Chars from wood gasification for removing H₂S from biogas

Biomass gasification is a mature thermochemical process used to produce a gaseous fuel to run burners, engines, and gas turbines. One of the byproducts of biomass gasification is char, which is a residue with low value and sometimes this material is even considered waste. Therefore, options for using gasification chars are required. On the other hand, there is a necessity of making biogas production and use more attractive by employing cheap materials for the biogas cleaning process. One of the promising options for using gasification chars is for cleaning biogas produced via anaerobic digestion (AD). The objective of this work was to assess the use of residual gasification chars from fast growing wood species (Eucalyptus Grandis-EG and Pinus Patula-PP) to remove hydrogen sulfide (H₂S) from biogas produced via AD. Gasification chars were produced employing a laboratory scale downdraft gasifier. EG char (EG-C30) was produced by gasification of EG using a 30 L min⁻¹ airflow, whereas the PP chars (PP–C20 and PP-C40) were produced from PP using 20 and 40 L min⁻¹ airflow. Results show that these three chars offer potential for biogas cleaning, although PP-derived chars produced at higher airflow rates are more effective. The H₂S removal capacity of the chars is ascribed to their large apparent surface area (up to 517 m² g⁻¹) and the presence of minerals and metals (e.g., Ca, K, and Fe) in the chars’ ash.