Adsorption of hydrogen sulfide (H2S) on zeolite (Z): Retention mechanism

• Physicochemical characterization of Z was performed before and after H2S adsorption.
• Water is present in Z pores and pH promotes H2S dissociation in HS−.
• After H2S adsorption, the adsorbate degraded between 300 and 630 °C in inert atmosphere.
• After H2S adsorption, the adsorbate could oxidize around 355 °C in air atmosphere.
• An adsorption–dissociation–oxidation mechanism led to the formation of elemental sulfur.

Zeolites are efficient adsorbents for the removal of hydrogen sulfide (H2S) – a trace compound commonly found in biogas. The assessment of zeolite regeneration potential is an important point to consider before using them in adsorption processes for biogas treatment. In this study, it was first shown that after adsorption of H2S, by heating a 13X zeolite at 350 °C, the desorbed quantities of sulfur compounds were very low. Afterwards, the objective was to understand H2S removal mechanism. Complementary physicochemical characterizations of the studied zeolite before and after H2S adsorption were performed: specific surface area, porosity, pH, infrared spectroscopy, thermogravimetry and differential scanning calorimetry. The speciation of sulfur in the studied zeolite after H2S adsorption was investigated and a retention mechanism was proposed. It was demonstrated that H2S was converted in elemental sulfur in the zeolite. This mechanism involves H2S adsorption at the zeolite surface, dissolution and dissociation of H2S in pore water, and oxidation to form elemental sulfur that can polymerize. The major formation of elemental sulfur limits the thermal regeneration of the studied zeolite and other regeneration methods should be considered.

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