Solvent equilibrium relation

With a reactive solvent, the mass-transfer coefficient may be enhanced by a factor E so that, for instance. Kg is replaced by EKg. Like specific rates of ordinary chemical reactions, such enhancements must be found experimentally. There are no generalized correlations. Some calculations have been made for idealized situations, such as complete reaction in the liquid film. Tables 23-6 and 23-7 show a few spot data. On that basis, a tower for absorption of SO9 with NaOH is smaller than that with pure water by a factor of roughly 0.317/7.0 = 0.045. Table 23-8 lists the main factors that are needed for mathematical representation of KgO in a typical case of the absorption of CO9 by aqueous mouethauolamiue. Figure 23-27 shows some of the complex behaviors of equilibria and mass-transfer coefficients for the absorption of CO9 in solutions of potassium carbonate. Other than Henry s law, p = HC, which holds for some fairly dilute solutions, there is no general form of equilibrium relation. A typically complex equation is that for CO9 in contact with sodium carbonate solutions (Harte, Baker, and Purcell, Ind. Eng. Chem., 25, 528 [1933]), which is... 

H2S is soluble in such a solution and the equilibrium relation may be taken as 7 = 2X, where 7 is kmol of H2S kmol inert gas and X is kmol of H2S/kmol of solvent. 

Mixture property Define the model to be used for liquid activity coefficient calculation, specify the binary mixture (composition, temperature, pressure), select the solute to be extracted, the type of phase equilibrium calculation (VLE or LLE) and finally, specify desired solvent performance related properties (solvent power, selectivity, etc.)... 

Gas, from a petroleum distillation column, has a concentration of H2S reduced from 0.03 (kmol H2S/kmol of inert hydrocarbon gas) to 1 per cent of this value by scrubbing with a triethanolamine-water solvent in a countercurrent tower, operating at 300 K and atmospheric pressure. The equilibrium relation for the solution may be taken as Ye = 2X. 

Because of the highly nonideal behavior of polymer-solvent solutions, polymer-vapor equilibrium relations account for the third major difference found in stripping operations with polymeric solutions. The appro-... 

Solvent extraction rarely involves gases, so that other cases should now be considered. Most liquid organic solutes are completely miscible with, or at least highly soluble in, most organic solvents. The case of a liquid solute that forms a solute-rich liquid phase that contains an appreciable concentration of the solvent is related to the mutual solubility of two solvents, and has been discussed in section 2.2. This leaves solid solutes that are in equilibrium with their saturated solution. It is expedient to discuss organic, nonelectrolytic solutes separately from salts or other ionic solutes. 

A method of prediction of the salt effect of vapor-liquid equilibrium relationships in the methanol-ethyl acetate-calcium chloride system at atmospheric pressure is described. From the determined solubilities it is assumed that methanol forms a preferential solvate of CaCl296CH OH. The preferential solvation number was calculated from the observed values of the salt effect in 14 systems, as a result of which the solvation number showed a linear relationship with respect to the concentration of solvent. With the use of the linear relation the salt effect can be determined from the solvation number of pure solvent and the vapor-liquid equilibrium relations obtained without adding a salt. 

The slope of line p (called the reaction constant) is a measurement of the sensitivity of such a reaction to the electronic effect of the substituents nevertheless, it can be explained as a proportionality constant pertaining to a given equilibrium (i.e., it depends on the reaction and the solvent), ft relates the effect of substituents on that equilibrium to the effect of those substituents on the benzoic acid equilibrium. That is, if the effect of substituents is proportionally greater than that on the benzoic acid equilibrium, then p > 1 if the effect is less than that on the benzoic acid equilibrium, then p < 1. By definition, for benzoic acid the parameter p is equal to 1 in water at 25°C. Many organic reactions proceed via a series of steps, each of which might have a different reaction constant p hence, to achieve a successful correlation, p must be at least roughly additive. 

