Oddelenie environmentálnej fyziky - Prihlásený: igor
Katedra astronómie, fyziky Zeme a meteorológie, FMFI UK, Bratislava,

Treatment of HCHO Using Corona Discharge and Pellet Catalysts

Hensel K., Pawłat J., Takashima K., Mizuno A.
30th IEEE International Conference on Plasma Science ICOPS 2003, Cheju (Korea), June 2-5, 276 (2003)

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Abstrakt:

Possibilities of formaldehyde (HCHO) treatment in dry airand nitrogen using discharge plasma of streamer coronadischarge was investigated and its treatment efficiency invarious conditions was evaluated. The effect of combination ofplasma and pellet catalysts for formaldehyde treatment wasexamined too.The reactor of multi-point-to-mesh geometry was used.The distance between electrodes was 16 mm. Initial concentrationof formaldehyde was 200 - 1000 ppm in dry air ornitrogen, and the gas flow was 0.25, 0.5 or 1.0 lpm. The analysisof gas composition was performed by FTIR and UV-VISspectrometry.Formaldehyde treatment efficiency of more than 80% usingdischarge only was obtained. The efficiency was better forsmaller initial concentrations of formaldehyde and smaller gasflow rates, although decrease of gas flow especially resulted inrapid increase of energy consumption. Formaldehyde decompositionresulted in formation of CO and HCOOH. The formationof CO occurs most probably by photolytic reactionse.g. HCHO+hν -> CO+H2. In air CO can be formed alsovia HCHO+hν -> H+HCO followed by HCO+O2 ->CO+HO2.Oxygen also supports formaldehyde oxidation to formic acidby HCHO+O -> HCOOH. On contrary, a reaction with ozoneappeared not to be effective. Due to existing oxidation processHCHO treatment is better in dry air, however also producesmore CO2, NO2 and N2O compared with nitrogen mixtures.Transformation of streamer into spark resulted in decrease ofHCHO treatment and CO production and increase of CO2 andNO2 productions.Combined effect of catalyst and plasma was investigatedtoo. An 8 mm thick layer of catalytic pellets of various materials(TiO2, Pt/Al2O3, MnO2, NaY, molecular sieves) wasplaced on the mesh electrode. At small discharge power thetreatment efficiency was relatively small due to desorption offormaldehyde adsorbed by pellets before application of thedischarge. Treatment efficiency however rapidly increasedwith discharge power as removal of formaldehyde dominatedits desorption. Increase of formaldehyde concentration, however,can also be attributed to interaction of the dischargewith pellets and or formaldehyde generation from methanoland formic acid. A combination of plasma and catalystsindicated surface process plays important role and affectsformaldehyde decomposition.