Claims:WE CLAIM:
1. A process for producing a chlorinated polymer, said process comprising the following steps:
a. mixing polymer granules with water under stirring in a reaction vessel equipped with a radiation source to obtain a suspension, wherein said polymer granules have porosity in the range of 0.01 mL/g to 0.22 mL/g and particle size in the range of 120 to 160 micron;
b. adding a chlorine based swelling agent to the suspension under slow stirring to form a slurry, wherein the weight ratio of said swelling agent to said suspension is in the range of 0.5:100 to 2:100;
c. heating the slurry at a temperature in the range of 40 to 80 °C;
d. introducing chlorine gas into the reaction vessel containing the heated slurry to obtain a reaction mixture, wherein the pressure of chlorine gas is in the range of 1.0 Kg/cm2 to 2.5 Kg/cm2;
e. irradiating the reaction mixture with radiation of wavelength in the range of 250 nm to 550 nm to obtain a product mixture comprising a chlorinated polymer; and
f. filtering the product mixture to obtain a residue, and
g. washing and drying the residue to obtain the chlorinated polymer.
2. The process as claimed in claim 1, wherein in step (a) stirring is carried out at a speed in the range of 700 rpm to 900 rpm, and in step (b) stirring is carried out at a speed in the range of 100 rpm to 300 rpm.
3. The process as claimed in claim 1, wherein said polymer is at least one selected from the group consisting of polyvinyl chloride, polybutadiene rubber, polypropylene, and polyethylene.
4. The process as claimed in claim 1, wherein the concentration of said polymer in said suspension is in the range of 15 wt% to 20 wt%.
5. The process as claimed in claim 1, wherein step (b) comprises purging inert gas into said suspension before addition of swelling agent.
6. The process as claimed in claim 1, wherein said swelling agent is chlorine based fluid medium selected from the group consisting of chloroform, and carbon tetrachloride.
7. The process as claimed in claim 1, wherein step (b) comprises stirring said slurry at a temperature in the range of 25 to 75 °C and for a time period in the range of 15 to 45 minutes.
8. The process as claimed in claim 1, wherein step (b) comprises stirring said slurry at a temperature in the range of 50 to 70 °C and for a time period in the range of 20 to 30 minutes.
9. The process as claimed in claim 1, wherein said inert gas is selected from nitrogen and argon.
10. The chlorinated polyvinyl chloride (CPVC) obtained by the process as claimed in claim 1 having:
• bulk density in the range of 0.5 to 0.6 g/ml;
• whiteness index in the range of 80 to 90;
• yellowness index in the range of 2.5 to 3.5; and
• thermal stability in the range of 500 to 650 sec.
, Description:FIELD
The present disclosure relates to a process for producing a chlorinated polymer.
DEFINITIONS
As used in the present disclosure, the following words and phrases are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used to indicate otherwise.
Swelling agent: A compound that is used in a fluid state for swelling a gel, network, or solid.
Chlorine based swelling agent: The swelling agent containing at least one chlorine atom in its molecule.
Porosity: It is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume.
Homolytic fission: It is chemical bond dissociation of a molecule by a process where each of the fragments retains one of the originally bonded electrons.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Chlorination is known to improve the properties of certain resinous polymers, notably polyvinyl chloride, polyethylene, polypropylene, and natural rubber. Chlorinated polymers are used as binders in paints, adhesives, and printing inks. Chlorinated polymers are usually prepared using gaseous chlorine or chlorinated hydrocarbons, such as carbon tetrachloride, trichloroethylene, chloroform, or tetrachloroethane.
Chlorination of polymer, particularly polyvinyl chloride (PVC) to generate chlorinated polyvinyl chloride (CPVC) is a mass transfer reaction that occurs by chlorination on the surface and inside the pores of PVC by introducing chlorine gas. After this reaction, the removal of chlorine gas from the pores of CPVC is necessary, as it might affect color and thermal stability of CPVC.
Swelling agents are used for the homogeneous chlorination of PVC. Conventionally, a large amount of swelling agent is used for chlorination. However, the chlorination of PVC using swelling agent is very slow reaction, and is therefore less economical. Further, the use of a significant amount of swelling agent is known to affect the rigidity of CPVC and therefore, CPVC must be freed from residual swelling agent. Moreover, in case of PVC having high porosity, there are chances of entrapping of higher amount of swelling agent in CPVC.
As it is well known in the art, preparation of high porosity PVC is associated with low monomer conversion, thereby making the process expensive. Due to the relatively high cost of PVC, it is essential that the cost of chlorination of PVC be minimized if the CPVC product is to be an affordable commodity.
