Effect of fiber surface modifications on the coalescence performance of polybutylene terephthalate filter media applied for the water removal from the diesel fuel

In this work the coalescence performance of the melt-blown structures applied for removal of emulsified water from the diesel fuel is studied. Fibrous polyester media (polybutylene terephthalate, PBT) were fabricated in-house using the melt-blow technique. Postproduction treatment towards the fiber modification involving hydrolysis of the surface with sodium hydroxide or exposure to a low temperature plasma was applied. Different properties of polymer surface were obtained for each modification method, which was verified by the capillary rise test with oil and water. The applied treatment had a significant impact on the coalescence performance comparing to the unmodified PBT structure. In contrary to numerous experimental studies the hydrophilic polyester media obtained by hydrolysis performed much worse than plasma treated filters. It was also shown that the combination of water wettable and non-wettable fibers respectively on the inlet and outlet can significantly improve the separation efficiency. However, in such case the pressure drop is significantly increased as the water captured and collected within the inlet layer is not effectively transported to the outlet. This confirmed that the wettability of fiber surface is not an independent parameter which affects the process. The filter material should be carefully selected with regards to both structural and surface properties of adjacent layers to form a reasonable saturation of the coalescence layer for the high efficiency and also enable the transport of collected liquid to the outlet. Both the structural and surface properties have a pronounced impact on the coalescence efficiency and detachment of droplets from the porous structure on the outlet.