GB339235A - Improvements in the manufacture and production of carboxylic acids from nitriles - Google Patents

Abstract

339,235. Johnson, J. Y., (I.. G. Farbenindustrie Akt.-Ges.). Dec. 18, 1929. Divided on 332,258. Acetic and other carboxylic acids are obtained by saponification of the nitriles by continuously passing the nitrile vapour in contact. with a current of a mineral acid such as a 50-90 per cent sulphuric or phosphoric acid. The vapour may pass in the same or opposite direction to the stream of acid. The acid may be used in excess, in which case the excess is neutralized by ammonia, or an ammonia base. The nitrile vapours as produced by the process of Specification 332,258 may be passed directly into the saponification vessel, or may be first condensed (especially when diluent reducing gases are present) the condensate being then vaporized, for instance by a stream of inert gas, and led into the saponification vessel; or the condensate may be introduced into the saponification vessel in liquid form in such conditions as to allow of vaporization in the saponification vessel. In the examples, (1) a mixture of acetylene and ammonia is passed over zinc chloride on silica gel at 400‹ C. and the vapours are passed through a vessel kept at 80‹ C. to remove any pyridine and then into an acid-proof tower containing Raschig rings of fireclay over which sulphuric acid trickles at 200-220‹ C.; the acetic acid vapour leaving the top of the tower is freed from hydrocyanic and sulphuric acid in a dephlegmator and yields on cooling an acid of 25-30 per cent; (2) the nitrile vapour is passed into the bottom of a tower containing lead Raschig rings fed with sulphuric acid of 70 per cent at 150‹ C., yielding acetic acid of 40 per cent; (3) a. mixture of 80 parts hydrogen, 5 parts nitrogen, 5 parts methane, 10 parts acetylene.. and 10 parts ammonia is passed at 380-400‹ C. over a granulated catalyst prepared from a paste of zinc oxide, chromium oxide and magnesium chloride, the vapours being passed through a packed tower to condense part of the nitrile while the remainder is collected in silica gel, active carbon, &c., the exit gas containing 75-80 per cent of hydrogen : the acetonitrile is evaporated, if desired with the aid of a current of air, and introduced into a tower containing porcelain or lead Raschig rings and fed with 80 per cent sulphuric acid at 170‹ C.; or the liquid nitrile may be introduced directly into the saponification vessel which is kept at a temperature above the boiling point of the nitrile; (4) the tower is fed with 90 per cent phosphoric acid at 190‹ C. yieding acetic acid of 50 per cent. The ammonium salts produced may be recovered.