setting up Sodium Hydroxide plant

1. SODIUM
HYDROXIDE
NaOH
(IIT Bombay)
Final Presentation
4th April 2022
GROUP 14
1

2. 2
Group Members
Samarth Doshi 180020089
Shubhanshi Asati 180020106
Rohit Yadav 180020084
Karan Desai 180020046
Shubham Kamble 180020105
Virat Rathor 170020067

3. Literature Review
&
Background Work
3

4. 4
Market Survey
China is the largest producer and consumer of Sodium Hydroxide. North America is
the second producer and consumer, and the American producers like Dow Chemical,
OxyChem, Axiall and Olin Corporation, are dominating the North America market,
these players also play important role in global market. The worldwide market for
Sodium Hydroxide is expected to grow at a CAGR of roughly 4.7% over the next five
years, will reach 39300 million USD in 2024, from 29800 million USD in 2019,
according to a new study.
Indian Caustic Soda market demand stood at 3.43 Million Tonnes in FY2021 and is
forecast to reach 5.52 Million Tonnes by FY2030. GACL is the largest Caustic Soda
Manufacturer in India with a capacity of 4,29,050 TPA. Spread over 2 complexes at
Vadodara and Dahej.

5. 5
Plant Capacity and Suitable Location
Capacity - 500 MT/day (50% w/w NaOH solution)
Location - Dahej, Gujarat
Advantages - Gujarat is the highest producer of salt in India accounting for 80% for NaCl production
in India
The major raw material for NaOH manufacturing using Membrane Cell Method is high purity brine
water. Brine water can be obtained from salt mines, evaporation of Seawater or Industrial Salt. As
Industrial Salt is of high purity of NaCl it is preferable save cost incurred for brine water purification
and reduce plant size.
Hence it is a preferable location for setting up the plant.The caustic soda market in India is growing
rapidly at 6% per year. Most of the caustic soda is used domestically and very little amount is
exported in forms of flakes.
Most of the operational cost for membrane cell method is electricity consumption. Gujarat has
cheaper electricity compared to most states in India

6. Detailed
Flowsheet
Development
6

7. 7
Process for NaOH Production
A. Castner Kellner’s Process B. Diaphragm Cell Method C. Membrane Cell Method
1. Environmental Performance - One of the major reasons for the trend of conversions has been
awareness about environmental regulations and the impact of mercury on human health and the
environment.
2. Demand growth and market price – capacity expansions - Another reason is growing demand of caustic
at a rate of 5% per year. After 1986, no mercury-cell units or expansions of existing mercury-cell units
were allowed in India. Therefore, only membrane cell units were constructed to meet the growing demand
for caustic
3. Energy savings - Converting to membrane cell technology yields net energy savings of 400 to 600
KWh/mt. The cost of electricity is very high in India (about $ 105/MWh compared to $63/MWh used in the
Appendix 1 analysis), and energy savings was one of the major reasons to opt for conversion, reducing
the cost of production and becoming more competitive in the market.
Hence, we go with the Membrane Cell Method.

8. 8

9. Mass
Balance
9

10. Assumptions
No material accumulation in the steady state
10
Stream Flow Rate (ton/hr)
1-aq.Nacl 15%(w/w) 51
2-Na2CO3 0.6
3-Pure aq.NaCl 28%(w/w) 94.1109
4-Sludge 10% 246.489
5-Feed aq.Nacl 14%(w/w) 287.56
6-Recycle Stream 21% w/w 52.44
Feed NaCl
15% * NaClFeed = 51
NaClFeed = 340 ton/hr

11. Balancing overall material
Feed (F) + Na2CO3 = |Sludgel| + |NaCI3|
340 + 0.6 = |Sludgel|4 + |NaCl|3 . . . . . . . . . . . . . . . . . . . . . . . . . equation(1)
11
Balancing NaCI
51 = 28%|NaCl| + 10%|Sludge|4
5100 = 28|NaCl|3 + 10|Sludge|4..............…equation(2)
Solving equation(1) & equation(2);
|NaCl|3 = 94.111ton/hr
|Sludge|4 = 246.489 ton/hr

