Transport properties of alkanes through ceramic thin zeolite MFI membranes

Abstract

Polycrystalline randomly oriented defect free zeolite layers on porous o~-A1203 supports are prepared with a thickness of less than 5/zm by in situ crystallisation of silicalite-1. The flux of alkanes is a function of the sorption and intracrystalline diffusion. In mixtures of strongly and weakly adsorbing gases and at high loadings of the strongly adsorbing molecule in the zeolite pore, the flux of the weakly adsorbing molecule is suppressed by the sorption and the mobility of the strongly adsorbing molecule resulting in pore-blocking effects. The separation of these mixtures is mainly based on the sorption and completely different from the permselectivity. At low loadings of the strongly adsorbing molecules the separation is based on the sorption and the diffusion and is the same as the permselectivity. Separation factors for the isomers of butane (n-butane/isobutane) and hexane (hexane/2,2-dimethylbutane) are respectively high (10) and very high (> 2000) at 200°C. These high separation factors are a strong evidence that the membrane shows selectivity by size-exclusion and that transport in pores larger than the zeolite MFI pores (possible defects, etc) can be neglected,

Separating mixtures by exploiting molecular packing effects in microporous materials

“…The MFI membrane permeation selectivity is found experimentally to be strongly in favor of the linear isomer. 67,70 A further point to stress is that nC4/iC4 separations using MFI in both fixed bed adsorbers and membrane devices benefit from the synergy between adsorption and diffusion; both of these act in favor of the linear isomer. This has been established in the MAS PFG NMR experiments of Fernandez et al 71 and the transient uptake data of Chmelik et al 72 Tijsebaert et al 73 have demonstrated the potential of RUB-41, which has the RRO zeolite structural topology, for separation of cis-2-butene and trans-2-butene from 1-butene; this separation is of industrial importance because 1-butene is needed in the production of e.g.…”

Simulating the Effect of Nonframework Cations on the Adsorption of Alkanes in MFI-type Zeolites

“…15 Moreover, experiments show that the linear/branched separation selectivity increases with increasing nonframework cation density inside MFI-type channels. 13,[26][27][28] To the best of our knowledge, only a few groups have performed molecular simulations in MFI-type structures with alkali metal nonframework cations. [29][30][31][32][33] This may be because the commercial interest for alkali-exchanged MFI zeolites has been less than that for LTA and FAU (structures used to separate oxygen from air in pressure swing adsorption 34 ).…”

Synthesis and perfection evaluation of NaA zeolite membrane

“…It will not only cut the equipment and operation cost off, but also be operated continuously if the zeolites can be configured into a membrane form. Since 1990s, much effort has been paid in the synthesis of zeolite membrane [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Till now, different types of zeolite membranes, e.g.…”

“…butane isomers. Although high separation factors have been obtained for these mixtures, the MFI zeolite membrane has not shown good separation performance for permanent gases or permanent gas/organic gas because of the large pore size and the hydrophobic nature of the zeolite [12][13][14][15]. Therefore, the investigation of the zeolite membranes with small pore size has attracted much attention [19][20][21][22][23][24][25].…”