Adsorption Henry constant

The pulse chromatographic technique was used to study low coverage adsorption of linear and monobranched alkanes in the CS-C8 range on two different 10-membered ring zeolites, ZSM-22 and ZSM-23. Henry adsorption constants, enthalpies of adsorption, preexponential Actors of the van t Hoff equation and separation fectors were determined. A detailed interpretation of the experimental data confirmed the previously proposed pore-mouth adsorption mode for branched alkanes on zeolite ZSM-22, where these molecules do not have access into the depth of the pores, but rather point their linear part herein. Zeolite ZSM-23 shows adsorption properties between zeolite ZSM-22 and zeolite ZSM-S, which is a shape selective zeolite where normal and monobranched molecules have both access into its pore system. 

Related to their similar pore diameter and pore structure, unsurprisingly the Henry adsorption constants for linear alkanes are very close to each other on zeolite ZSM-22 and ZSM-23 (Table I). Somewhat higher constants are obtained for 2- and 3-methylbranched alkanes on ZSM-23 compared to zeolite ZSM-22. The adsorption constants of linear alkanes are obviously hi er than branched alkanes on the two cases. The separation power of a zeolite between a linear and a branched hydrocarbon may be given by the separation factor (a), which is the ratio of Henry consteints of linear and branched molecules at a certain temperature, a values at 523 K are given for both zeolites in Table 1. For comparison, values for ZSM-5 are also included, which is one of the most popular shape selective catalyst used in isomerization reactions. From this table it can be seen that both ZSM-22 and ZSM-23 have higher separation constants compared to ZSM-5. The zeolites can be listed in the following order with respect to their separation capacity between linear and 2- and 3-methylbranched alkanes ZSM-22 > ZSM-23 > ZSM-5. In narrow pore structures such as zeolites ZSM-22 and ZSM-23 it is very probable that linear alkanes with smaller kinetic diameters have more access to the available adsorption sites compared to the more bulky branched molecules. This may be regarded as the first... 

The partial pressure of H2S on a volumetric basis in the atmosphere in equilibrium with a water phase of sulfide (H2S + HS ) is at a pH of 7, approximately equal to 100 ppm (gS m-3)-1 (Figure 4.2). It is clear that under equilibrium conditions, much lower concentrations than those corresponding to the values shown in Table 4.6 may result in odor and human health problems. This is also seen from the fact that Henry s constant for H2S is rather high, //H2S =563 atm (mole fraction)-1 at 25°C (Table 4.1). However, under real conditions in sewer networks, conditions close to equilibrium rarely exist because of, for example, ventilation and adsorption followed by oxidation on the sewer walls. Typically, the gas concentration found in the sewer atmosphere ranges from 2-20% and is normally found to be less than 10% of the theoretical equilibrium value (Melbourne and Metropolitan Board of Works, 1989). 

The extension of the ideas presented in Sections 5.8 and 5.10 to the theoretical treatment of isotope separation by gas chromatography is straightforward. The isotope effects observed in chromatography are governed by the isotopic ratio of Henry s Law constants (for gas-liquid separations), or adsorption constants (for... 

Adsorption constant, Henry s Law coefficient, slope of the chord of the isotherm, dimensionless... 

Just as the Henry law constant is used to quantify the partitioning between air and water, it is useful to define a parameter to quantify the partitioning between soil and water. The linear adsorption coefficient, Kd, has often been defined for this purpose ... 

The adsorption isotherm —Equation (8) —associated with this surface equation of state is called the Henry law limit, in analogy with the equation that describes the vapor pressure of dilute solutions. The constant m, then, is the adsorption equivalent of the Henry law constant. When adsorption is described by the Henry law limit, the adsorbed state behaves like a two-dimensional ideal gas. 

Here E ( y1 ) stands for the single-particle contribution to the total energy, allowing for molecule interaction with the surface <2 is the heat released in adsorption of molecules z on the /Lh site Fj the internal partition function for the z th molecules adsorbed on the /Lh site F j the internal partition function for the zth molecule in the gas phase the dissociation degree of the z th molecule, and zz the Henry local constant for adsorption of the zth molecule on the /Lh site. Lateral interaction is modeled by E2k([ylj ), and gj (r) allows for interaction between the z th and /Lh particles adsorbed on the /th and gth sites spaced r apart. In the lattice gas model, separations are conveniently measured in coordination-sphere numbers, 1 < r < R. For a homogeneous surface, molecular parameters zz and ej(r) are independent of the site nature, while for heterogeneous, they may depend on it. 

Numerical studies show that the UNILAN equation, although providing excellent overall correlation of adsorption data at low-to-moderate surface coverage, tends to underestimate Henry s constant. 

