(24b) Cellulose-Hemicellulose, Cellulose-Lignin Interactions During Fast Pyrolysis
Cellulose, hemicellulose and lignin are the major biopolymers in biomass and during their fast pyrolysis, each component generates distinct species, which leads to a complex chemical composition of the pyrolytic bio-oil product. Given this complexity, complete chemical speciation with a high mass balance closure can provide insight into the underlying chemical mechanisms during fast pyrolysis. Previously, the pyrolysis behavior of the pure biopolymers was studied to explore their thermal deconstruction mechanisms. The pyrolysis behavior of cellulose with different degrees of crystallinity and polymerization was also examined and it has been found that similar product distributions were obtained for all of the celluloses under fast pyrolysis conditions as long as it was appropriately demineralized. In the current work, the interaction effects between cellulose-hemicellulose and cellulose-lignin under fast pyrolysis conditions were determined by comparing the pyrolysis products from their native mixtures, physical mixtures and superposition of individual components. A micropyrolyzer-GC-MS/FID in conjunction with a gas analyzer was used for online pyrolysis product analysis. It was found that no apparent interaction exists for either the physical mixture or the native cellulose-hemicellulose mixture. However, in the case of the native cellulose-lignin mixture, the interaction effects depended on the type of biomass pyrolyzed. Herbaceous biomass exhibited an apparent interaction effect, represented by a diminished yield of levoglucosan and enhanced yield of low molecular weight compounds and furans. However, these interaction effects were not found for woody biomass. It is speculated that these results were due to a different degree of covalent linkage between cellulose and lignin in these biomass samples.