1 comparison of selected results for application of leading pretreatment technologies to corn stover...
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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, 2003Biomass Refining CAFI
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Outline of Talk• Pretreatment technologies studied
• Research approach
• Material balances
• Performance comparison
• Summary of trends
• Future plans
Biomass Refining CAFI
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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
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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
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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 %
Biomass Refining CAFI
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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: 120-200oC, 50 to 85% moisture, 0-1%
H2SO4
• Some degradation of liberated hemicellulose sugars Biomass Refining CAFI
Mineral acid
Biomass Stage 1. Pretreatment
Stage 2.Enzymatichydrolysis
Glucoseand ligninCellulose
and lignin
Hemicellulose sugars and oligomers
7Biomass Refining CAFI
Combined Stage 1 and Stage 2 Yields 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
8
Effect of Minerals and Temperature on Pretreatment pH
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
9
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
2Xkaea
10
Schematic of Flowthrough and SFS System
Back Regulator
Sand Bath
Valve-1
P
Cold WaterR
eact
or
T1
HPLC
Pump
Wateror
DiluteAcid
TC
Valve-2
Sample
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Total Xylose Fate for Batch, FT, and SFS Runs with Water at 200oC
0102030405060708090
100
%, o
f or
igin
al t
otal
xyl
ose
residual xylose in solids
total xylose in hydrolyzate
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Concentration of Xylose in Hydrolyzate for Pretreatment with Compressed Hot
Water at 200oC
02468
10121416
batch
, 20 m
inutes
batch
, 24 m
inutes
FT, 24 m
inutes
SFS1, 24
min
utes
SFS2, 24
min
utes
Con
cent
rati
on, g
/L monomer
oligomers
Note: 60, 50, and 40mL of wash water were used for batch, SFS1, and SFS2, respectively.
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Cellulose Digestibility for Batch, FT, and SFS Pretreatment ( 15 FPU/ gram cellulose, 72 h )
7880828486889092949698
%,
of
theo
ry y
ield
Water, 200oC 0.05wt% acid, 190oC
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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
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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 of Pretreated Corn Stover
6.42 FPU/g glucan, cellobiase 94.4 IU/g glucan, 48 hrs., 50°C
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Initial Rates of Hydrolysis at 50oC for Different Pretreatment Temperatures
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 8 16 24 32 40 48 56
Time (hrs)
Glu
can
Hyd
roly
zed
fro
m C
ellu
los
e (g
)
190-15200-5180-20170-20
Per gram glucan; 6.9 FPU cellulase, 94 IU cellobiase
190 C
200
180
170
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What is AFEX/FIBEX?
Reactor Explosion
AmmoniaRecovery
BiomassTreatedBiomass
LiquidAmmonia
GaseousAmmonia
Reactor Explosion
AmmoniaRecovery
BiomassTreatedBiomass
LiquidAmmonia
GaseousAmmonia
• Liquid “anhydrous” ammonia treats, explodes biomass, 99% of ammonia is recovered, remainder serves as N source downstream?
• No fermentation inhibitors formed, no wash stream, no overliming
• Conditions: 60-110oC (pressure up to 250 psig), sample moisture 20-60%, ammonia:biomass ratio 0.5-1.3:1.0 (dry basis), enzyme loadings of 15 FPU/gm glucan give theoretical yields of glucose and ~80% of theoretical for xylose
• Few visible effects of pretreatment, material is left dry and can be fed at very high solids loadings, stable for long periods of time
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0
10
20
30
40
50
60
70
80
90
100
60ºC 70ºC 80ºC 90ºC 100ºC Untreated
Glu
ca
n o
r X
yla
n C
on
ve
rsio
n (
%) Glucose yield
Xylose yield
Conditions:60% Moisture, 5 minutes Treatment1:1 Ammonia:Biomass168hr of Hydrolysis@15FPU
Conversion of Glucan and Xylan vs.AFEX Treatment Temperature
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Some Distinctive Features of AFEXNOT MUCH CHANGE
IN APPEARANCE- DRY PROCESS
Stover hydrolysis- 15 FPU @ zero hrs.
NOT MUCH EXTRACTED FROM TREATED STOVER
HPLC at 168 hours
Glucose, xylose, arabinose,Not much else
CLEAN SUGAR STREAMS FOR FERMENTATION
AFEX treated Untreated
21
Fed Batch SSF of AFEX Treated and Untreated Corn Stover (15 IU/g glucan)
AFEX treated stover in SSF24% solids loading
Untreated stover in SSF 24% solids loading
Flows very easily
Doesn’t flow worth a dang
Dark appearance is deceptive- caused by autoclaving and media
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N2 Gas
PG TG
TG
Vent
Oven
(Preheating Coil and Reactor)
Holding TankPumpPG : Press. Gauge
TG : Temp. Gauge
C.W.: Cooling Water
Aq
ueo
us A
mm
on
ia
Wa
ter
PG
C.W.
ARP Experimental Set-upTemp.
monitoring system (DAS)
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Enzymatic Hydrolysis of Representative ARP-Treated Sample
60 FPU/g of glucan
0
20
40
60
80
100
0 24 48 72
Time [h]
Dig
es
tib
ility
[%
]
ARP-treatedα-CelluloseUntreated
Pretreatment conditions: 170C, 3.3 mL of 15 wt% of ammonia per g of corn stover
Enzymatic hydrolysis conditions : 60 or 15 FPU/g glucan, pH 4.8, 50C, 150 rpm
95.3%@60FPU
15 FPU/g of glucan
0
20
40
60
80
100
0 24 48 72
Time [h]D
ige
sti
bil
ity
[%
]ARP-treateda-CelluloseUntreated
90.1%@15FPU
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ARP Summary• Representative ARP Process Conditions
–Liquid throughput: 3.3 mL of 15 wt.% NH3 per g of corn stover
–Dry feed is used without presoaking.
