Abstract
The CO2 solubilities (including CO2 Henry’s constants) and viscosities in ionic liquids (ILs)/deep eutectic solvents (DESs)-based hybrid solvents were comprehensively collected and summarized. The literature survey results of CO2 solubility illustrated that the addition of hybrid solvents to ILs/DESs can significantly enhance the CO2 solubility, and some of the ILs-based hybrid solvents are super to DESs-based hybrid solvents. The best hybrid solvents of IL–H2O, IL–organic, IL–amine, DES–H2O, and DES–organic are [DMAPAH][Formate] (2.5:1) + H2O (20 wt %) (4.61 mol/kg, 298 K, 0.1 MPa), [P4444][Pro] + PEG400 (70 wt %) (1.61 mol/kg, 333.15 K, 1.68 MPa), [DMAPAH][Formate] (2.0:1) + MEA (30 wt %) (6.24 mol/kg, 298 K, 0.1 MPa), [TEMA][Cl]-GLY-H2O 1:2:0.11 (0.66 mol/kg, 298 K, 1.74 MPa), and [Ch][Cl]-MEA 1:2 + DBN 1:1 (5.11 mol/kg, 298 K, 0.1 MPa), respectively. All of these best candidates show higher CO2 solubility than their used pure ILs or DESs, evidencing that IL/DES-based hybrid solvents are remarkable for CO2 capture. For the summarized viscosity results, the presence of hybrid solvents in ILs and DESs can decrease their viscosities. The lowest viscosities acquired in this work for IL–H2O, IL–amine, DES–H2O, and DES–organic hybrid solvents are [DEA][Bu] + H2O (98.78 mol%) (0.59 mPa·s, 343.15 K), [BMIM][BF4] + DETA (94.9 mol%) (2.68 mPa·s, 333.15 K), [L-Arg]-GLY 1:6 + H2O (60 wt %) (2.7 mPa·s, 353.15 K), and [MTPP][Br]-LEV-Ac 1:3:0.03 (16.16 mPa·s, 333.15 K) at 0.1 MPa, respectively.
Highlights
CO2 emission is an urgent issue due to its main contribution to global warming [1]
The absorption technology with 30 wt % MEA aqueous solution is the commercialized one. This technology with the corresponding solvent has the drawbacks of high energy demand (4.2 GJ/t CO2 ), high cost ($0.19–1.31/t CO2 ), low thermal and chemical stability, and high volatility and corrosion [3,4,5,6], which underlines the necessity for developing greener and more efficient solvent for CO2 capture
Zhang et al investigated the mass transfer feature in [BMIM][NO3 ] + H2 O, evidencing that mass transfer increases with the increase of water content, e.g., the mass transfer of [BMIM][NO3 ] (95 wt %) + H2 O (5 wt %) is 0.55 × 105 m·s−1, while it is 0.64 × 105 m·s−1 for [BMIM][NO3 ] (90 wt %) + H2 O (10 wt %), which may due to the decrease of viscosity that from 35.74 ([BMIM][NO3 ] (95 wt %) + H2 O (5 wt %)) to 12.65 mPa·s
Summary
CO2 emission is an urgent issue due to its main contribution to global warming [1]. It has been evidenced that CO2 capture is a promising route to mitigate CO2 emissions, and in general, cost, energy demand, and environmental impact need to be considered when for selecting the potential CO2 capture technologies [2]. To further take the benefits of both neoteric and conventional solvents, IL–amine-based and superbase–amine-based DES hybrid absorbents have been proposed and developed [19,20,21,22,23,24,25] These hybrid solvents possess certain advantages of low energy demand, low water evaporation, and high CO2 solubility compared to the commercialized MEA aqueous solution [26]. To develop the potential IL/DES-based hybrid solvents for CO2 capture, CO2 solubility (in accordance with Henry’s constant for physical absorption) and viscosity are two key properties. The best candidates for IL/DES-based hybrid solvents were obtained and compared with each other
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