Gas-liquid equilibrium constants

Ae=L/KV is the average effective absorption factor of each component, whereas K=y/x is the gas-liquid equilibrium constant. 

The relation between Henry s constant, Hoa, and the gas-liquid equilibrium constant,... 

For gas-liquid equilibria, it is very important to investigate how the gas-liquid equilibrium constant is defined. The constant for gas-liquid equilibrium (Ka) can be estimated from thermodynamic theories [9]. Henry s constant often yields an acceptable accuracy. Estimation methods for Henry s constant are discussed in reference [4]. There are several correlation equations for the liquid film coefficients (kcA and A la), phase area-to-reactor volume, and gas holdup. These correlations are discussed in reference [10] and in Appendix 7. Usually, correlations for the mass transfer parameter ki Uy are more reliable... 

In calculating the physical equilibrium, we made use of gas-liquid equilibrium constants, which are defined as... 

In Eq. (11.159), K is the gas-liquid equilibrium constant. When the volatifities of organic reactants and products are negligible, this expression should be used for hydrogen only, while for the organic compounds Ngli = 0. 

TABLE 4.1. Boiling Points and Gas-Liquid Equilibrium Characteristics (Henry s Law Constants) for Both Odorous and Nonodorous Compounds in Water at 25°C (Thibodeaux, 1996 Sander, 2000). 

Gas-liquid relationships, in the geochemical sense, should be considered liquid-solid-gas interactions in the subsurface. The subsurface gas phase is composed of a mixture of gases with various properties, usually found in the free pore spaces of the solid phase. Processes involved in the gas-liquid and gas-solid interface interactions are controlled by factors such as vapor pressure-volatilization, adsorption, solubility, pressure, and temperature. The solubility of a pure gas in a closed system containing water reaches an equilibrium concentration at a constant pressure and temperature. A gas-liquid equilibrium may be described by a partition coefficient, relative volatilization and Henry s law. 

An additional problem arises when the stability of the critical phase involving the gas-liquid equilibrium in a binary system is studied. The conditions of stability of a homogenous system at constant pressure are d2A/dV2)T x> 0 and d25/dx )T P > 0 from Equations (5.136) and (5.141), respectively. The question arises of which of the two conditions becomes zero first as the boundary between stable and unstable phases is approached. 

Bubble points for gas-liquid equilibrium were measured at constant temperature by observing the pressure at which the equilibrium gas phase disappeared upon injection of small amounts of solvent into the view cell. The equilibrium composition of the liquid phase was obtained from the known composition in the cell. Other pressures and corresponding compositions at this temperature were obtained by repeating the procedure for different porphyrin loadings. 

The regenerated extraction gas leaves the second regeneration column at its head and is cooled down in (WT3) to a temperature of approximately 20°C. Depending on the type of extraction solvent the buffer vessel (KP) contains liquid phase in equilibrium state with gas or merely gas of high density. In the last case a pressure controlled pneumatic pump feeds fresh solvent into the circular process. If a gas/liquid equilibrium is achieved in the buffer vessel the gas pressure remains constant until a minimal amount of liquid remains there. For this purpose two optical sensors are introduced into the buffer vessel registrating the minimum and maximum extraction liquid level If the level falls below minimum, fresh liquid extraction solvent is refilled. 

Here, V is the volume of the reactor, Qc, and QL are the gas and liquid flow rates, B is the vapor-liquid equilibrium constant (B = y/x, where y and x are mole fractions in vapor and liquid phase, respectively), and SL and va are the molar volumes of the liquid and gas phases, respectively, at reactor conditions. Similarly, for the gas phase, the following relation41 can be derived ... 

Where oil and gas phases occur in a reservoir, each compound will distribute itself between the two phases according to its vapour—liquid equilibrium constant. For a particular hydrocarbon, this constant is affected by all of the components present in each phase, as well as... 

In the above expression, C is a constant in the equation defining the gas-liquid equilibrium. It is assumed that a linear relationship exlssi between jr and y of die form y = nur + C, where y is the equilibrium concentration in the gas, m is the slope of tha equilibrium curve, and C is the y intercept. Nguyen gives the following example of the use of these equations. 

Table 8-5. Dissolution of Atmospheric Gases in Cloud and Rain Drops Time Constants for the Adjustment to Gas-Liquid Equilibrium... 

Absorption of sour gases (NH3, SO2, COj) in water at low pressures. Here gas/liquid equilibrium should be described correctly over a large concentration interval. Use of Henry constants without correction for concentration effects gives large errors. 

Group methods are limited to dilute systems, where A -values could be considered as constant. In the case of more concentrated mixtures we recommend the use of computer methods. Attention has to be paid care to correct description of gas-liquid equilibrium. The use of asymmetric convention for /C-values could overcome the drawback of using the Henry-law for concentrated solution (see Chapter 6). In the case of absorption with chemical reaction the methods based on the integration of mass transfer equations are recommended. Some specialised simulation packages have capabilities in this area. 

Equation (4.16) allows us to calculate liquid-phase reaction equilibria from gas-phase equilibrium constants and vice versa. 

The relative volatility is often constant, i.e., it does not depend on temperature. Therefore, application of (5.1-5) enables the calculation of gas-liquid equilibrium... 

The adsorption equilibrium constants Ka c a.c will be in different units for liquid systems than for gas systems. Equilibrium constants for several systems are listed in Table 18-2. 

Equilibrium ratio of component i in gas-liquid equilibrium Rate constant... 

The slope of this line is often referred to as Henry s constant, and Expression 6.5d as Henry s law for adsorption, in analogy to the corresponding case of gas-liquid equilibrium (see Equation 6.2). 

The gas-liquid equUihiium constants determine the solubility of gaseous molecule into the liquid phase so that they are important parameters for the kinetic analysis of multiphase reactions. Liquid reactions are important in the atmosphere for fog and cloud water droplets with the particle diameter of 1-100 pm. When those water droplets coexist in the atmosphere, water soluble molecules X in the gas phase is absorbed by the droplet, and the gas-liquid equilibrium,... 

Two-Phase Gas-Liquid Diffusional Operations The vapor-liquid equilibrium constant, defined as... 

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