Chaitanya Narula
led analysis of an ORNL biofuel-to-hydrocarbon conversion technology
to explain the
underlying process.
(November 3, 2015) A
new study from the Department of Energy’s Oak Ridge National Laboratory
explains the mechanism behind a technology that converts bio-based ethanol into
hydrocarbon blend-stocks for use as fossil fuel alternatives.
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 ORNL’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.
“It challenges a long-held but incorrect assumption,” said
ORNL coauthor Chaitanya Narula. “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.”
ORNL researchers tracked the molecular transition in
labeling experiments with deuterium, a hydrogen isotope, to confirm the
hydrocarbon pool mechanism.
The research, supported by DOE’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
ORNL’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.