Gasification of woody biomass char with CO 2: The catalytic effects of K and Ca species on char gasification reactivity

Abstract

The effects of alkali and alkaline earth metals such as potassium (K) and calcium (Ca) on CO 2 gasification reactivity of Japanese cypress (hinoki) char under various temperatures (1123–1223 K) and CO 2 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 CO 2 gasification catalytically. It was also confirmed that K and Ca compounds can be supported on char to exhibit an enhanced catalytic effect during CO 2 gasification of K-char and Ca-char. The char gasification rate increased with the increase of CO 2 concentration at higher temperatures (1173–1223 K), however at lower temperature (1123 K) the gasification rate decreased at 80% CO 2. The retardation of char gasification rate at higher CO 2 concentration is caused by the inhibition effect of CO: CO is disproportionated on alkali metal catalysts to CO 2 and carbon, and affected the CO 2 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.