Extraction of naphthenic acid from low-grade crude oil using diol compounds

The extraction of naphthenic acid from low-grade crudes offers economic and environmental advantages over chemical conversion or other separation processes. The properties of the solvent play critical roles for the successful implementation of the extraction process. Solvent screening techniques based on thermodynamic prediction can facilitate the selection of candidate solvents. This study first performed solvent screening based on thermodynamic property estimation using the COSMO-RS method and subsequently verified the solvent performances experimentally. The formation of liquid–liquid equilibrium (LLE), mutual solubility, and ternary LLE were predicted for n-octanol + n-octanoic acid + solvent mixtures. The predicted results were analyzed for the selection of the best candidates to remove acidic components from crude oil. From the theoretical calculations, 1,6-hexanediol was selected as the best candidate solvent. This result was experimentally verified by extracting reagent-grade naphthenic acid from diesel oil using the candidate solvents. The measured results were consistent with the trend observed in the theoretical calculations. Among the candidate solvents, 1,6-hexanediol reduced the acidic component composition corresponding to 5 mg KOH/g down to 1 mg KOH/g with a solvent fraction of 0.6.