12. Mass Balance - Membrane Cell
Assumptions -
1] Amount of liquid in the cell is constant throughout the
process, i.e., Q1 = Q4 + Q5 where Q = Vol Flow Rate
2] Slurry does not contain NaOH
3] The volume changes of liquid due to evolution of Cl2 and
H2 are negligible
12
Stream Flow Rate [tons/hr]
Pure aq NaCl 28%
[w/w]
94.11
H2 0.25
Cl2 8.72
aq. NaOH 35% [w/w] 28.31
Slurry (21% NaCl w/w) 65.55
Purge Stream (20%) 13.11

13. Finding NaOH|4 -
13
Amount of NaCl entering a membrane cell
= 28%*NaCl3 = 28%*94.11 = 26.35 tons/hr
Molar flow rate = 26.35/58.5 = 0.45 ton-mol/hr
No. of moles of NaOH produced = 55%* 0.45 =
0.25 ton-mole/hr
Amount of NaOH produced = 0.25*40 = 10 tons/hr
NaOH4 = 10/35% = 28.57 tons/hr
x = 0.2 for purge. It is 21% NaCl
26350.80 67759.80
58.5 18 40 2 70
450.42 3764.40
-247.71 -247.71 +247.71 +124.59 +124.59
11858.40 63300.30 9908.40 249.18 8721.30

14. Finding Waterin -
Amount of water entering a membrane cell = 72%* NaCl3 = 72%*94.11 = 67.76 tons/hr
Molar flow rate = 67.76/18 = 3.76 ton-mol/hr
Water is clearly in excess
Balancing total mass -
NaCl1 = H22 + Cl23 + NaOH4 + Slurry5
94.11 = 0.12 + 0.12 + 28.31 + Slurry5
Slurry = 65.55 tons/hr
14

15. Mass Balance - Evaporator
1] Amount of liquid in the evaporator is constant throughout the process
i.e. |NaOH|1 = |Steam|2 + |NaOH|3
2] No precipitation of NaOH is considered
15
Stream Flow Rate [tons/hr]
aq NaCl 35% [w/w] 28.31
steam 8.49
aq. NaOH 50% [w/w] 19.82
Assumptions

16. Balancing Across Evaporator
16
Amount of NaOH entering ( |NaOH|1 ) = 35% * |NaCl|1
= 0.35 * 28.31 tonnes/hr
= 9.91 tonnes/hr
NaOH exiting = NaOH entering = 9.91 tonnes/hr
50% * |NaOH|3 stream = 9.91 tonnes/hr
|NaOH|3 stream = (9.91/0.5) tonnes/hr
= 19.82 tonnes/hr
|NaOH|1 = |Steam|2 + |NaOH|3
|Steam|2 = 28.31 tonnes/hr - 19.82 tonnes/hr
= 8.49 tonnes/hr
Overall Mass Balance
NaOH Mass Balance

17. Steady State
Flowsheet
Simularion
17

18. DWSIM Simulation
18

19. Equipment
Sizing
19

20. 20
Equipments
❖ Saturator
❖ Heater
❖ Membrane Cell Reactor
❖ Evaporator
❖ Storage Tank

21. Saturator Sizing
Volumetric flow rate of the feed = 390 m3/hr
Diameter of the saturator = 1 m
Area = 3.14 m2
Uplift velocity = 2.07 m/min
From literature, we understand that the residence time is 5-10 minutes
We are taking it to be 7 minutes
So, the height of the saturator = uplift velocity * residence time
Height = 14.5 m
21

22. Heater Sizing
Heater is placed after the saturator to increase the temperature of the brine solution before it enters
Membrane Cell reactor.
We will perform energy Balance to see how much heat is needed to increase the temperature of the Brine
solution from 320C to 600C. Brine solution at 600C enters Membrane Cell reactor giving sodium hydroxide at
800C
Energy Balance:
Total Heat Needed = (flow rate)outlet (Enthalpy)outlet - (flow rate)inlet
(Enthalpy)inlet
Q = mout ΔHout - min ΔHin
From Material Balance of Saturator :
(flow rate)outlet = (flow rate)inlet = 94.111 ton/hr
Enthalpy of Brine solution:
22
Temperature (0C) Enthalpy of Brine Solution(KJ/Kmol)
32 -64288.9
60 -61974.3

