Desenvolvimento de catalisadores heterogêneos, à base de complexos de estanho(IV) ancorados em sílica, para produção de ésteres alquílicos

Abstract

In this study the anchorage of Sn (IV) complexes on silica gel to obtain heterogeneous catalysts with potential activity in transesterification was investigated. The Sif-DMTDU e Sif-TBTU catalysts were synthesized and anchored on silica modified with trimethoxysilane, and Si-TBTM e o Si-DBTDM were anchored without silica modification. The complexes formation was confirmed by spectroscopy in the mid-infrared region, optical atomic emission spectrometry, nitrogen physisorption and determination of the surface area of the catalyst by BET method, thermogravimetry and scanning transmission electron microscopy. The Si-DBTDM showed the largest tin content in silica, 17.3 %, followed by Sif-DMTDU with 12.0 %, Si-TBTM with 7.4 % and 5.0% for Sif-TBTU. The heterogenized compounds and their homogeneous equivalents, were tested for the transesterification of ethyl acetate in order to examine the catalytic behavior in this type of reaction. The transesterification were performed in vials, in order to convert the ethyl acetate in methyl acetate. The reaction products were characterized by gas chromatography. All homogeneous and heterogeneous catalysts tested, exhibit catalytic activity at the conditions employed. The reactivity order for homogeneous catalysts was DBTDM> DMTDU> TBTU> TBTM. When these species are heterogenized, the same order of reactivity was observed, but is necessary more time to achieve the same catalytic activity observed in the case of the homogeneous complex. In reuse and leaching tests, is observed the loss of Sn (IV) of the silica matrix, but the catalysts remained active for up to 10 reaction cycles, which represents 20 hours of reaction. The SIf-DMTDU and Si-DBTDM catalysts were more active than Sif TBTU and Si-TBTM, however Sif-TBTU was more advantageous, since from 4º reuse it showed the highest activity. Finally, at the conditions studied, the use of the complex base Sn (IV) anchored on silica proved to be very promising in the transesterification reaction.