Vapor Pressure Boiling Point Method

Rordorf, B.F. Prediction of vapor pressures, boiling points and enthalpies of fusion for twenty-nine halogenated dibenzo-p-dioxins and fifty-five dibenzofurans by a vapor pressure correlation method. Chemosphere, 18(l-6) 783-788,1989. Rosen, J.D. and Carey, W.F. Preparation of the photoisomers of aldrin and dieldrin. 7 Agric. Food Chem., 16(3) 536-537,1968. Rosen, J.D. and Strusz, R.F. Photolysis of 3-(p-bromophenyl)-l-methoxy-l-methylurea, 7 Agric. Food Chem., 16(4) 568-573, 1968. 

Rordorf, B.F. 1989. Prediction of vapor pressures, boiling points and enthalpies of fusion for twenty-nine halogenated dibenzo-p-dioxins and fifty-five dibenzofurans by a vapor pressure correlation method. Chemosphere 18 783-88. 

An alternative approach is based on the theoretical foundation described earlier for the colligative properties. If the solution is isotonic with blood, its osmotic pressure, vapor pressure, boiling-point elevation, and freezing-point depression should also be identical to those of blood. Thus, to measure isotonicity, one has to measure the osmotic pressure of the solution and compare it with the known value for blood. However, the accurate measurement of osmotic pressure is difficult and cumbersome. If a solution is separated from blood by a true semipermeable membrane, the resulting pressure due to solvent flow (the head) is accurately measurable, but the solvent flow dilutes the solution, thus not allowing one to know the concentration of the dissolved solute. An alternative is to apply pressure to the solution side of the membrane to prevent osmotic solvent flow. In 1877, Pfeffer used this method to measure osmotic pressure of sugar solutions. With the advances in the technology, sensitive pressure transducers, and synthetic polymer membranes, this method can be improved. However, results of the search for a true semipermeable membrane are still... 

Activity data for electrolytes usually are obtained by one or more of three independent experimental methods measurement of the potentials of electrochemical cells, measurement of the solubility, and measurement of the properties of the solvent, such as vapor pressure, freezing point depression, boiling point elevation, and osmotic pressure. All these solvent properties may be subsumed under the rubric colligative properties. 

In spite of the wealth of information available on the preparative and structural aspects of the lanthanide chlorides (1-3), experimental thermodynamic, and, in particular, high-temperature vaporization data are singularly lacking. The comprehensive estimates of the enthalpies of fusion, vaporization, heat capacities and other thermal functions for the lanthanide chlorides by Brewer et ah (4, 5) appear internally consistent, but the relatively few experimental measurements (6-/2) do not permit confirmation of the estimates due to the narrow temperature ranges of study. Additionally, the absence of accurate molecular data for the gaseous species has hampered third-law treatment of the limited experimental vapor pressure data available. The one reported study (12) of the vaporization of EuC12 effected by a boiling-point method lacks accuracy for these reasons. 

The heat of vaporization may be obtained accurately by direct calorimetric measurements or from the dependence of vapour pressure on temperature, and roughly by empirical methods using rates of vaporization, or by using empirical relationships between heat of vaporization and boiling point. 

Due to lack of data on vapor compositions over PbF2 at various temperatures, the total pressure measurements reported by Wartenberg and Bosse (2.), using boiling point method, and those of Nesmeyanov and lofa (2) are not used for evaluation. 

Boiling usually implies vapor bubble formation in a liquid. Since the method is also applicable to solid samples, it may seem inappropriate to call it the boiling point method. However, in this context, the term boiling may be taken to mean the evolution of vapor from a condensed sample when its saturated vapor pressure is equal to the external pressure. The term boiling point then refers to the temperature at which the vapor pressure equals an arbitrarily chosen external pressure, and not only 101.325 kPa. 

The boiling point method connected with the evaluation of experimental results according to the method of Motzfeldt et al. (1977) was applied to the determination of vapor pressure of various molten salt systems at a temperature range of 600-1200°C. The most accurate results were, however, obtained by computer fitting of the complete Eq. (7.19) using a sophisticated computer program developed by Hertzberg (1983). 

