JPS5910646B2 - Method for separating trace amounts of vinyl chloride monomer from wet vinyl chloride polymer slurry - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating trace amounts of vinyl chloride monomer from a wet vinyl chloride polymer slurry or emulsion.

A method of obtaining a slurry or emulsion of vinyl chloride polymer (hereinafter sometimes referred to as PVC) by suspension polymerization or emulsion polymerization of vinyl chloride monomer (hereinafter sometimes referred to as VCMR) in an aqueous medium. is publicly known.

Such a slurry or emulsion contains a trace amount of CVMR that cannot be separated by conventional separation or drying methods. The above-mentioned conventional separation method means to separate the VCMR remaining in the slurry or emulsion under normal pressure or reduced pressure at 70°C or lower, often at 65°C.
This method involves heating the material to a temperature below °C and, if necessary, blowing in an appropriate amount of inert gas. Depending on the separation method, the residual VCMR content in pVC is approximately 1000 to 20000 ppm (dry pVC).
VC standard). Moreover, the above-mentioned normal drying method is
By using the above separation method, the remaining VCMR content can be reduced to 1000 to 20
PVC slurry or PVC emulsion with a concentration of about 000 ppm is dehydrated by a known method, and then batch-processed under reduced pressure or normal pressure.
This is a method using a fluidized method or flash drying. Depending on the drying method, the residual VCMR content in PVC is 100~
It decreases to about 2000 ppm (based on dry PVC). The technical problems to be solved by the present invention are as follows: 1. Solving the insufficiency of the conventional separation method, and 2.
Prevention of trace amounts of VCMR released into the environment together with drying gas when drying VC slurry or latex;
3. Residual VCMR in PVC from the above-mentioned normal drying method may contaminate the atmosphere of the processing plant during PVC molding, or trace amounts of vinyl chloride monomer still remaining in PVC molded products resulting from said processing may The aim is to prevent the molded product from harming the health of the user.

In order to solve these problems, many methods have recently been proposed, such as heating a slurry containing a vinyl chloride polymer at 70°C to 125°C (Japanese Patent Application Laid-open No. 50-17288
No. 1), or by contacting a wet vinyl chloride polymer cake (powder aggregate) with water vapor (JP-A-51-17289).
), or wet vinyl chloride suspension polymer at a temperature of 80 to 15
This is a method such as passing water vapor at 0° C. (Japanese Patent Application Laid-open No. 18783/1983).

All of these methods use water vapor and PVC.
From the standpoint of thermal stability, the temperature is high (70°C to 150°C)
(hereinafter referred to as high-temperature treatment), it is possible to recover the VCMR separated along with the water vapor, and it is superior in that it is possible to reduce the amount of CMR in the dry PVC product to 10 ppm or less. . However, 70℃
Since high temperatures such as ~150°C are used, the thermal stability of PVC products is likely to be impaired. Therefore, the optimum application conditions for high-temperature steam treatment are based on individual batches of polymers even if they have the same polymerization recipe. The disadvantage is that there is variation depending on the
Furthermore, the thermal stability does not have to be good only during processing of the PVC product, but must not deteriorate during continued use of the PVC processed product. From the above point of view, high temperature treatment is not preferred, apart from steam treatment. The present inventor has researched a method for solving the technical problems 1 to 3 above without using such high temperatures, and has developed a method for desorbing and removing VCMR contained in a wet vinyl chloride polymer using a gas at 25°C or higher. When using hydrocarbons (hereinafter referred to as inert hydrocarbon gas), 7
Even when treated at temperatures below 0°C, results sufficiently comparable to the known methods described above can be obtained, and the thermal stability of the PvC product to be treated is superior to that of the known steam-treated products. With this result, the present invention was completed.

As is clear from the above description, the purpose of the present invention is, firstly, to provide a new method for removing trace amounts of VCMR in PVC products, and secondly, to provide a method for removing trace amounts of VCMR from PVC products that does not require heating to high temperatures. The object of the present invention is to provide a method for producing a PVC product with good thermal stability, and a third object is to provide a method for effectively recovering trace amounts of VCMR from wet PVC.

Other objects will become apparent from the following description of the invention. The present invention provides (1) a method for separating a trace amount of vinyl chloride monomer from a wet vinyl chloride polymer slurry;
A method characterized in that a hydrocarbon which is a gas at a temperature of 0.degree. C. or above is blown into the slurry at 25.degree. C. or below, or the slurry is blown into the slurry at 25.degree. C. or below and then heated to 25.degree.

