Prediction Thermodynamic Properties And Modeling Study On Anion-Cation Bifunctional Ionic Liquid And CO₂ Binary Hybrid System

With the development of economy,many global environmental crises,such as energy shortage and greenhouse effect,have gradually increased.The absorbent refrigeration system driven by low-quality heat source is rapidly developed.Many scholars have paid more attention to the study on natural refrigeration working pairs of CO₂-ionic liquid because of the effect of freon refrigerants on the environment.The thermodynamic properties of the refrigerant working pairs are one of the key factors for calculating the performance of an absorption refrigeration system and optimizing the system structure.Therefore,based on the vapor-liquid equilibrium theory,the equation of state+activity coefficient method is used to correlate the vapor-liquid equilibrium experimental data of 16 CO₂-ionic liquid working pairs,and the excess thermodynamics of these systems are calculated.There are 10 imidazole ionic liquids with[Tf₂N]^-,[BF₄]^-and[PF₆]^-as anions,3 pyrrole ionic liquids with[Tf₂N]^-as anions,and 3pyridine ionic liquids with[Tf₂N]^-as anions.SRK+WS+UNIFAC model and PR+WS+UNIFAC model are constructed by combining the UNIFAC activity coefficient model with the SRK EOS and the PR EOS combined with the WS mixing rule,which were used to calculate the vapor-liquid equilibrium of the binary mixed system of ionic liquids with different anion and cation types and CO₂.The research results show that when the two model are used to calculate the vapor-liquid equilibrium of 16 pairs of CO₂-ionic liquid binary mixed system,the calculation accuracy of CO₂-[BMP][Tf₂N]binary mixed system is higher,and the average relative deviations are 0.073 and 0.074,and the average relative deviations of the remaining 15 pairs of binary mixed systems were all less than 0.17.When the anions of the ionic liquid are the same,the calculation accuracy of the SRK+WS+UNIFAC model for 10[Tf₂N]^-type ionic liquids and CO₂binary mixed system is higher than that of the PR+WS+UNIFAC model.When the ionic liquid cations are the same,the PR+WS+UNIFAC model has higher computational accuracy than the SRK+WS+UNIFAC model in the calculation of the 6[BF₄]^-type,[PF₆]^-type imidazole ionic liquids and CO₂binary mixed systems.The interaction parameters k_ijof 16 ionic liquids and CO₂were regressed according to the two models.When the anion of the ionic liquid is the same,as the length of the alkyl chain on the cation increases,the interaction parameter k_ijbetween the ionic liquid and CO₂also increases,and the interaction parameter k_ijbetween[BMPY][Tf₂N]and CO₂is the smallest（0.05）,the interaction parameter k_ijof[OMIM][Tf₂N]with CO₂is the largest（0.61）.The excess Gibbs free energy（G^E）,excess enthalpy（H^E）and excess entropy（S^E）of 16pairs of CO₂-ionic liquid binary hybrid systems were predicted by the equation of state+activity coefficient method.The G^Evalues of 16 pairs of CO₂-ionic liquid systems are all negative,indicating that 16 kinds of ionic liquids have strong CO₂absorption capacity.Among the 16 pairs of CO₂-ionic liquid binary mixed systems,the G^Eof[Tf₂N]^-type pyrrole ionic liquid-CO₂system is the largest,the G^Eof[Tf₂N]^-type pyridine ionic liquid-CO₂system is the smallest,The G^Eof[Tf₂N]^-type imidazole ionic liquid-CO₂system is between the two.The CO₂-[EMIM][Tf₂N]system has the largest G^E（-1310.29～-1066.88 J/mol）,and the CO₂-[OMPY][Tf₂N]system has the smallest G^E（-6903.98～-5142.45 J/mol）.The 16 pairs of CO₂-ionic liquid systems have both positive and negative H^Evalues,indicating that the 16 kinds of ionic liquids have different types of ionic liquids,and absorb and release heat differently when absorbing CO₂.The H^Evalues of the three[Tf₂N]^-type pyrrole ionic liquids and CO₂binary mixed systems are all negative,indicating that these ionic liquids absorb CO₂exothermic,and the CO₂-[HMP][Tf₂N]system has the smallest H^E（-1038.75～464.58 J/mol）.The H^Evalues of the 10 imidazole-based ionic liquids and CO₂binary mixed systems have positive and negative values,among which the CO₂-[EMIM][Tf₂N]system has the highest H^Evalue（54.77～407.24 J/mol）.The S^Eof 16 pairs of CO₂-ionic liquid systems are all positive.Among the 16pairs of CO₂-ionic liquid binary hybrid systems,the S^Eof[Tf₂N]^-type pyrrole ionic liquid-CO₂system is the smallest,and the S^Eof the[Tf₂N]^-type pyridine ionic liquid-CO₂system is the largest,and the S^Eof the[Tf₂N]^-type imidazole ionic liquid-CO₂system is between the two.The S^Eof the CO₂-[OMPY][Tf₂N]system is the largest(15.92～21.6 J·mol^-1·K^-1),the S^Eof the CO₂-[BMP][Tf₂N]system is the smallest(1.76～4.78 J·mol^-1·K^-1).