Mahmood Moshfeghian

Prediction of equilibrium conditions for gas hydrate formation in the mixtures of both electrolytes and alcohol

Abstract Based on our previous method of prediction of equilibrium conditions in the separate solutions of electrolytes and alcohol, a combining rule for calculating hydrate formation temperature in the presence of both electrolytes and alcohol has been developed. In this method, the hydrate temperature in the presence of pure water is calculated and then this temperature is corrected for the presence of both electrolytes and alcohol. The average of absolute deviation for prediction of incipient of CO 2 and a typical natural gas hydrate in the mixtures of both electrolytes and alcohol was 0.96 K. The ability of the proposed model is also compared with other available methods.

A new approach for prediction of gas hydrate formation conditions in aqueous electrolyte solutions

Abstract A thermodynamic model for the calculation of hydrate formation temperatures of different hydrate formers in mixed electrolyte solutions is presented. The model uses the existing theory for the calculation of the water fugacity in single salt solutions and has been extended to mixtures of common electrolytes, i.e., NaCl, KCl and CaCl 2 . The present model, in contrast to previous models, needs no flash calculation procedure. The average absolute deviation of the model, using available experimental data, was about 0.4 K.

A new cubic equation of state for simple fluids: pure and mixture

Abstract A two-parameter cubic equation of state is developed. Both parameters are taken temperature dependent. Methods are also suggested to calculate the attraction parameter and the co-volume parameter of this new equation of state. For calculating the thermodynamic properties of a pure compound, this equation of state requires the critical temperature, the critical pressure and the Pitzer’s acentric factor of the component. Using this equation of state, the vapor pressure of pure compounds, especially near the critical point, and the bubble point pressure of binary mixtures are calculated accurately. The saturated liquid density of pure compounds and binary mixtures are also calculated quite accurately. The average of absolute deviations of the predicted vapor pressure, vapor volume and saturated liquid density of pure compounds are 1.18, 1.77 and 2.42%, respectively. Comparisons with other cubic equations of state for predicting some thermodynamic properties including second virial coefficients and thermal properties are given. Moreover, the capability of this equation of state for predicting the molar heat capacity of gases at constant pressure and the sound velocity in gases are also illustrated.

A saturated liquid density equation in conjunction with the Predictive-Soave–Redlich–Kwong equation of state for pure refrigerants and LNG multicomponent systems

Abstract An equation and a set of mixing rules for the prediction of liquid density of pure refrigerants and liquified natural gas (LNG) multicomponent systems have been developed. This equation uses the parameters of Mathias and Copeman [P.M. Mathias, T.W. Copeman, Fluid Phase Equilib. 13 (1983) 91–108] temperature dependent-term for the Predictive-Soave–Redlich–Kwong [T. Holderbaum, J. Gmehling, Fluid Phase Equilib. 70 (1991) 251–265] equation of state and hence it could be used together with this equation. The equation uses a characteristic parameter for each refrigerant; however, if it is not available, a value of zero is recommended. This model gives an average of absolute errors less than 0.42% for the prediction of liquid density of 28 pure refrigerants consisting of 2489 data points and 0.33% for 18 multicomponent LNG systems involving 132 data points. The model parameters were determined from pure component properties and reported. These parameters were then used without any adjustment to predict liquid density of multicomponent LNG mixtures and excellent results were obtained. The model was also compared with other available methods.

Evaluation of vapor—liquid equilibrium of CO2 binary systems using UNIQUAC-based Huron—Vidal mixing rules

Abstract Since Huron and Vidal [M.J. Huron, J. Vidal, Fluid Phase Equilib. 3 (1979) 255] developed the basic idea of the so-called GE mixing rules, similar models have been proposed by different authors. In most of them, a group-contribution method like the UNIFAC model is used with the equation of state to enable the description of vapor-liquid equilibrium (VLE) at high temperatures and pressures including supercritical compounds. In this work we intended to use the UNIQUAC instead of the UNIFAC method as GE model in SRK equation of state. For comparison between Huron-Vidal-type mixing rules, we selected the modified Huron-Vidal first-order (MHV1) and second-order (MHV2) mixing rules proposed by Michelsen [M.L. Michelsen, Fluid Phase Equilib. 60 (1990a) 213; M.L. Michelsen, Fluid Phase Equilib. 60 (1990b) 42.] and PSRK mixing rule proposed by Holderbaum and Gmehling [T. Holderbaum, J. Gmehling, Fluid Phase Equilib. 70 (1991) 251.]. In other words, this paper investigates the ability of several mixing rules to predict and correlate the high-pressure vapor-liquid equilibrium used in combination with the UNIFAC and UNIQUAC models. For comparison of these mixing rules, the carbon dioxide binary mixtures have been chosen because carbon dioxide has numerous applications in supercritical fluid processes. The missing interaction parameters of UNIFAC and UNIQUAC were estimated through the regression of experimental vapor-liquid equilibrium data. For comparison of UNIQUAC-based mixing rules with each other, the interaction parameters of 51 carbon dioxide binary systems have been determined. Furthermore, a comparison between UNIFAC- and UNIQUAC-based SRK equation of state is presented. The results show that all of the UNIFAC- and UNIQUAC-based mixing rules, with parameters derived from VLE, can be used for reliable calculations of phase equilibrium. It is shown that the PSRK/UNIQUAC mixing rule can correlate the data for the best VLE results. Also, it is shown that the use of the second-order mixing rule in UNIQUAC-based SRK equation of state does not necessarily improve the results of VLE calculations.

