GB1559334A - Polymerisation of vinyl chloride - Google Patents

Abstract

According to the invention, vinyl chloride monomer or a monomer mixture essentially comprising vinyl chloride is polymerised in a polymerisation reaction whose internal walls and stirrer and other surfaces which come into contact with the monomer or the monomers have been coated with a mixture of at least one electron-donor compound and at least one electron-acceptor compound. This method greatly reduces the deposition of polymer crusts on these surfaces, and a high-quality polymer can be produced.

Description

(54) POLYMERISATION OF VINYL CHLORIDE (71) We, SHIN-ETSU CHEMICAL COMPANY LIMITED, a Japanese Company, of 6-1, Otemachi 2-chome, Chiyoda-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an improvement for polymerization of vinyl chloride or a mixture of monomer or monomers composed mainly of vinyl chloride in the presence of a polymerization initiator in a polymerization reactor, whereby the deposition of polymer scale on the inner walls of the polymerization reactor and the surfaces of an agitator and other parts in contact with the monomer or monomers can be effectively prevented.

Known methods for the production of vinyl chloride polymer include suspension polymerization, emulsion polymerization, solution polymerization, gas-phase polymerization and bulk polymerization. These conventional polymerization methods have the defect that polymer scale deposits on the surfaces of the walls of the polymerization reactor and other parts including agitating blades in contact with the monomer, resulting in a reduction of the yield of polymer product and the cooling efficiency of the polymerization reactor. Further, the scale deposited on the surfaces tends to come off and enter the polymer product, resulting in a lowering of the product quality. Furthermore, all scale deposited on the surfaces has to be removed following each polymerization run with much labour and time. resulting in a reduction in productivity. Finally, the scale-removing operation involves a health problem owing to the carcinogenic properties of monomeric vinyl chloride.

Various proposals have been made to reduce or prevent unwanted polymer scale depose tion on the inner walls and other surfaces within the polymerisation reactor. British Patent Specification No. 1,291,145 discloses and claims a method of suspension-polymerising vinyl chloride monomer or a mixutre of vinyl monomers containing vinyl chloride as its main component, in an aqueous medium containing at least one suspension agent and at least one oil-soluble catalyst, in which, prior to the polymerisation, at least those parts of the inner walls of the polymerisation vessel that will come into contact with the vinyl monomer(s) are coated with one ore more coating compounds selected from nitrogen atom-containing organic compounds, sulphur atom-containing organic compounds, quinone compounds, ketone compounds, aldehyde compounds, alcohol compounds having at least six carbon atoms, carboxylic acid compounds having at least six carbon atoms, anionic and non-ionic surface active agents, indigoid dyes, sulphur dyes, diphenylmethane dyes, nitron dyes, thiazole dyes, xanthene dyes, acridine dyes, cyanine dyes, quinone dyes, phthalocyanine dyes, nitroso dyes, azo dyes, azine dyes, oxazine dyes, azomethine dyes, thiazine dyes, nitro dyes, aniline black, and inorganic pigments.

British Patent Specification No. 1,517,734 describes and claims a method for the bulk polymerisation of vinyl chloride monomer or a mixture thereof with a copolymerisable monomer or monomers, comprising providing inner surfaces of a polymerisation vessel coming into contact with the monomer or monomers, prior to polymerisation, with a coating comprising a non-metallic compound containing a ir-bond or at least one atom selected from nitrogen, sulphur, phosphorus and oxygen, said atom having lone pair electrons, the amount of said compound used for the coating being in the range from 0.001 to 100 g/m2.

British Patent Specification No. 1,521,058 describes and claims a method for the polymerisation of vinyl chloride monomer or a mixture of monomers composed mainly of vinyl chloride in the presence of a polymerisation initiator in a polymerisation vessel, in which a layer comprising a metal complex with at least one organic compound which is a polar compound and/or a dye is formed at least on the inner surfaces of the polymerisation vessel which come into contact with the monomer or monomer mixture, said metal complex being formed by treating said organic compound with a metal compound in a ratio of from 100:5 to 100:300 by weight, respectively.

British Patent Specification No. 1,536,160 describes and claims a method for the polymerisation of vinyl chloride or a mixture of monomers composed mainly of vinyl chloride in the presence of a polymerisation initiator in a polymerisation vessel, in which the surfaces of the vessel coming into contact with the monomer or monomers are treated, prior to polymerisation, with (a) an organic compound which is a polar compound and/or a dye and (b) a compound which is a metal halide, hydroxide, oxide or carboxylate, or an oxyacid, or an inorganic salt thereof, of an element of the second to sixth period of Group IIB of sub-group A or B of groups III to VII of the Periodic Table.

