Gasification of woody biomass char with CO2: The catalytic effects of K and Ca species on char gasification reactivity

The effects of alkali and alkaline earth metals such as potassium (K) and calcium (Ca) on CO2 gasification reactivity of Japanese cypress (hinoki) char under various temperatures (1123–1223 K) and CO2 concentration (20–80 vol.%) were studied using thermal gravimetric analysis. The presence of K and Ca compounds in char improved the reactivity of hinoki char for CO2 gasification catalytically. It was also confirmed that K and Ca compounds can be supported on char to exhibit an enhanced catalytic effect during CO2 gasification of K-char and Ca-char. The char gasification rate increased with the increase of CO2 concentration at higher temperatures (1173–1223 K), however at lower temperature (1123 K) the gasification rate decreased at 80% CO2. The retardation of char gasification rate at higher CO2 concentration is caused by the inhibition effect of CO: CO is disproportionated on alkali metal catalysts to CO2 and carbon, and affected the CO2 gasification rate. The dependence of char gasification rate on reaction temperature yielded a straight line in an Arrhenius-type plot which indicated that there was no significant change in the gasification mechanism in the temperature range of 1123–1223 K.