FI61036C - FOERFARANDE FOER POLYMERISATION AV VINYLKLORID I VATTENDISPERSION - Google Patents

Description

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Patent and Registration Office .... , _ . . . (44) Date of issue and date of issue. -

Patent- oeh registerstyrelsen v 'Antöktn utlagd oeh utl.tkrlfun publicend 29-01.82 (32) (33) (31) Requested privilege - Begird prforitet l8.08.75

Luxembourg (LU) 73211 (71) Solvay & Cie, 33, rue du Prince Albert, B-1050 Brussels, Belgium-Belgium (BE) (72) Daniel Tytgat, Brussels, Lucien Clerbois, Vilvoorde, Stephane Noel, Grimbergen, Belgium Belgien (BE) (7 * 0 Oy Kolster Ab '(5M Method for polymerisation of vinyl chloride in aqueous dispersion - Förfarande för polymerisation av vinylklorid i vattendispersion

The invention relates to a process for polymerizing vinyl chloride as a batch process in a reaction vessel in aqueous dispersion by means of an oil-soluble radical polymerization initiator and in the presence of an effective amount of an anti-scaling agent.

Vinyl chloride is generally polymerized in the form of small droplets dispersed in water by mechanical agitation in the presence of emulsifiers (emulsion polymerization) or dispersants (suspension polymerization), as well as water-soluble polymerization catalysts (emulsion polymerization) or fat polymerization (fat polymerization). The polymerization is generally carried out in batches in tank reactors with an impeller mixer.

Applying these prior art polymerization methods, solid deposits adhering to the polymers are formed on the inner surfaces of the reactors (tanks, stirrers, lids) during the polymerization. This phenomenon is called "scaling".

This scaling is very harmful. Due to the scaling that settles on the walls of the tank, the amount of heat that can be removed by the double casings of the 2,61036 reactors is reduced. As a result, lower polymerization rates are forced to be used, so reactor productivity must be reduced.

In addition, the precipitates often detach during polymerization and contaminate the polymers produced.

The formation of these precipitates, which always occurs randomly, makes it difficult to carry out and control the polymerization reactions.

For this reason, the reactors must be cleaned very carefully after each polymerization cycle. This cleaning is usually performed using hot solvents, mechanical devices such as water spray pipes, or even by hand. It is always a matter of time-consuming, cumbersome and expensive handling due to both material, power consumption and craftsmanship.

Various methods have already been proposed to reduce scaling, the simplest of which is based on the addition of an anti-scaling agent to the polymerization medium before or during polymerization. Examples of known anti-scaling agents include magnesium hydroxide (U.S. Patent 3,562,238, filed September 16, 1969 to THE BF Goodrich Company), certain cyanide compounds (JA Patent Application No. 34,976/72, filed April 16, 1971, to Mitsui Toatsu Chemical Company), e.g. nitrites (FR patent 2,185,638 filed on May 24, 1973 in the name of Wacker-Chemie GmbH).

However, none of these known inhibitors is effective enough to allow long sequential polymerization runs without occasional cleaning of the reactors.

Whereas the applicant has now invented a new class of anti-scaling agents which have significantly improved efficiency and which make it possible to extend the time between reactor cleaning cycles to a very large extent,

The invention is characterized in that before the vinyl chloride is charged to the reaction vessel, the inner walls of the reaction vessel are contacted with an anti-scaling solution which is bromide or iodide ions obtained from the dissociation of alkali metal or alkaline earth metal iodides or bromides.

However, the scaling problem is particularly pronounced in aqueous suspension polymerization and homogenized aqueous dispersion polymerization. The application of the method according to the invention is thus most interesting within the framework of these methods.

Any dispersant can be used in the aqueous suspension polymerization, especially finely dispersed solids, gelatin, polyvinyl alcohols of varying degrees of hydrolysis, water-soluble cellulose ethers and polyvinylpyrrolidones. These dispersants can optionally be used in combination with surfactants. The amount used can vary within wide limits and is usually 0.05 to 1.5% by weight, based on water.

