Ionic Liquid Solvents for Gas Sweetening Operations

1. Process System Engineering Group University of Twente Separation Technology Group Ionic Liquid Solvents for Gas Sweetening Operations Lara Galán Sánchez, G. Wytze Meindersma and André de Haan The Netherlands 11th July 2007 - Kingston, Canada

2. Contents • Room Temperature Ionic Liquids (RTILs) • Process advantages • Research • Gas absorption and selectivity • Conclusions • Acknowledgments

3. The choice of the cation and anion determines the physicochemical properties. Room Temperature Ionic Liquids (RTILs) • Organic salts with a melting point below 100 C • Wide liquid range: -96 C up to 300 C • Negligible vapour pressure • Non-volatile • Non-flammable • High thermal, chemical and electrochemical stability • Dissolution of many organic and inorganic compounds • Variable miscibility with water and organic solvents

4. Process features • Big volume operations: • No or very low vapour pressure • Reduction of volatile emissions and contamination • Decreased solvent inventory and solvent make-up volume • High thermal resistance • RTILs can be regenerated • Designer character: • Enhanced selectivity of a specific compound • Defined physical properties required for an economical operation • Promote specific interactions

5. Research • Identification of the potential of the designed RTILs as suitable solvents for CO2/CH4 separation • Comparison of performance to that of existing solvents: • NFM (N-formyl morpholine) • NMP (N-methyl pyrrolidone) • Sulfolane • Aqueous amine solutions

6. Room Temperature Ionic Liquids (RTILs) Tetrafluoroborate, BF4- 1-Butyl-3-methyl-imidazolium, [bmim]+ Bis(trifluoromethanesulfonyl)imide, [NTf2]-: N(CF3SO2)2-

7. [NH2-Im]BF4 [bmim]BF4 [NH2-Im]NTf2 [emim]NTf2 [NH2-Pyrr]BF4 Standard RTILs and NH2-functionalized: Tested RTILs Gravimetric Balance: IGA 002 - Hiden

8. Solvent Regeneration [NH2-Pyrr]BF4 Regenerated T > 353 K P < 10-2 MPa CO2 [NH2-Pyrr]BF4

9. CO2 absorption 343 K 344 K

10. CH4 absorption at 343 K CH4 solubility increases due to physical affinity with the liquid

11. CH4 absorption at 333 K [1]Henni, A., et al. 2006, J Chem. Eng. Data, 51, 64-67

12. CO2 volumetric load at 333 K

13. Selectivity • Individual gas absorption • Comparison at low and high CO2 concentration • Comparison of selectivity of standard ILs with functionalized ILs and physical solvents • Advantage of ILs for CO2 absorption: combination of physical and chemical interactions

14. CO2/CH4 selectivity [NH2-Pyrr]BF4 at 333 k

15. Selectivity individual gas 0.1 M Pa [2]Henni, A., et al. 2005, Canadian J Chem. Eng., 83, 358-361. [3] Murrieta, F., et al.1988, Fluid Phase Equilibria, 44, 105-115. T: 333 K

16. Selectivity individual gas 1 M Pa T: 333 K

17. Process selectivity – PTotal = 1 MPa

18. Process selectivity – PTotal = 1 MPa

19. Solvent effects in the process • Heat of absorption of CO2 and CH4: comparable with those of physical solvents • High viscosity affects mass transfer and kinetics: selection of equipment and operation conditions • Environmental aspects • Opportunity for design

20. Ethylene - ethane solubility [1]Henni, A., et al. 2006, J Chem. Eng. Data, 51, 64-67 [4] Rivas, O., Prausnitz, J., et al. 1979, AIChE J., 25, 975-984. T: 333 K

21. Solvent effects in the process • Solubility of ethane: comparable to NMP, NFM, sulfolane • Solubility of other gases: O2, H2 very low • Co-absorption effect needs to be studied

22. Conclusions • RTILs: good potential solvents for gas sweetening operations • Advantages of physical and chemical solvents are combined by the designed RTILs • The “designer ability” of the RTILs allows to have a suitable solvent for a specific process

23. Acknowledgments Special thanks to Jan de With from Shell Research & Technology Center, Amsterdam for the synthesis of the functionalised ILs Project funded by the Dutch EET program(Ecology, Economy, Technology)Cooperation with: ECNShellTNOHyflux CEPAration BV