Purification of 5-sulfoisophthalic acid by the use of an acetic acid wash on a crude cake

1. A method of purifying 5-sulfoisophthalic acid comprising the steps of:

obtaining a crude cake of 5-sulfoisophthalic acid having a sulfur compound as an impurity, and

washing said crude cake with acetic acid.

2. The method of claim 1 wherein said crude cake of 5-sulfoisophthalic acid contains sulfuric acid as an impurity.

3. The method of claim 1 wherein the step of obtaining a crude cake of 5-sulfoisophthalic acid comprises filtering a crude product of 5-sulfoisophthalic acid using solids isolation equipment.

4. The method of claim 1 further comprising the prior step of sulfonating isophthalic acid to obtain 5-sulfoisophthalic acid.

5. The method of claim 1 further comprising the step of recovering and recycling said acetic acid.

6. The method of claim 1 wherein the washing step is repeated.

7. The method of claim 3 wherein the washing step occurs while the crude product cake remains in the solids isolation equipment.

8. A method of manufacturing 5-sulfoisophthalic acid comprising the steps of:

sulfonating isophthalic acid to form 5-sulfoisophthalic acid,

isolating 5-sulfoisophthalic acid to form a crude cake;

washing the crude cake with acetic acid; and

drying the washed crude cake.

9. The method of claim 8 wherein the sulfonating step comprises contacting isophthalic acid with sulfuric acid.

10. The method of claim 8 wherein the isolating step and the washing step occur in the device utilized in the isolating step.

11. The method of claim 8 wherein said acetic acid is recovered and recycled.

12. A method of manufacturing 5-sulfoisophthalic acid comprising the steps of:

sulfonating isophthalic acid to form a 5-sulfoisophthalic acid product,

isolating said 5-sulfoisophthalic acid product to form a crude cake of 5-sulfoisophthalic acid product;

washing the crude cake with a liquid wherein said liquid does not dissolve a significant quantity of the product but is sufficiently polar to remove ionizable impurities from the product; and

drying the product wherein the wash liquid is acetic acid.

13. The method according to claim 12 wherein the steps of isolating and washing occur in the device utilized in the isolation step.

14. The method according to claim 12 wherein the impurity is a sulfur compound.

15. The method according to claim 12 in which the acetic acid is recovered and recycled.

16. The method according to claim 12 wherein the wash liquid does not significantly ionize the 5-sulfoisophthalic acid product.