Sustainable Alternative Jet Fuels
This chapter looks at alternative jet fuels that have lower carbon emissions than conventional petroleum-based fuels over the entire life cycle of the fuels. It discusses the challenges associated with their development and commercialization and outlines key needs for achieving significant production and use of drop-in sustainable jet fuels produced from feedstocks other than petroleum (see Box 5.1). If such commercialization takes place, aviation has the opportunity to significantly lower the net carbon emissions from aviation, potentially in a more aggressive and timely fashion than can be reasonably achieved with improved operations, infrastructure, and aircraft. This reduction can also be achieved without impacting the time frame or suitability of other potential carbon-lowering approaches.
Much has been accomplished over the last decade to validate the qualification, production, and usage of lower net carbon fuels. Some versions of these fuels are on the cusp of commercialization. However, many research, development, demonstration, and deployment challenges remain in moving these fuels to significant production and mainstream usage. This chapter addresses those challenges and related research projects.
It is not feasible for the aviation industry to switch from conventional jet fuel to a different fuel type, nor are
there readily identifiable, feasible, lower-carbon alternative fuel types that could be introduced in a reasonable time frame. Many entities have validated the technical viability of producing synthetic jet fuel (or jet fuel blending components) from a wide range of hydrocarbon sources other than petroleum, using a broad range of biochemical and thermochemical conversion processes. Several approaches to producing synthetic drop-in jet fuels have demonstrated not only a lower life-cycle carbon footprint than conventional petroleum-based jet fuel, but also other elements of sustainability—for example, social, environmental, or economic. This report refers to such fuels as sustainable alternative jet fuels (SAJF, see Box 5.2).
A wide array of organizations has been working for the last decade to support the development of SAJF and to create a framework by which such fuels can enter the marketplace. The SAJF community in the United States now includes a broad coalition federal agencies, state and local constituents, operators of aircraft powered by gas turbines (commercial, military, business, and general aviation), engine and aircraft manufacturers, some members of the petroleum industry, academia, nongovernmental organizations, and various public–private partnership efforts.
Civil and military users of jet fuel have engaged in several technical and commercial demonstrations of the production and use of SAJF and continue to do so worldwide. Even so, bringing SAJF to market at competitive prices remains an elusive goal for many reasons related to technological maturity, feedstock production and distribution systems, production infrastructure, conflicting market signals, policy issues, and depressed oil prices.
In the absence of government policies that mandate or strongly incentivize the use of SAJF, research and development (R&D) efforts continue on ways to lower the capital and operating costs of SAJF production, both for conversion processes that have already been developed and for entirely new conversion processes under development. A few SAJF producers have found unique ways to approach initial commercialization, for instance by using very inexpensive feedstocks (e.g., municipal solid waste, forestry residues, and other industrial waste streams). Initial production contracts and offtake commitments are in place for some of these processes, albeit for very modest quantities of SAJF. A new industrial sector with requisite supply-chain resources is needed to bring significant quantities of SAJF to the marketplace. Large commercial entities (e.g., existing jet fuel producers) could undertake such industrial development, but at present there are no large commercial entities driving SAJF development.
Policy elements are sometimes used to address the challenges of introducing new technologies, especially for products that deliver societal value (e.g., aviation safety and environmental protection) but are sold at a higher price than competing products. Several government agencies in the United States and elsewhere have been aiding the development of this new industrial sector. Much has been accomplished, but much remains to be done.
This committee, mirroring similar evaluations from others affiliated with the above developments, has identified high-priority research projects that could help facilitate the accelerated introduction and broad commercialization of SAJF. These projects are focused on four areas:
- Modeling and analysis of SAJF development,
- Feedstock development, production, and logistics,
- Conversion processes, fuel production, and scale-up, and
- Fuel testing, qualification, and certification.
Evidence suggests that efforts are needed in all these areas to truly enable a vibrant SAJF industry that might deliver significant quantities of appropriately priced fuel for the aviation enterprise in a timely fashion. Further, the work being done individually by multiple U.S. government agencies and SAJF developers could be made more effective through greater collaboration and alignment of efforts, as well as through increased engagement on the part of several agencies that have not had significant engagement to date.
Aircraft engines are designed to burn only a narrow range of fuels, and using fuels with characteristics that fall outside this range will detract from safety, efficiency, and/or operability. Operators of aircraft powered by gas turbines will continue to demand the use of hydrocarbon jet fuel for the foreseeable future. While burning SAJF will produce nearly the same amount of CO2 per unit of fuel as conventional jet fuel, the use of SAJF reduces net life-cycle carbon emissions because SAJF enable reusing or recycling carbon that is already in the biosphere to create the fuel.
Potential Alternative Drop-In Jet Fuels
Jet fuel comprises a distribution of hydrocarbons with typically 7 to 18 carbon atoms per molecule. Jet fuel is referred to as a middle distillate, or kerosene-type, fuel. It is typically produced by the distillation of petroleum in a refinery, falling between the products gasoline, on the higher end of the volatility range, and diesel, on the lower end. Jet fuel is often characterized as a pure hydrocarbon with an aggregate composition of C12H23.1
There is broad consensus in the aviation industry—and in the committee—that drop-in jet fuels are far superior to other alternative fuels based on five considerations: certification; lack of technically feasible alternatives; infrastructure; the existing and pending fleet; and SAJF specifications and qualification practices.
Gas turbine engines are certified to meet stringent performance and operability criteria to ensure safety. Engine manufacturers define what fuel types satisfy these criteria using fuel specifications. For already-certified aircraft types, using a different fuel type would require recertification of the aircraft to demonstrate that performance, operability, and safety are not compromised by the new fuel. Recertification may require modifications to the aircraft or engine, which would likely be prohibitively expensive. In contrast, a drop-in fuel that meets appropriate fuel specifications obviates the need for recertification or a large investment in aircraft or engine modifications.
