Experimental study on hydrogen production from heavy tar in biomass gasification furnace catalyzed by carbon-based catalysts

Abstract

High boiling point heavy tar compounds such as pyrene and naphthalene are key factors causing corrosion and blockage in the pipelines of biomass thermal utilization equipment, and catalytic reforming represents an effective means to address heavy tar issues. Biomass carbon, characterized by its cost-effectiveness, high efficiency, and environmental friendliness, is envisioned as a catalyst carrier with extensive application prospects. In this study, the tar produced by a biomass fixed-bed gasifier was investigated, with an initial analysis of the pyrolysis process and definition of its different stages conducted. It was discovered that the condensation and secondary cracking stages are the predominant phases for the formation of heavy tars, including polycyclic aromatic hydrocarbons (PAHs). Carbon-based carriers were prepared using apricot shell as the raw material, and biomass carbon-based catalysts were synthesized via impregnation methods. The heavy tar extracted from the original tar through distillation was utilized in the hydrogen production tests of steam catalytic reforming with biomass carbon-based catalysts. The investigation into the impact of temperature, steam-to-tar mass ratio (S/T), and tar-to-catalyst mass ratio (T/C) on the catalytic reforming of tar has been conducted. In considering a variety of parameters, including hydrogen production rate, tar conversion rate, and the volume of hydrogen generated, it was found that under the conditions of 800 °C, S/T = 3, and T/C = 2, the Ni/C catalyst yielded the highest amount of hydrogen (91.52 g H2/kg tar) with a tar conversion rate of 93.30 %. The Ni-Co/C composite catalyst exhibited stronger catalytic activity and superior deactivation resistance compared to the monometallic catalysts. For the latter, steam regeneration methods effectively restored the catalytic activity of the carbon-based catalysts, enhancing the hydrogen yield rates of Ni/C and Co/C catalysts by 2.74 and 1.55 times respectively.