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?