GB584601A - Production of butadiene - Google Patents

Abstract

1,3-Butadiene is produced by feeding 1,3-butylene glycol into a body of inert organic liquid containing a dehydrating catalyst at 220-350, preferably 260-285 DEG C., at substantially the rate at which conversion occurs, and separating butadiene from the withdrawn vapours. Suitable liquids, which may be miscible with the glycol or in which the latter may be slightly soluble, include diphenyl ethane, hexaethyl benzene, benzyl ether, "Dowtherm" (Registered Trade Mark, a mixture of diphenyl and diphenyl oxide), "Nujol" (Registered Trade Mark), various oil fractions, and "cyclic C18 alcohol." The preferred catalyst is ammonium phosphate including the tri-, di- and mono-ammonium salts or their mixtures or decomposition products formed at the reaction temperatures. Other catalysts are phosphoric acid, toluene sulphonic acid, ammonium sulphate, mixed calcium and ammonium phosphates, anilin phosphate, acid sodium phosphate, kaolin and clays. They may be mounted on supports, such as carbon, coke, kaolin, clay, "Filtercel" or "Celite" (Registered Trade Marks). The ratio of catalyst to heating liquid may be 2 per cent or less if finely divided and up to 50 per cent for larger pieces. A reactor fitted with heating jacket and stirrer contains the catalyst suspended or dissolved in the inert liquid, the glycol being introduced beneath the surface at the rate of reaction. The vapours produced pass to a reflux condenser for return of any glycol and heating liquid, and are further cooled to condense water and partially reacted glycol or butenol from the butadiene. The condensate is stratified, the upper butenol layer being recycled to the reactor while the upper layer is rectified to remove most of the water from residual butenol which is recycled. The heating liquid and catalyst may be drawn off periodically or continuously for reviving or replacing. In examples, diammonium phosphate in diphenyl ethane, diammonium phosphate on coke or "Filtercel" in a wash oil, anilin phosphate in a wash oil, and orthophosphoric acid in C18 alcohol are used.