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Advanced Biofuels 

Workshop/Fuel Ethanol 

Workshop

Daniel J. Schell

June 15, 2009

Integrating and Piloting Lignocellulose 

Biomass Conversion Technology

NREL/PR-510-46125
NREL Process Integration Project Goals 

• Investigate bioethanol production technology at the 

bench and pilot scales using corn stover 

• Produce integrated pilot-scale performance data, 

which when combined with a process design and a 

cost estimate validates a $1.49 (2007$) per gallon 

ethanol selling price

National Renewable Energy Laboratory Innovation for Our Energy Future
National Renewable Energy Laboratory Innovation for Our Energy Future

Key Process Performance Issues

Pretreatment Conditioning

Cofermentation

of C5 & C6

Sugars

Product

Recovery Products

By-products

Enzyme

Production

Enzymatic

Hydrolysis

Residue 

Processing

HSF

Ethanol Yields

Ethanol Concentration

Xylose Yield

Xylose Degradation

Reactor Costs

Solids Loading

Sugar Losses

Glucose Yield

Solids Loading (titer)

Feedstock Variation

Feedstock Quality

Enzyme Cost

Rate

Hydrolysate Toxicity

Feedstock Cost

Residual Xylose Yield

Recycle/Waste Streams

Energy Requirements

Separation Efficiencies

Impact on Yields
Process Configurations Investigated

National Renewable Energy Laboratory Innovation for Our Energy Future

Pretreatment Solid-Liquid 

Separation

Enzymatic 

Hydrolysis Fermentation

Conditioning Ethanol

Feed

Liquid

Acid

NH4OH or 

Ca(OH)2

Water Enzyme

30% Total Solids 

(TS) Loading

Glucose-xylose cofermenting bacteria, 

Zymomonas mobilis 8b

15% or 20% 

Total Solids 

Loading

Base Case (BC)

Hydrolysis Conditions:

• Genencor GC220 at 40 

mg protein/g cellulose

• 48°C

• 4 days 

Fermentation Conditions:

• Nutrients:10 g/L yeast 

extract + 2 g/L KH2PO4

• ~1.5 g/L initial cell 

density

• pH controlled at 5.8 

with 2N KOH

• 35°C

• 3 days 

Corn Stover
Process Configurations Investigated

National Renewable Energy Laboratory Innovation for Our Energy Future

Pretreatment Solid-Liquid 

Separation

Enzymatic 

Hydrolysis Fermentation

Conditioning Ethanol

Feed

Liquid

Acid

NH4OH or 

Ca(OH)2

Water Enzyme

30% Total Solids 

(TS) Loading

Glucose-xylose cofermenting bacteria, 

Zymomonas mobilis 8b

15% or 20% 

Total Solids 

Loading

Whole Slurry (WS)

Base Case (BC)

Hydrolysis Conditions:

• Genencor GC220 at 40 

mg protein/g cellulose

• 48°C

• 4 days 

Fermentation Conditions:

• Nutrients:10 g/L yeast 

extract + 2 g/L KH2PO4

• ~1.5 g/L initial cell 

density

• pH controlled at 5.8 

with 2N KOH

• 35°C

• 3 days 

Corn Stover

Pretreatment Conditioning Enzymatic 

Hydrolysis Fermentation

Ethanol

Feed

Acid

NH4OH or 

Ca(OH)2

Enzyme

Water

Corn Stover
Conditioning Technologies

National Renewable Energy Laboratory Innovation for Our Energy Future

Overliming Process (OL)

Ammonium Hydroxide Conditioning (AHC)

Advantages:

• Effectively detoxifies dilute acid (DA) hydrolysates

• Lime is inexpensive

Disadvantages:

• Soluble sugars are lost/degraded

• Requires additional filtration step to remove gypsum

• Need to dispose of insoluble gypsum

• Soluble gypsum remains in solution and can plate 

out in downstream equipment

Advantages:

• Effectively detoxifies DA hydrolysates

• No sugar degradation

• Insoluble solids are not produced

Disadvantages:

• NH4OH is expensive

• High ammonia salt concentrations are left 

in the treated liquor

Separation

Mixing (30°C, pH 8.5)

Mixing

Pretreated 

Feedstock

NH4OH

H2SO4

Liquor

Conditioned Liquor

Solids

Separation

Mixing (50°C, pH 10)

Mixing

Pretreated 

Feedstock

Ca(OH)2

H2SO4

Liquor

Conditioned Liquor

Solids

Filtration Gypsum
Conditioning Sugar Losses

National Renewable Energy Laboratory Innovation for Our Energy Future

Best Performance at pH 10

Ammonium Hydroxide Conditioning eliminates sugar losses during 

conditioning of dilute acid pretreated corn stover hydrolysates
Integrated Performance Results

National Renewable Energy Laboratory Innovation for Our Energy Future

Pilot scale production of 

pretreated corn stover 

Bench scale 

conditioning, enzymatic 

hydrolysis and 

fermentation
Fermentation Data

National Renewable Energy Laboratory Innovation for Our Energy Future

0

10

20

30

40

50

60

70

0 24 48 72

Sugar Concentration (g/L)

Time (h)

0

5

10

15

20

25

30

35

40

45

0 24 48 72

Ethanol Concentration (g/L)

Time (h)

0

10

20

30

40

50

60

70

0 24 48 72

Sugar Concentration (g/L) 

