JP2000198806A - Production of vinyl chloride polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject vinyl chloride polymer of lowered water content in the polymer cake after the dehydration of the polymer slurry with saved production cost by undergoing the suspension polymerization step, the unreacting monomer-stripping step and the dehydration step. SOLUTION: This vinyl chloride polymerization process comprises (A) the step wherein vinyl chloride or a mixture thereof with other monomers is suspension-polymerized in an aqueous medium, (B) the step wherein the unreacting monomer in the slurry is stripped, (C) the step wherein the stripped slurry is dehydrated at 80-95 deg.C within 60 minutes from the completion of the stripping. In a preferred embodiment, 1-300 ppm (in weight) of an antioxidant (for example, 2,6-di-t-butyl-p-cresol or the like) is added to the slurry of the vinyl chloride slurry after the completion of the step B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a vinyl chloride polymer by a suspension polymerization method.

[0002]

2. Description of the Related Art Generally, a vinyl chloride polymer is produced through the following steps. A step of suspending and polymerizing a vinyl chloride monomer or a monomer mixture containing the vinyl chloride monomer in an aqueous medium in a polymerization vessel to obtain a polymer slurry,
After recovering the unreacted monomers in the polymerization vessel by exhausting, removing the remaining unreacted monomers in the polymer slurry by stripping, dehydrating the polymer slurry that has undergone the stripping step, and The combined cake undergoes a step of drying with steam. Thus, the vinyl chloride polymer is obtained as a dried product.

In recent years, it has been desired to reduce the amount of energy used from the viewpoint of lowering manufacturing costs. As a-ring,
It has been desired to reduce the amount of steam used in the drying step when producing a dried vinyl chloride polymer product. To do this,
It is effective to reduce the water content of the polymer cake after the dehydration treatment supplied to the drying step. As a dehydration method for effectively reducing the water content of the polymer cake, a method using a centrifugal separator such as a screen bowl decanter type or a solid bowl decanter type continuous centrifuge is employed as a dehydration device. ing.

[0004]

However, even when these dehydrating machines such as centrifugal separators are used, the water content of the obtained polymer cake is in the range of 24 to 30% by weight. This water content is not enough to further improve the steam consumption rate in the drying step. Therefore, it has been desired to further reduce the water content of the polymer cake. Accordingly, an object of the present invention is to provide a method for producing a vinyl chloride-based polymer which can reduce the water content of a polymer cake obtained after dehydration treatment of a polymer slurry.

[0005]

In order to achieve the above object, the present invention provides (A) a step of subjecting a vinyl chloride monomer or a monomer mixture containing a vinyl chloride monomer to suspension polymerization in an aqueous medium to obtain a polymer slurry. (B) a step of stripping unreacted monomers in the polymer slurry, and (C) a step of heating the polymer slurry having undergone the step (B) to a temperature of 80 to 95 ° C. within 60 minutes from the end of the stripping. The present invention provides a method for producing a vinyl chloride-based polymer having a step of performing a dehydration treatment.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. (A) Suspension polymerization step: The conditions for suspension polymerization may be the same as those usually performed, and are not particularly limited. That is, first, a vinyl chloride monomer or a monomer mixture containing a vinyl chloride monomer, an aqueous medium, a polymerization initiator, and a dispersant are charged into a polymerization vessel, and a predetermined polymerization temperature (typically 30 to 75) is added while stirring.
C), the vinyl chloride monomer or monomer mixture is polymerized. A predetermined polymerization rate (usually 60 to
(98%), the polymerization is stopped. Termination of the polymerization can be performed, for example, by adding an antioxidant.

The monomer to be polymerized may be a vinyl chloride monomer alone, or a mixture of a vinyl chloride monomer and a copolymerizable monomer (comonomer) (the content of the vinyl chloride monomer is usually at least 50% by weight, preferably at least 50% by weight. 70% by weight or more). As the comonomer, ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-
Α-olefins such as heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-tridecene and 1-tetradecene; vinyl esters such as maleic acid and vinyl acetate; vinyl ethers such as lauryl vinyl ether and isobutyl vinyl ether; Maleic anhydride; vinylidene chloride and the like.

