Calcium zincate as precursor of active catalysts for biodiesel production under mild conditions

This work investigates the use of calcined calcium zincate as solid base catalyst for the methanolysis of sunflower oil to FAME (biodiesel). The precursor and catalyst were characterized by XRD, XPS, SEM, EGA-MS, FTIR and N2 adsorption. The thermal treatment at temperatures as low as 400 °C leads to a base catalyst which is very active and stable in biodiesel production from different vegetable oils (sunflower and soybean). The presence of carbonate on the calcium zincate, used as precursor, is negligible after remaining in contact with air for two weeks. The catalyst obtained at 400 °C shows FAME yields higher than 90% after 45 min of reaction, and the kinetic of the heterogeneous process (60 °C, methanol:sunflower oil molar ratio of 12, 3 wt.% of catalyst) is very close to that observed under homogeneous conditions (KOH dissolved in methanol). Under these experimental conditions, the catalyst is stable against lixiviation since it can be reutilized for three catalytic runs of 1 h, reaching yields higher than 85%. Moreover, by increasing the acidity of the oil until 1.1° (typical value of fried oils), the catalytic performance is maintained. The presence of water has a negative influence on the catalytic activity, since the addition of a 0.2 wt.% of water into the reaction medium decreases the FAME yield until 80% after 3 h of reaction, although this yield is still higher than 60% after adding a 1 wt.% of water. This catalyst is also very active in the transesterification of soybean oil.