Fabrication of Zeolite MFI Membranes on Low Cost Polymer Supports

Abstract

About 10~15% of total energy consumption in US is attributed to energy intensive chemical separation processes, such as distillation. The alternative membrane-based separation could save up to 90% energy consumption with outstanding separation performance. Zeolite MFI membranes have been demonstrated for xylene and butane isomer separations with high separation factors and permeances. However, high cost and scale-up difficulty prevent the commercialization of MFI membranes in industries. This dissertation attempts to explore the methods for MFI membranes supported on low cost polymer supports. The major challenge is the stability of polymer support during the detemplation treatment of the MFI membrane after secondary growth. Two mild detemplation methods, thermal treatment at 280 °C and UV/ozone treatment, were identified with sub-100 nm MFI membranes supported on quartz supports. These two methods were then applied to MFI membranes supported on mesh-polyethersulfone (PES) supports and MFI membranes supported on mesh-polybenzimidazole supports. However, cracks formed after the treatments due to the damage of polymer layer by UV light and the mismatch of linear thermal expansion co-efficient, respectively. Another approach, which utilizes the open-pore MFI nanosheets, have been demonstrated. The organic structure directing agents (OSDA) occluded inside the micropores of nanosheets were removed by successive piranha solution treatment, while the crystallinity and morphology were still preserved that confirmed by X-ray diffraction(XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and gas adsorption. The simple deposition of such open-pore MFI nanosheets on porous PBI support, without the need of secondary growth and detemplation, exhibited n-/iso-butane ideal selectivity of 5.4 with n-butane permeance of 3.5×10-7 mol/m2-s-Pa. In addition, the nanosheet exfoliation yield was significantly improved by an oligomeric polystyrene resin. Ultrafiltration polymer hollow fibers were also prepared as suitable supports for nanosheet coating.