JPS5814447B2 - 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 vinyl chloride (hereinafter simply referred to as polymerization), the inner walls of the polymerization tank, backflow condenser, stirring blades, baffle plates, and various attached piping connections, etc., are damaged during the polymerization operation. 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 the monomer, or the polymer that has once adhered and peeled off may be mixed into the vinyl chloride homopolymer or copolymer (hereinafter referred to as the product). Problems arise such as contamination and deterioration of product quality.

Therefore, it is customary to clean the interior 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.

Many methods have been proposed to prevent 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, starch or starch derivatives are applied in advance to the inner walls of the polymerization tank and other parts of the polymerization equipment and polymerization accessory equipment that come into contact with the monomer during the polymerization operation. We discovered that polymer adhesion can be greatly reduced if the polymer is left in place, and that even a small amount of adhering polymer can be easily removed by washing with water, and that there are no negative effects such as slowing down the polymerization reaction or deteriorating the physical properties of the product. invention has been achieved.

Starch as used in the present invention is a natural polymeric substance that is abundantly contained in plants, and corresponds to most of seeds, roots, underground stems, etc. in the mature stage.

It has an average molecular weight of 100,000 to 300,000, and its structure is a mixture of long-chain amylose and side-chain amylopectin, and is a polysaccharide with D-glucose as a unit.

The starch derivative referred to in the present invention is a derivative having the above-mentioned starch as a skeleton, and examples thereof include sodium starch phosphate, sodium starch glycolate, and carboxymethyl starch.

In carrying out the present invention, starch or starch derivatives (hereinafter collectively referred to as starches) 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 starch or starch derivatives can be dissolved, such as water or an alkaline aqueous solution, may be used.

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

It is not clear whether coating the starches of the present invention on the inner wall of a vinyl chloride polymerization tank will prevent accidental polymer adhesion, but it is likely that polar groups such as 10H groups that starches have It is thought that this is because it acts as a hydrophilic group and makes 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 of polymerization tanks and the like normally exhibit considerable water repellency, walls treated with the present invention have excellent wettability with water and exhibit hydrophilic properties. Ru.

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 containing dissolved starches is applied to the inner wall of the polymerization tank, etc., and the concentration of starch in the solution can range from 0.01 to 20% by weight. , preferably in the range of 0.05 to 5% by weight, which is convenient for coating operations.

In the present invention, application does not refer to the mode of work, but rather means that the starch is present on the vessel wall as a result, 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 0.05 to 10 g/m2.

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.

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

Furthermore, the present invention can be effectively applied to aqueous suspension polymerization of the above monomers, aqueous emulsion polymerization, and so-called bulk polymerization, in which only the above monomers are used without a polymerization medium, under 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 starch phosphate was dissolved in an aqueous solution of caustic soda, and sodium starch phosphate 1
A coating solution containing 2% by weight of caustic soda and 97% by weight of water was prepared.

This coating solution was sprayed onto the inner wall of a stainless steel polymerization tank having an internal volume of 7 m8.

After such treatment, 3,000 kg of deionized water, 2,000 kg of vinyl chloride, 0.6 kg of t-butyl peroxypivalate, and 2~2 of partially saponified polyvinyl alcohol with a degree of saponification of 80 mol% were charged and heated at 57°C under pressure. The reaction was continued until it reached 5 Ky/iG.

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. Ta.

The physical properties of the resulting product were also excellent.

Comparative Example: This is an example similar to the example except that no starch 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 a monomer that can be copolymerized with vinyl chloride in an aqueous medium or in bulk, starch or A method for monopolymerizing or copolymerizing vinyl chloride, which comprises applying a starch derivative.