CLIAMS:1. A process for chlorination of polyvinylchloride, said process comprising the following steps:
a. polymerizing vinyl chloride monomers in presence of an alcohol to obtain a reaction mixture;
b. separating unreacted vinyl chloride monomers from said reaction mixture to obtain a slurry comprising polyvinyl chloride;
c. chlorinating said slurry using chlorine gas and photo-irradiating to obtain chlorinated polyvinyl chloride.
2. The process of claim 1, wherein the reaction temperature for polymerization and chlorination is maintained at a temperature ranging from 60 to 80 °C.
3. The process of claim 1, wherein the photo-irradiation is carried out at a wavelength ranging from 254 to 530 nm, preferably at a wavelength ranging from 254 to 450 nm.
4. The process of claim 1, wherein the irradiation is carried out using a light source from the group comprising UV lamps, light emitting diodes and LASERs.
5. The process of claim 1, wherein the monomer conversion rate in the polymerization reaction is not less than 87%.
6. A chlorinated PVC having a chlorine content of 67 wt % prepared by the process as claimed in claim 1. ,TagSPECI:Field

The present disclosure relates to a process for chlorination of polyvinylchloride.

Background

Chlorinated polyvinyl chloride (CPVC) is a thermoplastic produced by chlorination of polyvinyl chloride (PVC) resin. CPVC can withstand a wider temperature range and contains more chlorine as compared to PVC. CPVC has an additional free radical chlorination process that adds chlorine to the material and increases its resiliency in terms of conveying hot materials like water. CPVC has a wide range of applications including pipes used for hot and cold water distribution in residential and industrial use, transportation of corrosive liquids, high tension cable protection pipe and the like.

Conventionally, PVC obtained by polymerization is filtered and dried; water is added to the dried PVC to make a slurry and the slurry is further used for carrying out chlorination reaction. However, the steps of filtration, washing drying and re-slurrying add up to overall the process time and running cost. The chlorination is carried out a temperature range of 50 to 70 °C or higher. CPVC tends to degrade at higher temperatures; additives and stabilizers are used to prevent the degradation of CPVC. Hence, PVC that has got less heat exposure would be preferable for preparing CPVC.

Therefore, there is felt a need for simple and economic process for preparation of CPVC directly from PVC.

Objects

Some of the objects of the present disclosure which at least one embodiment is adapted to provide, are described herein below:

It is an object of the present disclosure to provide a simple and economic process for preparation of chlorinated polyvinyl chloride.

It is another object of the present disclosure to provide a process for preparation of chlorinated polyvinyl chloride without using additional chemicals/reagents.

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

In accordance with the present disclosure there is provided a process for the preparation of chlorinated polyvinyl chloride, said process comprising the following steps: polymerizing vinyl chloride monomers in presence of an alcohol to obtain a reaction mixture; separating unreacted vinyl chloride monomers from said reaction mixture to obtain a slurry comprising PVC; chlorinating said slurry using chlorine gas and photo-irradiating at a wavelength ranging from 254 to 530 nm; to obtain chlorinated PVC. The polymerization and chlorination reaction is carried out at a temperature ranging from 60 to 80 °C

Detailed Description

In one aspect, the present disclosure provides a process for the preparation of chlorinated polyvinyl chloride.

