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

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