1. John Nowatzki NDSU Extension Service
Ethanol Production
John Nowatzki
NDSU Extension Service
2/21/2019

2. Introduction What is Ethanol? Ethanol Production From Biomass
Ethanol Production From Grains
Ethanol Engine Fuel Characteristics
Ethanol Strengths & Weaknesses
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3. What is Ethanol?
Ethanol is a clear liquid made from fermenting sugars from:
Grains – grain ethanol
Biomass – cellulosic ethanol
Ethanol is an engine fuel that burns to produce carbon dioxide and water
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4. Cellulosic Ethanol Production
Feedstock
2nd Pretreatment
(convert cellulose into
Glucose)
Glucose
fermentation
Lignin
1st Pretreatment
(convert hemi-cellulose
into xylose and reduce
size and open up
structure of cellulose)
Simultaneous
saccharification
& fermentation
Distillation
to recover
ethanol
Ethanol
Fuel for
heat and
electricity
Lignin
Hydrolysis
Hydrolysis is a chemical decomposition process that uses water to split chemical bonds of substances. There are two types of hydrolysis, acid and enzymatic. Feedstocks that may be appropriate for acid or enzymatic hydrolysis typically are plant-based materials containing cellulose. These include forest material and sawmill residue, agricultural residue, urban waste, and waste paper. All plants have structural components composed of lignocellulosic fibers, which in turn are comprised of three major fractions: cellulose, hemicellulose, and lignin. Cellulose and hemicellulose are chains of sugar molecules that can be broken down chemically or biologically into the component sugars. The sugars are then fermented using yeast or bacteria to produce ethanol, which is then distilled to a higher concentration for final use. Sugars can also be converted to levulinic acid and citric acid. Levulinic acid is a versatile chemical that is a precursor to other specialty chemicals, fuels and fuels additives, herbicides, and pesticides. The largest application for citric acid is in the beverage industry, which accounts for about 45 percent of the market for this product. Citric acid is also used in a wide variety of candies, frozen foods, and processed cheeses and as a preservative in canned goods, meats, jellies, and preserves.Lignin binds cellulose and hemicellulose together and cannot be broken down to form sugars. At this point, the most cost-effective use for lignins is as a fuel for biomass-to-energy facilities.
Reference: (California Integrated Waste Management Board )
Fermentation of
xylose and other simple sugars from hemi-cellulose
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5. Cellulosic Ethanol Production
1st Pretreatment
Convert hemi-cellulose into pentoses (5 carbon sugars) and partial breakdown of cellulose
Each type of cellulosic feedstock requires a unique combination of pretreatments.
Physical methods:
steam explosion
Chemical methods:
dilute acid, alkaline, organic solvent, ammonia, sulfur dioxide, carbon dioxide
Biological methods:
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6. Cellulosic Ethanol Production
2nd Pretreatment
Convert cellulose into hexoses (6 carbon sugars)
The cellulose fraction is hydrolyzed by acids or enzymes to produce glucose
Enzymatic hydrolysis – biological conversion of cellulose to sugars
Acid hydrolysis – acid concentrations to convert cellulose to sugars
Enzymatic Hydrolysis Enzymatic hydrolysis; simultaneous saccharification and co-fermentation (SSCF): The steps in the conversion of cellulosic materials to ethanol in processes featuring enzymatic hydrolysis includes pretreatment, biological conversion, product recovery, and utilities and waste treatment. SSCF is an adaptation to the process, which combines hydrolysis and fermentation in one vessel. Sugars produced during hydrolysis are immediately fermented into ethanol. By fermenting the sugars as soon as they form, eliminates problems associated with sugar accumulation and enzyme inhibition. 
Dilute Acid Hydrolysis  Dilute acid hydrolysis: This process uses low concentration acids and high temperatures to process the cellulosic biomass. Lignocellulose biomass is pretreated with approximately 0.5% acid in liquid at up to 200ºC to hydrolyze the hemicellulose and expose the cellulose for hydrolysis. The hemicellulose hydrolysis yields most pentose (C5) sugars, principally xylose and arabinose, which are fermented to ethanol and distilled. The remaining solids, cellulose and lignin, enter the second stage hydrolyzer where cellulose is converted to glucose with approximately 2% acid in liquid at up to 240º C. The resulting sugars are then fermented to ethanol and distilled. 
Concentrated Acid Hydrolysis  Concentrated acid hydrolysis: This process uses high concentration halogen acids and near ambient temperatures to convert cellulosic biomass to sugars. The decrystalization and hydrolysis of cellulose with nearly 100% yields may be accomplished with 40 wt% hydrochloric acid, 60 wt% sulfuric acid, or 90 wt% hydrofluoric acid. The liquid phase hydrochloric acid process is the only halogen process to have reached commercial development. 
