FORM -2
THE PATENTS ACT, 1970
(39 of 1970) & THE PATENTS RULES, 2006
COMPLETE SPECIFICATION
(See Section 10; rule 13)
A METHOD FOR RECOVERING CHLOROPRENE FROM AN AQUEOUS EFFLUENT
PIDILITE INDUSTRIES LIMITED
an Indian Company
of Regent Chambers, Nariman Point,
Mumbai - 400021, Maharashtra, India.
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TQ BE PERFORMED.

Field of invention
The invention relates to a method for recovering chloroprene from an aqueous effluent. The invention also relates to a system for carrying out the process,
Background
Chloroprene is used in large quantities for the synthesis of polychloroprene, a synthetic rubber. Polychloroprene is manufactured by emulsion polymerization of chloroprene. The unreacted chloroprene left out after polymerization is usually recovered from the polymer product by steam distillation under reduced pressure. Chloroprene is obtained from the organic fraction of the distillate while the aqueous fraction is disposed off in an effluent, which is further treated in the effluent treatment plant. Significant quantity of chloroprene is lost into the aqueous effluent. Further, the chemical oxygen demand (COD) of the aqueous effluent is significantly increased due to the presence of chloroprene. This necessitates intensive treatment in the effluent treatment plant. From the perspective of recovering and reusing chloroprene and from the perspective of safe and efficient disposal of the effluent, it is desirable to recover chloroprene from the aqueous effluent.
Detailed description
Accordingly, the invention provides a method for recovering chloroprene from an
aqueous effluent.
In one embodiment, the invention provides a method for recovering chloroprene from an aqueous effluent, the method comprising contacting the affluent with steam in a vessel

maintained at a pressure of around 0.2 bar, the container being equipped with a plurality of vacuumised overhead condensers, connected in series, adapted to draw in vapors stripped out of the effluent, the vapors being allowed to condense in the condensers to form a liquid condensate, the condensate being conveyed to a separating vessel capable of separating organic and aqueous phases of the condensate.
In another embodiment, the invention provides a method for recovering chloroprene from an aqueous effluent, the method comprising contacting the effluent with steam in a vessel maintained at a pressure of around 0.2 bar, the container being equipped with a plurality of vacuumised overhead condensers, connected in series, adapted to draw in vapors stripped out of the effluent, the vapors being allowed to condense in the condensers to form a liquid condensate, the condensate being conveyed to a separating vessel capable of separating organic and aqueous phases of the condensate wherein the aqueous affluent comprise aqueous fraction of effluent liquid generated in the process for polymerization of chloroprene.
In another embodiment, the invention provides a method for recovering chloroprene from an aqueous effluent, the method comprising contacting the effluent with steam in a container maintained at a pressure of around 0.2 bar, the vessel being equipped with a plurality of vacuumised overhead condensers, connected in series, adapted to draw in vapors stripped out of the effluent, the vapors being allowed to condense in the condensers to form a liquid condensate, the condensate being conveyed to a separating

vessel capable of separating organic and aqueous phases of the condensate wherein the aqueous affluent further comprise the aqueous phase of the condensate.
In another embodiment, the invention provides a method for recovering chloroprene from an aqueous effluent, the method comprising contacting the effluent with steam in a container maintained at a pressure of around 0.2 bar, the vessel being equipped with a plurality of vacuumised overhead condensers, connected in series, adapted to draw in vapors stripped out of the effluent, the vapors being allowed to condense in the condensers to form a liquid condensate, the condensate being conveyed to a separating vessel capable of separating organic and aqueous phases of the condensate wherein chloroprene is recovered from the organic phase of the condensate.
In another embodiment, the invention provides a method for recovering chloroprene from an aqueous effluent, the method comprising contacting the effluent with steam in a vessel maintained at a pressure of around 0.2 bar, the vessel being equipped with a plurality of vacuumised overhead condensers, connected in series, adapted to draw in vapors stripped out of the effluent, the vapors being allowed to condense in the condensers to form a liquid condensate, the condensate being conveyed to a separating vessel capable of separating organic and aqueous phases of the condensate wherein the plurality of condensers comprise a first condenser provided with a circulation of cold water, a second condenser provided with a circulation of chilled water and a third condenser provided with a circulation of brine having a temperature of around -20°C.

