A unified approach for prediction of thermodynamic properties of aqueous mixed‐electrolyte solutions. Part I: Vapor pressure and heat of vaporization

Patwardhan, V.S.; Kumar, Anil

doi:10.1002/aic.690320903

Cited by 93 publications

(80 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Patwardhan and Kumar (1986) introduced the concept of overall reduced activity coefficient, F*, for handling mixed electrolyte solutions, and derived the following predictive equation for the activity of water in such solutions, In Eq. 10, rnk is the modality of electrolyte k in the mixed solution, rnz is the molality of a solution containing only electrolyte k , which has the same ionic strength as that of the mixed solution and is the activity of water in the single salt solution.…”

Section: Single Electrolyte Solutionsmentioning

confidence: 99%

“…A number of models are available for calculating the activity of single salts in aqueous solutions, and recently an elegant method has been made available to account for the overall nonideal effects of salts in mixed salt solutions. The models have been used to develop (Zemaitis, 1986;Pitzer and Mayorga, 1973;Patwardhan and Kumar, 1986) expressions for the activity of water.…”

Section: Activity Of Water Amentioning

confidence: 99%

See 1 more Smart Citation

Prediction of gas hydrate formation conditions in aqueous electrolyte solutions

1988

View full text Add to dashboard Cite

Gas hydrates are solid clathratc compounds. They are formed by the enclosure of light nonpolar gases, such as natural gas components, in a lattice-like structure of water molecules. They have been extensively reviewed recently by Berecz and BallaAchs (1983). Hydrates are known to occur naturally in vast quantities on ocean floors and in the permafrost regions of the world (Makogon, 1974(Makogon, , 1987. Majority of the thermodynamic studies on gas hydrates have focused on formation from pure water. The methods for predicting the formation conditions are based on the statistical thermodynamics model of van der Waals and Platteeuw (1959). An algorithm for the predictions was developed by Parrish and Prausnitz (1972), and subsequently improved by Ng and Robinson (1976), Holder et al. (1980), and John et al.(1 985). When electrolytes or molecular species like methanol are present in the liquid water, the hydrate formation is inhibited. Inhibition of gas hydrate formation is of particular interest to the oil and gas industry. In the present work, only the studies on the effect of electrolytes are investigated. Makogon (1 974) and Berecz and Balla-Achs (1 983) discuss the inhibiting effects of various salts and classify them according to their inhibiting activities. Knox et al. (1961) investigated the seawater desalination process via propane hydrate formation. Recently Kubota et al. (1984) also studied the propane hydrate formation.In both studies, data are reported on the formation from sodium chloride solutions. Roo et al. (1983) studied methane hydrate formation from NaCl solutions. Their experimental data were useful in examining the possibility of gas storage in the crust of the earth. Menten (1979) and Menten et al. (1981) reported experimental data on the cyclopropane hydrate formation conditions from water containing KCI or CaCI,. In addition, they presented a predictive method for the calculation of the hydrate forming conditions in the single salt solutions. The method is based on calculating the activity of water by using freezing point depression data. This is the only available predict k e method for the effect of single electrolytes on gas hydrate formation. In the present work, a computer implementable methodology is developed (Engleios, 1987) for the prediction of hydrate formation conditions in systems containing light hydrocarbon gases and aqueous solutions of single or mixed electrolytes. No adjustable parameters are needed in addition to those for the thermodynamic model for predictions from pure water and for the activity coefficient models for the salts in aqueous solutions, which are available from the literature. Methodology water solution may be represented by the following equationEquilibrium among the solid hydrate, the gas, and the liquid &l:= p:.( 1 )In writing Eq. I the amount of water vapor present in the gas phase is considered negligible. In addition, it is assumed that the salts are present only in the liquid solution. Since the salts do not enter the hydrate lattice, the statistic...

show abstract

Section: Single Electrolyte Solutionsmentioning

confidence: 99%

Section: Activity Of Water Amentioning

confidence: 99%

Prediction of gas hydrate formation conditions in aqueous electrolyte solutions

1988

View full text Add to dashboard Cite

show abstract

“…For a common ion system, the vapor pressure of a mixed electrolyte solution can be predicted by (Patwardhan and Kumar, 1986a): where index J refers to the electrolytes actually used for preparing the solution. For a four-ion system, however, the equations stated in the previous section can be applied, by calculating the ionic composition of the final solution, calculating all y,J with Eq.…”

Section: Vapor Pressurementioning

confidence: 99%

Thermodynamic properties of aqueous solutions of mixed electrolytes: A new mixing rule

Patwardhan

Kumar

1993

AIChE Journal

Self Cite

View full text Add to dashboard Cite

The prediction of several thermodynamic properties of mixed aqueous electrolyte solutions has been considered earlier (Patwardhan and Kumar, 1986a,b). A unified set of predictive equations for several properties was presented by them and was tested against experimental data. These predictive equations require knowledge of properties of corresponding single electrolyte solutions. No further system-specific empirical constants are involved. The experimental data used for testing these equations involved mixed systems having a common ion in most cases, with only a few exceptions. It is thus clear that the equations developed earlier can be used with confidence for common ion systems. We consider here the application of these equations to mixed systems having no common ion, as well as several properties for which reliable data are available for different systems involving four ions. Process of MixingLet us consider the mixing of single electrolyte solutions of equal ionic strength which do not have any common ion, for example, mixing of NaCl solution and KBr solution. In the final solution, interactions of sodium ions with both chloride and bromide ions are present and may be important. A similar statement can be made about the potassium ions. If an equation involving only these two electrolytes were used for predicting the vapor pressure of the final mixture, then it would account for only the Na-Cl and K-Br interactions, leaving out the other two interactions, namely Na-Br and K-Cl. Therefore, even though the final mixed electrolyte solution has been actually prepared by mixing NaCl solution with KBr solution, it should be considered as obtained by conceptually mixing four single electrolyte solutions: NaC1, KCl, NaBr, and KBr. The amounts of these solutions have to be so selected that each mixing process involves a common ion or a common ionic atmosphere (cationic or anionic). These amounts can be calculated in the following manner. Consider a mixed electrolyte solution containing several species of cations and anions. Let i refer to cations and j refer to anions. The total anionic charge, ( C H ) , which is also equal to the total cationic charge, is given by:Correspondence concerning this work should be addressed to V. S. Patwardhan. I jThe cationic strength is:Z,=O.S c rnd 1 and the anionic strength is: Z,=O.S c m dThe total ionic strength is given by:Let the cationic strength fraction and the anionic strength fractions be defined as:and Let us consider a quantity of the mixed electrolyte solution which contains 1, OOO g of water. Consider a process whereby cation i in the solution is conceptually separated from other cations into a region containing (l,OOOyi) g water, keeping the anions well mixed where yi is unknown at present. The cationic strength in this region is XJc/Yi and the anionic strength in the same region is [mgi/( CH)]Z,/yi. We now select yi such that the total ionic strength in this region is equal to Z. Z=

show abstract

“…of 1.63 K and JMM with an a.a.t.d. of 3.13 K. The proposed model uses equation (12) while EB uses the equation of Patwarthan and Kumar (23) which is expressed by:…”

Section: Resultsmentioning

confidence: 99%