Oil-water separation using carbon – based membranes

Karen Tankus, Chemical engineering, Technion, Haifa, Israel



The oil industry's main side product is a mixture of water and oil, known as produced water. After primary separation of most oil, produced water still contains a combination of dissolved oil and residual oil in colloid form. Environmental reasons dictate a strict regulation, whereby the discharged water has to contain a low concentration of residual oil thereby an efficient technological solution for complete oil-water separation is required.
Filtration, regular or membrane, is a cost effective solution when it comes to water purification [1]. In current state-of-the-art produced water may be treated by two types of filters: dense membranes and coarse porous filters or membranes. Dense membranes, e.g., nanofiltration, allow high rejection of oil, however, they require high pressures and high energy consumption in order to produce acceptable fluxes due to high hydraulic resistance. On the other hand, porous membranes have low hydraulic resistance which leads to relatively high flux rates; however, oil rejection is not as high and can easily break through when a critical pressure is surpassed.
Porous, non-woven mats made of ultra-long carbon nanotubes (CNTs) made by Tortech Nano Fibers (Ma'alot, Israel) can offer a good compromise between the two, as their porosity and pore size of ~30 nm potentially offer both high filtration rates, thanks to its porosity, and a high oil rejection rate and high breakthrough pressure minimizing the risk of oil leaking through the membrane. Preliminary results on model oil-water mixtures demonstrate high water permeability and oil separation efficiency of CNT sheets and confirm their potential for treating produced water. This approach also has the potential to improve water treatment in other industries producing oily waste effluents that need to be treated prior to discharge.