Silica-rich geomaterials and their use as heterogeneous catalysts in the transesterification reaction to produce biodiesel

A silica-rich geomaterial of a mining tail was prepared and tested as a heterogeneous catalyst in the transesterification reaction in soybean oil to produce the corresponding fatty acid methyl esters (biodiesel). The dry raw geomaterial was characterized by powder X-ray diffractometry, scanning electron microscopy, energy dispersive X-ray (EDX) and 57Fe-Mössbauer spectroscopy. The raw mineral sample was then dispersed in aqueous solution containing 35 g KI 100 mL-1 to form the chemically active solid catalyst. The EDX data showed that the silica-rich material contained mainly silicon (87.3 mass%), iron (8.4 mass%) and aluminum (3.5 mass%). From the 298 K-Mössbauer spectrum, two sextets were attributed to hematite (αFe2O3) and goethite (αFeOOH). Meaning fully, although the silica-rich material, before being impregnated with KI, showed no chemical efficiency on the production of esters (biodiesel), the KI-impregnation made it an efficient catalyst: the biodiesel was produced after 7 h by the transesterification reaction using 5 mass% catalyst with respect to the oil mass; the reaction was performed with a methanol: soybean oil molar ratio 100:1, yielding 95 ± 2 mass% esters. These results encourage further essays focused not only on optimizing these reaction conditions but also on seeking for other formulations containing any silica-rich geomaterial as heterogeneous catalysts in transesterification.