Vapor-Liquid Equilibrium Based on Equations of State

6 VAPOR-LIQUID EQUILIBRIUM BASED ON EQUATIONS OF STATE 

Before an equation of state can be applied to calculate vapor-liquid equilibrium, the fugacity coefficient / , for each phase needs to be determined. The relationship between the fugacity coefficient and the volumetric properties can be written as  

For example, the Peng-Robinson equation of state for this integral yields2  

If an activity coefficient model is to be used at high pressure (Equation 4.27), then the vapor-phase fugacity coefficient can be predicted from Equation 4.47. However, 

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