Separation of liquid-liquid dispersions is important industrially and environmentally. Fibrous coalescing filters are used to separate liquid-liquid dispersions. Wettability of the fibers significantly influences the filter performance. The wettability of the filter media depends on surface properties of fiber materials and porosity of the filter medium. The wettability of filter media and interfacial tension of the liquid are the important factors in designing a coalescing filter media. It is generally accepted that the intermediate wettability gives best filter performance. However, the effect of wettability on filter performance is not well understood, especially at low interfacial tension liquids. In addition, wettability characterization techniques are not widely applied for fibrous filter media.
The goal of this work is to study the effect of wettability on filter performance and by evaluating filter media of varying wetting properties. In this work, filter media were prepared by mixing hydrophilic and hydrophobic fibers to control the wettability and to improve the performance of the filter media. The mixing of fibers was achieved by designing filter media in different geometries. The different geometries developed and evaluated are mixed, layered and radially layered hydrophilic/hydrophobic fiber media. The wettability of the filter media was characterized using modified Washburn's equation and expressed as the Lipophilic to Hydrophilic (L/H) ratio. Water and Viscor-1487 oil were used as test liquids for the wettability characterization. The developed geometries resulted in variation in wettability. The filter media were tested in liquid-liquid coalescence experiments in which fine emulsion was generated by dispersing water droplets in the Viscor-1487 oil.
The experimental results show that wettability of filter media can be controlled by constructing a media with different geometries and choosing a right composition of hydrophilic/hydrophobic fibers. The pressure drop of filter media was reduced with increase in L/H. The performance of filter hydrophilic/hydrophobic filter media was improved as compare to only glass fiber (hydrophilic) media. However, improvement in quality factor is mainly due to reduction in pressure drop. The best filter performance was achieved with layered and radially layered structures made of glass and polypropylene fibers having L/H between 2 to 10. The media developed with glass and electrospun polypropylene fibers shows significant improvement in separation efficiency but also increase in pressure drop. The results and approach of this work will be useful in designing and developing filter media for many industrial filtration applications.