Aviation biofuel

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Refueling an A320 with biofuel

An aviation biofuel or bio-jet-fuel[1] or bio-aviation fuel (BAF)[2] or sustainable aviation fuel (SAF) is a biofuel used to power aircraft. The International Air Transport Association (IATA) considers it to be one of the key elements to reduce the carbon footprint within the environmental impact of aviation.[3] Aviation biofuel could help decarbonize medium- and long-haul air travel generating most emissions, and could extend the life of older aircraft types by lowering their carbon footprint.

Biofuels are biomass-derived fuels, from plants or waste; depending on which type of biomass is used, they could lower CO₂ emissions by 20–98% compared to conventional jet fuel.[4] The first test flight using blended biofuel was in 2008, and in 2011 blended fuels with 50% biofuels were allowed in commercial flights. In 2019, the IATA was aiming for a 2% penetration by 2025.

Aviation biofuel can be produced from plant sources like Jatropha, algae, tallows, waste oils, palm oil, Babassu and Camelina (bio-SPK); from solid biomass using pyrolysis processed with a Fischer–Tropsch process (FT-SPK); with an alcohol-to-jet (ATJ) process from waste fermentation; or from synthetic biology through a solar reactor. Small piston engines can be modified to burn ethanol.

Sustainable biofuels do not compete with food crops, prime agricultural land, natural forest or fresh water. Sustainable aviation fuel are certified as being sustainable by a third-party organisation.

Environmental impact[edit]

Plants absorb carbon dioxide as they grow, meaning plant-based biofuels emit only the same amount of greenhouse gases as previously absorbed. Biofuel production, processing and transport however emit greenhouse gases, reducing the emissions savings.[2] Biofuels with most emission savings are those derived from photosynthetic algae (98% savings, technology not yet mature) and from non-food crops and forest residues (91-95% savings).[2]

Jatropha oil, a non-food oil used as a biofuel should lower CO₂ emissions by 50–80% compared to Jet-A1.[5] Jatropha, used for biodiesel, can thrive on marginal land where most cultures would produce low crop yields.[6][7] A life cycle assessment by the Yale School of Forestry on jatropha, one source of potential biofuels, estimated that using it could reduce greenhouse gas emissions by up to 85% if former agro-pastoral land is used, or increase emissions by up to 60% if natural woodland is converted to use.[8]

Palm oil cultivation is constrained by scarce land resources and its expansion to forestland cause deforestation and biodiversity loss, and direct and indirect emissions due to land-use change.[2] Neste's renewable products includes a refining residue of food-grade palm oil, and the oily waste skimmed from the palm oil mill’s wastewater.[9] Neste’s sustainable aviation fuel is used by Lufthansa.[10]

NASA has determined that 50% aviation biofuel mixture can cut particulate emissions caused by air traffic by 50–70%.[11] Biofuels do not contain sulfur compounds and thus do not emit sulfur dioxide.

Timeline[edit]

The first flight using blended biofuel took place in 2008.[12] Virgin Atlantic flew the first flight by a commercial airline to be powered partly by biofuel, while commercial biofuel flights were likely to use feedstocks such as algae.[13] By then, airlines representing more than 15% of the industry formed the Sustainable Aviation Fuel Users Group, with support from NGOs such as Natural Resources Defense Council and The Roundtable For Sustainable Biofuels. They pledged to develop sustainable biofuels for aviation.[14] That year, Boeing was co-chair of the Algal Biomass Organization, joined by air carriers and biofuel technology developer UOP LLC (Honeywell).[15]

In 2009, the IATA committed to achieve carbon-neutral growth by 2020, and to halve carbon emissions by 2050.[16]

In 2010, Boeing targeted of 1% of global aviation fuels by 2015.[17]

US Marine Corps AV-8B Harrier II test flight using a 50–50 biofuel blend in 2011

By June 2011, the revised Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons (ASTM D7566) allowed commercial airlines to blend up to 50% biofuels with conventional jet fuel.[18] The safety and performance of jet fuel used in passenger flights is certified by ASTM International.[19] Biofuels were approved for commercial use after a multi-year technical review from aircraft makers, engine manufacturers and oil companies.[20] Since then, some airlines have experimented with using biofuels on commercial flights.[21]

In December 2011, the FAA awarded US$7.7 million to eight companies to develop drop-in sustainable fuels, especially from alcohols, sugars, biomass, and organic matter such as pyrolysis oils, within its CAAFI and CLEEN programs.[22]

