Adsorption principles

Adsorption of fluids is based on the selective binding of components on the surface of a solid. In catalysis, adsorption is the essential first step followed by a chemical transformation of the adsorbed species (Section 4.5). In purification of gases and liquids, no further chemical reaction takes place, and the loaded solid, the 

If a gas is in contact with a solid, equilibrium is established between the molecules in the gas phase and the corresponding adsorbed species. An approach to 

We derive the Langmuir isotherm by treating the adsorption process like any other chemical equilibrium, except that it is established between gas molecules (species A), vacant surface sites of number Uvacam. and species adsorbed on the surface (number Ha). For a non-dissociative adsorption of species A, adsorption is represented by the following chemical equation  

The total number of surface sites, rtt, is equivalent to the sum of Uyacant and Ha, and so we inherently have assumed a fixed number of localized surface sites. We now formally define an equilibrium constant (e.g., here with n/A as a measure of the surface concentration in mol m )  

Equation (3.3.38) leads to the surface coverage 0a relative to the monolayer 

Physical adsorption occurs due to van der Waals (dispersion) or electrostatic forces. The attraction depends on the polar nature of the fluid component being adsorbed as well as that of the adsorbent. Van der Waals forces are directly related to the polarizability. An estimate of the relative strength of interaction is based on the sorbate size and polarizability. Electrostatic forces include polarization forces, field-dipole interactions and field gradient-quadrupole interactions. These forces arise when the surface is polar. In the case of a polar solvent like water with non-polar organic impurities, the organic molecules will prefer to stick to a non-polar adsorbent such as activated carbon rather than remain in the polar solvent. Physical adsorption is reversible. Physical sorption is sensitive to temperature, relatively non-specific regarding sorbates, relatively fast kineticaUy, and has a low heat of adsorption ( 2A//vap)- Multiple sorbate layers can form on the sorbent surface. 

Chemical adsorption (chemisorption) occurs when the attraction between the adsorbent and the adsorbate can form a covalent bond, or when a chemical reaction occurs between the adsorbent and adsorbate. Usually chemical adsorption will only allow a single layer of molecules (monolayer) to accumulate on the surface of the adsorbent. Chemical adsorption is usually irreversible. Chemisorption is typically more specific, kineticaUy slower and has a larger heat of adsorption ( 3AHvap). 

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Hyperbolic, based on the Langmuir adsorption principle for instance,... 

The sizing methods involve both classical and modem instrumentations, based on a broad spectrum of physical principles. The typical measuring systems may be classified according to their operation mechanisms, which include mechanical (sieving), optical and electronic (microscopy, laser Doppler phase shift, Fraunhofer diffraction, transmission electron miscroscopy [TEM], and scanning electron microscopy [SEM]), dynamic (sedimentation), and physical and chemical (gas adsorption) principles. The methods to be introduced later are briefly summarized in Table 1.2. A more complete list of particle sizing methods is given by Svarovsky (1990). 

High-performance liquid chromatography (or less common, high-pressure liquid chromatography, HPLC) is a preferred method of analysis for many compounds because it does not require the high temperatures used in gas chromatography. Separations in HPLC can be based on either a size exclusion or on an adsorption principle. The size exclusion mode is useful for separating fatty acids from... 

The surface of all inorganic materials exposed to ambient (humid) air is always covered with a thin layer of water adsorbed from the gas phase. The thickness of the adsorbed water layer varies with the humidity and surface chemistry. This water layer has been shown to reduce wear in MEMS operation. However, the high surface tension of the water film can cause an in-use stiction problem. The gas-phase lubrication concept discussed here employs the same equilibrium adsorption principle as the water adsorption in humid environments. The difference is that our approach utilizes a surfactant-like molecule that can provide low adhesion and good lubrication. The entry summarizes the advantages of gas-phase lubrication for MEMS devices and discusses the effect of alcohol adsorption on the adhesion and lubrication of silicon oxide surfaces. 

