Selection of adsorbents

It was shown that selectivity of adsorbents in liquid chromatography might be considered as sum of nonspecific and specific pai ts. The angulai factor of dependence E = f(Q,) determines nonspecific chai ge-controlled selectivity of adsorbents ... 

In a comprehensive study of a mixture having unknown chromatographic characteristics it is frequently desirable to be initially guided in the selection of adsorbents and solvents from information obtained by t.l.c. analysis using alumina or silica gel on microscope slides. Only if these prove unsatisfactory would recourse be made to the other adsorbents. 

The selection of adsorbent packing material is based on the polarity of pollutants to be analyzed. The nonpolar hydrophobic adsorbents retain the nonpolar analytes and allow the polar substances to pass through the column. The hydrophilic adsorbents adsorb the polar components, allowing the nonpolar materials to pass through. Various stationary phases for solid phase extraction are listed below in Table 1.5.1. 

In case of binaiy systems, co-adsorption was performed using three different initial mixtures - being equimolar (Z/ = Zz = O.S) and rich in component 1 and 2 (respectively Z/ = 0.85 and Z = 0.15) - whose molar ratio were formerly checked. The selectivity of adsorbent rn/2) was either directly represented in an X-Y isobaric equilibrium diagram, or determined using the following equation, where Xi and K are die adsorbed and gas phase molar fraction of f component, and plotted versus total amount adsorbed Qtad-... 

Selectivity of adsorbants vis a vis mercury. Attempts to remove toxic heavy metal ions, cadmium and lead, were made in order to check the specificity of modified corn--stick powder. 

The selection of adsorbents is critical for determining the overall separation performance of the above-described PSA processes for hydrogen purification. The separation of the impurities from hydrogen by the adsorbents used in these processes is generally based on their thermodynamic selectivities of adsorption over H2. Thus, the multicomponent adsorption equilibrium capacities and selectivities, the multi-component isosteric heats of adsorption, and the multicomponent equilibrium-controlled desorption characteristics of the feed gas impurities under the conditions of operation of the ad(de)sorption steps of the PSA processes are the key properties for the selection of the adsorbents. The adsorbents are generally chosen to have fast kinetics of adsorption. Nonetheless, the impact of improved mass transfer coefficients for adsorption cannot be ignored, especially for rapid PSA (RPSA) cycles. 

Selection of adsorbent is based on the same principles that are used for chromatography. Select the medium showing the strongest binding to the target protein which binds as few of the contaminants as possible i.e. the medium with the highest selectivity and/or capacity for the protein of interest. 

In addition, in order to improve the shape selectivity of adsorbents and catalysts, besides adjustment of pore size, the external surface of zeolites also needs to be modified to deactivate the adsorption sites and catalytically active sites present on the external surface which shows no shape selectivity. The external surface modification is especially important for small-particle and nano-sized zeolites. 

From the aforementioned examples, it is seen that through zeolite pore and surface modification, the shape selectivity of adsorbents and catalysts can be effectively improved, and consequently many practical problems can be solved. Especially, the discovery of the CLD method overcomes the shortcomings of the CVD method, clearing a series of obstacles for large-scale industrial applications, and therefore this new technique is very promising. 

Then the surface concentration is an informative value if only the surface accessible toward the molecules under study is known. In practice, the accessible surface is markedly decreased as the size of a modifier is increased. The surface areas accessible toward a selection of adsorbates and modifiers on silica are presented in Table 1. 

On separation of fullerenes on Silasorb Amin with bonded fullerene Ceo the selectivity of adsorbent is comparable with selectivity of adsorbents used for separation of fullerenes. 

These data clearly validate the logic for the selection of adsorbents for this application. 

Carey W P, Beebe K R, Kowalski B R, Illman D L and Hirschfeld T 1986 Selection of adsorbates for chemical sensor arrays by pattern recognition Anal. Chem. 58 149... 

Adsorption of dibenzothiophene (DBT) over FAU zeolites exchanged with alkali cations has been studied. Cristallinity (by XRD and IR), exchange level (XRF) and basic properties (CO2 TPD) of different adsorbents used have been determined. The influence of Si/Al molar ratio and type of cation exchanged in the zeolite as well as the presence of toluene in feedstock mixture on DBT adsorption capacity and selectivity of adsorbent has been also determined. Thermogravimetric analysis showed a stronger DBT adsorption over X zeolites. 

If only a small amount of one component is present in a mixture, changing the phase of the components in high concentrations should be avoided. In such a case, absorption, stripping, or selective adsorption best removes the minor component. Adsorption is particularly effective because of the high selectivity of adsorbents and is widely used for purification, where small amounts of a solute are removed from a liquid or vapor feed. 

Adsorbents, Selection of Adsorbent 291 Table 4-2. Actual data of a plant for subsequent treatment of 3000 ra /d wastewater. ... 

Small-scale spillages from leaking or broken containers on the road or in the air can readily be treated by having a specially selected adsorbent spill kit on the transport vehicle. This same approach would also apply to small spillages on-site. On a multipurpose chemical site, these small spills kits would contain a selection of adsorbent materials as outlined in Section 15.2.1. 

Ogino, H., and Oi, T., Extraction of lithium from LiMniOa by ammonium peroxodisulfate and lithium isotope selectivities of adsorbents thus obtained, Sep. Sci. Technol., 31(9), 1215-1232 (1996),... 

From this figure it clearly can be seen that the AC is selective for CO2 as both the N2 as well as the CH4 concentration in the adsorbed phase are considerably reduced compared to their values in the sorptive gas phase. Information of this kind is very valuable for the selection of adsorbents in gas purification and separation processes [3.37],... 

Carey WP, Beebe KR, Kowalski BR, lUman DL, Hirschfeld T (1986) Selection of adsorbates for chemical sensor arrays by pattern recognition. Anal Chem 58 149-153 Cheeke JDN, Wang Z (1999) Acoustic wave gas sensors. Sens Actuators B 59 146-153 Cheremisinof PN, Ellerbusch F (eds) (1980) Carbon adsorption handbook. Science, Ann Arbor, pp 241-279 Comyn J (ed) (1985) Permeation of gases and vapors in polymers. Elsevier, London... 

Several separations on PLOT columns are displayed in Figures 3.37 and 3.38. The selection of adsorbents currently available in a PLOT column format includes aluminum oxide-KCl, aluminum oxide-sodium sulfate, molecular sieves, alumina, graphitized carbon, and porous polymers. These columns are intended to be direct... 

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