Gujarat Cleaner Production Centre
CLEANER PRODUCTION
OPPURTUNITIES
CAUSTIC SODA /CHLOR
Gujarat Cleaner Production Centre – ENVIS CENTRE
CLEANER PRODUCTION
OPPURTUNITIES
IN
CAUSTIC SODA /CHLOR-ALKALI
INDUSTRIES
1
ALKALI
Gujarat Cleaner Production Centre
Introduction to Caustic soda / Chlor Alkali Industry
The Chlor-Alkali industry in India forms an important component of basic chemicals industry,
comprising around 74% of the basic chemicals production in India. Caustic soda, soda ash,
chlorine alongside hydrogen and hydrochloric acid comprise the
components. These chemicals find their applications in a number of industries such as textiles,
chemicals, paper, PVC, water treatment, alumina, soaps & detergents, glass, chlorinated paraffin
wax, among others. The demand for the two sub
increased significantly registering a
respectively, over the past five years.
The Chlor-Alkali Industry in the country produces mainly Caustic Soda, Chlorine and Soda Ash.
The products of the industry are of vital importance and their uses are:
a) Caustic Soda
• Soaps and Detergent Industry
• Pulp and Paper Industry
• Textile Processing Industry
• Aluminum Smelting
• Dyes and Dyestuff Industry
• Plastic Polymers
• Rayon Grade Pulp
• Pharmaceuticals
• Electroplating
• Adhesives/Additives.
b) Chlorine, By-product of Caustic Soda Industry is very important for manufacturing of
PVC, one of the five major Thermoplastic Commodity Plastics. Besides this, it is used in
disinfection of drinking water, pharmaceutic
industries. Because of the strong oxidizing properties of Chlorine, it is effectively used to
control bacteria and viruses in drinking water that can cause devastating illness such as
Cholera. Use of Chlorine is very
of floods. 85% of the pharmaceuticals rely on Chlorine Chemistry including medicines
that treat heart disease, cancer, AIDS and many other life threatening diseases. Chlorine
tablets are also used by public health workers in rural areas.
c) Soda Ash is used in Glass Industry, Soaps & Detergents, Silicates and various other
Chemical Industries.
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Caustic soda / Chlor Alkali Industry
lkali industry in India forms an important component of basic chemicals industry,
comprising around 74% of the basic chemicals production in India. Caustic soda, soda ash,
chlorine alongside hydrogen and hydrochloric acid comprise the Chlor-alkali industry
components. These chemicals find their applications in a number of industries such as textiles,
chemicals, paper, PVC, water treatment, alumina, soaps & detergents, glass, chlorinated paraffin
wax, among others. The demand for the two sub-segments – caustic soda & soda ash, has
increased significantly registering a compound annual growth rate (CAGR) of 5.6% and 4.7%
respectively, over the past five years.
Alkali Industry in the country produces mainly Caustic Soda, Chlorine and Soda Ash.
oducts of the industry are of vital importance and their uses are:-
Soaps and Detergent Industry
Pulp and Paper Industry
Textile Processing Industry
Dyes and Dyestuff Industry
Adhesives/Additives.
product of Caustic Soda Industry is very important for manufacturing of
PVC, one of the five major Thermoplastic Commodity Plastics. Besides this, it is used in
disinfection of drinking water, pharmaceutical industry and various other chemical
industries. Because of the strong oxidizing properties of Chlorine, it is effectively used to
control bacteria and viruses in drinking water that can cause devastating illness such as
Cholera. Use of Chlorine is very important for the Countries like India especially in case
of floods. 85% of the pharmaceuticals rely on Chlorine Chemistry including medicines
that treat heart disease, cancer, AIDS and many other life threatening diseases. Chlorine
by public health workers in rural areas.
is used in Glass Industry, Soaps & Detergents, Silicates and various other
2
lkali industry in India forms an important component of basic chemicals industry,
comprising around 74% of the basic chemicals production in India. Caustic soda, soda ash,
alkali industry’s
components. These chemicals find their applications in a number of industries such as textiles,
chemicals, paper, PVC, water treatment, alumina, soaps & detergents, glass, chlorinated paraffin
stic soda & soda ash, has
CAGR) of 5.6% and 4.7%
Alkali Industry in the country produces mainly Caustic Soda, Chlorine and Soda Ash.
product of Caustic Soda Industry is very important for manufacturing of
PVC, one of the five major Thermoplastic Commodity Plastics. Besides this, it is used in
al industry and various other chemical
industries. Because of the strong oxidizing properties of Chlorine, it is effectively used to
control bacteria and viruses in drinking water that can cause devastating illness such as
important for the Countries like India especially in case
of floods. 85% of the pharmaceuticals rely on Chlorine Chemistry including medicines
that treat heart disease, cancer, AIDS and many other life threatening diseases. Chlorine
is used in Glass Industry, Soaps & Detergents, Silicates and various other
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As stated above the growth of Caustic Soda and Soda Ash Industry is very important for the
Nation and if competitiveness of this Industry is maintained, it can certainly grow at a much
faster rate.
