Conversion interphase

After phase separation, two sets of equations such as those in Table A-1 describe the polymerization but now the interphase transport terms I, must be included which couples the two sets of equations. We assume that an equilibrium partitioning of the monomers is always maintained. Under these conditions, it is possible, following some work of Kilkson (17) on a simpler interfacial nylon polymerization, to express the transfer rates I in terms of the monomer partition coefficients, and the iJolume fraction X. We assume that no interphase transport of any polymer occurs. Thus, from this coupled set of eighteen equations, we can compute the overall conversions in each phase vs. time. We can then go back to the statistical derived equations in Table 1 and predict the average values of the distribution. The overall average values are the sums of those in each phase. 

Catalysis in Transacylation Reactions. The principal objective of the study was to evaluate 4 as an effective organic soluble lipophilic catalyst for transacylation reactions of carboxylic and phosphoric acid derivatives in aqueous and two-phase aqueous-organic solvent media. Indeed 4 catalyzes the conversion of benzoyl chloride to benzoic anhydride in well-stirred suspensions of CH2CI2 and 1.0 M aqueous NaHCC>3 (Equations 1-3). The results are summarized in Table 1 where yields of isolated acid, anhydride and recovered acid chloride are reported. The reaction is believed to involve formation of the poly(benzoyloxypyridinium) ion intermediate (5) in the organic phase (Equation 1) and 5 then quickly reacts with bicarbonate ion and/or hydroxide ion at the interphase to form benzoate ion (Equation 2 and 3). Apparently most of the benzoate ion is trapped by additional 5 in the organic layer or at the interphase to produce benzoic anhydride (Equation 4), an example of normal phase-... 

Epithelial cells express but do not apically localize Pins, and do not express Insc. We have previously shown that ectopically expressed Insc localizes to the apical cortex in wild-type epithelial cells (Kraut et al 1996). Interestingly, ectopic Insc expression causes Pins, which is normally localized to the lateral cortex, to localize to the apical cortex. Conversely, apical localization of ectopically expressed Insc is dependent on pins. Insc ectopically expressed in Pins- epithelial cells does not localize as an apical crescent it adopts a cytoplasmic distribution which is enriched towards the apical side of the cell during interphase and is undetectable during mitosis, presumably due to rapid degradation. This instability of ectopically expressed Insc may be why the 90° rotation in the mitotic spindles which occurs as a consequence of Insc ectopic expression in the wild-type epithelial cells no longer occurs when Insc is expressed in Pins-embryos. These results indicate that Insc is necessary and sufficient for the recruitment of Pins to the apical cortex of wild-type epithelial cells. 

By virtue of the conditions xi+X2 = 1>Xi+X2 = 1, only one of two equations (Eq. 98) (e.g. the first one) is independent. Analytical integration of this equation results in explicit expression connecting monomer composition jc with conversion p. This expression in conjunction with formula (Eq. 99) describes the dependence of the instantaneous copolymer composition X on conversion. The analysis of the results achieved revealed [74] that the mode of the drift with conversion of compositions x and X differs from that occurring in the processes of homophase copolymerization. It was found that at any values of parameters p, p2 and initial monomer composition x° both vectors, x and X, will tend with the growth of p to common limit x = X. In traditional copolymerization, systems also exist in which the instantaneous composition of a copolymer coincides with that of the monomer mixture. Such a composition, x =X, is known as the azeotrop . Its values, controlled by parameters of the model, are defined for homophase (a) [1,86] and interphase (b) copolymerization as follows... 

Fig. 9 Evolution with conversion p of composition distribution of the products of interphase copolymerization calculated at the initial monomer mixture composition x° = 0.6 and parameter a (Eq. 100) equal to 0.3...

Fig. 10 Dependence of the composition distribution of a copolymer formed under complete conversion of monomers on their initial composition x°. The diagrams are presented here for interphase copolymerization when at = 0.3... 

In many interfacial conversion processes, certainly those at biological interphases, the diffusion situation is complicated by the fact that the concentration at the organism surface is not constant with time (c°(f) not constant). However, in most cases of steady-state convective diffusion, the changes in the surface... 

Charged interphases may also be exploited to create high local concentrations of electron acceptors which affect the rate of electron transfer reactions confined within these restricted reaction volumes and diminish considerably the efficiency of the corresponding back-transfer [24], These results have been primarily applied in photochemical conversion projects [22,25], but technically more interesting applications may be found in their use for the development of new specific analytical procedures (e.g., optical or photoelectrochemical probes). High local concentrations are also of considerable interest in the optimization of photochemical dimerization reactions [22], as the rate of bimolecular reactions between excited and ground state molecules confined in an extremely restricted reaction volume (microreactor) will be considerably enhanced. In addition, spatial gradients of polarity may lead to preferential structures of the solvated substrate and, hence, to the synthesis of specific isomers [24, 22, 26], Similar selectivities have been found when monomolecular photochemical or photoinduced reactions [2,3] are made via inclusion complexes [27,28]. 

When heterogeneous mixtures are involved, the conversion rate often is limited by the rate of interphase mass transfer, so that a large interfacial surface is desirable. Thus, solid reactants or... 

Figure 24 illustrates the dependence of Type III selectivity on intraparticle and interphase diffusion effects by plotting the apparent overall selectivity from eqs 159, 167 and 168 for Bim/fa = 1, against the conversion of reactant Ai. From this figure, it appears that the influence of intraparticle diffusion may reduce the overall selectivity in Type III reactions by a factor of about two. Wheeler [113] reported that this degree of reduction is independent of the intrinsic selectivity factor AA . It may therefore serve as a general rule of thumb. 

In a well-stirred CSTR, intrareactor gradients will be absent, but interphase and intraparticle gradients may be present. Conversely, in a fixed-bed PFR with small catalyst particles, intraparticle gradients may be eliminated, although intrareactor gradients still occur. 

In a flow system, the flow rate can be varied while the space velocity is kept constant (Figure 6). If the conversion remains constant, the influence of interphase and intrareactor effects may be assumed to be negligible. A similar test can be done in a CSTR. In that case the absence of interphase and intrareactor effects can be assumed if the reaction rate is independent of the rate of agitation. 

If the conversion at any particular space velocity is independent of the linear velocity through the bed, interphase concentration gradients are absent. 

The large industrial fluid beds are normally operated with U/U exceeding 10, so that a large portion of the gas bypasses the bed in the form of bubbles. Also the diameter of the bubbles is fairly large, so that interphase mass transport is small compared to the rate of reaction. Under these conditions the extent of mixing in the emulsion phase is rather an unimportant parameter as far as the prediction of conversion is concerned. It would, however, have significant influence when non first-order reactions are involved. 

Even when the laboratory test reactor is intended to be representative in a reaction kinetic sense only (thus waiving the demand for correspondence in terms of pressure drop and hold-ups), the process performance data can be affected by differences in mass transfer and dispersion caused by scale reduction. When interphase mass transfer and chemical kinetics are both important for the overall conversions, the above test reactor, which is a relatively large pilot plant reactor, cannot be further reduced in size unless one accepts deviations in test results. 

---