M. Sadrzadeh, B. Khorshidi, H. Nazaripoor, A. Karkooti, A. Asad, A.M. Koupaei
University of Alberta,
Canada
Keywords: nanocomposite, membrane, water treatment, oil sands, produced water
Summary:
Membrane processes offer a promising alternative to current energy- and material-intensive water treatment processes in the oil sands industry, such as ion exchange and lime softener, by providing higher separation efficiency and a smaller footprint. However, the low thermal stability of polymeric membranes and their susceptibility to fouling has limited the development of sustainable and energy-efficient membrane processes for the well-known steam assisted gravity drainage (SAGD) process. Thermally tolerant nano-enabled membranes have the potential to improve heat integration in SAGD plants, thereby reducing boiler feed water heating requirements and greenhouse gas production. The major challenges to the successful incorporation of nanoparticles to polymer films are the severe aggregation of the nanoparticles and their weak compatibility with the structure of the polymer. These two phenomena lead to the formation of non-selective voids at the interface of the polymer and nanoparticles, which adversely affect the separation performance of the membrane. To overcome these challenges, we have developed strategies for the development of defect-free nanocomposite membranes for ultrafiltration and reverse osmosis processes. One of these approaches relied on the simultaneous synthesis, surface functionalization, and entrapment of nanoparticles within the polymer matrix. For example, TiO2 nanoparticles were synthesized and functionalized in an organic solvent (heptane) via biphasic solvothermal reaction. The resulting stable suspension of the nanoparticles in heptane was then utilized in the interfacial polymerization reaction where the nanoparticles were entrapped within the matrix of the polyamide membrane in reverse osmosis thin film nanocomposite membranes. TiO2 nanoparticles of 10 nm were effectively incorporated into the thin polyamide layer and improved the thermal stability and anti-biofouling properties of the resulting membranes. The prepared membranes were utilized for the treatment of oil sands produced water at 65 C and their performance was not negatively affected as compared to unmodified membranes. Surface patterning has been proven to be an effective method to enhance the permeate flux and lower the attachment of fouling materials on the membrane surface. The addition of patterns increases the surface area, which is directly proportional with the water permeate, also causes better recirculation/mixing of water which reduces the deposition of foulants on the membrane surface by distorting the feed streamlines. We developed two novel methods based on (a) hydrogel molding, that is a combined micro-molding and modified phase separation and (b) electrohydrodynamic lithography, which relies on the electrohydrodynamic-induced instabilities to generate features on the membranes. In hydrogel molding method, the thin polymer film is cast on a patterned hydrogel mold, and the controlled demixing of solvent and nonsolvent leads to the formation of patterned membranes leading to a thin dense layer on the patterned side. In the electrohydrodynamic lithography method, the thin polymer film is subjected to the electric field and patterns are self-organized to columnar structures. The performance of the patterned and the unpatterned membranes are examined in a cross-flow filtration system for the treatment of oil sands produced water; a significant increment in water flux and antifouling property was observed.