FORM 2
THE PATENTS ACT 70 ( ACT 39 of 70 )
COMPLETE SPECIFICATION (See Section 10)
AN IMPROVED PROCESS FOR RECOVERY OF SODIUM HYDROXIDE AND SODIUM CHLORIDE FROM EFFLUENTS
PIDIL1TE INDUSTRIES LIMITED, A COMPANY REGISTERED UNDER THE INDIAN
COMPANIES ACT 1956 HAVING ITS REGISTERED OFFICE LOCATED AT REGENT
CHAMBERS, NARIMAN POINT, MUMBAI-400021 MAHARASHTRA, INDIA.
The following specification describes the nature of the invention and the manner in which it is to be performed description

• Field of Invention
The invention relates to an improved process for the recovery of Sodium hydroxide and sodium chloride from effluents containing them. The present invention particularly relates to an improved process for the recovery of sodium hydroxide and sodium chloride from effluents, especially effluent coming out from chloroprene manufacturing process. The recovered sodium hydroxide can be recycled back to the chloroprene manufacture process and the recovered sodium chloride can be used as raw material for Caustic-Chlorine manufacture. Apart from recovering valuable components , the present invention facilitates solving the problem of disposing of the effluent from chloroprene manufacturing process thereby avoiding environmental problems
• Background of Invention
Chloroprene is manufactured from 3,4-dichlorobutene-1 by dehydrochlorination. Normally 48% Sodium hydroxide is used for dehydrochlorination. 48 % concentration is the maximum possible commercially available concentration of Sodium hydroxide. The reaction generates 1 mole of Sodium chloride for 1 mole of chloroprene. The effluent coming out of the process contains Sodium chloride in the range of up to 20 % and Sodium hydroxide in the range of 0 to 3%. Treatment of this effluent containing Sodium hydroxide and sodium chloride is complicated. Normally this effluent is diluted with other effluent from chloroprene manufacturing process having low TDS (Total dissolved solids) and treated in effluent treatment plant using Biological process wherein bacteria and other microorganisms used to remove contamination. Also discharge of the effluent containing high Sodium chloride content into the sea is not permitted because sodium chloride content in sea water is hardly 3-4%. The aqueous effluent of chloroprene manufacture contains Sodium chloride in the range of 15-20%. i.e. Sodium chloride content in aqueous effluent of chloroprene manufacture is much higher than sodium chloride content in sea water. There is loss of sodium hydroxide through this stream which is reactant in dehydrochlorination process of chloroprene manufacture.

• The Prior Art
There is very little specific information about prior art work is available for the treatment of aqueous effluent of Chloroprene manufacture. No prior art literature is available reference for the recovery and separation of Sodium hydroxide and sodium chloride as separate components. Very few literature references are available for recovery of Sodium hydroxide and Sodium chloride as a mixture.
US patent no. 4215078 describes electrolysis of aqueous effluent coming out of chlor /alkali cell during the manufacture of chloroprene These are recycled back to dehydrochlorination step of chloroprene manufacturing process. In the process dehydrochlorination is carried out with aqueous solution having concentration of chlor-alkali cell liquor. Typical cell liquor is an aqueous solution of about 6-12% sodium hydroxide and 10-18% of sodium chloride.
US patent no. 446495 describes the dehydrochlorination reaction in a chloroprene manufacturing process with n-butanol in anhydrous medium to generate chloroprene with solid sodium chloride . There is no generation of aqueous effluent in this process . Hence problems connected with the effluent does not arise
US patent no. 510897 describes treatment of dissolved organics in aqueous effluent coming out from the manufacturing process of chloroprene with ozone and chlorine. There is no information about recovery of sodium hydroxide form aqueous effluent in this patent.
US patent no. 5288472 describes treatment of aqueous effluent coming out from Diaphragm cell of the manufacturing process of chloroprene which contains sodium hydroxide and sodium chloride. The effluent is treated with carbon dioxide and ammonia to essentially convert the sodium hydroxide to sodium bicarbonate.
The process which is mentioned in US patent no. 4215078 gives large volumes of reaction mass associated with dehydrochlorination reaction due to 6 to 12 % Sodium hydroxide concentration. Also due to large volumes as mentioned in US patent no.

