Advanced Highly Permeable and Thermally Stable Polyamide Thin Film Composite and Thin Film Nanocomposite Membranes
Creators: Karami, Pooria
Publisher: name: University of Alberta Library
Year: 2022

<p>Treating contaminated hot streams is essential to reduce water cooling/re-heating needs and greenhouse gas emission in water reclamation processes, such as the Canadian in-situ oil-sand extraction processes that produce contaminated water at 80-90 C. Membrane separation processes have become one of the fastest growing methods for the desalination and treatment of water because they cost less, are more compact, and produce higher quality water than conventional processes. At the heart of this processes is the membrane. Thin film composite (TFC) membranes are the most common choices due to their high water recovery and contaminant rejection rates. However, commercially available TFC membranes do not perform well above 45 C. The objective of this PhD thesis is to make new classes of TFC polymeric membranes with high permeability and separation performance at high water temperatures. <br>
First, a novel reverse osmosis (RO) TFC membrane with enhanced thermal stability was made to address the limitation of available commercial TFC membranes. The goal was to make a new polymer with a rigid network, and therefore higher temperature resistance, as the selective layer. To reach this goal, triaminopyrimidine (TAP, a multifunctional amine) was added to the usual combination of m-phenylenediamine (MPD) and trimesoyl chloride (TMC) to crosslink the polymeric structure. The TAP-modified membranes had higher permeabilities and consistent permeate fluxes for 9 hours at high temperatures. <br>
These polymers were used to develop novel highly permeable and robust forward osmosis (FO) membranes. TAP-modified FO TFC membranes mediated with polydopamine (PDA)/graphene oxide (GO) interlayers were synthesized. The presence of an interlayer and a low reactive monomer (TAP) slowed down the interfacial polymerization, leading to forming a permeable, selective, and thermally stable polyamide layer. <br>
I also added nanodiamond (ND) particles with high thermal resistance into the polyamide layer. The surface of the ND particles was modified with MPD to covalently bond them in the polymer matrix. Thin film nanocomposite (TFN) membranes prepared with ND particles overcame the trade-off between water flux and NaCl rejection, and showed less flux decline at high temperature compared with a polyamide commercial membrane. <br>
In the next phase of this development, amine-modified ND particles were added to the polyamide layer to change its surface chemistry. The ND particles reduced fouling of the TFC membranes with sodium alginate (SA) and bovine serum albumin (BSA) foulants by decreasing the electrostatic and hydrophobic interactions between foulants and the membrane surface, and by reducing the membrane roughness. <br>
Finally, we provided guidelines to test TFC membrane at high temperatures. The performance of three commercial RO membranes were evaluated with a series of high-temperature filtrations including long-term operation, cyclic tests, controlled step-wise temperature increments, and permeability tests.</p>