Sung Yun Hong

Ether-functionalized ionic liquids as highly efficient SO2 absorbents

Room temperature ionic liquids (RTILs), ether-functionalized imidazolium methanesulfonates, exhibit extremely high SO2 solubility, at least 2 moles of SO2 per mole of RTIL at 30 °C and at atmospheric pressure. The solubility of SO2 in these RTILs increases with increasing number of tethered ether oxygen atoms and also with the pressure rise. FT-IR spectroscopic and quantum mechanical calculation results show that such high SO2 solubility is originated from the combined interactions of SO2 with methanesulfonate anion and ether oxygen atom or atoms on the imidazolium ring. The absorbed SO2 gas can be readily and completely desorbed from the RTILs by heating at 100 °C in a N2 flow, thereby allowing the RTILs to be reused up to 5 cycles without loss of their initial capacity.

Correlation between Hydrogen Bond Basicity and Acetylene Solubility in Room Temperature Ionic Liquids

Room temperature ionic liquids (RTILs) are proposed as the alternative solvents for the acetylene separation in ethylene generated from the naphtha cracking process. The solubility behavior of acetylene in RTILs was examined using a linear solvation energy relationship based on Kamlet-Taft solvent parameters including the hydrogen-bond acidity or donor ability (α), the hydrogen-bond basicity or acceptor ability (β), and the polarity/polarizability (π*). It is found that the solubility of acetylene linearly correlates with β value and is almost independent of α or π*. The solubility of acetylene in RTILs increases with increasing hydrogen-bond acceptor (HBA) ability of the anion, but is little affected by the nature of the cation. Quantum mechanical calculations demonstrate that the acidic proton of acetylene specifically forms hydrogen bond with a basic oxygen atom on the anion of a RTIL. On the other hand, although C-H···π interaction is plausible, all optimized structures indicate that the acidic protons on the cation do not specifically associate with the π cloud of acetylene. Thermodynamic analysis agrees well with the proposed correlation: the higher the β value of a RTIL is, the more negative the enthalpy of acetylene absorption in the RTIL is.

Steric hindrance-induced zwitterionic carbonates from alkanolamines and CO2: highly efficient CO2 absorbents

Sterically hindered amines such as 2-[(1,1-dimethylethyl)amino]ethanol (TBAE) and 1-[(1,1-dimethylethyl)amino]-2-propanol (TBAP) were found to reversibly interact with CO2 in a 1 : 1 molar ratio exclusively through the hydroxyl group, producing zwitterionic carbonate species, which lose CO2 at considerably lower temperatures than the CO2-adducts of other alkanolamines including monoethanolamine and diethanolamine. The formation of zwitterionic carbonate species from TBAE and TBAP was supported by spectroscopic and computational studies.

CO2 Absorption and Desorption in an Aqueous Solution of Heavily Hindered Alkanolamine: Structural Elucidation of CO2-Containing Species

The pathways for the CO2 absorption and desorption in an aqueous solution of a heavily hindered alkanolamine, 2-(t-butylamino)ethanol (TBAE) were elucidated by X-ray crystallographic and (13)C NMR spectroscopic analysis. In the early stage of the CO2 absorption, the formation of carbonate species ([TBAEH]2CO3) was predominant, along with the generation of small amounts of zwitterionic species. With the progress of the absorption, the carbonate species was rapidly transformed into bicarbonate species ([TBAEH]HCO3), and the amounts of the zwitterionic species increased gradually. During desorption at elevated temperature in the absence of CO2, [TBAEH]HCO3 was found to transform into [TBAEH]2CO3, where CO3(2-) strongly interacts with two [TBAEH](+) via hydrogen bondings.

Nitrile-functionalized tertiary amines as highly efficient and reversible SO2 absorbents.

Three different types of nitrile-functionalized amines, including 3-(N,N-diethylamino)propionitrile (DEAPN), 3-(N,N-dibutylamino)propionitrile (DBAPN), and N-methyl-N,N-dipropionitrile amine (MADPN) were synthesized, and their SO2 absorption performances were evaluated and compared with those of hydroxy-functionalized amines such as N,N-diethyl-N-ethanol amine (DEEA), N,N-dibutyl-N-ethanol amine (DBEA), and N-methyl-N,N-diethanol amine (MDEA). Absorption-desorption cycle experiments clearly demonstrate that the nitrile-functionalized amines are more efficient than the hydroxy-functionalized amines in terms of absorption rate and regenerability. Computational calculations with DBEA and DBAPN revealed that DBEA bearing a hydroxyethyl group chemically interacts with SO2 through oxygen atom, forming an ionic compound with a covalently bound OSO2(-) group. On the contrary, DBAPN bearing a nitrile group physically interacts with SO2 through the nitrogen and the hydrogen atoms of the two methylene groups adjacent to the amino and nitrile functionalities.

Carboxylate‐Assisted Formation of Alkylcarbonate Species from CO2 and Tetramethylammonium Salts with a β‐Amino Acid Anion

Tetramethylammonium-based molten salts bearing a β-amino acid anion (TMAAs) are synthesized through Michael addition reactions of amines with methyl acrylate followed by hydrolysis and subsequent neutralization by using aqueous tetramethylammonium hydroxide. The CO(2) capture performances of the TMAAs are evaluated and are shown to interact with CO(2) in a 1:1 mode in both water and alcohol. FTIR and (13)C NMR spectroscopic studies on the interactions of TMAAs with CO(2) indicate that the type of CO(2) adduct varies with the solvent used. When water is used as the solvent, a bicarbonate species is produced, whereas hydroxyethylcarbonate and methylcarbonate species are generated in ethylene glycol and methanol, respectively. Computational calculations show that the carboxylate groups of TMAAs contribute towards the formation and stabilization of 1:1 CO(2) adducts through hydrogen bonding interactions with the hydrogen atoms of the amino groups.