GB777087A - Improvements in or relating to the oxidation of cyclohexane - Google Patents

Abstract

A process for producing precursors of adipic acid which yield the acid on oxidation comprises the liquid phase oxidation of cyclohexane with a gas consisting of or comprising molecular oxygen characterized by the steps of effecting the oxidation at a temperature of from 50 DEG to 175 DEG C. under a pressure of 50 to 750 pounds per square inch in the presence of a cyclohexane-soluble compound of cobalt or chromium, said compound being present in an amount of from 1 to 5000 parts per million parts by weight of the oxidation mixture, heating at least a part of the resulting mixture containing cyclohexyl hydroperoxide in a separate step in the liquid phase at a temperature of 100 DEG to 300 DEG C. without any additional peroxide-decomposing catalyst, reducing agent or oxygen, and in the presence of at least a part of the unreacted cyclohexane, the amount of said cyclohexane being sufficient to avoid spontaneous violent decomposition of the peroxide present in the mixture, until most of the cyclohexyl hydroperoxide therein is decomposed, and then recovering adipic acid precursors from the resulting mixture by distillation. The initial oxidation of the cyclohexane is preferably carried out until from 1 to 12 per cent of the cyclohexane molecules have been oxidized and the adipic acid precursors (comprising cyclohexanol and cyclohexanone) obtained on distillation of the mixture resulting from the cyclohexyl hydroperoxide decomposition step may be converted to adipic acid by oxidation with nitric acid, e.g. by the method disclosed in Specification 633,354. The process of the invention may be carried out in a continuous or batchwise manner and the same reaction vessel may be employed in both the oxidation and hydroperoxide decomposition steps although it is preferred to use separate vessels for these steps. The cyclohexane oxidation may be effected with air, pure oxygen, oxygen-enriched air or air containing relatively inert gaseous diluents. In an example cyclohexane is oxidized with air in the presence of about 5 parts per million of cobalt naphthenate at 147-160 DEG C. under a pressure of about 150 pounds per square inch gauge, the oxidation being carried out in three successive vessels of equal size, each vessel being equipped with water take-off from a reflux condenser in the off-gas. The condensed hydrocarbon from the off-gas is returned to the first oxidizing vessel and the liquid effluent from the first vessel flows to the second vessel and that from the second vessel flows to the third vessel. For comparison, and in accordance with the invention, the same plant is operated with all of the conversion occurring in the first and second oxidizers, the third vessel being used as a hold-up tank in which the peroxide is decomposed in the liquid phase at the same temperature and without addition of oxygen. A table is given to show that the yield of adipic acid and steam-volatile adipic acid precursors is increased by including the peroxide decomposition step. It is stated that the steam-volatile fraction of the adipic acid precursors formed in the cyclohexyl hydroperoxide decomposition step may be oxidized, e.g. with nitric acid, to form adipic acid. Specification 767,348 also is referred to.