Properties of Molecular Sieves

N 2-recovery by PSA is performed predominantly on carbon molecular sieves 

Both adsorbents have high specific surfaces of 800-1500 g .  

The molesieve material is filled into horizontally or vertically orientated cylindrical vessels and the gas passes through the material either in axial or radial direction. Design criteria are pressure drop, the so-called lifting velocity above which the bed fluidizes, and the homogeneous distribution of the gas flow. 

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Hatori, H., H. Takagi, and Y. Yamada, Gas separation properties of molecular sieving carbon membranes with nanopore channels, Carbon, 42, 1169-1173, 2004. 

Tn presenting the adsorptive properties of molecular sieve zeolites, most authors (1, 2) report isosteric heats. These are obtained from the application of the thermodynamically derived Clausius-Clapeyron type equation to experimentally measured equilibrium data. At a constant... 

Financial support by the National Science Foundation and the State of Connecticut under its High Technology program are gratefully acknowledged. This article was written during a sabbatical at the University of California at Santa Barbara under the hospitality of Prof. R. Daniel Little. Joseph Leonetti provided some key references on the drying properties of molecular sieves. 

Guidelines for mastering the properties of molecular sieves, D. Barthomeuf et al. (Eds ), NATO ASI Series B Physics, 221, Plenum Press, New-York, 1990. 

Barthomeuf D. et al., eds., Guidelines for Mastering the Properties of Molecular Sieves, NATO ASI Series, B 221, (Kluwer). 

The most striking feature of Figure 8.2 is the effect of the additional degree of freedom provided by a parallel-sided slit. Indeed, this difference in the packing density in slits and cylinders will be seen to be of great importance when we consider the adsorptive properties of molecular sieve carbons and certain zeolites. 

Specific properties of molecular sieves are the reason for which these materials found application as adsorbents for separation of gas mixtures, especially air [2]. In fact, one can say that carbon-based molecular sieves played fundamental role in commercialisation of the pressure swing adsorption process (PSA) used for separation of nitrogen from air [3]. 

For description of textural properties of carbonaceous adsorbents, adsorption/desorption isotherms of vapours and gases in static conditions as well as mercury porosimetry are used. The latter method often leads to destruction of porous structure of investigated materials while the usage of the former one is affected by the specific properties of molecular sieves described above. Taking into account these limitations, in this work the authors have made an attempt of determination of porous structure of carbon molecular sieves with the used of the pycnometric technique. 

The growth in the use of molecular sieves as catalysts as compared with macro- and mesoporous oxides was stimulated by several factors (i) The high concentration of active sites (in comparison with oxides) results in very active catalysts, (ii) The defined pore structure allows to exclude reactants from being converted and/or products to be formed or transported out of the pores due to a too large size, (iii) The active site and the environment of that site can be designed on an atomic level for exEimple by ion exchange [9] or chemical functionalization of the framework [10]. (iv) It is possible to tailor the chemical properties of molecular sieves better than those of conventional macro and mesoporous oxides. 

We would like to emphasize that the global properties of molecular sieves, often described in terms of hydrophobicity and hydrophilicity [240] or fiamework polarity [241] will markedly influence the chemical preference for the sorption of molecules. This may lead to quite different relative concentrations of reactants in the zeolite pores (well demonstrated and discussed for the case of TS-1 in this review [163]) and in the intra ciystalline void space. The consequence of which is unexpected solvent-type effects. While these possibilities are hardly utilized up to now, one could think of systematically applying this approach for organic synthesis steps in which, for example, a high concentration of reactants is needed around the active site, but for which one wishes to dilute the products in the intra crystalline void to prevent further reaction. In such a case a solvent of different polarity than the reacting substrate should be chosen and the choice of the zeolite should be made in accordance to the polarity of the reactant(s). 

A. Corma, in "Guidelines for Mastering the Properties of Molecular Sieves" (D. 

M. Mertens, J.A. Martens, PJ. Grobet, and PA. Jacobs, Guidelines for Mastering the Properties of Molecular Sieves - Relationship between the Physicochemical Properties of Zeolite Systems and their Low Dimensionality. NATO ASI, Ser. B, ed. D. Barthomeuf, E.G. Derouane, and W. Holdrich, Plenum Press, New York, London, 1990, 221, 1. 

Transport Properties of Molecular Sieves Studied by the NMR Pulsed Field Gradient Technique... 

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