Method of continuously cleansing polyarylene sulfide

1. A process for continuously washing polyarylene sulfide, comprising a washing step of subjecting a polymerizate slurry to continuous countercurrent contact with a washing liquid; said polymerizate slurry containing polyarylene sulfide particles, a by-produced alkali metal salt and a polar organic solvent and obtained through a reaction of an alkali sulfide source and an aromatic dihalide compound in the polar organic solvent; wherein the washing step includes a step of moving the polyarylene sulfide particles as an upward flow countercurrently contacting the washing liquid, and the process further includes a step of continuing the upward flow of the polyarylene sulfide particles to separate the washing liquid therefrom and recover the polyarylene sulfide particles.

2. A process according to claim 1 , wherein the washing step includes a former step of moving the polyarylene sulfide particles as a downward flow countercurrently contacting the washing liquid, and a latter step of moving the polyarylene sulfide particles as an upward flow countercurrently contacting the washing liquid.

3. A process according to claim 2 , wherein the latter step is operated in an inclined tube provided with a conveying screw.

4. A process according to claim 2 , wherein in the latter step, at a point intermediate the upward flow of the polyarylene sulfide particles, the washing liquid is introduced and caused to start contacting the polyarylene sulfide particles.

5. A process according to claim 1 , wherein the washing step is performed in a generally V-shaped tubular apparatus including a downward tube and an upward tube provided with a conveying screw inside whereof; the polymerizate slurry is introduced at a point proximate to a lowermost part of the upward tube of the tubular apparatus so that the polyarylene sulfide particles are countercurrently contacted with the washing liquid; the washed polyarylene sulfide particles are recovered together with the by-produced alkali metal salt from a point proximate to a top of the upward tube; and a mixture liquid comprising the washing liquid and the polar organic solvent is recovered from a point proximate to a top of the downward tube.

6. A process according to claim 1 , wherein in the washing step, an organic solvent miscible with the polar organic solvent and water and having a lower boiling point than water is used as the washing liquid to recover the washed polyarylene sulfide particles accompanied with the by-produced alkali metal salt; and a second washing step is further included, wherein the thus-recovered polyarylene sulfide particles accompanied with the by-produced alkali metal salt are continuously and countercurrently contacted with an aqueous washing liquid to wash and recover the polyarylene sulfide particles.

7. A process according to claim 1 , further including a third washing step and a fourth washing step for sequentially washing the washed polyarylene sulfide particles with an acidic washing liquid and an aqueous washing liquid, respectively, countercurrently contacting the polyarylene sulfide particles.

8. A process according to claim 1 , further including prior to the washing step a preliminary (solid-liquid separation) step operated in a generally V-shaped tubular apparatus including a downward tube and an upward tube provided inside thereof with a conveying screw, wherein the polymerizate slurry is introduced at a point proximate to a top of the downward tube, and the polymerizate slurry with a reduced amount of the polar organic solvent is recovered from a point proximate to a top of the upward tube and supplied to the washing step.

9. A process according to claim 1 , further including prior to the washing step a preliminary step of mixing the polymerizate slurry with a portion of the washing liquid.

10. A process for treating a slurry, comprising: subjecting a slurry comprising a dispersion liquid medium and at least two types of solid particles dispersed in the liquid medium to sequential washing steps including:

a first washing step of washing the slurry by countercurrent contact with a first washing liquid which does not dissolve any of the solid particles but is miscible with the dispersion liquid medium, and

a second washing step of bringing the washed at least two types of solid particles into contact with a second washing liquid which selectively dissolves a part of the at least two types of solid particles and is also miscible with the first washing liquid;

wherein at least one of the first and second washing steps comprises a step of moving said at least two types of solid particles as an upward flow countercurrently contacting the washing liquid, and the process further includes a step of continuing the upward flow of the solid particles to separate the washing liquid therefrom the recover the solid particles.

11. A process according to claim 10 , wherein at least one of the first and second washing steps includes as a latter step a step of moving said at least two types of solid particles as an upward flow countercurrently contacting the washing liquid, and further as a former step preceding thereto a step of moving at least two types of solid particles as a downward flow countercurrently contacting the washing liquid.

12. A process according to claim 11 , wherein the latter step is operated in an inclined tube provided with a conveying screw.