Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2/00—Processes of polymerisation
  • C08F2/002—Scale prevention in a polymerisation reactor or its auxiliary parts
  • C08F2/004—Scale prevention in a polymerisation reactor or its auxiliary parts by a prior coating on the reactor walls
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus

Definitions

• the same are maintained in the form of discrete droplets in an aqueous suspension system by the use of suspending agents and agitation.
• the resultant polymer, or PVC is washed and dried.
• these suspension systems are often unstable and during the polymerization reaction vinyl chloride polymer builds up on the inner surfaces of the reactor. Obviously, this polymer buildup must be removed since it results in further formation of polymer buildup which in turn results in a crust formation that adversely affects heat transfer and contaminates
• a film or coating of a coating material made by reacting a thiodiphenol, or a derivative thereof, as hereinafter defined, with a bleaching material or agent, is applied to the inner surfaces of a polymerization reactor or vessel by merely contacting said surfaces with an aqueous solution of said coating material. All exposed surfaces in the interior of the reactor, such as the baffles, agitator or mixing mechanism, condensers, when the same are used, 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 be introduced to the reactor and the reaction started without the necessity of drying said surfaces beforehand.
• the surfaces are rinsed with water, such as by spraying, filling the reactor and draining, and the like, thereby, surprisingly, leaving on said surfaces a tightly adhering coating or film of the coating material which is not affected by the polymerization medium even though said medium is vigorously agitated during the polymerization reaction.
• Various bleaching materials or agents may be reacted with the thiodiphenols and derivatives thereof, such as chlorine, hypochlorites and chloramines, and chlorite and chlorine dioxide.
• the preferred bleaching materials or agents for use in the present invention are the hypochlorites, and in particular, sodium hypochlorite (NaOCl).
• the reaction is fairly simple and involves forming an alkali metal salt of the thiodiphenol, or derivative thereof, such as with sodium hydroxide, and the like, and then reacting said salt in an aqueous medium with the bleaching material while using good agitation.
• the useful thiodiphenols and derivatives thereof, for making the coating solutions for the practice of the present invention are those compounds represented by the following generic formula:
• R is -S-; or R 1 is -H; -OH; or an
• aqueous alkali metal or ammonium hydroxide solution containing about 2.0% to about 10.0% by weight as thiodiphenol and will have a pH in the range of about 10 to about 13 and the intermediate product need not be recovered.
• a separate aqueous solution containing about 2% to about 10% by weight of a bleaching material or agent, for example, NaOCl is made up at a temper ature in the range of about 5°C to about 50°C.
• the latter solution is slowly added to the former solution with good agitation at a temperature in the range of about 5°C to about 50°C.
• the final molar ratio of bleaching material or agent to thiodiphenol will be in the range of about 0.1 to about 2.0 and preferably in the range of about 0.4 to about 0.8.
• the resultant solution containing the reacted product is the master coating solution and will have a pH in the range of about 10 to about 13.
• This master coating solution is then further diluted with water to give a coating solution for application to the reactor surfaces having a total solids content, based on the weight of the thiodiphenol, or derivative thereof, reaction product in the range of about .1% to about 5% by weight.
• the final coating solution will contain from about .3% to about 1% by weight of the coating material as dry product.
• the pH of the final coating solution can be adjusted by means of an acid, such as hydrochloric acid, so as to fall within the range of about 9.7 to about 13.
• an acid such as hydrochloric acid
• HCl hydrochloric acid
• a precipitate forms locally but redissolves rapidly.
• the pH of the coating solution 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 of the thiodiphenol or derivative thereof, such as Na, K, Li, NH 4 , and the like.
• the inner surfaces thereof are water-wettable.
• An ordinary solid surface such as stainless steel, is non water-wettable due to the normal contamination of said surfaces with organic materials through contact with the atmosphere.
• the surfaces can be cleaned, such as with chromic acid or an abrasive cleanser, for example, and it will become water-wettable.
• cleaning alone does not solve the problem since the surfaces 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 polymerization cycle.
• ⁇ The angle formed between 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” ( ⁇ ).
• ⁇ The angle formed between the tangent of the side of the droplet and the metal or glass surface.
• ⁇ c The angle formed between the tangent of the side of the droplet and the metal or glass surface.
• the ⁇ is measured in dynes per centimeter. Using water as the standard, in order for a solid surface to be wettable, ⁇ must equal zero or be very close to it, and ⁇ c must be 72 dynes/cm. or greater.
• 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 mono-layer of the coating material applied which is 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.
• films of greater thickness can result when using higher solids content coating solutions, in accordance 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.
• the coating or film is resistant 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 solution is usually applied to the inner reactor surfaces by spraying it on. However, it is also possible to apply the coating solution by flooding the reactor and then draining, or painting or brushing on, but spraying is the most practical and economical method of application. After spraying the coating solution on the inner surfaces 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 reactor, 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 surfaces, such as stainless 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.
• 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 reactor periodically after several charges have been run therein, or after each charge, to insure uniform and efficient production.
• 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 invention does not adversely affect the heat stability or other physical and chemical properties of the polymers produced therein.
• the polymerization process is usually conducted 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 employed with some advantage with the more volatile monomers. 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 additional make-up liquid containing the monomer or monomers in the same proportions as at start-up. Upon the addition of a certain predetermined amount of liquid, the polymerization reaction is terminated, usually by the addition thereto of a short-stopping agent.
• EXAMPLE I In this example, the following were mixed together at a temperature of 23°C with stirring to form a clear solution having a pH of 11.95.
• the present invention has many advantages, principal among which is the ability to use very dilute coating solutions in polymerization reactors and still substantially reduce polymer buildup. By the use of dilute coating solutions, the adverse color problem is eliminated and the economics are greatly improved.
• Another advantageous feature of the present invention is the ease with which the coating material is prepared, that is, by a novel nearly instantaneous reaction in water at, or near, room temperature. Further, the present invention enables one to operate a closed reactor system thus eliminating the escape of any unreacted monomer into the surrounding atmosphere of the plant, which could be injurious to health. Numerous other advantages of the present invention will be apparent to those skilled in the art.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Health & Medical Sciences (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Polymerisation Methods In General (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)

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Citations (5)

• 1980
  • 1980-03-21 CA CA000348206A patent/CA1147098A/en not_active Expired
  • 1980-04-07 IN IN404/CAL/80A patent/IN151750B/en unknown
  • 1980-04-08 BR BR8008649A patent/BR8008649A/pt not_active IP Right Cessation
  • 1980-04-08 DE DE8080901046T patent/DE3062109D1/de not_active Expired
  • 1980-04-08 WO PCT/US1980/000393 patent/WO1980002388A1/en not_active Ceased
  • 1980-04-08 JP JP55501262A patent/JPH0134241B2/ja not_active Expired
  • 1980-04-08 EP EP80901046A patent/EP0027466B1/en not_active Expired
  • 1980-04-11 GR GR61656A patent/GR66625B/el unknown
  • 1980-04-15 PH PH23902A patent/PH19665A/en unknown
  • 1980-04-18 IT IT21511/80A patent/IT1141289B/it active
  • 1980-04-23 KR KR1019800001647A patent/KR830001026B1/ko not_active Expired
  • 1980-04-28 BE BE0/200398A patent/BE883017A/fr not_active IP Right Cessation
  • 1980-04-29 PT PT71159A patent/PT71159A/pt unknown
  • 1980-04-30 MX MX182183A patent/MX153932A/es unknown

Patent Citations (5)

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