CN1005717B - Process for polymerization of vinyl chloride monomer in aqueous medium - Google Patents

Abstract

The present invention is an improvement to the suspension polymerization of vinyl chloride in an aqueous medium in the presence of a monomer-soluble polymerization initiator. With this improvement, the polymer scale attached to the reactor wall The amount of greatly reduced, the present invention involves the following materials (a) and (b) are mixed together in the aqueous polymerization medium, wherein (a) is composed of unsaturated carboxylic acid monomers such as acrylic acid and such as divinyl ethylene A water-soluble cross-linked copolymer prepared by cross-linking monomers of two (methyl) allyl ethers of diols, and (b) is a nonionic surfactant.

Description

Method for polymerizing vinyl chloride monomer in aqueous medium

The present invention relates to an improved process for the polymerization of vinyl chloride monomers in an aqueous medium. More precisely, it relates to a process for the polymerization of vinyl chloride in an aqueous medium, which process is distinguished in that no polymer scale is deposited throughout the polymerization, either on the inner walls of the polymerization reactor or on the surfaces of the stirrer and all other parts in contact with the vinyl chloride monomer.

Needless to say, the most widely used method for polymerizing vinyl chloride or a vinyl chloride-based monomer mixture is known to date by suspension polymerization of the monomer or monomer mixture in an aqueous medium in the presence of a monomer-soluble polymerization initiator. It is known that in the suspension polymerization of vinyl chloride or its analogous monomers, the most serious problem exists in that, throughout the polymerization, polymer scale is deposited on the inner walls of the polymerization reactor, on the surfaces of the stirrer and all other parts in contact with the vinyl chloride monomer. Once the inner wall of the polymerization reactor is covered with the polymer scale, the cooling capacity of the polymerization reactor is greatly reduced, resulting in a decrease in productivity. When the polymer scale attached to the inner wall is detached and mixed in the polymer product, the product quality is inevitably reduced. In addition, in order to allow the batch polymerization operation to be continuously carried out, it is required to try to remove the polymer scale adhering to the contact surfaces in the reactor after each polymerization operation is completed. This is labor and time intensive. And there is a serious problem that the physical health of workers performing the above-mentioned descaling operation is affected due to the considerable amount of toxic vinyl chloride monomer absorbed in the polymer scale.

In order to avoid the deposition of polymer scale on the contact surfaces inside the reactor during the suspension polymerization operation of vinyl chloride, a measure is taken to coat the inner walls of the reactor with a covering agent of some compound in order to avoid the adhesion of polymer scale on the inner walls of the reactor. Various forms of surface covering agents have been proposed so far, including polar organic compounds such as amines, quinones, aldehydes and the like, dyes and pigments, reaction products of polar organic compounds or dyes with metal salts, mixtures of electron donors (electrondoner compound) and electron acceptors (electron acceptor compound), inorganic salts or complexes, and others.

In addition to the above-described method of coating the inner wall of the reactor, attempts have been made to reduce the adhesion of polymer scale to the inner wall of the reactor by improving the formulation of the polymerization mixture fed into the polymerization reactor. For example, japanese patent publication Nos. 57-5000614 and 57-5000650 disclose that an aqueous medium for suspension polymerization of vinyl chloride is mixed with a dispersant, which is a water-soluble crosslinked polymer prepared by crosslinking copolymerization of acrylic acid and a crosslinkable monomer such as allyl pentaerythritol, allyl sucrose, and the like. However, this method is unsatisfactory in that it is quite low in the effect of avoiding the deposition of polymer scale on the inner wall of the vessel.

The object of the present invention is to provide a novel and convenient and practical process for the suspension polymerization of vinyl chloride monomer in an aqueous medium without the attachment of polymer scale to all surfaces of the polymerization reactor which come into contact with the vinyl chloride monomer.

It is another object of the present invention to improve the suspension polymerization process of vinyl chloride. According to this method, the amount of polymer scale adhering to the reactor wall is greatly reduced by mixing the aqueous polymerization medium with specific additive compounds.

