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Green Chemistry for a Sustainable Future


The beginning of the chemical industry dates back to approximately 1850. ... Biodegradable polymers are very import to green chemistry ... – PowerPoint PPT presentation

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Title: Green Chemistry for a Sustainable Future

Green Chemistry for a Sustainable Future
  • Chapter 20

20.1 Introduction
  • The beginning of the chemical industry dates back
    to approximately 1850.
  • Since then it has arguably grown to become the
    most significant segment of the anthrosphere.

  • Laws have been set forth to regulate the usage of
    chemicals in production. Over a trillion dollars
    has been spent worldwide, trying to back these
  • Regulating was found to be very non-cost

The beginning of Green Chemistry
  • Practices of Green Chemistry began around 1990.
  • A broad definition the sustainable exercise of
    chemical science and technology within the
    framework of good practice of industrial ecology
    such that the use and handling of hazardous
    substances are minimized and such substances are
    never released to the environment.

  • Green Chemistry is self-sustaining Economic
    In strictly monetary terms, green chemistry is
    less costly. Materially Material usage is much
    lower than normal chemistry because use of raw
    materials is much smaller. Wastes Due to use
    of recycled and more natural materials, hazardous
    waste is avoided in great amounts.

20.2 The Key Concept of Atom Economy
  • Atom economy Molecular mass of desired
    product/total molecular mass of materials
  • (reagent)1(reagent)n ? product byproduct

Ideal Atom Economy
  • (reagent)1(reagent)n ? product. (zero
  • While the above reaction is difficult to achieve,
    having a reaction where byproduct ltlt productis
    very desirable.

Principles of Green Chemistry
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20.3 Hazard Reduction
  • Types of hazards 1. Combustible and flammable
    substances, strong reducers that burn readily or
    violently in the presence of atmospheric
    oxygen. 2. Oxidizers that provide oxygen for the
    combustion of reducers. 3. Reactive substances
    that are likely to undergo rapid, violent
    reactions, often in an unpredictable manner. 4.
    Corrosive substances that are generally sources
    of H ion or OH- ion and that tend to react
    destructively with materials, particularly metals.

The Big Three
  • Heavy Metals, Persistent Nonbiodegradable Organic
    Materials, and Volatile Organic Compounds (VOCs)
    are the top 3 candidates for reduction in our
  • An unrealistic goal, simple steps must be
    taken 1. Dont Use them 2. Dont Make them 3.
    If the above cannot be avoided, do not release
    the hazardous substances into the open.

  • Feedstock a raw material used in the industrial
    manufacture of a product.
  • Feedstock should place minimal demands on Earths
  • Should be as safe as possible.
  • Either from petroleum or biological materials

Source (lifetime, methods and environmental
impacts of extraction)
Separation of desired Components from waste or
byproduct matter
Conversion of isolated feedstock material
to desired product
Byproducts and Environmental Effects
The three major steps in obtaining a feedstock
and converting to a useful product.
Biological Feedstocks
  • Biological materials as feedstocks
  • Cellulose is generated in production of corn and

Bio Feedstocks cont.
  • Feedstocks from biological sources tend to be
    more complex than those from petroleum.
  • Offers the advantage of starting with a material
    in which most of the synthesis required has
    already been done by the plant.
  • However, this can be harder to manipulate as more
    complex is harder to alter that simpler feedstock

  • A substance taking part in a chemical reaction,
    especially one used to detect, measure, or
    prepare another substance
  • Use of a benign feedstock may be of little use if
    large quantities of hazardous reagents are
    required for its processing.

Reagent Selection
  • Two Factors
  • Product Selectivity High-Product Selectivity
    means higher conversion of raw material to the
    desired product
  • Product Yield High-Product Yield means a high
    percentage of the desired product is obtained
    relative to the maximum yield calculated from
    stiochiometric considerations.

  • Term used to refer to the matrix in which or on
    which chemical processes occur.
  • Most common type liquid solvents
  • Reagents are dissolved

Media Cont.
  • By their nature, they cause more health and
    environmental health problems than to other
    participants in the chemical synthesis process.
  • Volatile, flammable, cause photochemical smog,
    damages nerves, and can cause peripheral
    neuropathy as a few examples.

Importance of Solvents
  • Uniquely important type of media in which
    chemical processes are carried out
  • They go beyond a reaction media, they are used
    for separation, purification, and cleaning.

The Universal Solvent
  • Water!
  • Most abundant and safest solvent
  • Although, not everything dissolves in it, it is
    an excellent solvent
  • The geometry or the structure of the water
    molecule is what makes is so good

Other Solvent Examples
  • Benzene
  • n-Hexane
  • Glycol ethers

Synthetic and Processing Pathways
  • Ideally chemical synthesis begins with a readily
    available, inexpensive, nontoxic material and
    converts it in one step with 100 percent yield
    and 100 percent atom efficiency

Types of Processing Reactions
  • Addition reactions- all reagents are incorporated
    into product
  • Traditionally are the best because all starting
    materials end up in the product.
  • Substitution reactions- a reagent or parts of it
    replace groups on another reagent
  • Always generate at least some byproducts
  • Elimination reactions- substances are eliminated
    from the feedstock byproduct
  • Dont require input materials other than
    feedstock, but do generate byproducts

The Role of Catalysts
  • A substance that speeds up a reaction without
    being consumed by the reaction is a catalyst
  • Homogeneous catalysts can produce troublesome
    byproducts and product contaminants
  • Heterogeneous catalysts, such as molecular
    sieves, are the most amenable to the practice of
    green chemistry
  • Electrochemical oxidation and reduction is
    matter-free and comes close to the attainment
    of ideal green chemistry, other efficient methods
    of green chemistry catalysts are enzyme reactions
    and photochemical reactions

Biological Alternatives
  • A renewable , sustainable alternative to fuel is
    provided by photosynthetically produced biomass
    (consisting largely of biopolymeric cellulose,
    hemicellulose, starch, lignin, and protein)
  • Polymers are produced when small molecules called
    monomers bond together to form a much smaller
    number of very large molecules
  • Biopolymers are essential to green chemistry
  • Biodegradable polymers are very import to green
  • Examples of Biopolymers cellulose from wood and
    cotton, lignin in wood, and protein in wool and
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