In another embodiment, the invention provides a method for recovering chloroprene from an aqueous effluent, the method comprising contacting the effluent with steam in a vessel maintained at a pressure of around 0.2 bar, the vessel being equipped with a plurality of vacuumised overhead condensers, connected in series, adapted to draw in vapors stripped out of the effluent, the vapors being allowed to condense in the condensers to form a liquid condensate, the condensate being conveyed to a separating vessel capable of separating organic and aqueous phases of the condensate wherein the aqueous effluent in the container is agitated by an agitator operating at around 100-200 rpm.
In another embodiment, the invention provides a method for recovering chloroprene from an aqueous effluent, the method comprising contacting the effluent with steam in a vessel maintained at a pressure of around 0.2 bar, the vessel being equipped with a plurality of vacuumised overhead condensers, connected in series, adapted to draw in vapors stripped out of the effluent, the vapors being allowed to condense in the condensers to form a liquid condensate, the condensate being conveyed to a separating vessel capable of separating organic and aqueous phases of the condensate wherein the chloropene content in the aqueous phase is not greater than 5000 ppm.
In another embodiment, the invention provides a system for treatment of an aqueous effluent, the system comprising a first vessel adapted to convey the effluent to a second vessel equipped with a plurality of vacuumised overhead condensers, connected in series, adapted to draw in vapors stripped out of the effluent, the liquid effluent remaining after

stripping out the vapours being filtered, cooled and conveyed to a third vessel for further treatment thereof.
In another embodiment, the invention provides a system for treatment of an aqueous effluent, the system comprising a first vessel adapted to convey the effluent to a second vessel equipped with a plurality of vacuumised overhead condensers, connected in series, adapted to draw in vapors stripped out of the effluent, the liquid effluent remaining after stripping out the vapours being filtered, cooled and conveyed to a third vessel for further treatment thereof wherein the aqueous effluent comprise aqueous fraction of effluent liquid generated in the process for polymerization of chloroprene.
In another embodiment, the invention provides a system for treatment of an aqueous effluent, the system comprising a first vessel adapted to convey the effluent to a second vessel equipped with a plurality of vacuumised overhead condensers, connected in series, adapted to draw in vapors stripped out of the effluent, the liquid effluent remaining after stripping out the vapours being filtered, cooled and conveyed to a third vessel for further treatment thereof wherein the second container is provided with a short stop vessel maintained at a nitrogen pressure of around 3.2 bars.
The invention provides a method for recovering chloroprene from an aqueous effluent. The method of the invention is carried out in a vessel equipped with a plurality of overhead condensers. Advantageously, three overhead condensers are used. Typically, the vessel is a stripper tank working under vacuum. Usually, the vessel is operated with

50% fill and at a pressure of around 0.2 bars. The method of the invention involve contacting the aqueous effluent in the vessel with steam. The steam is usually bubbled from bottom into the aqueous effluent. The bubbling is carried out in such a way that the residence time for steam + water is around 30 minutes. The vessel used to carry out the method of the invention is also provided with an agitator having adjustable agitation speed. Advantageously, an agitation speed in the range of 100 to 200 rpm is selected for the agitator in the vessel. The aqueous effluent treated by the method of the invention is the aqueous fraction of effluent liquid generated in the process of polymerization of chioroprene. The aqueous effluent can also contain aqueous fraction of liquid condensates formed in the overhead condenser.
Chioroprene in generally recovered from the organic fraction of the effluent liquid. The aqueous and organic fractions of the effluent liquid as well as the aqueous and organic phases of the liquid condensate are usually separated using a separating vessel. A decanter vessel is the most commonly used separating vessel. The overhead condensers disposed over the container containing the aqueous effluent are usually cooled to different extents by different coolant liquids. Usually, the overhead condenser comprise a first condenser provided with a circulation of cold water, a second condenser provided with a circulation of chilled water and a third condenser provided with a circulation of brine having a temperature of around -20°C. The condensers are coupled to the vessel contacting the aqueous effluent on one side and is evacuated from the other side. This enables to draw in the vapours stripped out of the aqueous effluent in contact with steam. In the condensers, the vapours are condensed and a liquid condensate containing an

