Solvents binary adsorption

FIGURE 9.11 Classification of excess adsorption isotherms for binary solutions with o° solubility. After Kipling [39]. Reproduced by permission from Quantitative Review by Ripling Royal Society of Chemistry, Cambridge, UK, 1951. 

FIGURE 9.12 Excess adsorption isotherms for ideal bindary solution with infinite solubility for different values of K the adsorption distribution constant given by equation 9.44. 

FIGURE 9.13 Adsorption isotherms for a solute with a finite solubility and a Lanqmuir adsorption isotherm, equation 9.40, withX = C2/C, where Cx is the maximum concentration (i.e., solubility or critical micelle concentration) of the solute and b is K/oi (where K is the distribution constant and Oj is the activity of the solvent). This figure assumes that the solution is dilute where the activity 02 is equal to the concentration Cj. 

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Figure 5. TLC retention factor Rp for poly(methyl methacrylate) on silicagel, as a function of the elution strength of binary solvent (carbontetrachloride, CCl )/ displacer (1,4-dioxane) mixtures. Note the steep increase in Rj, at Efj w 0.38, indicating a sharp adsorption/ desorption transition.

Summary The classical treatment of the physicochemical behavior of polymers is presented in such a way that the chapter will meet the requirements of a beginner in the study of polymeric systems in solution. This chapter is an introduction to the classical conformational and thermodynamic analysis of polymeric solutions where the different theories that describe these behaviors of polymers are analyzed. Owing to the importance of the basic knowledge of the solution properties of polymers, the description of the conformational and thermodynamic behavior of polymers is presented in a classical way. The basic concepts like theta condition, excluded volume, good and poor solvents, critical phenomena, concentration regime, cosolvent effect of polymers in binary solvents, preferential adsorption are analyzed in an intelligible way. The thermodynamic theory of association equilibria which is capable to describe quantitatively the preferential adsorption of polymers by polar binary solvents is also analyzed. 

Polymers in Binary Solvents. Cosolvency Effect Preferential Adsorption Phenomena... 

In general, to explain the observed cosolvent effects, the preferential adsorption phenomena have been invoked. Flowever few topics in the physical chemistry of polymers have evoked so many theories but so little consensus as preferential adsorption. When a polymer is dissolved in a binary solvent mixture, usually one of the solvents preferentially solvates the polymer. This solvent will then be found in a greater proportion in the proximities of the macromolecule with respect to the bulk solution composition. This variation of the solvent composition can cause interesting phenomena such as cosolvency as was discussed before, [11, 91, 92] non - cosolvency [93, 94], and some times variation of the unperturbed polymer dimensions [95,96]... 

The preferential adsorption behavior of poly(vinylpyrrolidone) (PVP) in binary solvent containing aromatic components has been also studied [110]. In this case, it was concerned with the influence of the chemical structure of different binary solvents in the preferential adsorption of this polymer. 2 - propanol - cumene, 2 -propanol - mesitylene, 2 - propanol - p-xylene, 2 - propanol - ethylbenzene and 2 - propanol - toluene. Figure 1.15 shows the variation of X with the solvent composition. In both cases aromatic components are adsorbed in the range 0 to 40%, but the amount of adsorbed molecules is rather different for the two isomers. This result could be explained in terms of steric hindrance due to the isopropyl groups of cumene, which would be reflected in the lower X value. 

As it was noted before, Preferential or Selective Adsorption is a very common phenomenon in ternary systems composed of a polymer and a binary solvent mixture. There is a great variety of ternary systems that have been studied, mainly those containing at least one polar component [97], In many cases, specific interactions between polar groups are important, and the formation of hydrogen bonds have to be taken into account. This is the case, especially, when alcohols are components of the systems. 

The model has been further tested in terms of the behavior of solvent molecules isotherms for binary-solvent mixtures A/B adsorption energies (ch values) of the polar solvent B in such mixtures as a function of surface coverage 6b, etc. Again, good agreement of experimental data with calculated values is observed. An important requirement of the model and related experimental correlations is that the solvent molecule must be treated (thermodynamically) in the same manner as solute molecules. Thus, if. solute adsorption energies are measured for a molecule X, the behavior of X as a component (solvent) of the mobile phase should then be predictable. 

Those binary solvent systems causing the amylose component to precipitate as an adsorption complex with one of the constituents of the solvent system have, obviously, to be excluded here. 

Fig. 8-7. Binary solvent e" values versus solvent composition for adsorption on 3.8-3.9% HjO AI2O3. O, Pentane (/()-CCIi (B) (4) , pentane (/t)-n-propyi chloride (B) (/2) V, pentane (/tj-CH.CI, (B) (4,30) , pentane (/l)-acetone (B) (I2) , pentane (/t)-pyridine (B) (12) solid line, values calculated from Eq. (8-10).

The experimental e values of binary solvents in thin-layer systems often appear low because of solvent demixing. Preferential adsorption of B by the adsorbent depletes the advancing solvent front of B, leaving a solvent which is weaker than the original mixture. The seriousness of this effect can be estimated from the likelihood of extensive solvent demixing (see below). 

Binary Solvent Eluotropic Series for Adsorption on Water-Deactivated Alumina (a = 0.6) Calculated Values from Eq. (8-10)... 

Values of (the solvent strength parameter) for pure solvents on alumina can be obtained from Table 8-1. Similar values for adsorption on silica or other adsorbents are given in Tables 8-2 and 8-3, or can be estimated from e values for alumina through Eqs. (8-6a)-(8-6c). Values of e for a few binary solvents are listed in Appendix III. Other values can be calculated through Eq. (8-10) ... 

The dependence of e values (adsorption on polar adsorbents) on the molecular structure of the solvent is discussed in Section 8-4. The relationship between the e value of a binary or ternary solvent mixture and the e values of its constituent solvents is dealt with in Section 8-2A. A large number of binary solvent e values are tabulated in Appendix III. 

Binary Solvent Eluotropic Series for Adsorption on Water-Deactivated... 

P-15 - Simulation for removal of binary solvent vapor by adsorption onto high silica zeolite... 

Adsorption of some organic solvent vapours onto HSZ were studied. Binary adsorption equilibriums except azeotropic mixture-HSZ systems could be correlated by Markham-Benton equation for the whole concentration range, and the break times could be estimated well by using the Extended-MTZ-Method. For azeotropic mixture-HSZ systems, the equilibriums and the break times could be correlated and estimated only for a part of the all concentration range. Then, two azeotropic points appeared in the adsorption equilibriums for IPA-TCE -Y-type system. For this binary systems adsorption equilibrium data could be expressed by proposed equation, similar to liquid-vapour azeotropic equilibrium equation. Breakthrough curve could be simulated using the Stop Go method in the whole range for azeotropic mixture systems as well as for zeotropic systems. 

Adsorption chromatography is one of the more popular modern high-performance liquid chromatography (HPLC) techniques today. However, open-column chromatography and TLC are still widely used. - The adsorbents (stationary phases) used are silica, alumina, and carbon. Although some bonded phases have been considered to come under adsorption chromatography, these bonded phases will not be discussed. By far, silica and alumina are more widely used than carbon. The mobile phases employed are less polar than the stationary phases, and they usually consist of a signal or binary solvent system. However, ternary and quaternary solvent combinations have been used. 

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