23. Heater Sizing
Therefore,
(Enthalpy)outlet = -61974.3 KJ/Kmol
(Enthalpy)inlet = -64288.9 KJ/Kmol
So, Heat Required Q:
Q = mout ΔHout - min ΔHin
= 94111 Kg/hr *( -61974.3 -(-64288.9))KJ/Kmol = 2.17829 x 108 KJ-Kg/hr-
Kmol
Feed Brine solution is 89.3% water and 10.7% NaCl by moles
So, Average molar weight of brine solution = 58.5 * 0.107 + 18 * 0.893 = 22.3335 gm/mol
So, Q = 2.17829 * 108 KJ-Kg/hr-Kmol / (22.3335 Kg/Kmol)
Q = 9.75346 * 106 KJ/hr / (3600 sec/hr)
Q = 2709.3 KJ/sec = 2709.3 KW
So we would need to provide 2709.3 KW of heat to raise the temperature of Brine solution from 320C to
600C
23

24. Membrane Cell Sizing
The sizing of Membrane Cell in mainly affected by the type of arrangement of electrolysers.
There are two types of electrolysers monopolar and bipolar depending on the manner of electrical
connection is made between the electrolyser elements.
24
Due to the advantages of bipolar electrolyser we will
be considering it in our reactor. Some advantages are
:
● easier manufacturing,possibility to operate at
higher current density without dramatic effects
on energy consumption due to very efficient
internal recirculation
● membrane area more effectively used (from 85–
87 % to 90–92 %); better energy performance
due to smaller voltage drop
● shorter duration of shutdown and start-up
phases to replace membranes due to the easy
and simple filter press design;
● higher flexibility of operation (each electrolyser
could be operated independently of the others
due to a parallel connection)

25. Membrane Cell Sizing
The designation does not refer to the electrochemical reactions that take place, which of course
require two poles or electrodes for all cells, but to the electrolyser construction or assembly. In a
bipolar arrangement, the elements are connected in series with a resultant low current and high
voltage.Usually bipolar electrolysers are connected in parallel with a low current and high
voltage.
In commercial electrolysers sold we will be considering Uhde Bipolar Electrolyser.
The typical electrode active area is 2.7 m2 and the annual electrolyzer production capacity can
be up to 28,000 tons of NaOH (100% basis, with electrolyzers having 160 elements at 6.0kAm-
2).
It has length and width of 14 m and height of 8 m.
For our production we will need,
20*24*365/(28000*2) = 3.12 bipolar electrolysers
So we can add 4 bipolar electrolysers in parallel in the membrane cell room.
25

26. Evaporator Sizing
Inlet Flow rate = 28309.2 kg/hr
Q(kW) = 5501 kW
T1 = 75 degree C
T2 = 100 degree C
LMTD = 86.82
U = 2000
Q = U * A * LMTD LMTD = (T2 - T1)/ln(T2/T1)
Area = 31 m2
26

27. Storage Tank Sizing
Aq. NaCl Fresh Feed
Chlorine product
27
TANK DURATION VOLUME (tons) HEIGHT (m) DIAMETER (m)
Main 7 days 57,120 20.5 60
Day 24 hrs 8,160 12 30
Intermediate 8 hrs 2,720 10 19
TANK DURATION VOLUME (tons) HEIGHT (m) DIAMETER (m)
Main 15 days 3,139.20 10 20
Day 24 hrs 209.28 6 7
Intermediate 8 hrs 69.76 6 4

28. Economics
28

29. Saturator - Capital Cost
29
a b Length (m) n Cost in 2006 Cost in
2020
H-01 21000 340 14.5 1 $25930 $32301.433
Ce (cost) = a + b* Sn
CEPCI index
2006 2020
CEPCI Index 478.6 596.2

30. Heater - Capital Cost
30
a b S (Area - m2) n Cost in 2006 Cost in
2020
H-01 10000 88 42.3 1 $13722 $17094.22
Ce (cost) = a + b* Sn
CEPCI index
2006 2020
CEPCI Index 478.6 596.2

31. Heater Costing
31
From literature,
Cost of a 2700 kW Heater = $ 17094.22
Capital Cost of Heater = $ 17094.22
For Operating Cost,
Price of electricity in India per kWh = $ 0.109
Power of required electric heater = 2709.3 kW
If a plant runs for a day( 24 Hours)
Running Cost of Heater (per hour) = Power (kW) * Price of electricity per kWh
Running Cost (per day) = $ 2709.3 * 0.109 * 24
= $ 7087.44
Running Cost (per day) = $ 7087.44

