College of EngineeringCollege of Agriculture

Biochemical and Biomimetic Approaches to Saccharifying Biomass for Advanced BiofuelProduction

Center for direct

catalytic conversion

of biomass to biofuels

(C3Bio)

Nathan S. Mosier

Acknowledgements› Purdue University

– College of Agriculture

– College of Engineering

– C3Bio

– Energy Center

– Laboratory of Renewable Resources Engineering

› Funding Sources

– DOE-BES (C3Bio) DE-SC0000997

– NSF BES-9727096, IGERT-9987576

– Purdue Ag. Research Station

Value from Corn Lignocellulose

› Stover and Fiber

› Pathways to Value-added Products

– Biochemical

– Thermochemical

› Challenge is fractionation and conversion at low cost and high yield

CelluloseLignin

Hemicellulose

Simplified Impact of Pretreatment on Biomass

Mosier, N. et al. Bioresource Technology 96(6):673-686 (2005).

Pretreatment

555

Introduction Catalysts for Cellulosic Polysaccharide Hydrolysis

�H2SO4, HCl (mineral acids)

�H2O

O

H

H

�H2SO4, HCl (mineral acids)

�H2O

O

H

H

�H2SO4, HCl (mineral acids)

�H2O

O

H

H

�Cellulases�Cellulosomes

�Cellulases�Cellulosomes

Small molecular catalysts Protein catalysts

• Low selectivity;

• Low sugar yield;

• Fast reaction under severe

reaction condition (160-

250 °C, pH 0-2).

• High specificity & selectivity;

• Limited mass transfer (hindered

substrate access);

• Slow reaction under mild

condition (50 °C, pH 4.8).

Concept of a Biomimetic Catalyst

downsizing

MW 55kD

active site

Cellulolytic Enzyme

only active site

residue carboxylate

pair retained

downsizing

Thousands of Daltons

active site

Cellulolytic Enzyme Biomimetic Catalyst

only active site

residue carboxylate

pair retained

Hundreds of Daltons

Enhanced Activity - Control Catalyst Specificity- Higher Mass Transfer- Higher Temperatures

0

10

20

30

40

50

60

70

80

90

100

Corn Stover Switchgrass Poplar

% R

eco

ve

red

in

Aq

ue

ou

s P

ha

se

Xylose

Glucose

Maleic Acid: Selective Fractionation

50 mM

160 C

20 Min

Mosier, Purdue

Abu-Omar, Purdue

CONCLUSIONS

Maleic Acid Pretreatment

(170°C, 8min, 200 mM)

Sulfuric Acid Pretreatment

(179 °C, 6.2 min, 1.16%)

Xylose Yield ~95% ~68%

Furfural

Concentration~1.80 g/L ~8.00 g/L

• Fermentation of Resulting Xylose

– 87% of theoretical ethanol can be generated by Purdue-Ho yeast fermenting hydrolysate

– This yield is equivalent to pure xylose in YEP medium

ENZYME DIGESTABILITY OF PRETREATED CORN STOVER

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 12 24 36 48 60 72 84 96 108 120 132

GL

UC

OS

E Y

IEL

D

ENZYME HYDROLYSIS TIME, HOURS

MALEIC ACID PRETREATED

SULFURIC ACID PRETREATED

UNTREATED

Enzyme Hydrolysis of Three Types of Corn Stover in 120 Hours

(4% Solid-Loading for the Pretreatment)

Kinetics Analysis

Biomass

khydrolysis

khydrolysis is a function of H+

(independent of source)

pH Affects Dehydration of Xylose

Kinetics solely dependent on [H+],

indicating specific acid catalysis mechanism

y = -0.0075xR² = 0.9379

y = -0.0241xR² = 0.9863

y = -0.0468xR² = 0.9784

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0 5 10 15 20 25

ln (X

/X0)

