COATING POLYMERIZATION REACTORS WITH OLIGOMER COATINGS DERIVED FROM REACTION PRODUCTS OF SUBSTITUTED PHENOLS

Abstract: Polymerization reaction vessel having a coating on the inner surfaces thereof resulting from applying thereto a coating composition containing, as a primary ingredient, the reaction product or oligomers of (1) an alkyl or halogen substituted phenol, such as p-chlorophenol and the like, (2) a condensing agent, such as formaldehyde, and the like, and (3) a polyhydric phenol, such as resorcinol, and the like, dissolved in water or an aqueous alkaline solution. When polymerizing olefinic monomers, such as vinyl halides, vinylidene halides, and vinylidene monomers, having at least one terminal CH2=CH<group, and mixtures thereof, polymer buildup on the inner surfaces of the reaction vessel is substantially eliminated. Further, multiple charges or batches of polymer can be made in said internally coated reaction vessel without opening the same between charges thus preventing the escape of unreacted monomer (s) to the surrounding atmosphere.

Description: "COATING POLYMERIZATION REACTORS WITH OLIGOMER COATINGS DERIVED FROM REACTION PRODUCTS OF SUBSTITUTED PHENOLS" BACKGROUND OF THE INVENTION Various type chemical processes are commonly carried out in large, stirred vessels which are fre¬ quently provided with auxiliary equipment, such as baffles, agitator equipment, heat transfer coils which enable heat to be supplied or extracted from the con- tents of the vessels, 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 de¬ posits have a tendency to deteriorate and to partially fragment resulting in contamination of the reaction mixture and the products produced therefrom. This problem is particularly prevalent in polymerization type reactions, since the deposits, or buildup, of solid polymer on reactor surfaces, not only interferes with heat transfer, but decreases ' productivity and adversely affects polymer quality. The polymer buildup problem is particularly troublesome in the commercial production of polymers and copolymers of vinyl and vinylidene halides, when poly¬ merized alone or with other vinylidene monomers having a terminal CH 2 =C group, or with polymerizable polyole- finic monomers. For example, when polymerizing vinyl chloride, and other comonomers when used, the same are ' maintained in the form of discrete droplets in an aqueous suspension system by the use of suspending agents and agitation. When the reaction is complete, the resultant polymer, or PVC, is washed and dried. However, these suspension systems are often unstable and during the polymerization reaction, vinyl chloride OMPI polymer builds up on the interior surfaces of the re¬ actor, including the surfaces of the baffles and agita¬ tor. Obviously, 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 and contaminates the polymer being pro¬ duced. While various methods have heretofore been proposed to reduce the amount and nature of polymer buildup on polymerization reactor surfaces, such as solvent cleaning, various hydraulic and mechanical reactor cleaners, and the like, none has proved to be the ultimate in polymer buildup removal. That is to say, these various methods and apparatus have done an acceptable job, but there is still room for improvement in this area, particularly from an economic point of view. It has been proposed to coat the internal sur¬ faces of the reactor with various polymer buildup re¬ sistant coating materials. For example, in U.S. Patents No's. 4,024,330 and 4,024,301, various polyaromatic amines are shown as useful for coating reactors to sub¬ stantially eliminate buildup. Alkali soluble dyes have been shown to be useful for this purpose in U.S. Patent No. 4,068,059. Further, in U.S. Patent No. 4,080,173 there is shown and described -the use of selfcondensed polyhydric phenols and polyhydric naphthols as useful coating materials to prevent polymer buildup. While all these coating materials give good to excellent results, the search continues for new and improved polymer build- up resistant materials with which to coat reactors for • the purpose of preventing or eliminating polymer buildup on the inner surfaces thereof. SUMMARY OF THE INVENTION It has been found that if a polymerization reaction vessel, particularly one having inner surfaces of stainless steel, has been previously coated on said inner surfaces with the proper coating, undesirable buildup on said surfaces can be substantially decreased, and in many cases entirely eliminated, when polymerizing olefinic monomers therein. I have now found that when the interior surfaces of a polymerization reactor are coated with an aqueous or aqueous alkaline coating solution containing, as a primary ingredient, the re¬ action product or oligomers of (1) alk l or halogen substituted phenol, such as p-chlorophenol, arid the like, (2) a condensing agent, such as formaldehyde, and the like, and (3) a polyhydric phenol on said interior surfaces of the reactor is substantially eliminated. Due to the nature of the coating solution or composi¬ tion, it can be applied to the inner surfaces of the reactor without opening the same, thus providing a closed polymerization system. By