AU7456381A - Internally coated reaction vessel for use in emulsion polymerization of olefinic monomers - Google Patents

Description

"Internally Coated Reaction Vessel For Use In Emulsion Polymerization Of Olefinic Monomers"

Background of the Invention Various type chemical processes are carried out in large, stirred vessels, or reactors, which are frequently provided with auxiliary equipment, such as baffles, heat transfer coils which enable heat to be supplied to or extracted from the contents of the ves sels, and the like. In many cases, however, such processes eventually produce undesirable deposits on the surfaces of the equipment with which the reaction mixtures come into contact. Such deposits interfere with the efficient transfer of heat to and from the interior of the vessels. Further, these deposits have a tendency to deteriorate and partially fragment resulting in contamination of the reaction mixture and the products produced therefrom. This problem is particularly prevalent in the emulsion polymerization of unsaturated olefinic monomers to produce vinyl resin latices and vinyl dispersion or paste resins.

The problem of polymer buildup is very bad in the commercial production of polymers and copolymers of vinyl and vinylidene monomers having a terminal group, or with polymerizable polyolefinic monomers. In order to overcome this polymer buildup problem it has been, and is, the practice of many producers to coat the interior surfaces of the polymerization reactor with various materials prior to the start of the reaction. As examples of some of these coating materials, reference is made to U.S. Patents No's 4,024,330 - polyaromatic amines in organic solvents; 4,024,301 - polyaromatic amines in aqueous alkali; 4,080,173 - self-condensed polyhydric phenols in aqueous alkali; and 4,105,840 - aqueous solutions of tannins and tannates. All of these coating materials have proved to be very effective in reducing, and in many cases eliminating/ polymer buildup. However, the usefulness of these coating materials has been pretty well limited to aqueous suspension type polymerization systems.

In the emulsion polymerization systems wherein a vinyl polymer latex is produced and the polymer recovered therefrom, buildup is an extremely bad problem. When recovered, these polymers are referred to as dispersion or paste resins. This polymer buildup must be removed since it results in further formation of polymer buildup which in turn results in a crust that adversely affects heat transfer, contaminates the polymer being produced, and is extremely difficult to remove. Coatings have been used in these emulsion polymerization systems but not with very much success. For economic and other reasons the coatings are applied to the metal or glass surfaces in a very thin layer or monolayer. It is believed, that in the emulsion polymerization system the soaps in the emulsifier system may wash the coating off of the reactor surfaces. It has also been speculated that the monolayer of coating material is simply overwhelmed by the magnitude of the buildup that occurs in an emulsion polymerization system. Thus, there is a great need to find a means of substantially reducing and preferably, eliminating the polymer buildup in emulsion polymerization systems.

It should also be noted that the nature of the polymer buildup is such that it is very often necessary, after each polymerization reaction is completed, to open the reactor and scrape the polymer buildup off the walls and off the baffles and agitator. An operation such as this is not only costly, both in labor and in down-time of the reactor, but presents potential health hazards as well. Summary of the Invention It has been found that polymer buildup on the interior surfaces of a polymerization reactor, wherein an emulsion polymerization system is employed, can be substantially eliminated. This is accomplished by first coating the interior surfaces of the reactor with a heavy coating of an unneutralized condensed polyhydric phenol or naphthol dissolved in an organic solvent such as an alcohol and drying the coating prior to the intro duction of the reaction ingredients into the reactor. The coating can be applied to the inner surfaces of the reactor without opening the same thus providing a closed polymerization system. By "heavy coating" is meant one that is substantially thicker, or heavier, than a thin, or monolayer, coating.

