The molecular characteristics dominating the solubility of gases in ionic liquids

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1 The molecular characteristics dominating the solubility of gases in ionic liquids Yu-Feng Hu, * Zhi-Chang Liu, * Chun-Ming Xu, Xian-Ming Zhang State Key Laboratory of Heavy Oil Processing and High Pressure Fluid Phase Behavior & Property Research Laboratory, China University of Petroleum Beijing 09, China ( huyf358@sina.com; Fax: ; Tel.: ). Supporting information The solubilities of various gases in typical ionic liquids Table S Solubilities of various gases in typical ionic liquids ionic liquid(s) temperature(s) (K) pressure(s) a CO [C mim]([tf N], [TfO], [DCA]), [C mim][pf 6 ], [P 6,6,6, ][Cl] b mmhg 5 [C 7 mim][tf N], [P n mim][tf N] ( n = 3) c ~ atm 53 [C mim][meso ] [C mim][pf 6 ], TMGL d [C mim][pf 6 ] 33.5; ; ; ; ; 93 5; 95 and 5; ; [C mim][bf ], [C mim][pf 6 ] ([C 6 mim], [P, ], [ETT])[FEP] e [C mim]([tf N], [TfO], [DCA]), [P 6,6,6, ][Cl] , ,95 ([C mim], [C 3 --Memim], [C -3-MePy], ~ bar 77

2 [perfluoro-hmim])[tf N], [C mim][bf ] f [C mim]([pf 6 ], [BF ]) bar 7 ([C n mim], [C 8 H F 3 mim])[tf N] (n=3,, 6, 8), bar 00 [C 3 mim][pf 6 ], [,-dibutyl-3-phenylimidazolium][tf N], [-butyl-3-phenylimidazolium][tf N] g [C 6 mim][tf N] ; ; [C 6 mim][pf 6 ] bar 69 [C n mim][tf N] ( n =, 6, 0 ) [C mim][pf 6 ], [C mim]([tf N], [TfO], [DCA]), < atm 95 [P 6,6,6, ][Cl] [P 6,6,6, ]([C H 5 PhSO 3 ], [MeSO 3 ]) h [C mim]([tfa], [C 7 F 5 CO ]), ([C 8 H F 3 mim], [C 6 H F 9 mim], [C 6-3-MePy], [b -Nic], [Choline], [N,,, ], [Et 3 NBH mim])[tf N], [N,,, ][DOC], Ecoeng 500, Ecoeng M, [C 5 mim][(c F 9 ) 3 PF 3 ], [C 6 mim]([(c F 5 ) 3 PF 3 ], [(C 3 F 7 ) 3 PF 3 ], [Tf N], [ACE], [SAC]) i [C mim]([bf ], [Tf N]), [C mim][pf 6 ], [C 6 mim]([pf 6 ], [BF ], [Tf N]) [C mim][bf ], [C mim][dca] ~ 05 [C mim][y], ([C n mim], [C 6 --Memim])[Tf N] ( n = 6, 8) j HEF, HEA, HEL, THEAA, THEAL, HEAF, bar HEAA, HEAL k

3 [C mim][mdegso ] l [C mim][tfo] [C mim][bf ], [C mim]([bf ], [PF 6 ], [Tf N], 303.5, [TfO], and [DCA]) [C mim][tf N] kpa 30 ([C 8 mim], [C 0 mim], [C 8 H F 3 mim])[tf N] kpa 03 [C mim]([tf N], [B(CN) ]), [C mim]([dca], room temperature 09 0 atm 09 [C(CN) 3 ]) ([C -3-MePy], [C 8 mim], [C 6 mim])[bf ], bar 08 [C 6 mim][tf N], [C mim]([tf N], [BETI], [TFA], [TfO]) m [C mim][ac] [C mim]([tfsa], [NMes ]) n atm 0 [hemim]([pf 6 ], [TfO], [Tf N]) o CO, CF 3 CFH, SO, and NH 3 [C mim][tf N], [C mim]([pf 6 ] and [MeSO ]), [C 6 mim]([cl] and [Tf N]) [C mim][pf 6 ] CO [C mim][pf 6 ] H S [C mim][meso ] CO vapor liquid liquid equilibra 83. and and CO absorption isotherms ([C mim], [C --Memim])[Tf N], bar 7 ([C mim], [C --Memim])([PF 6 ], [BF ]) 3