use of the present coating composition, the necessary surface tension (γ ) for wetting of a solid surface by the water phase of the polymerization medium is obtained. In polymerizing the monomers in such a coated polymerization vessel or reactor, the same is done in an aqueous polymerization medium which is kept in contact with said coated sur¬ faces throughout the polymerization reaction. DETAILED DESCRIPTION In accordance with the present invention, a film or coating of a coating material, made by the reaction of an alkyl or halogen substituted phenol, a condensing agent and a polyhydric phenol, is applied to the inner surfaces of a polymerization reactor or vessel by merely contacting said surfaces with an aqueous solution or an aqueous alkaline solution of said coating material. All exposed surfaces in the interior of the reactor, such as the baffles, agitator or mixing mech¬ anism, etc., are likewise coated in the same manner. After the coating solution has been applied to the inner surfaces of the reactor, the polymerization medium can OMFI be introduced to the reactor and the reaction started without the necessity of drying said surfaces before¬ hand. However, it is preferred, when after the applica tion of the coating solution to the inner surfaces, tha the surfaces are rinsed with water, such as by spraying thereby, surprisingly, leaving on said surfaces a tightly adhering coating or film of the coating materia which is . not affected by the polymerization medium even though vigorously agitated during the polymerization reaction. The coating materials useful in the practice of the present invention have the following general structure: wherein R is halogen or an alkyl group containing from to 4 carbon atoms and R' is H, OH, halogen, or an alkyl group containing from 1 to 4 carbon atoms, R" is H or -CH^OH, and n is an integer from 1 to 20. Among the materials that may be employed in making the reaction products suitable as coating mater¬ ials in the present invention are the halogen or alkyl substituted phenols, such as p-chlorophenol, p-cresol, p-ethyl phenol, etc.; the condensing agents, such as formaldehyde, acetaldehyde, etc.; and polyhydric phenol such as resorcinol, hydroquinone, catechlor, phloro- glucinol, etc. A good example of a coating material having the above general structure is that formed by th reaction of p-chlorophenol, formaldehyde and resorcinol This material, or reaction product, is obtained in accordance with the following reaction: OMPI 1. In aqueous solution, p-chlorophenol is reacted with formaldehyde to form a bis-hydroxymethyl chlorophenol as follows: 2. Without isolating compound (A) , and still in aqueous solution, (A) is reacted with resorcinol giving precipitation of 3,4,5, etc. ring oligomers in accordance with the following equation showing the trimer (B) plus higher oligomers: The second reaction can also be carried out by fusion giving higher average molecular weight. A similar coat¬ ing material can be made by substituting p-cresol for p- chlorophenol in step 1. above. The material (B) above, is available under the trademark "Pexul" which is made and sold by I.C.I. , Ltd. of Great Britain * Pexul is supplied by I.C.I, as a 20% solution dissolved in 3 normal NH.OH, that is, as the ammonium salt at a pH of approximately 10. The histor- • ical development of Pexul is described in an article entitled "Development of a Polyester-Rubber Adhesive" which is found in British Polymer Journal, 1971, Vol. 3_, March, pages 58-62. In this article the author points out that with careful attention to reaction conditions and stoichiometry a consistent product can be obtained, OMFI IPO but the product always consists of a mixture of com¬ pounds or oligomers. However, the author further points out that it is possible to crystallize from an aqueous solution of the product of the above reaction a material 5 which is identified by analysis as the trimer, or product (B) above. In order to prevent polymer buildup in a poly¬ merization reactor, it is essential that the inner sur¬ faces thereof are water-wettable. An ordinary solid _ Q surface, such as stainless steel, is not water-wettable due to the normal contamination of said surface with organic materials through contact with the atmosphere. The surface can be cleaned, such as with chromic acid, or an abrasive cleanser, for example, and it will become __ ■ water-wettable. However, such cleaning alone does not solve the problem since the surface will not remain clean for a sufficient length of time, that is, for more than the duration of a single polymerization reaction. This necessitates recleaning the surface after each 20 polymerization cycle. Therefore, applying a coating to the surface which will be water-wettable and resist polymer buildup thereon and remain on said surface throughout multiple reaction cycles is most desirable. When a metal or solid surface is non-wettable, 25 a liquid thereon, such as water, will form droplets and not flow out into a smooth film. The angle formed be¬ tween the tangent of the side of the droplet and the metal or glass surface is called the "contact angle" and is referred to as "theta" (θ) . A further measurement