In one embodiment of the present disclosure the process comprises the following steps:
• polymerizing vinyl chloride monomers in presence of an alcohol to obtain a reaction mixture;
• separating unreacted vinyl chloride monomers from said reaction mixture to obtain a slurry comprising PVC; and
• chlorinating said slurry using chlorine gas and photo-irradiating at a wavelength ranging from 254 to 530 nm; to obtain chlorinated PVC.
The process in accordance with the present disclosure is carried out in the absence of the following four steps:
• cooling and filtering of PVC after the polymerization reaction;
• drying of the PVC obtained by the polymerization reaction;
• cooling to room temp and re-slurrying of the PVC for the chlorination reaction; and
• reheating the reaction mixture for the chlorination reaction.
Omission of the above mentioned four steps results in reducing the running cost, manpower and time; by reducing the numbers of unit operations involved. PVC obtained by suspension polymerization need not be dried before it can be used for chlorination to form chlorinated polyvinyl chloride. Thus, it reduces the number of cycles; the polymer is exposed to heat treatment and the CPVC so prepared has a better thermal stability. Also, the total batch time from the polymerization of vinyl chloride monomers to the chlorination of PVC to obtain CPVC is reduced.
The Whiteness Index (WI) and the Yellowness Index (YI) are the two color parameters to judge CPVC product quality. Higher values of WI and lower values of YI indicate better product quality whereas lower values of WI and higher values of YI indicate poor quality of product. CPVC products with WI values higher than 84 and YI values not higher than 4.5 are compoundable.
The process of the present disclosure is described hereinafter. Vinyl chloride monomer is polymerized under suspension polymerization in presence of partially hydrolyzed polyvinyl alcohol (PVA) to obtain a reaction mixture. The polymerization is carried out at a temperature ranging from 60 to 80 °C. The vinyl chloride monomer conversion rate in the polymerization reaction in accordance with the present disclosure is not less than 87%. Unreacted vinyl chloride monomer is separated from the reaction mixture leaving behind a slurry comprising PVA and partially hydrolyzed polyvinyl alcohol. Chlorination is carried out using chlorine gas and photo irradiating at a range from 254 to 530 nm, preferably the irradiation is carried out in the range of 254 to 450 nm. During chlorination of PVC, the temperature is maintained at a temperature ranging from 60 to 80 °C, preferably at a temperature of 70 °C. The PVC used directly in the present disclosure has better adsorption as compared to the conventional PVC slurry prepared using dried PVC and water.
PVA acts as a dispersing agent allowing uniform chlorination and reduces floating of CPVC during the chlorination process. Also, agglomeration of CPVC is not observed during the chlorination process. As the polymerization and chlorination reactions are carried out at a temperature ranging from 60 to 80 °C, there is no need to cool the PVC formed after polymerization step. Since, chlorinated polymers are vulnerable to degradation at high temperature, PVC formed at low temperature is preferred for CPVC manufacturing. The process of chlorinating PVC in accordance with the present disclosure does not include the steps of separation of PVC from the polymerization reaction mixture, washing, drying, re-slurrying for chlorination and therefore, saves time and lowers the running cost of the operation.
The process for the preparation of CPVC in accordance with the present disclosure is carried out without using additional chemicals/reagents. Also, a swelling agent or higher porosity PVC is not required for better adsorption of chlorine.
The process in accordance with the present disclosure can be carried out without the steps involving the separation of PVC from polymerization reaction mixture, washing, drying, and re-slurrying for chlorination. Both the polymerization and chlorination reactions in accordance with the present disclosure can be carried out at the same temperature range of 60 to 80 °C.

The disclosure will now be described with reference to the following non-limiting example:

Example 1

The setup consisted of a 5 L glass reactor quipped with irradiation source into which an aqueous slurry of 18 wt % PVC was added. The slurry was agitated at 800 rpm to obtain a uniform slurry and simultaneously nitrogen gas was purged into the slurry to remove oxygen. The temperature of the slurry was maintained at 70 °C. After 30 minutes, nitrogen purge was stopped and chlorine was purged into the slurry maintaining the same reaction conditions. Irradiation source rated at 450 nm was switched on, when the slurry and head space was saturated by chlorine. Start of irradiation was considered as the reaction start time.

The reaction was monitored periodically by titrating proportional amount of mother liquor with 0.1 N NaOH. The reaction was stopped when a titer value corresponding to 67 wt % chlorination was obtained and the irradiation was switched off.

Nitrogen gas was purged for 1 hour to expel free chlorine from the slurry.

The above slurry was filtered and the filtrate comprising CPVC was washed till a neutral pH was obtained. The wet cake obtained after the washing was dried under reduced pressure at 55 °C for 2 hours. The dried powder was further neutralized using 0.0125 N Ca(OH)2 at a concentration of 10 ml/g of CPVC for 10 minutes. The slurry formed after the neutralization step was filtered and washed with water at a concentration of 25 ml/g of CPVC. The CPVC obtained was dried at 70 °C for 3 hours.

The CPVC obtained had a chlorine content of 67.35 wt %, Apparent Bulk Density of 0.57 g/mL, Whiteness Index of 85.54, Yellowness Index of 2.91, and Thermal stability by Conductivity of 468 sec.

Example 2

The process of example 1 was repeated, except that 630 g PVC powder and 4 L water was taken in 5 L reactor. Nitrogen purging was carried out for 45 minutes.
The CPVC obtained had a chlorine content of 67.45 wt %, Apparent Bulk Density of 0.5 g/mL, Whiteness Index of 86.16, Yellowness Index of 3.25, and Thermal stability by Conductivity of 324 sec.

Example 3

The process of example 2 was repeated, except that the wavelength used was 450 nm.
The CPVC obtained had a chlorine content of 67.44 wt %, Apparent Bulk Density of 0.56 g/mL, Whiteness Index of 86.33, Yellowness Index of 3.08, and Thermal stability by Conductivity of 504 sec.

Technical advances

- The present disclosure provides a simple and economic process for the preparation of CPVC at a temperature of 70 °C.
- The present disclosure also provides a process for the preparation of CPVC without using additional chemicals/reagents.
- The present disclosure provides a CPVC with better thermal stability.

The exemplary embodiments herein quantify the benefits arising out of this disclosure and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the 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 will 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.

Any discussion of documents, acts, materials, devices, articles and 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.

While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications 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 modifications in the nature of the disclosure or the preferred embodiments 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.