GB369963A - Improvements in the manufacture and production of maleic acid or its anhydride - Google Patents

Abstract

Catalysts for the production of maleic acid and maleic anhydride by treating crotonaldehyde or crotonic acid or a mixture thereof in the vapour phase with oxygen comprise the lower oxides of vanadium or molybdenum (V2O4, V2O3, and MoO2) alone or preferably together with titanic oxide, and are prepared by heating to dryness aqueous dispersions of the oxides or salts of the corresponding metals together with aqueous oxalic acid. When porous diluents such as pumice are employed with the catalysts, the metal oxide may be fixed therein in this way, for example, a catalyst may be obtained by heating to dryness a mixture of granulated pumice, powdered ammonium vanadate and titanic oxide suspended in aqueous oxalic acid.ALSO:Maleic acid and maleic anhydride are obtained by bringing crotonaldehyde or crotonic acid or a mixture of both in the vapour phase and together with oxygen or gases containing oxygen, into contact with catalysts comprising at least one of the oxides or salts of vanadium or molybdenum, at temperatures between 200 and 500 DEG C., and preferably between 250 and 380 DEG C. The oxygen, which is preferably used in excess of the theoretical amount, may be diluted with inert gases such as nitrogen or carbon dioxide; air is preferably used. If quantities from about 56 to 480 grams of crotonaldehyde for 1 cubic metre of air are used, reduced pressure and lower temperatures should be employed to avoid explosions. Instead of crotonaldehyde, acetaldol, which is converted to crotonaldehyde at 84-85 DEG C., may be employed as a starting material. The oxides of vanadium or molybdenum employed as catalysts may be used alone, or in admixture with solid, inert, or promoting diluents, for example, granular aluminium, or difficultly reducible metal compounds including metal oxides such as titanic or hydrated titanic oxide, tungstic oxide or its hydrate, silica, or alumina. Small amounts of solid non-noble metal oxides, for example, oxides of zinc, cerium, chromium, cobalt, lead, zirconium, tin, potassium, sodium, lithium, rubidium, calcium, barium, strontium, or magnesium may be added to the catalysts. The basic oxides used as additions may be present in the catalysts in the form of their salts with the acidic oxides. Salts of vanadium and molybdenum such as alkali or alkaline earth metal vanadates or molybdates may be employed as the catalysts, mixed if desired with alkali or alkaline earth tungstates or silicates. Natural silicates such as pumice and kieselguhr may be employed as diluents, the metallic impurities therein acting as activators in some cases. Especially suitable catalysts are the lower oxides of vanadium and molybdenum (V2O4, V2O3, and MoO2 alone or mixed with titanic oxide, such catalysts being obtainable by evaporating aqueous dispersions of the oxides or salts of the corresponding metals with aqueous oxalic acid. When porous diluents are used, the catalysts may be fixed thereon in this way, for example, a catalyst may be obtained by heating granulated pumice, ammonium vanadate, and titanic oxide suspended in aqueous oxalic acid to dryness. The process may be carried out at atmospheric or any other pressure. Examples are given, in one of which a catalyst consisting of kieselguhr, potassium sulphate, and vanadic acid is employed.