1 Jet fuel is a generic term that encompasses many specific variants, such as Jet A, Jet A-1, JP-5, and JP-8. In most cases, the other names imply specific variants of the fuel, as often detailed in the specifications themselves. Jet A is the most common form of jet fuel used by commercial aviation in the United States, while Jet A-1 predominates in the rest of the world.
Lack of Technically Feasible Alternatives
Jet fuel helps meet the need for safe, efficient, and economic high-speed travel because it has a balance of appropriate fuel properties, such as high energy per unit mass, high energy per unit volume, stability, nonvolatility, low freezing point, low vapor pressure, materials compatibility, and low toxicity. Since the dawn of aviation, aviation equipment manufacturers, in conjunction with research institutions, academia, and other technology developers, have evaluated options for future fuels, engines, and vehicle configurations in an effort to improve efficiency, productivity, and economic returns. Many alternatives have been considered—including nuclear power, hydrogen, and compressed or liquefied natural gas—but not one has proved feasible for commercial aviation. Ethanol and biodiesel blending components have dominated consideration as alternative fuels for ground vehicles, but these fuels are not suitable for aviation due to issues with safety, operability, and/or performance. As discussed in Chapter 4, neither fuel cells nor batteries will advance enough to power large commercial aircraft within the 30-year time frame addressed by this report. Liquefied natural gas and liquid hydrogen both have higher energy content per unit mass than conventional jet fuel, but they require two to four times as much volume to hold the same amount of energy as jet fuel. In addition, liquefied natural gas and liquid hydrogen both introduce unique aircraft integration and substantial new safety challenges. Aircraft designed to use such fuels would have significantly larger fuels tanks and engine fuel systems, resulting in higher drag, weight, and complexity; much shorter range; and/or reductions in other operational capabilities, such as speed, payload, or altitude capability. Also, the net reduction in carbon emissions arising from the adoption of hydrogen-fueled aircraft, for example, could be quite small unless the hydrogen is produced with electricity generated by renewable or low-carbon-emission technologies or if it is produced from hydrocarbons such as methane.
Given the global nature of aviation and the tremendous investment in and long life span of aircraft and aviation infrastructure, switching fuel types would require significant modifications to the air transportation system and supporting services, including aircraft, airports, airport fuel delivery systems, and national pipeline systems. All this would be in addition to creating a new industrial sector for the production of the new fuel. There would also be a lengthy transition period, during which both the old and new fuel systems would need to operate, resulting in greater system complexity, higher costs, and longer time to completion.
Existing and Pending Fleet
New aircraft typically have production runs that last for 10-15 years, and then they remain in service for perhaps 25-30 years. This means that even with the introduction of a new engine or aircraft type with a new fuel or power source 15-20 years from now (to allow time for technology maturation and product development), conventional jet fuel would remain the primary source of aviation fuel perhaps through 2050 or longer, until aircraft using the new fuel became dominant in the fleet.
SAJF Specifications and Qualification Practices
ASTM International is a not-for-profit organization that develops voluntary, consensus standards for industrial processes, materials, and products. Two ASTM documents are of particular relevance to SAJF:
- ASTM D7566. Standard Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons.
- ASTM D4054. Standard Practice for Qualification and Approval of New Aviation Turbine Fuels and Fuel Additives.
Not every synthetic fuel production process creates the full range of molecules that are present in conventional jet fuel and are required to meet jet fuel specifications. This is the case for the five synthetic fuel production
TABLE 5.1 Approved Alternative Fuel Production Pathways
|Name (from ASTM D7566 Annex)||Description||Qualification Date||Blend Limitation (%)|
|A1: FT-SPKa||Fischer-Tropsch conversion of syngas to synthetic paraffinic kerosene||September 2009||50|
|A2: HEFA-SPKb||Hydroprocessed esters and fatty acids (lipids from plant and animal sources) to synthetic paraffinic kerosene||July 2011||50|
|A3: HFS-SIPc||Hydroprocessed fermented sugars to synthesized isoparaffins||June 2014||10|
|A4: FT-SPK/Ad||Fischer-Tropsch conversion of syngas to synthetic paraffinic kerosene and aromatics||November 2015||50|
|A5: ATJ-SPKe||Thermochemical conversion of alcohols (isobutanol only initially) to paraffinic kerosene||April 2016||30|
a In this process, syngas (a mixture of carbon monoxide and hydrogen) is processed in a Fischer-Tropsch catalytic reactor to produce a mix of longer-chain paraffinic hydrocarbons which are subsequently converted into jet fuel with typical refinery finishing processes. Common methods of producing syngas include gasification of solid forms of hydrocarbons (e.g., biomass residues, municipal solid waste, coal, or combinations thereof) and the conversion of natural gas or biogas into syngas (e.g., via steam methane reforming). Gasification entails processing feedstock in a high-energy, reduced-oxygen environment such that the feedstock does not combust but is thermally deconstructed into its constituent elements (hydrogen, carbon monoxide, nitrogen, water, methane, hydrogen sulfide, carbon dioxide, and other compounds). The gasifier output must be cleaned of particulate matter, sulfur, and other impurities. Syngas is also produced as a byproduct of various industrial processes.
b Waste fats, oils, and greases or plant-derived oils can be cleaned and treated with hydrogen to produce jet fuel. Some sources of plant-derived oils, such as soybeans, are so expensive that they exacerbate the challenge of producing cost-competitive SAJF. Other options are potentially more competitive. Examples include waste fats, oils, and grease and nonfood crops, especially those grown on land that is not suitable for growing food crops, are potentially more competitive.
c Biomass feedstocks can be converted to sugars using a variety of pretreatment technologies. Microorganisms have been developed that will convert the sugars directly into an isoparaffin for blending with jet fuel.
d This process is similar to FT-SPK, but it includes the addition of production methods that also produce aromatic hydrocarbons.
e Alcohols can be converted to pure hydrocarbons in the jet fuel range through a process of dehydration, oligomerization, hydrogenation, and fractionation.
pathways that have been approved to date under ASTM D7566 (see Table 5.1). Accordingly, as indicated in the table, they must be blended with conventional jet fuel, up to maximum allowable blending levels, for the synthetic blend to be considered a drop-in alternative jet fuel.
