Combination of molecular dynamics simulation, COSMO-RS, and experimental study to understand extraction of naphthenic acid

The forecast of an increase in the consumption of petroleum products, together with the growing scarcity of new deposits, makes it necessary to take full advantage of existing ones. The main problem faced by the petrochemical industry is high acid crude oils, which produce corrosion in equipment and high monetary losses. Crude oil acidity is usually calculated by making use of the total acid number (TAN). Current operations for the elimination of naphthenic acid (NA) have several drawbacks so at present this has led to new lines of research, among which the application of ionic liquids (ILs) in the extraction of this compound stands out. In this work, the extractive behavior of 6 different ILs has been analyzed with simulations of molecular dynamics (MD), a technique based on classical mechanics that allows visualizing the movement of molecules while they interact. This allows us to study the extraction mechanism of NA by ILs, as well as transport properties such as diffusion coefficients. In addition, it will be experimented in the laboratory with the same cases to contrast the results obtained, making use of a synthetic crude oil (SC, 150 g/mol, TAN equal to 3.8), which was treated with every IL at four different temperatures (30, 70, 90 and 120 °C). The IL/NA ratio implemented was 1:1 mol/mol, which corresponded more or less with the IL/crude ratio of 0.015 g/g. To support (MD) results and experimental results, the COSMO-RS model was used to characterize ILs analyzing the results obtained by the σ-profile. COSMO-Therm was put into practice to study the theoretical predictions of the TAN in the liquid/liquid phase equilibria where results were in agreement with the experimental ones except for acetate, whose extraction mechanism is supposed to be different (neutralization). Computer simulation suggests that a longer alkyl chain of [BMIm] respect [EMIm] behaves better in extraction, and it seems that the anion plays a major role in the extraction process of the NA than the cation of the ILs. This tendency has been correlated with the experimental results.