Non-thermal plasma treatment for the elimination of odorous compounds from exhaust air from cooking processes

Abstract

Non-thermal plasma technique can be a method to improve indoor air quality. In particular in cuisines, odorous emissions can be removed by non-thermal plasmas. In this study 2-methylthiophene, 2-methylpyrazine, 2-acetylthiazole, nonanal and trans-2-nonenal were used as target compounds in concentrations in the low ppmv range. These odorous compounds are emitted during cooking and frying processes. The oxidation of these target compounds as multi-component mixture in a non-thermal gas-phase plasma was studied in dry mixtures of argon and oxygen and in humid air. Complete oxidation of the odorous compounds to COX was achieved in both atmospheres. The energy efficiency was higher in the dry mixture of argon and oxygen, whereas the selectivity of the oxidation towards carbon dioxide was significantly higher in humid air. The main products of plasma treatment were identified as CO, CO2 and polymeric deposits. Some minor organic intermediates in the pptv range were also identified. Although odor carriers could be completely degraded and the concentrations of potentially harmful organic byproducts were several orders of magnitude below critical values, high ozone and CO emissions during plasma operation are critical for indoor application of non-thermal plasma as stand-alone technique. The combination with a catalytic step, either as in-plasma or post-plasma catalysis, might be a promising approach to tackle this problem.