Detailed Description

In accordance with the present invention, a heavy film or coating of an unneutralized condensed polyhydric phenol or naphthol is applied to the interior surface of a polymerization reactor or vessel by contacting said surfaces with an alcohol solution of said unneutralized condensed polyhydric phenol of naphthol. Likewise, all exposed surfaces in the interior of the reactor, such as the baffles, agitator or mixing mechanism, the condenser when one is employed, and the like, are also treated in like manner. After the alcohol coating solution has been applied to the interior surfaces, the heavy film or coating thereon is dried. Any suitable means may be employed for drying the coating, such as by flushing the reactor with hot air or steam to sweep the alcohol vapors out, by heating the reactor surfaces by circulating hot water through the jacket surrounding the reactor, and the like. The alcohol vapors can be sent to a recovery system but usually the same are vented to the atmosphere. After the coating has been dried the emulsion polymerization medium is charged into the reactor and the reaction started. The heavy coating or film is not substantially affected by the polymerization medium even though vigorously agitated during the polymerization reaction. The self-condensed and co-condensed polyhydric phenols useful in the present invention are made by heating any one or more of resorcinol, hydroquinone, catechol or phloroglucinol either with or without a suitable catalyst. The same is true for the self-condensed polyhydric naphthols, such as, for example, 2,7-dihydroxy naphthalene, 3 ,7-dihydroxy naphthalene, 2,6-dihydroxy naphthalene, and the like. The polyhydric phenol of naphthol is heated under an inert atmosphere, such as nitrogen, argon, and the like, at a temperature in the range of about 210°C. for a period of time ranging from about 10 minutes to about 500 minutes or 8 hours. Various catalysts may be employed in the reaction, such as zinc chloride, aluminum chloride, sodium hydroxide, and the like. It has been found that the sodium hydroxide catalyst gives the best results. A catalyst concentration of from about 0.05 mole to about 0.50 mole per mole of the compound or compounds being condensed is satisfactory. However, the amount of catalyst employed is not critical. It is understood, of course, that the particular time and temperature selected is dependent upon the catalyst employed and the final desired molecular weight of the condensation product.

The coating solutions of the present invention are made by conventional methods, using heat and agitation where necessary. Usually a temperature in the range of about 20°C. to about 30 °C. is satisfactory. Agitation during dissolution is desirable. The concentration of the condensation product in the coating solution will be in the range of about 1.0% to about 20.0% by weight, and preferably in the range of about 5.0% to about 10.0% by weight of the condensation product has an effect on the concentration of the condensation product in the coating solution of the total solids content of said solution. Since the molecular weight of the condensation product affects the total solids content in the coating solution, the concentration of the condensation product therein could, in certain instances, be greater than 20.0%.

Among the organic solvents that may be used in making the coating solutions of the present invention there may be named; saturated alcohols containing from 1 to 8 carbon atoms, such as methanol, ethanol, isopro panol, butanol, hexanol, 2-ethyl hexanol, and the like; ketones containing from 1 to 8 carbon atoms, such as methyl ethyl ketone, acetone, and the like; aldehydes containing from 1 to 8 carbon atoms, such as acetaldehyde, and the like; acetates, such as ethyl acetate, butyl acetate, and the like; and tetra-hydrofuran.

Unlike the monolayer coatings used in a suspension polymerization system, a sufficient amount of heavy coating solution is painted or brushed on the reactor surfaces or sprayed on and dried there in order for an effective film or coating to form. Spraying of the coating solution onto the reactor surfaces is preferred since it is the most practical and economical method of application. The thickness of the coating on the reactor surfaces is set by the concentration of the condensation product in the coating solution, the quantity of coating solution used, and the degree of run-off before the coating dries in place. The excess coating solution that runs off can be recovered and reused or it can be disposed of by usual methods, depending upon the amount that runs off prior to complete drying. It should be pointed out that the degree of run-off is low since the drying cycle is relatively short, that is, in reactors having a capacity of 3,000 gallons or more, the drying cycle will be in the range of about 1 minute to about 10 minutes. Usually with most coating solutions, the drying time will be about 2 minutes or less.

As pointed out above, various factors affect the thickness of the coating on the reactor surfaces, such as concentration of the condensation product in the coating solution. Usually, the thickness of the film or coating will be in the range of about 5 microns to about 50 microns, and preferably, in the range of about 5 microns to about 15 microns. As a practical matter, the coating should not be too thick due to the increased intensity of the color thereof with increased thickness. For example, a 5 micron thick film, which is tough and water-insoluble, is amber colored. The danger of the film or coating flaking off during the polymerization reaction is practically zero so that the color problem is not all that great. The thickness of the coatings of the present invention are in quite a contrast with the invisible, absorbed monolayer films used heretofore in suspension polymerization. For example, in the monolayer films or coatings, the average film thickness can be as low as 50Å which is 1/1,000th as thick as a 5 micron film.

