Experimental Research On The Demulsification And Separation Of Oil-Water Mixture With Super-hydrophobic Porous Plate

High-efficient separation of oil-water emulsion is of great significance and an important subject for resource recovery and environmental protection. With porous stainless steel plate as substrate, polytetrafluoroethylene (PTFE) and polyphenylene sulfite (PPS) as coating materials, the porous plate coating with super-hydrophobic membrane was prepared by a simple spraying-plasticizing method, and used for oil-water separation. The surface morphology and wettability was investigated by electron microscope and contact angle meter respectively. It is shown that, lots of microscale PTFE particles and nanoscale strip on these particles evenly distribute on the membrane surface and constitute the rough surface with micro-nano structure. The separation membrane shows a super-hydrophobic property, the contact angle for water on this membrane is 157.4°, and it also has strong adhesive force and wonderful chemical stability.The porous plate coating with super-hydrophobic membrane was installed in the separating unit to investigate its separation capacity for floating oil and dispersed oil. The results show that, the separation efficiency declines slightly with the increase of initial oil concentration and fewer separation stages, for the oil-water mixtures with the initial oil concentration of 5 g/L and 10 g/L, the residual oil concentration in the retentate water were both lower than 10 mg/L after a three-stage separation. Meanwhile, the influence of flow rate on separation effect for oil-water mixtures with initial oil concentration of 10 g/L was further investigated, it was found that when the quantity of flow is less than 20 L/h, the residual oil concentration in retentate water can be maintained at a low level, and the flow rate has little effect on the separation; but when the quantity of flow continues to increase, the residual oil concentration will show a sharp increase. Finally, the separation mechanism was briefly analyzed. Based on the wettability difference of oil and water on the super-hydrophobic surface, the oil droplet can penetrate through the separation membrane overcoming its own gravity, while the water can’t penetrate under the capillary resistance, so as to realize the separation of oil and water.Moreover, in the demulsification research, it can be found that, the flux increases with pressure, and tends to steady after the first decline with time. At the same time, effects of demulsification stages, flux and the size of emulsion droplets on the demulsification efficiency were also investigated respectively, we find the larger flux and the smaller size of emulsion droplets will lead to a poorer demulsification efficiency. Increasing the stages is an effective method to improve the demulsification efficiency, but an accompanying problem is the increasing of operating pressure. The demulsification mechanism of oil-water emulsions based on the membrane can be summarized into four processes, including deformation, adsorption, aggregation and breakaway. As the wetting and coalescence material of oil droplet, the demulsification membrane make the oil flow out of the hole channel slowly, while the water can flow out quickly, so as to achieve the purpose of demulsification.Based on the excellent effects of separation and demulsification, a further combined research on the emulsions separation was performed and delivered a high separation efficiency of 99%. This study could deliver an effective approach for the separation of oil-water emulsion and build up experimental experience for the technical innovation of oil-water separation.