Any monomer-soluble radical polymerization catalyst can be used in the aqueous suspension polymerization. Examples which may be mentioned are peroxide compounds such as di-tert-butyl peroxide, lauryl peroxide and acetylsulfohexylsulphonyl peroxide, azo compounds such as azo-bis-isobutyronitrile and alkyl borate. Fat-soluble radical polymerization catalysts which are very suitable in the process according to the invention are dialkyl peroxide carbonates whose alkyl radicals contain at most 5 carbon atoms. These catalysts can be used in conventional amounts, generally from 0.01 to 1% by weight of the monomers.

Polymerization in a homogenized aqueous dispersion, sometimes referred to as microsuspension polymerization, is based on mechanically homogenizing (emulsifying) an aqueous dispersion of one or more monomers in the presence of a surfactant (e.g., applying a very strong shear effect to the dispersion) to homogenize in the presence of a soluble catalyst.

Conventional emulsifiers and oil-soluble catalysts, such as sodium dodecylbenzenesulfonate-type anionic emulsifiers, and di-alkanyl peroxide-type peroxide catalysts, e.g. lauryl peroxide, can be used in the polymerization of the homogenized aqueous dispersion.

In addition to emulsifying or dispersing agents and catalysts, aqueous dispersions (suspensions and microsuspensions) may also contain a variety of additives normally used in prior art dispersion polymerization processes. substances.

The operating conditions of the polymerization carried out by the process according to the invention do not differ from the conventionally applied conditions. The temperature o 2 is usually U0 ... 75 C, and the pressure is usually less than 15 kp / cm. The pH is usually acidic, e.g. 2 ... 7. The amount of water used is also ordinary, so that the total weight of the monomers is 20 to 50% of the total weight of water and monomer.

The bromide or iodide ions used according to the invention can be added as a compound which is soluble in water and dissociates therein to form bromide or iodide ions.

Suitably bromides and iodides of alkali metals or alkaline earth metals are used, i.e. water-soluble salts which dissociate in water to form bromide or iodide ions and cations.

Namely, excellent results have been obtained with alkali and alkaline earth metal salts which dissociate in water to form bromide or iodide ions, as well as cations with an ion field (defined as the ratio of valence charge to ion beam) greater than 0.6.

Examples of suitable cations are K +, Na +, Li +, Ca2 ++,

Mg2 ++. Potassium, lithium, calcium and magnesium bromides and iodides are suitably used, and sodium, lithium and potassium iodides and bromides are suitably used.

The best results are obtained with potassium salts, the use of which is therefore very particularly advantageous. For reasons of efficiency, iodide ions are suitably used.

It has also been found that the way in which bromide or iodide ions are added to the aqueous dispersion forming the polymerization medium is an influential factor.

In a batch process, the inner surfaces of the reactor are suitably contacted with an aqueous solution containing bromide or iodide ions before the halogenated vinyl monomers are introduced into the reactor. Thus, the reactor can be rinsed with an aqueous solution to treat all internal surfaces, after which this solution is removed and the conventional polymerization components (water, dispersing or emulsifying agents, monomers, catalyst) are added. In doing so, it is found that the pre-rinsing causes the inner surfaces of the reactor to be covered by a sufficient amount of bromide or iodide ions by adsorption, so that these ions do not necessarily have to be added to the aqueous dispersion during the polymerization. However, for convenience, it is proposed to first add to the reactor the water used during the polymerization, possibly with the addition of other water-soluble components, such as emulsifiers or dispersants, and which contains bromide and iodide ions in solution. These can remain in the aqueous phase throughout the polymerization. The halogenated vinyl monomers, as well as possibly the catalyst, are added only after this.

