Separation through solid nonporous membrane

2 Oxygen separation through thick mixed-conducting solid oxide membrane 

In the examples considered in Section 5.4.4.6, the electrode (cathode) converted one of the gas species, e.g. O2, from a gas mixture to, say, OH in an electrochemical cell in the presence of an applied voltage. The hydroxyl ion so produced was transported through the SLM/ion exchange membrane to the other electrode to regenerate O2, which was evolved at the electrode as a pure gas the electron generated in the reaction was supplied to the external electrical circuit No electron transport was allowed through the SLM/ion exchange membrane. 

Mtxed-ronducting dense (nonporous) solid oxide membranes prepared out of appropriate perovskite ceramic materials are such that both ion induction and eleirtron transport can occur through the membrane at h temperatures the material is otherwise impermeable to gases. No voltage is applied across the membrane. 

Thus there are two mobile charged species in the membrane the oxygen vacancy and the electron hole. The membrane is chargewise neutral everywhere there is no macroscopic electrical field or potential gradient (V ) 

Quantitative descriptions of these transport processes are available in Heyne (1977) and Ceilings and Bouwmee-ster (1992). The net result of such analysis is an expression for oxygen flux through a membrane of thickness Sm subjected to a feed side oxygen partial pressure of and a permeate side partial pressure of Pq Pqj)  

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Thin, dense, nonporous polymeric membranes are widely used to separate gas and liquid mixtures. Diffusion of solutes through certain types of polymeric solids is more like diffusion through liquid solutions than any of the other solid-diffusion phenomena, at least for the permanent gases as solutes. Consider, for example, two portions of a gas at different pressures separated by a polymeric membrane. The gas dissolves in the solid at the faces exposed to the gas to an extent usually directly proportional to the pressure. The dissolved gas then diffuses from the high- to the low-pressure side in a manner describable by Fick s first law. 

In order to automate the analysis, these methods frequently combine immobilized enzymes with flow or sequential injection techniques. These methods may include a separation step such as solid-phase extraction, gas diffusion, or pervaporation. The latter is a nonchromatographic separation technique, which selectively separates a liquid mixture by partial vaporization through a nonporous polymeric membrane. Separation is not based on relative volatilities as in distillation, but rather on the relative rates of permeation through the membrane. 

Process Description Gas-separation membranes separate gases from other gases. Some gas filters, which remove liquids or solids from gases, are microfiltration membranes. Gas membranes generally work because individual gases differ in their solubility and diffusivity through nonporous polymers. A few membranes operate by sieving, Knudsen flow, or chemical complexation. 

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