Synthetic fuels produced from feedstocks other than petroleum do not necessarily guarantee sustainable, nor will they necessarily achieve the net carbon reduction required by policy measures targeting sustainability. For example, both of the Fischer-Tropsch pathways in Table 5.1 (FT-SPK and FT-SPK/A) use synthesis gas (syngas) which can be produced from various feedstocks including biomass, coal, natural gas, or waste gaseous streams from various industrial processes. To be considered sustainable, the input feedstocks for the syngas production would themselves need to be viewed as sustainable, and thus some sources of syngas (e.g., coal gasification with or without carbon capture and sequestration) could be precluded from use for the production of SAJF.
In the future some alternative fuels may qualify as drop-in fuels without blending, but that has not been the case to date.
SAJF State of Development
Although SAJF have been produced, the oil and transportation fuel industry is very competitive, increasingly so given low crude oil prices, making it very difficult for producers of SAJF to be economically competitive, especially given the capital costs of building large production facilities, the difficulty of establishing new supply chains, and the projected operating costs associated with proven feedstocks and conversion processes. In addition, the petroleum industry has been conservative in its engagement and support of alternative fuel development generally.
The U.S. aviation enterprise has demonstrated significant interest and engagement in the development, production, and use of SAJF over the past several decades. More than 20 airlines have flown more than 1,600 demonstration and proving flights using SAJF produced in limited production runs from pilot production facilities and facilities temporarily configured for SAJF production.2 The U.S. Navy and Air Force have been active in the testing of fuels in support of qualification activities, for both previous and pending qualification efforts.3 Even so, the Defense Logistics Agency has announced that it will purchase biofuel blends only if they are cost competitive with conventional fuels. Similarly, airlines have expressed interest in acquiring significant quantities of SAJF at petroleum parity pricing. Offers to purchase SAJF at higher prices will be evaluated subject to strategic interests of the airline. For example, the AltAir Biofuels facility in Paramount, California, is the first commercial production facility for SAJF (and for renewable hydrocarbon diesel, which is not a jet fuel).4 This facility, which was commissioned in late 2015, is now delivering SAJF to customers such as United Airlines and World Fuel Services, a jet fuel distributor.
The state of the art in sustainable fuels is advancing rapidly. In addition to the five qualified fuel production pathways listed in Table 5.1, three additional pathways could be approved before the end of 2017. Several additional pathways are also being developed by task forces within the ASTM community, while more than 10 additional pathways may be pursued based on comments by their technology developers.5,6,7,8 As each new pathway is approved, ASTM D7566 will be expanded to provide specifications that encompass all of the feedstocks and conversion processes approved for use in that pathway.
Several other producers, using a range of feedstocks and processes, are currently involved in the development of initial production facilities, including three companies with funding from the Defense Production Act: Fulcrum BioEnergy, Red Rock Biofuels, and Emerald Biofuels. These companies are targeting start of production in the 2017-2018 time frame, and two of them have agreements with major airlines to use the SAJF they produce. Altogether, these three facilities will likely produce no more than 50-100 million gallons of middle distillate (diesel and jet fuel blending components) per year, which would constitute perhaps 0.3 percent of the total U.S. demand for jet fuel. If U.S. commercial aviation consumes 20 billion gallons of jet fuel in 2020, 308 million gallons of conventional jet fuel would need to be replaced by SAJF with a 65 percent reduction in life-cycle carbon emissions to lower the total net carbon emissions of U.S. commercial aviation by 1 percent.
Life-Cycle Carbon Emissions
Any SAJF, by definition of it being a drop-in fuel, is expected to have an aggregate chemical composition that is essentially equivalent to petroleum-based jet fuel (i.e., C12H23). As such, the CO2 emissions from an engine burning SAJF will be practically equivalent to those from combustion of petroleum-based jet fuel.
Life-cycle analyses of alternative fuels determine the extent to which their production and use would reduce carbon emissions on a life-cycle basis compared to conventional jet fuel. Life-cycle analyses take into account all emissions associated with producing the final fuel from its initial form (e.g., an oil well, planting of oil seed crops, or conversion of municipal solid waste), as well as aircraft emissions. Biomass-derived alternative jet fuels have the potential to reduce life-cycle emissions compared to conventional jet fuel, since biomass-based hydrocarbons
2 IATA, “Alternative Fuels,” http://www.iata.org/whatwedo/environment/Pages/alternative-fuels.aspx, accessed May 14, 2016.
3 U.S. Government Accountability Office, 2015, Observations on DOD’s Investments in Alternative Fuels, GAO-15-674, Washington, D.C.
4 Because this facility is located in California, it benefits from the incentives provided by California’s low-carbon fuel standard.
5 Direct sugars to hydrocarbons. This pathway involves the direct catalytic conversion of sugars into hydrocarbons without the use of microorganisms.
6 Coprocessing of biocrudes at petroleum refineries. Biomass can be minimally treated to produce a biocrude that can be mixed with crude oil to form the input into an oil refinery. Depending on the quality of the biocrude it can also be inserted at the entry of the fluid catalytic cracker and/or the hydrotreater of a refinery. The refinery then produces the usual slate of gasoline, diesel, jet, and other products. The portion of biomass-based carbon molecules that constitute the jet fuel cut can be considered as an alternative fuel.
