Manufacture of t-butanol

A process for the manufacture of t-butanol by hydration of isobutylene comprising

• a. contacting in a hydrating stage an isobutylene-containing C.sub.4 -hydrocarbon mixture at temperatures of 20.degree. to 45.degree.C and at a pressure from 1 to 10 atmospheres gauge with a mixture of aqueous sulfuric acid and t-butanol, the concentration of the aqueous sulfuric acid being 25 to 45% w/w at the beginning of the reaction and the concentration of the t-butanol in the mixture of aqueous sulfuric acid and t-butanol being from 10 to 35% w/w at the beginning of the reaction,
• b. passing the mixture obtained in the hydrating stage to a separation stage to obtain an essentially isobutylene-free and t-butanol containing C.sub.4 -hydrocarbon mixture and a t-butanol/aqueous sulfuric acid mixture,
• c. introducing the essentially isobutylene-free and t-butanol containing C.sub.4 -hydrocarbon mixture and the t-butanol/aqueous sulfuric acid mixture of step (b) at separate points into an extraction stage and adding essentially isobutylene-free and t-butanol-free C.sub.4 -hydrocarbon mixture to the extraction stage to obtain an extracted mixture of t-butanol and C.sub.4 -hydrocarbon and a t-butanol/aqueous sulfuric acid mixture having a reduced content of t-butanol, said extraction stage being at 0.degree. to 50.degree. C, and
• d. recycling the t-butanol/aqueous sulfuric acid mixture having a reduced content of t-butanol to the hydrating stage and isolating the t-butanol from the extracted mixture of t-butanol and C.sub.4 -hydrocarbon mixture.