Electrolyte systems, prediction

Doyle et al. [40] used a mathematical model to examine the effect of separator thickness for the PVDF.HFP gel electrolyte system and found that decreasing separator thickness below 52 pm caused only a minor decrease in ohmic drop across the cell. The voltage drops in the electrodes were much more significant. They state that their model predictions were confirmed experimentally. 

Within the past few years the advances made in hydrocarbon thermodynamics combined wtih increased sophistication in computer software and hardware have made it quite simple for engineers to predict phase equilibria or simulate complex fractionation towers to a high degree of accuracy through software systems such as SSI s PROCESS, Monsanto s FLOWTRAN, and Chemshare s DISTILL among others. This has not beem the case for electrolyte systems. 

It is shown that the properties of fully ionized aqueous electrolyte systems can be represented by relatively simple equations over wide ranges of composition. There are only a few systems for which data are available over the full range to fused salt. A simple equation commonly used for nonelectrolytes fits the measured vapor pressure of water reasonably well and further refinements are clearly possible. Over the somewhat more limited composition range up to saturation of typical salts such as NaCl, the equations representing thermodynamic properties with a Debye-Hiickel term plus second and third virial coefficients are very successful and these coefficients are known for nearly 300 electrolytes at room temperature. These same equations effectively predict the properties of mixed electrolytes. A stringent test is offered by the calculation of the solubility relationships of the system Na-K-Mg-Ca-Cl-SO - O and the calculated results of Harvie and Weare show excellent agreement with experiment. 

Until recently the ability to predict the vapor-liquid equilibrium of electrolyte systems was limited and only empirical or approximate methods using experimental data, such as that by Van Krevelen (7) for the ammonia-hydrogen sulfide-water system, were used to design sour water strippers. Recently several advances in the prediction and correlation of thermodynamic properties of electrolyte systems have been published by Pitzer (5), Meissner (4), and Bromley ). Edwards, Newman, and Prausnitz (2) established a similar framework for weak electrolyte systems. 

Zemaitis, J.F., and M. Rafal, "ECES - A Computer System to Predict the Equilibrium Composition of Electrolyte Systems", 68th Annual Meeting, AICHE, Los Angeles, (.Nov, 1975)... 

Anderko and Lencka find. Eng. Chem. Res. 37, 2878 (1998)] These authors present an analysis of self-diffusion in multicomponent aqueous electrolyte systems. Their model includes contributions of long-range (Coulombic) and short-range (hard-sphere) interactions. Their mixing rule was based on equations of nonequilibrium thermodynamics. The model accurately predicts self-diffusivities of ions and gases in aqueous solutions from dilute to about 30 mol/kg water. It makes it possible to take single-solute data and extend them to multicomponent mixtures. 

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. 

This is identical with equation (6.9.1) in the case of 1-1 electrolytes. The predictions of the limiting law for the NaCl system are also shown in fig. 6.10. It is valid for concentrations up to 0.01 M. The success of the theory is clear from this result. First of all, it confirms that plots of A against the square root of ionic strength provide a valid route for determining Aq, the equivalent conductance in the limit of infinite dilution. In addition, it explains why the slope of the plot in the dilute solutions regime depends on the nature of the electrolyte. 

The theoretical basis of isotachophoresis has been elaborated to such an extent that relationships which permit the calculation of pH, mobilities, composition of zones, level of the separation reached etc., are available. These relationships have even been developed to routine computer procedures. Thus, not only a great deal of information on the substances to be separated can be gained but also theoretical predictions of the optimum electrolytic systems enabling successful separations can be made. 

In addition to nanostructural properties of the conducting polymer, considerable influence on actuation behavior has been demonstrated due to the choice of electrolyte. This has included properties of the solvent employed, and crucially the size of doping ions and their interaction with the conducting polymer. As mentioned above, PPy films doped with moderately small anions (e.g. CP) lead to actuation driven by anion movement. By contrast, it is generally found that the inclusion of a large dopant anion (e.g. DBS) within PPy leads to cation-driven actuation, typically when a smaller cation is employed (e.g. Na ). However, it is not always a simple matter of predicting which movement, anion or cation, will predominate for a particular electrolyte system, and for a particular type of... 

In order to better understand the basis for the chapters which follow, let us consider the formulation of a predictive model for a particular aqueous based electrolyte system. The example chosen involves water-chlorine. The reactions to be considered are ... 

In order to mathematically predict the state of electrolyte systems, there are three essential steps Involved. These are ... 

The Equilibrium Compositions of Electrolyte Solutions (ECES) Program is an extensive general purpose vapor-liquid-solid prediction program for aqueous electrolyte systems. The package has a number of special features, including ... 

Li JD, Lin YZ, Gmehling J (2005) g(E) model for single- and mixed-solvent electrolyte systems. 3. Prediction of salt solubilities in aqueous electrolyte systems. Ind Eng Chem Res 44 1602-1609... 

Experimental data including the acidic species in the vapor phase within the above concentration range are scarce. Only very few publications of VLE data in that range are available [168, 173]. In contrast, numerous vapor pressure curves are accessible in literature. Chemical equilibrium data for the polycondensation and dissociation reaction in that range (>100 wt%) are so far not published [148]. However, a starting point to describe the vapor-Uquid equilibrium at those high concentratirMis is given by an EOS which is based on the fundamentals of the perturbation theory of Barker [212, 213]. Built on this theory, Sadowski et al. [214] have developed the PC-SAFT (Perturbed Chain Statistical Associated Fluid Theory) equation of state. The PC-SAFT EOS and its derivatives offer the ability to be fuUy predictive in combination with quantum mechanically based estimated parameters [215] and can therefore be used for systems without or with very little experimental data. Nevertheless, a model validation should be undertaken. Cameretti et al. [216] adopted the PC-SAFT EOS for electrolyte systems (ePC-SAFT), but the quality for weak electrolytes as phosphoric... 

Farhad and Hamdullahpur (2010) propose a novel portable fuel cell plant fueled by ammonia. In this plant a solid-oxide fuel cell (SOFC) stack consisting of anode-supported planar cells with an Ni-YSZ anode, YSZ electrolyte, and YSZ-LSM cathode is used to generate electric power. An ammonia cylinder with a capacity of 0.8 L is sufficient to sustain full-load operation of the portable system for 9 hours and 34 minutes. Computer simulation of this system predicts that for a 100-W portable device operating at a voltage of 25.6 V (a single-cell voltage of 0.73 V), an energy efficiency of 41.1% and a fuel utilization ratio of 80% are attainable. 

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