Not all parts of a corn stalk are equal, and they shouldn’t
be treated that way when creating cellulosic ethanol, say Purdue University
researchers.
When corn stover is processed to make cellulosic ethanol,
everything is ground down and blended together. But a research team found that
three distinct parts of the stover—the rind, pith, and leaves—break down in
different ways.
Michael Ladisch, a distinguished professor of agricultural
and biological engineering and director of Purdue’s Laboratory of Renewable
Resources Engineering; Eduardo Ximenes, a Purdue research scientist in LORRE;
and doctoral graduate student Meijuan Zeng are trying to determine if there is
a better method to process corn stover and optimize efficiency.
Cellulosic ethanol is created by using enzymes to extract
sugars from cellulosic feedstocks, such as corn stover, grasses, and woods, and
then fermenting and distilling those sugars into fuels.
“Today, researchers grind the parts together and treat
it based on what’s needed to get at the hardest part,” Ximenes says.
“We show that there are major differences in degradability among the
tissues.”
Stover’s pith, the soft core that makes up more than half
the weight of a corn stalk, is the easiest for enzymes to digest, according to
the findings in two papers published in Biotechnology
and Bioengineering. Rind is the most difficult, while leaves fall in
between. Significant amounts of lignin, the rigid compound in plant cell walls,
make the cellulose resistant to hydrolosis, a process in which cellulose is
broken down into sugars.
Ximenes says converting the rinds only adds about 20% more
ethanol while requiring 10 times more enzymes, driving up the price of the
process.
“Is that extra 20% worth the added cost?” asks
Nathan Mosier, associate professor of agricultural and biological engineering
and coauthor of the study. “Because if there is a way to separate out
pith, you could burn the leftover rinds to generate steam, creating energy needed
to operate the plant.”
Ladisch adds that separating pieces of corn stover and
treating them differently would be a new way of approaching cellulosic ethanol
production.
“It uses existing conversion technology, but it enables
us to think about a new way of getting the most from that technology,”
Ladisch says. “There is absolutely no reason a ligno-cellulosic non-food
material such as corn stalk cannot be used to make ethanol if you understand
the science.”
Ladisch and Ximenes say they will next work with their colleagues
to explore ways to improve the ability of enzymes to create sugars from
cellulose and remove the compounds that inhibit those enzymes, as well as
adapting the findings for other feedstocks such as switchgrass and wood.
