There is a critical need for new energy-efficient solutions for separating liquid mixtures. Among the variety of current separation technologies, membrane-based operations are attractive because they are relatively energy-efficient, and are applicable to a wide range of industrial effluents. Our research explores the systematic design of membranes, as well as, the development of smart methodologies that enable separation of a wide variety of both immiscible and miscible liquid mixtures.
In this work we have developed novel membranes with hygro-responsive surfaces, which are both superhydrophilic and superoleophobic in air and underwater environments. Our membrane can separate several liters of oil-water mixtures, including surfactant-stabilized emulsions, solely using gravity, in a single-unit operation, with > 99.9% separation efficiency, by using the difference in capillary forces acting on the two phases. Our separation methodology is solely gravity-driven and consequently is expected to be highly energy-efficient. We demonstrate the separation of several liters of oil-water mixtures using a scaled-up apparatus. We also demonstrate continuous separation of oil-water emulsions for over 100 hours without a decrease in flux.
In addition to the separation of immiscible liquids such as oil and water, separation of miscible liquids is also important in various industries, including oil refining, biofuel production and food industry. Although distillation is one of the most widely used separation methods for separating miscible components from a liquid mixture, it has a high energy-cost, being a thermally driven process. Further, it is unsuitable for the separation of components with similar boiling points and azeotropes.
Liquid-liquid extraction, also known as solvent extraction, is typically used to separate azeotropes or components with overlapping boiling points when simple distillation cannot be used. For an efficient extraction of components, maximizing contact between the feed and the extractant is critical. Emulsions, especially those stabilized by surfactants, provide a large interfacial area and greatly enhance the mass transfer in extraction, the subsequent separation of emulsions can be energy-intensive and less economical. Consequently, there is a great need and a significant opportunity to develop a new energy-efficient separation methodology with enhanced mass transfer during extraction and facile separation of the surfactant-stabilized emulsion.
Here we have developed a new energy-efficient methodology that combines liquid-liquid extraction using surfactant-stabilized emulsions, and solely gravity-driven separation of these emulsions into a single unit operation, using membranes with hygro-responsive surfaces. We have demonstrated that our separation methodology is useful for a wide variety of separations, including the separations of azeotropes of alcohol-hydrocarbons, miscible dyes and sulfur compounds from oils. We anticipate that our separation methodology has numerous applications, including the production of diesel with ultra-low sulfur content, separation and purification of bio-fuels, removal of dyes from jet fuels and separation of azeotropes.
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