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Adsorption capacities

There are two methods for determining the adsorphon isotherm. The volumetric approach determines the quantity of gas present in the system by measurement [Pg.156]

Ammonia TPD is very simple and versatile. The use of propylamine as a probe molecule is starting to gain some popularity since it decomposes at the acid site to form ammonia and propene directly. This eliminates issues with surface adsorption observed with ammonia. The conversion of the TPD data into acid strength distribution can be influenced by the heating rate and can be subjective based on the selection of desorption temperatures for categorizing acid strength. Since basic molecules can adsorb on both Bronsted and Lewis acid sites, the TPD data may not necessarily be relevant for the specific catalytic reaction of interest because of the inability to distinguish between Bronsted and Lewis acid sites. [Pg.158]

As noted throughout this chapter, a single characterization technique caimot provide a full understanding or explain catalyst or adsorbent performance. The selection of an appropriate methodology requires (i) knowledge of the problem, [Pg.158]

Characterization techniques continue to develop and will impact their application to zeolitic systems. Aberration corrected electron microscopes are now being used to improve our understanding of catalysts and other nano-materials and will do the same for zeolites. For example, individual Pt atoms dispersed on a catalyst support are now able to be imaged in the STEM mode [252]. The application of this technique for imaging the location of rare-earth or other high atomic number cations in a zeolite would be expected to follow. Combining this with tomography [Pg.158]

Many of the characterization techniques described in this chapter require ambient or vacuum conditions, which may or may not be translatable to operational conditions. In situ or in opemndo characterization avoids such issues and can provide insight and information under more realistic conditions. Such approaches are becoming more common in X-ray adsorption spectroscopy (XAS) methods ofXANES and EXAFS, in NMR and in transmission electron microscopy where environmental instruments and cells are becoming common. In situ MAS NMR has been used to characterize reaction intermediates, organic deposits, surface complexes and the nature of transition state and reaction pathways. The formation of alkoxy species on zeolites upon adsorption of olefins or alcohols have been observed by C in situ and ex situ NMR [253]. Sensitivity enhancement techniques play an important role in the progress of this area. In operando infrared and RAMAN is becoming more widely used. In situ RAMAN spectroscopy has been used to online monitor synthesis of zeolites in pressurized reactors [254]. Such techniques will become commonplace. [Pg.159]


The total stationary-phase volume required to process a given feed stream is proportional to the inlet concentration and volume of the feed. For example, for a typical inlet concentration of protein of 10 g/L, in a 100 L volume of feed, a column volume of at least 100 L is needed for size-exclusion chromatography. In comparison, an ion-exchange column having an adsorption capacity of 50 g/L would only require 20 L of column volume for the same feed. [Pg.51]

This division is somewhat arbitrary siace it is really the pore size relative to the size of the sorbate molecule rather than the absolute pore size that governs the behavior. Nevertheless, the general concept is useful. In micropores (pores which are only slightly larger than the sorbate molecule) the molecule never escapes from the force field of the pore wall, even when ia the center of the pore. Such pores generally make a dominant contribution to the adsorptive capacity for molecules small enough to penetrate. Transport within these pores can be severely limited by steric effects, leading to molecular sieve behavior. [Pg.254]

The mesopores make some contribution to the adsorptive capacity, but thek main role is as conduits to provide access to the smaller micropores. Diffusion ia the mesopores may occur by several different mechanisms, as discussed below. The macropores make very Htde contribution to the adsorptive capacity, but they commonly provide a major contribution to the kinetics. Thek role is thus analogous to that of a super highway, aHowkig the adsorbate molecules to diffuse far kito a particle with a minimum of diffusional resistance. [Pg.254]

Fig. 6. Adsorption capacity of various dessicants vs years of service in dehydrating high pressure natural gas (39). a, Alumin a H-151, gas 27° C and 123 kPa, from oil and water separators b, siUca gel, gas 38° C and 145 kPa, from oil absorption plant c, sorbead, 136-kPa gas from absorption plant ... Fig. 6. Adsorption capacity of various dessicants vs years of service in dehydrating high pressure natural gas (39). a, Alumin a H-151, gas 27° C and 123 kPa, from oil and water separators b, siUca gel, gas 38° C and 145 kPa, from oil absorption plant c, sorbead, 136-kPa gas from absorption plant ...
The search for a suitable adsorbent is generally the first step in the development of an adsorption process. A practical adsorbent has four primary requirements selectivity, capacity, mass transfer rate, and long-term stabiUty. The requirement for adequate adsorptive capacity restricts the choice of adsorbents to microporous soUds with pore diameters ranging from a few tenths to a few tens of nanometers. [Pg.292]

Adsorption (qv) of gases has been reviewed (40,50) (see also Adsorption, gas separation). Adsorption, used alone or in combination with other removal methods, is excellent for removing pollutant gases to extremely low concentrations, eg, 1 ppmv. When used in combination, it is typically the final step. Adsorption, always exothermic, is even more attractive when very large gas volumes must be made almost pollutant free. Because granular adsorbent beds ate difficult to cool because of poor heat transfer, gas precooling is often practiced to minimize adsorption capacity loss toward the end of the bed. Pretreatment to remove or reduce adsorbable molecules, such as water, competing for adsorption sites should also be considered (41). [Pg.387]

