A PROCESS FOR OBTAINING 4,4'-DICHLORODIPHENYL SULFOXIDE

Abstract

The invention relates to a process for obtaining 4,4′-dichlorodiphenyl sulfoxide from a liquid mixture comprising dichlorodiphenyl sulfoxide and a solvent, comprising: (a) cooling the liquid mixture to a temperature below the saturation point of 4,4′-dichlorodiphenyl sulfoxide in the solvent to obtain a suspension comprising crystallized 4,4′-dichlorodiphenyl sulfoxide, (b) solid-liquid-separation of the suspension to obtain a residual moisture containing solid 4,4′-dichlorodiphenyl sulfoxide as a product and mother liquor, (c) concentrating the mother liquor, (d) recycling at least a part of the concentrated mother liquor into the cooling step (a).

Claims

1.-14. (canceled)

15. A process for obtaining 4,4′-dichlorodiphenyl sulfoxide from a liquid mixture comprising 4,4′-dichlorodiphenyl sulfoxide and chlorobenzene, comprising: (a) cooling the liquid mixture to a temperature below the saturation point of 4,4′-dichlorodiphenyl sulfoxide in the chlorobenzene to obtain a suspension comprising crystallized 4,4′-dichlorodiphenyl sulfoxide, (b) solid-liquid-separation of the suspension to obtain a residual moisture containing solid 4,4′-dichlorodiphenyl sulfoxide as a product and mother liquor, (c) concentrating the mother liquor, (d) recycling at least a part of the concentrated mother liquor into the cooling step (a).

16. The process according to claim 1, wherein the chlorobenzene is monochlorobenzene.

17. The process according to claim 1, wherein cooling step (a) is carried out in a gastight closed vessel (100) by (i) reducing the pressure in the gastight closed vessel (100); (ii) evaporating solvent; (iii) condensing the evaporated solvent by cooling; and (iv) returning the condensed solvent into the gastight closed vessel.

18. The process according to claim 17, wherein steps (ii) to (iv) are carried out during pressure reduction in step (i).

19. The process according to claim 17, wherein the pressure reduction in step (i) is continued until the pressure in the gastight closed vessel (100) reaches a predefined value in the range between 20 to 350 mbar(abs).

20. The process according to claim 17, wherein after the pressure reached the predefined value the process is finished, and the pressure is set to ambient pressure.

21. The process according to claim 17, wherein for initializing crystallization of the 4,4′-dichlorodiphenyl sulfoxide following steps are carried out before setting the reduced pressure in step (i): reducing the pressure in the gastight closed vessel such that the boiling point of the mixture is in the range between 80 and 95° C.; evaporating solvent until an initial formation of solids takes place; increasing the pressure in the vessel and heating the liquid mixture in the vessel to a temperature in the range between 85 and 100° C.

22. The process according to claim 15, wherein the mother liquor is concentrated by distillation or evaporation of solvent.

23. The process according to claim 22, wherein the distillation or evaporation is carried out at a pressure in the range between 20 and 800 mbar(abs).

24. The process according to claim 22, wherein the distillation is carried out in a distillation column with a bottom temperature in a range from 40 to 110° C. and a head temperature in a range from 30 to 100° C.

25. The process according to claim 22, wherein the evaporation or distillation is continued until the amount of mother liquor is reduced to 4 to 80 wt. % of the amount of mother liquor fed into the evaporation or distillation.

26. The process according to claim 22, wherein the evaporation or distillation is continued until the concentration of 4,4′-dichlorodiphenyl sulfoxide in the mother liquor is in the range from 6 to 60 wt. %.

27. The process according to claim 15, wherein the amount of concentrated mother liquor recycled into the cooling (a) is in the range from 10 to 95 wt. %.

28. The process according to claim 15, wherein the cooling (a) is continued until a solids content in the suspension in the range from 5 to 50 wt. % is achieved.

Description

[0093] In the drawing:

[0094] FIG. 1 shows a schematic flow diagram of the process for obtaining DCDPSO from a liquid mixture comprising DCDPSO and solvent,

[0095] FIG. 2 a vessel for crystallization of DCDPSO.

[0096] An embodiment of the inventive process for obtaining DCDPSO from a liquid mixture comprising DCDPSO and solvent is shown in FIG. 1.

[0097] A liquid mixture 1 comprising DCDPSO and solvent is fed into a crystallization step 3. In the crystallization step 3 the liquid mixture is cooled to a temperature below the saturation point of DCDPSO in the solvent. This has the effect that DCDPSO starts to crystallize and a suspension is formed comprising solid DCDPSO crystals in a liquid which contains solvent, DCDPSO which is not crystallized and liquid byproducts. This suspension is fed into a solid-liquid-separation step 5. By solid-liquid-separation, for example filtration, the solid DCDPSO crystals are separated from the liquid phase, obtaining DCDPSO crystals 7 as product and mother liquor.

