Adsorption of hydrogen sulfide in biogas using a novel iron-impregnated biochar scrubbing system

Hydrogen sulfide (H2S) in biogas is produced during anaerobic digestion of organic wastes and can lead to corrosion of generators used for energy production. Recently, there has been interest in utilizing biochar as a substitute for activated carbon (AC) to adsorb and remove H2S from biogas. This study was the first to test iron (Fe)-impregnation of biochar to increase H2S removal from biogas using a biogas scrubbing column. Two biochar substrates, corn stover biochar (CSB) and maple wood biochar (MB), with and without Fe-impregnation were evaluated for H2S adsorption from biogas. The H2S adsorption capacity was quantified using dynamic breakthrough experiments. Iron-impregnated maple biochar (MB-Fe) had the highest H2S saturation adsorption capacity (23.9 mg H2S g−1 biochar), which was 3.9 times higher than the unmodified MB (6.1 mg H2S g−1 biochar). The Fe-impregnated corn stover biochar (CSB-Fe) saturation H2S sorption capacity (8.2 mg H2S g−1 biochar) was 2.5 times higher than the unmodified CSB (3.3 mg H2S g−1 biochar). The presence of iron oxide (Fe3O4) was observed through X-ray diffraction and scanning electron microscopy in the Fe-impregnated biochar substrates, with ferrous sulfate (FeSO4) as one of the end products in the saturated biochar surface and elemental sulfur in the pores. The study showed how Fe-impregnation can result in a multifold increase in H2S adsorption from biogas compared to unmodified biochar.