3D Printed Spacers Modulate Selectivity in Membrane-Less Electrochemical Separation of Ammonium and Urea

Systems that simultaneously optimize transport and reaction parameters are crucial for chemical process intensification. In this talk, we discuss recent progress towards additively manufactured materials that control flow in electrochemical systems with forced convection. For example, we demonstrate how 3D printed porous spacers can modulate selectivity in the membrane-less electrochemical separation of ammonium and urea by tuning the relative rates of transport via diffusion and electromigration in an undivided cell. The separation of ammonium and urea, important in wastewater treatment applications, relies on the electromigration of ammonium under an electric potential gradient, while the neutral urea molecule does not experience electromigration. In contrast to typical electrodialysis systems, which make use of ion-exchange membranes, the membrane-less system relies on the geometry of a 3D printed spacer to adjust the flow fields within the system to mitigate diffusion-driven crossover from a feed stream to a receiving stream. This approach has the potential to not only reduce the cost of these types of reactors by obviating the need for a membrane, which can degrade and foul over time, but also yield strategies for increasing selectivity in many systems, including those that do make use of membranes.<br/><br/>Finite element simulations of flow and electromigration were used to computationally screen spacer designs to select for those that showed promise for the separation of urea and ammonium. Spacers were 3D printed using epoxy dual-cure resins which are stable under the acidic and/or basic conditions that are present in many electrochemical separation processes. Separation efficiency was measured experimentally for several spacer designs in flow cells with and without membranes. Finally, we demonstrate the ability to metalize 3D printed spacers through electroless deposition of nickel metal, showing a path towards using 3D printed parts not just as flow-directing spacers, but as “flow directing electrodes” in a variety of electrochemical systems, leading to the ability to explore an extensive landscape of multifunctional device designs.