Abstract
Ketonization of wet waste-derived carboxylic acids (volatile fatty acids, VFAs) constitutes the first step of a process to catalytically upgrade VFAs to an alkane sustainable aviation fuel blendstock. VFA ketonization has been demonstrated at near-theoretical yields at the lab scale, and robust operation of industrial-scale ketonization reactors is essential for the commercialization of VFA upgrading to sustainable aviation fuel. We present a ketonization kinetic study of hexanoic acid, a VFA model compound, over commercial ZrO2 and use the kinetic parameters derived from the study in an adiabatic packed-bed reactor simulation of hexanoic acid ketonization running to near-complete (98%) conversion. A key findings from the kinetic study is that ketonization rate is positive order in acid pressure at low (<10 kPa) pressures and transitions to zero order at higher pressures, conforming to a Langmuir–Hinshelwood surface coupling mechanism. Rates are inhibited by ketonization coproduct water but not by ketones themselves or coproduct CO2. Reactor simulations using these kinetics show that rate inhibition by water controls reactor size and that size requirements can be lessened by employing designs that allow for the removal of water from the partially converted acid stream.
Highlights
The accelerating pace and scale of climate change consequences stemming from anthropogenic greenhouse gas emissions emphasizes the need for decarbonization of fossil fuel-reliant industries.[1]
The trend in rates with hexanoic acid pressure is congruent with our assumed Langmuir−Hinshelwood kinetics, as ketonization rates steeply increased from 0 to 10 kPa, were constant at higher pressures, indicative of adsorbed hexanoic acid saturating active sites beyond 10 kPa
Volatile fatty acids can be upgraded to sustainable aviation fuel blends through catalytic ketonization followed by hydrodeoxygenation
Summary
The accelerating pace and scale of climate change consequences stemming from anthropogenic greenhouse gas emissions emphasizes the need for decarbonization of fossil fuel-reliant industries.[1] Aviation accounts for 2.5% of global greenhouse gas emissions[2] and the most promising near-term strategies for advancing aviation sustainability are through development of biomass-derived aviation fuels from abundant and inexpensive biomass sources.[3] Volatile fatty acids (VFAs, C2−8 carboxylic acids) generated from wet wastes such as food waste, animal manure, and wastewater sludge are a potential sustainable aviation fuel feedstock.[4,5] Anaerobic digestion of wet wastes by microbial consortia normally forms CO2 and. Upgrading of wet waste-derived VFAs for use as aviation fuel blendstocks is a promising decarbonization pathway
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