As momentum behind the sustainable aviation fuel (SAF) industry has grown, so has the need for nontraditional feedstocks. &nbsp;According to U.S. DOE’s 2023 Billion-Ton Report, there is up to 1.5 billion tons of biomass available on a &nbsp;sustainable basis in the U.S. each year, from waste to forest residuals to ag waste. Currently available but unused biomass resources can add around 350 million tons of additional biomass per year above current uses, according to the report, which indicates that 1 billion tons of biomass can produce about 60 billion gallons of biofuel, or 1.7 times the amount of sustainable energy needed to achieve the Sustainable Aviation Fuel Grand Challenge.With feedstock competition heating up, many are looking at new and unconventional feedstocks. SAF Magazine discussed some promising options with experts who will be making their cases at the upcoming SAF Conference &amp; Expo in St. Paul, Minnesota, Sept. 11-13.Milk Permeate&nbsp; The feedstock of choice for Omid McDonald, founder of Dairy Distillery, is a byproduct of the dairy production process called permeate. McDonald explains that there are two different types of permeate: whey and milk. Whey permeate is left over after the proteins are filtered out of the whey following cheesemaking. Similarly, the filtration process of &nbsp;skim milk to concentrate the proteins found therein leaves behind milk permeate, which is made up of lactose, water and some remaining minerals.Milk permeate is a waste product, meaning that it is not something any dairy producer makes intentionally. “No one milks cows or processes cheese to make permeate, and any value that dairy processors get from permeate is trivial, so from a carbon accounting point of view you could call it a waste,” McDonald says. This status means that none of the upstream carbon emission accounting needs to be done, giving ethanol made from milk permeate a low carbon intensity score of 15 grams CO2 per megajoule. When adding the generally used score of 15 grams CO2 per megajoule attributed to upgrading ethanol to jet fuel, this gives milk permeate-based SAF a score of 30 grams CO2 per megajoule, well below the threshold of 44.Although there is not enough milk permeate to meet all SAF demand, there is enough to make a difference. “American cows produce a lot of milk, and 4% of that milk by weight is lactose, which is the sugar in the permeate that we ferment,” McDonald says. “It’s going to be impossible to use every drop of lactose to make sustainable aviation fuel, but if you were [able to], just to give you an idea of scope, you’re talking about 370 million gallons of SAF.”Making 370 million gallons using milk permeate is the “theoretical maximum” he explains, however, it is plausible to reach 10% to 15% of that. Also, as demand for liquid dairy products fluid milk decreases and demand for dairy products (cheese, proteins) without lactose increases, the amount of permeate available will only increase.The other challenge of using milk permeate as a SAF feedstock is how spread out dairy processing plants farm locations are. “There isn’t a single dairy plant that could produce enough ethanol to be turned into SAF, and you need to get to a certain scale size for a SAF plant,” McDonald says. “We have to aggregate ethanol from a couple dairies, which is not a huge problem, but it is different than if you’re attaching a SAF plant to a giant corn ethanol plant.”Cassava&nbsp; One of the benefits of the cassava plant is its potential to be utilized as a feedstock under two different SAF processing methods, explains Jerome Friler, CEO of Satarem America. Cassava root holds a lot of starch, making it a great feedstock for ethanol production, which can then be upgraded to SAF using the alcohol-to-jet process. The stem of the cassava plant is essentially woody biomass, which can be gasified and turned into a syngas, which can be changed into SAF via the Fischer-Tropsch method. &nbsp;There are several key benefits of utilizing cassava as a feedstock, Friler explains. “First, it’s very easy to grow, and in Africa, they’ve been growing it for hundreds of years, so it grows well and [has] a good yield,” he says. “This is actually the best plant or the best seed to [make] alcohol. And then the alcohol-to-jet the process basically is the same, whether you make the alcohol from corn or from sugarcane or from cassava.”&nbsp;The stems of the plant are plentiful and underutilized, making them an ideal waste feedstock. Cassava roots are also being used to make bioethanol in Brazil and Thailand.&nbsp;Satarem is interested in pursuing both methods of production to both maximize market opportunities worldwide and the volume of SAF they are able to produce. “The ethanol part is already developed, but we are working full steam on the SAF part, alcohol-to-jet and [cassava] residue-to-SAF,” Friler says. The company is developing a SAF plant in the Tiebissou area of the Belier region of Ivory Coast.Cassava offers a great opportunity for project developers in parts of the African continent. All countries signed a mandate in November 2023 at an International Air Transport Association conference that states every airport on the continent must have a minimum of 5% SAF by 2030. “For Ivory Coast, we will need to produce approximately 50,000 [metric] tons per year of SAF for Abidjan [International] Airport, and we are planning on producing 100,000 altogether, so 50,000 for the local market and another 50,000 for export,” he says. Even 100,000 tons of SAF would only meet 20% of the Addis Ababa airport fuel needs.&nbsp;One of the benefits of developing this project in Ivory Coast is the availability of local manpower to harvest the cassava, explains Friler. However, building a plant in the country is challenging because of the complex land rights. “It’s a mixture of legal issues plus local issues and so on, so it takes quite some time to get the land,” he says. “Then you have to bring the fertilizers and the irrigation [because that equipment is not] over there. Apart from that—especially in Ivory Coast where we work—it rains a lot, and when it doesn’t rain you have a lot of sunshine, so things grow very, very fast, and that’s a good advantage.”Hybrid Hemp&nbsp; Although hemp was outlawed in the U.S. for several decades, a new hybrid strain of this oilseed offers U.S. farmers and SAF producers a unique opportunity to maximize SAF feedstock availability. John McKay, chief scientist at New West Genetics, explains that NWG hybrid hemp possesses more oil content than soybeans. Since hemp was made legal in 2014, New West Genetics has worked on developing a hybrid industrial hemp plant—titled Amplify—that yields double a standard plant’s yield. This makes it a great fit for project developers producing SAF through the hydroprocessed esters and fatty acids (HEFA) production process due to the increased yield and sustainability of the crop compared to standard hemp and other energy crops.