Mfg of Liquid Bromine (in brief) :-
Liquid bromine is produced from organic waste (acidic & alkaline) obtained from
pharmaceutical & fertilizer industries. NaBr obtained from waste is first acidified and then
treated with HBr and Cl2 gas to get gaseous bromine which when condensed in a
condenser gives Liquid Bromine.
Overall Reaction:-
NaBr + H2SO4 → HBr + Na2So4
HBr + Cl2 → HCl + Br2
Manufacturing Process:-
Raw Materials:-
Organic waste containing NaBr or HBr in significant quantity is obtained from fertilizer
and pharmaceutical industries.
Chlorine gas is used in substitution reaction to get liquid bromine.
Steam is used as heating medium as well as carrier gas.
Process: -
Reactor 1: -
Organic waste containing 10% to 25% concentration of NaBr is acidified in reactor 1. Due
to the corrosive nature of reactants reactor has to be glass lined. H2SO4 is added as a
acidifying medium. Acid used is of 98% conc. Steam of 1kg/hr mass flow rate is used to
attain reaction temperature of 110 oC and a pressure of 1kg/mm2.
Reaction taking place in the reactor is given by
NaBr + H2SO4 → HBr + Na2So4
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Since the reaction temperature is maintained at 110 oC all the organics having boiling
point less than that of water along with water and HBr get seperated and are sent to
condenser where hot vapours get condensed.
Filtration: -
The condensed liquid obtained is a mixture of HBr, water, & low boiling organics. Here
organics are undesired product therefore it needs to be removed.
Thus the liquid mixture is passed over a filter cloth in a filtration unit which acts under
vacuum. Here all the organics are removed from the mixture & HBr of approx. 30% conc.
is obtained. HBr obtained is pumped in reactor 2 for substitution reaction.
Reactor 2: -
Reactor 2 is made up of glass and is 6 m tall. Rasching rings are used as packing so as to
increase liquid gas contact time. Reaction temperature is 80 oC.
Liquid HBr is allowed to pass from the top and steam and Cl2 gas is passed through
bottom. Here, steam performs dual jobs firstly, of a heating medium & secondly, as a
carrier gas. The reaction taking place in the reactor is given by
HBr + Cl2 → HCl + Br2
HCl obtained is of 10% concentration which is of no significant use. It can either be
concentrated to 25% for sale or can be neutralised and discharged as an effluent. Br2
vapours along with unreacted Cl2 gas & H2O is condensed in a condenser & sent to a
distillation unit for further separation.
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Distillation Unit: -
Distillation unit is also made up of glass & is also 6 m tall. Packing used is rasching rings
and temperature is maintained 80oC.
The liquid mixture obtained from condenser is allowed to be heated using steam. Cl2 gas
having least boiling point in the mixture evolves first & is recycled back to reactor 2.
Around 62 to 65oC Br2 starts to evolve which is sent to the condenser where its
temperature is reduced below boiling point. Liquid bromine obtained is then stored in
amber coloured bottles. Water obtained from the bottom of distillation column and is
recycled for further use.
Page 3
INSTRUMENTATION AND PROCESS CONTROL
In any chemical industry quality has become the most important specification. This can be
achieved by proper instrumentation “Precise process control is a reward to Production”.
The measurement of the level of various energies and the control of the energy, which can
take place, is called instrumentation.
Instrumentation and process control are necessary in a plant for the following reasons:
1. Quality Control
2. Recording of certain variables (Viz. Temperature, Pressure, Viscosity, and pH) for
future analysis
3. To eliminate human errors while operating or running a plant
4. Safety of plant and efficient control
5. For controlling pollution free better control of plant emissions to meet more
stringent regulations
Since, in a chemical plant, the reactions are taking place in the reactor or column which
cannot be analyzed from outside and hence we have to rely on the reading indicated by
instruments and hence their reliability is to be accurately examined.
But only instrumentation cannot serve our purpose because instruments only indicated the
values of various parameters like pressure, temperature, level etc. And also, mere
indication is of no use. Sometimes there may be deflections in parameters and we have to
control it. So some systems are provided with these instruments and are termed as
“Process Control”.
In instrumentation and process control temperature, pressure, flow and level are the four
main variables, which are to be controlled for plant safety and from economic point of
view.
A well planned instrumentation and process control scheme leads to the following
advantages.
1. Saving of labour.
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2. Saving of service consumption.
3. Controlled speed of operation.
4. Accuracy
5. Continuous recording of process variables.
Instrumentation and process control does not mean automatic control of parameters.
Instrumentation also makes the use of local indicator. Local temperature and pressure
indicators are used to control the temperature and pressure indicators are used to control
the temperature and pressure manually in the emergency e.g. when there is power failure
at such time automatic controllers cannot work. Local indicators are installed with
equipments such as reactors, distillation columns, pumps, reboilers, heat exchangers etc.
