CO₂ Solubility in Hybrid Solvents Containing 1-Butyl-3-methylimidazolium Tetrafluoroborate and Mixtures of Alkanolamines

Abstract

To reduce the rate of climate change, feasible and energy-efficient solutions need to be found to capture CO 2 at low pressure from flue gas emitted by various industries and energy sectors worldwide. The use of solvents to selectively absorb CO 2 is a promising option for CO 2 capture. This research investigated the solubility of CO 2 in hybrid solvents containing the 1-butyl-3-methyl imidazolium tetrafluoroborate [bmim] [BF 4 ] ionic liquid with mixtures of up to three alkanolamine solvents, namely monoethanolamine (MEA), diethanolamine (DEA), and methyl-diethanolamine (MDEA). Gravimetric analysis was used to measure equilibrium CO 2 solubility in the hybrid solvents containing various compositions of the above components at CO 2 partial pressures of 0.05 MPa to 1.5 MPa and temperatures of 303.15 K to 323.15 K. CO 2 solubility in these solvents was benchmarked against pure ionic liquids, as well as conventional alkanolamine solvents, and modeled using the Posey−Tapperson−Rochelle model for the alkanolamines present and the SRK equation of state for the ionic liquid present in the hybrid solvents. It was found that the hybrid solvents achieved significantly higher CO 2 solubility at low pressure than pure ionic liquids and conventional alkanolamine solvents. Modeling, however, was found to be less accurate for hybrid systems than data modeled for pure ionic liquid systems.

Ionic-Liquid-Based CO2 Capture Systems: Structure, Interaction and Process

“…The designable properties of ILs and high CO 2 absorption performances of alkanolamines are combined, and the regeneration energy may be reduced without affecting the absorption performances in comparison with the aqueous alkanolamine solution. After that, many studies on the anhydrous IL–alkanolamine systems for CO 2 capture were reported in succession, such as the binary mixtures of [Bmim]­[BF 4 ]–MEA, [Bmim]­Cl–MEA, [Bmim]­[BF 4 ]–MDEA, [Bmim]­[BF 4 ]–DEA, trihexyl-tetradecylphosphonium 1,2,4-triazolide ([P 66614 ]­[124Triz])–MEA, and trihexyl-tetradecylphosphonium benzotriazolide ([P 66614 ]­[Bentriz])–MEA. − It was found that these hybrid solvents have higher CO 2 capacity than traditional alkanolamine solvents. Compared with pure ILs, the addition of alkanolamines to conventional ILs is favorable for increasing CO 2 capacity in hybrid solvents, but adding alkanolamines into chemisorption ILs has a different effect on CO 2 capacity.…”

Experimental Study of Carbon Dioxide Solubility in Aqueous N-Methyldiethanolamine Solution with 1-Butylpyridinium Tetrafluoroborate Ionic Liquid

“…Also, Ahmady et al ,, investigated the initial absorption rate, kinetics, and capacity of CO 2 absorption in the MDEA aqueous solution with [Bmim]­[BF 4 ], [Bmim]­[Ac], and [Bmim]­[DCA] and found that, by increasing the concentration of IL, the CO 2 loading was considerably reduced, but this decrease was observed to be lower in [Bmim]­[BF 4 ] solution than in other types of ILs. Osman et al examined six nonaqueous solutions of [Bmim]­[BF 4 ] with MEA, DEA, and MDEA in the forms of binary, ternary, and quaternary systems and reported the MEA + DEA + [Bmim]­[BF 4 ] mixture with a mass composition of 100w = 31.8:12.1:56.1 as the solution with the highest absorption capacity. A number of studies which have been carried out related to the CO 2 capture by alkanolamine + IL solutions are listed in Table .…”

“…Previous studies, which have been conducted on the solubility of CO 2 in mixtures of alkanolamine + IL, mostly concern up to low pressure ranges. Among the various types of ILs, numerous studies have been performed on gas solubility measurement in pure or aqueous ILs (such as imidazolium, − pyridinium, and ammonium , based cations with different anions) or addition of imidazolium-based RTILs − ,, to amine solutions due to their considerable solubility of CO 2 . However, the detailed CO 2 solubility measurement for a mixture of solvents containing pyridinium-based RTILs, which is helpful for deeply understanding the effect of adding this kind of IL to a mixture in CO 2 uptake, is scant.…”

Absorption Behavior of Acid Gases in Protic Ionic Liquid/Alkanolamine Binary Mixtures

“…Yu with co-workers investigated the CO 2 absorption capability of binary mixtures of 1-butyl-3-methylimidazolium hexafluorophosphate–monoethanolamine, 1-ethyl-3-methylimidazolium tetrafluoroborate–monoethanolamine, 1-butyl-3-methylimidazolium tetrafluoroborate–monoethanolamine and 1-ethyl-3-methylimidazolium hexafluorophosphate–monoethanolamine, and established that the CO 2 absorption capacity in ILs–MEA compositions became much higher than that in the neat ILs and was comparable to the values in some aqueous amines and mixture of ILs–amine–H 2 O. Ahmady et al investigated aqueous solution of methyldiethanolamine mixed with three types of ionic liquids: 1-butyl-3-methyl-imidazolium tetrafluoroborate, 1-butyl-3-methyl-imidazolium acetate and 1-butyl-3-methyl-imidazolium dicyanamide . Osman prepared hybrid solvents on the basis of [bmim]­[BF 4 ] combined with MEA, DEA, and MDEA with different concentrations, that achieved superior CO 2 absorption over alkanolamines …”

“…26 Osman prepared hybrid solvents on the basis of [bmim][BF 4 ] combined with MEA, DEA, and MDEA with different concentrations, that achieved superior CO 2 absorption over alkanolamines. 27 The protic ionic liquids were suggested in a range of reports as the acid gases absorbents with a low cost. An important feature thereof is the fewer amounts of basic amine groups in protic ILs than in amines, leading to the lower acidic gases capture ability and lower energies required for the desorption of gases.…”