Desulfurization of ultra-low-concentration H2S in natural gas on Cu-impregnated activated carbon: Characteristics and mechanisms

Characteristics and mechanisms of low-concentration H2S (4.5 ppmv) removal in balanced CH4 were investigated for Cu-impregnated activated carbon (Cu/AC). Herein, breakthrough experiments and analysis of the changes in the state of Cu and sulfur species on Cu/AC during a cyclic experiment comprising desulfurization, regeneration, and re-desulfurization were conducted. During desulfurization, catalytic oxidation, sulfate formation, and reactive adsorption resulted in the formation of elemental sulfur, CuSO4, and CuS, respectively. CuO acted as the catalyst, oxygen donor, and reactive adsorption site for the reaction. At 303 K, the low- concentration H2S was removed mainly through catalytic oxidation and sulfate formation. As the temperature was increased to 333 K, reactive adsorption and sulfate formation were promoted. The reactive adsorption was crucial for the complete removal of low-concentration H2S. The deposited sulfur was removed via vaporization, dissociation, and oxidation. The oxidative treatment using a dilute O2 mixture resulted in the effective removal of the thermally stable sulfur species and active regeneration of CuO. Furthermore, oxidative regeneration contributed to the high dispersion of CuO and enhanced the reactive adsorption. During desulfurization and regeneration, CuSO4 was formed by consuming oxygen species, which necessitates the use of an effective removal method for ensuring the reusability of adsorbents.