Abstract
Directional solvent extraction is one of the promising membrane-less seawater desalination method. This technique was not extensively investigated due the poor mixing and separation performances of its bench-scale system. It is believed that, overcoming these drawbacks is possible now with the rapid development of microfluidics technology that enabled high-precession micro mixing and separation. This work presents microfluidics chip for extracting and separating salt from seawater. The chip was designed with two sections for extraction and separation. In both sections, the liquids were separated using capillary channels perpendicular to the main stream. The main channels were designed to be 400 µm in width and 100 µm in height. Two streams inlets were introduced through a Y-junction containing octanoic acid as the organic phase and saltwater as the aqueous phase. The desalination performance was investigated at four different temperatures and five different solvent flow rates. Water product salinity was recorded to be as low as 0.056% (w/w) at 60 °C and 40 mL/h. A maximum water yield of 5.2% was achieved at 65 °C and 40 mL/h with a very low solvent residual (70 ppm). The chip mass transfer efficiency was recorded to be as high as 68% under similar conditions. The fabricated microfluidic desalination system showed a significant improvement in terms of water yield and separation efficiency over the conventional macroscale. The high performance of this microsystem resulted from its ability to achieve a high mixing efficiency and separate phases selectively and that will provide a good platform in the near future to develop small desalination kits for personal use.
Highlights
Microfluidics is a multidisciplinary technology which integrates several fields, including chemistry, biology, biotechnology, and medicine[8,9,10]
Gravitational forces are negligible in microfluidics, which makes a complete separation of two phases in a single step using surface forces possible[18]
Directional solvent extraction desalination method was briefly investigated in the past few decades as one of the promising membrane-less desalination techniques due to two major drawbacks
Summary
Microfluidics is a multidisciplinary technology which integrates several fields, including chemistry, biology, biotechnology, and medicine[8,9,10]. Microfluidics devices have shown a remarkable performance in specific phase separation[25,26]. In a study conducted by Castell and coworkers, microfluidics system for separating two immiscible liquids (chloroform and water) yielded an outstanding performance with 100% separation efficiency. According to their findings, the capillary section used to separate the liquids utilized the differences in the two phases wettability due to the advantage of miniaturized systems where the surface and intermolecular forces dominated. The present work introduces the first microfluidic system for directional solvent extraction desalination of saltwater with capillary separations. These capillaries selectively separated the two phases based on their hydrophobicity–hydrophilicity nature
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