Methods of separating catalyst in solution from a reaction mixture produced by oxidation of cyclohexane to adipic acid

Abstract

This invention relates to methods of controlling the oxidation of cyclohexane to adipic acid in the presence of a monobasic acid solvent, by separating the catalyst from the reaction mixture, outside the reaction zone. Substantially all the unreacted cyclohexane, the majority of adipic acid, and substantially all the monobasic acid solvent are preferably removed. A protic solvent, may be added intermittently or continuously in the reaction mixture during the removal of the monobasic acid solvent, preferably by distillation, for preventing solids precipitation. A dipolar aprotic solvent is then added in the presence of an adequate amount of the protic solvent to maintain a single liquid phase, followed by a step of formation of two liquid phases, a solids-free protic liquid phase containing substantially all the catalyst, and a solids-free aprotic liquid phase containing at least the majority of ingredients of the reaction mixture. The formation of the two phases is performed by a process selected from a group consisting of lowering the first temperature to a second temperature, adding additional protic solvent, adding an apolar aprotic solvent, and a combination thereof.