Ethanol Production from Lignocellulosics:

Sheldon Duff

EtOH

Outline

• Biorefinery/Biofuels

• Progress– Feedstocks– Pretreatment– Fermentation of hydrolysates– Process engineering

• Uncertainties/Current Status

Bioconversion

Pretreatment(chemical or

physical)Hydrolysis Fermentation

Plant Biomass ETHANOL

nzymes (Cellulase & b-Glucosidase)

Feedstocks

Feedstocks

• Partially pretreated– Clarifier sludges– SSL (knots/PCS)– Recycled fibre

• Urban cellulosic wastes

• Agricultural residues

Paper

Pretreatment

Pretreatment

• Focus on oxygen delignification

– Clean

– Proven

Flowsheet of MediumFlowsheet of Medium--consistency consistency OO22 DelignificationDelignification

To Bleach PlantD Eo H D E D

To Bleach PlantD Eo H D E D

Brown StockStorage

Brown StockStorage

No. 2 PressNo. 2 Press

No. 1 PressNo. 1 Press

O2 BlowTank

O2 BlowTank

O2 ReactorO2 Reactor

MC MixerMC Mixer

DeckerDecker

ScreensScreensO2O2

SteamSteam

NaOHNaOH

To Bleach PlantD Eo H D E D

To Bleach PlantD Eo H D E D

Brown StockStorage

Brown StockStorage

No. 2 PressNo. 2 Press

No. 1 PressNo. 1 Press

O2 BlowTank

O2 BlowTank

O2 ReactorO2 Reactor

MC MixerMC Mixer

DeckerDecker

ScreensScreensO2O2

SteamSteam

NaOHNaOH

Mill Oxygen Delignification

0

50

100

150

200

Lignin Sugar Rate

Reduction Increase Increase

Pe

rce

nt Mill A

Mill B

Mill C

Application of OD to Recovered Fibre

• Can be used across range of substrates

• Conditions can be extended

Application of OD to Recovered Fibre

• As with all most pulping / bleaching, limit is yield

Modelling OD Effects

• Can express sugar yield as a function of initial S, K and E

• Underpredicts high substrate case due to mixing limitations

Achievements

• Dramatic improvements in yield, using known, proven technology

• Allows reduction in enzyme loading

Fermentation

Fermentation-Challenges

• Inhibitors

• Pentose fermentation

Inhibitors

Fermentation Inhibitors

• Acetic acid

• Dissolved solids

• Furfural

pH 4 pH 6

ATP

ADP

H++CH3C

O

O-

CH3C

O

OH

H+

H+

H+

Acetic acid

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 1 2 3 4 5 6 7 8 9

Gro

wth

ra

te &

yie

ld

Undissociated acetic acid (g/L)

Maximum growth rate (/hr)

Biomass yield YX/S (g/g)

Ethanol yield YP/X (g/g)

1

X

dX

dtMAX

S

KS S

YX / SmHAc

Ac 110 pH pKa

1

X

dX

dtMAX

S

KS S

YX / SmHAc

Ac 110 pH pKa

Optimization of Prehydrolysate Fermentation

Yeast extract

Corn steepliquor

Fermaid - K

Achievements

• Mechanistic understanding of inhibitors

• Modelled using maintenance energy model

• Improved fermentation (including growth on hardwood)

Xylose Fermentation

Xylose fermentation• S. cerevisiae 259ST (Dr. N

Ho, Purdue U) NWY Ho, Z Chen, and AP Brainard, 1998

• Xylose Xylulose– xylose reductase– xylitol dehydrogenase

– xylulokinase

• Xylulose fermented via pentose phosphate pathway & glycolysis

Xylose fermentation

0

10

20

30

40

50

60

0.1

1

10

0 10 20 30 40 50 60

Eth

anol (g

/L)

Yeast bio

mass (

g/L

)

Time (hours)

Modified strain (259ST)

Parent strain (259A)

90 g/L glucose45 g/L xylose

Effect of Inhibitors

• Maintenance energy has little impact on hexose metabolism

• For xylose, metabolic rate is too slow to meet maintenance demand

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1 1.2T

heo

retic

al e

than

ol y

ield

(g/

0.51

g S

)

ms(g S/g X hr)

Hemicellulose Hydrolysate Fermentation

0

5

10

15

20

25

30

0 5 10 40 80 120

Su

ga

r, g

lyce

rol, x

ylit

ol, e

tha

no

l (g

/L)

Time (hours)

Glycerol

Xylose

Xylitol

Ethanol

• High [yeast] & high pH– Rapid hexose

fermentation

– Xylose fermentation

Achievements

• Xylose fermentation in SSL

– Yield on xylose increased from 0 to 80% yield

– Increased overall ethanol yield by 20 - 30%

Process Engineering

Modelling and Simulation

• Kinetics and yields from pretreatment, hydrolysis and fermentation used

• Output– M&E balances– Equipment sizing– Capital/operating

costs– Sensitivity analysis

Summary

• No full-scale cellulose-to-ethanol plants

• Any of several pretreatment technologies effective

• Enzyme costs high/uncertain ($2.40-$70/MFPU)

Summary

• C5 fermentation possible but has problems:– Slow– Metabolically challenged

• Moving toward simulation as a plant design tool

Acknowledgements

• NSERC, NRCan, P&P Companies

• Steve Helle (UNBC), David Cameron, Bob Benson

• Students: Janet Lam, Allison Murray, Kris Draude, Tony Lin, Rob Petretta, John Ruffell, John Moritz

Thank you