Diesel and jet fuels are notoriously difficult to obtain from non-oil plant-based sources, which is a major hurdle in biofuels research.
But “difficult” didn’t deter a group of undergraduate students in a process design course at the University of Wisconsin-Madison: In fact, the students made key initial steps toward overcoming that obstacle through their work on an open-ended class project aimed at producing a diesel fuel blendstock using readily available bio-ethanol as a starting point.
“What you try to do in the classroom is teach the fundamentals of engineering with real-world research projects,” says George Huber, the Richard Antoine professor of chemical and biological engineering at UW-Madison and a world expert in biofuels. “Here in our department, we have a long history of integrating teaching with research.”
For many of the students, the class was their first experience working on problems without predetermined solutions. Throughout the semester, the 82 students crunched real data from Huber’s lab to devise plans for a process so that ethanol refineries could one day produce high-value diesel and jet fuel.
They chose ethanol as a starting point because it is the most common biofuel and America is a top-producer of the corn-derived biofuel. The United States made nearly 16 billion gallons of ethanol in 2017, and fuel blends containing up to 15 percent ethanol are widely sold at gas stations around the country. The state of Wisconsin currently has 9 ethanol refineries that produce more than 500 million gallons of ethanol per year, contributing to some $4.2 billion of economic activity for the state including 19,000 jobs, $982 million in wages and $306 million in taxes, according to figures from the Wisconsin corn grower’s association.
Ethanol is the most commonly produced biofuel, and engineering students are using it as a starting point to synthesize high-demand diesel and jet fuels. Photo: Great Lakes Bioenergy Research Center.
Currently, ethanol is produced from corn and sugarcane; however, ethanol doesn’t work in diesel and jet engines. What’s more, demand for ethanol as an alternative is starting to dwindle as more and more people opt to drive hybrid and electric vehicles.
“We want to take advantage of the existing ethanol infrastructure to make diesel fuels,” says Nathaniel Eagan, a fifth-year PhD student whose research with Huber provided data for the course.
One measure of diesel fuel’s “bang for the buck” is a metric called the cetane number, and that number needs to be high for diesel fuels. Ethanol has a low cetane number, but it’s possible to convert this small molecule into a diesel fuel blendstock that has a higher cetane number.
Eagan’s research focuses on accelerants for chemical reactions called catalysts, which speed up the reactions without themselves being consumed in the process. He’s collaborated extensively with researchers at ExxonMobil to develop catalytic reactions to combine ethanol molecules into longer chemical chains that can be used as diesel fuel blendstocks.
Yet identifying effective catalysts is only one step in fuel production.
Biorefineries will need to perform a complicated series of chemical reactions, separations and purifications that are all integrated and optimized to minimize energy input to produce large quantities of usable diesel and jet fuel. Those processes haven’t yet been worked out.
Enter the undergraduates.
For 16 weeks, the students grappled with simulations, calculations and economic projections in hopes of sketching out workable and feasible designs.
“This is what real engineers do,” says Huber. “They analyze data and design a process in an open-ended way.”
Real engineers also collaborate, which is why the students spent the entirety of the semester working in small groups of four or five.
“It was different from other classes because of the group dynamics,” says Benjamin Moore, a senior majoring in chemical and biological engineering. “People became specialists for different parts of the process.”
The students had their work cut out for them: Ethanol tends to combine into complicated branched molecules instead of the linear chains that burn best in diesel engines. Complicating things further, strange interactions called azeotropes can make it difficult to achieve 100-percent purity when separating alcohols and water.
“It was a nightmare for us to figure out how to get all these separations to work,” says Moore.
But the students’ perseverance paid off. All the groups completed fully realized process designs, and Huber was impressed by the quality.
Now, Huber plans to collaborate with Associate Professor David Rothamer in the Department of Mechanical Engineering to study how ethanol-derived diesel fuels perform in real engines. Additionally, he’s working with chemical and biological engineering colleague Christos Maravelias to further analyze their economic feasibility and environmental impact.
Even though the semester ended in May 2019, the students’ groundwork will keep moving forward, with support from ExxonMobil and the Department of Energy.
“Now we have a much more rational way of designing this because of the undergraduates’ designs,” says Eagan.