GB606798A - Improvements relating to the production of pure hydrocarbons from petroleum naphtha and other hydrocarbon feedstocks - Google Patents

Abstract

Hydrocarbon mixtures containing methylcyclopentane, 2- and 3-methylpentanes, n-hexane, cyclohexane and benzene, and substantially free of olefins and hydrocarbons distilling above 74-75 DEG C. (other than cyclohexane and benzene) are fractionated to obtain a light fraction of F.B.P. not substantially above 69 DEG C. and containing branched hexanes, and at least one other fraction including a n-hexane fraction of B.R. about 69-72 DEG C. containing n-hexane, methylcyclopentane and benzene. Fractions obtained from naphthas, cracking or destructive hydrogenation products may be used, and fractions separated as follows: (1) an overhead up to about 66-69 DEG C.; (2) B.R. from about 66-69 DEG C. to 72 DEG C.; (3) B.R. about 72-76 DEG C. containing methylcyclopentane not removed in (2); (4) 1 B.P. about 76 DEG C. comprising a benzene, cyclohexane azeotrope; (5) substantially pure cyclohexane.ALSO:Pure hydrocarbons are produced from hydrocarbon mixtures containing methylcyclopentane, 2- and 3-methylpentanes, n-hexane, cyclohexane, and benzene, and substantially free of olefines and hydrocarbons distilling above 74 DEG -75 DEG C. (other than cyclohexane and benzene), by a process comprising fractionating with precision to obtain a light fraction of F.B.P. not substantially above 69 DEG C. and containing branched hexanes, and at least one other fraction including a n-hexane fraction of B.R. about 69 DEG -72 DEG C., containing n-hexane, methylcyclopentane, and benzene, and catalytically isomerizing the n-hexane fraction to convert n-hexane to branched hexanes and methylcyclopentane to cyclohexane, the product or part thereof being mixed with the initial hydrocarbon mixture feed. Fractions obtained from petroleum or coal tar naphtha, cracking products of mineral oils, or destructive hydrogeneration products of coal or tar may be used. Olefins may be removed by a preliminary hydrogenation. The fractionating zone may comprise one or more stages, and fractions may be separated as follows: (1) an overhead boiling up to about 66 DEG -69 DEG C. which may be isomerized in known manner to produce doubly branched hexanes; (2) B.R. from about 66 DEG -69 DEG C. to 72 DEG C., of low benzene content, which is the feed to the isomerizing zone; (3) B.R. about 72 DEG -76 DEG C. containing the methylcyclopentane not removed in (2); (4) I.B.P. about 76 DEG C. comprising an azeotropic mixture of benzene and cyclohexane; (5) substantially pure cyclohexane. In an example, the B.R. of each fraction is (1) 45.6-68.6 DEG , (2) 68.6-71.8 DEG , (3) 71.8-77.6 DEG , (4) 77.6-80.8 DEG , (5) 80.8 DEG C. If the amount of n-hexane in (2) is excessive, much may be included in (1), which then has a B.R. of, for example, 58.3 DEG -69.1 DEG C., and contains some benzene and naphthenes which may be recovered by extraction. The fractions (3), (4), and (5) may be treated separately or combined to recover pure benzene and cyclohexane as described in Specifications 585,850 and 606,797, [Group III]. Fraction (3) or fractions (3) and (4) may be extractively distilled to recover pure benzene. The isomerization of fraction (2) may be effected in liquid or vapour phase with metal halides, particularly a liquid complex of aluminium chloride and hydrocarbons at 60 DEG -200 DEG C. In examples, aluminium chloride is heated at 100 DEG C. with a liquid SO2 extract of a petroleum naphtha in presence of HCl, and the oily complex used, after adding further aluminium chloride, for isomerizing the fraction at 70 DEG -72 DEG C., the product being distilled and the distillate boiling below 75 DEG C. passed to the fractionating zone.