Valves are installed at inlet and outlet with all the units of POCl 3 plant to control the inlet
outlet flow rates of the process and utility lines.
INSTRUMENTATION FOR SPECIFIC EQUIPMENTS:-
Distillation Column: -
Distillation column should be provided with feed flow controllers by using flow-recording
controllers.
At the top of the distillation column a pressure relief valve is installed to release the excess
pressure and maintain the inside pressure.
Condenser & Preheater: -
Condenser and Preheater are installed as heat exchanging equipments. In both the units
utility inlet valves are controlled by process outlet temperature by means of a control loop.
Reboilers: -
At the bottom of the distillation column reboilers is placed. In reboilers steam flow is
controlled by process temperature level indicator controller is used with reboilers to
control the level of the process fluid in the reboilers.
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Pump: -
For transporting the process liquid positive suction centrifugal pump are used. Before a
pump a strainer is used to remove the solid particles or impurities. A nonreturnable valve
is also installed at the pump outlet.
Reactor: -
Flow:
Being a batch plant, the production capacity is fixed & hence the flow rate of raw material
plays an important role. Flow indicators & Controllers along with flow measuring devices
such as Rotameter have to be installed flow lines
Temperature:
The reaction taking place inside the reactor is endothermic and temperature is to be
maintained at 110˚C, which requires perfect process control to have higher conversion
hence for temperature measurement RTD or Thermocouple is satisfactorily used. The
temperature is sensed by the measuring unit & when it approaches 112˚C or 114˚C the
temperature is controlled to 110˚C. By altering the flow rate of chilled water flowing into
the internal coils which is a manipulated variable.
Level: -
Shaft & float type indicators are economically used as a level measuring devices
Page 6
MATERIAL BALANCE FOR REACTOR 1
Chemical reaction:-
2NaBr + H2SO4 → Na2SO4 + 2HBr
Required data:-
Chemicals Molecular weight
H2SO4 98
NaBr 103
HBr 81
Basis: 1000 kg solution of 10% NaBr and 10% organics.
i.e. 1000 kg of solution contains → 100 kg of NaBr, 100 kg of organics and 800 kg of
water.
100 kg NaBr → 971 mol of NaBr
From the stoichiometry of the reaction,
971 mol of NaBr → 485.5 mol of H2SO4
Amount of 98% H2SO4 required for 100 kg of NaBr
= (485.5 × 98)/.98
=48.55 kg
Similarly,
971 mol of NaBr → 485.5 mol of Na2SO4 and 971 mol of HBr
Amount of Na2SO4 formed = 485.5 × 142
= 68.94 kg.
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Amount of HBr formed = 971 × 81
=78.651kg.
From top we get 20% HBr solution.
Wt. of HBr solution = 78.651/.2
= 393.255 kg
Wt. of water in HBr solution = 393.255 – 78.651
= 314.6 kg
At bottom, we obtain
Wt. of organics + water = (Wt. of feed solution + Wt. of H2SO4 – Wt. of
HBr solution)
= (1000 kg + 48.55 kg – 393.255 kg )
= 655.295 kg
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MATERIAL BALANCE FOR REACTOR 2
Chemical reaction:
2HBr + Cl2 → 2HCl + Br2
Basis: - 1kmole of product POCl3
Compound Molecular Weight
Br2 80
HCl 36.5
HBr 81
Chlorine 35.5
From the stoichiometry of the reaction,
971 mol of HBr → 485.5 mol of Cl2
971 mol of HBr → 78.65 kg/hr of HBr
Amount of Cl2 required for 78.65 kg of HBr
= (485.5 × 71)
=34.47 kg
Similarly,
971 mol of HBr → 485.5 mol of Br2 and 971 mol of HCl
Amount of Br2 formed = 485.5 × 80
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= 38.84 kg.
Amount of HCl formed = 971 × 36.5
=35.44 kg/hr
At bottom, we obtain
Wt. of 12% HCl = 35.44/.12
= 295.33 kg/hr
Wt. of water in HCl solution = 295.33 – 35.44
= 259.9 kg/hr
For reaction, we provide
Cl2 flowrate = 50kg/hr
Steam flowrate = 16kg/hr
At top, we obtain
Wt. of Cl2 = 50 – 34.47
= 15.53 kg/hr
Wt of Br2 = 38.84
Wt. of steam = ( Wt.of water in HBr solution + steam feed – Wt. of
water in HCl solution)
= ( 314.6 + 16 - 259.9)
= 70.7 kg/hr
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MATERIAL BALANCE FOR DISTILLATION
Feed contains 38.84 kg of Br2 and 70.7 kg of water.
