Adsorption experimental system

The experimental investigation was performed by depositing copper films on the (100) -surface of a platinum single crystal. It was found that the reconstruction of the Pt surface was lifted upon Cu adsorption. The system was then heated to different temperatures and the formation of different ordered surface alloys was evidenced by... 

To run adsorption storage systems efficiently the appropriate adsorbent has to be used. The right choice is possible on the basis of the measured adsorption equilibrium. The adsorption equilibrium of water vapor and different adsorbents (zeolites and silica gels) was experimentally found [3,4], The differential heat of adsorption (AHd) was calculated from the equilibrium data. 

In order to test the reversibility of metal-bacteria interactions, Fowle and Fein (2000) compared the extent of desorption estimated from surface complexation modeling with that obtained from sorption-desorption experiments. Using B. subtilis these workers found that both sorption and desorption of Cd occurred rapidly, and the desorption kinetics were independent of sorption contact time. Steady-state conditions were attained within 2 h for all sorption reactions, and within 1 h for all desorption reactions. The extent of sorption or desorption remained constant for at least 24 h and up to 80 h for Cd. The observed extent of desorption in the experimental systems was in accordance with the amount estimated from a surface complexation model based on independently conducted adsorption experiments. 

Two general cases are considered (1) adsorption under conditions of constant or nearly constant external solution concentration (equivalent to infinite fluid volume) and (2) adsorption in a batch with finite volume. In the latter case, the fluid concentration varies from c°t to c7 when equilibrium is eventually attained. A = (c° - c /c = Ms(h7 — h0i)/(Vfc0i) is a partition ratio that represents the fraction of adsorbate that is ultimately adsorbed. It determines which general case should be considered in the analysis of experimental systems. Generally, when A90 > 0.1, solutions for the second case are required. 

To interpret the kinetics experimental data of an organic pollutant(s) or leachate from complex organic mixtures, it is necessary to determine the adsorption/ desorption process steps in a given experimental system which govern the overall adsorption/desorption rate. For instance, the adsorption process of an organic compound by a porous adsorbent can be categorized as three consecutive steps ... 

Free Energy of Adsorption, a) System with only one surfactant. Experimentally, it is found that the adsorption of the single surfactants is well described by an equation of the form... 

It might also be noted that K (Equation (62)) may be related to AG° for the adsorption process if the model applies to the experimental system. Therefore, from studies of adsorption at different temperatures, values of AH° and AS0 may be determined for the process described by Equation (61). It must be emphasized that compliance with the form predicted by the Langmuir isotherm is not a sensitive test of the model therefore interpretations of this kind must be used cautiously. 

Fiq. 13. Schematic diagram of experimental system used to study the adsorption of nitrogen on tungsten. 

A more complete and mechanistically explicit model has been described that allows for competitive adsorption to reactive and nonreactive sites on Fe°, as well as partitioning to the headspace in closed experimental systems and branching among parallel and sequential transformation pathways [174,175]. This model represents the distinction between reactive and nonreactive sites by a parameter called the fractional active site concentration. Simulations and sensitivity analysis performed with this model have been explored extensively, but application of the model to experimental data has been limited to date. 

In this section we give a selection of theoretical and experimental results for homopolymer adsorption. For a meaningful comparison between theory and experiment it is mandatory that the experimental system Is well defined, with as many parameters known as possible (chain length and chain-length distribution, solvency, adsorbent properties, etc.). Wherever feasible, we shall discuss theoretical predictions In combination with experimental data. However, this correspondence cannot be malnteiined in all cases there are useful theoretical predictions that, as yet, cannot be checked experimentally (for example, the relative contributions of loops and tails), whereas for some measurable quantities no quantitative theory has yet been developed (for example, most kinetic data). 

In most situations the experimental system is more complicated than one (homodisperse) polymer adsorbing from a single solvent. In multicomponent systems preferential adsorption always plays a role. A common example is the adsorption of a polydisperse polymer, where usually long chains adsorb preferentially over short ones, even if the adsorption energy per segment is the same. 

The Study of ammonia adsorption was carried out in a flow adsorption microcalorimeter under dynamic conditions. Some of the parameters from these experiments are collected in Table 2.. In all cases the amount desorbed was much smaller than the adsorbed one, and so was the absolute value of the heat evolved. This clearly points out that ammonia adsorption consists of two different components. One is related to chemisorption (irreversible adsorption) and the other one (more labile or reversible) to physisorption in the pores. Another important feature about these experiments is that heat was still released long afterwards the NH3 uptake was negligible. This heat evolution, already reported in other experimental systems [4,7,8], is due to diffusion of adsorbed ammonia from low energy sites to higher energy sites having low accessibility. The lack of further uptake of NH3 may be due to irreversibly adsorbed molecules on the borders of micropores blocking NH3 towards the end of the adsorption process. 

We proposed a novel method which can be used to for fast measurements of infinite dilution selectivity in binary gas adsorption. This experimental system can handle a wide range of pressure variation. Using the data obtained one can perform a quick characterization for selectivity. From the design point of view this method can be effectively employed to check validity of the model being used. 

Several experimental systems including inorganic sorbents are analyzed and their adsorption characteristics are estimated to illustrate the applicability of the presented theoretical relationships. 

Figures 1 and 2 show the results of our analysis for the literature system [8] butanol (1) + benzene (2) on silica gel at 298K. For illustrative purposes in Table 2 the results of analysis for experimental systems are presented. These systems were taken from the literature and investigated in terms of lAP adsorption model. Essential information about these systems is placed in Table 1.

Adsorption characteristics obtained for the experimental systems from Table 1 studied by means of Eqs. (7), (8) and (11)... 

The total mole fraction Xj depends on the bulk concentration x only and we can state that lnfj2i, vs. Xj is the function of the heterogeneity parameters n and m. For this reason this function is helpful for characterizing the liquid - solid experimental systems. The general form of the dependence lnfi2h vs. x obtained by means of Eqs. (13) and (14) has the following form (for the NBP-na model of adsorption system) ... 

Recent studies [6-14] on adsorption from electrolyte solutions on energetically homogeneous electrode surfaces, like the surface of the Hg electrode, show that at least for aqueous solutions the above approach should be re-examined in two respects first in what concerns the adsorption mechanism (1) and second the treatment of the intermolecular interactions at the surface solution. The adsorption mechanism (1) should be re-examined since, using a thermodynamic method proposed for the determination of the size ratio parameter ni, the value nj = 1 0.2 has been found for a variety of experimental systems, despite the fact that the adsorbate molecules can have dimensions considerably different from those of the solvent molecules [6-11]. In what concerns the intermolecular interactions, in the presence of polar molecules a significant contribution arises from the electric field across the surface solution, which is created by their dipoles [7,12-14]. Similarly, an electric field is established when ions, either from an electrolyte in the bulk solution or from impurities, penetrate the surface solution. In both cases this field is expected to have a dominant effect on the surface activities. 

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