Structural study of mixed metal oxide catalysts comprising Mg, Ca, and Al used for upgrading biodiesel byproduct glycerol to glycerol carbonate

Glycerol is a by-product in biodiesel production. It is possible to convert glycerol to glycerol carbonate by carbonylation with CO2. In this work, novel mixed metal oxides of Mg-Ca, Mg-Al, and Ca-Al were prepared by co-precipitation method, and used as catalysts for this reaction for the first time. Catalysts were characterized through XRD, BET surface area analyzer, XPS, ICP-OES, SEM, and CO2-TPD analyses. Mg0.75Ca0.25O catalyst showed the highest glycerol conversion of 18.2±0.7%, and glycerol carbonate yield of 12% at initial conditions. Reaction parameters including pressure, temperature, and catalyst loading were optimized, when Mg0.75Ca0.25O catalyst was used, to achieve the highest glycerol carbonate yield. The optimal reaction parameters were pressure of 7MPa, temperature of 180 ⁰C, and catalyst loading of 8.5%. Glycerol conversion was 25.7% and the glycerol carbonate yield was 16% at optimized condition. Morphology and chemical structure of Mg-Ca catalyst were also investigated.