Adsorption site energy, pre-exponential factor of Henry s constant and correlation between infinite and finite concentration... 

In the previous section, we have proposed the analytical method which can determine the adsorption free energy, j (or —AGa), based on the deformation polarizability, ao, and the dipole moment, n, of a molecule of solute, during the adsorption study on the solid surfaces as measured from inverse GC at infinite dilution. When the first value, i, of the adsorption free energy is equal to the energy measured at infinite dilution [i.e., the equilibrium concentration being extremely small, P = Pa in Eq. (95)], the pre-exponential factor of Henry s constant, K, can be obtained, depending on the experimental temperatures... 

While in the air compartment, the contaminant solubilizes in the vapor-liquid phase or is associated with aerosol particles by adsorption. It is also prone to desorption from the aerosol particles into the vapor phase. Relevant properties of the air used to model transport of partitioning of a contaminant in the air compartment include temperature, turbulence, wind speed, size and composition of aerosol particles, etc.16,19 Relevant properties of the contaminant that measure its tendency to partition among the vapor, liquid, and solid phases in the air include its aqueous solubility (Saq), vapor pressure (VP), Henry s constant... 

The high pressure adsorption of single gases and mixtures can be predicted from the low pressure (sub-atmospheric) data for the same systems. The optimum temperature for measuring the aulsorption of single gases is near their critical temperature where both the Henry s constant auid the absolute saturation capacity can be determined accurately. 

Selectivity is a key variable that affects the adsorption process and is essential for design. The variation of selectivity of ethane with pressure and composition is shown in a 3D graph in Fig. 2. Pure component data yields only the line AB at zero pressure, which is the ratio of Henry s constants. Using only this information it is not possible to accurately estimate the variation in selectivity. The two models differ substantially with respect to selectivity predictions. In the Langmuirian approach the selectivity is constant and is given by the ratio of Henry s constants (along a horizontal plane through AB). Selectivity by lAST approaches the same limit at zero pressure but rapidly decreases with pressure. 

There are several reports in the literature that measure binary adsorption equilibria using gas chromatography [4,S,6]. In GC techniques the adsorbent is equilibrated with a continuous flow of carrier gas (gas 1). Then a pulse of gas 2 is injected at the column inlet. A peak of the gas 2 is eluted at the exit of the column after some time. Net retention time (or volume) is calculated from the first moment of the peak after correcting for void volume (by measuring the retention time of a non-adsorbing species). If the carrier gas is inert (i.e. helium) the net retention time is related to the pure component Henry s constant. Typical binary measurements reported so r use a mixture of the two gases as carrier and introduce a small perturbation in composition. The net retention volume is related to the thermodynamic properties by [4]... 

Adsorption equilibrium and kinetics of Ar on the 4 adsorbents were measured by volumetric method at three temperatures. The constant volume apparatus and the calculation method have been described in detail elsewhere [3]. Small pressure steps ( 0.1 bar) were given to make sure that the measurements were in the linear range (q = Kc, where K is Henry law constant, q and c, in mmol/cc, are concentrations in adsorbed phase and gas phase). As such, constant, limiting kinetic parameters were extracted. 

The application of Equations (13)-(20) is illustrated for binary mixtures of ethylene (1) and ethane (2) adsorbed on NaX zeolite (faujasite). The constants for the singlegas adsorption equations of state are given in Tables 1 and 2. The selectivity of NaX for ethylene relative to ethane is a function of temperature, pressure, and the composition of the gas. The selectivity at constant temperature (20 °C) is shown in Figure 3. The selectivity at the limit of zero pressure is the ratio of Henry s constants (Xi/X2=33.7). At constant mole fraction of ethylene in the gas, the selectivity decreases rapidly with increasing pressure. At constant pressure, the selectivity decreases with increasing mole fraction of ethylene in the gas. The selectivity at constant pressure and gas composition decreases with temperature, as shown in Figure 4. Decrease of the selectivity with temperature, pressure, and the mole fraction of the preferentially adsorbed species is typical behavior for binary adsorption. 

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... 

Gas adsorption from the binary CO2/CH1, mixture to cellulose acetate was studied at different compositions. For this study, different volumes of gaseous mixtures of a given composition were injected into the column. A chromatogram with two peaks, one for CO2 and the other for CHi, was obtained for each injection and the method illustrated in Figure 1 for determining S ocug and h was applicable to both peaks. The latter SjOCU8 and h values were used to calculate Na, p and Henry s constant H Na/p. As a result of this calculation, Hqq and Hqj at different gas compositions were... 

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