PROCESS FOR PURIFYING 4,4'-DICHLORODIPHENYL SULFOXIDE

Abstract

The invention relates to a process for purifying 4,4′-dichlorodiphenyl sulfoxide comprising: (a) providing a suspension comprising particulate 4,4′-dichlorodiphenyl sulfoxide in monochlorobenzene, (b) solid-liquid separation of the suspension to obtain residual moisture containing 4,4′-dichlorodiphenyl sulfoxide, (c) washing residual moisture containing 4,4′-dichlorodiphenyl sulfoxide with monochlorobenzene, (d) optionally repeating steps (a) to (c).

Claims

1. A process for purifying 4,4′-dichlorodiphenyl sulfoxide comprising: (a) providing a suspension comprising particulate 4,4′-dichlorodiphenyl sulfoxide in monochlorobenzene, (b) solid-liquid separation of the suspension to obtain residual moisture containing 4,4′-dichlorodiphenyl sulfoxide, (c) washing the residual moisture containing 4,4′-dichlorodiphenyl sulfoxide with monochlorobenzene, (d) optionally repeating steps (a) to (c).

2. The process according to claim 1, wherein at least a part of the monochlorobenzene is purified after being used for washing the filter cake and recycled.

3. The process according to claim 2, wherein the monochlorobenzene is purified by distillation or evaporation.

4. The process according to claim 2, wherein at least a part of the purified monochlorobenzene is recycled into a process for producing the suspension comprising particulate 4,4′-dichlorodiphenyl sulfoxide in a monochlorobenzene.

5. The process according to claim 2, wherein at least a part of the purified monochlorobenzene is reused for washing the residual moisture containing 4,4′-dichlorodiphenyl sulfoxide.

6. The process according to claim 1, wherein solid-liquid separation and washing are carried out in one apparatus.

7. The process according to claim 1, wherein the solid-liquid separation is a filtration.

8. The process according to claim 7, wherein the filtration is carried out in an agitated pressure nutsche, a rotary pressure filter, a drum filter or a belt filter.

9. The process according to claim 1, wherein the monochlorobenzene used for washing the residual moisture containing 4,4′-dichlorodiphenyl sulfoxide comprises less than 1 vol-% impurities.

10. The process according to claim 1, wherein the suspension comprising 4,4′-dichlorodiphenyl sulfoxide and monochlorobenzene is produced by crystallization of 4,4′-dichlorodiphenyl sulfoxide in the monochlorobenzene.

Description

[0108] An illustrative embodiment of the invention is shown in the FIGURE and explained in more detail in the following description.

[0109] In the drawing:

[0110] FIG. 1 shows a schematic flow diagram of the process for purifying DCDPSO

[0111] The only FIGURE shows a schematic flow diagram of the process for purifying DCDPSO.

[0112] A suspension 1 comprising DCDPSO and MCB is fed into a filtration apparatus 3. In the filtration apparatus 3 the suspension 1 is separated into solid DCDPSO which forms a filter cake 5 and a mother liquor 7 as filtrate. The mother liquor 7 is withdrawn from the filtration apparatus 3.

[0113] In the embodiment shown in the FIGURE, the filter cake 5 afterwards is washed in the filtration apparatus. For washing the filter cake 5, MCB is fed into the filtration apparatus via MCB feed line 9. After the washing step, the filter cake 5 is removed from the filtration apparatus 3 which is depicted with arrow 6.

[0114] If the filtration and washing are carried out continuously in one apparatus, the filtration apparatus 3 preferably is a band filter. In the band filter the suspension is fed on one end of a filter band 11 and transported through the filtration apparatus 3. While being transported through the filtration apparatus 3, the suspension is filtered forming the filter cake 5 and the mother liquor 7. After a certain filtration duration which depends on the length and the speed of the filter band 11, MCB for washing the filter cake 5 is added. For washing the filter cake, MCB passes the filter cake and the filter band 11 on which the filter cake 5 lies and is collected below the filter band 11 and withdrawn from the filtration apparatus 3 via line 13.

