JPS58196211A - Method for removing scale stuck to polymerization vessel - Google Patents

Abstract

PURPOSE:To remove easily scales stuck to a vessel, by discharging an aqueous medium and the formed polymer after the polymerization of vinyl chloride, and bringing methylene chloride containing a specific amount of a surfactant into contact with the inner surface of the vessel. CONSTITUTION:Vinyl chloride is polymerized in an aqueous medium, and the aqueous medium and the formed polymer are dischrged from the polymerization vessel. Methylene chloride containing 0.1-20wt% surfactant, e.g. polyoxyethylene alkyl ether phosphate, and 5wt% or less water is then brough into contact with the inner surface of the vessel by spraying, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing nine-snars adhering to a polymerization vessel.

Vinyl chloride polymers are often produced by mixing vinyl chloride monomers alone or with other monomers and polymerizing them in an aqueous medium. In this pigeon house, an aqueous medium is first placed in a polymerization container, then vinyl chloride monomer is added to the aqueous medium, and a polymerization catalyst is added. It is dispersed in an aqueous medium and polymerized to obtain a vinyl chloride polymer.

When polymerizing vinyl chloride monomers in this way, when the produced vinyl chloride electropolymer is discharged from the polymerization vessel together with the aqueous medium, an electropolymer-like substance called scale often adheres to the inner surface of the vessel. are doing. If scale adheres, not only will the polymerization yield decrease, but the scale will also impede the conduction of heat from the container, making it difficult to control the temperature inside the polymerization container, making it impossible for the polymerization reaction to proceed as desired. It disappears. Additionally, scale sometimes flakes off from the inner surface of the container and becomes incorporated into the product polymer. If scale is mixed into the product, it will cause fish eyes and reduce the quality of the processed product.The adhesion of scale brings such disadvantages, so it is necessary to prevent scale from adhering as much as possible during polymerization. was there.

It has been proposed to coat the inner surface of the polymerization vessel with a specific compound in order to prevent scale from adhering.

Applying a specific compound will certainly reduce the amount of scale deposited. However, it was not possible to reduce scale adhesion as much as desired. Furthermore, if even a small amount of scale adheres to the inner surface of the container, it tends to accumulate in a particularly bulky manner on the inner surface of the container. In addition, scale has the property that when there is a scratch on the inner surface of a container, it tends to form at the scratched area. Therefore, after polymerization, it was necessary to completely remove the scale so as not to damage the polymerization container.

Several methods have been proposed so far for this purpose. One method is to have a person enter the polymerization container and manually scrape off the scale using a tool such as a scraper. Another method is to spray high-pressure water toward the inner surface of the container to remove scale using a stream of water. Another method is to dissolve the scale using an organic solvent.

However, all of these methods have advantages and disadvantages and are not satisfactory. In other words, the manual method tends to damage the inner surface of the container and, on the contrary, promotes the formation of scale.

Depending on the method using high aqua regia, scale tends to remain in some places and it is difficult to completely remove the scale, so instead the scale is deposited.

Depending on the method using a solvent, a thin film of [1iK polymers and coalesces] may be easily formed in the container, which may induce the formation of K and scale.

Among the methods using organic solvents, there is a method in which the organic solvent is mixed with heather and a surfactant.

This is described in the Japanese Patent Publication Shoda 2/RIG. In this method, it is necessary to fill a polymerization vessel with an organic solvent containing water and a surfactant, and to stir the mixture. Therefore, a large amount of organic solvent is required, which is uneconomical, and the dissolving power of the organic solvent is reduced by water.
Therefore, there was a drawback that it took time to remove the scale.

The inventors at Jin attempted to remove scale using a number of organic solvents. As a result, it was found that among solvents, methylene chloride has a great ability to moisten scale with Wl. In addition, using a solution obtained by dissolving methylene chloride in a substantially anhydrous state and dissolving polyoxyethylene alkyl ether 7-m-7 ate, which is a surfactant, a solution of nitrate was polymerized to remove scale. I tried to spray it into the container and clean it. As a result, it has been found that scale can be easily removed, and a thin film of polymer is not formed on the inner surface of the container, so that excessive scale can be prevented from forming during subsequent polymerization. This issue #4#-i was born based on such knowledge.

At this point, vinyl chloride is polymerized in an aqueous medium, and after discharging the aqueous medium and the produced polymer from the polymerization vessel, 0. This relates to a method for removing scale attached to a container WK, which is characterized by contacting the inner surface of a container with methylene chloride containing a surfactant of / or Q'IJiI% and a water content of 5 times ≦ or less. be.

