GB838854A - Improvements in the production of acrylic acid and its salts - Google Patents

Abstract

Acrylic acid or salts thereof are prepared by the reaction of acetylene, carbon monoxide and water in the presence of a carbonylation catalyst at a temperature above 180 DEG C. and at a minimum pressure of 75 atmospheres absolute using an acetylene-carbon monoxide containing gas mixture having not more than 23% by volume of acetylene based on the carbon monoxide-acetylene content, and if desired, converting the acrylic acid formed into a salt. The reaction may be effected in the presence of an alkaline agent such as an alkali carbonate, in an amount such that all or part of the acrylic acid formed is neutralized during the reaction. Reaction temperatures of 220-300 DEG C. are preferred. The carbon monoxide may contain inert gases. The catalyst may be a nickel salt such as those of acetic, propionic, acrylic, succinic, citric, tartaric, adipic, or phthalic acid; complex alkali nickel cyanides, which may be formed in situ from a nickel salt and an alkali cyanide, may also be used; activators such as cuprous salts may be present. Generally, the reaction is effected in the absence of organic solvents. The process may be effected continuously and unused carbon monoxide may be recycled. In typical examples: (1) an aqueous solution of nickel sulphate, potassium cyanide and sodium carbonate and a gaseous CO/C2H2 mixture containing 17% by volume of acetylene are passed upwardly through a stainless steel tube under a pressure of 200 atms. absolute at 245-250 DEG C., yielding a mixture of sodium, potassium and nickel acrylates from which acrylic acid is obtained on acidification; (4) an aqueous solution of nickel acrylate and a CO/C2H2 mixture containing 20% of acetylene are passed through a similar reactor at 280-290 DEG C. and 200 atms. yielding acrylic acid. A graph is given showing the relationship between the decomposition limiting pressure of a mixture of acetylene and carbon monoxide and the acetylene content of the mixture.