Removal of cyclohexanone in transition electric discharges atatmospheric pressure

Abstract

Two new types of streamer-induced electric discharges operating in anon-uniform electric field in air at atmospheric pressure were applied to theremoval of volatile organic compounds (VOCs). The first type is a pulseless dc discharge with physicalproperties corresponding to the glow discharge. The second, also supplied by adc high voltage of both polarities, is a spontaneously pulsing dischargeoperating in the regime of the streamer-to-spark transition, the spark phasebeing too short to reach local thermodynamic equilibrium conditions. Bothdischarges are able to generate a non-thermal plasma, as resolved from theirrotational and vibrational temperatures.The influences of these discharges on the removal of cyclohexanone at variousgas flow rates and concentrations (600-6000 ppm) were compared. The removalefficiencies achieved were about 50-60%, and the energy costs were16-100 eV/molecule at various energy densities. Special conditions whereCO2 and other gaseous products are minor and dominant products appear inthe condensed phase can be obtained, especially in the spontaneously pulsingtransition discharge.We explain some plasmochemical processes induced by the discharges byconsidering heterogeneous effects of the copper electrode surface. The role ofactive nitrogen and the formation of the NCO radical are probably key factorsleading to the formation of the condensation product based on amino acids,here produced for the first time from VOCs, as well as in the overall energycycle resulting in low energy costs of the process.The small pilot-scale reactor based on the spontaneously pulsing transitiondischarge has been successfully applied to the removal of cyclohexanone in themixture with other VOCs with no noxious gas output. This validates thepossibility of the application of such a type of reactor for larger scales.