Protic ionic liquid as excellent shuttle of MDEA for fast capture of CO2

Efficient Absorption of CO2 by Protic-Ionic-Liquid Based Deep Eutectic Solvents

Carbon capture, utilization, and storage (CCUS) are among the key technologies to achieve large-scale carbon emission reduction globally. Deep eutectic solvents (DESs) are considered as designable solvents, which has attracted intensive attention for CO2 capture. Here, a series of binary DESs are synthesized through one-step mixing with the starting materials of protic ionic liquid (PIL) and amine. The eutectic behavior was investigated by measuring the melting point of PILs and amine. The saturated vapor of these DESs and industrial MDEA solution were measured and compared. These DESs are investigated to have high absorption capacity (0.1 g ⋅ g-1 at 1.0 bar and 25 °C), superior apparent absorption rate constant (0.381 min-1 vs 0.012 min-1 of 70 wt.% MDEA), moderate interaction with CO2 (the enthalpy change is as low as -34.8 kJ ⋅ mol-1). The absorption mechanism is also investigated by NMR analysis. Eight absorption/desorption regeneration experiments are carried out to show their reversibility. Considering the advantages, including convenience of synthesis, large absorption capacity, fast absorption rate, and moderate interaction energy as well as good regeneration, these DESs are believed to be as potential CO2 absorbent in practical applications.

Molecular-Level Interactions in Binary Mixtures of 1-Ethyl-3-methylimidazolium Ethylsulfate and Propane-1,2-diol: The Interplay between Intermolecular and Intramolecular Hydrogen Bonding

In this study, volumetric properties of an ionic liquid, 1-ethyl-3-methylimidazolium ethylsulfate ([C2mim]C2H5SO4), propane-1,2-diol, and their binary mixtures were studied by measurements of density and viscosity. The excess molar volume (VmE), dynamic viscosity deviation (Δη), and excess molar Gibbs free energy of activation for viscous flow (ΔGm*) were calculated and fitted with the Redlich-Kister (RK) type polynomial equation. The results suggested that intermolecular interactions are weaker in the mixture compared to the pure components and the interactions decrease with increasing mole fraction of [C2mim]C2H5SO4. The thermodynamic activation parameters were also calculated from the Eyring equation, and their variations with mole fraction of [C2mim]C2H5SO4 were correlated to the molecular-level interactions. The near-infrared (NIR) spectroscopic measurements were carried out in the temperature range from 293.15 to 333.15 K. The raw NIR data were analyzed further by two-dimensional correlation spectroscopy and principal component analysis. When [C2mim]C2H5SO4 was introduced to the propane-1,2-diol system, the stronger intermolecular hydrogen bonds were destroyed. Propane-1,2-diol and [C2mim]C2H5SO4 produce some weaker hydrogen bonds, but the effect of breaking hydrogen bonds predominates. On the basis of volumetric and NIR spectroscopic investigations, molecular-level interactions are predicted. The interplay between intermolecular and intramolecular hydrogen bonding decides unique molecular-level interactions and dictates enhanced thermodynamic properties of the binary mixtures to make them tunable for a multitude of applications.

Highly Efficient Absorption of CO2 by Protic Ionic Liquids-Amine Blends at High Temperatures

In view of the increasingly serious harm of CO₂ to the environment, it is highly desirable to develop effective CO₂ absorbents. In this work, we demonstrated an efficient absorption of CO₂ by blends of protic ionic liquids (PILs) plus amines. The density and viscosity of investigative four PILs-amine mixtures were measured. By systematically studying the effects of the solution ratio, temperature, CO₂ partial pressure, and water content on the absorption of CO₂, it is found that the 3-dimethylamino-1-propylamine acetate ([DMAPAH][OAc]) plus ethanediamine (EDA) mixture shows the highest CO₂ uptake of 0.295 g CO₂ per g absorbent at 50 °C and 1 bar and a further increase in the absorption of CO₂ to 0.299 g/g by adding water with a mass fraction of 20%. Furthermore, the absorption mechanism of CO₂ in the presence and absence of water has also been investigated by FTIR and NMR spectra.

Investigation on Protic Ionic Liquids as Physical Solvents for Absorption of NO at Low Pressures

Nitric oxide (NO) absorption in ionic liquids (ILs) is an interesting issue, but little attention has been focused on the removal of NO at low partial pressures. Herein, a series of protic ionic liquids (PILs) based on polyamines as the cation and hydroxybenzenes as the anion were prepared for capturing low-concentration NO (0-0.6 bar). Triethylenetetramine phenolate ([TETAH][PhO]) showed an excellent absorption performance, with low viscosity, fast absorption rate, and high absorption capacity. The experimental solubility data were fitted by the Krichevsky-Kasarnovsky (K-K) equation, and the absorption enthalpy (ΔH) of NO in [TETAH][PhO] was thus calculated to be -43.60 kJ/mol. Density functional theory calculations were further performed to better understand the interaction of [TETAH][PhO] with NO on the molecular level, and the results suggest that the weak interaction of NO with the PIL was induced by the presence of H protons. It is believed that this work may provide a new method for the efficient and reversible absorption of low-concentration NO.

Binary System of Polyethylene Glycol 200 (1) + 3-Dimethylamino-1-propylamine (2) for CO2 Absorption: Thermophysical Properties and Spectroscopic Study

As the concentration of CO₂ in the atmosphere keeps increasing, the development of a highly efficient CO₂ absorbent is highly desired. In this work, a binary mixture system of polyethylene glycol 200 (PEG 200) (1) + 3-dimethylamino-propylamine (DMAPA) (2) was used for CO₂ absorption. Considering the importance of thermophysical properties to binary solutions, the densities and viscosities of the PEG 200 (1) + DMAPA (2) mixture were measured at T = (298.15, 303.15, 308.15, 313.15, and 318.15) K and atmospheric pressure over the entire composition range. Based on the density and viscosity data, the excess properties and viscous flow thermodynamic parameters were calculated, respectively. To obtain the coefficients and to estimate the standard deviations between the experimental and calculated quantities, the excess molar volume (V _m ^E), the viscosity deviation (Δη), and the excess Gibbs free energies of activation for viscous flow (ΔG* ^E) were fitted to the Redlich-Kister equation. Furthermore, based on the results of UV-vis, FTIR, and ¹H NMR spectra, the intermolecular interaction of PEG 200 and DMAPA was discussed. Particularly, a strong intermolecular bonding is formed when the molar ratio of PEG 200 to DMAPA is about 1:2 because of the excess molar volume (V _m ^E). On that account, a mixture of PEG 200 and DMAPA in a ratio of 1:2 was used for studying CO₂ absorption, and a CO₂ absorption of about 0.19 g per gram of absorbent was achieved at room temperature and atmosphere.

Ionic Liquids/Deep Eutectic Solvents-Based Hybrid Solvents for CO2 Capture

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.