GB735134A - Improved fuels for internal combustion engines - Google Patents

Abstract

A fuel composition boiling in the range from 100 DEG to 600 DEG F., particularly suitable for use in jet aircraft engines and spark ignition engines, comprises a major proportion of a mineral oil, at least 0.5 volume per cent of C8-C9 aromatic hydrocarbons and not more than 5 volume per cent of polycyclic aromatic hydrocarbons. The mineral oil may be a virgin or cracked stock and the fuel composition may be derived from petroleum feedstocks such as petroleum crude oils, virgin gas oils, kerosenes, residual oils and oils obtained by the cracking of petroleum fractions. A jet fuel composition according to the invention may be produced by blending various hydrocarbon fractions such as butanes, pentanes, light naphtha, heavy naphtha, heavy hydroformate, light hydroformate and kerosene. For example, a jet fuel composition may be produced by blending (1) a closely fractionated C4-C5 fraction; (2) a virgin naphtha boiling from about 120 DEG to 400 DEG F.; (3) a heavy hydroformate or a heavy catalytic naphtha rich in C8-C9 aromatics and boiling from 250 DEG to 400 DEG F.; and (4) a kerosene fraction boiling from about 400 DEG to 600 DEG F. and containing limited amounts of polycyclic aromatic hydrocarbons. An automotive fuel composition according to the invention may be produced by blending C4, C5, light naphtha and heavy naphtha fractions in the proper amounts. The fuel composition may contain additional ingredients such as anti-oxidants, ignition promoters, alkylate gasoline, propylene polymer, lead alkyls, solvent oil and alcohols. Specific C8-C9 aromatic hydrocarbons which may be present in the fuel composition are ethyl benzene, o-, m- and p-xylenes, mesitylene, pseudocumene, hemimellitene, o-, m- and p, ethyl toluenes, cumene, n-propyl benzenestyrene and o-, m- and p-vinyl toluenes. A process is described in which the fuel composition is produced from a virgin or cracked petroleum feedstock boiling in the range of 100-600 DEG F. by dearomatization. The dearomatization may be effected by solvent extraction (e.g. with sulphur dioxide, furfural, phenol, nitrated hydrocarbons or oxygenated hydrocarbons such as glycols), percolation through adsorbents (e.g. silica gel), extractive distillation, combined solvent extraction and distillation steps, or hydrogenation, and may completely remove aromatics or merely reduce the amount of polycyclic aromatic hydrocarbons present to the required degree. The dearomatized feedstock is then blended with other ingredients to make up the fuel composition. Where the feedstock is completely dearomatized the aromatics removed may be fractionated (e.g. by distillation, crystallization or solvent extraction) to separate the polycyclic aromatic hydrocarbons from the single ring aromatic hydrocarbons and the latter may be blended back into the dearomatized feedstock. In a modified process, the petroleum feedstock boiling in the range of 100-600 DEG F. is first fractionated to separate a fraction boiling above 350-375 DEG F., since this fraction contains substantially all of the polycyclic aromatics, and only this fraction is subjected to the partial or complete dearomatization mentioned above. The remaining fraction of the feedstock is blended with the dearomatized fraction either directly or after catalytic hydroforming of this remaining fraction. In another process, crude petroleum is fractionated into (a) gas and light naphtha; (b) heavy naphtha; (c) kerosene; (d) light gas oil; (e) heavy gas oil and (f) residuum, and these fractions are used in the production of automotive and jet fuel compositions according to the invention. Fraction (a) is further fractionated to yield gas and C4, C5 and light naphtha fractions, and the light naphtha may be catalytically hydroformed. Fraction (b) may be used as such or may first be catalytically hydroformed. Fraction (c) is dearomatized and the aromatics removed may be catalytically hydrogenated to naphthenes. Fractions (a), (b) and (c), treated as described, provide the main ingredients of the fuel compositions of the invention, while fractions (d), (e) and (f) may be employed as cracking stocks. For comparison purposes, the effect of the addition of various substances (viz., thiophene, vinylcyclohexene, dicyclopentadiene, alpha- or betamethylnaphthalene, indene, naphthalene, divinyl benzene and ethylvinyl benzene) to gasoline, and of various substances (viz., toluene, xylene, ethylbenzene, isopropylbenzene, trimethyl-benzene, sec.-butyl-benzene, triethylbenzene and benzene) to jet fuel is described. The purification of a heavy naphtha (prepared by catalytically cracking heavy gas oil) by washing with a mixture of aqueous caustic soda and methyl alcohol to remove acid oil, then treating with maleic anhydride to remove conjugated diolefins, and the subsequent chromatographic separation of the purified naphtha into (i) paraffins and naphthenes; (ii) olefins; (iii) monocyclic aromatics; and (iv) bicyclic aromatics and heterocyclics by percolation through silica gel is also described.