A role for ethanol in the roadmap to decarbonize aviation fuel.
Sustainable aviation fuel (SAF) announcements are being made weekly, if not daily, in the business news as airlines and technology developers announce new ventures.
The administration laid out its “SAF Grand Challenge Roadmap” goal last year — 3 billion gallons of domestic SAF produced by 2030, expanding to meet 100 percent of expected jet fuel use by 2050, projected to be 35 billion gallons. The plan includes achieving a minimum 50 percent reduction in lifecycle greenhouse gas (GHG) emissions compared to conventional fuel in the near term and supporting airline commitments to reach net zero by 2050.
Considering 2021 domestic production was a mere 5 million gallons, that will have to be one impressive hockey stick growth curve — something the ethanol industry is familiar with. But just what are ethanol’s prospects? After all, alcohol-to-jet (and specifically ethanol-to-jet) is one of nine ASTM-approved SAF pathways, and ethanol is one of the few — and arguably the only — renewable fuel commercially produced at relatively large scale and low price.
“If we could snap our fingers and all ethanol in the U.S. converted to SAF at 50 percent blend, we could meet 100 percent of the jet fuel needs of America. Just like that,” says technology developer Pat Gruber, CEO of Gevo Inc. He bases that on current U.S. jet fuel consumption of over 20 billion gallons and ASTM specifications allowing no more than a 50 percent blend of renewable jet fuel with petro-jet. A gallon of ethanol yields roughly two-thirds of a gallon of finished jet, so the U.S. ethanol capacity of 17 billion gallons would yield more than 10 billion gallons of renewable jet — enough to blend with petro-jet to get 20 billion gallons of SAF.
The administration’s SAF Grand Challenge, however, suggests lipid-based pathways converting fats, oils and greases will be the primary fuel pathway leading to the 2030 goals.
That’s because HEFA (hydrotreatment of esters and fatty acids) technology is already being commercialized at a rapid pace — primarily because of HEFA’s similarity to petroleum refining and growing demand for renewable diesel. (Recent record-high prices for distillers corn oil reflect that growing demand.) Diesel and jet overlap in the distillation curve and it’s a relatively simple retrofit to optimize for jet fuel production, though costly at refinery scale.
Commercialization of alcohol-to-jet (ATJ) is a step behind. A table of ASTM pathways in the administration’s roadmap lists six companies advancing projects: Gevo, LanzaTech, Cobalt, Honeywell UOP, Swedish Biofuels and Byogy. The roadmap discusses progress in all nine approved pathways, and others under research and development, predicting the momentum is building to meet the 2050 goals: “Technologies in this portfolio are expected to result in a dramatic buildout and expansion of alcohol, waste-based, lignocellulosic, and waste and captured carbon gas pathways.” The document also says there are ample feedstocks, citing the “Billion-Ton Report” that suggests about 1 billion dry tons per year of biomass can be grown or collected sustainably and converted into 50-60 billion gallons of advanced biofuels “without impacting agriculture, trade, or current uses of biomass.”
Last year’s SAF Grand Challenge Roadmap goals are backed by provisions in the 2022 Inflation Reduction Act that provide an immediate incentive for SAF production by including SAF in the current blenders tax credit program. That will be followed by SAF incentives in the Clean Fuels Production Tax Credit program of $1.25 per gallon producer tax credit for fuels with at least a 50 percent GHG reduction compared to conventional jet.
That’s a big deal, says Jill Blickstein, vice president of sustainability for American Airlines. “The policy incentives for renewable fuels were created before SAF was a possibility, so the framework for those incentives didn’t contemplate SAF – until Congress passed the Inflation Reduction Act.” There’s more work to do, she adds, because renewable diesel is still more profitable than SAF, but she’s pleased that the IRA’s tax credit is performance based.
The tax credit incentive for SAF increases by a penny with every percentage point of improved lifecycle GHG emissions over the 50 percent reduction threshold up to $1.75 per gallon. There lies the challenge for ethanol producers. To qualify as a feedstock for SAF conversion, which inherently adds carbon intensity (CI), corn ethanol must reduce its CI scores.
