Pyrolysis mechanism of cotton stalk catalyzed by bone char in situ: Py-GC/MS and DFT studies

This study investigated the effect of bone char on the conversion of cotton stalk pyrolysis tar components through pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and density-functional theory calculations. The results revealed that both bone char and bone char ash exhibit catalytic cracking effects on the chemical composition of tar. At 600 °C, cotton stalk pyrolysis tar mainly comprised ketones, phenols, esters, and hydrocarbons, with a low acid content. The addition of bone char enhanced esterification during cotton stalk pyrolysis, which converted gaseous tar into esters and reduced the levels of ketones and alcohols. Additionally, the content of phenolic compounds significantly decreased by 12.72 % and 11.9 %, respectively, and nearly disappeared. Moreover, the basic sites on the bone char surface facilitated acid reduction and deoxygenation through ketonization and aldol condensation reactions, which effectively reduced the oxygen content in the products (except for esters). Quantum chemical calculations further revealed that Ca2+ inhibited the retro-ene reactions, which suppressed the formation of ethylene and phenols, consistent with the Py-GC/MS results.