Thus, the present invention provides an improved process which comprises, in the suspension polymerization of vinyl chloride monomer in an aqueous medium in the presence of a monomer-soluble polymerization initiator, mixing the aqueous medium with:

(a) Water-soluble crosslinked copolymers of polymerizable unsaturated carboxylic acid compounds and crosslinking agents of the formula

Where Me is methyl, et is ethyl, R is a hydrogen atom or methyl, p, q and R are each zero or a positive integer, provided that p+q+r is a positive integer not exceeding 500.

(B) Nonionic surfactant

The polymerizable unsaturated carboxylic acids typically described above are olefinic acids and the crosslinking agent typically of formula (I) is a bis-allyl or bis-methallyl group of diethylene glycol.

From the foregoing, it will be appreciated that the present invention provides an improved process which comprises blending a specific water-soluble cross-linked copolymer prepared by polymerizing a polymerizable unsaturated carboxylic acid compound with a cross-linking agent of the formula (I), each symbol of the formula (I) being as noted above, each suffix p, q and r and zero or a positive integer, although as an average it may be a number with a fraction, with a nonionic surfactant.

Examples of the crosslinking agent represented by the formula (I) are diethylene glycol, bis allyl ether, that is, in the compound of the formula (I), R is a hydrogen atom, p=2, q=0 and r=0, diethylene glycol bis methyl allyl ether, that is, in the compound of the formula (I), R is methyl, p=2, q=0 and r=0, in the compound of the formula (I), R is a methyl, p is an average value of 4.5, q=0 and r=0, in the compound of the formula (I), R is a hydrogen atom, p= 8,q =2.6 and r=0, in the compound of the formula (I), R is a hydrogen atom, p=0, q=17 and r=0, in the compound of the formula (I), R is a methyl, p=0, q=2.6 and r=0, and the like, and the crosslinking agent may be used alone or in combination thereof, depending on the crosslinking agent.

Examples of the polymerizable unsaturated carboxylic acid compound are acrylic acid, methacrylic acid, itaconic acid, chloroacrylic acid, cyanoacrylate, α -benzylacrylic acid, crotonic acid, maleic acid, fumaric acid, sorbic acid and the like, and these polymerizable unsaturated carboxylic acids may be used either alone or in combination of two or more thereof as desired.

The ratio of the crosslinking agent represented by the formula (I) to the unsaturated carboxylic acid is 0.05 to 10 parts by weight, preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the crosslinking agent to 100 parts by weight of the unsaturated carboxylic acid. If the amount of the crosslinking agent used is less than the above-mentioned ratio, the degree of crosslinking in the resulting copolymer is too small to achieve the effect required for preventing the deposition of polymer scale, and if the amount of the crosslinking agent used is too large, the degree of crosslinking of the resulting copolymer is too large to render the copolymer water-insoluble, and the polymer cannot be applied by the method of the present invention.

Examples of nonionic surfactants suitable for use in the process of the present invention are polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polystyrenyl phenyl ethers, polyoxyethylene polyoxypropylene block copolymers, fatty acid-containing partial esters of glycerol, fatty acid-containing partial esters of sorbitan, fatty acid-containing partial esters of pentaerythritol, fatty acid-containing propylene glycol monoesters, fatty acid-containing partial esters of sucrose, fatty acid-containing partial esters of polyoxyethylene sorbitan, fatty acid-containing partial esters of glycerol, polyethylene glycol fatty acid-containing partial esters of polyglycerol, polyoxyethylene adducts of castor oil, fatty acid diethanol, N-N-bis (2-hydroxyalkyl) amines, polyoxyethylene alkylamines, fatty esters of triethanolamine, trialkylamine oxides and the like, either alone or in combination of two or more of these agents, as desired.

The components (a) and (b) are added together to the aqueous polymerization medium in such a proportion that, per 100 parts by weight of the vinyl chloride monomer or monomer mixture dispersed in the aqueous medium, the amount of component (a) is 0.01 to 2 parts, preferably 0.02 to 0.5 parts, and the amount of component (c) is 0.005 to 1 part, preferably 0.01 to 0.5 parts, these amounts being strictly defined so that the monomer can be dispersed in the aqueous medium in the form of very small droplets of high stability, so that only very small polymer scale deposits during the entire polymerization reaction.