Examples of the polymerization initiator include diacyl organic peroxides such as isobutyryl peroxide, 3,5,5-trimethylhexanoyl peroxide and lauroyl peroxide; cumyl peroxy neodecanoate, t-butyl peroxide. Peroxyester-based organic peroxides such as oxyneoheptanoate, t-butylperoxyneodecanoate, t-hexylperoxyneodecanoate; diallylperoxydicarbonate, di-2-ethylhexylperoxydi A peroxydicarbonate organic peroxide such as carbonate is exemplified. These polymerization initiators are added in an amount of 0.1 to 100 parts by weight of the total charged amount of the monomers.
It is added in an amount of from 0.01 to 0.3 part by weight, preferably from 0.03 to 0.2 part by weight.

Examples of the dispersant include cellulose derivatives such as methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose; water-soluble or oil-soluble partially saponified polyvinyl alcohol, acrylic acid polymers, gelatin and other water-soluble polymers. Is done. These can be used alone or in combination of two or more. These are nonionic emulsifiers such as sorbitan monolaurate, sorbitan trilaurate, glycerin tristearate, ethylene oxide / propylene oxide block copolymer; polyoxyethylene sorbitan monolaurate, polyoxyethylene glycerin oleate, sodium lauryl sulfate and the like. Can be used in combination with at least one kind of anionic emulsifiers. These dispersants are used in an amount of 0.1 to 100 parts by weight based on the total amount of monomers charged.
It is added in the range of 02 to 0.2 parts by weight, preferably 0.05 to 0.15 parts by weight.

Water is used as the aqueous medium. The water is usually used as deionized water or pure water.
The amount of the aqueous medium charged is in the range of 1.0 to 3.0 times by weight, preferably 1.1 to 2.0 times by weight of the monomer.

Any antioxidant can be used as long as it has a polymerization inhibiting action. For example, 2,6-di-t-butyl-p-cresol (BHT), 3-t-butyl-
4-hydroxy-anisole (3-BHA), 2-t-
Butyl-4-hydroxy-anisole (2-BHA),
2,2'-methylenebis (4-methyl-6-t-butylphenol) (MBMBP), 2,2'-methylenebis (4-methyl-6-t-butylphenol) (MBEB
P) 4,4'-butylidenebis (3-methyl-6-t
-Butylphenol) (BBMBP), 4,4'-thiobis (3-methyl-6-t-butylphenol) (SB
MBP), styrenated phenol, styrenated-P-cresol, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, tetrakis [methylene-3- (3 ′, 5 '-Di-1-butyl-4'-hydroxyphenyl) propionate] methane, octadecyl 3- (3,5
-Di-t-butyl-4-hydroxyphenylpropionate), 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-
-Butyl-4-hydroxybenzyl) benzene, 2,2'-
Dihydroxy-3,3'-di (α-methylcyclohexyl)
−5,5′-dimethyl-diphenylmethane, 4,4′-methylenebis (2,6-di-t-butylphenol), tris (3,5
-Di-t-butyl-4-hydroxyphenyl) isocyanurate, 1,3,5-tris (3 ', 5-di-t-butyl-4-hydroxybenzoyl) isocyanurate, bis [2-methyl-4- (3-n-alkylthiopropionyloxy)-
5-t-butylphenyl] sulfide, 1-hydroxy-3
-Methyl-isopropylbenzene, 2,5-di-t-butylhydroquinone, 2,2'-methylenebis (4-methyl-6-
Nonylphenol), alkylated bisphenol, 2,5
-Di-t-amylhydroquinone, polybutylated bisphenol A, bisphenol A, 2,6-di-t-butyl-p-ethylphenol, 2,6-bis (2'-hydroxy-
3-tert-butyl-5'-methyl-benzyl) -4-methylphenol, 1,3,5-tris (4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate, terephthaloyl-di (2,6-dimethyl-4-t-butyl-3-hydroxybenzyl sulfide), 2,6-di-t-butylphenol, 2,6-di-t-butyl-α-dimethylamino-
p-cresol, 2,2′-methylene-bis (4-methyl-6
-Cyclohexylphenol), tolethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], hexamethylene glycol-bis (3,5-di-t-butyl-4-) (Hydroxyphenyl) propionate, 3,5-di-t-butyl-4-hydroxytoluene, 6- (4-hydroxy-3,5-di-t-
(Butylaniline) -2,4-bis (octylthio) -1,3,5
-Triazine, N, N'-hexamethylenebis (3,5-di-
t-butyl-4-hydroxy-hydrocinamide), 3,5-
Di-t-butyl-4-hydroxy-benzyl-phosphoric acid diethyl ester, 2,4-dimethyl-6-t-butylphenol, 4,4′-methylenebis (2,6-di-t-butylphenol), 4,4 '-Thiobis (2-methyl-6-t-butylphenol), tris [β- (3,5-di-t-butyl-4
-Hydroxyphenyl) propionyl-oxyethyl]
Isocyanurate, 2,4,6-tributylphenol, bis [3,3-bis (4′-hydroxy-3′-tert-butylphenyl) -butylic acid] glycol ester, 4
-Hydroxymethyl-2,6-di-t-butylphenol,
Phenolic antioxidants such as bis (3-methyl-4-hydroxy-5-t-butylbenzyl) sulfide; N-phenyl-N′-isopropyl-p-phenylenediamine;
-Phenyl-N '-(1,3-dimethylbutyl) -P-phenylenediamine, N, N'-diphenyl-p-phenylenediamine, 2,2,4-trimethyl-1,2-dihydroquinoline polymer and the like Amine antioxidants; sulfur antioxidants such as dilauryl thiodipropionate, distearyl thiodipropionate and 2-mercaptobenzimidanol; phosphorus antioxidants such as distearyl pentaerythritol diphosphite And the like, but are not limited thereto. Among these antioxidants, in particular, toluethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 3,5
Di-tert-butyl-4-hydroxytoluene, 3-tert-butyl-4-hydroxy-anisole (3-BHA), 2,5-di-tert-butylhydroquinone and octadecyl 3- (3,5
-Di-tert-butyl-4-hydroxyphenylpropionate is preferred. These antioxidants may be used alone or in combination.
More than one species can be used in combination.

