JPS5814445B2 - Polymerization method of vinyl chloride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved process for the homo- or copolymerization of vinyl chloride.

When vinyl chloride is polymerized alone or together with a monomer that can be copolymerized with it (hereinafter simply referred to as polymerization), the monomer is removed during the polymerization process, such as on the inner wall of the polymerization tank, backflow condenser, stirring blades, baffle plates, and various attached piping connections. The cooling capacity of the polymerization tank may be reduced because the polymer adheres to the parts of the equipment that come into contact with it, or the polymer that has once adhered and peeled off is mixed into the vinyl chloride homopolymer or copolymer (hereinafter referred to as the product). This causes problems such as deterioration of product quality.

Therefore, it is customary to clean the inside of the polymerization tank after each polymerization and then perform the polymerization again, but this requires a great deal of labor and time, resulting in a decrease in the operating rate of the polymerization tank and an increase in product costs. There is.

Many methods have been proposed for polymer adhesion to the inner wall of the polymerization tank, but although these methods are effective in preventing polymer adhesion, they may slow down the polymerization rate or affect the physical properties of the product. There are various drawbacks such as deterioration, and none of these methods are satisfactory for industrial use.

An object of the present invention is to provide a practical polymerization method that does not cause the above-mentioned adverse effects and sufficiently prevents polymer adhesion during the polymerization of vinyl chloride.

As a result of repeated research, the present inventors have found that when polymerizing vinyl chloride, alginic acid or alginate metal salts are applied in advance to the inner walls of the polymerization tank and other parts of the polymerization equipment and equipment attached to the polymerization tank that come into contact with the monomer during the polymerization operation. By doing so, polymer adhesion will be greatly reduced, and even a small amount of adhering polymer can be easily removed by washing with water, etc., and there will be no negative effects such as slowing down the polymerization reaction or deteriorating the physical properties of the product. Heading, we arrived at the present invention.

The alginic acid referred to in the present invention is a natural polymer substance that is abundantly contained in seaweed.It is a highly viscous precipitate obtained by extraction from fresh seaweed with sodium carbonate and acid treatment, and has an average molecular weight of 50,000 to 200,000. It is.

In addition, the alginate metal salt referred to in the present invention refers to the above-mentioned alginic acid, lithium hydroxide, sodium hydroxide, potassium hydroxide,
Sodium alginate is the most typical example of products made with metal hydroxides such as rubidium hydroxide and cesium hydroxide.

That is, a commercially available product of alginic acid is sodium alginate, and industrially it is
It can be obtained from fresh seaweed by the ahec Herter method or the like.

In carrying out the present invention, alginic acid or alginic acid metal salts (hereinafter collectively referred to as alginic acids) are applied to the inner wall of a polymerization tank in the form of a solution dissolved in a solvent.

In this case, the medium of the coating liquid is not particularly limited, and any solvent in which alginic acids can be dissolved may be used, such as water or an alkaline aqueous solution.

There are no particular limitations on the preparation of the coating liquid, and it may be carried out under conditions such that the alginic acid is dissolved in the solvent.

It is not clear why polymer adhesion can be prevented by applying the alginic acids of the present invention to the inner wall of a vinyl chloride polymerization tank, but it is probably due to the Polar groups act as hydrophilic groups,
It is thought that this is to make the wall surface of the portion of the polymerization tank that comes into contact with the monomer hydrophilic.

In fact, it has been observed that while untreated walls such as polymerization tanks exhibit considerable water repellency, walls treated with the present invention have very good wettability with water and exhibit hydrophilic properties. .

Therefore, it can be considered that the monomer is prevented from approaching the wall surface during the polymerization reaction, which is effective in preventing polymer adhesion.

In carrying out the present invention, a solution in which alginic acids are dissolved is applied to the inner wall of the polymerization tank, etc., and the concentration of alginic acid can be in the range of 0.01 to 20% by weight, preferably 0. It is convenient for the coating work to use it in a range of .05 to 5% by weight.

In the present invention, application does not refer to the mode of work, but means that the alginic acid is present on the vessel wall, etc., and the method of application is not particularly limited, but is usually applied by brushing or spraying. The coating amount is not particularly limited, but it is usually preferably 0.005 to 10 g/m'.

Coating may be carried out before the start of polymerization for each batch, or polymerization may be continued for several batches or more by simply washing with water after coating.

Furthermore, the polymerization to which the present invention can be applied is not only the homopolymerization of vinyl chloride, but also monomers copolymerizable with vinyl chloride, such as olefins such as ethylene and propylene, vinyl acetate, etc.
It can be effectively applied to copolymerization with vinyl monomers such as styrene, dicarboxylic acid monomers such as maleic acid, maleic esters, fumaric acid, and fumaric esters.

Furthermore, the polymerization format applicable to the present invention can be effectively applied to aqueous suspension polymerization of the above monomers, aqueous emulsion polymerization, and so-called bulk polymerization containing only the above monomers without a polymerization medium under each of the usual polymerization conditions.

According to the method of the present invention, the effect of preventing polymer adhesion is much greater than that of conventional methods, and there are no adverse effects such as slowing down the polymerization rate or deteriorating various physical properties of the product.

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

Example Commercially available sodium alginate was dissolved in an aqueous solution of caustic soda, and 1% by weight of alginic acid, 2% by weight of caustic soda, and 97% by weight of water.
%wt% coating solution was prepared.

This coating liquid was sprayed onto the inner wall of a stainless steel polymerization tank having an internal volume of 7 m3.

After such treatment, deionized water 3000k
2000 g of vinyl chloride, 0.6 kg of t-butyl peroxypivalate, and 2 kg of partially saponified polyvinyl alcohol with a degree of saponification of 80 mol% were charged, and the pressure was 6.5 at 57°C.
The reaction was continued until kg/cm'G was reached.

After the reaction was completed, the unreacted vinyl chloride monomer was collected, and after the polymer slurry was discharged, the weight of the polymer adhering to the inner wall of the polymerization tank was determined.

The polymer slurry is obtained as a product by being dehydrated and dried, and as shown in Table 1, according to the method of the present invention, the amount of polymer adhesion is significantly small, and the adhering polymer can be easily washed away with simple water washing. did it.

The physical properties of the obtained product were also excellent. Comparative Example This example was the same as the example except that no alginic acid coating liquid was applied at all, but as shown in Table 1, there was an extremely large amount of polymer adhesion to the inner wall.

Claims (1)

[Claims] 1. When vinyl chloride is polymerized alone or together with monomers that can be copolymerized with it in an aqueous medium or in bulk, alginic acid or A method for monopolymerizing or copolymerizing vinyl chloride, which comprises applying a metal alginate.