That raises two points — just how does ethanol slash its CI score, and who will do the scoring?
CORSIA vs GREET
The IRA legislation instructs the Internal Revenue Service (IRS) to use GREET for determining lifecycle GHG emissions of renewable fuels, with the exception of SAF where it names CORSIA, although the legislation allows the use of “similar methodology” based on the statute.
CORSIA would be a problem for corn ethanol. The June 2022 publication of default values under the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) scores fuels produced with ETJ at 90.8 g/MJ for USA corn grain, of which 25.1 grams is the indirect land use charge (ILUC) and 65.7 is the core value. That compares with Brazil sugarcane at 32.8 g/MJ. Global corn grain-based ETJ fuel scores are even worse at 100.6 g/MJ. (An interesting side note: CORSIA’s default scores HEFA fuels using DCO at 17.2 g/MJ, compared to USA soybean oil at 64.9.)
Under GREET, ethanol would fare better, although still too high to qualify for IRA incentives. The 2021 Midwest GREET average for corn ethanol is 55.2 g/MJ, to which the CI of the SAF intensity needs to be added — an estimated 20-25 g/MJ. The GREET value includes 7.38 g/MJ as the ILUC penalty.
Gevo’s Gruber strongly suggests the ethanol industry get behind the use of GREET. “We need to have everybody pushing to use the full Argonne GREET, just like in diesel, gasoline, hydrogen or electricity. There shouldn’t be an exception for jet fuel.”
American Airline’s Blickstein supports the use of GREET. “It’s very important to measure the environmental impacts of SAF accurately and that the estimates are up to date using the best science available in a model that incentivizes all methods and approaches for reducing GHG emissions from the SAF supply chain and is transparent and well-understood. The GREET model, which was developed by and is regularly updated by the Department of Energy’s Argonne National Laboratory, meets that standard.
And we believe the government has the ability within the IRA to recognize the use of GREET for SAF, particularly because GREET is already required for other transportation fuels under the IRA.”
The American Coalition for Ethanol (ACE) concurs GREET must be used for the SAF tax credit. According to ACE CEO Brian Jennings, “The CORSIA model was developed by an international aviation safety organization who quite frankly lacks the experience and expertise of the scientists with the U.S. Department of Energy who developed the GREET model. What’s more, the SAF tax credit transitions into the 45Z Clean Fuel Production Tax Credit, which Congress requires the use of GREET by Treasury for making emission factor determinations. For these reasons and many more, GREET must be used for the SAF tax credit as well.”
Slashing CI to Zero
Gevo’s ETJ plant under construction in Lake Preston, South Dakota, is meant to showcase how corn-based ethanol converted to jet fuel can reach net zero—proclaimed in its name: Net-Zero One (NZ1). The 100 MMgy corn ethanol plant will be fully integrated with the ethanol-to-jet conversion process to produce 65 MMgy hydrocarbons, of which 60 MMgy will be renewable jet and the remainder renewable diesel and naphtha.
The yield loss from ethanol to jet is water produced in the first step in the ETJ process to create ethylene. The oxygen in ethanol (C2H4OH) is removed as water (H2O) leaving ethylene (C2H4) — a short hydrocarbon chain that is then catalytically combined into longer hydrocarbon chains and distilled.
Every step of the way is well-established technology, Gruber stresses. On the jet conversion side, Gevo has partnered with Axens. “They have something like 100 of these hydrocarbon plants working in the petrochemical industrial. It’s not new technology, they’ve done this for years, but from petrochemical raw materials.”
Similarly, the fermentation side uses known technologies, but configured in new ways. “That’s why we’re building a green field plant. We’ve cut thermal load by 80 percent, just by our designs,” he says, adding that when CI reduction is the goal, it’s all about efficiency. “We wind up spending more capital on equipment than you would if you were building a commodity ethanol plant. We also are able to use some of the chemical energy produced during the jet fuel production and integrate it back into the plant.”
