Biomass Refining CAFI
Overall Sugar Yields from Corn Stover via Thermochemical
Hemicellulose Hydrolysis Followed by Enzymatic Hydrolysis
Todd A. Lloyd and Charles E. Wyman
Thayer School of EngineeringDartmouth College
Hanover, New Hampshire 03755
AIChE Annual Meeting San Francisco, CA November 20, 2003
Biomass Refining CAFI
Biomass Refining CAFI
Objectives
• Determine pretreatment conditions that lead to highest overall sugar yields
• Develop comparitive information on a consistent basis
• Identify opportunities to lower production costs while maintaining high yields
Biomass Refining CAFI
Corn Stover Composition• NREL supplied corn stover to all project participants
(source: BioMass AgriProducts, Harlan IA)• Stover washed and dried in small commercial
operation, knife milled to pass ¼ inch screen
Glucan 36.1 %
Xylan 21.4 %
Arabinan 3.5 %
Mannan 1.8 %
Galactan 2.5 %
Lignin 17.2 %
Protein 4.0 %
Acetyl 3.2 %
Ash 7.1 %
Uronic Acid 3.6 %
Non-structural Sugars 1.2 %
Biomass Refining CAFI
Biomass Refining CAFI
Hydrolysis
Enzyme
BatchPretreatment
H2O or H2SO4(aq)
Corn Stover
Overall Flow Diagram for Dilute Acid Pretreatment
Fermentation
Ethanol
Pretreatment Sugars
Residue
Digestion Sugars
Stage 1 Stage 2
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Stage 1 – Summary of Pretreatment Conditions
• Steam Gun-no added acid– 150-220 oC– ~25% solids
• Dilute Acid– 140-200 oC– 0.22-1.0 % H2SO4
– 5-25% solids– Heated in sand bath
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• Batch Reaction Systems1. NREL steam gun
2. ½”o.d. batch tubes
3. 1l stirred autoclave
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NREL Steam Gun
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Biomass Refining CAFI
Batch Tube Experimental Apparatus for Dilute Sulfuric Acid
4 ”Biomass Refining CAFI
Biomass Refining CAFI
Parr Reactor Experimental Apparatus for Dilute Sulfuric Acid
Biomass Refining CAFI
Biomass Refining CAFI
Stage 2 – Enzymatic Digestion
• Spezyme from Genencor - used by all investigators
• NREL LAP-009 used to evaluate digestibility– 60 FPU/g original glucan used to determine
ultimate digestibility– 15 FPU/g tests done on selected samples
Biomass Refining CAFI
Severity Parameter• For no acid addition applied approach used by Overend
and Chornet
CS = t*Anexp[(T-100)/14.75]CS = Combined SeverityA = Added Acid, %n = Arbitrary exponentT = Reaction Temperature, oC
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• Modified equation including acid addition has the form:
Ro = t*exp[(T-100)/14.75]
• Provides useful tools to compare results from a broad range of conditions
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Combined Stage 1 and 2 Steam Gun Results - No Acid
Biomass Refining CAFI
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
3.2 3.4 3.6 3.8 4 4.2 4.4 4.6
Log (Ro)
Yie
ld, (X
/Xo +
G/G
o) Combined Xylose
Combined Glucose
Overall Combined
60 FPU/g original glucan
190 oC210 oC
Ro=t*exp((T-100)/14.75)
Biomass Refining CAFI
Stage 1 Pretreatment Yield for 0.49% H2SO4 Addition in Batch Tubes
Biomass Refining CAFI
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.00 1.50 2.00 2.50 3.00 3.50 4.00
Log CS
Yie
ld,
X/X
o o
r G
/Go
180 C Xylose Yield
180 C Glucose Yield
160 C Xylose Yield
160 C Glucose Yield
140 C Xylose Yield
140 C Glucose Yield
Batch Tube
CS=t*[aH+]0.5*exp((T-100)/14.75)
Biomass Refining CAFIBiomass Refining CAFI
Stage 2 Digestion Yield for 0.49% H2SO4 Addition in Batch Tubes
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.00 1.50 2.00 2.50 3.00 3.50 4.00
Log CS
Yie
ld,
X/X
o o
r G
/Go
180 C Glucose Yield
180 C Xylose Yield
160 C Glucose Yield
160 Xylose Yield
140 Glucose Yield
140 Xylose Yield
CS=t*[aH+]0.5*exp((T-100)/14.75)
60 FPU/g Original Glucan
Batch Tube
Biomass Refining CAFIBiomass Refining CAFI
Combined Stage 1 and Stage 2 Yield for 0.49% H2SO4 Addition in Batch Tubes
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.00 1.50 2.00 2.50 3.00 3.50 4.00
Log CS
Yie
ld,
(X+
G)/
(Xo
+ G
o)
180 C Combined Yield160 C Combined Yield140 C Combined Yield15 FPU/g glucan loading
