Solvent Model Selection And Capture Process Of Carbon Dioxide And Ammonia In Ionic Liquids

Capture and recovery of industrial NH₃,CO₂,CH₄,and C₂H₆ in waste gases can bring certain economic and environmental benefits.Compared with traditional solvents,ionic liquids do not produce environmental pollution and have high recycling rates.This paper combines the domestic and international research status,using ionic liquid as solvents for the industrial waste gas absorption and separation.Based on the solubility model of industrial waste gas in ionic liquids,the structural parameters of ionic liquids were calculated by the quantum mechanical method,and the the missing physical properties were estimated by thermodynamic model.Ionic liquid components were defined in Aspen Plus,the feasibility and economy of separation were evaluated through process simulation.The solubility of NH₃ in 6 kinds of imidazole ionic liquids was calculated.The thermodynamic model UNIFAC was used for the vapor-liquid equilibrium of NH₃ and ionic liquid.Based on the analysis of the influence of solubility,it was concluded that the order of the influence of anions on the solubility of ionic liquids was[BF₄]?>[Tf₂N]?>[PF₆]?,and the order of cations on solubility was[omim]⁺>[hmim]⁺>[bmim]⁺>[emim]⁺,therefore ammonia solubility can be increased by increasing the number of carbon atoms or by changing the ionic liquid anion.The COSMO-SAC software was used to calculate the selectivity of CH₄-CO₂ in different ionic liquids.Ionic liquid[bmim][Tf₂N]was selected as the appropriate absorbent.The NRTL model with wide applicability was used as a thermodynamic model.The binary interaction parameters between the ionic liquid and the gas are regressed by the binary gas-liquid equilibrium data between the gas and the ionic liquid.The separation process were simulated based on Aspen Plus software were conducted.The optimum operating parameters for the process were determined,the CO₂ purity captured reached 90%,and the high-purity recycling of the ionic liquid solvent 99.99%was achieved.Carbon dioxide and ethane easily form a binary azeotrope under liquefied conditions.An extractive distillation process for the separation of carbon dioxide and ethane using the ionic liquids[bmim][Tf₂N],[emim][Tf₂N]and[emim][EtSO₄]as solvents was explored.Based on the analysis of its physical properties and relative volatilities,[emim][Tf₂N]is the best option as a solvent for extractive distillation separation compared with other ionic liquids.Compared with traditional extraction distillation,the total annual cost and carbon dioxide emissions of the process using[emim][Tf₂N]as a solvent decreased by 62%and 31%,respectively.The thermodynamic efficiency（η）of the electricity generated from hydropower increase by0.7%.