NaOH production

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CH 1060 Process Engineering Fundamentals
Assignment
Group 13 : Sodium hydroxide Production
Group Members :
170070D : BENARAGAMA B.V.C.M.
170397K : NAOTUNNA L.W.
170230U : IMBULANA S.N.
170611N : SUMANASENA M.A.I.
Date of submission: 30/09/2018
Department of Chemical and Process Engineering
University of Moratuwa

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ASSIGNMENT 01
FEASIBILITY STUDY

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Sodium hydroxide is commonly known as caustic soda. Sodium hydroxide can be
normally seen as white solid forms and also as solutions of different concentrations in water.
It is a highly water-soluble substance and it also dissolves in alcohol, glycerin, fat and
grease. Sodium hydroxide can absorb carbon dioxide and moisture from air.
Since sodium hydroxide and chlorine are generated simultaneously by the
electrolysis of sodium chloride solution, this sodium hydroxide production is widely known
as chlor-alkali technology. One of the three cell types including mercury, diaphragm and
membrane cells is used in this process.
Importance of doing a feasibility study
A feasibility study is done to determine the success and minimize the risks related
to the project. A feasibility study is not only a project research, but also a framework or plan
on how to establish and run the particular process successfully all along. Here, we mainly
look at the following topics:
1. Demand and supply with justification
2. Raw material requirement
3. Energy requirement
4. Process selection based on internal and external constrains
5. Site selection
Introduction

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01. Demand and Supply with justification
1.1 : Production methods of NaOH
Sodium Hydroxide which is commonly referred as Caustic Soda is one of the highly
used chemical substances in the world. Sodium Hydroxide is the natural Co-Product of the
Chlorine Industry. Due to its high availability and the ease in production, Sodium
Hydroxide is a chemical substance that has a high supply and demand in the day to day
household activities.
Due to its extreme versatility as an alkali substance, NaOH is used across many
fields. Manufacture of pulp and paper, soap and detergents, petroleum and chemical
products are some of the commonly found industrial uses for NaOH. Water treatment, food,
textile and metal processing, glass making are some of the other applications of Sodium
Hydroxide.
Chart 1.1 : Common uses of Sodium Hydroxide
(“Sodium hydroxide.” : http://www.essentialchemicalindustry.org/chemicals/sodium-hydroxide.html.)

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As you can clearly see, the uses and applications of NaOH are quite common.
Therefore, the demand of NaOH takes higher values compared to other chemical
substances.
For most industrial purposes, Sodium Hydroxide can be directly replaced by Sodium
Carbonate (e.g. in pulp and paper, water treatment, and certain chemical sectors where
NaOH used as a neutralizing agent). Due to this, any kind of an increased demand for NaOH
could be remedied by the increased displacement of Sodium Carbonate.
However, in current global market, there’s an increase in the demand for Chlorine.
As mentioned in the beginning of the report, NaOH is a genuine co-product in the Chlorine
production. So, with the increased Chlorine production, the production of NaOH too have
risen and this continuous output of NaOH has resulted in the adequate supply of NaOH for
the essential production activities. Therefore, in any marginal increment of the demand for
NaOH will not be dealt with any other alternative NaOH production methods (i.e.-
Caustification Process, where NaOH is produced from lime and Soda). But for any further
increments in the NaOH demand, Caustification process will be used to increase the
production of NaOH.
( http://www.sundaytimes.lk/180121/business-times/raigam-wayamba-saltern-begins-
industrial-chlorine-production-277461.html )
Table 1.1 : The Annual Production of NaOH
World 70 million tons
US 11.4 million tons
Europe 10.7 million tons

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Just as there's a high demand for Sodium Hydroxide globally, there’s a high demand
for NaOH within Sri Lanka as well. Unlike other countries, Sri Lanka mainly import NaOH
from different parts of the world to counter the high demand. In theory, Sri Lanka can
produce NaOH substantially at a low price due to the location of the country. Sri Lanka is
an island surrounded by the ocean and more than 70% of the NaOH production comes from
sea water. Though the countries Geological positioning is not utilized to full effect at
present, back in the days it was used to greater effect. “Paranthan” Chemicals Corporation
established in 1954 was one of first state owned Chemical Factories that produced
Chlorine, Caustic Soda, Hydrochloric. Country’s’ demand for NaOH was kept well under
control by production factories like these. These practices have gradually diminished over
the years, thereby halting the production of NaOH in Sri Lanka. Small scale production
entities have survived over the years, but with the rise of the demand for industrial salts in
Sri Lanka, more production entities have entered the Caustic Soda production line. For an
example companies like Raigam Salts have now diversified their range of products to
include Caustic soda, Chlorine and Hydrochloric acid.
However still Sri Lankas majority of the NaOH demand is addressed by importing
NaOH from some of the major production countries like India and China. Here are some of
the companies in Sri Lanka who supply NaOH to the country through import export trade,
• Soap and Allied Industries (Pvt) Ltd
• Jayes Trading Company
• Glorchem
• Paranthan Chemicals
Research suggests that a ton of NaOH would cost 400$-600$ in the Sri Lankan
market. With the advantage that the country has over its Geological location, the sea water
can be utilized more to produce NaOH. So rather than importing of Caustic Soda, the
domestic large-scale production of NaOH is the answer for the rising national demand of
NaOH

