Alkylation and Other Processes for Refinery Propylene

Propylene, originating from catalytic and thermal cracking processes like Fluid Catalytic Cracking, FCC and Delayed Coking, DCU, presents a processing challenge for petroleum refineries. Fortunately, there are many options for handling and processing refinery propylene. If the demand from the petrochemical market is strong, refinery grade propylene can be recovered in a refinery gas plant processing unsaturated or olefinic feed. A refinery can produce chemical or polymer grade propylene by adding additional treatment and distillation equipment. Derivatives like isopropyl benzene are produced in refineries that recover benzene as well as propylene. Refineries have stayed away from adding the capability for converting propylene to polypropylene.

Lacking the existence or proximity to strong propylene or derivative demand, refiners have traditionally used processes for reacting propylene to maximize production of gasoline blend stocks. These processes have historically included catalytic polymerization and acid catalyzed alkylation of isobutane. More recently, to meet environmental regulation restricting benzene in gasoline, some refiners have implemented technology to alkylate dilute benzene streams with propylene, resulting in a benzene regulation compliant, higher octane product.

This paper will define and compare key characteristics and considerations for refinery propylene processes for both fuels and petrochemicals. The emphasis will be on alkylation of isobutane for fuel but will also include petrochemical alternatives that could increase product value and improve refinery profitability.