3D printed porous contactors for enhanced oil droplet coalescence

The fabrication of 3D printed porous contactors based on triply periodic minimal surfaces (TPMS) is reported here for the first time. The structures, based on the Schwarz-P and Gyroid TPMS, were tested for oil-in-water demulsification via oil droplet coalescence and compared to a contactor with cylindrical pores and natural separation. The contactors were characterized in terms of intrinsic permeability, resistance and oil separation efficiency, for different oil concentrations (0.3, 0.4, 0.5 vol%) in the oil-in-water emulsion, vacuum pressures (10 and 20 mbar) and thickness of the contactors (4.68 and 9.36 mm). Results show that while the Gyroid contactor has the highest resistance and lowest intrinsic permeability of all three structures, it has 18% and 5% higher separation efficiency than the cylindrical and Schwarz-P structures, respectively. These characteristics reflect the higher tortuosity and surface area of the Gyroid structure compared to the other two. At 90%, the Gyroid structure also has a 22% higher separation efficiency and a two order of magnitude higher separation rate for the permeate compared to natural coalescence, attributed to an 8-fold increase in oil droplet diameter of the permeate compared to the feed, as a result of passage through the contactor. Higher vacuum pressure and higher contactor thickness further increase the separation efficiency of all structures, but the effect is more pronounced for the Gyroid structure due to its higher tortuosity. These results show that 3D printing is an effective tool for the design of porous contactors where a high surface area of interaction is key to their success, paving their way to extended use in a variety of industrial applications.