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7. Cellulosic Ethanol Production
Lignin (By-product)
The solids remaining after the hemi-cellulose and cellulose are converted to sugars are washed, dried and used as fuel source for power production. 
Enzymatic Hydrolysis Enzymatic hydrolysis; simultaneous saccharification and co-fermentation (SSCF): The steps in the conversion of cellulosic materials to ethanol in processes featuring enzymatic hydrolysis includes pretreatment, biological conversion, product recovery, and utilities and waste treatment. SSCF is an adaptation to the process, which combines hydrolysis and fermentation in one vessel. Sugars produced during hydrolysis are immediately fermented into ethanol. By fermenting the sugars as soon as they form, eliminates problems associated with sugar accumulation and enzyme inhibition. 
Dilute Acid Hydrolysis  Dilute acid hydrolysis: This process uses low concentration acids and high temperatures to process the cellulosic biomass. Lignocellulose biomass is pretreated with approximately 0.5% acid in liquid at up to 200ºC to hydrolyze the hemicellulose and expose the cellulose for hydrolysis. The hemicellulose hydrolysis yields most pentose (C5) sugars, principally xylose and arabinose, which are fermented to ethanol and distilled. The remaining solids, cellulose and lignin, enter the second stage hydrolyzer where cellulose is converted to glucose with approximately 2% acid in liquid at up to 240º C. The resulting sugars are then fermented to ethanol and distilled. 
Concentrated Acid Hydrolysis  Concentrated acid hydrolysis: This process uses high concentration halogen acids and near ambient temperatures to convert cellulosic biomass to sugars. The decrystalization and hydrolysis of cellulose with nearly 100% yields may be accomplished with 40 wt% hydrochloric acid, 60 wt% sulfuric acid, or 90 wt% hydrofluoric acid. The liquid phase hydrochloric acid process is the only halogen process to have reached commercial development. 
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8. Cellulosic Ethanol Production
Hydrolysis (saccharification)
Hydrolysis breaks down the hydrogen bonds in the hemi-cellulose and cellulose fractions into their sugar components: pentoses and hexoses.
The yeast contains an enzyme called invertase, which acts as a catalyst and helps to convert the sucrose sugars into glucose and fructose (both C6H12O6)
The catalyst is dissolved in the alcohol using a standard agitator or mixer.
After the addition of alcoloh the reaction is closed to prevent the loss of alcohol.
Some processors use more heat to speed up the process.
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9. Cellulosic Ethanol Production
Fermentation
The fructose and glucose sugars reacts with an enzyme called zymase, which is also contained in the yeast, to produce ethanol and carbon dioxide.
The fermented mash, called beer, contains about 10% alcohol plus all the non-fermentable solids from the corn and yeast cells.
The mash and solids are separated
(After fermentation the cellulosic and grain ethanol production processes are similar and will be explained together.)
The catalyst is dissolved in the alcohol using a standard agitator or mixer.
After the addition of alcoloh the reaction is closed to prevent the loss of alcohol.
Some processors use more heat to speed up the process.
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10. Grain Ethanol Production Dry Milling Process
Hydrolysis
Hydrolysis is a chemical decomposition process that uses water to split chemical bonds of substances. There are two types of hydrolysis, acid and enzymatic. Feedstocks that may be appropriate for acid or enzymatic hydrolysis typically are plant-based materials containing cellulose. These include forest material and sawmill residue, agricultural residue, urban waste, and waste paper. All plants have structural components composed of lignocellulosic fibers, which in turn are comprised of three major fractions: cellulose, hemicellulose, and lignin. Cellulose and hemicellulose are chains of sugar molecules that can be broken down chemically or biologically into the component sugars. The sugars are then fermented using yeast or bacteria to produce ethanol, which is then distilled to a higher concentration for final use. Sugars can also be converted to levulinic acid and citric acid. Levulinic acid is a versatile chemical that is a precursor to other specialty chemicals, fuels and fuels additives, herbicides, and pesticides. The largest application for citric acid is in the beverage industry, which accounts for about 45 percent of the market for this product. Citric acid is also used in a wide variety of candies, frozen foods, and processed cheeses and as a preservative in canned goods, meats, jellies, and preserves.Lignin binds cellulose and hemicellulose together and cannot be broken down to form sugars. At this point, the most cost-effective use for lignins is as a fuel for biomass-to-energy facilities.
Reference: (California Integrated Waste Management Board )
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11. Grain Ethanol Production Grinding
The grain passes through a hammer mill which grinds it into a fine powder called meal.
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12. Grain Ethanol Production Liquify and Cooking
The meal is mixed with water and cooked to liquify the starch. Heat is applied to enhance liquefaction resulting in a mash.