Therefore, there is a need to provide an alternative process for the chlorination of polymers that can mitigate the drawbacks of the conventional processes.
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 a process for chlorination of a polymer.
Another object of the present disclosure is to provide a process for chlorination of a polymer that can be performed using a minimum amount of a swelling agent.
Yet another object of the present disclosure is to provide a process for chlorination of a polymer that can be performed using low porosity PVC.
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 relates to a process for producing chlorinated polymer. The process of the present disclosure involves following steps:
Initially, polymer granules are mixed with water under stirring in a reaction vessel equipped with a radiation source to obtain a suspension. The polymer granules have porosity in the range of 0.01 mL/g to 0.22 mL/g and particle size in the range of 120 to 160 micron. Chlorine based swelling agent is then added to the suspension under slow stirring to obtain slurry. The weight ratio of the swelling agent to the suspension is in the range of 0.5:100 to 2:100. The slurry is stirred for time period in the range of 15 minutes to 45 minutes and at a temperature in the range of 25 to 75 °C. The slurry is heated to attain a temperature in the range of 40 to 80 °C. Chlorine gas is introduced into the reaction vessel containing slurry to obtain a reaction mixture, wherein the pressure of chlorine gas is in the range of 1.0 Kg/cm2 to 2.5 Kg/cm2. The reaction mixture is irradiated with radiation of wavelength in the range of 250 nm to 550 nm to obtain a product mixture comprising a chlorinated polymer. The product mixture is filtered to obtain a residue, followed by washing and drying the residue to obtain the chlorinated polymer.
Typically, the chlorinated polyvinyl chloride obtained by the process of the present disclosure has bulk density in the range of 0.5 to 0.6 g/ml; whiteness index in the range of 80 to 90; yellowness index in the range of 2.5 to 3.5; and thermal stability in the range of 500 to 650 sec.
DETAILED DESCRIPTION
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.
Chlorination is known to improve the properties of certain resinous polymers, notably polyvinyl chloride, polyethylene, polypropylene, and natural rubber. The present disclosure relates to a process for producing a chlorinated polymer. In accordance with the present disclosure, there is provided a process for producing a chlorinated polymer. The process is carried out in the steps described herein below.
Initially, polymer granules are mixed with water under stirring at a speed in the range of 700 to 900 rpm in a reaction vessel equipped with a radiation source to obtain a suspension. The polymer granules have porosity in the range of 0.01.mL/g to 0.22 mL/g and size in the range of 120 to 160 micron.
After mixing the polymer granules with water, the reaction vessel containing the suspension is purged with the inert gas. Chlorine based swelling agent is then added to the purged suspension under slow stirring at a speed in the range of 100 to 300 rpm to obtain slurry. Typically, the slurry is stirred for time period in the range of 15 minutes to 45 minutes and at a temperature in the range of 25 to 75 °C.
The slurry is heated to attain a temperature in the range of 40 to 80 °C. The chlorine gas is introduced into the reaction vessel containing slurry, wherein the pressure of chlorine gas in the reaction vessel is in the range of 1.0 to 2.5 kg/cm2 to obtain a reaction mixture.
The reaction mixture is irradiated with radiation of wavelength in the range of 250 nm to 550 nm to obtain a product mixture comprising the chlorinated polymer. Further, the inert gas can be purged into the reaction vessel to remove the unreacted chlorine gas. The irradiation of the reaction mixture results in the formation of chlorine radicals, which reacts with the polymer to obtain the chlorinated polymer. The chlorinated polymer is isolated from the product mixture.
In accordance with the present disclosure, the polymer is at least one selected from the group consisting of polyvinyl chloride, polybutadiene rubber, polypropylene and polyethylene.
In accordance with the present disclosure, the optimum size of the polymer granules is in the range of 120 to 160 micron.
The process of the present disclosure is capable of chlorinating PVC with low porosity, such as 0.01.mL/g to 0.22 mL/g. The upstream process for obtaining high porosity PVC, typically greater than 0.22 mL/g is expensive. Preparation of high porosity PVC is associated with low monomer conversion, thereby making the process expensive. To obviate the problem, the inventors of the present disclosure developed a process for of chlorinating PVC having low porosity. Further, in case of PVC having high porosity, there are chances of entrapping of higher amount of swelling agent in CPVC. Thus, low porosity PVC becomes suitable for the formation of CPVC.
In accordance with the present disclosure, the swelling agent is at least one selected from chloroform and carbon tetrachloride. The swelling agent used in the process of the present disclosure can be directly recycled without any reduction in swelling efficiency thereof.
