Transcript Economics and environmental impact of bioethanol

Bioethanol production technologies:
Where are we? Where should we be?
W.D.S.S. Pemasinghe
BS/2004/233
Contents
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Why we need alternative fuels?
What are the main candidates for biofuels?
What is bioethanol?
What are the production schemes for bioethanol?
How does bioethanol become a good solution?
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economic issues
environmental issues
Problems and suggested solutions
Why we need alternative fuels?
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Continuous depletion of limited fossil fuel
stock (Global issue).
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Ensure protection and betterment of the
environment (Global issue).
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National security- to be dependent on foreign
nations for energy (USA and the European
Union)
Who are the main candidates for biofuels?
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Bioethanol
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Biodiesel
What is bioethanol?
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Ethanol derived from agricultural sources, as
distinct from petrochemical sources, is
referred to as bioethanol.
Esvc000085.wic012u.server-web.com/pubs/biofuels.doc
Production schemes for bioethanol
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Bioethanol is mainly produced in three ways.
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sugar
ethanol
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starch
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cellulose and hemicellulose
sugar
ethanol
ethanol
Direct conversion of sugar to ethanol
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This is usually done using molasses.
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Molasses is a thick dark syrup produced by boiling down juice from
sugarcane; specially during sugar refining.
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As molasses is a by product, ethanol production from molasses is
not done in a large scale around the world.
The main reaction involved is fermentation
yeast
C6H12O6
2 C2H5OH
sugar (e.g.:-glucose)
ethanol
+
2 CO2
carbon dioxide
Wet milling
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The process of separating the corn kernel into starch, protein, germ and
fiber in an aqueous medium prior to fermentation
The primary products
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starch and starch-derived products (e.g. high fructose corn syrup and
ethanol)
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corn oil, corn gluten, and corn gluten .
Dry milling
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The entire corn kernel is first ground into flour and the starch in the flour is
converted to ethanol via fermentation.
Other than ethanol
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carbon dioxide - carbonated beverage industry
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distillers dried grain with solubles (DDGS) - animal feed
Malting
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Steep the corn in water, start germination, stop germination at a particular
by drying to stop further growth.
Conversion of starch to sugar and then
sugar to ethanol
Eg:-1) wheat
Fermentation conditions
Temperature - 32˚C and 35˚C
pH - 5.2.
 Ethanol is produced at 10-15% concentration and the solution is distilled to produce ethanol at
higher concentrations
Eg:- 2) sugar cane
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Simplest of all the processes
• Fermentation conditions are similar to the above process
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Eg:- 3) Corn
The main producer - United States
http://www.dft.gov.uk/pgr/roads/environment/research.htm
Economics of non-cellulosic ethanol
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Ethanol production using sugarcane, sugarbeet,
corn are well established.
Rise of the Food vs. Fuel crisis and the
shift towards cellulosic ethanol
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"...large increases in biofuels production in
the United States and Europe are the main
reason behind the steep rise in global food
prices" -World Bank policy research working
paper July 2008
Food vs. Fuel crisis
Using crops that can be used for food, to produce bio-fuels
Government support of biofuels with tax breaks, mandated use, and
subsidies.
land that was also formerly used to grow crops for food is now used to grow crops
for biofuels
placing energy markets in competition with food markets
unintended consequence of diverting resources from food production and
leading to surging food prices and the potential destruction of natural habitats.
Challenge for the future…
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Improvement of the cellulosic ethanol
production process.
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Since it is produced from non-edible parts of
plants, cellulosic ethanol does not compete with
the production of food, resulting in no contribution
for the price surge of food.
Cellulosic ethanol
www.agwest.sk.ca/publications/documents/BPfeb05.pdf
Overview of the cellulosic ethanol production technology
Conversion of cellulose and hemicellulose
to ethanol
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1.
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3.
4.
4 steps
Pretreatment
Hydrolysis
Fermentation
Distillation of the product mixture to
separate ethanol
1) Pretreatment
The solubilization and separation of one or more of the four major
components of biomass – hemicellulose, cellulose, lignin, and
extractives – to make the remaining solid biomass more accessible to
further chemical or biological treatment.
2) Hydrolysis
The breaking down of the glycosidic bonds in cellulose and
hemicellulose
acid hydrolysis
Sugars made after acid hydrolysis get converted into furfural in the
acidic medium which can act as fermentation inhibitors.
Reaction should be rapid
Sugars should be rapidly removed
enzymatic hydrolysis
Dilute acid hydrolysis
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Done using dilute acid (1% sulfuric acid)
Two reaction chambers.
