Nitric acid oxidation design in the manufacture of adipic acid from cyclohexanol and cyclohexanone

Abstract

Summary Manufacturing routes from benzene through phenol or cyclohexane to adipic acid are discussed as background to the consideration of the liquid phase nitric acid oxidation of cyclohexanol and cyclohexanone. The influence of catalysts on the yield from these oxidations and on the temperature range over which high yield (over 00 %) can be obtained is marked, a mixed vanadium-copper catalyst being outstanding. The action of copper appears to be both catalytic and chemical. Associated by-products are glutaric, succinic and oxalic acids; the off-gases from the reaction being mainly of the type non-recoverable as nitric acid. In considering the design of a plant capable of producing at least a ton an hour of adipic acid the main factors which require consideration in relation to plant throughput and efficiency are tabulated and discussed. Reaction units for liquid phase nitric acid oxidation are described against the provisions they make for heat removal, off-gas separation, reaction contact time, and control of temperature, pressure and reactant concentration. The methods of isolating adipic acid from the product, the separation of by-products, and the recovery and re-use of nitric acid, the consumption of which is important to the economics of the process, are outlined. Corrosion data are given which emphasize the necessity of a full appreciation of materials of construction for acid-oxidation plant. Since the influence of products of the reaction and catalysts on nitric acid corrosion properties are diverse and in this case opposing, the importance of tests using the actual process liquors is shown in choosing a material of construction. Reasonably cheap materials of construction which can be fabricated for operation in the required temperature range of 70–85°C are shown to be 18·8 Ti or better 18·8 Nb austenitic chromium-nickel steels.