Research On Selection Of Extracting Agent Using Molecular Simulation And Validation

The selection of extraction agent is the first problem for the development of extractive distillation process.In this paper,we use the molecular simulation methods to study the interaction between the molecule of extraction agent and the binary system.Attempt to evaluate the merits of the extraction agent by using the molecular interaction energy and the difference of mixing energy between the two components and the extraction agent.Established a database of commonly used extraction agent,and using the thermodynamic NRTL equation to calculate the selectivity of the extraction agent as the comparison for molecular simulation model.The process of using different extraction agents for separate methanol-methyl acetate binary system was simulated as the verified for the molecular simulation model.Firstly,the interaction energy between the two molecules is calculated by the method of quantum mechanical simulation.The calculated results show that the interaction energy between hydrogen fluoride and water molecules can be in the 101 kcal/mol level,the interaction energy between aniline and benzene,aniline and cyclohexane,NMP and benzene,NMP and cyclohexane,phenol and benzene,water and benzene,water and cyclohexane are all in 100 kcal/mol level.The interaction energy between neopentane and benzene molecular are in 10-1 kcal/mol level.The interaction energy between propane and n-butane molecular are in 10-2 kcal/mol level.So it is preliminary to judge that the interaction between the molecules of the extraction agent and the molecule to be separated can be in the range of 100 kcal/mol.Then,the molecular simulation method was used to calculate the mixing energy between the two molecules and the extraction agent,and the extraction agent was evaluated by the difference of the two mixing energy.The selectivity of the extraction agent was calculated by using the thermodynamic NRTL equation as a comparison for model results.Taking benzene cyclohexane binary system as an example,the molecular dynamics simulation method was used to calculate the mixed energy of one type of alcohols,one type of carboxylic acid and the common extraction agent and some ionic liquid molecules.At the same time,the selectivity of the different extraction agent was calculated to verify the model results.The results show that the difference of mixing energy and the selectivity is linear,and the selectivity increases with the increase of the difference of mixing energy.Finally,the software of Aspen Plus was used to simulate the process of extractive distillation of methanol methyl acetate system.The separation effect for DMF,dimethyl sulfoxide,1,3-propanediol,1,4-butanediol,1,5-pentanediol as the extraction agent was calculated respectively.The calculation results show that the separation efficiency of the dimethyl sulfoxide is the best.In the paper,the process simulation of the 11 unknown extraction agents which was Calculated by molecular simulation method was carried out.The results show that the molecular simulation method is suitable for selection the extraction agent.