a b s t r a c tNatural 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.
In the present work, shell, which is available in abundance, low cost and non-toxicity, was used as a source of calcium for preparation of heterogeneous base catalysts. The catalyst was prepared by dissolution-precipitation method in which a calcined shell was mixed with Zn(NO3)2and Al2O3under acidic conditions, followed by calcination at 300-700 °C. ZSA-I was referred to as the catalyst attained under the suitable synthesis conditions. Physicochemical properties of ZSA-I were studied by using X-ray fluorescence spectroscopy (XRF), powder X-ray diffraction (XRD), thermogravimetric/ differential thermal analysis (TG/DTA) and CO2-pulse chemisorption analysis. ZSA-I gave the highest fatty acid methyl ester yield of 99 wt.% in the transesterification of palm oil with methanol and can be reused at least 5 times with a retention of the methyl ester yield higher than 96 wt.%.
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