Highlights of processes for Chloralkali/
The Chloralkali process (also chlor
electrolysis of sodium chloride
besides hydrogen can be produced. If the products are separated,
(caustic soda) are the products; by mixing,
depending on the temperature.
There are three basic processes for the electrolytic production of chlorine, the nature of the
cathode reaction depending on the specific process. These three processes are the diaphragm cell
process(Griesheim cell, 1885), the mercury cell process (Castner
membrane cell process (1970). Each process represents a different method of keeping
chlorine produced at the anode separate from the caustic soda and hydrogen produced, directly or
indirectly, at the cathode.
The basic principle in the electrolysis of a sodium chloride solution is the following:
- At the anode, chloride ions are o
- At the cathode: In the mercury process a sodium/mercury amalgam is formed and hydrogen
(H2) and hydroxide ions (OH-) are formed by the reaction of the sodium in the amalgam with
water in the denuder. In membrane and
(H2) and hydroxide ions (OH-) at the cathode.
For all processes the dissolving of salt, sodium chloride, is:
NaCl → Na+ + Cl-
The anode reaction for all processes is:
2 Cl-(aq) → Cl2(g) + 2 e
-
The cathode reaction is:
2 Na+(aq) +2 H2O + 2e
- → H2(g) + 2 Na
The overall reaction is:
2 Na+(aq) + 2 Cl
-(aq) + 2 H2O →
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As stated above the growth of Caustic Soda and Soda Ash Industry is very important for the
mpetitiveness of this Industry is maintained, it can certainly grow at a much
Highlights of processes for Chloralkali/ caustic soda
chlor-alkali and chlor alkali) is an industrial process for the
solution (brine). Depending on the method, several products
can be produced. If the products are separated, chlorine and sodium hydroxide
(caustic soda) are the products; by mixing, sodium hypochlorite or sodium chlorate
There are three basic processes for the electrolytic production of chlorine, the nature of the
pending on the specific process. These three processes are the diaphragm cell
process(Griesheim cell, 1885), the mercury cell process (Castner–Kellner cell, 1892), and the
membrane cell process (1970). Each process represents a different method of keeping
chlorine produced at the anode separate from the caustic soda and hydrogen produced, directly or
The basic principle in the electrolysis of a sodium chloride solution is the following:
At the anode, chloride ions are oxidised and chlorine (Cl2) is formed.
At the cathode: In the mercury process a sodium/mercury amalgam is formed and hydrogen
) are formed by the reaction of the sodium in the amalgam with
water in the denuder. In membrane and diaphragm cells, water decomposes to form hydrogen
) at the cathode.
For all processes the dissolving of salt, sodium chloride, is:
reaction for all processes is:
H2(g) + 2 Na+(aq) + 2 OH
-(aq)
→ 2 Na+(aq) + 2 OH
-(aq) + Cl2(g) + H2(g)
3
As stated above the growth of Caustic Soda and Soda Ash Industry is very important for the
mpetitiveness of this Industry is maintained, it can certainly grow at a much
) is an industrial process for the
). Depending on the method, several products
sodium hydroxide
sodium chlorate are produced,
There are three basic processes for the electrolytic production of chlorine, the nature of the
pending on the specific process. These three processes are the diaphragm cell
Kellner cell, 1892), and the
membrane cell process (1970). Each process represents a different method of keeping the
chlorine produced at the anode separate from the caustic soda and hydrogen produced, directly or
The basic principle in the electrolysis of a sodium chloride solution is the following:
At the cathode: In the mercury process a sodium/mercury amalgam is formed and hydrogen
) are formed by the reaction of the sodium in the amalgam with
diaphragm cells, water decomposes to form hydrogen
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(Flow diagram of the three main
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Flow diagram of the three main Chlor-alkali processes)
4
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(Simplified scheme of chlorine electrolysis cells)
The main characteristics of the three electrolysis processes are presented in Table
Mercury
Caustic quality
High, <30 ppm NaCl
5-150 µ
treatment the Hg level
is between 2.5
Hg/l)
Caustic
concentration
50%
Chlorine quality Contains low levels of
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chlorine electrolysis cells)
The main characteristics of the three electrolysis processes are presented in Table
Mercury Diaphragm Membrane
High, <30 ppm NaCl
150 µg Hg/l (Before
treatment the Hg level
is between 2.5-25 mg
1.0-1.5% by weight
NaCl (Before
treatment the NaCl
content is about 18%)
0.1% NaClO3 Not
suitable for some
applications
