Síntese e caracterização de catalisadores sulfonados suportados em carbono ativado e sílica mesoporosa para o processo de obtenção de biolubrificantes

Abstract

Over the years, homogeneous acid catalysts have been used in esterification reactions of fatty acid, aiming at high conversions of these acids. However, this type of catalysts results in some disadvantages in its use such as, large amounts of residual water, corrosion problems in the reactor and the impossibility of reusing homogeneous catalysts. In an attempt to convert these negative points into positives, heterogeneous acid catalysts gain space. Many researchers synthesize and functionalize these catalysts for high performance, especially with regard to thermal and catalytic stability, good selectivity and reuse of the material. Thereby, is this work the synthesis and characterization of sulfonated catalysts (based on carbon and silica) were carried out aiming the application in esterification reactions using long chain alcohols (octanol, 2-ethylhexanol and trimethylolpropane). Oleic acid was used as a model fatty acid. The commercial carbon “NORIT PLUS 1240” was modified with sulfuric acid in three different temperature, 100, 150 and 200 ºC named ACS1, ACS2 e ACS3, respectively. The silica-based catalyst is MCM-41, which was synthesized and modified in this work. The functionalization of this material was performed with organosilane (3-mercaptropopyl)trimethoxysilane – MPTS – and further oxidation with hydrogen peroxide. The catalysts were characterized by N2 adsorption/desorption, X ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG/DTG), scanning and transmission electron microscopy (SEM and TEM). All the catalysts were applied into the esterification reaction and the products were analyzed by hydrogen nuclear magnetic resonance (1H NMR). The characterization of the materials showed that all functionalization was successful and it was proved mainly by XPS through the peaks on region of 168 eV, that binding energy is concerning to sulfonic group (SO3H). The catalysts when applied in the esterification reaction, they obtained excellent catalytic activity with conversion close to 100% of the oleic acid and with ~ 70% of selectivity. ACS1 showed better performance when compared to other catalytics, but when it was reused the catalytic activity decreased showing that the catalyst was not stable in several cycles of use. In overview of this work, the synthesis and functionalization of the catalytics were carried out, both carbonaceous and silicate, and these materials displayed an excellent catalytic activity and a great selectivity in the esters desired.