Bio-avtur or SAF (Sustainable Aviation Fuel) will be the only decarbonization scenario in the aviation sector for the next few decades. The three leading production processes for SAF production are HEFA, FT and ATJ. And of the three processes, the HEFA process is the most efficient and most competitive at present, predicted to survive until 2030. The raw materials or feedstock for the HEFA process are mainly vegetable oil, used cooking oil, animal fat and so on. The HEFA process has also been approved by ASTM for use as aviation fuel (bio-jet fuel) based on ASTM D7566-14. In 2011 the latest version of the standard was published that allows up to 50% of HEFA aviation fuel products to be added to conventional jet fuel or petroleum-based fuel (avtur). ASTM itself, as an entity, does not have the authority or drive the development or qualification process of a new SAF technology, but only creates a framework, process, and repository that is the basis for the industry to create test methods, specifications, classifications, guidelines, and practices for their own needs.
Bio-avtur or SAF must have characteristics similar to conventional jet fuel so that it can be used anywhere in the world. Jet A fuel is primarily used in the US and jet A1 fuel is used in the rest of the world. The fuels are interchangeable. The main difference between the two types is that Jet A1 has a lower freeze point (-47oC, vs. -40oC) and usually has a static quenching additive (SDA) added to help reduce static buildup in the fuel during flight. Jet A1 is the fuel of choice for intercontinental flights. Given the volatility of jet fuel, the preferred components are hydrocarbons in the C10 to C15 paraffin range. Furthermore, to meet the freeze point specification (-47oC), these paraffins must be highly branched to achieve such a low freeze point. This means that bio-avtur or SAF must have carbon atom bonds or C bonds in the C10-C15 range, and in this range palm kernel oil (PKO) and coconut oil (CCO) are most suitable due to their high lauric acid composition which consists of 12 C atoms.
HVO / HEFA - SPK (Hydro-processed Esters and Fatty Acids-Synthesized paraffinic kerosene) is a renewable paraffin with combustion properties similar to other renewable paraffins such as Fischer-Tropsch fluids, produced by biomass gasification and chemical synthesis. HVO / HEFA can be produced in dedicated facilities producing 100% HVO, or it can be co-processed with fossil fuels in petroleum oil refineries. In co-processing, a bio-based feedstock of typically 5-10% is blended with the fossil feedstock. The HVO / HEFA process in addition to renewable diesel (which is different from biodiesel – FAME) can also be modified to produce bio-avtur / SAF for jet fuel applications. AltAir Fuels supplies HVO / HEFA based SAF and produces approximately 13 million liters per year.
HEFA is produced by hydrogenation and hydrocracking of vegetable oils and animal fats using hydrogen and catalysts at high temperature and pressure. In this hydrotreating process, oxygen is released from the feedstock consisting of triglycerides and / or fatty acids. This will produce straight chain hydrocarbons (paraffins) with various properties and molecular sizes depending on the characteristics of the raw materials and the operating conditions of the process being carried out. With the high lauric content in palm kernel oil (PKO) and coconut oil (CCO), the yield will be high because the oil content is in the bio-avtur range, namely C10 - C15. This is different if you use vegetable oil with a longer carbon chain, such as CPO, calophyllum inophyllum oil or canola oil. If you use vegetable oil with a long chain, the yield will be small and an extra cracking process is needed to increase the yield of bioavtur or SAF.
This conversion usually goes through two stages, namely hydrotreatment followed by hydrocracking/isomerization. This hydrotreatment process is usually carried out at a temperature of 300 -390 C and for triglyceride treatment, propane is usually produced as a by-product. The more hydrogen is added, the less propane is produced. The final product of the straight-chain hydrocarbon can be adjusted according to the type of fuel, for example for bio-avtur or bio jet fuel or SAF, namely by isomerization and the cracking process. The hydrogen used in HEFA production currently mostly comes from fossil sources or blue hydrogen. The catalyst for this can be a simple refinery hydro-processing catalyst. This catalyst can be adjusted to isomerize the paraffin chain to lower the melting point of the product. If necessary, a second isomerization stage is used to carry out this task in order to achieve the required jet fuel cold flow properties, namely Jet A or Jet A-1.
Currently, Pertamina (Indonesia's state-owned oil company) has succeeded in producing bio-avtur or SAF from palm kernel oil or PKO processing, namely refined bleached deodorized palm kernel oil (RBDPKO) called bioavtur J2.4 or containing vegetable oil ingredients in the form of RBDPKO 2.4%. The production of this bioavtur is carried out through the Hydrotreated Esters and Fatty Acids (HEFA) co-processing method and has a capacity of 9,000 barrels per day. The J.24 bioavtur has successfully undergone commercial flight tests on a Boeing 737-800 NG aircraft owned by PT Garuda Indonesia (Persero) Tbk. (GIAA) on October 4, 2023. And for the future, apart from the quantity aspect, namely the portion of vegetable oil (PKO) is larger, even the use of other vegetable oils such as coconut oil (CCO), CPO oil, calophyllum inophyllum oil and so on, it is also hoped that the quality of bioavtur will also improve. In addition, there are also plans from other institutions, namely the production of biovatur or SAF from coconut oil in collaboration with Japan.
In the aviation fuel industry, ASTM serves as the international standard for jet fuel quality, and plays a critical role in ensuring the safety, quality, and reliability of Sustainable Aviation Fuels (SAF). ASTM establishes requirements for criteria such as composition, volatility, fluidity, combustion, corrosion, thermal stability, contaminants, and additives, among others, to ensure that fuels are compatible when blended. ASTM International (American Society for Testing and Materials) is an international organization that develops technical standards for a wide range of materials, products, processes, systems, and services. Jet fuels must meet stringent quality specifications to be eligible for use in the aviation industry.
There are several ASTM standards related to this jet fuel, namely first, ASTM D1655: This is a conventional jet fuel specification that establishes requirements for Jet A and Jet A-1 produced from petroleum. This specification has been used globally by the aviation industry since 1959 to ensure the availability of safe and consistent jet fuel for all aircraft. Second, ASTM D4054: This ASTM standard practice defines the scope of fuel, rig, and engine property testing that should be considered when evaluating new synthetic jet fuels. This practice also describes the overall evaluation process and the important role of engine and aircraft manufacturers in ensuring a good jet fuel safety record is maintained with these new fuels. Third, ASTM D7566 Pathway: As per ASTM D4054, the pathway includes definitions of synthetic jet fuel blending components as defined by: permitted feedstocks; conversion processes and their attributes; and the final characteristics of the pure components. All of this is detailed in both the body of D7655 and its Appendices. The pathway will also define blending requirements.
In order for a new SAF production line to be included in D7566, it must undergo extensive testing to determine the maximum blend ratio with conventional jet fuel and demonstrate that the blend is suitable for its intended purpose. This procedure is outlined in ASTM D4054, ‘Standard Practice for Evaluation of New Aviation Turbine Fuels and Fuel Additives’.
Each batch of jet fuel needs to be certified before it can be used. While conventional jet fuel is certified as D1655 fuel (or a derivative), pure SAF is certified to the stringent specification requirements set out in Appendix D7566 which relates to the SAF production line. D7566 certified SAF is blended with conventional jet fuel to the maximum allowable blend ratio. The blended SAF is then certified to the D7566 blend requirements, and thus automatically receives D1655 certification, making it fully Jet A/A-1 compliant (‘drop-in fuel’) and ready for use in existing jet fuel infrastructure and equipment. In short, ASTM is vital to the aviation fuel industry as it is the basis for international standards for the quality of jet fuels, and SAF in particular.
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