[¦səl¦fyu̇r·ik ′as·əd ‚al·kə′lā·shən] (chemical engineering) A petroleum refinery alkylation process in which three-carbon, four-carbon, and five-carbon olefins combine with isobutane in the presence of a sulfuric acid catalyst to form high-octane, branched-chain hydrocarbons; used in motor gasoline.