GB2190604A - Process for the polymerization in aqueous suspension of halogen-containing vinylic monomers - Google Patents

Abstract

In the polymerization in aqueous suspension of halogen-containing vinylic monomers, the formation of crusts can be prevented or inhibited by treating the inner reactor walls (either of metal or vitrified) and the parts in contact with the reaction medium, before the polymerization reaction, with a solution or dispersion of an organic salt containing nitrogen in its cationic moiety. The anionic moiety of the salt is derived from a carboxylic acid of formula R1(COOH)n wherein R1 is C2 to C20-alkyl or an aryl or alkylaryl radical having 6 to 50 carbon atoms and n is from 1 to 4, or from a sulphonic acid of formula R1(SO3H)m where m is from 1 to 3. The cationic moiety is derived from an organic substance containing an =N-, =NH or -NH2 group.

Description

SPECIFICATION Processforthe polymerization in aqueoussuspen- sion of halogen-containing vinylic monomers The present invention relates to a processforthe polymerization in aqueous suspension of halogencontaining vinylic monomers.

The polymerization in aqueous suspension is a commonly used technique for producing polymers of halogen-containing vinylic monomers.

ltconsists in polymerizing the monomerorthe monomers in a stirred aqueous medium, and in the presence of one or more suspending agents and of one or more polymerization initiators, which act as free-radical generators. As the suspending agents, eithersynthetic or natural polymers are used which have colloid-protective properties, such as partly hydrolised polyvinyl acetate, cellulose ethers, gelatin, sorbitol esters with lauric acid, stearic acid and others.

As the polymerization initiators, organic peroxides are generally used, such as lauroyl peroxide, benzoyl peroxide, isopropyl peroxy-dicarbonates, acetyl cyclohexyl-sulphonyl peroxide, peresters, such astertbutyl per-neodecanoate, azo-compounds, such as azo-bis-isobutyronitrile, dimethyl valeronitrile, etc.

The polymerization is commonly carried out batchwise inside reactors equipped with blade stirrer and possibly baffle plates.

During the polymerization, especiallywhen steel reactors are used, polymer deposits, generally de nominated "crusts" are formed, which adhere, very strongly, to the surfaces of reactor, stirrer and baffle plates.

The formation of said crusts causes several negative effects. Firstly, the bad heat conductivity of the crusts makesdifficultthe heatexchangebetweenthereac- tion medium and the outer cooling wall, and this difficulty increases with increasing crusts surface areas and thicknesses during the polymerization.

It derives therefrom that the productivity of the reactor is reduced, in as much as operating at lower polymerization rates than those which could be had in the absence of crusts is necessary. It mayfurthrmore happen that a part of these crusts get detached during the time necessary for the polymerization, and contaminate the polymer, consistently worsening the quality thereof, by being difficultly melting and with different morphology.

Furthermore, to the purpose of carrying out subsequent polymerization, at the end of each run cleaning the reactor is necessary, such a cleaning being manually performed either with solvents orwaterjets.

These cleaning operations are very complex, burdensome, and involve a lengthening of the time during which the reactor remains out of commission. Fu rth ermore, as having access to the interior of the autoclave is necessary, forthe necessary cleaning at each polymerization end, operating according to the technology of sealed reactors is not possible; such a technoiogywould ailowa sourceof environmental pollution tp be removed.

Various trials have been made to the purpose of preventing or avoiding the formation of fouling. Thus, for instance, in U.K. patent No. 1,291,145, it is proposed to coat all of parts and walls which may come into contact with thevinylic monomerto be polymerized, before starting the polymerization reaction, with a coating composition which may be one or more of following compounds: an organic compound containing a nitrogen atom, such as azo-radicals, nitro-radicals, nitroso-radicals, azo-methines, azines, aminic compounds, an organic compound containing sulphur, a quinone, a ketone, an aldehyde, a 0s- alcohol, a cationic or anionic su rfactant com pou nd, or a dye of indigoid type, a sulphide dye, a nitro dye, a thiazole dye, a quinol dye, a di-azo dye, etc.

Tests carried out by the presentApplicant have however evidenced thatthe treatment of the reactor walls, and ofthe parts which come into contact with the liquid or gas monomer during the polymerization, with one or more of abovesaid compounds, is not completely efficacious in all cases, and with all polymerization formulations.

