Economical and environmental aspects are the main motivation for research on energy efficient processes and the search for environment friendly materials for CO2 capture. Currently, CO2 capture is dominated by amine-based (e.g., monoethanolamine) technologies, which are very energy intensive and less attractive from an environmental point of view due to emissions of the used volatile solvent components. Ionic liquids have been proposed as a promising alternative to the conventional volatile solvents, because of their low volatility and other interesting properties. This remarkable interest has led to a rapid growth of literature on this specific subject. The aim of the present review paper is to provide a detailed overview of the achievements and difficulties that has been encountered in finding a suitable ionic liquid for CO2 capture from flue-gas streams. A major part of this review includes an overview of the experimental data of CO2 solubility, selectivity, and diffusivity in different ionic liquids. ...

http://pubs.acs.org/doi/pdf/10.1021/ie3003705

State-of-the-Art of CO2 Capture with Ionic Liquids

Innovative off-the-shelf CO 2 capture approaches are burgeoning in the literature, among which, ionic liquids seem to have been omitted in the recent Intergovernmental Panel on Climate Change (IPCC) survey. Ionic liquids (ILs), because of their tunable properties, wide liquid range, reasonable thermal stability, and negligible vapor pressure, are emerging as promising candidates rivaling with conventional amine scrubbing. Due to substantial solubility, room-temperature ionic liquids (RTILs) are quite useful for CO 2 separation from flue gases. Their absorption capacity can be greatly enhanced by functionalization with an amine moiety but with concurrent increase in viscosity making process handling difficult. However this downside can be overcome by making use of supported ionic-liquid membranes (SILMs), especially where high pressures and temperatures are involved. Moreover, due to negligible loss of ionic liquids during recycling, these technologies will also decrease the CO 2 capture cost to a reasonable extent when employed on industrial scale. There is also need to look deeply into the noxious behavior of these unique species. Nevertheless, the flexibility in synthetic structure of ionic liquids may make them opportunistic in CO 2 capture scenarios.

Ionic liquids for CO2 capture—Development and progress

A predictive thermodynamic model for an aqueous blend of potassium carbonate, piperazine, and monoethanolamine for carbon dioxide capture from flue gas

Solubility of CO2 in 15, 30, 45 and 60 mass% MEA from 40 to 120 °C and model representation using the extended UNIQUAC framework

Densities and dynamic viscosities in liquid solutions of monoethanolamine (MEA), water, and carbon dioxide (CO2) have been measured. The mass fraction of MEA in water was (20, 30, and 40) %, and CO2 loading was between (0 and 0.5) mol CO2 per mole MEA; the temperature was varied between (25 and 80) °C. These measurements were compared with literature data of solutions without CO2 and with data for CO2 loaded solutions primarily at 25 °C. The results show that the densities and viscosities increase significantly with increasing CO2 loading at all temperatures. The measured data for the ternary system were compared with available density and viscosity correlations from Weiland et al. J. Chem. Eng. Data 1998, 43, 378−382. Agreement between the measurements and the Weiland correlations was satisfactory. The deviation increases with increased MEA concentration, CO2 loading, and temperature.

Density and Viscosity of Monoethanolamine + Water + Carbon Dioxide from (25 to 80) °C

The densities and viscosities of aqueous blends of N-methyldiethanolamine (MDEA) and 2-amino-2-methyl-1-propanol with monoethanolamine (MEA) and diethanolamine (DEA) have been measured at (25, 30, 35, 40, 45, and 50) °C. The total amine strength in the solution was kept at 30 mass % in view of recent interest in using concentrated amine solutions in gas treating. Correlations for the density and viscosity of the ternary mixtures are presented.

Density and Viscosity of Aqueous Solutions of (N-Methyldiethanolamine + Monoethanolamine), (N-Methyldiethanolamine + Diethanolamine), (2-Amino-2-methyl-1-propanol + Monoethanolamine), and (2-Amino-2-methyl-1-propanol + Diethanolamine)

In this work the physical solubility of N2O in (diethanolamine + water), (2-amino-2-methyl-1-propanol + water), (N-methyldiethanolamine + water), (N-methyldiethanolamine + diethanolamine + water), and (2-amino-2-methyl-1-propanol + diethanolamine + water) as well as the diffusivity of N2O in (N-methyldiethanolamine + diethanolamine + water) and (2-amino-2-methyl-1-propanol + diethanolamine + water) have been measured at (293, 298, 303, 308, and 313) K. For the binary mixtures the amine concentration ranges studied are (2.0, 2.5, and 3.0) kmol·m-3. For the ternary mixtures the total amine strength in the solution was kept at 30 mass %, in view of the recent interest in using concentrated amine solutions in gas treating. A solubility apparatus was used to measure the solubility of N2O in amine solutions. The diffusivity was measured with a wetted wall column absorber. The uncertainty of the measurement is estimated to be ±2%. A semiempirical model of the excess Henry's constant proposed by Wang et al. (Chem...

Physical Solubility and Diffusivity of N2O and CO2 into Aqueous Solutions of (2-Amino-2-methyl-1-propanol + Monoethanolamine) and (N-Methyldiethanolamine + Monoethanolamine)

The solubility of CO2 in aqueous solutions, 18 mass %, 25 mass %, and 30 mass % (2.0 M, 2.8 M, and 3.4 M), of 2-amino-2-methyl-1-propanol (AMP) has been measured over a temperature range of (303 to 323) K and a partial pressure range of (1 to 100) kPa. In this work, the modified Clegg−Pitzer equation is used to correlate and predict the vapor−liquid equilibria of the (CO2 + AMP + H2O) system. The model predicted results are in good agreement with the experimental vapor−liquid equilibrium (VLE) measurements in this work. A nontraditional optimization algorithm, simulated annealing (SA), has been used for the parameter estimation. It is observed that adopting the SA technique for the estimation of interaction parameters results in better VLE prediction accuracy than using the traditional deterministic techniques, such as Levenberg−Marquardt.

Bishnu P. Mandal

Papers

Density and Viscosity of Aqueous Solutions of (N-Methyldiethanolamine + Monoethanolamine), (N-Methyldiethanolamine + Diethanolamine), (2-Amino-2-methyl-1-propanol + Monoethanolamine), and (2-Amino-2-methyl-1-propanol + Diethanolamine)

Physical Solubility and Diffusivity of N2O and CO2 into Aqueous Solutions of (2-Amino-2-methyl-1-propanol + Monoethanolamine) and (N-Methyldiethanolamine + Monoethanolamine)

Vapor−Liquid Equilibrium of CO2 in Aqueous Solutions of 2-Amino-2-methyl-1-propanol†