Expanding the Feedstock Arsenal

by Katie Schroeder (SAF Magazine) ... According to U.S. DOE’s 2023 Billion-Ton Report, there is up to 1.5 billion tons of biomass available on a 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.

Milk Permeate
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 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.

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
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.

“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.

Hybrid Hemp
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.

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.”

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.

Hemp stalks also provide farmers with an additional revenue stream through utilization in making products like textiles, building materials and insulation.

Supply Chain and Preprocessing
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. READ MORE