JPS588406B2 - Apparatus and method for polymerizing vinyl chloride monomers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vinyl chloride monomer alone or a mixture of vinyl chloride as a main component and a monomer that can be polymerized with it (hereinafter referred to as
This invention relates to a polymerization apparatus and a polymerization method for vinyl chloride monomers.

More specifically, part or all of the inner wall of the polymerization tank and/or the surface of the polymerization tank ancillary equipment that comes into contact with the monomer (hereinafter referred to as the inner wall of the polymerization tank, etc.) is covered with a ferrite phase whose surface has a mirror finish. By using duplex stainless steel (hereinafter referred to as duplex stainless steel) consisting of austenite and austenite phases, it completely or substantially prevents the formation of polymer deposits (so-called scale), and virtually prevents corrosion caused by chlorine ions, etc. The present invention relates to a polymerization apparatus and method for vinyl chloride monomers that are not accompanied by other substances.

In the production of vinyl chloride monomers on an industrial scale, glass-lined polymerization tanks or austenitic stainless steel polymerization tanks have conventionally been used as polymerization equipment.

However, glass-lined polymerization tanks have drawbacks such as the glass layer being damaged by weak mechanical shock or thermal shock, and the heat transfer coefficient which determines production capacity being low. The advantages of being excellent in chlorine ion corrosion resistance are offset.

On the other hand, although austenitic stainless steel polymerization tanks have the advantage of having a higher heat transfer coefficient than glass-lined polymerization tanks, they suffer from corrosion due to chlorine ions, etc. generated during polymerization.
It has the fatal disadvantage of being weak against pitting corrosion, resulting in a large amount of scale adhesion and strong scale adhesion.

The adhesion of scale to the inner wall of the polymerization tank is undesirable from the viewpoint of industrial production because it causes a decrease in production capacity due to a decrease in heat transfer ability, a decrease in the polymerization cycle efficiency required for scale removal, and an increase in scale removal costs.

In view of these circumstances, the inventors of the present invention conducted extensive research to find a method for completely or substantially preventing the formation of scale and preventing corrosion of the inner walls of the polymerization tank due to chlorine ions, etc., and finally discovered the present invention. The invention was completed.

That is, the present invention provides that part or all of the inner wall of the polymerization tank and/or the surface of the polymerization tank ancillary equipment that comes into contact with the monomer is made of dual-phase stainless steel consisting of a ferrite phase and an austenite phase with a mirror finish. A polymerization apparatus for vinyl chloride monomers characterized by the following structure, and a polymerization apparatus for polymerizing vinyl chloride monomers, and a monomer mainly composed of vinyl chloride monomers or copolymerizable with vinyl chloride monomers The present invention provides a method for polymerizing vinyl chloride monomers, which comprises radically polymerizing a mixture in an aqueous medium in the presence of a radical-generating catalyst.

The stainless steel used in the present invention is a two-phase stainless steel consisting of a ferrite phase and an austenite phase (also known as ferritic-austenitic stainless steel).

The chemical composition of this duplex stainless steel usually has a Cr content of 17
-30% by weight, and 2-8% by weight of Nia.

In addition to the above components, the duplex stainless steel used in the present invention contains Mo, Zr, Cu, W, etc. to improve corrosion resistance and/or stabilize the structure, and further to improve strength. A material containing N can also be used.

In addition to using the above-mentioned duplex stainless steel, the present invention also requires that its surface be mirror-finished.

"Mirror finish" in the present invention refers to Japanese Industrial Standards JT
The specular gloss measured according to Method 2 of the specular gloss measurement method specified in S-Z-8741-1962 (however, the value with the silver deposited mirror as the reference surface and the gloss as 100%) is 7.
It is preferably 0% or more.

That is, by giving the duplex stainless steel a mirror finish with a mirror gloss of 70% or more, the purpose of completely or substantially preventing scale formation can be achieved.

