Transesterificação heterogênea catalisada por sílicas contendo sítios básicos e cátions cetilvinilimidazólio

Abstract

Homogeneous catalysis is the most used process in the production of biodiesel, although this process has several disadvantages such as: the catalyst cannot be easily reused and requires parallel processes for separation and neutralization. Thus, mesoporous molecular sieves stand out as heterogeneous catalysts, due to their physicochemical properties and have been preferentially studied as catalysts. Among the mesoporous molecular sieves, the family called M41S can be highlighted, with emphasis on MCM-41. MCM-41 hybrid silicas, containing cationic surfactants in their mesopores, have very strong basic sites, capable of promoting transesterification reactions. However, these materials have low catalytic stability, which hinders their reuse. Thus, this work aimed to evaluate the stability of MCM-41 hybrid silicas synthesized with a polymerizable surfactant, 1 cetyl 3 vinylimidazolium bromide (CVIMBr). The CVIMBr surfactant was synthesized by the quaternization reaction between 1-vinylimidazole and 1 bromohexadecane. The CVIM-MCM-41 hybrid silicas were synthesized, polymerized using ultraviolet irradiation, and evaluated in catalysis of the model transesterification reaction of ethyl acetate with methanol. The characterization results confirmed the formation of the CVIMBr surfactant. XRD analysis of hybrid silicas, containing CVIM+ cations, showed that the materials presented a typical structure of MCM 41. The CVIM MCM-41 and CTA-MCM-41 hybrid silicas were evaluated in catalysis of the model transesterification reaction of ethyl acetate with methanol. CVIM-MCM-41 showed lower catalytic activity but showed greater catalytic stability up to five successive uses. As the silica containing CTA+ cations showed good catalytic activity, and the silicas containing CVIM+ cations showed an improvement in stability, silicas were synthesized with different proportions of the CTABr and CVIMBr surfactants, in order to achieve a high catalytic activity and maintain stability. Thus, the catalytic activity of these silicas decreases with the content of CVIM+ cations and catalytic stability was reached when the hybrid silica was synthesized with 30% of the CVIM+ cations and 70% of the CTA+ cations.