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National Centre for Catalysis Research

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Pollution is the action of environmental contamination with man ... Bromine is regenerated. 2 HBr Br2 H2. H2S H2 1/2 S2. Electrochemical gas purification ... – PowerPoint PPT presentation

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Title: National Centre for Catalysis Research


1
National Centre for Catalysis Research
M. HELEN Research Scholar
2
Environment and Pollution
Pollution is the action of environmental
contamination with man-made waste
3
Possibilities offered by Electrochemistry
  • With a rapidly growing world population and an
    increasing number of reports on detrimental
    effects on the environment, its protection has
    become a major issue
  • The strategies for environmental protection in
    industry generally include processes for waste
    treatment as well as development of new processes
    or products which have no or less harmful effects
    on the environment
  • Electrochemistry has important roles to play in
    both types of strategies
  • Electrochemical processes can be used for
    recovery or treatment of effluents from
    industrial or municipal plants. Industrial
    electrochemistry has undergone a development
    towards cleaner processes and more
    environmentally friendly products
  • Electrochemical sensors are effective and
    inexpensive devices for environmental monitoring
    of an increasing range of toxic substances
  • A big and important class of environmental
    problems can be found in the energy and
    transportation sectors
  • Electrochemistry offers unique ways to generate
    pure electric power at high efficiency in fuel
    cells or to store it in batteries

4
Electrochemistry, with its unique ability to
oxidize or reduce compounds at a well-controlled
electrode potential and by just adding (at the
anode) or withdrawing (at the cathode) electrons,
offers many interesting possibilities in
environmental engineering
5
Standard Reduction Potentials (in Volts), 25oC
Reaction Eo
F2 2e- ---gt 2F- 2.87
Co3 e- ---gt Co2 1.80
Cl2 2e- ---gt 2Cl- 1.36
O2 4H 4e- ---gt 2H2O 1.23
NO3- 4H 3e- ---gt NO 2H2O 0.96
Ag e- ---gt Ag 0.80
Fe3 e- ---gt Fe2 0.77
I2 2e- ---gt 2I- 0.54
Cu e- ---gt Cu 0.52
Cu2 2e- ---gt Cu 0.34
Cu2 e- ---gt Cu 0.15
2H 2e- ---gt H2 0.00
Reaction Eo
Fe3 3e- ---gt Fe -0.04
Sn2 2e- ---gt Sn -0.14
Ni2 2e- ---gt Ni -0.25
Co2 2e- ---gt Co -0.29
Fe2 2e- ---gt Fe -0.41
Zn2 2e- ---gt Zn -0.76
2H2O 2e- ---gt H2(g) 2OH- -0.83
V2 2e- ---gt V -1.18
Mn2 2e- ---gt Mn -1.18
Al3 3e- ---gt Al -1.66
Strong oxidizing agents
Strong reducing agents
Na e- Na -2.71 Li
e- Li -3.04
6
Electrochemical processes for waste treatment
  • Anodic processes
  • To oxidize organic pollutants to harmless
    products
  • To remove toxic compounds from flue gases
  • Cathodic processes
  • To remove heavy metal ions from waste water
    solutions
  • In both types of electrode processes, the
    operating conditions must be carefully controlled
    in order to avoid side reactions.
  • In aqueous solutions, which are most often used,
    the side reactions are mainly oxygen evolution at
    the anode and hydrogen evolution at the cathode.
  • These side reactions lower the current efficiency
    thereby increasing the operating costs, and may
    disturb the process because of vigorous gas
    evolution or pH changes at the electrodes.
  • Not only can the two electrodes of the
    electrochemical cell be used in purification
    processes, but the ion-selective membranes that
    are often placed between the electrodes to have a
    selective transfer of only anions or cations can
    also.
  • New electrodialytic processes using such
    membranes have been developed, which can solve a
    variety of environmental problems.

7
Cyanide Poisoning
Electroplating - Zinc, copper, cadmium,
silver, gold, brass and nickel are
commonly plated using cyanide solutions Cyanide
solutions - intrinsic cleaning ability -
effective in keeping metals in solution during
the plating process - to obtain very
finely grained metal deposits
Cyanide
- harms the brain and heart, and may cause coma
and death
8
High concentration of cyanide (gt 1 M)
Electrochemical process Anode (graphite or
stainless steel) cyanide is oxidized CN-
20H- CNO- H20 2e- Cathode metal
deposition with hydrogen evolution as a side
reaction. Temperature - 50-90 ºC Current
density - 500 A m-2
Low concentration in outlet stream
9
Chlorine in Drinking Water
Effective disinfectant - destroy many of the
bacteria in your drinking
water  Chlorinated hydrocarbons - chlorine
reacts with decomposed plant and animal
materials
- solvents and disinfectants, bleaching
in the pulp and paper industry (chlorinated
phenols)
Chlorine - irritant to the eyes, skin, the upper
respiratory tract, and the lungs
Dechlorination
  • Combustion
  • membrane separation, adsorption on activated
    carbon and stripping, chemical oxidation with
    air, ozone or other oxidants
  • Chemical reduction techniques, such as catalytic
    dehalogenation with hydrogen or other reducing
    agents
  • Biological techniques using special
    microorganisms or enzymes
  • Electrochemical dechlorination - either
    anodically or cathodically