Mirror finishing methods include puff mechanical polishing of No. 400 or higher, followed by a mirror finish using an abrasive for stainless steel such as finishing blue rod, or after puff mechanical polishing of No. 300 or higher, further electrolysis. There is a method of polishing to obtain a mirror finish, and a method of performing puff mechanical polishing and electrolytic polishing at the same time to obtain a mirror finish.

However, 70% of the duplex stainless steel used in the present invention
The test piece, which had a mirror finish with the above specular gloss, showed no scale adhesion and excellent corrosion resistance.

This is due to the fact that even if regular austenitic stainless steel has a mirror finish, it will cause pitting corrosion due to chlorine ions, which will cause or even increase scale adhesion. This is thought to be because the corrosion resistance performance is not exhibited in the polymerization of vinyl chloride monomers.

On the other hand, the duplex stainless steel used in the present invention has significantly better stress corrosion cracking resistance than austenitic stainless steel under general usage conditions, but its pitting corrosion resistance and crevice corrosion resistance are the same. However, in experiments conducted by the present inventor, contrary to expectations, there was virtually no scale adhesion and excellent corrosion resistance was achieved.

This is due to the high mirror finish of duplex stainless steel, which forms a special dense and strong passive film on the surface of the stainless steel, which prevents scale adhesion and has better corrosion resistance than expected. It is imagined that this will be achieved.

Examples of the practical implementation of the present invention include a method in which all of the main structures of the polymerization tank are made of duplex stainless steel specified in the present invention, and a method in which the main structure is made of mild steel or high-strength steel and the inner wall etc. There are methods such as welding (strip lining) or explosion bonding of phase stainless steel, and methods of using so-called clad steel in which the stainless steel is bonded to the surface of mild steel etc. by explosion bonding or roll rolling. It is preferable to take the Sato Keizai surname into consideration and choose accordingly.

The method of the present invention is most effective in radical polymerization of vinyl chloride monomers in aqueous media, that is, suspension polymerization and emulsion polymerization.

However, similar effects can be expected in bulk polymerization and solution polymerization in which a small amount of water is added.

In the suspension polymerization method, oil-soluble catalysts and suspension stabilizers that are commonly used for suspension polymerization of vinyl chloride are used.

Such oil-injected catalysts include diacyl oxides such as lauroyl peroxide, alkyl peroxy esters such as t-butyl peroxy biparate, dialkyl peroxy dicarbonates such as diisopropyl peroxy dicarbonate, and acetyl peroxy dicarbonates. Oil-injected catalysts such as acetyl alkyl peroxides such as hexyl sulfonyl peroxide, ab-based catalysts such as azobis(2,4-dimethylvalenitrile), or mixtures thereof, but are not limited to these. It's not something you can do.

The catalyst can be used in an amount conventionally used in suspension polymerization of vinyl chloride, and is generally in an amount of 0.005 to
Used at 0.5% by weight.

Further, as suspension stabilizers, water-soluble synthetic polymers such as partially saponified polyvinyl alcohol, cellulose derivatives such as hydroxyproboxymethylcellulose, natural polymers such as gelatin, etc. are used.

In the emulsion polymerization method, water-soluble catalysts and emulsifiers that are commonly used for emulsion polymerization of vinyl chloride are used.

Examples of such aqueous injection catalysts include persulfates such as potassium persulfate, hydrogen peroxide, and redox systems in which these are combined with reducing agents.

Further, as the emulsifier, anionic surfactants such as alkali metal salts of alkyl sulfates such as sodium lauryl sulfate and alkali metal salts of alkylaryl sulfonates such as sodium dodecylbenzenesulfonate are used.

The polymerization reaction is generally carried out at a temperature of 40 to 80°C, and a chain transfer agent or a crosslinking agent may be added if necessary.

Monomers that can be copolymerized with vinyl chloride used in the present invention include, for example, ethylene, propylene, and α
Examples include -olefins, vinyl halides other than vinyl chloride, vinylidene halides such as vinylidene chloride, vinyl ethers such as methyl vinyl ether and lauryl vinyl ether, and vinyl esters such as vinyl acetate.

According to the method of the present invention detailed above, scale formation can be completely or substantially prevented.

