Binary permeation

Recent work of Van de Graaf et al. [209] and Kapteijn et al. [210] has shown that for diffusion of binary mixtures in Silicalite, the complete Maxwell-Stefan formulation, equation 5.14, tciking interchange into account provides a much better description of binary permeation experimental results across a Silicalite membrane than with a model ignoring the interchange mechanism (portrayed by D12). 

Lito P F, Santiago A S, Cardoso S P, Figueiredo B R and Silva C M (2011), New expressions for single and binary permeation through zeolite membranes for different isotherm models ,7 Membrane Sci, 367,21-32. 

In a binary separation, the highest purity of integrated permeate occurs at 0 = 0. Purity decreases monotonically until it reaches the feed purity at 0 = 1. In a ternary system, the residue concentration of the gas with the intermediate permeability will reach a maximum at some intermediate stage cut. 

Example 10.5 illustrates the trade-offs for gas permeation. The feed was assumed to be a binary mixture, which simplifies the calculations. For multicomponent mixtures, the same basic equations can be written for each component and solved simultaneously12. The approach is basically the same, but numerically more complex. 

Later Rytter et al. reported possible polymer chain exchange with polypropylene produced with a combination of 8 and 11 with TMA [32], The number of stereoerrors increased in the binary system at higher TMA levels. As discussed in the case of Przybyla and Fink (vida supra), pentad analysis is less compelling evidence for reversible chain transfer. In addition, the gel permeation chromatography (GPC) data showed bimodal peaks, indicating very limited reversible transfer. 

In various forms, lattice-gas models permeate statistical mechanics. Consider a lattice in which each site has two states. If we interpret the states as full or empty , we have a lattice-gas model, and an obvious model for an intercalation compound. If the states are spin up and spin down , we have an Ising model for a magnetic system if the states are Atom A and Atom B , we have a model for a binary alloy. Many different approximation techniques have been derived for such models, and many lattices and interactions have been considered. 

The lack of significant impact of CPEs on transdermal delivery vehicles is related to the inherent nonspecific activity of CPEs in the different strata of the skin, as discussed earlier. This limitation may be overcome by utilization of mixtures of CPEs. Research has already shown that binary mixtures of CPEs provide increased permeation enhancement as well as increased safety compared to single enhancers. Such unique chemical combinations, called synergistic combinations of penetration enhancers or SCOPE formulations, offer new opportunities in transdermal drug delivery (46). 

The phase map shown in Figure IB represents the skin permeation enhancement activity of the formulations containing binary mixtures of lauryl sarcosinate and sorbitan monolaurate at different concentrations and compositions. The region of maximum activity lies in a very narrow range of compositions. For such a nonlinear activity-composition behavior, it is very important to probe the binary phase map at as fine a resolution as possible, thus increasing the experimentation volume. 

Because of the long, narrow configuration, the equipment appears to function in countercurrent mode. Other data of experiments with gas permeators as continuous columns appear in Figures 19.6(b) and (c) the original paper has data on other binary and some complex mixtures. 

A permeation enhancer can be defined as a compound that alters the skin barrier function so that a desired drug can permeate at a faster rate. Dozens of enhancers are patented each year, and several books have been written summarizing the work and proposing mechanisms of enhancement.70-72 The permeation enhancers may be classified simply as polar and nonpolar ones. They can be used individually or in combination, such as binary mixtures. For several drugs, the flux across skin was observed to be linear with that of the most widely used enhancer, ethanol.73-75 Another polar enhancer, isopropanol, facilitated ion association of charged molecules and enhanced the transport of both neutral and ionic species across the stratum corneum.76 77 While polar enhancers traverse the skin, nonpolar enhancers are largely retained in the stratum corneum both aspects make the combination a superior enhancer to the individual enhancers.78... 

It can be shown that the composition of the permeate gas, P 11, for permeation of a binary gas mixture is given by the following quadratic equation ... 

The separation efficiency for a given membrane with a particular binary gas mixture will be dependent mainly upon three factors gas composition, the pressure ratio between feed and permeate gas, and the sepration factor for the two components. A higher separation factor gives a more selective membrane, resulting in a greater separation efficiency. This parameter is a function of the membrane material and is determined by the individual gas permeation rates. 

