Catalysis and process engineering for unconventional biomass conversion
Date
2021
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Abstract
Over the past few years, the concept of the biorefinery has grown significantly. A biorefinery is a facility that converts plant biomass into fuels, power, and value-added chemicals from biomass. It is analogous to today's petroleum refinery, which produces multiple fuels and products from crude oil, however, has a lower carbon footprint and enables a circular economy. Typical feedstocks include lignocellulosic biomass, food waste, algae, vegetable oils, sugars etc. While significant developments have been made in the field, the poor economic viability of many biorefineries has limited their widespread commercialization. To improve the economic potential of biorefineries and give them a standing chance against petroleum refineries, there is a need for more inexpensive and diverse feedstocks, energy and material efficient conversion processes as well as a slate of high value-added chemicals. To this end, the objective of this thesis is to investigate the conversion of unconventional biomass feedstocks into platform chemicals as well as upgrading the intermediate chemicals into high value products towards a viable biorefinery. ☐ Chapter 2 of this thesis begins by studying the hydrolysis of food waste derived starch towards producing renewable chemicals and fuels. The kinetics of glycosidic bond scission of malto-oligosaccharides in lithium bromide acidified molten salt hydrate (AMSH) medium is investigated. Findings supports the hypothesis that the terminal, non-reducing bonds hydrolyze faster than the interior and terminal reducing C-O bonds. The developed model is extended to simulate the hydrolysis of linear and cyclic saccharides of varying degree of polymerization and of potato starch. The model is in excellent agreement with the experimentally determined concentrations of glucose and other oligosaccharides. The chain length of saccharidesis found to be directly related to their hydrolysis rate constant, but inversely proportional to the glucose formation rate constant. ☐ In Chapter 3, inexpensive and abundant waste from bioethanol and agricultural processing are depolymerized, over Ru/C powder and Ru/Al2O3 pellets into phenolic monomers with high yields (~40 wt.% based on total (Klason + acid soluble) lignin and > 50 wt.% when stabilized using aldehydes), leaving behind a carbohydrate pulp residue. Batch reaction experiments, reaction kinetics analysis, machine learning, and catalyst characterization are employed to provide fundamental insights toward the reductive depolymerization of herbaceous biomass lignin which is structurally distinct from woody biomass lignin. Importantly, a polar solvent is sufficient to solubilize and fragment the lignin polymer into monomers without any catalyst. Contrary to woody biomass, where the monomer yields are positively correlated with the S-content of lignin, principal component analysis indicates that the monomer yields from herbaceous biomass depend on the content of lignin crosslinker – ferulate. Using NMR spectroscopy, I further identify α – 6 C-C linked oligomers formed from condensation reactions, explaining the unexpected low monomer yields of high β-O-4 herbaceous biomass. Recyclability experiments indicate that catalyst deactivation occurs through sintering, leaching, and fouling. ☐ Chapter 4 addresses food waste (FW) repurposing as an alternative waste management strategy towards meeting goal 12 of the United Nations sustainable development goals. An integrated biorefinery technology, repurposing potato peelwaste (PPW) for manufacturing multiple biobased value-added products is presented. This research provides salient information towards creating a circular economy, utilizing food waste in an integrated biorefinery or as a standalone energy feedstock, and provides an alternative to a make, use, dispose linear economy in which we keep resources in use for as long as possible. The integrated biorefinery comprises three stepwise processes: ultrasonic extraction to recover extractives, optimized hydrolysis and dehydration of glucose to 5-hydroxymethylfurfural (HMF), directly from potatopeels, and finally, pyrolysis of the residual lignin into biochar. As a best-case scenario, we obtain revenues of about $6,300 per MT of dry PPW, providing an opportunity for successful translation of the technology to an economically profitable process using zero value food waste. This study provides a sustainable valorization blueprint that can be extended to other types of FW for improving the economics of biomass-based biorefineries by manufacturing multiple renewable products. ☐ In Chapter 5, a data-driven quantitative synthesis-structure-property relation(QS2PRs) methodology is developed to elucidate correlations between catalyst synthesis conditions, structural properties as well as observed performance and to provide fundamental insights into active sites and a systematic way to optimize practical catalysts. We demonstrate the approach to the synthesis of nitrogen-doped catalysts (NDC) made via pyrolysis for the performance of the electrochemical hydrogen evolution reaction (HER), quantified by the onset potential and the current density. We demonstrated that an active learning-based optimization combined with various elementary machine learning tools (regression, principal component analysis, partial least squares) can efficiently identify optimum pyrolysis conditions to tune structural characteristics and performance with concomitant savings in materials and experimental time. Unlike previous reports on the importance of pyridinic or graphitic nitrogen, we discover that the electrochemical performance is not driven by a single catalyst property; rather, it arises from a multivariate influence of nitrogen dopants, pore structure and disorder in the NDC materials. ☐ In Chapter 6 of this thesis, we demonstrate a promising catalytic route to produce lubricant base oils from lignocellulosic biomass. A strategy is developed to synthesize branched benzene lubricant (BBL) and branched cyclic lubricants (BCL) lubricant base oils from lignin-derived monomers and aldehyde to replace current petroleum-derived lubricants. The reaction pathway involves carbon-carbon coupling through Brønsted acid-catalyzed hydroxyalkylation/alkylation (HAA) followed by hydrodeoxygenation (HDO). HAA reaction conditions are optimized to achieve a high guaiacol conversion into BBL and aldol condensation products. Subsequent HDO of HAA products over an Ir-ReOx/SiO2 catalyst produces a lubricant-ranged mixture of BCL (C24) and small fractions of dodecyl cyclohexane and C10 and C15 carbons alkanes. Quantification of kinematic viscosity, viscosity index, and Noack volatility indicates that the biobased lubricant base oils are comparable to commercial petroleum-derived poly α-olefin Group IV, and refrigerant base oil.
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Keywords
Biobased products, Biomass, Catalysis, Food waste, Kinetics, Process engineering