Basic Chemistry of Ethanol Production

presented at

CCURI Biofuels WorkshopMuskegon Community College

Muskegon, MIOctober, 17 – 20, 2013

by

Chuck CrabtreeDirector – Iowa BioDevelopmentIndian Hills Community College

Ottumwa, IA

Topics1. What are carbohydrates?2. What is glucose?3. Why is glucose important?4. What is starch?5. What is cellulose?6. How are the structures of starch and cellulose

similar and how are they different?7. How is starch used to make ethanol?8. How is cellulose used to make ethanol?9. What are some of the more common feedstocks

used for ethanol production?

Carbohydrates – Starch and Cellulose

What is a carbohydrate?• Organic compounds that contain only carbon,

hydrogen, and oxygen

What do carbohydrates do?• Store energy (food) – starch (corn, potatoes)• Structural – cellulose (plant stems, wood)

Basic component of both starch and cellulose?• Glucose

= Oxygen

= Carbon

Glucose Basic Structure

= Hydrogen

Glucose Basic Structure

= Oxygen

= Carbon

= Oxygen

= Carbon

Glucose Basic Structure

1

2

4

3

6

5

Glucose Basic Structure

Glucose – Important Facts• Also called “fermentable

sugar,” “dextrose,” “corn sugar” or “sugar”

• Used by biological systems as food

• It is a “monomer” – Mono means “one” or “single.”

• Starch is a “polymer” – Poly means “many.”

What is a monomer?• One unit of a string of units

Monomers

What is a monomer?• One unit of a string of units

• Example: Pearl necklace• If a monomer is 1 unit of a

string of units, then what is the monomer of a pearl necklace?

Monomers

What is a monomer?• One unit of a string of units

• Example: Pearl necklace• If a monomer is 1 unit of a

string of units, then what is the monomer of a pearl necklace?

• A pearl!

Monomers

What is a polymer?• A string of similar units

Polymers

What is a polymer?• A string of similar units

• Example: Pearl necklace• If a polymer is a string of

similar units, then what is the polymer of a pearl?

Polymers

What is a polymer?• A string of similar units

• Example: Pearl necklace• If a polymer is a string of

similar units, then what is the polymer of a pearl?

• A pearl necklace!

Polymers

• The pearl is a monomer– When connected with

other pearls they make a polymer called a pearl necklace

• Same principle applies to chemicals– Glucose is a monomer– When connected with

other glucose molecules they make a polymer called starch or cellulose

Monomers and Polymers

Starch is a polymer• > 500 glucose units • Two types of starch

Starch is a polymer• > 500 glucose units • Two types of starch

• Amylose – straight chains

Starch is a polymer• > 500 glucose units • Two types of starch

• Amylose – straight chains• Amylopectin – branched chains

Starch vs. Cellulose StructureStarch Structure

1

3 2

4

56

1

3 2

4

56

1

3 2

4

56

1

3 2

4

56

Cellulose Structure

1

3 2

4

5

6

1

3 2

4

5

6

1

3 2

4

56

1

3 2

4

56

Cellulosic Structure

Cellulose Structure

GlucoseMolecule

Cellulosic Structure

Cellulose Structure

GlucoseMolecule

IndividualCelluloseMolecules

Cellulosic Structure

Cellulose StructureIndividualCelluloseMolecules

GlucoseMolecule

Cellulosic StructureCellulose Structure

CelluloseMicrofibril

IndividualCelluloseMolecules

GlucoseMolecule

Lignin

Cellulosic StructureCellulose Structure

IndividualCelluloseMolecules

GlucoseMolecule

CelluloseMicrofibrils

CelluloseFiber

Non-cellulosePolysaccarides

Lignin

Lignin Structure

• Very complex structure

• Second most common molecule on earth.

• Lacks a defined structure

• Fills the spaces between cellulose

Hemicellulose Structure

• Enzymes are proteins that speed up chemical reactions, but are not altered themselves (catalysts)

Enzymes

• Enzymes are proteins that speed up chemical reactions, but are not altered themselves (catalysts)

Enzymes

• Enzymes are proteins that speed up chemical reactions, but are not altered themselves (catalysts)

Enzymes

• Enzymes are proteins that speed up chemical reactions, but are not altered themselves (catalysts)

Enzymes

Reaction can go either way

Glucose Linkages and Enzyme Active Sites

Glucose Linkages and Enzyme Active Sites

Glucose Linkages and Enzyme Active Sites

Glucose Linkages and Enzyme Active Sites

1

23

4

5

6

Named for the way two glucose molecules are attached to each other.

Glucose Linkages and Enzyme Active Sites

1

23

4

5

6

1,6 linkage1,4 linkage

Amylopectin – Branched Starch Molecule

Amylopectin – Branched Starch MoleculeIntroducing the enzyme α-amylase.

Amylopectin – Branched Starch MoleculeIntroducing the enzyme α-amylase.

α-amylase breaks down starch into shorter glucose chains called “dextrins.”Breaks 1,4 linkages that are not terminal.

