POLYMER SOLUBILITY THEORY PREDICTS EFFICIENCY OF RESIDUAL OIL EXTRACTION BY POLAR SOLVENTS

ABSTRACT

Light paraffinic solvents (C2 to C7) have traditionally been utilized by the petroleum refining industry to extract oils from crude distillation residua. Extracted oils constitute feedstock to lubricants manufacture and, to a lesser extent, additional cracking stock. More recent literature reveals a growing interest in polar, non-hydrocarbon partially oil-soluble solvents such as alcohols, ketones, and esters of lower carboxylic acids. In this work, articles and patents which report the separation of residua into asphalt and extracted oil by means of polar solvents are briefly reviewed, and the separation performance of same of those solvents is correlated to the solute-solvent interaction parameter (?) in the Flory-Huggins theory of polymer solubility. The three dimensional solubility parameter (δ) approach is followed to estimate ? for the solvents of interest at the appropriate operating conditions. The saturate, aromatic, and polar compounds fractions of a bitumen are characterized by solubility parameters equal to the values of δ of the solvents or mixtures thereof used by the standard ASTM D-2007 chromatographic fractionation of the deasphaltenated oil (DAO). A mean value of ? is found for every DAO-solvent pair, treatment ratio and temperature. For each solvent considered, yields of extracted oil at varying operating conditions (temperature, pressure, solvent /feed ratio) are found to be well correlated to ?, in according with theoretical predictions that the lower a value of ? a solvent has for a given solute, the better it dissolves the solute and the higher the yield.

It is suggested that this type of approach could supply criteria to select solvents and operating conditions for applications requiring high yields (to produce additional cracking stock) or lower yields but high rejection of metals and heteroatoms (e.g. for lube oil bases extraction).