(689a) Potential-Controlled Chromatography - a New Separation Method Based on Carbon Nanotubes

Separation and recovery of valuable organic products from wastewater or bio-broth is one of today's industrial challenges. An innovative expansion of common separation technologies is preparative potential-controlled chromatography, which combines the advantages of ion-exchange chromatography and capacitive deionization. The working principle of this versatile and cost-effective method is based on the system-specific formation of the electrochemical double layer, which triggers the adsorption and desorption process of various charged or polarized target species from aqueous systems to the charged electrode surface. To gain a multi-variant process description and optimize a recently developed potential-controlled chromatographic system using multi-walled carbon nanotubes as an electrode matrix, we investigate the interfacial effects on nano- and macroscale for aqueous systems. Therefore, we analyzed the influence of the electrode structure, the material and target species' properties, the attractive forces of the target species on the surface, and the environment's properties on the electrode performance.

We determined a distinct influence of the flow rate and the mobile phase media on the current response and the adsorption capacity of the macroporous electrode. With increasing attraction forces and higher electrolyte conductivity, capacitive and faradaic current increases. The electrolyte composition, the ion number and properties, affect the rearrangement time of the electrochemical double layer and can advantage the electrode's electric charge with increasing electrolyte concentration and higher ion charge density. A lower flow rate promotes the target-surface interactions and increases the column capacity. In contrast, a faster one benefits the desorption process diminishing mass transfer limitations. When DI-water is used as primary mobile phase media, the surface character of the electrode material is highlighted, observing a strong interference to the mobile phase protonation balance when the electrode works as a cathode. This effect can be disadvantageous for processing pH-sensitive proteins but can be compensated using buffers simultaneously increasing the column's total electric charge.

Based on these findings, we optimized the separation of maleic acid from aqueous solutions highlighting that the optimal column performance is always a trade-off of various process-operating parameters.