Vapor-Phase Dilution Systems

This section describes four additional techniques for mitigating releases of hazardous substances into the atmosphere. In addition to water, both steam and compressed air can be used to promote the movement of air to dilute a hazardous material. Foam can be used as a scrubbing medium to entrap a hazardous material in its structure. Foam scrubbing is often effective for materials that are soluble in water, or that are highly reactive with an additive contained in the foam. Lastly, dry powders can be used to capture a reactive chemical released into the air. 

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Outlined below are the steps required for of a X T.E calciilation of vapor-phase composition and pressure, given the liquid-phase composition and temperature. A choice must be made of an equation of state. Only the Soave/Redlich/Kwong and Peng/Robinson equations, as represented by Eqs. (4-230) and (4-231), are considered here. These two equations usually give comparable results. A choice must also be made of a two-parameter correlating expression to represent the liquid-phase composition dependence of for each pq binaiy. The Wilson, NRTL (with a fixed), and UNIQUAC equations are of general applicabihty for binary systems, the Margules and van Laar equations may also be used. The equation selected depends on evidence of its suitability to the particular system treated. Reasonable estimates of the parameters in the equation must also be known at the temperature of interest. These parameters are directly related to infinite-dilution values of the activity coefficients for each pq binaiy. 

The vapor-phase Badger process (Eigure 10-2), which has been commercialized since 1980, can accept dilute ethylene streams such as those produced from ECC off gas. A zeolite type heterogeneous catalyst is used in a fixed bed process. The reaction conditions are 420°C and 200-300 psi. Over 98% yield is obtained at 90% conversion." Polyethylbenzene (polyalkylated) and unreacted benzene are recycled and join the fresh feed to the reactor. The reactor effluent is fed to the benzene fractionation system to recover unreacted benzene. The bottoms... 

For treatment by the ZPU, a waste stream must be in the vapor phase at near-ambient pressure, at a temperature of less than 400°F, and relatively free of particulate matter. Each compound in the waste stream has unique requirements for destruction. Many compounds are destroyed with a low application of energy, while others require a stronger application. The dose required for a specific combination of contaminants must be determined experimentally. Moisture may either enhance or reduce system effectiveness depending on the mixture. Compounds that act as free-radical scavengers or reducing agents may diminish the process efficiency. Concentrations of vapors that produce temperatures above 400°F in the reaction chamber through exothermic reaction must be diluted to keep the temperature below 400°F. 

As already mentioned, the triplet state of benzene was identified by the cis-trans isomerization of the 2-butenes. Nevertheless, Wilzbach and Kaplan in the liquid phase, following work of Srinivasan,42 find a photochemical adduct of benzene to olefins. This adduct they find to be an adduct of benzvalene and not of benzene itself.414 There is also evidence of formation of a small amount of this adduct even in the vapor phase.35 Benzene exposed to ultraviolet radiation in a flowing system diluted with nitrogen and condensed shows compound formation with trifluoroethanol, CF3CH2OH. Again the adduct is one of benzvalene.410... 

From the isothermal vapor-liquid equilibrium data for the ethanol(l)/toluene(2) system given in Table 1.11, calculate (a) vapor composition, assuming that the liquid phase and the vapor phase obey Raoult s and Dalton s laws, respectively, (b) the values of the infinite-dilution activity coefficients, Y and y2°°, (c) Van Laar parameters using data at the azeotropic point as well as from the infinite-dilution activity coefficients, and (d) Wilson parameters using data at the azeotropic point as well as from the infinite-dilution activity coefficients. 

Activity Coefficients of Volatile Compounds. The headspace technique was used to determine the activity coefficients of volatile compounds as described previously (11). The headspace system flask contained 10 to 20 mL of the model wine with the diluted volatile compoimd, at 25°C. The flow rate of nitrogen gas in the flask was 5 to 10 mL/min. The concentration in volatile compound in the vapor phase was analysed by gas chromatography. The conditions were reported in a previous paper (11). The relative volatility of the volatile compound can be expressed as a partition coefficient K and activity coefficient y... 

