Feasibility assessment of pervaporation for desalinating high-salinity brines

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Pervaporation, which is a non-pressure driven membrane process, was evaluated to determine its viability for desalinating high-salinity source waters like those originating from oil and natural gas development (produced water). Two types of membrane material chemistries were studied in order to identify the optimal properties for maximizing the permeate flux under a given set of operating conditions. Permeate flux was determined to be a significant function of membrane thickness and the diffusion coefficient of water through the membrane. The diffusion coefficient is in turn a function of the membrane's affinity for water (hydrophilicity) and its fractional free volume space. A cellulose triacetate membrane (Membrane B) achieved fluxes of 0.06 m3m–2day–1 when treating solutions having salt concentrations of 100 g L–1, comparable to fluxes achieved by other types of non-pressure driven membrane processes. The flux increased in a linear fashion with decreasing ionic strength and improved through increases in the vapor pressure gradient and/or inclusion of a feed channel spacer into the test cell. Salt rejection efficiencies by all membranes were >99%; however, co-ions were able to penetrate into the membrane material matrix over time.

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