As has already been noted, the coatings of the present invention work equally well on glass or metal surfaces, such as stainless steel, and the like. While no special cleaning of said surfaces is necessary prior to application of the coating solution, it has been found that the most satisfactory results are obtained when the surfaces are first cleaned. The surfaces can be cleaned with chemical agents, such as chromic acid, etc. or with an abrasive cleaner, such as Ajax®, and the like, and then rinsed with water and dried prior to application of the coating solution. High pressure water cleaning of the surfaces can also be used. Starting with clean surfaces enhances the adhesion of the coating thereto. In the present invention, multiple polymeriza tions may be run without opening the reactor between charges. Although multiple charges may be run without recoating the surfaces, it has been found to be expeditious, and preferred, to recσat the internal surfaces of the reactor after each charge to insure uniform and efficient production. As previously pointed out, it is preferred to use spray nozzles in applying the coating solution to the inner surfaces of the reactor since, with this method, all inner surfaces of the reactor are more easily reached in the least amount of time which in turn reduces the amount of run-off of the coating solution. When it is decided to recoat the reactor, the reactor is drained, and the inner surfaces are flushed with water, that is, using a high pressure stream of water in order to remove any buildup that might have occurred and present a clean surface, when dried, for recoating. Using the spray nozzles, these steps can be accomplished without reopening the reactor. This process can be repeated after each charge or periodically after a certain number of charges, depending upon ones production schedule and the down-time allotted to each reactor. It is understood, of course, that one can recoat the reactor as often as desired without opening the same, even after every charge is polymerized, thus preventing the escape of unreacted monomer(s) to the atmosphere of the plant.

While the present invention is specifically illustrated hereinafter with regard to the emulsion polymerization of vinyl chloride, it is to be understood that the invention is likewise applicable to the emulsion polymerization of any polymerizable ethylenically unsaturated monomer or monomers wherein undesirable polymer buildup occurs. Examples of such monomers are other vinyl halides and vinylidene halides, such as vinyl bromide, vinylidene chloride, etc., vinylidene monomers having at least one terminal grouping, such as α , β-olefinically unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, ethacrylic acid. α-cyanoacrylic acid, and the like; esters of acrylic acid, for example methyl aerylate, ethyl aerylate, butyl aerylate, octyl acrylate, cyanoethyl aerylate, and the like; esters of methacrylic acid,, such as methyl methacrylate, butyl methacrylate, and the like; nitriles, such as acrylonitrile and methacrylonitrile; acrylamides, such as methyl acrylamide, N-methylol acrylamide, N-butoxy methacrylamide, and the like; vinyl ethers, such as ethyl vinyl ether, chloroethyl vinyl ether, and the like; the vinyl ketones; styrene and styrene derivatives including α-methyl styrene, vinyl toluene, chlorostyrene, and the like; vinyl naphthalene, allyl and vinyl chloroacetate, vinyl acetate, vinyl pyridine, methyl vinyl ketone, and other vinylidene monomers of the types known to those skilled in the art.

In using the aqueous emulsion polymerization technique, the aqueous reaction medium will contain one or more emulsifiers or an emulsifier system, such as a salt of a long chain fatty acid and a long straight chain saturated alcohol. Usually, an alkali metal or ammonium salt of a long chain saturated fatty acid is used as emulsifier or as part of the emulsifier system. The saturated fatty acids referred to may be either natural or synthetic and should contain from 8 to 20 carbon atoms. As examples of such acids there may be named lauric, myristic, palmitic, marganic, stearic, and the like, beef tallow, coconut oil, and the like. Excellent results have also been obtained when anionic emulsifiers are used, such as the alkali metal or ammonium salts of the suifates of alcohols having from 8 to 18 carbon atoms. As examples of such emulsifiers there may be named sodium lauryl sulfate, ethanolamine lauryl sulfate, ethylamine lauryl sulfate, and the like; alkali metal and ammonium salts of sulfonated petroleum and paraffin oils; sodium salts of hydrocarbon sulfonic acids, such as dodecane-1- sulfonic acid and octadiene-1-sulfonic acid; sodium salts of alpha-olefin sulfonates; aralkyl sulfonates, such as sodium isopropyl benzene sulfonate, sodium dodecyl ben zene sulfonate, sodium isobutyl nephthalene sulfonate, and the like; alkali metal and ammonium salts of sulfonate, and the like; alkali metal and ammonium salts of sulfonate dicarboxylic acid esters, such as sodium dio ctyl sulfosuccinate, disodium-n-octadecyl sulfosuccinata, and the like; alkali metal and ammonium salts of free acid of complex organic mono- and di-phosphate esters, and the like. Nonionic emulsifiers, such as octyl- or nonylphenyl polyethoxyethanol, may also be used. Vinyl polymer latices having excellent stability are obtained when employing the alkali metal and ammonium salts of aromatic sulfonic acid, aralkyl sulfonates and long chain sulfonates. The emulsifier is employed in an amount in the range of about 0.1% to about 5.0% by weight, based on the weight of monomer or monomers being polymerized, and preferably, an amount of emulsifier in the range of about 0.5% to about 1.5% is used. When employing more than one emulsifier in the system, the combined weight thereof will be in the same ranges.

