Eggshell Waste Valorization into CaO/CaCO3 Solid Base Catalysts

Eggshell waste is a biodegradable residue composed of more than 90% CaCO3, which makes it a great candidate to be converted into functional materials for diverse applications. Herein, domestic hen eggshell waste was dried and calcined in muffle under air at different temperatures (300 to 900 °C) and times (1 or 3 h) to achieve distinctive calcium species, compositions, and solid-phase transformations. The crystal structures achieved were characterized by X-ray diffraction (XRD), evidencing the transformation from CaCO3 (calcite) to CaO (lime) at high temperatures and the formation of Ca(OH)2 (slaked lime) due to the hydration of CaO facilitated by ambient water molecules. Considering this preliminary results, prepared solids could be useful as low-cost and metal-free (unsupported) catalysts for different heterogeneous reactions, such as the transesterification of vegetable oil and/or glycerol, where the presence of basic sites are needed.