COPLANAR INTERDIGITATED BAND ELECTRODES FOR ELECTROSYNTHESIS .3. EPOXIDATION OF PROPYLENE

Interdigitated coplanar band electrodes were made from platinum ink printed on alumina. Their application to the epoxidation of propylene was investigated under different experimental conditions, in both a tank cell and a flow cell. It was found for this coupled reaction that the agitation should be minimised to allow the products formed at the anodes to react with the products formed at the cathodes. The rate of bromine formation had to be high enough to allow a consequent production of propylene oxide, but low enough to avoid the formation of bromate. Therefore, the optimum potential was set between 3 and 4V, and the bromide concentration was found to be 1% by weight. The temperature was also optimised by choosing intermediate values between 6 and 10 degrees C. The compromise in this case lies between having fast reactions at high temperature and high propylene concentration at low temperature. The inter-electrode distance of the different arrays was varied between 250 mu m and 1 mm and figures of merit were improved by using smaller inter-electrode gaps. For an array used in a tank cell, with an inter-electrode gap of 250 mu m, an applied voltage of 3 V, a cell temperature of 10 degrees C and a bromide concentration of 1%, the current efficiency reached 68%, for an energy consumption of 2.0 kW h kg(-1) and a production rate of 0.12 mol h(-1) dm(-2), which compared well with results previously obtained in a pump cell or a trickle tower.