(557e) Mechanistic Modeling of Fast Pyrolysis of Glucose-Based Carbohydrates in the Presence of NaCl
Sodium ions, one of the inorganic constituents that naturally exist in lignocellulosic biomass, significantly alter pyrolysis behavior and resulting chemical speciation. In this work, experiments were conducted using a micropyrolyzer coupled to a gas chromatography−mass spectrometry/flame ionization detector system to investigate the catalytic effects of NaCl on fast pyrolysis of glucose-based carbohydrates including glucose, cellobiose, maltohexaose and cellulose, and on a major product of cellulose pyrolysis, levoglucosan. A mechanistic model that addressed the catalytic effects of NaCl on the quantitative pyrolysis product distribution was developed based on our previous model of fast pyrolysis of neat glucose-based carbohydrates. The model incorporated the interactions of Na+ with cellulosic chains and low molecular weight species formed in fast pyrolysis, reactions mediated by Na+ including dehydration, cyclic/Grob fragmentation, ring-opening/ring-closing, isomerization, and char formation, and a degradation network of levoglucosan in the presence of Na+. Kinetic parameters of each elementary step were specified in terms of the Arrhenius parameters. A computational framework based on continuous distribution kinetics and mass action kinetics was constructed to solve the mechanistic model. Agreement between model yields of various pyrolysis products with experimental data from fast pyrolysis of glucose-based carbohydrates dosed with NaCl ranging from 0−0.34 mmol/g at 500 °C validated the model and demonstrated the robustness and extendibility of the mechanistic model. The model was able to capture the yields of major and minor products as well as their trends across NaCl concentrations. Modeling results showed that Na+ accelerated the rate of decomposition and reduced the time for complete thermoconversion of carbohydrates. The sharp reduction in the yield of levoglucosan from fast pyrolysis of cellulose in the presence of NaCl was mainly caused by reduced decomposition of cellulose chains via endchain initiation and depropagation due to Na+ favoring competing dehydration reactions.
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