Thus, the fugacity of species i (in both the hquid and vapor phases) is equal to the partial pressure of species i in the vapor phase. Its value increases from zero at infinite dilution (jc, = y, -> 0) to Pj for pnre species i. This is illnstrated by the data of Table 12.1 for the methyl ethyl ketone(l)/toluene(2) system at 323.15 K (50°C). The first tlnee columns list a set of experimental P-x -y data and colunms 4 and 5 show ... 

Solubilitiesattemperaturesand pressures above the critical values of the solvent liave important applications for supercritical separation processes. Examples are extraction of caffeine from coffee beans and separation of asplraltenes from heavy petroleum fractions. For a typical solid/vapor equilibrium (SVE) problem, tire solid/vapor saturation pressure P is very small, and the saturated vapor is for practical purposes an ideal gas. Hence 0 for pure solute vapor at this pressure is close to unity. Moreover, exceptfor very low values of the system pressure P, the solid solubility yj is small, and can be approximated by j, the vapor-phase fugacity coefficient of the solute at infinite dilution. Finally, since is very small, the pressure difference P — in the Poyntingfactor is nearly equal to P at any pressure where tins factor... 

High temperature, steam dilution, and low system pressure produce an equilibrium more favorable to styrene. For endothermic vapor-phase reactions, the equilibrium constant increases with temperature and... 

Torress-Marchal, C., Cantalino, A. L., and De Brito, R. M., 1989. Prediction of vapor-liquid equilibria (VLE) from dilute systems data using the SRK equation of state Industrial applications. Fluid Phase Eq., 52 111-117. 

A substance in solution has a chemical potential, which is the partial molar free energy of the substance, which determines its reactivity. At constant pressure and temperature, reactivity is given by the thermodynamic activity of the substance for a so-called ideal system, this equals the mole fraction. Most food systems are nonideal, and then activity equals mole fraction times an activity coefficient, which may markedly deviate from unity. In many dilute solutions, the solute behaves as if the system were ideal. For such ideally dilute systems, simple relations exist for the solubility of substances, partitioning over phases, and the so-called colligative properties (lowering of vapor pressure, boiling point elevation, freezing point depression, osmotic pressure). 

Matching the lubrication equation to thermodynamic theory requires some caution, since thermodynamic theory yielding an expression for pL should be applied to the entire system including dense (liquid) and dilute (vapor) phases in equilibrium, whereas only the dense phase may have a suitable aspect ratio. To make the approximation applicable, one has to assume that the interface dividing the dense and the dilute phase is only weakly inclined relative to the substrate and weakly curved, so that its position can be expressed by a function h x, t) with derivatives obeying the above lubrication scahng. Thermodynamic theory, either local or nonlocal, can be used to compute an equilibrium density profile across the interface (in the vertical direction), po z — h x, t)), which is weakly dependent on the horizontal 2D position and time only through its dependence on h, e.g. 

The simplest example of such a system is the interface between a semiinfinite, bulk system and vacuum (or its own dilute, vapor phase) this interface is generally referred to as a surface. When this semi-infinite material coexists with another condensed phase, the separating surface is referred to as an... 

VLE data, the results of two thermodynamic consistency tests, and the parameters of different -models, such as the Wilson, NRTL, and UNIQUAC equation. Additionally, the parameters of the Margules [28] and van Laar [29] equation are listed. Furthermore, the calculated results for the different models are given. For the model which shows the lowest mean deviation in vapor phase mole fraction the results are additionally shown in graphical form together with the experimental data and the calculated activity coefficients at infinite dilution. In the appendix of the data compilation the reader will find the additionally required pure component data, such as the molar volumes for the Wilson equation, the relative van der Waals properties for the UNIQUAC equation, and the parameters of the dimerization constants for carboxylic acids. Usually, the Antoine parameter A is adjusted to A to start from the vapor pressure data given by the authors, and to use the -model parameters only to describe the deviation from Raoult s law. Since in this data compilation only VLE data up to 5000 mm Hg are presented, ideal vapor phase behavior is assumed when fitting the parameters. For systems with carboxylic acids the association model is used to describe the deviation from ideal vapor phase behavior. 

Calculate the Pxy-diagram at 70 "C for the system ethanol(l)-benzene(2) assuming ideal vapor phase behavior using the Wilson equation. The binary Wilson parameters and A 21 should be derived from the activity coefficients at infinite dilution (see Table 5.6). Experimentally the following activity coefficients at infinite dilution were determined at this temperature ... 

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