Time (h)

0

5

10

15

20

25

30

35

40

45

0 24 48 72

Ethanol Concentration (g/L)

Time (h)

15% TS, AHC

15% TS, OL

20% TS, AHC

20% TS, OL

Legend Base Case 

Process

Whole Slurry 

Process

Solid Lines: Glucose

Dashed Lines: Xylose
Enzymatic Cellulose Hydrolysis

National Renewable Energy Laboratory Innovation for Our Energy Future

50

60

70

80

90

100

BC 

15% 

AHC

BC 

15% 

OL

BC 

20% 

AHC

BC 

20% 

OL

WS 

15% 

AHC

WS 

15% 

OL

WS 

20% 

AHC

WS 

20% 

OL

Monomeric Glucose Yield (%)

Process Configuration:

Total Solids Loading (%):

Conditioning Technology:

Key Results:

• Cellulose to monomeric glucose yields improve at lower solids loadings

• Yields are independent of conditioning technology

• Yields are lower for the whole slurry process
Conversion of Sugars to Ethanol

National Renewable Energy Laboratory Innovation for Our Energy Future

30

40

50

60

70

80

90

100

BC 

15% 

AHC

BC 

15% 

OL

BC 

20% 

AHC

BC 

20% 

OL

WS 

15% 

AHC

WS 

15% 

OL

WS 

20% 

AHC

WS 

20% 

OL

Xylose-to-Ethanol Yield (%)

Process Configuration:

Total Solids Loading (%):

Conditioning Technology:

Xylose to Ethanol Yields:

• Yields are lower at high solids loadings

• Higher inhibitor concentrations

• Higher ethanol concentrations

• Conditioning technology and process 

configuration have little impact

30

40

50

60

70

80

90

100

BC 

15% 

AHC

BC 

15% 

OL

BC 

20% 

AHC

BC 

20% 

OL

WS 

15% 

AHC

WS 

15% 

OL

WS 

20% 

AHC

WS 

20% 

OL

Overall Ethanol Yield (%)

Process Configuration:

Total Solids Loading (%):

Conditioning Technology:

Overall Ethanol Yield:

• Base case process configuration outperforms 

whole slurry process configuration

• Conditioning technology has little impact on 

overall conversion yields 

*Assumes 90% glucose to ethanol yield

*
Constructing New Pilot Plant Capabilities

National Renewable Energy Laboratory Innovation for Our Energy Future

• Pilot plant expansion planned for substantial 

completion by May 2010

• New Equipment: Feedstock milling/handling 

system, versatile pretreatment systems, high 

solids enzymatic hydrolysis reactors

• Designed for parallel processing and flexible 

reconfiguration of unit operations with space for 

future equipment
National Renewable Energy Laboratory Innovation for Our Energy Future
Pretreatment

National Renewable Energy Laboratory Innovation for Our Energy Future

Single Horizontal Screw Reactor

Versatile Pretreatment System

• Residence times: minutes to 2 h

• Temperatures: 150° to 225°C

• Designed for a variety of 

pretreatment chemistries

Multi-Tube Reactor System Feedstock

Pretreated 

Feedstock

Pretreatment Chemicals
High Solids Enzymatic Hydrolysis

National Renewable Energy Laboratory Innovation for Our Energy Future

High Solids Enzymatic Hydrolysis Reactor

• Commercially available batch mixer

• No limitations on solids loading

• Thoroughly mixes

• Chemicals and enzyme added via a distributed 

spray system
Integrated Pilot Scale Processing

National Renewable Energy Laboratory Innovation for Our Energy Future

Main 

Feed 

Hopper

Pretreatment 

Feed Hopper

Weigh 

Belt

Pretreatment 

System

Flash 

Tank

Scrubber

S/L 

Separator

Enzymatic 

Hydrolysis 

Reactors

Main 

Fermentor 

Train

Seed 

Fermentor 

Train

Conditioning 

Tank

S/L 

Separator

Distillation 

Column

Catalyst and 

Chemical 

Tanks 

Enzyme 

Tank

Nutrient 

Tanks

S/L 

Separator

Recycle 

Water 

Tanks

Solids 

Tank

Dryer

Mill Condensers

Feedstock Steam

Catalyst/

Solvent

Water

Beer Well Bottoms 

Tank

Water Solids

Enzyme Chemical(s)

Feedstock

Nutrients/

Chemicals

Nutrients/ 

Enzyme

Solid 

Product Feedstock

Concentrated 

Ethanol

Liquor 

Tank

Water

Chemical

Inoculum

Pellets

Water

Water

Separator

Pelletizer

Solvent 

Recovery

Sterilizer

New Equipment

Existing Equipment

New piping

Existing piping

Future Equipment
National Renewable Energy Laboratory Innovation for Our Energy Future

Acknowledgements

Funding

• US DOE EERE Office of the Biomass Program

Contributors 

• NREL Project Members

• Nancy Dowe Farmer 

• Bill Bray

• Jody Farmer

• Wes Hjelm

• David Humbird

• Deb Hyman

• Ed Jennings

• Andrew Lowell

• Bob Lyons

• Gary McMillen

• Ali Mohagheghi

• Dave Sievers

• Millie Zuccarello

• Pilot Plant Designers/Builders
Questions?

National Renewable Energy Laboratory Innovation for Our Energy Future