aqueous phase and an organic phase are formed. The aqueous phase and the organic phases of the liquid condensate are separated using a separating vessel and the aqueous phase is recycled into the aqueous effluent that is contacted with steam. This cycle of stripping, condensing, separating and recycling is continued till the aqueous phase of the condensate has a chloroprene content of not greater than 5000 ppm.
The method of the invention is carried out in a system comprising vessels, condensers, filters and separating vessels. The method of the invention and the system for carrying out the method of the invention are further illustrated with reference to the accompanying drawing.
DESCRIPTION OF DRAWING
Figure 1 illustrates recovery process of Chloroprene from aqueous effluent. In the system of the invention, the aqueous fraction of effluent liquid obtained from the polymerization reactor and the aqueous phase of liquid condensates obtained from the condensers(2,4,6) are mixed together in a feeding tank. Flow going to stripping vessel (8) is fluctuating. Fluctuation is due to the continuous variation of the rate of the effluent liquid being decanted out of the separating vessel (The decanter) (10). The decanter collects the continuous and discontinuous water streams from the Polymerization section. The feeding tank must accept this fluctuation keeping a high efficiency. The feeding tank (12) helps in reducing the fluctuations in flow due to continuous variation of rate of decanted aqueous liquid effluent/aqueous phase of the liquid condensate which flows into the feeding tank by gravity.

The aqueous phase from decanter (10) is conveyed by gravity in feeding tank (12). The function of this feeding tank is to guarantee storage for the stripping and to ensure a good NPSH (net positive suction head) to the loading stripper pump without a generation of perturbation in the stripper. The feeding tank (12) is stirred with agitator (light axial agitation, to avoid the chloroprene malaxation and formation of a two phase system). The vapor phase is balanced with recovered monomer collection tanks using the VENT line. In case of foam formation, antifoam will be injected. High level in feeding tank will open valve on antifoam line. A very high level in feeding tank will close valves on the incoming effluent lines from Decanter (10) and stripper overhead condensers (22) and simultaneously opening of the valve on bypass line in order to divert water discharged from Decanter and stripper overhead condensers (22) to Effluent Treatment Plant (24). A short stop liquid addition with local flow control Rota meter will be available on feeding tank (12).
A vertical barrel mounted pump A (14) is connected to the bottom of feeding tank (12) to receive the liquid thereof and pump it toward the stripper tank (8). Pump A is supplied with its barrel to be installed in a sink hole. The level into the barrel will be controlled, in case of low level in the barrel; an alarm will stop the pump. Pump B will be the common spare for Pump A and Pump C, while Pump C (16) will be used to pump the stripped water to the heat exchanger before effluent discharge (Effluent cooler) (20).

The flow going to stripper tank is controlled by level control loop. Level control valve on pump A outlet has two different functions: it will control the level in feeding tank but also will be included into the automatic shutoff sequence in case of very high level in stripper tank. To protect the pump, a recirculation of 1 to 2 m3h on feeding tank must be assured. This wift be achieved using the Restriction Orifice on the feeding tank return line. For this application, a vortex pump has to be used because the presence of polymer is not excluded.
The stripper tank (8) is working under Vacuum. Operating pressure for shipper tank is 0.2 Bara. Content of stripper tank is bubbled with live steam from bottom. Agitator is provided to the vessel for proper mixing. The stripper tank will operate with 50% fill and 30 min. of resident time for Steam + water, Chloroprene mixture flow. Agitation speed will be adjustable in order to modify the operating conditions in the tank (flow rate and shear). A wide range of speed (100- 200 rpm) to be available at 50 Hz. A Gaseous short stop addition will be available on tank stripper tank. A double rupture disk system is provided for both vessels feeding tank and stripper tank; the discharge line will be connected to the vapor blow down tank.
The stripper tank (8) is provided with a pump C (16) to receive the stripped liguid phase there of and pump them to the effluent cooler before effluent discharge through basket type filters A & B (18). Filter A & B are provided for removal of any unwanted solid particles before going to Effluent cooler . The flow going to the effluent cooler is controlled by the valve of stripper tank. In effluent cooler, stripped liquid effluent will be cooled to temperature of 35°C and sent back to Effluent Treatment Plant for further

