Industrial olefin polymerization reactors

Processes for polyolefin production can be grouped into the following categories  

This variety of reactor configurations is unique for polyolefins among all commodity and specialty polymers. 

It is useful to separate the discussion into processes for polyethylene and polypropylene, as the requirements for these two polymers are different and have led to similar, but by no means identical, processes. A short discussion on the various reactor configurations will be presented first, followed by descriptions on how each reactor configuration is used in different polymerization processes throughout the world. Also listed are a few keys references at the end of the chapter for further reading [72-85]. Finally, the chapter will be concluded with a few considerations on the mathematical modeling of industrial olefin polymerization reactors. 

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Perhaps the most important reason leading to the industrial implementation of metallocene catalysts, in addition to their high activity and excellent microstructural control, is that they can be easily adapted to industrial olefin polymerization processes. The transition from Ziegler-Natta or Phillips catalysts to metaUocenes is sometimes called drop-in technology exactly to indicate that the new catalysts can simply be dropped in the existing reactor. Of course, reality is often not as simple as catchy terms may indicate, but the fact remains that metallocenes can be introduced into existing industrial processes without a prohibitively large number of adjustments. 

V. Touloupides et al.. Modeling and simulation of an industrial slurry-phase catal dic olefin polymerization reactor series, Chem. Eng. Sci., 65, 3208-3222 (2010)... 

Borstar is an industrial olefin polymerization plant/technology, which combines different polymerization processes and reactor units, utilizing an advanced catalytic system. In the present work, a detailed model for the dynamic and steady-state simulation of this industrial plant has been developed. A comprehensive kinetic model for the ethylene-1-butene copolymerization over a two-site catalyst was employed to predict the MWD and CCD in the Borstar process. The Sanchez-Lacombe equation of state (S-L EoS) was employed for the thermodynamic properties of the polymerization system and the phase equilibrium calculations in the process units. 

Emulsion polymerization is usually carried out isothermally in batch or continuous stirred-tank reactors. Temperature control is much easier than for bulk or solution polymerization because the small ( 0.5 fim) polymer particles, which are the locus of the reaction, are suspended in a continuous aqueous medium. This complex, multiphase reactor also shows multiple steady states under isothermal conditions. In industrial practice, such a reactor often shows sustained oscillations. Solid-catalyzed olefin polymerization in a slurry batch reactor is a classic example of a slurry reactor where the solid particles change size and characteristics with time during the reaction process. 

A complete phenomenological mathematical model for olefin polymerization in industrial reactors should, in principle, consider phenomena taking place from microscale to macroscale, but this is seldom the case. Most models assume that the conditions in the polymerization reactor are uniform and neglect any mesoscale phenomena, which may be a good approximation for solution polymerization reactors, but may not apply to polymerizations using heterogeneous catalysts. 

Polyolefins are produced in practically all types of reactor configurations -autoclaves, tubular reactors, loop reactors, fiuidized-bed reactors - making them a prime choice for polymer reaction engineering studies. Polymerization may take place in either gas or liquid phases. For liquid-phase reactors, the monomers can be either liquid (as in the case of propylene and higher a-olefins) or dissolved in an inert diluent. Industrial catalysts for olefin polymerization are mainly heterogeneous, but some processes also use soluble catalysts. There are many different types of catalysts for olefin polymerization and they can be used to synthesize polymer chains with very different microstructures and properties. 

The conventional stirred-tank reactor is an agitated vessel, typically a jacketed pressure vessel, and often with provisions for reflux of a solvent or monomer. The continuous-feed version is the CSTR. Continuous operation is typical of high-volume polymers but large batch and fed-batch stirred-tank reactors are occasionally used. Reactors other than stirred tanks may be functionally equivalent to stirred tanks. Loop reactors are widely used in the polymer industry, especially for solution and slurry olefin polymerizations the agitator in the stirred tank is replaced with a circulation pump. The loop many consist of jacketed pipe or there may be heat exchangers and even flash vessels in the loop. The loop may consist of many legs for space considerations, but the legs are connected in series and there is only one circulation pump. 

LLDPEs from tubular or cascade loop reactor have fewer LCB and broader MWD than autoclave products. Modeling of an industrial slurry-phase olefin catalytic polymerization of two loop reactors in series was carried out by U. Thessaloniki and Total Petrochemicals... 

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