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High temperatures and pressures
Disadvantages
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Chamber1- hydrolysis of hemicellulose (mild conditions)
Chamber2- hydrolysis of cellulose (harsh conditions)
Costs are high
Yields are quite low
Therefore concentrated acid hydrolysis is used
Concentrated acid hydrolysis
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Done using concentrated acid (70% sulfuric acid)
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Done in one reaction chamber
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Provides a complete and rapid conversion of cellulose and
hemicellulose to C6 and C5 sugars
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Advantages
 Optimize sugar recovery
 Cost effectively recover the acid for recycling
Acid hydrolysis of cellulose
http://www.turon.com/papers/ethanol.htm
Enzyme hydrolysis
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Bacteria and fungi are used as sources of
cellulases, hemicellulases that could be used
for the hydrolysis of pretreated lignocelulosics.
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There are two technological developments.
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Enzymatic conversion
Direct microbial conversion (DMC)
Direct microbial conversion (DMC)
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A single microorganism does both hydrolysis and
fermentation.
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Advantage
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Cellulose enzyme production or purchase is a significant
cost in enzymatic hydrolysis under development. With
DMC, a dedicated step for production of cellulase enzyme
is not necessary.
Disadvantage
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Currently available microbes cannot do both processes
at the required efficiencies
Enzymatic conversion
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The enzymes are extracted from microorganisms and
are modified genetically to increase efficiencies.
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For enzymes to work efficiently, they must obtain
access to the molecules to be hydrolyzed.
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This further asserts the necessity of pretreatment
process to remove crystalline structure of cellulose to
expose the molecules to the microorganisms.
Applications of enzymatic hydrolysis
(a) Simultaneous sacchrification and fermentation
(SSF)
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Cellulase enzymes and fermenting microbes are added
to one vessel - hydrolysis and fermentation happen in
one reaction vessel.
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Advantage
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Reduces cost
Disadvantage
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Cellulase enzymes and the fermentation enzymes have to
operate under the same conditions - decreases the sugar and
ethanol yields.
(b) Sequential hydrolysis and fermentation (SHF)
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Hydrolysis and fermentation are done in separate
reaction chambers.
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Advantage
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Enables optimization of conditions for the enzymes.
Disadvantage
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Operational and maintenance costs are high.
3) Fermentation
Fermentation of both C5 and C6 sugars
Problem
The ability to ferment pentoses along with hexoses is not
widespread among microorganisms.
Solution
Develop genetically modified microorganisms using recombinant
DNA technology which can ferment both forms of sugars.
Zymomonas mobilis - The National Renewable Energy Laboratory (NREL)
4) Distillation
This is done to separate ethanol from other products.
Ethanol & economy (e.g.-American economy)
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Creating new high-paying jobs
Increasing market opportunities for farmers
Generating additional household income tax and revenues
Stimulating capital investment
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In 2007, the ethanol industry provided employment for 238,000 workers in all
sectors of the U.S. economy, added $47.6 billion to the nation’s GDP, and put an
additional $12.3 billion into the pockets of American consumers.
(Source: Contribution of the Ethanol Industry to the Economy of the United
States)
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The increase in good paying jobs as a result of the facility boosted local
household incomes by more than $100 million.
(Source: "Contribution of the Ethanol Industry to the Economy of the United
States," LECG, LLC, Feb 2008.)
Environmental impact of bioethanol
technologies
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Positives
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Uses energy from renewable energy sources; no net CO2 is added
to the atmosphere, making ethanol an environmentally beneficial
energy source
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Toxicity of exhaust emissions is lower than that of petroleum sources
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Energy crops grown for the production of ethanol absorbs huge
amounts of green house gases (GHG) released by the burning of
fossil fuels.
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Ethanol contains 35% oxygen that helps complete combustion of
fuel and thus reduces particulate emission that pose health hazard
to living beings.
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Negatives
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Deriving ethanol from crops (eg:- corn) consumes copious amounts of
nitrogen fertilizer and extensive top-soil erosion associated with cultivation
of this particular crop.
 contamination of the Mississippi River -‘dead zone’
Recent researches
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Manipulate nitrogen metabolism and fixation pathways to
reduce the dependence on environmentally damaging
fertilizers.
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To enhance performance of enzymes, encapsulate
enzymes in silicon or carbon nanostructures, providing
enzymes with protection from pH and thermal
denaturation.
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Genetically manipulate Saccharomyces cerevisiae
(yeast) so that it can ferment both C5 sugars and C6
sugars
Fermentation
Glycolysis
Alcoholic fermentation
Inhibition by furfural