4215078, associated energy cost in distillation of organic matter from aqueous effluent is much more resulting in higher capital cost required for large volume equipments.
In the process there is also a loss of valuable Sodium hydroxide and sodium chloride in aqueous effluent. Sodium hydroxide and Sodium chloride are valuable components and hence they cannot afford to be lost. Therefore if a process is developed to recover Sodium hydroxide and Sodium chloride separately from the effluent, it would be beneficial as these valuable components can be used effectively for various purposes. So there is need of an improved process which will recover Sodium hydroxide and sodium chloride as separate components from the aqueous effluent coming out of the chloroprene manufacturing process.
Objectives of the present invention
Therefore the main objective of the present invention is to provide an improved process for the recovery of Sodium hydroxide and Sodium chloride separately from the aqueous effluent coming out of the chloroprene manufacturing process.
Another objective of the present invention is to provide an improved process for the recovery of Sodium hydroxide and Sodium chloride separately from the aqueous effluent coming out of the chloroprene manufacturing process which is simple & economical as the process requires very less energy
Still another objective of the present invention is to provide an improved process for the recovery of Sodium hydroxide and Sodium chloride from the aqueous effluent coming out of the chloroprene manufacturing process separately which solves environmental problems connecting with the effluent
The present invention has been developed by separating Sodium hydroxide and Sodium chloride as individual components from the aqueous effluent coming out of chloroprene manufacturing process using evaporation employing the fact that solubility of sodium chloride decreases with increase in the concentration of sodium hydroxide in water i.e. Sodium chloride concentration decreases with increase in concentration of sodium hydroxide and vice versa. When water in the aqueous effluent coming out of chloroprene manufacturing process is evaporated, Sodium chloride salt starts precipitating at saturation solubility of sodium chloride at that concentration of Sodium

hydroxide. Then Sodium chloride salt can be filtered and remaining filtrate solution is subjected to further evaporation and filtration till desired concentration of Sodium hydroxide is reached. Thus sodium chloride and sodium hydroxide solution are recovered separately.
The recovered Sodium hydroxide which has concentration of 48% and Sodium chloride content of 0.2-0.5% which is the saturation solubility of sodium chloride salt at this concentration of sodium hydroxide can be recycled back to dehydrochlorination process of chloroprene manufacture where . Sodium chloride acts as inert in dehydrochlorination process of chloroprene manufacture The recovered Sodium chloride salt can also be dried and used as raw material in Caustic-Chlorine manufacture plant. The evaporated and condensed water resulting from the process can be recycled back to chloroprene manufacturing process. This results in the complete recovery of sodium chloride, sodium hydroxide and water from the aqueous effluent stream coming out of the chloroprene manufacturing process. and if required , can be recycles to the chloroprene manufacturing process.
• Summary of Invention
Accordingly, the present invention provides an improved process for the recovery of
Sodium hydroxide and Sodium chloride as separate components from the aqueous
effluent coming out of chloroprene manufacturing process which comprises
(i) Evaporating the aqueous effluent of chloroprene manufacture by heating to a
temperature in the range of 105-115 Deg.C at atmospheric pressure for the period of 1-5
hours when Sodium chloride salt gets precipitated, the water condensed on evaporation
being collected
(ii) Filtering the precipitated Sodium chloride salt obtained in step (i) to get a first crop of
Sodium chloride
(iii) Evaporating the filtrate obtained in step (ii) by heating to a temperature in the range
of 95-102 Deg.C at a pressure of 450-700 mm Hg absolute for the period of 1-5 hours
when another quantity of Sodium chloride salt gets precipitated, the water condensed
on evaporation being collected
(iv) Filtering the precipitated Sodium chloride salt obtained in step (iii) to get a second
crop of Sodium chloride

