Chemistry, Catalysts, and Processes for Isoparaffin–Olefin Alkylation: Actual Situation and Future Trends

As a consequence of the Clean Air Act (CAA), beginning in 1990, USA refiners were forced to change their strategy in order to meet the new mandatory specifications on gasoline composition. The targets established by the CAA were directed to overcoming environmental problems by reducing the ground-level ozone-forming and carbon monoxide emissions from vehicles, as well as toxic hydrocarbons and SO, and NO, emissions in auto exhausts. In order to accomplish this, gasolines had to move in the following direction: Reduce volatility: that is, lower Reid vapor pressure (RVP), especially during summer months, in order to reduce ozone levels. This can be achieved by removing butanes and even C, from the gasoline. Limitations in the aromatic content, with special emphasis on benzene. This can be solved by reducing reformate severity and/or by reducing the upper cut of the fluid catalytically cracked (FCC) gas-oline. Increased amount ofoxygenates, in which MTBE and TAME are preferred, especially in the carbon monoxide and ozone nonattainment areas. Reduction of olefins: This will be achieved by separating the C, olefins from FCC gasoline. Meanwhile, the elimination of C, olefins from the gasoline will further reduce RVP, and the isoamylenes will be used as a raw material to produce TAME in sterification units. Reduction of sulfur: Hydrotreating of FCC feeds, or hydrotreating or removing part of the heavy-end FCC gasoline. Elimination of lead: This, which was already under way when the new regulations were announced, produces a decrease in octane which has to be compensated by other streams coming into the gasoline pool.