JPH0320401B2 - - Google Patents

Description

[Detailed description of the invention]

It is well known that polymer build-up occurs on the inner surface of the reactor in polymerization-type reactions, which not only obstructs heat transfer but also reduces productivity and adversely affects polymer quality. It is. This adhesion problem is a problem in the commercial production of vinyl halide and vinylidene polymers and copolymers, either singly or terminally with CH ₂ =
This is particularly harmful when polymerized with other vinylidene monomers or polymerizable monoolefin monomers with C< groups. For example, in the commercial production of vinyl chloride polymers, vinyl chloride polymers are usually produced in the form of discrete particles by polymerization in an aqueous suspension system. When using such polymerization systems, vinyl chloride and other comonomers, if used, are maintained in discrete droplets through the use of suspending agents and stirring. Upon completion of polymerization, the resulting polymer is washed and dried. This reaction is usually carried out under pressure in a metal reactor equipped with a baffle and a high speed stirrer. However, these polymerization systems are often unstable. As a result, polymer deposits form on the interior surfaces of the polymerization reactor, including the baffle and agitator surfaces. It goes without saying that this polymer deposit must be removed because of the deleterious effects it causes, especially on the quality of the polymer. Various methods have been proposed in the past to reduce or moderate the amount and nature of polymer deposition on polymerization reactor surfaces, such as solvent cleaning, various hydraulic and mechanical reactor cleaners, and the like.
See, for example, US Pat. No. 3,645,452 and US Pat. No. 3,741,808 for hydraulic reactor cleaners. Additionally, various methods have been proposed for coating reactor surfaces prior to polymerization. For example, US Pat. No. 4,024,330,
See No. 4024301 and No. 4081248. These various methods and devices have met with considerable success. However, the industry continues to strive for the ultimate prevention of polymer fouling, particularly from economic and environmental standpoints. Although the various coating solutions that have been proposed in the past have been quite satisfactory in achieving the desired results, experience on a commercial scale has shown that in order to reduce costs, and most importantly, these Since almost all coating solutions are colored, a more dilute coating solution was desired to reduce the color of the solution. Due to this coloration, in some cases, some of the polymer particles generated during the polymerization reaction in the presence of the coating on the inner surface of the polymerization vessel tend to fade or change color, which is of course undesirable and should be avoided if possible. Should. However, it must be pointed out that the effectiveness of coating solutions such as those described above in reducing and virtually eliminating polymer deposition is not affected by such discoloration problems. However, the search continues for the ultimate in reactor coatings, particularly those that eliminate the potential discoloration problems discussed above. If the inner surface of a polymerization reactor, especially one with an inner surface of stainless steel, has been previously provided with a suitable coating, undesirable polymers on the surface may be removed when the monoolefin monomer is polymerized therein. It has been found that fouling can be substantially reduced and in many cases completely eliminated. The present inventor has provided an aqueous solution containing a complex of an easily adsorbable polymer and a certain organic molecule selected from the group of polymerization inhibitors at a predetermined concentration on the inner surface of a polymerization reactor. It has been found that polymer deposition on the inner surface of the reactor is substantially eliminated when the reactor is coated with . Due to the nature of the coating solution, it can be applied to the reactor surface without opening the reactor, providing a closed polymerization system. When polymerizing monomers in such coated polymerization vessels or reactors, the polymerization is carried out in an aqueous polymerization medium that is maintained in constant contact with the coated surface throughout the entire polymerization reaction. According to the present invention, (A) water-soluble polyvinyl alcohol, hydroxylpropyl methylcellulose, polyvinylpyrrolidone, gelatin, acrylic acid polymer, methacrylic acid polymer, acrylic acid copolymer, methacrylic acid copolymer, maleic anhydride copolymer, soluble protein polymer, saponin , acrylamide polymer, acrylamide copolymer,
Water-soluble hydrophilic polymer selected from the group of hydroxyalkylacrylamide polymers and hydroxyalkylacrylamide copolymers from 0.01 to
2.5% by weight, and (B) bisphenol A salt, glucose thiosemicarbazone, 2,4-dinitrobenzene sulfonate, hydroquinone, hydroquinone methyl ether, acetone thiosemicarbazone, basic salt of phenol and aromatic amine. An aqueous coating solution containing a complex with 0.04-2.5% by weight of a polymerization inhibitor selected from the group of acid salts of A method of polymerization is provided which substantially prevents the adhesion of polymer to the inner surface of a polymerization reactor which comprises polymerizing while in constant contact with the coated inner surface. all exposed surfaces inside the reactor other than the inner walls;
For example, a baffle, a stirrer, etc. are treated in the same manner. After applying the aqueous solution of the hydrophilic polymer-inhibitor complex to these surfaces, the coated surfaces are rinsed with water to remove excess coating solution from the coated surfaces prior to introduction of the polymerization medium. This cleaning can be carried out by spraying the surface with water or by filling and draining the reactor with water. Surprisingly, this leaves in each case a tightly adhering coating or coating on the surface, so that even when agitated, the coating substantially reduces the adhesion of the polymer onto the surface. or unaffected by the polymerization medium in the sense of preventing deletion. Water-soluble polyvinyl alcohol (PVA) is used to prepare the hydrophilic polymer-inhibitor complexes useful in the practice of this invention. This polyvinyl alcohol is produced by hydrolyzing polyvinyl acetate from about 70% to about 100%. Most commercially available PVA
is about 88% saponified polyvinyl acetate, so for practical use it is about 85-90% saponified polyvinyl acetate.
