The effect of acid treatment and calcination on the modification of zeolite X in diesel fuel hydrodesulphurization

Faujasite (X, Y) zeolites are considered the main and important catalysts in hydrorefining processes. In order to obtain zeolites with higher acidity and volume of mesopores, post-synthesis modification, dealumination by different pickling techniques (using ethylenediamine tetraacetic acid [EDTA] chelating agent), and thermal treatment (calcination) were employed. The dealumination process led to the removal of the aluminum atoms from the zeolite structure and a rise in acidity while maintaining the zeolite crystalline lattice. X-ray diffraction (XRD), atomic absorption spectrometry (AAS), Fourier-transform infrared (FT-IR), field-emission scanning electron microscopy (FE-SEM), Brunauer–Emmett–Teller (BET), and temperature-programmed desorption of ammonia (NH3-TPD) analyses were performed to study the physicochemical characteristics of the zeolite and catalysts prepared. Atomic absorption spectroscopy showed an increase in the Si/Al ratio in the modified zeolites. Measuring the surface area of zeolite and the volume of the pores through BET-BJH and t-plot methods indicated a reduction in the surface area and an increase in the volume of the pores. Under the influence of the dealumination process, the volume of the mesopores in the modified zeolites increased from 0.056 cm3 g−1 in the initial zeolite (Na-X) to 0.2105 cm3 g−1 (zeolite X1). The acidity of the modified zeolites (X1) increased from 0.32–0.95 mmol NH3/g. The application of the catalysts containing X1 zeolite in the hydrodesulphurization (HDS) process yielded a product with less sulphur (conversion = 87.5%).