High Efficiency Chemical Synthesis Using Pulsed Plasma Gliding Arc Reactors with Water Spray

Pulsed plasma gliding arc reactors utilizing liquid spray have been demonstrated to lead to very high efficiency production of hydrogen peroxide from water with argon carrier gases, nitrates from water with air carrier gases, and molecular hydrogen from organic liquids, e.g. methanol, using argon carrier gases.  A gliding arc electrical discharge plasma is generated using two knife-edge electrodes separated by a small gap distance.  The carrier gas (2 lpm) containing micrometer size liquid droplets (20 ml/min) flows between the electrodes where a pulse forming circuit delivers relatively low power in the range 200 – 300 mW.   In the case of hydrogen peroxide generation, an energy yield of approximately 80 g/kwh has been obtained and this is close to 25% of the thermodynamic limits.  Survey of all plasma processes that have been reported to generate hydrogen peroxide show this method to be highly competitive.  This method has a major advantage over other chemical methods because only pure water and carrier gas are required in the feed.  The generation of nitrates from air is also potentially useful for fertilizer and disinfection processes.  The high solubility of products such as hydrogen peroxide and nitrate in the liquid droplets leads to rapid transfer of the plasma-formed products into the liquid phase, whereby they are protected from plasma degradation reactions and where they accumulate in significant amounts.  The water droplets also provide a significant source of the needed water reactant into the plasma.  The relatively low plasma and thermal reactor temperatures dramatically enhance the efficiency for generation of these species.  In the case of hydrogen generation from organic liquids, high efficiency, energy yields, have been demonstrated.  In all cases, the small liquid droplets lead to high efficiency due to rapid rates of mass transfer and large surface area contact with the surrounding plasma and gas phase.  Such plasma reactors have significant potential for high efficiency chemical synthesis in gas-liquid environments.