Novel System for Recalcitrance Screening Will Reduce Biofuels Production Costs; The Spectrum of Clean Energy Innovation (Fact Sheet) Page: 2 of 2
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The NREL and UCR scientists found that the key to a successful HTP system was to
perform the pretreatment, enzyme hydrolysis, and sugar assay steps all within the same
vessel. To accomplish this, the researchers adapted solids-dispensing robots to distrib-
ute biomass into custom 96-well reactor plates, and they developed a stackable plate
steam reactor capable of simultaneously pretreating 1,920 biomass samples. NREL's HTP
reactor plates were custom-fabricated from aluminum to withstand high pretreatment
temperatures and gold-plated for corrosion resistance. NREL researchers also custom-
ized the plates by boring steam channels between each of the wells so steam and
cooling water can circulate evenly through the reactor, resulting in uniform reaction
conditions for all samples. Another key development was effectively sealing the reactors
during pretreatment while maintaining robotic access to the samples inside the plate.
After pretreatment, enzymes are added into the sample wells and the plates are incu-
bated for three days while the enzymes break down the biomass into its component
sugars. The pretreatment and digestion conditions are defined to yield 50% to 70%
cellulose conversion, well above the conversion levels of raw material, yet below high
conversion levels that could mask sample variability and bias the analysis. The resulting
liquid hydrolysate is assayed for glucose and xylose, the primary sugars that result from
enyzme hydrolysis.
Putting the System to Use: Screening Poplar Tree Strains for
Conversion Efficiency
To demonstrate the new HTP platform, NREL researchers screened 755 poplar core
samples from the Pacific Northwest as part of an ongoing U.S. Department of Energy
BioEnergy Science Center study. Partial compositional analysis was performed on each
sample by HTP pyrolysis molecular beam mass spectroscopy, which provided informa-
tion about the chemistry of the cell wall, including the ratios of cellulose, hemicellulose,
and lignin.
The sugar release data from the poplar experiment provides a general idea of how the
recalcitrance varies within a large set of samples. In this case, there was a large variation
in conversion efficiency, more than 25%, which correlated with the chemical composi-
tion of the samples. Therefore, trends in recalcitrance were identified with respect to
a number of measurable characteristics, including the ratio of certain lignin species
known as syringyl and guaiacyl. The researchers found that the sugar release was
independent of overall lignin content, but that both the glucose and the xylose release
increased with increasing syringyl:guaiacyl ratio.
The results of NREL's HTP chemical and conversion analyses will be combined with
genetic information gathered by other BioEnergy Science Center researchers to dis-
cover the factors contributing to lower biomass recalcitrance. There is a large variation
in physical and chemical characteristics that can be exploited to develop improved
biomass feedstocks. This information provides the scientific basis for the rational
development of improved poplar trees and other potential feedstocks that can lead to
significant reductions in the cost of biofuel production.a
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NREL's custom-designed reactor
system, a high-throughput pre-
treatment and enzyme digestion
system, allows researchers to more
'apidly screen large numbers of
samples to identify the most prom-
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samples from the Pacific Northwest. ;stuckNational Renewable
Energy Laboratory
1617 Cole Boulevard
Golden, Colorado 80401-3305
303-275-3000 " www.nrel.gov
NREL is a national laboratory of the U.S. Department of
Energy, Office of Energy Efficiency and Renewable Energy,
operated by the Alliance for Sustainable Energy, LLC.
NREL/FS-6A4-47573 " June 2010
Printed with a renewable-source ink on paper containing at
least 50% wastepaper, including 10% post consumer waste.
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Novel System for Recalcitrance Screening Will Reduce Biofuels Production Costs; The Spectrum of Clean Energy Innovation (Fact Sheet), report, June 1, 2010; Golden, Colorado. (https://digital.library.unt.edu/ark:/67531/metadc1012954/m1/2/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.