With the increasing demand for net-zero sustainable aviation fuels (SAF), new conversion technologies are needed to process waste feedstocks and meet carbon reduction and cost targets. Wet waste is a low-cost, prevalent feedstock with the energy potential to displace over 20% of US jet fuel consumption; however, its complexity and high moisture typically relegates its use to methane production from anaerobic digestion. To overcome this, methanogenesis can be arrested during fermentation to instead produce C2 to C8 volatile fatty acids (VFA) for catalytic upgrading to SAF. Here, we evaluate the catalytic conversion of food waste-derived VFAs to produce n-paraffin SAF for near-term use as a 10 vol% blend for ASTM "Fast Track" qualification and produce a highly branched, isoparaffin VFA-SAF to increase the renewable blend limit. VFA ketonization models assessed the carbon chain length distributions suitable for each VFA-SAF conversion pathway, and food waste-derived VFA ketonization was demonstrated for >100 h of time on stream at approximately theoretical yield. Fuel property blending models and experimental testing determined normal paraffin VFA-SAF meets 10 vol% fuel specifications for "Fast Track." Synergistic blending with isoparaffin VFA-SAF increased the blend limit to 70 vol% by addressing flashpoint and viscosity constraints, with sooting 34% lower than fossil jet. Techno-economic analysis evaluated the major catalytic process cost-drivers, determining the minimum fuel selling price as a function of VFA production costs. Life cycle analysis determined that if food waste is diverted from landfills to avoid methane emissions, VFA-SAF could enable up to 165% reduction in greenhouse gas emissions relative to fossil jet.

https://www.pnas.org/content/pnas/118/13/e2023008118.full.pdf

Toward net-zero sustainable aviation fuel with wet waste–derived volatile fatty acids

A review on photo-, electro- and photoelectro- catalytic strategies for selective oxidation of alcohols

The thermochemical conversion of biomass is potentially vital to meeting global demand for sustainable transport fuels so besides combustion; torrefaction, liquefaction, pyrolysis and gasification are reviewed. The merits and demerits of these processes and examples of industrial applications are evaluated, and two promising avenues for future development are identified. The future of biomass upgrading via thermochemical processing will depend on sector coupling, both within the energy sector and with sectors such as food production. Owing to environmental constraints and the need to maintain food production, the availability of traditional feedstocks for biofuels, such as corn, will be limited in the future. Now given the ambitious targets for sustainable aviation fuel – a higher quality fuel – reserving appropriate feedstocks for aviation fuel will be necessary. Such a policy would open opportunities for the commercial development of the sustainable production of such liquid fuels via liquefaction and pyrolysis. The second avenue of opportunity links to the fact that biomass in the form of wooden pellets has established itself as an essential fuel. In the UK and elsewhere, it is already contributing to the decarbonisation of the electricity grids. So worldwide, a positive future for biomass combustion, aided where appropriate by torrefaction, is envisaged as increasingly crucial for the abatement of greenhouse gas emissions. Alongside battery storage and pumped hydroelectric storage, the contribution of biomass processes, such as torrefaction, to tackling the storage problem arising from the intermittent nature of wind and solar energy has been clarified for the first time. 

Thermochemical conversion of biomass: Potential future prospects

The current debate on the sustainability of bio-based products questions the environmental benefits of replacing fossil- by bio-resources. Here, we analyze the environmental trade-offs of 98 emerging bio-based materials compared to their fossil counterparts, reported in 130 studies. Although greenhouse gas life cycle emissions for emerging bio-based products are on average 45% lower (-52 to -37%; 95% confidence interval), we found a large variation between individual bio-based products with none of them reaching net-zero emissions. Grouped in product categories, reductions in greenhouse gas emissions ranged from 19% (-52 to 35%) for bioadhesives to 73% (-84 to -54%) for biorefinery products. In terms of other environmental impacts, we found evidence for an increase in eutrophication (369%; 163 to 737%), indicating that environmental trade-offs should not be overlooked. Our findings imply that the environmental sustainability of bio-based products should be evaluated on an individual product basis and that more radical product developments are required to reach climate-neutral targets. 

