Olefin polymerization solid-catalyzed

Solid-Catalyzed Olefin Polymerization. A third area where extremely challenging polymerization reaction engineering problems arise is in transition-metal catalyzed polymerization of olefins such as ethylene, propylene and their copolymers. 

Since mixing and good heat transfer are of vital importance in viscous polymerization reactions, a mechanically agitated continuous stirred-tank reactor is widely used in polymerization processes. Solution polymerization, emulsion polymerization, and solid-catalyzed olefin polymerization are all carried out in a mechanically agitated slurry reactor. 

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. 

The modeling of heterogeneous polymerization systems is generally more complicated than that of the homogenous systems because mass and heat transfer effects between two or more immiscible phases must be considered. Industrially important heterogeneous polymerization reactions include emulsion polymerization, suspension polymerization, precipitation polymerization, and solid-catalyzed olefin polymerization. The general polymerization rate equation is represented simply as... 

Oxidic catalysts with acidic properties catalyze many industrial reactions, including the dehydration of alcohols, the hydration of olefins, cracking processes, and olefin polymerization. How does the acidity of such solids arise ... 

Rhodium chloride catalyzes the polymerization of butadiene with high stereospecificity to trarw-poly( 1,4-butadiene) (4) and also the dimerization of ethylene and other olefins (2). Although certain oligomerizations are catalyzed by solid palladium and rhodium catalysts (9), polymerization to high molecular weight products is not generally observed. 

Three-c(H)rdinate carbenium ion and five-coordinate carbonium ion intermediates satisfactorily account for many of the acid-catalyzed reactions of hydrocarbons at high temperatures. Yannoni et al. have characterized the structure and dynamics of several carbenium ions trapped in (noncatalytic) solids at low temperatures [32,94,95), but lifetimes of such ions on active surfaces at higher temperatures would preclude NMR observation in all but special cases. Maciel observed triphenyl carbenium ion on alumina 196). The alkyl-substituted cyclopentenyl ions discussed earlier are also special ions they are commonly observed products in conjunct polymerization reactions of olefins in acidic solutions. The five member ring cannot easily rearrange to an aromatic structure, and ions like I and II are apparently too hindered to be captured by the framework to form alkoxy species. 

In a pioneering paper [97], Osakada has reported ethylene polymerization trials with a series of early-late heterobimetallic complexes, including a Co/Zr combination, and showed that some of these complexes enable the enchainment of the a-olefin or of the oligomer formed at the late metal center to the polymer grown at the Zr center. The synthesis of the Co/Zr heterobimetallic complex 49 is elegant and involves as key step the Ru-catalyzed cross metathesis of an ansa-zirconocene complex 47 with an allyl substituent and a Co complex 48 having a pendant acrylate (Scheme 31). In the solid state, both Zr and Co atoms were found far away from... 

Insertion polymerization is usually catalyzed by an organometallic compound and a monomer is inserted between the metal ion and the carbon atom adjacent to the metal (carboanion). As a result, the polymer chain is pushed out from the solid catalyst surface. Usually, addition polymerizations are involved in the polymerization of olefinic monomers. Polymerization occurs via an insertion of a monomer at the end of the growing chain, mediated by a catalyst. The catalyst stays at the end of the growing chain. Polymers synthesized by insertion polymerization are typically characterized by a very high stereo-regularity. An example of such a polymerization technique is the Ziegler-Natta-catalyzed polymerization. 

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