RATE AND MECHANISM OF BLACK LIQUOR CHAR GASIFICATION WITH CO2 AT ELEVATED PRESSURES

The kinetics of sodium-catalyzed CO2 gasification of carbon at elevate d pressures were investigated using a char, produced from spent kraft pulping liquor, in which the catalyst is distributed more uniformly in the carbon matrix than in alkali-metal-impregnated carbons. Gasificat ion measurements were carried out in a pressurized thermobalance at 70 0-degrees-C, 0.1-25 bar CO2 partial pressures, and 0-6 bar CO partial pressures. The rate of gasification was an order of magnitude or more higher than the rate of gasification of potassium-impregnated activate d carbon and several orders of magnitude greater than for alkali-metal -impregnated coal chars. It was less than first order in CO2, strongly inhibited by CO, and strongly temperature dependent. The gasification kinetics followed the same mechanism as reported previously for potas sium-catalyzed CO2 gasification of activated carbon in spite of large differences in the carbon source, catalyst type, and loading. The rate of gasification initially increased with increasing carbon conversion , but decreased with increasing conversion over most of the range of c onversion. The change in rate with carbon conversion is apparently rel ated to changes in the number of active carbon sites and catalyst site s. There was no loss of sodium from the char during gasification.