Mathematical modeling and mechanism of VUV photodegradation of H₂S in the Absence of O₂

The existence of H₂S has limited the biogas energy promotion. The traditional photodegradation of H₂S is usually conducted in the presence of O₂, yet this is unsuitable for biogas desulfurization which should be avoided. Therefore, the ultraviolet degradation of H₂S in the absence of O₂ was investigated for the first time in the present study from a mathematical point of view. Light wavelength and intensity applied were 185 nm and 2.16 × 10^-12 Einstein/cm²·s, respectively. Firstly, the mathematical model of H₂S photodegradation was established with MATLAB software, including the gas flow distribution model and radiation model of photoreactor, kinetics model, mass balance model, and calculation model of the degradation rate. Then, the influence of the initial H₂S concentration and gas retention time on the photodegradation rate were studied, for verification of the mathematical model. Results indicated that the photodegradation rate decreased with the increase in initial H₂S concentration, and the maximum photodegradation rate reached 62.8% under initial concentration of 3 mg/m³. In addition, the photodegradation rate of H₂S increased with the increase in retention time. The experimental results were in good accordance with the modeling results, indicating the feasibility of the mathematical model to simulate the photodegradation of H₂S. Finally, the intermediate products were simulated and results showed that the main photodegradation products were found to be H₂ and elemental S, and concentrations of the two main products were close and agreed well with the reaction stoichiometric coefficients. Moreover, the concentration of free radicals of H• and SH• was rather low.