Polyolefins reactor designs

Flego [1] recommends the use of micro devices for automated measurement and microanalysis of high-throughput in situ characterization of catalyst properties. Murphy et al. [5] stress the importance of the development of new reactor designs. Micro reactors at Dow were described for rapid serial screening of polyolefin catalysts. De Bellefon ete al. used a similar approach in combination with a micro mixer [6], Bergh et al. [7] presented a micro fluidic 256-fold flow reactor manufactured from a silicon wafer for the ethane partial oxidation and propane ammoxidation. 

Separation and recovery of contaminants, solvents and unreacted monomers are necessary steps in many bulk and solution polymerizations. The cost of these steps may dominate the overall economics. They should be considered as an integral part of reactor design since their economic importance may dictate the choice of a particular reaction scheme. As one example, gas-phase processes constitute an increasing segment of polyolefin production due to the simplicity of product recovery. The polymer is obtained directly from the reactor as a dry, free-flowing powder. There are no separation steps in this... 

An improved loop reactor design with cone-shaped zones that transition the loop to a wider diameter section was recently patented by Basell Polyolefine GmbH [29]. This design is illustrated in Figure 5.15. 

Polyolefins account for more than 50% of all synthetic polymers being produced today. The volume and applications of polyolefins have been substantially growing since the time of the Ziegler and Natta discoveries. With the introduction of metallocene and other single-site catalysts, polyolefins, with the simple chemistry of carbon and hydrogen, have evolved into complex microstructures that can be designed through multiple reactor-catalyst processes to achieve a desired performance for specific applications. 

Another important feature of a modem fluidized-bed reactor for polyolefin production is the disengaging zone the diameter of the reactor is increased at its topmost part to form the disengaging zone. This expanded cross section of the reactor slows down the upward movement of the polymer particles and prevents or minimizes them from being carried out by the fluidizing gas. Using this design procedure, the circulating gas velocity can be increased for better heat transfer. 

Olefin copolymerization and reactor blend formation are important processes to tailor polyolefins. Copolymer properties depend upon the sequence distribution of the comonomers, which is controlled by means of catalyst as well as process technology. Today most copolymers are produced either in solution processes or in solvent-free gas phase polymerization. Recent breakthroughs in catalyst development are stimulating production of a novel range of copolymers, especially of ethylene copolymers. In the past, special catalysts were designed to produce three classes of ethylene copolymers with different comonomer content ... 

Practically all industrial gas-solid fluidized bed reactors operate at temperatures well above ambient, and some, such as those used in the production of polyolefins, also operate at elevated pressures. It is therefore important to know how fluidized beds behave under high temperatures and/or pressures and if possible to predict this behavior from observations made under ambient conditions. The emphasis here will be on those aspects of the subject that are of direct relevance to the design and operation of fluidized bed plant a comprehensive review of the more academic aspects can be found in the review by Yates (1996). 

Ruff M, Paulik C (2013) Controlling polyolefin properties by in-reactor blending 2. particle design. Macromol React Eng 7 71-83... 

Some catalysts can now be regarded as mini-reactors and are designed that way. For example, the auto exhaust catalyst is supported on a monolith small enough to fit underneath an automobile. On a molecular scale, metallocene compounds are single-site catalysts that are now being used to make polyolefins more selectively. It is probably not necessary to emphasize that the industrial catalysts used in chemical and refining processes are not the same as the catalysts of theory. They all have well-defined features related to the basic demands of the process in order to achieve predictable and economic operation. These are shown in Table 1.3. 

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