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02. Raw Material Requirement
2.1 : Raw Material for Sodium Hydroxide Productions
The main raw material for Sodium hydroxide production is a brine solution.(Lanka,
1986) The three types of cells; mercury, diaphragm and membrane cells require different
degree of brine solution to electrolyze for a proper production of sodium hydroxide. This
brine solution is available in the form of Rock salt, Industrial salt and sea salt water.
Salt is the most important raw material for sodium hydroxide production. It can be
extracted by solar evaporation of sea water, inland brine, mining rock salt deposits and
solution mining. Since the diaphragm cell needs a low degree of purity, the brine which is
produced from solution mining can be directly used . The other types of cells require a
certain degree of purity.
(The Sri Lanka Forester, 1977)
2.1.1: Rock Salt
Rock salt, which is recovered by subsurface mining, is used as the primary source
for sodium hydroxide production. Certain applications, including Chlor-alkali
manufacturing can use the brine solution which is obtained directly from rock salt by
forcing water into the deposit to dissolve the salt. United States, Canada, Germany, Austria,
Brazil, Ethiopia, Pakistan, Poland, Spain, Thailand and United Kingdom have abandoned
rock salt. So, Sri Lanka have a huge opportunity to import rock salt from Pakistan, Ethiopia
or Thailand. This shows that, there is an opportunity to process rock salt as main raw
material.
(Industrial Chemistry, 1991)
.)

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2.1.2 : Solar Salt
Solar salt is a substance which is resulted from natural evaporation of seawater or
brine in large ponds. It is a slow process. Since the rate of evaporation and the success of
salt production depends on local weather patterns, the retention time from intake of seawater
to production of salt is several years. So, it is an uncertain business and one that must follow
a yearly cycle. Solar salt is never pure, and it contains impurities. So, treating of those
impurities need more process steps. Also, many solar salt plants make the product during
only a season of the year. This shows that some limitations can be occurred in producing
solar salt within the sodium hydroxide plant. Although there is an opportunity to purchase
solar salt from manufactures, it is difficult to take the required quality of salt.
Sea water contains more complex constitution other than NaCl: therefore, the
production of salt involves a sequence of fractional crystallization processes.
NaCl 77.8% (w/w)
MgCl2 10.9%
MgSO4 4.7%
CaSO4 3.6%
KCl 2.5%
CaCO3 0.3%
There are four different options to get raw material.
• Producing solar salt within the plant and itself
• Purchasing solar salt from local salterns in Sri Lanka
• Purchasing solar salt from foreign salterns
• Importing Rock salt from Pakistan or Thailand
Salt which is used in Sodium hydroxide production is not called as table salt; it is
called as industrial salt

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Raw material
Input
(mg)
Air 22000
Animal matter <1
Barytes 31
Bauxite <1
Bentonite <1
Biomass(including water) 11000
Calcium sulphate(CaSO4) <1
Chalk (CaCO3) <1
Clay <1
Cr <1
Cu <1
Dolomite 1
Fe 80
Feldspar <1
Ferromanganese <1
Fluorspar <1
Granite <1
Gravel <1
Hg 2
Limestone(CaCO3) 11000
Mg <1
Table 2.1 : Gross raw materials required to produce 1kg of Sodium
Hydroxide

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Raw material
Input
(mg)
N2 710
Ni <1
O2 2
Olivine 1
Pb 1
Phosphate as P2O5 <1
Potassium chloride (KCl) 2
Quartz (SiO2) <1
Rutile <1
S (bonded) <1
S (elemental) 1400
Sand (SiO2) 81
Shale <1
Sodium chloride (NaCl) 990000
Sodium nitrate (NaNO3) <1
Talc <1
Unspecified <1
Zn <1
Table 2.1 (cont’d) : Gross raw materials required to produce 1kg of
Sodium Hydroxide

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2.2 : Raw Material Selection
There are two different options for raw material. First one is Industrial Salt from
India and second one is solar salt from local market or local manufacturing. Due to High
Initial Investment on the salters and Less Quality/more Impurity in solar salt. It has been
suggested to avoid second option.
Solar salt processing within the plant and itself is an option to obtain raw material,
but Climate is more likely to control this process, so raw material supply is restricted to 6
months per year, but industrial salt can be used all over the year. To process sea water, a
huge land area is required, so producers will face problems. But if industrial salt is selected
as the raw material, some advantages can be taken, such as,
• No further cost for purifying
• No requirement of large area within the plant
• Can minimize the brine processing cost
Also, since South Asian countries like India and Pakistan have an excessive
industrial salt production, Sri Lanka can import industrial salt from there, so that the import
cost can be minimized. So, industrial salt is selected as the main raw material in the sodium
hydroxide production.
Component Percentage (%)
NaCl 97.94
MgCl2 0.74
MgSO4 0.32
NaOH 0
CaSO4 0.72
Insoluble 0.28
Table 2.2 : Typical chemical
composition of industrial salt

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03. Energy Requirement
Table 3.1 : Gross energy required to produce 1kg of sodium hydroxide
Fuel type
Fuel production
& delivery
energy
(MJ)
Energy
content of
delivered
fuel
(MJ)
Energy
use in
transport
(MJ)
Feedstock
Energy
(MJ)
Total
energy
(MJ)
Electricity 7.81 4.05 0.07 - 11.93
Oil fuels 0.15 1.11 0.03 <0.01 1.29
Other fuels 0.39 8.11 0.03 0.29 8.82
Totals 8.35 13.27 0.13 0.29 22.04
(Journal of the National Science Council of Sri Lanka, 1984)
Table 3.2 : Gross primary fuels used to produce 1kg of sodium hydroxide
Fuel type Input in mg
Crude oil 50000
Gas/condensate 170000
Coal 140000
Metallurgical coal 32
Lignite 12
Peat 1600
Wood 6300
(“Principles of Cattle Production - C. J. C. Phillips - Google Books,” n.d.)