(2) In a method for separating a trace amount of vinyl chloride monomer from a wet vinyl chloride polymer slurry, the vinyl chloride polymer slurry is heated to a temperature of 70°C or more and 110°C or less for 1 minute or more and 30 minutes or less, and then the temperature is lower than 70°C. A method characterized by blowing a hydrocarbon which is a gas at 25°C or higher into the slurry at 25°C or higher, or blowing into the slurry at 25°C or lower and then heating it to 25°C or higher.

It is. Hereinafter, the preceding statement α1) is defined as the first invention of the present invention and the above (α1).
2) is referred to as the second invention of the present invention. In the present invention, wet vinyl chloride polymer slurry refers to a vinyl chloride homopolymer produced by a suspension polymerization method or a monopolymer containing vinyl chloride containing 50% by weight or more of vinyl chloride and other monomers having ethylenically unsaturated bonds. It refers to wet powder or emulsion particles of a copolymer with a copolymer, which is suspended or emulsified in an aqueous medium.

It is known that such a slurry can be obtained by polymerizing vinyl chloride or a monomer having vinyl chloride and an ethylenically unsaturated bond while suspending it in an aqueous medium, or PVC obtained once as a dry powder from such a slurry. (including copolymers) may be dispersed again in an aqueous medium. Monomers having ethylenically unsaturated bonds include, for example, lower α-olefins such as ethylene and propylene, so-called vinyl monomers such as vinyl acetate and vinylidene chloride, acrylic acid esters, and acrylonitrile. Refers to acrylates and other copolymerizable monomers. In addition, the aqueous medium refers to water, a medium in which water and a suspension stabilizer, an emulsifier, a surfactant having an equivalent effect, and other necessary additives are dissolved or uniformly blended. The trace amount of vinyl chloride monomer is mostly contained in the wet PVC powder or emulsion particles in the slurry, and since PVC does not dissolve in CMR, the state in which it is contained is due to adsorption. It is understood that Next, the hydrocarbons that are gaseous at temperatures above 25°C used in the present invention include saturated aliphatic hydrocarbons such as methane, ethane, propane, and butane, and aliphatic unsaturated hydrocarbons such as ethylene, propylene, and butylene. Refers to hydrocarbons.

As is clear from the above description, the hydrocarbon used is at 25°C.
If it is less than that, it may be a gas or a liquid. These gases are VC adsorbed on the surface of wet PVC powder.
It functions to desorb a part of CMR that is adsorbed instead of MR, or to speed up the elution of adsorbed VCMR into an aqueous medium, and to dissolve and transport the eluted VCMR out of the system. Such desorption or adsorption CMR removal function has little or no effect at temperatures below 70° C. when a commonly used inert gas such as air nitrogen or argon is used. In addition, considerable effects can be obtained when water vapor is used at temperatures below 70°C and above 50°C, but it must be carried out under reduced pressure, and a large amount of water vapor is used per amount of VCMR to be removed and recovered compared to the hydrocarbons used in the present invention. Requires. 50 again
There is almost no effect below ℃. On the other hand, in the present invention, the VCMR removal effect can be achieved by blowing hydrocarbons that are gaseous at 25° C. or higher into a wet vinyl chloride polymer slurry at 25° C. or higher without any restriction on the blowing temperature. however,
Such treatment at a temperature of 7'C or higher, particularly 80C or higher, impairs the thermal stability of the PVC to be treated, and is therefore not preferred unless it is carried out separately from the hydrocarbon treatment as a requirement of the second aspect of the present invention. 25 to a wet vinyl chloride polymer slurry below 25°C.
The VCMR separation method of the present invention is effective even when gaseous hydrocarbons are blown at temperatures above .degree.

Therefore, it is possible to carry out the treatment as long as the slurry remains in a liquid state without freezing, but if the hydrocarbon used in the treatment is liquid or the amount of hydrocarbon dissolved in the aqueous medium constituting the slurry is Since the amount may be relatively large, in that case, the slurry may be
It is desirable to evaporate and separate the hydrocarbons by heating to 5° C. or higher. The method of using an inert gas or water vapor instead of hydrocarbons that are gaseous at temperatures above 25°C has the drawbacks mentioned above, and hydrocarbons that are gaseous at temperatures above 70°C cannot be treated at a treatment temperature of 70°C or above. or require depressurization.

Additionally, other low boiling point organic compounds such as hydrocarbons such as pentane, benzene, hexane, hexene can be used in the final CMR or wet PVC slurry to remove these hydrocarbons adsorbed on the wet PVC. 7
The treatment must be carried out at a temperature of 0° C. or higher for a certain period of time, which increases the risk of damaging the thermal stability of the PVC to be treated.

