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Comparison of Selected Results for Application of Leading Pretreatment
Technologies to Corn Stover Charles E. Wyman, Dartmouth College
Y. Y. Lee, Auburn UniversityBruce E. Dale, Michigan State University
Tim Eggeman, Neoterics International Richard T. Elander, National Renewable Energy Laboratory
Michael R. Ladisch, Purdue UniversityMark T. Holtzapple, Texas A&M University
2003 AIChE Annual MeetingSan Francisco, California
November 20, 2003
Outline of Talk
• Pretreatment technologies studied
• General research approach
• Material balance data
• Comparison of performance
• Needs for the future
USDA IFAFS Project Overview• Multi-institutional effort funded by USDA Initiative for Future
Agriculture and Food Systems Program for $1.2 million to develop comparative information on cellulosic biomass pretreatment by leading pretreatment options with common source of cellulosic biomass (corn stover) and identical analytical methods– Aqueous ammonia recycle pretreatment - YY Lee, Auburn University– Water only and dilute acid hydrolysis by co-current and flowthrough
systems - Charles Wyman, Dartmouth College– Ammonia fiber explosion (AFEX) - Bruce Dale, Michigan State University– Controlled pH pretreatment - Mike Ladisch, Purdue University– Lime pretreatment - Mark Holtzapple, Texas A&M University– Logistical support and economic analysis - Rick Elander/Tim Eggeman,
NREL through DOE Biomass Program funding• Emphasis on quality not quantity
USDA IFAFS Project Tasks1. Apply leading pretreatment technologies to prepare
biomass for conversion to products
2. Characterize resulting fluid and solid streams
3. Close material and energy balances for each pretreatment process
4. Determine cellulose digestibility and liquid fraction fermentability/toxicity
5. Compare performance of pretreatment technologies on corn stover on a consistent basis
Project period: 2000-2003
One Source of Corn Stover• 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 round 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 %
Dilute Acid Pretreatment
• Mineral acid gives good hemicellulose sugar yields and high cellulose digestibility
• Sulfuric acid usual choice because of low cost• Requires downstream neutralization and conditioning
• Typical conditions: 100-200oC, 50 to 85% moisture, 0-1%
H2SO4
• Some degradation of liberated hemicellulose sugars
Mineral acid
Hemicellulose sugarssolid cellulose and lignin
BiomassReactor
Reactor Systems Employed
5 inch long reactors
Sandbaths
NREL steam gun
Solubilized Xylan Partition vs. LogMo– Dilute Sulfuric Acid
0%
20%
40%
60%
80%
100%
2.5 3 3.5 4 4.5 5 5.5Log Mo
Max
Po
ten
tial
Xyl
ose
Yie
ld,
X/X0
140C, 0.5% H2SO4
160C, 0.5% H2SO4
180C, 0.5% H2SO4
140C, 1% H2SO4
160C, 1% H2SO4
180C, 1% H2SO4
Mo = t An exp{( T - 100)/14.75} – for acid
Fate of Xylan for Dilute Acid Hydrolysis
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 200Reaction Time, min
Max
Po
ten
tial
Xyl
ose
, X
/X0
Residual Xylan
Soluble Xylooligomers
Soluble Xylose + Xylooligomers
140 oC
0.5% H2SO4
Kh=.044 min-1
Ka=.232
Ko=.116 min-1
Kd=.0016 min-1
n:mj for
a1)C(jkaC2kdt
dCjh
n
1jiih
j :sEq.' Model
n
miia a1)C-(jk
dt
da
Schematic Diagram of Flowthrough Pretreatment
Back Regulator
Sand Bath
Valve-1
P
Cold WaterR
eact
or
T1
HPLC
Pump
Wateror
DiluteAcid
TC
Valve-2
Sample
Effect of Flow Rate and Acid on Residual Xylose at 180oC
1
10
100
0 4 8 12 16Time, minutes
% o
f p
ote
nti
al x
ylo
se
hot water only,0mL/min
hot water only,1mL/min
hot water only,10mL/min
0.05wt% acid,0mL/min
0.05wt% acid,1mL/min
0.05wt%acid,10mL/min
0.1wt% acid,0mL/min
0.1wt% acid,1mL/min
0.1wt% acid,10mL/min
Solubilization of Xylan and Lignin for Water Only Hydrolysis
0102030405060708090
100
0 10 20 30 40 50 60 70 80
Lignin removal (% of the original Klason lignin)
So
lub
iliza
tio
n o
f x
yla
n (
% o
f p
ote
nti
al x
ylo
se
)
180C, 0mL/min
180C, 1mL/min
180C, 10mL/min
200C, 0mL/min
200C, 1mL/min
200C, 10mL/min
220C, 0mL/min
220C, 1mL/min
220C, 10mL/min
Controlled pH Pretreatment
• pH control through buffer capacity of liquid• No fermentation inhibitors, no wash stream• Minimize hydrolysis to monosaccharides thereby
minimizing degradation
Water
Steam Stover Heat Recovery
Saccharification
Trim Heat Plug Flow
Reactor Coil
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
0 5 10 15 20 25Pretreatment Time (min.)