In addition to the compounds named above, it is very often desirable, in order to obtain certain desirable vinyl dispersion resin properties, to employ one or more long straight chain saturated alcohols, containing from 8 to 24 carbon atoms, in the emulsifier system. The addition of the alcohol (s) increases the colloidal stability of the polymerization system. As examples of such alcohols there may be named octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, heptadecanol, octadecanol, nonadecanol, eicosanol, heneicosanol, docosanol, tricosanol, tetracosanol, etc. As an example of a mixture of alcohols there may be mentioned the use of a 12 carbon alcohol olus an 18 carbon alcohol. Further, ethoxylated alcohols can be used, such as a mixture of ethoxylated linear primary alcohols containing from 12 to 15 carbon atoms, etc. The ratio of alcohol to emulsifier can range from 0.15 to 1.0 or greater depending upon the emulsifier being used. For example, when the emulsifier is an ammonium salt of a fatty acid the ratio of alcohol to fatty acid salt can be 1.0 but preferably the ratio is greater than 1.0. In the emulsion polymerization process of vinyl monomers, the same is conducted at a pH in the range of about 2.0 to about 10.0. If the pH is too high it takes too much alkali and if the pH is too low the coagulum increases. However, when employing the heavy or thick coating of the present invention in the emulsion polymerization process these undesirable effects are substantially overcome or eliminated. The amount of alkaline agent, needed to properly adjust and maintain the proper pH. will depend in part on the particular emulsifier system being used in the reaction mixture.

In all vinyl emulsion polymerization processes, the same are conducted in the presence of a compound capable of initiating the reaction. These compounds are free radical yielding initiators or catalysts that are normally used for polymerizing olefinically unsaturated monomers. The initiators or catalysts used will usually be water-insoluble. As examples of the initiators or catalysts that may be employed, there may be named the various peroxygen compounds, such as lauryl peroxide, isopropyl peroxydicarbonate, bis (4-tert-butyl cyclohexyl) peroxydicarbonata, di (2-ethyl hexyl) peroxydicarbonate, diisononanoyl peroxide, benzoyl peroxide, t-butyl hydroperoxide, t-butyl peroxypivalate, cumene hydroperoxide, cyclohexyl hydroperoxide, test-butyl peroxyneodecanoate, and the like; azo compounds, such as axodiiscbutyronitrile, dimethylazodiisobutyrate, and the like. Also useful initiators or catalysts are the water-soluble peroxygen compounds, such as hydrogen peroxide, persul fates, such as potassium persulfate, ammonium persulfate, and the like. Also, mixtures of catalysts or initiators may be employed, either water-insoluble or water-soluble or both. For example, a 50-50 mixture of di(2-ethyl hexyl) peroxydicarbonate and diisononanoyl peroxide can be used. Whether a single initiator, or a mixture of initiators,. is employed, the amount thereof will be in the range of about 0.01% to about 0.50% by weight, based on the weight of 100 parts of monomer or monomers being polymerized, and preferably in the range of about 0.015% to about 0.15% by weight.

While the initiators may be charged to the reactor after the reaction ingredients have been mixed or charged incrementally during the course of the reaction, usually, in most emulsion polymerization processes the initiators are charged completely at the outset of the polymerization by addition to the monomer premix with the other ingredients of the reaction mixture. The reaction ingredients are mixed to form the monomer premix prior to homogenization and introduction into the reactor. However, when adding the initiator to the monomer premix and then homogenizing, it is necessary that the temperature during the premixing and homogenization steps be kept below the minimum temperature of reactivity of the particular initiator or initiators being employed. Upon introduction of the homogenized mixture into the polymerization reactor, the temperature is then raised to that at which the reaction is to take place.

The choice of temperature at which to conduct the emulsion polymerization reaction is important since the inherent viscosity (IV) of the plastisols made with the vinyl dispersion resins thus produced is a direct function of the temperature of reaction. That is, the higher the reaction temnerature the lower the IV. Accord ingly, the end use for the vinyl dispersion resin being produced will normally dictate the emulsion polymerization reaction temperature. For the end uses to which the vinyl dispersion resins are particularly adapted, polymerization temperatures in the range of about 30°C. to about 70°C. are satisfactory. Preferably, however, a temperature in the range of about 40°C. to about 55°C. is employed. In some cases the vinyl polymer latices are sold as such, but in most instances the vinyl polymer or resin is sold in dry powder form. After the polymerization reaction is complete, the vinyl dispersion resin is isolated in powder form from the latex by means of spray drying. That is, a fine spray of the polymer latex is injected into a heated air chamber thereby removing the water, and any unreacted monomer, and recovering the dried resin in powder form.