In the case of using a catalyst which is somewhat soluble in water and capable of oxidizing bromide or iodide ions, e.g. diethyl peroxydicarbonate, the inner surfaces of the reactor are likewise suitably contacted with an aqueous solution containing the bromide or iodide ions before reactor. The addition is suitably carried out not only after the addition of bromide or iodide ions but also after the addition of monomers.

The amount of bromide or iodide ions used can vary within wide limits, depending in particular on the nature of the monomers and also on the polymerization conditions and the surface conditions of the reactor used. Optimal amounts can be easily determined experimentally. The total amounts used are suitably sufficient to cover the inner surfaces of the reactor as completely as possible by adsorption with bromide or iodide ions. The amounts to be used are. . . . . . 2 generally greater than about 1 mg of bromide or iodide ions per m of inner surface. When iodide ions are used, the maximum coverage of steel surfaces is achieved by using ions of about 5 mg / m,

When using alternative embodiments in which bromide or iodide ions are added directly to the aqueous phase of the polymerization medium, amounts of bromide-iodide ions greater than 1 ppm with respect to water are suitably used. Preferably amounts greater than 5 ppm are used and the best results are obtained are more than 10 ppm.

In the event that the reactor is rinsed with an aqueous solution of bromide or iodide ions as described above, the solution may suitably contain the same amounts of ions as described in the previous paragraph.

In principle, there are no upper limits on the amounts of bromide or iodide ions that can be used. In practice, however, some problems may arise if the concentrations of bromide or iodide ions in the aqueous phase are too high during the polymerization. In particular, a deterioration in the color of the polymer or the consumption of catalysts capable of oxidizing bromide or iodide ions are sometimes observed. For this reason, in practice, the concentration of bromide or iodide ions relative to 1000 ppm relative to water is seldom exceeded during polymerization. In most cases, a concentration of 200 ppm is not exceeded, and a concentration of 100 ppm is usually sufficient,

Obviously, it should finally be mentioned that in selecting the amounts to be added to the aqueous phase of the polymerization medium, account must be taken of the amounts of bromide or iodide ions adsorbed during the previous 6,61036 rinses or from previous polymerizations.

When applying the process according to the invention to a particular reactor, the inner surfaces of this reactor are preferably pre-cleaned with particular care. This can be done by using particularly effective solvents for scaling polymers, heating the walls at high temperature, pickling or polishing.

The efficiency of the method according to the invention is remarkably high. Applying the invention to the polymerization of vinyl chloride in aqueous suspension with diethyl peroxide carbonate using about 10 mg of potassium iodide / kg of water, several dozen successive polymerizations can be performed without manual purification of the reactor. In addition, it should be noted that the presence of potassium iodide in no way interferes with the polymerization reaction, and there is no need to change the conditions of use in any way because of this iodide. The polymers obtained are completely flawless and also free of any contaminants.

The following examples illustrate the invention.

Example 1 A stainless steel 3 liter laboratory reactor with a vane stirrer is used. The reactor is cleaned by washing with tetrahydrofuran, after which the waste is incinerated by heating at 600 ° C for 30 minutes. The reactor is then covered with a nitric acid-hydrofluoric acid bath. Finally, the reactor is flushed several times with demineralized water.

The reactor is rinsed with an aqueous solution of potassium iodide with an iodine content of 6.6 mg / l. 15 to 5 g of demineralized water to which 10 mg of potassium iodide and 1.65 g of polyvinyl alcohol have been added are then introduced into the reactor in turn. The mixer starts. The reactor is then evacuated twice (100 mm Hg abs.) And technical nitrogen is blown twice through the autoclave (pressure 1360 mm Hg abs.). 1030 g of vinyl chloride and then 310 mg of diethyl peroxydicarbonate are then introduced into the reactor, which is then heated to 6 [deg.] C. at a rate of 1 [deg.] C. / min and the polymerization medium is kept at this temperature of 61 [deg.] C. · 2

When the pressure in the reactor has dropped to 3.5 kp / cm abs, the polyraerisation is stopped (the pressure of the monomer is reduced), cooled and the polymer is recovered by filtration, followed by drying, 7 61036

Inspection of the inside surfaces of the reactor shows that there is no scum. The resulting polymer is impeccably white.