4 ([C mim], [C mim])([tfa], [Ac]), ([C mim], [C 6 mim])[tf N], [C mim]([pf 6 ], [BF ], [PRO], [ISB], [TMA], [LEV], [TFES], [SUC], [IAAc]), [TBP][FOR], [C 6 mim][fap], [C mim] [IDA] p [C mim]([tfa], [Ac]) [C mim][tfo], [C mim]([etso ], [DCA]) [Choline][Pro] q 33.5 ambient pressure [C 6 mim][tfo], [N,,,3 ][Tf N] bar [C n mim][bf ] ( n =, 6, 8) P[VBTMA][BF ], P[VBMI][BF ] r bar 5 [C n mim][(c n ) PO ] (n=,, ) s kpa 7 [C mim]([pf 6 ], [BF ]) phase behavior of the system(s) IL CO [C n mim][pf 6 ] (n=,, 6) [C mim]([pf 6 ], [NO 3 ]), [C 8 mim]([pf 6 ], [BF ]), bar 69 [C Py][BF ], [C mim][etso ] t ([C mim], [hpmim])[no 3 ] u [C 6 mim][br] 33.5, bar [C 0 mim][tf N] [C mim][pf 6 ]

5 bubble-point data for different CO mole fractions of CO in the system IL CO [C mim][bf ] [C n mim][tf N] ( n =, 5 ) [C mim]([ac], [TFA]) [C 6 mim][pf 6 ] [C mim][pf 6 ] [C 6 mim][bf ] [C mim][tf N] ; ; [C n mim][tf N] ( n =,, 6, 8 ) [C mim][tf N] [C n mim][tfo] ( n =,, 6, 8 ) [C mim]([tf N], [DCA]) [C 8 mim][bf ] [C mim]([bf ], [SCN]), [C mim][mp], [(ETO) IM][Tf N] v bar 59 [C mim][cl] [C 6 mim][tf N] m--heaa() w m--heaf() x CO ([C n mim], [C --Memim], [C --Memim], bar 50 [C m Py], [C --MePy], [C --MePy], [C -3-MePy], [C 8-3-MePy], [C --MePy], [C --MePy], [C 8 --MePy], [N,,,-OH ], 5

6 [N,,8,-OH ], [P, ])[Tf N] (n=,,, 6, 8; m=,, 6, 8), ([C mim], [C mim], [C mim], [C 6 mim], [C 8-3-MePy])[BF ], [C mim]([pf 6 ], [SbF 6 ], [CF 3 CO ]), [P, ][TFA], [C -3-MePy][DCA], and etc. y CO, CO, and H (molecular simulation results) [C mim][pf 6 ] CO, Ar, and H (molecular simulation results) [C 6 mim][tf N] bar 07 H O and CO (atomistic Monte Carlo simulation results) [C 6 mim][tf N] CO bar 5 [C 6 mim][tf N] H O kpa 5 CO, C H 6, and H [C 6 mim][tf N] kpa 8 CO, H, N, O, and CO [MDEA][Cl] z CO, ethylene, propylene, -butene, and,3-butadiene [C mim]([tf N], [TfO], [BETI]), [C mim][pf 6 ], ,97 atm 9,97 [P 6,6,6, ][Cl] ([N,,,3 ], [N 6,,,3 ], [N 0,,,3 ], [N,,, ], [N 6,,, ], atm 98 [N 0,,, ], [N,8,8,8 ], [N 6,,, ])[Tf N] [P 6,6,6, ]([Cl], [DCA], [Tf N]), [P,,, ][DBS] atm 3 [P,,, ][DEP] aa CO, CH, and N 6

7 [NC(CH ) n mim][tf N]( n =, 3, 5 ), atm 56 [HCC-C mim][tf N], ([C mim], [C mim], [C 6 mim])[tf N] [C mim]([tf N], [BF ]), ~ atm 3 [C mim][tf N] [C mim][bf ] CH and N [C mim]([tf N], [DCA], [TfO]), [C 6 mim][tf N] ~ atm 33 CO and H ([N,,, ], [C mim], [C mim])[tf N] kpa 3 CO, C H 6, CH, O, N, H, Ar, and CO [C mim][bf ] kpa 6 [C mim][pf 6 ] kpa 7 ethane, ethene, propane, propene, isobutane, butane, -butene,,3-butadiene, and CO [C mim]([dca], [Tf N], [TfO]), ~ atm 35 [C mim]([pf 6 ], [BF ]) [C mim][pf 6 ] ([C mim], [N 6,,, ])[Tf N] ~ atm 38 H O O [C mim]([pf 6 ], [BF ], [Tf N]), room temperature 70 ~ atm 70 [C --Memim]([PF 6 ], [BF ], [Tf N]), [bm im][tf N] ab SO 7

