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PPR78: New predictive equation of state for saturated hydrocarbons, aromatics and naphtenes

25/06/2007
ProSim, the French process simulation software house, announces the integration of PPR78, a new predictive equation of state, in ProSimPlus (software for steady state simulation of industrial processes) and in Simulis Thermodynamics (software component for thermodynamic properties calculation).


The objective of this integration is to ensure that the engineer who works with systems containing saturated hydrocarbons, aromatics and naphtenes is not constrained by a lack of data on properties and that he has predictive methods to estimate them. Thus, he can save time while preserving full reliability of the calculations.

Having access to reliable predictive methods in a thermodynamic library is essential. As Pr. Gmehling explained [1]: ”Reliable knowledge of the thermophysical properties of pure compounds and their mixture in the whole composition and a wide temperature and pressure range is a vital prerequisite for the computer aided synthesis, design and optimization of chemical processes”. In particular, “Because of the significance of separation processes during synthesis processes, reliable knowledge of the phase behavior is of special importance, whereby in most cases, the phase behavior of multi-component systems has to be known, for which nearly no data are available. Of course, the phase behavior can be measured today with the help of sophisticated often computer operated techniques. However, measurements are very time consuming. For example, the measurement of the vapor – liquid equilibria (VLE) behavior of a 10-component system at only atmospheric pressure in 10 mole % steps (in total 92 378 data points) would require approximately 37 years”.

The model integrated by ProSim comes from Jaubert et al. [3], [4], [5] group contribution method, which allows the estimation of the temperature dependent binary interaction parameters (kij(T)) for the widely used Peng–Robinson equation of state (EOS) [2]. Since the addition of a group contribution method to estimate the kij makes it predictive, this model was called PPR78 (Predictive 1978, Peng–Robinson EOS).

A key point in Jaubert et al. approach is that in the kij between two components, i and j are a function of temperature (T) and of the pure components critical temperatures (TCi, TCj), critical pressures (PCi, PCj) and acentric factors (ωi, ωj). This means that no additional properties besides those required by the EOS itself (TC, PC, ω) are required.

In a first paper [3], six groups were defined for application of the PPR78 model: CH3, CH2, CH, C, CH4 (methane), and C2H6 (ethane). The model was subsequently extended to systems containing aromatic compounds [4] (new groups: CHaro and Caro) and to systems containing naphtenic (cyclic hydrocarbons) compounds [5] (new groups: CH2, cyclic, CHcyclic and Ccyclic) and to gases (N2, CO2 and H2S). This makes it possible to estimate the kij for any mixture containing alkanes, aromatics, naphtenes and gases (N2, CO2, H2S) whatever the temperature.



Bubble and Dew Pressures at Given Temperature
n-Butane / n-Decane
Bubble and Dew Pressures at Given Temperature
Methane / Propane
Nitrogen / n-Butane Vapor Liquid equilibrium
 
Ethane / Hydrogen Sulfide Vapor Liquid equilibrium Methane / CO2 Vapor Liquid equilibrium  



[1] J. Gmehling
“Potential of thermodynamic tools (group contribution methods, factual data banks) for the development of chemical processes”
Fluid Phase Equilibria, vol. 210, pp. 161-173, 2003

[2] D.B. Robinson, D.Y. Peng
“The characterization of the heptanes and heavier fractions for the GPA Peng-Robinson programs”
Gas processors association, Research Report PR-28, 1978

[3] J.N. Jaubert, F. Mutelet
“VLE predictions with the Peng-Robinson equation of state and temperature dependant Kij calculated through a group contribution method”
Fluid Phase Equilibria, vol. 224, pp. 285-304, 2004

[4] J.N. Jaubert, S. Vitu, F. Mutelet
“Extension of the PPR78 model (Predictive 1978, Peng-Robinson EOS with temperature dependant calculated through a group contribution method) to systems containing aromatic compounds”
Fluid Phase Equilibria, vol. 237, pp. 193-211, 2005

[5] S. Vitu, J.N. Jaubert, F. Mutelet
“Extension of the PPR78 model (Predictive 1978, Peng-Robinson EOS with temperature dependant calculated through a group contribution method) to systems containing naphtenic compounds”
Fluid Phase Equilibria, vol. 243, pp. 9-28, 2006