Pervaporation is a membrane separation process where the liquid feed mixture is in contact with the membrane in the upstream under atmospheric pressure and permeate is removed from the downstream as vapor by vacuum or a swept inert gas. Most of the research efforts of the pervaporation have concentrated on the separation of alcohol-water system [1-20] but the separation of acetic acid-water mixtures has received relatively little attention [21-34]. Acetic acid is an important basic chemical in the industry ranking among the top 20 organic intermediates. Because of the small differences in the volatility s of water and acetic acid in dilute aqueous solutions, azeotropic distillation is used instead of normal binary distillation so that the process is an energy intensive process. From this point of view, the pervaporation separation of acetic acid-water mixtures can be one of the alternate processes for saving energy. 

B. Will, R.N. Lichtenthaler, Comparison of the separation of mixtures by vapor permeation and pervaporation using PVA composite membranes. Part I. Binary alcohol—water systems, J. Membr. Sci. 68 (1992) 119-125. 

Figure 9.19 Fraction of benzene in permeate as a function of feed mixture composition for pervaporation at the reflux temperature of a binary benzene/cyclohexane mixture. A 20-qm-thick crosslinked blend membrane of cellulose acetate and polystyrene phosphate) was used [54]. Reprinted with permission from I. Cabasso, Organic Liquid Mixtures Separation by Selective Polymer Membranes, Ind. Eng. Chem. Prod. Res. Dev. 22, 313. Copyright 1983 American Chemical Society...

C. K. Lee, T. Uchida, N. S. Kim, and S. Goto, Skin permeation enhancement of tegafur by ethanol/panasate 800 or ethanol/water binary vehicle and combined effect of fatty acids and fatty alcohols, J. Pharm. Sci. 82 1155-1159 (1993). 

The above-mentioned inverse selectivity/permeability relationship of polymers has been summarized by Robeson by means of log-log plots of the overall selectivity versus the permeability coefficient, where A is considered to be the more rapidly permeating gas. These plots were made for a variety of binary gas mixtures from the list He, H2, O2, N2, C02, and CH4, and for a large number of rubbery and glassy polymer membranes. Such representations, shown in Fig. 8 and Fig. 9 are often referred to as upper bound plots (Robeson, 1991). The upper bound lines clearly show the inverse selectivity/permeability relationship of polymer membranes. While these plots were prepared in 1991, only small advances have been made to push the upper bound higher since that time. 

Another aspect from the drug delivery point of view is the combined use of different types of permeation enhancers in the same formulation. Whitehead et al. (2008), for instance, could show a synergistic effect of binary combinations of hexylamine and chembetaine and ternary combinations of sodium laureth sulphate, decyltrimethyl ammonium bromide and chembetaine on the uptake of 70 kDa dextran from Caco-2 monolayer while inducing very little toxicity in Caco-2 cells. 

The chromatograms of cellulose triacetate (CTA) whole polymer (Ac w = 61.0 wt %, dotted curve) and its fractions (solid curves) are illustrated in Fig. 3. For the cellulose diacetate (CDA) and CTA fractions, the TLC becomes apparently sharp with an increase in Mw. The double-peaked form of the chromatograms is characteristic of the CTA samples, although their gel permeation chromatography (GPC) curves have been found to be single-peaked. This fact implies that the peak at the lower end of Rf corresponds to fully substituted CTA and the peak at the higher end is obviously due to the existence of not-fully substituted acetate. In this sense, real CTA is a binary mixture of ideal CTA and CDA. 

Chapter 3 described a new model for transport through porous media, developed recently by Kerkhof [5] and called the binary friction model (BFM). It is of interest to see how this model can be applied to the description of available experiments and to compare the results with those of the dusty gas model (DGM). Kerkhof [5] took the experimental data of Evans et al. [6,7] for the permeation of He and Ar through a low-permeability porous graphite septum. The experimental set-up, similar to the Wicke-Kallenbach diffusion cell, is sketched in Figure 9.7. Of interest are the steady... 

From Eqs. (7-1) and (7-2), it follows that the separation factor is purely based on the compositions of the entering and exit streams regardless of their flows. Another measure of the separation efficiency of a membrane process is the extent of separation proposed by Rony [1968]. In the context of applying this index of separation efficiency between two comfionents, it is assumed that there is no difficulty in separating the third component Thus the segregation fractions, fiy, are obtained from the molar flow rates of the permeate and retentate streams on the basis of only two components. The extent of separation is defined as the absolute value of a determinant of a binary separation matrix consisting of the segregation fractions as follows ... 

Figure 11 a) Transient permeation behaviour of a binary methan n-butane (50/50)... 

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