ZnO and Cu-based adsorbents for biogas desulfurization at room temperature

Synthesis and structural characterization of ZnO and Cu based materials were done in order to compare chemical, morphological and microstructural effects in sorbent materials for gas-phase desulfurization reaction at room temperatures as a potential application in biogas cleaning. The materials were synthesized through two wet chemical routes, firstly using zinc nitrate, hexamethylenetetramine and NaOH reagents at 70 and 90 °C for ZnO flower-like and rod-like structures, respectively; and secondly a typical calcination of metallic copper to obtain CuO. Powder X-ray diffraction, X-ray fluorescent spectroscopy analysis were realized. Results showed a unique zincite phase for ZnO and three phases in copper samples: Cu⁰, Cu₂O and CuO (76.3, 18.3 and 5.4 wt%). The size of crystal domains varied from 180 to 1600 nm, while the particle size varied from 660 to 1020 nm. These materials were tested in desulfurization reactions at room temperature using a fixed-bed glass reactor. In order to avoid poisoning and asphyxiation risks a non-desulfurized biogas influent was simulated by a gas mixture of N₂ and H₂S (100 ppm). The reactor was fed with the gas mixture at rate of 450 ml/min (GHSV 9120 h⁻¹). The composition of effluent gas was determined using a biogas detector, coupled with an electrochemical H₂S sensor. Results show that CuO and ZnO could be feasible adsorbents for the removal of hydrogen sulfide; however, they became saturated after 300 s while high surface area materials, evidenced by SEM, showed higher saturation capacity. Characterization of wasted adsorbents using electron microscopy techniques and fluorescence X-ray spectroscopy evidenced the presence of metallic sulfides at amounts less than 0.05 wt%, although no crystalline phases were detected in further analysis.