Xylene Vapor Permeation in MFI Zeolite Membranes Made by Templated and Template-Free Secondary Growth of Randomly Oriented Seeds: Effects of Xylene Activity and Microstructure

Abstract

Many studies have reported high p-xylene/o-xylene permselectivities with MFI zeolite membranes; however, these results were obtained at low xylene activity (<0.01). The present work investigates the vapor permeation of xylene isomers through MFI zeolite membranes at various xylene activities up to 0.033. Using MFI zeolite membranes synthesized with and without organic templates, the effects of xylene activity and membrane microstructure on separation performance in xylene vapor permeation were systematically studied. Both p-xylene and o-xylene permeances decrease with increasing xylene activity, but the decrease is more pronounced for p-xylene resulting in a reduction in p-xylene/o-xylene selectivity.The MFI zeolite membrane fabricated without template exhibits higher p-xylene selectivity than the templated membrane due to the presence of less intercrystalline gaps in the template-free zeolite layer, and the lesser decrease in p-xylene selectivity for the template-free membrane was confirmed with increasing xylene activity. A theoretical study using the transport model for MFI zeolite membrane reveals that the xylene activity dependence of xylene permeance and selectivity could be well explained by the decrease of both xylene solubility and diffusivity in zeolitic pores with increasing xylene activity. Also, the minimization of intercrystalline gaps in the zeolite layer weakens the unfavorable xylene activity dependence in xylene vapor separation.

Preparation of High Performance ZSM-5 Zeolite Membranes for CO2/H2 Separation

“…The microstructures of these membranes are different from those synthesized by large seeds (1.5 μm) at the primary layer. The XRD results in Figures 4 and S3 are also in good accordance with the SEM analysis in which the higher the intensity ratio of the (1 0 1) peak to that of the (0 2 0) peak (I 101 /I 020 ), the higher c-oriented degree of the membrane [18].…”

Calcination-Free Fabrication of Highly b-Oriented Silicalite-1 Zeolite Films by Secondary Growth in the Absence of Organic Structure-Directing Agents

“…Yang et al reported that b -oriented S-1 zeolite films could be successfully synthesized using microwave irradiation in the presence of TPAOH, Tsapatsis et al developed a designed trimer-TPAOH as an organic structure-directing agent (OSDA) for the fabrication of b -oriented S-1 zeolite films, Yoon et al employed TEAOH and (NH 4 ) 2 SiF 6 as co-OSDAs to synthesize the b -oriented S-1 zeolite films, and Zhou and Hedlund and Wang et al recently developed a solvent-free secondary growth of b -oriented S-1 zeolite films from the anhydrous synthetic powder. , Notably, the aforementioned syntheses of b -oriented S-1 zeolite films are always performed in the presence of OSDAs. The removal of these OSDAs by calcination at high temperatures sometimes results in the formation of cracks in the zeolite layer. − Despite the great progresses over the past 20 years in the fabrication of aluminosilicate MFI zeolite films from the OSDA-free synthesis methodology, − it has not been successful to fabricate the S-1 zeolite films in the absence of OSDAs.…”

Computational Evaluation of the Diffusion Mechanisms for C8 Aromatics in Porous Organic Cages

“…MFI zeolite membranes in particular have been extensively studied for pX production. 6,[15][16][17][18] The manufacture of crystalline zeolites and MOFs into large-scale and defect-free membranes remains challenging, however. Solution-processable polymers of intrinsic microporosity (PIMs) are a promising alternative for chemical separations.…”

“…Both zeolites and MOFs contain well-defined interconnected channels with nanometer-sized apertures that allow pX (kinetic diameter = 5.8 Å) to be separated from the bulkier mX and oX (kinetic diameter = 6.8 Å). MFI zeolite membranes, in particular, have been extensively studied for pX production. ,− The manufacture of crystalline zeolites and MOFs into large-scale and defect-free membranes remains challenging however. Solution-processable polymers of intrinsic microporosity are a promising alternative for chemical separations.…”