Microwave-assisted catalytic pyrolysis of refuse-derived fuel (RDF) to improve pyrolysis performance and biochar properties

This paper investigated the feasibility of microwave-assisted catalytic pyrolysis (MACP) of refuse-derived fuel (RDF) to produce high quality biochar for the first time. Two main catalysts, K2CO3 and K3PO4, and their combination with bentonite or clinoptilolite were selected to mix with RDF in a fixed bed reactor exposed to microwave radiation. By comparing heating rate and biochar properties, the promising catalyst was identified as 20 wt% K2CO3 + 10 wt% bentonite due to its high heating rate (163 °C/min) and large specific surface area (264 m2/g) of biochar obtained under relatively low temperature (500 °C) and short microwave radiation time (30 min), much higher than previously reported values of RDF derived biochar (6–25 m2/g). K2CO3 showed higher heating rate and larger specific surface area of biochar than that of K3PO4 due to its prominent activation effect. Synergistic effect was observed when bentonite or clinoptilolite was added into K3PO4 which significantly improved microwave heating rate. Biochar produced from K2CO3 acts as a potential sorbent for retaining heavy metals in the biochar and soil due to its better porosity, while K3PO4 remaining in the biochar serves as essential nutrients for plant growth.