Bioethanol

CE 521Shinnosuke Onuki

1. Introduction

A biofuel produced by the fermentation of plants rich in sugar/starch

Bioethanol

renewable resourcesimpact on air quality due to cleaner combustion reduced net carbon dioxide (greenhouse gas) emissionsexpanded market opportunity in the agricultural fieldenergy security: less dependence on crude oilMore than 90% of the bioethanol produced in the U.S. comes from corn

1. Introduction

Imports as a percentage of total U.S. crude oil supply (McMillan,1996)

2. Outline

1. Production process1. Grinding2. Cooking3. Fermentation4. Stress management5. Distillation6. Dehydration

2. Lignocellulosic biomass3. Immobilized Cell System 4. Energy Balance 5. Concerns

3. Production Process

Grain

Ethanol

1. Grinding

2. Cooking

3. Fermentation

4. Distillation

5. Dehydration

3-1. Grinding

Less energy consumptionProvide more uniform particles

Advantage

High set up costHigh maintenance costDifficult to grind small grainsDifficult to grind hard shell grains

Disadvantage

Roller mill (Kohl, 2003)

3-1. Grinding

Less set up costLess maintenance costEasier to grind small grainsEasier to grind hard shell grains

Advantage

Higher energy consumption ( about twice as much)

Provide less uniform particles

Disadvantage

Hammer mill (Kohl, 2003)

3-2. Cooking

Hot water treatment

Micro-crystalline area

Broken

Hot water85°C

20~60 min

Super heated water110°C

High pressure

3-2. Cooking

LiquefactionAttack α-1,4 linkageConvert Starch into Dextrinendoenzyme10 times faster than glucoamylase

Alpha-amylase

Starch (Kohl, 2003)

3-2. Cooking

SaccharificationexoenzymeAttack α-1,4 and α-1,6 linkageConvert Dextrin into Glucose

Glucoamylase

Dextrin (Kohl, 2003)

3-3. Fermentation

Facultative anaerobicConverts sugar into carbon dioxide and water in an aerobic environmentConverts sugar into carbon dioxide and ethanol in an anaerobic environmentPropagation tank

Yeast

S. cerevisiae

3-4. Stress management

Fermentation is exothermicCooling system is required

Temperature

Simultaneous increase in the both concentrations of sugar and ethanol should beavoidedThe simultaneous saccharification and fermentation (SSF)

Concentrations of sugar and ethanol

Byproducts produced by contaminated bacteriaLactic acid: lactobacilli bacteriaAcetic acid: acetobacter bacteriaClose control is required

Lactic acid and Acetic acid

3-5. Distillation

Distillation step (Kohl, 2004)

Multiple vaporization and concentrationIt burdens on the cost

Initial concentration of ethanol isimportant

3-6. Dehydration

Entrainer: benzene or cyclohexaneStrong intermolecular reaction between water and benzeneComplicatedToxicity problem

Azeotropic Distillation

Pore size of molecular sieves: 3 ǺEthanol: 4.4 ǺWater: 2.8 ǺHigh energy required to regenerateFlammability of superheated ethanol

Molecular sieves

4. Lignocellulosic Biomass

Agricultural residue: bagasse, wheat straw, wheat husk, wooden wastePretreatment required: solubilization of cellulose, hemicellulose, and lignin

Lignocellulosic biomass

Acid treatmentLow costHigh reaction

Alkaline treatmentBe able to remove lignin without having big effects on the other parts

Thermal treatmentSteam explosionLiquid hot water

Biological treatment

Pretreatment

5. Immobilized Cell System

(a) attachment to a surface (b) entrapment within a porous matrix(c) containment behind a barrier(d) self-agitation

Immobilization

Immobilization methods(Verbalen et al., 2006)

Provide high densityEnable high flow rate

and short time operation

Advantage

Affect on yeast: flavor, odor

Disadvantage

6. Energy Balance

2,373NANANANA31,961129.9113Average

16,19315,05682,82453,277 (HHV)2.5322,159124.5122This study (1995)

-4,00010,00090,00057,000 (LHV)NRNRNR90Ho (1989)

25,65324,95075,29746,297 (LHV)2.5531,000127.0120Morris and Ahmed (1992)

18,3248,12773,93440,105 (HHV)2.5031,135127.0119Marland and Turhollow (1991)

-8,4318,07291,12748,434 (LHV)2.5637,958135.0119Keeney and DeLuca (1992)

-33,51721,500131,01773,687 (LHV)2.5037,551136.0110Pimentel (1991)

Btu/galBtu/galBtu/galBtu/galgal/buBtu/lblb/acrebu/acre

Net energy value

Coproductsenergy credits

Total energy use

Ethanol conversion process

Corn ethanol conversion rate

Inputs for nitrogen fertilizer

Nitrogen fertilizer application rate

Corn yieldStudy/year

Energy balance of bioethanol (Shapouri et al., 1995)

Energy converted into ethanol or its coproductsminus energy used to produce ethanol

Net energy value (NEV)

6. Energy Balance

Development of technologiesCorn yieldFertilizer

EnergyApplication rate

Ethanol conversionFarm machineryCoproducts

Causes of discrepancies

6. Energy Balance

Change in NEV (Niven R.K., 2005 )

7. Concerns

Environmental impacts of ethanol in gasoline (Niven R.K., 2005)

8. Conclusion

Many sophisticated techniques for productionof bioethanolIts energetic efficiency and environmentalfriendliness are still controversial.

Thank you