Electrolyte-NRTL model

Electrolyte models Electrolyte NRTL Pitzer Bromley-Pitzer... 

Belveze, L.S., Brennecke, J.F., and Stadtherr, M.A., Modeling of activity coefficients of aqueous solutions of quaternary ammonium salts with the electrolyte-NRTL equation, Ind. Eng. Chem. Res., 43, 815, 2004. 

Reactive absorption processes occur mostly in aqueous systems, with both molecular and electrolyte species. These systems demonstrate substantially non-ideal behavior. The electrolyte components represent reaction products of absorbed gases or dissociation products of dissolved salts. There are two basic models applied for the description of electrolyte-containing mixtures, namely the Electrolyte NRTL model and the Pitzer model. The Electrolyte NRTL model [37-39] is able to estimate the activity coefficients for both ionic and molecular species in aqueous and mixed solvent electrolyte systems based on the binary pair parameters. The model reduces to the well-known NRTL model when electrolyte concentrations in the liquid phase approach zero [40]. 

The expression for the excess Gibbs energy is built up from the usual NRTL equation normalized by infinite dilution activity coefficients, the Pitzer-Debye-Hiickel expression and the Born equation. The first expression is used to represent the local interactions, whereas the second describes the contribution of the long-range ion-ion interactions. The Bom equation accounts for the Gibbs energy of the transfer of ionic species from the infinite dilution state in a mixed-solvent to a similar state in the aqueous phase [38, 39], In order to become applicable to reactive absorption, the Electrolyte NRTL model must be extended to multicomponent systems. The model parameters include pure component dielectric constants of non-aqueous solvents, Born radii of ionic species and NRTL interaction parameters (molecule-molecule, molecule-electrolyte and electrolyte-electrolyte pairs). 

We have seen many successful industrial applications of applied electrolyte thermodynamics models. In particular, the electrolyte NRTL activity coefficient model of Chen and Evans has proved to be the model of choice for various electrolyte systems, aqueous and mixed-solvent. However, there are unmet needs that require further development. 

First, we need a predictive activity coefficient model for electrolyte systems. The electrolyte NRTL model is correlative, and it requires extensive experimental data sets from which NRTL binary interaction parameters can be identified. The OLI electrolyte model, with its extensive parameter database, has been serving as a pseudo-predictive model. However, use of the OLI electrolyte model is limited to dilute aqueous electrolytes, its parameter database is not open to the public, and its electrolyte speciation is not supported by experiments. 

Second, we need an equation-of-state for electrolyte solutions. Equations-of-state are needed for modeling high-pressure applications with electrolyte solutions. Significant advances are being made in this area. Given that the electrolyte NRTL model has been widely applied for low-pressure applications, we are hopeful that, some day, there will be an equation-of-state for electrolytes that is compatible with the electrolyte NRTL activity coefficient model. 

The Electrolyte NRTL model " and the Extended UNIQUAC model" are examples of activity coefficient models derived by combining a Debye-Hiickel term with a local composition model. Equation of state models with electrostatic terms for... 

In the liquid phase, the simplest option is an ideal liquid, with an activity coefficient equal to 1.0. That choice leads to Raoult s law, which may suffice for similar chemicals. Other models include regular solution theory using solubility parameters (although not in Aspen Plus), NRTL, Electrolyte NRTL, UNIFAC, UNIQUAC, Van Laar, and Wilson. Characteristics of the models are ... 

Ammonia is removed by a IM H2SO4 water solution scrubber the liquid solution entering from the top of the tower (a SCDS column settled as packed column mass transfer simulation model) is continuously fed by a make-up quantity corresponding to the amount needed for the ammonia removal. At the bottom of the column gaseous ammonia enters at T = 95°C, it dissolves into the acid solution, diffuses and rapidly reacts with the H+ ions via ammonia protonation following thermodynamics of electrolyte non-random two liquid (Electrolyte NRTL) approach. 

