Incorporation of open-pore MFI zeolite nanosheets in polydimethylsiloxane (PDMS) to isomer-selective mixed matrix membranes

A mixture of H2SO4 and H2O2 (known as piranha solution) was used to remove organic structure-directing agents (OSDA) from multilamellar MFI zeolite (ML-MFI). An aqueous solution of MFI zeolite nanosheets was obtained via exfoliation of the OSDA-free ML-MFI zeolite through sonication in water followed by purification through sedimentation. The exfoliated MFI zeolite nanosheets were characterized by various techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and porosimetry by cryogenic N-2 adsorption-desorption, indicating that single-layer MFI nanosheets were obtained and the micropores were opened. MFI nanosheets/polydimethylsiloxane (PDMS) mixed matrix membranes (MMMs) were prepared by the solution casting method using the open-pore MFI zeolite nanosheets as the filler and PDMS as the continuous phase. The obtained MMMs exhibited greatly improved butane isomer permeabilities and ideal selectivities for n-butane over i-butane compared to the pure PDMS membrane. An ideal selectivity of 15.7 for n-butane/i-butane was achieved on the MMM at 1 wt% loading of MFI nanosheets, with a n-butane permeability up to 15615 Barrer.

Automated summary

The study successfully removed OSDA from multilamellar MFI zeolite using piranha solution, resulting in the preparation of single-layer MFI zeolite nanosheets. Mixed matrix membranes (MMMs) made from these nanosheets and PDMS showed greatly improved permeabilities and selectivities, particularly for n-butane separation.