Fixed-liquid compositions

A review is presented of techniques for the correlation and prediction of vapor-liquid equilibrium data in systems consisting of two volatile components and a salt dissolved in the liquid phase, and for the testing of such data for thermodynamic consistency. The complex interactions comprising salt effect in systems which in effect consist of a concentrated electrolyte in a mixed solvent composed of two liquid components, one or both of which may be polar, are discussed. The difficulties inherent in their characterization and quantitative treatment are described. Attempts to correlate, predict, and test data for thermodynamic consistency in such systems are reviewed under the following headings correlation at fixed liquid composition, extension to entire liquid composition range, prediction from pure-component properties, use of correlations based on the Gibbs-Duhem equation, and the recent special binary approach. 

The effect of a given salt on vapor composition in a given system is, of course, a function of the relative proportions of the two volatile components in the liquid as well as of salt concentration, and an equation for correlation of salt effect at other than fixed liquid composition should contain liquid composition as a factor. Hashitani and Hirata (18) reported some success with a purely empirical equation which related the improvement factor of Equation 1 both to salt concentration and to liquid composition. Guyer, Guyer, and Johnsen (19) proposed an empirical relationship between vapor composition change and the concentration... 

The data in Tables I-XVI (see Appendix for all tables) show the isobaric vapor-liquid equilibrium results at the boiling point for potassium, ammonium, tetramethylammonium, tetraethylammonium, tetra-n-propylammonium, and tetra-n-butylammonium bromides in various ethanol-water mixtures at fixed liquid composition ratios. The temperature, t, is the boiling temperature for all solutions in these tables. In all cases, the ethanol-water composition was held constant between 0.20 and 0.35 mole fraction ethanol since it is in this range that the most dramatic salt effects on vapor-liquid equilibrium in this particular system should be observed. That is, previous data (12-15,38) have demonstrated that a maximum displacement of the vapor-liquid equilibrium curve by salts frequently occurs in this region. In the results presented here, it should be noted that Equation 1 has been modified to... 

Salt Effect in Vapor-Liquid Equilibrium at Fixed Liquid Composition... 

The purpose of the present investigation was to extend the study of Equation 1 at fixed-liquid composition to salts in which the anion, rather than the cation, is organic. For this purpose, the sodium and potassium acetates were chosen, both having very high solubilities in ethanol-water... 

Isobaric vapor-liquid equilibrium data at atmospheric pressure are reported for the four systems of the present investigation in Tables I-VI. Salt concentrations are reported as mole fraction salt in the solution, while mixed-solvent compositions are given on a salt-free basis. A single fixed-liquid composition was used for potassium iodide and sodium acetate potassium acetate used three—all chosen from the region of ethanol-water composition where relative volatility is highest. In the... 

The k standard deviation data and R.A.A.D. values listed in Table VIII for the data of the present investigation and certain data from previous studies (3,4) demonstrate clearly that Equation 1 can satisfactorily correlate the salt effects of the inorganic salts tested at fixed-liquid composition in ethanol-water, at all salt concentrations up to saturation. The R.A.A.D. yields a critical evaluation of the applicability... 

A binary liquid solution, having mole fraction x of component 1, is in equilibrium with a vapor that has mole fraction v of that component. Show that for this mixture the.effect of a change in temperature on the equilibrium pressure at fixed liquid composition is approximately... 

For mixtures containing more than two species, an additional degree of freedom is available for each additional component. Thus, for a four-component system, the equihbrium vapor and liquid compositions are only fixed if the pressure, temperature, and mole fractious of two components are set. Representation of multicomponent vapor-hquid equihbrium data in tabular or graphical form of the type shown earlier for biuaiy systems is either difficult or impossible. Instead, such data, as well as biuaiy-system data, are commonly represented in terms of ivapor-liquid equilibrium ratios), which are defined by... 

Two phases are present in the region between the two curves the compositions of the two phases in equilibrium with each other are given by the intersection of a horizontal tie-line with the vapor and liquid curves. Lines cb and fd in Figure 8.13 are two examples. One degree of freedom is present in this region. Thus, specifying the pressure fixes the compositions of the phases in equilibrium conversely, specifying the composition of one of the phases in equilibrium sets the pressure and the composition of the other phase.w... 

Below the equilibrium lines, but above the eutectic temperature, a liquid and solid are in equilibrium. Under line ac, solid benzene, and liquid Li, whose composition is given by line ac, are present. Under line be, the phases present are solid 1,4-dimethylbenzene and liquid Li, whose composition is given by line be. Below point c, solid benzene and solid 1,4-dimethylbenzene are present. In the two phase regions, one degree of freedom is present. Thus, specifying T fixes the composition of the liquid, or specifying X2 fixes the temperature.cc Finally, at point c (the eutectic) three phases (solid benzene, solid 1,4-dimethylbenzene, and liquid with x2 = vi.e) are present. This is an invariant point, since no degrees of freedom are present. 

