Read Coordinated Development of Leading Biomass Pretreatment Technologies text version

Pretreatment: A Key to Low Cost Cellulosic Ethanol Production

Bin Yang Center for Bioproducts and Bioenergy 2710 University Drive-BESL Richland, WA 99354 Tel: 509-372-7640

WSU ChE 481/581 & UI BAE 504

Pretreatment

· Reduce biomass recalcitrance to attack by enzymes · High sugar yields are vital

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Disruption of Cellulosic Biomass by Pretreatment

Cellulose Lignin

Pretreatment

Hemicellulose

Mosier et al. (2007)

Central Role and Pervasive Impact of Pretreatment for Biological Processing

Enzyme production

Biomass production

Harvesting, storage, size reduction

Pretreatment

Enzymatic hydrolysis

Sugar fermentation

Hydrolyzate conditioning

Hydrolyzate fermentation

Ethanol recovery

Residue utilization

Waste treatment

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Pretreatment Classes

· Physical · Biological · Chemical · Physico-chemical

Physical Pretreatments

· Comminution

­ ­ ­ ­ ­ ­ ­ ­ ­ Hammer mills Knife mills Extruders Disc refiners Planer Ball mills Roll mills Dry mills Colloid mills

· Radiation

­ ­ ­ ­ Gamma rays Microwaves Electron beam Lasers

· Plasma

Biological Pretreatment

·

­ ­ ­

Microbial

White Rot Red Rot Brown Rot

·

­

Enzymatic

Peroxidases ­ Laccases ­ Manganases ­ Quinonereducing enzymes

Chemical Pretreatment I

· Oxidizing

­ ­ ­ ­ ­ ­ ­ ­ ­ ­ ­ Peracetic acid Ozone Hydrogen peroxide Chlorine Sodium hypochlorite Chlorine dioxide Sulfuric (55-75%) Phosphoric (79-86%) Nitric (60-88%) Hydrochloric (37-42%) Perchloric (59-61%)

· Cellulose solvents

­ Inorganic salts · Lithium chloride · Stannic chloride · Calcium bromide ­ Amine salts · Cadoxen (cadmium chloride + ethylenediamine) · Cooxen (cobalt hydroxide + ethylenediamine)

· Concentrated acid

· Ionic Liquids

· [C4min]Cl

Chemical Pretreatment II

· Delignification

­ Organosolv

· · · · · Ethanol Butanol Methanol Acetone acetic acid

· Alkaline

­ ­ ­ ­ ­ ­ ­ Sodium hydroxide Calcium hydroxide Kraft pulping Soda pulping Amines Lime Ammonia

· · · · · Gaseous Liquid Supercritical Aqueous Percolation

­ Triethylene glycol

· Cellulose modification

­ Carboxymethyl cellulose ­ Viscose ­ Mercerized

Chemical Pretreatment III

· Acids

­ Sulfite pulping ­ Dilute sulfuric or nitric acid ­ Autohydrolysis with natural acids ­ Liquid hot water ­ Gaseous

· · · · HCl SO2 NO2 CO2

· Neutral pH

Physico-Chemical Pretreatments

· Steam Explosion

­ ­ ­ ­ ­ ­ Steam only SO2 H2SO4 CO2 Lime others

· Ammonia Fiber Expansion

Cost Constraints for Pretreatment

· High yields are critical to distribute both operating and capital costs · Low operating costs essential to providing margin for return on capital

­ Low chemical, energy, and labor costs ­ Must be lower for overall process than for cash cows making conventional products

· Low capital costs essential to minimize exposure

­ Low cost containment, e.g., small size, low pressure, low temperature ­ Few steps, e.g., simple processes

Corn Stover

From BioMass AgriProducts, Harlan IA and Kramer Farm, Wray, CO

Component

Composition wt % Glucan 36.1 Xylan 21.4 Arabinan 3.5 Mannan 1.8 Galactan 2.5 Lignin 29.1 Protein nd Acetyl 3.6 Ash 1.1 Uronic Acids nd Extractives 3.6 Total maximum ethanol potential

