291959 An Improved Simple Method for Vapor Pressure Prediction From Cubic Equations of State

Monday, October 29, 2012
Hall B (Convention Center )
Minchul Kim and Michael J. Misovich, Engineering, Hope College, Holland, MI

Cubic equations of state, such as Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR), are commonly used to predict equilibrium properties of pure components such as vapor pressure. This work extended previous results which incorporate a quadratic approximation of the liquid density from a cubic equation of state into a vapor pressure prediction method.  Those results, derived from a low temperature and pressure limit method, give a relatively simple expression which predicts vapor pressures with deviations less than 35 percent of the exact predictions of the equation of state. A single empirical correction function for vapor pressure using a single similarity variable of temperature and acentric factor was determined. With the correction term, vapor pressures were estimated within less than one percent deviation from the exact values calculated by a SRK standard fugacity algorithm.   In the process of deriving the empirical correction, a new approach for defining the similarity variable was discovered.  Further research is planned with this new similarity variable with the goal of improving the empirical correction or possibly deriving an exact correction from theory.

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