7 Renewable diesel blending with jet fuel.
8 The qualification of a production pathway in accordance with ASTM D7566 does not imply that commercialization will follow soon or at all. It took 4 years and 6 months from the qualification of HEFA-SPK to begin using this method to produce commercial volumes of fuel (at the AltAir refinery).
absorbed CO2 from the atmosphere when they grew and the CO2 emitted during fuel combustion is equal to that absorbed during its growth (see Figure 5.1). The uptake of CO2 by the biomass is assumed to be “credit” that offsets (at least in part) the combustion CO2 in the life-cycle analysis. This biomass credit is the primary difference between biomass and fossil fuels in terms of their carbon emissions. However, a biofuel does not necessarily have life-cycle emissions that are below a petroleum-based baseline, since there can be emissions associated with acquiring a feedstock, with fuel production, with feedstock and fuel transportation, as well as with land-use change attributable to the production of biomass-based feedstocks. Similar CO2 emissions are also associated with the production of fossil fuels.9
SAJF produced from nonpetroleum hydrocarbon sources (feedstocks) can significantly reduce life-cycle emissions compared to conventional petroleum-derived jet fuel. Argonne National Laboratory has conducted life-cycle analysis of bio-based aviation fuel pathways and compared them with petroleum-based jet fuels (see Figure 5.2). The first column shows that for an alternative fuel that uses coal rather than biomass as the dominant raw material, CO2 emissions are 71 percent higher than with conventional jet fuel. For SAJF (that is, for alternative fuels derived entirely from biomass), depending upon the feedstock and conversion process, reductions in CO2 emissions relative to conventional jet fuel range from 41 to 89 percent. On a sector-wide basis, total reductions in life-cycle emissions will depend on rates of production and utilization, which are functions of the fuel’s commercial viability.
9 A. Elgowainy, J. Han, H. Cai, M. Wang, G.S. Forman, and V.B. DiVita, 2014, Energy efficiency and greenhouse gas emissions intensity of petroleum products at U.S. refineries, Environmental Science and Technology 48:7612-7624.
The commercialization of SAJF offers other potential societal benefits by expanding domestic energy sourcing; reducing greenhouse gases and other emissions that impact air quality; promoting economic development; promoting social welfare; and delivering other environmental services to the biosphere (e.g., improving water quality, reducing nutrient leaching, reducing erosion, restoring degraded soils, enhancing biodiversity, and assisting with reductions in pest and weed treatment for other crops). Many of these benefits arise from new agricultural opportunities in areas not amenable to the production of food crops. Given those potentials, SAJF development efforts are being supported by federal, state, and local government agencies that recognize the potential benefits:
- Environmental benefits—Lowering emissions around airports. SAJF blending components typically contain less sulfur than conventional jet fuel. As a result, their use will likely reduce emissions of oxides of sulfur (SOx), and because SOx is a precursor for secondary particulate matter, such emissions will also be reduced. SAJF blending components typically contain lower levels of aromatics (specifically, polycyclic aromatics), which improves combustion characteristics. Owing to this and other factors, SAJF tests have shown general reductions in aerosol emissions, particles, and black carbon.10
- Societal benefits—Jobs and rural development. Several examples of SAJF-focused feedstock development at various locations around the world are demonstrating the potential for growing feedstocks in ways that do not compete with food production, thereby providing societal benefits without unintended consequences such as food shortages. Examples include the use of family farming of a new type of tobacco in the South
10 Virent, Inc. “Virent Bio-Jet Provides more than 50% Reduction in Particulate Matter Emissions,” last update January 6, 2016, http://www.virent.com/news/virent-bio-jet-provides-more-than-50-reduction-in-particulate-matter-emissions.
African Solaris project,11 halophyte12 usage in saline environments in the Middle East and Mexico,13 and blighted citrus grove replacement in Florida.14
- Noncommercial aviation. SAJF developed for commercial aviation can also be used as a jet fuel for military, business, and general aviation. In fact, the Department of Defense is also supporting SAJF development, and the success of those efforts would also be broadly applicable.
The International Civil Aviation Organization has tasked its Committee on Aviation Environmental Protection to look at the feasibility of SAJF contributing significantly to the goals of capping net carbon emissions from 2020 onward and achieving a 50 percent reduction in net carbon emissions by 2050 from 2005 levels. In addition, the International Air Transport Association has examined issues related to SAJF and actions that national governments could take to address these issues.15
The majority of SAJF production could be distributed, with facilities geographically dispersed and located synergistically with feedstock supplies to keep costs and emissions to a minimum. Although the majority of efforts to date have been focused in the United States and Europe, there exist expectations that this production can proliferate around the world, with local governments attempting to capture some of the indirect benefits of such fuel production, as outlined previously. Recent announcements from Indonesia, Japan, China, and other countries provide support for these views.16,17,18
SAJF has the potential to provide commercial aviation with a low-carbon fuel with almost universal application. However, there are many economic, technical, and policy challenges that need to be overcome to achieve this vision. The economic challenges are taken up first because they constitute the largest barrier to the development and commercialization of SAJF.
The creation of a large-scale SAJF industrial sector will be difficult, especially given (1) the need to compete with producers of conventional jet fuel, (2) the barriers to entry, particularly for the production of a commodity product, and (3) the inability to capture sufficient value from the primary attribute of the new product, which is the inherent reduction in net carbon emissions resulting from the use of SAJF. The challenges associated with cost-competitiveness are illustrated in Figure 5.3, which shows that even with optimistic estimates of capital and operating expenses, SAJF costs more than conventional jet fuel, especially in the face of low crude oil prices. There are several SAJF technologies that can produce fuel for less than the price of conventional jet if the cost of crude oil is at least $120 per barrel. As of April 2016, however, the cost of crude oil was $36 per barrel and the cost of jet fuel was about $1 per gallon.19 As discussed in Chapter 2, predictions of future costs of crude oil are
11 Project Solaris website, http://www.projectsolaris.co.za/, accessed May 10, 2016.
12 Halophytes are plants that can grow in a salty environment such as areas exposed to salt spray, salt marches and mud flats, and other soils with high salt content.
