BRIDGING MICROBIAL FERMENTATION AND CATALYTIC OLIGOMERIZATION FOR SUSTAINABLE JET FUEL PRODUCTION FROM ORGANIC WASTE

Anthony T. Giduthuri

doi:10.7273/000007178

The increasing demand for aviation fuel coupled with stringent greenhouse gas reduction targets underscores the urgent need for sustainable jet fuels and presents a significant challenge. This dissertation explores a novel approach to producing sustainable jet fuels by combining microbial fermentation and catalytic upgrading processes to convert organic waste into jet fuel hydrocarbons. The research investigates various technologies within this hybrid pathway, including biomass pretreatment, anaerobic digestion (AD), modifying AD to produce volatile fatty acid (VFA) intermediates via arrested anaerobic digestion (AAD), process optimization of AAD to maximize VFA yield, and catalytic oligomerization of VFA-derived intermediates, i.e., olefins. The initial phase of this research focused on developing a pretreatment technology to enhance anaerobic digestion (AD), a widely practiced biochemical fermentation that produces biogas. A pretreatment technology was developed to improve biomass breakdown, assessed through kinetic studies on both control and pretreated green waste (GW), where the pretreated group improved biogas production by 28.3% compared to the control group (untreated GW). To further improve the biogas yield, co-digestion of GW and food waste (FW) was investigated. The combined effects of pretreatment and co-digestion was assessed via batch and semi-continuous reactor studies where an overall volatile solids (VS) reduction of 58% was observed. Subsequently, the research shifted to AAD by inhibiting methanogenesis. This modification led to a substantial increase in VFA production. Key process parameters, such as pH and hydraulic retention time were optimized to maximize VFA yield and productivity, where an overall substrate conversion of 55% to VFA was achieved, .establishing a foundation for overall conversion of GW and FW for producing VFA for subsequent catalytic upgrading. To further enhance VFA yield, bioaugmentation with Moorella thermoacetica was explored. To conclude the initial phase of research, Chapter 4 presents a comprehensive literature review encompassing previous AAD studies on various types of wastes, emerging VFA production technologies, and potential VFA separation methods. Chapter 5 presents a comparative analysis of existing and emerging catalytic technologies for converting VFA into jet fuel viz. via intermediates such as ketones, alcohols, and olefins. This chapter aims to bridge the gap between microbial fermentation derived VFA and their subsequent transformation into jet fuel precursors. Each pathway is evaluated based on catalyst requirements, carbon conversion efficiency, hydrogen consumption, and process complexity. The subsequent chapter focused on developing a catalytic reactor for co-oligomerizing light-olefins (C2-C5) into jet fuel range olefins (C8-C16). A catalyst screening process was conducted to identify the optimal catalyst based on their functional catalytic sites, followed by an evaluation of process parameters including temperature, pressure, weight hourly space velocity, and feed composition. The developed tandem catalytic reactor system demonstrated stable performance for over 100 hours in terms of selectively forming jet-range olefins. Subsequent hydrogenation of the jet fuel range olefins produced a 100% sustainable jet fuel product that met the American Society for Testing and Materials (ASTM) Tier alpha and Tier beta fuel specification at a 50% blend with conventional jet fuel. Catalyst deactivation studies were conducted to identify the root cause of performance decline for the catalysts employed in this research. Various factors influencing catalyst deterioration were investigated, and strategies to mitigate deactivation were proposed. In conclusion, this dissertation contributes to the burgeoning field of bio-based jet-fuel development by presenting a holistic framework for producing sustainable jet fuel from organic waste by integrating bio-based and catalytic processes. The research successfully addresses critical technical challenges and demonstrates the commercial potential of this approach. Future research should prioritize process scale-up, economic analysis, and life cycle assessment to fully realize the environmental and economic benefits of this technology.

BRIDGING MICROBIAL FERMENTATION AND CATALYTIC OLIGOMERIZATION FOR SUSTAINABLE JET FUEL PRODUCTION FROM ORGANIC WASTE

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