Scientists have experimented for decades with a class of catalysts known as zeolites that transform alcohols such as ethanol into higher-grade hydrocarbons. As ORNL researchers were developing a new type of zeolite-based conversion technology, they found the underlying reaction unfolds in a different manner than previously thought.
“For 40 years, everyone thought that these reactions must go first from ethanol to ethylene, and then from there it forms longer chains. We were able to show that it’s not how this occurs,” said the lab's Brian Davison, coauthor on the study published in Nature Scientific Reports.
The researchers’ analysis found that this energy-consuming intermediary step is not necessary for the conversion to happen. Instead, an energy-producing “hydrocarbon pool” mechanism allows the zeolite catalysts to directly produce longer hydrocarbon chains from the original alcohols.
Chaitanya Narula, another of the study's co-authors, said the conclusions reached in its pages challenge "a long-held but incorrect assumption.”
“It has been assumed that you must go from ethanol to ethylene, which is endothermic and requires energy. We showed this step doesn’t occur, and that the overall reaction is slightly exothermic,” Narula said.
Researchers at the laboratoty tracked the molecular transition in labeling experiments with deuterium, a hydrogen isotope, to confirm the hydrocarbon pool mechanism.
The research, supported by the Department of Energy's BioEnergy Technologies Office, has implications for the energy efficiency and cost of catalytic upgrading technologies proposed for use in bio-refineries. Uncovering the mechanism behind the reaction helps support the potential economic viability of the alboratory's direct biofuel-to-hydrocarbon conversion approach.
“Our method of direct conversion of ethanol offers a pathway to produce suitable hydrocarbon blend-stock that may be blended at a refinery to yield fuels such as gasoline, diesel and jet fuel or commodity chemicals,” Narula said.
The catalyst and conversion process were licensed in 2014 to Vertimass, a startup company based in Irvine, Calif. Laboratory researchers are working with Vertimass through a separate Department of Energy-funded project to scale the technology to the commercial level.
The paper is published in Scientific Reports and is titled “Heterometallic Zeolites, InV-ZSM-5, Enables Efficient Conversion of Biomass Derived Ethanol to Renewable Hydrocarbons.” Coauthors are the lab’s Chaitanya Narula, Zhenglong Li, Erik Casbeer, Robert Geiger, Melanie Moses-Debusk, Martin Keller, Michelle Buchanan and Brian Davison.
The study was supported by the BioEnergy Technologies Office in Department of Energy’s Office of Energy Efficiency and Renewable Energy. Initial funding came from the lab’s Laboratory Directed Research and Development program and the Department of Energy’s BioEnergy Science Center, which is supported by the Office of Biological and Environmental Research in the agency’s Office of Science.
The project used resources at the laboratory’s Center for Nanophase Materials Sciences, a Department of Energy Office of Science User Facility. The zeolite materials were originally developed with support from Department of Energy’s Office of Energy Efficiency and Renewable Energy.
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