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

摘要

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 CH3CHO was decomposed in N-2 using the head-on lamp (HL), CH4, CO, and CO2 were observed as products in FTIR spectra. The initial removal rate of CH3CHO in N-2 was ascertained as 0.37 min(-1). In air (1-20% O-2), HCHO, HCOOH, CO, and CO2 were observed as products in FTIR spectra. The removal rate of CH3CHO 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 CH3CHO concentration from 150 to 1000 ppm at 20% O-2. The best energy efficiency of the CH3CHO removal using the SL in a flow system was 2.8 g/kWh at 1% O-2. Results show that the contribution of O(D-1) and O-3 is insignificant in the initial decomposition of CH3CHO. It was inferred that CH3CHO is initially decomposed by the O(P-3) + CH3CHO 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 CH3CHO, it was oxidized further by reactions of O(P-3), OH, and O-3 with various intermediates such as HCHO, HCOOH, and CO, leading to CO2 as a final product.