Óxidos metálicos estruturados como catalisadores na produção de biodiesel etílico e metílico

Abstract

Biodiesel’s production is usually based on the catalytic transesterification of vegetable oils or animal fats. Usual heterogeneous catalysts lead to a lower reaction yield than homogeneous ones. However, they avoid corrosion problems, reduce the occurrence of side reactions such as saponification, and facilitate the performance of subsequent steps of the fuel purification, such as base neutralization, washes with hot distilled water and drying. This work focus on the development of new catalytic systems based on structured metal oxides for production of ethyl and methyl biodiesel as a replacement for the homogeneous alkaline catalysis. The compounds of hydrotalcite (layered double hydroxides, LDH's) were synthesized successfully using the co-precipitation method from aluminum and magnesium nitrates, in the presence of sodium carbonate. Synthesis in the presence of other metal nitrate ions (Ca2+, Cu2+, Fe3+ and Zn2+) and a directing agent (sucrose) were performed as well. All obtained materials were calcined at 450 °C to produce the corresponding mixed metal oxides, which were subsequently employed as catalysts for the transesterification reaction of soybean oil and the consequent production of biodiesel (methyl and ethyl routes). The materials’ characterization was held by TG, XRD, SEM, EDX, IR, BET and ICP. The quantitation of the methyl and ethyl esters was performed by Gas Chromatography (GC-FID). The analysis confirmed the formation of the double-layered hydroxides in all cases, with no segregated phase. In general, the employment of sucrose led to the formation of mixed oxides with greater specific surface area (250 m2/g), when compared to other HDL's, and to systems with the best catalytic yields, notably via ethylic route (92%) and the methyl route (98%).