The potential of emerging bio-based products to reduce environmental impacts

Ketonization reactions provide a feasible approach to remove oxygen and increase carbon chain length for conversion of biomass derived carboxylic acids. However, the reaction suffers from fast catalyst deactivation and low ketone selectivity. In this work, Lewis acidic heteroatom Ti-, Zr-, Ce-, and Sn-Beta zeolites were prepared using a two-step post-synthesis method and applied in vapor phase ketonization of propionic acid at 350 °C. Among these zeolites, Zr-Beta shows both the highest activity and selectivity. Characterizations indicate that Zr prefers the vacant tetrahedral site when the Zr content is 96% at a space time of 2 h. The amount of coke deposition on Zr-Beta is about 1/3 of that on H-Beta, and the structure of Zr-Beta is preserved after 60 h of reaction. The results of this work indicate that Zr-Beta zeolite is a promising catalyst for ketonization with good stability and high selectivity toward ketone.

Ketonization of Propionic Acid on Lewis Acidic Zr-Beta Zeolite with Improved Stability and Selectivity

Ketonization of (biomass) carboxylic acids is increasingly showing its potential as upgrading strategy to renewable fuels and chemicals. Due to the growing amount of recent studies, an updated and critical overview of the catalytic advancements are warranted. Metal oxide and zeolite catalysts are discussed, alongside their proposed mechanisms and elementary steps. Substrate-surface interactions, structure-function correlations and kinetic studies have contributed to a better understanding of the requirements for ketonization catalysis, though the mechanism and rate-determining step(s) are still under debate. As a result, targeted modifications to improve catalytic performance are being established. Furthermore, substrate properties such as chain length, branching, unsaturation and additional functionalities have been identified as crucial for their reactivity. However, additional research is necessary to better integrate ketonization into future biorefineries. This includes development of kinetic models for oleochemicals conversion, catalyst design and regeneration. Finally, techno-economic and sustainability assessments are lacking to incentivize industrial implementation.

Catalytic advancements in carboxylic acid ketonization and its perspectives on biomass valorisation

Catalytic ketonization of carboxylic acids is promising for the synthesis of renewable products. Despite its potential, fatty acid ketonization and its kinetics in the liquid phase are less investigated. This work encompasses kinetic evaluation of two TiO2 catalysts (anatase and rutile) for C-C coupling of C12-C18 fatty acids in inert dodecane solvent. The rutile catalyst, with higher Lewis acid density, showed higher intrinsic activity and more favorable activation energy barriers. Unfortunately, this material suffers from stronger product inhibition by ketone, water and carbon dioxide compared to anatase. Langmuir-Hinshelwood kinetic models were developed and validated against the experimental data, supporting that C-C coupling of adsorbed species is rate determining in the ketonization mechanism. The Lewis acid site density and distance between active Ti species at the surface were invoked to explain the activity patterns. The impacts of substrate chain length, solvent and liquid phase purging on the ketonization kinetics were investigated, showcasing potential for future improvements. 

/pdf/kinetics-of-fatty-acid-ketonization-in-liquid-phase-with-3qmoufse.pdf

Kinetics of fatty acid ketonization in liquid phase with anatase and rutile TiO2 catalysts

Assessment of the environmental sustainability of solvent-less fatty acid ketonization to bio-based ketones for wax emulsion applications

Metal-Free Reduction Creates Highly Active TiO2 Surfaces for Fatty Acid Ketonization

A method for the hydrophobization of wood-based materials wherein said wood-based materials are hydrophobized with an aqueous emulsion comprising an organic ketone composition comprising x percent by weight (wt %), relative to the total weight of the organic ketone composition, of at least one ketone having the formula R1-CO-R2, wherein R1 and R2 are hydrocarbon radicals which are independently selected from hydrocarbon radicals comprising from 6 to 24 carbon atoms, characterized in that the organic composition has a penetration value P mm of at least 40, measured in accordance with the ASTM standard method D1321 - 10 at 24 °C, and x is at least 32 when the penetration value P mm is equal to or higher than 110 and x > 3520/P when P is higher than 40 but lower than 110

Wood composite objects

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