Catalytic extraction of naphthenic acids from acidic petroleum crude oil utilizing an ethanolic 2- methylimidazole over Ca/Al₂O₃ and K/Al₂O₃ catalysts / Noraini Safar Che Harun

Naphthenic acids (NAs) corrosion is a major problem to the oil refinery equipment in the petroleum industry when processed at high temperature of 220-340oC. The acidity level in the crude oil is measured by the Total Acid Number (TAN) value. In this study, a catalytic extraction method was introduced to lower the TAN in crude oil to below than one mg KOH/g utilizing ethanolic 2-methylimidazole catalysed by Ca/Al2O3 and K/Al2O3 heterogeneous catalysts. The roles of 2-methylimidazole in ethanol was to help the reducing of TAN in crude oil by adding the catalysts and increasing the catalytic activity. Calcium nitrate (Ca (NO3)2) and potassium nitrate (KNO3) were utilized as a catalyst precursor and were supported onto alumina oxide (Al2O3). The Ca/Al2O3 and K/Al2O3 were successfully prepared by the Incipient Wetness Impregnation (IWI) method and calcined at different calcination temperature of 700, 900 and 1000oC. The parameters studied were the effect of reaction temperature, reaction time, catalysts without reagent, catalyst loading, calcination temperatures and reusability. The catalytic extraction reaction was fixed at a reaction time of 15 minutes at 35oC. The prepared catalyst were then characterized by using X-Ray Diffraction Spectroscopy (XRD), Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX), Fourier Transform Infrared Spectroscopy (FTIR) and Thermal Gravimetry Analysis Differential Thermal Analysis (TGA-DTA), and Brunauer-Emmett-Teller (BET) to obtained its physicochemical characteristic. Based on characterization of FTIR analysis, stretching mode of pure metal oxide (M=O) were detected for both fresh and used catalyst. Functional group of CH3, carboxylic acid (C=O), CH2, O-H and C-N were detected at the catalyst after reaction, which indicates that impurities have been adsorbed on both catalysts after reaction. Based on TGA-DTA analysis, temperature 700oC is suitable since all impurities in the precursor had been removed. XRD results of both catalysts showed a semicrystalline phase with the presence of Al2O3 rhombohedral, monoclinic and hexagonal species. SEM micrograph illustrated an inhomogeneous distribution of various particle sizes, which confirmed the presence of Ca and K metals on the prepared catalyst. EDX results confirmed the presence of 6.69% by weight composition of Ca and 6.50% for K metal in the prepared catalyst. Characterization using BET analysis showed the Ca/Al2O3 catalyst calcined at 700oC gave the highest surface area of 83.32 m2 /g and 120.11 m2 /g for K/Al2O3. The result shows that Ca/Al2O3 and K/Al2O3 catalysts had successfully reduced TAN value from acidic crude oil below one mg KOH/g. From the results, the Ca/Al2O3 catalyst gave a better reduction of TAN with 0.46 mg KOH/g compared to the K/Al2O3 catalyst which only reduced up to 0.93 mg KOH/g.In summary, the catalytic extraction reaction had successfully reduced the acid number in the crude oil sample to the lowest TAN value by operating at lower temperatures and cost-effective way to remove acid from crude oil.