GB567525A - Improved process for the manufacture of adipic acid - Google Patents

Abstract

<PICT:0567525/IV/1> A process for the manufacture of adipic acid which comprises continuously introducing cyclohexanol and a nitric acid solution into a reaction vessel, the rate of introduction of these reagents being adjusted so that the concentration of the nitric acid solution in the reaction vessel is maintained at 40-60 per cent by weight based on the nitric acid and water present, the temperature in the reaction vessel being maintained between 50 and 90 DEG C. and an oxidation catalyst being present, and continuously removing the reaction mixture from the reaction vessel and isolating the adipic acid therefrom by cooling and filtering. Any of the commonly used oxidation catalysts may be employed, such as one or more polyvalent metals, the oxides or salts thereof, for example, a vanadium compound such as ammonium vanadate and vanadium pentoxide. After isolating the adipic acid, the nitric acid filtrate may be fortified, for example, by concentration in a still, by addition of stronger nitric acid or by passage thereinto of oxides of nitrogen, until with additional catalyst it is suitable for re-use. In a process using the apparatus shown in the Figure, cyclohexanol containing 1.5 per cent water is passed at a rate of 12 lbs. an hour from a storage vessel A via a p flowmeter B into a primary reaction vessel F of capacity 5 gallons and having stirring and cooling means. From storage vessel C a 60 per cent nitric acid solution containing 0.1 per cent ammonium vanadate passes via a flowmeter D and a packed tower E, also to reaction vessel F at a feed rate of 132 lbs. per hour. The reaction vessel is maintained at a temperature of 60-63 DEG C. The quantity of nitric acid solution entering the reaction vessel is thus 11 times that of the cyclohexanol and the total quantity passed in 30 mins. approximately equals the reaction vessel capacity. The tower E serves as a scrubber to remove nitrous fumes and cyclohexanol and cyclohexyl nitrite vapours arising from the reaction vessel. A run-off, vented at the top to prevent air locking takes the reaction mixture from a point near the bottom of vessel F to a secondary reaction vessel G from which a similar run-off pipe passes the reaction mixture to the cooling vessels H. The material from the cooling vessels is filtered whilst the nitric acid filtrate is fortified and returned to storage vessel C. Any nitrous vapours evolved are passed to absorption towers and recovered. Examples of the process of the invention are given and also experiments are described of continuous processes in which the nitric acid concentration is maintained below 24 per cent. Specifications 265,959, [Class 2 (iii)], and 533,066 are referred to.