Al₂O₃-supported Mixed Ca and Zn Compounds Prepared from Waste Seashells for Synthesis of Palm Fatty Acid Methyl Esters

Waste mixed seashells of Perna viridis, Anadara granosa, Amusium pleuronectes, and Meretrix meretrix, as abundant, low-cost, and nontoxic calcium sources, were used as renewable raw materials in the preparation of a heterogeneous base catalyst for the transesterification of palm oil in refluxed methanol. The new mixed metal compound catalyst was prepared by mixing the calcined seashells with Zn(NO₃)₂ and Al₂O₃ in an acidic aqueous solution, followed by calcination at 500°C (ZSA-500). The ZSA-500 catalyst exhibited an enhanced surface area, dispersion, and total basicity compared to the parent calcined seashells. The fatty acid methyl ester (FAME) yield attained over ZSA-500 was 99 wt.% and dropped by 3% after five repetitive uses when the reaction was performed for 3 h at 60°C and ambient pressure with 10 wt.% catalyst and a methanol:oil molar ratio of 30:1. Structural and thermal analysis indicated that the active phases of ZSA-500 had a high stability against the glycerol adsorption as well as the phase transformation to calcium glyceroxides (Ca(C₃H₇O₃)₂).