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Table 3.3 : Gross primary fuels required to produce 1kg of sodium hydroxide
Fuel type
Fuel
production
& delivery
energy (MJ)
Energy
content of
delivered
fuel (MJ)
Fuel use in
transport
(MJ)
Feedstock
energy
(MJ)
Total
energy
(MJ)
Coal 1.63 2.02 <0.01 0.23 3.88
Oil 0.72 1.44 0.12 <0.01 2.27
Gas 1.53 7.44 <0.01 <0.01 8.98
Hydro 0.57 0.43 <0.01 - 1.00
Nuclear 3.67 1.81 <0.01 - 5.48
Lignite <0.01 <0.01 <0.01 - <0.01
Wood <0.01 <0.01 <0.01 0.06 0.06
Sulphur <0.01 <0.01 <0.01 0.01 0.01
Biomass(solid) 0.04 0.03 <0.01 <0.01 0.07
Hydrogen <0.01 0.48 <0.01 - 0.48
Recovered energy <0.01 -0.45 <0.01 - -0.45
Unspecified <0.01 <0.01 <0.01 - <0.01
Peat 0.01 0.01 <0.01 - 0.01
Geothermal 0.06 0.03 <0.01 - 0.08
Solar <0.01 <0.01 <0.01 - <0.01
Wave/tidal <0.01 <0.01 <0.01 - <0.01
Biomass(liquid/gas) 0.02 0.01 <0.01 - 0.03
Industrial waste 0.02 0.01 <0.01 - 0.03
Municipal Waste 0.05 0.02 <0.01 - 0.07
Wind 0.02 0.01 <0.01 - 0.03
Total 8.35 13.27 0.13 0.29 22.04

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Electricity
Basically, producing chlorine and caustic soda comes down to passing an
electric current through brine (a solution of salt – sodium chloride – in water). The brine
dissociates and recombines through exchange of electrons (delivered by the current) into
gaseous chlorine, dissolved caustic soda and hydrogen. By the nature of the chemical
reaction, chlorine, caustic soda and hydrogen are always manufactured in a fixed ratio: 1.1
tons of caustic and 0.03 tons of hydrogen per tons of chlorine. This product combination
is called an Electrochemical Unit or ECU. The average electricity consumption of a
chlorine electrolysis plant is about 3.3 MWh per ECU. About 90% of the electric current
is used as raw material which cannot be substituted. The reduction potential of the
consumption is therefore limited and is mainly due to technology shift from mercury cell
to membrane technology together with smaller efficiency measures in the production
units. About 10% of the electricity is used for lighting and operating pumps, compressors
and other necessary equipment.
(O’Brien, Bommaraju, & Hine, 2007)
So, electricity can be used as the main energy supply for chlor-alkali process and
electricity can be generated within the plant
.)

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04. Process Selection based on internal and external constrains
4.1 : Production methods of NaOH
The most commonly used and sold concentration of NaOH in world market is
50%(w/w), hence the processes should be designed to give out 50%(w/w) as the end-
product from the plant. It could be directly from the reactor or may be after some steps of
post-processing.
The most significant factors to be considered during selecting the process will be,
1. Production factors
• Raw Material
• Time required for processing
• Quality vs Expected use of the end-product
2. Overall Cost
• Principal Cost
• Manufacturing and Maintenance Cost
• Energy Consumption
3. Environment
• Waste produced by the process and the disposal
4. Technology
• Viability of the Technology
• Level of skilled labor required
NaOH can be produced using many methods depending on the quantity, necessity,
purity etc. Among them the three most commonly used methods for production in large
scale, in enough purity for general purposes, are given below.
1. Mercury Cell Method (Castner - Kellener Process)
2. Diaphragm Cell Method (Nelson Diaphragm Cell)
3. Membrane Cell Method

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All the three above mentioned processes involve electrolysis a solution of brine to
get Na+
/Na. OH-
ions are obtained through electrolysis of water or, reacting Na directly with
H2O.
4.2 : Mercury Cell Method
Consist of two cells where in first cell Cl- from the brine is removed at anode
while Na+ is discharged to get Na metal to the Mercury, at cathode.
2 Cl−
→ Cl2 + 2e−
(Titanium Anode)
Na+
+ e−
→ Na (Mercury Cathode)
Sodium-Mercury amalgam is sent to the decompose cell, where pure water its set-
in contact with amalgam for Sodium-water reaction which produces NaOH.
2 Na + 2 H2O > 2 NaOH + H2
Figure 4.1 : Mercury Cell

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As the concentration is 50%(w/w) anyway, it can directly be sold. Or else further
processing is done by evaporation to 75%(w/w), and then heated to 750-850K get the
solid.
Table 4.1 : Material used in Mercury Cell
Part of the reactor Material used
• Raw material • Saturated brine and water
• Mercury cell and the
Decomposer
• Rubber-lined or PVC-lined
steel
• Anodes • Titanium plates covered with
oxides of the precious metals
• Cathode • Mercury Liquid
• Energy fed to reactors • Electrical Energy
• As a catalyst in decomposer • Carbon Balls
(“Euro Chlor - The mercury cell process.” : http://www.eurochlor.org/the-chlorine-universe/how-is-
chlorine-produced/the-mercury-cell-process.aspx)
Increasing the Efficiency and the Output
• Brine is recirculated after pumping Oxygen for de-chlorination and adding solid
NaCl to maintain the level of saturation.
• Liquid Mercury is not used up in a one cycle hence can be recirculated.
• The gases Chlorine and Hydrogen can be used as raw material for other industries

