Catalysis in biomass gasification

Abstract

The objective of these studies is to evaluate the technical and economic feasibility of producing specific gas products by catalytic gasification of biomass. Catalyst performance is a key factor in the feasibility of catalytic gasification processes. The results of studies designed to gain a fundamental understanding of catalytic mechanisms and causes of deactivation, and discussion of the state-of-the-art of related catalytic processes are presented. Experiments with primary and secondary catalysts were conducted in a 5-cm-diameter, continuous-wood-feed, fixed-catalyst-bed reactor. The primary catalysts used in the experiments were alkali carbonates mixed with the biomass feed; the secondary catalysts included nickel or other transition metals on supports such as alumina, silica, or silica-alumina. The primary catalysts were found to influence wood pyrolysis as well as the char/steam reaction. Secondary catalysts were used in a fixed-bed configuration to direct gas phase reactions. Results of the performance of these catalysts are presented. Secondary catalysts were found to be highly effective for conversion of biomass to specific gas products: synthesis gases and methane-rich gas. With an active catalyst, equilibrium gas composition are obtained, and all liquid pyrolysis products are converted to gases. The major cause of catalyst deactivation was carbon deposition, or coking. Loss of surface area by sintering was also inportant. Catalyst deactivation by sulfur poisoning was observed when bagasse was used as the feedstock for catalytic gasification. Mechanisms of catalyst activity and deactivation are discussed. Model compounds (methane, ethylene, and phenol) were used to determine coking behavior of catalysts. Carbon deposition is more prevalent with ethylene and phenol than with methane. Catalyst formulations that are resistant to carbon deposition are presented. 60 references, 10 figures, 21 tables.