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

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.