In-situ corn-kernel fiber conversion has the potential to open the door to cellulosic ethanol volumes; however, analytical challenges have limited producers' ability to generate RINs from these technologies. A collaboration between Neogen and several key industry stakeholders saw the development of an analytical method that would enable producers to accurately determine how much ethanol is generated from starch versus from fiber when utilizing an in-situ fiber conversion process. The Neogen scientists involved in making this analysis a reality elucidate the history leading to its approval, as well as its current and future impacts on the ethanol industry.

Background
Anthropogenic (man-made) greenhouse gas emissions contribute significantly to global climate change. Numerous national and international governmental and scientific agencies have pinpointed internal combustion engine-based road vehicles as a major contributor to climate change, prioritizing the reduction of emissions through existing and innovative technologies. Policymakers and stakeholders have identified ethanol as a substantial means of reducing vehicular carbon emissions to achieve net zero and meet intermediate reduction targets for greenhouse gas emissions.

Ethanol has successfully reduced carbon emissions in the United States by using it blended with gasoline at a 10% ratio. There is an additional goal of advocating the usage of E15, a 15% ethanol blend. Most internal combustion engine vehicles manufactured since 2001 can utilize gasoline blended with 15% ethanol, representing another means to significantly reducing carbon emissions. The success of the ethanol industry in making notable reductions with existing ethanol blends and profitably producing ethanol is a testament to the industry’s ingenuity, continuous improvement and business acumen in challenging economic environments. While significant advancements have been made in starch-based ethanol, the cellulosic ethanol segment remains largely untapped and inaccessible to most of the industry.

Challenges in Cellulosic Ethanol Production
When the expanded Renewable Fuel Standard (RFS2) was enacted in 2007, it set ambitious targets of 15 billion gallons of cellulosic ethanol production by 2022. However, the technology to produce ethanol from cellulosic feedstocks, such as switchgrass and corn stover, has yet to become commercially viable. This is despite financial incentives available through the RFS program where D3 RINs, generated upon cellulosic ethanol production, consistently trade at a significant premium to D6 RINs, derived from traditional corn starch bioethanol processes.

Bioethanol Manufacturing Processes
Various modified processes exist within bioethanol manufacturing operations throughout the US, but for simplicity, we can categorize them into three broad types:

Type 1: The most widespread process involves converting the starch content in corn biomass to ethanol, generating D6 RINs. D6 RINs represent a 20% reduction in greenhouse gas emissions from baseline petroleum-based fuel.

Type 2: This process requires the separation of the residual, almost completely destarched biomass from a typical Type 1 process. This non-starch carbohydrate biomass can be degraded through chemoenzymatic hydrolysis to simple sugars, then fermented to produce bioethanol, generating highly valuable D3 RINs. D3 RINs represent a 60% reduction in greenhouse gas emissions from baseline petroleum-based fuel.

Type 3: This process involves the simultaneous conversion of the starch and non-starch components of corn kernel biomass in a single fermenter tank, often described as in-situ corn kernel fiber (CKF) fermentation. The major advantage of the Type 3 process is that it requires little to no additional capital investment for plants already operating the traditional Type 1 process. However, accurately determining the proportion of ethanol derived from starch (D6 RINs) versus corn kernel fiber (D3 RINs) presents a significant analytical challenge.

The Long Road to EPA Approval
Several analytical solution providers previously worked on methodologies to address this issue. In 2017, six ethanol plants were approved by the EPA to generate D3 RINs from in-situ CKF processes. However, within a year the EPA developed concerns about the analytical data supporting these plants and decided not to approve any new registrations for this process type.

In 2019, the EPA issued a guidance document describing options for the biofuel industry to obtain new facility registrations. The preferred approach recommended using a published voluntary consensus standard body (VCSB) method, but no such method existed.
In 2021, the National Renewable Energy Laboratory (NREL) published a seminal article describing a method for measuring cellulosic glucan content in corn biomass. This method, coupled with E-3181, seemed to be the key to unlocking EPA approval. Unfortunately, the analytical biases acknowledged by the authors in the NREL article, particularly the inability to differentiate between cellulosic content and yeast carbohydrates generated during fermentation, significantly masked the production of cellulosic ethanol, and it was not adopted by producers.

Around this time, Megazyme, an analytic reagent and method development SME, utilized its parent company Neogen's long-term relationships with industry stakeholders—established through Neogen's expertise in mycotoxins and food safety monitoring—to investigate the analytical challenge.

ASTM Standard E-3417
A working group led by David Mangan (Neogen/Megazyme) and Justin Sluiter (NREL) was established within ASTM. This group conducted a highly collaborative method development program over the past two years, finally resulting in the ASTM approval of a new standard, E-3417, in January 2024. This standard met the VCSB method requirement that the EPA first requested five years earlier. By July 2024, the EPA had approved 32 new bioethanol facilities for D3 RIN generation from in-situ CKF conversion processes, nearly eight years after their last approval for this application. Currently, many more facilities have registrations in process. This new ASTM method has the potential to be adopted by most bioethanol producers and bring significant financial benefits to the industry. One additional developmental area for this method is broadening the sample scope of E-3417 to include additional feedstocks such as milo.

Broader Perspectives for the Industry
While many producers in or near California have benefited from the Low Carbon Fuel Standard (LCFS) program for years, the RFS program's nationwide reach will impact producers across the US. The D3 RIN ethanol market requires production records to validate cellulosic ethanol production; however, it does not require physical delivery to California, unlike the LCFS.

With a 1% cellulosic ethanol production level, a D6-D3 RIN spread of $2.50, and a total market production capacity of 17 billion gallons, D3 RIN subsidies could be worth $425 million annually in financial uplift for the bioethanol industry. This direct fiscal benefit is supplementary to additional benefits, including reduced carbon intensity scores, increased corn oil yields, biofuel tax credits, and potential future access to new markets such as Sustainable Aviation Fuel with Alcohol to Jet processes.

Unlocking D3 RINs with in-situ ethanol production promises considerable financial benefits and a path toward a more sustainable future. For more information, contact Neogen at cellusmart@neogen.com.

Authors: Matt Nichols, Director of Biofuels Strategic Market
mnichols@neogen.com
David Mangan, R&D Director
dmangan@neogen.com

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