Effects of surface coating process conditions on the water permeation and salt rejection properties of composite polyamide reverse osmosis membranes
KAUST DepartmentAdvanced Membranes and Porous Materials Research Center
Physical Sciences and Engineering (PSE) Division
Chemical and Biological Engineering Program
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AbstractThe application of polymer surface coatings to improve the fouling resistance of reverse osmosis membranes tends to increase flow resistance across the membrane. This paper presents a systematic analysis on how membrane properties and performance are impacted by the coating process steps, and investigates how such effects could contribute to lower water flux. On one hand, simply pre-soaking dry aromatic polyamide composite membranes in aliphatic alcohols results in a significant increase in water flux, which is attributed to wetting of pores in the selective polyamide layer and to changes in the polymer structure. This flux increase was not readily reversible, based on a 300-h water permeation test. Conversely, drying a wetted membrane led to a decrease in water flux, which we hypothesize is caused by increased interchain hydrogen-bonding in the selective layer. This drop in water flux was not permanent; higher flux was observed if the same wetted/dried membrane was then re-soaked in ethanol prior to the water permeation experiment. An ethanol pre-soaking step also increased water flux of a PEBAX-coated membrane by nearly 70%. In contrast to the reduction in water flux caused by the specific treatment sequence of ethanol-swelling followed by drying, this same sequence actually increased gas transport. The eight- to ten-fold increase in Knudsen diffusion-based gas permeance after this pre-treatment was attributed to an increase in the number or size of membrane defects. © 2010 Elsevier B.V.
SponsorsThis work was funded by the Santa Clara Valley Water District (Agreement A2727A), the Metropolitan Water District (Agreement 41808), the California Department of Water Resources, the WateReuse Foundation (WRF-06-020) and Singapore Economic Development Board. Membranes used for this study were generously donated by Hydranautics (Oceanside, CA). Membrane Technology and Research, Inc. is gratefully acknowledged for providing water and gas permeation equipment.
JournalJournal of Membrane Science