Álvaro Cunha Neto

Stereoelectronic interaction and their effects on conformational preference for 2-substituted methylenecyclohexane: an experimental and theoretical investigation.

Conformational preferences for 2-substituted methylenecyclohexanes were determined using (3) J H 2 H 3 spin-spin coupling constants, while stereoelectronic interactions were obtained by means of theoretical calculations and NBO analysis. The conformational equilibrium of compounds studied can be represented by their axial and equatorial conformers, the axial conformers being the most stable form in polar and nonpolar solvents. These conformational preferences were attributed to the hyperconjugative interactions between the pi C-C-->sigma* C-Xax. and sigma C-H-->sigma* C-Xax. orbitals, and the repulsive steric interaction observed between sigma C-H-->n Xeq..

Methyl Esters Production by Heterogeneous Catalyst Mixtures of CaO/Nb2O5 with Simulation of Analysis of Environmental Impacts

The conventional biodiesel process, although it reaches high conversion yields and productivity, faces problems related to the use of homogeneous catalysts. This work aims to study mixtures of calcium oxide (CaO) and niobium oxide (Nb2O5) as the heterogeneous catalyst. It was used a full 2 factorial design with four central points to analyze how the mass percentage of the oxides, the molar ratio of reactants, and the reaction temperature affect the conversion yield to methyl esters. The best conversion yield was found near to 89% using 1.8% of catalyst, a 1:36 oil to methanol ratio and at 77 °C as reaction temperature. Finally, it was performed a simplified simulation to compare the heterogeneous catalyst process with the conventional process, and an algorithm to compare the effects of the exit streams of each process would have on the environment. The simulations results display a better performance for the heterogeneous catalyst process studied.

Studies on the synthesis of biodiesel catalyzed by Nb2O5.nH2O in transesterification reactions of cotton, coconut and flaxseed oils

Transesterification is the predominant process for converting vegetable oils into biodiesel. Nb2O5.nH2O is known to have strong surface acidity and it reportedly2 increases Lewis acid sites at temperatures higher than 500 oC, whereas Bronsted acid sites are more abundant at temperatures between 100 and 300 oC. This study, which is a continuation of other investigations of this research group3, aims to implement a methodology for preparing methylic biodiesel through transesterification process of cotton, coconut and flaxseed oils, monitoring heat treatment of Nb2O5.nH2O catalyst ratios and different proportions of catalyst mass/oil mass.