Sustainable Aviation Fuel: Review of Technical Pathways Report

September 10, 2020

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(U.S. Department of Energy) The Sustainable Aviation Fuel: Review of Technical Pathways report provides an overview of commercial jet aviation fuel and summarizes learnings from three BETO-supported workshops. In addition, the report focuses on insights for reducing costs and optimizing the value proposition of sustainable aviation fuel. Download the report to learn more.

Cost-competitive sustainable alternative jet fuels and high-performance fuels for aviation are needed to decouple carbon growth from market growth. With this in mind, the U.S. Department of Energy Bioenergy Technologies Office (BETO) published a report titled Sustainable Aviation Fuel: Review of Technical Pathways.

BETO's report describes potential pathways to produce sustainable alternative fuels suitable for use by the commercial aviation sector. It also presents a vision of low-cost, clean-burning, and low-soot-producing jet fuel uniquely available from renewable and wasted carbon sources. READ MORE

Sustainable Aviation Fuel: Review of Technical Pathways (U.S. Department of Energy)

Excerpt from report: The 106-billion-gallon global (21-billion-gallon domestic) commercial jet fuel market is projected to grow to over 230 billion gallons by 2050 (U.S. EIA 2020a). Cost-competitive, environmentally sustainable aviation fuels (SAFs) are recognized as a critical part of decoupling carbon growth from market growth. Renewable and wasted carbon can provide a path to low-cost, clean-burning, and low-soot-producing jet fuel. Research shows an opportunity to produce fuel in which aromatics are initially diluted with the addition of renewable iso-alkanes, aromatics are later fully replaced with cycloalkanes, and finally high-performance molecules that provide mission-based value to jet fuel consumers are introduced. Key to this fuel pathway is sourcing the three SAF blendstocks—iso-alkanes, cycloalkanes, and high-performing molecules—from inexpensive resources. When resourced from waste carbon, there are often additional benefits, such as cleaner water when sourcing carbon from wet sludges or less waste going to landfills when sourcing the carbon from municipal solid waste or plastic waste. Jet fuel properties differ from gasoline and diesel, so research will be most successful if it begins with the end result in mind.

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Executive Summary

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U.S. airlines have improved efficiency by 130% compared to 1978 levels (Airlines for America 2020). Additional efficiency improvements in planes and engines are not likely to be enough. Meeting the 2050 goal will required fuels that have a lower carbon footprint, referred to as sustainable aviation fuel (SAF)—defined by the International Civil Aviation Organization (ICAO) as alternative aviation fuels that “(i) achieve net GHG [greenhouse gas] emissions reduction on a life cycle basis; (ii) respect the areas of high importance for biodiversity, conservation and benefits for people from ecosystems, in accordance with international and national regulations; and (iii) contribute to local social and economic development, and competition with food and water should be avoided” (ICAO 2018).

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A second challenge is that the price of SAF today is higher than petroleum-based Jet A fuel. Fuel price is a hurdle because fuel is 20%–30% of the operating cost of an airline (IATA 2018). Research and development (R&D) can help bring the cost down.

Unlike light-duty vehicles, the low energy density of even the best batteries severely limits opportunities for electrification.1 While many are working on electrification, efforts are for smaller aircraft and airlines will have no alternative for some time but to use SAF to operate in a GHG-emission-constrained future.

Part I of this report provides an overview of commercial jet aviation fuel: how it compares to fuels for cars and trucks, its composition, its specification, and its certification process.

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Original equipment manufacturer (OEM)-led ASTM D4054 fit-for-purpose testing generally costs several million dollars and can require years to be approved (ASTM 2018). A fast-track approval process has been accepted for fuels in which the SAF blending component is limited to 10% and consists of the same types of molecules that are in petroleum-based jet fuel. A clearinghouse annex has also been proposed to reduce cost and time for approval.

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Part I finishes by summarizing the learnings from three BETO-supported workshops. These include the Alternative Aviation Fuel Workshop held in Macon, Georgia, in 2016, which focused on SAF production; the JET workshop held in Cleveland, Ohio, in 2017, which focused on high-performance fuels; and the Trilateral Biojet Workshop held in Richland, Washington, in 2018, which focused on jet fuel R&D collaborations between Canada, the United States, and Mexico. Some of the key learnings from these workshops include:

• The aviation industry seeks to reduce its GHG emissions significantly, decoupling airline growth from carbon growth.
• The current cost of SAF is high. Airlines are willing to support SAF development by purchasing some fuel at a higher price, but for SAF to scale, prices need to be reduced.
• OEM-led ASTM D4054 approval and evaluation process is expensive and time-consuming. Developing new engines is even more onerous regarding timescale and cost, and hence a program coupling fuel development and engine development R&D would not help overcome industry barriers.
• Existing engines can use fuels that have a much higher heat of combustion than Jet A, and specific energy (i.e., heat of combustion) increases can deliver greater range, higher payload capacity, or decreased fuel consumption.
• More sources of low-cost feedstock are required as fats, oils, and greases are not currently available in enough volume to meet SAF demand.
• The use of cover crops to increase availability of oil seeds while improving soil quality as well as use of other lipid-rich streams, such as manures and sludges, may increase availability. Processes for their conversion will need to be approved through ASTM.
• Techno-economic analysis (TEA) and life cycle analysis (LCA) are inconsistent across the SAF industry, but the consistent message from most models is that the main cost drivers are feedstock costs, yields, and plant capital recovery.
• Current policies are skewing renewable fuels towards diesel and away from the jet market.