A purpose of the present invention isto provide a simple and efficacious method to prevent or eliminate the formation of crusts inside the steel reactors used in the polymerization in aqueous suspension of halogencontaining vinylic monomers.

Another purpose of the present invention is to supplya methodforthe preparation in suspension of polymers of halogen-containing vinylic monomers withouttheformation of crusts, and withoutthe workability, the granulometricdistribution ofthe particles, the initial colourandthe heat stability of the polymer being impaired.

According to the present invention, these and other purposes are achieved in a process of polymerization in aqueous suspension of one or more halogencontaining vinylic monomers, in the presence of one or more free-radical-generator initiators and of one or more suspending agents, by treating the inner walls of the polymerization reactor (either of metal orvitrified) and all of parts which may come into contact with the polymerization medium, before starting the polymerization reaction, with a solution or dispersion of an organic salt having a pH value comprised within the range offrom 0 to 2 and wherein the anionic moiety is derived from a mono-or poly-carboxy acid of general formula R1~(COOHìn wherein R1 is an alkyl radical containing from 2 to 20 C atoms, a cyclo-alkyl radical containing from 3 to 30 C atoms or a simple or polycondensed aryl or alkylaryl radical containing from 6to 50 C atoms, and n is an integer comprised within the range of from 1 to 4, or from a sulphonic acid having the general formula R1-(SO3H)m' wherein R1 has the same meaning as above, andm is an integer comprised within the range of from 1 to 3; and the cationic moiety is derived from organic substances which contain nitrogen as =N-, =NH and/or-NH2 groups.

Forthe preparation ofthesolution or dispersion of the organic salt, any suitable solvent or diluent can be used such as, e.g., methyl alcohol, ethyl alcohol, water, acetone, water-acetone mixture, etc.

Examples of specific anions which can be used for the preparation of the organic salt, used in the process of the present invention, are those which derive from adipic acid, citric acid, oxalic acid, trimesic acid, p-toluenesulphonic acid, naphthalene-sulphonic acid, abietic acid, ortho- or meta-toluene-sulphonic acid, benzene-sulphonic acid, trimellitic acid, phthalic acid, terephthalic acid, tartaric acid, pyromellitic acid, benzoic acid, propionic acid, butyric acid, capronic acid, etc.

Examples of specific cations which can be used for the preparation ofthe organic salt used in the process ofthe present invention are those which derive from alpha-naphthyl-amine, anilene, m-toluenediamine, pyrrole, imidazole, pyrazole, pyrazine, pyrimidine, pyridazine, indole, indazole, purine, quinoline, phenanthroline, phenanthridine, carbazole, phenazine, piperazine, piperidine, organic dyes containing the N-, NH or -NH2 group, such as Nigrosine, etc.

The organic salt used in the subject process ofthe present invention is preferably obtained by dissoliving the basic compound into the selected solvent, and subsequently neutralizingthefree N-, = NH and/or NH2- groups by means ofthe addition ofthe organic acid.

According to the process of the present invention, the organic salt is applied asathin layer on reactor surface, on stirrer blades and on baffle plates, if present, by wetting or uniform spray-coating of said surfaces by the salt solution.

Such a treatment is also carried outonthewallsof the condenser and of the duct which connects this latter to the polymerization reactor, if present.

The salt amount necessary for obtaining the antifouling effect is very small. In practice, amounts hig her than 0.005 g/m2 are preferred, in as much as, by operating with amounts lowerthan such a threshold vale, the anti-fouling effect may result not satisfactory.

Vice-versa, no upper limits existforthe coating amount, on condition that no negative effects for copolymer properties occur. Even amounts higherthan 1 g/m2 can be used.

The process ofthe present invention can be applied tothe polymerization in aqueous suspension of halogen-containing vinylic monomers.

By the term "halogen-containing vinylic monom ers", as it is used in the instant specification and in the appended claims, all ofthose monomers are meant, which can be polymerized by free-radical-initiated polymerization, which have a terminal olefinic unsaturated bond, and contain at least a halogen as substituent. These monomers are preferably ethylene derivatives, and among them vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride, chloro-trifluoro-ethylene, tetrafluoroethylene, etc., can be mentioned. The chlorinecontaining vinylic monomers are particularly preferred, in particular vinyl chloride.

The term "polymerization", as it is used in the present specification and in the appended claims, comprises both the homopolymerization and the copolymerization oftwo or more halogen-containing vinylic monomers with one another, or of one or more of such monomers with one or more of other monomers copolymerizablewith them.

