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 products

2. Characterize resulting fluid and solid streams

3. Close material and energy balances for each pretreatment process

4. Determine cellulose digestibility and liquid fraction fermentability/toxicity

5. Compare performance of pretreatment technologies on corn stover on a consistent basis

Project 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, Genencor

Don Johnson, GPC (Retired)

Dale Monceaux, Katzen Engineers

John Nghiem, MBI

Rene Shunk, National Corn Growers Association

Joel Cherry, Novozymes

Leo 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 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

Mineral acid

Hemicellulose sugarssolid cellulose and lignin

BiomassReactor

Reactor Systems Employed

5 inch long reactors

Sandbaths

NREL steam gun

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

Po

ten

tial

Xyl

ose

Yie

ld,

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

Po

ten

tial

Xyl

ose

, X

/X0

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

dt

da

Schematic Diagram of Flowthrough Pretreatment

Back Regulator

Sand Bath

Valve-1

P

Cold WaterR

eact

or

T1

HPLC

Pump

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 p

ote

nti

al x

ylo

se

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

0.003640.00390

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

(m

m^2

/min

)Initial Mass Transfer Coefficient kd for 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 80

Lignin removal (% of the original Klason lignin)

So

lub

iliza

tio

n o

f x

yla

n (

% o

f p

ote

nti

al x

ylo

se

)

180C, 0mL/min

180C, 1mL/min

180C, 10mL/min

200C, 0mL/min

200C, 1mL/min

200C, 10mL/min

220C, 0mL/min

220C, 1mL/min

220C, 10mL/min

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

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

0 5 10 15 20 25Pretreatment Time (min.)

So

lub

iliza

tio

n (

%)

200°C190°C180°C170°C

Solubilization of Corn Stover by Controlled pH Pretreatment

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25

Pretreatment Time (min.)

Glu

cose

Yie

ld (

%)

200 °C

190 °C

180 °C

170 °C

Cellulose Digestibility vs Hemicellulose Solubilization

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25

Pretreatment Time (min.)

Xyl

ose

/Gal

acto

se Y

ield

(%

)

200 °C

190 °C

180 °C

170 °C

Controlled pH Hot Water Pretreatment (non flow-through) improves digestibility primarily by removal of hemicellulose without degrading the monosaccharides improved porosity / enzyme accessibility

Glucose Yields Xylose Yields

Fermentation of Pretreated, Saccharified Corn Stover

0

5

10

15

20

25

30

35

0 10 20 30 40 50 60

Time (hrs.)

Co

nce

ntr

atio

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 96 120 144 168 192

Time (hrs)

% G

luca

n C

onve

rsio

n

110ºC

100ºC

90ºC

Untreated

Kinetics of G lucan Hydrolysis

Conditions:5 m in A FEX treatm ent168 hrs hydrolysis60 % m oisture1:1 A m m onia: B iom ass@ 15 FPU /g of glucan

Conversion of G lucan 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 yield

Xylose yield

Conditions:5 min AFEX treatm ent168 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 delignification Volatile 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 15FPU

Note.; 1. All data based on original feed. 2. Enzymatic hydrolysis conditions; 60 or 15 FPU/g of glucan, pH 4.8, 50C, 150 rpm, at 72h

Glucan Xylan

2.5

5.15.1 35.635.6 10.310.3

6.4 35.9 10.7

5.05.07.5 5.6 35.7 10.1

0.50.5 10.110.1

0.5 10.6

0.8 10.591.391.3 86.986.9

91.5 83.2

93.4 86.9

Untreated 17.2 36.1 21.4 - - 21.2 15.7

• Pretreatment conditions Liquid throughput: 3.3 mL of 15 wt% NH3 per g of corn

stover at 170 C Air 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

es

tib

ilit

y [

%]

ARP-treatedα-CelluloseUntreated

Pretreatment conditions: 170C, 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, 50C, 150 rpm ; α

93.4%@60FPU

15 FPU/g of glucan

0

20

40

60

80

100

0 24 48 72

Time [h]D

ige

sti

bil

ity

[%

]ARP-treatedα-CelluloseUntreated

86.9%@15FPU

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

Reactor System for Lime Pretreatment

Pretreatment Time (weeks)

Kla

son

Lig

nin

Con

tent

(w

t %)

0

5

10

15

20

25

0 5 10 15 20

untreated

Pretreatment Time (weeks)

Kla

son

Lig

nin

Con

tent

(w

t %)

25oC35oC45oC55oC

0

5

10

15

20

25

0 5 10 15 20

untreated

No Air Air

Effect of Air/Temperature on Lignin

Enzymatic Digestibility for Lime Treated Biomass

Cellulase Loading (FPU/g dry biomass)

3-d

Sug

ar Y

ield

(mg

equi

v. g

luco

se/g

dry

bio

mas

s)

25oC 55oC

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

Sug

ar Y

ield

(mg

equi

v. g

luco

se/g

dry

bio

mas

s)

Hydrolysis

Enzyme

ResidualSolids

HydrolyzateLiquidAFEX

SystemTreatedStover

Ammonia

Stover

100.5 lb100 lb(dry basis)

21.4 lb xylan 3.5 lb arabinan 1.8 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 - Direct Purchased Equipment Installation - Indirect - Contingency - Start-up

Working

Revenues

Ethanol SalesElectricity Sales

Operating Costs

Variable - Stover Enzymes Other

Fixed - Labor Maintenance Insurance Depreciation

Discounted Cash Flow

2.5 yr Construction, 0.5 yr Start-up 20 yr Operation100% Equity, No Subsidy

Rational EtOH Pricing Rather Than Market Pricing10% Real After Tax Discount Rate

Performance Measures

Total 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 dry mtons/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

Acknowledgments The United States Department of Agriculture

Initiative for Future Agricultural and Food Systems Program through Contract 00-52104-9663 for funding this CAFI research

The United States Department of Energy Office of the Biomass Program and the National Renewable Energy Laboratory for NREL’s participation

Our team from Dartmouth College; Auburn, Michigan State, Purdue, and Texas A&M Universities; and the National Renewable Energy Laboratory

IFAFS Project Participants

Questions?