GB600551A - Improvements relating to the production of aviation or motor fuels - Google Patents

Abstract

<PICT:0600551/III/1> Aviation fuel of high octane number (90-100) is obtained from petroleum naphtha by distilling the naphtha and subjecting the vapours to precision fractionation in a number of successive columns so as to separate isopentane, an isohexane fraction of boiling range 45-64 DEG C. and an isoheptane fraction of boiling range 72-92 DEG C. from the fractions containing normal hydrocarbons and aromatic hydrocarbons and blending the above fractions together with tetraethyl lead so that the isopentane and isohexane fractions do not respectively exceed 20 and 25 per cent of the blend. The isohexane fraction is defined as comprising cyclopentane and dimethyl butanes and methylpentanes boiling in the range specified. A flow diagram is given in the Specification showing that the n-heptane and heavier hydrocarbon fraction is subjected to solvent extraction to remove aromatics which may be blended with the isohydrocarbon fractions. The crude oil is first treated to obtain two basic fractions by feeding it from a tank 1 to primary and secondary columns a, b, the column a having the equivalent of 20 theoretical plates operating at a reflux ratio of 2 : 1, a pressure of 40 lbs. per sq. inch, an overhead temperature of 98 DEG C. and a bottom temperature of 263 DEG C., while the column b operates with the equivalent of 24 theoretical plates at a reflux ratio of 4 : 1, atmospheric pressure, and overhead and bottom temperatures of 98 DEG and 263 DEG C. Under these conditions hydrocarbons having 1-6 C atoms are taken overhead through line 4 and constitute the primary flash distillate, while some of the C6 and all the C7 hydrocarbons are taken overhead from column b and constitute the "isoheptane base fraction"; this latter fraction is further fractionated in columns h, i, to separate n-hexane and n-heptane fractions through lines 16 and 19, while the isoheptane fraction is recovered through line 18. The primary flash distillate is subjected to further fractionation to remove hydrocarbons having less than 4 C atoms in column c and to debutanisation in column d, and is then fed to column e where the iso- and n-hexane fractions are separated and subjected to further purification in columns f, g. Details of the operating conditions for the columns are given in the Specification, also a table showing the hydrocarbon constituents of an Iranian crude and the fractions into which they may be separated according to the invention. Examples of the blends of the various fractions to constitute, after the addition of 4 ml. tetraethyl lead, 100 octane fuels are (1) 20 per cent isopentane, 10 per cent isohexane fraction, 50 per cent isoheptane fraction, 20 per cent toluene; (2) isopentane 10 per cent, isohexane 20 per cent, isoheptane 70 per cent; (3) isopentane 10 per cent, isohexane 20 per cent, isoheptane 50 per cent, aromatics 20 per cent; (5) 10 per cent isopentane, 20 per cent isohexane, 25 per cent isoheptane, 45 per cent alkylates.