Exploring Methodologies to Improve Lignin Utilization in Biorefineries

The increasing world population, coupled with an improving quality of life, has driven a rapidly increasing demand for fuels, chemicals, and materials. Fossil carbon feedstocks, such as petroleum, are currently being consumed to meet these demands. The utilization of these feedstocks has negative impacts on human and environmental health, which are undoubtedly intensifying as a result of the increased reliance required to meet these demands. As an alternative way to meet these demands, biorefineries generate a wide range of fuels, chemicals, and materials from biomass, a renewable and sustainable resource. Current second-generation biorefineries use a plant-based feedstock, lignocellulosic biomass, comprised of three main components: cellulose, hemicellulose, and lignin. Second-generation biorefineries focus on converting cellulose and hemicellulose into fermentative fuels, discarding lignin as waste. Lignin is a complex and recalcitrant random co-polymer that is difficult to isolate and process, but it is comprised of molecular sub-unit structures that are analogous to many high value components of petroleum. If biorefineries are to compete against and mitigate the harmful effects of petroleum refineries, they must efficiently utilize all three major biomass components to increase product diversity, value, and yields. This dissertation explores extracting and upgrading lignin to improve its utilization in biorefineries. The first study investigates the use of a series of organic solvent mixtures to extract usable lignin from the waste stream of an ammonia fiber explosion extraction (AFEX) biorefinery. It focuses on understanding the solvent characteristics that control the lignin yield and resulting physochemical properties. An ethanol:water mixture effectively separates lignin from the waste, with high yields and only minor chemical modifications. By utilizing a current waste stream, the technology is easily adopted without disrupting the biorefinery operation. The dissertation next explores the reactions occurring during organosolv pretreatment that control the lignin extraction efficiency, as well as reactions associated with key physiochemical characteristics. A ‘pseudo-first order in series’ reaction model was applied to nuclear magnetic resonance (NMR) data of extracted lignin and kinetics constants for lignin yields and the chemical moieties related to important physicochemical properties were elicited. This study provides guiding principles for designing future organosolv processes that obtain lignin streams with desired qualities. In a final study, Fourier Transform Ion Cyclotron Resonance High Resolution Mass Spectrometry (FT-ICR HRMS) is used to analyze lignin breakdown products after catalytic upgrading. FT-ICR HRMS overcomes many problems other characterization methods face, but a single analysis results in thousands of data points, making processing the data difficult, thus a petroleomic analysis is adopted to easily track key characteristics. In the study, FT-ICR HRMS and a petroleomic analysis are applied to a catalysis and stabilizing co-solvent system that effectively fragments the lignin while preserving important chemical moieties, as shown by petroleomic analysis of the FT-ICR HRMS data. All three of the technologies explored within this dissertation offer avenues to improve the technical and economic viability of biorefinerie