To ensure complete utilization of lignocellulosic biomass like lodgepole pine for biobased fuels and chemicals, pretreatment is usually carried out to separate the main components of the biomass namely: cellulose (40-60 wt%), hemicellulose (10-40 wt%) and lignin (15-30 wt%). In the traditional pulping industry, cellulose fibers are used in making paper, while the lignin generated is of low quality and is combusted to generate low-quality heat. However, since lignin could constitute up to 30 wt% of the material, and is the largest natural source of aromatics, it is finding applications in polymer blends, antioxidants, nanoparticles, and jet fuels. Hence the need for pretreatments that produce high-quality lignin and the development of organosolv pulping has helped in that regard. Organosolv pulping involves the use of organic solvents to break down lignin and dissolve it, leaving behind the cellulose fibers. The lignin can be recovered by solvent evaporation or the addition of water to the solution. However, most well-established organosolv processes utilize volatile organic compounds (VOCs), which not only require the use of specialized equipment because of their high vapors at temperatures required for effective pretreatment but also pose environmental concerns. Glycerol, a colorless, odorless, and viscous liquid, has been utilized as an alternative solvent for organosolv pulping processes. Glycerol organosolv pulping offers several advantages over traditional pulping methods, including reduced environmental impact, improved pulp quality, and the ability to utilize a wider range of biomass feedstocks. Additionally, glycerol, being a byproduct of biodiesel production and readily available, provides a cost-effective solvent option for this process. But glycerol is highly viscous and proves difficult to work with, especially at room temperature. Glycerol-derived compounds (GDCs) have been proposed to provide a way of tuning the properties of glycerol for effective pretreatment. These glycerol-derived solvents offer several advantages, including biodegradability, low viscosity, low toxicity, and renewable sourcing (since glycerol is often a byproduct of biodiesel production).
In this study, we investigate three of these glycerol-derived solvents namely: 1,3-Dimethoxypropanol (DMP) and 1,3-Diethoxypropanol (DEP), as well as 1,2,3-Triethoxypropane (TEP) are tested as potential solvent candidates for biomass pretreatment, with the addition of sulfuric acid as a catalyst. The impact of solvent speciation (DMP, DEP, or TEP), concentration (0-100 vol%), reaction conditions (temperature 120-180 °C, batch time 10-60 min, acid concentration 0-40 mN) are tested using the Klason lignin analysis method to quantify the extent of fractionation and delignification, surface morphology imaging using the scanning electron microscope (SEM) to understand changes in the surface features of the pine after pretreatment, spectroscopic analysis of the residual cellulose pulp to elucidate the removal of functionalities during pretreatment and appearance of functional groups in the precipitated lignin, X-ray diffraction to estimate changes in crystallinity of the residual pulps at different pretreatment conditions and 2D nuclear magnetic resonance imaging (NMR) to elucidate the structural features of the lignin precipitates. The goal is to help further develop the cocktail of renewable and eco-friendly solvents available for biomass fractionation/pretreatment.