So
lub
iliza
tio
n (
%)
200°C190°C180°C170°C
Solubilization of Corn Stover by Controlled pH Pretreatment
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25
Pretreatment Time (min.)
Glu
cose
Yie
ld (
%)
200 °C
190 °C
180 °C
170 °C
Cellulose Digestibility vs Hemicellulose Solubilization
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25
Pretreatment Time (min.)
Xyl
ose
/Gal
acto
se Y
ield
(%
)
200 °C
190 °C
180 °C
170 °C
Controlled pH Hot Water Pretreatment (non flow-through) improves digestibility primarily by removal of hemicellulose without degrading the monosaccharides improved porosity / enzyme accessibility
Glucose Yields Xylose Yields
Fermentation of Pretreated, Saccharified Corn Stover
0
5
10
15
20
25
30
35
0 10 20 30 40 50 60
Time (hrs.)
Co
nce
ntr
atio
n (
g/L
)
GlucoseXyloseGlycerolEthanol
Xylose Fermenting Recombinant Yeast 426A (LNH-87). Data provided by Dr. Nancy Ho.
What is AFEX/FIBEX?
• Liquid “anhydrous” ammonia treats and explodes biomass
• Ammonia is recovered and reused• Ammonia can serve as N source downstream• Batch process is AFEX; FIBEX is continuous version• Conditions: 60-110oC, moisture 20-80%, ammonia:biomass ratio 0.5-1.3 to 1.0 (dry basis)
• No fermentation inhibitors, no wash stream required, no overliming
• Only sugar oligomers formed, no detectable sugar monomers• Few visible physical effects
Reactor Explosion
AmmoniaRecovery
BiomassTreatedBiomass
LiquidAmmonia
GaseousAmmonia
Reactor Explosion
AmmoniaRecovery
BiomassTreatedBiomass
LiquidAmmonia
GaseousAmmonia
• Moderate temperatures, pH prevent/minimize sugar & protein loss
Experimental Ammonia Fiber Explosion (AFEX) System
0
10
20
30
40
50
60
70
80
90
100
0 24 48 72 96 120 144 168 192
Time (hrs)
% G
luca
n C
onve
rsio
n
110ºC
100ºC
90ºC
Untreated
Kinetics of G lucan Hydrolysis
Conditions:5 m in A FEX treatm ent168 hrs hydrolysis60 % m oisture1:1 A m m onia: B iom ass@ 15 FPU /g of glucan
Conversion of G lucan and Xylan vs.
AFEX Treatment Temperature
0
10
20
30
40
50
60
70
80
90
100 6
0ºC
70ºC
80º
C
90º
C
100
ºC
110
ºC
% G
luca
n or
Xyl
an C
onve
rsio
n
Glucose yield
Xylose yield
Conditions:5 min AFEX treatm ent168 hrs hydrolysis1:1 Ammonia: Biomass,60% moisture60 FPU/g glucan
Features of Ammonia Recycle Pretreatment (ARP)
• Aqueous ammonia is used as the pretreatment reagent: Efficient delignification Volatile nature of ammonia makes it easy to recover
• Flowthrough column reactor is used
• Value-added byproducts are obtained Low-lignin cellulose (“filler fiber” grade) Uncontaminated lignin
Composition and Digestibility for ARP Pretreatment
[mL/min]
Lignin Glucan XylanLiquid1Solid1Flow rate Digestibility2
60FPU 15FPU
Note.; 1. All data based on original feed. 2. Enzymatic hydrolysis conditions; 60 or 15 FPU/g of glucan, pH 4.8, 50C, 150 rpm, at 72h
Glucan Xylan
2.5
5.15.1 35.635.6 10.310.3
6.4 35.9 10.7
5.05.07.5 5.6 35.7 10.1
0.50.5 10.110.1
0.5 10.6
0.8 10.591.391.3 86.986.9
91.5 83.2
93.4 86.9
Untreated 17.2 36.1 21.4 - - 21.2 15.7
• Pretreatment conditions Liquid throughput: 3.3 mL of 15 wt% NH3 per g of corn
stover at 170 C Air dried corn stover is used without presoaking.
