Demulsification Effect And Mechanism Of O/W Emulsion Under Electric Field

Oil in water(O/W)emulsion has a wide range of sources and its property of physical chemistry is stable.If emulsion is allowed to discharge at will,it will waste resources,destroy the environment and endanger human health.Therefore,it is of great significance to deal with them effectively.Among many treatment methods,electric demulsification has attracted increasing attention for its simple structure,easy operation,environment-friendly and low cost.In this thesis,the effect and mechanism of O/W emulsion demulsification in electric field were studied in static and dynamic experiments.In the static experiment,the demulsification mechanism and characteristics of O/W emulsion were revealed with investigating the stratification,current change,and oil content and oil droplet diameter distribution of water layer after demulsification.At the same time,the reasonable operating condition parameters were determined.In the dynamic experiment,the effect of voltage,the spacing of the baffle plates and velocity on the demulsification of the emulsion was mainly investigated.The results of static experiment show that the demulsification process of dilute O/W emulsion is divided into three stages: water layer formation,re-emulsification with transverse diffusion and uplift-stabilization.There was a critical current density in the electro-demulsification of dilute O/W emulsion.When the current density through the emulsion was less than the critical current density,demulsification will not occur or stop.Some evidences confirmed that O/W emulsion system with surfactant produces a surface tension gradient in the height direction during the stratification process.The critical current together with the surface tension gradient caused different demulsification processes and current variation for emulsions with different additive.The change of oil content of water layer after demulsification coincided with the collision result of two droplets,and the minimum oil content was 60mg/L.The oil droplet diameter distribution of water layer after demulsification was less influenced by the voltage,and the diameter of the oil droplets was generally less than 7?mThe simulation results of a dynamic experimental device show that the maximum velocity appeared in the middle,and the velocity at the liquid level was minimal.The smaller the spacing of the baffle plate and the larger the flow was,the smaller the dead area was.At the same time,the high-speed area of the fluid flow was mainly on the right side of the flow direction.In dynamic electric demulsification experiments,the demulsification rate of the emulsion was more than 0.97,and the demulsification rate was only 0.33 for the experiment without voltage.Under flow condition,electric demulsification effect of emulsion had been strengthened,and the coalescence of small oil droplets was promoted.