Part II provides insights resulting from a study of the aviation fuel industry, challenges of and successes with
the approved pathways, and BETO capabilities and R&D portfolio.

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Examples of work could include the following:

• In the near term (0–5 years), research can help further reduce the cost of existing approved pathways to iso-alkanes and synthetic paraffinic kerosene molecules. Research could include low-cost routes to cycloalkanes, including alkylated cyclohexanes, and understanding the properties of molecules with various ring structures available from catalytic, biological, thermal, and hybrid approaches.
• Public–private partnerships and collaborations across agencies may accelerate cost reductions by ensuring a diverse set of stakeholders are involved early in the solution to ensure it can address barriers for industrywide use.
• In the longer term, as SAF volumes increase, aviation fuels may provide better performance and reduced emissions (i.e., soot).
• Use of nontraditional raw materials including carbon oxides, methane, deconstructed plastic, and other waste materials may keep cost in parity with conventional fuels.

BETO’s R&D capabilities and feedstock/technology portfolio provide tools for meeting the technical needs to overcome hurdles preventing SAF deployment, including cost reduction. READ MORE

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Table of Contents
Executive Summary ........................................................................................................................................... vi
Introduction..........................................................................................................................................................1
Part I – Background.............................................................................................................................................2
1 Jet Fuel Markets............................................................................................................................................3
1.1 Jet Fuel Versus Ground Transportation Fuel Markets.................................................................... 3
1.2 How Is Jet Fuel Similar to and Different from Other Transportation Fuels? ................................. 5
1.3 Why Invest in SAF? ....................................................................................................................... 7
2 Jet Fuel Specifications..................................................................................................................................7
2.1 Properties: Performance, Operability, and Drop-In Requirements................................................. 8
2.1.1 Performance ......................................................................................................................... 8
2.1.2 Operability ........................................................................................................................... 8
2.1.3 Drop-In................................................................................................................................. 9
2.1.4 Other Properties ................................................................................................................. 10
2.1.5 Fuel Properties Derived from Bulk Versus Trace Composition ........................................ 10
2.2 Molecular Families in Jet Fuel ..................................................................................................... 10
2.2.1 n-Alkanes and iso-Alkanes ................................................................................................ 12
2.2.2 Aromatics........................................................................................................................... 12
2.2.3 Cycloalkanes...................................................................................................................... 13
2.2.4 Blended Fuels..................................................................................................................... 14
2.3 Beyond Current Fuels – High Performance.................................................................................. 14
2.4 Review of Chapter 2..................................................................................................................... 15
3 Jet Fuel Certification ................................................................................................................................. 16
3.1 Getting a Fuel Approved .............................................................................................................. 16
3.2 A Fast Track to ASTM Approval................................................................................................. 18
3.3 Currently Approved and Emerging Fuels..................................................................................... 19
3.4 Summary of Current SAFs........................................................................................................... 20
4 Workshop Learnings ................................................................................................................................. 21
4.1 Alternative Aviation Fuel Workshop............................................................................................ 22
4.2 JET Workshop.............................................................................................................................. 23
4.3 Trilateral Canada–Mexico–U.S. Biojet Workshop....................................................................... 23
Part II – Analysis and Insights..................................................................................................................... 25
5 R&D – Fuel Molecules ............................................................................................................................. 26
5.1 Vision: Reduce Aromatic Content and Increase iso-Alkanes and Cycloalkanes ......................... 26
5.2 High-Quality iso-Alkanes............................................................................................................. 28
5.2.1 Crack Large Molecules...................................................................................................... 29
5.2.2 Build Up Small Molecules................................................................................................. 31
5.2.3 Direct Fermentation ........................................................................................................... 32
5.2.4 Summary............................................................................................................................ 32
Sustainable Aviation Fuel: Review of Technical Pathways