As a result, the cleaning work of the inner walls of the polymerization tank after the completion of the polymerization reaction can be done by spraying low-pressure water (50 kg/cm2 or less), which is extremely easy, and its industrial significance is extremely significant. .

Table 1 lists the names and chemical compositions of commercially available duplex stainless steels suitable for carrying out the present invention.

For comparison, the table also lists the chemical components of common austenitic stainless steels commonly used in equipment for polymerizing vinyl chloride monomers.

The present invention will be explained in more detail below using actual cases, but the present invention is not limited thereto.

Example 1 A glass-lined polymerization tank for producing vinyl chloride polymers with an internal volume of 22 m3 was filled with materials and surface finishes shown in Table 2 in the bottom part of the tank (the part that is completely immersed in the reaction solution during the polymerization reaction). Test piece (shape: 100mm x 100
mm x 2 mm> was installed.

The chemical composition of the stainless steel used here is as shown in Table 1.

The polymerization tank contained 10,000 kg of deionized water and an average degree of polymerization of 8.
50 Polyvinyl alcohol 5.6k9 with saponification degree 75%
After adding 2.8 units of a heavy salt% toluene solution of 1 diisopropyl peroxydicarbonate and degassing the inside of the polymerization tank,
7,000 kg of vinyl chloride monomer was charged and 57 kg was added under stirring.
The polymerization reaction was carried out by raising the temperature to ℃.

The pressure inside the polymerization tank was 8.7 kg/cm2G at the start of polymerization, but when this decreased to 2k9/cm2 after 7 hours, polymerization was stopped, unreacted vinyl chloride monomer was collected, and the contents were taken out. Afterwards, the inside of the polymerization tank was washed with low pressure water of 15ky/cm2G.

These series of operations were repeated for an average of 12 hours per cycle, and 360 batches of polymerization reactions were carried out over a period of about 6 months.

Meanwhile, remove the test piece at the time shown in Table 1.
After evaluating the scale adhesion and corrosion status, it was reinstalled and the test continued.

From the results shown in Table 2, the material and surface condition of test piece No. 1 according to the present invention. 1~No. 4. Substantial build-up of scale (15k
There is no observable hard scale adhesion that cannot be removed by low-pressure water washing at g/cm2G, and the progress of corrosion is minimal.

On the other hand, even though the material is duplex stainless steel specified in the present invention, test piece No. 1 has a poor surface finish. 5 and no. 6, and test piece No. 6 whose material is stainless steel other than that specified in the present invention. 7~No. In No. 9, strong scale adhesion was observed and corrosion progressed rapidly, and it was found that the condition worsened as the test period became longer.

Example 2 A strip-shaped thin plate (0.5 mm thick) made of NAR-F (chemical composition shown in Table 1) was welded to the entire inner wall of a SUS316L polymerization tank with an internal volume of 100 liters, and the inner surface was mechanically polished. After finishing it sufficiently smooth, add 45% by weight of phosphoric acid,
Electrolytic polishing was performed using a bath containing 35% by weight of sulfuric acid and 3% by weight of chromic acid at 70° C. and a current density of 50 A/dm.

The average value of specular gloss at five representative locations on the interior wall is 80%.
It was confirmed that it had a high degree of mirror finish.

45 kg of deionized water, 30 g of polyvinyl alcohol with an average degree of polymerization of 850 and an average saponification degree of 75 mol%, and 12 g of a 50% by weight toluene solution of diisopropyl peroxydicarbonate were added to this 100 liter polymerization tank, and the inside of the polymerization tank was degassed. After that, vinyl chloride monomer 30k9 was charged, and the temperature was raised to 57° C. with stirring to carry out a polymerization reaction.

At the start of polymerization, the pressure inside the polymerization tank was 8.7 kg/cm2G, but when this decreased to 2k9/cm2 after 7 hours, polymerization was stopped, unreacted vinyl chloride monomer was collected, and the contents were taken out. Afterwards, the inside of the polymerization tank was washed with low pressure water of 15 kg/cm2G.

