Study on heterogeneous catalysts from calcined Ca riched hydrotalcite like compounds for biodiesel production

Abstract Ca riched Hydrotalcite like compounds (HLCs) were synthesized by co-precipitation method to obtained Ca–Mg–Al mixed metal oxides with a view to produce biodiesel via methanolysis of microalgae. For this purpose, hydrotalcite-like catalysts containing Ca+2, Mg+2 and Al+3 metals were prepared with a molar ratio (x value) of Al+3/(Ca+2 + Mg+2 + Al+3) at 0.33. Ca/Mg molar ratio in the hydrotalcite like compounds was determined as 0, 0.5, 1, 2. Also, Mg-free CaAl HLCs was prepared at x = 0.33 value. The calcination process was carried out at 800 °C. Obtained catalysts were characterized by BET, XRD, TGA, FTIR, SEM and ICP-OES techniques. The basicity of the all catalysts were investigated by using TPD/CO2 technique and Hammett indicators. With increase in calcium amount on the HLCs, some evident features were observed such as high basicity and increase in basicity range with H_ values above 15, increase in pore diameter up to 18.37 nm, low pore volume and high catalytic activities. XRD analysis demostrated that the desired Ca–Mg–Al active metal oxide forms were formed after calcination. Catalytic activities of all the catalysts were examined in terms of conversion of microalgae oil to biodiesel and achieved up to 90% FAME yield under mild reaction conditions: 338 K for 5 h, methanol/microalgae oil molar ratio 6:1 and 3% catalyst amount. These results showed that the molar ratio of Ca–Mg in HLCs were significantly effective on the HLCs structure and catalytic activity.