Tar elimination from biomass gasification syngas with bauxite residue derived catalysts and gasification char

Efficient elimination of tar is a challenge to the development of biomass gasification as a viable clean energy technology. Catalytic reforming is effective in reducing biomass-derived tars. However, commercial metal-based catalysts are expensive and prone to deactivation. Developing economically viable and environmentally benign catalysts from renewable materials is therefore very attractive. This study focuses on the development of an effective tar elimination process utilizing alternative catalysts derived from bauxite residue, a solid waste material from the alumina production. In this work, the catalytic performance of reduced and activated bauxite residue in facilitating naphthalene (a model biomass tar compound) decomposition was studied in a fixed-bed reactor under cracking and reforming environments. Bauxite residue catalyst in reduced form was found to be active for naphthalene reforming, mainly due to its high metallic iron content. However, under wet syngas environments, bauxite residue catalyst was easily deactivated by steam. To address the steam deactivation of bauxite residue catalyst, biochar as a reducing agent, as well as a co-catalyst and adsorptive-support, was proposed to mix with bauxite residue. In this study, biochar from biomass gasification has been successfully employed as a reducing agent to reduce iron oxides in bauxite residue to metallic iron in an inert environment. Results from catalyst activity testing showed that the bauxite residue-biochar mixed catalyst led to highly effective and sustained naphthalene conversion in a reforming environment, since the iron content in bauxite residue was maintained in its reduced form in the presence of biochar.