Absorption/adsorption

See Absorption Adsorption Goad conversion processes, cleaning and desulfurization Gas, naturae. 

Ordinary diffusion involves molecular mixing caused by the random motion of molecules. It is much more pronounced in gases and Hquids than in soHds. The effects of diffusion in fluids are also greatly affected by convection or turbulence. These phenomena are involved in mass-transfer processes, and therefore in separation processes (see Mass transfer Separation systems synthesis). In chemical engineering, the term diffusional unit operations normally refers to the separation processes in which mass is transferred from one phase to another, often across a fluid interface, and in which diffusion is considered to be the rate-controlling mechanism. Thus, the standard unit operations such as distillation (qv), drying (qv), and the sorption processes, as well as the less conventional separation processes, are usually classified under this heading (see Absorption Adsorption Adsorption, gas separation Adsorption, liquid separation). 

Once an undesirable material is created, the most widely used approach to exhaust emission control is the appHcation of add-on control devices (6). Eor organic vapors, these devices can be one of two types, combustion or capture. AppHcable combustion devices include thermal iaciaerators (qv), ie, rotary kilns, Hquid injection combusters, fixed hearths, and uidi2ed-bed combustors catalytic oxidi2ation devices flares or boilers/process heaters. Primary appHcable capture devices include condensers, adsorbers, and absorbers, although such techniques as precipitation and membrane filtration ate finding increased appHcation. A comparison of the primary control alternatives is shown in Table 1 (see also Absorption Adsorption Membrane technology). 

The standard methods of drying can be classified as deposition of the moisture as either water or ice decomposition of the water chemical precipitation absorption adsorption mechanical separation and vaporization. The completeness with which dryness can be accomplished by any process depends upon the factors controlling the equilibrium conditions achieved in the operation. A brief discussion of each method is first given. 

Which mass-exchange operations should be used (e.g., absorption, adsorption) ... 

Air-purifying respirator A respirator that removes airborne contaminants, such as particulates, gases, vapors and fumes, from ambient air through filtration, absorption, adsorption, or chemical reactions on the media contained in the cartridge or filter. 

This chapter provides details on a number of commonly used process units reactors, heat exchangers, columns of various types (distillation, absorption, adsorption, evaporation, extraction), dryers, and grinders. The purpose of each unit or operation and the many configurations in which the units can be found are also discussed. 

The important physical separation processes, discussed here, are distillation, absorption, adsorption, and solvent extraction. 

It might be thought as a consequence of measurements such as these that leakage factors are the main issues in fuel containment. However, although obviously important, in some cases a leak might occur only at intermittent intervals, and the associated problem might well be easily resolvable by component replacement. In contrast, the relevance of permeation to fluid containment is its continuous nature—its rate may be low, but it occurs all the time that fluid is contacting elastomer. Hence, this phenomenon is now considered in association with related processes absorption, adsorption, and diffusion. 

Can the loss of useful material in the purge be avoided or reduced by additional separation on the purge The roles of refrigerated condensation, low-temperature distillation, absorption, adsorption and membranes in this respect have already been discussed. 

The technologies currently available for post-combustion capture are classified into five main groups absorption, adsorption, cryogenics, membranes and biological separation. The most mature and closest to market technology and so, the representative of first generation of postcombustion options, is capture absorption from amines. 

Unit operations Traditional - distillation, crystallization, extraction, absorption, adsorption, etc. Unconventional -granulation, milling, coating, etching, etc. 

The physical processes by which natural gas liquids are recovered include phase separation, cooling, compression, absorption, adsorption, refrigeration, and any combination of these. Obviously the definition already stated excludes refinery light volatiles produced by the destructive decomposition of heavy petroleum fractions and it also excludes liquids that may be produced synthetically from natural gas. These distinctions are of economic importance in considering our basic energy reserves. Both the refinery volatiles and the synthetic liquids represent conversion products from other hydrocarbons and the conversion is usually attended by a considerable loss. Thus it has been stated that only about 47% (17) of the energy of natural gas is realized in the liquid hydrocarbon products of the Fischer-Tropsch type of synthesis. 

Despite limitations, the most common sorption medium is activated charcoal — a form of carbon treated in such a way as to open a large number of pores. The surface energy of the material and the pores combine to produce a material that can first attract and then trap small organic molecules. The attraction is via adsorption rather than absorption. Adsorption applies to attachment to the surface absorption is a bulk effect. Extraction is a bulk phenomenon. Simply put, adsorption is a function of surface area while absorption is a mass effect. 

Figure 3.9—Adsorption and partition phenomena. Unlike absorption, adsorption is a surface phenomenon (reproduced by permission of M. Lagues, L Actualite Chimique 1990, (1) p. 17).

Fig. 46. Total amount (a) and absorption capacities (b) of Na and Cs salts of H3PW12O40 (O) Na, ( ) Cs. The acid amounts were measured by pyridine absorption (adsorption). (From Ref. 235.)...

One of these methods is called kinetic calibration, in which analyte absorption from the sample to the liquid coating (PDMS) on the fiber is related to analyte desorption from the coating to the sample. The isotropy of absorption and desorption in the kinetic calibration has been described by Chen et al.31 In kinetic calibration, also called in-fiber standardization, desorption of a radio-labeled standard (preloaded on the fiber coating) into the sample is used to calibrate the extraction (absorption/adsorption in the case of a liquid/solid coating) of analyte from the sample into the fiber. This calibration approach considerably facilitates the use of SPME for the on-site field sampling of water, where the control of flow velocity or addition of a standard to the matrix is very difficult. 

The classic sensitizer dye employed in DSC is a Ru(II) bipyridyl dye, cis-bis(isothiocyanato)-bis(2,2/-bipyridyl-4,4/-dicarboxylato)-Ru(II), often referred to as N3 , or in its partially deprotonated form (a di-tetrabutyl-ammonium salt) as N719. The structure of these dyes are shown in 2 and 26. The incorporation of carboxylate groups allows immobilization of sensitizer to the film surface via the formation of bidendate coordination and ester linkages, whilst the (- NCS) groups enhance the visible light absorption. Adsorption of the dye to the mesoporous film is achieved by simple immersion of the film in a solution of dye, which results in the adsorption of a dye monolayer to the film surface. The counter electrode is fabricated from FTO-coated glass, with the addition of a Pt catalyst to catalyze the reduc-... 

The primary pollution problem in nitric acid plants is the abatement of NOx in tail gases. Three options exist to reduce these emissions to acceptable levels 1) Capture the NOx and convert it to additional nitric acid, 2) Capture the NOx and convert it to nitrate-nitrite sales, or 3) Render the NOx harmless by converting it to non-polluting compounds. The processes that have been developed to reduce emissions at existing and new plants can be classified into four general categories Absorption, Adsorption, Selective Catalytic Reduction (SCR) and Non-Selective Catalytic Reduction91. 

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