Photochemical removal of acetaldehyde using 172 nm 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 172 nm 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 0.37 min⁻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 18.6 min⁻¹ with decreasing O₂ 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% O₂. The best energy efficiency of the CH₃CHO removal using the SL in a flow system was 2.8 g/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.