Preference is given to using PVA. most preferred
PVA is 88% saponified polyvinyl acetate. PVA
as well as hydroxylpropyl methylcellulose (Methocel); polyvinylpyrrolidone; gelatin (calfskin); acrylic or methacrylic acid polymers and copolymers; anhydrous maleic copolymers; soluble protein polymers such as albumin, ammoniated casein, etc.; Other water-soluble hydrophilic polymers such as saponins; acrylamide and hydroxyalkyl acrylamide polymers and copolymers can be used. A variety of inhibitors from various chemical classes can be used. Examples of polymerization inhibitors include disodium salt of bisphenol A (BPA); glucose thiosemicarbazone; 2,4-dinitrobenzenesulfonic acid-Na salt; hydroquinone, hydroquinone methyl ether; acetone thiosemicarbazone; glucose thio Semicarbazones; basic salts of phenols such as bishydroxyphenylthioether; or acid salts of certain aromatic amines such as the HCl salt of self-condensing metaphenylenediamine oligomers. of some substances
Although the Na salt is exemplified, it goes without saying that a variety of other salts that are water soluble in nature can be used, such as potassium, lithium, ammonium, ethanolamine, etc. salts. These salts generally produce solutions with a high PH up to 12.0. The low pH solution, which has been lowered to PH2.0, is an aromatic amine inhibitor.
Obtained by using HCl salt. A variety of other acid salts can be used as well, such as sulfates, phosphates, etc. The complexes of the invention are formed when mixed together in an aqueous medium in preparing the coating solution. For example, the easily adsorptive polymer PVA associates in water with approximately equimolar amounts of polymerization inhibitor organic molecules through hydrogen bonds and/or hydrophobic bonds. The said bond is
It is based on PVA repeating units ( _-CH2 -CHOH-). Usually equimolar amounts of substances are used, but
This varies depending on the components forming the complex. The hydrophilic polymer is about 0.01 to about 2.5% by weight, preferably
It has been found that it can be varied within the range of 0.02-1.0% by weight. the inhibitor is about 0.04 to about 2.5% by weight;
Preferably, it can vary within the range of 0.10 to 1.0% by weight. Importantly, the ratio of hydrophilic polymer to inhibitor should range from about 1:1 to about 1:13. In this range, the coating solution is colorless or only slightly colored so as not to have a detrimental effect on the polymer quality. Similarly, the pH of the resulting coating solution will vary depending on the materials used to form the complex. The coating solution may be either acid-side or base-side. PH is about 2.0~
May vary within the range of 13.0. For example, the pH of a coating solution containing PVA and 2Na salt of bisphenol A is
It will be 10.6. The coating solutions of the present invention are prepared by conventional methods, using heating and stirring if necessary. Generally, a temperature range of about 0° to about 100°C is sufficient. Stirring during dissolution is preferred. The complex concentration in the coating liquid can be varied. The inventor has determined that from about 0.05 to about 5.0
It has been found that hydrophilic polymer-inhibitor complex concentrations in the weight percent range satisfactorily achieve the objects of the present invention, and that such coating solutions range from colorless to very slightly colored, depending on the complexing substance. This is what I did. The preferred concentration range is 0.1 to 1.0 of the hydrophilic polymer-inhibitor complex.