Ethanol yield gal/ton 62.1 37.7 6.2 3.1 4.3

113.3

Poplar

Feedstock: USDA-supplied hybrid poplar (Alexandria, MN)

Debarked, chipped, and milled to pass ¼ inch round screen

Component

Composition wt % Glucan 43.8 Xylan 14.9 Arabinan 0.6 Mannan 3.9 Galactan 1.0 Lignin 29.1 Protein nd Acetyl 3.6 Ash 1.1 Uronic Acids nd Extractives 3.6 Total maximum ethanol potential

Ethanol yield gal/ton 75.4 26.1 1.1 6.8 1.8

111.1

Switchgrass

· Ceres, Inc supplied lowland variety switchgrass (harvested in 2006 from Ardmore, OK)

Component Glucan Xylan Arabinan Sucrose Acetyl Lignin Protein Ash Extractives

Composition (wt %) 35.0 21.8 3.5 1.5 2.8 21.4 1.4 3.3 8.1

Ammonia Recycle Percolation

· High degree of delignification by aqueous ammonia · Lignin removal improves enzyme efficiency and microbial efficiency · Ammonia is easily recycled · Uncontaminated lignin is coproduct · Can be combined with other pretreatment processes for near complete fractionation of biomass into hemicellulose, cellulose, and lignin · Developing a continuous co-current reactor with ammonia recycle

ARP Laboratory Reactor

Vent

Temp. monitoring system (DAS)

PG C.W.

N2 Gas

3-way v/v

PG : Press. Gauge TG : Temp. Gauge C.W.: Cooling Water

Aqueous Ammonia

PG

TG TG

Water

Pump

#1

#2

Oven

(Preheating Coil and Reactor)

Holding Tank

#1 : For ARP #2 : For Water or Acid

ARP Process Diagram

Ammonia recycling

Ammonia

Make-up water

Biomass

Reactor

Liquid

Evaporator

Steam water

Solid

Steam

Crystallizer Washing

Lignin & Other sugar

Steam

To Fermentor (SSF)

Soluble sugar Washing

Lignin (Fuel)

What is AFEX/FIBEX?

Liquid Ammonia

Ammonia Recovery

Gaseous Ammonia Treated Biomass

Biomass

Reactor

Explosion

· · · ·

Liquid "anhydrous" ammonia treats & "explodes" biomass, then ammonia is recovered & reused Batch process is AFEX, FIBEX is continuous version Conditions: 60-100 C, sample moisture 20-150%, ammonia to biomass ratio 0.5-1.3 to 1.0 (dry basis) Treatment time approx. 5 minutes

Ammonia Fiber Explosion (AFEX or FIBEX)

· Continuous or batch process with addition of liquid ammonia & ammonia recovery · No solids removed from the biomass: not a "wet" process­ material is left "dry" and can be batch fed to hydrolysis/fermentation at very high solids levels · Temperatures ambient to 80 C, wide range of moisture contents tolerated, ammonia levels between 0.3 ­ 1.0 kg/kg dry biomass · High yields of total carbohydrates, hemicellulose as oligomers, cellulose as glucose · Effective on many materials but must be "tuned" for each new raw material

SCHEMATIC OF THE FIBEX PROCESS

Liquid Ammonia Liquid Ammonia Tank Ammonia Metering Pump Ammonia Presized Biomass AFEX Reactor Water Metering Pump Water Tank Flash Tank Liquid Ammonia Liquid Compressor Liquid Ammonia

Precondenser Condenser Distillation Column

Heater Blower Dryer

Water

Reboiler Water (<500 ppm NH3)

Pretreated Biomass

Ammonia Fiber Explosion (AFEX) System

Neutral pH Pretreatment

· Pretreatment carried at pH between 4 and 7 · Conditions selected so that hydrolysis during pretreatment is minimized · Temperatures ranging from 180 to 200 C · Runs carried out at 180 C with 200 g corn stover/L of DI water · First step is to maximize loading (will be less than 400 g stover/L).

