Alkylation, first commercialized in 1938, experienced tremendous growth during the 1940s as a result of the demand for high-octane aviation fuel during World War II. During the mid-1950s, refiners' interest in alkylation shifted from the production of aviation fuel to the use of alkylate as a blending component in automotive motor fuel. Capacity remained relatively flat during the 1950s and 1960s due to the comparative cost of other blending components. The U.S. Environmental Protection Agency's lead phase-down program in the 1970s and 1980s further increased the demand for alkylate as a blending component for motor fuel. As additional environmental regulations are imposed on the worldwide refining community, the importance of alkylate as a blending component for motor fuel is once again being emphasized. Alkylation unit designs (grassroots and revamps) are no longer driven only by volume, but rather by a combination of volume, octane, and clean air specifications. Lower olefin, aromatic, sulfur, Reid vapor pressure, and drivability index specifications for finished gasoline blends have also become driving forces for increased alkylate demand in the United States and abroad.
The alkylation reaction combines isobutane with light olefins in the presence of a strong acid catalyst. The resulting highly branched, paraffinic product is a low-vapor-pressure, high-octane blending component. Although alkylation can take place at high temperatures without catalyst, the only processes of commercial importance today operate at low to moderate temperatures using either sulfuric or hydrofluoric acid catalysts. Several different companies are currently pursuing research to commercialize a solid alkylation catalyst. The reactions occurring in the alkylation process are complex and produce an alkylate product that has a wide boiling range. By optimizing operating conditions, the majority of the product is within the desired gasoline boiling range with motor octane numbers (MONs) up to 95 and research octane numbers (RONs) up to 98.
Reference: R. A. Myers: Handbook of petroleum refining processes, ISBN: 0-07-139109-6, 2003.