8 [C 6-3-MePy][Tf N], [C 6 mim][tf N] bar 70 [C mim]([pf 6 ], [BF ]), TMGL ~ atm 39 ([C mim], [TMGH])[BF ], bar 0 ([C mim], [TMGH])[Tf N] ac [C mim]([meso 3 ], [HSO ], [PF 6 ], [BF ], [Ac], ~ atm [Cl]), [C n mim][meso ] ( n =,,, 6 ) [C mim]([pf 6 ], [Tf N]), bar [C n mim][bf ] ( n =,, 6 ) [C mim][meso ] (from the reference 3 cited in ref. 0) [C 6 mim][tf N] [C mim]([bf ], [TFSA]), bar 63 [TMGH]([BF ], [TFSA]) H O, C 6 H 6, CO, N O, C H, C H 6, O, and Ar [C mim]([pf 6 ], [BF ], [Tf N]), ([N,,, ], bar 6 [P, ])[Tf N], [P,,, ][TOS] ad [C mim]([pf 6 ], [BF ]) room temperature atm 3 [C mim][pf 6 ] [C 6 mim][tf N] [X][Y] ae 93 and 98 6 atm 6 CH (bubble-point curves) [C mim][tf N] H [C 6 mim][tf N] CF 8

9 CHF 3 [C mim][pf 6 ] [C mim][pf 6 ] C H 6 [C 6 mim][tf N] CO, N, CH, and H ([C mim], [C 6 mim])[tf N], [C mim][bf ], ~ atm 9 [C mim][meso ] CO and O [C 6 mim][tf N] CO and O [C mim][bf ] CF, C F 6, and C 3 F 8 [P 6,6,6, ][Tf N] ~ atm 5 CH and Xe [C mim][meso ] [C 6 mim][tf N] H S [C mim]([tf N], [BF ], [PF 6 ]) kpa 5 [C 6 mim]([tf N], [BF ], [PF 6 ]) [C mim]([cl], [Tf N], [BF ], [PF 6 ], [TfO]), ([C mim], [C --Memim], [C --Memim], [C --MePy], [bnpy], [mbpy], [N,,,-OH ], 9

10 [N,,,-OH ], [C Py])[Tf N] af Supplementary Material (ESI) for Chemical Society Reviews CPL-TBAB ILs ag ~ atm 85 [C mim][meso ] [hemim]([pf 6 ], [TfO], [Tf N]) CO and H [C mim][meso ] [C mim][pf 6 ] bar 6 CO and C 3 H 8 [C 6 mim][tf N] CO and C H 6 ([P, ], [C mim], [N,,3,-OH ])[Tf N] ah kpa 6 H and CO [C mim][c 8 SO ], [C mim][etso ] CO and C H [C 8 mim][bf ], [CN-C 3 mim]([dca], [Tf N]), atm 66 [C mim]([n-c 6 H 3 OO], [n-c 8 H 35 OO], [Tf N], [BF ]), [CN-C 3 --Memim]([DCA], [Tf N]) ai CO and H S [C mim][etso ] kpa 57 bubble-point data of N O in the IL gas system [C mim]([bf ], [SCN]), [C mim][mp], bar 58 ([(OH) IM], [(ETO) IM])[Tf N] aj 0

11 C H and C H [C mim]([mehpo 3 ],[Me PO ]), [C mim]([mehpo 3 ], [BuHPO 3 ], [Me PO ], [Ac], kpa 8 [TFA], [MeSO ], [BF ], [Tf N]), [P, ]([BuHPO 3 ], [Ac], [Tf N]) ak NH 3 [C mim]([ac], [EtSO ], [SCN]), [N -OH,,,H ][Ac] al [C mim]([pf 6 ], [BF ]), [C mim][tf N], [C 6 mim][cl] [C n mim][bf ] ( n =,, 6, 8 ) CH 3 F, C H 5 F, and CHF CHF [C mim][pf 6 ] CO, CH F, CHF 3, C F 5 H, CF 3 CH F, CF 3 CH 3, and CHF CH 3 [C mim]([pf 6 ], [BF ]) CF 3 CH F [C mim]([pf 6 ], [HFPS], [TPES], [TTES]), [C mim][bei], [P 6,6,6, ][TPES], [P,,, ][HFPS] am [C 6 mim]([tf N], [BF ], [PF 6 ]) bar 76 CH F [C mim]([pf 6 ], [BF ], [Ac], [SCN], [MeSO ], [TFES], [HFPS], [FS], [TPES], [TTES]), [C 3 --Memim]([TMeM], [Tf N]), [C mim]([bei], [Tf N], [TFES]), [C 3-3-MePy][Tf N],

