Photochemical removal of acetaldehyde using 172 nm vacuum ultraviolet excimer lamp in N 2 or air at atmospheric pressure

The photochemical removal of acetaldehyde was studied in N 2 or air (O 2 1–20%) at atmospheric pressure using side-on and head-on types of 172 nm Xe 2 excimer lamps. When CH 3 CHO was decomposed in N 2 using the head-on lamp (HL), CH 4 , CO, and CO 2 were observed as products in FTIR spectra. The initial removal rate of CH 3 CHO in N 2 was ascertained as 0.37 min −1 . In air (1–20% O 2 ), HCHO, HCOOH, CO, and CO 2 were observed as products in FTIR spectra. The removal rate of CH 3 CHO in air using the side-on lamp (SL) increased from 3.2 to 18.6 min −1 with decreasing O 2 concentration from 20 to 1%. It also increased from 2.5 to 3.7 min −1 with increasing CH 3 CHO concentration from 150 to 1000 ppm at 20% O 2 . The best energy efficiency of the CH 3 CHO removal using the SL in a flow system was 2.8 g/kWh at 1% O 2 . Results show that the contribution of O( 1 D) and O 3 is insignificant in the initial decomposition of CH 3 CHO. It was inferred that CH 3 CHO is initially decomposed by the O( 3 P) + CH 3 CHO reaction at 5–20% O 2 , whereas the contribution of direct vacuum ultraviolet (VUV) photolysis increases concomitantly with decreasing O 2 pressure at < 5% O 2 . After initial decomposition of CH 3 CHO, it was oxidized further by reactions of O( 3 P), OH, and O 3 with various intermediates such as HCHO, HCOOH, and CO, leading to CO 2 as a final product.