An apparatus for the catalytic conversion of a hydrocarbon stream with a mineral acid catalyst comprising a vessel divided into an upper and lower chamber by an imperforate plate. The imperforate plate has a plurality of standpipe means connected thereto whereby hydrocarbon can pass into the upper chamber from hydrocarbon inlet means located in the lower chamber. A perforated plate is located in the upper chamber above the imperforate plate having flow guide conduits axially aligned above each of the standpipe means. A catalyst inlet means is located intermediate the imperforate and perforate plates and an emulsion outlet is located in the upper chamber. The flow guide conduits serve to promote eduction of acid-catalyst into the flow guide conduits by a high velocity hydrocarbon stream emitted from openings in said standpipe means, and to contain and confine the hydrocarbon stream and prevent contact of a resulting acidhydrocarbon emulsion with previously formed emulsion until the hydrocarbons and acid are thoroughly mixed and the hydrocarbons at least partially reacted.