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4.3 : Diaphragm Cell Method
A single cell with chambers separated by a permeable asbestos diaphragm where
anodic chamber is supplied with brine and cathodic chamber with water.
2 Cl−
→ Cl2 + 2e−
(Titanium Anode)
2H2O + 2e−
→ H2 + 2OH−
(Mild Steel Cathode)
Na+
travels through the diaphragm to form NaOH with OH-
. Membrane is
selectively permeable for Na+
Na+
+ OH−
→ NaOH
10-12% (w/w) dilute solution NaOH is obtained and concentration must be done by
in a separate large and complex unit to marketing NaOH of 50%(w/w)
Figure 4.2 : Diaphragm Cell

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Table 4.2 : Material used in Diaphragm Cell
• Raw material • Saturated brine and water
• Diaphragm • polytetrafluoroethylene with asbestos
• Anode • Titanium coated with a precious metal
oxide
• Cathode • Mild Steel
(“Euro Chlor - The diaphragm cell process.” :
http://www.eurochlor.org/the-chlorine-universe/how-is-chlorine-produced/the-diaphragm-cell-process.aspx )
• Impurity NaCl crystalized during the concentration of the output mixture is used for
saturation of brine again
• Liquid level at anode is kept at a higher level to avoid OH-
coming to anodic chamber
and react with Cl2
• The gases Chlorine and Hydrogen can be used as raw material for other industries
4.4 : Membrane Cell Method
A single cell with chambers separated by a polymer membrane selectively
permeable to Na+
, where anodic chamber is supplied with brine and cathodic chamber with
water same as in diaphragm cell. Despite the material used for electrodes, even the reactions
are same as in diaphragm cell.
30% (w/w) dilute solution NaOH is obtained and concentration to 50%(w/w)
NaOH is achieved in a simple evaporating unit with pressurized steam.

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Table 4.3 : Material used in Membrane Cell
• Raw material • Saturated brine, water, (Oxygen,
Hydrogen)
• Membrane • Perfluoro polymers
• Anode • Ruthenium dioxide coated titanium
• Cathode • Nickel
(“Euro Chlor - The membrane cell process.” :
http://www.eurochlor.org/the-chlorine-universe/how-is-chlorine-produced/the-membrane-cell-process.aspx )
Figure 4.3 : Membrane Cell

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• The membrane let only Na+
ions to pass via it, preventing reaction between Cl2 and
OH-
due to mixing and keeps the purity of the product.
• De-chlorinated brine can be recirculated after re-saturation with purified NaCl
formed in the same process.
• Using pressurized steam for evaporation reduces the energy consumption greatly
• Pumping Oxygen to Hydrogen evolving cathode, reduces the voltage needed for
process by third, reducing power needed, hence indirectly reduces CO2 evolved
during production of electricity.( an oxygen-depolarized cathode or ODC)
• The gas Chlorine can be used as raw material for other industries.

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4.5 : General Overview of the Processes
Before selecting a process and come to conclusions the processes should be
compared and observed under the factors mentioned first.
4.5.1 : Quality of the end-product and achieving the quality (Production Factors)
In Sri Lankan context the chemical productions which require high purity caustic
soda as a raw material are very less. Other than that, for general domestic and industrial
purposes, such as washing purposes, chemical pulping, water treatment etc., NaOH is
directly used and being contaminated with a little amount NaCl doesn’t matter because NaCl
is very neutral.
Given that the research sector of Sri Lanka is at a preliminary stage and that it doesn’t
need highly pure NaOH in huge amounts, bearing a huge cost and going for very
complicated mechanisms with high technological requirements is not necessary
Even if the global, market is aimed, most of the countries manufacture NaOH for their
requirements, and imports are rarely done. Hence when it comes to the quality of the end-
product, considering the factors given in the Table 4.4 and the requirements from the
chemical in Sri Lankan context, going for a mechanism with less trouble, to obtain NaOH
with moderate quality is advised.
• If solid caustic soda with very high purity is needed, then Mercury Cell
method must be used.
• For very general purposes where impurities don’t matter, diaphragm cell can
be used.
• On Sri Lankan context, Membrane Cell Method which provides enough
purity with less complicated process seems to be the best.

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Table 4.4 : Purity of the End Product in Different Process.
Name of the process Composition and the
quality of the directly
obtainable product
(w/w)
Composition and the
quality of the further
processed product
(w/w)
Additional Information
Mercury Cell Method
50% (pure)
solid NaOH (pure)
(30ppm NaCl)
• Concentration is done by evaporation and then
the solid is obtained heating to 750-850K.
Diaphragm Cell
Method 10-12% (impure)
(15% NaCl)
50% (impure)
(1% impurity)
• Concentration is done by evaporation at a
separate large and complex unit.
• Due to small amount of contamination in the
product, unsuitable for some purposes.
Membrane Cell
Method
30% (pure)
50% (pure)
(50ppm NaCl)
• Concentration is done by evaporation using
high pressure steam in a simple evaporator.

