Oxidation adsorbents

Fig. XI-7. Volume fraction profile of 280,000-molecular-weight poly(ethylene oxide) adsorbed onto deuterated polystyrene latex at a surface density of 1.21 mg/m and suspended in D2O, from Ref. 70.

Activated carbons contain chemisorbed oxygen in varying amounts unless special cate is taken to eliminate it. Desired adsorption properties often depend upon the amount and type of chemisorbed oxygen species on the surface. Therefore, the adsorption properties of an activated carbon adsorbent depend on its prior temperature and oxygen-exposure history. In contrast, molecular sieve 2eohtes and other oxide adsorbents are not affected by oxidi2ing or reducing conditions. 

If an adsorbed chemical group (anchor) is more strongly bound to the surface than a solvent molecule would be at that site, an equiHbrium expression may be written for the displacement of solvent by adsorbate. Adsorption is particularly strong if the chemical nature of the adsorbed group is similar to that of the particle surface for example, in aqueous systems perfluoroalkane groups adsorb weU on polytetrafluoroethene particles and aromatic polyethene oxides adsorb weU on polystyrene. 

Release of and regeneration of the metal oxide adsorbent in the stripper. 

The H2S comes out with the reactor products, goes through the product-recovery system of the FCCU, and eventually goes to a Claus plant for sulfur recovery. The metal oxide adsorbent recirculates with the spent cracking catalyst back to the regenerator for the next SO adsorption cycle. 

A sohd solution of a pure magnesium aluminate spiael (MgAl20 with MgO is an effective metal oxide adsorbent (43). Such a soHd solution (Mg2A10 ) does not destroy the spiael framework the MgO adsorbs SO and the adsorption activity of the dispersed MgO ia the spiael is much greater than that of pure MgO itself (43). 

Cobalt(Il) dicobalt(Ill) tetroxide [1308-06-17, Co O, is a black cubic crystalline material containing about 72% cobalt. It is prepared by oxidation of cobalt metal at temperatures below 900°C or by pyrolysis in air of cobalt salts, usually the nitrate or chloride. The mixed valence oxide is insoluble in water and organic solvents and only partially soluble in mineral acids. Complete solubiUty can be effected by dissolution in acids under reducing conditions. It is used in enamels, semiconductors, and grinding wheels. Both oxides adsorb molecular oxygen at room temperatures. 

Metal Oxide - Since metals are less electrophilic than silicon, metal oxide adsorbents show even stronger selectivity for polar molecules than do siliceous materials. The most commonly used metal oxide adsorbent is activated alumina, used primarily for gas drying. Occasionally, metal oxides find applications in specific chemisorption systems. For example, several processes are under development utilizing lime or limestone for removal of sulfur oxides from flue gases. Activated aluminas have surface areas in the range of 200 to 1,000 ftVft Average pore diameters range from about 30 to 80 A. 

Resin adsorption Aqueous solutions typical concentration < 8 % SS < 50 ppm no oxidants Adsorbate on resin always chemically regenerated... 

The Raman spectrum of an oxide sample after adsorption may be considered to consist of the spectrum of the adsorbed species superimposed on the spectrum due to the oxide adsorbent. In general, the Raman spectra of oxide adsorbents are sufficiently weak or sufficiently simple that they allow the detection of Raman lines due to the adsorbed species. This is one major advantage of Raman scattering over infrared absorption spectroscopy. The infrared spectra of most oxide adsorbents show strong absorptions which may obscure those arising from the adsorbates (Figs. 13,14). 

The ultimate result is that not only Fe, but most metals that interact strongly with organic matter or oxide adsorbents, are likely to settle out of the water column in estuaries. Not only does this process reduce the metal flux reaching the ocean, but 50% of the time the current at the bottom of an estuary actually facilitates the movement of metals upstream. 

In Chapter 1 we consider the physical and diemical basis of the method of semiconductor chemical sensors. The items dealing with mechanisms of interaction of gaseous phase with the surface of solids are considered in substantial detail. We also consider in this part the various forms of adsorption and adsorption kinetics processes as well as adsorption equilibria existing in real gas-semiconductor oxide adsorbent systems. We analyze the role of electron theory of chemisorption on... 