Examples of other monomers are: vinylic esters, such as vinyl acetate; acrylic esters, such as methyl acrylate and glycidyl acrylate; unsaturated diesters, such as dibutyl maleate; allyl-esters, such as allyl acetate; unsaturated amides, such as acrylamide; ,styrene; substituted styrene; alpha-olefins, such as ethylene or propylene, etc.

The present invention is preferably applied to the polymerization which generates polymers containing at least 50% by mol, and preferably more than 80% by mol ofvinyl chloride.

The anti-fouling action performed by the organic salt, according to the process of the present invention, is shown independently of the type of suspending agents used.

Specifically, used may be copolymers of vinyl acetate with vinyl alcohol or other types of alcohols, celluloses and/or cellulose ethers, polymers or copolymers containing acidic functions, esters of glycerol and/or sorbitol and still others, either alone or combined with one another. The amount of said suspending agents is generally comprised within the range of from 0.01 to 1% by weight relatively to the present monomer(s).

Any initiators, or initiator mixtures, can be used in the process of suspension-polymerization of the present invention, on condition that they are compati ble with the other substances present in the polymerization medium.

Among the known initiators, in practice the products of alkylperoxides, persters and perca rbonates classes have shown to be particularly interesting.

Besidesthe suspending agent and the polymeriza tl3FI initiator,the polymerization mixture can contain several other additives from those normally used in the polymerization in aqueous suspension as stabilizers, molecular weight regulators, buffer systems, and so forth.

The polymerization conditions are those generally used in the process of polymerization in aqueous suspension. The polymerization is generally carried out batchwise, and the inner coating of the reactor is usually applied after each polymerization batch.

In this way, it is possible to indefinitely keep spick-and-span all of the inner surfaces ofthe polymerization reactor and of all of parts into contact with the polymerization medium.

To the purpose of better understanding the present invention and of practically embodying it, hereunder some illustrative, but not iimitative, Examples are reported.

In the Examples, all parts are parts byweight, unless differently stated.

Examples from 1 to 12 To a polymerization reactor of steel, of 1500 litres of capacity, equipped with a blade stirrer, wherein the innerwalls and the stirrer had been spray-coated with a solution ofthe type as shown in Table 1, -720 litres ofwater; --480 kg of vinyl chloride; -675goflauryl peroxide; -96 g oftert-butyl-cyclohexyl peroxydicarbonate; -480 g of vinyl acetate-maieic an hydride copolymer, having a molecularweight of 1,200,000, and containing 52 mil % of acetate and 48 mol % of maleic anhydride; - 960 g of a copolymer of vinyl acetate and allyl alcohol, with an Mn of 6000, and a content of OH groups of 8.5%; were charged.

The temperature ofthe polymerization mass is increased up to 54"C. After 10 hours, the polymerization product is discharged, and the polymerization run is repeated until the reactor has to be cleaned due to the excessive presence offouling, either chemically, or manually, or by water jets.

The manual removal of the fouling evidenced that the total weight of the crusts results, when the cleaning is carried out, of about 1 kg.

If the polymerization runs with no need for cleaning exceed the number often, then the reactor is mechanically cleaned afterthe 10th batch and the collected crusts are weighed.

In Table 1 the numbers of polymerization runs carried out before the intervention for manual cleaning and the weight of collected crusts are reported, as a function of the type of solution applied to reactor walls.

Table 1 Applied solution Number Fouling, Compound Solvent of runs grams 1 1 3000 2 Adipicacid Methanol 1 2500 3 Trimesicacid Methanol 1 2500 4 p-Toluenesulphonicacid Methanol 1 1500 5 NigrosineB Methanol 1 1500 6 Alpha-Naphthilamine Methanol 1 2200 7 Adipic acid + alpha naphthylaminesalt Methanol 5 1100 8 Trimesicacid + alpha naphthylaminesalt Methanol 4 1200 9 p-Toluenesulphonicacid + alpha-naphthylamine salt Methanol 6 900 10 Adipicacid+ NigrosineBsalt Methanol 8 1000 11 Trimesic acid + NigrosineBsalt Methanol 10 100 12 p-Toluenesuiphonicacid + NigrosineBsalt Methanol 10 traces Examples 13 to 15 The operating modalities of Example 1 are repeated, with the 480 g ofvinyl acetate-maleic anhydride copolymerandthe960 g of vinyl acetate-allyl alcohol copolymer being replaced by a blend consisting of 960 g of a vinyl acetate-vinyl alcohol copolymer having an intrinsic viscosity of 20 ml/g, 30% hydrolysis and an index n = 0.35 and 750 g of anothervinyl acetate-vinyl alcohol copolymer having an intrinsic viscosity of 66.5 ml/g,72% hydrolysis and an index n of 0.40.

