Coalescence and Separation Properties of Fine Oil Droplets by Lipophilic Nanofiber Membrane

A coalescer is a useful device for removing oil from oil-in-water (O/W) emulsion, but it is unsuitable for the coalescence of fine oil droplets less than 10 μm. In this study, a nanofiber membrane was applied as a fibrous layer equipped in the coalescer to coalesce the fine oil droplets less than 10 μm, and the lipophilic polypropylene nanofiber membrane was selected in consideration of an affinity for oil. The O/W emulsion including the fine oil droplets was permeated through the membrane for evaluating the coalescence properties of fine oil droplets. In the initial stage of permeation, the oil droplets were strongly attracted to the lipophilic surface of nanofibers, and a thin oil film was formed on the entire fiber surface. Subsequent oil droplets were incorporated into the oil film, resulting in the growth of the oil film. When the fibers could no longer hold fully grown oil film, excess oil film was finally released from the outlet of the membrane. The released oil pieces floated and formed an oil layer on the surface of permeated fluid. In the steady state, the separation ratio of 83.3 % was observed under low pressure loss of 17 kPa. The size distribution data of droplets in the permeated fluid clearly demonstrated that the polypropylene nanofiber membrane used in this study could completely coalesce and separate the fine oil droplets of 2 to 10 μm.