Catalisadores heterogêneos derivados de hidróxidos duplos lamelares de Mg- Al e Ca-Al em reações de transesterificação para produção de biodiesel

Abstract

Biodiesel is a biofuel obtained by the transesterification and/or esterification of fatty materials with short molecular chain alcohol. It is a mixture of fatty acid esters. It has high environmental importance and is strategic from an energy policy point of view because it is a substitute for fossil diesel. The heterogeneous catalysts used in the transesterification reaction should be efficient and inexpensive. In this study, Mg-Al and Ca-Al layered double hydroxides were synthesized. Their thermal decomposition solid products were tested as catalysts in the transesterification of soybean oil and macauba kernel oil. The mixed oxides formed were characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy, thermogravimetry coupled to differential scanning calorimetry and mass spectrometry, specific surface area, CO2 temperature programed desorption and scanning electron microscopy. Analyzes of chemical-catalytic efficiency of the Mg-Al material using a fractional factorial design with soybean oil are described. We investigated the effect of temperature (80, 105 and 130°C), catalyst amount (1, 2, and 3% ro/m), time (2, 5 and 8 h) and Mg:Al catalyst ratios (2:1, 4:1 and 6:1). A response surface was constructed, obtaining an optimal reaction point. Under these conditions, we evaluated the effect of the acidic medium and the medium water content on the catalyst performance. The thermal decomposition products of the hydrocalumite-type compound were tested in transesterification reactions using alcohol reflux temperature and mechanical agitation at 600 rpm. The tests using the methyl route showed high conversion levels; with 1.5 h of reaction 97 and 95% were obtained using soybean and macauba oils, respectively. For the ethyl route, 12 h of reaction time were necessary to obtain 90% conversion using soybean oil. Hydrocalumite-type compounds intercalated with vinyl benzene sulfonate anions were also synthesized and this material showed a different morphology than hydrocalumite intercalated with chloride. Hydrocalumite intercalated with vinyl benzene sulfonate anions presented lower catalytic activity in the transesterification, 12 h of reaction were required to obtain 96% methyl conversion.