High, <50 ppm NaCl
12%, requires
concentration to 50%
for some applications
33%, requires
concentration
for some applications
Contains low levels of Oxygen content Oxygen content
5
The main characteristics of the three electrolysis processes are presented in Table
Membrane
High, <50 ppm NaCl
, requires
concentration to 50%
for some applications
Oxygen content
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oxygen
hydrogen
Brine feedstock
Some
required
but depends on purity
of salt or brine used
Variable electric
load performance
Good variable
electricity load
performance, down to
30 %
possible for some
cell rooms, which is
very important in
some European
countries
Auxiliary processes
There are various auxiliary processes attached to all the three technologies, which are listed
below:
• salt processing; unloading/storage
• brine purification and re-saturation
• chlorine processing
• caustic processing
• hydrogen processing
Caustic Processing
Process for Caustic Soda
Sodium hydroxide (caustic soda) is produced in a fixed ratio of 1.128 tonnes (as 100% NaOH)
per tonne chlorine produced.
The caustic soda solution from the three technologies is treated in slightly different ways due to
the difference in composition and concentration.
In the mercury cell process, 50% caustic soda is obtained directly from the decomposers. The
caustic soda is normally pumped through a cooler, then through a mercury removal system and
then to the intermediate and final storage sections. In some cases the caustic is heated before
filtration. The most common method for removal of mercury from caustic soda is a plate (or leaf)
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oxygen (< 0.1%) and
hydrogen
between 1.5-2.5%
between
2%, depending on
whether an acidified
electrolyte is used
Some purification
required
but depends on purity
or brine used
Some purification
required but depends
on purity of salt or
brine used
Very high purity brine
is
impurities affect
Membrane
performance
ood variable
electricity load
performance, down to
of full load
possible for some
cell rooms, which is
important in
some European
countries
Tolerates only slight
variation in electricity
load and brine flows
in order to maintain
diaphragm
performance
Variable electricity
load performance less
than for
60% depending
on design load),
affects
quality, and
efficiency at lower
loads
There are various auxiliary processes attached to all the three technologies, which are listed
salt processing; unloading/storage
saturation
Sodium hydroxide (caustic soda) is produced in a fixed ratio of 1.128 tonnes (as 100% NaOH)
The caustic soda solution from the three technologies is treated in slightly different ways due to
the difference in composition and concentration.
In the mercury cell process, 50% caustic soda is obtained directly from the decomposers. The
caustic soda is normally pumped through a cooler, then through a mercury removal system and
te and final storage sections. In some cases the caustic is heated before
filtration. The most common method for removal of mercury from caustic soda is a plate (or leaf)
6
between 0.5% and
2%, depending on
whether an acidified
electrolyte is used
Very high purity brine
required as
impurities affect
Membrane
performance
Variable electricity
performance less
than for mercury (40-
60% depending
on design load),
affects product
quality, and
efficiency at lower
There are various auxiliary processes attached to all the three technologies, which are listed
Sodium hydroxide (caustic soda) is produced in a fixed ratio of 1.128 tonnes (as 100% NaOH)
The caustic soda solution from the three technologies is treated in slightly different ways due to
In the mercury cell process, 50% caustic soda is obtained directly from the decomposers. The
caustic soda is normally pumped through a cooler, then through a mercury removal system and
te and final storage sections. In some cases the caustic is heated before
filtration. The most common method for removal of mercury from caustic soda is a plate (or leaf)
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filter with carbon precoat. Under normal operating conditions, mercury
100% NaOH) contains 20-100 ppm of sodium chloride and 40
In the case of diaphragm and membrane technologies the caustic soda is concentrated by
evaporation before final storage.
(The flow to storage of caustic soda from the diff
Emissions in Chlor Alkali Industry
Emission from Mercury cell process
Air Emission
Releases of mercury are
specific to the amalgam
technology. Air emissions
consist of mercury vapour
coming from:
- cell-room ventilation
- process exhausts
- brine purification
- stack of caustic evaporators
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filter with carbon precoat. Under normal operating conditions, mercury-cell caustic s
100 ppm of sodium chloride and 40-60 µg Hg/kg NaOH.
