The Research Of A New G~E-EoS Models Based On Elements And Chemical Bonds

Since the first GE-EoS(excess gibbs equation of state)model is proposed,GE-EoS model has been developed for over 30 years.GE-EoS model is the combination of equation of state and activity coefficient models and improvements to it are inevitably affected by the equation of states or activity coefficient models.Zhao Yajun(2013)proposed a new activity coefficient model based on elements and chemical bonds(UNAGEC model),in which elements and chemical bonds are considered as the basic contribution unit for molecular properties.Relative to the group contribution model of the most widely used now,UNAGEC model is more convient to split molecules.You can use fewer interaction parameters to predict properties of more kinds of compound,including the vapor-liquid equilibrium.So the problem of the existing group contribution model parameters are missing can be solved.Compared with the traditional methods of equation of state and activity coefficient models,the advantages of GE-EoS model in calculation of vapor-liquid equilibrium are a wider range of application in pressure and polarity.This paper shows a GE mixing rule,combining the SRK equation and the UNAGEC model,based on element and chemical bonds.A new GE-EoS model is obtained combining the above-mentioned GE mixing rule with SRK EoS.The new GE-EoS model is called SRK-RCB model and interaction parameter table of UNAGEC model is used here.In order to verify the prediction accuracy and the applicable scope in pressure of SRK-ECB model,phase equilibrium is forecasted for 229 groups of binary system(2869 points)and 12 groups of the ternary system(507 points)under low pressure,and 7 groups of binary system(44 points)under high pressures.A detailed comparison is made about predictions of SRK-ECB model and some other activity coefficient models.For binary and ternary systems under low pressure,the predictions are compared with the UNAGEC model,UNIFAC(1977)model,UNIFAC(2003)model,UNIFAC(DMD)model and UNIFAC(Larsen)model.For binary systems,the average absolute error of vapor composition and the average relative error of the bubble point are 0.0165,1.57%respectively.The result shows SRK-ECB model is better than the UNIFAC(1977)model,close to UNIFAC(2003)model.For ternary systems,the average absolute error of vapor composition and the average relative error of the bubble point are 0.0189,2.26%respectively,close to other activity coefficient models.For binary systems under high pressure,the predictions are compared with the UNIFAC(1977)model and UNIFAC(DMD)model.The average absolute error of vapor composition and the average relative error of the bubble point are 0.0165,1.57%respectively.The result shows the SRK-ECBmodel is better than the UNIFAC(1977)model and UNIFAC(DMD)model.SRK-RCB model is applicable to a larger pressure scope-from several kPa to several thousand kPa.And SRK-RCB model is also suitable for polar system and no-polarial system.It is more convient to split molecules and we can use fewer interaction parameter to predict vapor-liquid equilibrium of more different molecules,because of the introduction of UNAGEC models in the SRK-RCB model.SRK-RCB model can predict vapor-liquid equilibrium of multivariate system by vapor-liquid equilibrium datas of binary system.