DESC:FIELD
The present disclosure relates to 1,2-Chlorinated polyvinylchloride and a process for its preparation.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Chlorinated polyvinylchloride (CPVC) has high temperature tolerance for which the chlorine content plays primary role. CPVC displays its best properties at 66 to 68 wt% chlorine content, (specifically 67 wt % chlorine content) and is found to be processable and produce best performance at an optimum chlorine content of 67 wt% (± 2).
PVC consists of alternate -CH2- and -CHCl- units. Thus, both 1,2- and 1,1- chlorinated isomers of PVC are obtained during free radical chlorination of PVC. Addition of a chlorine to -CH2- provides 1,2-chlorinated PVC and addition of a chlorine to -CHCl- provides 1,1-chlorinated PVC, as described in the scheme below.

1,2-chlorinated PVC provides a thermally stable polymer chain whereas 1,1-chlorinated product provides an unstable polymer chain due to presence of geminal chlorine, which is susceptible to dehydrochlorination and lead to formation of undesirable unsaturation in the CPVC polymer chain. The unsaturation in chlorinated polymer chain is the genesis of degradation or oxidation. It is also a cause of yellowing. So, the formation of double bond in chlorinated polyvinylchloride must be avoided.
1,2-chlorinaed PVC can be prepared by chlorination of PVC, which is achieved by conducting chlorination by using chlorine gas in an organic solvent, in water slurry or in dry state of PVC.
In solution chlorination of PVC, that is chlorination of PVC in organic solvent, all the -CH2- groups are fully exposed for chlorination. So, there is more probability of getting 1,2-chlorinated PVC for solution chlorination. But the solution chlorination has major disadvantage that the organic solvent gets chlorinated and generates hazardous chlorinated solvent effluent. Solution based process is thus obsolete.
On the other hand, in case of heterogeneous chlorination that occurs in PVC-water slurry or in fluidized dry PVC, the accessibility of -CH2- to chlorine is limited. In this case, the chlorination occurs mostly at the surface. So, the -CH2- components available inside the PVC particle are not chlorinated and the desired chlorination of 67 wt% is not achieved. This forcibly leads to -CHCl- chlorination and yields 1,1-chlorinated product.
Fluidized dry chlorination also has noticeable limitations as it can be carried out only at smaller scale because of huge volume of fluidization; causes uneven chlorination; and requires PVC with high porosity which again necessitates upstream PVC manufacturing modification. All these drawbacks make dry chlorination process uneconomic.
Further, inherent viscosity of a polymer dictates the property of high mechanical strength of article made from polymer resin. Higher the viscosity, longer the chain length and greater the strength of the polymer. However, a prolonged reaction time lowers the inherent viscosity of resin due to chain degradation. This is a perennial problem of heterogeneous chlorination, as it is much slower than solution chlorination and takes longer time. Chlorination of PVC having greater inherent viscosity is the general practice for solving this problem. But this requires upstream modification of PVC which is a costly alternative.
Chlorination of PVC in water, using dispersing agent, swelling agent or an accelerator, may provide 1, 2-chlorinated polyvinylchloride at a faster rate. However, the addition of these foreign chemicals is unwanted, and it not only contributes to increase in operational costs but these chemicals remain as contaminants within the product.
The UV light mediated photochlorination is hazardous and the UV lamp does not last for long and needs to be replaced after 4000 hours. This reduces plant efficiency. Moreover, the use of UV lamp is hazardous to the environment, which undoubtedly necessitates the irradiation source alternative of UV lamp in the process.
There is, therefore, felt a need for a process for the preparation of 1,2-chlorinated polyvinylchloride , which overcomes the above mentioned drawbacks.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
Another object of the present disclosure is to provide 1,2-chlorinated polyvinylchloride.
Still another object of the present disclosure is to provide a process for the preparation of 1,2-chlorinated polyvinylchloride.
Yet another object of the present disclosure is to provide a process for the preparation of chlorinated polyvinylchloride, with high selectivity for 1,2-chlorinated polyvinylchloride (Vicinal chlorinated polyvinylchloride) as compared to geminal chlorinated polyvinylchloride.