of 30 the wettability of a solid surface is the critical surface tension for wetting a solid surface and is expressed as "γ c "• The γ c is measured in dynes per centimeter. Using water as the standard, in order for a solid surface to be wettable, θ must equal zero or be 35 very close to it, and Ύ _ must be 72 dynes/cm. or greate More importantly, the material being applied to the surface should not only form a wettable surface. but also form a layer or film thereon which is not readily removable. This film adheres to the solid or metal surface by adsorption and in many cases, the film is a onolayer of the coating material applied which is ' 5 of the order of a molecule in thickness. These films of such thickness are invisible to the naked eye thus eliminating any color problem, such as is the problem with many coatings heretofore used for the same purpose. Of course, films of greater thickness can result when 10 using higher solids content coating solutions, in accord¬ ance with the present invention, which films or coatings are visible to the naked eye. The film or layer formed by the coating solution is not removable by washing with water. That is to say, the coating or film is resistant 15 to removal from the surfaces when a turbulent aqueous reaction medium is in contact therewith, caused by the agitation of the polymerization mixture in the reactor. The coating solutions of the present invention are made by conventional methods, using heat and agita- 20 tion where necessary. In making said solutions, usually a temperature in the range of about 0°C. to about 100°C. is satisfactory. Agitation during dissolution is de¬ sirable. As previously pointed out, the coating ma¬ terial is dissolved in water or an aqueous alkaline 25 solution. It has been found that a concentration of coating material in the range of about 0.05% to about 3.0% by weight is satisfactory in accomplishing the objectives of the present invention and the coating solutions so produced are only slightly colored. To 30 insure against undesirable color, and for economic reasons, it is preferred to employ a concentration of coating material in said solutions in the range of 0.05% to 0.20% by weight. It is to be understood that since the molecular weight of the coating material affects the 32 total solids content in the coating " solution, the con¬ centration of said material could, in certain instances, be greater than 3.0% or less than 0.05% by weight. The coating solutions of the instant invention having a pH in the range of about 7.0 to about 13 are satisfactory. It is preferred, however, to operate at a pH in the range of 7.5 to 9.5. The pH is affected by the kind and number of -substituent groups attached to the aromatic nuclei of the coating material, and the cation used to form the salt, such as Na, K, NH 4 and the like. As previously pointed out, the coating solu- ' tion is usually applied to the inner reactor surfaces by spraying. However, it is also possible to apply the coating solution by flooding the reactor and then drain¬ ing, or painting or brushing on, but spraying is the most practical and economical method of application. After spraying the coating solution on the inner sur¬ faces and draining the reactor, the polymerization reaction can be started immediately without further treatment of said surfaces. However, it has been- found that excellent results are obtained when after applying the coating solution to the inner surfaces of the re¬ actor, the coated surfaces are sprayed with water and the reactor drained prior to charging the reactor with the polymerization mixture or recipe. It should also be pointed out that the coatings defined herein work equally well on glass or metal sur ces, such as stain¬ less steel, and the like. One important aspect of the present invention is that multiple polymerizations may be run without opening the reactor between charges since, with the spray nozzle or nozzles mounted at strategic points on the reactor, it is possible to reach all inner surfaces thereof while the reactor is closed. Although multiple charges may be run in a coated reactor without recoating the surfaces, it has been found to be expeditious, and preferred, to recoat the internal surfaces of the reacto .. I periodically after several charges have been run there¬ in, or after each charge, to insure uniform and effi ¬ cient production. When it is decided to recoat the reactor, the reactor is drained, and the inner surfaces of the reactor are flushed with water. The coating solution is applied to the surfaces, preferably by spraying, and the reactor is drained of the excess coating solution in such a way that the same can be sent to a recovery system, if desired. Then, optionally, the surfaces having -the coating thereon are sprayed with water and the effluent is discarded, or recovered if desired. Thereafter, the reactor is charged with the polymerization medium and ingredients in the usual manner and the reaction commenced immediately with no particular modification of processing techniques being required due to the presence of the coating. 