1. Initial Comparative Process Economics of Leading Biomass Pretreatment Technologies
Richard T. Elander, National Renewable Energy Laboratory
Charles E. Wyman, Dartmouth College
Bruce E. Dale, Michigan State University
Mark Holtzapple, Texas A&M University
Michael R. Ladisch, Purdue University
Y.Y. Lee, Auburn University
Tim Eggeman, Neoterics International
The International Symposia on Alcohol Fuels and Other Renewables XV
San Diego, CA
September 28, 2005
Biomass Refining CAFI

2. Pretreatment in a Biomass Conversion Process Context
Biomass Refining CAFI

3. Cellulosic Biomass Pretreatment Needs
High cellulose accessibility to enzymes
High sugar yields from hemicellulose
Low capital cost – low pressure, inexpensive materials of construction
Low energy cost
Low degradation
Low cost and/or recoverable chemicals
A large number of pretreatment technologies have been studied, but only a few show promise
Biomass Refining CAFI

4. Project Background: CAFI
Biomass Refining Consortium for Applied Fundamentals and Innovation organized in late 1999
Included top researchers in biomass hydrolysis from Auburn, Dartmouth, Michigan State, Purdue, NREL, Texas A&M, UBC, Univ. Sherbrooke
Mission:
Develop information and a fundamental understanding of biomass hydrolysis that will facilitate commercialization,
Accelerate the development of next generation technologies that dramatically reduce the cost of sugars from cellulosic biomass
Train future engineers, scientists, and managers
Biomass Refining CAFI

5. CAFI Approach Developing data on leading pretreatments using:
Common feedstocks
Shared enzymes
Identical analytical methods
The same material and energy balance methods
The same costing methods
Goal is to provide information that helps industry select technologies for their applications
Also seek to understand mechanisms that influence performance and differentiate pretreatments
Provide technology base to facilitate commercial use
Identify promising paths to advance pretreatment technologies
Biomass Refining CAFI

6. CAFI 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
Completed in 2004
Biomass Refining CAFI

7. Non-structural Sugars
CAFI USDA Project 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
Component
Composition (wt %)
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

8. Hydrolysis Stages Cellulase enzyme Stage 2 Stage 1 Residual solids:
Pretreatment
Stage 2
Enzymatic
hydrolysis
Residual solids:
cellulose,
hemicellulose,
lignin
Biomass
Solids: cellulose,
hemicellulose,
lignin
Chemicals
Dissolved sugars,
oligomers
Dissolved sugars,
oligomers, lignin
Stage 3
Sugar
fermentation
Biomass Refining CAFI

9. Dilute Acid Pretreatment
Stage 1.
Pretreatment
Stage 2.
Enzymatic
hydrolysis
Glucose
and lignin
Biomass
Cellulose
and lignin
Mineral
acid
Hemicellulose
sugars and oligomers
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: oC, 50 to 85% moisture, 0-1% H2SO4
Some degradation of liberated hemicellulose sugars

10. Schematic of Flowthrough Pretreatment System
Sample

11. Controlled pH Liquid Hot Water Pretreatment
pH control through buffer capacity of liquid
No fermentation inhibitors, no wash stream
Minimize hydrolysis to monosaccharides thereby minimizing degradation

12. The AFEX/FIBEX Process
Reactor
Explosion
Ammonia
Recovery
Biomass
Treated
Liquid
Gaseous •
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: oC, moisture 20-80%, ammonia:biomass ratio
to 1.0 (dry basis)
• Moderate temperatures, pH prevent/minimize sugar & protein loss
• No fermentation inhibitors, no wash stream required, no overliming
• Only sugar oligomers formed, no detectable sugar monomers
• Few visible physical effects

13. Ammonia Recycle Percolation (ARP)
Vent
Temp. monitoring system (DAS) PG
N2 Gas
C.W.
Aqueous Ammonia PG TG
Water TG
Pump
Oven
(Preheating Coil and Reactor)
Holding Tank
PG : Press. Gauge
TG : Temp. Gauge
C.W.: Cooling Water

