South Africans develop oil-water separation membrane
Researchers in South Africa have fabricated and tested a nanotube-infused membrane which could be used to treat polluted wastewater such as oil-containing waste from oil & gas operations.The research paper, A carbon nanotube-infused polysulfone membrane with polyvinyl alcohol layer for treating oil-containing waste water, was published in Scientific Reports (Nature Publishing Group) on 22 March 2013.
The researchers, primarily from the School of Chemical & Metallurgical Engineering, University of the Witwatersrand, Johannesburg, say that high volumes of wastewater in the form of oil-water emulsion are produced in various industries such as oil fields, petrochemical, metallurgical, pharmaceutical and others. Concentrations range from 50‑1,000 mg/L; however, the acceptable discharge limit is only 10-15 mg/L.
Membrane filtration, including microfiltration, ultrafiltration, nanofiltration and reverse osmosis, has been successfully used in the separation of oil from water, and is useful because of the high quality water produced, simpler module design, low amount of chemicals used and low energy consumption compared to other treatment techniques. However, these techniques are not without problems, including fouling and concentration polarization.
The team fabricated a carbon nanotube (CNT)-polymer composite membrane with a polyvinyl alcohol barrier layer and tested it for the separation of oil from water. At a concentration of 7.5% CNTs in the polymer composite, a 119% increase in the ultimate tensile strength, 77% increase in the Young's modulus and 258% increase in the toughness were seen indicating the suitability of the membrane in practical applications.
The permeate through the membrane showed oil concentrations below the acceptable 10 mg/L limit with an excellent throughput and oil rejection of over 95%. Depending on the application of the membrane, a balance between the metrics such as rejection and flux can be obtained by varying CNT concentration in the membrane and pressure.