A Comparison of Batch, Stop- Flow-Stop, and Flowthrough Pretreatments of Corn Stover Chaogang Liu, Charles E. Wyman Thayer School of Engineering Dartmouth

A Comparison of Batch, Stop-Flow-Stop, and Flowthrough Pretreatments of Corn Stover

Chaogang Liu, Charles E. WymanThayer School of Engineering

Dartmouth CollegeHanover, New Hampshire 03755

2003 AIChE Annual Meeting San Francisco, CA November 20, 2003

Biomass Refining CAFI

USDA IFAFS Project Overview

• Multi-institutional effort funded by USDA Initiative for Future Agriculture and Food Systems (IFAFS) Program to develop comparative information on cellulosic biomass pretreatment by leading options with common source of cellulosic biomass– 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 - 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


Flowthrough (FT) Pretreatment• Based on early work by Bobleter, Antal• Flows just hot water or very dilute acid solution

through stationary biomass• Removes large fraction of hemicellulose and lignin • Separates sugars from reactor, reducing time for

decomposition • Achieves high cellulose digestibility• Uses less chemicals than co-current process• Provides a less corrosive environment • However, high amounts of water are needed,

increasing energy for pretreatment and recovery


How are FT and Batch Different?

Batch FT

Xylose yield <~90% ~100%

Lignin removal <10% >50%

Digestion yield <~90% ~100% (by SSF) Digestion time 7 days ~2 days (by SSF)


Questions

• Why is FT so much different from batch?

• How can FT configuration make this difference?

• Can we combine the favorable features of FT and batch?


Objectives of This Study

• Evaluate effects of flow rate, temperature, and acid concentration on solubilization of hemicellulose and lignin in a flowthrough reactor

• Particularly focus on developing detailed time profiles of the fate of major biomass components and closing material balances

• Seek to understand mechanism responsible for much different behavior of batch and FT to develop advanced systems that can combine the best features of each while overcoming their limitations

• Evaluate the behavior of a novel approach called stop-flow-stop (SFS) and compare its performance with that for batch and FT


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 %


Schematic of FT System

Back Regulator

Sand Bath

Valve-1

P

Cold WaterR

eact

or

T1

HPLC

Pump

Wateror

DiluteAcid

TC

Valve-2

Sample


Flowthrough Reactors

Gasket filters ( Average pore size, 5 μm )

Internal volume : 37.8 mL

Biomass loading: ~6.5 g


Internal volume : 3.8 mL

Biomass loading: ~0.5 g

Small reactor Big reactor

Effect of Flow Rate and Temperature on Residual Xylose for Compressed Water

1

10

100

0 8 16 24 32 40 48 56 64

Time, minutes

% o

f p

ote

nti

al x

ylo

se

180C,0mL/min

180C,1mL/min

180C,10mL/min



1

10

100

0 8 16 24 32 40 48 56 64

Time, minutes

% 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



1

10

100

0 8 16 24 32 40 48 56 64

Time, minutes

% o

f p

ote

nti

al x

ylo

se

180C,0mL/min180C,1mL/min180C,10mL/min200C,0mL/min200C,1mL/min200C,10mL/min220C,0mL/min220C,1mL/min220C,10mL/min


Total Xylose Yield for 0.05wt% Sulfuric Acid Pretreatment at 180oC

0

20

40

60

80

100

0 4 8 12 16Time, minutes

% o

f po

ten

tial t

ota

l xyl

ose

0 mL/min

1 mL/min10 mL/min


Change in Lignin Removal with Flow Rate for Water Only and Very Dilute

Acid at 180oC after 16 minutes

0

10

20

30

40

50

60

flow rate,0mL/min

flow rate,1mL/min

flow rate,10mL/min

% o

f o

rig

inal

Kla

son

lig

nin

hot water only

0.05wt% sulfuric acid


Solubilized Xylan Vs Lignin Removal for Compressed Water Pretreatment

0

20

40

60

80

100

0 10 20 30 40 50 60 70 80

Lignin removal (% of the original Klason lignin)

So

lub

ilize

d x

ylan

(%

of

po

ten

tial

xyl

ose

)

180C, 0mL/min

180C, 10mL/min

200C, 0mL/min

200C, 10mL/min

220C, 0mL/min

220C, 10mL/min


Possible Pathway for Hemicellulose Hydrolysis

H OL O’L OS M D

H: Hemicellulose

OL : Undissolved long-chain oligomers

O’L: Dissolved long-chain oligomers

OS : Dissolved short-chain oligomers

M : Monomers

D : Degradation products

Mass transfer control

Reaction control

Reaction control

Reaction control

Reaction control


Reaction control

Mass Balance for FT Pretreatment with Compressed Hot Water at 15 FPU

FL reactorTreatedSolids

Hydrolysis

Enzyme @15FPU/g of glucan, 72h

Water

Corn Stover

ResidualSolids

Hydrolyzate

Fermentation

43.4 lb34.3 lb glucan

0.4 lb xylan

100 lb(dry basis)

36.1 lb glucan21.4 lb xylan

36.7 lb glucose0.31 lb xylose

4.45 gal ethanol

7.2 lbDissolved mass

96.5% glucan to glucose, 68.2% xylan to xylose at 15 FPU/ g of glucan97% overall glucan and xylan conversion92% theoretical ethanol yield from glucose + xylose96.3% overall mass balance closure (total dissolved mass+residual solids + G + X)

