Various type chemical processes are commonly carried out in large, stirred vessels which are frequently provided with auxiliary equipment, such as baffles, heat transfer coils which enable heat to be supplied or extracted from the contents 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 deposits 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.
This problem is particularly bad in the commercial production of polymers and copolymers of vinyl and vinylidene halides, when polymerized alone or with other vinylidene monomers having a terminal CH.sub.2 .dbd.C&lt; group, or with polymerizable polyolefinic monomers. For example, in the commercial production of vinyl chloride polymers, the same are usually produced in the form of discrete particles by polymerization in aqueous suspension systems. When employing such a polymerization system, the vinyl chloride, and other comonomers when used, are maintained in the form of small discrete droplets by the use of suspending agents and agitation. When the reaction is complete, the resultant polymer is washed and dried. These aqueous suspension system polymerization reactions are usually conducted under pressure in metal reactors equipped with baffles and high speed agitators. However, these suspension systems are inherently unstable and during the polymerization reaction, vinyl chloride polymer builds up on the interior surfaces of the polymerization reactor, including the surfaces of the baffles and agitator. Obviously, this polymer buildup must be removed since it results in further formation of polymer buildup on the reactor surfaces which results in a crust that adversely affects heat transfer and contaminates the polymer being produced.
The nature of the insoluble polymer buildup on the walls of the reactor is such that in the commercial production of polymers, as described above, it was the practice in the past to have an operator enter the reactor, after each polymerization reaction was completed, and hand scrape the polymer buildup off the walls and off the baffles and agitator. This procedure was not only costly, both in labor and down-time of the reactor, but most importantly, it has since been proven that this procedure has potential health hazards. Various methods have since 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, which have proved satisfactory to a certain extent but did not reach the ultimate in prevention of polymer buildup.
Subsequently, various methods of applying coating compositions to the inner surfaces of polymerization reactors have been developed which have represented a great step forward in the art. However, such coating methods require the installation of auxiliary equipment, more complex charging procedures and the danger of contamination of the polymer by coating ingredients. Accordingly, it would be most advantageous to have a polymerization recipe which would substantially eliminate polymer buildup and be readily adaptable to existing installations without addition of further equipment or alteration of existing equipment.
USPTO Backgrounds
USPTO Backgrounds