Pretreatment Modeling

C K C* k2 k2, k3, >> k1 k1 Gn k3 G k4

Degradation

Principles of Liquid Water Pretreatment

1. Controlled pH 2. High Temperature 3. Liquid Water (high pressure)

­ Water acts as acid

· kw = 10-14 to 6 · 10-12 from 20 C to 230 C.

pH of Liquid Water vs Temperature 7.5

7

6.5

pH

pH 5.66 at 190oC

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Minimum pH 5.62 at 230oC

5.5

5 0 50 100 150 200 250 300 350 Temperature (oC)

"Snake-coil" Plug Flow Pretreatment Reactor

Williams Bioenergy Pekin, IL

Why Lime?

·Alkaline treatments less damaging than acidic treatments ·Lime is the least expensive alkali ·Sodium hydroxide$0.68/kg ·Ammonia $0.25/kg ·Lime $0.06/kg ·Safe to handle ·No pressure vessel required (usually) ·Compatible with oxidants ·Available world wide

Schematic Reactor System for Lime Pretreatment

Reactor R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 Water Jacket

Manifold (Water)

Temperature sensor

Drain Water In

Temperature Controller

AM Pump

oC

T

Heat Element

Reactor System for Lime Pretreatment

Storage + Pretreatment + Fermentation

Tarp Cover

Air

Biomass + Lime + Calcium Carbonate

Gravel

Conclusions

· Lime alone is effective · Lime + air removes more lignin · Lime + air consumes more lime · Mixed acid (e.g., rumen) more effective than enzymes · Combine storage/pretreatment/fermentation · Low capital · High product concentrations (marine inoculum) · High conversion

Dilute Acid Pretreatment

· Similar to uncatalyzed pretreatment except with dilute acid · Temperatures of about 120 to 190oC · Times of about 10 minutes · Uses about 0.5 to 1.5% acid · Removes hemicellulose with about 80 to 90% yields · Produces digestible cellulose · Approach often favored for near term use · Using externally heated tubes by staged temperature sand baths and steam gun

Dilute Acid High Solids Pretreatment NREL

· On-going corn stover pretreatment work in support of Biofuels Program "Near Term" Project · Data will be included in USDA IFAFS comparative analysis · Sunds pilot-scale (1 ton/day) reactor

­ ~20% solids loading (higher on woody feedstocks)

· Sunds engineering-scale (200 kg/day) horizontal reactor

­ >25% solids loading with corn sover

· Bench scale steam gun (4 L capacity)

­ ~40% solids loading ­ Pre-impregnated corn stover

High Solids Pretreatment Reactors at NREL

4 L Batch Steam Digester Pilot Scale Sunds Reactor

Engineering Scale Sunds Horizontal Reactor

Flowthrough Reactor System at Dartmouth College

Flowthrough Dilute Acid Pretreatment NREL

· Initially developed in continuously flowing percolation and "shrinking bed" systems · Recently modified to high solids pretreatment followed by hot separation and washing of pretreated solids · Prevent re-precipitation/re-association of solubilized lignin upon pretreated solids · Lower liquid volumes and steam requirement than continuously flowing system · More rapid enzymatic hydrolysis and higher cellulose conversions demonstrated on hardwood · Concept beginning to be evaluated on corn stover · Commercial-scale separation/washing equipment option identified (Pneumapress pressure belt filter)

Flowthrough Pretreatment Systems at NREL

Percolation/Shrinking Bed Reactors Bench Scale Hot Wash System Pilot Scale Pneumapress

Shrinking Bed Concept

Pneumapress Filter Corporation, Richmond, CA

Acid Catalyzed Hemicellulose Hydrolysis

Xylan Oligomers Lower oligomers Xylose Furfural Char, Tar

Increasing severity

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First Order Hydrolysis Kinetics

· Hemicellulose (fast and slow hydrolysis fractions) rf,s = dHf,s/dt = - kHf,s AnHf,s Hf,s · Oligomers ro = dO/dt = + kHf AnH f Hf + kHs AnH s Hs - kO AnO O · Xylose monomers rx = dX/dt = + kO AnO O - kX AnX X · Furfural and other degradation products rF = dF/dt = + kX AnX X - kFAnFF All models assume first order homogeneous or pseudo homogeneous reactions

