PNNL-13501 - Pacific Northwest National Laboratory

Validation and Scale-Up of Monosaccharide Production from Grain Fiber
Study Control Number: PN00092/1499
Andrew J. Schmidt, Rick J. Orth
Renewable feedstocks, such as grain fiber, are a potential source for end products that would otherwise be produced from
fossil fuels. A key to using these renewable feedstocks is to economically break down the carbohydrate fractions to
soluble monosaccharides for further processing to the value-added chemicals. This project investigated various pathways,
methods, and operating conditions of using acid and enzyme hydrolysis to produce the monosaccharides from grain fiber,
in this case, corn fiber.
Project Description
The purpose of this project was to evaluate processing
options and operating conditions for breaking down the
carbohydrate fractions present in corn fiber to soluble
monosaccharides. This project also developed an
apparatus for continuous processing at a future date. Acid
and enzyme hydrolysis processes were investigated with
the main focus being on the breakdown of the
hemicellulose fraction in corn fiber to 5-carbon
monosaccharides (e.g., xylose and arabinose). Acid
hydrolysis conditions were identified where a significant
fraction of the corn fiber was solubilized, resulting in the
formation of soluble monosaccharides and
oligosaccharides. This acid hydrolysis work was
conducted in close collaboration with another LDRD
project (“Kinetics of Formation of Monosaccharides for
Grain Fiber and Related Constituents,” James A. Franz,
principal investigator). In addition, a variety of
commercially available enzymes was evaluated. Some of
the enzymes evaluated showed promise for breaking
down the hemicellulose fraction to monosaccharides. The
results from this project have provided valuable
information and capabilities that can be used to develop
and evaluate flowsheets using acid hydrolysis, enzyme
hydrolysis, or a combination for breaking down
hemicellulose in corn fiber to monosaccharides.
Introduction
The United States annually produces 13.9 billion pounds
of corn fiber from corn wet milling. This fiber is mixed
with protein to create a 21% protein feed for livestock,
and is sold primarily in Europe. However, the low value
of this byproduct and a recent boycott of genetically
modified food products in Europe creates a need to
generate a higher market value for corn fiber.
Hemicellulose, one of the major components of corn fiber
(Figure 1) is primarily composed of polymeric 5-carbon
sugars (e.g., arabinose and xylose). These
monosaccharides can be used as feedstocks for
downstream processing via catalytic processing to
produce chemicals such as polyols (e.g., ethylene glycol,
propylene glycol or glycerol), or via fermentation to
produce ethanol. To successfully use the hemicellulosic
fraction of corn fiber, the monosaccharides must be
recovered economically and without the production of
degradation products, such as furfurals, that can be
detrimental to downstream processing.
Starch
(17%)
Cellulose
(30%)
Approximately 35% of Corn Fiber is Composed of 5-Carbon Sugars
Protein
(11%)
Xylan
(35%)
Fiber
(59%)
Corn Fiber
8 lbs/bushel
Arabinan
(25%)
Hemicellulose Fraction
Ash
(6%)
Acid and enzyme hydrolysis processes were investigated
during this project to evaluate hydrolysis conditions for
breaking down the hemicellulosic fraction to soluble
monosaccharides. The yield of xylose, arabinose,
oligomers, and detection of detrimental breakdown
products were tracked during the testing. In addition, the
filterability and pumpability of the slurries were noted for
processing considerations.
Results and Accomplishments
Fat
(3%)
Galactan
(8%)
Figure 1. Major components in corn fiber
Other
(4%)
Mannan
(2%)
A literature review was conducted at the beginning of the
project to evaluate earlier work on corn fiber hydrolysis.
Many approaches used complete hydrolysis followed by
extensive downstream separations and purification of the
5-carbon and 6-carbon sugars. In most of the past work,
the goal was to recover all or nearly all of the
Separations and Conversions 439