Mechanism study on pyrolysis interaction between cellulose, hemicellulose, and lignin based on photoionization time-of-flight mass spectrometer (PI-TOF-MS) analysis

Abstract

It is critical to accurately reveal the interactions between biomass components for the selective preparation and directional exploitation of pyrolysis products. The rapid, simultaneous capture of the full mass spectrum of intermediates is advantageous for elucidating the interaction mechanism. To depict the real complicated pyrolysis reactions, a simplified coupled cross-pyrolysis process among the biomass components is examined. The interaction was studied by the examination of offline product distribution, bio-oil, and bio-gas composition, as well as the evolution of pyrolysis intermediates using an online photoionization time-of-flight mass spectrometer (PI-TOF-MS). Results indicate that the interaction only affects product distribution, rather than creating a new pyrolysis reaction pathway. The cracking of glycosidic bonds during low-temperature cellulose depolymerization provides hydrogen donor (H∙) and hydroxyl donor (OH∙) for the primary cleavage of hemicellulose and lignin. It increases the ring opening of C5 of hemicellulose and the cleavage of lignin's phenylpropane side chains, promoting the production of aliphatic compounds, guaiac-based phenols, and syringe-based phenols. CO cracking on the side chain of phenylpropane provides donors for the ring opening of cellulose’s secondary pyrolysis products, further promoting the production of aliphatic chains. High temperatures hasten the fragmentation of partial aliphatic chains and the demethylation of phenols, providing donors and molecular fragments (methyl and methoxy, etc.) for the aromatization of linear molecules and encouraging the generation of aromatic compounds. The study's findings will help to improve knowledge of the biomass pyrolysis interaction and be used as a reference for targeted biomass utilization and the optimization of catalytic pyrolysis strategies.