Microwave-induced cracking and CO2 reforming of toluene on biomass derived char

• Biomass derived char was utilized as a catalyst for toluene cracking and reforming.
• Microwave heating had a promoting effect on toluene conversion.
• Toluene reforming by CO2 could obtain more syngas production.
• An optimum CO2 flow rate, i.e., 80 mL min−1, was existed under microwave heating.
• Part of syngas production was derived from original carbon gasification.

The objective of this work was to investigate the ability of char from biomass microwave pyrolysis at 800 °C for tar removal, using toluene as the model compound. The experiments were conducted in a fixed bed with microwave heating and electrical heating, respectively. Carbon weight in biomass char was calculated after the experiments, and the chars were characterized by Brunauer–Emmett–Teller (BET) analysis and Scanning Electron Microscope (SEM) measurement. The results indicated that microwave heating had a promoting effect on toluene conversion. With the temperature increasing to 750 °C, cracking conversion and hydrogen selectivity rose respectively to 92.77% and 91.74%. CO2 reforming of toluene was effective to produce more syngas. An optimum CO2 flow rate, i.e., 80 mL min−1, was existed under microwave heating. In this case, toluene conversion reached a maximum of 92.03%, and the syngas yield also increased to 91.03%. The ratios of H2/CO exhibited a substantial reduction with increasing CO2 flow rate. At CO2 flow rate of 100 mL min−1, the ratio approached stoichiometric ratio in reforming reaction, and the ratio further reduced to 0.22 at CO2 flow rate of 120 mL min−1. Toluene reforming displayed a relative stable performance for the conversion of toluene, since the existence of CO2 efficiently relieved biomass char deactivation. Toluene reforming conversion retained at about 86% in a time range of 20–140 min. Carbon gasification during the reforming reaction possessed a resistance to carbon deposition, but it simultaneously caused carbon loss in biomass char. The most serious weight-loss ratio was 5.42% in this work, obtained at CO2 flow rate of 120 mL min−1. The consumed carbons were gasified into part of syngas production and provided the biggest contribution of 15.4% to final syngas production.