From the standpoint of quality and cost such as anti-initial coloring properties, the antioxidant is usually added in an amount of from 0.0001 to 0.0001 parts by weight based on 100 parts by weight of the total charged monomer at the time of addition.
0.5 parts by weight, preferably in the range of 0.001 to 0.05 parts by weight.

After the termination of the polymerization, unreacted monomers are recovered from the polymerization vessel by evacuation, and the obtained polymer slurry is extracted from the polymerization vessel, for example, to a blowdown tank. (B) Stripping step of unreacted monomer: Next, the polymer slurry obtained in step (A) is supplied to a monomer stripping tower, and stripping is performed. Unreacted monomers remaining in the polymer slurry in this step are almost completely removed, and the content becomes 50 ppm or less, preferably 10 ppm or less.

An antioxidant may be added to the polymer slurry before the stripping step and at least one time after the end of the step to suppress the initial coloration of the resulting polymer, For this purpose, it is desirable to add it before stripping. As described above, since the antioxidant is often used also for terminating polymerization, the polymer slurry after the completion of the unreacted monomer stripping usually contains the antioxidant. The content of the antioxidant in the polymer slurry after the completion of the stripping is preferably in the range of 1 to 3000 ppm (weight) including the antioxidant when added after the stripping. More preferably, it is in the range of 5 to 300 ppm.

As described above, since the polymer slurry after the completion of the stripping contains an antioxidant, the heat of the vinyl chloride-based polymer contained in the polymer slurry supplied to the next dehydration treatment step is reduced. Deterioration can be effectively prevented. For this reason, a decrease in the anti-initial coloring property of the obtained dried vinyl chloride polymer product can be sufficiently suppressed.

(C) Dehydration step: The method of the present invention is characterized in that the polymer slurry subjected to the step (B) is subjected to a dehydration treatment at a temperature of 80 to 95 ° C. within 60 minutes from the end of stripping. In the process. To elaborate further,
The polymer slurry obtained after the end of the stripping of the unreacted monomer (the temperature is usually 95 ° C. or higher) is supplied to, for example, a slurry tank equipped with an outer jacket and a stirrer, where the polymer slurry is optionally used. After being adjusted to a temperature range of 80 to 95 ° C. by cooling, it is supplied to the dehydration processor within the above temperature range within 60 minutes (including the temperature adjustment time) from the end of stripping, and is subjected to dehydration treatment.

