Adsorption components

The strong adsorption components (Cj Eg) are predominant on the surface adsorbed layer. Long hydrocarbon chain components are preferred In the micelle formation. 

A different concept dealing with highly adsorptive components is the so-called Flip-flop chromatography developed by Colin et al. (1991) (Fig. 5.8). The feed mixture is injected at the one end of the column and the early eluting components are pushed through the column (Fig. 5.8a) and collected at the other end (Fig. 5.8b). When the first components are withdrawn from the column the flow direction is reversed while the late-eluting component is still adsorbed on the column (Fig. 5.8c). After a predetermined time a new portion of feed mixture is injected and the elution is performed in the reversed flow direction (Fig. 5.8d). At the end of the column the late-eluting impurity from injection 1 is now eluted first (Fig. 5.8e) and afterwards the early-... 

Section I Desorption of the strongly adsorptive component Section II Desorption of the less adsorptive component Section III Adsorption of the strongly adsorptive component Section IV Adsorption of the less adsorptive component... 

In section I desorption of the more adsorptive component has to take place, therefore the elution capability should be the highest and thus the system pressure is also the highest. Through sections II and III towards IV the pressure can be constantly lowered due to adsorption and desorption requirements in the single sections. More detailed information about this process concept can be found in Clavier et al. (1996), Denet et al. (2001), Depta et al. (1999) and Giovanni et al. (2001). 

IIa(/i)— This adsorptive component of the disjoining pressure results from nonuniform concentrations in the film due to unequal interaction energies of solute and solvent with interfaces in nonionic solutions. (This is different than the nonuniform distribution of charged ions.) This component of the disjoining pressure is likely to become very important for interactions between nonpolar molecules (e.g., nonaqueous phase liquids) that give rise to repulsive forces in the liquid film [see discussion by Derjaguin et al. (1987, p. 171)]. 

The most suitable technique for chemically active and reactive trace components is the introduction of a more reactive compound into the carrier gas. This protects the trace components against moisture and trace amounts of oxygen, improves the shape of the chromatographic zones and prevents losses of the substance in the column and other units because the reactive and adsorptive component of the carrier gas poisons the adsorbing sites in the units and on the sohd support and reacts with contaminants in the carrier gas. To the best of our knowledge, one of the first applications of this method was the addition of 1% of boron trichloride to the carrier gas in the analysis of readily hydrolysable compounds. 

The feed stream is stoichiometric in terms of the two reactants. Diatomic A2 undergoes dissociative adsorption. Components B, C, and D experience single-site adsorption, and triple-site chemical reaction on the catalytic surface is the rate-controlling feature of the overall irreversible process. This Langmuir-Hinshelwood mechanism produces the following Hougen-Watson kinetic model for the rate of reaction with units of moles per area per time ... 

Section IV Adsorption ofthe less adsorptive component. 

Given the temperature and pressure range of study, we will assume that the adsorption component Va is negligible compared to Vd. 

The balance of the adsorptive component i in a system with the bonnding sntfaces according to this figure as part of the fixed bed with the external void vp is given by... 

Here c , is the concentration of the adsorptive component i at the entrance. The model is vahd if... 

Heat production due to the exothermal oxydation reactions between the oxygen of the gas and the carbon of the adsorbens and/or the adsorpt components. Additionally the heat of adsorption may play a role. 

Cu(I)— and Ag(I)—MFI ads. II isotherms (both volumetric and calorimetric) lie below the ads. I correspondent isotherms, indicating the presence of irreversible phenomena. The irreversible adsorption component was quantified by taking the (ads. I - ads. n) difference in the volumetric isotherms at pco = 90 Torr. It was 30 % of total uptake (ads. I) for copper- and % for silver-exchanged zeolites. 

The saturation mode (continuous-flow method) is more frequently used. Here changes in enthalpy and amount adsorbed of the solute correspond to the formation of a Solid-Liquid interface being in thermal and material equilibrium with the percolating stock solution of a given composition. Repeated adsorption and desorption cycles with the liquid phase in contact with the solid surface for a time required to reach equilibrium can be used to assess reversibility of the phenomenon, and quantify the reversible and irreversible adsorption components [79, 80]. In addition, the same equipment allows probing for some active sites in the solid surface. 

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