Although the current understanding of how the individual components of gasoline affect various environmental issues is very limited, several components in gasoline are now considered harmful to the environment if released to the atmosphere in high concentration as either spills, vaporization losses, or the result of incomplete combustion. They include aromatics, notably benzene, a carcinogenic reagent; high-vapor-pressure hydrocarbons such as butane; reactive hydrocarbons such as olefins; and sulfur compounds, which could promote the formation of smog and acids. The petroleum industry is responding to these concerns by directing its research toward the reformulation of gasolines. As discussed below, gasoline reformulation will require a number of advances in catalytic technology.
Innovations in catalytic cracking catalysts over the past 30 years have improved the conversion of the heavier components of crude oil to gasoline and diesel oil, allowing a reduction in crude imports of more than 400 million barrels a year. In the future, new types of cracking catalysts will be required to produce motor fuels that are environmentally more acceptable. To reduce the aromatics content of gasoline while at the same time providing higher-octane paraffinic components will require that fluidized catalytic cracking (FCC) catalysts produce more olefins. The highly reactive olefins can be isomerized, oligomerized, or alkylated with paraffins as well as reacted with methanol to produce a variety of high-octane ethers. For example, the zeolite ZSM-5 has been shown to be active in producing olefins when mixed with conventional faujasite-type cracking catalysts. ZSM-5 and other molecular sieves have also been proved active in isomerizing and oligomerizing olefins to a variety of liquid fuels.
Cracking catalysts will also have to become more rugged to endure the higher temperatures required to produce more olefins for subsequent processing into high-octane gasoline components. The catalytic cracking process has been the workhorse of modern refineries for 30 years and, with improved catalysts, will continue to be the main process for converting the heavier end of crude oil into more environmentally acceptable components for gasoline and diesel fuels.
The need to remove aromatics from gasoline has created a need for organic oxygenates as replacement octane enhancers. Today the two predominant