1 Comparison of Selected Results for Application of Leading Pretreatment Technologies to Corn Stover...

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Comparison of Selected Results for 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

2003 AIChE Annual MeetingSan Francisco, California

November 20, 2003Biomass Refining CAFI

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Outline of Talk• Pretreatment technologies studied

• Research approach

• Material balances

• Performance comparison

• Summary of trends

• Future plans

Biomass Refining CAFI

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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


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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


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One Source of 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

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 %


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Dilute Acid Pretreatment

• 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: 120-200oC, 50 to 85% moisture, 0-1%

H2SO4

• Some degradation of liberated hemicellulose sugars Biomass Refining CAFI

Mineral acid

Biomass Stage 1. Pretreatment

Stage 2.Enzymatichydrolysis

Glucoseand ligninCellulose

and lignin

Hemicellulose sugars and oligomers

7Biomass Refining CAFI

Combined Stage 1 and Stage 2 Yields for 0.49% H2SO4 Addition in Batch Tubes

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.00 1.50 2.00 2.50 3.00 3.50 4.00

Log CS

Yie

ld,

(X+

G)/

(Xo

+ G

o)

180 C Combined Yield160 C Combined Yield140 C Combined Yield15 FPU/g glucan loading

Batch TubeCS=t*[aH+]

0.5*exp((T-100)/14.75)

60 FPU/g glucan enzyme loading

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Effect of Minerals and Temperature on Pretreatment pH


0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

20 40 60 80 100 120 140 160 180

Temperature, oC

pH

0.98% H2SO4

0.45% H2SO4

0.22% H2SO4

25% solids20 mg/g Biomass Neutralization

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Modified Depolymerization Model 140 oC, 0.49% Added Acid


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 200Pretreatment Time, min

Yie

ld, X

/X0

Residual Xylan

Soluble Xylooligomers

Soluble Xylose + Xylooligomers

Kh=.516 min-1

Ka=7.9

Ko=.094 min-1

Kf=.0016 min-1

Assumptions:

Cutoff DP = 8Original DP = 100

n:mj for

1)Ca(jkCa2kdt

dCjh

n

1jiih

j

mj1 for

j)C-(1kC2kCa2kdt

dCjo

1-m

iio

n

iih

1

2m

1 for

jm

CkC2kCa2kdt

dC1d

1-m

iio

n

iih

1

2Xkaea

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Schematic of Flowthrough and SFS System

Back Regulator

Sand Bath

Valve-1

P

Cold WaterR

eact

or

T1

HPLC

Pump

Wateror

DiluteAcid

TC

Valve-2

Sample


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Total Xylose Fate for Batch, FT, and SFS Runs with Water at 200oC

0102030405060708090

100

%, o

f or

igin

al t

otal

xyl

ose

residual xylose in solids

total xylose in hydrolyzate


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Concentration of Xylose in Hydrolyzate for Pretreatment with Compressed Hot

Water at 200oC

02468

10121416

batch

, 20 m

inutes

batch

, 24 m

inutes

FT, 24 m

inutes

SFS1, 24

min

utes

SFS2, 24

min

utes

Con

cent

rati

on, g

/L monomer

oligomers

Note: 60, 50, and 40mL of wash water were used for batch, SFS1, and SFS2, respectively.


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Cellulose Digestibility for Batch, FT, and SFS Pretreatment ( 15 FPU/ gram cellulose, 72 h )

7880828486889092949698

%,

of

theo

ry y

ield

Water, 200oC 0.05wt% acid, 190oC


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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


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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 of Pretreated Corn Stover

6.42 FPU/g glucan, cellobiase 94.4 IU/g glucan, 48 hrs., 50°C


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Initial Rates of Hydrolysis at 50oC for Different Pretreatment Temperatures

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 8 16 24 32 40 48 56

Time (hrs)

Glu

can

Hyd

roly

zed

fro

m C

ellu

los

e (g

)

190-15200-5180-20170-20

Per gram glucan; 6.9 FPU cellulase, 94 IU cellobiase

190 C

200

180

170


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What is AFEX/FIBEX?

