Model CO2-C6F14 Vapor Liquid Equilibrium with an Equation of State

I'm trying to model the VLE for a binary mixture of CO2 and C6F14 using a cubic equation of state (e.g. Peng-Robinson) for both the liquid and the vapor phase (phi-phi approach).


From available data in literature I know that at 30°C and at a pressure ranging from 5 bar to 60 bar the system shows VLE.


In the first step I assume ideal mixture.


When I apply the equation of state to either C6F14 and CO2 to evaluate the fugacity coefficients for the liquid and for the gas phases I obtain only one root so that seems that there isn't any equilibrium.


Where am I wrong? Am I missing something from theory? 
Any help is appreciated.


