Abstract: Disclosed is a continuous process for the sulfonation of an alkylaromatic reactant involving heating liquid sulfur trioxide in a vaporizer and mixing this sulfur trioxide gas stream with a hexane-alkylaromatic stream containing about 1 to about 3 wt. % quantity of a promoter, which can be either sulfuric acid or an alkyl benzene sulfonic acid, in a sulfonator - static inline mixer, mixing water with the sulfonated product as it passes to the water reactor - static inline mixer, passing the aqueous sulfonated product through degassing column-heat exchanger apparatus and separating the sulfonated product from the aqueous sulfuric acid. The reaction is conducted under controlled temperature and pressure conditions.