According to the present invention, in a method for the polymerisation of vinyl chloride monomer or a mixture of monomers composed mainly of vinyl chloride in the presence of a polymerisation initiator in a polyermisation vessel, the surfaces of the vessel coming into contact with the monomer or monomers are treated, prior to polymerisation with (A) a basic nitrogen-containing dye selected from quinoneimine dyes containing an azine, oxazine or thiazine ring, azo dyes, diphenylemthane dyes, triphenylmethane dyes, oil-soluble aminocontaining azo dyes, xanthene dyes, thiazole dyes, stilbene dyes, phthalocyanine dyes and cyanine dyes, and (B) an acidic sulfonic acid group-containing dye selected from azo dyes, mordant azo dyes, triphenylmethane dyes, quinonimine dyes containing an azine, oxazine or thiazine ring, xanthene dyes, stilbene dyes and thiazole dyes.

The method of this invention can be used in any type of polymerization, i.e. suspension, emulsion, solution or bulk polymerisation and also in the copolymerisation of a monomer mixture composed mainly of vinyl chloride. The method of British Patent Specification No.

1,291,145, for example, is only effective in suspension polymerisation.

With regard to compounds of group (A), examples of suitable basic quinoneimine dyes containing an axine, oxazine or thiazine ring include Methylene Blue, Safranine, Nile Blue, Aniline Black, and the particularly preferred compounds Nigrosine Base, Spirit Black and Induline. Suitable basic azo dyes containing a monoazo-, bisazo- or polyazo- structure include Bismarck Brown R and Yellow AB. suitable basic diphenylmethane dyes include Auramine JD. Suitable basic triphenylmethane dyes include Magenta and Malachite Green (particularly preferred). Suitable basic oil-soluble, amino-containing azo dyes include Sudan Black B (particularly preferred), Oil Scarlet SN (particularly preferred) and Oil Yellow. Suitable basic xanthene dyes include Rhodamine B.

With regard to the compounds of group (B), suitable acid azo dyes include a-Napthol Orange, Amaranth (particularly preferred), Acid Brown GR (particularly preferred), Acid Cyanine GR, Acid Light Yellow and Milling Black VLG. Suitable acid mordant azo dyes include Chrome Black PB (particularly preferred). Suitable acidic triphenylmethane dyes include Acid Milling Green J and Acid Violet 4BN. Suitable acidic quinonemine dyes containing an axine, oxazine or thiazine ring include Nigrosine (particularly preferred) and Brilliant Alizaline Blue 3K. Suitable acid xanthene dyes include Rhodamine Base (particularly preferred). Suitable acid stilbene dyes include Chrysophenine. Suitable acid thiazole dyes include Diaresin Rose BD. Compounds (A) and (B) are conveniently mixed by dissolving or dispersing them together in a suitable medium. It is also possible to dissolve or disperse them separately, and then to mix the resulting two solutions or dispersions. Such dissolving or dispersing operations are usually carried out at room temperature or, sometimes, below 0 C or above 50"C, optionally under irradition with light. The light used in general is visible or ultra-violet light from fluorescent or mercury lamp.

Examples of media in which compounds (A) and (B) may be dissolved or dispersed are water; ethers, such as tetrahydrofuran and diisopropyl ether; alcohols, such as methanol ethanol and propanol; esters, such as methyl acetate and ethyl acetate; ketones, such as acetone and methyl ethyl ketone; hydrocarbons, such as benzene, toluene, xylene and hexane; chlorinated hydrocarbons, such as methylene chloride, carbon tetrachloride and trichloroethylene; and aprotic solvents, such as dimethylformamide, dimethylacetamide, dimethylisulfoxide and acetonitrile. These individual media can be used alone or in combinations.

In practising the method of the present invention, the deposition of polymer scale is prevented most effectively when the mixing ratio of compounds (A) and (B) is between 1:20 and 20:1, preferably 1:5 and 5:1, by weight.

The amounts of the mixture of compounds (A) and (B) which are used may be similar to those adopted in the prior art methods using conventional coating materials. In other words, polymer scale deposition can be sufficiently prevented when the mixture is applied on the surfaces in an amount of at least 0.01 g per m2 of coated area. It is recommended, however, that the thus coated surfaces are washed with water to remove any excessive coatings which would eventually come off and enter the polymer product.