From 2014, Solena planned to turn annually 500,000 tonnes of waste from the City of London that would normally go to landfill into biofuel to be used in the British Airways fleet.[23]

By 2015, cultivation of fatty acid methyl esters and alkenones from the algae, Isochrysis, was under research as a possible jet biofuel feedstock.[24]

By 2016, Thomas Brueck of Munich TU was forecasting that algaculture could provide 3-5% of jetfuel needs by 2050.[25]

In Fall 2016, to achieve its emissions reductions goals, the ICAO planned multiple measures including the development and deployment of sustainable aviation fuels.[26]

Dozens of companies received hundreds of millions in venture capital from 2005 to 2012 to extract fuel oil from algae, some promising competitively priced fuel by 2012 and a production of 1 billion US gal (3.8 million m3) by 2012-2014.[27] By 2017, nor were achieved and most companies had disappeared or changed their business plans to focus on cosmetics supplements, nutraceuticals, pet food additives, animal feed, pigments and speciality oils.[27]

In 2019, the International Air Transport Association (IATA) supports the adoption of Sustainable Aviation fuel, aiming in 2019 for a 2% penetration by 2025: 7 million m3 (1.8 billion US gal).[28] By then, more than 150,000 flights have used biofuels and five airports have regular biofuel distribution: Bergen, Brisbane, Los Angeles, Oslo and Stockholm, with others offering occasional supply.[12]

In 2019, United Airlines purchased up to 10 million US gallons (38,000 m3) of SAF from World Energy over two years.[29]

That year, Virgin Australia had fueled more than 700 flights and flown more than one million kilometers, domestic and international, using Gevo's alcohol-to-jet fuel.[30] Gevo is committed to going after the entire gallon of sustainable aviation fuel, potentially leading to a negative carbon footprint. Virgin Atlantic was working to regularly use fuel derived from the waste gases of steel mills, with LanzaTech.[31] British Airways wanted to convert household waste into jet fuel with Velocys.[31] United Airlines committed to 900 million US gal (3,400,000 m3) of sustainable aviation fuel for 10 years from Fulcrum BioEnergy (to be compared to its 4.1 billion US gal (16,000,000 m3) fuel consumption in 2018), after its $30 million investment in 2015, and will develop up to five biofuel factories near its hubs.[31]

From 2020, Qantas will start using a 50/50 blend of SG Preston’s biofuel on its Los Angeles-Australia flights, also providing fuel derived from non-food plant oils to JetBlue Airways during 10 years.[31] At its sites in Singapore, Rotterdam and Porvoo, Finland's Neste is expecting to improve its renewable fuel production capacity from 2.7 to 3.0 million t (6.0 to 6.6 billion lb) a year by 2020, and is increasing its Singapore capacity by 1.3 million t (2.9 billion lb) to reach 4.5 million t (9.9 billion lb) in 2022 by investing €1.4 billion ($1.6 billion).[31]

By 2020, International Airlines Group had invested $400 million to convert waste into sustainable aviation fuel with Velocys.[32]

Production[edit]

Jet fuel is a mixture of a large number of different hydrocarbons. The range of their sizes (molecular weights or carbon numbers) is restricted by the requirements for the product, for example, freezing point or smoke point. Jet fuels are sometimes classified as kerosene or naphtha-type. Kerosene-type fuels include Jet A, Jet A-1, JP-5 and JP-8. Naphtha-type jet fuels, sometimes referred to as "wide-cut" jet fuel, include Jet B and JP-4.

"Drop-in" biofuels are biofuels that are completely interchangeable with conventional fuels. Deriving "drop-in" jet fuel from bio-based sources is ASTM approved via two routes. ASTM has also found it safe to blend in 50% SPK into regular jet fuels.[33][34][35] Only tests have been done so far with blending in synthetic paraffinic kerosene (SPK) in considerably higher concentrations.[36]

