Deep Eutectic Solvents Composed of Urea and New Salts of a Choline Family for Efficient Ammonia Absorption

Abstract

Two new deep eutectic solvents (DESs) composed of urea (U) and salts of a choline family such as dimethyl-di(2hydroxyethyl)-ammonium chloride [Me 2 C OH 2 N]Cl and methyl-tri(2hydroxyethyl)-ammonium chloride [MeC OH3 N]Cl mixed in a 1:1 molar ratio were prepared. Their densities, viscosities, refractive indices, and properties related to the ammonia absorption were thoroughly investigated. We found that the obtained DESs show an absorption capacity of 2.078 and 2.632 mol NH3, respectively, at 313.2 K and 101.3 kPa, which is approximately two times higher than for the choline chloride/urea (2:3) DES at the same conditions. Also, the obtained Henry's law constants are of the same sequence; that is, they increase from [MeC OH3 N]Cl/U to [Me 2 C OH 2 N]Cl/U and finally to choline chloride/urea. The mentioned tendencies show good correlation with DES's molar volume and its free volume, and also with the number of the CH 2 CH 2 OH substituents in a quaternary ammonium salt cation. This suggests that the gas capture occurs via the interactions (most likely H-bonding) between an NH 3 molecule(s) and the hydroxyalkyl fragments. Indeed, the results of 1 H NMR and FTIR spectroscopy confirm strong coupling between ammonia and hydroxyls leading to a distortion of the inherent DES structure. This finding agrees well with the fact that an NH 3 dissolution process in the studied DESs is favored by an entropic contribution.

Remarkable NH3 absorption in metal‐based deep eutectic solvents by multiple coordination and hydrogen‐bond interaction

“…Therefore, the effect of water on NH 3 solubilities in metal‐based DESs prepared in this work is very minor. Table 2 presents the comparison of NH 3 solubilities in different DESs and ILs 25,36–50,65–76 . It is found that the solubilities of NH 3 in metal‐based DESs prepared in this work are remarkably high, especially at low pressures.…”

“…Therefore, DESs have the potential to replace ILs for highly efficient and reversible gas absorption 31–35 . As for the application of DESs in reversible NH 3 absorption, there have been some impressive examples such as ChCl + PhOH + EG DESs, 36 NH 4 SCN + Gly DESs, 37 EaCl + Gly DESs, 38 ChCl + TetrZ + EG DESs, 39 MAA + TetrZ DESs, 40 [Im][NO 3 ] + EG DESs, 41 [emim]Cl + BenTriz DESs, 42 [ImH]Cl + Gly DESs, 43 LiCl/EG DESs, 44 and [MeC OH 3 N]Cl/U 45 . After careful examination on these DESs, it can be found that they are typically constituted by one weak acidic compound (e.g., PhOH, NH 4 SCN, EaCl, TetZ, [Im][NO 3 ], BenTriz or [ImH]Cl) that enables acid–base interaction with NH 3 , and one or two hydroxyl compounds (e.g., ChCl, EG, or Gly) that enable hydrogen‐bond interaction with NH 3 .…”

“…[31][32][33][34][35] As for the application of DESs in reversible NH 3 absorption, there have been some impressive examples such as ChCl + PhOH + EG DESs, 36 NH 4 SCN + Gly DESs, 37 EaCl + Gly DESs, 38 ChCl + TetrZ + EG DESs, 39 MAA + TetrZ DESs, 40 [Im][NO 3 ] + EG DESs, 41 [emim]Cl + BenTriz DESs, 42 [ImH] Cl + Gly DESs, 43 LiCl/EG DESs, 44 and [MeC OH 3 N]Cl/U. 45 After careful examination on these DESs, it can be found that they are typically constituted by one weak acidic compound (e.g., PhOH, NH 4 46 EaCl + Res DESs, 47 and [TMPDA]Cl 2 + PhOH DESs 48 ). Thus, these DESs have two or three weak acidic sites, and exhibit higher NH 3 solubilities than those DESs having only one weak acidic site.…”

“…25,[36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][65][66][67][68][69][70][71][72][73][74][75][76] It is found that the solu-…”

An Efficient Technique for Ammonia Capture in the Haber–Bosch Process Loop—Membrane-Assisted Gas Absorption

“…At present, special attention is given to the deep eutectic solvents (DESs) [ 12 , 13 , 14 ], which seem to be a prospective alternative to recently widely studied room temperature ionic liquids (RTILs) [ 15 , 16 , 17 ], which have proven to be materials with high absorption capacity with regard to ammonia. Deep eutectic solvents possess both similar loading as RTILs and the merits of low cost.…”