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Table 4.5 : Energy Consumption of the End Product in Different Process.
Mercury Cell Method Diaphragm Cell Method Membrane Cell Method
Principal (Constructional) Cost Very High Cheapest
Cheaper relative to Mercury
Method
Operational Costs
to remove toxic Hg from
effluents
diaphragm must be frequently
replaced
low maintenance cost
Energy Consumption
(per ton of Cl2 produced)
3 360 kWh 2 720 kWh 2 500 kWh
(can be reduced to 2/3 using ODC)
Energy Requirement for
Concentration to 50%(w/w)
(per ton of Cl2 produced)
none 700 kWh 250 kWh
Labor force Required least more less
Raw Material Renewal
Brine, Hg can be reused
(though it is expensive)
No Brine, H2 can be reused
Time of processing least more less

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4.5.2 : Overview on Overall Cost and Expenditure
Principal cost is important only when starting the industry. Judging the process
depending only on principal cost is very risky. Hence before selecting the process the time
frame of how long the product is expected from the plant along with the maintenance cost
must be considered.
When considered only the principal cost diaphragm method seems to be the best but the
maintenance cost of the diaphragm is high compared to other methods. Even though Hg
method is a sophisticated method, to treat the effluents a high cost will have to be born.
The manufacturing cost and efficiency are affected by the factors such as Energy,
Raw Material, Labor cost, time of processing etc. When it comes to it, Diaphragm cell
method becomes very expensive to handle even if its principal cost is less. Least energy
consumption can be seen in membrane cell method. But considering other factors Hg cell
method also seems to be fine, because the cost could be covered by the high price that can
be obtained for highly pure NaOH produced.
4.5.3 : Effect on Environment and Ecological Balance
Taken, Diaphragm method and membrane method have the least impact to the
environment, provided that Cl2 and H2 produced are not released to atmosphere. Membrane
cell method has least energy consumption and hence the least CO2 amount produced on
energy generation. So, it is indirectly a better eco-friendly process than the other two.
Hg cell method seems to be the one that affects the environment the most, first by
the effluents containing Hg, a heavy metal, then by having a very high energy consumption,
hence releasing a very high amount of CO2 to the atmosphere indirectly.
Hence the most eco friendly process will be the Membrane cell method.

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4.5.4 : Viable Technology and Skilled Labor
Sri Lanka being a developing country, most of the technologies are in their early
transition period. Hence a process like Hg cell method will be difficult to be implemented
because of the unawareness of the technology and, not having experience personnel in the
field. Diaphragm method is too primitive that it has a lot of faults a malfunction. Hence it
is better to use moderately advanced technology of Membrane cell method.
4.5.5 : Statistical Analysis on Global Scale
The mostly used method of caustic soda production is Diaphragm cell method which
represents 50% of the global production. It is the oldest method of chlor-alkali process. But
at present European and Asian countries are moving towards the membrane cell method.
Only USA and Canada use diaphragm cell in great extent and show reluctance to change.
Membrane cell method is used in more than 30% of the productions globally. But
apparently it is increasing fast. Hg cell method is used in even less than 20% of the all
product population. And EuroChlor, the organization of European countries in industrial
productions related to chlor-alkali process, has made regulations and agreements to move
away from this method to environmental reasons. (“Resources - World Chlorine Council.” :
https://worldchlorine.org/publications/ )
4.6 : Conclusion
Apparently, all the factors above considered as a whole in Sri Lankan context
favours the fact that membrane cell method is the best process method to start a chlor-alkali
factory. Even the global trends and the statistics supports the process of membrane cell.
Diaphragm cell method is simple but, costly in wrong, it’s too primitive and
inconvenient. Hg cell method is sophisticated, but involves a high cost, plus the
environmental pollution could be significant. On Sri Lankan scale, and in globally accepted
trend, Membrane Cell method seems to be the best for a Chlor-Alkali production in Sri
Lanka.

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05. Site Selection
Site selection process is a major process when constructing a NaOH plant.
Following points can be considered.
• Location Factors
• Transporting options
• Waste Management
• Safety Options
5.1 : Location Factors :
To build a Sodium Hydroxide plant, it’s very useful to have a location near a coastal
area & harbor to import the raw materials and export the final products. And need a wide
area to build the plant. It’s necessary to be a desolated area for safety purposes with cheaper
land prices. The soil particles in that area should have the ability to absorb metal and
chemical compound. And Should have a proper weather conditions throughout the year.
(Zhuang, 2016)
5.2 : Transporting options :
A Range of different materials need to be transport into and out from the plant.
1. Starting raw materials and products: major raw material of Sodium
Hydroxide is industrial salt. So sometimes need to import it from abroad and
the products need to export.
2. Waste products and coproducts: some of the waste products should transport
to recycle centers as they may can’t recycling around the factory.

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For transport above mentioned things, following ways can be used.
1. Road transport & Highway Transport- Due to lack of highways in Sri Lanka,
must use normal roads most of time. So, it’s very important to have a location
which have access to major areas in the country to save the valuable time and
the cost.
2. Sea Transport: Sri Lanka has 7 ports around the country. That is great
advantage for this industry.
So, we must select a good location with sufficient transport options, otherwise we have to
estimate an extra cost for transport.
(https://en.wikipedia.org/wiki/Transport_in_Sri_Lanka)
5.3 : Waste Management :
Waste management is a huge part of any industry nowadays. And it is very important
to choose a place that can apply modern waste management options. Since Diaphragm cell
used in Sri Lanka to produce Sodium Hydroxide, following things are the major waste
generated from it.
5.3.1 : Waste Water: Ion exchange wash water, cell wash water, brine purge.
Salt has built up to such levels on water that the water is no longer can usable as
drinking water because of discharging brine purge into the water resources. it will be a threat
to every living beings and the nature.
5.3.2 : Solid Wastes: Used cell parts.
Ex: Asbestos: It is toxic material that cause medical problems like cancers.
5.3.3 : Hazardous Wastes: Chlorinated Hydrocarbon waste.

