A large-scale continuous-flow process for the production of adipic acidvia catalytic oxidation of cyclohexene with H2O2

Abstract

The demand for a clean production process of adipic acid (AA) can be achieved by developing a synthetic route using H₂O₂ as the oxidant. In this paper, a green process with a recyclable catalyst system consisting of H₂WO₄, H₂SO₄ and H₃PO₄ was developed for the production of AA via catalytic oxidation of cyclohexene. A continuous-flow reactor was set up for the optimization of the reaction parameters and developing the industrial operation of this green process. The mixture of H₂SO₄ and H₃PO₄ as acidic promoter displays a significant improvement in the activity of catalyst and the stability of H₂O₂. The catalyst could be recovered and reused 20 times, and no significant loss of catalytic performance can be observed. The effect of Fe³⁺ ion as a possible contaminant has no serious negative effect on this reaction, and the 316L stainless steel and glass-lined steel were selected as appropriate equipment material. Calorimetry and the scale-up in batch reactor demonstrate that the reaction could be operated safely on scale. The process was scaled up in a continuous-flow pilot plant, with excellent yield (94.7%) and purity (99.0%). Some advantages such as the solvent-, phase-transfer-catalyst-, and organic additive-free and low-cost light up the application of this process in the industrial production of AA.