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

Tsuji, Masaharu, Miyano, Masato, Kamo, Naohiro, Kawahara, Takashi, Uto, Keiko, Hayashi, Jun-ichiro, Tsuji, Takeshi
Environmental science and pollution research international 2019 v.26 no.11 pp. 11314-11325
Fourier transform infrared spectroscopy, acetaldehyde, air, atmospheric pressure, carbon dioxide, carbon monoxide, energy efficiency, formaldehyde, formic acid, lamps, methane, nitrogen, oxygen, ozone, photolysis
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.