Trafic fuel properties have become a major issue in the debate between air quality authorities and oil refining and car industries. California and the Nordic countries, Sweden and Finland in particular, have played a leading role in promoting lower emission fuels. Following the addition of oxygenates, growing demands for reducing olefin and aromatic levels in motor gasoline have begun to be heard in both areas.
One of the most economic methods of achieving this is to produce oxygenates from all potential tertiary olefins produced in FCC units. MTBE production based on FCC-isobutylene has reached a very high level, but it is nevertheless insufficient for a typical refinery and additional oxygenates must be purchased. The next phase will see the conversion of the isoamylenes in FCC light gasoline to TAME. Very little attention has been given to the heavier tertiary olefins present in the FCC light gasoline as tert-hexenes and heptenes. This route allows much higher levels of oxygenates production, thereby lowering the proportion of olefins and aromatics in the gasoline pool and maximizing the utilization of these potential feedstocks.
A new etherification process for TAME and heavier ethers has been developed in Neste Corporation's Technology Centre. This unique process configuration converts approx. 90% isoamylenes, 40-60% tert-hexenes and 20-40% heptenes to the corresponding ethers. Typical feed is FCC light gasoline with a cutpoint of 80–90°C.
This paper describes several alternative ways integrating ethers production, with and without skeletal isomerization or alkylation, to a typical refinery, and details their impact on gasoline pool quality and refinery economics. The tail pipe emission figures for vehicles using the new components are also given.
Although the final recipes for motor gasolines after the year 2000 have not been fixed, a lot of speculation on the subject has been published. A leading role will be played by the authorities in California and Sweden. Among the other issues concerned, the levels set for aromatics, light olefins, and oxygenates will be of the greatest interest for the refining industry. The methods for reducing sulphur and benzene content exist, and the only uncertainty with these issues will be the development of markets, tax incentives, and the timing of the investments required. More problematic for the industry will be the demands to achieve the proposed levels of light olefins, aromatics, and oxygenates. Table I illustrates the proposed values of the critical specifications for future motor gasoline.
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