Processes for the production of mixtures of caustic soda and hydrogen peroxide via the reduction of oxygen

The long history of the synthesis of hydrogen peroxide via the cathodic reduction of oxygen in caustic soda catholyte is reviewed. Recent progress is analysed on the electrochemical syntheses of mixtures of caustic soda and hydrogen peroxide in various by-weight ratios from 2.3: 1 NaOH to H₂O₂ to about 1 : 1. The analysis presented focuses primarily on published work concerning planar fuel cell type electrodes in membrane-divided cells and particulate bed electrodes in cells employing microporous separators with well-defined anolyte-to-catholyte flows. Potential ancillary technology for changing the ratios of products is also discussed. One configuration of the processes described encompasses the simultaneous near 50/50 use of two variations of generation technology. A highly desired product, for instance 1.2: 1 NaOH to H₂O₂, may be formed using the catholyte product of a membrane or diaphragm cell with a caustic anolyte as the catholyte feed stream for a membrane cell with an acidic anolyte. Although the particulate bed cathode approach has reached commercial trials, the planar cathode membrane cell approach may prove a difficult process to develop as the performance of electrodes optimized for realistic hydraulic depths may prove very different to that of electrodes used in small scale laboratory development.