DOEʻs Oak Ridge National Lab works on project for clean jet fuel

The U.S. Department of Energy is working on a project to convert ethanol into jet fuel to reduce carbon emissions.

While the decarbonization of air transportation is paramount to meeting U.S. climate goals, the clean energy technologies that are transforming automobiles are difficult to implement in aircraft. A battery powerful enough to fuel an airplane would be too heavy, and hydrogen would require large complex storage tanks onboard.

Thus, to reduce its emissions, the U.S. commercial aviation sector will need new methods of making sustainable aviation fuel. The ethanol market provides that opportunity, according to researchers at ORNL. The Department of Energy’s Office of Energy Efficiency and Renewable Energy Bioenergy Technologies Office is focused on developing industrially viable fuels using renewable biomass.

The first step in converting the ethanol-to-jet-fuel process is being done by the DOE’s Oak Ridge National Laboratory (ORNL) uses a catalyst to convert ethanol into butene-rich C3+ olefins. These are important intermediates that can then be processed into aviation fuels. Two more steps — oligomerization and hydrotreating — convert these intermediates into the liquid hydrocarbons used as fuels.

A team led by ORNL’s Zhenglong Li has been tasked with improving the current technique for converting ethanol to C3+ olefins.

Recent approaches to conversion have resulted in costs that are too high to compete with petroleum.

Li is committed to remake the standard process, producing C3+ olefins with high yield and without additional hydrogen.

“While we think of this as one process, from the chemistry side when you zoom in, there are several elementary steps,” Li said. “In the first step, we internally generate hydrogen — can we use that low concentration of hydrogen downstream where it is needed and avoid using additional hydrogen? To do this, we need to develop new catalysts; the current standards cannot do this conversion at the relative high temperature required.”

The team developed and tested a composite catalyst — a zinc-yttrium beta catalyst combined with a single-atom alloy catalyst.

“Single-atom alloys are used for low-temperature selective hydrogenation, but no one has yet reported its use in this kind of high temperature reduction,” Li said. “We also know that we could easily over-hydrogenate these molecules, which would not be usable. The critical thing here was modulating the ratio of hydrogen and butadiene generated during the reaction.”

The process has been a success thus far.

“We will continue to optimize this process to achieve even greater catalyst selectivity and higher olefin yield,” he said. “The aviation industry requires energy-dense liquid hydrocarbon fuels. This new catalyst technology is an important step toward achieving renewable, sustainable aviation fuel through ethanol conversion.”

The research was sponsored by the DOE Office of Energy Efficiency and Renewable Energy’s Bioenergy Technologies Office and conducted through the multi-laboratory Chemical Catalysis for Bioenergy Consortium.