Photochemical degradation of acrolein using VUV excimer lamp in air at atmospheric pressure

Abstract

The photochemical degradation of acrolein (C2H3CHO) was investigated in air at atmospheric pressure using a 172-nm Xe2 excimer lamp. When C2H3CHO was decomposed using the side-on type of lamp, HCOOH, CO, CO2, and O3 peaks were observed in FTIR absorption spectra. The dependence of product concentrations on the irradiation time indicated that HCOOH and CO intermediates are finally converted to CO2 via consecutive reactions. The degradation rate coefficient of C2H3CHO in the batch system increased from 8.4 to 19.3 min−1, as the O2 concentration was decreased from 20 to 1%. It increased also from 8.4 to 40.1 min−1 at 20% O2, as the chamber depth was decreased from 3.0 to 0.5 cm. The best energy efficiency of the C2H3CHO degradation was 3.4 g kW−1 h−1 at 1–20% O2 in a flow system. Besides direct VUV photodissociation of C2H3CHO, reactions of O(3P,1D) and O3, produced from photolysis of O2, can contribute to C2H3CHO degradation in the initial stage. Among them, the contribution of O(1D) and O3 was found to be insignificant on the basis of the total pressure dependence of removal amount of C2H3CHO and results obtained from the O3 + C2H3CHO reaction. It was concluded that at first C2H3CHO is decomposed by direct VUV photodissociation of C2H3CHO and the O(3P) + C2H3CHO reaction. It was further decomposed by secondary reactions of O(3P), OH, and O3 with such intermediates as HCOOH and CO and finally oxidized to CO2.