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Catalysis Looks to the Future
The alkylation of paraffins with olefins is one of the major refinery operations. The process reacts a paraffin, usually isobutane, with olefins, generally propylene and butenes, to produce highly branched C7 and C8 paraffins, respectively. They constitute a premium high-octane gasoline component (95-98 research octane number for C4 alkylate). The alkylation process is assuming increasing importance with increased olefin production from modern fluid catalytic cracking units and with recent emphasis on clean fuels of lower aromatics content.
Both of the currently used liquid acid catalysts, sulfuric acid and hydrogen fluoride, are very corrosive. Acid waste disposal in the sulfuric acid-catalyzed process is of increasing environmental concern, and liquid hydrogen fluoride is a potential health hazard. With increasing concerns and possible legislative action addressing environmental and safety issues, current alkylation processes may face critical scrutiny.
Exploratory studies have shown that new catalysts can be developed that are cleaner and safer than those presently used. However, it is also apparent that powerful acid catalysts are required for alkylation. It is a formidable challenge to produce a novel catalyst system that makes a new process economically feasible: high yield of alkylate, selectivity to produce high-octane gasoline, long life cycle, regenerability, and greatly reduced environmental and safety risks. This is a challenge that would benefit from broad-based fundamental studies of acid catalysis and from increased exploratory research. At the present time, no satisfactory solid alkylation catalyst exists.
Replacements for Chlorofluorocarbons
Chlorofluorocarbons (CFCs) are now believed to contribute to the seasonal ozone depletion over the Antarctic continent. However, because they are crucial to many aspects of modern society and have no available replacements, it is not practical to cease their production immediately. By 1988, total CFC consumption worldwide had grown to 2.5 billion pounds per year. The three major uses in the United States are as refrigerants (30%), foam blowing agents for polystyrene and polyurethane (28%), and industrial solvents and cleaning agents (19%).
Ironically, it is the high stability and inertness of CFCs, which make them so valuable, that has led to their downfall. Once released at ground level into the atmosphere, they rise slowly into the stratosphere where they are degraded by high-energy radiation from the sun, to release chlorine-containing free radicals that trigger a catalytic ozone depletion cycle. Following detailed though not definitive studies, agreement was reached on a