This work concerns the preparation, characterization and testing of a novel hydrophobic filter for oil-water separation through selective permeation, with particular focus on the effect of some parameters on the performance (hydrophobic coating, oil phase viscosity, water salinity, pressure on the filter). The filter material is made up of sintered stainless steel coated with a thin film of PDMS by a vapour deposition technique. Through SEM images it is pointed out that an increase of PDMS concentration in vapour phase and a longer deposition time induce a higher surface covering. From IR spectra it is evident the presence of silicone moieties grafted on the porous steel substrate. The contact angle measurements confirm the hydrophobic nature of the material (CA ~130°) and show no difference between poorly coated and highly coated samples, suggesting that a thin film of silicone is adequate to guarantee the hydrophobicity. As expected, the efficiency in oil-water separation, evaluated in term of selectivity and permeation flow, is satisfactory for all prepared samples. The diesel flow increases almost linearly with the pore diameter. Increasing viscosity (crude oil) the flow decreases. The flow is maintained for a working period longer than 250 hours with deionised water. In presence of seawater, the flow shows a decrease, probably because of salt precipitation on the surface and pores fouling. With a back-washing with solvent it is possible to restore the flow. By applying a small pressure between the two sides of the filter, it is possible to significantly increase the flow, maintaining selectivity.
The properties of the material have been tested with a prototype in a pilot tank; the encouraging results demonstrate the possibility of real application in oil-water separation processes.
