Lignin from energy plant (Arundo donax): Pyrolysis kinetics, mechanism and pathway evaluation

Pyrolysis of lignin was conducted and main decomposition temperature range was 250–500 °C and the maximum mass loss of lignin occurred at 300–350 °C (10–20 °C/min). Activation energy was ranged from 166 to 182 kJ/mol and lnA was ranged from 35 to 40. All fitting peaks described by mechanism function of random nucleation followed by growth. There was apparent infrared spectroscopy absorbance at 3565, 2950, 2367, 2182, 1775, and 1103 cm−1 because of vibrations of functional group in H2O, CH4, CO2, CO, CO and O-containing compounds. Main composition of bio-oil was phenols and main carbon distribution was ranged from C5 to C8. Ratio of p-hydroxyphenyl, guaiacyl and syringyl structures in bio-oil varied with pyrolysis temperature. Main pyrolysis mechanism of lignin was cracking of typical structure into phenols, cracking of carboxyl groups in side chains to form CO2 and carbonization of aromatic structure to biochar. Lignin showed higher biochar yield (up to 47.46%) and biochar from lignin pyrolysis have high carbon and low ash content. Comparing with direct pyrolysis, fermentation-pyrolysis pathway produced extra high-value products of ethanol (16.70%) and CO2 (8.5%). It indicated a potential and high-value pathway of lignin produced in cellulosic ethanol plants.