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Isotropic membrane

For dilute solutions at a homogeneous, isotropic membrane the transmembrane fluxes of water and solute in the steady state is given by Eqs. (8.69) and (8.70). [Pg.231]

In this chapter membrane preparation techniques are organized by membrane structure isotropic membranes, anisotropic membranes, ceramic and metal membranes, and liquid membranes. Isotropic membranes have a uniform composition and structure throughout such membranes can be porous or dense. Anisotropic (or asymmetric) membranes, on the other hand, consist of a number of layers each with different structures and permeabilities. A typical anisotropic membrane has a relatively dense, thin surface layer supported on an open, much thicker micro-porous substrate. The surface layer performs the separation and is the principal barrier to flow through the membrane. The open support layer provides mechanical strength. Ceramic and metal membranes can be either isotropic or anisotropic. [Pg.89]

Dense nonporous isotropic membranes are rarely used in membrane separation processes because the transmembrane flux through these relatively thick membranes is too low for practical separation processes. However, they are widely used in laboratory work to characterize membrane properties. In the laboratory, isotropic (dense) membranes are prepared by solution casting or thermal meltpressing. The same techniques can be used on a larger scale to produce, for example, packaging material. [Pg.90]

The new introduced parameter CLir = VA/5 is called clearance, and it has dimensions of flow, volume Xtime-1. The clearance has a bidirectional use and indicates the volume of the solution that is cleared from drug per unit of time because of the drug movement across the plane. For an isotropic membrane, structural and functional characteristics are identical at both sides of the membrane, CLir = CLri. In practice, the term clearance is rarely used except for the irreversible removal of a material from a compartment by unidirectional pathways of metabolism, storage, or excretion. The other new parameter P = T>/8 characterizes the diffusing ability of a given solute for a given membrane, and it is called permeability. Permeability has dimensions of length xtime-1. [Pg.29]

This equation shows that a stationary state imposes a relation between the diffusion and chemical reactions, and is of special interest in isotropic membranes where the coupling coefficients vanish. For a homogeneous and isotropic medium the linear phenomenological equations are... [Pg.528]

When the separating layer and the bulk support designed for mechanical strength are indistinguishable and show an integral, homogeneous structure and composition in the direction of the membrane thickness, it is called a symmetric or isotropic membrane. Since the flow rate through a membrane is inversely proportional to the membrane... [Pg.10]

Cabasso I. Organic liquid mixtures separation by permselective polymer membranes. 1. Selection and characteristics of dense isotropic membranes employed in the pervaporation process. Ind Eng Chem Prod Res Dev 1983 22 313-319. [Pg.266]

Most of the membranes listed in Table 5.20 are formed through phase separation processes, i.e., melt extrusion or coagulation of a polymer solution by a nonsolvent. In melt extrusion, a polymer melt is extruded into a cooler atmosphere which induces phase transition. The melt extrusion of a single polymer usually gives a dense, isotropic membrane. However, the presence of a compound (latent solvent) that is miscible with the polymer at the extrusion temperature but not at the ambient temperature, may lead to a secondary phase separation upon cooling. Removal of the solvent then yields a porous isotropic membrane. Anisotropic membranes may result from melt extrusion of a dope mixture of polymers containing plasticizers. [Pg.649]

Isotropic membranes are t5q)ically homogeneous/uniform in composition and structure. They are divided into three subgroups, namely micropo-rous, dense and electrically charged membranes. Isotropic microporous membranes have evenly distributed pores (Figure 9.10a). Their pore diameters range between 0.01-10 pm and operate by the sieving mechanism. The microporous membranes are mainly prepared by the phase inversion method albeit other methods can be used. Conversely, isotropic dense membranes do not have pores and as a result they tend to be thicker than... [Pg.182]

FIGURE 9.10 Schematic diagrams of isotropic membranes (a) microporous (b) dense and (c) electrically charged membranes. [Pg.183]

The invariants are needed to express the bending energy of membranes. This is because the bending energy density of a fluid, laterally isotropic membrane can consist only of terms that do not depend on the orientation of the xy cross. Multiplying each of them with a coefficient leads to one of the standard formulas for the bending energy surface density. [Pg.53]


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See also in sourсe #XX -- [ Pg.4 , Pg.190 , Pg.191 , Pg.192 , Pg.193 , Pg.194 , Pg.195 ]

See also in sourсe #XX -- [ Pg.7 ]




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