Valorization of lipid- and cellulose-rich biomass for sustainable fuel and chemical production

Abstract

As the demand for biodiesel has expanded due to the environmental issue related to the emission of greenhouse gases and the depletion of fossil fuel reservoirs, the interest in biodiesel valorization has spurred the search for non-debatable biomass, including microbial biomass, and biological refuse. This thesis covers the studies on the valorization of biomass such as microalgae or spent coffee grounds (SCG) in various ways and suggests sustainable routes for alternative fuels. In chapter 2, as a process intensification, a production of biodiesel (Fatty acid alkyl esters, FAAEs) via wet in situ transesterification (ISTE) of microalgae is suggested. Due to the costly process of drying and oil extraction, the concept of direct use of harvested microalgae via wet in situ transesterification has considered simplified yet economically viable process. Continue to chapter 3, wet ISTE process is modified by applying the concept of hydrothermal liquefaction to produce biodiesel without the addition of catalyst, and named this new process as iTHL. By controlling reaction variables such as reaction temperature, and the amount of solvent and water, solvothermal effect of chlorinated solvent, especially dichloroethane offers both biphasic and acidic environment which is favorable for the production of biodiesel. At this point, recent studies biodiesel production from microalgae via in situ transesterification were reviewed. Furthermore, not only microalgae but also SCG was applied in this process, and showed the way to sustainable production of biodiesel. Chapter 4 addresses the production of platform chemical, for example, levulinic acid (LA) and formic acid (FA) from untreated spent coffee ground (SCG) as a precursor of platform chemical. The previously suggested iTHL process was modified to study the mechanism of products and their distribution depending on the reaction variables such as temperature, the amount of solvent and water, and the pretreatment condition. In addition, the formation of humin, which leads to the decrease in the overall yield of LA and FA, depending on the reaction variables was dealt. Based on the experimental results, the optimum condition and mechanism for maximum LA and FA from raw SCG was confirmed.