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. Further, utilization of the internally coated reaction vessel of the present in¬ vention does not adversely affect the heat stability or other physical and chemical properties of the polymers produced therein. While the present invention is specifically illustrated with regard to the suspension polymerization of vinyl chloride, it is to be understood that the process and apparatus may likewise be applied in the dispersion, emulsion, or suspension polymerization of any polymerizable thylenically unsaturated monomer or monomers where 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 CH 2 =C ^grouping, such as esters of acrylic acid for example methyl acrylate, ethyl acrylate, butyl acrylate, octyl acrylate, cyanoethyl acrylate, and the like; vinyl acetate; acrylonitrile; esters of meth<- acrylic acid, such as methyl methacrylate, butyl meth- acrylate, and the like; styrene and styrene derivatives including α-methyl styrene, vinyl toluene, chlorostyrene vinyl naphthalene; diolefins including butadiene, iso- prene, chloroprene, and the like; and mixtures of any of these types of monomers and other vinylidene monomers copolymerizable therewith; and other vinylidene monomers of the types known to those skilled in the art. The present invention, however, is particularl applicable to the suspension polymerization of vinyl chloride, either alone or in a mixture with one or more other vinylidene monomers having at least one terminal CH 2 =C<^ grouping copolymerizable therewith in amounts as great as about 80% or more by weight, based on the weight of the monomer mixture, since polymer buildup in the reaction vessel is a bad problem here. The polymerization process is usually con¬ ducted at a temperature in the range of about 0°C. to about 100°C. depending upon the particular monomer or monomers being polymerized. However, it is preferred to employ temperatures in the range of about 40°C to about 70°C, since, at these temperatures, polymers having the most beneficial properties are produced. The time of the polymerization reaction will vary from about 2 to about 15 hours. The polymerization process may be carried out at autogenous pressures although superatmospheric pressures of up to 10 atmospheres or more may be em- ployed with some advantage with the more volatile mono- ■ mers. Superatmospheric pressures may also be employed with those monomers having the requisite volatilities at reaction temperatures permitting reflux cooling of the reaction mixture. Further, the polymerization process may be carried out utilizing a full reactor technique. , That is, the reaction vessel is completely filled with the polymerization medium and kept that way throughout the reaction by constant addition thereto of water or addi¬ tional make-up liquid containing the monomer or monomers in the same proportion as at start-up. Upon the addi¬ tion of a certain predetermined amount of liquid, the polymerization reaction is terminated, usually by the addition thereto of a short-stopping agent. The neces¬ sity for the addition of liquid is due to the shrinkage in volume of the reaction medium produced by the con¬ version of the monomer or monomers to the polymeric state. In order to rate the various coatings, as particularly set forth in the specific examples which follow hereinafter, there has been devised a rating scale with respect to "paper" and "sandy" buildup. An uncoated reactor referred to as the control, where normal amounts of both types of buildup occur, is given a rating of 1.5. Any rating below 1.0 is good ' or a definite improvement. In other words, 0.0 rating is perfect, and so on. In order to further illustrate the present invention, the following specific examples are given. It is to be understood, however, that this is merely intended in an illustrative and not limitative sense. In the examples, all parts and percents are by weight unless otherwise indicated. EXAMPLE I In this example, the coating material employed was the reaction product of p-chlorophenol, formalde¬ hyde, and resorcinol which product was made as set out hereinbefore. The reaction product was then dissolved in 3N H 4 OH, that is, as the ammonium salt, to give a 20% solution having a pH of 10. This solution is referred to as the concentrate. Sufficient of the concentrate was then mixed with demineralized water and the pH was adjusted to 7.6 to give a 0.10% reaction product coating solution. Thereafter, the inner sur¬ faces of the polymerization reactor, which had been previously cleaned with Ajax, were coated with said coating solution by spraying and the coating rinsed with water. The coating had a γ greater than 72 dynes/cm. Thereafter, the following recipe was charged to the coated reactor: Vinyl chloride 1000 grams Water (demineralized) 2055 grams 88% hydrolyzed polyvinyl acetate 0.5 gram di-secondary butyl peroxydi- carbonate 0.5 cc. A full reactor technique was used in the polymerization, sufficient water being added to keep the reactor full throughout the reaction cycle. The temperature of the reaction was maintained at 57°C and the reaction medium was agitated. The water was added during the reaction as the mixture shrank because of formation of polymer. Upon the addition of 400 grams of water, the reaction was discontinued. After removal of the contents of the reactor, in usual fashion, the internal surfaces were rinsed with water, then recoated and rinsed with water and a second charge made and polymerized in the same manner as above. After the second charge was polymer¬ ized, the reactor was recoated and a third was polymer¬ ized, all as was done before. Upon completion of the ' third charge, the internal surfaces of the reactor were classified in accordance with the aforementioned pro- cedure for rating said surfaces. The results were as follows: BUILDUP CONTROL FIRST SECOND THIRD (NO COATING) CHARGE CHARGE CHARGE Paper 1.5 0 .2 0. 