Comparative study of natural dolomitic rock and waste mixed seashells as heterogeneous catalysts for the methanolysis of palm oil to biodiesel

• After calcination at 800 °C, both dolomite and seashells gave the FAME yield >98%.
• Higher methanolysis rate was provided by the calcined dolomite catalyst.
• The FAME yield vs. the Ca content of the catalysts supported CaO as active site.
• The calcined dolomite exhibited a higher stability than the likewise seashells.

Natural dolomitic rock and waste mixed seashells were investigated as renewable sources for preparing heterogeneous catalysts for the methanolysis of palm oil to biodiesel as fatty acid methyl esters (FAME) at 60 °C and ambient pressure. After calcination at 800 °C, the dolomite as the mixed CaO·MgO catalyst possessed smaller CaO crystallites, a higher thermal stability and higher basicity than the pure CaO catalyst derived from the seashells. Although both catalysts gave the FAME yield >98% (w/w), the calcined dolomite exhibited a faster methanolysis rate and higher stability in use than the likewise calcined seashells. The linear correlation of the FAME yield to the amount of CaO phase containing in both catalysts supported that CaO was the active site. The catalyst deactivation was relevant to the formation of calcium glyceroxides. The presence of MgO dispersed in the CaO matrix was important for the superior physicochemical and catalytic properties of the natural dolomite calcined at 800 °C.