32. Evaporator
32
a b S (Area - m2) n Cost in 2006 Cost in 2020
E-03 17000 13500 31.0 0.6 $122962.15 $153176.01
Ce (cost) = a + b* Sn
CEPCI index
2006 2020
CEPCI Index 478.6 596.2

33. Storage Tank Costing
33
TANK DURATION VOLUME
(tons)
HEIGHT (m) DIAMETER
(m)
Cost ($)
Main 15 days 7,135.20 15 25 1885655
Day 24 hrs 475.68 6 10 151342
Intermediate 8 hrs 158.56 6 6 54982
𝐶 = 𝐹𝑀*𝑒𝑥𝑝(11. 662 − 0. 6104(𝑙𝑛𝑉) + 0. 04536(𝑙𝑛𝑉) 2 , V-volume in gallons
MoC factor for Carbon steel SS-316 FM=2.7
Aq. NaOH Product Feed

34. Storage Tank Costing
34
TANK DURATIO
N
VOLUME (tons) HEIGHT
(m)
DIAMETER
(m)
Cost ($)
Main 7 days 57,120 20.5 60 3025774
Day 24 hrs 8,160 12 30 2299763
Intermediate 8 hrs 2,720 10 19 138776
Aq. NaCl Fresh Feed
Chlorine product
TANK DURATIO
N
VOLUME
(tons)
HEIGHT
(m)
DIAMETER
(m)
Cost ($)
Main 15 days 3,139.20 10 20 1662451
Day 24 hrs 209.28 6 7 145674
Total = $9364417

35. Major Equipment Costing
Thus, the total cost of the equipments is = $9501101.15
35
Capital Investment Evaluation
Total purchased equipment costs calculated in the earlier sections are used to calculate the total
capital investment in the plant. The plant is considered to be a Fluid-Fluid Processing plant.
Working capital is taken to be as 15% of the total capital investment. The total capital investment
is determined using the method of percentage of delivered equipment cost. India factor is
considered to be 0.7.

36. 36
Direct Cost Percentage Normalized Cost in Million
Dollar as in 2002
Purchase equipment delivered 100 0.2 9.5
Purchase equipment installation 47 0.09 4.47
Instrumentation and Controls 36 0.07 3.42
Piping 11 0.13 1.05
Electrical systems 68 0.02 6.46
Buildings 18 0.04 1.71
Yard improvements 10 0.02 0.95
Service facilities 70 0.14 6.65
Land 5 0.01 0.48
Total direct plant cost 365 0.72 34.675

37. 37
Indirect cost Percentage Normalized Cost in million dollar
as in 2002
Engineering and supervision 33 0.06 3.14
Construction expenses 41 0.08 3.89
Legal expenses 4 0.01 0.38
Contractor’s fee 22 0.04 2.09
Contingency 44 0.09 4.18
Total indirect plant cost 144 0.28 13.68
Fixed capital investment 509 1 48.36
Working capital 90 0.18 8.55
TCI [acc to USA 2002] 56.91
India factor 0.7
TCI [ acc to india 2002] 39.837
TCI [ acc to india 2020 ] 49.625

38. Raw Material Cost
Assuming 8000 Hrs of Running hours annually
38
Raw Material Per kg Cost
(₹/kg)
Amount Required
(tonnes/yr)
Cost
(crore ₹/yr)
Industrial Salt 1.5 4,08,000 61.2
Na2CO3 36.5 4,800 17.52
Total Raw Material
Cost
78.72
Total = $1023500

39. Revenue Calculation
According to 8000 hours of annual running time. The main product in the operation of the plant is 50%(w/w) NaOH and the by-products are
Hydrogen and Chlorine gas.
39
Product Production
(tonnes/yr)
Cost/kg
(₹/kg)
Revenue
(crore ₹/yr)
50%(w/w) NaOH 1,58,560 25 396.4
Cl2 69,770.4 20 139.5
H2 1998.48 116 23.18
Total Revenue 559.08
Total = $7335000