Yet another object of the present disclosure is to provide a process for the preparation of 1,2-chlorinated polyvinylchloride that is processable.
Yet another object of the present disclosure is to provide a process for the preparation of 1,2-chlorinated polyvinylchloride that reduces the content of unsaturated polymer.
Yet another object is to provide a process for uniform and alternate distribution of chlorine in the carbon chain backbone of the PVC polymer.
Yet another object of the present disclosure is to provide a process for the preparation of 1,2-chlorinated polyvinylchloride that does not use additives.
Yet another object of the present disclosure is to provide a process for the preparation of 1,2-chlorinated polyvinylchloride that is simple, efficient, economic and environment friendly.
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.
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 a schematic representation for proximity of -CH2- and -CHCl- protons towards chlorination by chlorine radical;
FIGURE 2 illustrates a graph representing a drop in inherent viscosity during chlorination, when the chlorination is conducted using chlorine at atmospheric pressure;
FIGURE 3 illustrates a graph representing the dynamic mechanical analysis (DMA) of 1,2-CPVC obtained by conducting chlorination reaction at 1.9 kg/cm2 chlorine pressure;
FIGURE 4 illustrates a graph representing the dynamic mechanical analysis (DMA) of 1,2-CPVC obtained by conducting chlorination reaction at 3.0 kg/cm2 chlorine pressure;
FIGURE 5 illustrates a graph representing the glass transition temperature of 1,2-CPVC obtained by conducting reaction at different chlorine pressures;
FIGURE 6 illustrates a spectrum representing 13C solid state CP MAS NMR of 1,2-CPVC obtained by conducting chlorination reaction at 1.9 kg/cm2 chlorine pressure;
FIGURE 7 illustrates a spectrum representing 13C solid state CP MAS NMR of 1,2-CPVC obtained by conducting chlorination reaction at 3.0 kg/cm2 chlorine pressure;
FIGURE 8 illustrates a graph representing selectivity (%) of -CHCl-, -CCl2- and -C=C- during chlorination at different chlorine pressures. Values are obtained from 13C solid state CP MAS NMR spectra; and
FIGURE 9 illustrates a graph representing the inherent viscosity of 1,2-CPVC obtained by conducting chlorination at different chlorine pressures.
SUMMARY
The present disclosure relates to a process for the preparation of 1,2-chlorinated polyvinylchloride (1,2-CPVC). The process comprises the step of preparing an aqueous slurry of polyvinylchloride (PVC) under nitrogen atmosphere followed by heating the aqueous slurry at a temperature in the range of 50 to 90 °C to obtain a heated slurry. A predetermined amount of chlorine gas is passed into the heated slurry at a pressure in the range of 2 to 3.5 kg/cm2 for a predetermined time period to obtain a chlorine saturated slurry. The chlorine saturated slurry is irradiated with LED as an irradiation source having a wavelength in the range of 400 nm to 500 nm to obtain a product mixture comprising 1,2-chlorinated polyvinylchloride (1,2-CPVC). 1,2-chlorinated polyvinylchloride (1,2-CPVC) is then separated from the product mixture. The so obtained CPVC has an amount in the range 90 to 95 wt% of 1,2-chlorinated polyvinylchloride along with 5 to 10 wt% of 1,1-chlorinated polyvinylchloride, a chlorine content in the range of 67 - 68% and has no unsaturation in the polymer chain of CPVC. The process of the present disclosure is devoid of any chemical agent selected from neutralizing agent, stabilizer and processing additives.
1,2-chlorinated polyvinyl chloride (1,2-CPVC) is characterized by having;
i. no unsaturation in the molecular chain of the CPVC;
ii. a chlorine content in the range of 67 to 68%;
iii. an inherent viscosity in the range of 0.825 to 0.850;
iv. a thermal stability in the range of 800 seconds to 1200 seconds; and
v. a glass transition temperature (Tg) in the range of 150 to 155 °C.
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.
