Sustainable Organosolv Pretreatment and Fractionation of Lignocellulosic Biomass with the Aim of Subsequent Utilization of the Fractionated Components

Lignocellulosic biomass is the most abundant biomass species on Earth. However, lignocellulose biomass is challenging to exploit because the biochemical components (cellulose, 40-60 wt.%; hemicellulose, 10-40 wt.%; and lignin, 15-30 wt.%) form the lignin-carbohydrate complex (LCC) that supports the growth of the plant/crop but also makes them recalcitrant to valorization. To overcome this recalcitrance and to exploit lignocellulose biomass for biofuels and biochemicals, pretreatment (fractionation or pulping) is often carried out. This procedure is aimed at breaking apart the lignin-carbohydrate linkages (LCC) and dissolving the lignin, leaving a pulp rich in cellulose. In traditional pretreatment methods, the lignin fractions are usually of low grade, primarily due to their condensed nature and the incorporation of sulfur in some cases. One of the major ways to sustainably pretreat biomass and produce high-quality lignin is through organosolv pulping. Traditional organosolv processes utilized volatile solvents (VOCs) like ethanol, methanol, and acetone, but, due to the rising concerns about the release of these VOCs into the environment, alternative high-boiling point solvents are being proposed. Hence, this research started by using available high-boiling point polar aprotic solvents as sustainable options for organosolv pretreatment of lodgepole pine (a representative lignocellulose). It was shown for the first time that the combination of these solvents with organic bases as additives effectively removes lignin from biomass. Concurrently, a modeling approach was employed to study the kinetics of lignin removal from lodgepole pine using these polar aprotic solvents. Thereafter, the research extended to using novel biobased solvents based on the glycerol backbone and termed glycerol-derived ethers (GDEs) as sustainable solvent options for organosolv fractionation of lodgepole pine. The dried pulp and the isolated lignin were extensively analyzed, demonstrating for the first time a novel solvent system for biomass fractionation. Furthermore, to improve the utilization of fractionated lignocellulose components (cellulose, lignin), this work extends to integrating them into biobased composite materials, specifically, lignin-based epoxides and cellulosic materials with improved mechanical and barrier properties. Finally, future research goals related to improving the sustainability of the novel solvent systems for biomass fractionation and materials utilization were proposed.