Example 2 R

This example is presented for comparison. The procedure is as in Example 1, except that the reactor is not rinsed with aqueous potassium iodide and potassium iodide is not added to the polymerization water.

Inspection of the reactor after polymerization shows that the inner surface of the tank is covered by an adhering polymer film, that there is adhering polymer on the agitator shaft, that there is also adhering polymer in the reactor lid, and that the outward opening lines in the reactor are partially blocked by adhering polymer.

Example 3

The procedure is as in Example 1, except that the washing solution contains 0.66 mg of potassium iodide per liter of water and that 1 mg of potassium iodide is added to the polymerization water.

Very weak scum is observed on the inner surfaces of the reactor. This example shows that even a very small amount of potassium iodide is sufficient to significantly reduce scaling.

Example 4

The procedure is as in Example 1, except that the rinsing solution contains 66 mg of potassium iodide / liter of water and 100 mg of potassium iodide are added to the polymerization water.

No scum is observed on the inner surfaces of the reactor. However, the polymerization rate is slightly lower than in the case of Example 1.

This example shows that excessive amounts of potassium iodide lead to the consumption of diethyl peroxide carbonate (soluble in water and oxidizes iodine).

Example 5

The procedure is as in Example 1, except that the reactor is rinsed with a solution of 660 mg of potassium iodide per liter and that potassium iodide is not added to the polymerization water.

Namely, the observed scaling is small with a light film adhering to the agitator shaft, and a few polymer granules are adhered to the wall.

This example shows that pre-rinsing with an aqueous solution of potassium iodide is already sufficient to quite significantly reduce scaling.

8 61036

Example 6

The procedure is as in Example 1, except that the reactor is not rinsed with potassium iodide solution, but that the stirrer is allowed to run for 15 minutes before 1545 g of demineralized water and 10 mg of potassium iodide are added. In addition, 4-tert-butylcyclohexyl peroxydicarbonate is used as a catalyst.

No scaling is observed.

Example 7

The procedure is as in Example 1, except that the reactor is rinsed with a solution of 1000 mg of potassium iodide / liter of water and that 1050 mg of potassium iodide is added to the polymerization water. In addition, 1050 mg of disethyl peroxydicarbonate are used as catalyst.

No scaling fades.

This example shows that higher doses of potassium iodide can be used in the case of water-insoluble catalysts.

Example 8

The procedure is as in Example 7f except that 515 mg of azo-bis-valeronitrile are used as catalyst.

No scaling is observed.

This example shows that higher doses of potassium iodide can be used in the case of a catalyst which does not oxidize iodide. Example 9

The procedure is as in Example 1, except that the reactor is rinsed with a solution of 10 mg of sodium iodide per liter of demineralized water and 15 mg of sodium iodide are added to the polymerization water.

A fairly slight scaling is observed, limited to the polymer lines adhering to the top of the container wall.

Example 10

The procedure is as in Example 1, except that the reactor is rinsed with a solution of 10 mg of potassium bromide per liter of demineralized water and 15 mg of potassium bromide is added to the polymerization water.

Polymer streaks are observed which form a light scum on the inner surfaces of the reactor.

Example 11 This example relates to the homopolymerization of vinyl chloride in a homogenized water dispersion.

1500 g of demineralized water to which 10 mg of potassium iodide, 10 mg of sodium dodecylbenzenesulfonate and 2 g of lauryl peroxide have been added in turn to the mixing autoclaves. The reactor is then pressurized twice (100 mm Hg abs) and between these two pressures the reactor is purged with clean nitrogen (pressure about 1036 mm Hg abs). Then 1000 g of vinyl chloride are added and stirred for 15 minutes to obtain a homogeneous mixture. This mixture is mechanically emulsified by means of a homogenizer and transferred to a three-liter polymerization autoclave equipped with a stirrer, which has been pre-purified, washed and then rinsed with an aqueous solution of potassium iodide in the same manner as described in Example 1.