Weight%. Additionally, the molecular weight of the complex affects the concentration of the complex in the coating solution or the total solids content of the solution. The total solids content of the polymer-inhibitor complex in the coating fluids of the present invention will be within the range of about 0.08 to about 6.0% by weight. However, since the molecular weight of the complex affects the total solids content in the coating solution, in some cases the total solids content is 0.08% by weight.
It can be less than 6.0% by weight or more than 6.0% by weight. As previously indicated, the coating solution of the present invention is typically applied to the reactor interior surfaces by spraying. However, the coating liquid can also be applied by flooding the reactor and then draining out, or by painting or brushing. However, spraying is the most practical and economical method of application. After applying the coating liquid to the reactor internal surfaces, the coating surfaces are sprayed with water and drained before charging the reactor with the polymerization mixture or formulation. It should also be pointed out that the coating of the invention works equally well on metals such as glass or stainless steel and other surfaces. The exact mechanism of adhesion of the coating of the present invention to the reactor surface is not clear, but some type of electrical force or adsorption occurs between the reactor surface and the hydrophilic polymer-inhibitor complex. It seems so. In any event, the coating composition of the present invention substantially eliminates polymer adhesion to the reactor surfaces and, if any polymer adhesion occurs, it is removed from the reactor without the need for manual stripping. It is sand-like in nature and can be easily removed from surfaces. The polymer build-up that must be avoided is the so-called paper build-up. This is because this deposit is very difficult to remove and usually requires manual stripping or the use of a high pressure jet stream of water or other liquid. In either case, the reactor must be opened for cleaning, which releases harmful unreacted monomers, such as vinyl chloride, into the atmosphere. According to the invention, multiple polymerizations can be carried out without opening the reactor between each charge.
Multiple charge polymerizations can be carried out without recoating the inner surface of the reactor, but recoating the inner surface of the reactor after each charge polymerization ensures homogeneous and efficient production. We have found that it is quick and suitable for As previously pointed out, by fixing spray nozzles at strategic points in the reactor, it is possible to reach all internal surfaces of the reactor.
When the reactor is to be recoated, drain it and rinse its interior surfaces with water. Spraying the coating liquid onto the inner surface of the reactor using a spray nozzle means,
If desired, excess liquid is withdrawn from the reactor so that it can be sent to a recovery system. The surface is then optionally sprayed with water and the effluent discarded or collected if desired. Thereafter, the reactor is charged with the polymerization medium and components in the conventional manner and the polymerization reaction is initiated. It goes without saying that the reactor can be recoated as often as desired, even after each initial polymerization, without opening the reactor. Applying the coating composition of the present invention to the inner surface of the reactor,
After spraying with water, the reactions to be carried out in the device can be started immediately without any special process procedure changes due to the presence of the coating. Furthermore, by utilizing the internally coated reactor of the present invention, the thermal stability or other physical and chemical properties of the polymers produced therein are not adversely affected. Although the present invention is specifically described with respect to the suspension polymerization of vinyl chloride, the apparatus and process of the present invention are suitable for the dispersion polymerization, emulsion, and emulsion of any polymerizable ethylenically unsaturated monomer or monomers that result in undesirable polymer deposition. It goes without saying that it can be similarly applied to polymerization or suspension polymerization. Examples of such monomers include other vinyl halides and vinylidene halides, such as vinyl bromide, vinylidene chloride, etc.; vinylidene monomers having at least one terminal CH ₂ =C< group, such as methyl acrylate. , ethyl acrylate, butyl acrylate, octyl acrylate, cyanoethyl acrylate, etc.; vinyl acetate;
Methacrylic acid esters such as methyl methacrylate, butyl methacrylate, etc.; styrene and α
- styrene derivatives, including methylstyrene, vinyltoluene, chlorostyrene, etc.; vinylnaphthalene; diolefins, including butadiene, isoprene, chloroprene, etc.; mixtures of any type of monomer with other vinylidene monomers copolymerizable therewith; and those skilled in the art and other types of vinylidene monomers known in the art. However, the present invention uses vinyl chloride alone or at least one terminal copolymerizable with vinyl chloride.
