Method of separating petroleum-containing material into fractions, extraction system, and extraction fluid therefor

A method of separating a petroleum-containing material into at least two fractions, including the steps of:

• introducing into an extraction column petroleum-containing material as well as a solvent mixture comprising 50%-90% by volume sub-critical carbon dioxide and 1%-50% by volume of at least one co-solvent selected from the group consisting of propane, ethane, butane, propylene, 2 methylpropane, 2,2 dimethylpropane, propadiene, dimethylether, chlorodifuoromethane, difluoromethane and methylfluoride, wherein said introducing step comprises introducing both said petroleum-containing material and said solvent mixture into a top portion of said extraction column;
• allowing the petroleum-containing material to percolate down through said extraction column;
• removing from a lower portion of said extraction column a fraction containing solvent mixture and solvated petroleum-containing material;
• withdrawing from a bottom portion of said extraction column a dense fraction of said petroleum-containing material;
• and
• conveying said removed fraction of solvent mixture and solvated petroleum-containing material to a recovery unit for separating solvent mixture from solvated petroleum-containing material.