Photochemical removal of acetaldehyde using 172nm vacuum ultraviolet excimer lamp in N2 or air at atmospheric pressure.

Abstract

The photochemical removal of acetaldehyde was studied in N2 or air (O2 1-20%) at atmospheric pressure using side-on and head-on types of 172nm Xe2 excimer lamps. When CH3CHO was decomposed in N2 using the head-on lamp (HL), CH4, CO, and CO2 were observed as products in FTIR spectra. The initial removal rate of CH3CHO in N2 was ascertained as 0.37min-1. In air (1-20% O2), 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 18.6min-1 with decreasing O2 concentration from 20 to 1%. It also increased from 2.5 to 3.7min-1 with increasing CH3CHO concentration from 150 to 1000ppm at 20% O2. The best energy efficiency of the CH3CHO removal using the SL in a flow system was 2.8g/kWh at 1% O2. Results show that the contribution of O(1D) and O3 is insignificant in the initial decomposition of CH3CHO. It was inferred that CH3CHO is initially decomposed by the O(3P) + CH3CHO reaction at 5-20% O2, whereas the contribution of direct vacuum ultraviolet (VUV) photolysis increases concomitantly with decreasing O2 pressure at < 5% O2. After initial decomposition of CH3CHO, it was oxidized further by reactions of O(3P), OH, and O3 with various intermediates such as HCHO, HCOOH, and CO, leading to CO2 as a final product.