It is particularly applicable to the suspension polymerization of mixtures containing up to about 80% by weight or more of one or more vinylidene monomers with CH ₂ =C< groups, based on the total monomer mixture. This is because polymer adhesion to the reactor is a particularly detrimental problem in these polymerizations. In the present invention, the polymerization reaction is usually carried out at about 0° to 0° depending on the specific monomer or monomers to be polymerized.
Conducted in a temperature range of approximately 100°C. However, about 40°~
It is preferred to use a temperature range of about 70°C as this range produces polymers with the most advantageous properties. The polymerization reaction time will be on the order of about 2 to about 15 hours. Although the polymerization process can be carried out at autogenous pressures, superatmospheric pressures of up to 10 atmospheres or more can be advantageously used for volatile monomers. Pressures above atmospheric pressure can also be used for monomers with volatilization requirements that cause reflux cooling of the reaction mixture at the reaction temperature. Furthermore, the process of the present invention is compatible with full reactor technology (full reactor technology).
It can be carried out using a reactor technique). That is,
The reactor is completely filled with polymerization medium and this condition is maintained during the reaction by constant addition to the polymerization vessel of water or an additional make-up liquid containing the same proportions of monomers or monomer mixtures as at the beginning of the polymerization. The polymerization reaction is usually started by adding a certain amount of liquid.
Polymerization is terminated by adding a terminator. This additional addition of liquid is necessary because of the volumetric contraction of the reaction medium caused by the conversion of one or more monomers into the polymer state. A percent scale based on the degree of release of attachment was devised to grade the various coatings specifically listed in the specific examples below. That is, if the reactor was rated 100%, the reactor was completely free of fouling. Controls, ie, reactors without internal coatings, will typically be less than 75%. A rating of 75% or higher is good or indicates a definite improvement. Specific examples are presented below to further illustrate the invention. However, it goes without saying that these examples are merely illustrative and do not limit the present invention to these examples. In the examples, all "parts" and "percents" are based on weight unless otherwise specified. Example In this example, PVA/bisphenol A2Na
A salt complex was used in the coating solution. of bisphenol A
An aqueous coating solution containing 0.50% of 2Na salt and 0.10% of PVA (88% saponified polyvinyl acetate) was prepared under stirring.
The ratio of inhibitor to polymer in the resulting coating solution was 5:1. The pH of the coating liquid was 10.6. Clean two 3 liter reactors with polishing powder,
One was left uncoated (control) and the other was coated with the coating solution described above. The coating liquid was sprayed onto the inner surface of the reactor and the coating was then rinsed with water. After the reactors were then purged with nitrogen and vacuum applied, the following formulations were charged to each reactor. Vinyl chloride 1000gr Water (desalted) 2055gr Vinol540 ^*1 0.5gr SBP ^*2 0.5cc *1 Vinol540: 88% saponified polyvinyl acetate *2 Di-secondary butyl peroxydicarbonate. A full reactor technique was used for the polymerization reaction, with enough water added to keep the reactor full. The temperature of the reaction medium was maintained at 57°C and the reaction medium was stirred.
According to the shrinkage of the mixture for the production of polymers,
Water was added during the reaction. The reaction was stopped by adding 400 gr of water. The contents of each reactor were then removed in the usual manner. After removing the polymerization mixture from the reactor, the internal surfaces were rinsed with water and, in the case of one reactor, recoated and rinsed with water before a second charge was introduced and polymerized. After the second polymerization, a third polymerization was carried out following the same procedure as above.
After completion of the third charge polymerization, the interior surfaces of the reactor were graded according to the method previously described for grading interior reactor surfaces. The uncoated control developed significant fouling after the second charge polymerization, with a rating of less than 75%. On the other hand, the coated reactor remained very clean with no adhesion even after the third charging polymerization, and its grading was 97.5%, which was almost perfect. More importantly, the coating liquid used in this example is colorless. Similarly good results were obtained using more dilute solutions using the above components. This coating solution contains 0.10% 2Na salt of bisphenol A and
It contained 0.02% PVA and was colorless. The reactor surface rating after the second charge polymerization using the procedure as described above was 95%. The above data demonstrate the superior results of the coated reactor according to the invention over the uncoated reactor. EXAMPLE The inhibitor used was a 1% solution of glucose thiosemicarbazone. This is 0.20% in water.
