The Experimental Approach Of A Hydrophobic Membrane In The Demulsification Of Oil-Water Emulsions

The hydrophobic composite coating membrane was successfully prepared by multi-layer spraying and plasticizing method on the stainless steel mesh. The surfaces of prepared composite coating membrane were analyzed through scanning electron microscopy (SEM). It shows a three-dimensional and multi-layer fiber network structure on the surface. The maximum pore size of the membrane is less than10μm. This membrane also shows hydrophobic and oleophilic properities. Contact angle of this membrane is131.6°for water. The oil droplet is spreaded on the surface of this membrane once they meet.Preparation process and performance of hydrophobic composite coating membrane was studied. Effects of the membrane thickness and sintering time on wettability of this membrane and the maximum pressure that the membrane can endure were investigated. It is shown that contact angle of membrane increases slightly. And the maximum pressure that the membrane can endure increased with the increase of membrane thickness while have slight or almost no effect.The membrane can be applied to the separation of oil-water emulsions. The membrane was installed on the oil-water separator to test the demulsification performances for oil/water emulsions. Orthogonal test is carried out in order to investigate the effect degree of operating condition on demulsification. The membrane flux and oil content in permeated water were investigated. It shows that the lower pressure and thicker membrane have positive effect on demulsification, but negative effect on membrane flux. In the condition of thickness0.3mm or0.4mm, pressure difference80KPa, oil content in permeated water can be less than50mg/L. When the thickness is0.4mm, and pressure difference is40KPa, oil content in permeated water can be reduced to7.62mg/L. According to the above content, the pressure and thickness of membrane should be chosen carefully.The membrane was installed on the improved oil-water separator to text the demulsification performances for water/oil emulsions. Methods to determine water content in permeated oil by using Karl Fischer’s reagent. The membrane flux changes with the pressure, but the change is not very obvious. The experiments should be operated under low pressure difference. Once the pressure difference is too large, emulsions can permeate with sudden increased water. The membrane flux increases with increasing the flow velocity. The higher pressure difference and flow velocity, the higher water content in permeated oil. The water content in permeated oil can be reduced to140mg/kg, when initial concentration of the feed is50mg water/g oil. And the membrane has99%retention for water.A new concept "membrane fouling index" is proposed to investigate the degree of membrane fouling. It was found that small oil particles were adsorbed on the membrane surface at the early stage of membrane fouling, and the membrane fouling index decreases sharply. And then smaller oil particles were main adsorbed in membrane pore, the reduction of the membrane fouling index become gently. The membrane must be washed once the membrane fouling index decreases below0.4.