Ethanol-water composition, solute

Evidence for an Interfacial Tension Mechanism. The mechanism was later tested with longer Pt/Au rods, various diameters and finally solutions of ethanol/water made up in varying ethanol concentrations. Ethanol was chosen because literature values exist for the interfacial tension of various ethanol/water compositions. Figure 3.3 shows the variation of the product of tension and the oxygen flux with particle speed as evidence in support of a interfacial tension mechanism. 

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... 

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... 

In the crystallization of RRR, the initial solution in ethanol is seeded (2%) and aged for 1 hour at 40°C. After aging, the slurry is cooled linearly to 20°C, followed by a linear addition of antisolvent (water) over 5 hours. A final cool-down to O C is performed to minimize the mother liquor loss. The final ethanol/water composition is 55/45. 

B.-B. Li et al. [64] have studied the separation of EtOH-H20 solutions by pervaporation (PV) using chitosan (CS), poly (vinyl alcohol)-poly(acrylonitrile) (PVA-PAN) and chitosan-poly(vinyl alcohol)/poly(acrylonitrile) (CS-PVA/PAN) composite membranes. It was found that the separation factor of the CS-PVA/PAN composite membrane increased with an increase of PVA concentration in the CS-PVA polymer from 0 to 40 wt%. With an increase in the membrane thickness from 12 to 18 pm, the separation factor of the CS-PVA/PAN composite membrane increased and the permeation flux decreased. With an increase of ethanol-water solution temperature, the separation factor of the CS membrane decreased and the permeation flux of the CS membrane increased while the separation factor and the permeation flux of PVA/PAN and CS-PVA/PAN composite membranes increased. 

Most frequently, volume data for solutions are tabulated as density p as a function of composition. The procedure for obtaining y i2 is illustrated by reference to the densities and weight percent concentrations of ethanol-water mixtures (Table 18.1, Columns 1 and 4 at 25°C). 

FIGURE 3.12 Surface composition (A) of pure water, (B) of an ethanol-water solution (shaded = ethanol). 

The LLE for another ternary system, ethyl terf-butyl ether (ETBE) -t ethanol -l- [C4CiIm][TfO], at 298.15 K was studied by Arce et al. [35]. To determine the tie-line compositions, they used the NMR spectroscopy. The values of the solute distribution ratio fi = XEtoH V. EtoH / where II refers to an IL-rich phase) and selectivity (S = /SEtoH// EXBE) were calculated from tie-line data. In general, both the solute distribution ratio and the selectivity decreased as the molar fraction of efhanol in the organic-rich phase increased, the maximal values being ca. 3.5 and ca. 22, respectively. The ETBE + ethanol + IL system was compared to the ETBE + ethanol + water system. 

From experimental data for the ethanol-water system without salt, obtained at 700 and 760 mmHg, it can be seen that within this pressure range the effects of pressure on the equilibrium data are small enough to be within the experimental scatter. In fact, in previous works (8,11,12,13,18,19,23,24,27) there seems to be no clear difference between the equilibrium data at 700 and at 760 mmHg. Errors obtained in the determination of liquid and vapor compositions are approximately 0.05 wt % for the systems without salt. For salt-saturated systems, the same error prevails for the vapor phase, while the error is between 0.1 and 0.2 wt % for liquid phase compositions. The error for the boiling temperature is less than 0.1 °C for the systems without salt, but for saturated solutions the error is much greater from 0.2°C for nonconcentrated solutions to 3°C or more for highly concentrated solutions. 

The salt effects of potassium bromide and a series office symmetrical tetraalkylammonium bromides on vapor-liquid equilibrium at constant pressure in various ethanol-water mixtures were determined. For these systems, the composition of the binary solvent was held constant while the dependence of the equilibrium vapor composition on salt concentration was investigated these studies were done at various fixed compositions of the mixed solvent. Good agreement with the equation of Furter and Johnson was observed for the salts exhibiting either mainly electrostrictive or mainly hydrophobic behavior however, the correlation was unsatisfactory in the case of the one salt (tetraethylammonium bromide) where these two types of solute-solvent interactions were in close competition. The transition from salting out of the ethanol to salting in, observed as the tetraalkylammonium salt series is ascended, was interpreted in terms of the solute-solvent interactions as related to physical properties of the system components, particularly solubilities and surface tensions. 

P12.5 The following data taken from the Handbook of Chemistry and Physics demonstrate how the surface tension at 323.15 K of (methanol + water) and (ethanol + water) solutions changes with composition... 

A composite obtained from aerosil and an ethanol-water (2 1) mixture with a total porosity of 65% was used as the matrix to be impregnated with polystyrene solutions. The impregnation time was 7 and 24 h. 

