GB732476A - Process for the separation of meta-dialkylbenzenes from hydrocarbon mixtures containing the same - Google Patents

Abstract

A m-dialkylbenzene is separated from a hydrocarbon mixture as herein defined by extracting at a temperature not above atmospheric with an extraction agent comprising a compound of aluminium chloride or bromide with a m-dialkylbenzene or a higher alkyl benzene, i.e. containing more than two alkyl substituents. The hydrocarbon mixture contains m-dialkylbenzene(s) with one or more monoalkylbenzenes and/or other dialkylbenzenes. It may contain saturated hydrocarbons but substantially no unsaturated aliphatic hydrocarbons or higher alkylbenzenes should be present. In particular, narrow boiling range fractions, especially xylene mixtures which may include ethylbenzene, are treated. The aluminium halide compound generally contains 2 mols. of halide to 1 of the alkylbenzene with a small deviation in either direction. HCl or HBr may also be present, e.g. in an amount of 1 mol. per mol. of alkylbenzene. The extraction agent can be made by leading HCl or HBr through the aluminium halide and alkylbenzene at, say, 0 DEG C. It takes up further m-dialkylbenzene from the hydrocarbon mixture to form a complex of the type Al2Cl6, m-xylene, (m-xylene)n, where n may be 1-5. These n molecules are easily split off and recovered as by extracting with a saturated hydrocarbon and distilling the extract. Extraction of the hydrocarbon mixture may be effected in presence of a saturated hydrocarbon, suitably using the two extraction agents in counter-current to one another. A diluent may be added, e.g. liquid HCl or HBr when, however, pressure is required to maintain the liquid state. In examples p- and m-xylene mixtures dissolved in n-heptane are extracted with Al2Cl6 m-xylene containing HCl, at 0 DEG C. in one stage or in a 12-stage system wherein the mixture is introduced in the 5th stage, the halide compound + HCl in the 12th, and n-heptane + HCl in the 1st.