Selective separation of aliphatic and aromatic amines with CO2 switchable ionic liquids aqueous two-phase systems

Abstract

In many practical processes, separation of aliphatic amines from aromatic amines in water is imperative to obtain the desired products. In this work, a novel strategy was proposed for selective separation of aliphatic amines from aromatic amines with CO 2 switchable ionic liquids (ILs) aqueous two-phase systems (ATPSs). It was shown that upon introduction of CO 2 into an aqueous solution containing the IL, aliphatic amine and aromatic amine at 25 °C and atmospheric pressure, an ATPS could be formed with an IL-rich top phase and an ammonium-salt-rich bottom phase. Under these circumstances, the aromatic amine was largely partitioned in the IL-rich phase, while the aliphatic amine was transformed into the ammonium salt by the reaction with CO 2 . Thus the aliphatic amine was well separated from the aromatic amine in aqueous solution. The distribution ratios of aromatic amines between the two phases were found to increase with increasing hydrophobicity of ILs and aromatic amines, pK a values of aliphatic amines and tie-line length of the systems. Moreover, aliphatic amines retained in the ammonium-salt-rich phases were regenerated by bubbling N 2 under heating, while aromatic amines in the IL-rich phases were removed by simple steam distillation. The recovery efficiency for aliphatic amines was as high as 99.0%. The regenerated ILs could then be reused in the next separation process, and no decrease in the distribution ratios of aromatic amines was observed after six cycles.

Continuous-Flow Hydrogenation of 4-Phenylpyridine to 4-Phenylpiperidine with Integrated Product Isolation Using a CO2 Switchable System

“…Taking advantage of different basicity of pyridines versus piperidines, a purification and isolation procedure based on a liquid-liquid extraction in a CO 2 -switchable system was conceived as illustrated in Scheme 2 [35,36]. The biphasic system comprises an organic solvent containing the product mixture and an aqueous layer.…”

Recovery and purification of ionic liquids from solutions: a review

“…Carbon dioxide (CO 2 ) is nontoxic, cheap and recyclable, thus it is oen used as the trigger for process switching in many cases. Introduction of CO 2 can induce either the formation of IL-based ATPS, 53,199 or the direct phase transition of the IL/water mixture. 63 Xiong et al 53 investigated the phase separation of aqueous solutions of ILs and amines upon the introduction of CO 2 at 25 C and ambient pressure.…”

Recovery and Recycling of CO2/N2‐Switchable Anionic Surfactants in Emulsions

“…and/or TMEDAH 2 2? [17][18][19][20][21][22]. This subsequently boosts the hydrolysis of the deprotonated DSA to the insoluble acid form of DSA [34,35], because DSA (pK a = 6.98 ± 0.06) [31] is a weaker acid than H 2 CO 3 (pKa 1 = 6.38).…”

“…Switchable surfactants can undergo reversible conversions between active (ON state) and inactive (OFF state) forms upon application of the appropriate stimuli, including light [6][7][8], pH [8][9][10][11][12], temperature [8,13], CO 2 [2][3][4][5][14][15][16][17][18][19][20][21][22][23][24], host-guest interactions [25], magnetism [26,27] and redox reactions [22,[28][29][30][31][32]. Thus, emulsions formed by switchable surfactants are also switchable [2-7, 15, 16, 20-22, 30, 31].…”