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Characteristics of Biomass Pretreatments Studied by the CAFI
Bruce E. Dale, Richard T. Elander, Mark T. Holtzapple, Michael R. Ladisch, Yoon Y. Lee and
Charles E. Wyman
ISAF XVInternational Symposia on Alcohol Fuels
September 26-28, 2005 San Diego, CA
Biomass Refining CAFI
Brief History of Biomass Refining Consortium for Applied Fundamentals
and Innovation (CAFI)
• Pretreatment researchers working together in a coordinated, disciplined way to understand the fundamentals underlying lignocellulosic biomass pretreatment and hydrolysis
• Organized in late 1999, early 2000• CAFI recognizes that pretreatment operates as
part of a system that includes hydrolysis and fermentation—pretreatment effects on downstream processes must be better understood
Biomass Refining CAFI
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 %
Pretreatment system
Temperature, oC
Reaction time,
minutes
Chemical agent used
Percent chemical
used
Other notes
Dilute acid1 160 20 Sulfuric acid 0.49 25% solids concentration during run in batch tubes
Flowthrough2 200 24 none 0 Continuously flow just hot water at 10mL/min for 24minutes
Partial flow pretreatment2
200 24 none 0 Flow hot water at 10mL/min from 4-8 minutes, batch otherwise
Controlled pH3 190 15 none 0 16% corn residue slurry in water
AFEX4 90 5 Anhydrous ammonia
100 62.5% solids in reactor(60% moisture dry weight basis), 5 minutes at temperature
ARP5,6 170 10 ammonia 15 Flow aqueous ammonia at 5 mL/min without presoaking
Lime7 55 4 weeks lime 0.08 g CaO/g biomass
Purged with air.
Characteristics of CAFI Pretreatments
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
Mineral acid
Biomass Stage 1. Pretreatment
Stage 2.Enzymatichydrolysis
Glucoseand ligninCellulose
and lignin
Hemicellulose sugars and oligomers
Glucose and Xylose Yields in Pretreatment and Enzymatic
Hydrolysis
Co
mb
ine
d S
tag
e 1
an
d s
tag
e 2
Yie
lds
Sta
ge
2 Y
ield
s
Sta
ge
1 Y
ield
s0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Yie
ld (
% o
rig
inal
glu
co
se +
xylo
se)
GlucoseXylose
Maximum potential glucose
Maximum potential xylose
Schematic of Flowthrough Pretreatment System
Back Regulator
Sand Bath
Valve-1
P
Cold WaterR
eact
or
T1
HPLC
Pump
Wateror
DiluteAcid
TC
Valve-2
Sample
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
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
Stepwise Process Yields & Mass Balance for 15 FPU Spezyme (168 hrs)
Controlled pH Liquid Hot Water
TreatedStoverSlurry
HydrolysisCellulase Enzyme2209 FPU per lb stover (30 FPU/ml)
Water
Stover
ResidualSolids
HydrolyzateLiquid
Fermentation
62.8 lb undissolved solids37.2 lb dissolved solids620 lb water
100 lb (dry basis)36.1 lb glucan21.4 lb xylan
36.32 lb glucose19.89 lb xylose
Ethanol90.5% total glucan conversion (raw stover basis)81.8% total xylan conversion (raw stover basis)88% of theoretical ethanol yield from glucose + xylose
620 lb
22.0 lb25.2 lb
Cellobiase Enzyme 5891 IU per lb
stover (309 IU/ml)
The AFEX/FIBEX Process
• 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
AFEX Process Mass Balance
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
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)
Preliminary Mass Balance for ARP Pretreatment
Biomass
Ammonia recycling
