Continuous extraction of naphthenic acid from low-grade oil using 1,6-hexanediol in an ammonia solution

•Searching for the best solvent for the acid removal from the High-Acid Crudes (HAC)•The previous computational solvent selection study was verified using an experimental study.•Solvents were tested using a batch-type and bench-scale continuous removal apparatus.•1,6-hexanediol with 3% ammonia solution was found to be the best solvent.•Regeneration scheme was suggested. The efficient use of low-quality crude oil is one short-term solution to overcoming the imminent energy crisis due to the depletion of fossil resources. Several methods have been developed to upgrade low-quality oil, the most important part of which is the removal of acidic components. High-acid crudes can be converted to lower-acid crudes using various methods based on physical and chemical principles. In this contribution, we suggest an efficient and economical method based on liquid–liquid extraction. The candidate solvent was screened from a thermodynamic analysis in a previous study, and the additives and process conditions were adjusted according to experimental results. As the final solvent choice, 1,6-hexanediol in an aqueous ammonia solution showed the best performance with the minimal amount of solvent (weight fraction of 0.6). Experiments showed that the proposed solvent can be used to treat real crude oil used in the industry. A continuous operation scheme was suggested with solvent regeneration and recycling combined with separation of the acidic residue. The results showed that the proposed extraction process can reduce 85% of the acidic component in high-acid crudes and that repeated use of the solvent is possible.