In the case of diaphragm and membrane technologies the caustic soda is concentrated by
(The flow to storage of caustic soda from the different technologies)
Emissions in Chlor Alkali Industry
Emission from Mercury cell process
Water emissions
- the process: bleed from brine purification,
condensate from hydrogen drying,
condensate from caustic soda concentration
units, brine leakage, ion-exchange eluate
from process water
Treatment.
- the wash water from the cell cleaning
operations: inlet and outlet boxes
- the rinsing water from the electrolysis hall:
7
cell caustic soda (as
g Hg/kg NaOH.
In the case of diaphragm and membrane technologies the caustic soda is concentrated by
Solid Waste
- Solids from brine
purification
- Solids from
caustic filtration
- Graphite and
activated carbon
from treatment of
gaseous streams
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- hydrogen burnt or vented to
atmosphere
- mercury retorting
-maintenance outside cell
room
Emission from Diaphragm cell process
Air Emission
Three sources of asbestos
emission can be identified in
the cell room maintenance
area:
- from the off-gas compressor,
- from the off-gas drying
oven,
- from the off-gas asbestos
weighing room
Emission from the Membrane Cell Process
Air Emission
Water emissions
- Waste water from the membrane cell process
originates from
- caustic evaporation,
- chlorine
- Wash
used to purify the brine.
Environmental Issues in Chlor alkali/
• Implementation of cleaner processes and pollution prevention measures can yield both
economic and environmental benefits. In MBCP (membrane process), the chlorine (at the
anode) and the hydrogen (at the cathode) are kept apart by a selective polymer membra
allows sodium ions to pass into the cathodic compartment and react with the hydroxyl ions to
form caustic soda. The depleted brine is de
major waste stream from the MBCP consists of brine mud
purification step, which may contain magnesium, calcium, iron, and other metal hydroxides,
depending on the source and purity of the brine.
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cleaning of the floors, tanks, pipes and
dismantled apparatus
- the rinsing water from maintenance areas
outside the electrolysis hall, if they are
cleaned with water
Emission from Diaphragm cell process
Water emissions
Waste water streams from the diaphragm cell
process mainly originate from
- the condenser
- caustic soda evaporation,
- chlorine drying,
- brine purification of salt recovered
from
The evaporators.
Emission from the Membrane Cell Process
Water emissions Solid Waste
Waste water from the membrane cell process
originates from
caustic evaporation,
chlorine drying and
Wash water from the ion exchange resin
used to purify the brine.
- precoat and body feed
material made of cellulose
- Spent membranes and
gaskets from membrane
cells
Environmental Issues in Chlor alkali/ caustic soda Industry and CP options
Implementation of cleaner processes and pollution prevention measures can yield both
economic and environmental benefits. In MBCP (membrane process), the chlorine (at the
anode) and the hydrogen (at the cathode) are kept apart by a selective polymer membra
allows sodium ions to pass into the cathodic compartment and react with the hydroxyl ions to
form caustic soda. The depleted brine is de-chlorinated and recycled to the input stage. The
major waste stream from the MBCP consists of brine mud - the sludge from the brine
purification step, which may contain magnesium, calcium, iron, and other metal hydroxides,
depending on the source and purity of the brine.
8
Solid Waste
- Bagged asbestos
from scrap
diaphragms
Solid Waste
precoat and body feed
material made of cellulose
Spent membranes and
gaskets from membrane
Industry and CP options
Implementation of cleaner processes and pollution prevention measures can yield both
economic and environmental benefits. In MBCP (membrane process), the chlorine (at the
anode) and the hydrogen (at the cathode) are kept apart by a selective polymer membrane that
allows sodium ions to pass into the cathodic compartment and react with the hydroxyl ions to
chlorinated and recycled to the input stage. The
ludge from the brine
purification step, which may contain magnesium, calcium, iron, and other metal hydroxides,
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• The pollution emission target namely wastewater generation target of 0.1 m
1. Having an emergency preparedness and response plan for potential uncontrolled chlorine
and other releases.
