Abstract
Biodiesel, a mixture of fatty acid (methyl) esters (FAME), is a renewable fuel produced from the homogeneous catalytic transesterification of vegetable oils and animal fats, using basic hydroxides as catalysts.
Advantages such as product separation, catalyst reuse and favorable reaction conditions, inherent in the heterogeneous catalytic transesterification process, have led to the development of various solid catalysts to carry out this reaction.
The hydrotalcite has been considered of great interest in the transesterification reaction due to its strong basicity, high surface area and pore volume. It consists of a natural anionic clay containing carbonate anions intercalated between lamellar double hydroxide, magnesium and aluminum. The lamellar double hydroxides, although not abundant in nature, can be synthesized in the laboratory at a relatively low cost. Thus, this study investigated the transesterification of soybean oil to produce biodiesel using methanol and Mg/Al hydrotalcite as a basic catalyst solid.
In this work, hydrotalcite was synthesized using the co-precipitation method with Mg/Al molar ratio of 3.0 and calcined at 450 °C (723 K), under Ar flow, for 6 h. The obtained solid was characterized by X-ray powder diffraction and temperature-programmed desorption of CO2 (CO2-TPD). The reactions of transesterification were carried out at atmospheric pressure and at 64 °C (337 K) in a jacketed reactor coupled to a condenser, under magnetic stirring, by varying the molar ratio methanol/oil and the reaction time. The obtained ester phase was characterized by viscosity and gas chromatography.
The best condition was achieved with a methanol/oil molar ratio of 20:1, 5.0 % catalyst (w/wt), for 10 h, which resulted in the highest FAME conversion of 94.8 %. The result was showed that the proposed solid catalyst is a promising for the production of biodiesel via heterogeneous catalytic transesterification under milder reaction conditions.