treatment. The cooling fluid flow rate will be controlled by temperature control loop in case of breaking vacuum, a security valve at outlet of Effluent cooler (Process side) will close. The vapor phase corning out of stripper tank (8) will be passing through the mist eliminator (26) to eliminate any foam or liquid carry over to condensers. However flow rate and composition of this vapor phase should not be constant at all. They will depend on stripping parameters. The size of the each overhead condenser (3 condensers in series, condenser (2) working with cooling water, condenser (4) working with Chilled water and condenser (6) working with -20 Deg C Brine) is to be design larger enough to condense full water vapor load at outlet of third condenser C. Temperature control loop on utility side of these condensers will control the process outlet temperature at each condenser outlet. Care to be taken not to use direct brine at (-20°C) on third condenser to avoid icing. Circulation pump to be provided with temperature Control loop valve at outlet and inlet (-2o°Q brine on pump suction. Vacuum pump package unit with frequency and flow control is used to develop vacuum at striper tank. Non-condensable outlet from condenser c is passed through vacuum Pump (28). Dedicated short Stop vessel is provided for aqueous effluent stripper unit to avoid any polymerization reaction inside the system. Short Stop vessel is pressurized with 3.2 bar Nitrogen. Short stop will be transferred to feeding tank with nitrogen pressure.
Technical advantages
The process and system of the invention ena6/es recovery and reuse of cn/oroprene in the aqueous effluent generated during the polymerization of chloroprene. Chloroprene is a valuable chemical and, therefore, its recovery enables savings in cost. The system of the invention allows recycling of the aqueous phases of the liquid condensate generated from

the vapours stripped out of the aqueous effluent by steam. By reducing the chloroprene load in the effluent that is finally disposed off, for effluent treatment, the process and system of the invention reduces the burden of effluent treatment and on the environment. Thus the effluent discharge contains less than 50ppm chloroprene.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the invention. These and other changes in the preferred embodiment of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim:
1. A method for recovering chloroprene from an aqueous effluent, the method comprising contacting the effluent with steam in a vessel maintained at a pressure of around 0.2 bar, the container being equipped with a plurality of vacuumised overhead condensers, connected in series, adapted to draw in vapors stripped out of the effluent, the vapors being allowed to condense in the condensers to form a liquid condensate, the condensate being conveyed to a separating vessel capable of separating organic and aqueous phases of the condensate.
2. The method as claimed in claim 1 wherein the aqueous affluent comprise aqueous fraction of effluent liquid generated in the process for polymerization of chloroprene.
3 The method as claimed in claim 1 or 2 wherein the aqueous affluent further comprise the aqueous phase of the condensate.
4. The method as claimed in anyone of the claims 1 to 3 wherein chloroprene is recovered from the organic phase of the condensate.
5. The method as claimed in any one of the preceding claims, wherein the plurality of condensers comprise a first condenser provided with a circulation of cold water, a second condenser provided with a circulation of chilled water and a third condenser provided with a circulation of brine having a temperature of around -20°C.
6. The method as claimed in any one of the preceding claims, wherein the
aqueous effluent in the container is agitated by an agitator operating at around 100-200 rpm.

7. The method as claimed in any one of the preceding claims, wherein the chloropene content in the aqueous phase is not greater than 5000 ppm.
8. A system for treatment of an aqueous effluent, the system comprising a first vessel adapted to convey the effluent to a second vessel equipped with a plurality of vacuumised overhead condensers, connected in series, adapted to draw in vapors stripped out of the effluent, the liquid effluent remaining after stripping out the vapours being filtered, cooled and conveyed to a third container for further treatment thereof.
9. The system as claimed in claim 8 wherein the aqueous effluent comprise aqueous fraction of effluent liquid generated in the process for polymerization of chloroprene.
10. The system as claimed in claim 8 or 9 wherein the second vessel is provided with a
short stop vessel maintained at a nitrogen pressure of around 3.2 bars.