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Adsorption configuration integral

The use of statistical calculations of configuration integrals to determine thermodynamic adsorption characteristics of zeolites dates back to the late 1970s (49). Kiselev and Du (22) reported calculations based on atom-atom potentials for Ar, Kr, and Xe sorbed in NaX, NaY, and KX zeolites. Then-calculations, which included an electrostatic contribution, predicted changes in internal energy in excellent agreement with those determined experimentally. The largest deviation between calculated and experimental values, for any of the sorbates in any of the hosts, was a little over 1 kJ/mol. [Pg.53]

In Silicalite. A variety of papers are concerned with sorption of methane in the all-silica pentasil, silicalite. June et al. (87) used a Metropolis Monte Carlo method and MC integration of configuration integrals to determine low-occupancy sorption information for methane. The predicted heat of adsorption (18 kJ/mol) is within the range of experimental values (18-21 kJ/ mol) (145-150), as is the Henry s law coefficient as a function of temperature (141, 142). Furthermore, the center of mass distribution for methane in silicalite at 400 K shows that the molecule is delocalized over most of the total pore volume (Fig. 9). Even in the case of such a small sorbate, the channel intersections are unfavorable locations. [Pg.66]

For NaA zeolite, an approximate calculation of the configurational integrals was made in Ref. 19 on the basis of potential curves for 3 symmetry axes of the second, third, and fourth order. All together, 26 directions were taken into account. In a subsequent work, 482 directions have been considered (17). It was assumed that during the adsorption the... [Pg.52]

CO oxidation to CO2 involves 2 electrons. If one CO molecule occupies one Pt atom in a linear adsorption configuration (Pt-COad), the ECSA would be calculated by dividing the integrated CO oxidation charge area by 0.42 mC cm Pt. If one CO molecules occupies two Pt atoms in a bridge adsorption configuration (2Pt-COad),... [Pg.562]

Deviations from the two-dimensional approximation can be studied by introducing more terms into the configuration integral perturbation expansion, which includes the effects of the periodic nature of real solid surfaces. Although some preliminary results were obtained by Monson et al. [182,224] through a certain munber of simphfications, more extensive calculations are needed in order to estimate the contribution of each of the terms and to give a more realistic statistical-mechanics description of adsorption phenomena. [Pg.494]

The experimental rig and process configuration for integrated bead milling and fluidised bed adsorption is shown in Figure 17.5. [Pg.406]

Fig. 17.5. Experimental configuration for integrated bead milling and fluidised bed adsorption 1. Feedstock 2. peristaltic pump 3. bead mill 4. flow through/waste 5. fluidised bed contactor 6. elution buffer 7. fraction collector/ waste 8. loading buffer. Fig. 17.5. Experimental configuration for integrated bead milling and fluidised bed adsorption 1. Feedstock 2. peristaltic pump 3. bead mill 4. flow through/waste 5. fluidised bed contactor 6. elution buffer 7. fraction collector/ waste 8. loading buffer.
For any dynamical simulation, a continuous representation of the PES is mandatory since the potential and the gradients are needed for arbitrary configurations. One can in fact perform ab initio molecular dynamics simulations in which the forces necessary to integrate the classical equations of motion are determined in each step by an electronic structure calculations. There have been few examples for such an approach [35-37], However, in spite of the fact that electronic structure calculations can nowadays be performed very efficiently, still there is a significant numerical effort associated with ab initio calculations. This effort is so large that in the ab initio dynamics simulations addressing molecular adsorption and desorption at surfaces the number of calculated trajectories has been well below 100, a number that is much too low to extract any reliable reaction probabilities. [Pg.6]

Enthalpies of wetting are sometimes used to obtain (integral) enthalpies of adsorption by subtracting the enthalpy of condensation. This procedure is not exact because it presupposes a model in which the interaction between the first and the second surface layer is Interpreted as purely identical to that in condensation (BET theory assumes the same). However, the heat of adsorption of the second layer Is not exactly Identical to the heat of liquefaction and the configuration of the first layer is affected by the presence of a second. In other words, entropic factors also have to be considered, and. in this connection, the packing in the first layer must be known to convert A H (in J m ) into A H (in J mol 2). Notwithstanding these reservations, a certain similarity may be expected. [Pg.69]

A second approach is the triangle method which was developed based on the equilibrium theory model which assumes that the adsorption equilibrium is established everywhere at any time in the column. The equivalent TMB configuration with a four-section emit will be considered here. The model equations consist in four sets of mass balance equations, one for each section j j = 1,- , 4), with the relevant boundary conditions and the integral material balances at the column ends and at the nodes of the unit [16,28]. These equations were given earlier, in Section 17.2 (Eqs. 17.4 to 17.6). [Pg.817]


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See also in sourсe #XX -- [ Pg.8 ]




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