12 [C -3-MePy][Tf N], [C 7 mim][tfes], [C mim][tfes] an CFCl 3, CHCl 3, CDCl 3, CFCl CF Cl and CHCl CF 3 (VLLE data of the system IL gas) [C mim][pf 6 ] ~ atm 75 CO, propane, propene, butane, and -butene [C mim][tf N] CO, C H, C H 6, CH, Ar, O, CO, H, and N [C mim][pf 6 ] bar 9 a Unit: MPa unless otherwise noted. b [C n mim] + =-alkyl-3-methylimidazolium cation, [Tf N] = bis(trifluoromethylsulfonyl)imide anion, [TfO] =trifluoromethanesulfonate anion, [DCA] =dicyanamide anion, [ P n, n, n 3, n ] + =quaternary phosphonium cation. c [P n mim] + =-(Oligo(ethylene glycol) monomethyl ether)-3-methylimidazolium cation. d TMGL=,,3,3-tetramethylguanidium lactate e [P, ] + =N-butyl-N-methylpyrrolidinium cation, [ETT] + =S-ethyl-N,N,N,N -tetramethylthiouronium cation, [FEP] =tris(pentafluoroethyl)trifluorophosphate anion. f [C n --Memim] + =,-dimethyl-3-alkylimidazolium cation, [C n -3-MePy] + =-alkyl-3-methylpyridinium cation, [perfluoro-hmim] + =-(3,,5,6-perfluorohexyl)-3-methylimdazolium =-methyl-3-(3,3,,,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)imidazolium cation. cation. g [C 8 H F 3 mim] + h [C H 5 PhSO 3 ] = dodecylbenzenesulfonates anion. i [TFA] =trifluoroacetate anion, [C 7 F 5 CO ] = pentadecafluorooctanoate anion, [C 6 H F 9 mim] + =-methyl-3-(3,3,,,5,5,6,6,6-nonafluorohexyl) imidazolium cation, [b -Nic] + =-butyl-nicotinic acid butyl ester cation, [ N n, n, n 3, n ] + =quaternary ammonium cation, [Et 3 NBH mim] + =(-methylimidazole)(triethylamine)boronium cation, [DOC] =docusate anion, Ecoeng 500=PEG-5 cocomonium methylsulfate, Ecoeng M=-butyl-3-methylimidazolium -(-methoxyethoxy)ethylsulfate, [(C F 9 ) 3 PF 3 ] = tris(nonafluorobutyl)trifluorophosphate anion, [(C F 5 ) 3 PF 3 ] =tris(pentafluoroethyl)trifluorophosphate anion, [(C 3 F 7 ) 3 PF 3 ] =tris(heptafluoropropyl)trifluorophosphate anion, [ACE] =acesulfamate anion, [SAC] =saccharinate anion. j [Y]=[BF ], [PF 6 ], [TfO], [NO 3 ], [Tf N], [DCA], and [methide]([methide] =tris(trifluoromethylsulfonyl)methide anion). k HEF=-hydroxy ethylammonium