10
p-chlorophenol and pentachlorophenol - anodically
on lead dioxide
First step chlorine is substituted by hydroxyl
radicals formed from water Subsequent
steps further oxidation yields quinone, which
decomposes into maleic acid, oxalic acid
(primarily) and carbon dioxide. Oxygen and
significant amounts of ozone were formed as
by- products at the anode Risk chloride ions
formed may be oxidized to hypochlorite, which can
then form chlorinated organic compounds
Cathodic Electrochemical Dechlorination RCl
H 2e- RH C1- Electrode material - thin
graphite/carbon fibres high specific surface area
and high overpotential for the competing
hydrogen evolution reaction
11
Removal of heavy metal ions
Cu, Hg, Zn, Cr and Cd
Waste waters containing heavy metal ions -
generated in metallurgical and electroplating
industries and in the manufacture of printed
circuit boards. Conventional purification -
uses hydroxide precipitation gives voluminous
metal hydroxide sludge that has to be
disposed of Complexed metal ions in alkaline
solutions-hydroxide precipitation is not a
viable method Cathodic removal of heavy metal
ions attractive alternative process Metal
can be recovered in its pure metallic form
12
Anode - three-dimensional electrode or
just a planar electrode for e.g. oxygen
evolution Cathode - graphite particles, expanded
metal, metal wool graphite fibres
  • Three-dimensional electrodes -offer both a high
    specific surface area and high mass transport
    rate conditions.
  • Metal concentration can be reduced from 100 to
    0.1 ppm at a residence time of a few minutes
  • Operational costs are favourable compared with
    classical waste water treatment systems
  • the space required by the process is low
  • deposited metal in the cathode may be recovered
    as a concentrated solution by chemical dissolution

13
Electrodialytic processes
  • Aqueous streams containing e.g. NaCl and Na2S04 -
    chemical processing operations
  • Flue gas scrubbing
  • Metal pickling
  • Fermentation
  • Rayon manufacture

Splitting of sodium sulfate solutions into sodium
hydroxide and sulfuric acid solutions
Applications
  • Large scale brackish and seawater desalination
    and salt production.
  • Small and medium scale drinking water production
    (e.g., towns villages, construction military
    camps, hotels hospitals)
  • Water reuse (e.g., industrial laundry wastewater,
    produced water from oil/gas production, metals
    industry fluids)

14
Electrochemical remediation of soils
Restoration of contaminated soils Anode -oxygen
evolution H20 1/2 02 2H
2e- Cathode- hydrogen evolution H20 2e-
H2 20H-
Ions will move due to migration, diffusion
and convection Heavy metal ions - move to the
cathode Organic compounds - by means of the
electroosmotic flow
15
Electrochemical gas purification
I step Absorption of the gaseous species in a
liquid II step Electrochemical conversion of
them to less harmful products
  • Reduction of chlorine to chloride
  • Oxidation of nitrous oxides to nitric acid
  • Sulfur dioxide to sulfuric acid

The reduction or oxidation - directly at the
electrode or indirectly via a redox mediator
Chemically Bromine as a mediator to oxidize SO2
SO2 Br2 2H20 H2S04 2HBr
Electrochemically Bromine is
regenerated 2 HBr Br2 H2
H2S H2 1/2 S2
16
Electrochemical power sources for cleaner
electrical energy
  • Thermal combustion of fossil fuels in power
    plants and vehicles is a major environmental
    problem in modern society
  • The immediate damage of air pollution has been
    estimated to cost about three times more than the
    fossil fuels themselves
  • The most important gaseous impurities in the flue
    gas from electricity generation plants are C02,
    NO, SO2 and dust particles
  • C02 is a major contributor to the greenhouse
    effect and NO, contributes to the acidification
    of water and soil, eutrophication, and the
    formation of smog

17
Global warming and climate change
18
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19
Battery
  • Road traffic alone generates more than 50 of
    the total emissions of nitrogen oxides, carbon
    monoxide and hydrocarbons.
  • The only vehicles that are likely to meet zero
    emission vehicles demands are electric vehicles.
  • In order to meet these new regulations The Big
    Three, General Motors, Ford and Chrysler in the
    USA decided in January 1991 to form a consortium,
    The United States Advanced Battery Consortium (US
    ABC), for cooperation towards improved power
    sources for electric vehicles.

