Mechanism and Kinetic Modeling of Ethanol Conversion to 1-Butanol over Mg and Al Oxide Derived from Hydrotalcites

Utilizing a mixed Mg/Al oxide derivate from hydrotalcites as catalyst for the ethanol conversation to 1-butanol, catalytic tests were performed using a tubular quartz reactor at different reaction temperatures and following the central composite design for experiment design to evaluate ethanol feed molar fraction and nitrogen (carrier gas) feed flow rate. Reaction products were analyzed by gas chromatography, being qualitatively and quantitatively identified by mass spectrometer detection and by flame ionization detection, respectively. Experimental data was used to propose a mechanism of elementary reactions, which were analyzed thermodynamically to select thermodynamically favorable reactions. With the proposed mechanism, parameter estimation was performed using a particle swarm algorithm, minimizing a least-squares objective function. Results were also compared by analyzing the estimated parameters and Fisher’s test. With the best elementary reaction mechanism, a heterogeneous mechanism, which considers the adsorption, desorption, and surface reaction steps, was also proposed, and its parameters were also estimated. Despite high standard deviations of its estimated parameters, the Fisher’s test proved that it was the best model compared in this work to fit the experimental data. Finally, the results suggest that the 1-butanol production over this catalyst does not follow the Guerbet reaction scheme, because the direct condensation of two ethanol molecules is the most favorable path.