The swelling agent is added to the suspension in an amount in the range of 0.5 weight% to 2 weight% of the amount of the polymer. The weight ratio of the swelling agent to the suspension can be in the range of 0.5:100 to 2:100. The present disclosure uses optimum amounts of the swelling agent, which prevents phase separation in the water. In accordance with the present disclosure, the swelling agent is used within its solubility limit, therefore no phase separation is observed and the step of stripping can be avoided. Further, the swelling agent also reduces byproduct generation, thereby obviating the step of post reaction work up.
In accordance with the present disclosure, the swelling agent is stirred in a mixture of polymer and water for a pre-determined time period, to enable soaking. The step of soaking before the photo-chlorination reaction is carried out for a time period in the range of 20 to 40 min, preferably 30 min.
In accordance with the present disclosure, the soaking temperature is the temperature at which chloroform is allowed to penetrate the PVC solid particle before the reaction start, and the corresponding time is termed as soaking time or period.
Swelling agent when added in water can be homogeneously mixed with PVC. At higher temperature, the pore diameter of PVC particle increases, which leads to effective adsorption of the swelling agent or chloroform, which leads to efficient swelling of PVC. Chlorine diffuses very efficiently in the swollen PVC particles thereby facilitating the reaction to proceed faster. Once the reaction is faster, the chain degradation is less and thermal stability can be higher.
Conventionally, the aqueous chlorination of PVC having porosity less than 0.22 ml/g takes longer time of 7 hours to achieve 67% chlorination (by weight). To overcome this problem, 20% by weight of swelling agent (chloroform) can be added to water to reduce the time period. However, the addition of 20% by weight of chloroform in water leads to the generation of unwanted products, making the process uneconomic. In addition, use of the higher amount of swelling agent (chloroform) affects the structural rigidity of PVC thereby affecting the processibility. To overcome this problem, the amount of swelling agent used is in the range of 0.5 wt% to 2 wt%, which is quite low as compared to the amount of conventionally used swelling agent. The lower amount of the swelling agent also helps to avoid a step of stripping, which is used to remove the swelling agent after the process of chlorination.
Swelling agent is absorbed by the PVC particles, which eventually enhances the porosity of the PVC. The enhanced porosity facilitates the diffusion of the chlorine gas into the PVC, thereby leading to the higher rate of the chlorination reaction.
In accordance with the present disclosure, initiation of chlorination reaction is driven by homolytic fission of the Cl - Cl bond of the chlorine molecule by irradiating the reaction mixture comprising polymer, water and chlorine gas, which gives rise to chlorine radicals.
During chlorination, hydrogen of C-H in the polymer is replaced by chlorine. The aqueous chlorination of polyvinyl chloride (PVC) particles using chlorine gas is a three phase (Gas-Liquid-Solid) system.
Further, the radiation used in the process of the present disclosure is visible light. The high intensity radiation accelerates the rate of reaction to an extent, but it has disadvantages like high electrical power consumption, poor product quality in terms of color, intrinsic viscosity (IV) and thermal stability. The process of the present disclosure is performed using the visible part of light to ameliorate the problems associated with using high intensity radiations.
In accordance with the embodiments of the present disclosure, the inert gas purged in the reaction vessel while containing the suspension, and the inert gas purged in the reaction vessel for removing the unreacted chlorine gas can be same or different.
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 experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
Experimental Details
Experiment 1: Chlorination of PVC in accordance with the present disclosure
The experiment was carried out in a reaction vessel equipped with a radiation source. The reaction vessel was charged with polyvinyl chloride (PVC) granules (630 g) having porosity of 0.1 mL/g and particle size of 140 micron. To the reaction vessel was added water (4000 mL). PVC and water were mixed in the reaction vessel at a stirring speed of 800 rpm to obtain a suspension. The reaction vessel was purged with nitrogen gas.
Chloroform (swelling agent, 32 mL) was added to the suspension (Ratio of swelling agent to suspension 0.6: 100) in a drop wise manner at room temperature to obtain slurry. The so obtained slurry was stirred at room temperature at speed of 200 rpm for a time period of 15 minutes to enable soaking of the swelling agent into the polymer.
After 15 min, the temperature of the slurry was increased from room temperature to 70 °C and the stirring speed was further increased to 300 rpm, and the stirring speed of 300 rpm was maintained for a time period of 30 minutes.