In the conventional processes for the preparation of chlorinated polyvinylchloride (CPVC) by using solution based chlorination, the organic solvent gets chlorinated and generates hazardous chlorinated solvent effluent. In the heterogeneous chlorination, the -CH2- components available inside the PVC particles are not chlorinated and the desired chlorination of 67 wt% is not achieved. This forcibly leads to -CHCl- chlorination and yields 1,1-chlorinated product. The fluidized dry chlorination also has noticeable limitations as it can be carried out only at smaller scale because of huge volume of fluidization, thereby resulting in an uneven chlorination. Fluidized dry chlorination requires PVC with high porosity which again necessitates upstream PVC manufacturing modification.
Further, chlorination of PVC in water, using dispersing agent, swelling agent and/or an accelerator, provides 1,2-chlorinated polyvinylchloride at a faster rate. However, addition of these foreign chemicals is unwanted, because it not only contributes to increase in operational costs but these chemicals remain as contaminants within the product.
Still further, the UV light mediated photochlorination is hazardous and the UV lamp does not last for long and needs to be replaced after 4000 hours. This reduces plant efficiency. Moreover, the use of UV lamp is hazardous to the environment, which undoubtedly necessitates the irradiation source alternative of UV lamp in the process.
The present disclosure therefore, provides 1,2-chlorinated polyvinylchloride (CPVC) and a process for its preparation, to overcome the limitations mentioned hereinabove.
In an aspect, the present disclosure provides a process for the preparation of 1,2-chlorinated polyvinylchloride (1,2-CPVC). The process comprises the following steps:
a) preparing an aqueous slurry of polyvinylchloride (PVC) under nitrogen atmosphere;
b) heating the aqueous slurry at a temperature in the range of 50 °C to 90 °C to obtain a heated slurry;
c) passing a predetermined amount of chlorine gas into the heated slurry at a pressure in the range of 2 to 3.5 kg/cm2 for a predetermined time period to obtain a chlorine saturated slurry;
d) irradiating the chlorine saturated slurry, with a LED as a irradiation source having a wavelength in the range of 400 nm to 500 nm to obtain a product mixture comprising 1,2-chlorinated polyvinylchloride; and
e) separating 1,2-chlorinated polyvinylchloride (1,2-CPVC) from the product mixture.
The process is described in details as given below.
Firstly, an aqueous slurry of PVC is prepared under nitrogen atmosphere. In an embodiment, the aqueous slurry is prepared by mixing polyvinyl chloride (PVC) and water in a predetermined weight ratio at a predetermined temperature and at a predetermined agitation speed.
The predetermined weight ratio of the PVC to water is in the range of 1:80 to 1:8. In accordance with an exemplary embodiment, the weight ratio of the PVC to water is 0.15:1. In another exemplary embodiment, the weight ratio of the PVC to water is 0.18:1.
The predetermined agitation speed is impeller tip speed in the range of 1 to 6 m/s. In an exemplary embodiment, the predetermined agitation speed is impeller tip speed of 2 m/s. The predetermined temperature is in the range of 25 °C to 35 °C. In an exemplary embodiment, the predetermined temperature is 30 °C.
In accordance with an embodiment of the present disclosure, PVC has a porosity in the range of 0.21 to 0.25 ml/g. In an exemplary embodiment of the present disclosure, the porosity of PVC is 0.23 ml/g.
Porosity allows chlorine adsorption and enables 1,2-chlorination inside the pores. PVC having porosity below 0.21 ml/g leads to very low adsorption resulting into incomplete chlorination. PVC having porosity higher than 0.25ml/g may be better for 1,2- chlorination but PVC with this high porosity requires upstream modification in manufacturing process.
The aqueous slurry is agitated under the nitrogen atmosphere.
In the next step, the slurry is heated to a temperature in the range of 50 to 90 °C to obtain a heated slurry followed by passing nitrogen gas for a time period in the range of 20 minutes to 40 minutes.
In the next step, nitrogen is purged using chlorine and then, a predetermined amount of chlorine gas is passed through the heated slurry at a pressure in the range of 2.0 to 3.5 Kg/cm2 for a predetermined time period to obtain a chlorine saturated slurry.
In an embodiment of the present disclosure, the predetermined amount of chlorine is in the range of 66 to 68 wt%. In an exemplary embodiment of the present disclosure, the predetermined amount of chlorine is 67 wt%.
