Study On The Activity Coefficient Of Ionic Liquids [C_nmim][Pro](n=3,5) Dilute Solutions By The Method Of Freezing Point Depression

The pollution brought by the traditional chemical industry to the environment has been very serious,at present the world produces 0.4 to 0.5 billion tons of hazardous waste per year,causing serious harm to the environment and threatening the survival of mankind.In our country,the "green chemistry" has been one of the main directions of chemical development in the new century.Ionic liquid as a new green solvent has many excellent properties,which requires us to study the ionic liquid dilute solution properties,as in its application to provide a theoretical basis.In this paper,the 1-propyl-3-methylimidazolium propionate salt([C3mim][Pro])and 1-pentyl-3-methylimidazolium propionate salt([C5mim][Pro])were prepared by two step synthesis method,and characterized by1 H NMR spectroscopy and DSC trace.The freezing point data of KCl dilute solutions in the molality range of 0.1000mol·kg-1-0.5000 mol·kg-1 was measured using a freezing point analyzer.The osmotic coefficients of KCl dilute solutions at a temperature of 273.15 K were calculated by the freezing point depression data,which were in good agreement with the literature values.So the measurement method is effective.The freezing point data of different molality of [Cnmim][Pro](n = 3,5)dilute solutions were measured by a freezing point analyzer,using the freezing point depression data through the Pitzer equation to calculate the activity coefficients of [Cnmim][Pro](n = 3,5)dilute solutions.The determination and theoretical calculation of the activity coefficients are of great practical value and theoretical significance in the fields of marine chemistry,salt lake chemistry,pollution control,hydrometallurgy and so on.As green solution with many excellent properties of ionic liquid,is worth studying the osmotic coefficients and the activity coefficients.Therefore,using the freezing point depression data to calculate activities and osmotic coefficients of [Cnmim][Pro](n = 3,5)dilute solutions,Pitzer equation was used to determine the parameters of Pitzer at the temperature of Tf and further calculating activity coefficients.This is a very crucial thermodynamic model for using the method of freezing point depression to calculate activitycoefficients of ionic liquid dilute solutions.