Friederike Agel, Peter Schulz, Peter Wasserscheid, Fee Pitsch, Florian Krull, Thomas Melin, Matthias Wessling:
Ag[NTf2]-olefin as ionic liquid in immobilised liquid membranes (ILM) for olefin-paraffin separation
EUCHEM Conference on Molten Salts and Ionic Liquids 2010, Bamberg, 14-19.03.2010
Olefin-paraffin separation is one of the most important processes in petrochemical industry. At present it is done by a highly capital and energy intensive low temperature distillation. For this reason many efforts in research are made in finding alternative processes. One approach is separation through immobilised liquid membranes (ILM). They are made up of porous supports whose pores are impregnated with a liquid. This liquid separates gaseous feed molecules by a solution and diffusion mechanism. Since vaporisation of this liquid in the feed and purge gas streams has always been a problem, the negligible vapour pressure of ionic liquids opens a very promising research field for gas separations. For the separation of olefins and paraffins selectivities can be tremendously increased by dissolving olefin complexing salts of silver or copper(I) in the liquid. They do not only effect a higher solubility of the olefins but also open the possibility of a facilitated transport through the membrane. However, a high metal content in the liquid is required for such a transport mechanism. We here present a new ILM system for the separation of olefins and paraffins based on the neat silver salt AgNTf2 which has a much higher silver content than systems with dissolved silver salts in liquids. The synthesis of AgNTf2 is very simple and upscaling causes no problems. AgNTf2 liquefies in contact with propene by building π-complexes. A very small partial pressure of propene is sufficient to achieve room temperature ionic liquid [Ag(C3H6)xNTf2]. We determined the properties of AgNTf2 and its propene complexes. Propene and propane uptake were measured over the full pressure range. In order to elucidate the transport mechanism we carried out 1H-, 19F- and 109Ag-NMR diffusion measurement at different partial pressures of propene and propane.
olefin-paraffin separation, liquid membrane, ionic liquids