Permeation reduction coefficient

Permeation reduction coefficient Equivalent coefficient Considered phenomena... 

Caravella, A., Scura, F., Barbieri, G., Drioh, E. (2010). Inhibition by CO and polarization in Pd-based membranes a novel permeation reduction coefficient. Journal of Physical Chemistry B, 774(38), 12264-12276. 

Similarly to what was done for the coefficients CPC and IC, also for PRC some permeation reduction maps were calculated and developed. These maps are reported and discussed in Section 14.6.4.2. 

In this section, the reduction coefficients introduced before CPC, IC and PRC) are presented in the form of the so-called permeation reduction maps , which... 

In this chapter, an innovative approach dealing with the combined effect of concentration polarization and inhibition by CO in Pd-based membranes is discussed and analyzed by means of appropriate coefficients measuring the permeation reduction due to these phenomena. 

All reduction coefficients dealt with in this chapter were calculated from the numerical solution of a complex hydrogen permeation model, opportunely validated by a number of experimental data, and reported in form of permeation reduction maps for several operating conditions. From these maps, the values of CPC, IC and PRC can be read directly and used simply in the modified forms of Sieverts law shown above to evaluate the hydrogen permeating flux, providing in this way a possible novel strategy of membrane module design. 

FIG. 13 Reduction of the relative permeability coefficient is dependent on the clay platelet aspect ratio in the system of polyimide-clay hybrid with water vapor as the permeate. Each hybrid contains 2 wt% clay. The aspect ratios for hectorite, saponite, montmorillonite, and synthetic mica are 46, 165, 218, and 1230, respectively. (From Ref. 71.)... 

The permeability of solutes across lipid bilayers is a product of the partition coefficient and the transverse diffusion coefficient [30]. Bilayer polymerization can alter solute diffusion by modifying either or both of these processes. In order to examine the effect of polymerization on bilayer permeability a nonionic solute of moderate permeability, [3H-glucose], was encapsulated in the vesicles prior to polymerization, removed from the exterior after polymerization, and its permeation across the bilayer was measured periodically [31]. Quantitative measurements of the 3H-glucose leakage revealed that the formation of linear polymer chains from methacryloyl lipids reduced the permeability coefficient to 0.3 to 0.5 of that of the unpolymerized lipid vesicles. A larger reduction (two orders of magnitude) was only found when crosslinked polymer networks were formed [31]. 

Mengual et al. have observed an Arrhenius type of dependence of the permeate flux on the feed temperature. An increase in the feed circulation velocity increases the heat transfer coefficient in the liquid boundary layer, which in turn increases the VMD flux due to the reduction in the temperature polarization. Concentration factors increased with a decrease in feed temperature during VMD, and for a decrease of 30°C to 10°C, increase in concentration factors from 7-15.5 to 21-31 were obtained for a highly volatile black currant aroma ester [17]. 

Ross, J.S. and Shah, J.C. (2000). Reduction in skin permeation of iV,iV-diethyl-/n-toluamide (DEET) by altering the skin/vehicle partition coefficient, J. Controlled Release, 67, 211-221. 

Accordingly, the permeation kinetics is improved at 37°C and Cr increases more rapidly than at 25°C. An inspection of Table 15.2 reveals that the theophylline diffusion coefficient (Dj) does not sensibly vary with %P, regardless of the temperature. This can be explained with the fact that the %P increase, in the l%-4% range, does not substantially reflect in an increase of the polymeric network cross-link density, responsible for a reduction of the network mesh size, but it reflects in a higher membrane thickness. Nevertheless, it cannot be also excluded that, due to reduced theophylline dimension ( 3.8 A [118,120]), polymeric network meshes are... 

The effect of inhibition by CO on hydrogen permeation has recently become the object of several investigations, since CO is typically present in significant amounts in the hydrogen streams to be separated. In particular, a macroscopic model equation was developed to describe the influence of CO on permeation. This equation modifies Sieverts law to take into account the permeance reduction due to CO as reported in eqn (14.15), where the quantities a, and 6co represent a coefficient accounting for other additional effects of CO on adsorbed hydrogen and the membrane surface coverage by CO, respectively ... 

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