Abstract
Asymmetric plate-type micro-channels (APM) have one hydrophobic wall and one hydrophilic wall. By flowing through APM, a kerosene-in-water emulsion can be de-emulsified in one second. To date, however, the demulsification process in the APM is still a black box. In order to observe the demulsification process directly, transparent asymmetric plate-type micro-channels (TAPM) were fabricated with two surface-modified glass plates. Emulsions with oil contents of 10%, 30%, and 50% were pumped through TAPM with heights of 39.2 μm and 159.5 μm. The movement and coalescence of oil droplets (the dispersed phase of a kerosene-in-water emulsion) in the TAPM were observed directly with an optical microscope. By analyzing videos and photographs, it was found that the demulsification process included three steps: oil droplets flowed against and were adsorbed on the hydrophobic wall, then oil droplets coalesced to form larger droplets, whereupon the oil phase was separated. The experimental results showed that the demulsification efficiency was approximately proportional to the oil content (30–50%) of the emulsions and increased when the micro-channel height was reduced.
Highlights
Since the 1990s, studies on micro-fluid systems have gradually increased in popularity and micro-channels have drawn worldwide attention due to their unique flow pattern, high surface area and process intensification [1,2,3]
With a residence time of less than 0.01 s, almost 100% demulsification efficiency was achieved by the micro-channels
These results showed that factors of higher oil-to-water ratio, larger droplet size and smaller micro-channel depth contributed to demulsification efficiency with micro-channels, and were in accordance with the previous result [14]
Summary
Since the 1990s, studies on micro-fluid systems have gradually increased in popularity and micro-channels have drawn worldwide attention due to their unique flow pattern, high surface area and process intensification [1,2,3]. Two main structural types of micro-channels have been applied in demulsification: linear micro-channels [12,13,14,15] and arc or spiral micro-channels [16]. Asymmetric linear micro-channels [12,13,14,15,16] have been utilized to de-emulsify oil-in-water emulsions since 2004. Okubo et al [12] used linear glass-polytetrafluoroethylene (PTFE) micro-channels with a height of 5–12 μm to de-emulsify octanoldodecanese in water emulsions with a median droplet diameter (D50) of 60 μm. With a residence time of less than 0.01 s, almost 100% demulsification efficiency was achieved by the micro-channels. Droplets of emulsions through the micro-channel were directly observed with a Leica DM2500 optical microscope. The demulsification efficiency of emulsions with different oil content was investigated
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