13 Masdar Institute, “Abu Dhabi’s Innovative Bioenergy Project Highlighted at Leading Bioenergy Conference,” last update October 31, 2015, http://www.masdar.ac.ae/component/k2/item/6594-abu-dhabi-s-innovative-bioenergy-project-highlighted-at-leading-bioenergy-conference.
14 Treasure Coast Research Park, “Biofuel Feedstocks Research Takes Off in Fort Pierce,” last update 2013, http://www.treasurecoastresearchpark.com/biofuel-research-takes-off-in-ft-pierce.
15 International Air Transport Association (IATA), 2015, Report on Alternative Fuels, 10th Edition, Montreal, Canada, http://www.iata.org/publications/Documents/2015-report-alternative-fuels.pdf.
16 Federal Aviation Administration, “U.S./Indonesia Agreement on Sustainable Air Transportation and Aviation Alternative Fuels,” last update October 23, 2015, http://www.faa.gov/news/updates/?newsId=84086.
17 Initiatives for Next-Generation Aviation Fuels (INAF), 2015, Roadmap for Establishing Supply Chain for Next-Generation Aviation Fuels, Japan, http://aviation.u-tokyo.ac.jp/inaf/roadmap_en.pdf.
18 Xinhua News Agency/China Finance Corporation (CFC), “China Grants 1st Bio Jet Fuel Airworthiness Certificate to Sinopec,” last update February 13, 2014, http://en.xinhua08.com/a/20140213/1299111.shtml.
19 Energy Information Agency, 2016, “Petroleum and Other Liquids: Spot Prices,” Washington, D.C. https://www.eia.gov/dnav/pet/xls/PET_PRI_SPT_S1_D.xls.
highly uncertain: the U.S. Energy Information Administration projects that the spot price of crude oil in 2040 will be 2 to 7 times as much as current prices.20
The economic challenges to widespread use of SAJF are spread across the business model: high capital expense, high operating expense (including feedstock cost), and the relative immaturity of the systems, machinery, and processes required to enable robust supply chains for these processes. Research could address cost reductions for many of these elements, but demonstration and deployment efforts will also be needed to address fully all of the economic challenges.
Feedstock Price and Availability
Currently achievable refinery-gate feedstock prices are expensive relative to the final product, which is driven in part by immature or nonexistent feedstock supply chains.
Well-defined, well-established supply chains are needed for large-scale, dedicated production of SAJF feedstocks, particularly agricultural and wood products. Economies of scale are not yet achievable.
It remains questionable whether all feedstocks of interest (initial and envisioned) will be able to deliver enough energy per unit cost to the various conversion processes, especially for “first-unit” production, because much of the demonstration work completed to date for any specific feedstock has been done on a limited basis.
20 Energy Information Agency, 2015, Annual Energy Outlook 2015 with Projections to 2040, DOE/EIA-0383(2015), Washington, D.C., http://www.eia.gov/forecasts/aeo/pdf/0383(2015).pdf, Figure 3.
Developing an SAJF enterprise that can provide fuel globally, throughout the year, will be extremely complex. Sustainable feedstocks are typically only applicable on a regional basis, so different types of feedstocks and conversion processes will be needed. Also, within an agricultural feedstock family, individual feedstocks are typically only available during certain times of the year. Thus, for any particular SAJF production facility to maintain operations throughout the year, either it will probably need to store large quantities of feedstock to sustain itself throughout the year, or it will need to access multiple feedstocks and/or import feedstocks from other regions with different growing seasons, using multiple supply chain concepts. This same issue applies to many nonagricultural feedstocks, too, where intermittency issues may be driven by factors other than harvest availability.
Many feedstocks are diverse and unique; harvest, handling, storage, and processing technologies are needed for multiple feedstock types, as well as for the manufacture of such equipment. Important advances are being made, for example, with the harvest, storage, and transport of cellulosic plants in support of pilot plants. Nonetheless, appropriately affordable, robust, and producible conversion equipment, and the facilities and systems to enable production of such equipment at sufficient scale, are not available, and future availability is uncertain at best.
There are varying models for the envisioned development of full-scale SAJF production capabilities, but because key technologies related to fuel conversion and associated infrastructure have not yet been optimized, models cannot be validated, and as a result research may not be targeting the best solutions.
With no large vertical integrator driving the overall development of the entire supply chain, it is proving tremendously difficult to manage the simultaneous and independent growth of the feedstock supply chains and conversion facilities at appropriate scales. This may prove particularly challenging for feedstock systems that take several years to achieve scale or maturity and have no other viable customers. If the feedstock is available prior to being needed in the conversion facility, who will buy it, and at what price? Can it be stored without degradation? Who will pay for the storage? And so on. Conversely, who will capitalize and build a production facility without the assurance that feedstocks will be available when needed? Some feedstocks (e.g., crop residues or municipal waste, which are a byproduct of other activity) may prove significantly easier to address than others (e.g., crops, such as oilseeds, that would be grown specifically as a feedstock).
Industrial Sector Collaboration
This nascent industry lacks the elements of collaboration that are inherent in a fully defined industrial sector which enable system optimization, or even the initial matching of supply and demand signals.
The establishment of a new industrial sector, with its requisite resources (e.g., supply chain, equipment, facilities, personnel, equity, etc.) entails the fostering and bringing together of organizations who have not worked with one another previously. Large producers of conventional jet fuel, who are perhaps in the best position to address this challenge, currently seem to have little motivation to do so, given that SAJF by design is interchangeable with their current products, but its production comes with uncertain margins, higher investment, and higher risk.
Lack of technoeconomic assessments and comparative understanding of various approaches impedes the ability of industry and the researchers and agencies that support SAJF R&D to make practical decisions about the prioritization of R&D and demonstration and deployment efforts.