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Yield Profiles for 170° C, 1.5% 100% Acid 90%

80%

Yield, percent

Fast Xylan Left Slow Xylan Left Total Xylan Left Oligomers Xylose Monomers Monomers+Oligo mers

70% 60% 50% 40% 30% 20% 10% 0% 0 2 4 6 8 10

Overall Degraded

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Time, minutes

Fate of Xylan vs. Time during Dilute Acid Hydrolysis

1 0.9 0.8

n dC j Model Eq.' s : = 2k h Ci a - k h (j - 1)C j a dt i = j +1 n da = -k a (j - 1)Ci a dt i =m

for j = m : n

140 oC 0.5% H2SO4

Max Potential Xylose, X/X0

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 20 40 60 80 100 120 Reaction Time, min 140 160 180 200

Kh=.044 min-1 Ka=.232 Kd=.0016 min-1 Ko=.116 min-1

Residual Xylan Soluble Xylooligomers Soluble Xylose + Xylooligomers

Cellulose Hydrolysis

Hydrolytic methods and temperature effect Cellulose

High T Low T Low T

Dilute Acid

Concentrated Acid

Enzyme

Glucose

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43

Cellulose Hydrolysis

Effect of severity factor on hydrolysis

Glucan

Oligomers

Lower oligomers

Glucose

HMF

LA

Char, Tar, Humins Increasing severity

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44

Effect of Flow Rate on Xylan Removal from Corn Stover and Oat Spelt Xylan 100

Xylan/2mL/min 90 Xylan/25mL/min Xylan/0mL/min Corn stover/25mL/min 60 50 40 30 20 10 0 0

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Percent of potential total xylose, %

80 70

Corn stover/2mL/min Corn stover/0mL/min

2

4

6

8

10

12

Time, minutes

Yield of Xylan Oligomers and Total Xylan Recovery in Hydrolysate

Feedstock Flow rate mL/min Total xylan recovery1 Yield, % DP1 to 30 Long Ratio of chain shorter chain 2 oligomer to longer chain oligomer 10.0 2.8 27.9 0.7 64.2 0.1 43.0 0.7 91.8 0.003 90.8 0.004

Corn stover

Oat spelt xylan

0 (Batch) 2 25 0 (Batch) 2 25

38.1 48.2 73.3 73.1 92.1 91.1

28.1 20.3 9.1 30.1 0.3 0.4

1. 2.

Total xylan recovery = yield of xylose in hydrolysate+ yield of oligomers in hydrolysate (xylose equivalent); Yield of long chain oligomer (DP>30) = total xylan recovery ­ yield of DP130.

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Effect of Xylan Removal on Digestibility of Corn Stover for Batch and Flowthrough Reactors

100 90 80

Enzymatic digestibility,%

70 60 50 40 30 20 10 0 20 40

Uncatalyzed batch tube (160-220C, 5% solid loading) Catalyzed batch tube (160-220C, 5% solid loading, 0.1% acid) Uncatalyzed flowthrough (160-220C, flow rate of 2ml/min) Uncatalyzed flowthrough (160-220C, flow rate of 7.5ml/min) Uncatalyzed flowthrough (160-220C, flow rate of 25ml/min) Catalyzed flowthrough (160-220C, flow rate of 2ml/min) Catalyzed flowthrough (160-220C, flow rate of 7.5ml/min) Catalyzed flowthrough (160-220C, flow rate of 25ml/min)

60

80

100

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Xylan removal,%

Effect of Lignin Removal on Digestibility of Corn Stover for Batch and Flowthrough Reactors

100 90 80

Enzymatic digestibility,%

70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90

Uncatalyzed batch tube (160-220C, 5% solid loading) Catalyzed batch tube (160-220C, 5% solid loading, 0.1% acid) Uncatalyzed flowthrough (160-220C, flow rate of 2ml/min) Uncatalyzed flowthrough (160-220C, flow rate of 7.5ml/min) Uncatalyzed flowthrough (160-220C, flow rate of 25ml/min) Catalyzed flowthrough (160-220C, flow rate of 2ml/min) Catalyzed flowthrough (160-220C, flow rate of 7.5ml/min) Catalyzed flowthrough (160-220C, flow rate of 25ml/min)

