Nanosizing zeolite 5A fillers in mixed-matrix carbon molecular sieve membranes to improve gas separation performance

Abstract

Zeolite 5A with particle sizes of 100 nm and 1 μm were synthesized and leveraged as filler materials in carbon molecular sieve membranes (CMSMs) using Matrimid® 5218 as the polymeric precursor. Our results show that nanosized zeolite 5A fillers are capable of creating substantially improved CO2 and O2 permeability as compared to the large-sized zeolite 5A at 1 μm, owing to an increase in interfacial surface areas between the filler and carbon matrix. Accordingly, the mixed-matrix CMSMs with 20 wt% loading of nanosized zeolite 5A at 100 nm demonstrated up to 2 orders of magnitude higher permeability than the unfilled CMSM, which not only compensated for the marginal drop in membrane selectivity (between 34 to 41%), but also resulted in performances that transcend the 2008 Robeson upper bound for CO2/CH4 separation. From a different perspective, the effectiveness of the fillers at different loadings was also confirmed using a filler enhancement index, Findex, which is a new composite rating that accounts for both permeability and selectivity enhancements. Our evaluations showed that nanosized zeolite 5A fillers at 100 nm are indeed more competent than the large-sized zeolite 5A crystals in improving the separation performances of the mixed-matrix CMSMs. Essentially, nanosizing filler materials for mixed-matrix CMSMs is a straightforward and effective strategy to elevate separation performances of CMSMs, making this approach highly relevant for biogas (CO2/CH4) and air (O2/N2) separations.