UC Riverside

Lignocellulosic biomass is an abundant renewable resource that can be converted into liquid transportation fuels to reduce greenhouse gas emissions and global dependence on petroleum. Cellulose, hemicellulose, and lignin, the three primary components in most forms of lignocellulosics, provide plants with structural rigidity and protection against microbial attack. Cellulose can be broken down to glucose and hemicellulose to up to five different sugars that can be fermented to ethanol and other products. However, these sugars can be converted to such fuels and chemicals with industrially competitive yields, the complex lignocellulosic matrix in biomass must be disrupted by application of various pretreatment technologies followed by application of enzymes to breakdown the cellulose left in pretreated solids to glucose.

UCR recently invented a novel pretreatment named Co-Solvent Enhanced Lignocellulosic Fractionation (CELF) that uses an acidic THF:water mixture at elevated temperatures and pressures to dissolve and recover lignin and hemicellulose sugars with high yields and leave solids that are highly enriched in cellulose and highly susceptible to breakdown into glucose with economically viable enzyme loadings. CELF’s efficacy is attributed to its unique THF-water co-solvent properties that facilitate acid cleavage of lignin bonds. The exposed cellulose-rich solids can then be saccharified by low doses of cellulase enzymes. The resulting glucose can then be isomerized to fructose which can then be easily converted to 5-HMF, a platform chemical that is used in the pharmaceutical, plastics, and fuels industry.

This thesis reports on the application of novel kinetic models to understand how temperature and time impact lignin and hemicellulose removal during CELF pretreatment. Calculated rate constants helped elucidate underlying mechanisms responsible for CELF’s efficiency. Additionally, the kinetic models were applied to cellulose solubilization during pretreatment and to subsequent enzymatic hydrolysis and consolidated bioprocessing to understand what pretreatment parameters impact cellulose solubilization most. Lastly, fructose production was combined with enzymatic hydrolysis of cellulose to glucose in a novel simultaneous saccharification and isomerization process for the first time.