&nbsp;According to the GREET Feedstock Carbon Intensity Calculator, NWG Amplify has a much more favorable CI score than other oilseeds serving fuel. Hemp’s profile in general yields more oil than soybeans, with 30% of the seed being made of oil compared to 20% for soybeans. “[Basically,] we made a competitor to soy in terms of yield of oil per acre,” says Wendy Mosher, CEO of New West Genetics. "The sustainability and water needs are lower, drought and frost tolerance are better, as well as the carbon sequestration potential—it is much greater than most annual crops.”&nbsp;This hybrid hemp is an attractive option for farmers desiring to grow two crops in the same field each growing season. New West Genetics’ scientists have also worked to improve the cold hardiness of the plant, allowing it to be planted earlier so that winter wheat or another crop could be planted after the hemp is harvested.AMPLIFY’s higher yield is also an advantage over some other low-CI crops frequently discussed in the SAF space. “[Higher yields] make it an attractive crop for this supply chain,” McKay says. “Obviously, lower-yielding crops are not in favor with farmers; the processors don’t like them because you’re only getting 500 to a thousand pounds of the oilseed per acre. The farmer can’t possibly make that much money.”Mosher explains that hemp faces the same challenges as any new crop in the current day agriculture supply chain: scaling up. New crops are not favored under the crop insurance programs benefitting farmers in the U.S., and this makes planting a new crop inherently risky for farmers—even crops with clear economic potential.&nbsp;Hemp stalks also provide farmers with an additional revenue stream through utilization in making products like textiles, building materials and insulation.&nbsp;“I think people are very excited about hemp,” Mosher says. “We’ve seen larger-scale adoption of hemp than these other crops over the past 10 years. Farmers like the rotation; there’s benefits to it. I’m really excited about the AMPLIFY hybrids, and ... [if] we can add soil sequestration and soil carbon credits—there are some private markets popping up for that—I see a lot of potential.”Supply Chain and Preprocessing&nbsp; Novel biogenic feedstocks such as municipal solid waste (MSW), corn stover and wood residuals often come with unique feedstock supply chain and processing challenges. Idaho National Laboratory is dedicated to understanding problems and identifying solutions to help producers mitigate the risk involved in using these feedstocks. Luke Williams, senior research engineer with INL, explains that preprocessing and supply chain considerations are often overlooked when considering a potential feedstock. “People often assume that the [currently] available, industrial size-reduction equipment will produce a viable feedstock that will feed and handle well,” he says. “What gets missed is how much wear they’re going to have on their equipment and how often their hoppers, feed systems and screens will break or plug as the moisture content on their corn stover changes with harvest conditions or biologically degrades. There are a lot of logistical challenges around solids handling that I think are underappreciated broadly in the biomass industry, and that is what we are trying to help solve.”INL’s team thoroughly examines feedstock characteristics, runs technoeconomic analyses and lifecycle assessments to help fuel producers understand the feedstock’s logistics and processing needs to make a conversion-ready feedstock. His team has assessed feedstock supply, logistics and preprocessing for everything from corn stover, loblolly pine residues, ocean plastics, cover crops and more. “At our processing facility, we take power consumption measurements, processing throughputs, failure modes, initial and final particle sizes, as well as chemical and mechanical analysis so you know how much it takes to transform a raw waste into something that is useful that we can then tie to lifecycle assessments,” Williams says.&nbsp;INL does not study feedstock conversion past gram-scale screening experiments, and instead partners with the National Renewable Energy Laboratory and other conversion facilities to understand how feedstocks convert into fuels and chemicals. INL does perform contract research for companies, because the lab does not compete with industry, so the researchers there do not perform services like sample testing alone.&nbsp;Raw biomass is an attractive feedstock for SAF producers, but in some cases, only 30% of raw biomass gathered fits into a biorefinery’s specifications and it needs to be engineered into a much narrower specification, Williams explains. Adhering to these narrow specifications is vital, because producers must be able to efficiently convert their feedstock and ultimately keep their CI scores low by avoiding process upsets and increasing operational reliability. INL performs the breadth of research needed to understand the challenges associated with turning a waste stream into well-characterized, conversion-ready feedstocks. &nbsp;Although it is almost certain that no individual biogenic feedstock is available at the scale needed to supply the entire global aviation industry, as McDonald says, every little bit counts. Whether that feedstock is available in millions or billions of tons, there could be a place for each one within the SAF industry. Economics, supply chain logistics and processing technology will determine which feedstocks will gain the most momentum in the market. Author: Katie Schroeder&nbsp; Associate Editor, SAF Magazine&nbsp; Katie.schroeder@bbiinternational.com

2024-08-26 - Expanding the Feedstock Arsenal (SAF Magazine)

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New and unique feedstocks abound for the SAF industry, offering significant carbon reduction potential for the aviation industry. 

Expanding the Feedstock Arsenal

Expanding the Feedstock Arsenal

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