40. Total
Production
Cost
40
Item Percentage of total
product costs
Normalized value Cost - $/yr
Raw material 50 0.345 511750
Operating labor 15 0.1 153525
Supervising labor 3 0.021 30705
Utilities 15 0.1 153525
Repairs and maintenance 7 0.05 71645
Operating supplies 1.05 0.01 10746.75
Laboratory charges 1 0.007 10235
Patents 3 0.021 30705
Fixed charges 15 0.1 153525
Plant overhead costs 15 0.1 153525
Admin expenses 3.75 0.026 38381.25
Distribution and marketing 11 0.076 112585
RnD cost 5 0.034 51175
Total product cost 144.8 1 1482028
Total costs 2810531

41. Payback Period Calculation
The following assumptions have been made while calculating the payback period:
1. FCI excluding the land is considered to be depreciable over a period of 10 years
2. Average depreciation is calculated using a linear depreciation model
3. Bank interest rate of 8% over the total capital used
4. Capacity is 70 % 1st year, 80 % 2nd year, and 90% from 3rd year onwards
41
The following values are in Crore INR, at 100% production:
Total depreciable FCI = INR 363.89 Crore
Total depreciable per yr = INR 36.39 Crore
Tax rate = 30 % (Turnover > 250 Crore)
Gross Profit before depreciation = Revenue-Total product cost = INR
44.48 Crore
Net Profit= (Gross profit-depreciation)*(1-tax rate) = INR 5.663 Crore

42. Payback Period Calculation
42
Year Capacity Investment Cost Revenue Gross Profit Depreciation Net Profit Cash Flow Cumulative
position
0 -377.15cr -377.15cr -377.15cr
1 70 -7.88 39.02 31.14 36.39 3.964 40.354 -336.796
2 80 -9.01 44.59 35.58 36.39 4.53 40.92 -295.876
3 90 -10.13 50.17 40.04 36.39 5.097 41.49 -254.389
4 90 -10.13 50.17 40.04 36.39 5.097 41.49 -212.896
5 90 -10.13 50.17 40.04 36.39 5.097 41.49 -171.406
6 90 -10.13 50.17 40.04 36.39 5.097 41.49 -129.16
Hence the Payback Period comes out
to be approximately 10 years.

43. Payback Period Calculation
43

44. Detailed
Design of One
Equipment
44

45. Membrane Cell Reactor
The sizing of Membrane Cell in mainly affected by the type of arrangement of electrolysers.
There are two types of electrolysers monopolar and bipolar depending on the manner of electrical connection is made
between the electrolyser elements.
45
Due to the advantages of bipolar electrolyser we will
be considering it in our reactor. Some advantages
are :
● easier manufacturing,possibility to operate at
higher current density without dramatic
effects on energy consumption due to very
efficient internal recirculation
● membrane area more effectively used (from
85–87 % to 90–92 %); better energy
performance due to smaller voltage drop
● shorter duration of shutdown and start-up
phases to replace membranes due to the
easy and simple filter press design;
● higher flexibility of operation (each
electrolyser could be operated
independently of the others due to a parallel
connection)

46. Membrane Cell Reactor
The designation does not refer to the electrochemical reactions that take place, which of course require two poles or electrodes for all cells,
but to the electrolyser construction or assembly. In a bipolar arrangement, the elements are connected in series with a resultant low current
and high voltage.Usually bipolar electrolysers are connected in parallel with a low current and high voltage.
In commercial electrolysers sold we will be considering Uhde Bipolar Electrolyser.
The typical electrode active area is 2.7 m2 and the annual electrolyzer production capacity can be up to 28,000 tons of NaOH (100% basis,
with electrolyzers having 160 elements at 6.0kAm-2).
It has length and width of 14 m and height of 8 m.
For our production we will need,
20*24*365/(28000*2) = 3.12 bipolar electrolysers
So we can add 4 bipolar electrolysers in parallel in the membrane cell room.
46

47. Membrane Cell Reactor
47
Number of cells 160
Density (kAm-2) 2-6
Energy consumption 2100 kWhr/ton
Length 4.85 m
Width 2.38 m
Height 1.6 m
Weight of electrolyzer 3600 kg (when full)
Temperature 60 degree celsius
Concentration 28% NaOH [w/w]
Anode/Cathod bonding Bipolar elements
Anode gasket EPDM
Cathod gasket EPDM
Anode coating Ti based coating
Electrode size 2.7 m2
Method of electrolyte level control Overflow
Gaskets EPDM
Sealing force for gaskets Hydraulic