Reaction time, minutes

10mM

50 mM

100 mM

y = 0.473xR² = 0.9896

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

0 0.05 0.1 0.15

kd

eg, m

in-1

[H+], mole

Organic/Weak Acids

Kinetics dependent on [Acetic acid] at constant pH,

indicating general acid catalysis mechanism

y = -0.0081xR² = 0.9634

y = -0.0111xR² = 0.9493

y = -0.0178xR² = 0.9944

-0.4

-0.4

-0.3

-0.3

-0.2

-0.2

-0.1

-0.1

0.0

0 5 10 15 20 25

ln (

X/X

0)

Reaction time, minutes

10mM

50 mM

100 mM

y = 0.1763xR² = 0.9628

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02

0 0.05 0.1 0.15

kd

eg, m

in-1

[Acetic acid], mole

Unexpected Results

Kinetics inversely dependent on [Maleic acid] at constant pH,

Indicating inverse general acid catalysis mechanism

y = -0.007xR² = 0.9228

y = -0.003xR² = 0.7713

y = -0.0011xR² = 0.0211

-0.30

-0.25

-0.20

-0.15

-0.10

-0.05

0.00

0 10 20 30 40

ln (

X/X

0)

Reaction time, minutes

10mM

50 mM

100 mM

y = -0.0475x + 0.0062R² = 0.994

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0 0.05 0.1 0.15

kd

eg, m

in-1

[Maleic acid], mole

What the Kinetic Analysis Tells Us

� Maleic Acid Inhibitions Degradation of Xylose

� Inhibition of dehydration to furfural less than

degradation to humins

� Activation Energy of Dehydration Higher

� Activation Energy of Degradation to Humins

Lower

� Selectivity of Reactions of Xylose in

Presence of Maleic Acid Controlled by

Temperature

Thermochemical Route to Platform

Chemicals

15

18 MJ/kg

Xylose3H2O

24 MJ/kg

Furfural

100% C33% Higher Energy Density

Catalysis

Furans (precursor for levulinic acid, THF)

Bozell and Petersen, 2010

Selective hydrolysis and conversion: Tandem Catalysis

~170 °C, 10 min

+

Biomass Lignin & Cellulose Xylose≥ 80% yield

filter

~200 °C, 5-10 min

furfural≥ 60% yield

Maleic acid& 10 mol% ZnCl2

Maleic acid Pd/C

~ 10 min

Me-THF

H2

Pure sugar and biomass are NOT the same!

Sample Catalyst t/ min Xylose %

conversion

% Yield

furfural

Pure xylose

(10 g/L)

ZnCl2

0.25 M Maleic acid

0.25 M H2SO4

10

10

5

100

100

100

50

66

65

Corn Stover 0.25 Maleic acid

0.25 M H2SO4

10

5

100

100

69

55

Salts (especially halides) strongly affect

thermocatalytic processes

Conversion of Cellulose Difficult

– Not Just Recalcitrance

Nate Mosier

Mahdi Abu-Omar

Eurick Kim

Sugar kdeg

(*10-4s-1)

@ 180 C

Ea

(kJ/mol)

Glucose 1.0 120.0

Xylose 5.8 121.0

Fructose 123.0 18.1

Conversion of Cellulose Requires Paired Catalysis

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20

HMF %

Glu %

Fru %

LA %

180 C 2 phase solution

25mM AlCl3 H2O:MTHF

50mM Maleic Acid

AlCl3 Isomerizes Glucose to Fructose

Time, minutes

% in

itia

l C

Hydrolysis of Cellulose is Rate Limiting

0

10

20

30

40

50

60

70

% Y

ield

HMF

Ff

180 C, 60 minutes 2 phase solution

25mM AlCl3 H2O:MTHF

50mM Maleic Acid

Conclusions

• Mimetic approach attempts to achieve

catalytic selectivity similar to enzymes

• Maleic acid can fractionate biomass sugars at

high yields for biochemical and

thermocatalytic conversion

• Corn-derived sugars good feedstocks for

value-added chemicals and fuels