Biogas use in high temperature fuel cells: Enhancement of KOH-KI activated carbon performance toward H2S removal

Activated carbons (ACs) treated with KOH-KI are very effective sorbents for deep H₂S removal, as required by biogas use in high temperature fuel cell systems. For this application, the performance of a commercial KOH-KI treated AC was investigated through a systematic study based on dynamic adsorption tests. With reference to the composition of a real biogas produced in a wastewater treatment plant located in Barcelona, the present work presents a sensitivity performance analysis on singular and synergetic effects of gas matrix, humidity and oxygen on AC KOH-KI performance.The results revealed a positive role of water (up to 90% of relative humidity (R.H.)) for different gas matrices, enhanced by the simultaneous presence of small percentages of oxygen (2%_v). A relevant influence of gas matrix composition was found (except for the case of oxygen addition to dry inlet streams), specifically in terms of a marked negative effect of CO₂ and a significant sorption capacity increase for high percentage of methane. Sulfur dioxide was not detected in the outlet gas-phase for the investigated operating parameters (O₂ 2%_v, R.H. 0–90%, H₂S 100 ppm_v, temperature 45 °C). Therefore, even in the case of further oxidation of adsorbed elemental sulfur to SO₂, this product could be completely removed by AC KOH-KI.