Comparison of pure component thermodynamic properties from CHEMCAD with direct calculation using the Peng-Robinson equation of state

Abstract

• A systematic analysis of thermodynamic properties calculated using the CHEMCAD process simulator was undertaken to assess the accuracy of the results. • The results were very good with a few small yet significant discrepancies for the molecules nitric oxide, dinitrogen tetroxide, nitrogen dioxide, and sulfur dioxide. Accurate calculations of properties such as enthalpy, entropy, and fugacity are crucial for chemical process design. These properties are calculated from equations of state in commonly used process design software such as CHEMCAD[1], and software-based calculations of properties have been routine for decades. Correct application of chemical thermodynamics by the user is a requirement for successful process simulations. Users should be able to easily reproduce the calculations to verify choices made during the development of a simulation. In a previous study [4], we reproduced the compressibility factors, enthalpy, entropy, and fugacity coefficients from CHEMCAD using the Lee-Kesler method. In this paper, we extend our study to include the Peng-Robinson equation of state [5]. We compare the thermodynamic properties of 48 molecules at two different states. Our results show good consistency for most of these molecules, with percent errors generally less than 1%. The property changes for the difference between the two states show deviations for hydrogen, nitric oxide, and water. For absolute (stream) enthalpies, we observe deviations for air, hydrogen sulfide, nitrogen, oxygen, and water. For absolute (stream) entropies, we observe deviations for hydrogen, hydrogen chloride, nitric oxide, and water.