JPS6117841B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for aqueous suspension polymerization of vinyl chloride in the presence of at least one of a cellulose derivative and partially saponified polyvinyl alcohol using a polymerization machine equipped with a reflux condenser.

Industrially, polyvinyl chloride (hereinafter referred to as PVC) is produced by polymerizing vinyl chloride, mainly by a batch aqueous suspension polymerization method, but a relax condenser is used to remove the heat of polymerization. There are many things. In this suspension polymerization method, a suspension stabilizer for polymerization is usually used, and particularly cellulose derivatives and partially saponified polyvinyl alcohol are used as suspension stabilizers for polymerization that have excellent plasticizer absorption properties and provide PVC with good fiber properties. It is widely used as an agent.

However, when carrying out suspension polymerization of vinyl chloride using cellulose derivatives or partially saponified polyvinyl alcohol as a suspending agent, if a reflux condenser is used to remove part of the polymerization heat,
PVC scale adheres to the reflux condenser itself, its piping, conduits, etc., and in extreme cases, the inside of the pipe may even become clogged with PVC scale, making continuous industrial production difficult.

In order to elucidate the cause of this, the present inventors conducted a suspension polymerization test of vinyl chloride using a test device in which the polymerization machine and reflux condenser were equipped with a pressure-resistant see-through glass that allowed the inside to be observed.
The cause of scale buildup in the pipes mentioned above is related to the foaming properties of the cellulose derivatives and partially saponified polyvinyl alcohol used as suspending agents.Furthermore, during the polymerization reaction, vaporized vinyl chloride polymerizes in the reflux condenser, causing scale buildup. was found to be increasing. Aqueous solutions of cellulose derivatives and partially saponified polyvinyl alcohol are highly foamable, and so are vinyl chloride polymerization suspensions prepared using at least one of cellulose derivatives and partially saponified polyvinyl alcohol.

As a result of observation by the present inventors using the above-mentioned pressure-resistant see-through glass test device, it was found that during the process of heating the polymerization suspension to a preset polymerization temperature at the start of polymerization, the suspension temporarily became violently foamy. In extreme cases, it could even fill the inside of the capacitor. This overflow of the polymerization suspension into the reflux condenser may cause the polymerization of vinyl chloride to progress in the condenser itself or in the parts of the polymerization equipment that come into contact with vinyl chloride during the polymerization operation, such as its piping and conduits. PVC adheres to these areas as scale.

Furthermore, after the polymerization suspension reaches the polymerization temperature, the temperature at which PVC scale adheres varies greatly depending on the temperature of the reflux condenser, specifically the temperature of its jacket, and the temperature is 15 degrees higher than the polymerization temperature on the Celsius scale. When temperatures exceed low temperatures, PVC scale build-up becomes significant. Therefore, in the case of a production method in which a reflux condenser is used to remove part of the polymerization heat in suspension polymerization of vinyl chloride using a cellulose derivative or partially saponified polyvinyl alcohol as a suspending agent, the reflux condenser and its PVC to appurtenances
In order to prevent scale adhesion and continue industrial production, it is necessary to prevent the polymerization suspension from overflowing into the condenser and to suppress the polymerization of vinyl chloride in the condenser during the polymerization reaction. is necessary.

Conventionally, in order to prevent overflow of a polymerization suspension during a polymerization reaction, a method has been proposed in which water is sprayed into the interior of a reflux condenser or ancillary equipment. However, when a cellulose derivative or partially saponified polyvinyl alcohol is used as a suspending agent, the foaming property of the polymerization suspension is so great that it cannot be practically prevented by water spraying as described above.

Regarding the relationship between the temperature of the reflux condenser during the polymerization reaction and the adhesion of PVC scale,
Conventionally, this was not recognized at all, and the system was normally operated at a temperature approximately 5 degrees lower on a Celsius scale than the polymerization temperature. Therefore, it always encouraged the adhesion of PVC scale and accelerated its accumulation in the reflux condenser and its ancillary equipment.

