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Economics and environmental impact of bioethanol production


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									Bioethanol production technologies:
Where are we? Where should we be?

      W.D.S.S. Pemasinghe
   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?
       economic issues
       environmental issues
   Problems and suggested solutions
Why we need alternative fuels?

   Continuous depletion of limited fossil fuel
    stock (Global issue).

   Ensure protection and betterment of the
    environment (Global issue).

   National security- to be dependent on foreign
    nations for energy (USA and the European
Who are the main candidates for biofuels?

                  Bioethanol

                  Biodiesel
What is bioethanol?

   Ethanol derived from agricultural sources, as
    distinct from petrochemical sources, is
    referred to as bioethanol.

Production schemes for bioethanol

   Bioethanol is mainly produced in three ways.

       sugar            ethanol

       starch           sugar        ethanol

       cellulose and hemicellulose        ethanol
Direct conversion of sugar to ethanol
   This is usually done using molasses.

   Molasses is a thick dark syrup produced by boiling down juice from
    sugarcane; specially during sugar refining.

   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
    C6H12O6                    2 C2H5OH    +   2 CO2
    sugar (e.g.:-glucose)      ethanol         carbon dioxide
       Wet milling

         The process of separating the corn kernel into starch, protein, germ and
          fiber in an aqueous medium prior to fermentation
         The primary products
            starch and starch-derived products (e.g. high fructose corn syrup and
            corn oil, corn gluten, and corn gluten .

       Dry milling

         The entire corn kernel is first ground into flour and the starch in the flour is
          converted to ethanol via fermentation.
         Other than ethanol
           carbon dioxide - carbonated beverage industry
           distillers dried grain with solubles (DDGS) - animal feed

       Malting

         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

   Simplest of all the processes

     • Fermentation conditions are similar to the above process
   Eg:- 3) Corn
       The main producer - United States

Economics of non-cellulosic ethanol
   Ethanol production using sugarcane, sugarbeet,
    corn are well established.
Rise of the Food vs. Fuel crisis and the
shift towards cellulosic ethanol

   "...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

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…

   Improvement of the cellulosic ethanol
    production process.

       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

Overview of the cellulosic ethanol production technology
Conversion of cellulose and hemicellulose
to ethanol
    4 steps
1.   Pretreatment
2.   Hydrolysis
3.   Fermentation
4.   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
              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

   Done using dilute acid (1% sulfuric acid)
   Two reaction chambers.
           Chamber1- hydrolysis of hemicellulose (mild conditions)
           Chamber2- hydrolysis of cellulose (harsh conditions)
   High temperatures and pressures
   Disadvantages
       Costs are high
       Yields are quite low

   Therefore concentrated acid hydrolysis is used
    Concentrated acid hydrolysis

   Done using concentrated acid (70% sulfuric acid)

   Done in one reaction chamber

   Provides a complete and rapid conversion of cellulose and
    hemicellulose to C6 and C5 sugars

   Advantages
     Optimize sugar recovery

     Cost effectively recover the acid for recycling
Acid hydrolysis of cellulose

    Enzyme hydrolysis

   Bacteria and fungi are used as sources of
    cellulases, hemicellulases that could be used
    for the hydrolysis of pretreated lignocelulosics.

   There are two technological developments.
       Enzymatic conversion
       Direct microbial conversion (DMC)
Direct microbial conversion (DMC)

   A single microorganism does both hydrolysis and

   Advantage
       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
       Currently available microbes cannot do both processes
        at the required efficiencies
Enzymatic conversion

   The enzymes are extracted from microorganisms and
    are modified genetically to increase efficiencies.

   For enzymes to work efficiently, they must obtain
    access to the molecules to be hydrolyzed.

   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

   Cellulase enzymes and fermenting microbes are added
    to one vessel - hydrolysis and fermentation happen in
    one reaction vessel.

   Advantage
       Reduces cost

   Disadvantage
       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)

   Hydrolysis and fermentation are done in separate
    reaction chambers.

   Advantage
       Enables optimization of conditions for the enzymes.

   Disadvantage
       Operational and maintenance costs are high.
3) Fermentation
Fermentation of both C5 and C6 sugars

     The ability to ferment pentoses along with hexoses is not
     widespread among microorganisms.

     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)
   Creating new high-paying jobs
   Increasing market opportunities for farmers
   Generating additional household income tax and revenues
   Stimulating capital investment

       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

       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
   Positives
   Uses energy from renewable energy sources; no net CO2 is added
    to the atmosphere, making ethanol an environmentally beneficial
    energy source

   Toxicity of exhaust emissions is lower than that of petroleum

   Energy crops grown for the production of ethanol absorbs huge
    amounts of green house gases (GHG) released by the burning of
    fossil fuels.

   Ethanol contains 35% oxygen that helps complete combustion of
    fuel and thus reduces particulate emission that pose health hazard
    to living beings.
   Negatives
   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
   Manipulate nitrogen metabolism and fixation pathways to
    reduce the dependence on environmentally damaging

   To enhance performance of enzymes, encapsulate
    enzymes in silicon or carbon nanostructures, providing
    enzymes with protection from pH and thermal

   Genetically manipulate Saccharomyces cerevisiae
    (yeast) so that it can ferment both C5 sugars and C6

          Alcoholic fermentation
Inhibition by furfural

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