In an exemplary embodiment of the present disclosure, the chlorine pressure is maintained at 2.5 kg/cm2. In another exemplary embodiment of the present disclosure, the chlorine pressure is maintained at 3.0 kg/cm2.
The predetermined time period is in the range of 20 to 40 minutes. In an exemplary embodiment of the present disclosure, the predetermined time period is 30 minutes.
In an embodiment of the present disclosure, the chlorine gas is passed through the heated slurry at a chlorination rate in the range of 2 x 10-3 to 4 x 10-3 L/mol/min. In an exemplary embodiment of the present disclosure, the chlorination rate is 3 x 10-3 L/mol/min.
In accordance with an embodiment of the present disclosure, a weight ratio of the PVC to the chlorine gas is in the range of 1:3 to 1:1. In an exemplary embodiment, the weight ratio of the PVC to the chlorine gas is 1:2.
The chlorine saturated slurry is irradiated with LED as an irradiation source having a wavelength in the range of 400 nm to 500 nm to obtain a product mixture comprising 1,2-chlorinated polyvinylchloride .
In an embodiment of the present disclosure, the LED light source emitting visible wavelength of 450 nm used as an irradiating source is equally distributed around periphery of the reactor. The LED used in the process of the present disclosure, has a power output in the range of 1 watt/kg to 5 watt/kg of polyvinyl chloride.
The wavelength has significant role in conducting chlorination of PVC because inherent viscosity of PVC decreases during chlorination due to high energy UV wavelength. The visible wavelength of 450 nm is chosen so that it is just required to break the Cl-Cl bond and create chlorine radical and does not have deleterious effect on PVC chain.
Chlorination reaction occurs by interaction of photons and chlorine molecule to generate chlorine radical, which initiates the chlorination reaction of the PVC. To achieve chlorination inside the pores of the PVC, diffusion of chlorine as well as penetration of photons is imperative. As a matter of fact, during chlorination of PVC using chlorine at an atmospheric pressure, the reaction sluggishly reaches 67% chlorination or sometime even ceases due to pore closure caused by chlorination of PVC on the surface. Therefore, the chlorination at high pressure is desirable to keep enough Cl2 concentration available inside the pore. However, too high pressure results in liquefaction of chlorine, which is not preferred choice in the present invention, as it is highly hazardous and uneconomic. On the other hand, LED has higher penetrating ability inside the PVC pore. So, chloriation inside the pore is feasible, in combination of LED and the high pressure of chlorine gas. Figure 2 elucidates the drop in inherent viscosity during chlorination conducted at atmospheric chlorine pressure.
In an embodiment of the present disclosure, the temperature of reaction medium is controlled by absorbing the heat of reaction using water having temperature in the range of 10 to 15 ?C at a flow rate of 6000L/h for initial 30-45 minutes of chlorination reaction.
During chlorination reaction it is essential to control the temperature of reaction medium. Due to exothermicity of chlorination reaction, heat builds up in the reaction medium that raises reaction temperature which is detrimental to the resin properties, as it causes dehydrochlorination and change in PVC morphology. If the reaction temperature is not maintained, it would result into incomplete chlorination of the product with lower thermal stability and non processable CPVC. So, it is required to remove the heat of reaction by passing cooling water through reactor jacket, which was achieved by using water having temperature in the range of 10 to 15 ?C at a flow rate of 6000 L/h. It is observed that the CPVC prepared by chlorination of PVC at 3 Kg/cm2 shows absence of unsaturation in CPVC (Figure 7). However, when the CPVC is prepared by chlorination of PVC at 1.9 Kg/cm2, it shows the presence of unsaturation in CPVC (Figure 6).
In the present disclosure, the chlorine in the vessel is monitored by using an ammonia torch. Start of irradiation is considered as a reaction start time.
In an embodiment, the chlorination reaction is monitored periodically by titrating a proportional amount of mother liquor against 0.1N NaOH, and the reaction is stopped by switching off the irradiation, at a titer value corresponding to 67% chlorination (by weight) of PVC to obtain a product mixture comprising 1,2-CPVC.
If excess chlorine remains in the product mixture or in the vessel, it can be removed by passing nitrogen gas through the slurry for a time period in the range of 30 minutes to 90 minutes to obtain CPVC slurry that is free of chlorine.
