Properties Prediction Of Ionic Liquids System And Its Application For Gas Separations

The combination of cations and anions can yield 1018 ionic liquids?ILs?systems,and thus it is experimentally time consuming,expensive and impossible by measuring all possible ILs for a special purpose.Therefore,it is necessary to predict the properties of ILs using computational methods.Recently,ILs have attracted much attention for absorbing and separating gases in both academic and industrial communities.However,a systematic database and screening method is scarce as well as the mechanism study of gas separation is not in depth.In this study,some predictive models for properties of ILs are established firstly,and then a new,systematic,and efficient screening method for ILs selection for absorption and separation of gases subject to important target properties is proposed.Finally,the mechanism study of gas separation is studied using the quantum chemistry calculation method.The main innovative work and results of the dissertation are as follows:?1?Physicochemical properties prediction of pure ionic liquids.Firstly,two models,integrating the fragment contribution-corresponding states?FC-CS?method with multiple linear regression?MLR?and support vector machine?SVM?algorithms,are proposed to predict the viscosity of imidazolium-based ILs.The average absolute relative deviation?AARD?of the entire data set of the MLR and SVM is 24.2%and 3.95%,respectively.Then,two novel QSPR models are developed to predict the viscosity of ILs using the MLR and SVM algorithms based on S?-profile molecular descriptors.The AARD of the total data set?89 ILs,1502 data points?of the MLR and SVM is 10.68%and 6.58%,respectively.Thirdly,In order to estimate the heat capacity of ILs,statistical models have been proposed using the S?-profile and MLR and relatively new ELM algorithms.The AARD of the total data set?46 ILs,2416 data points?of the MLR and ELM is 2.72%and 0.60%,respectively.The above results suggest that the established nonlinear models have better predictive performance.?2?Phase equilibrium study of ionic liquid system?H₂S solubility is selected as case study?.This study firstly established a comprehensive database on the H₂S solubility in ILs,which includes 1334 pieces of data covering the period from 2007 to 2016.Based on the database,a new model is proposed using the ELM intelligence algorithm and number of fragments as input parameters.A total of 1282 pieces of data for 27 ILs is used to build and test the model.The AARD of the entire set of the ELM model is 4.12%.Because the information of the fragments is not very rich,two novel models are developed using the ELM algorithm and S?-profile descriptors.The AARD of the two ELM models of the entire data set is 3.73%and 3.80%,respectively.These results suggest that proposed ELM models can be useful for the prediction of the H₂S solubility in ILs.?3?Systematic screening method for gas separation.In this study,an extensive database of estimated Henry's law constants of twelve gases in more than ten thousand ILs through the COSMO-RS method,is established?including 163020 data points?.Based on the database,a new,systematic,efficient and reliable screening method considering various important properties such as toxicity,bioaccumulation potential,viscosity,melting point,molality and molarity absorption capacity and separation performance,has been proposed.In addition,a new concept,namely,absorption separation index?AS I?is proposed in the above mentioned screening method.Application of the database and the screening method is highlighted through case studies involving two important gases separation problems?C02 from CH₄ and C2H₂ from C2H₄?.The results demonstrate the effectiveness of the screening method together with the database to explore and screen novel ILs meeting specific requirements for absorption and separation of gases.?4?Mechanism study of gas separation.Based on the above mentioned work,three representative ILs?[S221][CCN3],[S222][Ace]and[OHemim][NTf2]?are selected for studying the mechanism of the corresponding gases separation problems?CO2/CH₄,C2H₂/C2H₄ and NH₃/CH₄?using the quantum chemistry calculation method.The results show that hydrogen bond?HB?is very important for gas separation,and the HB is mainly electrostatic dominant,sometimes even covalent dominat for strong HB.Meanwhile it is found that there may exist linear relationships between the distance of HB and electron density ?BCP/Laplacian value ?2?BCP Through symmetry adapted perturbation theory?SAPT?it is found that electrostatic energy plays main role in total attractive energy of ILs and ILs-gases?[OHemim][NTf2]-NH₃,[S221][CCN3]-CO2 and[S222][Ace]-C2H₂?.