The exact calculation equations are given in [25], where it has also been proved that the Gibbs-Duhem equation is fulfilled. As well, NRTL parameters have been fitted up to molalities of 30mol/kg for a number of systems. Together with the ionic diameters, they are listed in [25]. Osmotic and mean ionic activity coefficients could be reproduced in an excellent way for a number of systems. Furthermore, the parameters fitted to binary systems have been successfully applied to ternary systems, that is, one salt in a binary solvent mixture, which always causes problems with the Electrolyte NRTL model [25]. 

Calculate the saturation pressure of an aqueous NaOH solution at = 100 C at NaOH concentrations of 10, 30, and 50wt%. Use the Electrolyte NRTL model. The necessary parameters are given in Example 7.2. 

Calculate the liquid heat capacity of a 20wt% NaCl solution at iJ = 80 " C using the Electrolyte NRTL model. The required parameters can be downloaded from the textbook page on www.ddbst.com. 

Calculate the saturation pressure of a 20 wt% ammonia solution using the NRTL equation and the Electrolyte NRTL model at = 20 C. An ideal vapor phase can be assumed. The pKb value of ammonia at 25 ""C is 4.75. Further required parameters can he downloaded from the textbook page on www.ddbst.com. Do you think that the use of the electrolyte model is necessary in this case. How is the situation affected if significant amounts of CO2 are added to the system. ... 

For selected salts and ions in water the thermodynamic standard properties are listed in Table 8.1. To be able to determine the salt solubility from the solubility product, only an electrolyte model, such as Pitzer, Electrolyte NRTL, LIQUAC [8], or LI FAC [9] for the calculation of the mean activity coefficients y , and in the case of hydrated salts additionally the activity of water is required (see Chapter 7). 

Nonelectrolyte G mcxlels only account for the short-range interaction among non-charged molecules (—One widely used G model is the Non-Random-Two-Liquid (NRTL) theory developed in 1968. To extend this to electrolyte solutions, it was combined with either the DH or the MSA theory to explicitly account for the Coulomb forces among the ions. Examples for electrolyte models are the electrolyte NRTL (eNRTL) [4] or the Pitzer model [5] which both include the Debye-Hiickel theory. Nasirzadeh et al. [6] used a MSA-NRTL model [7] (combination of NRTL with MSA) as well as an extended Pitzer model of Archer [8] which are excellent models for the description of activity coefficients in electrolyte solutions. Examples for electrolyte G models which were applied to solutions with more than one solvent or more than one solute are a modified Pitzer approach by Ye et al. [9] or the MSA-NRTL by Papaiconomou et al. [7]. However, both groups applied ternary mixture parameters to correlate activity coefficients. Salimi et al. [10] defined concentration-dependent and salt-dependent ion parameters which allows for correlations only but not for predictions or extrapolations. 

Chen CC, Mathias PM, Orbey H (1999) Use of hydration and dissociation chemistries with the electrolyte-NRTL model. AIChE J 45 1576-1585... 

Simoni LD, Lin Y, Brennecke JF, Stadtherr MA (2(X)8) Modeling liquid-liquid equilibrium of ionic liquid systems with NRTL, electrolyte-NRTL, and UNIQUAC. Ind Eng Chem Res 47 256-272... 

Figure 8.3 shows a decision tree to help in the choice for the thermodynamic property model. Besides the four factors mentioned earlier, this decision tree takes into account the polarity of the mixture. Another feature of the mixture considered is the existence of pseudocomponents and the possibility of some of the components being electrolyte. The most common electrolyte methods are the Pitzer model and the electrolyte NRTL. 

The most sophisticated, and probably the most accurate model available at this time was proposed by Austgen et al. (1991). This model is based on the electrolyte-NRTL model of... 

Danner et al. express the short-range contribution using a modification of the electrolyte-NRTL equation of Chen and Evans [109] and take the long-range contribution from Manning s model (for the case of infinite dilution of a... 

