JPS588405B2 - Equipment and method for polymerizing vinyl chloride monomers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a polymerization apparatus for a vinyl chloride monomer alone or a mixture of vinyl chloride as a main component and a monomer copolymerizable therewith (hereinafter referred to as a vinyl chloride monomer); Regarding polymerization methods.

Furthermore, in detail, 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 made of ferrite stainless steel with a mirror finish. An apparatus and method for polymerizing vinyl chloride monomers that completely or substantially prevents the formation of polymer deposits (so-called scale) by being constructed of steel and is substantially free from corrosion by chlorine ions, etc. Regarding.

In the production of vinyl chloride polymers on an industrial scale, glass-lined polymerization tanks or austenitic stainless steel (Cr--Ni 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 or thermal shocks, and a low heat transfer coefficient that determines production capacity. The advantage of superior ionic corrosion resistance is offset by this.

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 are susceptible to corrosion and pitting caused by chlorine ions, etc. generated during polymerization, and as a result, the amount of attached scale is large. It also has the fatal disadvantage of 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, in the present invention, a 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 mirror-finished and has a Cr content of 15 to 40% by weight.
, MO content is 0.5 to 5% by weight, Ni content is 0.5% by weight or less, C content is 0.05% by weight or less, and N content is 0.5% by weight.
A system for polymerizing vinyl chloride monomers, characterized in that it is composed of 0.05% by weight or less of ferritic stainless steel, and using this polymerization system, it is possible to polymerize vinyl chloride monomers alone or with vinyl chloride monomers as a main component. Provided is a method for polymerizing vinyl chloride monomers, which comprises radically polymerizing a mixture with a copolymerizable monomer in an aqueous medium in the presence of a radical generating catalyst.

In the ferritic stainless steel used in the present invention, the Cr content is 15 to 40% by weight, preferably 17 to 40% by weight.
It is 35% by weight.

Materials with a Cr content of less than 15% by weight have poor chloride ion corrosion resistance and cannot be put into practical use, while materials with a Cr content of more than 40% by weight are undesirable because they become too expensive.

The Mo content is 0.5 to 5% by weight, preferably 1 to 3% by weight.

If the Mo content is less than 0.5% by weight, the effect of improving corrosion resistance due to interaction with Cr will be insufficient;
Even if the weight percentage is exceeded, the effect of improving corrosion resistance is not as remarkable as compared to the increase in material prices.

The Ni content is 0.5% by weight or less, preferably 0.3% by weight or less.

If it exceeds 0.5% by weight, the stress corrosion cracking resistance is significantly reduced, which is not preferable.

The contents of C and N are each 0.05% by weight or less, preferably 0.02% by weight or less each.

When the content of C and N exceeds 0.05% by weight, corrosion resistance
It is not preferred because the workability and weldability are significantly inferior.

Of course, in addition to the above components, other elements may be included in an amount of several percent or less.

For example, a few percent of titanium, niobium, zirconium, etc., which are normally added to ferrite stainless steel as stabilizing elements, are added.
There is no restriction in any way to include the following amounts.

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

The "mirror finish" used in the present invention refers to the specular gloss measured according to Method 2 of the specular gloss measurement method specified in the Japanese Industrial Standard JISZ-8741-1962 (however, a silver-deposited mirror is not used). Use as reference surface, gloss level 100%
value) is preferably 70% or more.

Ferrite stainless steel with the above composition has a specular gloss of 70%.
As described above, the objective of completely or substantially preventing scale formation can only be achieved by achieving a mirror finish of preferably 75% or more.

Methods for mirror finishing 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, and electrolytic polishing after puff mechanical polishing of No. 300 or higher. There are two methods: a method of performing polishing to obtain a mirror finish, and a method of performing electrolytic polishing at the same time as puff mechanical polishing to obtain a mirror finish.

However, the test pieces in which the ferrite stainless steel used in the present invention was made into a mirror finish with a mirror gloss of 70% or more showed no scale adhesion and excellent corrosion resistance.

This is due to the fact that even if austenitic stainless steel is mirror-finished, it will suffer pitting corrosion due to chlorine ions, which will cause or even increase scale adhesion, and the general corrosion resistance of austenitic stainless steel. This is presumably because this ability is not exhibited in the polymerization of vinyl chloride monomers.

On the other hand, the ferritic stainless steel used in the present invention has significantly better stress corrosion cracking resistance than austenitic stainless steel under general usage conditions, but is inferior in pitting corrosion resistance and crevice corrosion resistance. has been considered.

However, in experiments conducted by the present inventor, contrary to expectations, there was virtually no scale adhesion, and the results showed excellent corrosion resistance.

By giving the ferrite stainless steel a highly mirror-finished surface, a special, dense and strong passive film is formed on the surface of the stainless steel, which prevents scale adhesion and exhibits better corrosion resistance than expected. It is imagined that it will be done.

A practical embodiment of the present invention includes a method in which all of the main structures of the polymerization tank are made of ferrite 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 walls etc. are made of ferrite stainless steel. There are methods such as welding and pasting steel (strip lining) or explosion bonding, and methods of using so-called clad steel, which is made by bonding the stainless steel to the surface of mild steel etc. by explosion bonding or roll rolling. It is preferable to select the appropriate size in consideration of size and economical efficiency.

