Synthesis of acidic modified UiO‐66 by concentrated sulphation form and its application in the production of fatty acids ethyl esters

Abstract

In this article, UiO‐66 metal–organic frameworks containing structural modifications were synthesized and characterized to increase acidic surface behaviour for application in heterogeneous acid catalysis to produce fatty acid ethyl esters (FAEE) from degummed soybean oil. The solvothermal route synthesized UiO‐66, and the post‐synthesis acid modifications were done by sulphation reaction in strong acidic medium. The synthesized materials were characterized by physicochemical techniques such as X‐ray diffraction (XRD), C‐ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectrometer (FTIR), and N2 physisorption, observing a strong structural modification of the original UiO‐66, but no signal of sulphated ZrO2 was presented. However, the acidic characteristics on the material's surface were increased. A central compound centred on face 23 experiments design was carried out to evaluate three essential reaction variables: temperature, time, and alcohol/oil ratio, obtaining an optimized fit for the UiO‐66‐S35 of temperature at 140°C, time of 3 h, and molar ratio of 16. The optimized statistical adjustment was applied in the reuse cycles assays in three catalyst cycles, reaching the maximum yield of 95% in FAEE, keeping the catalyst active at the end of 3 cycles.