Batch TubeCS=t*[aH+]
0.5*exp((T-100)/14.75)
60 FPU/g glucan enzyme loading
Biomass Refining CAFIBiomass Refining CAFI
Combined Stage 1 and Stage 2 Yield for 0.98% H2SO4 Addition in Batch Tubes
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.00 1.50 2.00 2.50 3.00 3.50Log CS
180 C Combined Yield
160 C Combined Yield
140 C Combined Yield
15 FPU/g glucan loading
Batch Tube
CS=t*[aH+]0.5*exp((T-100)/14.75)
60 FPU/g glucan enzyme loading
Biomass Refining CAFI
84.2% glucan to glucose + 54.5% xylan to xylose conversion at 15FPU/g glucan
89.7% mass balance closure ( all solids + G + GO + X + XO)92% theoretical ethanol yield from glucose + xylose
Hydrolysis
Enzyme@ 15 FPU/g of glucan, 48h
Residual Solids
HydrolyzateLiquidParr Reactor
Pretreatment
1 wt% H2SO4
Corn Stover100 lb(dry basis)
21.4 lb xylan
0.2 lb gluco-oligomer (GO)
21.8lb xylose (X)
64.0 lb
36.1 lb glucan
Fermentation
4.08 galEthanol
1.3 lb xylose (X)30.9 lb glucose (G)
0.1 lb xylo-oligomer (XO)3.0 lb glucose (G)
32.4 lbTreated Solids
2.1 lb xylan33 lb glucan
2.29 gal ethanol
1.79 gal ethanol
140 oC
Mass Balance for Dilute Acid Pretreatment with Digestion (15 FPU/ g of glucan) in Parr Reactor
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Summary of Batch Tube Dilute Acid
Performance at 15 FPU/g Glucan
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T, oC A, % t, min X Yield, % G Yield, %
140 0.98 40
Stage 1 - 85
Stage 2 - 8
Total - 93
Stage 1 - 8
Stage 2 - 82
Total - 90
160 0.49 20
Stage 1 - 85
Stage 2 - 9
Total - 94
Stage 1 - 6
Stage 2 - 85
Total - 91
Biomass Refining CAFI
Understanding Role of Dilute Acid and Oligomer Release
• Why does acid enhance performance?
• What is the role of oligomers in sugar release?
Biomass Refining CAFI
Biomass Refining CAFI
Understanding Role of Dilute Acid and Oligomer Release
• Why does acid enhance performance?
• What is the role of oligomers in sugar release?
Biomass Refining CAFI
Biomass Refining CAFI
Predicting pH at Elevated Temperature
442
1
HSOHSOHK
44
2
SOHHSOK
(1)
(2)
][
]][[
4
42
HSO
SOHK (3)
Biomass Refining CAFI
][
][
4
42
SON
SOHM
2
8][ 2
222 MKNMKNMK
H
(4)
(Amount of Acid Neutralized)
Assume reaction (1) goes to completion
(Amount of Added Acid)
Biomass Refining CAFIBiomass Refining CAFI
I
I
IAzi 2.0
1log 2
Expression Empirical Davies'
molarity ion
charge ionic
tcoefficien activity ionic
m
z
T
TxA
zmI
i
ii
208.88.132
10825.1
2
1
5.16
2
*Marshall and Jones
444
41
)10(1 )0065./9.2307log9.199.56(
222
SO
TTT
SO
th
SOH
HSOth KKK
)0065./9.2307log9.199.56(log* ][
]][[2
4
42
4
4 TTTKHSO
SOHK th
HSO
SOHth
Predicting pH at Elevated Temperature
Biomass Refining CAFIBiomass Refining CAFI
HHHapH ][loglog
H
MKNMKNMKpH
2
8log 2
222
Predicting pH at Elevated Temperature
• Similar to approach used by Bienkowski et al. to predict the sulfuric acid degradation of glucose at elevated temperature and of Springer and Harris for the hydrolysis of wood
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Predicted pH vs. Temperature
Biomass Refining CAFI
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
20 40 60 80 100 120 140 160 180
T emperature, oC
pH
0.98% H2SO 4
0.45% H2SO 4
0.22% H2SO 4
5% solidsNo Neutralization
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Predicted pH vs. Temperature
Biomass Refining CAFI
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
20 40 60 80 100 120 140 160 180
Temperature, oC
pH
0.98% H2SO4
0.45% H2SO4
0.22% H2SO4
5% solids10 mg/g Biomass Neutralization
Biomass Refining CAFI
Predicted pH vs. Temperature
Biomass Refining CAFI
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
20 40 60 80 100 120 140 160 180
Temperature, oC
pH
0.98% H2SO4
0.45% H2SO4
0.22% H2SO4
5% solids20 mg/g Biomass Neutralization
Biomass Refining CAFI
Predicted pH vs. Temperature
Biomass Refining CAFI
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
20 40 60 80 100 120 140 160 180
Temperature, oC
pH
0.98% H2SO4
0.45% H2SO4
0.22% H2SO4
25% solids20 mg/g Biomass Neutralization
Biomass Refining CAFI
Understanding Role of Dilute Acid and Oligomer Release
• Why does acid enhance performance?
