In defining these quantities, a new variable SRC appears which is the normalized pellet SO2 concentration at the sulfation interface within the pellet. It is defined asThe expressions for the preceding variables are derived by solving the Laplace equations which result from the pseudo steady state pellet gas phase material balances and their boundary conditions (Bourgeois, 1972).Experimental data are presented for five systems, each consisting of water, an alcohol (methanol or ethanol), and an inorganic salt dissolved to saturation in the boiling liquid phase. The data confirm and extend knowledge of recently discovered anomalies to the general theory of salt effect in vapor-liquid equilibrium. A partial accounting for the observed anomalies is attempted based on recent advances in the understanding of the structural nature of alcohol-water mixtures. SCOPEExtractive distillation employing a dissolved salt in place of the conventional liquid solvent as the separating agent is capable of yielding higher separation efficiency, and with lower energy requirements, than conventional extractive distillation processing. A recent review of the theoretical and technical aspects of extractive distillation by salt effect has been published (Furter, 1972). Before large-scale commercialization is feasible, however, the theory of salt effect on vapor-liquid equilibrium must be better understood than at present. When a salt is dissolved in a boiling solution of two liquid components, there are several salt effects that may occur. These include alterations in the boiling point, in the mutual solubilities of the two liquid components in each other, and in the composition of the equilibrium vapor phase. It is with the latter effect that this paper is concerned. Studies of salt effect in vapor-liquid equilibrium involve, in the simplest case, a two-component vapor phase in equilibrium with a three-component liquid phase, one of the components of the latter being the dissolved salt. The salt does not appear in the vapor.At least until recently, it has been generally held that the presence of a salt in the liquid would result in an Electric Power Commission, Toronto, Ontario, Canada.the component in which the salt was less soluble, with

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Isobaric vapor-liquid equilibrium data at atmospheric pressure are reported for seven systems, each consisting of water, an akohol (methanol or ethanol), and an anhydrous acetate salt (of sodium, potassium, barium, or calcium) dissolved to saturation in the boiling liquid phase. These systems are intended to complete a matrix about the single system ethanol-water-potassium acetate for which data were reported previously.Solubility data are reported in terms of saturation salt concentration as a function of alcohol-water proportionality in the liquid. Sodium acetate as well as potassium acetate was found capable of eliminating completely the ethanol-water azeotrope.Mojor differences in the effects of these salts as compared to those reported for other salts in the ralt-effect literature were observed. Systems were discovered in which the salt appeared to cause both salting out and salting in of the alcohol in differing composition regions of the same system, the predominating effect depending on the relative proportions of alcohol and water. Systems were also discovered in which the s a l t salted-in the component in which it was less soluble. Both observed effects are in contradiction with previously accepted theories of salt effect in vapor-liquid equilibrium.In a previous study (1 ) , potassium acetate dissolved to saturation was observed to exert a very large effect on the relative volatility of the ethanol-water system. Relative volatility was enhanced as much as fourfold and more at certain ethanol-water ratios. The magnitude of the effect was attributed to a combination of the very high solubility of potassium acetate in the system and the large difference in solubilities of potassium acetate in pure water and pure ethanol. Such a system consists of a two-component vapor phase and a three-component liquid phase, a consequence of the salt being nonvolatile and hence appearing only in the liquid.Extractive distillation employing a dissolved salt as separating agent is a novel unit-operation of great promise for application in certain specific systems where relatively small concentrations of salt are capable of effecting, through selective association in the liquid phase, large alterations in the vapor-liquid equilibrium relationship. One advantage of using a dissolved salt rather than a liquid is that an overhead product completely free of separating agent is yielded directly from the rectification column, a consequence of the separating agent's residing in its entirety in the liquid phase. Another lies in substantially lower energy requirements for achievement of the separation. A typical application, based on the system of the previous study ( I ) , has been described by Cook and Furter ( 2 ) .Recent interest in extractive distillation by salt effect has led to an expansion of the ethanol-water-potassium acetate system to a matrix of eight systems involving water, two alcohols, and four acetates. Of the seven additional systems, isobaric vapor-liquid equilibrium data have been reported for only one, the eth...

Isobaric vapor-liquid equilibrium data at atmospheric pressure are reported for 17 systems, each consisting of water, an alcohol (methanol or ethanol), and either a salt or a mixed pair of salts having a common anion, dissolved to saturation in the boiling liquid phase. The matrix of four salts employed consisted of the sodium and potassium bromides and iodides. Solubility data are reported in terms of saturation salt concentration as a function of alcohol-water proportionality in the liquid.Some of these salts and salt mixtures were found copable of eliminating the ethanol-water azeotrope completely. Relative volatility was observed to be enhanced by as much as threefold in certain coses. Orders of effectiveness of both the cations and anions were in agreement with those observed by previous investigators of the effects of electrolytes in mixed solvents.The value of the salt effect parameter was observed to undergo major variation as a function of alcohol-water mixed solvent proportionality in the methanol-water-salt systems, but to be remarkably constant throughout the ethanol-water-salt systems. Synergistic effects of mixed salts on vapor-liquid equilibrium were observed in certain systems despite their apparent lack in the corresponding salt solubility relationships. In systems where synergistic effects did exist they were found to be dependent strongly on liquid composition, largely lacking in waterrich regions, and evident only in midrange and alcohol-rich regions of binary solvent composition. In some of these systems the salt appeared to cause both salting out and salting in of the alcohol in differing composition regions of the same system, the predominating effect depending on the relative proportions of alcohol and water present. This latter effect i s in general contradiction with the accepted theories of salt effect i n vapor-liquid equilibrium.The unit operation of extractive distillation employing dissolved salts, rather than liquid solvents, as separating agents for effecting separations in systems exhibiting either azeotropes or low relative volatility in composition regions critical to the separation is an unusual operation which has been a subject of continuing interest in the literature.Recent industrial interest in achieving extractive distillation by salt effect has led to the present investigation into the efficacies of mixed salts, as compared with single salts, to serve as separating agents for such an operation. For this study, a matrix of systems was chosen, each consisting of water, an alcohol (methanol or ethanol), and either a single salt or a mixture of two salts having a common anion, dissolved to saturation in the boiling liquid phase. The individual salts employed were sodium bromide, potassium bromide, sodium iodide, and potassium iodide. The mixed salt pairs used were the two bromides and the two iodides. All salts were anhydrous. In all, the matrix consisted of 17 separate systems, eight with single salts and nine with mixed salt pairs. Each system was studied with the salt co...

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Isobaric vapor‐liquid equilibrium data at atmospheric pressure are reported for the system ethanol‐water saturated with potassium acetate. Solubility data for potassium acetate in boiling solutions of aqueous ethanol, as a function of ethanol concentration, are also reported. Potassium acetate, a salt highly soluble in aqueous solution, was observed to exert a very large effect on relative volatility.