HEFA-SPK
Hydroprocessed Esters and Fatty Acids Synthetic Paraffinic Kerosine (HEFA-SPK) is a specific type of hydrotreated vegetable oil fuel used in aviation.[2] As of 2020 this is the only mature technology.[12][2] HEFA-SPK fuel is considered as leading alternative replacements for conventional jet fuel by the CAA because of its sustainability.[37] HEFA-SPK was approved by Altair Engineering for use in 2011.[38] HEFA-SPK is produced by the deoxygenation and hydroprocessing of the feedstock fatty acids of algae, jatropha, and camelina.[39]
Bio-SPK
This route involves using oil which is extracted from plant sources like Jatropha, algae, tallows, other waste oils, Babassu and Camelina to produce bio derived synthetic paraffinic kerosene (bio-SPK) by cracking and hydroprocessing. The growing of algae to make jet fuel is a promising but still emerging technology. Companies working on algae jet fuel are Solazyme, Honeywell UOP, Solena, Sapphire Energy, Imperium Renewables, and Aquaflow Bionomic Corporation. Universities working on algae jet fuel are Arizona State University and Cranfield University Major investors for algae based SPK research are Boeing, Honeywell/UOP, Air New Zealand, Continental Airlines, Japan Airlines, and General Electric.
FT-SPK
The second route involves processing solid biomass using pyrolysis to produce pyrolysis oil or gasification to produce a syngas which is then processed into FT SPK (Fischer–Tropsch Synthetic Paraffinic Kerosene).
ATJ-SPK
Research is also being done on the alcohol-to-jet (ATJ) pathway where alcohols such as ethanol or butanol are de-oxygenated and processed into jet fuels.[40] Some companies such as LanzaTech have already managed to create ATJ-SPK from CO2 in flue gases.[41] The ethanol is hereby produced from CO in the flue gases using microbes (clostridium autoethanogenum to be exact). LanzaTech has successfully demonstrated its technology at Pilot scale in NZ –using Industrial waste gases from the steel industry as a feedstock for its microbial fermentation.[42][43][44]
Future production routes
Routes that use synthetic biology to directly create hydro-carbons are being researched. Also, the production of Fischer-Tropsch hydro-carbon fuels (i.e. FT-SPK, referred to as "solar kerosine" by the project) through the use of a solar reactor is being researched by the SUN-TO-LIQUID project.[45][46][47]
Piston engines
Small piston engines can be modified to burn ethanol as a fuel.[48] Swift Fuel, a biofuel alternative to avgas under development, was approved as a test fuel by ASTM International in December 2009, aiming for a comparably priced, environmentally friendlier and more fuel-efficient general aviation fuel.[49][50]

Technical challenges[edit]

Nitrile-based rubber materials expand in the presence of aromatic compounds found in conventional petroleum fuel. Pure biofuels that aren't mixed with petroleum and don't contain paraffin-based additives may cause rubber seals and hoses to shrink.[51] Manufacturers are starting[needs update] to use synthetic rubber substitutes which are not adversely affected by biofuels, such as Viton, for seals and hoses.[52] The United States Air Force has found harmful bacteria and fungi in their biofueled aircraft, and use pasteurization to disinfect them.[53]

Economics[edit]

The International Energy Agency forecast SAF production should grow from 18 to 75 billion litres between 2025 and 2040, representing a share of aviation fuel getting from 5% to 19%.[12] By 2019, fossil jet fuel production cost was $0.3-0.6 per L given a $50–100 crude oil barrel, while aviation biofuel production cost was $0.7-1.6, needing a $110–260 crude oil barrel to break-even.[12]

As of 2020 aviation biofuel is more expensive than fossil jet kerosene,[1] considering aviation taxation and subsidies at that time.[54]

Sustainable fuels[edit]

Oslo Airport was the first international airport to offer Sustainable aviation fuel as part of the fuel mix since 2016

Sustainable biofuels do not compete with food crops, prime agricultural land or fresh water. Sustainable aviation fuel (SAF) are certified as being sustainable by a third-party like the Roundtable For Sustainable Biofuels. The sustainable aviation fuels certification and production pace seems insufficient to meet the International Air Transport Association target of halving the CO₂ emissions by 2050.[55]

Certification[edit]

A SAF sustainability certification verifies that the fuel product, mainly focussing on the biomass feedstock, has met criteria focussed around long-term global environmental, social and economic "triple-bottom-line" sustainability considerations. Under many carbon emission regulation schemes, such as the European Union Emissions Trading Scheme, a certified SAF product may be granted an exemption from an associated carbon compliance liability cost.[56]  This marginally improves the economic competitiveness of environmentally favourable SAF over traditional fossil-based jet fuel. However, in the near term there are several commercialisation and regulatory hurdles that are yet to be overcome through the collaboration of a variety of stakeholders for SAF products to meet price parity with traditional jet fuel and to enable widespread uptake.[57]

