WO2020194140A1

WO2020194140A1 - A process for preparing chlorinated polyvinyl chloride (cpvc)

Info

Publication number: WO2020194140A1
Application number: PCT/IB2020/052512
Authority: WO
Inventors: Pradip Munshi; Ninad Deepak INGLE; Santosh AGRWAL; Uttam MAITY; Raksh Vir Jasra; Sunil PETER
Original assignee: Reliance Industries Ltd.
Priority date: 2019-03-25
Filing date: 2020-03-19
Publication date: 2020-10-01

Abstract

The present disclosure relates to a process for preparing chlorinated polyvinyl chloride (CPVC) from polyvinyl chloride (PVC). The process comprises mixing PVC with water to obtain an aqueous slurry of PVC which is introduced into a reactor. The slurry is agitated and an inert gas is simultaneously purged through the slurry to de-oxygenate the slurry to form de-oxygenated slurry which is warmed to a temperature in the range of 40 °C to 49 °C. Chlorine gas is introduced into the slurry. The slurry is warmed to a temperature in the range of 50 °C to 70 °C, followed by irradiation with visible light radiations, to obtain a product mixture. The product mixture is filtered to obtain solid residue of CPVC which is treated with alkali and hypochlorite. The process of the present disclosure is simple, economical and avoids use of additives.

Description

A PROCESS FOR PREPARING CHLORINATED POLYVINYL CHLORIDE (CPVC)

FIELD

The present disclosure relates to a process for preparing chlorinated polyvinyl chloride (CPVC).

DEFINITIONS

As used in the present disclosure, the following term is generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.

TSC as used herein refers to Thermally stimulated conductivity (TSC) which is the conductivity measured (in seconds) as a result of transport of charged carriers, ions electrons or holes that are thermally released by decomposition, from trapping states to a medium, solution, or excitation states.

BACKGROUND

The background information herein below relates to the present disclosure but is not necessarily prior art.

Chlorinated polyvinyl chloride (CPVC) is a thermoplastic polymer produced by the chlorination of polyvinyl chloride (PVC). CPVC is fire resistant, chemical corrosion resistant material and is used in plumbing, fitting, injection molding and sheet extrusion.

Conventionally, chlorination of PVC is carried out by photochlorination using ultra-violet radiations and/or at higher temperature. However, CPVC obtained by chlorination under these conditions has undesired properties, such as low inherent viscosity (IV), reduced thermal stability, reduced mechanical strength, and yellowish tint.

Undesired properties of CPVC can be attributed to inefficient and uneven chlorination of PVC, which occurs due to inadequate diffusion of chlorine gas in the pores of PVC. The inadequate diffusion of chlorine gas is a major concern in the case of PVC having a lower particle size and having a large amount of fines, wherein the diffusion of chlorine gas is even more difficult. Therefore, there is felt a need, to provide an efficient process for chlorination of PVC.

OBJECTS

Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.

It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.

An object of the present disclosure is to provide an efficient process for manufacturing CPVC polymer.

Another object of the present disclosure is to provide an efficient process for manufacturing CPVC polymer with high thermal stability.

Still another object of the present disclosure is to provide an efficient process for manufacturing CPVC that gives uniform chlorination.

Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY

The present disclosure provides a process for preparing chlorinated polyvinyl chloride (CPVC) by chlorination of polyvinyl chloride (PVC).

In the process of the present disclosure, PVC is mixed with water to obtain an aqueous slurry of PVC having concentration in the range of 5 wt.% to 15 wt.%. The aqueous slurry is introduced into a reactor followed by agitating the slurry and simultaneously purging an inert gas through the slurry to de-oxygenate the slurry to form de-oxygenated slurry. The de- oxygenated slurry is warmed at a temperature rate in the range of 0.15 °C to 0.25 °C per minute to a temperature in the range of 40 °C to 49 °C to form warm slurry. Chlorine gas is introduced in the warm slurry at a pressure in the range of 0.5 Kg/cm to 2.0 Kg/cm to obtain a reaction mixture. The reaction mixture is warmed to a temperature in the range of 50 °C to 70 °C to form warm reaction mixture. The warm reaction mixture is irradiated with visible light radiations having wavelength in the range of 390 nm to 700 nm and intensity in the range of 2 Watt/Kg to 8 Watt/Kg of PVC, to obtain a product mixture. The temperature of the product mixture is lowered to a temperature in the range of 20 °C to 45 °C and the product mixture is filtered to obtain a solid residue of CPVC.

