Using simple technology developed primarily for producing electricity
from hydrogen, a team of researchers from the University of Wisconsin-Madison, University
of Massachusetts-Amherst, and Gwangju Institute of Science and Technology of
South Korea has developed what could be a commercially viable, continuous
process for converting biomass and electricity into renewable liquid
George Huber, a UW-Madison professor of chemical and
biological engineering, and his collaborators have demonstrated they can use a
proton-exchange-membrane fuel cell to convert the model biomass compound
acetone into isopropanol, a chemical compound with a wide variety of
pharmaceutical and industrial applications, including as a gasoline additive.
The advance paves the way for researchers to convert biomass
molecules such as glucose into hexanes, which are significant components of
gasoline currently derived by refining crude oil. “Essentially, we are
making renewable liquid fuel that fits into the existing infrastructure,”
says Huber, whose team published its results in ChemSusChem.
Unlike other technologies that use large quantities of
expensive hydrogen gas to convert biomass to biofuels, the team’s process is
driven by electricity, which is inexpensive and readily available in rural
areas. “And, we’re storing the electrical energy as chemical energy,”
A fuel cell converts chemical energy into electrical energy,
or vice versa. Reactions in a proton-exchange-membrane fuel cell require only
water, electricity, and the biomass-derived molecule.
The proton-exchange-membrane fuel cell consists of two
“halves,” separated by the proton-exchange membrane, which looks
somewhat like a thin sheet of plastic wrap. On one side-the anode side-there is
a positive electrode coupled with a catalyst that facilitates the chemical
reaction. The other side-the cathode-consists of a negative electrode and a
To reduce biomass molecules into fuel, Huber’s team feeds
water into the anode side and passes an electric current through the water to
generate protons and electrons. The electrons run through a circuit and the
protons pass through the proton-exchange membrane to the cathode side, where
they generate hydrogen. The hydrogen reacts with the biomass molecule and
reduces it to fuel, while oxygen exits the system.
Huber’s team demonstrated the biomass-to-biofuel reduction
process in a continuous-flow reactor, which continuously and efficiently moves
reactants through the system. Another advantage is that the process yields 50%
more liquid fuel over ethanol fermentation processes.
At the production level, the process also could be modular,
says Huber. “This is potentially a scalable technology where you could
make these proton-exchange-membrane-type reactors in the field, close to the
biomass, and run them at night when you have cheap electricity,” he says.
In future work, Huber hopes to improve the catalysts and
membranes in the fuel cell to make the process more efficient. And, while his
team used acetone and a few other molecules as their proof of concept, one of
Huber’s goals is to repeat the process with sugar. “With this approach,
you could take water and glucose and run it through the fuel cell circuit to
make hexane and oxygen,” he says.