Process for reacting sulfuric acid and an aromatic hydrocarbon to purify a disulfonic acid product of an aromatic hydrocarbon

A chemical purification process for removing unreacted sulfuric acid from a meta-benzene disulfonic acid product, which product is useful in the caustic fusion method of making resorcinol, the meta-benzene disulfonic acid product produced by reacting benzene or benzene monosulfonic acid with an excess of oleum, said purification process comprising:

• (a) providing a mixture containing at least about 20 percent by weight of meta-benzene disulfonic acid and an amount of unreacted sulfuric acid;
• (b) adding benzene to said mixture in an amount providing a molar ratio of said benzene to said unreacted sulfuric acid in said mixture in a range from about 0.25 to one to about 2 to one;
• (c) maintaining the temperature of said mixture in a range from about 130.degree. C. to about 200.degree. C. during the reaction of said benzene and said unreacted sulfuric acid;
• (d) allowing the reaction to proceed without removing water formed during reaction of said benzene and said unreacted sulfuric acid;
• whereby there is produced purified meta-benzene disulfonic acid having little or no unreacted sulfuric acid.