compared to the use of corrosion resistant alloys in the isostripper overhead which is a larger item of equipment the acid treatment tower operates at a higher temperature than the isostripper so that the composition of the overhead can approach azeotropic in a way that is not possible in the isostripper the number of stages of separation required in the tower will be dependent on the desired degree of separation between hydrocarbon alkylate polymer and acid in the simplest case a flash drum can be used which will send more hydrocarbon overhead alternatively a refluxed tower with many stages minimizes the amount of hydrocarbon going overhead in either case some butane and light alkylate will end up condensing in the overhead receiver drum because this fraction will contain dissolved acid it will need to be reinjected back into the isostripper tower via line 23 for removal of the acid at that point the remainder of the hf alkylation process including identities and feed hydrocarbons temperatures and equipment items can be conventional in type the olefin feed will typically be c 2 c 4 olefins with preference being given to butylenes although propylene and ethylene may also be used with corresponding changes in product properties and in the appropriate process conditions as is known the iso paraffin most favored for use in the hf alkylation process is isobutane the alkylate product may be treated in the conventional way in the product recovery.