Reaction media employed polymerization reactors

Polymers can be classified according to the techniques used during the polymerization of the monomer. In bulk polymerization, only the monomer (and possibly eatalyst and initiator, but no solvent) is fed into the reactor. The monomer undergoes polymerization, at the end of whieh a (nearly) solid mass is removed as the polymer product. As we shall see later, bulk polymerization is employed widely in the manufacture of condensation polymers, where reactions are only mildly exothermic and viscosity is mostly low thus enhancing ready mixing, heat transfer, and bubble elimination. Solution polymerization involves polymerization of a monomer in a solvent in which both the monomer (reactant) and polymer (product) are soluble. Suspension polymerization refers to polymerization in an aqueous medium with the monomer as the dispersed phase. Consequently, the polymer resulting from such a system forms a solid dispersed phase. Emulsion polymerization is similar to suspension polymerization but the initiator is located in... 

During the late 1970s, Union Carbide developed a low-pressure polymerization process (Unipol process) capable of producing polyethylene in the gas phase that required no solvents. The process employed a chromium based catalyst. In this process (Figure 4.1) ethylene gas and solid catalysts are fed continuously to a fluidized bed reactor. The fluidized material is polyethylene powder which is produced as a result of polymerization of the ethylene on the catalyst. The ethylene, which is recycled, supplies monomer for the reaction, fluidizes the solid, and serves as a heat-removal medium. The reaction is exothermic and is normally run at temperatures 25-50°C below the softening temperatures of the polyethylene powder in the bed. This operation requires very good heat transfer to avoid hot spots and means that the gas distribution and fluidization must be uniform. 

Polymerization of the quarterpolymers took place in a stirred reactor in an aqueous or a nonaqueous reaction medium. Preferred organic solvents were fluoroalkanes or chlorofluoroalkanes and their mixtures with water. Polymerization reaction could be carried out by bulk, solution, suspension, emulsion, or vapor phase polymerization methods. The reaction conditions depended on the selected polymerization process. The reaction temperature was in the range of 20°C to 100°C. An organic solvent medium required the use of organic peroxy or azo compounds as the reaction initiator. In aqueous media, water-soluble initiators such as ammonium persulfate could be employed. The best initiators for aqueous media were acids of manganese and their salts, such as potassium permanganate. The total pressure was in the range of 0.2-10 MPa. 

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