2. Using carbon tetrachloride with levels below 4% to avoid explosion.
3. Using metal rather than graphite anodes in DCP to reduce lead and chlorinated organics.
4. Re-saturate brine in closed vessels to reduce the generation of salt sprays.
5. Use non-contact condensers to reduce the amount of process wastewater.
6. Scrub chlorine tail-gases to reduce chlorine discharges and to produce hypochlorite.
Scrub chlorine tail-gas using suitable quantity of water for preparation of caustic solution
for pH maintenance to reduce chlorine discharge and to produce sodium hypo chloride
7. Recycle condensates and waste process water to the brine system, if possible.
8. Recycle brine wastes, if possible
9. Preferable use of substitutes for carbon tetrachloride as this is hazardous
10. chlorine produced can be achieved by adopting preventive measures such as:
• Indian Chlor-alkali plants have achieved huge benefits through
Technology shift from Mercury cell to Membrane cell, which are tabulated below:
1. Given the fact that Chlor
technology, approximately 70
costs in case of mercury cell based technology. On the other hand in case of membrane cell
technology, there is a significant reduction in energy consumption and the total energy cost
only constitutes 60% of the production cost. Therefore, immediate reduction of produ
cost of about 24% can be achieved by technology shifts.
2. The membrane cell plant is an environment friendly and energy efficient technology. Any
end products or gas, generated
chances of mercury contamination to the soil or water;
3. The membrane cell based plant would ensure no emission of mercury into the air;
4. No chances of negative impacts on humans as well as the environment remains as the
mercury itself is a toxic element;
5. Net energy saving of about 24 percent, thereby reducing the amount of carbon foot print
• Mercury cell Chlor-alkali plants are subject to special regulations due to the use of mercury.
the case of mercury as well as membrane cell process, the initial investment on pollution
control measures remains unchanged; thereby the conversion in technology did not envisage
any additional investment. Converting to a mercury free process will lead
several relevant costs, which in approximate order of economic significance include:
1. Avoiding costs of recycling, retorting, transporting, inventorying and/or disposing of
mercury wastes;
2. Elimination of the mercury wastewater treatment facility;
3. Reduced labor costs due to reduced need for maintenance;
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The pollution emission target namely wastewater generation target of 0.1 m3 per ton of
an emergency preparedness and response plan for potential uncontrolled chlorine
Using carbon tetrachloride with levels below 4% to avoid explosion.
Using metal rather than graphite anodes in DCP to reduce lead and chlorinated organics.
saturate brine in closed vessels to reduce the generation of salt sprays.
contact condensers to reduce the amount of process wastewater.
gases to reduce chlorine discharges and to produce hypochlorite.
using suitable quantity of water for preparation of caustic solution
for pH maintenance to reduce chlorine discharge and to produce sodium hypo chloride
Recycle condensates and waste process water to the brine system, if possible.
possible
Preferable use of substitutes for carbon tetrachloride as this is hazardous
chlorine produced can be achieved by adopting preventive measures such as:
alkali plants have achieved huge benefits through technology shift i.e.
y shift from Mercury cell to Membrane cell, which are tabulated below:
Given the fact that Chlor-alkali production relies on energy intensive electrochemical
technology, approximately 70-75% of the production cost primarily comprises of energy
e of mercury cell based technology. On the other hand in case of membrane cell
technology, there is a significant reduction in energy consumption and the total energy cost
only constitutes 60% of the production cost. Therefore, immediate reduction of produ
cost of about 24% can be achieved by technology shifts.
The membrane cell plant is an environment friendly and energy efficient technology. Any
gas, generated from this plant are completely free of mercury with no
ontamination to the soil or water;
The membrane cell based plant would ensure no emission of mercury into the air;
No chances of negative impacts on humans as well as the environment remains as the
mercury itself is a toxic element;
about 24 percent, thereby reducing the amount of carbon foot print
alkali plants are subject to special regulations due to the use of mercury.
the case of mercury as well as membrane cell process, the initial investment on pollution
control measures remains unchanged; thereby the conversion in technology did not envisage
Converting to a mercury free process will lead to the savings of
several relevant costs, which in approximate order of economic significance include:
Avoiding costs of recycling, retorting, transporting, inventorying and/or disposing of
Elimination of the mercury wastewater treatment facility;
Reduced labor costs due to reduced need for maintenance;
9
per ton of
an emergency preparedness and response plan for potential uncontrolled chlorine
Using metal rather than graphite anodes in DCP to reduce lead and chlorinated organics.
saturate brine in closed vessels to reduce the generation of salt sprays.
contact condensers to reduce the amount of process wastewater.
gases to reduce chlorine discharges and to produce hypochlorite.
using suitable quantity of water for preparation of caustic solution
for pH maintenance to reduce chlorine discharge and to produce sodium hypo chloride
Recycle condensates and waste process water to the brine system, if possible.
chlorine produced can be achieved by adopting preventive measures such as:
technology shift i.e.