(v) Evaporating the filtrate obtained in step (iv) by heating at a temperature in the range
of 80-90 Deg.C at a pressure in the range of 100-450 mm Hg absolute for the period of
1-5 hours when yet another quantity of Sodium chloride salt gets precipitated, the water
condensed on evaporation being collected
(vi) Filtering the precipitated Sodium chloride salt obtained in step (v) to get a third crop
of sodium chloride
vii) Mixing the sodium chloride obtained in steps ( ii), (iv) and (vi) to get the total
recovered sodium chloride
viii) Mixing the condensed water obtained in steps (i), (iii) and (v) to get the total
recovered water
ix) Filtrate solution obtained in step (vi) being Sodium hydroxide solution, and
if desired evaporating the filtrate obtained in step (vi) at a temperature in the range of
90-120 Deg. C at a temperature in the range of 100-600 mm Hg absolute for a period in
the range of 1-6 hours to get solid sodium hydroxide
In a preferred embodiment , the evaporation in step (i) ,may be done at a temperature in the range of 107-112 Deg.C at atmospheric pressure and for the period of 2-4 hours In another preferred embodiment , the evaporation in step (ii) may be done at a temperature in the range of 97-100 Deg.C at a pressure of 500-600 mm Hg absolute and for the period of 2-4 hours
In yet another embodiment the evaporation in step (iv) may be done at a temperature in the range of 85-90 Deg.C at a pressure of 100-200 mm Hg absolute and for the period of 2-4 hours
The feed solution used which is the effluent of chloroprene manufacturing process may have concentrations of sodium hydroxide preferably of 1-3% and that of sodium chloride 15-20% chloroprene manufacturing process. During the first evaporation the feed solution may be concentrated upto 18% Sodium hydroxide For the second evaporation of aqueous effluent of chloroprene manufacture, the filtrate solution obtained from the first evaporation is taken again to the feed tank and evaporation procedure is repeated in the above mentioned apparatus. In the second evaporation of filtrate solution may be concentrated upto 42% Sodium hydroxide . For the third evaporation of aqueous effluent of chloroprene manufacture, the filtrate solution obtained from second evaporation is taken again to the feed tank and evaporation

procedure is repeated in above mentioned apparatus. In the third evaporation of filtrate by heating with steam, Solution may be concentrated to 48% Filtered sodium chloride salt from each evaporation step is mixed together.
After the filtration of sodium chloride salt, the filtrate solution from third evaporation step the resultant product is sodium hydroxide solution preferably of 48% concentration.
The known evaporator used in the process of the present invention is shown in fig 1 of the drawing accompanying this specification The evaporation apparatus used for carrying out the process of the present invention comprises a feed tank FT(-01) being connected to a pump (P-01), the pump (P-01) being connected to vapor liquid separator (VLS-01), the condenser (SC-01) being provided at the top with an inlet and out let for passing cooling water to the condenser and taking out of the cooling water respectively, the condenser also being provided with a port for connecting to a vacuum pump , the condenser being provided with an outlet at its bottom to take out the condensate Vapor liquid separator (VLS -01) being connected to the condenser through its top for vapors , the Vapor liquid separator (VLS -01) being also connected to evaporator( E - 01) through the pump ( P-02), evaporator(E-O1) being also connected to a centrifuge ( CF-01 ) for collecting solids, the evaporator being a shell and tube design, the feed solution being passed through the tube of the evaporator and steam being passed through shell side of evaporator(E-O1), the evaporator ( E-01) also being connected to the Vapor liquid separator (VLS -01) at its top for vapor outlet, the evaporator (E-01) also being provided with an out let at its bottom for taking out the condensed steam (condensate).
• Detailed description of invention
The process of the present invention can be performed employing an apparatus described above
Feed tank FT-01 stores the effluent of chloroprene manufacturing process. The effluent from the feed tank FT-01 is passed on to the Vapor liquid separator VLS -01 through the pump P-01. From the Vapor liquid separator VLS -01 the effluent solution is pumped by pump P-02 to the evaporator E-01. Steam is applied at the shell side of evaporator E-01. The applied steam converts the water present in the effluent solution into vapor. The

evaporator temperature and pressure are maintained at particular temperature and pressure mentioned above The Vapor Liquid separator VLS 01 serves the purpose to separate the vapors and the liquid, and the vapors are condensed in the Condenser SC-01. Condenser SC-01 is supplied with cooling water at the top. The cooling water is taken out also from the top of the condenser. Vacuum is applied at the condenser. Concentrated solution after evaporation of water is taken to centrifuge CF-01 and precipitated sodium chloride salt is filtered in the Centrifuge CF-01. The solution coming out of the centrifuge CF-01 is the solution of Sodium hydroxide of desired concentration.
The above description defines the procedure for the first evaporation of aqueous effluent of chloroprene manufacture. For the second and third evaporations, above procedure is repeated in the same evaporator. The filtrate solution resulting from the first evaporation is taken again to the feed tank and the evaporation procedure described above is repeated . Thus all the three stages of evaporation are carried out in the same evaporator.
Recovery of Sodium hydroxide and Sodium chloride is verified by doing pilot trials in each stage of evaporation.
Multiple effect evaporation technology for recovery of Sodium hydroxide and Sodium chloride salt can be designed to optimize energy consumption. Evaporations carried out in a single vessel are called single effect evaporations, and evaporations carried out in multiple vessels in series is called multiple effect evaporation.
The boiling point of water decreases as pressure decreases. Due to this, pressure decreases with increase in number of effects. Thus, the First effect is at highest pressure and last effect is at lowest pressure. The water vapor boiled off in first effect can be used to heat the next effect, and only the first effect at the highest pressure requires an external source of heat. Quadruple effect {four effects) evaporator can be used to minimize the energy requirement.
In the first effect of evaporation, the feed solution which is aqueous effluent of chloroprene manufacture will be concentrated upto 9% Sodium hydroxide concentration Saturation solubility of sodium chloride salt at this concentration of Sodium hydroxide is 18%. Precipitated Sodium chloride salt is filtered. In the second effect of evaporation,

