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Phase-Change Reversible Absorption of Hydrogen Sulfide by the Superbase 1,5-Diazabicyclo[4.3.0]non-5-ene in Organic Solvents

Xu, Zhiyong, Zhao, Wenbo, Xie, Xuhao, Li, Yanhong, Chen, Yuan
Industrial & engineering chemistry process design and development 2019 v.58 no.4 pp. 1701-1710
absorbents, absorption, desulfurization, energy, hexadecane, hexanols, hydrogen sulfide, nitrogen, phase transition, process design, solvents
Phase-change absorption has shown a promising application prospect for acid gas capture because only the gas-rich phase needs to be transported to the stripper for recovery, which could drastically reduce the energy consumption of the regeneration process. In this study, the liquid–liquid phase-change behavior of a new recyclable ternary system, composed of 1,5-diazabicyclo[4.3.0]non-5-ene (DBN)/hexadecane/hexanol, was evaluated for capturing H₂S. The absorption adduct was the [DBNH]⁺[SH]⁻ salt, and the cause of the phase change was attributed to the polarity difference between the upper and lower phases. Furthermore, considering that only the lower phase needed to be heated for regeneration, the gravimetric absorption capacity was calculated to be 0.205 g H₂S/g lower phase at 1 bar and 293.15 K. To the best of our knowledge, this is the largest gravimetric absorption capacity for H₂S capture obtained to date. Additionally, when the absorption reached equilibrium, DBN, hexanol, and H₂S were concentrated in the lower phase, while hexadecane mostly remained in the upper phase. The DBN/hexadecane/hexanol system showed that the benign desulfurization efficiency was nearly 100% under the condition that the molar ratio of H₂S gas to DBN is not more than 0.6 mol/mol. The cyclic absorption experiments showed that the H₂S gas could be easily released by bubbling N₂ at 80 °C, which indicated the low energy requirement for the regeneration of the absorbent.