Modified polyethersulfone membranes for micellar enhanced ultrafiltration of chromium
Advancing the chemical engineering fundamentals
Filtration (T2-11P)
Keywords: polyethersulfone, ultrafiltration, chromium
The increasing contamination of water by toxic heavy metals, such as chromium, is a serious environmental problem. Chromium exists in nature mostly in two valence states: Cr(VI) and Cr(III). Membrane separation processes play today an important role in the field of wastewater purification and reuse. This technology is being more ecological than conventional separation techniques.
The micellar enhanced ultrafiltration (MEUF) has been shown to be a promising method for removal of low levels of toxic heavy metal ions from industrial effluents. In MEUF an ionic surfactant at a concentration higher than the critical micelle concentration (cmc) is added to the aqueous stream containing the dissolved solutes. The charged micelles cause the ions to bind or adsorb at the micelle interface. Micelles containing absorbed ions are then separated by UF using membrane of suitable porosity, capable of retaining micelles.
Thermo-resistant polymers of good mechanical strength, biological and chemical stability and film-forming properties are the most frequently used materials for membrane preparation. Among them polyethersulfone (PES) is a popular one in last time. However, it has hydrophobic character that facilitates adsorption of many substances during filtration processes. Deposition of solute on/in membrane causes the negative effect - a significant drop of the permeate flux. This harmful phenomenon is called membrane fouling. There are many ways to protect membrane from fouling, one of them is introduction of ionic groups. Porous ion exchange membranes prove to be very useful in ultrafiltration of charge-bearing solutes. The decrease in the membrane fouling ability is the main profit of these membranes.
Transport properties of membranes made from PES, aminated (APES) and sulfonated polyethersulfone (SPES) in MEUF of Cr(VI) and Cr(III) in presence of hexadecylpyridine chloride (CPC) and sodium dodecyl sulfate micelles (SDS), respectively, were characterized. It was found that separation of investigated metal ions by MEUF depends on the kind of membrane and concentration of surfactant. At concentration of surfactants equal to 5 x cmc the best results for separation of Cr(III) through SPES membrane and Cr(VI) through APES membrane were obtained. Additionally, the effect of ligand (EDTA) added to a receiving solution with SDS on Cr(III) ions transport through SPES membrane was studied. The ligand forms a complex with the targed ion of interest and becomes incorporated in the micelles. In ligand-modified micellar enhanced ultrafiltration (LM-MEUF), the best rejection of Cr(III) at concentration of SDS equal to 1 x cmc was obtained. In comparison with unmodified PES, aminated and sulfonated membranes show a significant improvement of performance in micellar enhanced ultrafiltration of chromium.
Acknowledgement:
This work was supported by the Polish Committee for Scientific Research grant 3 T09B 047 28.
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Presented Tuesday 18, 13:30 to 15:00, in session Filtration (T2-11P).
