Abstract
Rapid and efficient demulsification (destabilizing of an emulsion) processes of a water in oil (W/O) emulsion were carried out in a three-dimensional electric spiral plate-type microchannel (3D-ESPM). In this experiment, the demulsifying efficiency of emulsions by 3D-ESPM was compared with that by gravity settling, the factors influencing demulsifying efficiency were investigated, and the induction period, cut size and residence time in the demulsification process were studied. The results showed that in contrast to the gravity settling method, 3D-ESPM can directly separate the disperse phase (water) instead of the continuous phase (oil). The maximum demulsifying efficiency of W/O emulsion in a single pass through the 3D-ESPM reached 90.3%, with a microchannel height of 200 μm, electric field intensity of 250 V /cm, microchannel angle of 180°, microchannel with 18 plates and a flow rate of 2 mL /min. An induction period of 0.6 s during the demulsification process was simulated with experimental data fitting. When the residence time of emulsion in 3D-ESPM was longer than the induction period, its demulsifying efficiency increased as the increase of the flow velocity due to the droplet coalescence effects of Dean vortices in the spiral microchannel. For this device a cut size of droplets of 4.5 μm was deduced. Our results showed that the demulsification process of W/O emulsion was intensified by 3D-ESPM based on the coupling effect between electric field-induced droplets migration and microfluidic hydrodynamic trapping.
Highlights
Emulsions are widely used and play a vital role in industrial processes, agricultural industry and daily life
The results revealed that the dual coupling of this direct current (DC) electric field and spiral microchannel within the 3D-ESPM can demulsify the water in kerosene emulsions with high efficiency
Xiao Chen designed and manufactured a plate-type PTFE-SS microchannel to achieve the continuous demulsification for kerosene in water emulsions with emulsifier, and the demulsification process was repeated 5 to 20 times, and its demulsification efficiency can be up to 90% [19]
Summary
Emulsions are widely used and play a vital role in industrial processes, agricultural industry and daily life. The results revealed that the dual coupling of this DC electric field and spiral microchannel within the 3D-ESPM can demulsify the water in kerosene emulsions with high efficiency. The 3D-ESPM employs a special spiral inner microstructure and a DC electric field at the same time, and shows an efficient demulsification action on W/O emulsions [16]; the demulsifying process and the mechanism still deserve to be studied especially, how the induction period. Under the Dean-coupled inertial migration principle from the spiral microchannel [37,38] and the electrostatic forces from the DC electric field [39], different particle sizes resulting in different movement speeds, the droplets are after the gravity settling, the water droplets were still stable and not broken into a continuous phase. Effect of the plate number of 3D-ESPM and the flow rate of W/O emulsion on demulsifying efficiency were studied under the condition of a microchannel height of 200 μm, arc radian of 180◦ and
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