Investigation of slowing-down and speeding-up effects in binary mixture permeation across SAPO-34 and MFI membranes

Abstract

Permeation experiments for Ar/CH₄ and CO₂/H₂ mixtures across a SAPO-34 membrane were performed with the objective of highlighting their distinct diffusion characteristics. For the Ar/CH₄ mixture, the effective transport coefficients of the individual components in the mixture were found to be practically the same as those obtained from unary permeation experiments, when compared at the same total loading at the upstream face of the membrane. There is no speeding-up of the tardier CH₄. Only at the high loadings is there evidence of a small, about 10%, slowing-down of the more mobile Ar. A different picture emerges for permeation of CO₂/H₂ mixtures across SAPO-34 membrane. While the transport coefficient of CO₂ is practically identical to those obtained from unary experiments, there is a significant slowing-down of the more mobile H₂. At the highest loading, the transport coefficient of H₂ is about a third of the value of the pure component. Permeation of CO₂/CH₄ mixtures across an MFI membrane showed that there is a significant slowing-down of the more mobile CH₄ with concomitant speeding-up of the tardier CO₂. The incorporation of the Vignes interpolation formula for the exchange coefficient Ð₁₂in the Maxwell-Stefan equations does not adequately reflect the slowing-down and speeding-up phenomena for either SAPO-34 or MFI membranes.