Study on selective hydrogen sulfide removal over carbon dioxide by catalytic oxidative absorption method with chelated iron as the catalyst

• Selective desulfurization can be achieved by catalytic oxidative absorption method.
• High concentration of chelated iron is desired for the selective desulfurization.
• The optimum EDTA-Fe concentration for selective desulfurization is 0.084 M.
• pH at 7.8 and G/L ratio of 55 are the optimized selective H2S removal conditions.

H2S is a detrimental impurity that must be removed for upgrading biogas to biomethane. H2S removal selectivity over CO2 employing catalytic oxidative absorption method and its influence factors were studied in this work. The desulfurization experiments were performed in a laboratory apparatus using EDTA-Fe as the catalyst and metered mixture of 60% (v/v) CH4, 33% (v/v) CO2 and 2000–3000 ppmv H2S balanced by N2 as the simulated biogas. It was found that for a given catalytic oxidative desulfurization system, it exists a critical pH, at which desulfurization selectivity achieves the highest. It was also observed that desulfurization selectivity increased along with the increase of chelated iron concentration, gas flow rate, and ratio of gas flow rate to liquid flow rate (G/L). This demonstrated that high selectivity and high efficiency for biogas desulfurization could both be achieved through optimizing these parameters. Specific to the desulfurization system of this work, when the gas flow rate was set as 1.1 L/min, after optimizing the above mentioned parameters, i.e. EDTA-Fe concentration of 0.084 mol/L, absorption solution pH of 7.8, and G/L of 55, the desulfurization selectivity factor reached 142.1 with H2S removal efficiency attained 96.7%.