A comprehensive set of common-baseline, comparative technoeconomic assessments of current and projected pathways and feedstocks is needed to provide insights into the technical and economic feasibility of proposed SAJF production pathways. These assessments are not necessarily associated with “picking winner and losers” (an issue of some sensitivity among government agencies and policymakers). For a given pathway and feedstock, technoeconomic assessments of discrete technology elements can ascertain where the most gain might be achieved for a given level of research effort.
Hydrogen Price and Availability
Hydrogen is needed for almost all SAJF production, and in several conversion processes (those with potentially the lowest feedstock costs) it represents a significant portion of operating cost.
Hydrogen is needed for SAJF production because the ratio of hydrogen atoms to carbon atoms in jet fuel molecules is typically higher than the hydrogen-to-carbon ratio in feedstocks. Thus, in almost all cases, hydrogen is a key input to the feedstock conversion process. In many regions associated with abundant supplies of feedstock, hydrogen is not readily accessible, particularly at reasonable cost. In many cases, hydrogen can be supplied from the conversion of natural gas, but natural gas infrastructure is also limited. Biogas (e.g., from manure digesters, waste-water treatment plants, landfills, or other biomass conversion techniques) could facilitate production of the large amounts of hydrogen typically needed for SAJF production, and it could do so with minimal increase in life-cycle carbon emissions. Even in that case, however, infrastructure could still be an issue, for example, to transfer locally produced biogas from a very large number of broadly distributed sources into distribution pipelines.
SAJF Development and Demonstration Projects
Additional, affordable SAJF demonstration and deployment efforts are needed to adequately address economic and technical risks.
After several decades of on-again, off-again development of SAJF, coupled with some well-publicized commercialization failures, major SAJF economic and technical challenges persist. As a result, members of the investment and finance community are generally uncomfortable with the risk associated with development of commercial facilities. The engagement of large, well-respected commercial engineering and construction companies who could provide turnkey project development and performance guarantees would help to alleviate such concerns, but unresolved risks have likewise dissuaded these companies from taking on such a role, implying that demonstration and deployment efforts executed to date have not been successful enough to move to the next step.
Funding for SAJF Capital Investments
Uncertainty about economic viability of SAJF production has impeded engagement from the petroleum industry or other large industrial entities that could bring appropriate resources to bear on addressing economic challenges.
Some incremental capital costs are driven by perceptions of unabated high risk resulting from uncertainties about the economic viability of SAJF.
Challenges for Small SAJF Start-Ups
Start-ups are unable to explore and leverage the full range of technical and economic opportunities that might provide sufficient economic benefit to facilitate commercialization.
The likelihood that small, underresourced entrepreneurs will be able to successfully commercialize new SAJF technology would be greatly enhanced if R&D organizations had more insight into opportunities to minimize the risks and maximize the economic returns of a new SAJF endeavor. Mechanisms that could provide that insight (e.g., national databases of opportunities, foundational analytical work, and feasibility studies) are lacking. Areas of potential interest include the following:
- Use of idled brownfield or other distressed properties to lower capital requirements, receive favorable tax treatment, and/or reduce operating expense (e.g., through the use of excess hydrogen capacity from an adjacent industrial process).
- The pursuit of technology refinements and/or scale that would reduce capital and operating expenses (e.g., through less expensive catalysts, more efficient processes, or a reduced need for consumables such as water, chemical reagents, and catalysts).
- Use of lower cost feedstocks (e.g., municipal solid wastes, steel mill offgases, and other waste streams).
- Reducing the cost of more traditional feedstocks, either through commercial mechanisms (e.g., long-term contracting, vertical integration, and use of aggregators) or actual reduction in costs (e.g., improvements in agronomy).
- Development of new feedstocks that can be delivered to the refinery gate with more accessible energy content per unit cost by, for example, fostering the breeding or development of new species of biomass with more useful energy content per unit volume or mass.
- Development of high-value products that can be coproduced with SAJF.
Several SAJF production pathways have been demonstrated, and others are in varying stages of development. Even so, several remaining technical challenges need to be overcome to enable economically competitive large-scale production of SAJF using a wide range of promising feedstocks.
Despite progress to date in developing feedstocks, in many cases, SAJF feedstocks are widely dispersed, they are unwieldy (e.g., they may have low bulk density, small seed size, and/or high moisture content), and/or they are not easily collected, transported, stored, or pre-processed with existing equipment.
Feedstock Conversion Technologies
Cost-effective conversion technologies are not available for some promising feedstocks.
SAJF Fuel Testing, Qualification, and Certification Processes
It takes longer than it should to commercialize new SAJF production methods, in part because of the cost and time required to complete current fuel qualification and certification processes. Improvements to the qualification process are also needed to enable compositionally based evaluation of additional SAJF production pathways.
Fuel qualification and certification processes are costly, fuels required for testing are difficult to produce in sufficient quantities in reasonable amounts of time, and the entities pursuing qualification are typically small, underfunded start-up organizations that will also need to deal with the many other technical and economic challenges that a start-up company usually encounters.
An industry process has been established through the use of standard ASTM practices and specifications, and it is being used to qualify production pathways for alternative jet fuels. The ASTM testing and qualification process, however, has limited throughput, it is highly dependent on physical testing for validation, and it is insufficiently based on science (chemistry and combustion sciences). Progress is being made, but key shortfalls exist in several areas: (1) lack of testing facilities, (2) lack of fundamental understanding of the impact of chemical composition on physical properties, (3) uncertainties about the compatibility of various fuel molecules and combinations of molecules with materials generally used in aircraft fuel systems, gas turbines, and existing fuel supply and storage infrastructure, and (4) lack of pilot scale research and process demonstration facilities. These shortfalls are impeding the broad commercialization of such fuels. For example, equipment and infrastructure owners are uncertain about the direct impact of various SAJF compositions, so they typically request a full set of materials compatibility testing for each proposed fuel conversion process. Further, the industry would benefit from a more
compositionally-based specification to allow for expedited consideration of fully synthetic fuels and to allow the blending of various synthetic blending components.
