Membrane Engineering Progress and Potentialities in Gas Separations

Adele Brunetti Paola Bernardo, Enrico DriolP and Giuseppe Barbiert National Research Council - Institute for Membrane Technology (ITM-CNR), The University of 

Membrane Gas Separation Edited by Yuri Yampolskii and Benny Freeman 2010 John Wiley Sons, Ltd 

The membranes used in GS can be distinguished in two main categories, polymeric and inorganic. Polymeric membranes, specifically used for GS, are generally asymmetric or composite and based on a solution-diffusion transport mechanism. These membranes, made as flat sheet or hollow fibres, have a thin, dense skin layer on a micro-porous support that provides mechanical strength [7]. Typically, polymeric membranes show high, but finite, selectivities with respect to porous inorganic materials due to their low free-volume 

Zeolite membranes show high thermal stability and chemical resistance compared with those of polymeric membranes. They are able to separate mixtures continuously on the basis of differences in the molecular size and shape [18], and/or on the basis of different adsorption properties [19], since their separation ability depends on the interplay of the mixture adsorption equilibrium and the mixture. Different types of zeolites have been studied (e.g. MFI, LTA, MOR, FAU) for the membrane separation. They are used still at laboratory level, also as catalytic membranes in membrane reactors (e.g. CO clean-up, water gas shift, methane reforming, etc.) [20,21]. The first commercial application is that of LTA zeolite membranes for solvent dehydration by pervaporation [22], Some other pervaporation plants have been installed since 2001, but no industrial applications use zeolite membranes in the GS field [23]. The reason for this limited application in industry might be due to economical feasibility (development of higher flux membranes should reduce both costs of membranes and modules) and poor reproducibility. 

Ion transport membranes are new dense inorganic membranes able to be permeated only by oxygen (or hydrogen). They show good performance in terms of permeability and selectivity at a very high temperature ( 600 °C) however, the main problem is related to their durability. Once the time of operation is passed, the formation of micro-pinholes depletes the membrane properties, significantly reducing the selectivity [28]. 

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Source Branetti, A., Bernardo, P., Drioli, E., and Barbieri, G./Yampolskii, Y. and Freeman, B. (eds.) Membrane Gas Separation, Membrane engineering progresses and potentialities in gas separations, pp. 281-312. 2010. Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with... 

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