Industrial & Engineering Chemistry Research, Vol.59, No.52, 22605-22618, 2020
Absorption of Toluene Using Deep Eutectic Solvents: Quantum Chemical Calculations and Experimental Investigation
For the treatment of toluene exhaust gas, absorption is widely applied because of its advantages of mature technology and high efficiency, and research for the development and performance of absorbents is one of the focuses in this field. Deep eutectic solvents (DESs), which are emerging as efficient green solvents, were introduced as the toluene absorbent in this work. The effects of the structures and compositions of hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) on toluene affinities were explored. It was found that both the HBAs and HBDs with longer alkyl chains have higher affinities to toluene; in addition, the solubility of toluene in DESs increases with the increase of the ratio of long-chain-fatty-acid HBDs. Tetraethylammonium chloride (TEACl) and oleic acid (OA) were selected as the HBA and HBD, respectively, in a molar ratio of 1:3 to form DES TEACl-OA. A quantum chemistry method was adopted to study the noncovalent interactions between molecules to gain insights into the microscopic mechanism. Results demonstrated that weak hydrogen bonds (HBs) dominated by the dispersion attraction are formed between toluene and other systems, while strong HBs of the nature of the electrostatic interaction are formed between the HBA and HBD. In addition, the interaction between toluene and DES is stronger than that between toluene molecules, which is the essential reason for toluene removal by TEACl-OA. Furthermore, the excellent absorption performance of the DES was confirmed by experiments of solubility and dynamic absorption, in which Henry's law constant at 298.2 K is 2.53 Pa.m(3)/mol and the removal efficiency in the first 10 min of the continuous bubbing absorption process can reach 99.7%. The proposed DES TEACl-OA is proved to be a promising solvent for toluene absorption; furthermore, the theoretical research and experimental data are significant for the development of DES absorbents and revealing the absorption mechanism on a molecular scale.