SOLID ACID CATALYTIC ALKYLATION: A MEANS FOR GASOLINE-AROMATICS REDUCTION

摘要

Aromatics have been traditionally used as octane-enhancing components in gasoline. However, their impact on human health and the environment has led many countries to develop legislation to reduce aromatic content, with special emphasis on benzene, in their gasoline pool. Aromatics cause significant health hazards. Benzene, for instance, is a potent carcinogen and ranks among priority pollutants. Aromatic content is not an issue in North Americans gasoline pool, while EU regulations dictates the refiners to reduce the aromatic content of the gasoline pool significantly. This in the coming years may lead to oversupply of toluene and xylenes as petrochemical feed stocks, and for some refiners this may cause difficulties in meeting the volume. The reduction of aromatics alone implies that the gasoline pool would suffer both quantitatively and qualitatively. Alkylates (highly branched paraffinic hydrocarbons) are ideal substitutes because of their, high octane numbers, and environmental friendly characters. Alkylates have played significant roles in US gasoline pool, while in Europe alkylates have a lesser important role. The phase out of lead and the increased capacity of FCC units for making more gasoline from heavier petroleum cuts have enhanced the validity of alkylation processes in petroleum refineries. Current technologies based on concentrated sulfuric acid and hydrofluoric acid catalysts are adequate for production of alkylates. However, the serious environmental concerns and high costs associated with the use of these acids in alkylation processes are the major drawbacks and impose limitations toward future expansion of liquid acid catalyzed plants. Technological difficulties in development of the more environmental benign and cost effective solid acid catalyzed process have delayed commercialization of such processes. However, after many years of endeavors, solid acid alkylation process is moving from laboratory to pilot plant stage and beyond. The developments have been aimed at both the catalyst type and process parameters. Patents are now available in the market. This paper will fully discuss the challenges, status, and process principles of solid acid catalyzed alkylation as well as the main parameters governing the kinetics and catalysis. Based on the data obtained in our own laboratory on a new developed catalyst, it is predicted to behave as a successful catalyst for C_4 alkylation to produce high-octane branched chain hydrocarbons from petroleum refinery gases.