JPH07206907A - Production of polyvinylchloride having low fish eye content - Google Patents

Abstract

PURPOSE:To obtain the subject polymer having less fish eye content, by an aqueous suspension polymerization of vinyl chloride or vinyl chloride and its comonomers in a polymerization vessel equipped with a reflux condenser having a heat exchanging tube and its supporting board, where water can be passed over their outer surfaces. CONSTITUTION:In a production of poly (vinyl chloride) by an aqueous suspension polymerization of monomeric vinyl chloride or a mixture of vinyl chloride and a monomer copolymerizable with vinyl chloride (e.g. ethylene, etc.) by using a polymerization vessel equipped with a reflux condenser directly connected to the vessel, having a heat exchanging tube and its supporting board, and during a period from a completion of the polymerization and an initiation of next monomer charge, where no refluxing is conducted, water is passed over the outer surfaces of the heat exchanging tube of the condenser and of the tube supporting board in a rate of 0.5-100l/min.m<2> per unit heat conducting surface area of the heat exchanging tube, 0.5-30l/min per one tube, and 200-2000l/min.m<2> per unit area of the supporting board to obtain the objective polymer of less fish eye content.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing polyvinyl chloride or a polyvinyl chloride copolymer having a low fisheye content by an aqueous suspension polymerization method using a polymerization machine provided with a direct coupling type reflux condenser. Regarding

[0002]

BACKGROUND OF THE INVENTION Polyvinyl chloride of the present invention means polyvinyl chloride or a polyvinyl chloride copolymer. Polyvinyl chloride is industrially polymerized mainly by the batch type aqueous suspension polymerization method, but the productivity is improved and the inner volume of the polymerization machine is 40%.
Along with the increase in size of m ³ or more, it is common practice to use a reflux condenser directly connected to a polymerization machine for the purpose of removing heat of polymerization. The reflux condenser directly connected to the polymerization machine usually has a heat exchange tube and a supporting plate for the tube. However, if an attempt is made to remove a part of the heat of polymerization using a reflux condenser, vinyl chloride polymer or vinyl chloride copolymer will accumulate or become polychlorinated on the heat exchange tube of the reflux condenser or the supporting plate of the tube. Vinyl scale may adhere and may block if it is too large. Further, even if the blockage did not occur, if the polymerization was carried out by using such a polymerization machine, the quality of the product, especially the fish eye characteristic was deteriorated, and continuous production of polyvinyl chloride was difficult. One of the causes of the accumulation of polyvinyl chloride or the adhesion of scale thereof is considered to be the effect of foaming of the suspension during the polymerization. As a method of suppressing the foaming, for example, Japanese Patent Publication No. 12963/1990 discloses a method of suppressing the foaming by raising the polymerization temperature at a polymerization conversion rate of 50% or more.

[0003]

However, the above-mentioned production method is a method of suppressing foaming by raising the polymerization temperature during the polymerization, and the obtained polyvinyl chloride is obtained by keeping the polymerization temperature constant. There is a problem that the distribution of the degree of polymerization becomes wider than that of vinyl chloride. Further, since the temperature of the reflux condenser also rises as the polymerization temperature rises, there is a problem that the scale easily adheres to the heat exchange tube and the fish eye characteristic is often deteriorated. Therefore, there has been a demand for a method capable of continuously producing polyvinyl chloride with good quality by using a polymerization machine having a reflux condenser. The present invention provides a manufacturing method for continuously producing polyvinyl chloride having good fish eye characteristics by a simple operation and using a polymerization machine provided with a direct coupling type reflux condenser.

[0004]

In the present invention, as a result of intensive studies to solve the above-mentioned problems, it was found that polyvinyl chloride remaining on the outer surface of the heat exchange tube of a reflux condenser is a problem. The present invention has been completed and the present invention has been completed. That is, the present invention is a method in which a vinyl chloride monomer, or a mixture with a monomer copolymerizable therewith, is subjected to aqueous suspension polymerization using a polymerization machine equipped with a direct coupling type reflux condenser to obtain polyvinyl chloride or polyvinyl chloride. In the method for producing a vinyl copolymer, the heat exchange tube of the condenser and the A method for polymerizing vinyl chloride, characterized in that water is passed through the outer surface of a tube support plate or the like. That is, not only will the deterioration of the fisheye characteristics of the product obtained by carrying out the subsequent polymerization with the polyvinyl chloride produced by the previous polymerization remaining in the reflux capacitor, but also that of polyvinyl chloride in the reflux capacitor. It has been found that it promotes the accumulation or adhesion of scale and reduces its heat removal capacity, and eventually causes clogging of the reflux condenser.