The CPVC slurry is filtered and the CPVC cake is washed with water to remove any acidic impurities until the wash water displayed neutral pH, to obtain a wet CPVC cake.
The wet CPVC cake is dried at a temperature in the range of 50 to 90 °C for 3h to obtain 1,2-CPVC. The so obtained 1,2-CPVC has a chlorine content in the range of 67 to 68% and has no unsaturation in the molecular chain of the CPVC.
In another aspect, the present disclosure provides 1,2-chlorinated polyvinyl chloride (1,2-CPVC).
1,2-chlorinated polyvinyl chloride (1,2-CPVC) of the present disclosure is being characterized by having;
i. no unsaturation in the molecular chain of the CPVC;
ii. a chlorine content in the range of 67 to 68%;
iii. an inherent viscosity in the range of 0.825 to 0.850;
iv. a thermal stability in the range of 800 seconds to 1200 seconds; and
v. a glass transition temperature (Tg) in the range of 150 °C to 155 °C.
1,2-chlorinated polyvinyl chloride (1,2-CPVC) of the present disclosure exhibits good processability. 1,2-chlorinated polyvinyl chloride (1,2-CPVC) of the present disclosure does not contain any dispersant, swelling agent and any unsaturated CPVC.
In an embodiment of the present disclosure, 1,2-CPVC has a glass transition temperature (Tg) at 151 °C. In another embodiment of the present disclosure, 1,2-CPVC has a glass transition temperature (Tg) at 154 °C.
In an embodiment of the present disclosure, 1,2-CPVC has intrinsic viscosity of 0.828. In another embodiment of the present disclosure, 1,2-CPVC has intrinsic viscosity of 0.837.
The chlorinated polyvinyl chloride (CPVC) obtained by the process of the present disclosure has 90 to 95 wt% of 1,2-chlorinated polyvinylchloride and 5 to 10 wt% of 1,1-chlorinated polyvinylchloride. Thus, the process of the present disclosure has very high selectivity for 1,2-chlorinated polyvinylchloride (Vicinal chlorinated polyvinylchloride) with respect to 1,1-chlorinated polyvinylchloride (geminal chlorinated polyvinylchloride) and no unsaturation present therein.
The process of the present disclosure provides uniform chlorination of PVC particle with good processability of the material. In the process of the present disclosure, the rate of chlorination is high to obtain high productivity of the process and 1,2-CPVC so obtained is processable and delivers the properties of high viscosity and high thermal stability.
Furthermore, 1,2-Chlorinated polyvinylchloride (1,2-CPVC) has higher temperature tolerance than the mixed CPVC i.e. mixture of 1,2-CPVC and 1,1-CPVC which is the result of annonymous chlorination of PVC.
The process of the present disclosure uses no chemicals other than water, PVC, and chlorine, thereby eliminating the possibility of leaving behind any contaminants in 1,2-CPVC formed.
The process of the present disclosure is scalable for commercial preparation, discharges very less effluent and avoids use of UV irradiation.
The invention is demonstrated by Figure 5, which explains that higher glass transition temperature of same chlorine content of 1,2-CPVC (67 wt%) is achieved by conducting reaction at higher pressure. This is possible due to high reaction rate, high inherent viscosity (Figure 9) and very high selectivity for 1,2- CPVC.
The reaction at high pressure eventually helps to attain the desired rate of reaction and importantly the required viscosity of 1,2-CPVC resin by not allowing the chain degradation that happens during longer reaction times required as a result of slower rate of reaction. The photoirradiation source having a narrow spectral band width, for example LED, is used to penetrate inside the PVC pores and react with photons and chlorine present in the pore. Formation of unsaturation is prevented by facilitating greater -CH2- chlorination and reducing the chlorination of -CHCl-, which results in formation -CCl2- and leads to dehydrochlorination to form a polymer with a double bond (unsaturation). Water is used in chlorination reaction of PVC, as water is a less hazardous easily treatable effluent followed by solid state neutralization without using water making the process highly economic, with less space and equipment, better product quality and high productivity.
High viscosity is achieved by using visible irradiation of 450 nm and completing the reaction at shorter time by achieving high reaction rate.
