Heterogeneous polymerization solid catalysts

Rate of polymerization. The rate of polymerization for homogeneous systems closely resembles anionic polymerization. For heterogeneous systems the concentration of alkylated transition metal sites on the surface appears in the rate law. The latter depends on the particle size of the solid catalyst and may be complicated by sites of various degrees of activity. There is sometimes an inverse relationship between the degree of stereoregularity produced by a catalyst and the rate at which polymerization occurs. 

Equipment for heterogeneous reactions is particularly flexible, since each phase can be processed more or less independently. In the fluidized-bed reactor (Fig. 1-4) the reactants flow continuously through and out of the reactor, but the solid-catalyst phase is withdrawn, regenerated, and returned. In the lime kiln (an example of a gas-solid noncatalytic reactor) the two phases pass continuously and countercurrently through the reactor. In heterogeneous liquid-solid polymerization systems the slurry of catalyst and reaction mixture flow together through the reactors. Walas, Brotz, and particularly van Krevelen have summarized the various types of... 

Polymerization reactors are a specific kind of chemical reactors in which polymerization reactions take place therefore, in principle, they can be analyzed following the same general rules applicable to any other chemical reactor. The basic components of a mathematical model for a chemical reactor are a reactor model and rate expressions for the chemical species that participate in the reactions. If the system is homogeneous (only one phase), these two basic components are pretty much what is needed on the other hand, for heterogeneous systems formed by several phases (emulsion or suspension polymerizations, systems with gaseous monomers, slurry reactors or fluidized bed reactors with solid catalysts, etc.), additional transport and/or thermodynamic models may be necessary to build a realistic mathematical representation of the system. In this section, to illustrate the basic principles and components needed, we restrict ourselves to the simplest case, that of homogeneous reactors in other sections, additional components and more complex cases are discussed. 

Commercial eoordination catalysts (except the homogeneous metalloeene/aluminoxane eatalysts) are heterogeneous solids. During the polymerization the catalyst particles eonvert from pure catalyst to catalyst+polymer particles by a repliealion ptoeess [20]. The overall shape of the parliele is maintained as the polymerization continues. The ehaiacteristics of the final polymer parliele are... 

Zohuri et al. (2013) synthesized novel 2,9-dihydro-2-oxo-4-aryl-l//-pyrido[2,3-fc] indole-3-carbonitrile derivatives by condensation of substituted (triethoxymethyl) arene, l-methyl-lH-indol-2-ol, and cyanoacetamide using catalytic amounts of crosslinked poly(2-acrylamido-2-methyl propane sulfonic acid) (AMPS) as an efficient and heterogeneous catalyst (Scheme 2.10). This polymeric solid acid catalyst is stable and can be easily recovered and reused without significant change in its... 

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