Avaliação do catalisador CTA-MCM-41, modificado por poliacrilatos, na transesterificação de monoéster

Abstract

The silica hybrid CTA-MCM-41 (where CTA is the cetyltrimethylammonium cation) was synthesized and used in the transesterification of ethyl acetate with methanol. This is a model reaction used to test basic catalysts for the production of biodiesel from vegetable oils and fats. The basic sites in the catalyst consist of siloxy anions associated with CTA cations. In earlier work, it was found that progressive deactivation of the catalyst occurred when it was reused, due to leaching of the CTA cations located within the pores and on the external surface, resulting in partial loss of the basicity required for this type of reaction. The challenge of the present work was to stabilize the catalytic activity of CTA-MCM-41 by restricting the loss of cations from its interior (since the basicity derives from the interaction between the CTA cation and the siloxy anion). To this end, novel modifications were made to the synthesis of CTA-MCM-41, involving the encapsulation of acrylate monomers in the hydrophobic interior of the micelles followed by their subsequent polymerization using the application of ultraviolet irradiation together with a photoinitiator. The polymers formed then interacted with the hydrophobic tails of the micelles, which restricted the exit of CTA from the interior of the pores, hence improving the stability of the catalyst. The combination of the traditional synthesis method with polymerization using a microemulsion is innovative, because there are no reports in the literature that describe a synthesis in which the initial step is performed using emulsified polymers. The emulsions and the synthesized solids were evaluated using small angle X-ray scattering (SAXS). The materials were also analyzed by Xray diffraction, elemental (CHN) analysis, infrared absorption spectroscopy, scanning electron microscopy, and thermogravimetry. All these techniques helped to identify the presence of the monomer, as well as the polymer, in the channels of the CTA-MCM-41. It was confirmed that the presence of the polymer increased the catalytic stability of these new silica hybrids applied in the transesterification reaction.