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.
EXPERIMENTS:
Example 1. Process for the preparation of 1,2-CPVC at atmospheric pressure
Polyvinyl chloride (PVC) (630 g, K 67 PVC having porosity of 0.23 ml/g) and water (4 Kg) were mixed at 30 °C in a glass vessel to obtain an aqueous slurry. The slurry was agitated at impeller tip speed 2 m/s under nitrogen. The aqueous slurry was heated at 70°C to obtain a heated slurry. After 30 minutes nitrogen was purged by passing chlorine through the slurry for 30 minutes until the slurry was saturated with chlorine. The chlorine saturated slurry was irradiated with a visible light of wavelength 450 nm using a LED source, and the chlorine in the vessel was monitored using an ammonia torch. Start of irradiation was considered as reaction start time. To remove the exothermic heat generated from the chlorination reaction and to maintain the reaction temperature, the reactor was cooled by using cold water having temperature of 10-15 ?C at a flow rate of 6000 L/h in a reactor jacket for intial 30 minutes. The reaction was monitored periodically by titrating a proportional amount of mother liquor against 0.1N NaOH, and the reaction was stopped by switching off the irradiation, at a titer value corresponding to 67% chlorine (by weight) of PVC to obtain a product mixture comprising 1,2-CPVC. Excess chlorine in the product mixture and the vessel was purged/removed by passing nitrogen gas through the slurry for 1 h to obtain CPVC slurry free of chlorine. The CPVC slurry was filtered and the CPVC cake was washed with water to remove any acidic impurities until the wash water displays neutral pH, to obtain a wet CPVC cake. The wet CPVC cake was dried at 70 °C for 3h to obtain 1,2-CPVC. The chlorine content was checked by using oxygen flask method as per reference: IS-15778-2007. Dry material i.e. 1,2-chlorinated polyvinylchloride was analyzed, and the results are presented in Table 1 and Table 2.
Example 2. Process for the preparation of CPVC at chlorine pressure 1.9 kg/cm2
PVC (130 Kg) and water (720 Kg) were mixed in a reactor equipped with self-induction agitator and LED lights source emitting visible wavelength of 450 nm as an irradiating source, to obtain an aqueous slurry. The slurry was agitated at impeller tip speed 2m/s under nitrogen. Temperature of the slurry was raised to 50 °C. The aqueous slurry including the headspace was deoxygenated using nitrogen gas through pressurization at 1.5 kg/cm2 and depressurization at ambient under constant agitation. Temperature of the nitrogen purged slurry was raised to 70 °C, after 30 minutes nitrogen was purged by passing chlorine through the slurry for 30 minutes until the reactor head space and the slurry were saturated with chlorine while maintaining the chlorine pressure at 1.9 kg/cm2 (± 0.1). The chlorine saturated slurry was irradiated with a visible light of wavelength 450 nm using a LED source, and under a constant supply of chlorine gas. The chlorine pressure was maintained using a digital pressure meter with the accuracy of ±0.1. Chlorine consumption was noted through mass flow meter reading in kg/h with the accuracy of ±0.05. Of the 77 Kg chlorine required as per stoichiometric calculation, on the consumption of 73 Kg of chlorine gas, chlorine supply was stopped while keeping the LED light on. The reaction is complete after 4 Kg chlorine remaining inside the reactor was consumed. To remove the exothermic heat generated from the chlorination reaction and to maintain the reaction temperature, the reactor was cooled by using cold water having temperature of 10-15 ?C at a flow rate of 6000 L/h in a reactor jacket for intial 30 minutes. Under above conditions the total 77 Kg of chlorine was required to obtain CPVC with 67% chlorine content by weight.
The CPVC thus obtained was filtered and washed with fresh water (at least one cycle) under a pressure gradient of 5 kg/cm2. The wet CPVC obtained hereinafter was dried with the aid of hot nitrogen at 80 °C under flow of 100 kg/h and back pressure of 2.2 kg/cm2. Moisture content of solid dry CPVC obtained was less than 0.1 % by weight. Inherent viscosity of solid dry CPVC obtained was 0.82. Thermal stability (as per DIN 53381 Part 1) of solid dry CPVC obtained was 1019 sec. Dried material was analyzed and the results are tabulated below.
