Process and apparatus for suspension polymerization

Abstract

Abstract In a suspension polymerization process which comprises polymerizing an ethylene halide by itself or a mixture of an ethylene halide and a monomer copolymerizable therewith in an aqueous medium in the presence of a suspending agent and an oil-soluble catalyst under pressure, a pressure polymerization vessel the internal exposed surfaces of which are wholly or at least partially lined with wood is used so as to prevent adhesion of the resulting polymer to the exposed area. BACKGROUND OF THE INVENTION The present invention relates to a suspension polymerization process in which an ethylene halide or a mixture of an ethylene halide and a monomer copolymerizable therewith is continuously suspension polymerized while adherence of the polymerization component to the wall of the polymerization apparatus is prevented and to a polymerization apparatus therefor. That is, as is well known, in the suspension polymerization of at least one monomer selected from ethylene halides including vinyl chloride, vinyl fluoride, vinylidene chloride, vinylidene fluoride, tetrafluoroethylene, or mixtures thereof or mixtures of an ethylene halide and a monomer copolymerizable therewith in an aqueous medium in the presence of an oil-soluble catalyst and a suspending agent, the resulting polymer adheres to the inner wall of the polymerizatiton vessel and to the internal accessory devices such as agitating vanes, baffle plates, a temperature detector, and the like. This adhesion of the polymer reduces the yield of the polymer and a polymerization temperature adjusting ability and gives rise to problems such as difficulty in adjusting the polymerization temperature and mixing of the adhering material into the product thereby to cause deterioration of the physical properties of the product. Further, there is caused another problem from the standpoint of operation of a polymerization vessel in that removal of the adhering material requires an excessive amount of labor and time, reducing the rate of production. In addition, occurrence and growth of the adhering material is a great obstacle to continuation of the suspension polymerization operation. That is, in order to insure good quality of the product produced by a continuous suspension polymerization process, it is necessary to use a so-called multi-vessel type reactor so as to reduce reverse mixing as much as possible. For this purpose, a passage of a very small area must be formed at least between adjacent vessels, which in turn gives rise to the problem of plugging, whereby normal operation is hindered. It is known that the occurrence of the sticking material depends upon the material from which the polymerization vessel used is made and the content contained in the polymerization vessel. In general, with a polymerization vessel made of stainless steel severe sticking occurs. In the case of a polymerization vessel lined with glass, the degree of sticking is slightly reduced, but when this type of vessel is used, the polymerization vessel must be cleaned after every polymerization operation and, thus, operated by a batch operation. It is not suitable for a continuous operation. Although various attempts have been long made to prevent such sticking, a satisfactory method is still to be found, and this lack is a great obstacle to the continuous operation of the suspension polymerization described above. It is considered that the adhesion of a polymer to the inner wall of the polymerization vessel in the suspension polymerization process is caused by the monomer being first adsorbed on the inner wall and then being polymerized on the surface. In view of this consideration, as one measure for preventing adhesion in the suspension polymerization of the ethylene halide in an aqueous medium, coating of various materials capable of adsorbing water and forming a film of water on the inner wall of the polymerization vessel has been heretofore practiced. However, in all cases, the film of water formed on the surface is composed of a monomolecular layer or at most 20 layers, and this film may be easily removed depending on change in the conditions surrounding the film, whereby it is thus impossible to maintain the film for a long period of time. Therefore, it is possible to attain temporary adhesion prevention using the prior art, but it is almost impossible to expect a continuous effect. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide a process for the continuous suspension polymerization of the ethylene halides mentioned above and an apparatus therefor. That is, in the suspension polymerization of at least one monomer selected from ethylene halides including vinyl chloride, vinyl fluoride, vinylidene chloride, vinylidene fluoride, tetrafluoroethylene, or mixtures thereof or mixtures of an ethylene halide and a monomer copolymerizable therewith in an aqueous medium containing an oil-soluble catalyst and a suspending agent, polymerization under pressure is carried out in a pressure polymerization vessel in which the whole or at least adhesion susceptive surfaces of the inner wall and accessory instruments contained therein are lined with wood or are constructed of wood. As to the ability of wood to prevent adhesion in the process of the present invention, it is considered that because of its tendency to adsorb water, the wood forms a film of water on the surface thereof which acts as a barrier to a sticking polymer. The wood used in the process of the present invention adsorbs water within the interior thereof and forms a film of water. As compared with the prior method in which a film of water is formed on the inner wall of the polymerization vessel merely using a thin coating of a wettable material, the process of the present invention provides a film of water which is thicker and not easily removed, and, accordingly, adhesion is effectively prevented. Moreover, this effect lasts for a long time.

Inventors

• 👤 Hiroyuki Noziri
• 👤 Mituaki Sugahara
• 👤 Hirotada Tanno

Bibliographic Details