Production of hydrogen via microalgae air gasification over acid mine sludge waste coated on monolith

In this study, air gasification of microalgae employing Nickel-loaded acid mine sludge waste (Ni/AMS) with the packed bed and monolith-type reactor designs was performed for the first time. The effects of various factors such as reaction temperature, equivalence ratio (ER), and AMS-to-biomass ratio were also evaluated. The gas yield and H₂ selectivity greatly increased over the Ni/AMS catalyst compared to those produced using the AMS catalyst owing to the dual function of the Fe₂O₃ redox properties and metallic Ni. By applying monolith-type supports (M-AMS and M-Ni/AMS), the yield of gas and H₂ selectivity significantly increased compared to those obtained using packed bed reactors. The gas yield and H₂ selectivity reached 74.30 wt% and 42.32 vol%, respectively, employing monolith-type Ni/AMS (M-Ni/AMS). This can be ascribed to the augmented mass and heat transfer in the monolithic structure. Increasing the reaction temperature also increased gas yield and H₂ selectivity. Furthermore, although the gas yield gradually increased with increasing ER, the selectivity of H₂ increased with increasing ER till 0.3 and then decreased with further enhancement of the ER. However, decreasing the AMS-to-biomass ratio reduced the gas yield and selectivity of H₂. As a result of microalgae water-washing pretreatment, the gas yield and H₂ selectivity enhanced favorably. Overall, this study provides new prospects for the use of waste, such as AMS, and monolith frameworks for the air gasification of microalgae to increase H₂ production.