Valorization of biodiesel byproduct glycerol to glycerol carbonate using highly reusable apatite-like catalyst derived from waste Gastropoda Mollusca

Predominantly, calcium oxide from the calcined waste Gastropoda Mollusca (Achatina fulica sp.) was post-functionalized and stabilized using trisodium phosphate to obtain an apatite-like catalyst (snail shell apatite, SNS-AP) to tailor the synthesis of glycerol carbonate (GC) from abundant biodiesel byproduct glycerol. Textural properties, crystal structure, and morphology were characterized by different techniques. The turnover frequency (TOF) and E-factor green metrics were determined, and plausible reaction mechanisms elucidated. The results show that the transformation of the crystalline phases of the snail shell consisting of aragonite and dolomite phases to apatite-like glaserite after functionalization with trisodium phosphate promoted stability and enhanced basicity of the catalyst to tailor the transesterification reaction. Thus, about 94.3% glycerol conversion and 96.5% GC yield were achieved under best reaction conditions of 80 °C, 90 min, DMC/glycerol molar ratio of 4, and 4 wt% catalyst weight. The TOF and E-factor were 12.533 h⁻¹ and 0.5322, respectively. Also, the catalyst was stable over eight successive cycles of reuse sustaining about 80.34% GC yield. The results show the potential of this environmentally friendly strategy to prepare stable heterogeneous catalyst from natural wastes to promote the upgrading of oversupplied glycerol.

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