Comparative Data from Application of Leading Pretreatment ... · of Leading Pretreatment...
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Comparative Data from 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
25th Symposium on Biotechnology for Fuels and ChemicalsBreckenridge, Colorado
May 7, 2003
Outline of Talk
• Overview of Consortium• USDA IFAFS project overview• Participants and Advisory Board• Pretreatment technologies• Selected results and preliminary material
balances to date• Preliminary economic comparisons• Future work
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
• IFAFS opportunity arose in March 2000, and a subset of CAFI pursued and won an award
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 products2. Characterize resulting fluid and solid streams3. Close material and energy balances for each
pretreatment process 4. Determine cellulose digestibility and liquid fraction
fermentability/toxicity5. Compare performance of pretreatment technologies on
corn stover on a consistent basisProject period: 2000-2003
USDA IFAFS Project Advisory BoardServe as extension agents for technology transfer
Provide feedback on approach and resultsMeet with team every 6 months
Mat Peabody, Applied CarboChemicals
Greg Luli, BC InternationalParis Tsobanakis, CargillRobert Wooley, Cargill DowJames Hettenhaus, CEAKevin Gray, DiversaPaul Roessler, DowSusan Hennessey, DuPont
Michael Knauf, GenencorDon Johnson, GPC (Retired)Dale Monceaux, Katzen
EngineersJohn Nghiem, MBIRene Shunk, National Corn
Growers AssociationJoel Cherry, NovozymesLeo Petrus, Shell
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 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
Hemicellulose sugarssolid cellulose and lignin
Biomass Reactor
• Mineral acid gives good hemicellulose sugar yields and high cellulose digestability
• 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
Reactor Systems EmployedNREL steam gun5 inch long reactors
Sandbaths
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
Pot
entia
l Xyl
ose
Yiel
d, 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
Pot
entia
l Xyl
ose,
X/X
0
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
dtda
Schematic Diagram of Flowthrough Pretreatment
Back Regulator
Sand Bath
Valve-1
P
Cold WaterR
eact
or
T1
HPLCPump
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 pot
entia
l xyl
ose
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
0.00250 0.00252 0.00259
0.00364 0.00390
0.00579265
0.0106
0.000
0.002
0.004
0.006
0.008
0.010
0.012
20% solids 10% solids 5% solids Batch 25%sol0.1%acid
1ml/min 1000 rpm 10ml/min
Batch Batch Batch FT Parr FT
Kd
(mm
^2/m
in)
Initial Mass Transfer Coefficient kdfor Water Only Hydrolysis Changes
with Reactor Type (180oC)
k1 = 0.1272 min-1
without acid
Solubilization of Xylan and Lignin for Water Only Hydrolysis
0102030405060708090
100
0 10 20 30 40 50 60 70 80Lignin removal (% of the original Klason lignin)
Solu
biliz
atio
n of
xyl
an (%
of p
oten
tial x
ylos
e) 180C, 0mL/min180C, 1mL/min180C, 10mL/min200C, 0mL/min200C, 1mL/min200C, 10mL/min220C, 0mL/min220C, 1mL/min220C, 10mL/min
Controlled pH Pretreatment
Water
Steam Stover Heat Recovery
Saccharification
Trim Heat Plug Flow Reactor Coil
• pH control through buffer capacity of liquid• No fermentation inhibitors, no wash stream• Minimize hydrolysis to monosaccharides thereby
minimizing degradation
0%5%
10%15%20%25%30%35%40%45%50%
0 5 10 15 20 25Pretreatment Time (min.)
Solu
biliz
atio
n (%
)
200°C190°C180°C170°C
Solubilization of Corn Stover by Controlled pH Pretreatment
Cellulose Digestibility vs Hemicellulose Solubilization
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25Pretreatment Time (min.)
Glu
cose
Yie
ld (%
)
200 °C190 °C180 °C170 °C
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25Pretreatment Time (min.)
Xylo
se/G
alac
tose
Yie
ld (%
)
200 °C190 °C180 °C170 °C
Glucose Yields Xylose Yields
Controlled pH Hot Water Pretreatment (non flow-through) improves digestibility primarily by removal of hemicellulose without degrading the monosaccharides → improved porosity / enzyme accessibility
Fermentation of Pretreated, SaccharifiedCorn Stover
0
5
10
15
20
25
30
35
0 10 20 30 40 50 60
Time (hrs.)
