GB925495A - A process for preparing unsaturated nitriles - Google Patents

Abstract

Bismuth tungstate is prepared by (1) adding to a solution of tungstic acid (H2WO4) in ammonium hydroxide a solution of bismuth nitrate in concentrated nitric acid or (2) mixing yellow tungstic acid to a paste with a solution of bismuth nitrate in nitric acid. In both cases the product is dried at 120 DEG C. and then calcined to remove any ammonia and nitrates from the product. Specifications 709,337 and 912,795 are referred to.ALSO:In a process for preparing unsaturated nitriles, ammonia and an olefin are reacted together in the gaseous phase at a temperature of 300-700 DEG C. in the presence of a catalyst which contains only Bi and W, in chemical combination with oxygen. The gaseous reactants are passed under a pressure of between 1 to 18 atmospheres (preferably 1-3 atm) over the catalyst which may be present in a fixed or fluidised bed and which is maintained at a temperature between 300 DEG C. and 700 DEG C., preferably 550-650, the flow rate of the gases being adjusted so that 1 unit vol. of gas is in contact with 1 unit vol. of catalyst for between 0.01 and 10 secs., preferably 0.05-2 secs. The process may be operated continuously or intermittently. The molar ratio of oxygen (generally in the form of air) to olefin in the feed to the reaction zone should preferably be in the range 0.5 : 1-3 : 1, more preferred ratios being 1 : 1-2 : 1. When using pure oxygen it may be desirable to dilute the oxygen with a substantially inert gas, e.g. steam, paraffin hydrocarbon vapours, carbon dioxide or nitrogen. The molar ratio of ammonia : olefin must preferably be at leat 0.05 : 1, there being no upper limit. The reaction products are recovered by known methods. The catalyst present in the reaction is based on tungsten oxide promoted with bismuth oxide alone or supported on a carrier, e.g. alumina. Preferably the catalyst must include Bi W O in such a proportion that it may be regarded as bismuth tungstate. The effective proportion of the elements Bi and W present in the catalyst correspond generally in their limits to those represented by the various compounds of Bi3+ and BiO+ cations and one of the anions WO42-W7O246- W12O4110 - W12O408-W12O396-as well as other possible more complicated compounds. When bismuth tungstate is used with a supporting material it is preferable to have the bismuth present in excess of the theoretical quantity necessary to form the true salt. Experiments I to IV describe how the catalyst may be prepared and further examples show the effectiveness of the catalyst in the preparation of acrylonitrile from propylene, NH3 and air (Table I) and also from propylene, NH3, air and steam (Table II). Other suitable olefins are isobutylene which gives methacrylonitrile and those olefins derived from petroleum oil refining. Specifications 709,337 and 912,795 are referred to.