Catalytic pyrolysis of biogas residues with incineration bottom ash by TG-MS: Kinetics analysis and biochar stability

Catalytic pyrolysis is an efficient disposal technology for multiple solid wastes. In this work, biomass incineration bottom ash (ASH) was added into the pyrolysis of biogas residues (BR) to suppress the over reactions for high quality biochar yield, and the pyrolysis behavior and non-condensable gases release behavior were investigated by Thermogravimetrice-Mass spectrometry (TG-MS). Kinetics of pyrolysis and carbon sequestration potential of biochar were studied to reveal the mechanism of pyrolysis and the properties of solid product. The addition of ASH showed an inhibitive effect on BR pyrolysis, while it favored the biochar formation and stability. The kinetics analysis by Starink method confirmed that average activation energy increased with ASH blending, where the highest average activation energy was 209.06 kJ/mol of catalytic pyrolysis with 10 wt% of ASH. Kinetics data by Coats-Redfern method showed that the first-order reaction function performed well fitting at low temperature region, while the second-order reaction fitted well at high temperature. MS analysis detected the main release of CO2 during catalytic pyrolysis. The ASH addition made a slight influence on thermal-decomposite reactions including tar cracking reactions. Composite biochar derived from BR pyrolyzed with 20 wt% of ASH had the preferable carbon sequestration potential of 27.29%. According to the expected output of biogas in 2030 by Chinese government, once all the biogas residue were pyrolyzed with 20 wt% of ASH to produce agricultural biochar, a potential of 8.11 million tons of equivalent carbon dioxide could be prevented to emmision and storaged in biochar as carbon sink. This work provides an important reference to understand fundamental characteristics of pyrolysis of BR with ASH.

Automated summary

This study investigates the addition of biomass incineration bottom ash (ASH) into the pyrolysis of biogas residues (BR) to enhance the formation of high quality biochar. The kinetics of pyrolysis and carbon sequestration potential of biochar were analyzed. The results show that the addition of ASH inhibits over reactions, increases biochar stability, and improves carbon sequestration potential.