(620b) Influence of Lignin-Carbohydrate Complex (LCC) Linkages on the Pyrolytic Decomposition of Carbohydrates in Biomass

Development of the pyrolysis process to improve the quality and yield of bio-oil is hindered by the limited knowledge of the underlying chemistry. The multiscale nature of biomass and the presence of lignin-carbohydrate complex (LCC) linkages between its components contribute to the complexity. To delineate the influence of lignin in carbohydrate decomposition, a multiscale investigation, based on first principles modeling, is conducted. First-principles based search is performed to identify the lowest energy LCC conformations bonded at the thermodynamically most stable sites. Subsequently, key glycosidic bond cleavage mechanisms in cellulose are simulated using DFT and comparison with non-LCC bonded cellulose is made to evaluate the effects of LCC linkages on cellulose decomposition. The presence of LCC linkages also affects the temperature-dependent crystallinity and density of cellulose microstructure. These condensed phase effects of LCC are studied using ReSolv method, a recently developed approach in our group to calculate free energy barriers. Two condensed phase lignin + carbohydrate environments, with and without LCC linkages are modelled. The effect of condensed phase composition, LCC linkages and that of temperature on cellulose decomposition kinetics is evaluated. To validate computational findings, thin film pyrolysis experiments are performed on physically mixed Cellulose-Hemicellulose-Lignin (CHL, without LCC linkages) and bagasse (real biomass with with LCC linkages). Significantly higher yield of anhydrosugars is observed in CHL while higher yield of phenolic compounds is observed in bagasse. The lower yield of anhydrosugars in bagasse compared to mixed CHL at 300Ö¯ C is in good qualitative agreement with the calculated high free-energy barriers for the primary decomposition of cellulose in LCC. This novel, combined computational and experimental approach can be further exploited to investigate pyrolytic decomposition chemistry of real biomass.