[0098] The solid-liquid-separation step 5 can be carried out in any suitable apparatus, particularly in a filtration apparatus, for example an agitated pressure nutsche, a rotary pressure filter, a drum filter or a belt filter or a centrifuge. The differential pressure in the filtration apparatus preferably is in the range between 100 and 6000 mbar, more preferred between 300 and 2000 mbar and particularly in the range between 400 and 1500 mbar. The filtration preferably is carried out at ambient temperature. Due to the necessary differential pressure in the filtration step, ambient pressure either can be set on the feed side which means that the pressure on the filtrate side is below ambient pressure, or ambient pressure is set on the filtrate side and a pressure above ambient pressure is set on the feed side.

[0099] The solid DCDPSO 7 is removed from the process and the mother liquor is fed into a concentrating step 9. In the concentrating step 9, solvent is removed from the mother liquor and withdrawn from the process as stream 11.

[0100] To remove by-products and impurities from the process which are not removed with the solvent, a part of the concentrated mother liquor is withdrawn as stream 13. The rest 15 of the concentrated mother liquor is recycled into the crystallization step 3.

[0101] The concentrating step 9 for example is a distillation or evaporation. In the distillation or evaporation solvent as low boiler is removed in gaseous form and the concentrated mother liquor containing the high boilers is removed in liquid form. If the mother liquor is concentrated by evaporation or distillation, the distillation or evaporation preferably is carried out at a pressure in the range between 20 and 800 mbar(abs), more preferred in a range between 50 and 500 mbar(abs), and particularly in a range between 100 and 350 mbar(abs). The bottom temperature if the concentrating step is operated by distillation or the temperature for evaporation preferably is in the range between 40 and 110° C., more preferred in the range of 55 and 100° C. and in particularly in the range between 55 and 80° C.

[0102] FIG. 2 shows a vessel for cooling and crystallizing DCDPSO.

[0103] To avoid fouling on cooled surfaces of a cooling and crystallization apparatus, it is preferred to use a gastight closed vessel 100 as shown in FIG. 2 for carrying out cooling and crystallization of DCDPSO. The cooling is performed by pressure reduction and the lowering of the boiling point due to the reduced pressure.

[0104] The liquid mixture comprising DCDPSO and solvent is fed into the vessel 100 via feed line 101. To achieve a homogeneous temperature and concentration in the liquid in vessel 100, the vessel 100 preferably is a stirred tank comprising at least one stirrer 103. By stirring the liquid mixture in the vessel further crystallized DCDPSO is kept in the forming dispersion and precipitation of crystallized DCDPSO and thus fouling is avoided.

[0105] For cooling the liquid mixture in the vessel 100 by dropping the boiling point of 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 vessel 100 and the vacuum pump 107, a condenser 109 is accommodated in the exhaust gas line 105. In the condenser 109 solvent which is evaporated from the boiling liquid mixture in the vessel 100 is condensed by cooling. The condensed solvent then is returned into the vessel 100 via line 111. Further, to remove low boilers from the crystallization or to increase the concentration of DCDPSO in the liquid mixture to facilitate crystallization and thus increase the yield of solid DCDPSO obtained by crystallization, a withdrawing line 113 is provided via which condensed solvent and low boilers, if present, can be removed from the process.

[0106] By a drain line 115 suspension comprising crystallized DCDPSO is withdrawn from the vessel 100. The drain line 115 is connected to the filtration step 5 to feed the suspension into the filtration step 5.

[0107] The vessel 100 for cooling and crystallization can be operated either batchwise or continuously. If the vessel 100 for cooling and crystallization is operated batchwise, in a first step the liquid mixture is fed into the vessel 100. After a predefined filling level is reached, feeding of the liquid mixture is stopped. In a next step, the pressure in the vessel 100 is reduced using the vacuum pump 107 until a pressure in the vessel 100 is reached at which the boiling point of the liquid mixture is in a range between 80 and 95° C. Due to pressure reduction the liquid mixture starts boiling and solvent and low boilers evaporate. Once the saturation point of the DCDPSO in the solvent is reached, the pressure in the vessel is increased and the liquid mixture is heated to a temperature between 85 and 100° C. to dissolve partially the DCDPSO to achieve crystal nuclei of a homogeneous size. After this heating phase, the pressure in the vessel 100 is reduced again. By this pressure reduction the boiling point of the liquid mixture drops, solvent evaporates and is withdrawn from the vessel 100 via exhaust gas line 105. In the condenser 109 the evaporated solvent is condensed by cooling and the condensed solvent is recycled into the vessel 100. This recycling of solvent results in cooling of the liquid mixture leading to crystallization of DCDPSO. The temperature reduction in the 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.

[0108] After this temperature is reached, the pressure in the vessel is increased until ambient pressure is reached without heating the liquid mixture. Therefore, the suspension produced in the vessel 100 preferably has ambient temperature and ambient pressure before it is withdrawn from the vessel 100 via drain line 115.

[0109] By this process for cooling the liquid in the vessel 100 no cooled surfaces have to be provided on which DCDPSO would crystallize. Therefore, during crystallization no solid deposits on walls are formed.