Although Johnson and Furter (1,2), among others, observed a surprising insensitivity of k to mixed-solvent composition in many alcohol-water-inorganic salt systems, such does not appear to be the case with ammonium bromide-ethanol-water. A linear dependence of k with x was observed and is demonstrated in Figure 4. The slope of this dependence is 2.63 and the intercept with the y-axis occurs at approximately a value of unity. This extrapolated salt effect when x = 0, that is, with water as the single solvent, is consistent with Raoult s Law in that the vapor pressure of the aqueous salt solution depends directly on the salt concentration. However the same behavior has not been observed for the ammonium chloride-ethanol-water system (3) as seen in Table VIII its salt effect parameter shows essentially no dependence on the liquid composition. Therefore the two systems differ in this respect. 

Similarly, Sano et al. [1994] added colloidal silica to a stirred solution of tetrapropylammonium bromide and sodium hydroxide to synthesize a hydrogel on a stainless steel or alumina support with a mean pore diameter of 0.5 to 2 pm. The composite membrane is then dried and heat treated at 500 C for 20 hours to remove the organic amine occluded in the zeolite framework. The silicalite membranes thus obtained are claimed to be free of cracks and pores between grains, thus making the membranes suitable for more demanding applications such as separation of ethanol/water mixtures where the compound molecules are both small. The step of calcination is critical for synthesizing membranes with a high permselectivity. 

Gutbezahl and Grunwald considered liquid-junction potentials between a solution of aqueous potassium chloride and solutions of acids in ethanol-water mixtures both theoretically and experimentally. They concluded that for mixtures containing up to 33% ethanol the liquid-junction potential should be 6 mV or less. For solvents containing higher percentages of alcohol, the liquid-junction potential increases rapidly—25 mV for 50%, 44 mV for 65%, and 75 mV for 80% ethanol. These numerical values should not be interpreted too literally, particularly as the composition approaches 100% ethanol. Calculated liquid-junction potentials contain an indeterminate term that involves all quantities other than those arising from unequal transfer activity coefficients (such as dipole orientation effects). 

Not all liquids form ideal solutions and conform to Raoult s law. Ethanol and water are such liquids. Because of molecular interaction, a mixture of 95.5% (by weight) of ethanol and 4.5% of water boils below (78.15°C) the boiling point of pure ethanol (78.3°C). Thus, no matter how efficient the distilling apparatus, 100% ethanol cannot be obtained by distillation of a mixture of, say, 75% water and 25% ethanol. A mixture of liquids of a certain definite composition that distills at a constant temperature without change in composition is called an azeotrope 95% ethanol is such an azeotrope. The boiling point-composition curve for the ethanol-water mixture is seen in Fig. 4. To prepare 100% ethanol the water can be removed chemically (reaction with calcium oxide) or by removal of the water as an azeotrope (with still another liquid). An azeotropic mixture of 32.4% ethanol and 67.6% benzene (bp 80.1 °C) boils at 68.2°C. A ternary azeotrope (bp 64.9°C) contains 74.1% benzene, 18.5% ethanol, and 7.4% water. Absolute alcohol (100% ethanol) is made by addition of benzene to 95% alcohol and removal of the water in the volatile benzene-water-alcohol azeotrope. 

For the dioxin binder screening, some changes were made as shown in Fig. 8.6. A new pentapeptide library was prepared because a strong affinity is required, to detect dioxins at the ppb level. The design of the screening solution is very important since it determines which peptides can be screened. Also, the composition of the screening solution may restrict the detection conditions of the sensor. For the herbicide binder screening, ethanol was used to dissolve the herbicide in an aqueous buffer. The refractive index of ethanol (1.3623) is not very different from that of water (1.3335) therefore, the ethanol-based buffer solution could be used in the... 

Ethanol, with a boiling point of 78.3°C, has a vapor pressure of 760 mmHg at this temperature and consequently forms a higher mole fraction in the vapor space above a heated ethanol/water mixture than it does in the liquid phase. Condensation of the alcohol-enriched vapor mixture obtained in this way produces a solution of ethanol in water again, but now enriched in the concentration of ethanol. In a laboratory batch distillation the process described above may be carried out very easily, but this only achieves a limited (by the liquid-vapor composition diagram) improvement in concentration of ethanol obtained with each repetition of the distillation (Eig. 16.5a). Also, as the distillation proceeds, the concentration of alcohol in the distilling vessel becomes depleted. Consequently there is also a gradual depletion in the alcohol concentration obtained in the vapor, and the condensate from this. Despite these problems, many small distilleries still use batch distillation to raise the alcohol concentrations to the requirement of their product [44]. 

Figure 8.40 Approximate trajectory taken in ethanol-water-CTAB phase space during the EISA process. Point A corresponds to the initial composition of entrained solution, Point B is near the drying line, and Point C corresponds to the dried product. Reproduced with permission from [180]. Copyright (1999) Wiley-VCH...

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