Applications of adsorption

Widespread adsorption occurs when a gas or a solution meets an interface. Here we mention only a few cases where adsorption is of practical interest. 

Adsorption from the gas phase is commonly applied in determining the specific surface area of finely dispersed materials. For that purpose, assumptions have to be made concerning the dimensions of the gas molecules and the structure of the adsorbed layer under saturation conditions (fully packed monolayer, multilayer, etc.). Small gas molecules may enter pores and capillaries in porous materials. Hence, by comparing the surface area determined by gas adsorption with the outer surface area obtained from, for example, electron microscopy, the porosity of the material can be estimated. Moreover, by using different types of gas having different molecular dimensions, an impression of the pore size distribution may be obtained. 

Gas adsorption is also applied to aid mechanical pumps in achieving ultrahigh vacuum. Further, surfaces may act as catalysts for reactions that occur relatively 

Activated charcoal is often used as an adsorbent in air and water filters as well as in medical preparations to eliminate poisonous substances. 

Various applications of adsorption are based on the concomitant reduction of the interfacial tension. The inflation of the lungs of newborns requires a large fluid/air interface. Formation of that interface is facilitated by the adsorption of lung surfactant that is released to the alveoli. Other examples of interfacial tension reduction are found in wetting phenomena such as impregnation, flotation, cleansing, and so on. These phenomena are explained and discussed in Section 8.7. Finally, adsorption of surfactants at gas/liquid and liquid/liquid interfaces to prepare foams and emulsions should be mentioned (see Chapter 18). 

Hydrocarbon trapping during engine cold starting 

Separation of para-xylene from other xylenes and ethylbenzene 

Na-A is t5 pically used for drying, because of its high capacity for water adsorption and narrow pore openings. 

There is a need for specially designed adsorbents for halocarbon refrigerant fluids, to avoid decomposition of the zeolite. 

Once CO2 is largely removed by adsorption in basic solution, residua] CO2 and H2O are removed by molecular sieves to 1 ppm CO2 and N2 removed non-cryogenically over molecular sieves 

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The enhanced concentration at the surface accounts, in part, for the catalytic activity shown by many solid surfaces, and it is also the basis of the application of adsorbents for low pressure storage of permanent gases such as methane. However, most of the important applications of adsorption depend on the selectivity, ie, the difference in the affinity of the surface for different components. As a result of this selectivity, adsorption offers, at least in principle, a relatively straightforward means of purification (removal of an undesirable trace component from a fluid mixture) and a potentially useflil means of bulk separation. 

Adsorption — An important physico-chemical phenomenon used in treatment of hazardous wastes or in predicting the behavior of hazardous materials in natural systems is adsorption. Adsorption is the concentration or accumulation of substances at a surface or interface between media. Hazardous materials are often removed from water or air by adsorption onto activated carbon. Adsorption of organic hazardous materials onto soils or sediments is an important factor affecting their mobility in the environment. Adsorption may be predicted by use of a number of equations most commonly relating the concentration of a chemical at the surface or interface to the concentration in air or in solution, at equilibrium. These equations may be solved graphically using laboratory data to plot "isotherms." The most common application of adsorption is for the removal of organic compounds from water by activated carbon. 

The application of adsorption to contaminated groundwater remediation is not only an important subject, but one we could expand upon into several volumes unto itself. At best, all we can do is try to provide a concise overview in this volume. 

Adsorption phenomena from solutions onto sohd surfaces have been one of the important subjects in colloid and surface chemistry. Sophisticated application of adsorption has been demonstrated recently in the formation of self-assembhng monolayers and multilayers on various substrates [4,7], However, only a limited number of researchers have been devoted to the study of adsorption in binary hquid systems. The adsorption isotherm and colloidal stabihty measmement have been the main tools for these studies. The molecular level of characterization is needed to elucidate the phenomenon. We have employed the combination of smface forces measmement and Fomier transform infrared spectroscopy in attenuated total reflection (FTIR-ATR) to study the preferential (selective) adsorption of alcohol (methanol, ethanol, and propanol) onto glass surfaces from their binary mixtures with cyclohexane. Om studies have demonstrated the cluster formation of alcohol adsorbed on the surfaces and the long-range attraction associated with such adsorption. We may call these clusters macroclusters, because the thickness of the adsorbed alcohol layer is about 15 mn, which is quite large compared to the size of the alcohol. The following describes the results for the ethanol-cycohexane mixtures [10],... 