The process further comprises sequential steps of treatment of the solid residue of CPVC with alkali and hypochlorite solution to obtain CPVC having purity greater than 97 %.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

The present disclosure will now be described with the help of the accompanying drawing, in which:

Figure 1 illustrates Dynamic mechanical analysis (DMA) graph of CPVC obtained in experiment 8;

Figure 2 illustrates Dynamic mechanical analysis (DMA) graph of CPVC obtained in experiment 9;

Figure 3 illustrates Dynamic mechanical analysis (DMA) graph of CPVC obtained in experiment 10; and

Figure 4 illustrates Dynamic mechanical analysis (DMA) graph of CPVC obtained in comparative example 2.

DETAILED DESCRIPTION

Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.

Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details, are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.

The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising,"“including,” and“having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.

The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.

The conventional process to prepare chlorinated polyvinyl chloride (CPVC) involves photo chlorination using ultra-violet radiations wherein the process is usually conducted at higher temperatures. The use of high temperature is usually done to improve the rate of chlorination reaction. However, the raw material PVC has low heat capacity and is highly temperature sensitive. Hence, chlorination at high temperatures does not result in efficient chlorination as chlorine intake almost ceases before desired chlorination is achieved. This leads to PVC having low inherent viscosity (IV), reduced thermal stability, reduced mechanical strength, and yellowish tint. Therefore, adequate control of the reaction temperature is necessary to achieve desired level of chlorination of PVC.

The present disclosure envisages a process for preparing chlorinated polyvinyl chloride (CPVC) having desired inherent viscosity, mechanical properties and thermal properties.

In an aspect, the present disclosure provides a process for chlorinating PVC. The process is described in detail.

PVC and water are mixed to obtain an aqueous slurry of PVC having concentration in the range of 5 wt.% to 15 wt.%. In an embodiment, the concentration of PVC in the aqueous slurry is 10 wt.%.

The aqueous slurry is introduced into a reactor followed by agitating the slurry and simultaneously purging an inert gas through the slurry to de-oxygenate the slurry to form de- oxygenated slurry.

In accordance with one embodiment of the present disclosure, the aqueous PVC slurry is low molecular weight PVC or suspension grade PVC, which is characterized by (i) having degree of polymerization of the vinyl chloride monomer (VCM) of less than 900; (ii) inherent viscosity (IV) greater than 0.6 dL/g; (iii) having porosity in the range of 0.23 to 0.29 mL/g; and (iv) at least 60 weight% PVC resin particles are retained at 100 micron sieve.

In an embodiment, the step of agitating the slurry is done using a self-induction agitator. The self-induction agitator provides better diffusion of chlorine through the pores of PVC, thereby resulting in rapid and efficient chlorination of PVC.

The step of purging the inert gas through the slurry is carried out till the oxygen content of the slurry is in the range of 10 ppm to 250 ppm. In an embodiment, the step of purging the inert gas through the slurry is carried out till the oxygen content of the slurry is in the range of 200 ppm to 250 ppm. In an exemplary embodiment, the oxygen content of the slurry is 230 ppm by mass.

In an embodiment, the inert gas used for purging is nitrogen. The de-oxygenated slurry is warmed at a temperature rate in the range of 0.15 °C to 0.25 °C per minute, to a temperature in the range of 40 °C to 49 °C to form warm slurry. In an embodiment, the de-oxygenated slurry is warmed to a temperature of 45 °C and at a temperature rate of 0.2 °C per minute.

The step of deoxygenation is necessary for chlorination reaction as it enables to improve the quality of CPVC formed.

