CARBON REMOVAL

Carbon removal is the process by which humans actively and intentionally remove carbon dioxide (CO2) from the atmosphere and store it in longer-lived reservoirs.

SAF (Sustainable Aviation Fuel)

SAF, which stands for sustainable aviation fuel, is an alternative fuel derived from renewable/clean sources that reduces carbon emissions from air transport.

Video caption

SAF, which stands for sustainable aviation fuel, is an alternative fuel derived from renewable/clean sources that reduce carbon emissions from air transport. SAF powers aircraft with similar performance as conventional petroleum-made fuel, but can reduce up to 85% of the emissions.

99% of SAF today are biofuels made from renewable biomass and waste sources. Bio-made SAF includes resources such as agricultural products, cooking fats/oils, municipal waste streams. However, there are several emerging technologies poised to make up a large share of the SAF market. These include renewable carbon feedstocks produced from the electrochemical conversion of carbon dioxide and other carbon waste.[1]

Curated by:

Dr. Staff Sheehan

Co-founder and CTO

Air Company

With help from:

Albert Gang

Example of a sustainable aviation fuel (SAF) production cycle. Fuels are derived from atmospheric carbon dioxide, creating a circular carbon life cycle.[a]

Benefits of SAF beyond lowering emissions:

increased profits for agricultural workers
environmental protections
fewer pollutants in the atmosphere besides greenhouse gas emissions, such as sulfur oxides

Why do we need SAF?

The transportation sector plays an important role in our energy systems and significantly contributes to greenhouse gas emissions. Transportation accounts for 12% of global emissions; aviation alone contributes to 2% of global emissions. Transportation — aviation in particular — will require innovative solutions to decarbonize and reduce their emissions. Most airlines have committed to net-zero carbon emissions by 2050, and most will rely on SAF to achieve this ambitious goal.

Most modes of transportation will decarbonize by electrification; however, the aviation sector cannot be fully electrified with current technology. The amount of electricity required to power standard commercial aircraft would have to be stored in extremely large and weighty batteries or hydrogen storage, so large and weighty that a plane could not fly. Furthermore, electric airplanes would require significant retrofitting of aviation infrastructure, introducing additional costs. Thus, decarbonization of air transport will require carbon-neutral "drop-in" fuels: liquid fuels which contain the same chemical composition and functionality as standard jet fuel, but are derived from non-petroleum sources.[2]

Examples of SAF production methods include:

Cooking oils

Vegetable oils and similar products can be refined into biofuels.

Agricultural waste

Agricultural waste includes any unwanted or unprofitable parts of a crop that are not used for consumption, typically vines, stems, or leaves.

Algae

Micro-algae farming yields large amounts of biomass precursor that can be processed into SAF.

Carbon conversion

Carbon dioxide is chemically converted into other ethanol and other carbon feedstocks that can be used as SAF.

Animal waste fat

Animal fat generated as waste by-products of the meat industry, including fat from pigs and cows, are incorporated in biofuels.

Municipal waste

Municipal waste includes residential and commercial garbage as well as sewage sludge.

Energy crops

Oil seed cover crops can be grown in rotation during the year with other cereal crops, when that land would otherwise be unused.

Green hydrogen

Electricity produced from renewable sources splits water molecules into oxygen and hydrogen. The latter only emits water when burned as a fuel.

Emerging Technologies: Power-to-Liquid

Power-to-liquid (PtL) jet fuel is a type of SAF produced through the conversion of renewable electricity into liquid hydrocarbons. PtL technologies are relatively newer than their biofuel counterparts, but they have potential for much greater emission reductions. PtL fuel production first begins with using renewable energy sources, such as wind or solar, to produce hydrogen through electrolysis. This hydrogen is then combined with captured carbon dioxide in a chemical synthesis process, such as a Fischer-Tropsch synthesis, to create liquid hydrocarbons that can be refined into jet fuel. PtL fuel companies such as Air Company offer promising solutions for decarbonizing the aviation industry, as it uses renewable electricity and recycles atmospheric CO2, creating a nearly closed carbon cycle.[3]

What are the challenges of SAF?

Incorporation of SAF into our energy systems presents several challenges. In order to be used as a "drop-in" fuel that functions in existing airplane infrastructure, SAF must be blended with conventional aviation fuel. Current regulations limiting SAF blending to a maximum 50% component of the fuel. This demands extensive testing and investment to ensure compatibility without compromising safety or performance. Additionally, there are high costs associated with SAF production, hindering widespread adoption. To address this, new financing models and government incentives are needed to drive down costs and incentivize investment in SAF production technologies.

Moreover, expanding the range of usable waste products to meet SAF demand introduces logistical and environmental considerations. Increasing the sources of feedstock for SAF production must be done carefully to avoid disrupting the food supply chain or triggering detrimental land use changes. The graph above projects a three-fold increase in land use for biofuels from 2010 to 2050.[4] The delicate balance between the needs of waste stream sources, food security, and natural ecosystems is paramount. Collaborative efforts between industry stakeholders, policymakers, and environmental advocates are necessary to navigate these challenges and realize the potential of SAF as a viable alternative to traditional jet fuels.

Projected land use changes for different biofuel sources from 2010 to 2050.[b]

Here are some useful resources to learn more about SAF:

Footnotes

[1] U.S. Department of Energy, Alternative Fuels Data Center. Sustainable Aviation. Fuel. https://afdc.energy.gov/fuels/sustainable-aviation-fuel

[2] International Civil Aviation Organization, Environmental Protection. Sustainable Aviation Fuel. https://www.icao.int/environmental-protection/pages/SAF.aspx

[3] Airbus, Power-to-Liquids, Explained.

https://www.airbus.com/en/newsroom/news/2021-07-power-to-liquids-explained

[4] World Economic Forum, What is Sustainable Aviation Fuel.

https://www.weforum.org/agenda/2023/11/what-is-sustainable-aviation-fuel/

[a] Omnagen, Ltd.

[b] International Energy Agency, Technology Roadmap, Biofuels for Transport.