In addition, low-boiling organic compounds having polar groups are easily adsorbed to wet PVC and are difficult to desorb, and their presence in PVC in trace amounts is harmful in terms of environmental protection. The use of hydrocarbons that are liquid at temperatures above 25° C., as used in the present invention, has little or no of these drawbacks. The blowing method is to blow a gaseous hydrocarbon into a wet vinyl chloride polymer slurry at a predetermined temperature for a predetermined time at 25° C. or lower with or without stirring, and then dehydrate and dry the slurry in the same manner as in a known method.

The preferred treatment temperature is from 25 to less than 70°C, and the treatment time is from 10 minutes to 300 minutes. Higher temperatures generally allow relatively short processing times to achieve the objective. The hydrocarbon exhaust gas can be compressed and liquefied to easily separate and recover vinyl chloride monomers. The present invention (especially the first invention) described above has the following effects compared to the known method.

Since the process can be carried out continuously at room temperature or below 65°C, which is the usual polymerization temperature, there is no time loss.

2.Since no steam is used, there is no need for extra steam generation heat or extra cooling water after treatment.

3 VCMR concentration after wet treatment is 100-200
At 0 ppm, there is no difference from the known high-temperature steam treatment, but the subsequent dehydration and drying by the known method has a high VCMR removal effect.

Even if trace amounts of gaseous hydrocarbons may remain in the PVC product below 425°C, there is little or no toxicity compared to VCMR adsorption.

5 Even if variations in the polymerization recipe or between rods are taken into consideration, PVC products with poor thermal stability will not occur.

Next, the differences from the first invention regarding the second invention of the present invention will be explained.

In this invention, the wet PVC slurry is heat-treated at 70° C. or higher and 110° C. or lower for 1 minute or more and 30 minutes before hydrocarbon treatment. This process is not intended for direct VCMR removal. That is, there is no need to forcefully generate water vapor.
This is done for the purpose of softening the surface of the wet PVC particles and reducing the surface area, thereby reducing the adsorption power of VCMR. Therefore, especially when the temperature is 80°C or higher, preliminary tests should be carried out to keep the temperature within a range that does not affect the thermal stability. On the other hand, at temperatures above 70°C and below 80°C, there is no problem with thermal stability in most cases even if the reaction is carried out for 30 minutes. However, VC in wet PVC slurry after treatment with hydrocarbons that are gaseous above 25°C
Although the MR is not particularly significantly reduced, a final product (PVC) with a lower VCMR is obtained in the product that is subsequently dried. Therefore, for example, the amount of residual VCMR in the product PVC is 5
This is particularly effective when obtaining a product with a small residual amount of VCMR, such as not detectable below ppm.

The present invention will be explained below with reference to Examples.

Examples 1 to 5, Comparative Examples 1 to 3 Produced by suspension polymerization method, unpolymerized monomers were released at 65°C, and the VCMR concentration was 11000 ppm (dry PVC
wet PVC slurry (700 kg of aqueous medium,
PVC3OOkg) was obtained.

This slurry was maintained at a predetermined temperature while stirring, and 15 k9 of each predetermined hydrocarbon gas was blown into the slurry at a uniform rate within a predetermined time.
During this time, the VCMR concentration in the slurry was measured. Then, the slurry after the treatment was centrifugally dehydrated and soaked with nitrogen at 70°C for 1 hour.
A dry PVC product with a water content of about 0.5% was obtained by time-flow drying. On the other hand, in the comparative example, steam treatment was performed at a predetermined temperature and for a predetermined time, and then dehydration and drying were performed in the same manner. Hydrocarbons at the end of the treatment were collected in a gas holder. The predetermined conditions and results are shown in Table 1. Note 1 The thermal stability test was conducted using the following method.

Quality test method () Color of dry resin: Judgment with naked eye indoor light (
The one with the highest whiteness as a vinyl chloride resin powder under daylight (daylight color) was classified as pure white, and the one with the next highest rank of slightly yellowish tinge than pure white was classified as faint yellow.

(b) Thermal stability of dry resin: 100g of vinyl chloride polymer
r. Dioctyl phthalate 50 gr) Barium stearate 0.3 gr) Cadmium stearate 0.5 gr
．． After mixing, the mixture was kneaded with rolls at 150° C. for 20 minutes and taken out as a 1 m771 sheet, and the transparency and degree of coloring of the resulting film were compared using the following criteria.

As is clear from Table 1, the VCMR value of the wet slurry after the hydrocarbon gas treatment of the present invention is generally inferior to that of each comparative example, but after dehydration and drying using a known method. obtained results that were equal to or superior to those of the comparative examples, and in terms of thermal stability, whereas the comparative examples sometimes showed a tendency to color, the results obtained when carried out by the method of the present invention (first invention) All were in good condition. This shows the effectiveness and practicality of the present invention. Examples 7 to 12, Comparative Example 4
~6 The same wet slurry as used in Example 1 (aqueous medium 700k9, PVC3OOk9) was treated at 80° C. for 20 minutes with stirring.