filtrate solution from first effect will be concentrated upto 15% Sodium hydroxide concentration by evaporating water vapor Saturation solubility of Sodium chloride salt is 13 % at this concentration of Sodium hydroxide. In the third effect of evaporation, filtrate solution from second will be concentrated upto 23% Sodium hydroxide concentration Saturation solubility of Sodium chloride salt is only 8% at this concentration of Sodium hydroxide. In the fourth effect of evaporation, filtrate solution from third effect will be concentrated to 48% Sodium Hydroxide concentration Precipitated Sodium chloride salt is filtered. The Filtrate solution will be 48% Sodium hydroxide solution
Vapors from previous effect of evaporation are used as heating medium for next effect of evaporation. Thus by using four effects of evaporation the energy required is only for first effect of evaporation. This gives minimum energy requirement as steam is required only for first effect. Total evaporated water to steam ratio which is called steam economy will be maximum which is 3.8
The details of the invention is given in the Example provided below which is given to illustrate the invention only and therefore should not be construed to limit the scope of the invention
Example 1 1000 Kg of aqueous effluent of chloroprene manufacture of 2.6% Sodium hydroxide and 17% Sodium chloride salt from the feed tank FT-01 is passed on to the Vapor liquid separator VLS -01 through the pump P-01. From the Vapor liquid separator VLS -01 the effluent solution is pumped by pump P-02 to the evaporator E-01. Steam is applied at the shell side of evaporator E-01. The applied steam converts the water present in the effluent solution into vapor. Evaporator Temperature was maintained at 107 Deg.C and pressure was at atmospheric. The Vapor Liquid separator VLS 01 serves the purpose to separate the vapors and the liquid, and the vapors are condensed in the Condenser SC-01. Condenser SC-01 is supplied with cooling water at the top. The cooling water is taken out also from the top of the condenser. Vacuum is applied at the condenser. Concentrated solution after evaporation of water is taken to centrifuge CF-01 and precipitated sodium chloride salt is filtered in the Centrifuge CF-01. The solution coming out of the centrifuge CF-01 is the solution of Sodium hydroxide of desired concentration. This is the first evaporation of aqueous effluent of chloroprene manufacture.

During the first evaporation of the effluent solution, water evaporated was 692 Kg by heating with steam for the period of 3 hours. Concentrated solution after evaporation of water was filtered. 162.3 Kg of Sodium chloride salt having moisture of 6% was obtained. Balance solution after filtration of sodium chloride was 145 Kg of 18% Sodium hydroxide concentration. Saturation solubility of Sodium chloride salt at this concentration of Sodium hydroxide was 12%.
The filtrate solution from first evaporation was taken again to the feed tank FT-01 and the evaporation procedure described above was repeated in above mentioned apparatus. This is the second evaporation of the aqueous effluent. During the second evaporation of the filtrate (feed) solution from first evaporation, total water evaporated was 65 Kg by heating with steam for the period of 2 hours. Temperature was 98 Deg.C and pressure was at 500 mm Hg absolute. Concentrated solution after evaporation of water was filtered. 17.4 Kg of Sodium chloride salt having moisture of 6% was obtained. Balance solution after filtration of sodium chloride was 62 Kg of 42% Sodium hydroxide concentration. Saturation solubility of Sodium chloride salt at this concentration of Sodium hydroxide was 1.7%.
The filtrate solution from the second evaporation was taken again to feed tank FT-01 and evaporation procedure was repeated in above mentioned apparatus. This is the third evaporation of aqueous effluent.
During the third evaporation of the filtrate solution from second evaporation, water evaporated was 7 Kg by heating with steam for the period of 2 hour. Temperature used was 88 Deg.C and pressure was at 150 mm Hg absolute. Concentrated solution after evaporation of water was filtered. 0.74 Kg of Sodium chloride salt having moisture of 6% was obtained. Balance solution after filtration of sodium chloride was 54 Kg of 48% Sodium hydroxide concentration. Saturation solubility of Sodium chloride salt at this concentration of Sodium hydroxide was 0.5%. Total filtered sodium chloride salt from all three evaporation steps was mixed and quantity was 180.4 Kg having moisture of 6% was obtained Total condensed water from all three steps was mixed and quantity was 764 Kg. 54 Kg of 48% Sodium hydroxide solution was obtained with sodium chloride content of 0.5%.

