Cuprous‐based composite ionic liquids for the selective absorption of CO: Experimental study and thermodynamic analysis

Abstract

Three cuprous-based composite ionic liquids (ILs) [EimH][OAc]-xCuOAc (x = 0.5, 0.6, 0.7) were prepared and employed for efficient absorption of CO. It is shown that the cuprous composite IL [EimH][OAc]-0.6CuOAc exhibited the largest absorption capacity for CO (0.031 g/g at 293.15 K and 1 bar) and had a record CO/N 2 selectivity of 967, which is better than most of common ILs and solvents reported in the literature. The results of Fourier transform infrared (FTIR) spectra, electrospray ionization mass spectrometry (ESI-MS) analysis, and theoretical calculations reveal that such superior CO capacity mainly resulted from two kinds of chemical interaction between CO and the active anionic species [Cu(OAc) 2 ] À in [EimH][OAc]-0.6CuOAc. Furthermore, a "deactivated IL model" was further proposed to accurately describe the absorption behavior of CO in [EimH][OAc]-0.6CuOAc, in which the thermodynamic parameters including Henry's law constants, reaction equilibrium constants, and absorption enthalpies were estimated by the correlation of the experimental solubilities of CO.

Equimolar CO Capture by Cuprous-Based Quaternary Deep Eutectic Solvents

“…It is found that the quaternary DES [Emim]­Cl-CuCl-ZnCl 2 -EG showed an extremely low capacity in the capture of pure N 2 or CO 2 or H 2 in comparison with efficient absorption of CO. The ideal absorption selectivities of CO 2 /CO, H 2 /CO, and N 2 /CO were calculated to be 23, 18, and 943 at 298.2 K and 1.0 bar, respectively, indicating that [Emim]­Cl-CuCl-ZnCl 2 -EG is much better than many reported DESs or ILs in the literature. − ,,,, The quaternary DES [Emim]­Cl-CuCl-ZnCl 2 -EG thus shows remarkable potential for selective absorption of CO from other competitive gases.…”

“…This suggests that the π-complexation between CO and Cu + species in [Emim]­Cl-CuCl-ZnCl 2 -EG is relatively slow, requiring enough and long contact time. In addition, the CO uptake capacities and rates of [Emim]­Cl-CuCl and [Emim]­Cl-CuCl-ZnCl 2 -EG were compared with those of reported ILs and DESs such as [Bmim]­[Tf 2 N], [P 4448 ]­[Pen], [EimH]­[CuCl 2 ], [TEA]­[CuCl 2 ], [EimH]­[OAc]–0.6CuOAc, and [BimH]­Cl-CuCl-1.0ZnCl 2 . ,− ,, As seen from Table , the solubility of CO in [Emim]­Cl-CuCl-ZnCl 2 -EG at 298.2 K was 1–2 orders higher than the cases of all the current reported absorbents. The CO absorption equilibrium time of 20 min for binary DES [Emim]­Cl-CuCl was comparable to that of the reported composite IL [EimH]­[OAc]–0.6CuOAc.…”

“…Also, the quaternary DES [Emim]Cl-CuCl-ZnCl 2 -EG could be stable enough for the absorption and desorption of CO in the temperature range of this work. In addition, the melting temperatures of EG and [Emim]Cl-CuCl were found to be 262 and 217 K, respectively (Figures S4 and S5 12,[14][15][16][17][18]23,26 As seen from Table 2, the solubility of CO in [Emim]Cl-CuCl-ZnCl 2 -EG at 298.2 K was 1−2 orders higher than the cases of all the current reported absorbents. The CO absorption equilibrium time of 20 min for binary DES [Emim]Cl-CuCl was comparable to that of the reported composite IL [EimH][OAc]−0.6CuOAc.…”

“…Moreover, compared to the free CO (2143 cm −1 ), the vibration frequency of captured CO from the complex of Cu(CO) + in the liquid phase was obviously red-shifted, confirming the chemical interaction of [Emim]Cl-CuCl-ZnCl 2 -EG with CO to form the complex of Cu(CO) + . 16,18 XPS characterization for CuCl, ZnCl 2 , [Emim]Cl-CuCl-ZnCl 2 , and [Emim]Cl-CuCl-ZnCl 2 -EG was carried out to obtain the detailed valence states of Cu and Zn elements (Figure 6). The binding energy characteristic of Cu 2p of CuCl is located at 932.5 eV.…”

“…Being a type of advanced solvents, ionic liquids exhibit a variety of unique properties such as tunable designability, high dissolvability, and negligible volatility. − So far, many ILs have been reported and employed for CO absorption. − For example, Ohlin et al used a common IL [Bmim]­[Tf 2 N] to reach a very low CO absorption capacity of 1.25 × 10 –3 mol/mol at 303.2 K and 1.0 bar. Tao et al designed a kind of carbanion-based ILs for reversibly capturing CO with a capacity of 0.046 mol/mol at 298.2 K and 1.0 bar.…”