So far, two examples of natural abundance 13C imaging have been reported. The first was an extension of the work of Yuen et al.31 which had provided a clear demonstration of the heterogeneity in conversion within a fixed bed. As mentioned previously, this early study had only been successful because the reaction mixture was associated with a relatively simple H NMR spectrum the spectrum gave only 4 spectral peaks with the chemical shift of one being a direct measure of the interparticle liquid composition and hence extent of conversion. Akpa et al.29 extended that work by using 13C spatially-resolved spectroscopy to follow a reaction in which... 

The temperature of distillation is fixed by safety considerations at 410 K and, from a knowledge of the vapour pressures of the three components, the pressure in the still is found to be about 6 kN/m2. The composition of the vapour in the still is found from the relation yso = ce0xS0/T,axs. The liquid composition on the first plate is then found from equation (i) and for ortho ... 

Typically, adsorption isotherms are generated using a batch experiment at a fixed temperature and a fixed feed composition. These experiments include exposing a known amount of adsorbent to a known concentration of adsorbate at a constant temperature. Once equilibrium is established, the net adsorbate concentration in the liquid is measured. This process is repeated at multiple adsorbate concentrations and temperatures. A plot of adsorbate loading (g adsorbate/g adsorbent) versus adsorbate concentration reveals the adsorption isotherm with the shape of the isotherm determining the suitability of a particular adsorbent for a particular system [20]. 

For any fixed gas composition, the dewpoint la a function of both the pressure and temperature of the gas. The question of what gas dewpoint limitation is necessary to prevent condensation of liquids in the gas pipeline Introduces a somewhat complex problem of vapor-liquid phase equilibrium under high pressure pipeline conditions, and the interrelated problem of the flowing pressure-teoperature profile for the gas in a pipeline. Gas of different compositions will behave somewhat differently, but we can... 

An offline measurement apparatus is usually not directly mounted on the reactor, but is fed with samples withdrawn from it manually or automatically. This is the typical case of chromatography, a widely used measurement device for gas and liquid composition. Both gas and liquid chromatographies are based on the separation of the sample by means of selective adsorption on a solid substrate posed in a fixed bed column, and on the detection of the change of a suitable property of the (gas or liquid) carrier, usually thermal conductivity. 

In a natural gasoline fractionation system there are usually six chemical species present in appreciable quantities methane, ethane, propane, isobutane, n-butane, and n-pentane. A mixture of these species is placed in a closed vessel from which all air has been removed. If the temperature and pressure are fixed so that both liquid and vapor phases exist at equilibrium, how many additional phase-rule variables must be chosen to fix the compositions of both phases ... 

For mixtures containing more than two species, an additional degree of freedom is available for each additional conmonent. Thus, for a four-component system, the equilibrium vapor and liquid compositions are fixed only if the pressure, temperature, and mole fractions of two com-... 

For a fixed reflux ratio for a column, the operating line remains a line in higher-dimension composition space, as it too is a line passing through the sequence of liquid compositions appearing on the trays as we move up or down a column. 

The system is constrained to obey the Gibbs Phase Rule. In the most common application, with methane (or a fixed gas composition) and water, the two components will form the three phases of hydrates, vapor, and liquid with one degree of fi eedom. Fixing the temperature (or the pressure) determines the pressure (or the temperature) at the three-phase condition. 

With a constant but low exhaust gas stream and a fixed catalyst composition and concentration, the kinetics of the reaction being discussed are strongly dependent on the oxygen mass transfer rate. In this case, the rate of oxidation is faster than the transport rate of oxygen into the reaction phase. Thus the oxygen concentration in the liquid phase is near zero, the concentration of oxygen in the exhaust gas is less than 0.1 %. As a result, side reactions may occur colored products are often obtained. 

I have fixed the composition of the liquid obtained as above described, and proved it to be a compound of one atom of zinc and and one atom of methyl, by the following experiments —... 

For a BUBL P calculation, the temperature and the liquid composition are known, and this fixes the location of the PV isotherm for the composition of the liquid phase (solid line). The problem then is to locate a second (dashed) line for a vapor composition such that the line contains a dew point D on its vapor segment that lies at the pressure of the bubble point B on the liquid segment of the solid line. This pressure is the phase equilibrium pressure, and the composition for the dashed line is that of the equilibrium vapor. This equilibrium condition is shown by Fig. 4-9. 

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