Solvent Extraction - Viscosity Index Control

Extraction is typically the second process although this is not always the case. The primary goal of extraction is to remove aromatics and polar molecules. This is accomplished through solvent extraction of the distillate using NMP, furfural, or phenol. By removing aromatics, the VI is raised. Secondary effects of extraction include reduction in the refractive index, reduction in density, reduction in Conradson carbon and improvement in color, color stability and oxidative stability. 

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Ionic liquids have been described as designer solvents [11]. Properties such as solubility, density, refractive index, and viscosity can be adjusted to suit requirements simply by making changes to the structure of either the anion, or the cation, or both [12, 13]. This degree of control can be of substantial benefit when carrying out solvent extractions or product separations, as the relative solubilities of the ionic and extraction phases can be adjusted to assist with the separation [14]. Also, separation of the products can be achieved by other means such as, distillation (usually under vacuum), steam distillation, and supercritical fluid extraction (CO2). 

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