PNNL-13501 - Pacific Northwest National Laboratory

carbohydrate value from the corn fiber, including the
glucose from hydrolysis of the cellulose fraction. In this
project, selective hydrolysis was evaluated to recover
monosaccharides from the hemicellulosic component.
Development of Novel and Simple Processing Strategies
Based in part on the literature and on testing both under
this project and under a separate LDRD project led by
James Franz, three hydrolysis processing strategies were
developed, and portions of the processing strategies were
further tested (see Figure 2).
Corn
Fiber
Corn
Fiber
Corn
Fiber
(Step 1) (Step 2)
Prehydrolysis
(Thermochemical)
Hydrolysis
(Enzymatic)
Prehydrolysis (Step 1) and Enzymatic Hydrolysis (Step 2)
1-Step Hydrolysis
(Step 1)
Hydrolysis
(Thermochemical)
Prehydrolysis
(Thermochemical)
2-Step (Thermochemical) Hydrolysis
Filtration
(Step 1) (Step 2)
Optional
Separations
Step(s)
Filtration
Residual Solids
(To Upgraded Livestock Feed)
C-5’s and C-6’s
(To Product Conditioning/
Catalytic Conversion or Fermentation)
Hydrolysis
(Thermochemical)
Figure 2. Hydrolysis processing strategies
Residual Solids
(To Upgraded Livestock Feed)
C-5’s and C-6’s
(To Product Conditioning/
Catalytic Conversion or Fermentation)
Filtration
Residual Solids
(To Upgraded Livestock Feed)
C-5’s and C-6’s
(To Product Conditioning/
Catalytic Conversion
or Fermentation)
The first approach included both acid and enzyme
hydrolysis. The fiber was first subjected to selective acid
hydrolysis to solubilize the hemicellulosic fraction of the
corn fiber. Next, enzymes were added to further break
down the solubilized hemicellulosic fraction to the
monomers. (An alternative to this flowsheet is to conduct
two acid hydrolysis steps, the first to solubilize the
hemicellulosic fraction, with a filtration to remove the
solids, and the second hydrolysis to convert the
oligosaccharides in solution to monosaccharides. With
this approach, however, the conditions of the second
hydrolysis were needed to control and prevent the
formation of degradation products.)
The second approach involved a one-step acid hydrolysis
at selected conditions. This approach was simpler than
the first; however, if the conditions were not right, total
conversion to the monosaccharides did not occur, or
degradation products could form.
The third approach used a two-step thermochemical
method. In the first step, the hemicellulose component
was solubilized, and an optional polishing step was
employed to remove the monosaccharides (e.g.,
440 FY 2000 Laboratory Directed Research and Development Annual Report
ultrafiltration), then the slurry was subjected to further
hydrolysis to break down the oligosaccharides to the
monomers. By removing the monosaccharides after the
first hydrolysis, the formation of degradation products
was minimized, while monosaccharide production is
maximized.
Acid Hydrolysis Testing
During evaluation of some of the acid hydrolysis
conditions, significant solubilization was observed
without the formation of degradation products. This
testing was conducted at the micro-scale and bench-scale.
The bench-scale results illustrated in Figure 3 were
obtained by operation at elevated temperatures without
acid addition. Even without acid addition, approximately
25% solubilization took place, with the solubilized
fraction mainly consisting of oligomers. At higher
temperatures, significantly more solubilization took place,
but degradation products also formed. The micro-scale
testing (Figure 3) was conducted under selective
hydrolysis conditions with the addition of acid.
Approximately 50% solubilization took place, and no
degradation products (e.g., furfural) were detected.
Approximately half of the solubilized fraction was
monosaccharides, and the remainder was
oligosaccharides.
Corn Fiber Solubilized (%)
70
60
50
40
30
20
10
0
Bench-scale Testing Results
Operation without acid at lower temperatures
Operation at low temperatue with acid addition
allows for approximately 25% solubilization
allows for approximately 50% solubilization
(Mostly as soluble oligomers) (25% soluble sugars and 25% soluble oligomers, no detectable furfural)
Increasing Temperature
Shorter Hold Time Longer Hold Time
Enzyme Hydrolysis Testing
Micro-scale Kinetic Testing Results
Enzyme hydrolysis testing was conducted, using several
commercially available enzymes. These enzymes are
relatively inexpensive and readily available. As can be
seen in Figure 4, three of the enzymes tested showed
promise for converting hemicellulose to the monomer
sugars (xylose and arabinose). In these tests, the corn
fiber itself was treated with the enzymes. If the corn fiber
were first treated via selective thermochemical (with or
%Yield, g/g Fiber
10
9
8
7
6
5
4
3
2
1
0
Increasing Hold Time
Arabinose
Galactose
Xy lose
Glucose
(a): Micro-scale kinetic testing results
provided by Jim Franz and Miikhail Alnajjar
Figure 3. Acid/thermochemical hydrolysis of corn fiber