Xenon adsorption experimental

Figure 1 shows the representation of the experimental isotherm (B. G. Aristov, V. Bosacek, A. V. Kiselev, Trans. Faraday Soc. 1967 63, 2057) of xenon adsorption on partly decationized zeolite LiX-1 (the composition of this zeolite is given on p. 185) with the aid of the virial equation in the exponential form with a different number of coefficients in the series i = 1 (Henry constant), i = 2 (second virial coefficient of adsorbate in the adsorbent molecular field), i = 3, and i = 4 (coefficients determined at fixed values of the first and the second coefficients which are found by the method indicated for the adsorption of ethane, see Figure 4 on p. 41). In this case, the isotherm has an inflection point. The figure shows the role of each of these four constants in the description of this isotherm (as was also shown on Figure 3a, p. 41, for the adsorption of ethane on the same zeolite sample). The first two of these constants—Henry constant (the first virial constant) and second virial coefficient of adsorbate-adsorbate interaction in the field of the adsorbent —have definite physical meanings. 

Remarkable improvements have been reported experimentally regarding the optimization of the reaction yield, such as variations in the reaction temperature and solvent, and the introduction of special techniques (e.g. dry stage adsorption conditions , ultrasonication and photoirradiation employing a Xenon lamp ). 

In the field emission microscope observations are made on the properties of the adsorbed layer itself. This technique therefore should not suffer from the difficulties experienced in flash desorption of xenon it should, moreover, yield detailed information on the structural dependence of the interaction. Two problems might prevent useful results (1) The field required for emission may seriously affect the surface distribution of a weakly adsorbed gas. The importance of such field effects can only be estimated experimentally. (2) Adsorption of a rare gas may not affect the electron emission sufficiently to permit significant observations. Previous work on evaporated films by Mignolet (54) established quite significant work function changes in physical adsorption and makes it clear that lack of sensitivity should not prove a limitation. 

In the adsorption experiments, only a small portion of the surface was filled when brought to a steady state at p = 10-7 mm. If this concentration were to correspond to saturation of the entire surface the xenon adsorbed would have a cross-sectional area of 50A2, more than three times the gas kinetic value. A more reasonable view is that only the rougher, stepped planes are filled. From the calculated binding energy ratios which appear in fair agreement with experimental results found by field emission for the 111 and 130, we can estimate for Xe a heat of 5.4 kcal/mole on the 100 and 4.5 kcal/mole for the 110 plane. 

The adsorption isotherm of xenon on graphite has been measured at different temperatures [56-60]. Review the experimental results and discuss the surface phases of xenon that were detected. Would you expect krypton to behave similarly on the same substrate Explain. 

The diffusion of gaseous benzene and paraxylene during their adsorption in a fixed bed of HZSM-5 zeolite crystallite has been studied by Xe NMR of adsorbed xenon used as a probe. The equations of diffusion in the macropores and micropores have been analytically solved, giving the hydrocarbon concentration profiles against time in both types of pores and allowing the simulation of the Xe NMR spectra. The comparison of simulated and experimental spectra leads to the value of the intracrystallite diffusion coefficients which are in good agreement with the literature. 

After 30 years of continuing investigation, the adsorption properties of the noble ses on metal and semiconductor surfaces have recently attracted renewed interest. On the one hand, some fundamental aspects have come within the reach of modem experimental and theoretical techniques, sueh as the very nature of physisorption and the noble gas - substrate interaction, the possibility to study growth and surface kinetics at the atomic scale, and the recent interest in nanoscale surface friction and related tribological issues, where noble gas adlayers serve as model systems [99P]. On the other hand, noble gas adsorption is being used as a non-destmctive and quantitative surface analytical tool as, for instance, in photoemission of adsorbed xenon (PAX) [97W] and for titration analysis of heterogeneous surfaees based on the site specificity of the interaction strength [96S, 98W]. 

It is instructive to compare the results of simulations obtained using spherical representations of the sorbates with those firom nonspherical (structured) representations. We need also to consider the influence of the rigidity of the lattice, which can be constrained to be completely rigid or flexible. June et al. were able to reproduce experimental self-diffusivities and isosteric heats of adsorption of methane and xenon in silicalite by employing a rigid but structured methane molecule despite the neglect of the Coulomb term in their poten-tial.244 Even when methane is treated as a nonstructured sphere, it was still possible to predict experimentally observed diffusion coefficients well. " ... 

Activated charcoal is thus a class of substances whose chemical and physical properties may vary within rather wide limits, Let us hasten to add that this does not really impair its usefulness as an adsorbent. The adsorptive properties of charcoals in separation systems are usually not so critical that even variations like factors of two or more will result in loss of separation, though such variations certainly affect the procedure in detail. The intent is to point out that the experimenter should pot be surprised if the adsorptive properties of his charcoal differ from those he sees quoted in the literature. In one study of the adsorption of xenon on seven charcoals at room temperature, the amount per gram of charcoal adsorbed at a given pressure varied as much as a factor of five.. These charcoals were of course chosen on the basis of differences in materials and preparations expected to produce a range of adsorption characteristics. In order that early experience maybe used to predict with fair accuracy the course of separations in systems built at later dates, it is probably wise to originally purchase a quantity of charcoal sufficient for many years needs. 

Experimental study of adsorption of fission product gases. Evaluation of various ad. orbcr materials based on experimental measurements of the equilibrium adsorption of krypton or xenon under static conditions is in progress [7]. Results in the form of adsorption isotherms of various solid adsorber materials are presented in Fig. 6-8. 

The HRE-2 charcoal beds were designed [42] on the basis of adsorption equilibrium data of krypton and xenon from the literature, with a safety factor of six to compensate for lack of experimental data on the particular conditions. An HRE-2 bed to process 2.50 cc/min of off-gas oxygen contains 13.3 fU of 8- to 14-mesh activated cocoanut charcoal, i here are four such beds immersed in a water-cooled underground concrete tank. In the HRE-1, 13,9 ft of charcoal were used for a design flow rate of 470 cc/min. The HRE-1 beds operated successfully. 

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