If the temperature of the polymer slurry supplied to the dehydration processor is less than 80 ° C., the water content of the obtained polymer cake is not sufficiently reduced, and a sufficient effect of reducing the amount of steam used in the drying step is obtained. If the temperature is higher than 95 ° C., it is not preferable because the anti-initial coloring property of the dried vinyl chloride polymer decreases. On the other hand, if the polymer slurry that has passed through the step (B) is supplied to the dehydration processing machine for more than 60 minutes from the end of the stripping, the anti-initial coloring property of the obtained vinyl chloride-based dried polymer rapidly deteriorates.

As the dehydration treatment machine used in the step (C), a centrifuge such as a screen bowl decanter type or a solid bowl decanter type continuous centrifuge is exemplified. The continuous centrifuge is preferably of the solid bowl decanter type. The water content of the polymer cake obtained by the dehydration treatment as described above, as shown in the Examples below,
It is lower than before. Next, the polymer cake is supplied to, for example, a fluidized drier and dried at a drying temperature of 50 to 100 ° C., preferably 60 to 80 ° C. until the water content becomes 0.3% by weight or less, and a vinyl chloride-based heavy A combined dried product is obtained.

[0019]

EXAMPLES The present invention will be described below in detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. [Examples 1 to 5, Comparative Examples 1 to 6] As a polymerization vessel for performing suspension polymerization of a vinyl chloride monomer, a stainless steel polymerization vessel having an internal volume of 80 m ³ equipped with a reflux condenser, an outer jacket and a stirrer was used. Was.

35.5 tons of deionized water were charged into the polymerization vessel, and then 300 kg of an aqueous solution in which 10.7 kg of a water-soluble partially saponified polyvinyl alcohol and 4.6 kg of a water-soluble cellulose ether were dissolved as a dispersant were charged and stirred. . After the polymerization vessel was evacuated to 56 mmHg, 30.5 tons of vinyl chloride monomer was charged with stirring, and 17.4 kg of t-butyl peroxy neodecanoate and cumyl peroxy neodecanoate were added as polymerization initiators. 48.8 kg of an aqueous emulsion in which 7.0 kg was dispersed was injected by a pump to form a charged mixture. Simultaneously with the injection of the polymerization initiator, the internal temperature was raised to a predetermined polymerization temperature of 56 ° C. by passing heated water through the outer jacket to start polymerization. Cooling water was passed through the outer jacket from near the end of the temperature increase, and heat removal by the reflux condenser was started 20 minutes after the internal temperature reached the predetermined 56 ° C, and the internal temperature was maintained at 56 ° C. The polymerization was continued. The internal pressure in the polymerization vessel is 5.5kg / c
At the time of drop to m ² (polymerization rate: 87.0%), an antioxidant having a polymerization inhibiting action shown in Tables 1 and 2 was added to the polymerization mixture to terminate the polymerization.

After the termination of the polymerization, unreacted monomers were recovered from the polymerization vessel by evacuation, and the obtained polymer slurry was withdrawn from the polymerization vessel to a 150 m ³ blowdown tank.
Further, in order to remove the remaining unreacted monomer in the polymer slurry, the polymer slurry in the tank was supplied to a monomer stripping tower.

Polymer slurry after stripping of unreacted monomer (concentration of unreacted monomer: 10 ppm, solid content of vinyl chloride polymer: 41.2% by weight, temperature: 92 ° C., degree of polymerization of vinyl chloride polymer: 1000;
The concentration of the antioxidant is shown in Tables 1 and 2), and a speed of 13.5 m ³ / h [slurry linear velocity (V1)] was applied to a 19 m ³ slurry tank provided with an external jacket and a stirrer.
V1 = 0.82 m / s]. The residence time (pipe length / pipe linear speed) of the polymer slurry in the pipe between the monomer stripping tower and the slurry tank was 30 seconds. After the polymer slurry has been supplied to the slurry tank, when the slurry has accumulated in the slurry tank at 12.0 m ³ , the solid bowl decanter-type continuous centrifugal separator (Tomo Kogyo Co., Ltd., horizontal super decanter) is used. Was started at the temperatures shown in Tables 1 and 2 and at a speed of 13.5 m ³ / h (pipe linear speed (V2) was V2 = 0.82 m / s).

The pipe length (L1) from the unreacted monomer stripping tower to the slurry tank is L1 = 25 m, the pipe length (L2) from the slurry tank to the continuous centrifuge is L2 = 75 m, and the slurry volume in the slurry tank ( Q)
Is set to Qm ³ , and the slurry flow rate (q) supplied to and withdrawn from the slurry tank is q = 13.5 m ³ , the residence time (Ta) in the pipe between the unreacted monomer stripping tower and the slurry tank, and continuous centrifugation from the slurry tank The residence time (Tb), the average residence time (Tc) in the slurry tank, and the total residence time (T) in the slurry tank were calculated according to the following equations.