The polyvinyl chloride remaining in the reflux condenser can be roughly classified into a substance adhered as a powder and a substance adhered as a scale. If the next polymerization is carried out once even in the presence of the former, it becomes a substance causing fish eyes and is easily peeled off from the heat exchange tube. The polyvinyl chloride slurry mixed with the peeled off fisheye causative substance is recovered and dried to separate coarse products with a sieving machine, but the size of the fisheye causative substance has the same size as the product, I found it difficult to separate. The present inventor can sufficiently prevent generation of a fish eye-causing substance by passing water to the outer surface of the heat exchange tube of the reflux condenser after the completion of polymerization and before starting the charging of the next raw material for polymerization. And has reached the present invention. On the other hand, the substances attached as the latter scale can hardly be removed even if water is passed through the outer surface of the heat exchange tube. It was found that even if it peels off, it cannot be a causative substance of fish eyes because it is much larger than the product and separated by a sieving machine.

If the amount of water to be passed is too small, the effect is insufficient, and if it is too large, the amount of water used increases and it is not economical. Therefore, the following range is preferable. That is, the outer surface of the heat exchange tube of the reflux condenser has a heat transfer area of 0.
5 to 100 liters / min · m ² , 0.5 to 30 liters / min per tube, and 200 to 2000 liters / per unit area of the outer surface of the tube support plate
min · m ² , more preferably 1.
0 to 50 liters / min · m ² , 1.0 to 10 liters / min per tube, and 500 to 1000 liters / min · m per unit area of the tube support plate
^{Is 2} . The water flow may be such that water flows uniformly on the outer surfaces of the tubes and the tube support plate, and includes a mode in which water is sprinkled or irrigated. Examples of the method of passing water include, but are not particularly limited to, methods performed by a fixed spray nozzle, a slit type rinse valve, a rotary nozzle, or the like.

As the polymerization is approaching completion, the generation of reaction heat is reduced and the reflux is lowered, and the reflux is stopped when the polymerization is completed. When the reflux is reduced or stopped, the polyvinyl chloride attached in the powder state in the reflux condenser becomes a causative substance of fish eyes. Therefore, the time of passing water is generally the time when the reflux is reduced or stopped. More specifically, the time of passing water is between the completion of polymerization and the start of charging the raw materials for the next polymerization, but preferably immediately after the completion of polymerization, and more preferably immediately after the completion of polymerization. It is good to use the liquid (hereinafter referred to as slurry) while transferring the liquid from the polymerization machine to another tank in terms of water use efficiency. The water to be passed is not particularly limited, but the reuse of the wastewater generated when the obtained slurry is centrifuged is compared with the addition of new water in terms of water use efficiency and economic efficiency. Is preferable.

The method of the present invention can be used in the aqueous suspension polymerization method generally used in the art. That is, the ratio of vinyl chloride to water is generally 80 to 300 parts by weight of water with respect to 100 parts by weight of vinyl chloride, and the polymerization temperature is usually 35.
C to 75C. The vinyl chloride used in the present invention, or a monomer copolymerizable with vinyl chloride,
For example, ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1
Α-olefins having 2 to 12 carbon atoms such as nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, acrylic acid and its esters, methacrylic acid and its esters, Examples thereof include maleic acid and its esters, vinyl compounds such as vinyl acetate, vinyl propionate, and alkyl vinyl esters, and mixtures thereof.

The initiator used in the present invention is an initiator usually used in vinyl chloride suspension polymerization, for example,
Percarbonates such as diisopropyl peroxydicarbonate and dioctyl peroxydicarbonate, peresters such as tertiary butyl peroxyneodecanate and amyl peroxyneodecanate, diacyl peroxides such as lauroyl peroxide and diisobutyl peroxide. , 2,2'azobisisoptyronitrile, 2,2'azobis-2,4 dimethylvaleronitrile azo compounds, potassium persulfate, ammonium persulfate and other water-soluble peroxides such as water-soluble azo compounds These may be used alone or in combination to make the polymerization reaction rate uniform. The dispersant used in the present invention may be a known dispersant, for example, partially saponified polyvinyl alcohol, polyvinylpyrrolidone, cellulose derivative, vinyl acetate-maleic anhydride copolymer, maleic anhydride-styrene copolymer, gelatin. Etc.

[0010]

EXAMPLES The present invention will be described in detail below with reference to examples, but these examples do not limit the scope of the present invention. The tests and measurement methods of the polymers obtained in Examples and Comparative Examples were carried out by the following methods. (1) Fish eye: A polymer in which a predetermined amount of a plasticizer, a heat stabilizer and the like were mixed and kneaded at 145 ° C. for 5 minutes to give a thickness of 0.
Create a 3mm sheet. Then, visually, 10 cm
The number of seeds present in an area of × 10 cm is measured, and this is defined as the number of fish eyes. (2) Foreign matter: A foreign matter is an object which has a color distinctly different from the color of the obtained polymer and can be visually confirmed,
It is indicated by the number of foreign matters contained in 100 g of the polymer.

