Incomplete reactions, homogeneous

Morphology of the cured samples was analyzed by SEM of the fractured samples etched with tetrohydrofuran (THE), which is a solvent for the rubber. Figure 11.24 shows the fracture surfaces of the PWE and PNE specimens. Whereas the PWE fracture surface presents an essentially homogeneous surface with only a few small voids present, small yet uniformly distributed cavities are seen in PNE samples. The PWE morphology is consistent with the high degree of intermolecular link between rubber and epoxy macromolecules. The PNE morphology indicates incomplete reaction between epoxy and rubber. 

The reasons for this lack of work are manifold The problem is quite complex and difficult to tackle. The information in reaction databases is inherently biased only known reactions, no reactions that failed, are stored. However, any learning also needs information on situations where a certain event will not happen or will fad. The quality of information stored in reaction databases often leaves something to be desired reaction equations are incomplete, certain detads on a reaction are often incomplete or missing, the coverage of the reaction space is not homogeneous, etc. Nevertheless, the challenge is there and the merits of success should be great ... 

Danckwerts, P.V., 1958. The effect of incomplete mixing on homogeneous reactions. Chemical Engineering Science, 8, 93-99. 

In this context we postulated that the shift reaction might proceed catalytically according to a hypothetical cycle such as Scheme I. There are four key steps in Scheme I a) nucleophilic attack of hydroxide or water on coordinated CO to give a hydroxycarbonyl complex, b) decarboxylation to give the metal hydride, c) reductive elimination of H2 from the hydride and d) coordination of new CO. In addition, there are several potentially crucial protonation/deprotonation equilibria involving metal hydrides or the hydroxycarbonyl. The mechanistic details have been worked out (but only incompletely) for a couple of the alkaline solution WGSR homogeneous catalysts. In these cases,... 

The effect of incomplete mixing on homogeneous reactions. Chemical... 

At the same symposium, Danckwerts (D2) drew attention to the effect of incomplete mixing on homogeneous reactions. He introduced the concept of segregation, which indicates that in the same vessel there are clumps of fluid which have different concentrations, caused by incomplete mixing. The effect on the conversion of chemical reactors is again an increase in conversion for reactions of an order greater than 1 and a decrease in conversion when the order is less than 1. 

Both fractions were characterised by NMR spectroscopy and mass spectrometry. Fraction A mainly consists of silsesquioxane a7b3 (Fig. 9.5) [38], while fraction B is a mixture of different silsesquioxanes, mostly incompletely condensed species, with the main species assigned to silsesquioxane structure 6i>2 (Fig. 9.5). Finally, both fractions were reacted with a titanium alkoxide and tested for catalytic activity in the epoxidation of 1-octene as a function of the reaction time and the results compared with those of HTE lead (all three catalysts are homogeneous) (Fig. 9.6). 

In FIA, the sample and reagents are incompletely mixed and there is a concentration gradient that varies along the system as a function of time. The continuous detectors provide a transient signal, which is recorded. Neither physical equilibrium (homogenization of a portion of the flow) nor chemical equilibrium (reaction completeness) is attained by the time the signal is detected. Hence, FIA can be considered a fixed-time analytical methodology. The main elements of these analyzers are... 

---