Towards understanding the role of K during biomass steam gasification

Abstract

Steam gasification is known to be catalyzed by K. However, the exact mechanisms are not identified to this day. In the present study, the catalytic influence of K on biomass steam gasification and its interaction with Si was investigated. The study was conducted through thermogravimetric analysis (TGA) on rice husks as a Si-rich biomass and K2CO3 as a model K-compound. Experiments were conducted in three different configurations: biomass or inorganic compound alone; mixtures of biomass and inorganic powders; biomass and inorganic compound without contact in a two-compartment crucible. It was shown that K has a catalytic effect on both the pyrolysis and the gasification steps. These effects occur even when the K-compound is not in direct contact with the biomass. Therefore, it demonstrates that the mechanisms involve the gas phase through the volatilization of a K-compound, most likely KOH(g). However, the observed catalytic effect on rice husks was weaker than the effect obtained in the case of beech wood, a Si-poor and more generally ash-poor biomass, under the same conditions. It shows that there is a competition between i) the influence of K on the biomass pyrolysis and char gasification kinetics and ii) the interaction of K with SiO2 inherent to the biomass.