Evaluation and fabrication of pore‐size‐tuned silica membranes with tetraethoxydimethyl disiloxane for gas separation

Abstract

Organic/inorganic hybrid silica membranes were prepared from 1,1,3,3‐tetraethoxy‐1,3‐dimethyl disiloxane (TEDMDS) by the sol‐gel technique with firing at 300–550°C in N2. TEDMDS‐derived silica membranes showed high H2 permeance (0.3–1.1 × 10−6 mol m−2 s−1 Pa−1) with low H2/N2 (∼10) and high H2/SF6 (∼1200) perm‐selectivity, confirming successful tuning of micropore sizes larger than TEOS‐derived silica membranes. TEDMDS‐derived silica membranes prepared at 550°C in N2 increased gas permeances as well as pore sizes after air exposure at 450°C. TEDMDS had an advantage in tuning pore size by the “template” and “spacer” techniques, due to the pyrolysis of methyl groups in air and SiOSi bonding, respectively. For pore size evaluation of microporous membranes, normalized Knudsen‐based permeance, which was proposed based on the gas translation model and verified with permeance of zeolite membranes, reveals that pore sizes of TEDMDS membranes were successfully tuned in the range of 0.6–1.0 nm. © 2011 American Institute of Chemical Engineers AIChE J, 2011

Review on Mechanisms of Gas Permeation through Inorganic Membranes

“…From the results, dp was numerically fitted using Eq. (36) to be 0.34 nm, which is comparable to that of a sol-gel silica membrane from TEOS 11), 19) . Although the method can be used for the data obtained here, and gives a reasonable estimate of the pore diameter, if there were pores.…”

“…Very recently, the group of Tsuru proposed a novel method for the determination of pore size which they call a normalized Knudsen-based permeance (NKP) derived from the GT model 19) . The NKP, f, is the ratio of the permeance of a target component to that predicted from a reference component (He) based on the Knudsen diffusion mechanism (Eq.…”

Structure–property tuning in hydrothermally stable sol–gel-processed hybrid organosilica molecular sieving membranes

“…The organic groups are incorporated in the silica network on a molecular level, and this makes them more stable than analogous pure organics, but they cannot withstand the same temperatures as fully inorganic silica. For example, the methyl groups in methylated silica are reported stable up to 450-550°C under inert atmosphere [19,[37][38][39][40] and up to 350-400°C in the presence of oxygen [38,40]. Placing organic groups in bridged configuration improves their thermal stability; methylene groups are reported stable up to 650°C under inert atmosphere [41].…”

Micropore Filling Phase Permeation of a Condensable Vapor in Silica Membranes: A Molecular Dynamics Study

“…Here, ρ is the moving probability in a 3-dimensional space including the effective pore cross-sectional area, πd e 2 /4, and the activation energy for diffusion (Shelekhin et al, 1995;Lee et al, 2011).…”

“…In order to design a porous inorganic membrane unit and to determine the optimized operating conditions for such separation processes, an understanding of the transport mechanisms of molecules within micropores is indispensable. The gas permeation mechanisms for microporous inorganic membranes with pores less than 1.0 nm in diameter have been extensively investigated in experimental and theoretical manners by many groups using zeolite, sol-gel derived, or CVD-modified glass membranes (Xiao and Wei, 1992;De Lange et al, 1995;Shelekhin et al, 1995;Burggraaf, 1999;Yoshioka et al, 2001aYoshioka et al, , 2013Lee et al, 2011). Gas permeation and separation mechanisms through a micropore are normally classified into Knudsen diffusion, surface diffusion, multilayer diffusion, capillary condensation, and molecular sieving (Uhlhorn et al, 1992;Gilron and Soffer, 2002).…”