Kinetic study of ethyl ester transesterification using a hybrid silica catalyst

CTA-MCM-41 hybrid silica was prepared using a 40 °C non hydrothermal method for 2 h and was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and thermogravimetric analysis. Using these techniques was possible to confirm the structural organization with a highly organized hexagonal matrix of the MCM-41 type, quantify the presence of hexadecyltrimethylammonium cations present in the pores of silica and, consequently, to measure the concentration of the catalytic sites present in the material, 1.83 mmol g −1 . This catalyst was used in the transesterification of the esters with the aim of determining the influence of the length of the ester side-chain on the reaction kinetics. The ethyl esters tested had the length of the ester side-chain in the range 1–4 carbons. The catalytic tests were performed at temperatures ranging from 20 to 50 °C, employing a methanol/ester molar ratio of 6:1 and 4% of catalyst relative to the total reactants mass. Conversion close to 80% was observed for the ethyl acetate at 40 °C and decreased as the length of the ester side-chain increased. Fitting using a pseudo-homogeneous reversible first order model enabled determination of the kinetic parameters for each reaction with activation energies between 41.3 and 48.3 kJ mol −1 . Inductive and diffusional effects explain the slower reaction rate and higher activation energy as the size of the molecule increase.