When it is desired to further enhance the effect of preventing polymer scale from depositing on the walls, we can of course also use conventional methods of preventing polymer scale from depositing on the walls, i.e. coating the reactor walls and other relevant surfaces with known coating compositions, in combination with the above-described inventive method. Japanese patent publication No. 45-30343,45-30835,56-5442,56-5444 describes suitable coating compositions. Polar organic compounds are most suitable as such coating components, for example dyes, such as direct dyes, acid dyes, basic dyes, vat dyes, sulfur dyes, mordant dyes, disperse dyes, oil-soluble dyes, reactive dyes and the like, amine compounds, quinone compounds, aldehyde compounds and the like. Among these, organic dyes containing one or more azine rings in their molecules are particularly desirable.

As in the case of the conventional suspension polymerization method of vinyl chloride monomer, the polymerization reaction is carried out in the presence of a monomer-soluble polymerization initiator according to the method of the present invention, and the kind of the monomer-soluble polymerization initiator is not particularly limited. Examples of the polymerization initiator used in the process of the present invention are organic peroxides such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, caproyl cyclohexylsulfonyl peroxide, t-butyl peroxypivalate, benzyl peroxide, lauroyl peroxide and the like, and azo compounds such as azobisisobutyronitrile, azo-bis-2, 4-dimethylbutyronitrile, azo-bis-4-methoxy-2, 4-dimethylbutyronitrile and the like.

The process of the invention is suitable not only for the homopolymerization of vinyl chloride, but also for the copolymerization of vinyl chloride with other known copolymerizable monomer(s), examples of which are vinyl esters, such as vinyl acetate, vinyl ethers, acrylic acid and methacrylic acid, and esters thereof. Maleic acid and fumaric acid, and esters thereof, maleic anhydride, aromatic vinyl compounds such as styrene, unsaturated nitrile compounds such as acrylonitrile, vinylidene halides such as vinylidene fluoride and vinylidene chloride, olefins such as ethylene, propylene and the like.

In practicing the process of the present invention, the effect of preventing the deposition of copolymer scale walls is enhanced if small amounts, e.g., 1% by weight or less, of water-soluble alkaline or strong gangue compounds are blended in the aqueous medium.

In addition to the above-described method of adding the mixed components (a) and (b) in combination to the aqueous polymerization medium, the polymerization of the present invention can be carried out under generally usual polymerization conditions, such as the amount of the polymerization initiator, the polymerization temperature and reaction time, and other conditions.

Hereinafter, the method of the present invention will be described in detail with reference to examples.

Examples 1-5 and comparative examples 1-2.

60 Kg of deionized water, 14 g of di-2-ethylhexyl peroxydicarbonate as a polymerization initiator, 30 g of any one of the below-shown crosslinked copolymers I, II, III, IV and V and 30 g of any one of the below-shown nonionic surfactants I, II and III were charged together into a stainless steel polymerization reactor having a capacity of 100 liters, and after the reactor pressure was pulled to 50 mmHg, 30 kg of vinyl chloride monomer was charged into the reactor, and the polymerization mixture in the polymerization reactor was stirred at a temperature of 57℃to start the polymerization reaction.

After about 6 hours from the start of the polymerization, the pressure in the polymerization reactor was reduced to 6.0 kg/cm ² gauge, at which point the polymerization was terminated, unreacted vinyl chloride monomer was recovered, and the polymerization product slurry in the reactor was poured out to observe the deposition of polymer scale on the reactor wall.

The above procedure was regarded as a run and the above test was repeated until it was observed that polymer scale deposited on the reactor wall. The number of times of repeating the test run was recorded, and the test results are shown in Table 1.

Crosslinked copolymers

I. a copolymer prepared from 100 parts by weight of acrylic acid and 1 part of diethylene glycol bis allyl ether.

Copolymers made from 100 parts by weight of acrylic acid and 2 parts of diethylene glycol bis allyl ether.

