TG-FTIR and thermodynamic analysis of the herb residue pyrolysis with in- situ CO2 capture using CaO catalyst

Thermochemical conversion technology can be employed for the utilization of biomass resource, which not only disposes of the waste polluting the environment but also produces biomass gas and bio-oil for industrial applications. In this work, CaO catalyst was used to catalyze the pyrolysis of herb residues to produce biobased gas. The mechanism of biomass pyrolysis with in-situ CO2 capture was studied by experimental investigation and thermodynamic simulation. The results of the thermogravimetric and infrared analysis showed that CaO could promote biomass pyrolysis, water gas shift reaction, methanation reaction, and macromolecular transformation, thus significantly improving the quality of catalytic cracking gas. The further mechanistic study indicated that in-situ CO2 capture promoted by CaO relieved the thermodynamic constraints of methanation at high temperature and achieved a high CH4 selectivity in the temperature range of biomass pyrolysis and tar catalytic cracking, which is consistent with the result of the thermodynamic analysis. Mechanistically, CaO promotes the water gas shift reaction by absorbing CO2, reduces the volume contents of CO2 and CO in gas and improves H-2 and CH4 concentration to afford high-quality gas.