GB900829A - Process for the manufacture of acetaldehyde and acetic acid - Google Patents

Abstract

A catalyst for the oxidation of ethylene, in neutral to acid medium, to acetaldehyde and/or acetic acid comprises an inorganic redox system containing at least one compound of a metal which is capable of existing in different valency states under the reaction conditions. Suitable compounds are those of copper, iron, cobalt, nickel, manganese, mercury, cerium, titanium, uranium, bismuth, tantalum, tin, lead, chromium, molybdenum, vanadium or antimony. The catalysts may also contain silver, zinc or cadmium salts. The catalyst may be used as an aqueous or watercontaining suspension or solution, or as a solid which may be supported, for example, on silica gel, pumice, silicates, titanium dioxide, kieselguhr, alumina or carbon. The catalyst is regenerated by treatment with oxygen or an oxygen-containing gas, and, if desired, an additional oxidizing agent, e.g. ozone, oxygen compounds of nitrogen, a peroxidic compound, free halogens, halogenoxygen compounds or selenium dioxide.ALSO:Acetaldehyde and/or acetic acid are produced by bringing ethylene into contact with oxygen or an oxygen-containing gas as oxidising agent in the absence of a noble metal at raised temperature and in the presence of water and an inorganic redox system comprising at least one compound of a metal capable of existing in different stages of valency under the reaction conditions. The ethylene and the oxidising agent may be brought into contact with the catalyst simultaneously or the catalyst may be first reacted with the ethylene and subsequently regenerated by means of the oxidising agent. Suitable redox systems are, for example, compounds of copper, iron, cobalt, nickel, manganese, mercury, cerium, titanium, uranium, bismuth, tantalum, tin, lead, chromium, molybdenum, vanadium and antimony and mixtures of these. In addition the catalysts may contain salts of silver, zinc, or cadmium. It is particularly advantageous to use a catalyst containing mercuric sulphate. The preferred temperatures for carrying out the process are in the range 50-250 DEG C. and the preferred pressures up to 400 atm. gauge. The catalyst may be present as an aqueous or water-containing solution or suspension or as a solid, which may be supported on, for example, silica gel, pumice, silicates, titanium dioxide, kieselguhr, alumina or carbon. When the catalyst is in aqueous solution the solution may also contain, for example, acetic acid, glycol, glycerol, dioxan, methyl ethyl ketone, acetone, a higher ketone or a mixture of such solvents. The ethylene used may be mixed, for example, with paraffins, nitrogen, carbon dioxide, cyclohexane, benzene or toluene. The regeneration of the catalyst may be assisted by adding a further oxidising agent, for example ozone, a peroxide compound, oxygen compounds of nitrogen, free halogens, halogen-oxygen compounds or selenium dioxide. When metal halides are used as redox systems, volatile halogen compounds may be formed and to counteract the halogen depletion of the redox system it is advantageous to add free halogen, a hydrogen halide or a compound which splits off a halogen or hydrogen halide under the reaction conditions. Acetic acid may be formed in addition to acetaldehyde and if desired the oxidation of acetaldehyde to acetic acid by a known process may be combined with the oxidation step already described. The preferred pH value of the reaction solution is between 1 and 5. If cuprous chloride is formed from the redox system during the reaction it is advisable to add hydrochloric acid, a halogenated acetic acid or a metallic chloride which increases the solubility of the cuprous chloride. The reaction mixture may be irradiated by ultra-violet light or X-rays. It is advisable to use an apparatus lined with titanium, a titanium alloy, tantalum, resins or ceramic materials.