14. Lime Pretreatment Typical Conditions: Temperature = 25 – 55oC
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

15. Process Modeling in CAFI 1 Project
Thermodynamics
Process
Analogies
Chemistry
Pretreatment Model
Aspen Plus
Design Methods
CAFI
Researcher
Bioethanol Plant Model
2001 NREL Design Case
2000 Metric Ton (dry)/Day Stover
Stover Cost: $35/ton
Enzyme Cost: ~$0.15/gal ethanol
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16. General Process Flow Diagram
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17. Hydrolysis Stages Cellulase enzyme Stage 2 Stage 1 Residual solids:
Pretreatment
Stage 2
Enzymatic
hydrolysis
Residual solids:
cellulose,
hemicellulose,
lignin
Biomass
Solids: cellulose,
hemicellulose,
lignin
Chemicals
Dissolved sugars,
oligomers
Dissolved sugars,
oligomers, lignin
Stage 3
Sugar
fermentation
Biomass Refining CAFI

18. Pretreatment Yield Comparisons at 15 FPU/g Glucan
System
Xylose yields*
Glucose yields*
Total sugars*
Stage 1
Stage 2
Total
xylose
glucose
Combined
total
Maximum possible
37.7
62.3
100.0
Dilute acid
32.1/31.2
3.2
35.3
3.9
53.2
57.1
36.0/35.1
56.4
92.4/91.5
Flowthrough
36.3/1.7
0.6/0.5
36.9/2.2
4.5/4.4
55.2
59.7/59.6
40.8/6.1
55.8/55.7
96.6/61.8
Controlled pH
21.8/0.9
9.0
30.8
3.5/0.2
52.9
25.3/1.1
61.9
87.2
AFEX
34.6/29.3
59.8
94.4/89.1
ARP
17.8/0
15.5
33.3/15.5
56.1
71.6
89.4/71.6
Lime
9.2/0.3
19.6
28.8/19.9
1.0/0.3
57.0
58.0/57.3
10.2/0.6
76.6
86.8/77.2
Increasing pH
*Cumulative soluble sugars as total/monomers. Single number = just monomers.
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19. Pretreatment Yields at 15 FPU/g Glucan
Maximum possible
Dilute acid
Flowthrough
Controlled pH
ARP
AFEX
Lime

20. Pretreatment Yields at 15 FPU/g Glucan

21. Pretreatment Yield Comparisons at 15 FPU/g Glucan—Alternative Basis
System
Xylose Yields,
% of Theoretical*
Glucose Yields,
After Pretreatment
After Enzymatic Hydrolysis
Dilute Acid
90.2 / 89.7  
95.6 / 95.1  
 8.0 / 7.5
85.1 / 84.6  
Controlled pH
50.8 / 7.3
81.8 / 38.3
4.5 / 2.0
90.5 / 88.0
AFEX
0 / 0
92.7 / 77.6
95.9
ARP
47.2 / 0
88.3 / 41.1
1.4
90.1
Lime
24.3 / 0.8
75.3 / 51.8
1.6 / 0.5
92.4 / 91.3
No Pretreatment
8.5
15.7
Ideal Pretreatment -
100
*Cumulative soluble sugars as (oligomers+monomers) / monomers. Single number = just monomers.
Biomass Refining CAFI

22. Capital Cost Estimates
Pretreatment
System
Pretreatment Direct Fixed Capital ($MM)
Pretreatment Breakdown,
(% Reactor/% Other)
Total Fixed Capital ($MM)
Ethanol Production (MM gal/yr)
Total Fixed Capital ($/gal Annual Capacity)
Dilute Acid
25.0
64/36
208.6
56.1
3.72
Hot Water
4.5
100/0
200.9
44.0
4.57
AFEX
25.7
26/74
211.5
56.8
ARP
28.3
25/75
210.9
46.3
4.56
Lime
22.3
19/81
163.6
48.9
3.35
No Pretreatment -
200.3
9.0
22.26
Ideal Pretreatment
162.5
64.7
2.51
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23. Minimum Ethanol Selling Price (MESP)
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24. Effect of Oligomer Conversion
Biomass Refining CAFI

