Magnetically-Responsive Membranes for Water Treatment

Magnetically-Responsive Membranes for Water Treatment

Heath H. Himstedt^*, Xianghong Qian⁺, Mathias^# Ulbricht, Qian Yang+, S. Ranil Wickramasinghe⁺

^*Department of Chemical and Biological Engineering, Colorado State University ⁺Ralph E. Martin Department of Chemical Engineering, University of Arkansas

^#Lehrstuhl für Technische Chemie II, Universität Duisburg-Essen, Essen, Germany

Membrane processes are used increasingly in water treatment because they often require less energy than alternative unit operations.  Unfortunately membrane fouling often limits the use of membrane separations for water treatment. Development of advanced antifouling membranes will be essential if the potential for low energy membrane separations is to be used for water treatment.  We have created a novel filtration membrane which responds to an external magnetic field.  Here results will be presented for surface modification of commercially available nanofiltration membranes in order to make them responsive to an oscillating magnetic field. 

Commercially available nanofiltration membranes (NF 270) have been modified using atom transfer radical polymerization to grow poly(2-hydroxyethyl methacrylate) chains from the surface of the membrane. Next a Gabriel synthesis reaction was used to convert the alkyl halide end group of the polymer chains to primary amines. Carboxylic acid coated iron oxide nanoparticles were then attached to the chain ends through an amide linkage.  Spectroscopy and microscopy was used to verify surface funtionalization.

Movement of the magnetically responsive brushes has been visualized using particle image velocimetry which shows that the movement of brushes in an oscillating field causes mixing above the membrane surface. Our data indicate that this motion is sufficient to cause mixing up to a distance of 0.5 mm from the membrane surface.

Treatment and handling of oily waters produced during alternative fuel exploration (produced waters) is costly and difficult.  Membranes have been investigated to treat produced waters; however, membrane fouling limits membrane lifetime and performance.  An idealized produced water feed was treated using the magnetically-activated membranes.  Our results show less severe flux decline and improved permeate quality compared to nonfunctionalized NF 270 membranes.  Additionally, the modified membranes were more easily cleaned and maintained higher performance over numerous filtration/washing cycles.  It is believed that the mixing generated by the polymer brushes in an alternating field reduces concentration polarization (and by extension colloidal fouling) leading to improved performance and easier maintenance.