To illustrate the present invention, the following specific examples are given, it being understood that this is merely intended in an illustrative and not a limitative sense. In the examples all parts and precents are by weight unless otherwise indicated.

Example I

In this example there is shown the recipe and polymerization procedure for making a vinyl dispersion resin or PVC from vinyl chloride monomer. This same recipe and procedure was followed in making all of the PVC resins shown in all of the examples that follow hereinafter. The polymerization recipe employed was as follows:

All of the ingredients of the recipe were charged to a premix tank with the vinyl chloride being charged last after the tank had been placed under vacuum. The mixture was then stirred or agitated for 15 minutes at a temperature of 20°C. Then the premix was homogenized in a two stage Manton-Gaulin homogenizer at a temperature of 20°C. into the polymerization reactor. The first stage of the homogenizer was set at 700 psig. and the second stage at 600 psig. The reactor was evacuated prior to the addition of the homogenized premix. After charging of the reactor, the reaction mixture therein was heated to the reaction temperature of 45°C. and the reaction was conducted at this temperature with stirring until completion. After the reaction was complete, the reactor was cooled and the PVC latex was removed from the reactor and spray-dried to recover the dry PVC or resin.

Using the above recipe and procedure, 2 runs were made in a previously cleaned 3300 gal. stainless steel reactor in order to establish a control. No coating was used and the reactor was rinsed after each charge in order to measure the polymer buildup. The results were as follows :

The nature of the buildup was very bad. It was a tightly held paper buildup on the surfaces. Due to the nature of the buildup and being so tightly held on the walls, it precluded the continuation of further runs.

Example II In this example, a series cf 4 runs were made using a coated reactor. The polymerization procedure of Example I was employed in each ofi the runs. Before coating, the reactor surfaces were super cleaned and then coated with a 5% solution of self-condensed resor cinol in ethanol. The coating solution was applied by means of spraying and then dried. It took about 4 to 5 pounds of coating solution. Thereafter, the first run was made. After each run the reactor was rinsed with water to remove any buildup prior to- starting the next run. No further coating solution was applied between runs. Results were tabulated after each run and these results are shown in the following table:

From the above Table it can be seen, when compared to the control in Example I, that the present heavy coating greatly reduces polymer buildup in emulsion polymerization systems.

Besides substantially reducing polymer buildup in emulsion polymerization, where a little polymer buildup does occur, it is not of the hard, rough difficult-to-ramove type and is easily removed without employing difficult and tedious scraping methods. Further, the present invention enables one to operate a closed polymerization system. Numerous other advantages of the present invention will be apparent to those skilled in the art.

While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the appended claims.

Claims (10)

1. A process for substantially eliminating the buildup of polymers on the internal surfaces of a polymerization reaction vessel for use in emulsion polymerization systems which comprises applying to said surfaces a coating solution comprised of an organic solvent solution containing an unneutralized condensation product selected from the group consisting of (1) the self-condensation product of a polyhydric phenol, (2) the condensation product of two or more polyhydric phenols, and (3) the self-condensation product: of a polyhydric naphthol, wherein said polyhydric phenol (s) is selected from the group consisting of resorcinol, hydroquinone, catechol and phloroglucinol, drying said coating solution on said surfaces to produce a coating thereon having a thickness in the range of about 5 microns to about 50 microns, and emulsion polymerizing one or more polymerizable ethylenically unsaturated monomers while in contact with said coating.

2. A process as defined in claim 1 wherein the polymerizable ethylenically unsaturated monomer is vinyl chloride.

3. A process as defined in claim 1 wherein the solvent is methanol.

4. A process as defined in claim 1 wherein the solvent is ethanol.

5. A process as defined in claim 1 wherein the solvent is isopropanol.

6. A process as defined in claim 1 wherein the polyhydric phenol is resorcinol.

7. A process as defined in claim 1 wherein the polyhydric phenol is hydroquinone.

8. A process as defined in claim 1 wherein the polyhydric phenol is catechol.

9. A process as defined in claim 1 wherein the coating solution contains from about 1.0% to about 20.0% by weight of said unneutralized condensation product.

10. A process as defined in claim 1 wherein the condensation product is the self-condensation product of a polyhydric phenol.