Policy elements (and subsequent rule making) can clearly impact the potential for SAJF development and commercialization, particularly if they are able to assist in closing any portion of an existing price gap between the price of petroleum-based jet fuel and SAJF. It is beyond the scope of this study to assess or recommend new policies that would incentivize the production of SAJF; however, the committee has identified two policy challenges to implementing SAJF technologies.
Renewable Fuel Standard
Uncertainties about the long-term impact of the U.S. Renewable Fuel Standard, which provides indirect incentives for the production of SAJF, limit its effectiveness in fostering the development of an SAJF industry.
As in any industry, investment and engagement are enhanced by long-term, well-defined policies that provide stability. Stability lowers risk, and gives investors, developers, and financiers the certainty that their business models are sound for the life of the project. This has proven to be problematic with the current U.S. Renewable Fuel Standard, which sets annual minimum requirements for the distribution of biofuels as a ground transportation fuel. (In 2022, the requirement amounts to about 7 percent the expected U.S. demand for gasoline and diesel fuel.21) Uncertainty has arisen because of delays to the implementation of the biofuel mandate, because of congressional debate about its value, and because of uncertainties about fuel standards for 2023 and beyond, which have yet to be defined.
Sustainability Assessment Models and Requirements
There is no well-defined, internationally adopted framework for sustainability analysis of alternative jet fuels.
The variability in the many different sustainability frameworks complicates the process of developing SAJF that can be widely marketed as meeting “sustainability needs,” and it increases uncertainty about the economic feasibility of SAJF. The variability and uncertainty might also influence policy or decisions that have established relatively high hurdles for various metrics. For example, both the U.S. Renewable Fuel Standard and the independent Roundtable on Sustainable Biomaterials have established the need for advanced fuels to achieve at least a 50 percent reduction in life-cycle CO2 emissions.22 This disincentivizes the potential of some synthetic fuel production pathways that could produce lesser but still substantial reductions in life-cycle carbon emissions.
ONGOING EFFORTS TO DEFINE A FEDERAL ALTERNATIVE JET FUEL R&D STRATEGY
In 2013 several government agencies and their public–private partnerships involved in the development and commercialization of SAJF recognized the need to further coordinate the broad range of activities occurring in the public and private sectors to improve the focus, effectiveness, and timeliness of such efforts. Discussions among involved federal agencies23 led to an agreement to develop and initiate a Federal Alternative Jet Fuel R&D Strategy
21 In the United States, there is no mandate for the production of SAJF. The Renewable Fuel Standard provides a mechanism that allows the production of SAJF to indirectly contribute to a fuel producer’s obligations under the Standard to produce biofuel for ground transportation.
22 For cellulosic biofuel pathways, the minimum acceptable reduction is 60 percent.
23 Department of Commerce, Department of Defense, Department of Energy, Department of Transportation, Environmental Protection Agency, NASA, National Science Foundation, and the Department of Agriculture.
under the leadership of the White House Office of Science and Technology Policy (OSTP).24 This new strategy will target the following objectives:
- Identify key scientific and technical barriers to development of SAJF.
- Provide federal agencies with detailed national goals and objectives to inform their R&D program decisions, including budgeting and prioritization.
- Promote crosscutting and collaborative R&D activities by both federal and nonfederal stakeholders.
The process of developing the strategy has included workshops, meetings, and other interactions with stakeholders from industry, nongovernmental organizations, academia, state and local governments, and potential producers of SAJF. The strategy is intended to be a comprehensive document that provides a shared and actionable SAJF R&D plan that mobilizes public and private stakeholders to address key scientific and technical challenges over the near-, mid-, and far-terms.
RATIONALE FOR SUSTAINABLE ALTERNATIVE JET FUELS
Finding. Rationale for Sustainable Alternative Jet Fuels. Sustainable alternative jet fuels (SAJF) will be able to reduce life-cycle CO2, emissions, and in some cases the reductions may be substantial. SAJF have the potential to immediately lower net global CO2 emissions from commercial aviation because, as drop-in fuels, they are compatible with existing aircraft and infrastructure. Thus, their widespread use will not be limited by the rate at which new aircraft replace existing aircraft. The combustion of SAJF will likely also produce lesser amounts of other harmful emissions, such as oxides of sulfur and particulate matter, than the combustion of equivalent amounts of conventional jet fuel. SAJF are also compatible with and complementary to the three other high-priority approaches recommended in this report for reducing carbon emissions.
RECOMMENDED HIGH-PRIORITY RESEARCH PROJECTS
The high-priority research projects described below are necessary but not sufficient to enable broad development, commercialization, and use of SAJF; sustained progress is required over a wide range of interrelated efforts. Furthermore, the recommended research projects will not address all of the economic and policy challenges discussed above, because not all of them can be overcome solely through typical R&D.
SAJF Industry Modeling and Analysis
This project would undertake research to enable detailed and comprehensive modeling and analysis of SAJF development efforts and impacts at microscale (individual projects) and macroscale (nationwide or worldwide) levels to support the needs of policymakers and industry practitioners.
Key tasks to execute this research project are listed below. Relevant federal agencies include the U.S. Department of Energy (DOE), Department of Transportation (DOT), Federal Aviation Administration (FAA), and U.S. Department of Agriculture (USDA).
- Conduct comprehensive comparative technoeconomic assessments of potential SAJF feedstocks and conversion processes.
—Develop models for, and conduct comparative technoeconomic assessments of, SAJF feedstocks and conversion processes.
—Use these models, along with existing frameworks and databases, to create a comprehensive database
24 Committee on Technology, National Science and Technology Council, OSTP.
of relevant SAJF feedstocks and conversion processes. Use the results of technoeconomic assessments to inform R&D prioritization to improve the effectiveness of integrated R&D efforts.
