Direct synthesis of methane-rich gas from reed biomass pyrolysis volatiles over its biochar-supported Ni catalysts

Abstract

Thermochemical conversion of biomass into methane is a promising way for bioenergy recovery and alleviate natural gas shortage; however, the available technologies are queried by the complex procedures. This paper proposed a new approach for the direct synthesis of methane-rich gases from reed pyrolysis volatile at atmospheric pressure, according to which the reed pyrolysis volatiles are catalyzed over reed biochar-supported Ni catalysts in two stages to be converted. Seawater and freshwater reeds were compared for preparing effective catalysts, and the influences of inorganic salts in reed biomass on the catalytic performance were explored. The reed biochar-supported Ni catalysts were also compared with γ-Al2O3-supported Ni catalyst (Ni/γ-Al2O3) to evaluate their activities. It has been found that freshwater reed biochar-supported Ni catalysts (Ni/FWBs) performed better than seawater reed biochar-supported catalysts (Ni/SWBs) and Ni/γ-Al2O3 owing to their large specific surface areas, uniform Ni particle dispersions, and appropriate Ni/biochar interactions. The Ni/FWB with biochar support produced at 600 °C (Ni/600FWB) was the best, and its corresponded tar-free gas product was characterized by a methane yield of 188.38 L/kg reed after two-stage catalytic conversion. The SWBs with higher alkali metal contents corresponded to larger Ni loading amounts than that of FWBs under the same conditions; however, they suffered from Ni particle aggregation and fusion, which deteriorated their catalytic activities. The findings indicated that the inexpensive Ni/FWBs were effective for the direct synthesis of methane from biomass pyrolysis volatiles, and the approach developed in this study provides an alternative to produce methane from biomass economically.