Here, we describe the application and typical modelling results for a G model (MSA-NRTL) as well as for an EOS (ePC-SAFT). In addition to strong electrolytes which are almost fully dissociated, we also consider some weak electrolytes (acids like HE or ion-paired electrolytes) that do only partially dissociate in aqueous solution. Here, ion pairing is accounted for by an association/dissociation equilibrium between the ion pair and the respective free ions in solution. 

As mentioned before, ion-specific instead of salt-specific parameters are used here for both models. Thus, the ionic parameters determined for an ion are applicable to all electrolytes containing this ion. Obtaining such a universal set of parameters requires a simultaneous regression of several electrolyte solutions, which is described in Refs. 5 and 15 for both models, MSA-NRTL and ePC-SAFT. 

It is estimated that half of all pharmaceuticals are formulated as salts, to achieve increased stability and bioavailability [13]. Predictive solubility methods are very limited for this area, and the development of new models to address this category is very important. The NRTL-SAC model has recently been extended by C.-C. Chen, and Y. Song to represent such electrolytic solutes, that partly dissociate to ions in solution. This extension has been achieved by the addition of one new segment type into the preceding NRTL-SAC model. NRTL-SAC thus becomes a limiting case of the eNRTL-SAC formulation [27]. 

About the same time Beutier and Renon (11) also proposed a similar model for the representation of the equilibria in aqueous solutions of weak electrolytes. The vapor was assumed to be an ideal gas and < >a was set equal to unity. Pitzer s method was used for the estimation of the activity coefficients, but, in contrast to Edwards et al. (j)), two ternary parameters in the activity coefficient expression were employed. These were obtained from data on the two-solute systems It was found that the equilibria in the systems NH3+ H2S+H20, NH3+C02+H20 and NH3+S02+H20 could be represented very well up to high concentrations of the ionic species. However, the model was unreliable at high concentrations of undissociated ammonia. Edwards et al. (1 2) have recently proposed a new expression for the representation of the activity coefficients in the NH3+H20 system, over the complete concentration range from pure water to pure NH3. it appears that this area will assume increasing importance and that one must be able to represent activity coefficients in the region of high concentrations of molecular species as well as in dilute solutions. Cruz and Renon (13) have proposed an expression which combines the equations for electrolytes with the non-random two-liquid (NRTL) model for non-electrolytes in order to represent the complete composition range. In a later publication, Cruz and Renon (J4J, this model was applied to the acetic acid-water system. 

Among the various models incorporating the local composition concept for short-range interactions, the NRTL equation is adopted in this study. Electrolyte systems are characterized by extraordinarily large heats of mixing. 

Jefferson Tester I would like to shift gears and direct a question to John Prausnitz regarding his comments. You didn t talk very much about some of your own contributions and those of your students, for instance, the NRTL equation and UNIQUAC-UNIFAC models for nonideal solutions now in widespread use throughout the chemical industry and certainly employed by many people making practical calculations. There have been extensions of that local composition approach, in particular to electrolyte systems, by C. C. Chen and others. I wonder how you personally feel about that and... 

Medications in this class include delavirdine, efa-virenz, and nevirapine. Similar to the NRTls, these agents bind to viral reverse transcriptase and block DNA polymerase activity. A key difference is that NNRTIs do not require intracellular phosphorylation and are not incorporated into viral DNA. Clinically significant kidney toxicities or specific fluid-electrolyte complications have not been reported with this class of agents. In the rat model, efavirenz was associated wifh a species specific dependent kidney toxicity which occurred secondary to the development of a unique glutathione conjugate produced as a metabolite of efavirenz associated with renal tubular epifhelial cell necrosis [125-126]. This toxicity has not been observed in humans. One patient was recently reported to have reversible nephrotic-range proteinuria attributed to efavirenz use, in which a kidney biopsy showed diffuse podocyte foot process effacement [127]. Another report noted the development of rhabdomyolysis and acute tubular necrosis as a result of a drug interaction between delavirdine and atorvastatin [128]. Kidney toxicity due to nevirapine has not been reported. 

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