Con
cent
ratio
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 192Time (hrs)
% G
luca
n C
onve
rsio
n110ºC100ºC90ºCUntreated
Kinetics of Glucan Hydrolysis
Conditions:5 min AFEX treatment168 hrs hydrolysis60 % moisture1:1 Ammonia: Biomass@ 15 FPU/g of glucan
Conversion of Glucan 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 yieldXylose yield
Conditions:5 min AFEX treatment168 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 delignificationVolatile 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 15FPUGlucan Xylan
Note.; 1. All data based on original feed. 2. Enzymatic hydrolysis conditions; 60 or 15 FPU/g of glucan, pH 4.8, 50°C, 150 rpm, at 72h
2.5Untreated 17.2 36.1 21.4 - - 21.2 15.7
6.4 35.9 10.7 0.5 10.6 91.5 83.25.05.0 5.15.1 35.635.6 10.310.37.5 5.6 35.7 10.1
0.50.5 10.110.10.8 10.5
91.391.3 86.986.993.4 86.9
• Pretreatment conditionsLiquid throughput: 3.3 mL of 15 wt% NH3 per g of cornstover at 170 °CAir 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
estib
ility
[%]
ARP-treatedα-CelluloseUntreated
93.4%@60FPU
15 FPU/g of glucan
0
20
40
60
80
100
0 24 48 72
Time [h]D
iges
tibili
ty [%
]ARP-treatedα-CelluloseUntreated
86.9%@15FPU
Pretreatment conditions: 170°C, 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, 50°C, 150 rpm ; α
Lime Pretreatment
Biomass + Lime
Gravel
Air
Typical Conditions:Temperature = 25 – 55oCTime = 1 – 2 monthsLime Loading = 0.1 – 0.2 g Ca(OH)2/g biomass
Reactor System for Lime Pretreatment
Effect of Air/Temperature on LigninNo Air Air
Pretreatment Time (weeks)
Kla
son
Lign
in C
onte
nt (w
t %)
0
5
10
15
20
25
0 5 10 15 20
untreated
Pretreatment Time (weeks)
Kla
son
Lign
in C
onte
nt (w
t %)
0
5
10
15
20
25
0 5 10 15 20
untreated
25oC35oC45oC55oC
Enzymatic Digestibility for Lime Treated Biomass
55oC25oC
(mg
equi
v. g
luco
se/g
dry
bio
mas
s)
(mg
equi
v. g
luco
se/g
dry
bio
mas
s)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
Suga
r Yie
ld
3-d
Suga
r Yie
ld
Cellulase Loading (FPU/g dry biomass)
Hydrolysis
Enzyme
ResidualSolids
HydrolyzateLiquidAFEX
SystemTreatedStover
Ammonia
Stover
100.5 lb100 lb(dry basis)
21.4 lb xylan3.5 lb arabinan1.8 lb mannan
38.3 lb glucose (G)16.6 lb xylose (X)1.11 lb arabinose(A)1.92 lb mannose (M)38.7 lb
95% glucan to glucose, 68% xylan to xylose(93% overall glucan + xylan solubilization)97% overall mass balance closure (All solids + G + X + A + M)3.76 gallons ethanol (90% yield of glucose plus xylose)
Wash
2 lb
98.5 lb
Removed Solids
36.1 lb glucan
Preliminary Mass Balances:Example for AFEX Pretreatment
15 IU/g glucan
Preliminary Yield ComparisonsProcess Xylose yields Glucose yields
Dilute acid ~85% increasing to ~95% w cellulase @ 60 FPU/g glucan
~90 @ 15 FPU/g SSF1 to 95% w cellulase @ 60 FPU/g glucan
Flowthrough ~97-98% in pretreatment ~93-98% @ 15 FPU/g glucan cellulase
Controlled pH ~62% after pretreatment and enzyme
~73% @ ~30 FPU/g glucan
AFEX ~68% after both steps ~95% @ 7.5 FPU/g glucan
ARP ~70% from both steps at 15 FPU/g glucan
~87% at 15 FPU/g glucan~95% at 60 FPU/g glucan
Lime ~77-93% overall as cellulase raised from ~2 to 20 FPU/g glucan
Increasing pH
1 – NREL data on Sunds
NREL CAFI Project Contributions
• Properly store and provide feedstock • Provide/monitor cellulase preparation• Train students on analytical procedures, etc.• Perform process engineering evaluations• Conduct periodic comparative SSF
evaluations• Supported by US DOE Office of the
Biomass Program
Economic Modeling MethodologyCapital Costs
Fixed - DirectPurchased EquipmentInstallation
- Indirect- Contingency- Start-up
Working
RevenuesEthanol Sales
Electricity Sales
Operating CostsVariable - Stover
EnzymesOther
Fixed - LaborMaintenanceInsuranceDepreciation
Discounted Cash Flow2.5 yr Construction, 0.5 yr Start-up 20 yr Operation
100% Equity, No SubsidyRational EtOH Pricing Rather Than Market Pricing
10% Real After Tax Discount Rate
Performance MeasuresTotal Fixed Capital Per Annual Gallon of CapacityMinimum Ethanol Selling Price (MESP)—$/gallon
Plant Level Cash Costs
Based on NRELeconomic modelfor ethanol from cellulosics
-Pricing per 2001NREL design-2,000 drymtons/day stover
MESP and Cash Cost
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2001 NRELDesign
AcidCocurrent
AutoCocurrent
Neutral pHHot Water
ARP AFEX Lime Corn DryMill
Net Stover Other Variable Fixed w/o Depreciation Depreciation Income Tax Return on Capital
CashCostPlantLevel
MESP
Proof Year: 4th Year of Operation$/gal EtOH
Caveats About Economic Projections
• Current economic models…Not final!– Pretreatment assumptions: Modeling currently based on
many assumptions—will be updated with more data at conclusion of project
– Assumptions in other areas: All cases have similar assumptions….thus similar performance—will be updated with additional data
• No distinctions for level of development
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 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• Complete pretreatments with each technology• Complete data on enzymatic digestibility
– Gather max yield data at 15 and 60 FPU/g glucan– Determine yields in SSF configuration
• Characterize hydrolyzate toxicity to organisms• Characterize pretreated materials to improve
picture of key differences and similarities, e.g., acetyl content, crystallinity
• Update process economic models with more developed pretreatment and enzymatic digestibility performance data
AcknowledgmentsThe United States Department of Agriculture Initiative for Future Agricultural and Food Systems Program through Contract 00-52104-9663 for funding this CAFI researchThe United States Department of Energy Office of the Biomass Program and the National Renewable Energy Laboratory for NREL’s participationOur team from Dartmouth College; Auburn, Michigan State, Purdue, and Texas A&M Universities; and the National Renewable Energy Laboratory
IFAFS Project Participants
Questions?