Chlorine gas is introduced in the warm slurry at a pressure in the range of 0.5 Kg/cm² to 2.0 Kg/cm to obtain a reaction mixture. In an embodiment, the pressure is 1.9 Kg/cm .

The pressure at which chlorine is introduced is optimum for efficient functioning of the self- induction agitator.

The reaction mixture is warmed to a temperature in the range of 50 °C to 70 °C to form warm reaction mixture. In an embodiment, the reaction mixture is warmed to 65 °C.

The PVC material has shorter chain length, low heat capacity and it is highly temperature sensitive. Therefore increasing temperature for better rate of chlorination rather leads to incomplete chlorination, because chlorine intake almost completely ceases before desired chlorination is achieved. The rise in temperature in two separate steps at a specific heating rate avoids degradation of the PVC polymer and allows greater diffusion of chlorine inside PVC pores. The chlorine diffusion step increases the glass transition temperature as well as raises the heat capacity of PVC, thereby allowing the rise in temperature in the next step.

The warm reaction mixture is irradiated with visible light radiations having wavelength in the range of 390 nm to 700 nm and intensity in the range of 2 Watt/Kg to 8 Watt/Kg of PVC, to obtain a product mixture. In an embodiment, the wavelength of the visible light radiations is 450 nm. In an embodiment, the intensity of the visible radiations is 4.2 W/Kg.

In an embodiment, the step of irradiating the reaction mixture is done by using a light emitting diode (LED).

The irradiation with visible light ensures that the chain termination is minimum and the drop is inherent viscosity is less. In accordance with the present disclosure, the step of irradiation leads to formation of CPVC having chlorine content in the range of 65% to 70%. In an embodiment, the chlorine content of CPVC is 67%.

The temperature of the product mixture is lowered to a temperature in the range of 20 °C to 45 °C and the product mixture is filtered to obtain a solid residue of CPVC. In an embodiment, the temperature of the product mixture is lowered to 40 °C.

The temperature of the product mixture is lowered at a temperature rate in the range of 0.15 °C to 0.25 °C per minute.

In an embodiment, the solid residue of CPVC is washed with water.

The process further comprises treating the solid residue of CPVC with an alkali, followed by washing with water to obtain alkali treated CPVC.

The alkali treatment is done to remove the HC1 formed during the process of preparation of CPVC.

Typically, the alkali is an aqueous solution of at least one compound selected from the group consisting of calcium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, sodium carbonate, sodium bicarbonate, calcium carbonate, magnesium carbonate and sodium acetate. In an embodiment, the alkali is an aqueous solution of calcium hydroxide.

The alkali treated CPVC is treated with an aqueous hypochlorite solution, followed by washing with water to obtain hypochlorite treated CPVC.

The treatment with hypochlorite enables to reduce the yellowness index of CPVC and thereby improve the aesthetic characteristics of CPVC.

In an embodiment, the aqueous hypochlorite solution is aqueous sodium hypochlorite solution.

The hypochlorite treated CPVC is dried at a temperature in the range of 40 °C to 55 °C under reduced pressure to obtain CPVC having purity greater than 97 %. In an embodiment, the purity of the so obtained CPVC is 98 %. In an embodiment, the hypochlorite treated CPVC is dried at 45 °C under reduced pressure.

The inherent viscosity (IV) of CPVC having purity greater than 97 % is in the range of 0.65 to 0.70 dL/g. The thermal stability (TSC) of the CPVC is in the range of 550 seconds to 700 seconds. The CPVC obtained is found to be uniformly chlorinated, with high stability and having white color.

Using the process of the present disclosure, the low molecular weight PVC or suspension grade PVC is chlorinated to obtain CPVC. The CPVC obtained has similar values for degree of polymerization and IV values as compared to the PVC, which indicates that there is no degradation of polymer during the chlorination process of the present disclosure. Thus, the suspension grade PVC can be chlorinated using the process of the present disclosure to obtain CPVC having high thermal stability and desired mechanical properties.