The technological appHcations of molecular sieves are as varied as their chemical makeup. Heterogeneous catalysis and adsorption processes make extensive use of molecular sieves. The utility of the latter materials Hes in their microstmctures, which allow access to large internal surfaces, and cavities that enhance catalytic activity and adsorptive capacity. [Pg.443]

Hydrogels are used ia the refining of edible oils to adsorb phosphohpids, trace metals, and soaps (103). The adsorption capacity depends on the ease of hydration of the adsorbates, so best performance demands careful control of moisture content ia the system (104). Sihca hydrogel ia combination with alumiaa has beea fouad to be useful for purifyiag used cooking oils ia order to extead their life and enhance the quahty of the fried food (105). [Pg.480]

Characterization. When siHca gel is used as an adsorbent, the pore stmcture determines the gel adsorption capacity. Pores are characterized by specific surface area, specific pore volume (total volume of pores per gram of solid), average pore diameter, pore size distribution, and the degree to which entrance to larger pores is restricted by smaller pores. These parameters are derived from measuring vapor adsorption isotherms, mercury intmsion, low angle x-ray scattering, electron microscopy, gas permeabiHty, ion or molecule exclusion, or the volume of imbibed Hquid (1). [Pg.491]

The sulfur is thus removed from the gas stream and trapped in the sorbent as iron sulfide [1317-37-9]. Over time all of the iron oxide becomes sulfided and the adsorptive capacity of the sorbent becomes exhausted. The bed can be partially regenerated by oxidation, as follows ... [Pg.209]

In carbon adsorption, contaminants are physically attracted or adsorbed on the surface of the carbon. Adsorption capacities are high for carbon because its porous nature provides a large surface area relative to its volume. Activated carbon is prepared from lignite, bituminous coal, coke, wood, or other organic materials such as coconut shells. [Pg.160]

When the adsorption capacity of a carbon unit is exceeded, there is breakthrough of the contaminant in the treated stream. Eixed beds may be operated in series to allow continuous treatment while spent or exhausted units are replaced with fresh carbon. In series operation, there are two or more units. The majority of the contaminant is removed by the first unit in the series with the downstream units acting as polishing units. When breakthrough occurs in the first or primary unit, it is replaced with fresh carbon and becomes a polishing unit while the next unit in the series takes over and becomes the primary treatment unit. An example of this round-robin operation of a three-carbon bed is shown in Eigure 2. [Pg.160]

Design criteria for carbon adsorption include type and concentration of contaminant, hydrauhc loading, bed depth, and contact time. Typical ranges are 1.4—6.8 L/s/m for hydrauhc loading, 1.5—9.1 m for bed depth, and 10—50 minutes for contact time (1). The adsorption capacity for a particular compound or mixed waste stream can be deterrnined as an adsorption isotherm and pilot tested. The adsorption isotherm relates the observed effluent concentration to the amount of material adsorbed per mass of carbon. [Pg.161]

Compound Adsorption capacity, mg/g Compound Adsorption capacity, mg/g... [Pg.226]

Table 8. Adsorption Capacity of Amberlite XAD-4 Polymeric Resin ... Table 8. Adsorption Capacity of Amberlite XAD-4 Polymeric Resin ...
Compounds Maximum solubiUty in water, g/L Influent concentration, mg/L Adsorption capacity, kg/m ... [Pg.227]

Other Fiber Evaluation Methods. The extent of fiber separation (fiber openness) is an important evaluation criteria that is commonly measured by several techniques, namely ak permeabiUty, adsorbed gas volume, bulk density, and residence (compression and recovery). The adsorption and retention of kerosene is also used as a measure of fiber openness and fiber adsorption capacity (34). [Pg.353]

The main characteristic properties of asbestos fibers that can be exploited in industrial appHcations (8) are their thermal, electrical, and sound insulation nonflammabiUty matrix reinforcement (cement, plastic, and resins) adsorption capacity (filtration, Hquid sterilization) wear and friction properties (friction materials) and chemical inertia (except in acids). These properties have led to several main classes of industrial products or appHcations... [Pg.354]

Determination of Adsorptive Capacity of Carbon by Isotherm Technique Determining Operating Performance of Granular Activated Carbon... [Pg.532]

Since adsorption takes place at the interphase boundaiy, the adsorption surface area becomes an important consideration. Generally, the higher the adsorption surface area, the greater its adsorption capacity. However, the surface area has to be available in a particular pore size within the adsorbent. At low partial pressure (or concentration) a surface area in the smallest pores in which the adsorbate can enter is the most efficient. At higher pressures the larger pores become more important at very high concentrations, capiDaiy condensation will take place within the pores, and the total micropore volume becomes the limiting factor. [Pg.2186]

The adsorptive capacity of activated carbon for some common solvent vapors is shown in Table 25-27. [Pg.2187]

TABLE 25-27 Adsorptive Capacity of Common Solvents on Activated Carbons ... [Pg.2188]

Adsorbents, and activated carbon in particular, are typically characterized by a highly porous structure. Adsorbents with the highest adsorption capacity for gasoline or fuel vapors have a large pore volume associated with pore diameters on the order of 50 Angstroms or less. When adsorption occurs in these pores, the process is comparable to condensation in which the pores become filled with hquid adsorbate. Fig. 5 depicts the adsorption process, including transfer of adsorbate molecules through the bulk gas phase to the surface of the solid, and diffusion onto internal surfaces of the adsorbent and into the pores. [Pg.247]


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