In the method invented by Jin, methylene quaride is used as the organic solvent to be brought into contact with the polymerization capacity K. For scale removal, as mentioned above, Patent Publication No. 1/2/I/Z proposes the use of a chlorinated hydrocarbon mixed with water and a surfactant. Methylene chloride is not exemplified as the chlorinated hydrocarbon in that case. In that publication, trichlorethylene, dichloroethane, carbon tetrachloride,
Dichloropropane, trichloropropane, /, /, /-
Only compounds with high boiling points and relatively large molecular weights, such as trichloroethane, are listed. Therefore, it was not known that methylene chloride is particularly suitable for removing scale. In the method of this invention, methylene chloride, which is under such circumstances, is used in particular. 1,1 Methylene chloride, also called dichloroethane, is a liquid with a boiling point of about 0°C and is used as a general Ks agent. However, methylene acrylide is not named as a solvent for removing scale as mentioned above. The inventor has found that methylene chloride is superior to other chlorinated hydrocarbons in its ability to swell scale, and has confirmed that it is particularly effective for removing scale. Therefore, this invention decided to use only methylene chloride.

Methylene chloride is compatible with a small amount of water, but if water coexists, the ability to swell scale will be poor, so it is better not to coexist with water.

The coexistence of water is allowed to be less than 1% relative to methylene chloride. Among these, the water content is preferably 2% by weight or less, more preferably 11% by weight or less. In the method of this invention, a surfactant is used together with methylene chloride. The surfactant used is one that essentially dissolves in methylene chloride. The surfactant is, for example, polyethylene glycol alkyl ether, polyethylene glycol alkyl phenyl ether, polyethylene glycol alkyl amine ether, polyethylene glycol alkyl ether 7-mole 7-ate, polyethylene glycol alkyl allyl 7-m 7-E F1 dialkyl sulfosuccinic acid. etc. All of these dissolve in methylene chloride at 20°C by more than O1/electromechanical equipment.

If the solubility of the surfactant in methylene chloride is low, even if a large amount of surfactant is used, the surfactant will remain in the methylene chloride as a solid or in the form of surfactant droplets, thus making the surface active. The effect of the agent will not be fully demonstrated.

Therefore, as the surfactant, one having the highest possible solubility in methylene acrylide is selected and used.

The amount of surfactant used is O
/ or coO amount of electricity%. Among these, preferred is Fio, j to /j weight lII%.

Generally, when the amount of surfactant used is small, a polymer film tends to form on the inner surface of the container. Therefore, in order to prevent the formation of this film, it is necessary to use a surfactant with a weight ratio of KSO or higher. Even if 20% by weight or more of surfactant is used, there is no difference in the effect from using CoQ weight.
, PVA and become a residue, which is discarded, which is economically disadvantageous. Therefore, the maximum amount of surfactant is limited as described above.

In the method of this invention, there are no particular limitations regarding the temperature at which methylene chloride is brought into contact with the inner surface of the polymerization vessel. Although there is no problem as long as the temperature is above room temperature, it is preferably within the range of Fi Mig to 20°C.

Among these, high temperatures are desirable because they facilitate the removal of scale. However, since methylene chloride has a boiling point of about 910°C, if the temperature is too high, a high pressure is required to keep it in a liquid state, which is undesirable in terms of excessive iA heat.

To bring methylene chloride into contact with the inner surface of the polymerization vessel, methylene chloride may be collected in the vessel and stirred, but this requires a large amount of methylene chloride and is not advantageous. A preferred contact method is to insert a nozzle into the container and spray methylene chloride in liquid form from the nozzle, and the sprayed methylene chloride becomes a thin film that flows down along the inner surface of the container and washes away the inner surface. It's a method.

To inject methylene chloride, attach a fine injection nozzle to the upper part of the polymerization container in advance, and make sure that methylene chloride can be injected from this nozzle toward the inner surface of the container and the stirrer inside the container. This is desirable.

The time period for which methylene chloride is brought into contact with the inner surface of the container varies depending on the amount of scale attached, the properties of the inner surface of the polymerization container, the material constituting the polymer, etc., but is usually within the range of 3θ to 270 minutes.

When bringing methylene chloride into contact with the inner surface of the polymerization container, prepare a solvent container to contain the methylene chloride separately from the polymerization container, store methylene chloride containing a surfactant in the solvent container, and complete the polymerization reaction. It is preferred that methylene chloride is subsequently allowed to flow into the polymerization vessel from the S-mesh vessel.

Also, prepare two solvent containers, and when recovering methylene chloride from the polymerization container, put methylene chloride containing a large amount of scale into one solvent container, and put methylene chloride containing a small amount of scale into another solvent container. It is preferable to change the storage container depending on the scale content. In this way, methylene chloride can be easily recovered and reused.

