Selective separation of aliphatic tertiary amines and aromatic amines by using CO2

Abstract

In many practical processes, it is necessary to separate the aliphatic amine from the aromatic amine from water to obtain the desired product. A simple and effective strategy was proposed for selective separation of aliphatic amines from aromatic amines by using CO2. With the introduction of CO2 into the aqueous solution, aliphatic amines can be switched from hydrophobicity to hydrophilicity but aromatic amines cannot due to their different pKa. The separation performance associated with product purity cannot be explained by pKa or log Kow. Thus, solubility parameter was employed to explain the separation performance of these amines. The relationship between solubility parameter and separation performance was investigated by gas chromatography and ultraviolet spectrophotometry, which established the concentration of each aliphatic amine in aromatic amine and that of aromatic amine in water. This relationship can guide the selection of appropriate switchable-hydrophilicity solvents (SHSs) to acquire better quality products. In addition, aliphatic amines dissolved in water could be regenerated by removing CO2 and the recovery of aliphatic tertiary amines was up to 93.4%.