It is observed that the concentration of PVC and the intensity of visible light irradiations are important parameters for achieving the desired level of chlorination of PVC and obtaining CPVC with high thermal stability. Further, during the process of the present disclosure, temperature control is important. The change in temperature is carefully controlled during the steps of heating the de-oxygenated slurry, irradiating the reaction mixture, cooling the product mixture and drying CPVC.

The increase and decrease in temperature during the process is slow and gradual. Also, the temperature of each step in the process is not allowed to fluctuate. While increasing and decreasing temperature, the temperature is slowly changed at a rate in the range of 0.15 °C to 0.25 °C per minute. Further, during these steps the temperature is maintained in such a way that the fluctuation in temperature is less than 2 °C. As a result, the CPVC is obtained without degradation or yellowing.

The process of the present disclosure is carried out without the use of an additive such as swelling agent, dispersing agent, or a chemical initiator. Therefore, the process of the present disclosure is simple and economical.

The irradiations used in the process of the present disclosure have visible light wavelength, which are safe. Conventional processes use a spurger or reaction system under high pressure, which lead to non-uniform chlorination. In the process of the present disclosure, a self-induction agitator was used, which ensures better diffusion, uniform chlorine distribution through pores of PVC, thereby resulting in rapid and efficient chlorination of PVC.

The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.

The present disclosure is further described in light of the following laboratory scale experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. These laboratory scale experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.

Experimental Details

Experiment 1:

A slurry containing 85 Kg of PVC (grade K 57) in 765 liters of water, i.e. 10 wt% of PVC (having inherent viscosity as 0.71 dL/g and thermal stability derived from TSC as 450 sec), was introduced into a reactor equipped with an self induction agitator and LED lights. The slurry was agitated at 100 rpm with agitator tip speed of 2 m/s, while purging nitrogen through the slurry to obtain a de-oxygenated slurry having oxygen content of 230 ppm. The temperature of the de-oxygenated slurry was slowly raised to 45 °C at a rate of 0.2 °C per minute to obtain warm slurry.

Chlorine gas was introduced in the reactor till a chlorine pressure of 1.9 Kg/cm was attained in the reactor, to obtain a reaction mixture. Speed of rotation was increased to 200 rpm and the reaction mixture was irradiated using LED lights emitting visible light radiations having a wavelength of 450 nm and an intensity of 360 watt (4.2 W/Kg of PVC). The temperature of the reaction mixture was maintained at 65 °C. The LED lights were switched off to obtain a product mixture comprising CP VC with chlorine content of 67 %. The product mixture was slowly cooled to a temperature of 40 °C and filtered, wherein the residue was washed with water to obtain CPVC. The CPVC was neutralized using 0.0125 M calcium hydroxide, followed by washing with water to obtain neutralized CPVC. The neutralized CPVC was washed with aqueous 0.1 weight% sodium hypochlorite solution, 5 followed by washing with water to obtain a hypochlorite treated CPVC.

The hypochlorite treated CPVC was dried at 45 °C under reduced pressure to obtain CPVC having purity of 98 %.

The chlorine content was measured as per standard reference method IS15778:2007.

The results are summari ed in Table 1.

10 Experiment 2:

Experiment 2 was carried out following the procedure of experiment 1, except that the concentration of the PVC slurry was 8 wt.% instead of 10 wt.%. The results are summari ed in Table 1.

Experiment 3:

15 Experiment 3 was carried out following the procedure of experiment 1, except that the concentration of the PVC slurry was 12 wt.% instead of 10 wt.%. The results are summarized in Table 1.

Table 1: Effect of the PVC concentration

It is clear from Table 1 that the CPVC with higher thermal stability was obtained using PVC concentrations of 10 wt.% and 12 wt.% as compared to CPVC obtained using the PVC concentration of 8 wt.%.

Moreover the thermal stability values of the CPVC samples obtained from Experiments 1-3 5 are much higher in comparison to the starting PVC material. The values of the inherent viscosity also did not drop much in comparison to the starting PVC material, having IV value as 0.71 Kg/cm².

