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Enhanced NH3 capture by imidazolium‐based protic ionic liquids with different anions and cation substituents

Shang, Dawei, Bai, Lu, Zeng, Shaojuan, Dong, Haifeng, Gao, Hongshuai, Zhang, Xiangping, Zhang, Suojiang
Journal of chemical technology and biotechnology 2018 v.93 no.5 pp. 1228-1236
absorbents, absorption, ammonia, anions, cations, desorption, hydrogen, ionic liquids, liquids, nitrates, solubility, temperature, thermal degradation, vapors, viscosity
BACKGROUND: Ionic liquids have become potential absorbents to treat exhausted gases containing NH₃, which threatens the living environment of human beings. RESULTS: In this study, 10 kinds of protic and conventional ILs were synthesized and characterized and their densities, viscosities and thermal decomposition temperatures measured. The NH₃ solubility in ILs from the vapor liquid equilibrium (VLE) experiments revealed that the chain length of cations had little influence on the NH₃ solubility of the protic ILs because of the high NH₃ capacities in protic ILs resulting from protic hydrogen atom compared with conventional ILs. The 2‐H atom on the cation influenced the NH₃ solubility in both protic and conventional ILs with different trends as the pressure was increased. Considering the effect of anions with the same cation [Bim]⁺, the order of NH₃ solubility in protic ILs was [Bim][NTf₂] > [Bim][SCN] > [Bim][NO₃]. Dynamic absorption of NH₃ in [Eim][NTf₂] preliminarily revealed that the absorption was fast under ambient pressure and through 5 cycles of absorption and desorption, the NH₃ absorption ability remained stable. CONCLUSIONS: The relationship between the NH₃ solubility and the structures of both protic and conventional ILs was revealed, indicating the protic ILs as an alternative material for the treatment of NH₃‐containing exhaust gases. © 2017 Society of Chemical Industry