Patent GB-728366-A (GB)
Title: Improvements in or relating to process for separation of c hydrocarbons and solvent therefor
IPC: C07C7/08
Filed: 1952-07-08
Abstract: A mixture of C4 hydrocarbons comprising principally n-butane and butene-2 is separated by extractive distillation with a solvent comprising a mixture of furfural, C5-C10 hydrocarbons comprising principally butadiene dimer, and liquid polydimethyl siloxane of the formula <FORM:0728366/IV (b)/1> where n is a large number resulting in a compound having a viscosity ranging from 1 c.s. at 25 DEG  C. to a million c.s., the siloxane being in a concentration effective in reducing the foam height of the furfural system so as selectively to dissolve butene-2, and stripping the dissolved butene-2.  The mixed solvent is used in the manufacture of butadiene from n-butenes or n-butane.  Thus, butane may be dehydrogenated to butenes in a first stage, the product fractionated to remove butene-1 overhead and give a bottoms which is extractively distilled with a solvent consisting of furfural, 1-15 per cent of hydrocarbons formed in the process comprising principally butadiene dimer, and the specified siloxane to dissolve butene-2, combining the stripped butene-2 with the butene-1, dehydrogenating to butadiene in a second stage, recovering a C4 fraction, extractively distilling with the said solvent to dissolve the butadiene and some butene-2, stripping, and fractionating to recover butadiene. The concentration of the siloxane is preferably 1-20 p.p.m. based on the weight of solvent.  Its viscosity is preferably at least 100 c.s.  Very viscous siloxanes may be mixed with those of lower viscosity or may contain a wetting agent, e.g. alkali metal, ammonium, ethanolamine, and guanidine salts of alkylaryl sulphonic acids, the alkyl containing 12-16 carbon atoms, in an amount of 0.1-5 weight per cent.  The siloxane may be dissolved in the fractionator bottoms and added, preferably, to the lean furfural stream to the absorbers.ALSO:A mixture of C4 hydrocarbons comprising principally n-butane and butene-2 is separated by extractive distillation with a solvent comprising a mixture of furfural, C5-C10 hydrocarbons comprising principally butadiene dimer, and liquid polydimethyl siloxane of the formula <FORM:0728366/III/1> where n is a large number resulting in a compound having a viscosity ranging from 1 c/s. at 25 DEG  C. to a million c/s., the siloxane being in a concentration effective in reducing the foam height of the furfural system so as selectively to dissolve butene -2, and stripping the dissolved butene -2.  The mixed solvent is used in the manufacture of butadiene from n-butenes or n-butane. Thus, butane may be dehydrogenated to butenes in a first stage, the product fractionated to remove butene-1 overhead and give a bottoms which is extractively distilled with a solvent consisting of furfural, 1-15 per cent. of hydrocarbons formed in the process comprising principally butadiene dimer, and the specified siloxane to dissolve butene-2, combining the stripped butene-2 with the butene-1, dehydrogenating to butadiene in a second stage, recovering a C4 fraction, extractively distilling with the said solvent to dissolve the butadiene and some butene-2, stripping, and fractionating to recover butadiene.  The concentration of the siloxane is preferably 1-20 p.p.m. based on the weight of solvent.  Its viscosity is preferably at least 100 c/s.  Very viscous siloxanes may be mixed with those of lower viscosity or may contain a wetting agent, e.g. alkali metal, ammonium, ethanolamine, and guanidine salts of alkylaryl sulphonic acids, the alkyl containing 12-16 carbon atoms, in an amount of 0.1-5 weight per cent.  The siloxane may be dissolved in the fractionator bottoms and added, preferably, to the lean furfural stream to the absorbers.