Specific energy/ W h kg-1 Peak specific power/ W kg-1 Discharge cycles
US ABC 80-100 150-200 600
US ABC 200 400 1000
Pb/PbO2 35-40 150-300 100-1000
lithium-metal sulfide, lithium-polymer,
lithium-ion batteries, metal hydride-nickel
oxide, zinc-air and zinc-nickel oxide
20
Representation of a lead acid battery
Charging of the battery
Discharging of the battery
Anode Sponge metallic lead Cathode Lead dioxide
(PbO2) Electrolyte aqueous sulfuric
acid Applications Motive power in cars, trucks,
standby/backup systems
21
Battery vs Capacitors
  • Batteries - used in all-electric vehicles or in
    hybrid vehicles that use also combustion engines
    for propulsion.
  • The batteries are then mainly used for
    acceleration and for citydriving, while the
    combustion engine gives a reasonable range.
  • In this application, a high peak power density of
    the battery is a major requirement, while the
    energy density, which determines the all-electric
    range, is less important compared to all-electric
    vehicles.
  • An interesting alternative, or complement, to
    batteries is elctrochemical capacitors (also
    called ultra capacitors or supercapacitors),
    which can give peak power densities greater than
    1 kW kg-l while the energy density is only 2-10
    of that stored in a battery)

Applications
  • Regenerative backing in hybrid vehicles,
  • cold engine starting,
  • backup power systems and
  • digital electronic devices

22
Electrochemical capacitor
  • An electrochemical capacitor stores the
    electrical energy electrostatically by charging
    of the electrochemical double layer at the
    electrode/electrolyte interface
  • In some systems intermediates are adsorbed on the
    electrode surface or intercalated into the
    electrode material, which gives an additional so
    called pseudo-capacitance that may be 10 to 100
    times higher than the double layer capacitance
  • In a finely porous electrode with a high specific
    surface area, fairly high amounts of electrical
    energy may be stored per unit volume or mass
  • Research and development has been going on since
    the early 1990s to develop ultracapacitors using
    various types of carbon, doped conducting
    polymers, and metal oxides as electrode materials
  • The electrolyte may be aqueous, organic or a
    solid polymer
  • Ultracapacitors with aqueous electrolyte can
    store 1.5 W h kg-1 and deliver 1 kW kg-1, while
    the best values reported for devices using an
    organic electrolyte are 5-7 W h kg-l and 2 kW kg-1

23
Fuel Cells
Direct Energy Conversion vs Indirect Technology
Applications
Submarine with fuel cell propulsion - German Navy
24
Electrochemical sensors
  • Monitoring of toxic compounds - Electrochemical
    sensors are convenient and effective devices
  • An electric signal can be related directly to the
    concentration of the compound being measured
  • Sensing pollutants - as potentiometric,
    amperometric or voltammetric sensors

Potentiometric Sensors
  • These sensors measure the electrical potential of
    an electrode when no current is flowing. The
    signal is measured as the potential difference
    (voltage) between the working electrode and the
    reference electrode
  • The working electrode's potential must depend on
    the concentration of the analyte in the gas or
    solution phase
  • Ion-selective electrodes can be used to determine
    for example pH, fluoride and cyanide
    concentrations in water
  • The concentration of toxic gases such as sulfur
    and nitrogen oxides can also be determined with
    potentiometric sensors

25
Amperometric sensors
  • These sensors measure current at a fixed
    potential
  • The current is then proportional to the
    concentration of the measured species
  • The Clark electrode for measuring oxygen
    concentration is the classic example
  • Its general principle also works for toxic gases
    like CO, NO, NO, SO2 and H2S
  • A sensor can be made selective by a suitable
    choice of electrode potential and electrode
    material
  • An array of such selective sensors can be built
    into one device for monitoring flue gases and
    other gas streams containing several toxic
    components