52.1 lb22.2 lb xylose oligomers1.2 1b xylose monomer

2.1 lb glucose

1.81 gal ethanol

2.64 gal ethanol

Mass Balance For FT Pretreatment with Very Dilute Acid at 15 FPU

FL reactorTreatedSolids

Hydrolysis

Enzyme@15FPU/g of glucan, 72h

0.05wt %wt H2SO4

Corn Stover

ResidualSolids

Hydrolyzate

Fermentation

46.6 lb33.2 lb glucan0.43 lb xylan

100 lb(dry basis)

36.1 lb glucan21.4 lb xylan

36.1 lb glucose0.39 lb xylose

13.4 lbDissolved mass

4.50 gal ethanol

97.8% glucan to glucose, 80% xylan to xylose at 15FPU/g of glucan97.5% overall glucan and xylan conversion92% theoretical ethanol yield from glucose + xylose 98.1% overall mass balance closure (total dissolved mass+residual solids + G + X)

48.2 lb21.5 lb xylose oligomers1.5 Ib xylose monomer

3.2 lb glucose

1.91 gal ethanol

2.59 gal ethanol

Liquid Fraction Concentrations Over 4 Minute Intervals for FT with

Compressed Water at 200oC

0

5

10

15

20

25

30

35

0 1 2 3 4 5 6Fraction numbers

Co

nce

ntr

atio

n,

g/L

overall sugars

other substances

total dissolved mass


Sugar Concentrations in Liquid Fraction Over 4 Minute Intervals for FT Pretreatment with

0.05wt% Acid at 190oC

0

5

10

15

20

25

30

0 1 2 3 4 5 6

Fractions

Xyl

ose

co

nc,

g/L monomeric xylose

xylose oligomers

total xylose


Stop-Flow-Stop (SFS) Test Modes

0

10

0 4 8 12 16 20 24

Time, minutes

Flo

w r

ate

, m

L/m

in

SFS 1

0

10

0 4 8 12 16 20 24

Time, minutes

Flo

w r

ate

, m

L/m

in

SFS 2


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

0102030405060708090

100

Batch

, 20m

inute

s

Batch

, 24 m

inute

s

FT, 24m

inute

s

SFS1, 24

min

utes

SFS2, 24

min

utes

%, o

f or

igin

al t

otal

xyl

ose

residual xylose in solids

total xylose in hydrolyzate


Residual Xylan for Batch, FT, and SFS Runs with 0.05wt% Acid at 180oC

0

20

40

60

80

100

0 4 8 12 16Time, minutes

% o

f o

rig

inal

to

tal x

ylan

batchFT, 10 mL/minSFS1SFS2


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 monomeroligomers

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

Hydrolyzate Sugar Concentration for Pretreatment of Corn Stover with

Hot Water at 200oC

Modes

Hydrolyzate

Volume

mL

Xylose monomer

g/L

Xylose

Oligomers

g/L

Total

Xylose

g/L

Total xylose

Yield

%

Batch,

20 minutes

60 0.6 10.7 11.3 46.6

Batch,

24 minutes

60 0.1 2.8 2.9 12.1

FT, 10 mL/min 240 0.4 5.4 5.8 96.2

SFS 1 90 1.2 12.3 13.5 83.5

SFS 2 120 0.8 10.0 10.8 88.6


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

Lignin Removal for Batch, FT, and SFS Runs with Water at 200oC

010203040506070

Batch

, 20 m

inutes

Batch

, 24 m

inutes

FT, 24 m

inute

s

SFS1, 24

min

utes

SFS2, 24

min

utes

% o

f or

igin

al K

laso

n l

ign

in


Lignin Removal for Batch, FT, and SFS Runs with 0.05wt% Acid

at 180oC after 16 minutes

0

10

20

30

40

50

60

Batch FT SFS1 SFS2

% o

f or

igin

al K

laso

n li

gnin


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

7880828486889092949698

%

of

theo

reti

cal

yie

ld

Water, 200oC 0.05wt% acid, 190oC


Comparison of Batch, FT, and SFS with Hot Water at 200oC

Total xylose

yield, %

Total xylose

conc, g/ L

Lignin removal,

%

Cellulose digestibility

, %

Batch ~ 46 ~ 11 ~ 10 ~ 85

FT ~ 96 ~ 6 ~ 55 ~ 95

SFS 83~ 88 10 - 13 40 - 45 88 ~ 90


Summary• Flow rate acts somewhat like temperature and acid in effect on

solubilization of hemicellulose and lignin• Increase in xylan removal with flow rate is inconsistent with

traditional first order kinetic models, suggesting that other factors like mass transfer may also play an important role in hemicellulose hydrolysis, especially in the early reaction times

• Compared with batch, FT can significantly increase the yields of hemicellulose sugars, lignin removal, and cellulose digestibility, but the hydrolyzate is very dilute

• SFS can significantly reduce the amount of water consumption while realizing good hemicellulose sugar yields and cellulose digestibility

• In the future, we will optimize the SFS operation and investigate mechanisms responsible for the better performance of FT and SFS so that we can develop a more effective process.


Acknowledgments

The United States Department of Agriculture Initiative for Future Agricultural and Food Systems Program through Contract 00-52104-9663 for funding our research

The United States Department of Energy Office of the Biomass Program and the National Renewable Energy Laboratory

Our partners from Auburn, Michigan State, Purdue, and Texas A&M Universities and the National Renewable Energy Laboratory

The National Institute of Standards and Technology through award 60NANB1D0064 for funds for some equipment used

The Thayer School of Engineering at Dartmouth College


Questions?


Documents

A Comparison of Batch, Stop- Flow-Stop, and Flowthrough Pretreatments of Corn Stover Chaogang Liu, Charles E. Wyman Thayer School of Engineering Dartmouth