Synthesis of ethylene glycol monomethyl ether monolaurate catalysed by KF/NaAlO2 as a novel and efficient solid base

Abstract

A novel solid base catalyst of NaAlO₂ modified with KF (x-KF/NaAlO₂) was prepared using a wet-impregnation method and used for the synthesis of ethylene glycol monomethyl ether monolaurate (EGMEML) via transesterification of ethylene glycol monomethyl ether (EGME) and methyl laurate (ML). The catalyst was characterized using the Hammett indicator method, X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy with an energy dispersive spectrometer. The effect of the reaction parameters such as the amount of KF loading, molar ratio of EGME to ML, dosage of the catalyst, reaction time and temperature on the yield of EGMEML was investigated. These characterizations led to a conclusion that the reaction between NaAlO₂ and KF mainly generates fluoroaluminates, which act as the main active sites for the transesterification. The catalyst shows excellent catalytic activity and good stability. The highest yield of 91% was obtained over 30%-KF/NaAlO₂ at an EGME/ML molar ratio of 3.0, a catalyst amount of 5 wt%, and a reaction time of 4 h at 120 °C. A yield of 80% was obtained after use for three consecutive rounds without reactivation. Furthermore, a desirable yield of 88.0% of a novel biodiesel of ethylene glycol methyl ether soybean oil monoester was obtained with 30%-KF/NaAlO₂ as a catalyst. Moreover, it was found that the reaction follows second-order kinetics, the activation energy (E_a) of the reaction of EGME with ML equals 56.54 kJ mol⁻¹, and the thermodynamic parameters of activation were evaluated based on an activation complex theory of the reaction, and the following data were obtained: ΔG^‡ > 0, ΔH^‡ > 0 and ΔS^‡ < 0, indicating the unspontaneous and endergonic nature of the reaction of EGME with ML. A Koros–Nowak test was conducted and the results confirmed that the diffusion limitations did not affect the catalytic activity. Finally, a few of the physicochemical properties of the EGMEML as biodiesel were determined, and the values were within those of European standards.