Comparative Analysis of Green Solvent Efficacy in Biomass Pretreatment Processes

Thesis Abstract

The increasing global demand for sustainable biofuel production necessitates efficient biomass pretreatment methods that minimize environmental impact while maximizing biomass digestibility. Traditional pretreatment chemicals often pose environmental and health risks, prompting a shift towards environmentally friendly, or "green," solvents. This study aims to conduct a comparative analysis of the efficacy of selected green solvents—namely, deep eutectic solvents (DES), supercritical carbon dioxide (scCO?), and aqueous ionic liquids—in the pretreatment of lignocellulosic biomass, specifically corn stover and rice husks. The specific objectives are to evaluate the pretreatment efficiency of these solvents based on delignification, cellulose accessibility, and subsequent enzymatic hydrolysis yields; to optimize pretreatment parameters for each solvent type; and to model the relation between solvent properties and biomass conversion efficiency. The research adopts an experimental research design, integrating quantitative laboratory-based procedures. The population comprises lignocellulosic biomass samples (corn stover and rice husks), with a purposive sampling approach to select representative samples characterized by similar moisture content and particle size distribution. A total of 120 biomass samples—60 per biomass type—are subjected to pretreatment using each of the three green solvents across varying conditions, including temperature (50–150°C), solvent-to-biomass ratio (101 to 301), and treatment time (30–120 minutes). Data collection involves measuring lignin content, cellulose accessibility, and enzymatic hydrolysis yields, using techniques such as Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and High-Performance Liquid Chromatography (HPLC). Additionally, solvent properties like polarity and viscosity are characterized and correlated with pretreatment outcomes. Methodologically, the study employs Analysis of Variance (ANOVA) to compare the efficacy among solvents under different conditions and regression analysis to model the relationship between solvent properties, pretreatment parameters, and biomass conversion efficiency. The Theory of Green Chemistry guides the selection and evaluation of solvents, emphasizing principles of minimization of hazardous substances, energy efficiency, and product safety. Optimization techniques such as Response Surface Methodology (RSM) facilitate the identification of optimal pretreatment conditions for each solvent. Expected results include statistically significant differences in pretreatment efficacy among the solvents, with specific conditions enhancing delignification and enzymatic digestibility. It is anticipated that deep eutectic solvents will outperform ionic liquids and scCO? in terms of biomass digestibility and process sustainability, owing to their tunable properties and biodegradability. Findings will reveal how physicochemical attributes of solvents influence biomass structural disruption and enzyme accessibility. This study contributes new insights into the comparative performance of emerging green solvents, providing a scientific basis for selecting environmentally benign pretreatment methods for lignocellulosic biomass. It advances understanding of the interplay between solvent chemistry and biomass transformation, filling existing gaps in knowledge regarding scalability and process optimization of green pretreatment technologies. The outcomes will inform policymakers, researchers, and industry practitioners seeking sustainable alternatives to conventional chemicals in biomass pretreatment. The main conclusion underscores the potential of specific green solvents, particularly deep eutectic solvents, to serve as efficient, eco-friendly pretreatment agents, thereby supporting the development of sustainable bio-refineries. Recommendations include further exploration of solvent recovery processes, techno-economic assessments, and pilot-scale studies to facilitate commercial adoption of the most promising pretreatment options identified in this research. Future investigations should also examine long-term environmental impacts and life cycle assessments to ensure comprehensive sustainability evaluations.