Synthesis of adipic acid via nitric acid oxidation of cyclohexanol in a two-step continuous process

Abstract A continuous process is described for the production of adipic acid via the reaction of cyclohexanol and/or cyclohexanone with fairly strongly diluted (45 – 55 wt.%) HNO 3 in two reactors, the first being operated at a rather low temperature (of 35 to 45 °C), in the presence of a V 5+ -containing catalyst, and the second at a temperature between 90 and 95 °C. The contact times of the reagents are 7.5 to 25 min. in step I and 10 to 60 min. in step II. In the first process step soluble oxidized intermediates are formed, which are then converted into adipic acid in the second step. The optimized reaction conditions (time and temperature, HNO 3 concentration, type of catalyst) are compatible with the material requirements of the usual commercial plants and lead to a 20 % reduction in specific HNO 3 consumption as well as a further improvement of the selectivity towards adipic acid (97 %). The procedure does not present the disadvantages of earlier continuous processes.