Example 1 A direct coupling type reflux condenser having a heat exchange tube, a support plate for the heat exchange tube and an auxiliary pipe, and a polymerization machine having an internal volume of 150 m ³ provided with a rotary nozzle on the upper side of the reflux condenser. Using. First, 50 tons of deionized water from a manhole in a polymerization machine, 640 kg of a 5% aqueous solution of partially saponified polyvinyl alcohol having a saponification degree of 80 mol% and an average degree of polymerization of about 2,000, and a saponification degree of 70 mol% and an average degree of polymerization of about 700. Partially saponified polyvinyl alcohol 5
% Aqueous solution 800 kg, 70% di-2-ethylhexyl peroxydicarbonate 12 kg, 70% cumyl peroxyneodecanoate 8 kg, the air inside is removed by a vacuum pump, and then 40 tons of vinyl chloride monomer is charged. did. The polymerization temperature was set to 52.4 ° C., the reaction was allowed to proceed, and when the internal pressure reached 6 kg / cm ² -G, the reaction was stopped and unreacted vinyl chloride was recovered. In addition,
The reaction time was 7.5 hours. Then, the polymer slurry was discharged. From the start to the end of discharge, a rotary nozzle at the upper part of the reflux condenser was used to heat the outer surface of the heat exchange tube of the reflux condenser at 10 liter / min · m ² , The flow rate per exchange tube is 1.5 liters / min, and 1000 liters / min · m ^{2 with} respect to the outer surface of the support plate of the heat exchange tube.
Water was passed. The discharged slurry was dehydrated with a decanter and then dried to obtain 34 tons of polyvinyl chloride. After the production of the first batch, the heat exchange tubes of the reflux condenser, the tube support plate, and the like were examined, but adhesion of polyvinyl chloride was not recognized. Also, 3 polyvinyl chloride fish eyes obtained in the first batch,
There were zero foreign matter. The same operation was performed twice a day, and the heat exchange tube and tube support plate of the reflux condenser after 6 months were examined, but adhesion of polyvinyl chloride and blockage of the tube were hardly observed. The amount of polymer adhering to the heat exchange tube and tube support plate of the reflux condenser is 0.1 g / unit heat transfer area.
m ^2, the 6 months after the obtained polyvinyl chloride fisheye 8, the foreign matter was zero.

Comparative Example 1 Vinyl chloride was polymerized in the same manner as in Example 1 except that water was not passed from the rotary nozzle above the reflux condenser to the reflux condenser from the beginning to the end of discharging the polymer slurry. . After the production of the first batch, the heat exchange tubes and the tube support plate of the reflux condenser were examined, and as a result, the amount of polyvinyl chloride deposited was 3 g / m ² per unit heat transfer area of the reflux condenser. The polyvinyl chloride obtained in the first batch had 3 fish eyes and 0 foreign matters. When the same reaction was continued twice a day, the heat exchange tube of the reflux condenser was clogged after 2 months. At the time of blockage, the amount of polymer attached to the heat exchange tube of the reflux condenser and the tube support plate was 300 g /
The polyvinyl chloride obtained after m ² and 2 months had 85 fish eyes and 6 foreign matters.

[0013]

According to the method of the present invention, it is possible to continuously produce polyvinyl chloride having a good fish eye characteristic for a long period of time without clogging or adhesion of the heat exchange tube of the reflux condenser directly connected to the polymerization machine. became.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiko Takahashi 1-6 Takasago, Takaishi-shi, Osaka Mitsui Toatsu Chemical Co., Ltd.

Claims (3)

[Claims] 1. A polymerization machine equipped with a reflux condenser of direct polymerization type, which comprises a vinyl chloride monomer or a mixture with a monomer copolymerizable therewith and which has a heat exchange tube and a supporting plate for the tube. In the method for producing polyvinyl chloride by aqueous suspension polymerization, the method of supplying water to the outer surface of the heat exchange tube of the condenser and the outer surface of the support plate of the tube in a period in which no reflux is performed. A method for producing polyvinyl chloride having a low content of fish eyes. 2. The period during which the reflux is not performed is
The method according to claim 1, which is a period from immediately after the completion of the polymerization to the start of charging the next raw material for the polymerization. 3. An amount of water to be passed is 0.5 to 100 liter / min · m ² per unit heat transfer area of the heat exchange tube,
0.5 to 30 liters / min per tube and 200 to 200 per unit area of the tube support plate
The method according to claim 1, which is 0 liter / min · m ² .