Henry constant, modified

Eq. (2) does not contain any adjustable parameter and can be used to predict the gas solubility in mixed solvents in terms of the solubilities in the individual solvents (1 and 3) and their molar volumes. Eq. (2) provided a very good agreement [9] with the experimental gas solubilities in binary aqueous solutions of nonelectrolytes a somewhat modified form correlated well the gas solubilities in aqueous salt solutions [17]. The authors also derived the following rigorous expression for the Henry constant in a binary solvent mixture [9] (Appendix A for the details of the derivation) ... 

Henry constant for absorption of gas in liquid Free energy change Heat of reaction Initiator for polymerization, modified Bessel functions, electric current Electric current density Adsorption constant Chemical equilibrium constant Specific rate constant of reaction, mass-transfer coefficient Length of path in reactor Lack of fit sum of squares Average molecular weight in polymers, dead polymer species, monomer Number of moles in electrochemical reaction Molar flow rate, molar flux Number chain length distribution Number molecular weight distribution... 

Figure 14.5 depicts the predicted vs. observed permeability constants (log Kp) for all 288 treatment combinations studied without taking into account the specific mixtures at which these chemicals were dosed. The residuals of this model showed no further correlation to penetrant properties. However, when vehicle/mixture component properties were analyzed, trends in residuals became evident. An excellent single parameter explaining some variability of this residual pattern (R of 0.44) was log (1 /Henry constant) (1/HC). Figure 14.6 depicts the modified LFER model including an MF = log (1/HC). 

As can be recognized from the results shown before, modified UNI FAC is a very powerful predictive model for the development and design of chemical processes, in particular separation processes. However, modified UNIFAC is a g -model. This means that it cannot handle supercritical compounds. For supercritical compounds either Henry constants have to be introduced or Approach A has to be used. In the latter case, an equation of state is required, which is able to describe the PvT behavior of both the vapor (gas) and the liquid phase. 

For gas-liquid solutions which are only moderately dilute, the equation of Krichevsky and Ilinskaya provides a significant improvement over the equation of Krichevsky and Kasarnovsky. It has been used for the reduction of high-pressure equilibrium data by various investigators, notably by Orentlicher (03), and in slightly modified form by Conolly (C6). For any binary system, its three parameters depend only on temperature. The parameter H (Henry s constant) is by far the most important, and in data reduction, care must be taken to obtain H as accurately as possible, even at the expense of lower accuracy for the remaining parameters. While H must be positive, A and vf may be positive or negative A is called the self-interaction parameter because it takes into account the deviations from infinite-dilution behavior that are caused by the interaction between solute molecules in the solvent matrix. 

Most agricultural pyrethroids have a very low vapor pressure (Vp) - around 10 8 mmHg at an ambient temperature - which is usually measured by the gas saturation method [8] and, therefore, its distribution to an air compartment is considered less important, as listed in Table 1. Tsuzuki [27] has improved the modified Watson method to estimate the vapor pressure of pyrethroids with reasonable precision just from their chemical structures. The volatilization from water can be conveniently evaluated by the Henry s law constant defined as vapor pressure divided by water solubility [28] and the small values of synthetic pyrethroids... 

Henry s law constants are reported in a modified exponential form. For example, the experimentally determined Henry s law constant of benzene is 5.48 x 10 atm-mVmol however, this valne is reported as 5.48 (x 10 atm-m /mol). 

In addition, the high concentrations of ions in solutions of high ionic strength such as sea salt particles (especially near their deliquescence point) can alter gas solubility. In this case, the Henry s law constants must be modified using Setchenow coefficients to take this effect into account (e.g., Kolb et al., 1997). 

In this chapter we will focus on another special case, that is, the case in which we assume that Yu is different from 1 but is constant over the concentration range considered. This situation is primarily met when we are dealing with dilute solutions. As we have seen for the solvent water (Table 5.2), for many organic compounds of interest to us, Ylw does not vary much with concentration, even up to saturated solutions. Hence, for our treatment of air-water partitioning, as well as for our examples of air/organic solvent partitioning at dilute conditions, we will assume that Yu is constant. This allows us to modify Eq. 6-1 to a form known as Henry s Law ... 