TT Then salt is added to a volatile solvent mixture, there is a salt effect—a change in the vapor-liquid equilibrium relation. This salt effect occurs because salt forms a preferential solvate with a particular component of the solvent mixture, causing a drop in partial pressure of the particular component which forms the preferential solvate. Results of the studies conducted based on this idea are reported by the author in References 1 and 2. In the past studies, the vapor-liquid equilbrium relation of the system for which formation of preferential solvate had been expected was observed, preferential solvation number was calculated based on the actually observed values, and further, salt effect was predicted based on the preferential solvate number. The author has... 

When a preferential solvate is formed across salt and a particular component in a solvent mixture, the preferentially solvated component is assumed to be nonvolatile. Hence, the essential concentration of the preferentially solvated component in the solvent mixture is reduced as much as the solvated component. The vapor-liquid equilibrium relation obtained under the addition of a salt may well be considered to be the same as the vapor-liquid equilibrium without the salt for liquid-phase composition from which the solvents forming solvates are excluded. Based on this idea, the essential concentration at the time when salt forms a preferential solvate with the primary component is given by Equation 1. Then we can obtain the preferential solvation number from the observed values of the salt effect. As the concentration of solvent is decreased by the number of solvated molecules, the actual solvent composition participating in the vapor-liquid equilibrium is changed. Assuming that a salt forms the solvate with the first component, the actual composition Xia is given by... 

If there is no doubt that many Friedel-Crafts halides can undergo selfdissociation in certain solvents (particularly halogenated hydrocarbons), and that this ionc enic reaction is not due to basic impurities in the system, the attainment of the equilibrium relating ions to undissociated molecules often requires a long time This... 

Sorption of VOCs involves the processes of adsorption and partitioning. Partitioning is the incorporation of the VOC into the natural organic matter associated with the solid and is analogous to the dissolution of an organic compound into an organic solvent. Adsorption is the formation of a chemical or physical bond between the VOC and the mineral surface of a solid particle (Rathbun, 1998). The equilibrium relation between aqueous and solid phase concentrations then is expressed as... 

The thermodynamic modeling and calculation procedures for S-L-V equilibrium in binary systems for RESS/PGSS involve simultaneous solution of the phase equilibrium relations for the two components, namely, the SCF solvent, 1, and the solid solute, 3, for all three phases, S, L, and V, as given by the following equations ... 

In a chemical processing plant, the acetone concentration in a water-acetone solution stream must be lowered. Acetone extraction using vinyl trichloride (VTC) as the solvent is considered, and the required number of equilibrium stages in a countercurrent liquid-liquid extraction system must be determined. Equilibrium relations were developed based on available data at the expected operating conditions. The extract and raffinate phase and tie-line equations are expressed in terms of the extract component (acetone) and raffinate component (water) weight fractions in each phase. 

This equation is solved together with the equilibrium relations for the solvent species,... 

The simplest type of solute distribution problem occurs when A i moles of a solute are completely dissolved and distributed between two immiscible solvents. The. equilibrium di.sEribution of the solute is determined from the single equilibrium relation... 

The equilibrium saturated solvent concentration is related to the concentration of solvent at the coating surface by thermodynamic equilibrium relations, such as Henry s law, Raoult s... 

The condition needed for an osmotic membrane equilibrium related to the solvent can be written... 

Solvent or liquid extraction is another widely used industrial separation technique that lends itself to the staged operation approach. In these systems the solution to be separated is contacted with a solvent in a stage. The products of this operation are a solvent-rich phase (the extract) and a solvent-lean phase (the raffinate). Because thermal effects are not usually large, only the material or mass balance and the equilibrium relation are used to determine ideal stages. 

To develop an estimate of the solute mole fraction xu in the SCF solvent in equilibrium with a solid mixture, the equilibrium relation is... 

The simplest explanation for why the vapor pressure of a solution is lower than that of the pure solvent is related to the concept of dynamic equihbrium itself. Consider the following representation of a liquid in dynamic equilibrium with its vapor. Here the rate of vaporization is equal to the rate of condensation. 

In each of these steps the product is moved from the phase in which penicillin is present in low concentration to one in which its concentration is much higher, mostly by adjusting pH, sometimes by changing the solvent. For more complex separations various kinds of chromatography are used. All of these steps obey the thermodynamic equilibrium relations shown in the previous chapters. 

---