[0110] If the vessel 100 is operated continuously, liquid mixture is continuously fed into the vessel 100 via feed line 101 and suspension comprising crystallized DCDPSO and solvent is continuously removed from the vessel 100 via drain line 115. In a continuous process preferably at least two vessels 100 connected into series are used. In the first vessel 100 the pressure in the vessel is kept constantly at a value at which the temperature is in a range from 65 to 85° C. and in the last vessel the pressure is kept such that the temperature is in the range from 0 to 45° C. If more than two vessels are used, the pressure in the vessels between the first and the last vessel is between the temperature in the first and in the last vessel and the temperature in all vessels decreases from the first to the last vessel. In each 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 vessel 100 via line 111.

[0111] 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

[0112] Influence of final crystallization temperature (without concentrating and recycling of mother liquor) on the 4,4′-dichlorodiphenyl sulfoxide yield

[0113] A liquid mixture comprising 25 wt % DCDPSO based on the total amount of the liquid mixture was cooled to a desired temperature according to Table 1 at a cooling rate of 15 K/h by which a suspension formed. The suspension was filtrated to obtain a filter cake. The filter cake was washed with monochlorobenzene (100 g) and dried at 80° C. and 20 mbar(abs) overnight which yielded the desired product 4,4′-dichlorodiphenyl sulfoxide (4,4′-DCDPSO) as a fine white crystalline powder (1st isolated yield).

[0114] The mother liquor was distilled and concentrated to 20 wt % of the original amount. The concentrated mother liquor was cooled to 20° C. by which a suspension formed. This suspension was filtered to obtain a filter cake which was washed with chlorobenzene (100 g) and dried at 80° C. and 20 mbar(abs) overnight which yielded the desired product 4,4′-DCDPSO as a fine white crystalline powder (2nd isolated yield).

TABLE-US-00001 TABLE 1 Variation of crystallization temperatures Crystallization 1.sup.st and 2.sup.nd Purity temperature Isolated 4,4′-DCDPSO Experiment [° C.] Yield [%] [wt %] 1 0  78.3/n.d. 100/— 2 20 77.9/5.5 100/92 3 30 77.9/7.7 100/95 4 40  74.5/11.5 99.5/96 

[0115] Crystallization without concentrating and recycling the mother liquor (comparative example)

[0116] A liquid mixture comprising 25.2 wt % DCDPSO, 72.9 wt % monochlorobenzene, 0.2 wt % 4,4′-dichlorodiphenylsulfide and 1.7 wt % 2,4′-dichlorodiphenylsulfoxide which was obtained in a reaction for obtaining DCDPSO was subjected to a distillation. Monochlorobenzene was distilled from the liquid mixture until saturation was reached at about 88° C. (monitored via a turbidity probe, distillation conditions: 200 mbar(abs)). Then the liquid mixture was cooled by reducing the pressure until the temperature reached 30° C. By the cooling a suspension comprising crystallized DCDPSO was obtained which was objected to a filtration process to obtain a filter cake comprising crystallized DCDPSO.

[0117] After filtration and washing of the filter cake with monochlorobenzene the crystalline solid was dried at 100° C. and 100 mbar(abs).

[0118] The 4,4′-dichlorodiphenyl sulfoxide was obtained in 83.2% yield, with a purity of 98.8 wt %, containing 0.6 wt % monochlorobenzene, 0.2 wt % 4,4′-dichlorodiphenylsulfide and 0.4 wt % 2,4′-dichlorodiphenylsulfoxide.

[0119] Influence of concentrating and recycling the mother liquor into the crystallization process (inventive example)

[0120] A liquid mixture comprising 26.7 wt % DCDPSO, 66.3 wt % monochlorobenzene, 0.5 wt % 4,4′-dichlorodiphenylsulfide and 6.5 wt % 2,4′-dichlorodiphenylsulfoxide which was obtained in a reaction for obtaining DCDPSO was subjected to a distillation. Monochlorobenzene was distilled from the liquid mixture until saturation was reached at about 88° C. (monitored via a turbidity probe, distillation conditions: 200 mbar(abs)). Then the liquid mixture was cooled by reducing the pressure until the temperature reached 30° C. By the cooling a suspension comprising crystallized DCDPSO was obtained which was objected to a filtration process to obtain a filter cake comprising crystallized DCDPSO.

[0121] After filtration and washing of the filter cake with monochlorobenzene the crystalline solid was dried at 100° C. and 100 mbar(abs). The combined mother liquor and washing filtrate were subjected to a distillation. In the distillation monochlorobenzene was removed until the amount of combined mother liquor and washing filtrate was reduced to 25 wt %. The distillation was operated at a bottom temperature of 90° C. and 200 mbar(abs).

[0122] 80 wt % of the obtained bottom product were transferred into the crystallization of the next batch.

[0123] The 4,4′-dichlorodiphenyl sulfoxide yield in the steady state with loop crystallization were 1232 g which corresponds to 91.3%.

[0124] The 4,4′-dichlorodiphenyl sulfoxide had a purity of 98.9 wt %, containing 0.5 wt % monochlorobenzene, 0.3 wt % 4,4′-dichlorodiphenylsulfide and 0.3 wt % 2,4′-dichlorodiphenylsulfoxide.