D. A. Sams

Kinetics of catalyst loss during potassium-catalysed CO2 gasification of carbon

A significant fraction of the potassium catalyst can be lost by vaporization during catalysed carbon gasification. The extent of this loss depends primarily on the reaction start-up procedure. Temperature programmed experiments show that, under inert atmospheres, both KOH and K2CO3 react with carbon to give a reduced form of potassium-carbon complex. The formation of this complex appears to be a prerequisite for the vaporization of potassium. The rate of vaporization at 800 °C follows a first-order expression. Under gasification conditions, only a fraction of the catalyst is in this reduced form; therefore, the rate of catalyst loss during gasification is lower than that under inert atmospheres. The effect of catalyst loss on both the initial gasification rate and the variation in rate with conversion has been determined.

Catalytic effect of potassium on the rate of char-CO2 gasification

The effect of potassium on the rate of char-CO2 gasification at 800 °C was investigated. The instantaneous rate depends on both catalyst concentration (KC) and the internal porous structure of the solid. At low values of KC atomic ratio, the rate increases sharply with the addition of catalyst. As catalyst concentration is increased, the rate first levels off and then decreases. The levelling off is attributed to the saturation of the surface with catalytic sites. The subsequent decrease in rate seems to be due to the plugging of micropores by catalyst deposits. The reaction rate changes significantly during gasification and drops sharply before gasification is completed. The drop in rate before total conversion can be explained by catalyst accumulation and pore plugging.

Variation of rate during potassium-catalysed CO2 gasification of coal char

Abstract The instantaneous rate of catalysed CO 2 gasification of char at 800 °C was measured at various levels of conversion. One important reason for the change in rate during the gasification is the change in the solid surface area, measured in the present study by CO 2 adsorption at 25 °C. The models which have been successful in representing the char porous structure under noncatalytic conditions were found inadequate for catalytic gasification at low conversions. Other important factors contributing to the variation in rate during conversion are the catalyst loss and the change in the catalyst/carbon ratio. A model is presented which combines the effects of these contributing factors and gives a satisfactory representation of the experimental data.

Significance of the reduction of alkali carbonates in catalytic carbon gasification

Abstract The catalytic effect of alkali carbonates on carbon gasification depends not only on the initial catalyst loading but also on how these carbonates are reduced to surface complexes during the initial heating of the samples. This effect is primarily due to three important processes which take place simultaneously during the initial heat treatment: 1, catalyst re-distribution on the surface; 2, catalyst loss by vaporization; and 3, change in the substrate surface area due to carbon conversion.