Sweet Sorghum Ethanol: In-Field Fermentation Issues

Dani Bellmer1, Ray Huhnke2

1Assoc. Professor, Biosystems Engineering & Food and Agricultural Products Center

2Professor, Biosystems Engineering

Oklahoma State University

In the US, we currently import over 60% of our petroleum

needs

Current U.S. Ethanol Production Facilities

117 operational, 57 under construction

Sweet Sorghum Has Great Potential as an Energy Crop

Can be grown in temperate climates

“More Crop Per Drop” - Low irrigation needs (1/2 corn and 1/3 sugarcane)

Drought tolerant

12-21% directly fermentable sugar (i.e. no starch to convert)

Traditional Sugar Processing

Sugarcane

Central FacilityOn-Farm

Press

Juice

Bagasse

Fermentation Distillation &Dehydration

Heat Energy

In-Field Production of Ethanol from Sweet Sorghum

Harvesting, pressing, & fermenting the juice in the field…

Potential In-Field Processing

SorghumPres

s

Juice

Bagasse

Fermentation Dewatering/Distillation

Dehydration

Central FacilityOn-Farm

Field Residue

Silage

Heat Energy

Potential In-Field Storage Bladders

Possible System Scenario in OK

Begin planting ~ mid April

Stagger plantings April- June

Harvest July – mid-November (4.5 month harvest window)

Producers owns 1 week juice storage capacity + partial dewatering system

Final dehydration conducted at central site

Evaluate Sweet Sorghum Ethanol Potential in Oklahoma

Goals:

• Evaluate In-Field Fermentation Issues

• Determine Factors Affecting Juice Extraction Efficiency

• Evaluate Potential for Expanded Harvest Window

Fermentation

Theoretical Ethanol Production

Stoichiometry of sugar fermentation:

C6H12O6 2C2H5OH + 2CO2

Theoretical Conversion: 0.51 g etoh/ g sugar

In-Field Fermentation

Superstart Distillers Yeast/pH5.4/NoUrea

0

50

100

150

200

Time (h)

To

tal

Su

gar

E

than

ol,

g/L

-2.0

0.0

2.0

4.0

6.0

8.0

Bio

mas

s, g

/L

Total Sugar Ethanol Cell Count

Total Sugar 161.52 107.16 60.70 33.45 11.92 0.00

Ethanol 0.01 9.93 33.90 56.17 68.54 76.95

Cell Count 0.54 1.56 3.52 6.07 5.76 6.36

0 24 48 72 96 120

Ethanol Production Results

Treatment [Yeast, pH, Urea]

Avg. EtOH, g/L

Conversion Efficiency

Fermax, 4.5, U 79.0 97% Fermax, 4.5, NU 79.5 97% Fermax, 5.3, U 77.5 95%

Fermax, 5.3, NU 78.0 96% SS, 4.5, U 78.1 96%

SS, 4.5, NU 76.8 94% SS, 5.3, U 74.7 92%

SS, 5.3, NU 76.9 94%

Ethanol Production at Different Harvest Times (1 month apart)

Harvest 1 vs. Harvest 2Stillwater

0

1

2

3

4

5

6

7

8

9

Dale Keller M81 Theis Topper

Variety

Per

cen

t E

than

ol

Harvest 1

Harvest 2

Effect of Inoculation Time on Ethanol Production

0

10

20

30

40

50

60

70

0 10 20 30 40

Inoculation Time (hrs)

Eth

an

ol P

rod

uc

tio

n (

g/l)

Effect of Leaf Stripping on Ethanol Production

20

30

40

50

60

70

With

Lea

ves

With

Lea

ves

With

Lea

ves

No Le

aves

No Le

aves

No Le

aves

Eth

an

ol P

rod

uc

tio

n (

g/l)

Effect of Storage Fermentation samples after 5

monthsHaskell

(all without acid)

0

1

2

3

4

5

6

7

8

Dale 1 Dale 2 M81 1 M81 2 Theis 2 Topper 1 Topper 2

Variety

Per

cen

t E

than

ol

Original

May

Effect of Storage Fermentation samples after 5

monthsStillwater

(all without acid)

0

1

2

3

4

5

6

7

8

Dale 1 Dale 2 Keller 1 Keller 2 M81 1 M81 2 Theis 1 Theis 2 Topper 1 Topper 2

Variety

Per

cen

t E

than

ol

Original

May

Juice Extraction Efficiency

Compare roller press and screw press

Evaluate juice yield as affected by time of harvest

Effect of stalk diameter on juice expression

Small Scale Roller Press

Screw Press

Finely Chopped Bagasse Out of Screw Press

Screw Press vs Roller Press

Juice Expression Ratio (g juice/g biomass)

Roller Press: .36 - .4

Screw Press: .45 - .5

Whole Stalks in Screw Press: Effect of Pressure

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0 10 20 30 40

Pressure (psi)

Ju

ice

Ex

pre

ss

ion

Ra

tio

Effect of Harvest Time on Juice Expression(Roller Press)

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

5-Oct 15-Oct 25-Oct 4-Nov 14-Nov

Harvest Date

Juic

e E

xpre

ssio

n R

atio

Trt 8

Trt 10

Trt 11

Trt 12

Effect of Stalk Diameter on Juice Expression

0 0.1 0.2 0.3 0.4

Small 1

Large 1

Small 2

Large 2L

arg

e &

Sm

all

Sta

lk S

ize

s

Juice Expression RatioLarge ~ 3 cmSmall ~ 1.5 cm

Additional Ongoing Research

Determine level of sterilization needed between fermentation cycling in storage bladders

Develop on-farm partial dewatering process

Evaluate staggered plantings to determine effect of extended harvest window

Three Different Planting Dates

Potential Ethanol Yield(gallons/acre)

Sorghum Juice Sugar Content

Biomass Yield 15% 17% 19%

25 tons/acre 288 326 372

35 tons/acre 404 457 511

45 tons/acre 518 586 656

* Assumes 0.55 juice expression ratio and 90% conversion efficiency

Trade-Offs Between Processing Scenarios

Central FacilityOn-Farm

- Lower Transportation Costs

- Lower Capital Costs

- More Feasible in Reduced Harvest Window Scenarios

- Value to Rural Economies

- Higher Juice Extraction Efficiency

- Higher Conversion Efficiency

- Economies of Scale

Critical Process Questions Remaining

Best technology for in-field, single pass pressing

Determination of extent of dewatering to be completed on-farm, and best technology

Sterilization Requirements

The Future is Sweet…

Acknowledgements

OSU Collaborators: Ray Huhnke, Dimple Kundiyana, Chad Godsey, Bill Raun, Rodney Holcomb, students

Lee McClune, LeeMax Energy, Knoxville, IA

Kerr Center for Sustainable Agriculture, Poteau, OK

OK Field Research Station Superintendents

Oklahoma Food and Agricultural Products Center, Stillwater, OK

Sugar Content Monitoring

Dale Variety

0

5

10

15

20

25

8/11/06 8/31/06 9/20/06 10/10/06 10/30/06 11/19/06 12/9/06

Date

Av

era

ge

Su

ga

r C

on

ten

t (o

Bri

x)

Haskell

Perkins

Fort Cobb

Stillwater

115 Days After Planting