48. Environmental
Impact
Assessment
48

49. 49
Waste Emissions
There are mainly two emissions :
1. Waste from saturator - Sludge
1. Waste from membrane cell - Slurry

50. 50
Sludge Formation
In primary brine plant, saturation of brine, purification of brine, settling, filtration, acidification, de-chlorination are
performed.
The return brine from cell plant (190-200 gpl) is re-saturated in the saturator by addition of NaCl / KCl salt to
achieve brine concentration of 300gpl to 315gpl. The salt contains unwanted impurities Ca2+, Mg2+ and
SO42-. These impurities are removed by adding Na2CO3, NaOH and BaCO3. The mixture are agitated and
allowed for coagulating the precipitate. The precipitated impurities are dragged towards the settler bottom by
the rotation of the arm.
The settled liquid is allowed to overflow through the launder into the surge tank. The settled precipitates are
periodically removed.
The clarified brine from the settler is pumped to the filters from the surge tank. The suspended particles are
filtered in brine tanks. Filters are periodically backwashed to remove the arrested impurities. In membrane
system, the stored brine is sent to secondary brine plant for further treatment (to convert the brine to ppb
quality). The feed brine after electrolysis gets depleted to 50 gpl and also gets contaminated with free Cl2 to the
extent of 500-600 ppm. Hence de-chlorination system for removal of free Cl2. Dechlorination is done by
vacuum system. Return brine from cell plant is acidified to pH 2.0 and collected in lean brine tank where from it
is pumped into the saturator after neutralization.
This cycle is continued.
The Sludge is mainly formed from precipitate and sediments from Classifier and Saturator.

51. 51
Sludge Composition
Component Percentage (%)
Moisture 37.57
NaCl 12.73
Acid Insoluble 19.70
BaSO4 2.10
CaSO4 5.80
CaSO3 15.70
Mg(OH)2 6.40
Chlor-alkali industry, being red category industry,
generating huge wastewater and solid waste like
brine mud. High TDS, TSS, Chloride, free
chlorine are the main problem. Mercury is
present in the waste generated from mercury
and diaphragm process.

52. Brine Treatment
We do brine treatment to reuse water in the system and prevent waste of water in the system
being discharged in the environment.There are many technology options to concentrate brine,
reduce its volume and disposal costs, or to produce solids for zero liquid discharge.
Methods to desalt brine released in environment :
1. Membrane Treatment System
2. Thermal Treatment System
52
Membrane Treatment Systems
Reverse osmosis (RO) is the membrane system most widely used to
desalt brine waters. RO produces freshwater and more concentrated
brine often referred to as RO brine, reject, or concentrate. This brine
concentrate will usually reach concentrations of dissolved salts and
chemicals that will be near scaling limits. This requires treatment to
relieve the scaling potential if you will use a thermal system to further
concentrate the brine or to produce solids. Alternatively, you could
consider thermal systems that can operate under scaling conditions, such
as seeded slurry evaporators or a SaltMaker, to eliminate the thermal
pretreatment step.

53. Thermal Treatment Systems
If you are considering thermal evaporative systems,
maximizing freshwater recovery from lower cost membrane
systems before using expensive thermal systems will
deliver the best project economics. In general, there are two
types of thermal systems based on their residual outputs:
1. evaporators that produce concentrated, low volume
brine but do not precipitate solids;
2. crystallizers that exceed salt saturation and produce
solids. For high flow rate zero liquid discharge
applications, evaporators are used to preconcentrate
the brine prior to the crystallizer for final solids
production. At lower flows, the waste brine can be sent
directly to the crystallizer after treating with a
membrane system.
53

54. 54
Liquid Waste from Membrane Cell
Slurry
❏ The slurry mainly constitutes NaCl, water and chlorates(in a very low quantity). So, it is essential
that the chlorate doesn’t accumulate.
❏ We purge out a certain amount of stream and recycle the remaining stream back to the
saturator.
Hazardous effects of Chlorates -
❏ Contact can irritate and burn the skin and eyes
❏ Inhaling sodium chlorate can irritate the nose and throat causing coughing and wheezing
❏ It can cause nausea, vomiting and diarrhea and abdominal pain
❏ High levels of this substance can reduce the blood's ability to transport oxygen, causing
headache, fatigue, dizziness and blue colour to the skin and lips
❏ sodium chlorate can damage kidneys and affect the liver
❏ It is not combustible, but it is a strong oxidizer that enhances the combustion of other substance

