Microwave-Assisted Nickel and Vanadium Removal from Crude Petroleum Oil Using Bis(2-ethylhexyl)phosphoric Acid: A Kinetic Study

Among the various metals in crude oils, nickel (Ni) and vanadium (V) exist as oil-soluble organic compounds, making them extremely difficult to remove. The presence of these metals has been proven to have deleterious effects, such as catalyst poisoning and corrosion in crude refinery processes. This study aimed for Ni/V removal from Iranian crude oil using bis(2-ethylhexyl)phosphoric acid (D2EHPA) under microwave heating. The impact of primary process parameters, such as temperature, residence time, and D2EHPA dosage, on Ni and V removal efficiencies was studied. The demetallization reaction kinetics and mechanism were investigated at 230–250 °C and optimized conditions. The findings demonstrated that at low microwave powers of 40–50 W, Ni and V removal efficiencies could reach up to 63% and 72%, respectively, after a reaction time of 1 h at 250 °C. The kinetics of demetallization reactions was found to be of first-order, and the activation energies and pre-exponential factors for Ni and V were estimated to be 29.8 and 34.7 kJ/mol and 16.5 and 66.2 min–1, respectively. A well-fitted kinetic model was proposed based on the coefficients of determination. The reaction between the metalloporphyrins in crude oil and D2EHPA resulted in the substitution of Ni and V with protons provided by D2EHPA, leading to the formation of metal salts that are soluble in water. The formation of N–H bonds in the treated oil, as confirmed by the FTIR analysis results, indicated the occurrence of the demetallization reaction.