Evaluation of saturated liquid density prediction methods for pure refrigerants

Abstract Fourteen correlations and four equations of state (EOS) have been used to predict the liquid density of 15 refrigerants. Overall, Hankinson and Thomson correlation [R.W. Hankinson, G.H. Thomson, AIChE J., 26 (1979) 653–663] with an average of absolute percent deviation of 0.381 is the best for the prediction of liquid density of the refrigerants. The Chain of Rotator Group Contribution (CORGC) equation of state [J.D. Pults, R.A. Greenkorn, K.C. Chao, Chem. Eng. Sci., 44 (1989) 2553–2564] with an average of absolute percent deviation of 1.227 is the best among the equations of state and the fourth in overall.

A compressed liquid density correlation

Abstract A new correlation is developed for calculation of the compressed liquid density of pure compounds and mixtures. This correlation is used together with the Hankinson–Thomson (COSTALD) correlation of saturated liquid density and the Riedel equation for the calculation of vapor pressures. The range of application of this correlation is quite wide; from freezing point temperature to critical point temperature and from saturation pressure to 500 MPa. The average of error for the prediction of the compressed liquid volume of 31 compounds consisting of 3324 experimental data points is 0.77% with −0.24% bias from the experimental data. For mixtures, the average of error for the prediction of the compressed liquid volume of 13 mixtures consisting of 2101 experimental data points is 1% with −0.22% bias from the experimental data. The comparison with other correlations shows that the new correlation is somewhat better and quite reliable to very high pressures.

Generalized saturated liquid density prediction method for pure compounds and multi-component mixtures

A generalized saturated liquid density equation in conjunction with the Predictive-Soave–Redlich–Kwong (PSRK) equation of state has been developed. This equation uses the Mathias and Copeman temperature dependent term in addition to the critical temperature, critical density and dipole moment for prediction of saturated liquid density of pure compounds. The average absolute error for prediction of the saturated liquid density of 4745 experimental data points for hydrocarbons, halogenated paraffins, liquefied inorganic gases, alcohols, ethers and acids was 0.91%. The equation was then used with the equation and mixing rules of Nasrifar and Moshfeghian to predict the saturated liquid density of multi-component mixtures. The average absolute error for prediction of saturated liquid density of 87 multi-component systems containing nitrogen, hydrocarbons, alcohols, H2S, CO2 and halogenated paraffins was 1.11% for 1407 experimental data points.

Prediction of refrigerant thermodynamic properties by equations of state: vapor liquid equilibrium behavior of binary mixtures

Abstract The ability of three equations of state (EOS) for describing the vapor-liquid equilibria of refrigerants has been studied for several binary mixtures. The three uations of state studied were the Soave-Redlich-Kwong (SRK), Peng-Robinson (PR) and Parameters From Molecule Contribution (PFMC). For azeotropic mixtures, the bubble point pressure, vapor molar volume, saturated liquid density, and heat of vaporization were calculated and compared with the values reported in the ASHRAE hand- book. Binary interaction parameters for each equation of state were optimized to achieve better agreement between calculated values and the reported experimental data. The optimized binary interaction parameters for several binary mixtures are presented. Sample graphical error analyses are shown.

Vapor-liquid equilibria of LNG and gas condensate mixtures by the Nasrifar-Moshfeghian equation of state

Abstract The Nasrifar–Moshfeghian (NM) equation of state (EOS) is used to predict vapor–liquid equilibria (VLE) of multi-component mixtures. The systems under study consist of liquefied natural gases (LNG), gas condensates, an asymmetric system, slightly polar systems and gas/water systems. van der Waals mixing rules are used and no pure component parameter is adjusted; however, the predictions compare well with experimental data, in particular, the solubility of CO 2 , H 2 S, CO and some hydrocarbon gases in water are calculated quite accurately. The average absolute error was found to be 7% for calculating gas solubility in water. For some systems, the volumetric properties were also predicted. The saturated liquid density of LNG systems is predicted with an average absolute error less than 0.6%.