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Lignin removal,%

· Historically divergent opinions on role of lignin versus hemicellulose in access of enzymes to cellulose in pretreated biomass · Our results suggest that lignin must be disrupted to achieve high enzymatic hydrolysis

­ Hemicellulose removal serves as a marker of lignin disruption but is not the cause of better digestion ­ Even better results if remove lignin ­ Lignin-xylan oligomers and their solubility could have a large effect on the rates and yields of lignocellulosic biomass pretreatment

Role of Lignin in Pretreatment

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Key Features of CAFI Leading Pretreatments for Corn Stover

Acid

Pretreatment system Dilute acid Flowthrough Temperature, oC 160 200 Reaction time, minutes 20 24 Chemical agent used Sulfuric acid none Percent chemical used 0.49 0 Other notes

25% solids concentration during run in batch tubes Continuously flow just hot water at 10mL/min for 24minutes

Partial flow pretreatment Controlled pH AFEX

200

24

none

0

Flow hot water at 10mL/min from 4-8 minutes, batch otherwise

190 90

15 5

none Anhydrous ammonia ammonia lime

0 100

16% corn residue slurry in water

62.5% solids in reactor (60% moisture dry weight basis), 5 minutes at temperature Flow aqueous ammonia at 5 mL/min without presoaking Purged with air.

ARP Lime

170 55

10 4 weeks

15 0.08 g CaO/g biomass

Base

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Overall Yields for Corn Stover at 15 FPU/g Glucan

Xylose yields* Pretreatment Total system Stage 1 Stage 2 xylose Maximum 37.7 37.7 37.7 62.3 62.3 62.3 100.0 100.0 100.0 1 Stage Stage 2 glucose Total Stage 1 Stage 2 total Combined Glucose yields* Total sugars*

Increasing pH

possible Dilute acid SO2 Steam 14.7/1.0 explosion Flowthrough Controlled 21.8/0.9 pH AFEX ARP Lime 17.8/0 9.2/0.3 34.6/29.3 15.5 19.6 34.6/29.3 33.3/15.5 28.8/19.9 1.0/0.3 59.8 56.1 57.0 59.8 56.1 58.0/57.3 17.8/0 10.2/0.6 94.4/89.1 71.6 76.6 94.4/89.1 89.4/71.6 86.8/77.2 9.0 30.8/9.9 3.5/0.2 52.9 56.4/53.1 25.3/1.1 61.9 87.2/63.0 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 20.0 34.7/21.0 2.5/0.8 56.7 59.2/57.5 17.2/1.8 76.7 93.9/78.5 32.1/31.2 3.2 35.3/34.4 3.9 53.2 57.1 36.0/35.1 56.4 92.4/91.5

*Cumulative soluble sugars as total/monomers. Single number = just monomers.

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Sugar Yields for CAFI Standard Poplar at 15 FPU/g Glucan

Xylose yields Pretreatment Total system Stage 1 Stage 2 xylose Maximum 25.7 possible SO2 Steam 19.2/14.0 explosion Dilute acid 16.1 (Sunds) Controlled 21.2/1.0 pH AFEX AFEX with 76.9/55. cellulase + xylanase ARP 9.6/0.0 8.2/8.0 17.7/8.0 0.4/0.0 36.3 74.4/72. Lime 1.1/0.0 20.1/17.1 21.2/17.1 0.2/0.0 5 74.6/72.5 1.3/0.0 94.5/89.6 95.8/89.6 36.6/36.3 10.0/0.0 44.5/44.3 54.5/44.3 0.0 17.5/13.0 17.5/13.0 0.0 0 76.9/55.0 0.0 94.3/68.0 94.3/68.0 0.0 13.4 13.4 0.0 39.4 39.4 0.0 52.8 52.8 8.8 30.0/9.8 1.4/0.1 42.3 43.7/42.4 22.6/1.1 51.1 73.7/52.2 2.4 18.5 17.7 46.6 64.3 33.8 49.0 82.8 2.4 21.6/16.4 2.3 72.0 74.3 21.6/16.3 74.4 95.9/90.7 25.7 25.7 74.3 74.3 74.3 100 100 100 Stage 1 Stage 2 glucose Total Stage 1 Stage 2 total Combined Glucose yields Total sugar monomers

*Cumulative soluble sugars as total/monomers. Single number = just monomers.

