Desorption-adsorption relationship

The desorption-adsorption relationship for mucin and collagen on mica is represented in Figure 8. This relationship for mucin is linear and clearly indicates that half of the adsorbed quantities can be desorbed. On the contrary, for collagen, this relationship shows a threshold value (1.1 mg/m ) corresponding to the maximum irreversibly adsorbed value. Above this value all adsorbed collagen can be desorbed (the slope of the straight line is one). 

Finally, Figure 9 presents the desorption-adsorption relationship for mucin and collagen on polyethylene and surface-modified polyethylene. The adsorption of mucin on untreated polyethylene is typically irreversible and the maximum adsorbed quantity is equal to 2.2 mg/m2. In contrast, low but continuous desorption of mucin with increasing adsorbed concentrations is observed on surface oxidized polyethylene. 

Figure 8. Desorption-adsorption relationships on mica surfaces, (t) mucin (a) collagen. Adsorption time 20 hrs temp. 20°C. Adsorption conditions as indicated in Figure 7.

Solution The elementary reaction steps of adsorption, reaction, and desorption are now reversible. From this point on, we will set ai = a, pi = P, and so on, since the intrinsic kinetics are desired. The relationships between ai, a, and a are addressed using an eflectiveness factor in Section 10.4. The various reaction steps are... 

Modification techniques for activated carhon were used to increase the removal capacity by surface adsorption and to improve the selectivity to volatile organic compounds (VOCs). Modified activated carbons (MACs) were prepared by modifying the purified activated carbon with various acids or bases. The effects of adsorption capacity and modified contents on the textural properties of the MACs were investigated. Furthermore, VOC adsorption and desorption experiments were carried out to determine the relationship between the adsorption capacity and the chemical properties of the adsorbents. High adsorption capacity for the selected VOCs was obtained over lwt%-H3P04/AC (lwt%-PA/AC). As a result, MAC was found to be very effective for VOC removal by adsorption with the potential for repeated use through desorption by simple heat treatment. 

The reaction is carried out in close-loop reactor connected to a mass spectrometer for 1S02, 180160 and 1602 analyses as a function of time [38], The gases should be in equilibrium with the metallic surface (fast adsorption/desorption steps 1 and f ) If the bulk diffusion is slow (step 6) and the direct exchange (step 5) does occur at a negligible rate, coefficients of surface diffusion Ds can be calculated from the simple relationship between the number of exchanged atoms Ne and given by the model of circular sources developed by Kramer and Andre [41] ... 

The adsorption of fully and partially hydrolyzed (88%) polyvinyl alcohol (PVA) on 190-1lOOnm monodisperse polystyrene latex particles was investigated. The effect of molecular weight was investigated for 190 nm-size particles using the serum replacement adsorption and desorption methods. The adsorption density at the adsorption-isotherm plateau followed the relationships for the fully hydrolyzed... 

If, on the timescale of observation, the degree of coverage of any site type becomes appreciable, the precise nature of the relationship between Fi, F2 and has to be taken into account. For the case of a Langmuirian isotherm (implying sufficiently fast kinetics of adsorption/desorption) this means that equations in (2) are applicable. Two particular cases are described here ... 

A mechanism is determined from these data by choosing one which is consistent with the overall equilibrium behavior and which correctly matches the rate relationships derived for the postulated mechanism e.g., assuming the bimolecular adsorption/desorption reaction mechanism, as given in Equation 1, and using the kinetic model described above, the following relationship between xp and reactant and product concentrations can be derived (see Appendix C) ... 

If the adsorption-desorption relationship is hnear, then n is equal to 1 and Eq. (3.18) would be the same as... 

The origin of the relationship between Kp and temperature in Eq. (YY) can be seen by reexamining equations (RR) and (SS), which show that Kp is directly proportional to bL, i.e., to the ratio of the rate constants for adsorption and desorption, k, k, . The rate constant for desorption from the surface, k, can be expressed as a function of the heat of desorption, A7/d (Adamson, 1982) ... 

The rate of adsorption and the rate of desorption are assumed to be dependent on the geometric relationship of the rock and solution (i.e., dependent upon the volume of solution and on the shape and area of the solid medium in contact with the solution). Because the dependence of sorption kinetics on the geometric relationship is not known, the rates for sorption are determined by experiment for the particular geometry (surface area of rock to volume of solution) for which the prediction of nuclide migration is desired. 

Kinetic Considerations. The reaction kinetics are masked by a desorption process as shown below and are further complicated by rate deactivation. The independence of the 400-sec rate on reactant mole ratio is not indicative of zero-order kinetics but results because of the nature of the particular kinetic, desorption, and rate decay relationships under these conditions. It would not be expected to be more generally observed under widely varying conditions. The initial rate behavior is considered more indicative of the intrinsic kinetics of the system and is consistent with a model involving competitive adsorption between the two reactants with the olefin being more strongly adsorbed. Such kinetic behavior is consistent with that reported by Venuto (16). Kinetic analysis depends on the assumption that quasi-steady state behavior holds for the rate during rate decay and that the exponential decay extrapolation is valid as time approaches zero. Detailed quantification of the intrinsic kinetics was not attempted in this work. 

The half-band width is constant below PIP, = 0.37, and then suddenly drops with the increase of P/P,. The relationship between the half-band width and PIP, has a clear hysteresis corresponding to that of adsorption isotherm. The half-band width upon desorption is smaller than that upon adsorption. 

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