CO2 absorption features of 1-ethyl-3-methylimidazolium ionic liquids with 2,4-pentanedionate and its fluorine derivatives

Tuning Functionalized Ionic Liquids for CO2 Capture

The increasing concentration of CO₂ in the atmosphere is related to global climate change. Carbon capture, utilization, and storage (CCUS) is an important technology to reduce CO₂ emissions and to deal with global climate change. The development of new materials and technologies for efficient CO₂ capture has received increasing attention among global researchers. Ionic liquids (ILs), especially functionalized ILs, with such unique properties as almost no vapor pressure, thermal- and chemical-stability, non-flammability, and tunable properties, have been used in CCUS with great interest. This paper focuses on the development of functionalized ILs for CO₂ capture in the past decade (2012~2022). Functionalized ILs, or task-specific ILs, are ILs with active sites on cations or/and anions. The main contents include three parts: cation-functionalized ILs, anion-functionalized ILs, and cation-anion dual-functionalized ILs for CO₂ capture. In addition, classification, structures, and synthesis of functionalized ILs are also summarized. Finally, future directions, concerns, and prospects for functionalized ILs in CCUS are discussed. This review is beneficial for researchers to obtain an overall understanding of CO₂-philic ILs. This work will open a door to develop novel IL-based solvents and materials for the capture and separation of other gases, such as SO₂, H₂S, NOx, NH₃, and so on.

Enrichment in CO2 Absorption by 2-Methyl Piperazine-Activated Tertiary Amines, Physical Solvents, and Ionic Liquid Systems

One of the ever-demanding research fields is the development of new solvents with better properties for mitigation of CO₂ compared to existing solvents. This work reports the measurement and modeling of CO₂ solubility in newly proposed aqueous solvent blends of 2-methyl piperazine with N-methyldiethanolamine (MDEA), sulfolane (TMSO₂), and 1-butyl-3-methyl-imidazolium acetate ([bmim] [Ac]). The operating temperature and CO₂ partial pressure conditions chosen were 303.2-323.2 K and 2-370 kPa, respectively. Along with this, qualitative ¹³C NMR and FTIR analysis were also performed to consider the proposed reaction scheme. The experimental vapor-liquid equilibrium data were modeled by a modified Kent-Eisenberg equilibrium model. The equilibrium constants associated with 2-methyl piperazine (2-MPZ) and [bmim] [Ac] deprotonation and carbamate formation reactions were regressed to fit the experimental CO₂ solubility data. In addition, the CO₂ cyclic capacity and heat of absorption were evaluated for the aq (MDEA + 2-MPZ) blend.

Cooperative CO2 absorption by amino acid-based ionic liquids with balanced dual sites

In this study, a variety of functionalized ILs with dual sites including amino acid group (AA) and basic anion (R) were synthesized to investigate the suppression and cooperation between the sites in CO₂ absorption. The basic anions selected in this study with different basicity include sulfonate (Su), carboxylate (Ac), imidazolium (Im), and indolium (Ind). These ILs ([P₆₆₆₁₄]₂[AA-R]) were applied to CO₂ absorption. The results present that CO₂ capacity increases first and then decreases later with the continuous increase in the activity of the anion site. Combined with CO₂ absorption experiments, IR and NMR spectroscopic analyses and DFT calculation demonstrate that the ability of one site to capture CO₂ would be suppressed when the activity of another site is much stronger. Thus, the cooperation of dual site-functionalized ILs and high CO₂ capacity might be achieved through balancing the two sites to be equivalent. Based on this point, [P₆₆₆₁₄]₂[5Am-iPA] was further synthesized by taking the advantage of the conjugated benzene ring. As expected, [P₆₆₆₁₄]₂[5Am-iPA] showed capacity as high as 2.38 mol CO₂ per mol IL at 30 °C and 1 bar without capacity decrease even after 10 times recycling performance of CO₂ absorption and desorption.