Solid adsorbents characteristics

A variety of experimental data has been found to fit the Langmuir equation reasonably well. Data are generally plotted according to the linear form, Eq. XVn-9, to obtain the constants b and n from the best fitting straight line. The specific surface area, E, can then be obtained from Eq. XVII-10. A widely used practice is to take to be the molecular area of the adsorbate, estimated from liquid or solid adsorbate densities. On the other hand, the Langmuir model is cast around the concept of adsorption sites, whose spacing one would suppose to be characteristic of the adsorbent. See Section XVII-5B for an additional discussion of the problem. 

Arbitrary the book can be divided into two complementary parts. The first one describes the physical and chemical basics leading to description of the method of semiconductor sensors. The mechanisms of underlying processes are given. These processes involve interaction of gas with the surface of semiconductor adsorbent which brings about tiie change of electric and physics characteristics of the latter. Various models of absorption-induced response of electric and physics characteristics of semiconductor adsorbent are considered. Results of numerous physical and chemical experiments carried out by the authors of this book and by other scientists underlying the method of semiconductor sensors are scrupulously discussed. The possibility of qualitative measurements of ultra-small concentrations of molecules, atoms, radicals as well as excited particles in gases, liquids and on surfaces of solids (adsorbents and catalysts) is demonstrated. 

In industrial operations, adsorption is accomplished primarily on the surfaces of internal passages within small porous particles. Three basic mass transfer processes occur in series (1) mass transfer from the bulk gas to the particle surface, (2) diffusion through the passages within the particle, and (3) adsorption on the internal particle surfaces. Each of the processes depends on the system operating conditions and the physical and chemical characteristics of the gas stream and the solid adsorbent. Often, one of the transfer processes will be significantly slower than the other two and will control the overall transfer rate. The other process will operate nearly at equilibrium. 

The characteristics of solid adsorbents that are pertinent to accumulation are (1) functionality, (2) surface area, (3) pore size, (4) particle size and shape, (5) chemical stability, and (6) solubility. The first three characteristics are the most important, and these are compared for several solid adsorbents as part of Table I. Certain features of this table will be explained before discussing the six pertinent characteristics of solid adsorbents. 

Functionality. Surface affinity to different solutes is the most important characteristic of solid adsorbents. These affinities depend on the chemical functionality and the surface orientation of the polymer. Affinity can be estimated in the static mode by measuring adsorption isotherms for different organic solutes. 

For the in situ product separation of plant cell culture, liquid-solid culture systems for plant cells consisting of an aqueous nutrient phase and polar solid adsorbents have been preferred because many products of plant cells are expected to be polar in character and bound weakly to the lipophilic phase of liquid-liquid systems. The differences in the acid-base properties and sorption characteristics of alkaloids further offer the potential for selectively absorbing specific alkaloids from a mixture. 

This equation is written on the basis of a unit mass, usually a gram or a kdogram, of solid adsorbent. Thus n is the specific amount adsorbed, i.e., the number of moles of adsorbate per unit mass of adsorbent. Moreover, area A is defined as the specific surface area, i.e., the area per unit mass of adsorbent, a qrrantity characteristic of a particular adsorbent. The molar area, a = A/ , is the surface area per mole of adsorbate. 

Tamon, H. and Okazaki, M. (1996). Desorption characteristics of aromatic compounds in aqueous solution on solid adsorbents. /. Colloid Interface Sci., 179, 181—7. 

Sample Preparation Slurries, Solvent Evaporated Samples and Equilibrium Samples. The adsorption of probes on microcrystalline cellulose or native cellulose, on the surface of different pore size silicas or alumina, and on silicalite surfaces (or other zeolites) has to be made in a differentiated manner, according to each s adsorbent characteristics. Adsorption of probes onto these powdered solids can be performed from a solution containing the probe or from a gas phase. 

The NMR results are in agreement with results from DRS, TSDC, DSC, XRD, and other methods with respect to clusterization of the adsorption layers. It is possible to estimate the size distribution functions of water clusters that become (melting) or remain (freezing) liquid at T<273 K (NMR) or relaxing (TSDC, DRS, DSC) at different temperatures. TSDC and NMR cryoporometry give results for solid adsorbents in agreement with the structural characteristics estimated from nitrogen adsorption isotherms. However, NMR and TSDC cryoporometry can be applied to systans (e.g., seeds, cells, tissues) which cannot be studied by conventional adsorption methods to determine their structural and textural characteristics. 

MOR depends on whether the silver is reduced. Table 14.9 summarizes the solid adsorbents available for iodine capture. The silver-based alumina, silica, and mordenite adsorbents have comparable characteristics and are the currently preferred sorbents. An advantage of the mordenite is that the regeneration of the sorbent is possible, thereby utilizing the silver over the course of several cycles. The stripped iodine is then available for sorption using a cheaper metal or conversion to a waste form preferred for long-term storage. 

The significance of pores in the adsorption processes largely depends on their sizes. Because sizes of micropores are comparable to those of adsorbate molecules, all atoms or molecules of the adsorbent can interact with the adsorbate species. That is the fundamental difference between adsorption in micropores and larger pores like meso- and macropores. Consequently, the adsorption in micropores is essentially a pore-filling process in which their volume is the main controlling factor. Thus as the essential parameter characterizing micropores is their volume usually referred to a unit of the solid and characteristics of their sizes. This characteristics is expressed by the so-called micropore - distribution function evaluated mainly from the low concentration adsorption data [25], Determination of microporous adsorbent specific area from generally accepted adsorption equations is only of a formal character. 

Chemical methods based on the study of extractant distribution (TBP) on TVEX-TBP resins were used to demonstrate that TBP is adsorbed by the TVEX porous matrix by physical adsorption. Extractant wash-out from the TVEX matrix is an important characteristic for metal extraction applications of solid adsorbents as TVEX since it may influence the physical-chemical properties of the extraction process. Infrared (IR) spectroscopy analysis of TVEX-TPB resins show the absence of shift for stretching frequency of the P = O group in comparison to the stretching frequency assignment for liquid TBP as an indication that TBP is hold by matrix surface due to physical adsorption as was confirmed from the by enthalpy values of TBP distribution from the TVEX matrix of 45.0 0.5 kJ/mol [10]. 

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