Experiment 4:

Experiment 4 was carried out following the procedure of experiment 1, except that the LED 0 intensity was 576 W (6.8 W/Kg) instead of 360 W (4.2 W/Kg). The results are summarized in

Table 2.

Experiment 5:

Experiment 5 was carried out following the procedure of experiment 1, except that the LED intensity was 576 W (6.8 W/Kg) instead of 360 W (4.2 W/Kg). Further, the temperature of 5 the de-oxygenated slurry was raised to 58 °C instead of 45 °C and the temperature of the reaction mixture was maintained at 70 °C. The results are summarized in Table 2.

Experiment 6:

Experiment 6 was carried out following the procedure of experiment 1, except that the LED wattage was 576 W (6.8 W/Kg) instead of 360 W (4.2 W/Kg). The PVC slurry concentration 0 was 15.3 weight% instead of 10 weight%. The temperature of the de-oxygenated slurry was raised to 56 °C instead of 45 °C. Further, the temperature of the reaction mixture was maintained at 65 °C. The results are summari ed in Table 2. Table 2: Chlorination of PVC using higher intensity of irradiations

It is evident upon comparing the data of experiment 1 (in Table 1) and experiment 4 (in table 2) that the thermal stability of CPVC increases with an increase in the intensity of the visible irradiations, for the same concentration (10 wt.%)

5 However, at higher reaction temperature the thermal stability of CPVC decreases (as observed from the experiments 5 and 6).

Experiment 7:

Experiment 7 was carried out following the procedure of experiment 1, except that the chlorine gas pressure was 0.5 Kg/cm 2 instead of 1.9 Kg/cm 2. The results are summarized in

10 Table 3.

Table 3: Effect of chlorine pressure

It is evident from Table 3 that the thermal stability of CPVC is higher with a lower chlorine pressure.

Experiment 8:

Experiment 8 was carried out following the procedure of experiment 1 , except that the step of 5 drying was carried out using hot nitrogen gas in such a way that the temperature of CPVC being dried does not exceed 45 °C. Dynamic mechanical analysis (DMA) graph of CPVC obtained in experiment 8 is shown in Figure 1. The TGA spectrum showed smooth transition of glass transition temperature (T_g) which indicates uniform material and uniform distribution of chlorine.

10 Experiment 9:

Experiment 9 was carried out following the procedure of experiment 1 , except that the step of drying was carried out using hot nitrogen gas in such a way that the temperature of CPVC being dried reaches up to 60 °C. Dynamic mechanical analysis (DMA) graph of CPVC obtained in experiment 9 is shown in Figure 2. The DMA graph showed uneven transition of 15 T_g which indicates non-uniform material.

Experiment 10:

Experiment 10 was carried out following the procedure of experiment 1, except that the temperature of the de-oxygenated slurry was raised to 65 °C instead of 45 °C. Further, the temperature of the reaction mixture was maintained at 65 °C. Dynamic mechanical analysis (DMA) graph of CPVC obtained in experiment 10 is shown in Figure 3. The DMA graph showed two glass transition temperatures, which indicates non-uniform material.

Comparative experiment 1:

Comparative experiment 1 was carried out using PVC having a higher degree of 5 polymerization. The PVC having an inherent viscosity (IV) of 0.90 was used for this experiment.

Comparative experiment 1 was carried out following the procedure of experiment 1, except that the temperature of the de-oxygenated slurry was raised to 65 °C instead of 45 °C. Further, the temperature of the reaction mixture was maintained at 70 °C. The results are 10 summarized in Table 4.

Table 4: Chlorination at 65 °C

Comparative experiment 2:

Comparative experiment 2 was carried out following the procedure of comparative experiment 1 , except that the step of drying was carried out using hot nitrogen gas in such a 15 way that the temperature of CPVC being dried does not exceed 45 °C. Dynamic mechanical analysis (DMA) graph of CP VC obtained in comparative experiment 2 is shown in Figure 4. The (DMA) graph showed a smooth transition at glass transition, which indicates uniform material.

