Abstract

In this work, a data bank consisted of the experimental enthalpy departure data from ideal gas state for several pure and binary, and ternary systems was used to evaluate the accuracy of the modified Nasrifar-Moshfeghian (MNM) EoS. The impact of binary interaction parameters which were optimized based on vapor-liquid-equilibrium (VLE) data on enthalpy departure was also studied. In each case, the accuracy of MNM EoS has been compared with the Peng-Robinson and Soave-Redlich-Kowng EoSs and for each cases, the average absolute deviations are reported.

The overall analysis of the results indicates that the accuracy of MNM EoS in predicting enthalpy departures is in the same order of magnitude as for the SRK and PR EoSs for light hydrocarbon systems such as natural gas and LNG.

Introduction

Many equations of state (EoSs) are developed based on the pressure-volume-temperature (PVT) behavior and properties for pure compounds. Once the EoS was developed, expressions for enthalpy and entropy departures from ideal gas state, i.e., isothermal effect of pressure on enthalpy and entropy, can be used for calculation of these two properties. Accurate prediction of enthalpy and entropy is very important for design and simulation of unit operations such as compressor, turbine, expansion valve, distillation column, refrigeration cycles, and etc. When these EoSs are used to predict thermodynamic properties and vapor-liquid-equilibrium (VLE) behavior of binary and multicomponent systems, their accuracy deteriorates due to the dissimilarities in size, shape and interaction forces among the different molecules. In order to overcome this deficiency, a common practice is to introduce binary interaction parameters, kij., which are normally determined from the binary experimental VLE data Therefore, the industrial application of any cubic EoS with better accuracy requires the kij values. This work was undertaken to evaluate the accuracy of the Modified-Nasrifar-Moshfeghian (MNM) EoS [1] for prediction of enthalpy departure from ideal gas state of pure compounds, binary, ternary and multicomponent systems. The effect of kij values on prediction of enthalpy departure prediction was investigated. The optimized values of binary interaction parameters reported by Moshfeghian and Nasrifar [2] were used for this evaluation. In addition, the accuracy of the MNM EoS is compared with the two widely used SRK [3] and the PR [4] EoSs.

The same data bank of experimental enthalpy data was used for the MNM, SRK and the PR EoSs. In addition, for each case, the average absolute deviations are calculated and reported.

THE MNM EQUATION OF STATE

Nasrifar and Moshfeghian [1,5,6,7] used the following generalized cubic EoS:

(Equation 1) (Available in full paper)

Using a Pressure-Volume- Temperature (PVT) data bank of pure compounds, they developed a set of correlations to calculate the parameters a and b [1, 5]. Their proposed correlations are presented by Eqs 2 through 10.

(Equation 2) (Available in full paper)

(Equation 3) (Available in full paper)

(Equation 4) (Available in full paper)

(Equation 5) (Available in full paper)

(Equation 6) (Available in full paper)

(Equation 7) (Available in full paper)

(Equation 8) (Available in full paper)

(Equation 9) (Available in full paper)

(Equation 10) (Available in full paper)

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