Fast pyrolysis, a potential strategy for the production of transportation fuels from biomass, involves a complex network of competing reactions, which result in the formation of bio-oil, non-condensable gaseous species, and solid char. Bio-oil is a mixture of anhydro sugars, furan derivatives, and oxygenated aromatic and low molecular weight (LMW) compounds. Previously, the successful modeling of fast pyrolysis reactors for biomass conversion was hampered by lumped kinetic models, which fail to predict the bio-oil composition. Hence, a fundamental understanding of the chemistry and kinetics of biomass pyrolysis is important to evaluate the effects of process parameters like temperature, residence time and pressure on the composition of bio-oil. In this work, we describe a mechanistic model that we recently developed to characterize the primary products of fast pyrolysis of pure cellulose. The model incorporates the following condensed phase reactions for the formation of various LMW products in bio-oil: glucosidic bond cleavage, retro-aldol, retro-Diels-Alder, 1,2-dehydration, 1,3-dehydration, hydrolysis, cyclic Grob fragmentation and enol-keto transformation reactions. The kinetic rate coefficients were primarily obtained from the literature, based on either experimentally determined Arrhenius parameters for cellulose and model compounds, or theoretically computed values using quantum chemical calculations. A computational framework based on continuous distribution kinetics was constructed to solve the kinetic model. We are now extending the kinetic model of pyrolysis of pure cellulose to describe cellulose decomposition in the presence of sodium salts.  To quantify the effect of sodium ion, a density functional theory study of glucose dehydration, an important class of decomposition reactions of a cellulose-derived intermediate, is being carried out. The initial theoretical results reveal an increase in the reaction rate coefficients when Na+ was present and a change in the relative rates of different dehydration reactions.  These kinetic parameters are then being used in the kinetic model to describe Na+-mediated pathways.

Mechanistic modeling of the decomposition of glucose-based carbohydrates: Effect of sodium ion

246th National Meeting (2013)

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