Dextrins

Dextrins

Dextrins

Amylopectin – Branched Starch MoleculeIntroducing the enzyme α-amylase.

α-amylase breaks down starch into shorter glucose chains called “dextrins.”Breaks 1,4 linkages that are not terminal.

Dextrins

Dextrins

Dextrins

Introducing the enzyme glucoamylase.

Glucoamylase breaks down dextrins into individual glucose molecules.Acts on 1,4 and 1,6 terminal linkages.

Introducing the enzyme glucoamylase.

What about CelluloseSince starch and cellulose are glucose polymers, why is cellulose so much harder to break down into glucose?

So how do we get through the other stuff to get to the cellulose?

Once we get to the cellulose, will the same enzymes work?

Cellulose Pretreatment OptionsPhysical Breakdown (heat/pressure, grinding, chopping, sonication)

Weak Caustic (NaOH, Ammonia)

Weak Acid (Sulfuric, HCL)

Heat with caustic and acid

Pressure and heat with caustic and acid

Enzymatic cocktails (cellulases, zylases, gluconases, ligases, hemicellulases, etc). Usually used after at least one of the above.

Time can vary on all of these.

Cellulose as Other Forms of FuelStraight Combustion – Most common

Pyrolysis (bio-oil)– Usually high temps and pressures. Some low temp technologies.

Syngas – Gasification of organic material at high temps (without combustion) with oxygen and steam to produce CO, H, and CO2

Ethanol Feedstocks

FeedstocksThree Types of Feedstocks• Starch-rich feedstocks• Sugar-rich feedstocks• Cellulosic feedstocks

Sugar Cane

Cellulose Corn

Starch-Rich FeedstocksTwo Types of Starch-rich Feedstocks

• Tubers• Cassava• Potato

• Cereal grains• Corn• Wheat• Barley• Rye• Grain Sorghum• Triticale

Potato

Barley

Triticale

Cassava

Sorghum

Wheat Corn

Starch-Rich Feedstocks

Tubers• Cassava• Potato

PotatoCassava

Starch-Rich Feedstocks

Cereal Grains• Wheat• Barley

Barley

Wheat

Starch-Rich Feedstocks

Cereal Grains• Rye• Grain Sorghum• Triticale

Rye

Grain Sorghum

Triticale

Sugar-Rich Feedstocks

Three Primary Sources• Sugar Cane• Sugar Beets• Sweet Sorghum

Sugar Cane

Sugar Beets Sweet Sorghum

Sugar-Rich Feedstocks

Different process than for starch-rich feedstocks.

Sugar Feedstock Process

• Washing• Breaking• Milling• Straining• Clarification• Evaporation• Mash Preparation• Fermentation• Distillation/Dehydration

Starch Feedstock Process

• -• -• Milling• -• -• -• Mashing/Cooking/Liquifaction• Fermentation• Distillation/Dehydration

Sugar juice/syruppreparation

Sugar-Rich FeedstocksSugar Cane

Sugar-Rich FeedstocksSugar BeetsSweet Sorghum

Sweet Sorghum

Sugar Beets

Cellulosic FeedstocksCellulose• What is it?

• General term – Biomass• Straight chain polymer of

glucose molecules• Used by plants in cell walls

Wood Chips

Hay

Cellulosic FeedstocksCellulose

• Where does it come from?• Plant material• Wood• Grasses (e.g.,

switchgrass)• Crop residue (e.g., corn

stover)

Cellulosic FeedstocksCellulose

• Where does it come from?• Plant material• Wood• Grasses (e.g.,

switchgrass)• Crop residue (e.g., corn

stover)

• Advantages• No food vs. fuel issues• Worldwide distribution• High glucose density

Cellulosic FeedstocksCellulose

• Where does it come from?• Plant material• Wood• Grasses (e.g.,

switchgrass)• Crop residue (e.g., corn

stover)

• Advantages• No food vs. fuel issues• Worldwide distribution• High glucose density

• Disadvantages• Difficult to breakdown• Bulky

Sources of InformationThe Alcohol Textbook, Fifth Edition, W.M Ingledew, D. R. Kelsall,

G. D. Austin and C Kluhspies, eds. Nottingham University Press, Nottingham, UK, 2009.

Portaria Nº 143, de 27 de Junho de 2007 (in Portuguese). Ministério da Agricultura, Pecuária e Abastecimento. Retrieved 2008-10-05.  This decree fixed the mandatory blend at 25% starting July 1st, 2007

Luiz A. Horta Nogueira (2004-03-22). "Perspectivas de un Programa de Biocombustibles en América Central: Proyecto Uso Sustentable de Hidrocarburos" (in Spanish) (PDF). Comisión Económica para América Latina y el Caribe (CEPAL). Retrieved 2008-05-09. 

UNICA: venda de veículos flex no Brasil cresce 13,9% em 2009 e frota ultrapassa 9 milhões de unidades (in Portuguese). UNICA. 2010-01-11. Retrieved 2010-02-09.