Ian Foerster

Date of Award

January 2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

First Advisor

Wayne Seames

Abstract

Widespread concern with the impacts of global emissions and climate change plays an active role in driving global renewable markets, developing scientific research communities, and setting environmental pollution regulations. Efforts to confront this rise in global emissions are primarily focused on the reduction and replacement of non-renewable fuels and materials. It has become increasingly apparent that reducing global greenhouse gas emissions will require more than just the replacement of fossil fuels, but the development of technologies to convert a diverse set of renewable feedstocks into fuels, chemicals, and materials.The goal of the work documented herein, was to expand the breadth of knowledge associated with transforming renewable feedstocks into renewable chemicals and materials. This dissertation is organized into three chapters each of which focuses on initial or developmental research for technologies to transform three different renewable feedstocks into fuels, chemicals, and materials. Specifically, this research will focus on soybeans, micro-algae, and forage sorghum as feedstocks to produce carbon fibers, fatty acid-based oils, and chemical intermediates, respectively. Chapter II, “Production of Mesophase Pitch from Renewable Sources of Tar,” documents initial research efforts for the design, commissioning, and utilization of a novel lab-scale extruder-based reaction system to convert tars generated from the non-catalytic cracking of soybean oil into a mesophase pitch suitable for processing into continuous carbon fibers. This research looks to replace traditional petroleum-based carbon fiber precursors with renewably sourced materials. Mesophase pitch formation from pyrolysis of soy tars was performed at temperatures of 325, 350, 375, and 390 °C. It was observed that increasing the processing temperature led to increased mesophase pitch formation, with 390 °C providing the only solid pitch products. The preliminary results demonstrate that this approach is technically feasible and recommends additional development towards commercialization. Chapter III, “The Extraction of Fatty Acids from Algae Oils” details a comparative study evaluating the most viable methods and conditions identified by previous researchers for the extraction of lipids from microalgae biomass in a single, consistent study. The interest in microalgae to produce third generation biofuels has developed entire research fields focused on the recovery of recoverable chemicals and components from their biomass using the most heavily researched, the lipids. The use of microalgae as a renewable feedstock faces several barriers to commercialization including the complexity of lipids extraction from the microalgae biomass. Many researchers have published techniques, with varying success. However, with differing methodologies and analytical methods, it is difficult to determine the relative merits of these techniques or of combinations of these techniques. The goal of this research was to perform a study that investigates all of the primary methods identified by earlier researchers, separately and in certain combinations, in order to provide a consistent comparison of the methods for the efficient extraction of lipids from microalgae. The lipid extraction techniques investigated were solvent selection coupled with microwave, sonication, or in situ transesterification assisted extraction. Methanol was found to be the best performing solvent for lipid extraction from Chlorella Vulgaris microalgae. Methanol consistently outperformed the other solvents examined, namely: Bligh Dyer, ethanol, chloroform, acetonitrile, and hexane. Methanol was the top solvent for use with both microwave and sonication assisted extraction, as well as, for in-situ transesterification assisted extraction. Of the techniques investigated, methanol solvent with in situ transesterification followed by ultrasonication provided the highest recovery of lipids from microalgae biomass with 35% of the initial lipids recovered. Chapter IV includes two distinct studies involving the transformation of the lignocellulosic biomass forage sorghum. Lignocellulosic biomass is one of the most extensively researched and promising renewable feedstocks for fuels, chemicals, and material products traditionally sourced from nonrenewable sources. The work was divided into two efforts, the production of organic acids from the carbohydrates and decomposition of the remaining lignin. The first section of Chapter IV, “Production of Organic Acids from Sorghum Carbohydrates,” documents a study of the catalytic decomposition and transformation of into building block acids, with a focus on lactic acid. Both model sugar solutions plus those derived from forage sorghum carbohydrates were utilized. For the actual samples, the carbohydrates were extracted from the biomass and the cellulose and hemi-cellulose hydrolyzed into glucose and xylose. The glucose and xylose monomers were catalytically transformed into the acids. Experiments were performed to investigate catalyst doping factors and performance, specifically dopant selection and silica-to-alumina ratios. Additional experiments were performed to determine xylose decomposition products and biomass sourced carbohydrate decomposition products. Batch catalytic decomposition reactions of model glucose in water solutions were performed to determine differences in the impact of using Sn (II) or Sn (IV) as the catalyst dopant, as well as the impact from varying the silica-to-alumina ratio in catalyst scaffold. It was determined that both Sn (II) and Sn (IV) are equally effective at providing Lewis acid sites necessary for the decomposition of carbohydrates to lactic acid. The silica-to-alumina ratio of the catalyst scaffold was a significant factor in the performance of carbohydrate decomposition reactions. Increasing the alumina content within the catalysts leads to increased Brønsted acid sites causing an increase in levulinic acid formation. Using a xylose in water solution, it was found that the Sn-Beta catalytic decomposition of xylose leads to increased lactic acid and decreased levulinic acid, when compared to glucose. This is attributed to differences between the proposed reaction pathways for xylose and glucose. It was also found that forage sorghum-derived glucose and xylose mixtures were acceptable feedstocks for Sn-Beta decomposition reactions to form lactic acid. The neutralization step for acid hydrolysis used to generate the mixtures modifies the Sn-Beta catalyst to provide increased lactic acid formation and decreased levulinic acid formation, when compared to model solutions. It was also observed that decreasing sugar-to-catalyst ratios in biomass sourced carbohydrate decomposition reactions leads to increased lactic acid formation, with the highest observed conversion of carbon to lactic acid of 64%. The second section of Chapter IV, “Base Facilitated Decomposition of Forage Sorghum Lignin” documents experiments with a novel, continuous flow reactor designed to decompose the lignin from forage sorghum. Lignin is one of the most abundant natural polymers, behind cellulose and hemicellulose. Unique amongst renewable biomass, lignin is considered the most promising non-petroleum source of renewable aromatic compounds. Currently, lignin is considered a waste product, with most of its production being burnt for heat and electricity. In order to better exploit the unique phenolic content of lignin, it is necessary to liberate these desirable monomer compounds from the polymer. Given the complex nature of lignin, an efficient method to decompose it into chemical intermediates does not currently exist. A novel non-catalytic decomposition reactor was utilized and evaluated for the decomposition of softwood kraft lignin and forage sorghum extracted lignin. Initial experiments using softwood kraft lignin were performed to determine an optimum decomposition temperature. Temperatures of 335, 340, and 350 °C were examined. It was determined that 340 °C provided the highest conversion to monomer and oligomer components. When compared to forage sorghum-derived lignin, Kraft lignin maintains a more complex, recalcitrant nature. Sorghum-derived lignin shows significantly higher oligomer and monomer carbon fractions, when compared to Kraft lignin. The fraction of monomers and oligomers generated in this novel system are higher than those from acid and base catalyzed polymerization methods reported in the literature. This demonstrates that this system has the potential to be used for the decomposition of reactive lignin.

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