Catalytic decomposition of biomass tars with dolomites

Catalytic gasification of wood biomass was carried out using a double-bed microreactor in a two-stage process. Temperature-programmed steam gasification of biomass was performed in the first bed at 200-850 °C. Following in series was isothermal catalytic decomposition and gasification of volatile compounds (including tars) in the second bed containing various dolomites. Dolomites from Canada, Australia, and Japan were examined for their effects on tar conversion and the overall gaseous product. A total of 74% of biomass carbon was emitted as volatile matter during tar gasification (200-500 °C biomass bed temperature). Dolomites improved tar conversion to gaseous products by an average of 21% over noncatalytic results at a 750 °C isothermal catalyst bed temperature using 1.6 cm³ dolomite/g of biomass. The iron content in dolomite was found to promote tar conversion and the water-gas shift reaction, but the effectiveness reached a plateau at 0.9 wt % Fe in Canadian dolomites. The maximum tar conversion of 66% was achieved at 750 °C using a Canadian dolomite with 0.9 wt % Fe (1.6 cm³/g of biomass). Carbon conversion to gaseous products increased to 97% using 3.2 cm³ dolomite/g of biomass at the same temperature. The dolomite seemed stable after 15 h of cyclic use at 800 °C.