The process of the present disclosure is carried out without the use of any additives. Moreover, the process provides CPVC with desired characteristics by controlling the reaction parameters. Therefore, the process of the present disclosure is simple and economical.

TECHNICAL ADVANCEMENTS

The process of the present disclosure described herein above has several technical advantages including but not limited to the realization of:

- an efficient process for chlorination of PVC;

- a process for chlorination of PVC without use of additives; and

- a safe process for chlorination of PVC.

Throughout this specification the word“comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

The use of the expression“at least” or“at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary. While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure 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 disclosure and not as a limitation.

Claims

CLAIM:

1. A process for preparing chlorinated polyvinyl chloride (CPVC) by chlorination of polyvinyl chloride (PVC), said process comprising the following steps:

a) mixing PVC with water to obtain an aqueous slurry of PVC having concentration in the range of 5 wt.% to 15 wt.%;

b) introducing said slurry into a reactor followed by agitating said slurry and simultaneously purging an inert gas through said slurry to de-oxygenate said slurry to form de-oxygenated slurry;

c) warming said de-oxygenated slurry, to a temperature in the range of 40 °C to 49 °C at a temperature rate in the range of 0.15 °C to 0.25 °C per minute, to form warm slurry;

d) introducing chlorine gas into said warm slurry at a pressure in the range of 0.5 Kg/cm to 2.0 Kg/cm to obtain a reaction mixture;

e) warming said reaction mixture to a temperature in the range of 50 °C to 70 °C to form warm reaction mixture;

f) irradiating said warm reaction mixture with visible light radiations having wavelength in the range of 390 nm to 700 nm and intensity in the range of 2 Watt/Kg to 8 Watt/Kg of PVC, to obtain a product mixture; and g) lowering the temperature of said product mixture to a temperature in the range of 20 °C to 45 °C, and filtering said product mixture to obtain a solid residue of CPVC.

2. The process as claimed in claim 1, wherein said process comprises the following steps:

i) treating said solid residue of CPVC with an alkali, followed by washing with water to obtain alkali treated CPVC;

ii) treating said alkali treated CPVC with aqueous hypochlorite solution, followed by washing with water to obtain hypochlorite treated CPVC; and iii) drying said hypochlorite treated CPVC under reduced pressure at a temperature in the range of 40 °C to 55 °C to obtain CPVC having purity greater than 97 %.

3. The process as claimed in claim 2, wherein the purity of the CPVC is 98%.

4. The process as claimed in claim 2, wherein said alkali is an aqueous solution of at least one compound selected from the group consisting of calcium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, sodium carbonate, sodium bicarbonate, calcium carbonate, magnesium carbonate and sodium acetate.

5. The process as claimed in claim 2, wherein said hypochlorite is aqueous sodium hypochlorite.

6. The process as claimed in claim 2, wherein the inherent viscosity (IV) of said CPVC is in the range of 0.65 dL/g to 0.70 dL/g.

7. The process as claimed in claim 2, wherein the thermal stability (TSC) of said CPVC is in the range of 550 seconds to 700 seconds.

8. The process as claimed in claim 1, wherein said step of agitating the slurry is done using a self-induction agitator.

9. The process as claimed in claim 1, wherein the step of purging said inert gas through said slurry is carried out till the oxygen content of the slurry is in the range of 10 ppm to 250 ppm.

10. The process as claimed in claim 1, wherein the step of purging said inert gas through said slurry is carried out till the oxygen content of the slurry is in the range of 200 ppm to 250 ppm.

11. The process as claimed in claim 1, wherein the step of purging said inert gas through said slurry is carried out till the oxygen content of the slurry is 230 ppm.

12. The process as claimed in claim 1, wherein said inert gas is nitrogen.

13. The process as claimed in claim 1, wherein the step of irradiation of said reaction mixture is done by using a light emitting diode (LED).

14. The process as claimed in claim 1, wherein said step of irradiation leads to formation of CPVC having chlorine content in the range of 65 % to 70 %.