Kinetic analysis of the photochemical decomposition of gas-phase chlorobenzene in a UV reactor: Quantum yield and photonic efficiency

The destruction of a chlorinated aromatic compound by UV photolysis and advanced oxidation was examined for potential use in air emissions treatment. The fluence rate distribution in a photoreactor was analyzed by a finite model, and this was used to estimate quantum yield and photonic efficiency for the photochemical decomposition of chlorobenzene in air. The analysis indicates that the quantum yield was constant at approximately 115%, but the presence of the common flue gas components sulfur dioxide and water could increase it to approximately 145%. Ozone, which strongly absorbs UV photons and promotes radical chain reactions, enhanced the quantum yield to 1534% when present at 2253 ppm. When SO2 or ozone are present, “effective” quantum yield may be more informative for analysis, since it includes the number of photons absorbed by all reacting species. In this work, the effective QY ranged from 3.9% to 108.7%, with low values indicating that photons were wasted in processes that did not degrade the target organic. An analysis of photonic efficiency shows that the photo-reactor is more efficient at high concentrations of the target organic pollutant, and when ozone or sulfur dioxide are present.

• UV photolysis of chlorobenzene in air occurs with a 115% quantum efficiency. • The presence of SO2 and water increases quantum efficiency to 145%. • High ozone concentrations increased quantum efficiency to 1541%. • The photoreactor photonic efficiency was improved by SO2 and ozone.