Extraction/adsorption as applied to the dearomatization of white mineral oil

Abstract

Cyclic adsorption units can be considered as an alternative for the regeneration of the solvent being continuously recycled to extraction units. The concept was studied here with an example of dearomatization of mineral oil. Thermodynamic and kinetic parameters of the units were determined in single experiments. The operation of an extraction/adsorption process was then simulated. A model contaminated oil was purified from aromatics by extraction with ethylene glycol (EG)in a stirred tank. The aromatic impurity was ethylbenzene (EB), which was added to a USP grade mineral oil feedstock. The partition coefficient for the EB:EG:oil system and the global mass transfer coefficient for the stirred tank were measured. The solvent was regenerated by adsorption of the aromatic impurity over a fixed bed of activated carbon. The adsorption isotherm was found to be almost linear in the range of interest. Mass transfer kinetics were described with the approximate model of linear driving force. Regeneration of the bed by flushing with hot solvent was tried and the feasibility of regeneration and cyclic operation was demonstrated. A plant with 3 countercurrent mixer-settlers and a packed bed with activated carbon granules was used as example. The process was modelled by the corresponding set of differential equations which were solved by finite differences. Process variables were thus estimated as a function of time and space. The results indicate that this process combination is feasible and convenient.