Green Chemistry for a Sustainable Future

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Green Chemistry for a Sustainable Future

• Chapter 20

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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.

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20.1

• 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
  regulations.
• Regulating was found to be very non-cost
  efficient.

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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.

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Sustainability

• 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.

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20.2 The Key Concept of Atom Economy

• Atom economy Molecular mass of desired
  product/total molecular mass of materials
  generated.
• (reagent)1(reagent)n ? product byproduct

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Ideal Atom Economy

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

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Principles of Green Chemistry

• http//interface.audiovideoweb.com/lnk/il80win1011
  5/video_converted_wm/intro/windowshigh_str.wmv/pla
  y.asx
• https//portal.acs.org/portal/Navigate?nodeid1415
  
• http//pubs.acs.org/cen/coverstory/7929/7929greenc
  hemistry.html

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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.

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The Big Three

• Heavy Metals, Persistent Nonbiodegradable Organic
  Materials, and Volatile Organic Compounds (VOCs)
  are the top 3 candidates for reduction in our
  environment.
• 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.

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20.4

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

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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.
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Biological Feedstocks

• Biological materials as feedstocks
• Cellulose is generated in production of corn and
  wheat

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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

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Reagents

• 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.

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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.

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Media

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

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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.

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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.

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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

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Other Solvent Examples

• Benzene
• n-Hexane
• Glycol ethers

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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

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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

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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

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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
  chemistry
• Examples of Biopolymers cellulose from wood and
  cotton, lignin in wood, and protein in wool and
  silk