A copolymer prepared from 100 parts by weight of acrylic acid and 2 parts of diethylene glycol dimethyl allyl ether.

Copolymers made from 100 parts by weight of acrylic acid and 0.3 parts of allyl pentaerythritol.

V. copolymer made from 100 parts by weight of acrylic acid and 1.3 parts of allyl sucrose.

Nonionic surfactant

I. Sorbitan glycerol laurate (Span 20)

II. Polyoxyethylene sorbitan monolaurate (Tween 20)

III Polyoxyethylene sorbitan oleate (Tween 80)

Examples 6 to 8

A surface covering agent was applied to the inner wall of a polymerization reactor and the surface of the stirrer, which were the same as those used in the previous examples, in an amount of 0.001 g/m, as shown in Table 2 below, and a drying agent

TABLE 1

Non-ionic surface Scale deposition test of crosslinked copolymer

Number of active agent processes

Example 1I I12

Example 2I II 15

Example 3 III 16

Example 4 II III 14

Example 5 III III 10

Comparative 1 IV III 4

Example 2V III 3

Then, 60 kg of deionized water, 16 g of a 1:1 mixture of azobis-2, 4-dimethylbutyronitrile and di-2-ethylhexyl peroxydicarbonate as a polymerization initiator, 30 g of the crosslinked copolymer 1 used in the preceding example and 30 g of the nonionic surfactant III used in the preceding example were charged into a polymerization reactor, and after removing the oxygen in the reactor by evacuation, 30 kg of a vinyl hydride monomer was further added, and the polymerization mixture was heated to a temperature of 57℃under stirring to start the polymerization. After 6 hours of reaction, the pressure was reduced to 6.0 kg/cm. The polymerization reaction was terminated, unreacted vinyl chloride monomer was recovered, and then the slurry of the polymerization product in the reactor was poured out, and the inner wall of the reactor was visually observed.

The above polymerization test procedure was repeated until the adhesion of the polymer scale to the reactor wall was visually observed, and the number of times of the test run and the results thereof were recorded in table 2 below.

TABLE 2

Example No. 67 8

Coating agent solvent black 7 solvent black 5 acid black 2 and

(Solvent phytic acid Black 7) Black 5)

Scale deposition 100 100 115

Number of tests

Claims (6)

1. In a process for suspension polymerization of vinyl chloride monomer or monomer mixture consisting essentially of vinyl chloride in an aqueous medium in the presence of a monomer-soluble polymerization initiator, the improvement comprising blending into the aqueous medium:

(a) Water-soluble crosslinked copolymer prepared from polymerizable unsaturated carboxylic acid compound and crosslinking agent represented by the following chemical formula

CH₂＝CR-CH₂-（O-CH₂-CH₂）_p-（0CH₂-CHMO）q-O-CH₂-CR＝CH₂,

Wherein Me is a methyl group, R is a hydrogen atom or a methyl group, and p and q are each zero or a positive integer, provided that p+q is a positive integer of not more than 20, and

(B) Nonionic surfactants.

2. The improved process of claim 1 wherein the water-soluble cross-linked copolymer is a copolymer prepared from 100 parts by weight of acrylic acid and 0.05 to 10 parts by weight of bis allyl ether or bis methallyl ether of diethylene glycol.

3. The improvement as claimed in claim 1 wherein component (a) is added to the aqueous medium in an amount of 0.01 to 2 parts by weight of the mixed component (a) per 100 parts by weight of the vinyl chloride monomer or monomer mixture.

4. The improved process of claim 1 wherein component (b) is added to the aqueous medium in an amount of from 0.005 to 1 parts by weight of mixed component (b) per 100 parts by weight of vinyl chloride monomer or monomer mixture.

5. The improved process of claim 1, further comprising coating the interior walls of the polymerization reactor with an organic dye or an organic polar compound.

6. The improved process of any one of claims 1 to 4 wherein the nonionic surfactant is sorbitan monolaurate, polyoxyethylene sorbitan monolaurate or polyoxyethylene sorbitan monooleate.