GB767348A - Improvements in or relating to the preparation of adipic acid - Google Patents

Abstract

In a process for manufacturing adipic acid by oxidizing cyclohexane in the liquid phase with molecular oxygen to yield primary oxidation products comprising chiefly cyclohexanol and cyclohexanone, followed by oxidation of said primary oxidation products to adipic acid by means of nitric acid, there is employed as the oxidizable feed to the nitric acid oxidizer the steam-distillable oil component of the residue obtained by stripping substantially all of the hydrocarbon from the mixture obtained by injecting water into the effluent from the liquid phase cyclohexane oxidation reaction vessel. In a modification, the steam distillable oil component used as feed to the nitric acid oxidizer is obtained by separating the hydrocarbon and aqueous phases in the mixture obtained by injecting water into said effluent, removing steam distillable oil from the said aqueous phase, adding said oil to the hydrocarbon phase, stripping substantially all of the hydrocarbon from the resulting mixture, and steam distilling the resulting residue. In this modification a part, but not all, of the nonsteam-distillable residue obtained from the aqueous phase may be included in the nitric acid oxidizer feed. In a further modification, the said steam distillable oil component is obtained by separating the hydrocarbon and aqueous phases in the mixture obtained by injecting water into the effluent from the liquid phase cyclohexane oxidation reaction vessel, stripping substantially all of the hydrocarbon from the hydrocarbon phase and steam distilling the residue to yield a first oil distillate, steam distilling the separated aqueous phase to yield a second oil distillate, and combining the first and second oil distillates. The liquid phase oxidation of the cyclohexane may be carried out at between 50 DEG and 175 DEG C. and 50-250 pounds per square inch pressure and the oxidation continued until 5 to 30 per cent preferably 5 to 12 per cent of the cyclohexane is oxidized. The nitric acid oxidation step may be carried out in two stages, the temperature in the first stage being between 40 DEG C. and 90 DEG C. and in the second stage between 90 DEG and 120 DEG C. The weight ratio of nitric acid to organic feed in the nitric acid oxidizers is preferably from 2.5 : 1 to 6.5 : 1 and the pressure in the nitric acid oxidation may be from 2 to 10 atmospheres. The oxidation of the cyclohexane may be carried out in the presence of an oxidation catalyst, e.g. a cobalt salt such as cobalt naphthenate whilst the nitric acid oxidation step may be carried out in the presence of copper oxide and ammonium vanadate. In examples: (1) cyclohexane is oxidized with air in a continuous manner in batteries of three autoclaves connected in series, each autoclave being equipped with a condenser for the removal of water as formed. The cyclohexane conversion is 11 per cent and the whole of the product after injection of water is distilled to remove hydrocarbon and the residue subjected to steam distillation to yield an oil phase and an aqueous phase, the oil phase being subjected to the nitric acid oxidation to form adipic acid. A table is given to show that the adipic acid yield based on the feed to the nitric acid oxidation step is higher and that the amount of succinic and glutaric acids is lower in this case than when the hydrocarbon-freed residue from the primary oxidation is used as feed in the nitric acid oxidation; (2) as in (1) except that the feed to the nitric acid oxidation is that described in the first modification referred to above. The recovery of the steam distillable oil components from the cyclohexane oxidation product and a method for their oxidation with nitric acid and for the recovery of adipic acid from the products are described in detail with the aid of flow sheets. Specification 633,354 is referred to.