Surface reactivity was measured on selected samples by Pt(acac)2 adsorption. In order to homogenize the surface of the samples, the tested solids were exposed 12 h to a water saturated air at room temperature before calcination 2 h at 500 °C in a diy air stream. The composite was cooled down to room temperature overnight in the same air stream. After the pre-treatment, the solid was impregnated during 8 h at room temperature with a 4 mM solution of platinum bis-acetylacetonate (R(acac)2) in toluene with a solvent to solid ratio of 5 mL g" The kinetics of Pt(acac)2 impregnation, i.e. the evolution of Pt precursor concentration in solution, was followed by UV-vis. Spectra were recorded in transmission mode on a PERKIN-ELMER Lambdall UV-vis spectrometer, using a 1 mm quartz cells. Pt(acac)2 adsorption principle and details on the data treatments can be found in [11]. 

The postulate of Vroman addresses only one variable, namely concentration, that may be expected to influence a protein s adsorption competitiveness. From known adsorption principles we may reasonably assume that protein affinity for the surface (free energy of adsorption), protein-protein interactions in the layer, and kinetic factors such as activation energy of adsorption will also influence competitive adsorption. The idea of a sequenced based at least partly on concentration seems reasonable, since initially difTusion would ensure relatively high concentrations of the abundant proteins, and only later would the true relative affinities of the proteins for the surface be expressed. This idea raises tantalizing questions such as whether all surfaces end up with the same protein layer or whether the sequence stops at different points on different surfaces. 

The advantages of ion-exchange chromatography are its straightforward adsorption principle that is based on the Coulomb interaction that can be adjusted according to the isoelectric point (pl) of the proteins to be separated. The binding mechanism can be tuned over a wide area of conditions by choosing different types... 

Finally, when dealing with a complex mineral/organic matrix, the combination of separations according to size exclusion and adsorption principles is possible on the same column packing. 

Further purification of HP-j8-CDs can be carried out through the thin layer chromatography. A formula for developing was propanol, ethyl acetate, aqua ammonia and water were prepared by 6 1 1 3, or acetonitrile, water, aqua ammonia was mixed by 6 3 1, the latter formula has a shorter developing time. The color development reagents are cerous sulfate 1 g, ammonium molybdate 24 g, concentrated sulfuric acid 50 mb, 450 mL deionized water. Because of the adsorption principle of the silica gel, the more the substituent on the HP- -CDs, the faster the molecules will move. Therefore, the high DS HP-)3-CDs move a long distance. Furthermore, HP-j8-CDs can be purified by sihca column. The mobile phase was chloroform/methanol (100 1) [26]. 

ABSTRACT Based on low-temperature nitrogen adsorption principle, the pore structure of coal particles is tested and adsorption isotherms of coal particles with different size are obtained by Quantachrome Autosorb-iQ automatic specific surface area and pore size distribution analyzer. Then, microstructure characteristic parameters such as specific surface area, pore volume and average pore size of coal particles are calculated. Besides, fractal dimension of the internal surface of coal particles is calculated with FHH fractal theory. The relationship between fractal dimension and pore structure parameters together with the adsorption capacity of coal particles is analyzed. Studies show that fractal dimension can characterize the variation of characteristic parameters such as specific surface area and total pore volume of coal particles. In addition, with the increase of fractal dimension, the surface heterogeneity of pore structure is strengthened and so is adsorption capacity. The findings can provide a certain theoretical foundation for mechanism study on coal gas adsorption, desorption and seepage. 

The adsorption isotherm of coal particles with different size were studied using Autosorb-iQ automatic specific surface area and pore size distribution analyzer based on low temperature nitrogen adsorption principle. 

The test is based on the adsorption principle of clay minerals using methylene blue dye. During the test, the quantity of methylene blue required to cover all clayey ingredients is measured. The quantity of methylene blue dye adsorbed is related to the specific surface of the clay mineral (montmorillonite, illite and kaolinite). Active clay minerals have a large specific surface in contrast to inactive clay materials. As a result, the required methylene blue quantity will be proportional to the quantity and the type of clay minerals. 

Adsorption principles, design data and adsorbent materials for industrial applications A Bibliography (1967-1997)... 

Thin layer chromatography may be either carried out by the adsorption principle (if the thin layer is prepared by an adsorbent such as Kieselguhr, or alumina) or by the partition principle (if the layer is prepared by a substance such is silica gel which holds water like the paper). More recently, thin layer gel filtration chromatography Is also performed as we will see later. In this case, the layer is made up of controlled pore beads of various gels. 

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