The invention provides an improved alkylation process and reactor apparatus. The invention utilizes a vessel (19) containing a riser-reactor conduit (50), an acid settler (60) and an acid cooler (70). Hydrocarbons are introduced beneath said riser-reactor conduit (50), mixed with acid catalyst, and passed generally upwards through the riser-reactor conduit (50) to enter the acid settler (60). Within the acid settler (60), alkylate is separate from the acid catalyst and is removed from the vessel (19). Acid catalyst from the acid settler (60) is cooled in the internal acid coolers (70) and returned to the region beneath the riser-reactor conduit (50).