Improved process for the production of aviation gasoline

摘要

A catalytically cracked naphtha or gasoline is separated into a light fraction boiling between 60 DEG and 150-200 DEG F., the upper limit being chosen so as to exclude aromatics, and a heavy fraction boiling between 170-220 DEG and 350-410 DEG F., the light fraction is alkylated with isobutane, the heavy is catalytically cracked, and fractions of aviation gasoline boiling range separated from the products are combined. The products of recracking the heavy fraction may be fractionated to separate a C4 fraction, a light naphtha, and/or ethylene which may be alkylated with isobutane to increase the yield of gasoline. An intermediate fraction of the catalytically cracked feedstock boiling between about 160 DEG or 170 DEG and 220 DEG F. is of low octane number, improving little on cracking and is preferably discarded. A heavy oil such as gas oil may be cracked at 900-1000 DEG F., preferably using silica-alumina gel as "fluidized" catalyst, and the products, after separating catalyst, fractionated to give the light and heavy fractions required, and uncondensed gases which may be treated to separate ethylene and a C4 fraction. The latter, if desired after scrubbing with sulphuric acid and steam-treating the extract to recover isobutene for rubber production, is mixed with the light fraction and alkylated with isobutane using a suitable catalyst such as sulphuric acid of above 82 per cent at 45-80 DEG F. The ethylene is alkylated, using aluminium chloride at 100-150 DEG F. and 250-350 p.s.i. The alkylates are fractionated together to separate an aviation gasoline fraction generally boiling up to 300-330 DEG F. The heavy fraction from the first fractionation is recracked in a manner similar to the initial cracking, but generally at 700-950 DEG F., whereby isoparaffins and aromatics are produced and olefins removed. From the products, an aviation naphtha fraction mainly boiling at 190-335 DEG F. is separated and blended with the light alkylate fraction. Isobutane and olefins may be recovered for use in the alkylations. Examples compare the results of alkylation and recracking of selected light and heavy fractions, viz. 60-150 DEG and 220-410 DEG F. fractions of catalytically cracked naphtha.