N-Doped Biochar as H2s Adsorbent for the Biogas-Fueled SOFC

Abstract

The reliability of a biogas-fueled SOFC depends directly on the purity of the biogas. To prevent performance degradation caused by H2S poisoning, this study aimed to develop a nitrogen (N)-doped carbon derived from biomass feedstock using the digested liquid as the N source, which acted as an adsorbent material to reduce the H2S concentration in biogas to below the sub-ppm level. Biochar (BC) derived from rice husk (RH) treated with 25 vol% NH3 gas (balanced with N2) at 900°C for 120 min, RH-BC(N900-120), exhibited the largest H2S breakthrough capacity (APCH2S(0) ) of 8.02 mg H2S g-BC−1 and a total H2S adsorption capacity (ACPH2S ) of 9.58 mg H2S g-BC−1. The largest ACPH2S , 23.0 mg H2S g-BC−1, was obtained for the RH-BC treated with NH3 evaporated from a 10 wt% NH3 solution (simulating a concentrated digested liquid) at 850°C for 270 min, RH-BC(EN850-270), with an APCH2S(0) of 3.96 mg H2S g-BC−1. For a strongly N-doped BC such as RH-BC(N900-120), the formation of surface sulfate after H2S adsorption was more significant compared to a mildly N-doped BC, i.e. RH-BC(EN850-270), in which the interaction of the surface with H2S was moderately weakened, preventing the blockage of micropore openings by the accumulation of sulfate. Consequently, the H2S molecules could be adsorbed into the micropores, resulting in a higher ACPH2S .