Hybridizing zeolite MFI nanosheets with PTMSP membranes for enhanced butane isomer separations

Abstract

Hybridizing zeolite nanosheets with a high aspect ratio has the potential to improve the gas separation performance of polymeric materials due to their good mechanical strength, thermal stability, and well-defined microporous structure. However, the use of zeolite-nanosheet-based mixed matrix membranes (MMMs) has been limited, and their effects on polymeric materials have not been studied thoroughly. In this study, zeolite MFI nanosheets were directly synthesized and introduced into PTMSP polymer using the shear-coating method. This resulted in a horizontally aligned structure with preferentially b-oriented zeolite MFI fillers. The straight b-channels of zeolite MFI facilitated fast gas permeation, while the high aspect ratio increased the tortuosity for non-permeable gases. The elastic modulus of the composite increased from 306 MPa to 2069 MPa as the zeolite MFI nanosheet content was increased to 50 wt%. The membrane was thermally stable up to 285 °C due to the protection provided by the zeolite MFI filler, which prevented thermal degradation by oxygen. The gas separation performance was improved, with a butane isomer selectivity of 7.3 and a permeability of 5400 barrer, a 20% increase from the neat PTMSP membrane. The selectivity was well preserved even in the binary mixture of butane isomers gas permeation test at 1 bar, while the neat PTMSP membrane showed a dramatic decrease in selectivity under this condition. The compatibility between the nanosheets and the polymer is expected to be important in achieving high separation performance of the composite membrane, as can be inferred from the large difference between the performance predicted by the modified Cussler model and the actual performance.