Fabrication and molecular transport studies of highly c-Oriented AFI membranes

Abstract

The AFI membrane with one-dimensional straight channels is an ideal platform for various applications. In this work, we report the fabrication of a highly c-oriented, compact and stable AFI membrane by epitaxial growth from an almost close-packed and c-oriented monolayer of plate-like seeds that is manually assembled on a porous alumina support. The straight channels in the membrane are not only aligned vertically along the membrane depth, but are also continuous without disruption. The transport resistance is thus minimized and as a result, the membrane shows almost two orders of magnitude greater permeance in pervaporation of hydrocarbons compared to reported values in the literature. The selectivity of p-xylene to 1,3,5triisopropylbenzene (TIPB) is approximately 850. In addition, through gas permeation studies on a number of gas and liquid molecules, different transport mechanisms including activated Knudsen diffusion, surface diffusion and molecular sieving were discovered for different diffusion species. The ratio of kinetic diameter to channel diameter, d m /d c , and the ratio of the Lennard-Jones length constant to channel diameter, σ m /d c , are found very useful in explaining the different transport behaviors. These results should be useful not only for potential industrial applications of the AFI membranes but also for the fundamental understanding of transport in nanoporous structures.

Noble gas separation by a MOF with one-dimensional channels

“…Therefore, porous materials with uniform sized 1-dimensional (1D) channels ( Fig. 1b) are attractive to achieve high adsorption ability by providing strong and uniform adsorption potentials [15] if the channel size is well constrained to angstrom level, such as < 3.9 Å (equals to the molecular size of Xe) for noble gas separation. One of promising porous materials exhibiting such uniform 1D channels is SIFSIX-3-Zn MOF with a channel size of 3.84 Å, closing to the kinetic diameter of Xe (3.9 Å) [16,17].…”

Helium separation using membrane technology: Recent advances and perspectives

“…Zeolites have been widely studied as membrane materials due to their unique advantages, including uniform pores with molecule-size dimensions, high porosity, and excellent thermal and chemical stability [121]. Many different types of zeolite membranes have been developed, such as LTA [122], FAU [123], MOR [124], FER [125], MEL [126,127], CHA [128,129], SAPO-34 [130,131], DDR [132], and AFI [133]. There are several review articles about zeolite membrane fabrication, separation mechanism, and applications [121,134,135].…”

Kinetic Molecular Sieving of Cyclopentane/Neohexane Mixtures by the MFI Zeolite with Intersecting 10-Ring Channels

“…Different from that in the pure component vapor atmosphere, in liquid adsorption, the adsorbates were diluted in a solvent. In order to minimize the competitive adsorption between the adsorbates and solvent, 1,3,5-trimethylbenzene (kinetic diameter = 7.5 Å) 33 was employed as the solvent because the molecule is excluded by the narrow pores of silicalite-1, 34 and thus, its sorption only occurs on the outer surface of the material. With an equilibrium time of ∼4 h, the cyclopentane uptake (1.31 mmol/g at 1.80 M) is much higher than that of neohexane (0.07 mmol/g at 1.59 M) at 298 K (Figure 2), consistent with the single-phase vapor adsorption results.…”