Comparison for the compositions of fast and slow pyrolysis oils by NMR characterization

The pyrolysis of softwood (SW) kraft lignin and pine wood in different pyrolysis systems were examined at 400, 500 and 600 °C. NMR including quantitative 13C and Heteronuclear Single-Quantum Correlation (HSQC)–NMR, and Gel Permeation Chromatography (GPC) were used to characterize various pyrolysis oils. The content of methoxyl groups decreased by 76% for pine wood and 70% for lignin when using fast pyrolysis system. The carbonyl groups also decreased by 76% and nearly completely eliminated in 600 °C pine wood fast pyrolysis oil. Compared to the slow pyrolysis process, fast pyrolysis process was found to improve the cleavage of methoxyl groups, aliphatic CC bonds and carbonyl groups and produce more polyaromatic hydrocarbons (PAH) from lignin and aliphatic CO bonds from carbohydrates. Another remarkable difference between fast and slow pyrolysis oils was the molecular weight of fast pyrolysis oils increased by 85–112% for pine wood and 104–112% for lignin.