y shift from Mercury cell to Membrane cell, which are tabulated below:
alkali production relies on energy intensive electrochemical
75% of the production cost primarily comprises of energy
e of mercury cell based technology. On the other hand in case of membrane cell
technology, there is a significant reduction in energy consumption and the total energy cost
only constitutes 60% of the production cost. Therefore, immediate reduction of production
The membrane cell plant is an environment friendly and energy efficient technology. Any
from this plant are completely free of mercury with no
The membrane cell based plant would ensure no emission of mercury into the air;
No chances of negative impacts on humans as well as the environment remains as the
about 24 percent, thereby reducing the amount of carbon foot print
alkali plants are subject to special regulations due to the use of mercury. In
the case of mercury as well as membrane cell process, the initial investment on pollution
control measures remains unchanged; thereby the conversion in technology did not envisage
to the savings of
several relevant costs, which in approximate order of economic significance include:
Avoiding costs of recycling, retorting, transporting, inventorying and/or disposing of
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4. Reduced labor costs due to reduced need for monitoring mercury emissions and
occupational exposures, health testing, reporting and abatemen
5. Avoidance of costs of storage of residual mercury;
6. Elimination of mercury monitoring equipment, as well as equipment for cleaning mercury
from product streams, flue exhausts, other clean
7. This cannot be easily quantified; however, at least 5% of the total benefits listed above, can
be achieved, which include, improved community relations, decreased legal liability,
improved public/investor image of the company, improved attractiveness of the company
as a place to work (employee satisfaction), reduced energy demand during the time of
raised energy consciousness, reduced CO
8. Reduced costs on medical testing of workers and relevant insurances as well as costs
related to potential need of rehabilitation in case workers had to take time off.
• Fundamental research programmes related to mercury technology are not being developed
since it is very unlikely that any new mercury plants will be built. The only recent
improvements in mercury cells concerns the anode geometry with the aim of improving gas
release in order to decrease electrical energy usage and increase anode coating life. In
diaphragm technology, with the exception of non
improvements are minor and related to reducing power consumption in the cell. An interesting
example is a specific development of activated cathode technology which is the pre
concept.
• Oxygen depolarized cathodes in membrane cells have the potential to save
kWh/tonne of chlorine produced and are now being tested at the industrial scale.
• The membrane is being developed that can produce high concentration (50%) caustic soda
and believes that it could be available at an acceptable cost within a fe
• For MBCP (membrane technology) the cleaner options include:
1. Minimizing the discharge of chlorate and bromate to water by applying: acid conditions in
the anolyte (pH: 1-2) to minimize the formation of chlorate (ClO3
chlorate destruction in the brine circuit to remove chlorate before purging.
2. The acidity of the anolyte is a design parameter of membrane cell plant and cannot be
adjusted without affecting the operation of the membrane cell. If this is not the chosen
option, a chlorate decomposer may be necessary to remove chlorate before purging.
3. The chlorate level associated with BAT in the brine circuit is 1
bromate level is 2-10 mg/l (note that the bromate level depends on the bromide level in the
salt).
4. Appropriate handling of spent membranes and gaskets.
Environmental Issues in Caustic Soda Manufacturing
• Steam is used as the source of evaporative energy. The presence of salt in the diaphragm cell
liquor requires that the evaporator is
the precipitated salt. This high quality sodium chloride can then be used to enrich depleted
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Reduced labor costs due to reduced need for monitoring mercury emissions and
occupational exposures, health testing, reporting and abatement measures;
Avoidance of costs of storage of residual mercury;
Elimination of mercury monitoring equipment, as well as equipment for cleaning mercury
from product streams, flue exhausts, other clean-up related costs (spillages) etc;
quantified; however, at least 5% of the total benefits listed above, can
be achieved, which include, improved community relations, decreased legal liability,
improved public/investor image of the company, improved attractiveness of the company
to work (employee satisfaction), reduced energy demand during the time of
raised energy consciousness, reduced CO2 emissions related to energy demand etc.
Reduced costs on medical testing of workers and relevant insurances as well as costs
ntial need of rehabilitation in case workers had to take time off.
Fundamental research programmes related to mercury technology are not being developed
since it is very unlikely that any new mercury plants will be built. The only recent
rcury cells concerns the anode geometry with the aim of improving gas
release in order to decrease electrical energy usage and increase anode coating life. In
diaphragm technology, with the exception of non-asbestos technology referred earlier,
s are minor and related to reducing power consumption in the cell. An interesting
example is a specific development of activated cathode technology which is the pre
Oxygen depolarized cathodes in membrane cells have the potential to save
kWh/tonne of chlorine produced and are now being tested at the industrial scale.
