Thin film composite nanfiltration membranes for extreme conditions

Abstract

The research presented in this thesis focuses on development and performance evaluation of thin film composite (TFC) nanofiltration (NF) membranes, with special attention to extreme pH applications. In Chapter 2 a new method that allows molecular weight cut off (MWCO) characterization of NF membranes as a function of pH is presented. Performance evaluation of a well-known commercial NF membrane (NF-270, Dow Filmtec™) via this method reveals reversible changes with respect to pH, signifying the relevance of performance characterization at the relevant conditions. The developed method is thus also used in the following chapters for characterization of in-house developed NF membranes. In Chapter 3 the above mentioned method illustrates the effect of pH on the performance of in-house developed polyamide TFC NF membranes, fabricated via the interfacial polymerization (IP) route. Following an investigation of optimal fabrication parameters the performance of the developed membranes has been compared to commercial NF membranes currently used in the industry. Using the Donnan steric partitioning pore model, the pH induced performance changes have been correlated to morphological changes in the membrane matrix. TFC’s presented in Chapter 4 were prepared by spin coating sulfonated poly (ether ether ketone) (SPEEK) solutions on ultraporous polyethersulfone (PES) supports. The optimal fabrication parameters required for obtaining stable membranes were determined and the resulting performance was benchmarked against several commercial NF membranes. The developed membranes reveal excellent stability in the entire pH range from 0-14, even under prolonged exposure (up to several weeks). Permeance and MWCO analysis at varying pH indicate that charge effects induce reversible changes in the membrane properties. In Chapter 5 novel hybrid TFC membranes containing Polyhedral oligomeric silsesquioxanes (POSS) are presented. Inorganic POSS cages have been linked together via the classical polycondensation chemistry widely used for IP polyamide membrane fabrication. Both, free standing as well as substrate supported films could be obtained. In depth analysis to confirm the chemistry was carried out via Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy. NF permeation experiments were performed on the substrate supported films and the effect of some important fabrication parameters are discussed.