Volatilization from pure phase liquids

The concentration of the chemical at the base of the stagnant air layer, just above the surface of the NAPL, is determined from the vapor pressure of the chemical as 

The rate of volatilization from a NAPL surface is then given by the following expression, as compared with Eq. [2-32]  

The quantity Da/8a is the same as previously discussed, and can be estimated from empirical equations. This velocity is larger for chemicals having larger diffusion coefficients in air, and is smaller for larger slicks or pools, because vapor advected over a downwind point has the effect of de- 

A layer of NAPL floating on water can also lose mass by dissolution into the water body. If the NAPL is denser than water (in which case it is abbreviated DNAPL, for dense NAPL), it will sink through the water body to the bottom sediments. Most halogenated solvents are denser than water (see Table 1-3) and therefore have greatly diminished volatilization rates from water bodies relative to loss rates for floating NAPLs. 

Benzene is spilled onto a lake from an overturned tanker truck. Given a 3 m/sec wind speed at a 10-m height, what will be the flux density from the slick  

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Modeling Volatilization from Pure Phase Liquids... 

A review is presented of techniques for the correlation and prediction of vapor-liquid equilibrium data in systems consisting of two volatile components and a salt dissolved in the liquid phase, and for the testing of such data for thermodynamic consistency. The complex interactions comprising salt effect in systems which in effect consist of a concentrated electrolyte in a mixed solvent composed of two liquid components, one or both of which may be polar, are discussed. The difficulties inherent in their characterization and quantitative treatment are described. Attempts to correlate, predict, and test data for thermodynamic consistency in such systems are reviewed under the following headings correlation at fixed liquid composition, extension to entire liquid composition range, prediction from pure-component properties, use of correlations based on the Gibbs-Duhem equation, and the recent special binary approach. 

Jaques and Furter (37,38,39,40) devised a technique for treating systems consisting of two volatile components and a salt as special binaries rather than as ternary systems. In this pseudo binary technique the presence of the salt is recognized in adjustments made to the pure-component vapor pressures from which the liquid-phase activity coefficients of the two volatile components are calculated, rather than by inclusion of the salt presence in liquid composition data. In other words, alteration is made in the standard states on which the activity coefficients are based. In the special binary approach as applied to salt-saturated systems, for instance, each of the two components of the binary is considered to be one of the volatile components individually saturated with the... 

The vapor pressure, Pvp, of a liquid or solid is the pressure of the compound s vapor (gas) in equilibrium with the pure, condensed liquid or solid phase of the compound at a given temperature [5-9]. Vapor pressure, which is temperature dependent, increases with temperature. The vapor pressure of chemicals varies widely according to the degree of intermolecular attractions between like molecules The stronger the intermolecular attraction, the lower the magnitude of the vapor pressure. Vapor pressure and the Henry s law constant should not be confused. Vapor pressure refers to the volatility from the pure substance into the atmosphere the Henry s law constant refers to the volatility of the compound from liquid solution into the air. Vapor pressure is used to estimate the Henry s law constant [equation (2.4)]. 

The stationary phase consists of a thin layer (ca. 0.2 pm) of a non-volatile liquid, such as methylsilicone or methylphenylsilicone, tightly adsorbed to the inert surfaces of the column. The liquid stationary phases are classified according to their polarity, non-polar phases are used most often because they are easier to handle and are stable over a wide temperature range. The mobile phase is an inert carrier gas such as nitrogen, helium or hydrogen which flows at a constant, but adjustable rate through the column. Current capillary columns, with internal diameters between 0.1-0.6 mm, are constructed of fused silica, specially prepared from pure silicon tetrachloride, and formed into spirals up to 100 m long. Injectors, columns and detectors are located in separately thermostatable compartments. 

In geologic conditions nonpolar, hydrophobic substances under consideration, depending on pressure and temperature are capable of changing their phase state and can be gaseous, liquid or even solid. In gas state they form underground gas whose composition is dominated by such components as CH, more rarely and very rarely CO. Liquid nonpolar substances are mobile solutions (crude oil, oil products, residual oil, etc.,) whose composition is dominated by complex non-volatile organic compounds, namely, liquid alkanes (from pentane to heptadecane), almost all naphthenes, numerous aromatic hydrocarbons (benzene, toluene, isopropyl benzene, etc.), which in pure form may have melting temperature below 0 °C. 

Apart from pure analytical apphcations, HSGC has found wide usage among thermodynamicists for the study of mixed phases where it is used to determine physicochemical data on vapour-solid or vapour-liquid systems (Hachenberg and Schmidt, 1977). Van Boekel and Lindsay (1992) studied the partition of some volatiles of cheese in equilibrium with its... 

Polymeric adsorbents modified with stationary liquid phase are widely used in chromatographic practice. Having proposed the use of porous sorbents based on styrene and divinyl benzene copolymers in gas chromatography, Hollis simultaneously demonstrated the feasibility of these sorbents modified with stationary liquid phase for GS separation of volatile compounds [16]. Studying water determination in various liquid specimens Hollis and Hayes found out [17] that the chromatographic properties of a modified adsorbent differ from both the pure initial polymeric adsorbent and the pure stationary liquid phase. 