Other plant-scale applications to pollution control include the flotation of suspended sewage particles by depressurizing so as to release dissolved air [Jenkins, Scherfig, and Eckhoff, Applications of Adsorptive Bubble Separation Techniques to Wastewater Treatment, in Lemlich (ed.). Adsorptive Bubble Separation Techniques, Academic, New York, 1972, chap. 14 and Richter, Internat. Chem. Eng, 16,614 (1976)]. Dissolved-air flotation is also employed in treating waste-water from pulp and paper mills [Coertze, Prog. Water TechnoL, 10, 449(1978) and Severeid, TAPPl 62(2), 61, 1979]. In addition, there is the flotation, with electrolytically released bubbles [Chambers and Cottrell, Chem. Eng, 83(16), 95 (1976)], of oily iron dust [Ellwood, Chem. Eng, 75(16), 82 (1968)] and of a variety of wastes from surface-treatment processes at the maintenance and overhaul base of an airline [Roth and Ferguson, Desalination, 23, 49 (1977)]. 

J.A. (1992) Applications of adsorption microcalorimetry to the study of heterogeneous catalysis. Adv. Catal.,... 

The primary area of application of adsorption chromatography on polar stationary phases is in the separation of nonpolar to moderately polar organic compounds. A preliminary decision on whether or not this system is adequate can be based on sample solubility in such "nonpolar" solvents as aliphatic or aromatic hydrocarbons, haloalkanes, perhaps with the addition of a few percent of esters, acetonitrile, or even alcohols. When the sample is soluble or miscible with these eluents, the use of a polar stationary phase may be the best approach to chromatographic separation. 

Many problems that arise in the application of adsorption chromatography can be related to the slow attainment of equilibrium distribution of the omnipresent water and other modulators tetween eluent and stationary phase. With suitable precautions, such as moisture control, reproducible work is possible with both silica and alumina as the stationary phase. 

An apparatus with high sensitivity is the heat-flow microcalorimeter originally developed by Calvet and Prat [139] based on the design of Tian [140]. Several Tian-Calvet type microcalorimeters have been designed [141-144]. In the Calvet microcalorimeter, heat flow is measured between the system and the heat block itself. The principles and theory of heat-flow microcalorimetry, the analysis of calorimetric data, as well as the merits and limitations of the various applications of adsorption calorimetry to the study of heterogeneous catalysis have been discussed in several reviews [61,118,134,135,141,145]. The Tian-Calvet type calorimeters are preferred because they have been shown to be reliable, can be used with a wide variety of solids, can follow both slow and fast processes, and can be operated over a reasonably broad temperature range [118,135]. The apparatus is composed by an experimental vessel, where the system is located, which is contained into a calorimetric block (Figure 13.3 [146]). 

Purification of liquids by solid adsorbents has been practiced from early times, and even today, with the tremendous expansion of chemical industry, the removal of undesired components from liquids is the main practical application of adsorption phenomena at solid-liquid interfaces. Both the range of substances to be purified by adsorption and the range of appropriate adsorbents has increased immensely, and thus the number of experimental investigations has also. 

J. Wang, B.S. Grabaric, Application of adsorptive stripping voltammetry for indirect measurement of nonelectroactive ions using competitive complex formation reactions, Mikrochim. Acta 100 (1990) 31-40. 

In this work, we will show that the addition of TCM to the feedstream in the methane conversion process results in the enhancement of the conversion of methane and the selectivity to C2 hydrocarbons on praseodymium oxide primarily as a result of the formation of praseodymium oxychloride, in contrast with the production of carbon oxides on praseodymium oxide in the absence of TCM (8-10). The surface properties of these catalysts are characterized by application of adsorption experiments and X-ray photoelectron spectroscopy (XPS). 

Application of adsorptive stripping analysis to the determination of nucleic acids at mercury electrodes has also been reported [195]. Tomschik etal. [196] have studied reduction and oxidation of peptide nucleic acid and DNA at mercury and carbon electrodes. The authors have utilized cyclic and square-wave voltammetries to study reduction and oxidation signals of single-stranded peptide nucleic acid and DNA decamers and pentadecamers. 

These early applications of adsorption were based on intuition and not on a systematic study. It was in 1773 that Scheele made the first quantitative observations in connection with adsorption, whereas F. Fontana in 1777 reported his experiments on the uptake of gases from charcoal and clays. However, the modern application of adsorption is attributed to Lowitz. Lowitz used charcoal for the decolorization of tartaric acid solutions in 1788. The next systematic studies were published by Saussure in 1814. He concluded that all types of gases can be taken up by a number of porous substances and this process is accompanied by the evolution of heat (Dabrowski, 2001). 