The homogenized aqueous dispersion is heated to 55 ° C. After the reaction proceeded 1? hours the polymerization is stopped (the pressure of the monomer is reduced), cooled and the polymer is recovered.

Inspection of the inside surfaces of the polymerization reactor shows that they contain only relatively light scum. The scales are scraped off and weighed to give a weight of 0.05% by weight of the vinyl chloride monomer. Example 12 R

This example is presented for comparison. It is carried out in all respects in the same manner as in Example 11, except that the polymerization reactor is not rinsed with aqueous potassium iodide and potassium iodide is not added to the polymerization water.

Inspection of the polymerization reactor shows much stronger scaling in all parts of the reactor. The pastes are scraped off and weighed and found to be 1.5% by weight of the vinyl chloride used.

Example 13 5 This example is presented for comparison. The procedure is as in Example 6, except that the reactor is first rinsed with a solution of 100 g of potassium sulfocyanide per liter of demineralized water, then rinsed a second time with a solution of 6.5 mg of sulfocyanide per liter and 10 mg of calcium sulfocyanide are added to the polymerization water.

Excessive scaling of the inner surfaces of the reactor is observed, with the top of the tank and the lid covered with adhering polymer film.

This example shows that potassium sulfocyanide inhibits scaling much worse than the inhibitors used according to the invention.

Example 14 R

This example is presented for comparison. The procedure is as in Example 6, except that the first rinsing of the reactor is carried out with a solution of 6.5 mg of sodium nitrite per liter of demineralized water and 10 mg of sodium nitrite are added to the polymerization water.

Significant scaling of the reactor interior surfaces is observed, with the tank walls covered with significant polymer streaks, and the tank 10 61 0 36 lid, top of the walls, and agitator covered with copious scum.

This example shows that the nitrile is an anion which has a much weaker antifouling effect than the anions used according to the invention.

Claims (10)

11 61036 A method for polymerizing vinyl chloride as a batch process in a reaction vessel in an aqueous suspension with an oil-soluble radical polymerization initiator and in the presence of an effective amount of antifouling agent, characterized in that the inner walls of the reaction vessel are contacted obtained from the dissociation of alkali metal or alkaline earth metal iodides or bromides. Process according to Claim 1, characterized in that the anti-scaling agent is iodide or bromide ions obtained from the dissociation of alkali metal iodides or bromides. Process according to Claim 2, characterized in that the anti-scaling agent is iodide ions obtained from the dissociation of sodium, potassium or lithium iodide, i.e. Process according to Claim 3, characterized in that the anti-scaling agent is iodide ions obtained from potassium iodide dissociation. Process according to Claim 1, characterized in that the inner walls of the reaction vessel are rinsed with an aqueous solution containing an anti-scaling agent before being charged for polymerization. Process according to Claim 1, characterized in that the anti-scaling agent is added to the water used as the aqueous phase in the polymerization. Process according to one of Claims 1 to 6, characterized in that the anti-scaling agent is used in an amount of more than 1 mg of bromide or. . . . . 2 iodide ions per m inside the reaction vessel. Process according to one of Claims 1 to 7, characterized in that the aqueous phase of the polymerization contains, as an anti-scaling agent, bromide or iodide ions in an amount of more than 1 ppm, based on the amount of water. Process according to Claim 8, characterized in that the amount is from 10 to 100 ppm. Process according to one of Claims 1 to 9, characterized in that aqueous suspension polymerization is used and in that the initiator is a dialkyl peroxide carbonate whose alkyl moieties contain at most 5 carbon atoms.