Arrow-shaped patterned microchannel for enhancing droplet coalescence and demulsification of oil-in-water emulsions with high oil content

The direct discharge of industrial emulsified wastewater critically threatens the environment and human health. Emulsified wastewater must be demulsified before discharge. Inspired by the applications of microchannels in oil-in-water (O/W) emulsion separation and patterned wettable surfaces to manipulate droplet formation, an arrow-shaped patterned microchannel (APM) was designed to enhance the droplet coalescence and demulsification of O/W emulsions with high oil content. The APM demulsification efficiency with 15 arrows of 5 patterns attained 70 % within 4.5 s when handling the O/W emulsion of 40 % (v/v) oil content. The experimental and simulation results revealed that the arrow-shaped patterns provided a series of inducing effects for dispersed droplets, enabling the coalesced droplets to form "oil-droplet-string flows". These positive inductions improved the efficiency of droplet coalescence and phase separation, thereby markedly enhancing the demulsification effect. By introducing the arrow-shaped wettable patterns, APM achieves the highest single demulsification efficiency of 70 % known at present for surfactant stabilized O/W emulsion with high oil content. This study provides a new technical approach for the treatment of industrial emulsified wastewater with high oil content.