The transpiration method is a simple and versatile method for vapor pressure measurement at high temperatures. An inert carrier gas is passed over the condensed substance in a constant temperature furnace zone. The flow rate of the carrier gas is constant and sufficiently small so that the carrier gas is saturated with vapor, which condenses at some point downstream. The mass of vapor transported by a known volume of carrier gas is determined. If the total vapor pressure is known, from the boiling point method, the results from the transpiration method may be used to calculate the average molar mass of the vapor. 

Saturated vapor pressures of [BMIm]BF4 + 2,2,2-trifluoroethanol (TFE) and [BMImJBr + TFE mixtures were measured by KS. Kim et al. [4] using the boiling point method in the concentration range of 40.0 90.0 mass% of ionic liquids and in the temperature range of 298.2 K 323.2 K. The data were correlated with an Antoine-type equation. The average absolute deviations between experimental and calculated values were 0.6% and 0.4% for the [BMIm]BF4 + TFE and the [BMImJBr + TFE system, respectively. As shown in Figure 3, the [BMIm]Br + TFE system was found to be more favorable as working pairs in absorption heat pumps or chillers than the [BMIm]BF4 + TFE from the results of VLE. 

At low temperatures, using the original function/(T ) could lead to greater error. In Tables 4.11 and 4.12, the results obtained by the Soave method are compared with fitted curves published by the DIPPR for hexane and hexadecane. Note that the differences are less than 5% between the normal boiling point and the critical point but that they are greater at low temperature. The original form of the Soave equation should be used with caution when the vapor pressure of the components is less than 0.1 bar. In these conditions, it leads to underestimating the values for equilibrium coefficients for these components. 

Maxwell and Bonnel (1955) proposed a method to calculate the vapor pressure of pure hydrocarbons or petroleum fractions whose normal boiling point and specific gravity are known. It is iterative if the boiling point is greater than 366.5 K ... 

The only method utilized commercially is vapor-phase nitration of propane, although methane (70), ethane, and butane also can be nitrated quite readily. The data in Table 5 show the typical distribution of nitroparaffins obtained from the nitration of propane with nitric acid at different temperatures (71). Nitrogen dioxide can be used for nitration, but its low boiling point (21°C) limits its effectiveness, except at increased pressure. Nitrogen pentoxide is a powerful nitrating agent for alkanes however, it is expensive and often gives polynitrated products. 

An overview of some basic mathematical techniques for data correlation is to be found herein together with background on several types of physical property correlating techniques and a road map for the use of selected methods. Methods are presented for the correlation of observed experimental data to physical properties such as critical properties, normal boiling point, molar volume, vapor pressure, heats of vaporization and fusion, heat capacity, surface tension, viscosity, thermal conductivity, acentric factor, flammability limits, enthalpy of formation, Gibbs energy, entropy, activity coefficients, Henry s constant, octanol—water partition coefficients, diffusion coefficients, virial coefficients, chemical reactivity, and toxicological parameters. 

Various methods are available for estimation of the normal boiling point of organic compounds. Lyman et al. review and give calcula-tional procedures for the methods of Meissner, Miller, and Lydersen/ Forman-Thodos. A more recent method that has been determined to be more accurate is the method of Pailhes, which reqmres one experimental vapor pressure point and Lydersen group contributions for critical temperature and critical pressure (Table 2-385). 

When criticals cannot he estimated with reasonable accuracy, the method of Maxwell and BonnelP is recommended. The normal boiling point and the specific gravity at 60 F (15.5 C) are required inputs. According to what vapor pressure range is expected, the vapor pressure is calculated from Eqs. (2-34), (2-35), or (2-36). If the wrong range is selected, the procedure will need to be repeated. 

For nonKydi ocai bon organics for which normal boiling points are unknown or expected vapor pressures are below 15 kPa, the reference substance method of Othmer and YiF as given by Eq. (2-44) is recommended. 

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