SELECTIVE ELECTROCHEMICAL OXIDATION OF COAL IN AQUEOUS ALKALINE ELECTROLYTE

In this study, we report on the selective electrochemical oxidation of coal at room temperature in an alkaline slurry at 1.0 V (vs. SCE) with little or no oxygen production. Electrode activities and selectivities toward coal oxidation and oxygen evolution were determined by monitoring and analyzing anodic and cathodic gas products. The activities of platinum and various nickel surfaces were compared. Results indicate that coal reacts predominantly with OH radicals during the first 300 to 400 C/g of coal at an initial rate of 0.23 A/cm(2) in a slurry containing 14.3 g of coal per liter. After the 400 C/g level is achieved, the rate of coal oxidation begins to decrease, and oxygen evolution becomes appreciable. Coal oxidation continues to greater than 900 C/g coal. The 900 C/g reaction level corresponds to approximately one electron per six carbon atoms in the coal substrate and exceeds that expected for any type of surface passivation/functionalization. The rate-controlling steps in the coal reaction sequence appear to be OH radical formation on the electrode surface during the first 400 C/g of reaction and contacting of unreacted coal particles with the electrode thereafter. Coal oxidation competes with oxygen evolution, but the latter becomes significant only after the coal substrate has been depleted.