Permselectivity improvement in membranes for CO2/N2 separation

Abstract

In this work, small-pore zeolites of different topology (CHA, LTA5, Rho), all with Si/Al ratio of 5, have been added to highly permeable poly(1-trimethylsilyl-1-propyne) (PTMSP) to increase its selectivity and thermal and mechanical stability. Membranes were characterized by TGA, XRD, SEM and CO2 and N2 single gas permeation measurements at different temperatures. TGA reveal that the thermal resistance of the mixed matrix membranes (MMM) is as good as that of pure PTMSP polymer membranes. XRD and SEM results reflect that there is good interaction between the fillers and the membrane matrix, at 5 and 10 wt.% zeolite loadings, while at 20 wt.% a dual layer structure is formed, when Rho zeolite is the filler, because the particle size of Rho is higher than those of LTA5 or CHA, and voids appear that limit the permselectivity performance. In single gas permeation of N2 and CO2, the influence of temperature, zeolite loading and type is analyzed. The selectivity of pure PTMSP is considerably enhanced with the addition of the zeolites and the increase of temperature, and the MMM loaded with 5 wt.% zeolite surpassed the Robeson's upper bound for CO2/N2 separation, without decreasing the permeability too much. Upon increasing temperature from 298 to 333 K, the permselectivity is enhanced even further without loss of permeability. The 5 wt.% loaded membranes were tested in CO2/N2 mixed gas separation experiments at 333 K and 12.5 wt.% CO2 in the feed, and the permselectivity of LTA5- and Rho-PTMSP membranes was further enhanced, compared with the single gas permeation experiments.