Removal of hydrogen sulfide from biogas using sweet potato’s leaves derived activated carbon

Hydrogen sulfide gas contained in biogas is both corrosive and poisonous. In this study a performance of sweet potato leaves activated carbon for hydrogen sulfide removal from biogas was evaluated. The samples were synthesized through chemical activation method using potassium hydroxide as an activating agent. The study focused on the understanding of the effect of carbonization temperature during activated carbon making, KOH: C activation ratio, the flow rate of biogas and mass of sweet potato leaves activated carbon on adsorption capacity. The Brunauer-Emmett-Teller analysis was performed for both fresh and spent activated carbon as well as for carbonized sample, which was not activated. The activated carbon was also characterized by X-ray fluorescence and Carbon, Hydrogen, Nitrogen and Sulfur techniques for elemental analysis. The adsorption tests were conducted at the on-site biogas digester at ambient conditions. The adsorbent was packed into the reactor bed, biogas allowed to pass through the adsorbent, and the inlet and outlet concentrations of H2S were monitored. The results showed that the removal efficiency of hydrogen sulfide increased with increase carbonization temperature from 600 to 800 °C. The increase in the mass of sorbent from 0.4 g to 1.0 g also brought to the rise in removal efficiency from 88% to 95% under the lowest flow rate of about 0.02 m3 /h with activation ratio 1:1 KOH: C at 800 °C which made a sorption capacity of approximately 1.9 g S/100 g, activated carbon. As per the mechanism of the hydrogen sulfide removal, it is not only contributed by the adsorption process with the pores available but also by the presence of iron in the sample that reacted with hydrogen sulfide. The regeneration test was done for the saturated sample to check the regenerative ability of the material and the result indicated that the sorption capacity of the regenerated sample was lower compared to the freshly prepared sample. Therefore, upon successful hydrogen sulfide sorption, sweet potato leaves activated carbon is viable adsorbent for removing H2S from biogas.