Characteristics of Biomass Pretreatments Studied by the CAFI

Bruce E. Dale, Richard T. Elander, Mark T. Holtzapple, Michael R. Ladisch, Yoon Y. Lee and

Charles E. Wyman

ISAF XVInternational Symposia on Alcohol Fuels

September 26-28, 2005 San Diego, CA

Biomass Refining CAFI

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

Biomass Refining CAFI

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 %

Pretreatment system

Temperature, oC

Reaction time,

minutes

Chemical agent used

Percent chemical

used

Other notes

Dilute acid1 160 20 Sulfuric acid 0.49 25% solids concentration during run in batch tubes

Flowthrough2 200 24 none 0 Continuously flow just hot water at 10mL/min for 24minutes

Partial flow pretreatment2

200 24 none 0 Flow hot water at 10mL/min from 4-8 minutes, batch otherwise

Controlled pH3 190 15 none 0 16% corn residue slurry in water

AFEX4 90 5 Anhydrous ammonia

100 62.5% solids in reactor(60% moisture dry weight basis), 5 minutes at temperature

ARP5,6 170 10 ammonia 15 Flow aqueous ammonia at 5 mL/min without presoaking

Lime7 55 4 weeks lime 0.08 g CaO/g biomass

Purged with air.

Characteristics of CAFI Pretreatments

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

Mineral acid

Biomass Stage 1. Pretreatment

Stage 2.Enzymatichydrolysis

Glucoseand ligninCellulose

and lignin

Hemicellulose sugars and oligomers

Glucose and Xylose Yields in Pretreatment and Enzymatic

Hydrolysis

Co

mb

ine

d S

tag

e 1

an

d s

tag

e 2

Yie

lds

Sta

ge

2 Y

ield

s

Sta

ge

1 Y

ield

s0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Yie

ld (

% o

rig

inal

glu

co

se +

xylo

se)

GlucoseXylose

Maximum potential glucose

Maximum potential xylose

Schematic of Flowthrough Pretreatment System

Back Regulator

Sand Bath

Valve-1

P

Cold WaterR

eact

or

T1

HPLC

Pump

Wateror

DiluteAcid

TC

Valve-2

Sample

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

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

Stepwise Process Yields & Mass Balance for 15 FPU Spezyme (168 hrs)

Controlled pH Liquid Hot Water

TreatedStoverSlurry

HydrolysisCellulase Enzyme2209 FPU per lb stover (30 FPU/ml)

Water

Stover

ResidualSolids

HydrolyzateLiquid

Fermentation

62.8 lb undissolved solids37.2 lb dissolved solids620 lb water

100 lb (dry basis)36.1 lb glucan21.4 lb xylan

36.32 lb glucose19.89 lb xylose

Ethanol90.5% total glucan conversion (raw stover basis)81.8% total xylan conversion (raw stover basis)88% of theoretical ethanol yield from glucose + xylose

620 lb

22.0 lb25.2 lb

Cellobiase Enzyme 5891 IU per lb

stover (309 IU/ml)

The AFEX/FIBEX Process

• 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

AFEX Process Mass Balance

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

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)

Preliminary Mass Balance for ARP Pretreatment

Biomass

Ammonia recycling

Fermention

ARP Reactor

Soluble sugar

Ammonia

Washing100 lb (dry

basis)

G:36.1 lb X: 21.4 lb O: 7.8 lb

G: Glucan X: Xylan

O: Other sugar

Liquid

G: 0.5 lb X: 10.6 lb

Lignin12.1 lbResidual solid 19.3 lb

G: 35.6 lb X:10.8 lb

Treated stover Hydrolysis

Hydrolyzate

Glucose 34.9 lb Xylose 17.0 lb

SSF

Ethanol 23.4 lbConversion Efficiency:87% glucan + 70% xylan conversion at 15 FPU/g of gulcan3.56 gallons ethanol (90% of theoretical yield, glucan+xylan)95% mass balance closure (solids + G + X + EtOH + Others)Other sugar is excluded for Ethanol production

Others 20.8 lb

Residual solids 18.9 lb

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

Lime System

Solids

LiquidHydrolysis

EnzymeLime + air

Stover

ResidualSolids

HydrolyzateLiquid

Fermentation

43 lb carb.4 lb lignin

100 lb(dry basis)58 lb carb.19 lb lignin

Ethanol3.8 – 4.1 gal

27 lb

To date:

80 – 90% overall carbohydrate conversion

15 lb sugars15 lb lignin

55-60 lb sugars15 lb lignin

Mass Balance for Lime Pretreatment

Pretreatment Yields-Stage 1 and Overall*

Pretreatment system

Xylose yields (38% max) Glucose yields (62% max) Total sugars (100% max)

Stage 1 Total xylose Stage 1 Total glucose Stage 1 Combined

Dilute acid1 32.1/31.2 35.3/34.4 3.9 57.1 36.0/35.1

92.4/91.5

Flowthrough2 36.3/1.7 36.9/2.2 4.5/4.4 59.7/59.6 40.8/6.1 96.6/61.8

Partial flow pretreatment2

31.5/2.8 34.1/5.2 4.3/4.2 55.5/55.4 35.8/7.0 89.6/60.6

Controlled pH3 21.8/0.9 30.8/9.9 3.5/0.2 56.4/53.1 25.3/1.1 87.2/63.0

AFEX4 nil 34.6/29.3 0 59.8 nil 94.4/89.1

ARP5,6 17.8/0 33.3/15.5 0 56.1 17.8/0 89.4/71.6

Lime7 9.2/0.3 28.8/19.9 1.0/0.3 58.0/57.3 10.2/0.6 86.8/77.2

* Soluble oligomers plus monomers/monomers only

Pretreatment system

Temperature, oC

Reaction time,

minutes

Chemical agent used

Percent chemical

used

Other notes

Dilute acid1 160 20 Sulfuric acid 0.49 25% solids concentration during run in batch tubes

Flowthrough2 200 24 none 0 Continuously flow just hot water at 10mL/min for 24minutes

Partial flow pretreatment2

200 24 none 0 Flow hot water at 10mL/min from 4-8 minutes, batch otherwise

Controlled pH3 190 15 none 0 16% corn residue slurry in water

AFEX4 90 5 Anhydrous ammonia

100 62.5% solids in reactor(60% moisture dry weight basis), 5 minutes at temperature

ARP5,6 170 10 ammonia 15 Flow aqueous ammonia at 5 mL/min without presoaking

Lime7 55 4 weeks lime 0.08 g CaO/g biomass

Purged with air.

Characteristics of CAFI Pretreatments

Acknowledgments US Department of Agriculture Initiative for Future

Agricultural and Food Systems Program, Contract 00-52104-9663

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

First group publication: Bioresource Technology vol. 96 #18 pgs. 1959-2032 December 2005

Biomass Refining CAFI

IFAFS Project Institutions

Purdue University

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

Cellulose Digestibility of Pretreated Corn Stover

190C – 15 minute

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180

Hydrolysis Time (hrs)

Glu

co

se

Yie

ld (

%)

60 FPU/g15 FPU/g7.5 FPU/g

Error bars represent 95% confidence intervals