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. 2021 Mar 30;118(13):e2023008118.
doi: 10.1073/pnas.2023008118.

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

Nabila A Huq  1 , Glenn R Hafenstine  1 , Xiangchen Huo  1 , Hannah Nguyen  1 , Stephen M Tifft  1 , Davis R Conklin  1 , Daniela Stück  1 , Jim Stunkel  1 , Zhibin Yang  2 , Joshua S Heyne  2 , Matthew R Wiatrowski  1 , Yimin Zhang  1 , Ling Tao  1 , Junqing Zhu  3 , Charles S McEnally  3 , Earl D Christensen  1 , Cameron Hays  1 , Kurt M Van Allsburg  1 , Kinga A Unocic  4 , Harry M Meyer 3rd  5 , Zia Abdullah  1 , Derek R Vardon  6
Affiliations

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

Nabila A Huq et al. Proc Natl Acad Sci U S A. .

Abstract

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.

Keywords: biojet; decarbonization; food waste; ketonization.

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Conflict of interest statement

Competing interest statement: N.A.H., X.H., H.N., and D.R.V. are inventors on a patent application submitted by the Alliance for Sustainable Energy on methods for the production of VFA-SAF (US 17/121,336 filed on December 14, 2020).

Figures

Fig. 1.
Fig. 1.
Overview scheme of the major oxygenate and hydrocarbon molecules produced when converting wet waste VFA into Fast Track VFA-SAF that is composed of normal paraffin-rich hydrocarbons (Top Right) and Aldol Condensation VFA-SAF composed of isoparaffin-rich hydrocarbons (Bottom Right).
Fig. 2.
Fig. 2.
Modeled and experimental VFA ketonization carbon yields. For the C6/C8 VFA feed, (A) VFA carbon chain length distribution, (B) ketone and CO2 carbon yield, and (C) model and experimental ketone carbon number profile. Similar values are reported for the C4/C6 VFA feed (D–F). Blue represents ≥C8 ketone carbon chain lengths suitable for Fast Track VFA-SAF, while orange represents ≤C7 ketones that require coupling for Aldol Condensation VFA-SAF. Values are rounded to whole number.
Fig. 3.
Fig. 3.
Ketonization catalyst performance with the biogenic C6/C8 VFA sample. (A) Complete conversion conditions with near theoretical yields. Reaction conditions: catalyst loading 5 g ZrO2, Ar flow 166 mL(STP)/min−1 at 1 atm, bed temperature 350 °C, and weight hourly space velocity (WHSV) 3.1 h−1 based on VFA mass flow rate. (B) XPS survey spectra of fresh, spent, and regenerated ZrO2. (C) Ketonization catalyst stability under partial conversion conditions before and after regeneration using the spent full conversion catalyst. Reaction conditions: catalyst loading 2 g ZrO2, Ar flow 166 mL(STP)/min−1 at 1 atm, bed temperature 290 °C, and WHSV 7.7 h−1 based on VFA mass flow rate. Regeneration conditions: 5 °C/min to 500 °C, hold 12 h, cool naturally, and in flowing air.
Fig. 4.
Fig. 4.
VFA-SAF fuel properties relative to fossil Jet A are shown, prescreened for composition, chemical and physical properties, and distillation analysis. The first row shows Fast Track VFA-SAF blend produced from the C6/C8 VFA sample (A) neat carbon distribution, (B) 10 vol% blend fuel properties (σ = surface tension, ρ = density, μ = viscosity, nHOC = net heat of combustion, and CN = cetane number), and (C) 10 vol% blend simulated distillation curves. Equivalent data are shown for the Aldol Condensation VFA-SAF produced from the C4/C6 VFA sample (D–F). The 20%/50% Fast Track/Aldol Condensation blend result is shown for all three of its panels (G–I). The gray region represents the range of conventional fuels, namely, POSFs 10325, 10264, and 10289. The red regions represent out-of-specification ranges. The carbon distribution for representative fossil jet POSF 10325 is tabulated in SI Appendix, Table S6, with fuel properties in SI Appendix, Table S8. Predicted data are shown with an open circle.
Fig. 5.
Fig. 5.
Techno-economic analysis of VFA-SAF Fast Track process. (A) Simplified process flow diagram for the downstream catalytic Fast Track VFA-SAF production via ketonization (KET) and hydrodeoxygenation (HDO), with light ≤C7 ketones being converted to naphtha. (B) VFA biofuel minimum fuel selling price as a function of VFA production cost and assumed LCFS credit of $3.71/gallon. (C) Sensitivity analysis of major downstream catalytic process parameters for VFA biofuel production.
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References

    1. Holladay J., Abdullah Z., Heyne J., “Sustainable aviation fuel: Review of technical pathways” (DOE/EE-2041 8292, USDOE Office of Energy Efficiency and Renewable Energy (EERE), Bioenergy Technologies Office (EE-3B) (Bioenergy Technologies Office Corporate), DOE EERE, 2020).
    1. ICAO , Assembly Resolutions in Force. https://www.icao.int/Meetings/GLADs-2015/Documents/A38-18.pdf. Accessed 1 March 2021.
    1. Lee D. S., et al., The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018. Atmos. Environ. (1994) 244, 117834 (2021). - PMC - PubMed
    1. ICAO , Resolutions Adopted by the Assembly: Provisional Edition. 38th Session, Montreal, Canada. September 24 - October 13 (2013).
    1. Zhang L., Butler T. L., Yang B., Recent Trends, Opportunities and Challenges of Sustainable Aviation Fuel (Green Energy to Sustainability, 2020), pp. 85–110.

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