Sorption effect

Pr q/Pro = 5,0 are relevant sorption effects of CO- but not of H2 thus only the 1 wavefronts represent rather tne shift conversion). Therefore it seems conceivable that there are two different mechanisms which participate in the CO shift conversion which is also in agreement with the established two different sorption mechanisms for 1 0 and with the transient behavior, depicted on Figure 6. 

Ellis AS, Johnson,TM, Bullen TD (submitted) Using chromium stable isotope ratios to quantify Cr(VI) reduction lack of sorption effects. Environ Sci Technol submitted 9/2003 Ellis AS, Johnson TM, Bullen TD, Herbel MJ (2003) Stable isotope fractionation of selenium by natural microbial consortia. Chem Geol 195 119-129... 

This method has the advantage that, after reaching a state of equilibrium, sorption effects can be ignored and this procedure can therefore be used for calibrating gauges at very low pressures. 

PhI02 is rather bulky and plugs the pores, thus preventing further access of reactants to the active sites [49-50,63-64]. Therefore turn-overs are quite low when PhIO is used as oxidant. For the oxidation of methyl cyclohexane on TMPcY [49-50,63-64] and of cyclohexane on Fet.BuPcY [67] turn-overs are 5.6 and 7.6 respectively. It should be noted that the reported turn-overs for oxidations with PhIO correspond to conversions of less than 1 substrate molecule per two supercages, or to total conversions of less than 0.1 %. Therefore the observed activities and selectivities may be influenced by sorption effects. Furthermore iodosobenzene is a rather expensive oxidant and not practical to use because of its low solubility in solvents. Therefore some researchers tend to use other oxidantia such as air [65,66] and tertiary butyl hydroperoxide (t-ButOOH) [57]. In the oxidation of n-octane with t-ButOOH turn-overs as high as 6000 have been reported [57]. 

The ketone/alcohol ratio in methyl cyclohexane oxidation with PhIO is systematically higher on THPc zeolites than on the homogeneous FePc [63], as shown in Figure 7. This is explained by the authors by a sorption effect, since... 

All elution curves were reproducible at 0.2% (or better), practically independently on the sample concentration from 0.5 to 5 mg/ml. A concentration-dependent knick occurred in these curves after replacing a 1 cm3 of the covered glass beads by uncovered ones. It is well known that sorption effects are concentration-dependent... 

Other, secondary effects skew the response of the piezoelectric sensor when it is used as a gas sensor. These can be described phenomenologically as the hydrostatic effect (p), the frictional effect (x), and the sorption effect (m) ... 

When the gas or vapor feed stream contains a component that is highly soluble in the polymer membrane and causes plasticization, then the selectivity as defined by Equation 4.6 will depend on the partial pressure or the amount of the plasticizing component sorbed into the membrane. Furthermore, pure-gas permeation measurements are generally not a good indicator of the separation performance, and mixed-gas permeation measurements will be needed [21-23]. Often, the mixed-gas selectivity is less than predicted from pure-gas measurements [8] however, the opposite has been observed [24], Competitive sorption effects can also compromise the prediction of mixed-gas behavior from pure-gas measurements [25], For gas pairs where each component is less condensable than C02, like 02/N2, it is generally safe to conclude that the selectivity characteristics can be accurately judged from pure-gas permeabilities at all reasonable pressures. When the gas pair involves a component more condensable than C02, plasticization is likely to be a factor and pure-gas data may not adequately reflect mixed-gas selectivity. When C02 is a component, the situation depends on the partial pressures and the nature of the polymer. 

Sorption effects in the macroscopic scale are usually used for non-continuous pumping. They contain a highly porous sorption material like activated carbon or zeolites with a huge inner surface. The sorption material is usually cooled down by liquid nitrogen. They are regenerated by heating the sorption material to temperatures of several hundred degrees Celsius after a disconnection of pump and vacuum-chamber. 

The remaining vacuum pumps to be discussed in this chapter fall into a group which remove gas particles from systems by sorption effects such as adsorption, chemisorption/gettering and implantation. They tend to be used on systems where any contamination of the vacuum by pump fluids, lubricants, etc. must be avoided. However, those pumps that remove gas particles exclusively by temperature-dependent gas adsorption on molecular sieves or A1203 (adsorption pumps) will not be discussed. 

Chapter 3 also considered those entrapment pumps that remove gas particles by sorption effects such as gettering and implantation. The operating principles of sputter ion pumps were explained (Example 3.26) and some typical calculations performed (Examples 3.27-3.29). Aspects of the use of titanium sublimation pumps were dealt with (Examples 3.30-3.33). 

The catalytic activity of MePc depends on the nature of the ligand in the apical position and should therefore be solvent dependent.[56] From the chromatographic determination of the respective adsorption coefficients of the reaction partners in pre-catalytic conditions, a very pronounced activity difference is found depending on the nature of the solvent used.[64] However, the sequence of the adsorption coefficients is of zeolitic origin and reflects a sorption effect rather than a coordination effect. The respective values of the adsorption coefficients indicate that for the oxidation of alkanes, cyclohexane, with organic peroxide for example, in acetone the oxidant is enriched in the intracrystalline voids, resulting preferentially in peroxide decomposition. In excess cyclohexane, the substrate is enriched in the pores, so that every adsorbed peroxide molecule results in an efficient oxygenation. 

The fulfillment of Equation 9.13, within experimental error, is obvious from the analysis of the data reported in Ref. 100 (see Figure 9.5). As a result, sorption effects are responsible for the changes in the reaction rates for monomolecular paraffin cracking. 

Polymerization frequently is performed in gas-phase reactors at intermediate pressures. The role of heterogeneous catalysts and the interaction between reaction kinetics and mass transfer can only be understood if sorption effects, solubilities of gases in solids, volume changes, and diffusivities at reactor conditions are known. 

The third mechanistic jq>proach has been proposed by Bidlingmeyer et al. and Deming et al. (B6-B8, K24). In the ion-interaction approach i i pairs do not form in the mobile phase rather it is assumed that there is a dynamic equilibrium of lipophilic ions. This results in the formation of an electrical double layer on the hydrocarbonaceous stationary phase. Retention is based, therefore, upon an electrostatic attraction due to surface charge density of the ion-pairing ions and from a sorption effect onto the nonpolar stationary phase. 

The authors have developed an expression to modify kinetic rate constants for surface-sorption effects. Corrections to rate constants have not been made in the calculations reported here, but the experimental values for rate constants are within a few percent of those which would be appropriate for the Rainier Mesa aquifer. The basic methodology reported here is believed valid only minor changes in the computed values are expected from more precise calculations. 

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