–Temperature:170 C, Residence Time: 10 minutes
• ARP treatment of corn stover results:
–63-70% delignification
–High retention of glucan
–Partial solubilization of hemicellulose
• ARP raises the digestibility of corn stover to above 95% with 60 FPU/g of glucan and above 90% with 15 FPU/g of glucan.
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Lime Pretreatment
Biomass + Lime
Gravel
Air
Typical Conditions: Temperature = 25 – 55oC Time = 1 – 2 months Lime Loading = 0.1 g Ca(OH)2/g biomass
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Reactor System for Lime Pretreatment
27
0
5
10
15
20
25
0 5 10 15 20
untreated
0
5
10
15
20
25
0 5 10 15 20
untreated
Pretreatment Time (weeks) Pretreatment Time (weeks)
25oC35oC45oC55oC
No Air Air
Effect of Air/Temperature on Lignin
Kla
son
lign
in c
onte
nt
g K
laso
n li
gnin
g dr
y bi
omas
s tr
eate
d×
100
recommendedK
laso
n li
gnin
con
tent
g K
laso
n li
gnin
g dr
y bi
omas
s tr
eate
d×
100
28
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)
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Mass Balance Approach: AFEX Example
Hydrolysis
Enzyme (15 FPU/g of Glucan)
ResidualSolids
HydrolyzateLiquidAFEX
SystemTreatedStover
Ammonia
Stover
101.0 lb100 lb
(dry basis)36.1 lb glucan21.4 lbxylan 39.2 lb
95.9% glucan conversion to glucose, 77.6% xylan conversion to xylose
99% mass balance closure includes:(solids + glucose + xylose + arabinose )
Wash
2 lb
99.0 lb
Solids washed out
38.5 lb glucose18.9 lb xylose (Ave. of 4 runs)
Very few solubles from pretreatment—about 2% of inlet stover
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Yield Comparisons at 60 FPU/g glucan
Increasing pH 93.4/90.94.5/2.081.3/37.850.8/7.3Controlled pH
99.5/94.45.2/5.197.8/6.296.2/4.6Flowthrough
95.31.492.3/45.147.2/0ARP
97.1/96.01.6/0.577.8/54.324.3/0.8Lime
99.40/080.40/0AFEX**
95.8/95.38.0/7.5 98.8/98.390.2/89.7 Dilute acid
EnzymaticPretreatmentEnzymaticPretreatment
Glucose yields –
% of total potential*
Xylose yields -
% of total potential*
Process
*Cumulative soluble sugars as total/monomers. Single number = just monomers. ** Dry process- no free water in pretreatment
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Yield Comparisons at 15 FPU/g glucan
Increasing pH 90.5/88.04.5/2.081.8/38.350.8/7.3Controlled pH
96.8/91.75.2/5.197.5/5.996.2/4.6Flowthrough
90.11.488.3/41.147.2/0ARP
92.4/91.31.6/0.575.3/51.824.3/0.8Lime
95.90/077.60/0AFEX**
85.1/84.68.0/7.5 95.6/95.190.2/89.7 Dilute acid
EnzymaticPretreatmentEnzymaticPretreatment
Glucose yields –
% of total potential*
Xylose yields -
% of total potential*
Process
* Cumulative soluble sugars as total/monomers. Single number = just monomers.** Dry process-no free water in pretreatment
32
Pretreatment Water:Solids
Ratio
% Solids
Solubilized
Dilute acid 1.5 36
Flowthrough ~37 52
Controlled pH 6.2 37.7
AFEX 0.6 2.0
ARP 3.3 40.0
Lime 10.0 23.0
Water Loadings and Stover Solids Made Soluble by Pretreatments
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Trends• Dilute acid and neutral pH pretreatments solubilize mostly
hemicellulose while ammonia and lime remove mostly lignin. AFEX removes neither and flowthrough removes both.
• All these pretreatments result in high glucose yields via enzymatic hydrolysis with somewhat better results for higher pH and flowthrough methods, possibly due to effect on lignin (cellulase adsorption and interference)– Lignin removal (ARP, lime, flowthrough) or modification (AFEX)
• Xylose remaining in the solids is solubilized during enzymatic hydrolysis for all methods– Enhanced hemicellulase activity could improve yields for all
methods and could have particularly important benefits as pH increases and for flowthrough approach
• It is important to consider the sugar release pattern and solids concentrations for each pretreatment in the selection of process, enzymes, and fermentative organisms to maximize yields
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Future Work• Evaluate performance differences in more depth
– Apply hydrolyzate conditioning– Ferment hydrolyzate with recombinant organism– Determine differences in pretreatment effects on
cellulase effectiveness– Add hemicellulases to improve performance– Work with Genencor as enzyme supplier– Understand how pretreatment affects substrate features
and their effect on digestibility– Broaden scope to hardwoods– Expand team to include University of British Columbia
and University of Sherbrooke in Canada• To be funded by Office of the Biomass Program
of the Department of Energy
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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
Biomass Refining CAFI
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IFAFS Project ParticipantsBiomass Refining CAFI
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Questions?
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