i.e. .41% of Br2 and 59% of water
At top,
Wt. of 98% Br = 38.84/.98
= 39.63 kg
Wt. of water = 39.63 – 38.84
= .8 kg
Wt of water at bottom= 70.7 - .8
= 69.9 kg
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ENERGY BALANCE FOR REACTOR 1
Reaction 1
2NaBr + H2SO4 → Na2SO4 + 2HBr
Chemicals Standard heat of reaction Heat Capacity
(KJ/mol) (cal mol-1K-1)
H2SO4 -814 25
NaBr -361 11.74 + .00233T
HBr -36.4 6.8 + .000084T
Na2SO4 -1387.1 32.8
Total heat of reaction at standard temperature
ΔHR 0 = ∑ΔHo PRODUCTS - ∑ΔHoREACTANTS
= [ 2(-36.4) + (-1387.1) ] - [ 2(-361) + (-184) ]
= 76.1 KJ/mol
= 18200 cal/mol
Total heat of reaction at operating temperature i.e. at 383 K
ΔHR383 = ΔHR 0 + ∫ ΔCp dt
= 18200 + ( 2.08T + .00298T2/2]383298
= 18200 - ( 176.8 + 86.248 )
= 17936.952 cal/mol of H2SO4
= 8708413 cal
Steam required is given by
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ΔHR383 = mass of steam * Latent heat of vaporisation
ΔHR383 = m * λ
8708413 = m 540
m = 16 kg/hr of steam
ENERGY BALANCE FOR REACTOR 2
Reaction 2
2HBr + Cl2 → 2HCl + Br2
Chemicals Standard heat of reaction Heat Capacity
(KJ/mol) (cal mol-1K-1)
HCl -72.31 6.7 + .00084T
Cl2 0 8.28 + .00056T
HBr -66.36 6.8 + .000084T
Br2 30.91 9
Total heat of reaction at standard temperature
ΔHR 0 = ∑ΔHo PRODUCTS - ∑ΔHoREACTANTS
= [ 2(-72.31) + (30.91) ] - [ 2(-66.36) + 0 ]
= 18.41 KJ/mol
= 4400 cal/mol
Total heat of reaction at operating temperature i.e. at 353 K
ΔHR353 = ΔHR 0 + ∫ ΔCp dt
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= 4400 + ( .54T + .000056T2/2]353298
= 18200 + ( 29.7 - 10 )
= 4419.7 cal/mol of Cl2
= 2145910 cal
Steam required is given by
ΔHR353 = mass of steam * Latent heat of vaporisation
ΔHR353 = m * λ
2145910 = m 540
m = 3.97 kg/hr of steam
ENERGY BALANCE FOR DISTILLATION TOWER
Balance on Bromine, bromine loss at bottom is neglected.
38.84 = D .98
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ENERGY BALANCE for POCl3
HR (333K) = - 279.5kJ/mole
Total heat of reaction at (333K) Reaction temperature
=No. of moles of POCl3 × (279.5) kJ/mole
No. of moles of POCl3 = (6281.54kg/ batch)/157.5
= 39.883 × 103 gm mole
HR (333K) = 39.883 × 103 × (279.5) kJ/mole
= -11.147 × 103 kJ/mole
HR (333K) = Q = Heat evolved = Heat absorbed
During reaction by cold water
Q = mW CpW T
Where mw = Mass flow rate of chilled water
Cpw = Specific heat of water
T = (Inlet temperature – Outlet temperature)
-11,147.17 × 103 = mw × 4.182 × (25-35)
mw = 266.551 × 18 kg/batch
mw = 4797.92 kg/batch
Mass flow rate of water required = 599.74 kg/ hr
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PROJECT COST ESTIMATION
The cost of the individual equipment is calculated on the basis of the Weight of the
equipment and the material of construction required for the particular equipment. The cost
is rounded up to the higher Value depending upon the complexity of the equipment.
The basic purchase of equipment used in the plant is calculated.
Equipment Cost Rs. Lakhs
Demister Tank 4.0
POCl3 Reactor with Jacket and 2.0
Agitators
Condenser 8.0
Distillation Tower 5.0
Disaster Vessel 1.0
Noah Scrubber 0.8
Packed Tower along with Packing 1.2
Silica Gel Column 2.0
Storage of PCl3 & POCl3 2.0
Liquid O2 storage 8.0
Pump (4) 3.2
A= 35.20
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INSTALLATION
Piping 8,80,000
Insulation 70,000ll
Utilities 7,04,000
Electrical 5,28,000
Instruments 3,52,000
Effluent treatment plant 5,28,000
B= 3,06,24,000
MAN POWER EMPLOYED
Manager 3,25,000
Plant Superintendent 1,95,000
Engineer × 2 3,90,000
Skilled workers × 10 3,90,000
Office staff × 8 2,60,000
Transportation × 4 6,24,000
C= 2,18,40,000
Total Cost = A + B + C = Rs.5,39,84,000
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