Catalytic alkylation apparatus

A continuous process for alkylating an alkylatable hydrocarbon in the presence of a acid-type catalyst in which the alkylatable hydrocarbon is contacted with an alkylating agent in the presence of a catalyst in a reaction zone so as to alkylate the alkylatable hydrocarbon. The reaction product is separated in an acid settler vessel into an alkylate product phase, located in the upper portion of the first separation zone, and a catalyst phase located in the lower portion of the first separation zone. The catalyst phase is further separated into a first portion and second portion, such that the first portion is cooled and recycled for use in the alkylation reaction zone as a catalyst recycle, and the second portion is passed into a second separation zone, wherein the catalyst phase is further separated into a rerun catalyst stream containing acid-type catalyst and an acid soluble oil stream. The rerun catalyst stream is passed into the hydrocarbon phase of the acid settler vessel. In order to prevent excessive pressure in the acid settler vessel as a result of the hot rerun catalyst stream, two liquid hydrocarbon drawoffs from the acid settler vessel are employed. The warm upper drawoff of the acid settler vessel is charged as feed to a depropanizer and stripper and the cool lower drawoff of the acid settler vessel is charged as reflux feed to an isostripper. The acid settler vessel contains a pressure controller set to the desired pressure to be maintained in the upper portion of the acid settler vessel. As the pressure in the acid settler vessel increases, a valve connected to the cool lower drawoff is closed and a valve connected to a conduit attached to the warmer upper drawoff is further opened such that an increased amount of hot hydrocarbon is shifted to the isostripper so as to lower the heat in the acid settler vessel thereby maintaining the desired pressure in the acid settler vessel.