The reaction was monitored by calculating the chlorine content using the formula mentioned below.
% ???? ???? ????????=??????.??-????.?? (??/??+??.?????? ??)
A = Wt of PVC taken and W = wt of Chlorine consumed in reaction.
Example 3. Process for the preparation of 1,2-CPVC at chlorine pressure 2.5 kg/cm2
In this example, 1,2-CPVC was prepared according to the process of Example 1, except the chlorine pressure inside the reactor was maintained at 2.5 Kg/cm2.
Example 4. Process for the preparation of 1,2-CPVC at chlorine pressure 3 kg/cm2
In this example, 1,2-CPVC was prepared according to the process of Example 1, except the chlorine pressure inside the reactor was maintained at 3.0 Kg/cm2.
Table 2, presents the results of chlorination conducted at different pressure to achieve 67 wt% chlorinated 1,2-CPVC.
Comparative example:
CPVC resin of H829 grade produced by Kaneka Corporation, which is available in the market, was analyzed and compared with the present data.
Table 1. Change in inherent viscosity, chlorine content and glass transition temperature during chlorination at atmospheric chlorine pressure.
Reaction time (h) Intrinsic Viscosity Wt% Chlorine Tg (°C)
0 0.922 56.7 92
0.5 0.885 57.2 108
1 0.867 58.61 114
1.5 0.855 61.25 127
2 0.832 62.17 140
2.5 0.82 64.56 137
3 0.803 66.15 135
3.5 0.801 67.59 145
Table-1 clearly shows decrease in intrinsic viscosity (IV), with increase in the chlorine content of the CPVC.
The glass transition temperature (Tg) of PVC is 85 °C, which increases with % chlorination as the results shown in Table 1 when the chlorination is conducted using chlorine at an atmospheric pressure.
Table 2. Results of chlorination conducted at different pressure to achieve 67% chlorinated 1,2-CPVC.
S. No Cl2 pressure
(atm) CHCl (%) CCl2 (%) C=C (%) IV Tg
(°C) Chlorination Rate (L/mol/min) % Cl Thermal Stability (TSC results) (sec)
Example 1 1 74.32 16.67 9 0.811 145 4.2 x 10-7 67.32 540
Example 2 1.9 88.38 11.12 0.5 0.820 148 1.9 x 10-3 67.23 800
Example 3 2.5 92.23 7.77 0 0.828 151 2.5 x 10-3 67.31 900
Example 4 3 93.05 6.95 0 0.837 154 3 x 10-3 67.30 1029
Comparative example Not available 87.80 11.09 1.11 0.800 146 Not available 67.22 779
*IV-Intrinsic viscosity; Tg- glass transition temperature.
Selectivity (in %) of -CHCl-, -CCl2- and -C=C- during chlorination at different chlorine pressures (Figure 10). Values are obtained from 13C solid state CP MAS NMR spectra.
13C solid state NMR is used as tool to determine selectivity of 1,2-chlorinated PVC by monitoring -CHCl-, -CCl2- and -C=C- peaks. The analysis was conducted in 500 MHz Bruker NMR.
In Table 2, Examples 3 and 4, when 1,2-CPVC is prepared by chlorination of PVC at a chlorine pressure of 2.5 Kg/cm2, and 3 Kg/cm2, respectively, it clearly shows the absence of unsaturation in 1,2-CPVC samples. Thus, 1,2-CPVC prepared by the process of the present disclosure contains 1,2-Chlorinated polyvinylchloride or Poly (1,2-dichloroethylene) with 93% selectivity in comparison to 1,1-chlorinated polyvinylchloride or poly (vinylidene chloride), and having no unsaturation present in the polymer chain.
However, in Examples 1 and 2, when CPVC is prepared by chlorination of PVC at a chlorine pressure below 1.9 Kg/cm2, it clearly shows the presence of unsaturation in CPVC samples.
