GB820125A - Process for the manufacture of benzonitrile - Google Patents

Abstract

Benzonitrile is manufactured by a continuous process, wherein an aromatic hydrocarbon capable of yielding phthalic anhydride by oxidation is subjected in the vapour phase to catalytic oxidation with air, and the oxidation product so obtained, and without being cooled or isolated, is converted in the vapour phase by reaction with ammonia in the presence of a dehydration catalyst into benzonitrile. Suitable aromatic hydrocarbons are naphthalene and ortho-xylene, and suitable catalysts for the oxidation step are vanadium pentoxide supported on e.g. silica gel, or alumina, to which phosphorus pentoxide, potassium hydrogen sulphate or potassium sulphate may be added. Suitable dehydration catalysts are aluminium oxide or silica gel. The process may be carried out by preheating a gaseous mixture of air and naphthalene in a ratio within the range 20:1 to 50:1 at a temperature up to 350 DEG C. and passing the mixture at a space velocity within the range of 500-4000 parts by volume per volume of catalyst per hour, over the catalyst heated at 300-500 DEG C. At least 1 mol. of ammonia per mol. of naphthalene is then added and the gaseous mixture is then passed at a space velocity of 100-1000 volumes per volume of catalyst per hour over e.g. silica gel, and is heated at 360 DEG to 500 DEG C. Examples are given of the preparation of benzonitrile from (1) naphthalene with a catalyst of vanadium pentoxide, potassium sulphate and silica gel mixture, for the oxidation step, and silica gel of bulk density 0.4 for the dehydration step; (2) ortho xylene with a catalyst of vanadium pentoxide on pumice; (3) naphthalene with active alumina as the dehydration catalyst.