In Table 2 the numbers of polymerization runs carried out before the intervention for manual cleaning and the weight of collected crusts are reported, as a function ofthe type of solution applied to reactor walls.

Table 2 Applied solution Number Fouling, Compound Solvent of runs grams 13 Adipicacid + alpha naphthylaminesalt Methanol 4 1300 14 Trimesicacid + aipha naphthylaminesalt Methanol 4 1300 15 p-Toluenesulphonicacid + NigrosineBsalt Methanol 10 traces Examples 16 to 18 The operating modalities of Example 1 were repeated, with the 480 g of vinyl acetate-maleic anhydride copolymer and the 960 g of vinyl acetate allyl alcohol copolymer being replaced by 400 9 of methyl-hydroxypropyl-cellulose having a methyl content of 28% and a hydroxypropyl content of 5%, and 750 g of a vinyl acetate-vinyl alcohol copolymer having an intrinsic viscosity of 20 mI/g, 55% hydroly- sis and an index n = 0.35.

In Table 3the numbers of polymerization runs carried out before the intervention for manual cleaning and the weight of collected crusts are reported, as afunction ofthetype of solution applied to reactor walls.

Table 3 Applied solution Number Fouling, Compound Solvent of runs grams 16 Adipicacid + alpha naphthylamine salt Methanol 4 1100 17 Tnmesicacid + alpha naphthylaminesalt Methanol 4 1000 18 p-Toluenesulphonicacid + Nigrosine B salt Methanol 10 traces Examples 19 to 22 The operating modalities of Example 1 were repeated, with the 480 g of vinyl acetate-maleic anhydride copolymerand the 960 g of vinyl acetate allyl alcohol copolymer being replaced by 160 g ofthe same vinyl acetate-maleic anhydride copolymer, 200 g of a vinyl acetate-vinyl alcohol copolymerhaving an intrinsic viscosity of 20 mllg, 25% hydrolysis and index n equal to 0.40 and 250 g of sorbitan monostearate.

In Table 4the numbers of polymerization runs carried out before the interventrion for manual cleaning and the weight of collected crusts are reported, as a function ofthe type of solution applied to reactorwalls Table4 Applied solution Number Fouling, Compound Solvent of runs grams 19 Adipic acid + alpha- naphthylaminesalt Methanol 5 1300 20 Trimesicacid + alpha naphthylaminesalt Methanol 6 1000 21 Tnmesicacid + Nigrosine B salt Methanol 10 traces 22 p-Toluenesulphonicacid + Nigrosine B salt Methanol 10 traces Examples 23 to 25 The operating modalities of Example 1 are repeated, with the 96 g oftert-butyldohexyl-peroxy- dicarbonate being replaced by 22 g of lauroyl peroxide.

The grams of crusts collected as a function of the type ofsolution applied to reactorwalls are reported in Table 5.

Table 5 Applied solution Number Fouling.

Compound Solvent of runs grams 23 Adipicacid + Nigrosine B salt Methanol 8 950 24 Trimesicacid + Nigrosine B salt Methanol 10 traces 25 p-Toluenesulphonicacid + NigrosineBsalt Methanol 10 traces Example 26 The same results as reported in Tables 1 and 5 were obtained by carrying outthe copolymerization of a mixture of monomers constituted by 87% byweight of vinyl chloride and 13% by weight of vinyl acetate, under the same operating conditions as reported in Examples 1-12 and 32-37.

Examples 27 to 29 The operating modalitiesofExample 15 were repeated atdifferentvaluesofpH of suspension water.

In Table 6,the number of runs carried out, and the collected crusts are reported as a function of solution pH.

Table 6 Applied solution Number Fouling, Compound Solvent pH of runs grams 27 p-Toluenesulphonicacid + NigrosineBsalt Methanol 2 10 traces 28 p-Toluenesulphonicacid + Nigrosine B salt Methanol 6 10 traces 29 p-Toluenesulphonicacid + NigrosineBsalt Methanol 10 10 traces Examples 30 and 31 The operating modalities of Example 15 were repeated by using different types of solvents for the preparation of salt solution.