• What is the role of oligomers in sugar release?
Biomass Refining CAFI
Biomass Refining CAFI
Typical Stage 1 Yield vs Time Data
0
20
40
60
80
100
0 20 40 60 80 100 120 140 160 180 200
Reaction Time, min
% M
axim
um
Po
ten
tial
Xylo
se
Residual Xylan
Soluble Monomers and Oligomers
Soluble Xylooligomers
Batch Tube Reactors
140 oC
0.49% Sulfuric Acid
Biomass Refining CAFI
Models to Predict Hemicellulose Hydrolysis
• Abundance of literature data• Most kinetic studies neglect oligomers• Saeman model:
H M Dk h k d
Hf M D
Hs
k f
k s
k d
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• Have also added consideration of two fractions of hemicellulose in biphasic reaction (Kobayashi et al.)
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Hemicellulose Hydrolysis Kinetics
• A few models in literature include oligomers
• These treat oligomers as only one or possibly two species
• In fact, we would expect a number of different species of oligomers with varying chain lengths
• Some inconsistencies among models
Hf O MH s
k f
k s
k h
Dk d
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Biomass Refining CAFI
Hemicellulose Hydrolysis Kinetics
• A few models in literature include more than one species of oligomer and suggest that oligomers may react directly to degradation products without first forming xylose monomer
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XOH
MH s
k fk s k h
Dk d
XO L
k Od
Garrote et. al, 2000, Process Biochemistry, 36/571-78
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Structure of Hemicellulose
p-Coumaric Acid
Xylose
Acetyl
Arabinose
Ferulic Acid
Glucuronic Acid
Fragmentation Products
+ H2O
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Biomass Refining CAFI
Polymer Degradation1
N-mer
dCN/dt = -kh(N-1)CN
CN = CN0exp[-kh (N-1) t]
Assumes random bond scission and uniform rate constant
1 Simha, R., (1941), Journal of Applied Physics, 12:569-578
Biomass Refining CAFI
Biomass Refining CAFI
Generalized Form for j-mer Distribution
dCj/dt = 2kh Ci - kh(j-1)Cji=j+1
N
Cj = CN0 [1 – ](j-1)[ 2 + (N-j-1) ] 1< j < N-1
Where = 1 - exp[ -kht ]
@ t=0, CN=CN0; Cj=0
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hd
tktk
hd
tktkh
kk
eeN
kk
eeN
N
kC
dhdh
2
212 2
1
For reactive monomer:
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Depolymerization Model 140 oC, 0.49% Added Acid
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 20 40 60 80 100 120 140 160 180 200
Pretreatment Time, min
Yie
ld,
X/X
0
Residual Xylan
Total Xylose and Xylooligomers
Xylooligomers
kh=0.126
kd=0.0016 AssumptionsOriginal DP = 100Cutoff DP = 8
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Modified Depolymerization Model
n
mi
kaa0
1X e wher;i
iX
C
Ce
n:mj for
1)Ca(jkCa2kdt
dCjh
n
1jiih
j
• Assumes a change in activation energy with conversion
Biomass Refining CAFI
Modified Depolymerization Model 140 oC, 0.49% Added Acid
Biomass Refining CAFI
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 20 40 60 80 100 120 140 160 180 200Pretreatment Time, min
Yie
ld, X
/X0
Residual Xylan
Soluble Xylooligomers
Soluble Xylose + Xylooligomers
Kh=.516 min-1
Ka=7.9
Ko=.094 min-1
Kf=.0016 min-1
Assumptions:
Cutoff DP = 8Original DP = 100
n:mj for
1)Ca(jkCa2kdt
dCjh
n
1jiih
j
mj1 for
j)C-(1kC2kCa2kdt
dCjo
1-m
iio
n
iih
1
2m
1 for
jm
CkC2kCa2kdt
dC1d
1-m
iio
n
iih
1
2
Xkaea
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Conclusions
• Water only hydrolysis with a steam gun produced a maximum yield of about 60% X+G with 60 FPU/g glucan.
• For dilute acid pretreatment conditions for >95% yield of glucan and xylan ranged from 140oC with 0.98% added acid for 40 minutes to 180oC with 0.49% added acid for 5 minutes
• Xylanase activity in stage 2 enhances xylose yields • Neutralization of added acid can have a significant
effect on pH• Hydrolysis can be viewed as a depolymerization
process
Biomass Refining CAFI
Biomass Refining CAFI
Acknowledgements The United States Department of Agriculture Initiative for
Future Agricultural and Food Systems Program through Contract 00-52104-9663 for funding our research
The United States Department of Energy Office of the Biomass Program and the National Renewable Energy Laboratory
Our partners from Auburn University, Michigan State, Purdue, and Texas A&M Universities and the National Renewable Energy Laboratory
The National Institute of Standards and Technology for funds to purchase some of the equipment used in this research
The Thayer School of Engineering at Dartmouth College
Biomass Refining CAFI
Biomass Refining CAFI
Questions?
Biomass Refining CAFI