Hydrogen Sulfide Removal from Biogas using Biochar made from Cow Dung and Jackfruit Tree Waste

Abstract

The presence of >1ppm concentrations of hydrogen sulfide (H2S) in biogas can pose a challenge for the implementation of off-grid biogas-SOFC energy systems in rural Uganda. This study investigated the potential of biochars made from cow dung (CB), jackfruit tree leaves (LB) and jackfruit tree branches (TB) to remove H2S from biogas to below the 1 ppm threshold and compared the findings to the use of commercially available activated carbon (AC). The surface area, pore structure, particle size, trace-metal content, pH and alkalinity were characterized and their influence on the H2S adsorption capacity was qualitatively evaluated. Furthermore, a Central Composite Design (CCD) was used to determine the influence of the gas hourly space velocity (GHSV) and inlet H2S concentration on the H2S adsorption capacity. AC was observed to exhibit the highest H2S adsorption capacity, followed by CB, LB and TB, in that order. The specific surface area (SSA) and micropore volume were argued to be the determining factors to explain the differences in H2S adsorption capacity. Furthermore, the GHSV and inlet H2S concentration were both found to be negatively correlated to the H2S adsorption capacity. The interaction effect between both parameters was observed to be insignificant and no optimum was found by the response surface analysis. The comparison of the research findings with similar studies highlighted the complexity involved in comparing the H2S adsorption capacities of biochars between studies. It is therefore suggested that a reference benchmark breakthrough test should be created and used by future studies. Ultimately, the insights of this study may contribute to the implementation of cost-effective biogas-SOFC systems in rural Uganda.