Gusev and Suter calculation of the diffusion coefficients of light gases in silicalite-1 membrane and silica-sodalite zeolite

• Published in: Separation and purification technology 2004-05, Vol.36 (3), p.215-228
• Main Authors: De Luca, Giorgio, Pullumbi, Pluton, Barbieri, Giuseppe, Famà, Angelo D, Bernardo, Paola, Drioli, Enrico
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemical engineering; Diffusion coefficients; Exact sciences and technology; Silica-sodalite zeolite; Transition-state theory (TST)
• ISSN: 1383-5866; 1873-3794
• DOI: 10.1016/j.seppur.2003.07.002

Transition-state theory (TST) as implemented by Gusev and Suter was applied to calculate the zero-loading-diffusion coefficients of 12 gases (He, Ne, Ar, Xe, H 2, N 2, O 2, CO 2, SF 6, CH 4, CF 4, and i-C 4H 10) in two different zeolites, silicalite-1 and silica-sodalite. Gusev–Suter (GS) model was and is widely and successfully used for polymeric matrixes. Therefore, the reliability of this method was studied for gas diffusion in silicalite-1 and silica-sodalite using CVFF_aug and CVFF force fields and two simulation cells. The results were compared with diffusion coefficients used to reproduce the permeance in a silicalite-1 membrane. Model limits were also tested comparing the H 2, He and Ne diffusion in silica-sodalite with previous calculations of classical and quantum TST. Gusev–Suter method systematically underestimates the average diffusion coefficients of the considered gases; underestimation was less marked for species larger than methane. The ratio between D x and D y components in silicalite-1 was found near one differently from the expected result. The diffusion coefficients obtained using Gusev–Suter approach in silicalite-1 and silica-sodalite can be improved with an appropriate average displacements definition, set in this work equal to 0. Concerning the anisotropy diffusion in silicalite-1, this work shows that correlated jumps in a Gusev–Suter procedure would also be considered. Gusev–Suter computational time for diffusivity estimation of Xe, CF 4, CO 2 and SF 6 is much shorter than the corresponding molecular dynamics (MD) simulation time.