Effects of Citric Acid as a Chelating Agent on the Performance of a Heavy Oil Hydrotreatment Catalyst

Hydrotreatment catalyst was prepared by adding citric acid to improve the metal dispersion and reduce the metal-support interaction (MSI) of the catalyst. The catalyst was characterized by the method of Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), NH3-temperature-programmed desorption (NH3-TPD) and thermogravimetry-differential scanning calorimetry (TG-DSC). Experimental and characterization results showed that citric acid intensively interacted with the active metal components of a catalyst. This interaction improved metal dispersion, and lessened the amount by which the specific surface area and pore volume decreased after corresponding decreased amounts of support-loaded metal components. The addition of citric acid favored the interaction of Ni and W with the support. The hydrotreatment performance of the citric acid-modified catalyst CMcat was higher than that of Ni-W/CYCTS. The hydrotreatment performances of the catalysts modified with citric acid were higher than that of the unmodified catalyst. The catalyst with 5% citric acid showed the highest HDS and HDN conversions, reaching 96% and 63%.