55. 55
Hazardous Effects of Chemicals in Air
❖ Chlorine and Hypochlorites : The corrosiveness of wet chlorine is due to its hydrolysis to hydrochloric
and hypochlorous acids. It is rated as extremely dangerous health hazard. Chlorine is a strong oxidiser
and its reaction with other materials can also generate dangerous byproducts. It irritates mucous
membranes, the respiratory tract and the eyes. Inhaling can cause vomiting, chest pain, headache,
anxiety and feeling of suffocation. The safety limit of chlorine is 0.2 - 0.5 ppm in air.
Area monitoring to discover and track leaks as useful methods to prevent accidents. Electrochemical
Sensors are worn by workers to monitor exposure to chlorine. Various national exposure limits are
between 0.5 and 1 ppm averaged over an 8 hr day.
Most of the chlorine released to the atmosphere reacts to form HCl and returns to earth as acid rain
causing environmental damage.
❖ Caustic and Potash : Caustic and potash are classified as corrosive materials. Both NaOH and KOH
are very strong alkalis and are corrosive to human tissue. The concentration of 1 mg/m3 of NaOH in
the air can cause mild watering of eyes. A concentration of 2 mg/m3 is taken as an average or a ceiling
exposure limit.
❖ Hydrogen : Other than being a simple asphyxiant, hydrogen does not present a personal hazard.
Hydrogen also has explosion hazard but being light gas it disperses quickly in atmosphere hence it is
not very dangerous.

56. 56
Waste Minimization and Disposal
❖ Membranes :
➢ Membranes are generally inert and contain no hazardous material. They are considered
safe to handle, and only the most basic precautions, such as avoiding prolonged contact
with the skin, are necessary.
➢ Membranes to be removed from the cells will be wet and swollen with electrolytes and
should be handled accordingly. Rinsing and soaking relieve this particular hazard.
➢ Used membranes can be sent to a sanitary landfill. Another possible method of disposal is
incineration. Off-gases must then be scrubbed with an alkaline medium to prevent the
escape of HF and other corrosive or toxic gases.
❖ Miscellaneous Solids :
➢ Miscellaneous solids include auxiliary materials used in the process, small parts being
replaced, packages and wrappings, and everyday trash.
➢ Carbon, other adsorbents, filter aids, and ion-exchange resins used to treat water and brine
are examples of materials removed from the process. Consumable parts include valves,
gaskets, packings, cell renewal material, etc.
➢ Materials in these two categories should be rinsed or washed to remove process materials.
All miscellaneous solids should then be disposed of properly, according to their respective
properties. Segregation of the various types can simplify the procedures.

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Waste Minimization and Disposal
❖ Spent Sulfuric Acid :
➢ The sulfuric acid used to dry chlorine gas becomes a waste product. The quantity of waste acid
generated is inversely related to the difference between the concentrations of feed acid and waste
acid.
➢ Production of a more dilute waste acid means generation of less waste product. This is
constrained by the ability of the drying system to produce chlorine gas of satisfactory quality, the
increasing corrosivity of the chlorine-containing acid, and the method of disposal of the waste
acid.Possible means of disposal include :
■ productive use as a neutralizing agent for alkaline waste streams
■ dechlorination of waste condensate from a chlorine cooling system
■ return to the sulfuric acid supplier for disposal or reconstitution
■ neutralization by alkaline material for disposal
❖ Waste Water :
➢ A lot of water is wasted in the plant daily as cooling water, Steam, Sludge and Slurry.
➢ It is treated to bring the pollutants to safety level and are disposed of in stream or it is treated to
remove solid waste and then recycled.

58. 58
References
1. Handbook of Chlor Alkali Technology_Thomas F. O'Brien, Tilak V. Bommaraju, Fumio Hine
1. Manufacture of chlorine-caustic soda using Electrolysis Process R. K. Kulkarnee
1. ESF flowsheet simulation Application Brief, OLI systems Inc.
1. Sodium Chloride Article Online library
1. Handbook_of_Chlor_Alkali_Technology by Vladimir Lora