Patent GB-570870-A (GB)
Title: Recovery of hydrogen halides from mixtures with olefines
IPC: C01B7/07
Filed: 1943-05-10
Abstract: Hydrogen halide is recovered in substantially anhydrous form from a gaseous mixture with an olefin by extracting the latter with a selective solvent consisting of a liquid hydrocarbon containing at least 4 carbon atoms or a liquid halogenated hydrocarbon, said solvent having a boiling point above that of the olefin, and separating the hydrogen halide from the solution. The initial mixture may be that obtained in the halogenation of olefins, the dehydrogenation of C3-C5 paraffins or olefins in the presence of halogen to yield diolefins or the dehydrohalogenation of dihalogenated and unsaturated monohalogenated hydrocarbons.  The olefins may be mono-, di- or cyclo-olefins, and include ethylene, propene, butenes, allene and butadiene, as well as the normally liquid amylenes, cyclopentene, piperylene and isoprene.  Saturated hydrocarbons and halo-substituted hydrocarbons may also be present. Selective solvents specified include paraffins and iso-paraffins, naphthenes and aromatics, for example, dimethylcyclopropane, methylcyclobutane, cyclopentane, methylcyclopentane, cyclohexane, isopropylcyclobutane, cycloheptane, cyclo-octane, benzene, ethylbenzene, toluene, xylene and other polyalkylbenzenes, carbon tetrachloride and halogen derivatives of unsaturated hydrocarbons, for example, dihaloalkanes.  They may consist of one or more of the reaction products separated from the mixture being treated, for example unsaturated monochlorides produced in the dehydrohalogenation of dihalogenated hydrocarbons. Preferably, the solvent boils at about 40-250 DEG  C. and extraction is effected at about 25-250 DEG  C. and 1-4 atm.  Counter-current extraction may be used or, preferably, extractive distillation, wherein the solvent flows down a column as the mixture is distilled and the solution is partially stripped in the lower and hotter portion.  A gaseous mixture of butadiene, hydrogen chloride, 1-chlor-and-2-chlor-butene-2, 3-chlor-butene-1, and dichlorbutanes, obtained by pyrolysis of dichlorbutanes at about 575-675 DEG  C., is fed through a condenser to remove the chlor-butenes and butanes, and then to the central portion of a distilling column whose upper portion has a cooling jacket.  The solvent, which may be one or more of the chlorbutenes in the pyrolysis product or the "heavy ends" consisting of trichlorbutane with higher chlorinated butanes and butadiene polymers or, preferably, the initial dichlorbutanes, is fed near the top of the column, and the extract led to a stripper to recover butadiene, the solvent, if dichlorbutanes, being recycled to the pyrolysis stage. In examples, a dichlorbutane pyrolysis mixture is extracted in a column of the above type with (1) 1 vol. of liquid dichlorbutane to 20 vols. of gaseous feed using a bottom temperature of 97 DEG  C.; (2) octane made by polymerization and hydrogenation of a butanebutene fraction in the same ratio with a temperature of 86 DEG  C.; (3) octane in the ratio of 1 vol. to 45 and a temperature of 66 DEG  C. A further example (4) uses a gasoline fraction boiling at 150-175 DEG C. and a temperature of about 60 DEG  C. to separate a synthetic mixture of butadiene and hydrogen chloride.