Effect of cellulose-lignin interactions on char structural changes during fast pyrolysis at 100-350 °C

This study investigates the cellulose-lignin interactions during fast pyrolysis at 100-350 degrees C for better understanding fundamental pyrolysis mechanism of lignocellulosic biomass. The results show that co-pyrolysis of cellulose and lignin (with a mass ratio of 1:1) at temperatures < 300 degrees C leads to a char yield lower than the calculated char yield based on the addition of individual cellulose and lignin pyrolysis. The difference between the experimental and calculated char yields increases with temperature, from-2% 150 degrees C to-6% at 250 degrees C. Such differences in char yields provide direct evidences on the existence of cellulose-lignin interactions during co-pyrolysis of cellulose and lignin. At temperatures below 300 degrees C, the reductions in both lignin functional groups and sugar structures within the char indicate that co-pyrolysis of cellulose and lignin enhances the release of volatiles from both cellulose and lignin. Such an observation could be attributed to two possible reasons: (1) the stabilization of lignin-derived reactive species by cellulose-derived reaction intermediates as hydrogen donors, and (2) the thermal ejection of cellulose-derived species due to micro-explosion of liquid intermediates from lignin. In contrast, at temperatures > 300 degrees C, co-pyrolysis of cellulose and lignin increases char yields, i.e., with the difference between the experimental and calculated char yields increasing from-1% at 300 degrees C to-8% at 350 degrees C. The results indicate that the cellulose-derived volatiles are difficult to diffuse through the lignin-derived liquid intermediates into the vapor phase, leading to increased char formation from co-pyrolysis of cellulose and lignin as temperature increases. Such an observation is further supported by the increased retention of cellulose functional groups in the char from co-pyrolysis of cellulose and lignin. Crown Copyright (c) 2020 Published by Elsevier Inc. on behalf of The Combustion Institute. All rights reserved.