Bases, adsorption

The conformity to laws of adsorption, in particular their thermodynamic fundamentals, is independent of whether a water-air or a water-apolar oil interface is considered, provided that the surfactant is soluble only in one phase. If the oil phase in a liquid two-phase system is apolar, this condition is valid for many surfactants. Thus, all surfactants with an adequate solubility in water are almost insoluble in the hydrocarbon phase. If this condition is not met, e.g., in the system water-amyl alcohol, the thermodynamically based adsorption isotherms are more complicated to set up [39]. 

The major processes affecting the geochemical fate of hazardous inorganics are acid-base adsorption-desorption, precipitation-dissolution, complexation, hydrolysis, oxidation-reduction, and catalytic reactions. The significance of these processes to inorganic wastes is discussed only briefly here additional information on individual elements is given in Table 20.16. 

In Part Four (Chapter eight) we focus on the interactions of mixed systems of surface-active biopolymers (proteins and polysaccharides) and surface-active lipids (surfactants/emulsifiers) at oil-water and air-water interfaces. We describe how these interactions affect mechanisms controlling the behaviour of colloidal systems containing mixed ingredients. We show how the properties of biopolymer-based adsorption layers are affected by an interplay of phenomena which include selfassociation, complexation, phase separation, and competitive displacement. 

Resin-Based Adsorption Processes for Reactions in High-Temperature Water... 

Physicochemical methods, i.e. adsorption of probe molecules followed by varied analytical techniques (gravimetry, chromatography, calorimetry, spectroscopic techniques, etc.) are currently used for estimating more precisely the concentration of the potential active sites.[34 36] However, very few methods are well adapted for this purpose most of the methods employed for the characterization of the acidity of solid catalysts lead to values of the total concentrations of the acid sites (Brpnsted + Lewis) and to relative data on their strength, whereas few of them discriminate between Lewis and Brpnsted acid sites. It is however the case for base adsorption (often pyridine) followed by IR spectroscopy, from which the concentrations of Brpnsted and Lewis sites can be estimated from the absorbance of IR bands specific for adsorbed molecules on Brpnsted or Lewis sites. 

The acid properties of NaH zeolite (NaHY, NaHMOR, NaHMFI) series with different Na contents were investigated with adsorption microcalorimetry23. Whatever the zeolite, the initial heat of base adsorption (NH3, pyridine, etc.) as well as the total acidity increases with the exchange of Na+ by FT Thus for a series of NaHMOR zeolites24, the initial heat of ammonia adsorption passes from 145 to 184 kJ mol"1 when the exchange rate passes from 33 to 98 % and the number of acid sites with adsorption heat greater than 110 kJ mol 1 passes from 0.4 to 9.3 1020 g"1 i.e. from 7% of the theoretical number of protonic sites to 56 %. 

Avramescu ME, Sager WFC, Bomeman Z, and Wessling M. EVAL-based adsorptive membranes for bilimbin removal. J. Chromatogr. B 2004 803 215-223. 

In addition to pore size distribution, the surface chemistry of the activated carbon can have an important influence on the adsorption of certain compounds. As the adsorptive surface of most activated carbons is hydrophobic, they are best suited for the removal of neutral organic molecules, while polar and ionic compounds show much less affinity for adsorption. For the adsorption of polar compounds such as phenol, research has shown that the carbon surface chemistry is more relevant than the total available adsorption capacity or surface area [72-74]. It has been found that the presence of acidic surface oxides, whose concentration can be increased by oxygen adsorption or chemical treatment, leads to a decrease in adsorptive capacity for compounds such as phenols and increases the base adsorption capacity [75 [. 

Here Xa, Ya are strictly equilibrium mole fractions for component A in the adsorbed phase and adsorbate (fluid) phase, respectively as are Xb, Fb for component B. For equilibrium-based adsorptive separation process, the adsorbent selectivity is the same as the separation factor as defined in Eq. (1). Apparently, this definition is not applicable to other processes based on kinetic and steric effects. In a kinetically controlled adsorption process, the adsorbent selectivity depends on both equilibrium and kinetic effects. A simplified definition for adsorbent separation factor is given by Ruthven et al. ... 

