(A) potentiostatic study on the electrolysis of coal-water slurry

Abstract

A potentiostatic study on the electrolysis of coal-water slurry was performed to investigate the effects of oxidation potential, particle size, coal concentration, temperature, and electrolyte. The experiment was performed by the use of potentiostat in the three-electrode electrolytic cell which contains the coal-water (1M $H_2SO_4$) slurry in the anode compartment and the water (1M $H_2SO_4$) in the cathode compartment. The pulse and sweep methods were used to obtain the current-potential curve, while the potentiostatic operation was performed to determine the effect of potential on the anodic gas composition. It has been observed that the evolution of carbon dioxide occurred at -10 mV (vs SCE) and that of carbon monoxide occurred at 400 mV (vs SCE). The evolution of oxygen occurred at 1.1 V (vs SCE) for a platinum anode, but oxygen evolution did not occur at a graphite anode because of direct formation of carbon oxides on the electrode surface. The mean current efficiency for hydrogen evolution was 99.97\% with a standard deviation of 1.90\%. Larger coal particles provide higher rates during electro-oxidation. This means that the site of electro-oxidation is the electrode and larger coal particles encounter the anode more effectively. In the potential range where only carbon dioxide evolved, the reaction order with respect to coal concentration was in the range of 0.820 to 0.867 for the platinum anode and 0.787 to 0.873 for the graphite anode. In the potential range where carbon dioxide and carbon monoxide simultaneously evolved, the reaction order with respect to coal concentration was in the range of 0.685 to 0.851 for the platinum anode and 0.466 to 0.891 for the graphite anode. The higher the temperature the greater the oxidation current. The activation energy of electrochemical coal gasification was in the range of 10.7 to 12.5 Kcal/g-mol for the graphite anode and 7.4 to 7.7 Kcal/g-mol for the platinum anode at the potential range of carbon dioxide evol...