Unveiling the low-temperature window in alkali-glycerol organosolv pretreatment: insights from process severity modeling, porosity, and adsorption kinetics.

Conventional alkali-catalysed glycerol organosolv pretreatments typically operate at high temperatures (>190 °C) to deconstruct lignocellulosic biomass, where delignification often fails to correlate with glucose yield. Rigorous evaluations of process severity and its relation with delignification and glucose yield remain scarce. This study addresses these gaps by evaluating alkali-glycerol pretreatment of jute (Corchorus olitorius) biomass across a wide range of pretreatment severity using a response surface design. Boundary conditions for temperature, duration and catalyst concentration were established prior to optimization. While alkali catalysts outperformed acids, delignification deteriorated sharply at 210 °C. Crucially, glucose yield maximized at an unprecedentedly low temperature (150 °C, 1.5% NaOH, 43.6 min) compared to peak delignification (190 °C, 1% NaOH, 44.2 min). Cellulose recovery and hemicellulose content peaked in the central conditions (170 °C, 1% NaOH, 45 min) of the BBD. Process severity was strongly correlated with delignification and cellulose recovery but decoupled from glucose yield. Through multi-criteria desirability analysis and Pareto optimization we delineated a stable, low-severity operating window previously uncharacterized for alkali-glycerol pretreatment for achieving simultaneously high glucose yield (>78.5%) and delignification (>75.5%). Model-based predictions confirmed that this low-severity window remains highly stable for glucose yield across diverse input conditions. Cong red dye adsorption kinetics, electron microscopy and spectroscopic profiling revealed that biomass pretreated at 150 °C exhibited higher adsorption capacity, increased porosity and a preferential loss of S-lignin functional groups. Collectively, these findings indicate that low-temperature alkali-glycerol pretreatment promotes more efficient biomass accessibility through synergistic structural loosening and lignin redistribution, rather than increased delignification alone.