Unlike weak bases adsorption of acetonitrile reveals Lewis acid sites responsible for the IR-band at 2310-2305 cm (Fig.3b). The appearance of... 

The characteristics of the oxide produced at one temperature are altered when a carbon is reheated at a different temperature. A carbon prepared at 400° C, with base-adsorbing properties, when subsequently heated to 900° C becomes acid-adsorbing. If this carbon is again reheated in air at 400° C, base-adsorption reappears. This last change also occurs slowly at room temperature in the presence of moist oxygen. Thus it appears that the surface oxides are reversible from one form to another although the effect is not entirely independent of previous treatment. 

The factors affecting the hydrogen sulfide removal from Elkton field gas were evaluated in the extensive optimization study [70]. It was carried out to apply activated carbon based adsorption/oxidation to the industrial environment. In order to make the process as simple and economical as possible the temperature, pressure, O/H2S ratio, water vapor content in the feed gas, minimizing production of SO2 and time achieving high conversion of H2S to sulfur and water were varied [70], Moreover, the efficiency of using thermally regenerated carbon was evaluated. 

Many studies have been undertaken during the last decade to develop new methods of acid strength measurement. In these studies it was assumed that such parameters as the differential heat of base adsorption, the quantity of irreversibly bonded base, the shift of i.r. bands of OH groups or adsorbed bases, the chemical shift 5 of surface H" ", the catalytic activity or the selectivity of test reactions could be used to describe the acid strength of surface centres. 

Base Adsorption.- Deeba and Hall, proposed description of a catalyst s acid strength by the value of P 3h+ irreversibly... 

The acid strength of surface BreSnsted centres can be followed by measurements of the OH band shift caused by weak base adsorption. Bellamy, Hallam and Williams, have shown that relative... 

Anatase is another interesting phase of Ti02- The natural crystallographic faces are the (101) and (100) orientations. The acid-base adsorption mechanism is very similar to the one of the metal/oxide already discussed. On the (101) surface, molecular adsorption is exothermic (16.6 kcal/mol for full coverage) [99]. In contrast, water dissociates on the (001) plane, which is more reactive [100]. It is worth noticing that the surface morphology has a very important effect on the hydroxyl coverage [100]. 

Li Z (2000) Theory and large-scale application prospect of carbon-based adsorptive hydrogen storage materials. Mater Rev 14 3-5. 

FIGURE 1.8 Base adsorption capacity in relation to evacuation temperature. (From Bansal, R.C., Bhatia, N., and Dhami, T.L., Carbon, 16, 65, 1978. With permission.)... 

FIGURE 6.8 Relationship between the maximum amount of Cu(II) ions adsorbed and base adsorption capacity. (Source Goyal, M., Rattan, V.K., Aggarwal, D., and Bansal, R.C., Colloids and Surfaces, A. Physico-Chem. and Engg. Aspects, 190, 229, 2001. With permission.)... 

Karanfil and Kilduff studied the adsorption of two synthetic organic contaminants, trichloroethylene (TCE) and trichlorobenzene (TCB), on coal-based and wood-based granulated activated carbons. The activated carbon surface was modified by liquid-phase oxidation with nitric acid and by degassing in an inert atmosphere. The activated carbons were characterized by elemental analysis, surface area and pore-size distribution, and acid-base adsorption techniques. The adsorption isotherms were determined by equilibrating a known weight of the carbon sample with different concentrations of TCE and TCB solutions, and analyzing the solution by gas chromatography. 

The dependence of organic base adsorption on pH is illustrated by the case of benzidine. This base is adsorbed from aqueous solutions on Ca- and Na-montmorillonite as a mixture of monovalent and divalent cations at pH 3 and as neutral molecules when the pH is higher. Aniline is also adsorbed as a mixture of monovalent cations and neutral molecules at pH = 3.2. Amounts adsorbed are in excess of the exchange capacity of the clay, and in both cases intermolecular association by hydrogen bonds (see Fig. 1) is assumed to exist between cations and molecules in the interlayer space (23). 

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