GB576480A - Process for producing olefinic hydrocarbons - Google Patents

Abstract

Olefinic hydrocarbons are produced by dehydrating a monohydroxy alcohol containing at least 4 carbon atoms with an aqueous solution containing less than 5 per cent by weight of a mineral acid. Normal, secondary or tertiary, aliphatic, naphthenic, terpenic or aromatic alcohols may be treated, generally at about 100-400 DEG C. and superatmospheric pressures below about 300 atm. Ethers are also obtained from some primary and secondary alcohols. The mineral acid such as hydrochloric, hydrobromic, arsenic, sulphuric, boric, ortho- and other phosphoric acids may be introduced as such or formed in situ by hydrolysis of salts such as halides or sulphates of Fe, Zn, Al, Mg, Cu, Mn, Ni and Co. The weight ratio of alcohol to the acid catalyst solution may be about 1 : 1. Batch or continuous operation may be used, unconverted alcohol and catalyst solution being separated and re-used. The olefins may be simultaneously isomerized, for example n-butyl alcohol with ferric chloride solution gives butene-2 and butene-1 in a molar ratio of about 3 : 1. Naphthenic and terpenic alcohols, e.g. borneol, isoborneol and terpineol give cyclic olefins, while aromatic alcohols give arylalkenes. Examples describe the dehydration of normal, secondary and tertiary butyl, tertiary amyl and cetyl alcohols, borneol and isoborneol to yield butenes-1 and -2, isobutene, pentenes, cetene and camphene, the catalysts consisting of various aqueous solutions of ferric chloride, hydrochloric acid, magnesium chloride, sulphuric acid, ferric sulphate, boric acid, arsenic pentoxide or potassium acid sulphate. Where a stainless steel autoclave containing traces of metal halides, probably iron and nickel chlorides, is used, the addition of water only gives satisfactory results. The effects of reducing the concentration of acid catalyst and of water in the reaction system are shown.