Green Mg-Ca-Al Mixed Oxide Catalyst for Synthesis of Glycerol Carbonate

Abstract

This study aims to investigate the transesterification of glycerol with dimethyl carbonate (DMC) to produce glycerol carbonate (GLC) using a heterogeneous Mg–Ca–Al mixed-oxide catalyst. Catalysts with different molar ratios of Mg, Ca, and Al (Mg₃.₅ₓCa₀.₅ᵧAlₓO₃) were synthesized and calcined at 500 °C for 5 hours to determine the optimal composition for achieving a high GLC yield. Among the synthesized catalysts, Mg₁.₀₅Ca₀.₇₅Al₀.₃O₃ was identified as the most effective. The results revealed that the Mg₁.₀₅Ca₀.₇₅Al₀.₃O₃ catalyst exhibited higher catalytic activity when calcined at an elevated temperature of 800 °C. Characterization techniques, including SEM, HRTEM, BET, XRD, and FTIR, were employed to analyze the structure, morphology, composition, porosity, and surface functionality of the catalysts. All transesterification reactions were conducted in a batch process under varying conditions: catalyst loading (2–5 wt%), DMC-to-glycerol molar ratio (1:1–4:1), reaction temperature (65–80 °C), and reaction time (0.5–2.0 hours). The optimum reaction conditions were identified as a catalyst loading of 3 wt%, reaction temperature of 70 °C, DMC-to-glycerol molar ratio of 3:1, and reaction time of 1.5 hours. Under these conditions, a GLC yield of 75% was achieved, with a glycerol conversion of 76%. The stability of the Mg₁.₀₅Ca₀.₇₅Al₀.₃O₃ catalyst was evaluated over three consecutive cycles. The results indicated that aluminium plays a crucial role in enhancing catalyst stability by providing a high surface area and acting as a support. Furthermore, the presence of aluminium reduces the basicity of the catalyst, thereby minimizing the formation of glycidol.