Enzymes are added to facilitate starch breakdown
Liquefaction. The meal is mixed with water and alpha-amylase, then passed through cookers where the starch is liquefied. Heat is applied at this stage to enable liquefaction. Cookers with a high temperature stage ( degrees Celsius) and a lower temperature holding period (95 degrees Celsius) are used. High temperatures reduce bacteria levels in the mash.
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13. Grain Ethanol Production Saccharify
An enzyme is added to the mash to convert the liquefied starch to fermentable sugars
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14. Grain Ethanol Production Fermentation
Yeast is added to the mash to ferment the sugars to ethanol and carbon dioxide.
In a batch process, the mash stays in one fermenter for about 48 hours before the distillation process is started.
Fermentation. Yeast is added to the mash to ferment the sugars to ethanol and carbon dioxide. Using a continuous process, the fermenting mash is allowed to flow through several fermenters until it is fully fermented and leaves the final tank. In a batch process, the mash stays in one fermenter for about 48 hours before the distillation process is started.
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15. Distillation (Cellulosic or Grain)
Ethanol Production
Distillation (Cellulosic or Grain)
The distillation involves boiling the water and ethanol mixture. Since ethanol has a lower boiling point (78.3C) than water (100C), ethanol vaporizes before water and can be condensed and separated
The distilled alcohol is about 96% strength.
Fractional Distillation Process The ethanol, which is produced from the fermentation process, still contains a significant quantity of water, which must be removed. This is achieved by using the fractional distillation process. The distillation process works by boiling the water and ethanol mixture. Since ethanol has a lower boiling point (78.3C) compared to that of water (100C), the ethanol turns into the vapour state before the water and can be condensed and separated.
Dehydration. The alcohol from the top of the column passes through a dehydration system where the remaining water will be removed. Most ethanol plants use a molecular sieve to capture the last bit of water in the ethanol. The alcohol product at this stage is called anhydrous ethanol (pure, without water) and is approximately 200 proof.
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16. Ethanol Production Drying & Denaturing
(Cellulosic or Grain)
Most ethanol plants use a molecular sieve to water from the distilled ethanol.
Fuel ethanol must be denatured, or made unfit for human consumption, with a small amount of gasoline (2-5%)
Fractional Distillation Process The ethanol, which is produced from the fermentation process, still contains a significant quantity of water, which must be removed. This is achieved by using the fractional distillation process. The distillation process works by boiling the water and ethanol mixture. Since ethanol has a lower boiling point (78.3C) compared to that of water (100C), the ethanol turns into the vapour state before the water and can be condensed and separated.
Dehydration. The alcohol from the top of the column passes through a dehydration system where the remaining water will be removed. Most ethanol plants use a molecular sieve to capture the last bit of water in the ethanol. The alcohol product at this stage is called anhydrous ethanol (pure, without water) and is approximately 200 proof.
7. Denaturing. Ethanol that will be used for fuel must be denatured, or made unfit for human consumption, with a small amount of gasoline (2-5%). This is done at the ethanol plant.
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17. Grain Ethanol Production
Dried Distillers Grains (DDG)
DDG is a by-product of grain ethanol production.
Drying the distillers grain increases its shelf life and reduces transportation costs
A bushel of corn (56 lbs) yields about 2.8 gallons of ethanol and 17 pounds of distillers grain
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18. Grain Ethanol Production
Dried Distillers Grains with Solubles (DDGS)
DDGS is a by-product of grain ethanol production.
The liquid that is separated from the mash during the distilling process is partially dehydrated into a syrup, then added back onto the dried distillers grain to create DDGS
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19. (Cellulosic or Grain) Carbon Dioxide (CO2)
Ethanol Production
(Cellulosic or Grain) Carbon Dioxide (CO2)
CO2 is given off during fermentation
Ethanol production plants collect, compress, and sell it for use in other industries
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20. Ethanol Fuel Characteristics
Ethanol E100
E85
85 % Ethanol – 15 % Gasoline
Gasohol
10 % Ethanol – 90 % Gasoline
Gasoline
BTU,s/Gal
84,400
90,000
120,900
125,000
Octane Number
100 98 94
Equitable Value (BTU)
$2.02/gal
$2.16/gal
$2.90/gal
$3.00/gal
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21. Ethanol Strengths & Weaknesses
Potential Strengths
Fewer air pollutants
Renewable sources
Potential Weaknesses
Fewer BTU’s per gallon
Higher ethanol blends require engine modification
Fuel line heaters
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22. More Information http://www.ag.ndsu.nodak.edu/abeng
John Nowatzki, NDSU Extension State Specialist
Telephone:
References
The Institute for Energy and Environment, within the RAE '5' rated Electronic and Electrical Engineering Department at Strathclyde University, has established itself as one of the leading centres of its kind internationally.
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