Ta (minute) = L1 / (V1 × 60) Tb (minute) = L2 / (V2 × 60) Tc (minute) = Q / q × 60 T (minute) = Ta + Tb + Tc The results are shown in Tables 1 and 2. It is shown in FIG.

After completion of the dehydration, the water content of the obtained polymer cake was calculated according to the following equation. Water content (%) = [W1 / (W1 + W2)] × 100 W1: Weight of water in cake W2: Weight of vinyl chloride polymer The results are shown in Tables 1 and 2.

Further, the obtained polymer cake is supplied to a fluidized drier (manufactured by Nara Machinery Co., Ltd.) at a rate of 6.1 t / h with a vinyl chloride polymer in terms of dry weight, and vinyl chloride is discharged from a dryer outlet. So that the water content of the polymer is 0.1%,
Steam drying was performed at a temperature in the dryer of 75 ° C. to obtain a dried vinyl chloride polymer. At this time, the temperature inside the dryer is 75
Steam (gauge pressure 3.5kg)
/ cm ² , temperature 147 ° C.)
Shown in

The obtained dried vinyl chloride polymer was tested and evaluated for anti-initial coloring properties according to the following method.
The results are shown in Tables 1 and 2. Anti-initial coloring: 100 parts by weight of vinyl chloride polymer, 1 part by weight of tin laurate, 0.5 part by weight of cadmium-based stabilizer and 50 parts by weight of dioctyl phthalate are mixed, and the mixture is rolled at 160 ° C. for 5 minutes using a two-roll mill. After kneading, a thickness of 0.
It was formed into an 8 mm sheet. Next, this sheet was cut and stacked, and placed in a 4 × 4 × 1.5 cm formwork,
The sample was formed by heating and pressing at 65 to 70 kgf / cm ² at ℃. This measurement sample was measured using a photoelectric colorimeter (manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS Z 8730 (198).
Lightness index L in the Hunter's color difference equation defined in 0)
Was determined, and a value and b value were measured, and the anti-initial coloring property was evaluated based on the following criteria. Evaluation criteria: ◎: Excellent ○: Good △: Somewhat bad ×: Bad

[0028]

[Table 1]

* List of antioxidant symbols a. Toluethylene glycol-bis [3- (3-t-butyl-5
-Methyl-4-hydroxyphenyl) propionate] b. 3,5-di-t-butyl-4-hydroxytoluene c. 3-t-butyl-4-hydroxy-anisole (3-BHA) d. 2,5-di-t-butylhydroquinone e. Octadecyl 3- (3,5-di-t-butyl-4-hydroxyphenylpropionate)

[0030]

[Table 2]

[0031]

According to the method of the present invention, the water content of the polymer cake obtained after the dehydration treatment of the polymer slurry can be reduced as compared with the conventional one, so that the energy consumption in the drying step can be reduced, and thus the production can be reduced. Cost reduction is achieved.
In addition, the addition of the antioxidant has the advantage that a dried vinyl chloride polymer having excellent anti-initial coloring properties can be obtained.

 ────────────────────────────────────────────────── ─── Continuing on the front page F term (reference) 4J011 AA01 JA07 JA08 JA10 JA13 JB09 JB26 PA33 PB24 PC02 PC07 4J100 AA02Q AA03Q AA04Q AA07Q AA15Q AA16Q AA19Q AA21Q AC03P AC04Q AE05Q AE06Q AG04 FA03

Claims (2)

[Claims] (A) a step of subjecting a vinyl chloride monomer or a monomer mixture containing a vinyl chloride monomer to suspension polymerization in an aqueous medium to obtain a polymer slurry; and (B) a step of removing unreacted monomers in the polymer slurry. Production of a vinyl chloride polymer having a step of ripping and (C) a step of subjecting the polymer slurry subjected to the step (B) to a dehydration treatment at a temperature of 80 to 95 ° C. within 60 minutes from the end of stripping. Method. 2. The method for producing a vinyl chloride polymer according to claim 1, wherein after the step (B) is completed, the vinyl chloride polymer slurry contains 1 to 3000 ppm (by weight) of an antioxidant.