Further, the effect of preventing the deposition of polymer scale in accordance with the resent invention can be enhanced by adding one or more alkaline substances, such as oxides, hydroxides, carbonates, phosphates, bicarbonates, silicates and carboxylates of alkali metals, alkaline earth metals and ammonium to the polymerization mixture. In this case, however, it is preferred that the amount of such additives is always smaller than 1% by weight based on the monomer or monomers so that the quality of the resulting polymer should not be degraded and the polymerization reaction is not disturbed.

The method of the present invention is effective to all types of polymerization of vinyl chloride including suspension, emulsion, solution and bulk polymerization. Further, the method of the present invention is not limited by polymerization conditions, such as polymer ization temperatures and agitation conditions, or by the kinds of additives to the polymerization mixture, for example, suspending agents, such as partially saponified polyvinyl alcohol and methylcellulose, anionic emulsifiers, such as sodium lauryl sulfate, sodium dodecyl benzene sulfonate and sodium dioctyl sulfosuccinate, nonionic emulsifiers, such as sorbitan monolaurate and polyoxyethylene alkyl ether, chain transfer agents, such as trichloroethylene and mercaptans, and initiators, such as diisopropyl peroxydicarbonate, lauroyl peroxide and dimethyl valeronitrile. The effect of the method of the invention is not affected by the presence of certain processing additives, such as fillers (e.g. calcium carbonate and titanium dioxide), stabilizers (e.g. tribasic lead sulfate, calcium stearate and dibutyltin laurate), lubricants (e.g. rice wax and stearic acid) and plasticizers (e.g. dioctyl phthalate and dibutyl phthalate).

Furthermore, the present invention can attain an excellent effect not only in the homopolymerization of vinyl chloride but also in the copolymerization of vinyl chloride with one or more monomers copolymerizable with vinyl chloride, for example, vinyl esters, vinyl ethers, acrylonitrile, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, maleic acid, maleic acid esters, maleic anhydride fumaric acid, fumaric acid esters, aromatic vinyl monomers, vinyl halides other than vinyl chloride, vinylidene halides, and olefins.

The present invention will now be further illustrated by the following Examples.

Examples 1 to 5 and Controls A to F Various coating solutions were prepared by mixing compounds (A) and (B) in the solvents, as set forth in Table I, at room temperature with agitation for 3 hours, followed by filtration, to give a concentration of 1% by weight based on the solvent.

Each coating solution thus obtained was applied to the surfaces of the inner walls of a 1,000-liter stainless steel polymerization reactor in an amount of 0.1 g/m2 (as solid). The surfaces so treated were then dried and washed with water.

Thereupon, 500 kg of deionized water, 0.5 kg of hydroxypropylmethylcellulose, 0.5 kg of sorbitan monolaurate, 200 g of dimethyl valeronitrile and 200 kg of vinyl chloride were introduced into the polymerization reactor, and polymerization was then conducted at 57"C for 10 hours. After completion of the polymerization, the amount of polymer scale deposited on the surfaces was determined with the results given in Table I.

In Table I, any mixtures of compounds used as (A) or (B) were mixed in a 1:1 ratio, by weight. Solvent (a) is a mixture of toluene and methanol; solvent (b) is methanol; solvent (c) is dimethylformamide; and solvent (d) is a methylene chloride.

Table I Exp. Scale No. Compound (A) Compound (B) Solvent (g/m22 A Nigrosine Base None a 25 B None Oil Scarlet 308 b 300 C None Rhodamine Base (b) 410 1 Nigrosine Base Nigrosine (b) 0 2 Oil Scarlet SN Nigrosine (b) 0 3 Malachite Green Oil Scarlet 308 b 0 4 Induline Amaranth (c) 0 5 Nigrosine Base Oil Scarlet 308 (d) 0 D Nigrosine Base/ None (b) 280 Sudan Black B E None Rhodamine Base/ (b) 320 Nigrosine F Induline/ None (b) 300 Spirit Black Examples 6 to 17 and Controls G to I Coating solutions were prepared by mixing Sudan Black B as compound (A) and Nigrosine as compound (B) in the various proportions (by weight, in certain solvents under specific conditions, as set forth in Table II, followed by filtration, to give a concentration of 1% by weight based on the solvent.

Each coating solution thus obtained was applied to the surfaces of the inner walls of 1,000-liter stainless steel polymerization reactor and the agitator blades in an amount of 0.1 g/m2 (as solid). The surfaces so treated were then dried and washed with water. Thereupon, 500 kg of deionized water, 0.5 kg of partially saponified polyvinyl alcohol, 100 g of diisopropyl peroxydicarbonate and 200 kg of vinyl chloride were introduced into the polymerization reactor, and polymerization was then conducted at 570c for 10 hours with agitation at 100 r.p.m. After completion of the polymerization, the amount of polymer scale deposited on the surfaces was determined with the results as given in Table II.