No steam was blown in, so no steam was distilled off. Thereafter, the mixture was cooled to 65° C. or lower, and 15 kg each of a predetermined hydrocarbon gas at a predetermined temperature and a predetermined amount were blown into the reactor at a uniform speed for a predetermined time while stirring. During this time, the VCMR concentration in the slurry was measured. The slurry was then centrifugally dehydrated and dried with nitrogen at 70°C for 1 hour.
A dried PVC product having a moisture content of approximately 0.5% was obtained by fluidized drying for hours. On the other hand, in Comparative Examples 4 to 6, the 80°C,
After heat treatment for 20 minutes, steam treatment was performed at a predetermined temperature for a predetermined time, and then dehydrated and dried in the same manner. The predetermined conditions and results are
Shown in the table. As is clear from Table 2, the CMR values in the wet slurry after preheating and hydrocarbon gas treatment according to the second invention of the present invention are generally inferior to those of the comparative examples, but After dehydrating and drying this material by a known method, results were obtained that were equal to or superior to those of each comparative example, and in comparison with the corresponding example in Table 1 (first invention of the present invention) (Example 1). and Example 7 and the following), the effect of the second invention of the present invention is obvious. Furthermore, as in Table 1, the thermal stability also shows better results than the comparative examples. Example 13, Comparative Example 7 A wet vinyl chloride/vinyl acetate copolymer produced by a suspension polymerization method and having a CMR concentration of 8500 ppm (based on dry vinyl chloride/vinyl acetate copolymer) by releasing the monomer at 65°C. Slurry (aqueous medium 700k9, the copolymer 300kg,
A copolymer containing 10% by weight of vinyl acetate was obtained.

Keep this slurry at a predetermined temperature and use 200ml each of propylene gas
kg was injected at a uniform rate within a predetermined time. During this time, the VCMR concentration in the slurry was measured. Then, the slurry after the treatment was centrifugally dehydrated and fluidized for 1 hour with nitrogen at 70° C. to obtain a dry PVC product with a water content of about 0.5%.

On the other hand, in a comparative example, the same treatment was performed using nitrogen gas instead of propylene gas, followed by dehydration and drying. In addition, the propylene at the end of the process was collected in a gas holder. Table 3 shows the predetermined conditions and results. As is clear from Table 3, the VCMR value of the wet slurry after hydrocarbon gas treatment of the present invention is generally superior to that of each comparative example; & Toge Comparative results have been obtained that are significantly superior to each example.

Claims (1)

[Claims] 1. A method for separating a trace amount of vinyl chloride monomer from a wet vinyl chloride polymer slurry, characterized by blowing a hydrocarbon that is a gas at 25°C or higher into the slurry at 25°C or higher. how to. 2. The method according to claim 1, wherein the vinyl chloride polymer is a vinyl chloride homopolymer or a copolymer of vinyl chloride and an ethylenically unsaturated compound containing 50% by weight or more of vinyl chloride. 3 Hydrocarbons that are gaseous at temperatures above 25°C are methane, ethane, propane, butane, ethylene, propylene,
The method according to claim 1, wherein the compound is one or more compounds selected from butylene. 4. The method according to claim 1, wherein the temperature at which the hydrocarbon, which is a gas at 25°C or higher, is blown into the wet vinyl chloride polymer slurry is 40°C or higher and lower than 70°C. 5 In a method for separating a trace amount of vinyl chloride monomer from a wet vinyl chloride polymer slurry, the vinyl chloride polymer slurry is heated to 70°C or more and 110°C or less for 1 minute or more and 30 minutes or less, and then cooled to less than 70°C. , a method characterized in that a hydrocarbon which is a gas at 25°C or higher is blown into the slurry at 25°C or higher. 6. The method according to claim 5, wherein the vinyl chloride polymer is a vinyl chloride homopolymer or a copolymer of vinyl chloride and an ethylenically unsaturated compound containing 50% by weight or more of vinyl chloride. 7 Hydrocarbons that are gaseous at temperatures above 25°C are methane, ethane, propane, butane, ethylene, propylene,
The method according to claim 5, wherein the compound is one or more compounds selected from butylene. 8. The method according to claim 5, wherein the temperature at which the hydrocarbon, which is a gas at 25°C or higher, is blown into the wet vinyl chloride polymer slurry is 40°C or higher and lower than 70°C.