The first reputable body to launch a sustainable biofuel certification system applicable to SAF was the academic European-based Roundtable on Sustainable Biomaterials (RSB) NGO.[58] This multi-stakeholder organization set a global benchmark standard on which the sustainability integrity of advanced aviation biofuel types seeking to use the claim of being a Sustainable Aviation Fuel can be judged. Leading airlines in the aviation industry and other signatories to the Sustainable Aviation Fuel Users Group (SAFUG) pledge support the RSB as the preferred provider of SAF certification.[59] These airlines believe it important for any proposed aviation biofuels have independently certified sustainable biofuel long term environmental benefits compared to the status quo in order to ensure their successful uptake and marketability [60]

Sustainability Criteria[edit]

EU RED II Recast (2018)
GHG reduction - Greenhouse gas emissions from aviation sustainable fuels must be lower than those from the fossil fuels they replace: at least 50% for production facilities prior to 5 October 2015, a mandatory reduction of 60% for production facilities after that date and 65% for sustainable fuels (SAF) produced in facilities starting operations after 2021.
Land use change - Carbon stocks and biodiversity: raw materials for sustainable fuel production cannot be sourced from land with high biodiversity or high carbon stocks (i.e. primary and protected forests, biodiversity-rich grasslands, wetlands and peatlands).
Other sustainability issues are set out in the Governance Regulation and may be covered by certification schemes on a voluntary basis.
ICAO ‘CORSIA’
GHG Reduction - Criterion 1: Sustainable alternative fuel for reactors will generate net GHG reductions of at least 10% compared to fossil fuel for reactors, based on the life cycle.
Carbon Stock - Criterion 1: Sustainable alternative Fuel will not be produced from biomass obtained from land whose uses changed after 1st January 2008 and which has been from primeval forests, wetlands or peatlands, as all these lands have high carbon stocks. Criterion 2: In the case of a change in land use after 1st January 2008, as defined on the basis of the IPCC land categories, emissions from direct land use change (DLUC) shall be calculated. If the greenhouse gas emissions from a DLUC exceed the default value of the land use change induced (ILUC), the value of the DLUC will replace the default value of the ILUC.

Global impact[edit]

Sustainable Aviation Fuel development in Europe.[61]

As emissions trading schemes and other carbon compliance regimes are emerging globally, certain biofuels are likely to be exempted ("zero rated") by governments from having an associated carbon compliance liability due to their closed-emissions-loop renewable nature, if they can also prove their wider sustainability credentials. For example, in the European Union Emissions Trading Scheme it has been proposed by SAFUG that only aviation biofuels that have been certified as sustainable by the RSB or similar bodies would be zero rated.[62] This proposal has been accepted.[63] SAFUG was formed by a group of interested airlines in 2008 under the auspices of Boeing Commercial Airplanes and in cooperation with support from NGOs such as Natural Resources Defense Council. Member airlines represent more than 15% of the industry, and all member CEOs have signed a pledge to work on the development and use of Sustainable Aviation Fuel.[64][65]

In addition to SAF certification, the integrity of aviation biofuel producers and their product can be assessed by further means, such as by using Richard Branson's Carbon War Room,[66] or the Renewable Jet Fuels initiative.[67] The latter currently cooperates with companies such as LanzaTech, SG Biofuels, AltAir, Solazyme, and Sapphire. A leading independent NGO focused on this issue is the Sustainable Sky Institute.[68]

Certified processes[edit]

Abbreviation Conversion Process Possible Feedstocks Blending Ratio Commercialization Proposals / Projects
HEFA-SPK Synthesized paraffinic kerosene produced from hydroprocessed esters and fatty acids Bio-Oils, Animal Fat, Recycled Oils 50% World Energy, Universal Oil Products, Neste, Dynamic Fuels, EERC
FT-SPK Fischer-Tropsch hydroprocessed synthesized paraffinic kerosene Coal, Natural Gas, Biomass 50% Fulcrum Bioenergy, Red Rock Biofuels, SG Preston, Kaidi Finland, Sasol, Shell Oil Company, Syntroleum
SIP-HFS Synthesized kerosene isoparaffins produced from hydroprocessed fermented sugars Biomass used for sugar production 10% Amyris (company), Total S.A.
SPK/A Synthesized kerosene with aromatics derived by alkylation of light aromatics from non-petroleum sources Coal, Natural Gas, Biomass 50% Sasol
ATJ-SPK Alcohol-to-jet synthetic paraffinic kerosene Biomass from ethanol or isobutanol production 50% Gevo, Cobalt, Universal Oil Products, Lanzatech, Swedish Biofuels, Byogy

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Further reading[edit]

External links[edit]