The treatment of Debye and Hiickel is based on the assumption of an electric field which is constant everywhere and on the supposition that all parts of any spherical shell can move with the same velocity in a given direction. The presence of the particle must, however, distort the electrical field and the hydrodynamic currents, and it is only when the particles are very small in comparison with the thickness of the double layer that the Debyc-Hiickcl result would be expected to hold. Since the value of 1/k increases with increasing dilution, it follows that equation (23) should be applicable to small particles in very dilute solutions. For the case of relatively large particles, Henry has derived the modified equation... 

When the amount of modifier on the montmorillonite surface increases, a regular decrease in differential heats of adsorption is observed, with the simultaneous increase of the specific retention volumes per unit area of external surface and Henry s constants for the hydrocarbons considered (Tables 7, 8). At the same time, an increase in the amount of long-chain cationic surfactants on the kaolinite surface leads to the decrease in both differential heat of adsorption and Henry s constant for benzene (Table 8), not surprisingly, because of a more complete covering of the kaolinite surface hy the presorbed modifying layer and a decrease in the charge of the polar NHj groups of the modifier [41]. 

Specific retention volumes V , (cm /g), Henry s constants Ki (mm) and differential heats of adsorption Qa (kJ/mol) of benzene on organo-substituted kaolinite and montmorillonite samples with different amounts of presorbed modifier a (meq/g) at 120°C... 

Using the value of the specific surface area of the kaolinite specimen prior to modification (70 m /g), the area occupied by each cation (1.2 nm ) and the amount of adsorbed modifier, we have estimated the thickness of the modifying layer covering the surface of the silicate, assuming that no defects exist in this layer. The resulting values, together with the experimental data on the Henry s constants and the differential heats of adsorption obtained as reported in [47] are listed in Table 10 for the two specimens considered. 

Experimental, calculated and estimated values of Henry s constant Ki (/um) and differential heat of adsorption Qa (kJ/mol) for n-hexane adsorbed on montmorillonite modified by cetyl-pyridinium (1.1 mol/kg) at 393 K... 

Hs)ai surface average modified Henry s law constant for species s In the mixture (—)... 

Predict (using the modified Huron-Vidal second order (MHV2) mixing rule) the sorption of CO2 in polyethylene glycol over extended pressure ranges Predict (using EoS/G mixing rules) Henry s law constants for different polymer solutions... 

Zhong, C. and Masuoka, H., Prediction of Henry s constants for polymer-containing systems using the SRK equation of state coupled with a new modified UNIFAC model. Fluid Phase Equilibria, 126, 1, 1996. 

Many chemicals escape quite rapidly from the aqueous phase, with half-lives on the order of minutes to hours, whereas others may remain for such long periods that other chemical and physical mechanisms govern their ultimate fates. The factors that affect the rate of volatilization of a chemical from aqueous solution (or its uptake from the gas phase by water) are complex, including the concentration of the compound and its profile with depth, Henry s law constant and diffusion coefficient for the compound, mass transport coefficients for the chemical both in air and water, wind speed, turbulence of the water body, the presence of modifying substrates such as adsorbents in the solution, and the temperature of the water. Many of these data can be estimated by laboratory measurements (Thomas, 1990), but extrapolation to a natural situation is often less than fully successful. Equations for computing rate constants for volatilization have been developed by Liss and Slater (1974) and Mackay and Leinonen (1975), whereas the effects of natural and forced aeration on the volatilization of chemicals from ponds, lakes, and streams have been discussed by Thibodeaux (1979). 

Depending on the system at hand, the equilibrium ratio AT, may be either constant (as in Henry s law), or a function of temperature, pressure, and/or composition. In this book, the following phase equilibrium models are primarily models dealt with (1) constant relative volatilities, (2) ideal solutions using Raoult s law, and (3) nonideal solutions using a modified Raoult s law and the NRTL activity coefficient model, although other activity coefficient models are also applicable. Each of these three models is briefly discussed here. 

This modified rule was successfully applied to vapor-liquid equilibria of numerous mixtures [39-41]. Here, the binary parameter was adjusted to one experimental data point for vapor pressure or Henry s law constant of the smdied binary mixture. 

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