13 formate, HEA=-hydroxy ethylammonium acetate, HEL=-hydroxy ethylammonium lactate, THEAA=tri-(-hydroxy ethyl)-ammonium acetate, THEAL=tri-(-hydroxy ethyl)-ammonium lactate, HEAF=-(-hydroxy ethoxy)-ammonium formate, HEAA=-(-hydroxy ethoxy)-ammonium acetate, HEAL=-(-hydroxy ethoxy)-ammonium lactate. l [MDEGSO ] =-(-methoxyethoxy) ethylsulfate anion, m [BETI] =bis(pentafluoroethylsufonyl)imide anion. n [TFSA] = bis(trifluoromethanesulfonyl)amide anion, [NMes ] =bis(methanesulfonyl)amide anion. o [hemim] + =-(-hydroxyethyl)-3-methylimidazolium cation. p [PRO] =propionate anion, [ISB] =isobutyrate anion, [TMA] =trimethylacetate anion, [LEV] =levulinate anion, [TFES] =,,,-tetrafluoroethanesulfonate anion, [SUC] =succinamate anion, [IAAc] =iminoacetic acid acetate anion, [TBP][FOR]=tetrabutylphosphonium formate, [FAP] = tris(pentafluoroethyl)trifluorophosphate anion, [C mim] [IDA]=bis(-butyl-3-methylimidazolium) iminodiacetate. q [Choline][Pro]=(-hydroxyethyl)-trimethyl-ammonium(S)--pyrrolidine-carboxylic acid salt. r P[VBTMA][BF ]=poly(pvinylbenzyltrimethyl ammonium tetrafluoroborate), P[VBMI][BF ]=poly(-(p-vinylbenzyl)-3-methyl-imidazolium tetrafluoroborate). s [(C n ) PO ] =dialkylphosphate anion. t [C n Py] + =-alkylpyridinium cation. u [hpmim] + =-(3-hydroxypropyl)-3-methylimidazolium cation. v [SCN] =thiocyanate anion, [MP] =methylphosphonate anion, [(ETO) IM] + =,3-diethoxyimidazolium cation. w m--heaa=n-methyl--hydroxy ethylammonium acetate. x m--heaf=n-methyl--hydroxy ethylammonium formate. y [C n --MePy] + =-alkyl--methylpyridinium cation, [C n --MePy] + =-alkyl--methylpyridinium cation, [N,,,-OH ] + =,-dimethyl--butyl--(-hydroxyethyl) ammonium cation, [N,,8,-OH ] + =,-dimethyl--octyl--(-hydroxyethyl)ammonium cation. z [MDEA][Cl]=-(-hydroxyethyl(methyl)amino) ethanol chloride. aa [DBS] =dodecylbenzenesulfonate anion, [DEP] =diethylphosphate anion. ab [bm im] + =-butyl-,3,,5-tetramethylimidazolium cation. ac [TMGH] + =,,3,3-tetramethylguanidinium cation. ad [P,,, ][TOS]=tri-isobutyl-methyl phosphonium p-toluenesulfonate. ae [X][Y]=[C mim]([bf ], [PF 6 ], [Tf N], [SbF 6 ], [TFA] and [TfO]), [C --Memim][Tf N], ([C 6 mim], [C 8 mim])[bf ], ([C Py], [P, ])[Tf N], [P 6,6,6, ][(C F 5 ) 3 PF 3 ]. af [bnpy] + =-benzylpyridinium cation, [mbpy] + =-benzyl--methylpyrrolidinium cation, [N,,,-OH ] + =,-dimethyl--ethyl--(-hydroxyethyl)ammonium cation. ag ILs based on different mole 3

14 ratios of caprolactam and tetrabutyl ammonium bromide. ah [N,,3,-OH ] + =,-dimethyl--propyl--(-hydroxyethyl)ammonium cation. ai [CN-C 3 mim] + = -butyronitrile-3-methylimidazolium cation, [n-c 6 H 3 OO] =palmitate anion, [n-c 8 H 35 OO] =stearate anion, [CN-C 3 --Memim] + =-butyronitrile-,3-dimethylimidazolium cation. aj [(OH) IM] + =,3-dihydroxyimidazolium cation. ak [MeHPO 3 ] =methylphosphonate anion, [BuHPO 3 ] =butylphosphonate anion. al [N -OH,,,H ] + =-(-hydroxyethyl)-,-dimethylammonium cation. am [HFPS] =,,,3,3,3-hexafluoropropanesulfonate anion, [TPES] =,,-trifluoro--(perfluoroethoxy) ethanesulfonate anion, [TTES] =,,-trifluoro--(trifluoromethoxy)ethanesulfonate anion, [BEI] =bis(pentafluoroethylsulfonyl)imide anion. an [FS] = -(,,,-tetrafluoroethoxy)-,,,-tetrafluoroethanesulfonate anion, [TMeM] =tris(trifluoromethylsulfonyl)methide anion. Experimental Procedures Samples. CHCl 3 was supplied by Beijing Xiandaidongfang Chmical Ltd. [C 6 mim][(c F 5 ) 3 PF 3 ], [C mim][tf N], and [C 6 mim][tf N] were purchased from MercK with the claimed purity more than 99%. [P, ][Br] was prepared according to literature methods. 8,66 [P, ][Tf N], [C mim][dca], and [C mim][pf 6 ] were prepared with the well-established procedures of our and other previous works. 8,66 68 The ILs before use were dried under vacuum over CaCl for days at 353 K, and were further dried with 3 Å molecular sieve for days immediately. The water content after drying before use, measured by Karl Fisher titration, was less than 0.0 wt%. Raman spectra measurements. The Raman spectra were obtained using a HR800 micro-raman spectrometer (Jobin Yvon, France) employing a 785 nm laser beam, and the instrument resolution is 0.5 cm. 3 The temperatures ranging from 73 to 353 K on the sample were controlled using a Linkam TS600 hot stage with a temperature stability of ± 0.5 K. The temperature was held for at least 5 min at each selected temperature point in order to get more accurate temperature value of the sample. The Raman spectra were

