Reduction of adsorption capacity

A considerable reduction in pumping speed and failure to reach the ultimate pressure which is normally attainable in spite of thermal regeneration having been carried out indicates that the zeolite being used has become contaminated by outside substances. It does not make good sense to attempt to rejuvenate the contaminated zeolite with special thermal processes. The zeolite should simply be replaced. 

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Coconut shell-based carbon seems to be less susceptible to fouling by NOM and other background water quality parameters, e.g., the precipitation of manganese, iron, or calcium carbonate [28] however, a decrease in adsorption performance correlating with the TOC content of three different natural waters was observed as well [55]. Knappe and Rossner [54] found a reduction of adsorption capacity of up to 60% for the coal-based activated carbons, for the coconut shell-based carbons of around 20%. The presence of NOM in values of 0.5 mg/L TOC resulted in a decrease in adsorption capacity of coconut-based carbons [28,53]. 

Zeolites were found tobealmostunaffectedbythepresenceofNOM [52,54]. A maximum reduction of adsorption capacities of 0-23% for ZSM-5 was observed by Knappe et al. [54]. 

The incorporation of element in a given structure may well modify the effective free volume but only to a reasonable extent. Therefore the adsorption capacity of a given compound usually (toluene, cyclohexane and 2-methyl pentane) may not vary too much with respect to the parent aluminosilicate. Drastic reduction of adsorption capacity may be ascribed to an extensive amorphization or to occlusion of non framework material. Additional structural examination will remove any ambiguity in this respect and specific washing may increase the adsorption capacity. 

The titer reduction and adsorption capacities of the T2 phage and HSV-1 are compared in Table 3. For similar initial titers (10 PFU/ml), the survivor titer of HSV-1 was at least 2 orders of magnitude lower than that of T2. For similar equilibrium titer remaining in the solution (10 PFU/ml), the adsorption capacity (PFU/ml) of HSV-1 was 2 orders of magnitude higher than that of T2. Evidently, HSV-1 is much more susceptible to the surface-bonded QAC than T2. Since HSV-1 is an enveloped virus, the lipid bilayer surroimding the capsid binds strongly to the QAC-treated surface due to additional hydrophobic interaction. It should be noted that the adsorption experiments of T2 were carried out in buffer solutions without proteins, while those of HSV-1 were in buffered 1 vol% FBS solution. 

Table 3. Comparison of Titer Reduction and Adsorption Capacity Between HSV-1 and T2 Phage Using Surface-Bonded QAC...

But not only the activated carbons are subject to the impact of co-solutes. Bi et al. [56] showed that in a binary solution of MTBE and o-xylene the latter is preferentially adsorbed on carbonaceous resin leading to a reduction in adsorption capacity for MTBE. Similar results are found for m-xylene [28,47] and other BTEX [58]. Davis and Powers [47] showed, however, that the influence is more pronounced on activated carbon (F-400) than on the carbonaceous resin Ambersorb (35% reduction vs. 11% reduction). 

The substitution of phosphorus in the framework structure of Type L zeolite results in reduced adsorption capacity (—50% ) and a reduction in apparent pore size from about 10 to 6-7 A. Na+-exchange of P-L zeolite results in a further reduction in adsorption capacity except for water. Ca2+-exchange of P-L results in an increased adsorption capacity for KUO and 02 to about 90% of that of phosphorus-free L zeolite, but reduces... 

In the case of P-A zeolite, although some reduction in adsorption capacity is observed in the case of some cation forms of P-A and with... 

There is some evidence (see Table 6) that raising the reduction temperature from 573 to 723 K decreases the amount of H2 adsorbed. However, the decrease is less than a factor of two, and interpretations other than SMSI could be offered to account for such a small effect. The only evidence for a marked loss of adsorption capacity comes from the work of Mustard et al. However, it is possible that at temperatures as high as 1023 K there is a migration of the Ni into the support. 

The adsorption capacity of the adsorbent increases with pressure because the partial pressure of the solvent increases. An increase in adsorber temperature causes a reduction in adsorption capacity. Because the equilibrium capacity is lower at higher temperatures, the dynamic capacity (working capacity) of the activated carbon adsorber will also be lower. To enhance adsorption, the inlet temperature of the adsorber should be in the range of20-40°C. In Figure 22.1.13 the adsorption isotherms of tetrahydrofuran on activated carbon D43/3 for several temperatures are shown. 

Activated carbon in solvent recovery service will have a useful service life of 1 to 10 years, depending on the attrition rate and reduction in adsorption capacity. 

An increase in temperature also increases the speed of adsorption, that is the time to approach equilibrium, because of the two factors the increase in diffusivity and the reduction in adsorption capacity. This has been demonstrated in Figure 9.2-4 where the apparent diffusivity increases monotonically with temperature. Although the increase in temperature makes the system to approach equilibrium... 

The influence of the presence of sulfur adatoms on the adsorption and decomposition of methanol and other alcohols on metal surfaces is in general twofold. It involves reduction of the adsorption rate and the adsorptive capacity of the surface as well as significant modification of the decomposition reaction path. For example, on Ni(100) methanol is adsorbed dissociatively at temperatures as low as -100K and decomposes to CO and hydrogen at temperatures higher than 300 K. As shown in Fig. 2.38 preadsorption of sulfur on Ni(100) inhibits the complete decomposition of adsorbed methanol and favors the production of HCHO in a narrow range of sulfur coverage (between 0.2 and 0.5). 

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