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.
5.3.4 : Chlorine Gas :
Since chlorine is highly toxic gas which has a unique penetrating odor and can
cause problems like coughing, lung problems so should have precautions to minimize
the risk.
( https://www.ncbi.nlm.nih.gov/pubmed/27955969 )
(https://www.researchgate.net/publication/319466961_4_Waste_Treatment_and_Management_in
_Chlor-Alkali_Industries )
5.4 : Safety Options :
Safety Is the main part of anything. Not only the safety of workers but also the people
around selected location. Sodium Hydroxide production is chemical process, so it should
follow the international safety standards. Any accident inside the plant will make a huge
impact to the reputation of the products as well..
5.5 : Site Selection Justification :
Paranthan is the major place that manufacture NaOH in Sri Lanka which established in
1954. It is located in Kilinochchci district and its very near to sea. So, it’s easy to import
and export. Normally there is a bright temperature in this area and helpful conditions for
this industry at all. There are no reports on safety problems so that means they use enough
safety management options.
( http://paranthanchemicals.gov.lk/eng / )
❖ Coastal Areas like Puttalam, Hambantota, Trincomalee are good as well for build
the plant.

30
Example : Let’s take Hambantota area as recommendation.
• Hambantota is a city in the border of Sri Lanka with fort and airport that constructed
in few years ago.
• Since this city is very near to the sea, Nacl can be taken very easily.
• Nacl and other raw materials can be imported from abroad with having fort facilities
and airport facilities.
• Hambantota is a city which has no larger population with respect to other areas in
Sri Lanka. it’s always a great factor to build a such plant.
• With the availability of southern Express highway, it’s easier to transporting to
Colombo or any other area through Colombo.
• Basically, Hambantota has a sunny and windy whether condition in most of time in
the year. So, it’s a good advantage too.

31
References
1. Supply and Demand
• “Sodiumhydroxide.”
http://www.essentialchemicalindustry.org/chemicals/sodium-hydroxide.html
• “Raigam Wayamba Saltern begins industrial chlorine production”
http://www.sundaytimes.lk/180121/business-times/raigam-wayamba-saltern-
begins-industrial-chlorine-production-277461.html
2. Raw Material Requirement
• “The Sri Lanka Forester, 1977
• “Industrial Chemistry, 1991”
3. Energy Requirement
• “Journal of the National Science Council of Sri Lanka, 1984”
• “Principles of Cattle Production - C. J. C. Phillips - Google Books,”
• “O’Brien, Bommaraju, & Hine, 2007”
4. Process Selection
• “Euro Chlor - The mercury cell process.”
http://www.eurochlor.org/the-chlorine-universe/how-is-chlorine-
produced/the-mercury-cell-process.aspx
• “Euro Chlor - The diaphragm cell process.”
produced/the-diaphragm-cell-process.aspx
• “Euro Chlor - The membrane cell process.”
produced/the-membrane-cell-process.aspx
• “Resources - World Chlorine Council.”
https://worldchlorine.org/publications

32
5. Site Selection
• “Zhuang, 2016”
• “Transport_in_Sri_Lanka”
https://en.wikipedia.org/wiki/Transport_in_Sri_Lanka
• “Environmental challenges of the chlor-alkali production”
https://www.ncbi.nlm.nih.gov/pubmed/27955969
• “Paranthan Chemicals”
http://paranthanchemicals.gov.lk/eng

ASSIGNMENT
SODIUM HYDROXIDE PRODUCTION
Group Members
DATE OF SUBMISSION 14/10/2018
DEPARTMENT OF CHEMICAL AND PROCESS ENGINEERING
UNIVERSITY OF MORATUWA

ASSIGNMENT 2
PROCESS DESCRIPTION

Unit Operations Based On NaOH Production
❖ Brine Saturation
❖ Brine Purification
❖ Electrolysis
❖ Concentration
❖ Cooling and Filtration
❖ Drying
❖ Compression
❖ Liquefaction
Brine Saturation
• This process is helping to bring the undersaturated brine up to saturation conditions.
• Brine liquid is brought into a holding tank and recycled to keep the solids suspended in the
liquid. Part of the recycling salt stream is diverted to a saturator unit which have an upright
column and a slurry feed tube mounted inside and coaxial with the column.
• The slurry passes downwardly through the feed tube. Then it mixes with an undersaturated
brine stream entering through the bottom of the column. This mixture flows upwardly through
an annulus section defined between the feed tube and saturator column, with the salt dissolving
in the brine during the upward flow.
• Saturated brine is removed at the top of the column.
Brine Purification
• This process is for the purification of raw brines which containing impurities like Strontium,
Calcium and Magnesium.
• In this process raw brine is treated by contacting it with,
✓ sodium carbonate for precipitation of carbonates of strontium and calcium.
✓ sodium hydroxide for precipitation of magnesium hydroxide.

Electrolysis
• Normally Titanium anode and Nickel or Steel cathode is use in Membrane cell as well as an ion
exchange column which made by some polymeric material to separate anode and cathode.
• By this it prevents unwanted secondary reaction in the cell.
• Brine water should be applying into the cathode while water is applying to the anode loop.
Anode reaction:
2Cl-
Cl2 + 2e-
Cathode reaction:
2H2O+ 2e-
H2 +2OH-
• Between the reactions Na+ is moving to the cathode through the ion exchange column.
• So NaOH is producing as a result of combinations in the anode loop.

