Insights on the Mechanisms of H₂S Retention at Low Concentration on Impregnated Carbons

Adsorption of H₂S onto porous materials is as an attractive technology for fine biogas cleaning. Three activated carbon samples were studied as adsorbents for biogas desulfurization at low concentration (100 ppm), in order to better understand the underlying mechanisms and provide a basis for the development of new materials. One of the carbons is impregnated with NaOH, another with Fe₂O₃ and the third one is the parent material. Molecular simulation was performed to distinguish the retention mechanism. Textural characterization revealed high surface areas and the existence of ultramicropores with sizes below 4 Å in all samples. The possibility of discriminating the retention regimes emphasized the great influence of the chemisorption in these systems increasing up to 50 times the capacity of retention of H₂S for the sodium-impregnated sample (from 0.3 to 15.64 mg g^–1). Surprisingly, both physisorption and chemisorption could be unequivocally detected for the nonimpregnated sample by evaluating breakthrough curves in different temperatures (up to 423 K). The evaluation of regeneration by heat indicated that the adsorbents can recover about 50% and 20% of their initial capacity for nonimpregnated and impregnated samples, respectively.