5.3 Alkylcycloalkanes, Six-Carbon Rings.......................................................................................... 33
5.3.1 Zeolite-Catalyzed Aromatization Followed by Hydrotreating........................................... 34
5.3.2 Phenol Hydrogenation........................................................................................................ 35
5.4 Cycloalkanes, Other Ring Sizes, and Fused Rings....................................................................... 36
5.4.1 Ring Contraction................................................................................................................ 36
5.4.2 Ring-Forming Reactions.................................................................................................... 36
5.4.3 Ring Motifs in Wood Extractives and Fermentation.......................................................... 36
5.4.4 Esoteric Cycloalkanes........................................................................................................ 37
5.5 Low-Aromatic, High-Energy-Content Fuel Properties ................................................................ 38
5.5.1 Gaps in Understanding Cycloalkane Properties................................................................. 38
5.5.2 Quantifying the Value of SAF ........................................................................................... 39
5.6 Quantifying the Value Added with SAFs..................................................................................... 40
5.7 Summary of Fuel Molecules......................................................................................................... 40
6 R&D -- Cost Reduction............................................................................................................................. 41
6.1 Feedstock-Related Research......................................................................................................... 41
6.1.1 “Solve Another Problem” .................................................................................................. 41
6.1.2 Collected Carbon from Existing or Developing Processes................................................ 42
6.1.3 Waste Gases....................................................................................................................... 42
6.1.4 CO2 as a Carbon Source..................................................................................................... 42
6.2 Reducing Capital Cost.................................................................................................................. 44
6.2.1 Use Current and Distressed Infrastructure ......................................................................... 44
6.2.2 Petroleum Refinery Integration.......................................................................................... 45
6.2.3 Separations......................................................................................................................... 45
6.2.4 R&D Needs for Small-Scale Distributed Refineries.......................................................... 45
6.3 Rethinking Biorefineries............................................................................................................... 46
6.3.1 Sugars to Products, Lignin to Fuels ................................................................................... 46
6.3.2 Focus R&D on Conversion Platforms That Provide Product Flexibility ........................... 46
6.3.3 Feedstock Flexibility to Use Full Capacity........................................................................ 47
6.4 Sourcing Hydrogen....................................................................................................................... 48
6.5 Analysis of Cost Reduction .......................................................................................................... 48
6.6 Summary of Cost Reduction......................................................................................................... 49
7 Summary and Insights............................................................................................................................... 49
7.1 An R&D Strategy for SAF ........................................................................................................... 49
7.2 Insights on R&D........................................................................................................................... 50
7.2.1 Focus R&D on Low-Cost iso- and Cycloalkane Production ............................................. 50
7.2.2 Focus on Low-Cost Feedstocks ......................................................................................... 51
7.2.3 Focus R&D on Conversion Platforms that Provide Product Flexibility ............................ 51
7.2.4 Provide Replacement for Hydrogen Gas in Distributed Processing .................................. 51
7.2.5 Refine and Expand Analysis.............................................................................................. 51
7.2.6 Sequencing R&D to Achieve Impact in the Short, Medium, and Long Term ................... 52
7.3 Cooperative Opportunities for R&D ............................................................................................ 52
7.3.1 Collaboration Between the National Laboratories............................................................. 52
7.3.2 Intersection with FAA Center of Excellence and USDA................................................... 52
Sustainable Aviation Fuel: Review of Technical Pathways

7.3.3 Intersection with North American Partners........................................................................ 53
7.3.4 SAF Working Group.......................................................................................................... 53
References......................................................................................................................................................... 54
Appendix 1. Bioenergy Technologies Office Mission................................................................................... 58
Appendix 2. ASTM Fuel Approval Prescreening Tests ................................................................................ 59
Appendix 3. Workshop Learnings................................................................................................................... 60
A3.1 Macon Workshop ........................................................................................................................ 60
A3.2 Cleveland Workshop ................................................................................................................... 61
A3.2.1 Two Schools of Thought.......................................................................................................... 61
A3.2.2 High-Performance Fuel Options.............................................................................................. 61
A3.2.3 Engine and Combustor Options............................................................................................... 62
A3.2.4 Aircraft On-Board Considerations........................................................................................... 64
A3.2.5 High-Performance Fuel Development to Deployment............................................................. 65
A3.2.6 Key Takeaways........................................................................................................................ 66
A3.3 Richland Workshop..................................................................................................................... 66
A3.3.1 Synopsis of the Workshop Report............................................................................................ 67
A3.3.2 Key Takeaway Messages......................................................................................................... 67

Tags

Aviation Fuel/Sustainable Aviation Fuel (SAF) Jetfuel (Sustainable Aviation Fuel (SAF)) Department of Energy (DOE) soot particulates waste-to-fuel markets/sales market forces alkanes recycled plastics MSW (Municipal Solid Waste) aviation fuel (SAF) price ASTM GHG (Greenhouse Gas Emissions) heat of combustion jet A aviation fuel (SAF) benefits FOG (Fats/Oils/Grease) Feedstocks cover crops oil seed crops soil health manure sludge life cycle analysis (LCA) tax incentives Transportation Fuels Policy Renewable Diesel/Green Diesel/HVO/Paraffinic Diesel Investing drop-in biofuels/hydrocarbons ASTM standards ASTM D7566 (Standard Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons) aromatics Federal Aviation Administration (FAA) Engine/Fuel Co-optimization Sustainability

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