The PVA was mixed in an amount sufficient to provide a 5/1 ratio of glucose thiosemicarbazone to PVA in the coating solution. Coating the inner surface of the reactor using the example procedure, rinsing with water and charging the example formulation;
Then it was polymerized. This sequence was repeated for two cycles. The grade of the reactor internal surface after the second cycle is:
95%, demonstrating superiority over the control. EXAMPLES In this example, several coating solutions were prepared as in the examples using various hydrophilic polymers and inhibitors. Again using the example procedure, the reactors were applied with these coating solutions and the example formulations were polymerized multiple times in the coating reactor. The reactor was evaluated after each polymerization was completed and compared to a control. The coating composition and results are shown in the table below.

Table: As is clear from the results in the table above, the superior results of the coated reactor over the uncoated reactor (control) are evident. Coating an internal surface of a polymerization reactor according to the invention substantially reduces, and in many cases practically eliminates, the deposition of polymer on that surface during the polymerization reaction, and thus This results in an increase in per unit production. Even if small amounts of polymer deposits do occur on the internal surfaces, they are not hard, rough, and difficult to remove using the difficult and time-consuming stripping methods traditionally used. It can be easily removed. Furthermore, the coating liquid of the present invention is colorless, and even if slight coloration is observed, it does not affect the quality of the produced polymer. Furthermore, the invention allows closed polymerization system operation, which has the advantage that in the case of vinyl chloride polymerization, the PPM of vinyl chloride in the plant atmosphere is significantly reduced. Declining vinyl chloride concentrations in the atmosphere have recently been recognized by OSHA (Occupational Safety and
Health Administration) and EPA
(Environmental Protection Agency). Numerous other features of the invention will be apparent to those skilled in the art. Although the present invention has been described in terms of specific embodiments thereof, it will be obvious to those skilled in the art that modifications thereto and equivalents thereto will be obvious to those skilled in the art. shall be included within the scope.

Claims (1)

[Scope of Claims] 1 (A) Water-soluble polyvinyl alcohol, hydroxylpropylmethylcellulose, polyvinylpyrrolidone, gelatin, acrylic acid polymer, methacrylic acid polymer, acrylic acid copolymer,
Water-soluble hydrophilic polymers selected from the group of methacrylic acid copolymers, maleic anhydride copolymers, soluble protein polymers, saponins, acrylamide polymers, acrylamide copolymers, hydroxyalkylacrylamide polymers and hydroxyalkylacrylamide copolymers.
0.01 to 2.5% by weight, and (B) bisphenol A salt, glucose thiosemicarbazone, 2,4-dinitrobenzene sulfonate, hydroquinone, hydroquinone methyl ether, acetone thiosemicarbazone, basic salt of phenol and aroma. An aqueous coating solution containing a complex with 0.04-2.5% by weight of a polymerization inhibitor selected from the group of acid salts of group amines is applied to the inner surface of the polymerization reactor, the coating is rinsed with water, and the monomers are removed from the reaction. A polymerization method which substantially prevents the adhesion of polymer to the inner surface of a polymerization reactor, which comprises polymerizing while constantly in contact with the coated inner surface of the vessel. 2. The method of claim 1, wherein said aqueous coating fluid contains from about 0.05 to about 5.0% by weight of said complex. 3. The method according to claim 1, wherein the hydrophilic polymer is polyvinyl alcohol. 4. The method according to claim 1, wherein the hydrophilic polymer is hydroxypropylmethylcellulose. 5. The method according to claim 1, wherein the polymerization inhibitor is a disodium salt of bisphenol A. 6. The method according to claim 1, wherein the polymerization inhibitor is glucose thiosemicarbazone. 7. The method according to claim 1, wherein the polymerization inhibitor is 2,4-dinitrobenzenesulfonic acid-Na salt. 8. The method according to claim 1, wherein the polymerization inhibitor is hydroquinone. 9 The ratio of hydrophilic polymer to polymerization inhibitor is approximately 1:1.
2. The method of claim 1, wherein the ratio is about 1:13. 10. The method of claim 1, wherein the pH of the coating solution is within the range of about 2.0 to about 12.0. 11. The method of claim 2, wherein the hydrophilic polymer is polyvinyl alcohol and the polymerization inhibitor is bisphenol A disodium salt. 12. The method of claim 2, wherein the hydrophilic polymer is polyvinyl alcohol and the polymerization inhibitor is glucose thiosemicarbazone.