For Examples 6 and 11 to 16, the coating compounds were mixed in the solvent and the mixture was agitated for 3 hours at room temperature. For Examples 7 and 8, the same procedure was carried out except that the temperture during agitation was 0 and 90"c, respectively. For Examples 10 and 17, the same procedure was carried out except that, respectively, ultraviolet light was used and the mixing period was one hour. For example 9, the coating compounds were individually disolved in the solvent with agitation for 3 hours at room temperature, and the two solutions were then mixed.

Table II Exp. Sudan Nigro- Scale No. Black B sine Solvent G None None None H 100 None Methanol 420 I None 100 Methanol 460 6 100 100 Methanol 0 7 100 100 Methanol 0 8 100 100 Methanol 18 9 100 100 Methanol 5 10 100 100 Methanol 0 11 100 5 Methanol 85 12 100 20 Methanol 15 13 100 50 Methanol 0 14 5 100 Methanol 60 15 20 100 Methanol 12 16 50 100 Methanol 0 17 100 100 Ethylene- 0 diamine Examples 18 to 29 and Controls J to V Using the coating solution of Example 6, the surfaces of the inner walls of a 1,000-liter stainless steel polymerization vessel and the agitator having paddle-type blades 600 mm in diameter were coated in an amount of 0.1 g/m 2 (as solid). The surfaces so treated were then dried and washed with water.

Thereupon, 100 kg of vinyl chloride, 200 kg of deionized water and various amounts of various processing additives, together with various amounts of polymerization initiators and dispersing agents, as set forth in Table III, were introduced into the polymerization reactor, and polymerization was then conducted at 57"C for 10 hours with agitation at 100 r.p.m.

After completion of the polymerization, the amount of polymer scale deposited on the surfaces was determined with the results as given in the table under the heading "Present Invention".

For comparison, the same procedure as above was repreated except that.the coating solution was a solution of Nigrosine Base alone, and the amount of polymer scale was determined with the results as given in the same table under the heading "Control".

In Table III, DVN means dimethylvaleronitrile, LPO means lauroylperoxide, BPO means benzoylperoxide, IPP means diisopropylperoxydicarbonate, PVA means partially saponified polyvinyl alcohol, HPMC means hydroxypropylmethycellulose, SLS means sodium lauryl sulphate, CA means cetyl alcohol, and DOP means dioctyl phthalate. In Example 21 and control M, the monomer mixture comprised 85 kg of vinyl chloride and 15 kg of vinyl acetate.

In Example 22 and control N, a mixture of 95 kg of vinyl chloride and 5 kg of vinyl acetate was used. Vinyl chloride alone was used in all the other experiments. In Example 29 and control U, the agitation speed was 30 r.p.m.

When a control was carried out using 0.03 kg of DVN as the initiator at 0.1 kg of PVA as the dispersing agent, without any processing additives, the amount of scale deposited was 1200 g/m2.

Table III Scale (g/m) Processing Present Exp. Initiator Dispersing additive(s) in No. (kg) agent (kg) (kg) vention Control 18/J DVN(0.03) PVA(0.1) Stearic acid (0.1) 0 310 19/K -do- -do- Calcium stearate 0 300 (0.1) 20/L -do- -do- Zinc oleate (0.1) 0 230 21/M -do- -do- - 0 170 22/N -do- -do- - 0 130 23/O -do- HPMC (0.1) Sodium 2-ethyl- 0 330 hexyl-sulfosuccinate (0.1) 24/P LPO(0.5) PVA (0.1) - 0 330 25/Q BPO(0.7) -do- - 0 300 26/R IPP(0.02) -do- Tribasic lead 0 360 stearate (1.2) Calcium carbonate(3.0) DOP (2.0) Stearic acid (0.5) Calcium stearate (0.7) Titanium dioxide (1.5) 27/S -do- -do- Dibasic lead 0 410 stearate (0.7) Tribasic lead stearate (1.0) Polyethylene was (0.5) Lead Stearate (1.4) Barium stearate(0.2) Stearic acid (0.1) 28/T -do- -do- Calcium 0 390 stearate (1.0) Rice wax (1.2) Octyl mercaptide (0.7) Polyethylene wax (0.1) 29/U DVN(0.03) S.L.S.(1.0) - 27 450 C.A. (1.5) Examples 30 to 37 The coating solution of Example 6 was applied to the surfaces of the inner walls of a 5-liter stainless steel polymerization reactor and the agitation blades in an amount of 0.1 g/m2, and the surfaces so treated were dried and then washed with water. Thereupon, 1,800 g of vinyl chloride, 2,700 g of deionized water, 0.1 g of partially saponified polyvinyl alcohol, 0.1 g of sodium stearate and 0.03 g of dimethyl-valeronitrile were introduced into the polymerization reactor and subjected to polymerization at 570c in the presence of alkaline substances which were added in the amounts and at the times, after the start of polymerisation, indicated in Table IV. Runs of such polymerization were repeated with the same polymerization reactor until polymer scale depositing on the coated surfaces was found to exceed 1 g/m2 or observed with the naked eye. The number of runs just prior to that run where the polymer scale deposition was so found or observed was recorded. The results are given in the table.

