Modification of ultrafiltration membranes with block copolymer nanolayers for produced water treatment: The roles of polymer chain density and polymerization time on performance

This contribution describes the development of advanced membranes for produced water treatment through modification of low molecular weight cut-off regenerated cellulose ultrafiltration membranes with uniquely structured block copolymer nanolayers. Poly(N-isopropylacrylamide)-block-poly((polyethylene glycol) methacrylate) (PNIPAAm-b-PPEGMA) nanolayers were grafted from the membrane using surface-initiated atom transfer radical polymerization. A focus of this study was to better understand the role of polymer nanolayer structure on performance. Specifically, the objective of this work was to use initiator grafting density and PNIPAAm and PPEGMA polymerization times as independent variables to optimize the performance of the surface-modified membranes. Membrane performance was evaluated by measuring water flux using deionized water, synthetic produced water developed from an oil-in-water emulsion, and actual oil-field produced water. Optimization of nanolayer structure yielded membranes with stable permeabilities that compare well to commercial membranes used for removal of organics with high salt passage. The results show that nanolayer structure plays an important role in determining the effectiveness of a polymer coating for fouling prevention, even for polymers that are recognized by the community to have good antifouling characteristics. The membrane surface modification protocol allows optimization of nanolayer structure in ways not achievable by standard coating methods. Visualization by confocal laser scanning microscopy shows that the modification occurs at the membrane external surface and internally within the porous cellulose layer. The modification protocol was used in this study to design highly advanced membranes to separate emulsified oils from produced water.