Incomplete mixing, influence

It was postulated that the aqueous pores are available to all molecular species, both ionic and non-ionic, while the lipoidal pathway is accessible only to un-ionised species. In addition, Ho and co-workers introduced the concept of the aqueous boundary layer (ABL) [9, 10], The ABL is considered a stagnant water layer adjacent to the apical membrane surface that is created by incomplete mixing of luminal contents near the intestinal cell surface. The influence of drug structure on permeability in these domains will be different for example ABL permeability (Paq) is inversely related to solute size, whereas membrane permeability (Pm) is dependent on both size and charge. Using this model, the apparent permeability coefficient (Papp) through the biomembrane may therefore be expressed as a function of the resistance of the ABL and... 

In fact, it is extremely complex to predict the influence of mixing on product selectivity. This would require detailed modeling of an incompletely mixed reactor and kinetic data, difficult to obtain for multistep reactions, without any prohibitive effort. However, with knowledge of the reaction mechanism, but withoutthe kinetics, a simple method can be applied which does not determine quantitatively the extent of a mixing effect but rather indicates qualitatively how partial segregation and feed configuration influence the rates of formation of the desired and undesired products and hence the selectivity [66, 67]. 

The selectivity of rapid reactions may be sensitive to mixing conditions, particularly in the case of competitive and competitive-consecutive reactions. A detailed description of all the relevant phenomena may be quite complicated. However, we can see a priori that good mixing and well controlled feed rates will generally be favourable for the selectivity of semi-batch processes, hi section 3.4 the relation between the selectivity and the degree of conversion was calculated for a few types of reaction pairs, for batch (or plug-flow) reactors, and for CSTR s. In sections 5.2.2 and 5.2.3 the influence of incomplete micro-mixing on selectivity was briefly discussed, for turbulent and laminar flow, respectively. 

Jerome et al. reported on the influence of the mixing sequence on the phase morphology of the previously discussed (SAN-X/SAN)/(EP-g-MA/EPDM) reactive blends. The particle-in-particle phase morphology, could be forced by melt blending the reactive SAN diluted by a small part of neat SAN with the pre-mixture of EPDM and EP-g-MA. This reactive pre-dispersion of SAN in the polyolefinic rubber was then added by the rest of neat SAN, so that the phase inversion occurred, although incompletely, with part of SAN remaining occluded in the dispersed mbber phase. The faster NH2/MA interfacial reaction (compared to the slow carbamate/MA reaction) was more favorable to the retention of the occluded SAN, as a result of more efficient stabilization of the interface between these occlusions and the host phase [119]. 

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