Enzymatic Hydrolysis of a Representative ARP Sample (15 wt% NH3, 170ºC)
60 FPU/g of glucan
0
20
40
60
80
100
0 24 48 72
Time [h]
Dig
es
tib
ilit
y [
%]
ARP-treatedα-CelluloseUntreated
Pretreatment conditions: 170C, 3.3 mL of 15 wt% of ammonia per g of corn stover, 2.3 MPa; Enzymatic hydrolysis conditions : 60 or 15 FPU/g cellulose, pH 4.8, 50C, 150 rpm ; α
93.4%@60FPU
15 FPU/g of glucan
0
20
40
60
80
100
0 24 48 72
Time [h]D
ige
sti
bil
ity
[%
]ARP-treatedα-CelluloseUntreated
86.9%@15FPU
Lime Pretreatment
Biomass + Lime
Gravel
Air
Typical Conditions: Temperature = 25 – 55oC Time = 1 – 2 months Lime Loading = 0.1 – 0.2 g Ca(OH)2/g biomass
Reactor System for Lime Pretreatment
Pretreatment Time (weeks)
Kla
son
Lig
nin
Con
tent
(w
t %)
0
5
10
15
20
25
0 5 10 15 20
untreated
Pretreatment Time (weeks)
Kla
son
Lig
nin
Con
tent
(w
t %)
25oC35oC45oC55oC
0
5
10
15
20
25
0 5 10 15 20
untreated
No Air Air
Effect of Air/Temperature on Lignin
Enzymatic Digestibility for Lime Treated Biomass
Cellulase Loading (FPU/g dry biomass)
3-d
Sug
ar Y
ield
(mg
equi
v. g
luco
se/g
dry
bio
mas
s)
25oC 55oC
0
100
200
300
400
500
600
700
1 10 100
0
100
200
300
400
500
600
700
1 10 100
Air
No Air
untreated
Cellulase Loading (FPU/g dry biomass)
0
100
200
300
400
500
600
700
1 10 100
0
100
200
300
400
500
600
700
1 10 100
Air
No Air
3-d
Sug
ar Y
ield
(mg
equi
v. g
luco
se/g
dry
bio
mas
s)
AFEX Process Yields and Material Balance
Hydrolysis
Enzyme (15 FPU/g of Glucan)
ResidualSolids
HydrolyzateLiquidAFEX
SystemTreatedStover
Ammonia
Stover
100.5 lb100 lb
(dry basis)36.1 lb glucan21.4 lbxylan 38.7 lb
95.9% glucan conversion, 77.6% xylan conversion (up-dated on 9/10/03)
99% mass balance closure includes:(solids + glucose + xylose + arabinose )
Wash
2 lb
98.5 lb
Solids washed out
38.5 lb glucose18.9 lb xylose (Ave. of 4 runs)
Yield Comparisons at 60 FPU/g glucan
Increasing pH
Process Xylose yields -
% of total potential*
Glucose yields –
% of total potential*
Pretreatment Enzymatic Pretreatment Enzymatic
Dilute acid
Flowthrough
Controlled pH
AFEX
ARP
Lime
* Listed as total/monomers/oligomers in each step
Yield Comparisons at 15 FPU/g glucan
Increasing pH
Process Xylose yields -
% of total potential*
Glucose yields –
% of total potential*
Pretreatment Enzymatic Pretreatment Enzymatic
Dilute acid
Flowthrough
Controlled pH
AFEX
ARP
Lime
* Listed as total/monomers/oligomers in each step
Yield Comparisons in SSF at 15 FPU/g glucan
Increasing pH
Process Xylose yields -
% of total potential*
Glucose yields –
% of total potential*
Pretreatment Enzymatic Pretreatment Enzymatic
Dilute acid
Flowthrough
Controlled pH
AFEX
ARP
Lime
* Listed as total/monomers/oligomers in each step
Some Conclusions to Date• Dilute acid and neutral pH pretreatments solubilize
mostly hemicellulose while ammonia and lime remove mostly lignin. AFEX removes neither.– Hemicellulose hydrolysis to monomers can reduce post
processing– Lignin removal can reduce cellulase use although AFEX
reduces cellulase without lignin removal• Greater hemicellulase activity would improve yields
from higher pH and controlled pH approaches• All are capital intensive for differing reasons
– Costly reactor materials and waste treatment, in some cases– Pretreatment catalyst recovery, in others
• Some advantages in operating costs– e.g., low waste generation with AFEX
Future Work• Evaluate performance differences in more depth
– Apply hydrolyzate conditioning– Ferment hydrolyzate with recombinant organisms– Evaluate effect of pretreatment approach on cellulase
effectiveness– Apply hemicellulases to improve performance– Work with Genencor as enzyme supplier– Understand effect of how pretreatment affects substrate
features and digestibility– Expand research to hardwoods– Expand team to include University of British Columbia
and University of Sherbrooke in Canada• Funded by Office of the Biomass Program of the
Department of Energy
Acknowledgments The United States Department of Agriculture
Initiative for Future Agricultural and Food Systems Program through Contract 00-52104-9663 for funding this CAFI research
The United States Department of Energy Office of the Biomass Program and the National Renewable Energy Laboratory for NREL’s participation
Our team from Dartmouth College; Auburn, Michigan State, Purdue, and Texas A&M Universities; and the National Renewable Energy Laboratory
IFAFS Project Participants
Questions?