Advantages of the invention
1. The process is simple
2. The process requires very less energy.
3. The process solves the problem of disposing of the effluent coming out of chloroprene manufacturing process
4. The Process recovers the Sodium hydroxide and sodium chloride separately. The Sodium hydroxide if desired recovered can if desired be recycled back to dehydrochlorination process of chloroprene manufacture.
5. The Sodium chloride salt recovered can be if desired, used as raw material for Caustic-chlorine manufacture. The recovered water can be recycled back to chloroprene manufacturing process.

We claim
1. An improved process for the recovery of Sodium hydroxide and Sodium chloride as
separate components from the aqueous effluent coming out of chloroprene
manufacturing process which comprises
(i) Evaporating the aqueous effluent of chloroprene manufacture by heating to a
temperature in the range of 105-115 Deg.C at atmospheric pressure for the period of 1-5
hours when Sodium chloride salt gets precipitated, the water condensed on evaporation
being collected
(ii) Filtering the precipitated Sodium chloride salt obtained in step (i) to get a first crop of
Sodium chloride
(iii) Evaporating the filtrate obtained in step (ii) by heating to a temperature in the range
of 95-102 Deg.C at a pressure of 450-700 mm Hg absolute for the period of 1-5 hours
when another quantity of Sodium chloride salt gets precipitated, the water condensed
on evaporation being collected
(iv) Filtering the precipitated Sodium chloride salt obtained in step (iii) to get a second
crop of Sodium chloride
(v) Evaporating the filtrate obtained in step (iv) by heating at a temperature in the range
of 80-90 Deg.C at a pressure in the range of 100-450 mm Hg absolute for the period of
1-5 hours when yet another quantity of Sodium chloride salt gets precipitated, the water
condensed on evaporation being collected
(vi) Filtering the precipitated Sodium chloride salt obtained in step (v) to get a third crop
of sodium chloride
vii) Mixing the sodium chloride obtained in steps ( ii), (iv) and (vi) to get the total
recovered sodium chloride
viii) Mixing the condensed water obtained in steps (i), (iii) and (v) to get the total
recovered water
ix) Filtrate solution obtained in step (vi) being Sodium hydroxide solution, and
if desired evaporating the filtrate obtained in step (vi) at a temperature in the range of
90-120 Deg. C at a temperature in the range of 100-600 mm Hg absolute for a period in
the range of 1-6 hours to get solid sodium hydroxide
2. An improved process as claimed in claim 1 wherein the evaporation in step (i) is
done at a temperature in the range of 107-112 Deg.C at atmospheric pressure and for
the period of 2-4 hours

3. An improved process as claimed in claims 1 & 2 wherein the evaporation in step (ii) is done at a temperature in the range of 97-100 Deg.C at a pressure of 500-600 mm Hg absolute and for the period of 2-4 hours
4. An improved process as claimed in claimsl to 3 wherein the evaporation in step (iv) is done at a temperature in the range of 85-90 Deg.C at a pressure of 100-200 mm Hg absolute and for the period of 2-4 hours
5. An improved process as claimed in claims 1 to 4 wherein the feed solution used which is the effluent of chtoroprene manufacturing process has concentrations of sodium hydroxide preferably of 1-3% and that of sodium chloride 15-20%

6. An improved process as claimed in claimsl to 5 wherein the dduring the first evaporation the feed solution is concentrated upto 18% Sodium hydroxide
7. An improved process as claimed in claims 1 to 6 wherein the during the second evaporation , the filtrate solution is concentrated upto 42% Sodium hydroxide

8. An improved process as claimed in claimsl to 7 wherein the d uring the third evaporation the Solution is concentrated upto to 48%
9. An improved process for the recovery of Sodium hydroxide and Sodium chloride as separate components from the aqueous effluent coming out of chloroprene manufacturing process substantially as herein described with reference to the Example