Comparative microwave catalytic pyrolysis of cellulose and lignin in nitrogen and carbon dioxide atmospheres

In this paper, a cleaner pyrolysis strategy combining microwave heating, catalyst and carbon dioxide was explored for converting biomass components into higher quality products. Catalytic pyrolysis was more favorable for the decomposition and conversion of complex biomass structures. For furfural residue pyrolysis, potassium sulfate contained in sample served as the main catalytic component. Potassium sulfate promoted the increase of phenols in bio-oil. Notably, carbon dioxide atmosphere promoted the decomposition of substances and exerted a significant effect on biomass pyrolysis, which increased bio-oil yield and declined gas yield. When the pyrolysis atmosphere was changed from nitrogen to carbon dioxide, the ID/IG ratio decreased from 1.07 to 0.74, indicating that carbon dioxide decreased defect structure in biochar. Carbon dioxide enriched the porous structure and surface roughness of biochar. Also, carbon dioxide as a carrier gas was found to be more effective than nitrogen in improving the heating values of biochar and the acidity of bio-oil under carbon dioxide was lower than that under nitrogen, which was conducive to the subsequent utilization of biochar and bio-oil. Carbon dioxide promoted the production of alcohols, alkenes, and alkanes in bio-oil. Beneficially, the interaction of cellulose and lignin inhibited the release of hydrogen chloride. At last, this study also provides insights into the mechanism of catalyst and CO2 on biomass microwave pyrolysis.