26
Photoelectrochemical methods
Photoanode 2h H2O 2H ½
O2 Cathode 2e- 2H H2
  • Recent advances in photoelectrochemistry have led
    to new, interesting possibilities, both for
    treatment of pollutants and for conversion of
    solar energy from light to electricity
  • In the first case, suspensions of semiconductor
    particles can be used to harness the light with
    production of electrons and holes in the solid,
    which can destroy pollutants by means of
    reduction and oxidation, respectively
  • In this way, air or water containing organic,
    inorganic or microbiological pollutants can be
    effectively treated
  • Photoelectrochemical cells for electricity
    production offer a sustainable way to generate
    electricity, e.g. for charging batteries in
    electric vehicles
  • With semiconductor electrodes using dye
    sensitized nanocrystalline Ti02 films an
    efficiency of 12 has been reported
  • Compared to conventional photovoltaic cells, this
    type of photoelectro-chemical cell is less
    expensive, since it uses inexpensive raw
    materials, is easily fabricated

27
In brief
  • A variety of selected electrochemical processes
    and devices for environmental protection have
    been presented
  • Some, but not all of them, have also been tested
    at pilot scale and some have reached
    commercialization
  • In some cases, it is only a matter of time,
    further development work (and investment) being
    required
  • In other cases, chemical or biological processes
    are preferred because they are competitive and do
    not require expertise in electrochemistry and
    electrochemical engineering
  • It may be expected that the number of
    electrochemical processes for treatment or
    prevention of pollution will increase in the
    future due to their specific advantages in a
    number of applications
  • A major beneficial impact of electrochemistry on
    the environment would be the future introduction
    of fuel cell or battery driven vehicles

28
Thank you
29
(No Transcript)
30
Delhi to observe Earth Hour every month
The Delhi government has proposed to hold an Earth Hour on the last working day of every month, urging residents to switch off non essential lights to save power on the lines of the recently held global campaign.
31
India is a signatory to the United Nations
Educational, Scientific and Cultural
Organization's (UNESCO) World Heritage Convention
adopted in 1972. The main goal of the World
Heritage Convention is to identify and protect
monuments of great cultural and natural heritage
throughout the world. In signing the Convention,
a country pledges to conserve the World Heritage
sites located in its own territory and protect
its national heritage. The application for a site
to be accepted as the World must come from the
country itself. The application process includes
submission of a plan detailing how the site is
managed and the measures assuring its continued
protection. In some cases, UNESCO identifies
conditions to a country before accepting a site
as a world heritage monument. For example, at
the time Delphi was nominated by Greece, a plan
was in the works to build an aluminum plant
nearby. The Greek government was asked to find an
alternative location for the plant, did so, and
Delphi was accepted onto the World Heritage List.
In other cases, such as the Giza Pyramids, UNESCO
asks the country for remediation of potential
threats. In 1995, the Pyramids were threatened by
a highway project near Cairo which would have
seriously damaged the monument. Negotiations with
the Egyptian government resulted in a number of
alternative solutions which replaced the disputed
project. Ultimately, the treaty is not binding by
the force of an ultra-national body but rather
left to the discretion of the country. The Agra
area currently has three world heritage sites
the Taj Mahal, Agra Fort and Fatehpur Sikri.
32
The Issue Environmental pollution spurred by
industry and automobiles has long been observed
to be progressively destroying the Taj Mahal's
white marble surface. Petitions of Indian
environmentalists have led to a series of court
challenges in the Indian Supreme Court and lower
courts. The conflict has often pitted business
and labor interests against environmentalists and
preservationists as well as India's need to
protect its cultural heritage versus its need to
provide jobs for its citizens. 2. Description
Mark Twain once remarked the world is divided
between two types of people those who have seen
the Taj Mahal and those who have not. The Taj is
one of the most recognizable landmarks in the
world and the image most associated with India.
The Mughal emperor Shah Jahan erected the Taj
Mahal at Agra as a mausoleum in memory of his
beloved wife, Arjumarid Bano Begum (popularly
known as Mumtaz Mahal "favored of the court"),
who died in A.D. 1630. Begun in 1632 AD, it took
20,000 men working every day over 22 years to
complete. It is heralded by many as the greatest
work of Mughal architecture. India has
experienced exponential industrial growth in
recent years. Increasingly, people have left
villages for urban centers in order to try and
find work. The result of this industrialization
has often been overcrowded cities and dense
pollution. Agra is no exception. It has been
identified as a "pollution intensive zone" by the
World Health Organization (WHO). It is estimated
that the area around the Taj contains five times
the amount of suspended particles (such as sulfur
dioxide) that the Taj Mahal could handle without
sustaining everlasting damage. India has been
involved in a "greening" campaign particularly in
regards to its national monuments. More
recently, India has begun to try and attract more
tourists this has created a dilemma how to
market its best Tourist attraction without
causing significant damage to it in the process.
 
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