A detailed kinetic modeling of subcritical water hydrolysis of sweet sorghum bagasse: From sugar formation to inhibitor decomposition

Sweet sorghum bagasse (SSB) is a promising lignocellulosic feedstock for the sustainable production of fermentable sugars and bio-based chemicals. In this study, a comprehensive kinetic model was developed to describe the subcritical hydrolysis of SSB in a batch reactor at 100 bar and three temperatures: 200, 240, and 280 °C. The model integrates the simultaneous hydrolysis of cellulose and hemicellulose, sugar production, and the formation and degradation of key inhibitory compounds, such as furfural and 5-hydroxymethylfurfural (HMF). The kinetic parameters were estimated using Particle Swarm Optimization (PSO), followed by statistical analysis. The model satisfactorily reproduces the experimental transient concentration profiles of sugars and inhibitors at all tested temperatures, achieving a close fit to the experimental data for cellobiose, glucose, xylose, arabinose, HMF, and furfural contents. The results confirmed that hemicellulose is preferentially hydrolyzed at lower temperatures, while significant cellulose conversion (~95%) occurs only at 280 °C. Inhibitor formation was well represented, with rapid accumulation of furfural and HMF followed by secondary degradation, especially at higher temperatures. Statistical analyses suggest that most of the estimated kinetic parameters are reliable, with low to moderate parameter correlations and well-defined confidence intervals. The proposed model effectively captures the competitive and sequential nature of the hydrolysis and degradation pathways and provides a complete mass balance for cellulose and hemicellulose consumption. The proposed kinetic model satisfactorily reproduces the experimental concentration profiles under the investigated conditions and provides a mechanistic framework that may support further studies of lignocellulosic biomass hydrolysis and degradation.