The mechanism of extraction of organic compounds using polyurethane membranes

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Rzeszutek, Kathy
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The main focus of this research has been to investigate the process by which organic compounds in solution are taken up by polyurethane membrane under various chemical and physical conditions. This extensive mechanistic study involved examining the effect of solution conditions on extraction (presence of salts, pH), the size and polarity of the organic species, the type and position of substituents on the molecule, membrane properties (active surface area, thickness), and temperature on the sorption of pollutants and industrially important compounds such as various phenols, benzoic acids, organic dyes, organometallic ion-association complexes, and organic solvents. It was found that the formation of a neutral species in solution and the ability to engage in hydrogen-bonding with the membrane is essential for extraction into polyurethane to occur. The size of the organic species is not as important as its overall polarity and the relative solubility in the solvent and in the membrane. Increased removal of species from solution can be attained by providing either a larger surface area exposed to the sample solution, a thicker membrane, or a receiving solution into which the compound can be desorbed from the membrane. Higher temperature can be used to accelerate the entire sorption process. The mechanism by which organic compounds are removed from solution by the polyurethane membrane can be subdivided into three separate phenomena, namely, the transfer of species from bulk solution to the solution-membrane interface and the reverse, adsorption onto the membrane surface, and transport into the bulk of the polymer.