Peracetic acid is prepared on-site and on-demand in a continuous process and at a controlled rate to meet the demand of a downstream operation. In one aspect, a continuous tank reactor is used to produce quantities of peracetic acid at a controlled rate in liquid or vapor form. In another aspect, the use of super acid catalysts enhances the production of peracetic acid under milder conditions, for example, than those typically encountered when using sulfuric acid catalysts alone.