At a $850 million capital investment, Gruber admits it’s expensive. “The reason we do a vertically integrated plant is that I have many levers to adjust CI score. Our jet fuel is just jet fuel. The only thing that makes it interesting is the CI score. It’s all about how to drive that carbon reduction downward and keep the optionality for the future, because these are 20-year investments, and we know things will change.”
Many in the ethanol industry think carbon capture use and sequestration is going to be the best solution for driving down CI, but Gruber says that’s not going to be enough. While CCS saves about 30 CI points, it gets offset by the 20-25 CI points added when ethanol is converted to jet.
The key is to go after all renewable energy, Gruber says. “Everything we touch will be tied to renewable energy. That’s the real problem. It’s not the corn. Accounting for the corn is the problem, it’s not the corn. Energy is the real problem. That’s how we drop the CI score, by decarbonizing the energy.”
The electricity for NZ1 will be generated from wind from 20 turbines to be built and operated by Zero6 Energy (formerly Juhl Energy). A key to getting interest from power companies, Gruber adds, is to make the wind farm big enough. Wind will not only power the NZ1 plant, but it will produce the hydrogen it needs for the ethanol-to-ethylene step, with surplus hydrogen sold as a new coproduct. The ethanol-to-ethylene step also generates energy, which is recycled in the plant to replace fossil natural gas.
Gevo landed a USDA grant to help with another aspect of its CI reduction approach — paying farmers a premium for supplying sustainably produced corn feedstock. Gevo’s Verity Tracking platform has about 60,000 acres enrolled this year, Gruber says, demonstrating Verity’s use of block chain technology to verify farmers’ tillage and fertilizer practices, as well as other inputs.
Modern agriculture is misunderstood, Gruber says, with too many urban folks thinking all corn is all bad. “We’re out to make a transparent system, tracking how something is grown straight through to all the energy used in the plant, all the way to the marketplace and out to burning the fuel. Completely transparent. That’s the way you stop the arguments.”
When NZ1 becomes operational in 2024, Gevo won’t be done. NZ2 is on the drawing boards — a 300 MMgy ethanol equivalent to make 195 MMgy of hydrocarbons. “We’ve got several sites that could fit and ways to do it. We’ve begun the engineering. We’ve sold almost 400 MMgy jet on take or pay contracts. We make it. They buy it. That’s an important point for financing.”
Gruber also anticipates working with Gevo’s partners, Axen and Praj, to help other ethanol producers reduce their carbon intensity and diversify into hydrocarbons.
SAF Roadmap
While the roadmap document dances around the term “corn ethanol,” calling it “the current fermentation-based fuel industry” or “the existing starch ethanol industry,” it is clear the departments involved in writing the administration’s SAF Challenge Roadmap — DOE, DOT, USDA, EPA — see fostering ethanol-to-jet as important to achieving the goal of 35 billion gallons of SAF. The document calls for reducing the carbon intensity of the existing starch ethanol industry while increasing capacity without planting additional corn.
Other measures include:
—Conducting a market analysis of starch-based ethanol, the supply/demand impact of increased SAF demand, the availability of feedstocks, as well as R&D and policy needs.
—Reducing GHG emissions through the agricultural practices of corn production.
—Developing supply chains for bio intermediates such as cellulosic sugars, alcohols, bio-oils or biocrude, that are sufficiently stable to be stored and transported to another entity for further processing.
— Reducing ethanol-based SAF’s CI and increasing carbon efficiency by integrating carbon capture and sequestration, reducing energy for concentration of alcohols following fermentation and improving the tolerance of ATJ catalysts to impurities and water.
As ground transport electrifies, the document says, “SAF presents a potential market for existing biofuels.” It suggests that more than 400 biorefineries will be needed to produce 35 billion gallons per year, bringing new economic opportunities to rural America.
“There is sufficient feedstock to meet the projected needs of the U.S. aviation industry if cost, sustainability and production barriers can be addressed.”