Table IV Exp. Alkaline Amount Addition Time, No. of No. Substance weight % hours Runs 30 None - - 2 31 Sodium hydroxide 0.01 0 6 32 - do - 0.01 2 5 33 - do - 0.01 4 3 34 - do - 0.1 0 12 35 Sodium acetate 0.1 0 9 36 -do- 0.1 2 7 37 Calcium hydroxide 0.05 0 10 Example 38 The coating solution of Example 6 was applied to the surfaces of inner walls of two polymerization reactors, one being a vertical-type 2-liter stainless steel reactor and the other being a horizontal-type 4-liter stainless steel reactor and other parts coming into contact with monomer, in an amount of 0.1 g/m2. The coated surfaces were dried and then washed with water. Thereupon, 800 g of vinyl chloride and 0.4 g of dimethylvaleronitrile were introduced into the first 2-liter polymerization reactor, and polymerization was then conducted at 600c for 2 hours with agitation at 900 r.p.m. The resulting reaction mixture was transferred to the second 4-liter polymerization reactor which had been charged with 800 g of vinyl chloride and 0.4 g of dimethylvaleronitrile, to carry out a further polymerization at 570c for 10 hours with agitation at 100 r.p.m. No scale was deposited in either rector.

For comparison, two similar tests were carried out, one without a coating solution and the other with a coating solution consisting of Nigrosine Base alone. In the first test, the amounts of scale deposited in the first and second reactors were 1400 and 2040 g/m2, respectively.

The respective results in the second test were 70 and 80 g/m2.

Claims (12)

WHAT WE CLAIM IS:

1. A method for the polymerisation of vinyl chloride monomer or a mixture of monomers composed mainly of vinyl chloride in the presence of a polymerisation initiator in a polymer isation vessel, in which the surfaces of the vessel coming into contact with the monomer or monomers are treated, prior to polymerisation, with (A) a basic nitrogen-containing dye selected from quinoneimine dyes containing an axine, oxazine or thiazine ring, azo dyes, diphenylmethane dyes, triphenylmethane dyes, oil-soluble amino-containing azo dyes, xanthene dyes thiazole dyes, stilbene dyes, phthalocyanine dyes and cyanine dyes, and (B) and acidic sulfonic acid group-containing dye selected from azo dyes, mordant azo dyes, triphenylmethane dyes, quinoneimine dyes containing an azine, oxazine or thiazone ring, xanthene dyes, stilbene dyes and thiazole dyes.

2. A method according to claim tin which compound (A) is selected from Nigrosine Base. Oil Scarlet SN, Malachite Green, Spirit Black, Induline and Sudan Black B.

3. A method according to claim 1 or claim 2 in which compound (B) is selected from Rhodamine Base, Nigrosine, Acid Brown GR, Chrome Black PB and Amaranth.

4. A method according to any preceding claim in which the weight ratio of compound (A) to compound (B) is from 1:20 to 20:1.

5. A method according to claim 4 in which the weight ratio is from 1:5 to 5:1.

6. A method according to any preceding claim in which the amount of compound (A) plus compound (B) is at least 0.001 g. solid/m2.

7. A method according to any preceding claim in which compounds (A) and (B) are used as a solution in a solvent selected from water, alcohols, esters, ketones, hydrocarbons, chlorinated hydrocarbons and aprotic salts.

8. A method according to any preceding claim in which the polymerisation mixture is a dispersion of the monomer or monomers in an aqueous medium to which an alkaline substance has been added.

9. A method according to any preceding claim in which the polymerisation mixture contains at least one processing additive.

10. A method according to any preceding claim in which, prior to the polymerisation, the said surfaces of the vessel are washed with water.

11. A method according to claim 1 substantially as described in any of the Examples.

12. A vinyl chloride polymer prepared by a method according to any preceding claim.