(359c) The Direct Activation of Targeted Partial Oxidation Reactions in Liquid Phase Via Enhanced Corona Discharge Techniques From Nanofibrous Emitter Electrodes in Microreactor Channels

In this study, the application of carbon nanotubes, grown with randomly dispersed diameters ranging from 10 to 50 nanometers, has been extended to the microscale for liquid phase corona discharge. Metal nanowires and nanotubes have also been examined. While the length scale of the diameter of the nanostructures are hardly on the atomic scale as at the tips of most of the atomically-sharp metal emitters, the material properties of the carbon nanotube emitters is a relativistic playground for electrons and have displayed durability up to 100 h in corona discharge process. A surface covered with a forest of the nanofibrous emitter electrodes activates a larger portion of the fluid than did the single atomically fine metal tips. The application of these discharge processes to the microscale invokes the typical improvements in heat and mass transfer to cool the anode (where the majority of the heat dissipation occurs), the ability to activate these reactions at extremely low electric potentials, and effectively transfer reactive species into the fluid. Flow through systems use forced convection to cool the anode emitter which allows nearer separations. The carbon nanotube allows the turn-on electric potential to be reduced. These enhancements have grand implications for phenomena such as frothy electric discharge which occurs in conducting aqueous fluids and for dc corona discharge in gas phase. The energy requirements of which have been reduced by several orders of magnitude (typical reports list 150 mA at 900 V and hour scale treatment times depending on whether the study is examining glow discharge electrolysis or arc discharge-this study reports 6 mA at almost any desired electric potential (depends on the distance of the carbon nanotube covered wire to the pin and material constraints) and minute scale residence times for similar degradation ratios). This is the first attempt in literature to take nanostructured emitters down to microscale dimensions for liquid phase corona discharge reaction engineering to the author’s knowledge.

The target reaction is the oxidative destruction of organics in groundwater with phenol being the example organic. The advantages of the corona discharges at low turn-on electric field strengths will be discussed with respect to the sanitization of groundwater. The ability to operate at 50 V rather than 10 kV at the same current density as at the macroscale is powerfully important both when considering the simplicity of the required pulsing technology, effectiveness of the corona process and reactor design. This improvement is made viable by understanding the corona discharge mechanism, microreactor technology and enhanced nanofibrous electrodes. The application of microscale reaction engineering technology and the nanofibrous emitter electrode corona discharge process to aqueous systems will have remarkable implications in every area of the chemical industry. Purifications, reaction chemistry and separations can be accomplished using the enabling techniques developed during this study to achieve energy savings two orders of magnitude greater than currently available world-wide for electric discharge technologies.