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
(No Transcript)
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.