Reactor Explosion

AmmoniaRecovery

BiomassTreatedBiomass

LiquidAmmonia

GaseousAmmonia

Reactor Explosion

AmmoniaRecovery

BiomassTreatedBiomass

LiquidAmmonia

GaseousAmmonia

• Liquid “anhydrous” ammonia treats, explodes biomass, 99% of ammonia is recovered, remainder serves as N source downstream?

• No fermentation inhibitors formed, no wash stream, no overliming

• Conditions: 60-110oC (pressure up to 250 psig), sample moisture 20-60%, ammonia:biomass ratio 0.5-1.3:1.0 (dry basis), enzyme loadings of 15 FPU/gm glucan give theoretical yields of glucose and ~80% of theoretical for xylose

• Few visible effects of pretreatment, material is left dry and can be fed at very high solids loadings, stable for long periods of time


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0

10

20

30

40

50

60

70

80

90

100

60ºC 70ºC 80ºC 90ºC 100ºC Untreated

Glu

ca

n o

r X

yla

n C

on

ve

rsio

n (

%) Glucose yield

Xylose yield

Conditions:60% Moisture, 5 minutes Treatment1:1 Ammonia:Biomass168hr of Hydrolysis@15FPU

Conversion of Glucan and Xylan vs.AFEX Treatment Temperature


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Some Distinctive Features of AFEXNOT MUCH CHANGE

IN APPEARANCE- DRY PROCESS

Stover hydrolysis- 15 FPU @ zero hrs.

NOT MUCH EXTRACTED FROM TREATED STOVER

HPLC at 168 hours

Glucose, xylose, arabinose,Not much else

CLEAN SUGAR STREAMS FOR FERMENTATION

AFEX treated Untreated

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Fed Batch SSF of AFEX Treated and Untreated Corn Stover (15 IU/g glucan)

AFEX treated stover in SSF24% solids loading

Untreated stover in SSF 24% solids loading

Flows very easily

Doesn’t flow worth a dang

Dark appearance is deceptive- caused by autoclaving and media


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N2 Gas

PG TG

TG

Vent

Oven

(Preheating Coil and Reactor)

Holding TankPumpPG : Press. Gauge

TG : Temp. Gauge

C.W.: Cooling Water

Aq

ueo

us A

mm

on

ia

Wa

ter

PG

C.W.

ARP Experimental Set-upTemp.

monitoring system (DAS)


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Enzymatic Hydrolysis of Representative ARP-Treated Sample

60 FPU/g of glucan

0

20

40

60

80

100

0 24 48 72

Time [h]

Dig

es

tib

ility

[%

]

ARP-treatedα-CelluloseUntreated

Pretreatment conditions: 170C, 3.3 mL of 15 wt% of ammonia per g of corn stover

Enzymatic hydrolysis conditions : 60 or 15 FPU/g glucan, pH 4.8, 50C, 150 rpm

95.3%@60FPU

15 FPU/g of glucan

0

20

40

60

80

100

0 24 48 72

Time [h]D

ige

sti

bil

ity

[%

]ARP-treateda-CelluloseUntreated

90.1%@15FPU


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ARP Summary• Representative ARP Process Conditions

–Liquid throughput: 3.3 mL of 15 wt.% NH3 per g of corn stover

–Dry feed is used without presoaking.

–Temperature:170 C, Residence Time: 10 minutes

• ARP treatment of corn stover results:

–63-70% delignification

–High retention of glucan

–Partial solubilization of hemicellulose

• ARP raises the digestibility of corn stover to above 95% with 60 FPU/g of glucan and above 90% with 15 FPU/g of glucan.


