Simultaneous Removal of Toluene (Model Tar), NH₃, and H₂S, from Biomass-Generated Producer Gas Using Biochar-Based and Mixed-Metal Oxide Catalysts

Abstract

Effectiveness of four catalysts (biochar, activated carbon, acidic surface activated carbon, and mixed metal oxide) was studied for simultaneous removal of toluene, NH3, and H2S from biomass-generated producer gas. NH3 (0.03%), H2S (0.015%), and toluene at a flow rate of 2 mL/h were mixed with a synthetic producer gas composition (H2: 8.5%, N2: 58%, CO: 17%, CH4: 2%, and CO2: 11%) and passed over a catalyst bed in a fixed-bed reactor tube maintained at 800 °C. Results indicate that simultaneous removal of contaminants from producer gas is feasible using biochar-based catalysts. High surface area mixed metal oxides synthesized using microwave and ultrasonication were also effective for simultaneous removal of contaminants. Among the four catalysts, acidic surface activated carbon resulted in the highest toluene removal efficiency of 97.5% and highest breakthrough time of 145 min for NH3. For H2S removal, mixed metal oxides resulted in the highest breakthrough time of 105 min. For simultaneous removal of toluene, H2S and NH3, activated carbon showed good removal capacity (91% toluene removal efficiency; NH3 adsorption capacity of 0.03g-NH3/g-activated carbon; H2S adsorption capacity of 0.008 g-H2S/g-activated carbon), whereas biochar had moderate removal capacity (86% toluene removal efficiency; NH3 adsorption capacity of 0.008 g-NH3/g-biochar; H2S adsorption capacity of 0.008 g-H2S/g-biochar).