The Solvent Extraction Approach to Petroleum Demetallation

Metals are present in petroleum depending on age and conditions of diagenesis, and concentrate during refining in heavy fractions and residua. Nickel and vanadium show particularly deleterious effects on catalysts, such as poisoning, excessive gas and coke formation. Besides, removing vanadium from fuel oils reduces the environmental impact of “acid rain” due to the oxidation of sulphur dioxide in the atmosphere. In this paper, research and industrial practice literature concerning the removal. of nickel and vanadium from petroleum and its fractions by solvent extraction and related techniques is reviewed and arranged into four groups as follows: i) Processes employing hydrocarbon solvents, used to modify the oily matrix solubility parameter in such a way that asphalt/enes be separated. Because a fraction of total metals present are associated to asphalt/enes, deasphaltation implies partial demetallation. ii) Processes using polar solvents, scarcely miscible with petroleum and able to selectively extract from it metallic complexes of heteroatomic ligands (e.g. metalloporphyri ns). iii) Processes not based on molecular phase equilibria like i) and ii) but on the formation, by contact with aqueous solutions, of a separate, colloidally stabilized phase. Either surface active agents are added or the surface activity of substances naturally occurring in petroleum is promoted. iv) Processes based on extraction with chemical reaction (oxidation, chelation) orion exchange between organometallic species in petroleum and ligandsin solution of non-miscibile media.