Many contaminants exist as immiscible nonaqueous phase liquids (NAPLs) in soil. These liquids do not fully solubilize in water and exist as a separate phase due to physical and chemical differences from water. NAPLs can be classified as light (less dense than water) nonaqueous phase liquids (LNAPLs) and dense (more dense than water) nonaqueous phase liquids (DNAPLs). A list of typical NAPLs and their important properties is presented in Table 8.8. As described elsewhere in this book (Chapter 15), NAPLs may solubilize, volatilize, and otherwise partition among phases. This section focuses on the advective transport of pure-phase NAPL. 

In the first class, azeotropic distillation, the extraneous mass-separating agent is relatively volatile and is known as an entrainer. This entrainer forms either a low-boiling binary azeotrope with one of the keys or, more often, a ternary azeotrope containing both keys. The latter kind of operation is feasible only if condensation of the overhead vapor results in two liquid phases, one of which contains the bulk of one of the key components and the other contains the bulk of the entrainer. A t3q)ical scheme is shown in Fig. 3.10. The mixture (A -I- B) is fed to the column, and relatively pure A is taken from the column bottoms. A ternary azeotrope distilled overhead is condensed and separated into two liquid layers in the decanter. One layer contains a mixture of A -I- entrainer which is returned as reflux. The other layer contains relatively pure B. If the B layer contains a significant amount of entrainer, then this layer may need to be fed to an additional column to separate and recycle the entrainer and produce pure B. 

When a mixture contains components with a broad range of volatilities, either a partial condensation from the vapor phase or a partial vaporization from the liquid phase followed by a simple phase split often can produce an effective separation. This is in essence a single-stage distillation process. However, by its very nature, a single-stage separation does not produce pure products hence further separation of both liquid and vapor streams is often required. 

Volatilization — Volatilization is a physico-chemical phenomenon of particular interest to environmental managers as well as safety managers. It is the tendency of a material to transfer from a liquid phase (either pure or dissolved as in aqueous systems) to a gaseous phase (commonly air). The volatilization, or evaporation as it is more commonly called, is controlled by a number of factors, the most important of which are the vapor pressure of the material, temperature (vapor pressure increases with temperature), and air/material interfacial surface area, and the action of active mass transfer agents such as wind. 

Condensed phase interactions can be divided roughly into two further categories chemical and physical. The latter involves all purely physical processes such as condensation of species of low volatility onto the surfaces of aerosol particles, adsorption, and absorption into liquid cloud and rainwater. Here, the interactions may be quite complex. For example, cloud droplets require a CCN, which in many instances is a particle of sulfate produced from SO2 and gas-particle conversion. If this particle is strongly acidic (as is often the case) HNO3 will not deposit on the aerosol particle rather, it will be dissolved in liquid water in clouds and rain. Thus, even though HNO3 is not very soluble in... 

In an SVE system, the primary mechanism for contaminant removal from the soil to the vadose zone is the volatilization of contaminants present in the pure or adsorbed phase onto soil into the vapor phase, as the vapor phase is continually extracted. The property that shows the extent to which this transfer can take place during SVE is vapor pressure, which provides an indication of the extent to which each contaminant will partition between the liquid phase and the vapor state at equilibrium conditions. Generally, a contaminant with a greater vapor pressure more readily volatilizes than one with a lesser vapor pressure. 

While this technique can be used for gas solubility in volatile liquids, where the vapor pressure of the liquid is determined prior to the introduction of the gas, it is uniquely suited for fhe measurement of gas solubilities in ILs because the gas phase remains pure. This is the technique used by Costa Gomez and coworkers [8-10] to measure the solubility of various gases in ILs and a schematic of the apparatus is shown in Figure 8.3. These apparatuses are frequently made entirely from glass and, therefore, are limited to low-pressure operation. Nonetheless, this makes them ideal for determining Henry s law constants. 

This chapter shows how a biphasic medium can help in reducing loss of volatile compounds in a gaseous phase exiting from a bioreactor, in comparison with pure aqueous systems. It also emphasises the usefulness of solvents having low vapour pressure (heavy organic solvents or ionic liquids) in the reduction of the release of compounds into the environment. There are, from this point of view, common interests between engineering needs and environmental concerns in the flavouring industry. 

The distillation technique is not used to separate complex mixtures, but finds its acceptance more for the preparation of large quantities of pure substances or the separation of complex mixtures into fractions. The technique depends on the distribution of constituents between the liquid mixture and component vapors in equilibrium with the mixture two phases exist because of the partial evaporation of the liquids. How effective the distillation becomes depends upon the type equipment employed, the method of distillation, and the properties of the mixture components. The distinguishing aspects of distillation and evaporation are that in the former all components are volatile, whereas in the latter technique volatile components are separated from nonvolatile components. An example of distillation would be the separation of ethyl alcohol and benzene. An evaporative separation would be the separation of water from an aqueous solution of some inorganic salt, for example, sodium sulfate. 

A rather broad applicability of FTIR as a detector in liquid chromatography can be achieved when the mobile phase is removed from the sample prior to detection. In this case the sample fractions are measured in a pure state without interference from solvents. Experimental interfaces to eliminate volatile mobile phases fromHPLC effluents have been tried with some success [133-135] but the breakthrough towards a powerful FTIR detector has only been achieved by Gagel and Biemann, who formed an aerosol from the effluent and sprayed it on a rotating aluminum mirror. The mirror was then deposited in a FTIR spectrometer and spectra were recorded at each position in the reflexion mode [136-138]. 

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