Spheripol bulk polymerization reactor

Refinement of the bulk polymerization reactor and of the gas-phase reactor led to the development of the Spheripol process in 1982 (Figure 17.2). 

By far the most commonly used PP-process is Montell s Spheripol Process. The first reaction stage consists of one or two tubular loop reactors where bulk polymerization of homopolymers, random and terpol5nners is carried out in liquid propylene. The prepolymerized catalyst, liquid propylene, hydrogen for controlling molecular weight and eventually comonomers are continuously fed into the reactor in which polymerization takes place at temperatures of 60-80°C and pressures of 35-40 bar. The tubular configuration enables a perfect heat transfer and control of the reaction temperature. 

In PP manufacture, modern bulk (liquid monomer) and gas-phase processes have largely replaced the earlier slurry processes in which polymerization was carried out in hydrocarbon diluent. The most widely adopted process for PP is Basell s Spheripol process.317 Homopolymer production involves a pre-polymerization step at relatively low temperature, followed by polymerization in a loop reactor using liquid propylene random co-polymers are produced by introducing small quantities of ethylene into the feed. The pre-polymerization step gives a pre-polymer particle with the capacity to withstand the reaction peak, which occurs on entering the main loop reactor. The addition of one or two gas-phase reactors for EP co-polymerization makes it possible to produce heterophasic co-polymers containing up to 40% of E/P rubber within the homopolymer matrix. 

One particular development was the commercialization of the Spheripol process by Himont (now licensed by Basell) in 1982. This process combines bulk phase polymerization in loop reactors with gas phase polymerisation and has become the most dominant licensed process. More recently. Borealis has taken a similar route with the adaptation of its Bor-star bimodal PE process to produce PP. 

In order to fully exploit this catalyst system a unique commercial polymerization process was developed, Himont s Spheripol process is, in practice, a two-stage hybrid process consisting of both liquid and gas phases. Homopolymerization takes place in the liquid slurry phase, and after removal of unreacted monomer and solvent, the solid, porous particles pass into the gas phase part of the process in which the introduction of other monomers allows copolymerization to take place within the solid, spherical particle. This growing polymer particle has become a "reactor granule" and represents a revolution in the development of Ziegler-Natta catalysis. Since polymerization can take place within a solid polymer shell, the mechanical containment aspects of the polymerization process became secondary. Bulk, gas phase, and slurry processes are all equally adaptable for use with this catalyst system and are chosen based on economics, mechanical reliability and reaction control criteria in order to maximize reactivity and productivity. It removes almost all of the previous process constraints on Ziegler-Natta catalysis, allowing reactor-made resins to be produced with... 

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