An Empirical Correction for Determining SRK and PR Vapor Pressures

Faculty Mentor(s)

Dr. Michael Misovich, Hope College

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This material is based upon work supported by Hope College and the Hope College Engineering Department.


The Soave-Redlich-Kwong (SRK) and Peng-Robinson (PR) equations of state are commonly used methods for estimating vapor pressure of pure substances at any temperature, typically by a fugacity-based numerical algorithm. Recent work shows that a simple expression derived from a low temperature and pressure limit gives results within 35 percent of a standard fugacity algorithm for reduced temperatures below approximately 0.8. An empirical correction term for this simple expression was determined in this project, allowing estimation of vapor pressure with less than 0.1 percent deviation from the result given by a fugacity-based algorithm. Another empirical method was developed to estimate vapor pressure with similar accuracy for temperatures up to the critical point. Both empirical corrections were functions of a single variable combining temperature and acentric factor. Using these approaches, SRK and PR vapor pressures were accurately estimated at any temperature by a simple, non-iterative calculation.

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