Purification of sulfuric acid containing acetic acid

A process for purifying dilute sulfuric acid contaminated with acetic acid and hydrogen chloride with the resultant formation of concentrated sulfuric acid of about 94-96 % strength and acetic acid, the sulfuric acid to be purified forming part of a mixture consisting substantially of about 30-60 weight % of concentrated sulfuric acid, about 20-50 weight % of acetic acid, about 10-40 weight % of water, and about 2-10 weight % of hydrogen chloride, which process comprises:

• heating, in a first step, the contaminated sulfuric acid to a temperature of at most about 60.degree. C under a pressure of about 25-30 mm Hg and thereby expelling all of the hydrogen chloride together with minor proportions of acetic acid and water;
• heating, in a second step, the sulfuric acid to a temperature of at most 165.degree. C under a pressure of about 20-25 mm Hg and thereby distilling off the bulk of acetic acid together with water with the resultant formation of (a) sulfuric acid containing at most 1.3 up to 1.6 weight % of residual acetic acid and (b) of acetic acid of about 70-80 weight % strength;
• cooling, in a third step, the sulfuric acid down to a temperature of about 60.degree.-90.degree. C, diluting it with about 10-30 weight % of water with agitation and while cooling is continued, and then heating the sulfuric acid to a temperature of about 160.degree.-165.degree. C under a pressure of about 20-25 mm Hg and thereby freeing it from the water and residual acetic acid.