Figures 3 and 4 illustrate graphs representing the dynamic mechanical analysis (DMA) of CPVC obtained by conducting chlorination reaction at 1.9 kg/cm2 chlorine pressure and 3 kg/cm2 chlorine pressure respectively. Dynamic mechanical analysis (DMA) measures the damping in terms of Modulus (pa) and tan delta, which is a critical test to check processability of a material. Smooth transition in DMA curve with no additional peaks represents uniform chlorination of solid particle indicating good processability of the material.
For CPVC obtained by chlorination of PVC by using chlorine at a pressure of 1.9 Kg/cm2, in Figure 3, appearance of a peak at 88 °C represents residual PVC component, near to the low Tg peak of CPVC and appearance of a peak at 148 °C, represents uneven chlorination, which means that the CPVC material is difficult to process.
For 1,2-CPVC obtained by chlorination of PVC by using chlorine at a pressure of 3 Kg/cm2, in Figure 4 shows smooth transition and high Tg of CPVC, at 154 °C, indicating good processability.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of process for the preparation of 1,2-chlorinated polyvinyl chloride (1,2-CPVC), wherein the process provides:
- 93% selectivity for 1,2-Chlorinated polyvinylchloride;
- 1,2-CPVC with uniform chlorination;
- no unsaturation in the molecular chain of the CPVC
- 1,2-CPVC having high inherent viscosity (> 0.83 ± 0.02);
- 1,2-CPVC having thermal stability in the range of 800 to 1200 seconds; and
- 1,2-CPVC having high glass transition (Tg > 152 °C ± 0.05).
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 invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
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 disclosure. These and other changes in the preferred embodiment 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:WE CLAIM:
1. A process for preparing 1,2-chlorinated polyvinylchloride (1,2-CPVC), said process comprising the following steps:
a) preparing an aqueous slurry of polyvinylchloride (PVC) under a nitrogen atmosphere;
b) heating said aqueous slurry at a temperature in the range of 50 °C to 90 °C to obtain a heated slurry;
c) passing a predetermined amount of chlorine gas into said heated slurry at a pressure in the range of 2 to 3.5 kg/cm2 for a predetermined time period to obtain a chlorine saturated slurry;
d) irradiating said chlorine saturated slurry with LED as an irradiation source having a wavelength in the range of 400 nm to 500 nm to obtain a product mixture comprising 1,2-chlorinated polyvinylchloride; and
e) separating the 1,2-chlorinated polyvinylchloride (1,2-CPVC) from said product mixture;
wherein the 1,2-CPVC has a chlorine content in the range of 67% to 68% and has no unsaturation in the polymer chain of CPVC; and
wherein said process is devoid of any chemical agent selected from neutralizing agent, stabilizer and processing additives.
2. The process as claimed in claim 1, wherein said aqueous slurry is prepared by mixing polyvinyl chloride (PVC) and water in a predetermined weight ratio at a temperature in the range of 25 °C to 35 °C and at an agitation speed in the range of 1 m/s to 6 m/s.
3. The process as claimed in claim 2, wherein said predetermined weight ratio of the PVC to water is in the range of 1:80 to 1:8.
4. The process as claimed in claim 1, wherein said PVC has a porosity in the range of 0.21 to 0.25 ml/g.
5. The process as claimed in claim 1, wherein said predetermined amount of chlorine is in the range of 66 to 68 wt%.
6. The process as claimed in claim 1, wherein said predetermined time period is in the range of 20 to 40 minutes.
7. The process as claimed in claim 1, wherein said chlorine gas in step (c) is passed into said heated slurry at a pressure in the range of 2.5 to 3 kg/cm2.
8. The process as claimed in claim 1, wherein a chlorination rate in step (c) is in the range of 2 x 10-3 to 4 x 10-3 L/mol/min.
9. The process as claimed in claim 1, wherein said LED has a power output in the range of 1 watt/kg to 5 watt/kg of polyvinyl chloride.
10. 1,2-chlorinated polyvinyl chloride (1,2-CPVC) being characterized by having;
i. no unsaturation in the molecular chain of said CPVC;
ii. a chlorine content in the range of 67 to 68%;
iii. an inherent viscosity in the range of 0.825 to 0.850;
iv. a thermal stability in the range of 800 seconds to 1200 seconds; and
v. a glass transition temperature (Tg) in the range of 150 to 155 °C.