Inorganic Materials for Gas-separation Membranes

The interested reader is referred to some good reviews on inorganic membrane materials [295-299]. 

In this chapter, three examples of inorganic membranes or hybrid organic/in-organic membranes for gas separation that might find industrial applications in the future will be discussed. 

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T.T. Moore, W.J. Koros, Non-ideal effects in organic-inorganic materials for gas-separation membranes. Journal of Molecular Structure 2005, 739 (1-3),... 

Moore, T.T. and Koros, W.J. 2005. Non-ideal effects in organic—inorganic materials for gas separation membranes.Mol. Struct. 739(1-3) 87-98. 

C.L. Lin, D.L. Flowers and P.K.T. Liu, Characterization of ceramic membranes. II. Modified commercial membranes with pore size imder 40 A. /. Membr. Sci., 92 (1994) 45. J. Luyten, J. Cooymans, R. Persons, R. Leysen and J. Sleurs, A New Ceramic Support Material for Gas Separative Membranes. Paper presented at the 3rd International Conference on Inorganic Membranes, July, 1994, Worcester, MA, USA. 

Numerous studies on inorganic membranes have shown that the separation factor is limited and not far from that predicted by the Knudsen diffusion. This primarily reflects the current status of material developments of inorganic membranes. The majority of commercial and developmental inorganic membranes contain macropoies or mesopores. These pore sizes fall within the dominant regime of Knudsen diffusion which is of limited use for many gas separation applications from the standpoint of process economics. To break this barrier, finer pore sizes or transport mechanisms more effective than Knudsen diffusion for gas separation is essential. 

Yet another unique class of inorganic membrane materials called pillared clay and carbon composite membranes has been studied for gas separation [Zhu et al., 1994]. The permeation rates of benzene, chlorobenzene and 1,3-dichlorobenzene vapors through these membranes can be different by orders of magnitude as indicated earlier. This may open the door for these types of membranes for separating organic mixtures. 

Dense inorganic or metallic membranes for gas separation are usually ion-conducting materials, while membranes with carriers are polymers or supported liquid membranes (SLM). For transport through these materials, different flux equations should be applied. Figure 4.2 sums up and generalizes the various types of transport, which may take place in gas-separation membranes [21]. 

The last category of inorganic membranes used for gas separation is constituted of dense materials including metals and ceramics [127]. 

Fain DE (1991) Technical and economic aspects and prospects for gas separation with inorganic membranes. Key Eng Materials 61/62 327-336... 

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