Chlorine gas was introduced into the reaction vessel containing the slurry to obtain a reaction mixture, wherein the pressure of the chlorine gas is 1.5 Kg/cm2. Visible light source was switched on so as to emit a radiation of 410 nm in the reaction vessel. The initiation of irradiation was considered as the initiation time of the reaction. The progress of the reaction was monitored periodically by titrating proportional amount of mother liquor against 0.1 N NaOH. The reaction was stopped at the titer value corresponding to 67% chlorination (by weight) of PVC by switching off the visible light to obtain the chlorinated PVC (CPVC) was formed. Inert gas purging was continued for 1 hour to expel out chlorine from CPVC.
The content of the reaction vessel was filtered and the solid obtained after filtration was washed with water till pH showed litmus neutral. The solid was dried under reduced pressure at 55 °C for 2 hours. The dried solid was further neutralized by using 0.0125(N) Ca(OH)2 at 10mL/g of solid for 10 minutes. Filtration followed by washing (25mL/g CPVC dry basis) after neutralization gave chlorinated polyvinyl chloride (CPVC) which was dried at 70 °C for 3 hours.
% chlorine content (by weight) was determined by using the method as per reference: IS-15778-2007. The calculation was executed by using the following formula:
% Chlorine in CPVC = [102.9 – 46.2(A/B)]
where A = weight of PVC in grams, B = weight of CPVC obtained in grams.
The chlorine present in A grams CPVC was 0.567A grams. The result was obtained within ± 0.5 % accuracy.
The thermal stability of CPVC was measured by a conductivity meter using a PVC thermometer (Metrohm 895), as per DIN53381, ISO 182-3.
Chlorinated PVC obtained in experiment has apparent bulk density was 0.55 g/mL, whiteness index was 85.26, Yellowness Index was 3.15, and the thermal stability as measured by conductivity meter was 504 seconds.
Experiment 2: Chlorination of PVC in accordance with the present disclosure
The process of chlorination was carried out under similar conditions as that of experiment 1 except that the wavelength of the radiation source was 450 nm.
The Results are given in table 1 below.
Experiment 3: Chlorination of PVC in accordance with the present disclosure
The process of chlorination was carried out under similar conditions as that of experiment 1 except that soaking was done at 50 °C.
The Results are given in table 1 below.
Experiment 4: Chlorination of PVC in accordance with the present disclosure
The process of chlorination was carried out under similar conditions as that of experiment 1 except that soaking was done at 60 °C.
The Results are given in table 1 below.
Experiment 5: Chlorination of PVC in accordance with the present disclosure
The process of chlorination was carried out under similar conditions as that of experiment 1 except that the soaking was done at 50 °C but the polymerization reaction was done at 70 °C.
Experiment 6: Chlorination of PVC in accordance with the present disclosure
The process of chlorination was carried out under similar conditions as that of experiment 1 except that soaking and reaction both were done at 70 °C.
The Results are given in table 1 below.
Table 1: Chlorination of PVC in accordance with the present disclosure
Sr. No. Experiment Soaking temp.
(°C) Reaction temp.
(°C) Wavelength
(nm) Time
(hours) Chlorine Content
(%) Thermal Stability
(sec) Yellowness Index

1. Experiment 1 RT 70 410 5.5 67.4 504 3.15
2. Experiment 2 RT 70 450 5.4 67.34 540 2.9
3. Experiment 3 50 70 410 5.0 67.23 588 2.7
4. Experiment 4 60 70 410 4.75 67.3 600 2.5
5. Experiment 5 50 70 410 4.5 67.33 612 2.3
6. Experiment 6 70 70 410 4.25 67.43 640 2.0

From table 1, it is evident that the higher soaking temperature leads to the lower reaction time and the enhanced thermal stability of the chlorinated PVC obtained. At higher temperature pore size of PVC particle increases, which helps in effective absorption of the swelling agent, which further leads to efficient diffusion of chlorine gas in PVC in comparatively shorter period. The lower reaction time results in reduction in chain degradation and increased thermal stability.
Following the experimental procedure as disclosed in exp. 1 to 6, other polymers such as polybutadiene rubber, polypropylene, and polyethylene can also be chlorinated with similar results.
Similarly, instead of chloroform, carbon tetrachloride can be equally effectively used as swelling agent.
Further, argon can be used as inert gas although it is more expensive.

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for chlorination of polymer, which
• is carried out using less amount of swelling agent within its solubility limit; thereby obviating step of stripping to remove residual swelling agent in CPVC;
• incorporates chlorine based swelling agent, which enhances the porosity of the PVC; thereby leading to the higher rate of the chlorination reaction;
• is capable of chlorinating low porosity PVC; and
• is economical and efficient.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
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.