Abstract
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.
Highlights
During anaerobic digestion which is considered as one of the most important biomass-based renewable energy techniques to reclaim clean fuel of biogas [1], hydrogen sulfide (H2S) is produced in addition to CH4 and CO2, with content of 0.3%–0.4% [2]
In order to investigate the degradation efficiency of H2S with only the high-frequency electrodeless vacuum ultraviolet (VUV) lamp without addition of O3, OH, and photocatalyst, the reactor was firstly dried, and Ar was flushed into the reactor with a 10 L/min flow rate for an hour to expel the residual O2 and H2O in the pipeline
As the diameter of the reactor and the UV lamp were 15 cm and 4 cm, respectively, the rate of the gas flow was calculated as 20–40 L/min when the retention time was set as 3–6 s
Summary
During anaerobic digestion which is considered as one of the most important biomass-based renewable energy techniques to reclaim clean fuel of biogas [1], hydrogen sulfide (H2S) is produced in addition to CH4 and CO2, with content of 0.3%–0.4% [2]. When the biogas containing H2S is utilized as energy (such as burning, power generation, etc.), H2S will be converted into SO2 and cause serious air pollution [3]. H2S treatment methods include physical, chemical, biological, and combinatorial technologies. The direct degradation of H2S for production of hydrogen and sulfur has been the research focus of domestic and foreign researchers, since it can effectively control the H2S pollution produced during oil, gas, coal, and mineral processing and achieve the recycling of hydrogen energy. The main methods of H2S degradation for hydrogen and sulfur production include thermal degradation [4, 5], electrochemical degradation [6], photocatalytic degradation [7,8,9], and plasma degradation [10, 11]. Photocatalytic degradation of H2S is the most promising technology due to the high treatment efficiency and reaction rate
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