Separation of olefins from paraffins using ionic liquid solutions

Abstract

Methods for separating olefins from non-olefins, such as paraffins, including cycloparaffins, oxygenates and aromatics, are provided. The methods use metal salts to complex olefins, allowing the non-olefins to be separated by a variety of methods, including decantation and distillation. The metal salts are dissolved in ionic liquids, which tend to have virtually no vapor pressure, and which poorly solubilize the non-olefins. Accordingly, the non-olefins phase separate well, and can be distilled without carrying over any of the ionic liquid into the distillate. Preferred salts are Group IB salts, more preferably silver salts. A preferred silver salt is silver tetrafluoroborate. Preferred ionic liquids are those which form stable solutions or dispersions of the metal salts, and which do not dissolve the non-olefins. Further, if the olefins are subject to isomerization, the ionic liquid is preferably relatively non-acidic. The methods involve forming a solution of a suitable olefin-complexing salt in an appropriate ionic liquid. An olefin-containing mixture is contacted with the ionic liquid/salt solution, and the olefins are adsorbed. After the paraffins are removed, the olefins can be isolated by desorption. The olefin-containing mixture can be in the gas phase, or in the liquid phase. The flow of olefin-containing mixtures over/through the ionic liquid can be, for example, co-current, counter-current, or staged in stirred tanks. Countercurrent is preferred as it is the most efficient. The methods can be optimized using combinatorial chemistry.

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