and 102 and suspension comprising crystallized DCDPS and organic solvent is continuously removed from the crystallization vessel 100 via drain line 115. In a continuous process preferably at least two crystallization vessels 100 connected into series are used. In the first crystallization vessel 100 the pressure in the crystallization vessel is kept constantly at a value at which the temperature is in a range from 40 to 90° C. and in the last crystallization vessel the pressure is kept such that the temperature is in the range from −10 to 50° C. If more than two crystallization vessels are used, the pressure in the crystallization vessels between the first and the last crystallization vessel is between the temperature in the first and in the last crystallization vessel and the temperature in all crystallization vessels decreases from the first to the last crystallization vessel. In each crystallization vessel 100 the temperature is set by withdrawing evaporated solvent via the exhaust gas line 105, condensing the evaporated solvent in the condenser 109 by cooling and returning the condensed solvent into the crystallization vessel 100 via line 111.

[0124] To keep a constant gas flow into the condenser 109 for continuous operation it is preferred to place an additional pump into the exhaust gas line 105 between the vessel 100 and the condenser 109 or into the line 111 between the condenser 109 and the vessel 100.

EXAMPLES

Example 1

[0125] For producing 4,4′-dichlorodiphenyl sulfone (DCDPS), 1098 g 4,4′-dichlorodiphenyl sulfoxide (DCDPSO) were dissolved in 2917 g n-heptanoic acid. Additionally, 7.2 g sulfuric acid were added. Over a period of 3 h 197 g H.sub.2O.sub.2 were added to oxidize the DCDPSO in the solution.

[0126] To the resulting organic mixture comprising DCDPS and n-heptanoic acid, 881 g water were added with a temperature of 97° C. The thus obtained mixture was cooled by reducing the pressure according to the cooling profile shown in table 1.

TABLE-US-00001 TABLE 1 cooling profile time [h] temperature [° C.] pressure [mbar] 0:00  97 760 0:50 81 380 01:15  90 580 1:45 90 580 2:45 81 370 3:40 61.5 175 4:35 43 70 6:00 18 980

[0127] A suspension comprising 2480 g n-heptanoic acid and DCDPS was obtained by this process.

[0128] The suspension then was filtered at ambient temperature to obtain a filter cake comprising about 80 wt % DCDPS, 16 wt % n-heptanoic acid and 4 wt % water. The mother liquor which was separated off the filter cake in the filtration process contained about 78 wt % n-heptanoic acid, 20 wt % water and about 2.5 wt % DCDPS. For filtering the suspension, a glass nutsche was used which was covered with a Sefar® Tetex DLW 17-80000-SK 020 Pharma filter cloth. For filtering, an absolute pressure of 500 mbar was set below the nutsche. After filtration, the filter cake was treated with dry air for 30 s.

[0129] The crystallizate obtained contained 99.724 wt % 4,4′-dichlorodiphenyl sulfoxide, 0.031 wt % 2,4′-dichlorodiphenyl sulfoxide and 0.24 wt % heptanoic acid and had a color index APHA=17.

Example 2

[0130] For producing DCDPS, 1000.2 g DCDPSO were dissolved in 3000 g n-heptanoic acid. Additionally, 1.2 g sulfuric acid were added. Over a period of 3 h 40 min 197.1 g H.sub.2O.sub.2 were added to oxidize the DCDPSO in the solution. The resulting organic mixture comprising DCDPS had a temperature of 93° C.

[0131] For separating the DCDPS, the organic mixture comprising DCDPS was cooled to a temperature of 20° C. by a cooling ramp of 73 K in 2 h 38 min and then the temperature was maintained at 20° C. for additional 2 h 34 min.

[0132] The suspension obtained by this process was filtered at ambient temperature to obtain a filter cake comprising the DCDPS. The filter cake was washed with 1.3 kg 5% aqueous NaOH and then two times with 1.3 kg water, each. The washed filter cake was dried for 16 h at a temperature of 60° C. to obtain dried DCDPS.

[0133] The dried DCDPS had a color index APHA=99 and a residual content of n-heptanoic acid of 0.23 wt %.

Example 3

[0134] For producing DCDPS, 1000.3 g DCDPSO were dissolved in 3000 g n-heptanoic acid. Additionally, 1.3 g sulfuric acid were added. Over a period of 3 h 40 min 197.1 g H.sub.2O.sub.2 were added to oxidize the DCDPSO in the solution. The resulting organic mixture comprising DCDPS had a temperature of 94° C.

[0135] To the resulting organic mixture comprising DCDPS and n-heptanoic acid, 794 g water were added with a temperature of 90° C. The thus obtained mixture was cooled by reducing the pressure over a time period of 5 h 12 min in such a way that the temperature was reduced by 74 K. During cooling, the organic mixture was agitated.

[0136] The suspension obtained by this process was filtered at ambient temperature to obtain a filter cake comprising the DCDPS. The filter cake was washed with 1.3 kg 5% aqueous NaOH and then two times with 1.3 kg water, each. The washed filter cake was dried for 16 h at a temperature of 60° C. to obtain dried DCDPS.

[0137] The dried DCDPS had a color index APHA=31 and a residual content of n-heptanoic acid of 0.16 wt %.