The membrane is being developed that can produce high concentration (50%) caustic soda
and believes that it could be available at an acceptable cost within a few years
For MBCP (membrane technology) the cleaner options include:
Minimizing the discharge of chlorate and bromate to water by applying: acid conditions in
2) to minimize the formation of chlorate (ClO3-) and bromate (BrO3
destruction in the brine circuit to remove chlorate before purging.
The acidity of the anolyte is a design parameter of membrane cell plant and cannot be
adjusted without affecting the operation of the membrane cell. If this is not the chosen
lorate decomposer may be necessary to remove chlorate before purging.
The chlorate level associated with BAT in the brine circuit is 1-5 g/l and the associated
10 mg/l (note that the bromate level depends on the bromide level in the
Appropriate handling of spent membranes and gaskets.
Caustic Soda Manufacturing and CP options
Steam is used as the source of evaporative energy. The presence of salt in the diaphragm cell
liquor requires that the evaporator is equipped with scraper blades or other devices to draw off
the precipitated salt. This high quality sodium chloride can then be used to enrich depleted
10
Reduced labor costs due to reduced need for monitoring mercury emissions and
t measures;
Elimination of mercury monitoring equipment, as well as equipment for cleaning mercury
up related costs (spillages) etc;
quantified; however, at least 5% of the total benefits listed above, can
be achieved, which include, improved community relations, decreased legal liability,
improved public/investor image of the company, improved attractiveness of the company
to work (employee satisfaction), reduced energy demand during the time of
emissions related to energy demand etc.
Reduced costs on medical testing of workers and relevant insurances as well as costs
ntial need of rehabilitation in case workers had to take time off.
Fundamental research programmes related to mercury technology are not being developed
since it is very unlikely that any new mercury plants will be built. The only recent
rcury cells concerns the anode geometry with the aim of improving gas
release in order to decrease electrical energy usage and increase anode coating life. In
asbestos technology referred earlier,
s are minor and related to reducing power consumption in the cell. An interesting
example is a specific development of activated cathode technology which is the pre-cathode
Oxygen depolarized cathodes in membrane cells have the potential to save around 500-600
kWh/tonne of chlorine produced and are now being tested at the industrial scale.
The membrane is being developed that can produce high concentration (50%) caustic soda
w years
Minimizing the discharge of chlorate and bromate to water by applying: acid conditions in
) and bromate (BrO3-) −
The acidity of the anolyte is a design parameter of membrane cell plant and cannot be
adjusted without affecting the operation of the membrane cell. If this is not the chosen
lorate decomposer may be necessary to remove chlorate before purging.
5 g/l and the associated
10 mg/l (note that the bromate level depends on the bromide level in the
Steam is used as the source of evaporative energy. The presence of salt in the diaphragm cell
equipped with scraper blades or other devices to draw off
the precipitated salt. This high quality sodium chloride can then be used to enrich depleted
Gujarat Cleaner Production Centre
brine, sometimes it is used as a raw material for an amalgam or membrane process. The
residual level of sodium chloride in sodium hydroxide from diaphragm cell is about 1% and
sodium chlorate 0.1%. For this reason, it is unsuitable for certain end applications such as the
manufacture of rayon.
• Salt and sodium chlorate in the caustic soda from diaphragm cells
extraction to increase marketability, but at increased cost.
• The caustic soda from membrane cells is of high quality, although the caustic soda produced
(usually around 33% NaOH) needs concentration to 50% NaOH for some applicatio
salt content of the membrane-cell caustic soda lies between 20
is on average slightly higher than mercury cell caustic
• In some plants the caustic soda is further concentrated to a 73% solution and to 100% as solid
caustic prills or flakes.
• Some Chlor-alkali production facilities can combine the caustic production process from
mercury and membrane cells in order to
caustic from the membrane cells to the decomposer to produ
for evaporation.
