Polyimide and PEBAX flat and hollow fiber membranes for gas separation

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Chemical Engineering, Turkey

Approval Date: 2017




This thesis analyzes the effect of polyimide (PI) hollow fiber membrane spinning conditions including dope solution flow rate, bore liquid flow rate, addition of more volatile solvent to dope solution, air gap height and heating zone temperature on the ideal gas separation performance and membrane morphology. The effect of PEBAX1657 coating of PI hollow fiber membrane was also investigated. The effect of incorporation of ZIF-8 crystals to PEBAX1657 flat sheet membrane, the effect of coagulant type for the preparation of porous polyethersulfone (PES) flat sheet membrane, the effect of PEBAX1657 and PEBAX1657/ZIF-8 coating of PES flat sheet membrane on the membrane gas separation performance and morphology were investigated. In this study, asymmetric PI hollow fiber membranes were produced by dry-wet spinning method via twin orifice spinneret at room conditions from dope liquid containing dimethylformamide (DMF) and tetrahydrofuran (THF) and bore liquid solution containing 90 wt. % of DMF and 10 wt. % of distilled water. Tap water was used as non-solvent in the coagulation bath. Gas separation membrane performance of virgin hollow fiber membranes were not sufficiently high for biogas refining. PEBAX1657 coating enhanced gas separation performance of the virgin hollow fiber membranes. PEBAX1657 and PEBAX1657/ZIF-8 coating of porous PES flat sheet membranes increased ideal CO2/N2 and CO2/CH4 selectivity. Hollow fiber membranes were characterized by scanning electron microscopy (SEM). Flat sheet membranes were characterized by SEM, Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA). ZIF-8 crystals were characterized by N2 adsorption desorption isotherms, SEM, X-ray diffraction (XRD). ZIF-8 particles having high crystallinity was synthesized with average size of 69 ± 14 nm