Catalytic Reforming of Tars Formed During Black Liquor/ Biomass Gasification, 2003 Fall Technical Conference

Formation of tars during black liquor/ biomass gasification presents a significant hurdle in the commercialization of integrated combined cycle gasification technology. This work is aimed at developing catalytic pathways to destroy tar species under conditions where catalytic activity can be maintained in the presence of alkali and sulfur species. Steam reforming of tar species was investigated in a packed-bed reactor operating at atmospheric pressure and at temperatures between 600 oC and 900 oC. The feed consisting of ~ 2400 ppm benzene (model tar compound) was reacted over Group VIII metals and Group VIB-VIII metal sulfides as catalysts. These catalysts undergo slow carbon deactivation at the reaction conditions, but can be regenerated by oxidation treatment.

The presence of alkali species results in the formation of various phases and structures depending on the alkali species. These slow solid state transformations cause complex transient activity behavior. The presence of 225 ppm H2S leads to the formation of sulfide and sulfate phases of Group VIII transition metals (e.g., Pt, Ni etc.), and this results in an almost complete and irreversible loss of catalytic activity for tar reforming. However, Group VIB-VIII sulfided catalysts maintain a stable catalytic activity in the presence of H2S and show promise as potential catalytic candidates.