The separation of O/W dispersions is an important operation in many industrial processes related to water treatment technologies, e.g., to meet discharge limits to the environment or comply with technological standards for the recirculated water. Due to their advantages, coalescence separators have been widely used for the deoiling of water, especially for the separation of secondary dispersions and small-sized droplets, which do not settle down and are spontaneously separated by gravity.

The coalescence that takes place when fluid flows through a filter element means the merging of droplets into larger ones. Many factors affect the efficacy of the process, which are related to operating conditions, physicochemical properties of liquids and the design of fibrous filtration material, including both structure and surface properties. During experiments, the detrimental effect of oil film stretching instead of large droplets formation on the outlet from the drain layer was observed at certain conditions, which significantly affected the separation efficacy. This research aimed to determine the correlation between process conditions and material properties and the structure of the dispersed phase (oil) on the outlet.

The first series of experiments were conducted for two types of nonwoven filter native polymer material – polypropylene (PP) and polyamide 6 (PA6), which were fabricated using the melt-blow technique. The separation efficacy was significantly affected by differences in the form the oil droplets are detached from the filter element. In the case of polypropylene nonwovens, the formation of foam-like structures was observed, which subsequently broke. This caused a decrease of the separation efficacy due to the release of fine oil droplets on the outlet. For polyamide nonwovens, large oil droplets were detached from the outlet layer of filter, and they were easily separated by gravity. These phenomena are...

Although the PA6 media possesses inherent surface properties more suitable for the oil from water separation, the PP is much cheaper and easier for melt-blow processing, including the manufacturing of high-efficiency structures made of fine fibers. Therefore, a modification of the outlet layer made of polymer was considered to improve the drainage. The fibers were coated with various metallic layers using the magnetron sputtering technique, which was proved to be suitable for thermally unstable polymers such as PP.

To verify the effect of treatment and obtain a qualitative measure of surface properties, the material wettability with the oil and the water was determined by measuring the static contact angle or kinetic of liquid transport at the capillary rise test. Moreover, the coating was analyzed using...

The experiments of the oil separation from water were carried out in a test tig, in which the emulsion was created by a single pass of injected oil through a centrifugal pump. Depending on the pump speed different size distribution of oil droplets was obtained (two pump speeds corresponding to 40% and 80% of the maximum were applied). The flow rate was controlled independently of the pump speed by throttling using the membrane valve, and was equal to 50, 100 and 200 L/h, while the oil concentration was set constant and equal to 2500 mg/L.

The results confirmed that ...