[0115] Besides using one apparatus for filtration and washing as shown in FIG. 1, it is also possible to use one filtration apparatus in which the suspension is filtered forming a filter cake and mother liquor and a second apparatus into which the filter cake is transferred and then washed. Further, if the filtration and washing are carried out batchwise, first the suspension is filtered and the filter cake obtained by the filtration is washed in the same apparatus. In the batchwise process, however, unlike in a continuous process it is not necessary to transport the filter cake. Therefore, also filter apparatus can be used which do not convey the filter cake, for example an agitated pressure strainer, a rotary pressure filter or a drum filter.

[0116] The mother liquor 7 and MCB used for washing 13 are withdrawn from the filtration apparatus 3 and fed into a purifying step 15. Purifying of the mother liquor and MCB used for washing can be performed for example by evaporation or distillation. Generally, MCB is low boiler and thus evaporated and withdrawn as vapor 17. Subsequently the vaporous MCB is condensed and can be reused, for example for producing the suspension or for washing the filter cake.

[0117] In the evaporation or distillation, the high boilers are concentrated in MCB. This concentrated solution 19 is withdrawn from the purification step 15 and can be recycled into a process for producing the suspension, for example by cooling and crystallization of 4,4′-dichlorodiphenyl sulfoxide.

[0118] Besides adding the mother liquor obtained in the filtration and MCB from the washing step to one purifying step as shown in FIG. 1 it is also possible to concentrate the mother liquor and to purify MCB from the washing step separately. In this case concentrating the mother liquor and purifying MCB preferably both are carried out by distillation or evaporation, wherein MCB in both distillations and/or evaporations is the low boiler and withdrawn in gaseous form and the concentrated mother liquor and the impurities from the washing process are the high boiler and in liquid form, respectively. The concentrated mother liquor can be used in the step for producing the suspension and the high boilers which are obtained by distillation or evaporation in the purifying step of MCB used for washing are removed.

[0119] Further, it is also possible to carry out the concentration of the mother liquor and the purification separately. To further purify MCB removed from the mother liquor in the concentrating process, the MCB removed from the mother liquor is added into the process for purifying MCB, too.

Examples

[0120] 5.5 mol aluminum chloride and 40 mol MCB were fed into a stirred tank reactor as first reactor. 5 mol thionyl chloride were added to the reaction mixture in 160 min. The reaction in the first reactor was carried out at 10° C. Hydrogen chloride produced in the reaction was withdrawn from the process. After finishing the addition of thionyl chloride the reaction mixture was heated to 60° C.

[0121] After finishing the reaction in the first reactor, the resulting reaction mixture was fed into a second stirred tank reactor which contained 3400 g hydrochloric acid with a concentration of 11 wt %. The second stirred tank reactor was heated to a temperature of 90° C. After 30 min the mixing was stopped and the mixture separated into an aqueous phase and an organic phase.

[0122] The aqueous phase was withdrawn and the organic phase was washed with 3000 g water while stirring at 90° C. After washing, stirring was stopped and the mixture separated into an aqueous phase and an organic phase.

[0123] The aqueous phase was removed and the organic phase was subjected to a crystallization. At 30° C. the resulting suspension was filtered. By the filtration a filter cake was obtained which was washed with monochlorobenzene (MCB). Table 1 compiles the results regarding the composition of the filter cake depending on the amount of washing liquid used.

TABLE-US-00001 TABLE 1 Composition of the filter cake depending on the amount of MCB used for washing Filter Cake Composition 4,4′- 2,4′- 4,4′- Ratio [g/g] MCB DCDPSO DCDPSO dichlorodiphenylsulfide Example MCB:filter cake [wt %] [wt %] [wt %] [wt %] 1 no washing 8.5 83.7 3.8 4.0  2* .sup. 2:1 10.2 89.7 0.2 0.2  3* .sup. 1:1 10.9 88.3 0.2 0.1 4 0.45:1  11.3 87.9 0.3 0.2 5 0.4:1 10.5 89.3 0.2 0.1 6 0.2:1 10.6 88.8 0.3 0.2 *results achieved by simulation