Volatility enhancement factors

It has been established that the apparent volatilities of transition and rare-earth metal halides are increased by several orders of magnitude through reactions of type (1) and (2) giving rise to vapor complex formation. The enhancement of the vapor densities of transition metal and/or rare-earth metal ions has commonly (see for example Papatheodorou 1982) been reported in the form of the uolatility enhancement factor. That is, when a reaction occurs between a solid rare-earth halide with low vapor pressure Ps (e.g. NdCb) and a more volatile salt (carrier gas) with partial pressure P (e.g. AlCl3,NaCl), and the partial pressure of the vapor complex is Pq, then the volatility enhancement factor is determined at unit pressure of the carrier gas as ... 

By factoring out solute volatility, the enhancement factor allows comparison of solvent and secondary solute effects. Empirically, there is a linear relationship between the log of the enhancement factor and solvent density. For nonpolar and polar solutes in supercritical carbon dioxide, plots of enhancement factor coincide, indicating that differences in solubility are primarily due to vapor-pressure differences. Nonlinear behavior is noted in the case of high solubilities. The enhancement m pure fluids is relatively independent of solute structure but is sensitive to solvent polarity and density. 

A cosolvent used as a miscible additive to CO2 changed the properties of the supercritical gas phase. The addition of a cosolvent resulted in increased viscosity and density of the gas mixture and enhanced extraction of the oil compounds into the C02-rich phase. Gas phase properties were measured in an equilibrium cell with a capillary viscometer and a high-pressure densitometer. Cosolvent miscibility with CO2, brine solubility, cosolvent volatility, and relative quantity of the cosolvent partitioning into the oil phase are factors that must be considered for the successful application of cosolvents. The results indicate that lower-molecular-weight additives, such as propane, are the most effective cosolvents to increase oil recovery [1472]. 

The pressure generated in a reaction vessel, and hence the rate enhancement, depends on a number of factors including the MW power level, the volatility of the solvent, the dielectric loss of the reaction mixture, the size of the vessel and the volume of the reaction mixture [7, 20]. Gedye et al. [20] found that, in the esterification of benzoic acid with a series of aliphatic alcohols (Scheme 4.1) in closed Teflon vessels, the most dramatic rate enhancements were observed with methanol (the most volatile solvent). 

Confinement—Deflagration rates of substances such as azo compounds, peroxides, and certain lead oxides may accelerate by pressure increase, especially when the governing decomposition reaction is gas-phase controlled [28]. Initiation of a deflagration at the bottom or at the center of a closed or partially closed vessel may lead to an increase of eh deflagration rate by a factor of more than 100 in comparison with top initiation. Autocatalytic decomposition by a volatile catalyst is enhanced by confinement. 

The volatility of ammonia can be significantely affected by high concentrations of dissolved ions in the liquid phase. In sodium acetate the volatility increases by a factor of 1.9 at 25 wt % of salt. In sodium hydroxide the volatility is enhanced to a lesser degree with an increase of 1.25 at 22.5 wt % NaOH. Both electrolytes produce ions with only one electronic charge, but their effects on the volatility of ammonia are significantly different. Thus the effects of various ionic components must be studied individually in order to determine their effect on the volatility of NH3. 

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