Fermention
ARP Reactor
Soluble sugar
Ammonia
Washing100 lb (dry
basis)
G:36.1 lb X: 21.4 lb O: 7.8 lb
G: Glucan X: Xylan
O: Other sugar
Liquid
G: 0.5 lb X: 10.6 lb
Lignin12.1 lbResidual solid 19.3 lb
G: 35.6 lb X:10.8 lb
Treated stover Hydrolysis
Hydrolyzate
Glucose 34.9 lb Xylose 17.0 lb
SSF
Ethanol 23.4 lbConversion Efficiency:87% glucan + 70% xylan conversion at 15 FPU/g of gulcan3.56 gallons ethanol (90% of theoretical yield, glucan+xylan)95% mass balance closure (solids + G + X + EtOH + Others)Other sugar is excluded for Ethanol production
Others 20.8 lb
Residual solids 18.9 lb
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
Lime System
Solids
LiquidHydrolysis
EnzymeLime + air
Stover
ResidualSolids
HydrolyzateLiquid
Fermentation
43 lb carb.4 lb lignin
100 lb(dry basis)58 lb carb.19 lb lignin
Ethanol3.8 – 4.1 gal
27 lb
To date:
80 – 90% overall carbohydrate conversion
15 lb sugars15 lb lignin
55-60 lb sugars15 lb lignin
Mass Balance for Lime Pretreatment
Pretreatment Yields-Stage 1 and Overall*
Pretreatment system
Xylose yields (38% max) Glucose yields (62% max) Total sugars (100% max)
Stage 1 Total xylose Stage 1 Total glucose Stage 1 Combined
Dilute acid1 32.1/31.2 35.3/34.4 3.9 57.1 36.0/35.1
92.4/91.5
Flowthrough2 36.3/1.7 36.9/2.2 4.5/4.4 59.7/59.6 40.8/6.1 96.6/61.8
Partial flow pretreatment2
31.5/2.8 34.1/5.2 4.3/4.2 55.5/55.4 35.8/7.0 89.6/60.6
Controlled pH3 21.8/0.9 30.8/9.9 3.5/0.2 56.4/53.1 25.3/1.1 87.2/63.0
AFEX4 nil 34.6/29.3 0 59.8 nil 94.4/89.1
ARP5,6 17.8/0 33.3/15.5 0 56.1 17.8/0 89.4/71.6
Lime7 9.2/0.3 28.8/19.9 1.0/0.3 58.0/57.3 10.2/0.6 86.8/77.2
* Soluble oligomers plus monomers/monomers only
Pretreatment system
Temperature, oC
Reaction time,
minutes
Chemical agent used
Percent chemical
used
Other notes
Dilute acid1 160 20 Sulfuric acid 0.49 25% solids concentration during run in batch tubes
Flowthrough2 200 24 none 0 Continuously flow just hot water at 10mL/min for 24minutes
Partial flow pretreatment2
200 24 none 0 Flow hot water at 10mL/min from 4-8 minutes, batch otherwise
Controlled pH3 190 15 none 0 16% corn residue slurry in water
AFEX4 90 5 Anhydrous ammonia
100 62.5% solids in reactor(60% moisture dry weight basis), 5 minutes at temperature
ARP5,6 170 10 ammonia 15 Flow aqueous ammonia at 5 mL/min without presoaking
Lime7 55 4 weeks lime 0.08 g CaO/g biomass
Purged with air.
Characteristics of CAFI Pretreatments
Acknowledgments US Department of Agriculture Initiative for Future
Agricultural and Food Systems Program, Contract 00-52104-9663
US Department of Energy Office of the Biomass Program, Contract DE-FG36-04GO14017
Natural Resources Canada Genencor International Our team from Dartmouth College; Auburn, Michigan
State, Purdue, and Texas A&M Universities; the University of British Columbia; and the National Renewable Energy Laboratory
First group publication: Bioresource Technology vol. 96 #18 pgs. 1959-2032 December 2005
Biomass Refining CAFI
IFAFS Project Institutions
Purdue University
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
Cellulose Digestibility of Pretreated Corn Stover
190C – 15 minute
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100 120 140 160 180
Hydrolysis Time (hrs)
Glu
co
se
Yie
ld (
%)
60 FPU/g15 FPU/g7.5 FPU/g
Error bars represent 95% confidence intervals