By washing with the low-pressure water, the polymer particles slightly adhering to the inner walls of the polymerization tank could be easily and completely removed.

These series of operations were repeated at an average cycle of 12 hours per cycle, and a total of 20 batches of polymerization reactions were carried out over 10 days. However, even after the completion of 20 cycles, no adhesion of polymer particles or scale was observed, and no surface corrosion was observed. A detailed observation of the situation revealed no pitting or other corrosion spots, and it was confirmed that a healthy surface condition was maintained.

Leprosy Example 3 After completing the series of suspension polymerization experiments shown in Leprosy Example 2, a polymerization experiment using emulsion polymerization was conducted using the same polymerization tank.

That is, 45 kg of deionized water, 24 g of potassium persulfate, and 80 g of sodium lauryl sulfate were added to the above 100 L polymerization tank, and after the inside of the polymerization tank was deaerated and replaced with nitrogen, 34 kg of vinyl chloride monomer was charged, and the temperature was heated to 53°C with stirring. The polymerization reaction was carried out by raising the temperature.

Polymerization was stopped when the pressure inside the polymerization tank decreased by 1 kg/cm2, and after recovering unreacted vinyl chloride monomer, the contents were taken out.

As a result, a vinyl chloride polymer latex with an average particle size of 0.4μ was obtained, and after the contents were taken out, the thin film-like scale that had adhered to the inner wall of the polymerization tank was reduced to 30kg/c.
It was possible to completely remove it by washing with low pressure water of m2G.

These series of operations were repeated at an average cycle of 12 hours per cycle, and a total of 20 batches of polymerization reaction were performed in 10 days, but even after the completion of 20 cycles, no significant scale accumulation was observed and the surface gloss state was maintained. .

In addition, detailed observation of the surface corrosion revealed that no corroded areas such as pitting corrosion or crevice corrosion were observed, and that a healthy surface condition was maintained.

Comparative Example 1 Suspension polymerization of vinyl chloride was carried out under the same conditions as in Example 1 using a polymerization tank made of SUS316L and having an internal volume of 100 liters (inner wall surface was finished with Puff No. 300, specular gloss 63%).

After the polymerization reaction was completed, the inner wall of the polymerization tank was cleaned by jetting water at 100 kg/cm2G, but the thin but firmly adhered scale on the inner wall could not be completely removed, and the remaining scale was removed by scraping. When I weighed it, it was 1
It was 60g.

Comparative Example 2 Using the same apparatus as that used in Comparative Example 1, emulsion polymerization of vinyl chloride was carried out under the same conditions as in Example 3.

After the polymerization reaction was completed, the inner wall of the polymerization tank was cleaned by jetting water at 100 kg/cm2G, but most of the thin but very firmly fixed scale on the inner wall could not be removed, and the remaining scale was removed by scraping. When one bottle was removed and weighed, it was 330 g.

Claims (1)

[Claims] 1. Part or all of the inner wall of the polymerization tank and/or the surface of the polymerization tank ancillary equipment that contacts the monomer is made of a ferrite phase and an austenite phase with a mirror finish. 2.
An apparatus for polymerizing vinyl chloride monomers, characterized in that it is constructed of phase stainless steel. 2 @ The degree of surface finish is determined by specular gloss (JISZ-874
1-1962, method 2, the vinyl chloride type according to claim 1, characterized in that the glossiness is 70% or more when expressed using a silver-deposited mirror as a reference surface and a gloss level of 100%). Equipment for polymerization of monomers. 3 A polymerization device in which part or all of the inner wall of the polymerization tank and/or the surface of the polymerization tank ancillary equipment that comes into contact with the monomer is made of two-phase stainless steel consisting of a ferrite phase and an austenite phase with a mirror finish. In the presence of a radical-generating catalyst, radical polymerization of vinyl chloride monomer alone or a mixture of vinyl chloride monomer and a monomer that can be copolymerized with vinyl chloride monomer is carried out in an aqueous medium in the presence of a radical-generating catalyst. Characteristic method for polymerizing vinyl chloride monomers.