In order to solve these problems, the present inventors conducted extensive research based on the above observation results, and found that at the start of polymerization, the reflux condenser and its piping are By heating incidental equipment such as conduits to a temperature higher than the polymerization temperature, and after the polymerization suspension reaches the polymerization temperature, the temperature of the reflux condenser is kept at least 15 degrees lower than the polymerization temperature in degrees Celsius. It has been found that it is possible to prevent PVC scale from adhering to condensers and their auxiliary equipment, making it possible to continue industrial production.

That is, in the method of the present invention, the condenser and its associated equipment such as piping and conduits are heated above the polymerization temperature until the polymerization suspension reaches the polymerization temperature at the start of polymerization. This is accomplished by running hot water through the jacket of the reflux condenser and by steam tracing the piping and conduits. The temperature is at least the polymerization temperature or higher, preferably 10° or more higher than the polymerization temperature. This prevents the suspension from overflowing into the condenser even if the polymerization suspension temporarily becomes violently foamy at the start of polymerization. Furthermore, when the temperature of the polymerization suspension reaches the polymerization temperature, the supply of hot water to the jacket of the reflux condenser is stopped, and the supply of hot water is gradually switched to cooling water. In this case, if the hot water is suddenly switched from the cooling water, it is not preferable because the vinyl chloride vaporizes violently and becomes temporarily foamy. Cooling water is gradually passed in accordance with the exothermic state of the polymerization reaction, and within one hour after the polymerization suspension reaches the polymerization temperature, the temperature of the jacket of the reflux condenser is set to 15 degrees or more on the Celsius temperature scale above the polymerization temperature. Keep the temperature low. Practically speaking, the temperature difference between the polymerization temperature and the cooling water temperature of the reflux condenser may be 15° or more. By doing so, it is possible to prevent vinyl chloride vaporized from the polymerization suspension from polymerizing inside the reflux condenser and forming scale.

As described in detail above, the present invention prevents the suspension from overflowing into the condenser by heating the reflux condenser above the polymerization temperature until the polymerization suspension reaches the polymerization temperature at the start of polymerization. In addition, after the polymerization suspension reaches the polymerization temperature, the temperature of the reflux condenser is maintained at a temperature lower than the polymerization temperature by 15 degrees or more on the Celsius temperature scale, thereby preventing vaporized chloride from flowing. A method of preventing polymerization within a vinyl reflux condenser is provided.

By applying the method of the present invention, it is possible to prevent PVC scale from adhering to the reflux condenser itself or its piping/conduits, so the polymerization machine can be used continuously for the next batch without cleaning them. I can do it.

The cellulose derivatives that can be used in the present invention may be those already known as suspending agents for vinyl chloride polymerization. Examples include methylcellulose, ethylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, and carboxymethylcellulose. Further, partially saponified polyvinyl alcohol may also be used as a suspending agent for vinyl chloride polymerization. Generally, a saponification degree of 90 mol % or less and an average polymerization degree of 2,400 or less are preferred. These cellulose derivatives and partially saponified polyvinyl alcohols can be used alone or in combination. The amount used is preferably 0.01 to 0.2 parts by weight per 100 parts by weight of vinyl chloride. Furthermore, the effects of the present invention are not hindered by the concomitant use of other known suspending agents such as gelatin, maleic anhydride-styrene copolymer, polyvinylpyrrolidone, etc.

The method of the present invention can be applied to aqueous suspension polymerization methods commonly practiced in the art. That is, the ratio of vinyl chloride and water is generally 80 to 300 parts by weight of water to 100 parts by weight of vinyl chloride, and the polymerization temperature is usually 35 parts by weight.
℃~70℃.

Further, the polymerization catalyst is appropriately selected from known catalysts and used.

In addition to vinyl chloride, other monomers copolymerizable with vinyl chloride, such as ethylene, propylene,
Vinyl acetate, acrylic acid or its esters, methacrylic acid or its esters, fumaric acid or its esters, maleic acid or its esters, alkyl vinyl ethers, etc. can also be present.

