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Experimental and theoretical approach for evaluation of porous support resistance on the permeation of oxygen separation membranes

pubblicazioni - Poster

Experimental and theoretical approach for evaluation of porous support resistance on the permeation of oxygen separation membranes

Il lavoro presentato descrive la procedura sviluppata nel progetto europeo GREEN-CC per la valutazione della resistenza del supporto poroso sulla permeazione delle membrane per separazione di ossigeno.L’approccio descritto consente una stima della resistenza al trasporto di massa globale del supporto direttamente confrontabile con i dati sperimentali. Inoltre permette di effettuare uno studio parametrico sulle caratteristiche del supporto, in modo da indirizzare il design del supporto della membrana e massimizzare il flusso di ossigeno.

Perovskite materials are widely studied as membranes for oxygen separation, thanks to their high oxygen transport rate through the crystal lattice oxygen vacancies at high temperature.

During the last years, research efforts have been directed towards the manufacturing of asymmetric membranes, where a thin dense layer is deposited on a porous support, both for an increase of the membrane permeation and a cost reduction.

The high temperature oxygen transport through an asymmetric membrane is a combination of several steps, which can be considered as a series of resistances.

When the permeation rate is relatively high, the gas transport through the porous support may cause significant limitations to the oxygen permeation, in particular in the presence of a binary gas mixture. Literature data show that concentration polarization inside the porous support can be avoided by the use of pure oxygen instead of air as feed gas on the support side.

In the European project GREEN-CC a procedure to evaluate the resistance of a porous support on the membrane permeation has been developed.

In this work the support is considered as a homogeneous medium and the oxygen partial pressure in the feed and sweep gas are supposed to be uniform. Oxygen permeated flux through the asymmetric membrane is described by a semi-empirical correlation (Arrhenius’ law), as a function of the temperature and the driving force, ln(p’O2/p”O2 ):

Activation energy and pre-exponential factor, Eact and k0 respectively, can be estimated by the regression of experimental data of the oxygen flux versus the inverse of the temperature. The estimated value of Eact and k0 are affected by the mass transfer resistance of oxygen through the support, which can be evaluated as an increase of the oxygen partial pressure at the interface between membrane layer and porous support (piO2 in Figure 1), but it is not directly measured experimentally.

Starting from experimental results and by knowing the permeance of the bare support, it’s possible to evaluate the oxygen partial pressure at the interface between membrane and porous support and the permeation law of the asymmetric membrane, in the absence of any limitation.

This approach allows an evaluation of the overall mass transfer resistance of the support layer directly comparable to experimental data. Moreover, a parametric study on the support characteristics can be performed, in order to address the membrane support design and to maximize the oxygen flux.

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