Determination of active sites during gasification of biomass char with CO2 using temperature-programmed desorption. Part 2: Influence of ash components

Abstract

The present work is the second part of a study conducted with the aim to determine the amount of active sites present on the surface of a biomass char participating in the gasification reaction with CO2 using the temperature programmed desorption (TPD) technique. In part 1, the methodology and experimental results during TPD of partially gasified samples of beech wood char (WC1600) using CO2 as gasification agent are presented. This work focusses on the influence of the main inorganic ash components of WC1600 on the CO2 and CO signals obtained during TPD of partially gasified char samples. Furthermore, an activated carbon with ash content lower than 1 wt-% is impregnated with Ca and K and partially gasified followed by a TPD analysis. CO2 and CO signals obtained during TPD result from decomposition of oxygenated surface complexes and decomposition reactions of ash components. During gasification, three different kinds of sites are present on the surface of the char: stable, reactive and catalytically active sites. The latter are a measure of the catalytic influence of inorganic matter during char gasification. From the analysis of the TPD spectra, it can be concluded that gasification of WC1600 is dominated by the catalytic influence exerted by Ca and K. Formation of oxygenated surface complexes on WC1600 is limited, possibly due to the high temperature at which the sample was pyrolyzed (1600 °C). However, a direct correlation between specific conversion rate and the amount of reactive and catalytically active sites is developed from the experimental results, corrected by the contribution of ash decomposition.