Effects of Endogenous Potassium and Calcium Ions on the Yields and Characteristics of Products from Corn Stalk Pyrolysis
Endogenous alkali and alkaline earth metals (AAEMs) in biomass ash and pyrolysis temperature significantly influence the properties of pyrolysis polygeneration products. This study selected potassium (K+) and calcium (Ca2+) as representative AAEMs, added them at mass ratios of 2%, 5%, and 7% to corn stover via impregnation, and conducted fixed-bed pyrolysis at 400, 500, and 600 °C to investigate the yields and compositions of gas, liquid, and solid products. Results showed that increasing metal ion concentration significantly increased biochar yield, with Ca2+ at 7% achieving 24.96% biochar yield, while bio-oil yield generally decreased. Ca2+ strongly promoted H2 formation due to its Lewis acidity, reaching 32.49% in gas at 7% concentration, and facilitated furan enrichment to 65.88%. K+ at low concentrations favored phenolic formation, while high concentrations promoted ketones and intensified bio-oil cracking. Increasing temperature from 400 to 600 °C decreased biochar yield and increased gas yield, with high temperatures enhancing secondary cracking and reforming, significantly raising H2 and CH4 yields while suppressing oxygenates. At 600 °C, K+ catalysis increased acids to 39.41%, while Ca2+ maintained furans at 65.89%. This study demonstrates that adjusting metal ion concentration and temperature enables directional regulation of high-value bio-oil components and high-energy gases, providing a theoretical basis for optimized biomass pyrolysis utilization.