15 measured in the crossed Z( XY ) Z ( VH ) and parallel Z( XY ) Z ( VV ) polarizations, where X, Y, and Z are the cubic axes. All these samples were sealed under vacuum in glass tubes for the Raman measurements. Analysis of the variation of G c with σ The G c is expressed as 3 G c 6y 8y πpσ 3 = ( r r) + r ln ( y) + r r + r RT y ( y) kbt 3 6 () σ+ σ σ It follows from r = that σ = σ r and r σ σ = + > () We then obtain σ σ σ = = r 3 6 r r + r 3 6 (3) πpσ πpσ r r + r = kt 3 6 6kT B B () and G c 6y 8 = ( r r) + r ln y + RT y ( y) 6k T 3 y πpσ ( ) B (5) If y is approximately regarded as a constant, then the effect of r on the G c is πpσσ = + + > 0 dr y ( y) kbt dgc 6y 36y RT ( r ) r (6) It is clear that, the r and thereby the G c is decreasing with increasing the σ. Comparisons of the solubilities of CO in [C mim][pf 6 ] and [C 6 mim][tf N] reported 5

16 in the literatures Pressure, MPa CO, mole fraction Fig. S The CO solubilities in [C mim][pf 6 ] at 33 K: ( ) ([Cl] :.7 mg L ); 90 ( ) (H O: <00 ppm, [Br] : <50 ppm); 9 ( ) ([Cl] : 3 ppm) Pressure, MPa CO, mole fraction Fig. S The CO solubilities in [C mim][pf 6 ] at 98 K: ( ) ([Cl] :.7 mg L ); 90 ( ) (H O: <00 ppm, [Br] : <50 ppm); 9 ( ) (H O: <00 ppm, halogen: <0 ppm); 03 ( ) (H O: ppm, [Cl] : <0 ppm); 66 ( ) ([Cl] : 3 ppm). 9 6

17 6 5 Pressure, MPa CO, mole fraction Fig. S3 Comparison of the CO solubilities in [C 6 mim][tf N] in the K range: ( ); 03 ( ); 67 ( ); 0 ( ); 0 ( ); 66 ( ) fitted values calculated using eqn (0). Comparisons of measured and fitted solubilities of CO in [C n mim][bf ] ( n =, 6 ), [C n mim][tf N] ( n =, 8), and [C 6 mim][pf 6 ] at different temperatures and pressures Pressure, MPa CO, mole fraction Fig. S Comparisons of measured 3 (symbols) and fitted (lines) solubilities of CO in [C mim][bf ]:( ) K; ( ) 3.5 K; ( ) 37.5; ( ) 3.5 K. 7

18 9 8 7 Pressure, MPa CO, mole fraction Fig. S5 Comparisons of measured 3 (symbols) and fitted (lines) solubilities of CO in [C 6 mim][bf ]: ( ) 3.5 K; ( ) 37.5 K; ( ) 3.5 K. Pressure, MPa CO, mole fraction Fig. S6 Comparisons of measured 66 (symbols) and fitted (lines) solubilities of CO in [C mim][tf N]: ( ) 98. K; ( ) 33.3 K; ( ) K. 8

19 9 8 7 Pressure, MPa CO, mole fraction Fig. S7 Comparisons of measured 66 (symbols) and fitted (lines) solubilities of CO in [C 8 mim][tf N]: ( ) 98. K; ( ) 33.3 K; ( ) K Pressure, MPa CO, mole fraction Fig. S8 Comparisons of measured 88 (symbols) and fitted (lines) solubilities of CO in [C 6 mim][pf 6 ]: ( ) 33.5 K; ( ) 33.5 K; ( ) 333.5; ( ) 33.5 K. 9

20 References 66. A. K. Burrell, R. E. Del Sesto, S. N. Baker, T. M. McCleskey and G. A. Baker, Green Chem., 007, 9, D. R. MacFarlane, J. Golding, S. Forsyth, M. Forsyth and G. B. Deacon, Chem. Commun., 00, J. Dupont, C. S. Consorti, P. A. Z. Suarez and R. F. de Souza, Org. Synth., 00, 79, 36. 0