Bibliography
Books
1. Kirk-Othmer, Encyclopedia,
2. Lindley Encyclopedia, 1997,
3. Ullmann’s Encyclopedia1996
4. Research and Markets: Indian Chlor
hydrogen December 08, 2011 09:28 AM Eastern Standard Time
5. Pre-Budget Memorandum
6. Technical EIA guidance manual for Chlor Alkali Industry Prepared for The Ministry of
Environment & Forests Government of India
7. Chlorine Industry: Economics Of Conversion In India Study By: Toxics Link, New
Delhi Supported By Zero Mercury, 2012
8. BREF document on Chlor Alkali Manufacturing Industry
9. Cost Benefit Analysis for Changeover of Hg
Alkali Industry, by Central Pollution Control Board (CPCB);
10. The effects of Environmental Regulation on Technology Diffusion: The Case of Chlorine
Manufacturing, by Lori Snyder, Nolan Miller, Robert Stavins, Aug, 2003: Resources
The Future;
Gujarat Cleaner Production Centre – ENVIS CENTRE
sometimes it is used as a raw material for an amalgam or membrane process. The
odium chloride in sodium hydroxide from diaphragm cell is about 1% and
0.1%. For this reason, it is unsuitable for certain end applications such as the
Salt and sodium chlorate in the caustic soda from diaphragm cells can be reduced by ammonia
extraction to increase marketability, but at increased cost.
The caustic soda from membrane cells is of high quality, although the caustic soda produced
(usually around 33% NaOH) needs concentration to 50% NaOH for some applicatio
cell caustic soda lies between 20-100 ppm (in 100% NaOH), but
average slightly higher than mercury cell caustic.
In some plants the caustic soda is further concentrated to a 73% solution and to 100% as solid
alkali production facilities can combine the caustic production process from
mercury and membrane cells in order to minimize energy costs. It is possible to feed 33%
caustic from the membrane cells to the decomposer to produce 50% caustic without the need
Encyclopedia,1991,
, 1997,
1996
Research and Markets: Indian Chlor-Alkali Industry: caustic soda, soda ash, chlorine and
December 08, 2011 09:28 AM Eastern Standard Time
Budget Memorandum 2012-2013 by Alkali Manufacturers’ of India
Technical EIA guidance manual for Chlor Alkali Industry Prepared for The Ministry of
Environment & Forests Government of India by IL&FS Ecosmart Hyderabad
Economics Of Conversion In India Study By: Toxics Link, New
Delhi Supported By Zero Mercury, 2012
BREF document on Chlor Alkali Manufacturing Industry.
Cost Benefit Analysis for Changeover of Hg-Cell to Membrane Cell technology in Chlor
Alkali Industry, by Central Pollution Control Board (CPCB);
The effects of Environmental Regulation on Technology Diffusion: The Case of Chlorine
Manufacturing, by Lori Snyder, Nolan Miller, Robert Stavins, Aug, 2003: Resources
11
sometimes it is used as a raw material for an amalgam or membrane process. The
odium chloride in sodium hydroxide from diaphragm cell is about 1% and
0.1%. For this reason, it is unsuitable for certain end applications such as the
can be reduced by ammonia
The caustic soda from membrane cells is of high quality, although the caustic soda produced
(usually around 33% NaOH) needs concentration to 50% NaOH for some applications. The
100 ppm (in 100% NaOH), but
In some plants the caustic soda is further concentrated to a 73% solution and to 100% as solid
alkali production facilities can combine the caustic production process from
energy costs. It is possible to feed 33%
ce 50% caustic without the need
Alkali Industry: caustic soda, soda ash, chlorine and
Technical EIA guidance manual for Chlor Alkali Industry Prepared for The Ministry of
Ecosmart Hyderabad , 2010
Economics Of Conversion In India Study By: Toxics Link, New
e Cell technology in Chlor-
The effects of Environmental Regulation on Technology Diffusion: The Case of Chlorine
Manufacturing, by Lori Snyder, Nolan Miller, Robert Stavins, Aug, 2003: Resources For
Gujarat Cleaner Production Centre
Website
1. http://www.adityabirlachemicals.com/products/chlor_alkali/companies_producing_chlor_
alkalis.html
2. http://www.businesswire.com/news/home/20111208005754/en/Research
Indian-Chlor-Alkali-Industry
3. http://www.ama-india.org/
4. http://www.greenbuildingcongress.com/site/superdirectory/suppliers.jsp?sector=3&
er=3
Gujarat Cleaner Production Centre – ENVIS CENTRE
http://www.adityabirlachemicals.com/products/chlor_alkali/companies_producing_chlor_
http://www.businesswire.com/news/home/20111208005754/en/Research
Industry-caustic-soda#.UrvzyvtgCho
india.org/
http://www.greenbuildingcongress.com/site/superdirectory/suppliers.jsp?sector=3&
12
http://www.adityabirlachemicals.com/products/chlor_alkali/companies_producing_chlor_
http://www.businesswire.com/news/home/20111208005754/en/Research-Markets-
http://www.greenbuildingcongress.com/site/superdirectory/suppliers.jsp?sector=3&suppli
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