According to the method of this invention, the solvent that comes into contact with the inner surface of the polymerization vessel is methylene chloride, which has a high rate of swelling the scale, and also contains a surfactant.
The rate at which the scale swells is even higher, and therefore the scale attached to the inner surface of the container can be easily and reliably removed. Since there is no water or only a small amount of water exists, the swelling ability of methylene chloride is not reduced, and scale can be easily and reliably removed. Therefore, the time required to clean the polymerization container can be shortened, and subsequent scale adhesion can be reduced. Thus, according to the method of this invention, a high quality vinyl chloride polymer can be efficiently produced.

In this respect, the method of this invention is highly effective.

Next, the details of the method of this invention will be explained with reference to Examples and Comparative Examples, and the superiority of this method will be clarified.

Example / Put a stainless steel container eK with an internal volume of 10 /, 2 kg of M water, 102 parts of polyvinyl acetate, and 2 pieces of lauroyl peroxide, reduce the pressure inside the container, and reduce the pressure at 3θ''C. ■ After culling, K j j, j in the container
Vinyl chloride monomer Kf and ethylene monomer J, J' Kf were charged. Thereafter, polymerization was carried out at Jj'C for 2 hours. The vinyl chloride polymer produced by polymerization was taken out, and the inside of the polymerization container was washed with water.

Then, the same polymerization reaction was further repeated five times in total. Thereafter, the vinyl chloride polymer was taken out from the polymerization container, and the inside of the container was washed with water. At this time, a large amount of thick and hard scale was attached to the inner surface of the container. Therefore, in order to remove this scale, methylene chloride was injected toward the inner surface of the polymerization vessel while circulating methylene chloride containing a surfactant.

Methylene chloride containing a surfactant was prepared in advance in a solvent container prepared separately from the polymerization container. For the preparation, methylene chloride daKf and polyoxyethylene alkyl ether 7m, 7m) were used, and these were placed in a solvent container and stirred thoroughly to form a solution.

After the polymerization volume W is heated to a temperature of 5/ko''CK through a jacket attached to the polymerization vessel, the solution is supplied to the inner surface of the polymerization vessel from a wide-angle injection nozzle attached to the upper part of the polymerization vessel. KSJ under a discharge pressure of j Kg / tyi G, with a circulating volume of 750
It was sprayed cyclically for minutes. Thereafter, collect as much of the methylene chloride solution as possible from the polymerization container into the original solvent container.

Almost all of the scale had been removed. I found that some traces of l'i polymer remained on the inner surface of the polymerization container. The amount of scale removed at this time was Fi/Coco OP, and the amount of methylene chloride solution recovered was #i, IKfI. Next, the inside of the polymerization container! Washed with jKt/ala pressurized water. As a result, the wall surface was clean and free of any Snarl-tun polymer film. The amount of scale and electric composite film removed at this time was I/i/koθe.

Comparative Example/ This comparative example was carried out using less surfactant than the specified amount.

That is, in Example/, except that the amount of polyoxyethylene alkyl ether 7-mole 7-ate used was t2θ2 (0.05% by weight relative to methylene chloride),
It was carried out in exactly the same manner as in Example.

In the scale removal process, scale i! is removed by contact with surfactant-containing methylene chloride.
#, is QF, υl is recovered methylene chloride solution is JK9, and in this point Fi Example/
Almost the same results were obtained. However, although the inner surface of the polymerization vessel was subsequently washed with pressurized water of 1,000 kg/cwt a, some scale still remained on the inner surface in some places, and although the polymer film was partially removed, It remained in some places. The amount of scale and film removed at this time was da θ2.

Comparative Example In this comparative example, a surfactant that is not soluble in methylene chloride was used.

Example 1 was carried out in exactly the same manner as in Example 1, except that sodium stearate was used instead of the surfactant polyoxyethylene alkyl ether 7-mole 7-ate.

Sodium stearate did not dissolve in methylene chloride and was suspended in solid form.

During the scale removal process, when the surfactant-containing methylene chloride comes into contact with K, the amount of scale removed is /joy, and the recovered methylene chloride solution is Vj, 0 kg, and Fi is carried out at this point. Similar results were obtained for Example/ and #. However, the inner surface of the polymerization vessel was subsequently washed with pressurized water of 2 j Kg/da, but
Parts of the scale remained here and there on the inner surface, and on top of that, the polymer film remained on the entire inner surface. The amount of scale and polymer film removed at this time was 33y.

Comparative Example J In exactly the same manner as in Example, the polymerization reaction was carried out five times in succession, and a thick scale was deposited on the inner surface of the polymerization container.

