Tungstic Acid-Functionalized Natural Zeolite as a Solid Acid Catalyst for Levulinic Acid Esterification

The investigation of the process of converting levulinic acid (LA) into ethyl levulinate (EL) using tungstic acid (TA)-functionalized activated natural zeolite (AZ) was systematically conducted. The aims of this work were to synthesize and characterize the activated zeolite modified by tungstic acid (TA-AZ) and also evaluate its performance in LA esterification. We employed the wet impregnation approach and ultrasonication-assisted method to produce TA-AZ catalyst with different concentrations of TA (15, 20, and 25 wt%). Fourier transform infrared (FTIR), ammonia-temperature programmed desorption (NH₃-TPD), X-ray diffraction (XRD), scanning electron microscope with an energy dispersive X-ray spectrometer (SEM-EDX), transmission electron microscope (TEM), and surface area analyzer (SAA) were among the analytical methods used to investigate the chemical and physical characteristics of AZ and TA-AZ catalysts. The liquid yields from LA esterification were analyzed by GC-FID. The findings indicated that the 25TA-AZ catalyst exhibited the highest acidity, reaching 3.65 mmol/g. The presence of TA in AZ resulted in an enhancement of LA conversion and an increase in EL yield. The LA esterification process, employing a 25TA-AZ catalyst with a reaction temperature of 150 °C and a weight% of 0.5 wt%, produced 91.72% for LA conversion and 82.65% for EL yield.