Heterogeneous-homogeneous reactions chain branching

Chain termination may be either heterogeneous or homogeneous in nature. At low pressure the chain carriers and branching agents may diffuse to the walls of the reactor where they are destroyed either by capture or conversion to inactive products. These heterogeneous termination reactions are either diffusion-controlled in which case the rate coefficient is given by the expression... 

This article surveys the research work on the synthesis and modification reactions of poly(ethyleneimine) as well as its applications to metal complexation processes. Poly-(ethyleneimine), one of the most simple heterochain polymers exists in the form of two different chemical structures one of them is branched, which is a commercially available and the other one linear which is synthesized by cationic polymerization of oxazoline monomers and subsequent hydrolysis of polyf(/V acylimino)cthylcne]. The most salient feature of poly(ethyleneimine) is the simultaneous presence of primary, secondary, and tertiary amino groups in the polymer chain which explains its basic properties and gives access to various modification reactions. A great number of synthetic routes to branched and linear poly(ethyleneimine)s and polymer-analogous reactions are described. In addition, the complexation of polyfethyleneimine) and its derivatives with metal ions is investigated. Homogeneous and heterogeneous metal separation and enrichment processes are reviewed. 

Metal-oxides of the type (Al203)x(Sn0)Y(Zn0)z were also studied as heterogeneous catalysts for the transesterification reaction of soybean oil (Macedo et al., 2006). It was observed that these materials are active for soybean oil alcoholysis with different alkyl-chain alcohols using several alcohols, including branched ones. The best result was achieved using methanol, with conversion yields up to 80% in 4 h. As observed for the complex 1 in homogenous conditions, the catalytic activities are strongly dependent on the nature of the alcohol. For alcohols with a linear chain, the reaction activities decrease with... 

Chain initiation occurs by surface reaction, as in this example, or homogeneously, as in the CO + Og chain.Since heterogeneous processes are very significant in the kinetics of branching chains great care in surface preparation is required to achieve reproducible results. The propagation... 

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