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-soluble catalysts include diacyl oxides such as lauroyl peroxide, alkyl peroxy esters such as 1-butyl peroxypiparate, diakyl peroxy dicarbonates such as diisopropyl peroxy dicarbonate, Oil-injected catalysts such as acetyl alkyl peroxides such as acetyl hexyl sulfonyl peroxide, azo catalysts such as azobis(2,4-dimethyl nitrile), 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 hydroxypropoxymethyl cellulose, 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 water-soluble 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.

This makes it very easy to clean the inner walls of the polymerization tank after the completion of the polymerization reaction by rinsing them off with a jet of low-pressure water (50 kg/cm2 or less), and its industrial significance is extremely significant.

Actual winding example 1 The material and surface finish shown in Table 1 were placed in the bottom part (the part completely immersed in the reaction solution during the polymerization reaction) of a glass-lined polymerization tank for producing vinyl chloride polymers with an internal volume of 22 m3. test piece (shape: 100mm x 100x
m x 2 mm) was attached.

The chemical composition of the stainless steel used here is shown in Table 2.

The polymerization tank contained 10,000 kg of deionized water and an average degree of polymerization of 8.
50, polyvinyl alcohol with saponification degree of 75%5. 6
kg, 5 of diisopropyl peroxydicarbonate
After adding 2.8 kg of 0% by weight toluene solution and deaerating the inside of the polymerization tank, 7.000 kg of vinyl chloride monomer was charged.
A polymerization reaction was carried out by raising the temperature to 57° C. while stirring.

The pressure inside the polymerization tank at the start of polymerization was 8. 7 kg/cm2G, but when this decreased to 2kg/cm2 after 7 hours, the polymerization was stopped and unreacted vinyl chloride monomer was collected.
After taking out the contents, the inside of the polymerization tank was washed with low pressure water of 15 kg/cm2e.

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 1, test piece No. 1 of the material and surface condition obtained by the method of the present invention. 1~No. 6. Substantial build-up of scale (1
No hard scale adhesion that could not be removed by low-pressure water cleaning at 5ky/cm2G was observed, and corrosion progress was minimal.

On the other hand, even if the material is the specific ferrite stainless steel specified in the present invention, test piece No. 1 has a poor surface finish. 7~No. 9, and test piece No. 9 whose material is stainless steel other than that specified in the present invention. 10~N
o. In No. 13, strong scale adhesion was observed and corrosion progressed rapidly, and the condition worsened as the test period became longer.

Actual winding example 2 A thin rectangular plate (0.5 mm thick) made of YUS190 (chemical composition shown in Table 2) was welded to the entire inner wall of a polymerization tank made of SUS316L with an internal volume of 100 liters, and the inner surface was mechanically polished. After making it smooth enough, 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 an electrolyte density of 50 A/dm 2 .

The average value of specular gloss at five representative locations on the interior wall is 81%.
It was confirmed that it had a high degree of mirror finish.

To this 100 liter polymerization tank, 45 g of deionized water, 80 g of polyvinyl alcohol with an average degree of polymerization of 850 and an average degree of saponification of 75 mol%, and 12 g of a 50% by weight solution of diisopropyl peroxydicarbonate in toluene were added, and the inside of the polymerization tank was cooled. After degassing, add 80 kg of vinyl chloride monomer and stir for 5 minutes.
The polymerization reaction was carried out by raising the temperature to 7°C.

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 15ky/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 for an average of 12 hours per cycle, and a total of 20 batches of polymerization reaction were performed in 10 days. However, even after the completion of 20 cycles, no polymer particles or scale adhesion 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 Persimmon Example 2, a polymerization experiment was conducted using emulsion polymerization using the same polymerization tank.

That is, 45k9 of deionized water, 24g of potassium persulfate, and 80g of sodium lauryl sulfate were added to the above 100L polymerization tank, and after the inside of the polymerization tank was deaerated and replaced with nitrogen, 34kg of vinyl chloride monomer was charged, and the temperature was raised to 53°C while stirring. The polymerization reaction was carried out at warm 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 every week for an average 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 Emulsion polymerization of vinyl ferrite was carried out using the same apparatus as that used in Comparative Example 1 and 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 the thin but very firmly adhered scale on the inner wall could hardly be removed, and the remaining scale was removed by scraping. When it was weighed, it was 380 g.

Claims (1)

[Scope of Claims] 1 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 mirror-finished with a Cr content of 15 to 40% by weight, Mo It is characterized by being made of ferrite stainless steel having a Ni content of 0.5 to 5% by weight, a Ni content of 0.5% by weight or less, a C content of 0.05% by weight or less, and a N content of 0.05% by weight or less. Equipment for polymerizing vinyl chloride monomers. 2 Cra amount is 17 to 3 as ferrite stainless steel
5% by weight, MO content 1-3% by weight, Ni content 0.3
% by weight or less, a C content of 0.02% by weight or less, and a N content of 0.02% by weight or less. equipment for polymerization. 3 The degree of mirror finish is measured by specular gloss (JISZ-874
1-1962, method 2, using a silver vapor-deposited mirror as a reference surface and a gloss level of 400%), the glossiness is 75% or more. Equipment for polymerizing vinyl chloride monomers. 4 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 has a mirror finish with a Cr content of 15 to 40% by weight and an MO content of 0.
．． Using a polymerization apparatus made of ferrite stainless steel with a Ni content of 0.5% by weight or less, a C content of 0.05% by weight or less, and a N content of 0.05% by weight or less, A vinyl chloride monomer characterized by radical polymerization of a monomer alone or a mixture of a vinyl chloride monomer as a main component and a monomer copolymerizable with the monomer in an aqueous medium in the presence of a radical generating catalyst. Body polymerization method.