0 0 . 0 Sandy 1.5 0 .0 0 .5 0 . 5 -^U REA OMPI The superior results of the coated reactor over the un¬ coated reactor are evident from the above data. Sub¬ stitution of p-cresol for p-chlorophenol in making the reaction product for the coating will give like bene- ficial results. EXAMPLE II In this example the same recipe and procedure described in Example I was used, except that a 5 gal. solution of the reaction product (20% in NH 4 0H) was diluted 200/1 with demineralized water. This gave a coating solution of 0.10% with a pH of 9.35. Three charges were run n the reactor and the internal sur¬ faces were classified after each charge with the follow¬ ing results. BUILDUP CONTROL FIRST SECOND THIRD (NO COATING) CHARGE CHARGE CHARGE Paper 1 . 5 0 .3 0 . 7 0 . 7 Sandy 1 . 5 0 .0 0 . 0 0 . 0 Again, the superior results of the coated reactor are apparent from the above data. One of the principal advantages of the present invention is that in using the invention, polymer build¬ up on the inner surfaces of the polymerization reactor is substantially reduced, and in many cases, practically eliminated. This results in increased production over a unit period of time. More importantly, the present invention enables one to operate a closed polymerization system, which, in the case of vinyl chloride polymeriza¬ tion, has the advantage of reducing drastically the parts per million of vinyl chloride in the atmosphere of- the plant. Such reduction in vinyl chloride in the atmosphere is extremely helpful in meeting recent Governmental requirements. Numerous other advantages of the present invention will be apparent to those skilled in the art. While the present invention has been described cations and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention, which is to be limited only by the scope of the appended claims.

Claims: CLAIMS 1. A process for substantially eliminating the buildup of polymers on the internal surfaces of a polymerization reaction vessel which comprises applying to said surfaces an aqueous coating solution containing an oligomer having the general structure wherein R is halogen or an alkyl group containing from 1 to 4 carbon atoms and R' is selected from the group consisting of H, OH, halogen and an alkyl group contain¬ ing from 1 to 4 carbon atoms, R" is selected from the group consisting of H and -CH 2 OH, and wherein n is an integer from 1 to 20, and conducting the polymerization of monomer(s> while in contact with the coated internal surfaces of said vessel. 2. A process as defined in Claim 1 wherein the monomer is vinyl chloride. 3. A process as defined in Claim 1 wherein the oligomer is formed by the reaction of a halogen or alkyl substituted phenol, a condensing agent, and a polyhydric phenol. 4. A process as defined in Claim 1 wherein the coating solution contains from about 0.05% to about 3.0% by weight of the oligomer. 5. A process as defined in Claim 1 wherein the coated internal surfaces are rinsed with water prior , to conducting the polymerization of monomer(s) . 6. A process as defined in Claim 1 wherein the coating solution has a pH in the range of about 7.5 to about 9.5. 7. A process as defined in Claim 3 wherein the halogen or alkyl substituted phenol is p-chlorophenol, 8. A process as defined in Claim 3 wherein the halogen or alkyl substituted phenol is p-cresol. . A process as defined in Claim 3 wherein the condensing agent is formaldehyde. 10. A process as defined in Claim 3 wherein the polyhydric phenol is resorcinol. 11. A process as defined in Claim 1 wherein the oligomer is the reaction product of p-chlorophenol, formaldehyde and resorcinol. 12. A polymerization reaction vessel having on all the internal surfaces thereof a coating comprised of an oligomer having the general structure wherein R is halogen or an alkyl group containing from 1 to 4 carbon atoms and R' is selected from the group consisting of H, OH, halogen, an alkyl group containing from 1 to 4 carbon atoms, R" is selected from the group consisting of H and -CH 2 OH, and wherein n is an integer from 1 to 20. 13. A polymerization reaction vessel as defined in Claim 12 wherein the oligomer is the reaction product of p-chlorophenol, formaldehyde and resorcinol. 14. A polymerization reaction vessel as defined in Claim 12 wherein the coated surfaces are characterized by having a critical surface tension of at least 72 dynes/centimeter and a contact angle with water of about zero.

Inventors: COHEN L
Applicants: GOODRICH CO B F
Application year: 1979
Main classification: B05D7
IPC codes: B05D7, C08F2, C08F14