Molecular dynamics studies on gas permeation properties through microporous silica membranes

Citation
T. Yoshioka et al., Molecular dynamics studies on gas permeation properties through microporous silica membranes, SEP PURIF T, 25(1-3), 2001, pp. 441-449
Citations number
20
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemical Engineering
Journal title
SEPARATION AND PURIFICATION TECHNOLOGY
ISSN journal
1383-5866 → ACNP
Volume
25
Issue
1-3
Year of publication
2001
Pages
441 - 449
Database
ISI
SICI code
1383-5866(20011001)25:1-3<441:MDSOGP>2.0.ZU;2-Y
Abstract
Gas permeation mechanisms through a micropore of a vitreous silica (v-SiO2) membrane were studied using a molecular dynamics (MD) simulation. Virtual v-SiO2 membranes were prepared by the melt-quench methods using the modifie d Born-Mayer-Huggins pair potential and Stillinger-Waber three-body interac tions. The particle-generating non-equilibrium MD technique was employed in order to simulate gas permeation phenomena, where permeating molecules wer e modeled as Lennard-Jones particles. This simulation method accommodates a change in the number of particles in a unit cell and, hence, an accurate s imulation of the steady-state process of permeation can be achieved, The de pendencies of permeance on temperature and pressure were discussed. For cyl indrical pores of about 5 Angstrom in diameter, the calculated temperature dependencies of the permeance of He-like LJ particles were similar to those predicted by the normal Knudsen permeation mechanism, while, for CO2 perme ation, a temperature dependency larger than He and a significant deviation from the Knudsen's could be observed. In the relatively high-temperature re gion (400-800 K), the simulated permeance of CO2 was nearly independent of the upstream pressure, while at the temperature below 300 K, a pressure dep endency of permeance was observed. Simulations of adsorption conducted on t he same unit cell yielded a Henry-type isotherm at 400 K and a Langmuir-typ e isotherm at 260 K. These results indicate that gas-Eke permeation occurre d in the higher-temperature region, where the permeation flux is proportion al to the pressure drop across the pore. However, at lower temperatures, th e transports of molecules as some type of adsorption phase might be dominan t in such a small pore. A simple gas permeation model, considering the effe ct of the pore wall potential field and Langmuir type adsorption within a m icropore explained those permeation properties of CO2 well. (C) 2001 Elsevi er Science B.V. All rights reserved.