The first practical applications of adsorption were based on the selective removal of individual components from then- mixtures using other substances. The first filters for water treatment were installed in Europe and the United States in 1929 and 1930, respectively. Activated carbon was recognized as an efficient purification and separation material for the synthetic chemical industry in the 1940s. By the late 1960s and early 1970s, activated carbon was used in many applications for removing a broad spectrum of synthetic chemicals from water and gases. 

There ate many environmental applications of adsorption in practice and many others are being developed (Noble and Terry, 2004). Activated carbons and clays are frequently used for the removal of organic contaminants, such as phenol and aniline, both of which are prevalent in industry wastewaters and are known to have a significant negative impact on marine life and human health (IRIS, 1998 Dabrowski et al., 2005). Moreover, the adsorption on inexpensive and efficient solid supports has been considered a simple and economical viable method for the removal of dyes from water and wastewater (Forgacsa et al., 2004). Activated carbon, clays, coal, vermiculite, and other adsorbents have been used for this purpose. Specifically, adsorption can be employed in (Noble and Terry, 2004 Dabrowski, 2001) ... 

Other important applications of adsorption are the control of greenhouse gases (CO, CH4, N20), the utilization of CH4, the flue gas treatment (SOx, N()x, Hg removal), and the recovery of the ozone-depleting CFCs (Dabrowski, 2001). Activated carbons and hydrophobic zeolites are used for the adsorption of HCFCs (Tsai, 2002). 

Another special application of adsorption in space is presented by Grover et al. (1998). The University of Washington has designed an in situ resource utilization system to provide water to the life-support system in the laboratory module of the NASA Mars Reference Mission, a piloted mission to Mars. In this system, the Water Vapor Adsorption Reactor (WAVAR) extracts water vapor from the Martian atmosphere by adsorption in a bed of type 3A zeolite molecular1 sieve. Using ambient winds and fan power to move atmosphere, the WAVAR adsorbs the water vapor until the zeolite 3A bed is nearly saturated, and then heats the bed within a sealed chamber by microwave radiation to drive off water for collection. Tire water vapor flows to a condenser where it freezes and is later liquefied for use in tire life-support system. 

Development of solvent extraction processes in the petroleum industry and theoretical aspects of solvent extraction are reviewed. Six extraction processes which have received industrial acceptance are described and performance characteristics of furfural, phenol, and Duosol processes are compared. Data are presented to demonstrate the applicability of adsorption analyses for stock evaluation and prediction of commercial extraction yields. Correlations for predicting solvent requirements and layer compositions and process design and engineering considerations are included. The desirability of further fundamental work to facilitate design calculations from physical data is suggested. 

Finally, the material may also be regarded as a mixture of fundamentals and applications. Although the entire book stresses principles, applications are considered from time to time as examples of more abstract ideas. This is also the intent of the sections on applications in this chapter. In addition, however, many applications of adsorption phenomena are the basis of large and important areas of technology. To omit mention of them would lead to a very incomplete picture of these fields. As it is, many important applications must be omitted for lack of space, and those mentioned are sketched in only a superficial way. 

Davies, J. T., and Rideal, E. K., Interfacial Phenomena, Academic Press, New York, 1961. (Undergraduate level. A standard reference on interfacial phenomena. Somewhat outdated, but has good discussions on many of the conventional applications of adsorption of surfactants... 

F. L. Slejko, ed., Adsorption Technology, Marcel Dekker, Inc., New York, 1985, pp. 23—32. A good account of the theory, design, and application of adsorption systems. 

To a large extent, the discovery and application of adsorption phenomena for the modification of electrode surfaces has been an empirical process with few highly systematic or fundamental studies being employed until recent years. For example, successful efforts to quantitate the adsorption phenomena at electrodes have recently been published [1-3]. These efforts utilized both double potential step chronocoulometry and thin-layer spectroelectrochemistry to characterize the deposition of the product of an electrochemical reaction. For redox systems in which there is product deposition, the mathematical treatment described permits the calculation of various thermodynamic and transport properties. Of more recent origin is the approach whereby modifiers are selected on the basis of known and desired properties and deliberately immobilized on an electrode surface to convert the properties of the surface from those of the electrode material to those of the immobilized substance. 

Berger LM (1993) Application of Adsorption for the Characterization of Solids in Ceramic and Related Technologies. In Aldinger F (ed) PTM 93, DGM Information-sgesellschaft, Oberursel, p 677... 

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