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Increasing pH

Projected Costs Virtually the Same with Oligomer Utilization (Black Bars) for Corn Stover

1.75

MESP, $/gal EtOH

1.50

1.25

1.00 Dilute Acid Hot Water w/o Oligomer Credit AFEX ARP w/ Oligomer Credit Lime

· Need to reduce cost from the operation units:

­ ­ ­ ­ Energy use Costs of chemicals Containment costs Size reduction requirements

Opportunities to Reduce Pretreatment Cost

­ Prefermentation conditioning

· Achieve high yields for multiple crops, sites, ages, harvest times · While increasing yields · And limiting inhibitors to bioprocessing · Advanced pretreatment processes will pay big dividends

· Key: understand pretreatment mechanisms and how to improve yields 54

Process Modeling

Thermodynamics Chemistry Process Analogies Design Methods

Pretreatment Researcher

Pretreatment Model

Aspen Plus

Bioethanol Plant Model

2001 NREL Design Case 2000 Metric Ton (dry)/Day Stover

Block Flow

Enzymes CO2 Water Stover

Feed Handling

Pretreatment

Hydrolysis + Fermentation

Recovery

Syrup + Solids

EtOH

Chemicals

Water

Boiler + Generator

Steam Power

Major Process Assumptions

· Pretreatment

­ Estimated Performance (Yield, Solids Loading, etc.) ­ Conceptual Process Configuration

· Reactor · Recovery Systems

­ Minimal Conditioning Required ­ Sterilization Required for Low Temperature Pretreatments

· Other Areas

­ ­ ­ ­ ­ Simultaneous Saccharification and Fermentation (SSF) 15 FPU/gram Cellulose $0.15 per gal EtOH Hemicellulase Activity Glucose and Xylose are Converted to EtOH Excess Power is Sold to Grid @ $0.04 per kWh

Economic Modeling

Capital Costs

Fixed - Direct Purchased Equipment Installation - Indirect - Contingency - Start-up Working

Operating Costs

Variable - Stover Enzymes Other Fixed - Labor Maintenance Insurance Depreciation

Revenues

Ethanol Sales Electricity Sales

Discounted Cash Flow

2.5 yr Construction, 0.5 yr Start-up 20 yr Operation 100% Equity, No Subsidy Rational EtOH Pricing Rather Than Market Pricing 10% Real After Tax Discount Rate

Performance Measures

Total Fixed Capital Per Annual Gallon of Capacity Minimum Ethanol Selling Price (MESP) Plant Level Cash Costs

Fixed Capital

Capital Cost and Yield Comparison

$/gal EtOH

MESP and Cash Cost

Proof Year: 4th Year of Operation

1.75

1.50

1.25

1.00

MESP

0.75

0.50

Cash Cost

Plant Level

0.25

0.00 2001 NREL Design Acid Cocurrent Auto Cocurrent Neutral pH Hot Water ARP FIBEX Corn Dry Mill

Net Stover

Other Variable

Fixed w/o Depreciation

Depreciation

Income Tax

Return on Capital

Closing Thoughts

· Biology provides a powerful platform for low cost fuels and chemicals from biomass

­ Can benefit both crop production and conversion systems

· The resistance of one biological system (cellulosic biomass) to the other (biological conversion) requires a pretreatment interface · Advanced pretreatment systems are critical to enhancing yields and lowering costs · Not all pretreatments are equally effective on all feedstocks · Focus on 2 biologies - plants and biological conversion without integrating their interface ­ pretreatment ­ will not significantly lower costs

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Information

Coordinated Development of Leading Biomass Pretreatment Technologies

62 pages

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