Study On The Capture Of Acidic Gases By Ionic Liquids

At present,there are many methods for capturing acidic gases in the world,which can be divided into chemical absorption and physical absorption of traditional absorbents.However,the physical absorption of traditional absorbents needs to be carried out under low temperature and high pressure conditions,and the actual operating conditions are harsh;chemical absorption is easy to produce by-products,desorption requires a lot of energy consumption,increases industrial costs,and corrodes equipment.Combining the above two absorption methods,the traditional method of capturing acidic gases by absorbents obviously cannot meet the current stage of acidic gas absorption.In order to solve the above problems,two kinds of high-efficiency ionic liquid absorbents were synthesized in this paper,which were alkaline salt iron-based ionic liquid（triethylamine hydrochloride iron-based ionic liquid rFeCl₃/Et₃NHCl）and alkaline ionic liquid（N-butyl-N-methylmorpholine acetate ionic liquid[Bmmorp][OAc]）.The iron content analysis,infrared and nuclear magnetic characterization and structure analysis were carried out.For better application,its physical properties（density,viscosity）were measured.The alkaline salt iron-based ionic liquid（rFeCl₃/Et₃NHCl）was used to capture the acidic gas H2S,and the solubility data were correlated by the RETM model.Based on the simulation results,the effects of temperature,pressure and iron-amine ratio r on the solubility were discussed,and the effects of the fitted apparent Henry’s constant₍（6,）and the apparent chemical reaction equilibrium constant₍（6,）on the solubility were discussed.Compared with the solubility of H₂S in other chemically absorbed ionic liquids under the same conditions.The physical absorption enthalpy and chemical absorption enthalpy in the absorption process were calculated,which provided a data basis for the application of the alkaline salt iron-based ionic liquid in capturing acidic gas.Alkaline ionic liquid aqueous solution（20%,30%,40%water content of[Bmmorp][OAc]）was used to capture acid gas H₂S.The solubility of[Bmmorp][OAc]was fitted by RETM model and NRTL model respectively.The reaction mechanism of[Bmmorp][OAc]aqueous solution with H₂S was discussed.The reaction mechanism of[Bmmorp][OAc]aqueous solution with H₂S was speculated by RETM model fitting.It was found that the 2:1 binding mode was better than the 1:1 binding mode.In addition,the effects of water content,temperature and pressure on the solubility of H₂S were discussed.The solubility of pure[Bmmorp][OAc]for H₂S was predicted by COSMO-SAC.The critical properties of[Bmmorp][OAc]were estimated by group contribution method,and the Henry constant parameters were obtained according to the predicted solubility.The experimental data of NRTL model were regressed to obtain the binary interaction parameters of the system.The binary interaction parameters were used to regress the ternary system（[Bmmorp][OAc]-H₂S-H₂O）.The predicted solubility was compared with the results obtained by RETM model fitting.It was found that the RETM model was more suitable for the system and the fitting effect was higher.The solubility data are provided for the application of the alkaline salt iron-based ionic liquid in capturing acidic gas.The reaction mechanism was studied by quantum chemistry at the micro level.The reaction mechanism was discussed by quantitative analysis（interaction energy）and qualitative analysis（IRI analysis,AIM analysis）.Compared with the combination of N-propyl-N-methylmorpholine acetate（[Pmmorp][OAc]）and H₂S,[Bmmorp][OAc]and H₂S,[Bmmorp][OAc]and CO₂,it is proved that[Bmmorp][OAc]has a greater advantage in capturing H₂S.In order to prove that the reaction of[Bmmorp][OAc]with H₂S is a 2:1reaction,the interaction energy of the 1:1 and 2:1 reaction is compared.It is found that the2:1 reaction is more stable and easier to carry out,which is consistent with the results predicted by the RETM model.It provides an important basis for the future industrial prospects of[Bmmorp][OAc]in capturing acidic gases.