A detailed description is given to the role of point defects available in the volume and on the surface of oxide adsorbents on adsorption-induced change of electrophysical characteristics. We try to deduce the impact of the proper nature of adsorbent as well as the nature of adsorption centers. 

We consider problems related to electrophysical properties of sintered polycrystalline oxides as well as their adsorption changes. We also analyze the difference in adsorption induced changes of electrophysical characteristics of stoichiometric and non-stoichiometric partially reduced oxide adsorbents. 

We shall note that there are numerous experimental papers dealing with studies of effect of adsorption on other electrophysical characteristics of oxide adsorbents such as thermal electromotive force [107], Hall effect [108 - 110], volt-ampere [58, 111] and frequency [112] characteristics. The availability of results of these studies makes one expect that in near future the adequate theoretical model describing adsorption-induced changes in electrophysical characteristics of semiconductor adsorbent will be developed. 

Summing up the above said we examined in our experiments the adsorption-caused change in ohmic electric conductivity and the inclination angle of pre-relaxation VAC of polycrystalline oxide adsorbents. 

In above sections the main attention has been paid to adsorption-caused change in electrophysical characteristics of semiconductor adsorbent caused by surface charging effects. However, as it was mentioned in section 1.6, the change in electrophysical characteristics of such adsorbents can be caused by other mechanisms, e.g. by direct interaction of absorbate with the surface defects provided (as in the case of oxide adsorbents) by superstoichiometric atoms of metals and oxygen... 

An a priori information on the centers of adsorption of various particles on oxide adsorbents is important from the standpoint of having an option of separate detection of various particles in their mixtures [200]. 

On the basis of consideration of this model one can easily obtain expressions describing kinetics of the change in electric conductivity of sintered partially reduced oxide adsorbent during development of direct and inverse reaction described by expression (2.17). The consumption of superstoichiometric metal atoms which takes place during adsorption of O2 is described by equation... 

As it has been shown in Section 1.11 a comparison of experimental data on effects of adsorption of various particles on electric conductivity of oxide adsorbents results in conclusion that the dominant role in this... 

We should note that expressions similar to (2.100) and (2.101) obtained in paper [120] have been experimentally confirmed in numerous systems free radical - oxide adsorbent [1, 34, 57, 120]. 

These expressions describe the kinetics and the value of response of electric conductivity in oxide adsorbent during adsorption of atomic hydrogen. In general case they are applicable for adsorption of any radical particles of the donor type. However, in each specific case any of the processes of schematics (2.114) controlled by specificity of each system [129] may be a dominant process controlling both the kinetics and the stationary value of electric conductivity. 

Thus, we have considered in detail various theoretical models of effect of adsorption of molecular, atom and radical particles on electric conductivity of semiconductor adsorbents of various crystalline types. Special attention has been paid to sintered and partially reduced oxide adsorbents characterized by the bridge type of intercrystalline contacts with the dominant content of bridges of open type because of wide domain of application of this very type of adsorbents as sensitive elements used in our physical and chemical studies. 

V.N. Tsivenko, Adsorption of Nitrogen Atoms and Nitrogen-Hydrogen Radicals on Oxide Adsorbents by Electxoconductivity Technique, PhD (Chemistry) Thesis, Moscow, 1973... 

V.I. Tsivenko, Studies of Adsorption Nitrogen Atoms and Nitrogen-Hydrogen Radicals on Oxide Adsorbents by Electroconductivity Technique, PhD (Chemistry) Thesis, Moscow, 1973 B.S. Agayan, I.A. Myasnikov and V.I. Tsivenko, Zhum. Fiz. Khimii, 47 (1973) 1292 - 1296... 

Gas compressibility correction factor (GC) 4 Gas purifier 233, 764 Gas-solid chromatography 199 carbosieves 204 glassy carbon 204 graphitlzed carbon blacks 202 modifiers 204 inorganic oxide adsorbents 200... 

TYPICAL PROPERTIES OF INORGANIC OXIDE ADSORBENTS USED FOR TLC... 

The ferric oxide adsorbent, once it has been transformed chemically, can be regenerated in an oxidation step ... 

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