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 Grift is co-author on a new study, published in Bioresource
Technology Reports, that takes a look at the bioconversion
efficiency of two products often used as biomass for energy
production, miscanthus giganteus and sugarcane bagasse.
“Our goal was to determine how much energy it takes to prepare
these materials. It’s a comprehensive look at various
preprocessing methods and their relationship to conversion
efficiency,” he explains.
The two materials were chosen because of their importance for
energy production. Miscanthus is typically grown as an
ornamental crop, but it has a high amount of biomass and grows
easily with very little nitrogen use. Sugarcane bagasse is the
byproduct left over after sugarcane is crushed to extract the
juice for sugar.
The study was done in collaboration with chemists from
University of California at Berkeley. Grift says the
interdisciplinary approach makes the research unique, because it
considers the whole energy balance. The U of I researchers,
including Grift and postdoc research associate Zewei Miao (now
at Bayer Company), studied the energy expenditure of harvesting
and preprocessing materials. The Berkeley chemists focused on
converting the biomass to glucose, which is used to make
ethanol.
The researchers defined the percentage of inherent heating value
(PIHV), which measures the amount of energy going into and out
of the production process. “It tells you that you have a certain
amount of biomass, which contains a certain amount of energy.
How much energy do you spend on processing? You don’t want to
spend more than 5% of the total energy value,” Grift says.
The researchers subjected the two materials to nine different
preprocessing methods, either separately or as a blend.
Preprocessing is done for various reasons, Grift explains. After
the crop is harvested, it needs to be transported to a
processing plant, and to make transportation efficient, the
material first undergoes a process called comminution, in which
is it chopped or cut into smaller pieces, and then it is
compressed.
Grift explains that harvesting and compression do not add much
to the energy equation. The main source of energy expenditure is
comminution, or size reduction. That brings the energy
expenditure to 5%.
“Smaller particle sizes make compression easier,” he says. “It’s
also better for energy production, because it provides a larger
surface area for enzymes to attach to in the conversion process.
But comminution takes a certain amount of energy, so there is a
tradeoff.”
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The preprocessing methods included chopped and cut
stems, pelletization, comminution, and various levels of
compression. Of the nine treatment groups, five included miscanthus,
three included sugarcane bagasse, and one included a blend of the
two products. The processed materials were all subjected to the same
chemical processes to release the glucose.
The researchers also evaluated the effects of particle size,
compression level, and blending on biomass conversion efficiency.
The results showed that comminution had a positive effect on the
efficiency of miscanthus but not sugarcane bagasse, while the
opposite was the case for pelletization. The researchers also found
that a 50/50 blend of the two materials had higher conversion
efficiency than sugarcane bagasse, but there was no significant
difference compared to miscanthus alone.
The results can be used to help make biomass energy production more
efficient, Grift says.
“The differences are not huge. But if you want to do something on a
larger scale it’s actually quite important to figure these things
out,” he explains.
Grift emphasizes that the results are preliminary and should be
examined in further studies.
Continued research is needed to substantiate the findings and to
broaden the knowledge base to other products and other preprocessing
methods.
The article, “Measuring the influence of biomass preprocessing
methods on the bioconversion efficiency of miscanthus giganteus and
sugarcane bagasse,” is published in Bioresource Technology Reports.
[https://doi.org/10.1016/j.biteb.2019.100301] Funding was provided
by the Energy Biosciences Institute.
Authors include Zewei Miao, formerly a postdoc research associate at
the U of I, now at Bayer Company, Stefan Bauer and Ana B. Ibáñez,
University of California at Berkeley, and Tony Grift, Department of
Agricultural and Biological Engineering and Grainger College of
Engineering, U of I.
[Source: Tony Grift
News writer: Marianne Stein] |
