Mixed oxides tuned with alkaline metals to improve glycerolysis for sustainable biodiesel production

Abstract

In this study, monoglycerides were produced as glycerol value-added products via transesterification reaction of methyl stearate. This green and selective process involved catalysis from hydrotalcite-like compounds with different metals incorporated (Li, K or Cs) to improve their basic properties. Layered double hydroxides were obtained by two different methods and activated by calcination. All samples were examined by X-ray diffraction, specific surface area determined by the BET method, temperature-programmed desorption of CO2 and infrared absorption spectroscopy with Fourier transform for basic sites measurement. Metal content was determined by inductively coupled plasma optical emission spectroscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The hydrotalcite-like compounds modified with monovalent metal ions (Li, K or Cs) with the lamellar structure were synthesized. The metal percentage incorporated was higher for materials modified with Li than for those modified with K and Cs. This fact can be attributed to the lower size of their ionic radii. All mixed oxides presented basic properties. The products were analyzed by gas chromatography. The correlation between the basic properties of the solid catalysts and the activity in the transesterification reaction was investigated. The highest activity was found for the catalyst with Li incorporated by the co-precipitation method with yield values around 78% for monoglycerides. Which also showed the greatest Lewis medium basic sites density, a 31% more than the rest of the materials.