Concentration
• An aqueous solution of sodium hydroxide containing soluble impurities such as a concentrated
catholyte produced by a diaphragm electrolysis is cooled by a coolant or a heat-exchanger to
form a slurry containing sodium hydroxide hydrate crystals and fine impurity crystals. The fine
impurity crystals are adsorbed on bubbles which are formed by vaporizing a dissolved coolant
or introducing a gas in the slurry and separated from the slurry.
• The caustic solution leaves the cell with about 30% concentration and, at a later stage in the
process, is usually concentrated to 50%
Cooling and Filtration process
• The chlorine gas coming from electrolysis is normally about 80-90c and it should be cooled
before the compression process.
• And the brine mist must be removed by filtration process.
• This cooling process can be done by 2 steps. For these two heat exchangers named as Cooler 1
and cooler 2 can be used. These coolers are operated with cooling water system. the chlorine
gas is cooled down,
• to 40ºC inside the cooler 1.
• to 15ºC inside the cooler 2.
Drying
• The chlorine gas coming after the cooling process is dried by help of Sulphuric acid to a final
moisture content of max. 12.5 w/w ppm. The drying is performed in one single Cl2 drying
tower which consists of two drying sections.
✓ In the first section Cl2 gas is dried by using 78% H2SO4
✓ In the second section Cl2 gas is dried by using 98% H2SO4

Compression
• The chlorine gas coming after the drying process compressed from about 0.02 barg to 3 barg.
• This process is occurred in in a liquid piston type compressor.
Liquefaction
• The chlorine gas contains some oxygen and must often be purified by liquefaction.
• The dried and compressed chlorine gas is liquefied in the Chlorine Liquefier.
• The liquefied chlorine flows by gravity thorough a siphon in to the Chlorine Storage Tanks.
The siphon must be always vented to the compressor discharge.

Summary of Unit operations
Unit Operation Necessity
Brine Saturation Help to bring the undersaturated brine up to saturation conditions
Brine Purification Purifying raw brines which containing impurities
Electrolysis Building the atmosphere to occur chemical reactions
Cooling and Filtration Remove the brine mist
Reduce the heat of the gas
Concentration Increase the NaOH concentration of the brine.
Drying Removing the moisture
Compression Decrease the volume of the gasses.
Liquefaction Removing the oxygen content

PROCESS BLOCK DIAGRAM
SOLID SALT + WATER IMPURITIES
HCl Water
Cooling Water Chlorine Gas Hydrogen Gas
Caustic Solution
H2S04
Caustic Solution
BRINE
SATURATION
BRINE
PURIFICATION
CONCENTRATION
COOLING &
FILTERATION
ELECTROLYSIS COOLING
COOLING
DRYING
LIQUEFACTION
COMPRESSION
LIQUID
HYDROGEN
N
NaOH
LIQUID
CHLORINE

References
1. http://www.freepatentsonline.com
2. www.fumatech.com
3. https://worldchlorine.org
4. http://www.eurochlor.org
5. https://www.youtube.com

ASSIGNMENT
SODIUM HYDROXIDE PRODUCTION
Group Members
DATE OF SUBMISSION 21/10/2018
DEPARTMENT OF CHEMICAL AND PROCESS ENGINEERING
UNIVERSITY OF MORATUWA

ASSIGNMENT 3
PROCESS FLOW DIAGRAM

FLOW DIAGRAM
(SOFTWARE: MICROSOFT VISIO 2016)
BRINE SATUARATOR
COOLING TOWER 1COOLING TOWER 2
Salt + Water
Caustic Solution
H2
Cl2
H2SO4
LIQUID
CHOLORINE
NaOH
MEMBRANE CELL
DRIER
COMPRESSER
CONDENSER
EVAPORATOR
CONDENSER
OPEN TANK
Brine Solution
WATER

REFERENCES
1. http://www.freepatentsonline.com
2. www.fumatech.com
3. https://worldchlorine.org
4. http://www.eurochlor.org
5. https://www.edrawsoft.com/pfdsymbols.php

1
Assignment
Group Members :

2
ASSIGNMENT 04
Material Balance

3
Objective of this report is to provide detail material and energy balance for the proposed
Sodium hydroxide plant. Capacity of the plant is 6000 MT per day. Chlorine and
hydrogen are the byproducts and hence not considered in the balances in the steps
involving their processing. Approximately it is prepared to install 1.5 tons per hour.
4.1: Brine Saturator
Assumptions
No material accumulation in the steady state.
Feed NaCl:
15/100 x Feed =1700
NaClFeed = 11333.33 kg/hr.
Stream Flow rate (kg/hr)
1- aq. NaCl 15%(w/w) 1700
2- Na2CO3 20
3- Pure aq.NaCl 28%(w/w) 3137.03
4- Sludge 10% NaCl (w/w) 8216.30
Mass Balance

5
Assumptions
1. Amount of liquid in the cell is constant throughout the process
ie: Q1 = Q4 + Q5 (Q = Volume Flow rate)
2. Slurry doesn’t contain NaOH
3. The volume changes of liquid due to evolution of Cl2 and H2 are negligible.
finding |NaOH|4;
Amount of NaCl entering a membrane cell
= 28% * |NaCl|3 = 28% * (3137.03) = 878.368 kg/hr
Molar flow rate = 878.368 / 58.5 = 15.014 kmol/hr
No of moles of NaOH produced
= 55% * (15.014) = 8.257 kmol/hr
Amount of NaOH produced
= 8.257 * 40 = 330.28 kg/hr
|NaOH|4 = 330.28 / 35% = 943.66 kg/hr
1- Pure aq.NaCl 28%(w/w) 3137.03
2- H2 8.256
3- Cl2 290.71
4- aq. NaOH 35%(w/w) 943.66
5- Slurry 2185.06