Thereafter, the substitution of methylene chloride and polyoxyethylene alkyl ether in Examples/1) K, Special Publication I
! Example 2 except that a solution consisting of 20 KF of trichlorethylene, water, 20 KF, and polyvinyl alcohol da 2 recommended in Publication No. 2-/R-G was injected.
The scale was removed in exactly the same way. However, at this time, if the trichlorethylene and water were allowed to stand still, the mixture would separate into two phases, so the injection was carried out with thorough stirring.

The amount of scale removed by contact with trichlorethylene or the like was /jO. Subsequently, the inner surface of the polymerization vessel was washed with pressurized water at 2 j Kg/dia.

At this time, a large amount of scale still remained, and when this was scraped off, a school of jlof was obtained.

Comparative Example The polymerization reaction was carried out j times in a row in exactly the same manner as in Example 2, and a thick scale was deposited on the inner surface of the polymerization container.

Thereafter, in place of methylene chloride and dioxyethylene alkyl ether in Example/, silylchlorethylene I recommended in Japanese Patent Publication No.
Using a solution consisting of J' j Kt, water J' j Kf, and polyvinyl alcohol/l, ty, this solution was filled into a polymerization container and stirred to remove scale. Specifically, the temperature of the jacket of the polymerization container was raised by jθ”CK to 11
After stirring for 0 minutes, the solution was drained. At this time, the scale removed is the glue 102, and the inner surface F of the polymerization container
There were scales scattered here and there.

From the comparison between the above Examples and Comparative Example/Seishida, a methylene chloride solution containing 0.7% by weight or more of a surfactant soluble in methylene chloride is sprayed onto the scale and brought into contact with it, and then the scale is Approximately ko θ or j OK
It can be seen that when washed with pressurized water of f/cdck, the polymer film as well as the scale can be easily removed. On the other hand, it can be seen that scale cannot be removed so easily using conventional methods.

Example Using the polymerization vessel used in Example, the nine-electrode reaction carried out in Example was repeated j times. Thereafter, the polymer was taken out from the polymerization container and the inside of the container was washed with water. At this time, a large amount of thick and hard scale was attached to the inner surface of the container.

Therefore, a methylene chloride solution containing one surfactant was used to remove the scale, but in this example, two types of methylene chloride solutions were used. First Mononoke, methylene chloride/7. <KfK Polyoxyethylene Alkyl Ether 7 Male 7 Eto DaK
t (21.2 g&) for methylene chloride
and further contains 3 weights of scale. The second one contains scale and is of great quality, methylene chloride/! ? 0KtK polyoxyethylene alkyl ether 7 phosphate o, yb<0.3% by weight relative to methylene chloride) was dissolved.

First, the above-mentioned first product was put into the polymerization container, and then the second product was put therein. Specifically, the first methylene chloride solution was charged into the polymerization volume ax, and the temperature of the reaction volume was raised to 60°C using a jacket attached to the container, and the mixture was stirred for 40 minutes to bring the methylene chloride solution into contact with the scale. . The methylene chloride solution was then drained from the polymerization vessel and collected in another storage tank KN. Although most of the scale had been removed, a polymer film had been formed on the inner surface of the container. At this time, the amount of scale removed was Fi/j10f. 30″ jacket
While maintaining CK, the second methylene chloride solution was subsequently charged into the polymerization container and stirred for jO minutes. The second methylene chloride solution was then drained from the polymerization vessel and collected into yet another storage tank. Then,
The inner surface of the polymerization vessel was free of scale and polymer film. The scale and polymer film removed at this time weighed 2 oy.

Based on this result, we first filled a polymerization vessel with scale with a methylene chloride solution containing a surfactant (which may contain some impurities) and stirred it. It can be seen that by filling the tube with a methylene chloride solution and stirring it, the scale can be completely removed and a clean inner surface without an electrolyte film can be obtained.

Claims (1)

[Claims] / After polymerizing vinyl chloride in an aqueous medium and discharging the aqueous medium and the produced electrified vinyl polymer from the polymerization container, 0. A method for removing scale attached to a polymerization container, the method comprising: bringing into contact with the inner surface of the container methylene chloride containing a surfactant with a weight of / or θ and a water content of less than a weight of J. The method according to claim 1, wherein the methylene chloride is injected toward the inner surface of the container and allowed to flow down along the inner surface. 3. Divide the above methylene chloride into a polymerization container, add the first methylene chloride, bring them into contact by stirring, discharge the methylene chloride, and then add particularly clean methylene as the next methylene chloride. A method according to claim 1, wherein the chloride is introduced and brought into contact by stirring.