In table 7,the number of runs carried out, and the collected crusts are reported as a function of the type of solvent.

Table 7 Applied solution Number Fouling, Compound Solvent of runs grams 30 p-Toluenesulphonicacid + NigrosineBsalt Ethanol 10 traces 31 p-Toluenesulphonicacid + NigrosineBsalt Acetone 10 traces Examples 32 to 33 By the operating modalities as of Example 1, to a vitrified polymerization reactor of 500 litres of capacity, provided with impeller-stirrer, wherein the inner walls were spray-coated with a solution of the type as reported in Table 8, charged are:: 225 litres of water 150 kg of vinyl chloride 211 g of lauroyl peroxide 30 g oftert-butyl-cyclohexyl-peroxydicarbonate 50 g ofvinyl acetate-maleic anhydride copolymer 62.5 g of a vinyl acetate-vinyl alcohol copolymer having an intrinsic viscosity of about 20 ml/g,25% hydrolysis and index n equal to 0.4 78 g ofsorbitan monostearate.

In table8the numbers of polymerization runs carried out before the intervention for manual cleaning and the weight of collected crusts are reported, as a function ofthetype of solution applied to reactor walls.

Table 8 Applied solution Number Fouling, Compound Solvent of runs grams 32 Trimesic acid + Nigrosine B salt Methanol 10 traces 33 p-Toluenesulphonicacid + Nigrosine B salt Methanol 10 traces

Claims (10)

1. A processforthe polymerization in aqueous suspension of one or more halogen-containing vinylic monomers in the presence of one or more free-radical-generator initiators and of one or more suspending agents, wherein at least part ofthat surface ofthe reactor in which the polymerization is carried outwhich in use comes into contact with the polymerìzation medium, and/or at least part of that surface other equipment used in the polymeriza tionwhich in use comes into contact with the polymerization medium, is wetted, before starting the polymerization reaction, with a solution or dispersion of an organic salt having an anionic moiety derived from a mono- or poly-carboxy acid of the general formula:: R1 (COOH)n wherein R1 is an alkyl radical containing from 2to 20 carbon atoms or an aryl or a simple or polycondensed aryl oralkylaryl radical containing from 6to 50 carbon atoms, and n is an integeroffrom 1 to 4, orfrom a sulphonicacid having the general formula: R1 (SO3H)m wherein R1 is as defined above, and m is an integer of from 1 to 3; and having a cationic moeity derived from an organic substance which contains nitrogen asan=N-,=NHand/or-NH2group.

2. A process according to claim 1, wherein the anionic moiety ofthe organic salt is derived from at least one offollowing acids: adipic acid, citric acid, oxalic acid, trimesic acid, p-toluenesulphonic acid, naphthalene-sulphonic acid, abietic acid, ortho-or meta-toluene-sulphonic acid, benzene-sulphonic acid, trimellitic acid, phthalic acid, terephthalic acid, tartaric acid, pyromellitic acid, propionic acid, butyric acid, capronic acid, orthe like.

3. A process according to claim 1 or 2, wherein the cationic moiety ofthe organic salt is derived from at least one offollowing compounds: alpha-naphthylamine, aniline, m-toluenediamine, pyridinic bases, pyrrole, imidazole, pyrazole, pyrazine, pyrimidine, pyridazine, indole, indazole, purine, quinoline, phe nanthroline, phenanthridine, carbazole, piperazine, piperidine, and organic dyes containing an =N-, =NH or-NH2group.

4. A process according to claim 3, wherein the cationic moiety ofthe organic salt is derived from Nigrosine.

5. A process according to any the preceeding claims, wherein the solvent or diluent ofthe organic salt is methyl alcohol, ethyl alcohol, propyl alcohol, water, acetone, a water-acetone blend, orthe like.

6. A process according to any ofthe preceeding claims, wherein the wetting is carried out bywashing, spray-coating or atomization of the solution or suspension bythe use of an inert gas orvapour.

7. A process according to anyofthe preceding claims, wherein the solution or dispersion is used in an amount higherthan 0.005 g/m2.

8. A process according to any of the preceeding claims, wherein that surface ofthe reactorwhich in use comes into contact with the polymerization medium is metallicorvitreous.

9. A process according to any of the preceeding claims, wherein the equipment includes a condenseirn

10. A process according to claim 1, substantially as described in any of the foregoing Examples.