Heterogeneity of lignocellulose must be considered for kinetic study: A case on formic acid fractionation of sugarcane bagasse with different pseudo-homogeneous kinetic models

Sugarcane bagasse was fractionated by 60–90 wt% formic acid (FA) under mild (<105 °C) conditions. Several pseudo-homogenous models including Saeman’s model, two-fraction model and “potential degree of reaction” model were employed to determine the kinetic parameters. Saeman’s model showed satisfying prediction to experimental results when the data of xylose and solubilized lignin concentrations in the liquid phase were used for fitting; however, significant deviation was found when the data of xylan and lignin contents in the residual solids were used for fitting. Two-fraction model that divided the components as fast-reacting and slow-reacting fractions showed good degree of fitting. The determined average fast-reacting fractions for xylan and lignin of sugarcane bagasse were 0.733 and 0.685, respectively. Potential degree of reaction model that introduced a parameter termed as potential degree of xylan solubilization or delignification demonstrated the best degree of fitting. The obtained rate constants was in the range of 4–14 h−1 with an observed activation energy of 20.7 kJ/mol for xylan solubilization, and 4–15 h−1 with an observed activation energy of 43.5 kJ/mol for delignification. This study is believed to provide deeper understanding of heterogeneity of lignocellulose, which is promising to enhance biorefinery and biofuel production based on sugarcane bagasse. The finding of this work also may provide useful information for kinetic modelling of chemical pretreatment and fractionation of lignocellulosic biomass.