Basic Chemistry of Ethanol
Production
presented at
CCURI Biofuels Workshop
Muskegon Community College
Muskegon, MI
October, 17 – 20, 2013
by
Chuck Crabtree
Director – Iowa BioDevelopment
Indian Hills Community College
Ottumwa, IA
Topics
1. 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
Glucose Basic Structure
= Oxygen
= Carbon
= Hydrogen
Glucose Basic Structure
= Oxygen
= Carbon
Glucose Basic Structure
6
= Oxygen
= Carbon
5
1
4
3
2
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.”
Monomers
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!
Polymers
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!
Monomers and 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
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 Structure
Starch Structure
6
6
6
5
5
5
4
1
3
6
4
1
3
2
5
4
1
3
2
4
2
1
3
2
3
2
Cellulose Structure
6
6
5
3
4
1
3
4
1
5
2
6
5
2
1
4
3
4
1
5
2
6
Cellulosic Structure
Cellulose Structure
Glucose
Molecule
Cellulosic Structure
Cellulose Structure
Individual
Cellulose
Molecules
Glucose
Molecule
Cellulosic Structure
Cellulose Structure
Individual
Cellulose
Molecules
Glucose
Molecule
Cellulosic Structure
Cellulose Structure
Cellulose
Microfibril
Lignin
Individual
Cellulose
Molecules
Glucose
Molecule
Cellulosic Structure
Cellulose Structure
Cellulose
Microfibrils
Lignin
Individual
Cellulose
Molecules
Non-cellulose
Polysaccarides
Cellulose
Fiber
Glucose
Molecule
Lignin
Structure
• Very complex
structure
• Second most
common molecule
on earth.
• Lacks a defined
structure
• Fills the spaces
between cellulose
Hemicellulose Structure
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
• Enzymes are proteins that speed up chemical reactions, but
are not altered themselves (catalysts)
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
6
5
1
4
3
2
Glucose Linkages and Enzyme Active Sites
Named for the way two glucose molecules are attached to each other.
6
5
1
4
3
1,4 linkage
1,6 linkage
2
Amylopectin – Branched Starch Molecule
Amylopectin – Branched Starch Molecule
Introducing the enzyme α-amylase.
Amylopectin – Branched Starch Molecule
Introducing the enzyme α-amylase.
α-amylase breaks down starch into shorter glucose chains
called “dextrins.”
Breaks 1,4 linkages that are not terminal.
Amylopectin – Branched Starch Molecule
Introducing the enzyme α-amylase.
Dextrins
Dextrins
Dextrins
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.
Introducing the enzyme glucoamylase.
Glucoamylase breaks down dextrins into individual glucose molecules.
Acts on 1,4 and 1,6 terminal linkages.
What about Cellulose
Since 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 Options
Physical 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 Fuel
Straight 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
Feedstocks
Three Types of Feedstocks
• Starch-rich feedstocks
• Sugar-rich feedstocks
• Cellulosic feedstocks
Cellulose
Corn
Sugar Cane
Starch-Rich Feedstocks
Two Types of Starch-rich Feedstocks
• Tubers
• Cassava
• Potato
• Cereal grains
• Corn
• Wheat
• Barley
• Rye
• Grain Sorghum Triticale
• Triticale
Barley
Cassava
Potato
Wheat
Sorghum
Corn
Starch-Rich Feedstocks
Tubers
• Cassava
• Potato
Cassava
Potato
Starch-Rich Feedstocks
Cereal Grains
• Wheat
• Barley
Wheat
Barley
Starch-Rich Feedstocks
Cereal Grains
• Rye
• Grain Sorghum
• Triticale
Rye
Triticale
Grain Sorghum
Sugar-Rich Feedstocks
Three Primary Sources
• Sugar Cane
• Sugar Beets
• Sweet Sorghum
Sugar Beets
Sugar Cane
Sweet Sorghum
Sugar-Rich Feedstocks
Different process than for starch-rich feedstocks.
Sugar Feedstock Process
•
•
•
•
•
•
•
•
•
Sugar juice/syrup
Washing
preparation
Breaking
Milling
Straining
Clarification
Evaporation
Mash Preparation
Fermentation
Distillation/Dehydration
Starch Feedstock Process
•
•
•
•
•
•
•
•
•
Milling
Mashing/Cooking/Liquifaction
Fermentation
Distillation/Dehydration
Sugar-Rich Feedstocks
Sugar Cane
Sugar-Rich Feedstocks
Sugar Beets
Sweet Sorghum
Sugar Beets
Sweet Sorghum
Cellulosic Feedstocks
Cellulose
• What is it?
• General term – Biomass
• Straight chain polymer of
glucose molecules
• Used by plants in cell walls
Hay
Wood Chips
Cellulosic Feedstocks
Cellulose
• Where does it come from?
• Plant material
• Wood
• Grasses (e.g., switchgrass)
• Crop residue (e.g., corn
stover)
Cellulosic Feedstocks
Cellulose
• 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 Feedstocks
Cellulose
• 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 Information
The 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 2008-1005. 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.