Selective oxidation of carbohydrates with gold catalysts: Continuous-flow reactor system for glucose oxidation

For the first time, a continuous-flow liquid-phase oxidation using a gold catalyst is described. A 0.25% Au/Al2O3 catalyst was investigated in the continuous-flow carbohydrate oxidation using glucose as the model compound. To achieve this, a continuous stirred tank reactor (CSTR) system was developed in which the powdered catalyst was separated by a combination of an ultrasonic separator and a separation vessel. The continuous-flow glucose oxidation was carried out at 40 °C, pH 9 and 1 bar oxygen partial pressure and maintained for 70 days. During this run-time the residence time and glucose concentration were varied. The alumina-supported gold catalyst showed very high activity and selectivity to gluconic acid. The long-term stability of the gold catalyst was excellent as no loss in activity or selectivity occurred during 70 days of continuous operation.