Kinetics of spontaneous liquid-gas imbibition in carbon molecular sieves used for O2/N2 separation

Abstract

The kinetics of spontaneous liquid-gas imbibition in micropores of carbon molecular sieves (CMSs) used for air separation has been investigated. Based on the kinetics, the microporous textures of CMSs could be estimated, and a new assessment method for O2/N2 separation performance of CMSs in pressure swing adsorption (PSA) was established. Water was chosen as the imbibition liquid probe, and N2 and O2 were chosen as the gas probes. The pseudo-second-order (PSO) kinetic model and the linear driving force (LDF) model were employed to confirm that the rate-limiting steps of the spontaneous water-O2/N2 imbibition were mainly attributable to the surface adsorption of water and the diffusion of gas through the micropore entrence or interior in CMSs. Water molecules invade into the narrower micropore mouths prior to the wider micropore mouths. An O2/N2 selectivity coefficient K was established to assess the air separation performance of CMSs. When the K value is equal to zero, the size distribution of micropore mouths in CMSs is the fittest for the air separation and the highest N2 production can be obtained. But with K gradually deviating zero, the air separation performance of CMSs decreases.