SYNTHESIS OF ADIPIC ACID VIA THE NITRIC-ACID OXIDATION OF CYCLOHEXANOL IN A 2-STEP BATCH PROCESS

It has proved possible to improve the traditional process for the production of adipic acid (AAD) via the nitric acid oxidation of cyclohexanol in such a manner as to arrive at a significant reduction in HNO3 consumption while maintaining a high level of product selectivity. The procedure consists of a first oxidation step at T1 = 25 - 40-degrees-C, which results in intermediates that are then rapidly oxidized to AAD at a higher temperature (T2 > 75-degrees-C), in the presence of a vanadium catalyst, without extraction or separation. At the low T1 cyclohexanedione and NO(X) are formed rather than adipomononitrolic acid and N2 + N2O. The new production method leads to a reduction in HNO3 consumption of about 0.2 kg HNO3/kg AAD because it favours the formation of nitrogen oxides, which are easily reoxidized, whereas the traditional process leads to non-regenerable nitrogen compounds (N2, N2O). The selectivity towards AAD (up to 97.8%) is the same as or even higher than that of the traditional process. By-products are 2 - 3% succinic acid and about 1% glutaric acid.