6
2NaCl + 2H2O → 2NaOH + H2 + Cl2
(Mass)in flow
(kg/hr)
878.36 2258.66
Molecular Weight
(g/mol)
58.5 18 40 2 70
(Moles)in flow
(kmol/hr)
15.014 125.48
Production
Rate at 55%
(kmol/hr)
-8.257 -8.257 +8.257 +4.153 +4.153
(Mass)out flow
(kg/hr)
395.28 2110.01 330.28 8.306 290.71
finding Waterin;
Amount of Water entering a membrane cell
= 72% * |NaCl|3 = 72% * (3137.03) = 2258.66 kg/hr
Molar flow rate = 2258.66 / 18 = 125.48 kmol/hr
Water is clearly in excess
Balancing total mass;
|NaCl|1 = |H2|2 + |Cl2|3 + |NaOH|4 + |Slurry|5
3137.03 = 4.153 + 4.153 + 943.66 + |Slurry|5
|Slurry|5 = 2185.06

8
References
1. O’brien, T. F., Bommaraju, T. V, & Hine, F. (n.d.). Handbook of Chlor-Alkali
Technology Volume I: Fundamentals. Retrieved from
https://link.springer.com/content/pdf/bfm%3A978-0-306-48624-1%2F1.pdf
2. MANUFACTURE OF CHLORINE - CAUSTIC SODA USING
ELECTROLYSIS PROCESS (ME…. (n.d.). Retrieved November 5, 2018, from
https://www.slideshare.net/AnkushGupta40/phase23?from_action=save
3. Chlor alkali Market - Detailed Study Analysis and Forecast by 2023. (n.d.).
Retrieved November 5, 2018, from
https://www.slideshare.net/PriyankaThombare3/chlor-alkali-market-detailed-
study-analysis-and-forecast-by-2023?qid=a2cb2180-69a7-4af5-87ec-
b9630f39adec&v=&b=&from_search=6
4. ESP FLOWSHEET SIMULATION APPLICATION BRIEF Chlor-Alkali
Simulation. (n.d.). Retrieved from
http://support.olisystems.com/ApplicationBriefs/Briefs - Chlor Alkali.pdf
5. Westphal, G., Kristen, G., Wegener, W., Ambatiello, P., Geyer, H., Epron, B., …
Götzfried, F. (2010). Sodium Chloride. In Ullmann’s Encyclopedia of Industrial
Chemistry. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA.
https://doi.org/10.1002/14356007.a24_317.pub4

1
Assignment
Group Members :

2
ASSIGNMENT 05
Energy Balance

3
Objective of this report is to provide detailed energy balance for the proposed Sodium
hydroxide plant. Chlorine and hydrogen are the byproducts and hence not considered
in the balances in the steps involving their processing.
4.1: Brine Saturator.
From material balance data,
Assumptions
1. No material accumulation in the steady state.
2. Energy Consumption in the saturator unit is negligible.
Energy Balance
Stream Flow rate
(kg/hr)
1- aq. NaCl 15%(w/w) 1700
2- Na2CO3 20
3- Pure aq.NaCl 28%(w/w) 3137.03
4- Sludge 10% NaCl (w/w) 8216.30

4
4.1: Membrane Cell
Assumptions
1. Datum Temperature : 250
C
2. Change in specific heat capacity values with temperature are
negligible.
3. The No energy / work loss in the cell.
Stream Specific Heat 600C
(kJ/kg K)
Flow rate
(kg/hr)
Temperature
Change (K)
Water (250
C) 4.185 270.252 35
1- Pure aq.NaCl 28%(w/w) 3.247 3137.03 35
2- H2 14.430 8.256 55
3- Cl2 0.480 290.71 55
4- aq. NaOH 35%(w/w) 3.594 943.66 55
5- Slurry 3.247 2185.06 55
Efficiency : 55%

5
Input Power = Stream 1 + Water Stream = 396092.9 kJ/hr
Output Power = Stream 2 + Stream 3 + Stream 4 + Stream 5 = 590979.3 kJ/hr
The remaining power for output must be obtained from Electricity.
Electric Power needed = 590979.3 - 396092.9 = 194886.4 kJ/hr
Stream Heat Content
(kJ/hr)
Water (250
C) 39585.16
1- Pure aq.NaCl 28%(w/w) 356507.8
2- H2 6552.374
3- Cl2 7674.744
4- aq. NaOH 35%(w/w) 186533.3
5- Slurry 390218.9

6
4.3: Evaporator
Stream Specific Heat
600C (kJ/kg K)
Flow rate
(kg/hr)
Temperature
Change (K)
1- aq. NaOH 35%(w/w) 3.594 943.66 55
3- aq. NaOH 50%(w/w) 3.564 660.56 85
2- Steam 1.996 283.10 10
Latent Heat of
Vaporization
(kJ/kg)
Flow rate
(kg/hr)
2- Steam 2231.86 283.10
Assumptions
1. Change in specific heat capacity values with temperature are negligible.
2. The No energy / work loss in the Evaporator.
3. No energy/ heat loss in transfer process from Cell to Evaporator.
.

7
Input Power = Stream 1 = 186533.3 kJ/hr
Output Power = Stream 2 + Stream 3 = 837600.3 kJ/hr
The remaining power for output must be given as heat.
Heat Power needed = 837600.3 - 186533.3 = 651067 kJ/hr
4.4: Conclusion
• Electric Power needed = 194886.4 kJ/hr
• Heat Power needed = 651067 kJ/hr
Stream Heat Content
(kJ/hr)
1- aq. NaOH 35%(w/w) 186533.3
2- Steam 637490.2
3- aq. NaOH 50%(w/w) 200110.0

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