—Institute a process to periodically refresh technoeconomic assessments and to evaluate new SAJF production pathways of interest as they are identified, for example, through interactions with organizations such as the ASTM International Committee on Petroleum Products, Liquid Fuels, and Lubricants, the Coordinating Research Council, the Commercial Aviation Alternative Fuels Initiative, and the Federal Aviation Administration’s Center of Excellence for Alternative Jet Fuels and Environment.
- Enhance system modeling and analysis capabilities for microscale (individual projects) and macroscale (nationwide or worldwide) evaluations of potential impacts and benefits of SAJF development and commercialization to support for policy and business decision making.
- Advance the science, application, and harmonization of sustainability analysis, particularly with regard to life-cycle CO2 modeling.
Support continued development of sustainable, low-cost feedstocks and associated systems that have the potential to enable the large-scale production of economically viable SAJF.
Key tasks to execute this research project are listed below. Relevant federal agencies include DOE, DOT, the Environmental Protection Agency (EPA), and USDA.
- Identify and develop feedstocks that could enable economically viable and sustainable production of SAJF. For example, efforts to develop feedstocks from agricultural and wood products could target reductions in input requirements, enhancements in recoverable energy content, or those with attributes that enable lower cost processing.25
- Develop strategic approaches to more fully explore viable usage of waste streams that are large in volume, relatively constant in supply, ubiquitous in availability, low in cost, and have established production and/ or collection systems in place. Waste streams of potential interest include:
—Municipal solid waste, including a comprehensive approach to utilization of nonrecyclables (organics, plastics, tires, etc.).
- Human waste and sanitary waste treatment (e.g., gasification or other conversion of sludge, and use of biogas from digesters).
—Animal waste, especially since waste disposal, groundwater contamination, and nutrient leaching are becoming significant issues that could negatively impact the availability of low-cost food production.
—Food processing waste.
—Gaseous waste such as carbon monoxide, hydrogen, CO2, and methane, which in some cases arise from the above sources.
- Use the results of feedstock evaluations performed under the SAJF Industry Modeling research project, above, to inform and prioritize feedstock development activities, within existing programs.
Conversion Processes, Fuel Production, and Scale-Up
Develop technologies and processes for cost-effective feedstock conversion, fuel production, and scale-up from pilot and demonstration facilities to enable full-scale production of SAJF.
Key tasks to execute this research project are listed below. Relevant federal agencies include the Department of Defense (DOD) and DOE.
25 U.S. Department of Energy, 2015, Advanced Feedstock Supply System Validation Workshop Summary Report: Mobilizing the Billion Tons, INL/EXT-10-18930, Washington, D.C., https://www.bioenergykdf.net/system/files/1/15-50315-R3_Summary_Report_Only_ONLINE.PDF.
- Create additional process development facilities26 to enhance the ability of SAJF conversion technology developers to move expeditiously from bench-top to pilot scale with minimal capital and operating expenses.
—Design facilities to be of sufficient flexibility and complexity to enable R&D (fundamental and applied) on an extremely broad range of thermochemical and biochemical conversion, and fuel finishing processes.
—Design facilities of sufficient scale to allow for production of sufficient quantities of SAJF to complete qualification processes in accordance with relevant ASTM standards (i.e., ASTM D4054 and D7566).
—Enhance the ability of facilities to access applicable human and technical resources from the National Labs, from a broad range of disciplines.
- Pursue development of fuel conversion and finishing processes and equipment, focusing first on processes common to multiple conversion processes.
- Foster the development of lower-cost hydrogen production to provide the hydrogen that is needed for almost all SAJF production.
SAJF Fuel Testing, Qualification, and Certification
Improve fuel testing, qualification, and certification processes to lower testing costs, increase throughput, and enhance understanding of fuel properties.
Key tasks to execute this research project are listed below. Relevant federal agencies include the Department of Commerce, DOD, DOE, DOT, NASA, the National Science Foundation.
- Eliminate or reduce time-consuming and costly physical testing by developing a low-cost, high throughput approach to meeting ASTM specifications and qualifications standards relevant to SAJF (i.e., ASTM D4054 and D7566). This will likely require determining which molecular components in the family of molecules in SAJF are causes for concern with respect to material compatibility.
- Bolster current efforts, such as those by the FAA Aviation Sustainability Center’s National Jet Fuels Combustion Program, to develop a research program to improve the ability to characterize combustion attributes of properties of various SAJF constituents using analysis and simpler testing. Similar work could focus on qualification and quantification of environmental effects (nearer term) and turbomachinery health and performance benefits (longer term) of potential SAJF pathways. This would likely enable the SAJF community to move away from a reliance of rote physical testing, which is costly and timely, to more of an analytical approach, and better optimize the type of engine, auxiliary power unit, and/or rig testing that is needed to resolve any outstanding issues. This would also support the development of a more-compositionally based specification, and facilitate the development of concepts for 100 percent drop-in fuels from single SAJF sources, as well as blends from multiple SAJF sources.
- Assess the environmental effects (nearer term) and turbomachinery performance benefits (longer term) of potential SAJF pathways.
- Develop a database, made broadly available to the members of the SAJF community, of fuel feedstocks, processes, fuel properties, and combustion emission characteristics to facilitate utilization of alternative jet fuels.
26 This is envisioned as enabling similar success to what has been previously demonstrated (e.g., what the Assured Aerospace Fuels Research Facility at Wright Patterson Air Force Base has done for HEFA-SPK development, and what the Alternative Fuels User Facility and Thermochemical Pilot and Users Facility at the Department of Energy’s National Renewable Energy Laboratory and the Advanced Biofuels Process Demonstration Unit at Lawrence Berkeley National Lab have done for biologic conversion development.