Co-pyrolysis of Chinese herb residue and reused polypropylene: Comparison of pyrolysis product diversification and upgrading over metal/ ZSM-5 and metal/biochar catalysts

Cheap biochar-supported catalyst has a large application prospect in catalytic pyrolysis. Compared with X/ZSM-5 (X = Ni, Fe, Co, Cu), the catalytic activity of X/biochar in the catalytic thermal conversion of Chinese herb residue (CHR) and reused polypropylene (PP) to prepare high-value fuels and carbon nanotubes (CNTs) was determined. The biochar support had higher specific surface area (SBET) and more strong acid sites, exhibiting stronger secondary pyrolysis capacity. Metal/biochar groups obtained lower pyrolysis oil yield and higher CNTs yield. Fe-loaded catalysts obtained the lowest pyrolysis oil yield, while that of Co-loaded catalysts was the opposite. Fe-loaded and Co-loaded groups had low CNTs yield, indicating that extremely strong and weak cracking capacity are unfavorable to the formation of CNTs at the back-end. Cu/biochar (Cu-C) obtained the highest yield of CNTs, which also had the lowest ID/IG ratio (0.758). In addition, Cu-C group had the highest content of H2 (35.11%) in biochar support groups. Therefore, Cu-C can be used as a cheap and efficient catalyst to produce high-value products (hydrogen-rich pyrolysis gas and CNTs) and facilitate the industrial application of biomass pyrolysis technology.