Co-Solvent Enhanced Production of Platform Fuel Precursors From Lignocellulosic Biomass
Lignocellulosic biomass is the most abundant source of organic carbon on Earth with the highest potential to economically and sustainably replace fossil resources for large-scale production of liquid fuels. However, although lignocellulosic biomass itself is much less expensive than petroleum, its natural resistance to chemical and biological breakdown is the major obstacle that must be overcome for biomass-derived fuels to be economically competitive. This dissertation outlines the inception, development, and application of a novel biomass conversion technology called Co-solvent Enhanced Lignocellulosic Fractionation, or CELF, that applies tetrahydrofuran (THF) as a miscible aqueous co-solvent to greatly augment the dilute acid-catalyzed deconstruction of lignocellulosic biomass to enable production of renewable fuels and chemicals at unprecedented yields. CELF directly enhances the production of primary fuel precursors such as monomeric sugars and secondary fuel precursors such as furfural, 5-HMF, and levulinic acid (LA) from biomass to integrate with downstream catalytic and biological processes to convert the fuel precursors into liquid fuels and renewable chemicals. In this dissertation, three different process configurations for CELF are evaluated. First, coupling CELF with sulfuric acid at higher reaction severities achieved 87% furfural yield from maple wood and produced a glucan enriched solid that was further reacted to LA at 75% yield in a subsequent reaction. Second, coupling CELF with metal halides achieved simultaneous production of furfural at 95% yield and 5-HMF at 51% yield from maple wood and corn stover. Third, reducing the reaction severity of CELF with dilute sulfuric acid drastically improved total sugar recovery, achieving 95% xylose recovery from corn stover after first stage pretreatment and subsequent > 99% glucose recovery after enzymatic hydrolysis of the remaining solids at an enzyme dosage of only 2 mg-protein g-glucan-1. In all cases, CELF was effective at de-lignifying the biomass, dissolving up to 90% of the lignin into the liquid phase. Afterwards, recovery of THF by low temperature distillation caused the dissolved lignin to precipitate as a solid. In addition to enhancing fuel precursor yields, CELF can also serve as a valuable tool to help understand biomass recalcitrance and deconstruction.