The method of the present invention makes it possible to continuously use a backflow condenser for the polymerization of vinyl chloride without cleaning it, and therefore has great industrial significance.

The present invention will be specifically explained below using Examples.

Example 1 Heat transfer area of 300 polymerization machine equipped with pressure-resistant transparent glass, also equipped with pressure-resistant transparent glass
A 0.2 m ² vertical reflux condenser was installed and the condenser was heated to 70°C by passing hot water at 90°C through the jacket of the condenser. In this polymerization machine, 150 kg of water, 50 g of hydroxypropyl methyl cellulose, saponification degree of 73 mol%, and an average polymerization degree of 800.
After charging 50 g of partially saponified polyvinyl alcohol and 25 g of dioctyl peroxydicarbonate and removing the air inside with a vacuum pump, the vinyl chloride
100Kg was charged. Set the polymerization temperature to 57 °C and incubate at 30 °C.
The temperature was raised to this temperature in minutes, but the reflux condenser was constantly kept at 70°C during this time. Fifteen minutes after the start of heating, the polymerization suspension remained in a foamy state for 3 minutes, but the suspension did not overflow into the reflux condenser. When the temperature of the polymerization suspension reached 57°C, the 90°C hot water that had been passed through the jacket of the reflux condenser was gradually switched to 30°C cooling water over 45 minutes, and from then on the cooling water was turned off. The temperature was always maintained at 35°C.
A part of the heat of the polymerization reaction was removed by a reflux condenser, and the polymerization was continued until the internal pressure of the polymerization machine reached 5 kg/cm ² G. In this way, a total of 60 batches of polymerization can be made without cleaning the reflux condenser.
After repeated cycles, the reflux condenser was disassembled and the inside was inspected, but no PVC scale was found inside the condenser.

Comparative Example 1 Polymerization was initiated in the same manner as in Example 1 using the same polymerization test equipment as in Example 1, except that the reflux condenser was not heated to 70°C. Fifteen minutes after the start of temperature rise, the polymerization suspension became violently foamy, and two minutes later, the suspension filled up to the top of the reflux condenser. When the temperature of the polymerization suspension reaches 57°C, pour 5°C cooling water into the reflux condenser jacket.
Afterwards, the temperature of the cooling water outlet is always set at 50°C.
It was kept at ℃. A part of the polymerization reaction heat is removed by a reflux condenser, and the internal pressure of the polymerization machine is reduced to 5Kg/cm ² G.
Polymerization was continued until . After repeating the next polymerization batch five times without cleaning the reflux condenser in this way, a large amount of PVC scale adhered to the inside of the condenser, making it impossible to operate the condenser.

Examples 2 and 3 Instead of 50 g of hydroxypropyl methyl cellulose and 50 g of partially saponified polyvinyl alcohol with a saponification degree of 73 mol% and a polymerization degree of 800, 80 g of hydroxypropyl methyl cellulose (Example 2) or a saponification degree of 73 was used.
Example 1 except that 120 g of partially saponified polyvinyl alcohol (Example 3) with a degree of polymerization of 800 in mol% was used.
The same results as in Example 1 were obtained.

Comparative Examples 2 and 3 In Examples 2 and 3, when polymerization was initiated without heating the reflux condenser to 70° C. as in Comparative Example 1, the same problems as in Comparative Example 1 arose.

Claims (1)

[Claims] 1 Vinyl chloride or a mixture of vinyl chloride and a monomer that can be copolymerized with vinyl chloride is aqueous-based using at least one of a cellulose derivative and partially saponified polyvinyl alcohol using a polymerization machine equipped with a reflux condenser. When performing suspension polymerization, at the start of polymerization, a reflux condenser is heated above the polymerization temperature until the polymerization suspension reaches the polymerization temperature, and after the polymerization suspension reaches the polymerization temperature, the reflux condenser is heated. 1. A method for the suspension polymerization of vinyl chloride, characterized in that the temperature of the Tux condenser is kept lower than the polymerization temperature by at least 15° on the Celsius temperature scale.