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Lime Pretreatment

Biomass + Lime

Gravel

Air

Typical Conditions: Temperature = 25 – 55oC Time = 1 – 2 months Lime Loading = 0.1 g Ca(OH)2/g biomass

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Reactor System for Lime Pretreatment

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0

5

10

15

20

25

0 5 10 15 20

untreated

0

5

10

15

20

25

0 5 10 15 20

untreated

Pretreatment Time (weeks) Pretreatment Time (weeks)

25oC35oC45oC55oC

No Air Air

Effect of Air/Temperature on Lignin

Kla

son

lign

in c

onte

nt

g K

laso

n li

gnin

g dr

y bi

omas

s tr

eate

d×

100

recommendedK

laso

n li

gnin

con

tent

g K

laso

n li

gnin

g dr

y bi

omas

s tr

eate

d×

100

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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)


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Mass Balance Approach: AFEX Example

Hydrolysis

Enzyme (15 FPU/g of Glucan)

ResidualSolids

HydrolyzateLiquidAFEX

SystemTreatedStover

Ammonia

Stover

101.0 lb100 lb

(dry basis)36.1 lb glucan21.4 lbxylan 39.2 lb

95.9% glucan conversion to glucose, 77.6% xylan conversion to xylose

99% mass balance closure includes:(solids + glucose + xylose + arabinose )

Wash

2 lb

99.0 lb

Solids washed out

38.5 lb glucose18.9 lb xylose (Ave. of 4 runs)

Very few solubles from pretreatment—about 2% of inlet stover

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Yield Comparisons at 60 FPU/g glucan

Increasing pH 93.4/90.94.5/2.081.3/37.850.8/7.3Controlled pH

99.5/94.45.2/5.197.8/6.296.2/4.6Flowthrough

95.31.492.3/45.147.2/0ARP

97.1/96.01.6/0.577.8/54.324.3/0.8Lime

99.40/080.40/0AFEX**

95.8/95.38.0/7.5 98.8/98.390.2/89.7 Dilute acid

EnzymaticPretreatmentEnzymaticPretreatment

Glucose yields –

% of total potential*

Xylose yields -


Process

*Cumulative soluble sugars as total/monomers. Single number = just monomers. ** Dry process- no free water in pretreatment

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Yield Comparisons at 15 FPU/g glucan

Increasing pH 90.5/88.04.5/2.081.8/38.350.8/7.3Controlled pH

96.8/91.75.2/5.197.5/5.996.2/4.6Flowthrough

90.11.488.3/41.147.2/0ARP

92.4/91.31.6/0.575.3/51.824.3/0.8Lime

95.90/077.60/0AFEX**

85.1/84.68.0/7.5 95.6/95.190.2/89.7 Dilute acid

EnzymaticPretreatmentEnzymaticPretreatment

Glucose yields –


Xylose yields -


Process

* Cumulative soluble sugars as total/monomers. Single number = just monomers.** Dry process-no free water in pretreatment

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Pretreatment Water:Solids

Ratio

% Solids

Solubilized

Dilute acid 1.5 36

Flowthrough ~37 52

Controlled pH 6.2 37.7

AFEX 0.6 2.0

ARP 3.3 40.0

Lime 10.0 23.0

Water Loadings and Stover Solids Made Soluble by Pretreatments

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Trends• Dilute acid and neutral pH pretreatments solubilize mostly

hemicellulose while ammonia and lime remove mostly lignin. AFEX removes neither and flowthrough removes both.

• All these pretreatments result in high glucose yields via enzymatic hydrolysis with somewhat better results for higher pH and flowthrough methods, possibly due to effect on lignin (cellulase adsorption and interference)– Lignin removal (ARP, lime, flowthrough) or modification (AFEX)

• Xylose remaining in the solids is solubilized during enzymatic hydrolysis for all methods– Enhanced hemicellulase activity could improve yields for all

methods and could have particularly important benefits as pH increases and for flowthrough approach

• It is important to consider the sugar release pattern and solids concentrations for each pretreatment in the selection of process, enzymes, and fermentative organisms to maximize yields


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Future Work• Evaluate performance differences in more depth

– Apply hydrolyzate conditioning– Ferment hydrolyzate with recombinant organism– Determine differences in pretreatment effects on

cellulase effectiveness– Add hemicellulases to improve performance– Work with Genencor as enzyme supplier– Understand how pretreatment affects substrate features

and their effect on digestibility– Broaden scope to hardwoods– Expand team to include University of British Columbia

and University of Sherbrooke in Canada• To be funded by Office of the Biomass Program

of the Department of Energy


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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


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IFAFS Project ParticipantsBiomass Refining CAFI

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