25. Solids Loading and Ethanol Concentration—Energy Impacts
Pretreatment
System
Pretreatment Effluent (wt % Liquid)
Fermentation Titer (wt % Ethanol in Liquid)
Process Steam Usage
Electrical Power
HP Steam (kg/hr)
LP Steam (kg/hr)
VLP Steam (kg/hr)
Total Generated (Mwe)
Process Needs (Mwe)
Dilute Acid
66.8
5.07
14,663
83,377
16,426
42.1
14.0
Hot Water
83.7
3.09
34,281
146,580
48,374
42.2
13.5
AFEX
61.2
4.62
154,980
31,932
35.6
17.4
ARP
74.5
5.06
112,330
56,972
11,469
38.0
11.9
Lime
80.0
3.16
160,540
42,265
14.4
No Pretreatment
0.92
59,697
51,477
88.8
13.9
Ideal Pretreatment
5.86
71,230
20,160
45.2
32.4
Biomass Refining CAFI

26. Key Findings from USDA CAFI Project
Initial set of comparative pretreatment data has been developed
1st generation economic models developed
Significant differences in pretreatment and enzymatic hydrolysis yields observed
Especially, when and to what extent xylan is converted
Pretreatment capital costs more similar than anticipated
High costs for catalyst recovery or regeneration
Findings to be published in a special issue of Bioresource Technology (December, 2005)
Data gaps remain (addressed in current CAFI DOE Project)
Optimal enzyme types for each pretreatment
Hydrolyzate fermentability at relevant sugar concentrations
Rigor of economic models (esp. pretreatment area capital costs)
Biomass Refining CAFI

27. DOE Office of the Biomass Program Project: April 2004 Start
Funded by DOE Office of the Biomass Program for $1.88 million through a joint competitive solicitation with USDA
Using identical analytical methods and feedstock sources to develop comparative data for corn stover and poplar
Determining more in-depth information on:
Enzymatic hydrolysis of cellulose and hemicellulose in solids
Conditioning and fermentation of pretreatment hydrolyzate liquids
Predictive models
Added University of British Columbia to team through funding from Natural Resources Canada to
Capitalize on their expertise with xylanases for better hemicellulose utilization
Evaluate sulfur dioxide pretreatment along with those previously examined: dilute acid, controlled pH, AFEX, ARP, lime
Augmented by Genencor Int’l to supply enzymes
Biomass Refining CAFI

28. Objectives of CAFI DOE Project
Cellulosic biomass will be pretreated by leading technologies to improve cellulose accessibility to enzymes.
Conditioning methods will be developed as needed to maximize fermentation yields by a recombinant yeast, the cause of inhibition will be determined, and fermentations will be modeled.
Cellulose and hemicellulose in pretreated biomass will be enzymatically hydrolyzed, as appropriate, and models will be developed to understand the relationship between pretreated biomass features, advanced enzyme characteristics, and enzymatic digestion results.
Capital and operating costs will be estimated for each integrated pretreatment, hydrolysis, and fermentation system and used to direct research.
The proposal team will work with an Industrial and Agricultural Advisory Board and others to evaluate these findings; identify opportunities to utilize the pretreatment technologies; define opportunities to improve coupled pretreatment, fermentation, and enzymatic hydrolysis; and disseminate the results widely.
Biomass Refining CAFI

29. Acknowledgements
US Department of Agriculture Initiative for Future Agricultural and Food Systems Program, Contract
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
Biomass Refining CAFI