Adsorbents zeolite adsorbent

To run adsorption storage systems efficiently the appropriate adsorbent has to be used. The right choice is possible on the basis of the measured adsorption equilibrium. The adsorption equilibrium of water vapor and different adsorbents (zeolites and silica gels) was experimentally found [3,4], The differential heat of adsorption (AHd) was calculated from the equilibrium data. 

Concerning the application of these adsorbents as thermal energy storages the amount of water, which can be adsorbed is the most important property. Figure 238 shows the maximum water uptake of some commercially available adsorbents. Zeolite A can reach 25% and Zeolite 13X up to 32% of its dry weight. Narrow pore Silicagel can adsorb 38% water. Two special adsorbents Sizeo, which is a mixture of Zeolite and Silicagel, and SWS, which is a wide... 

Haines A process for recovering sulfur from natural gas, using a zeolite adsorbent. The hydrogen sulfide in the gas is adsorbed on the zeolite when the bed is saturated, hot sulfur dioxide is passed through it. The zeolite catalyzes the reaction between hydrogen sulfide and sulfur dioxide to fonn elemental sulfur, which sublimes out and is condensed. The process was invented by H. W. Haines in 1960 it was developed by Krell Associates and piloted in Canada from 1961 to 1962, but not commercialized because of problems caused by fouling of the zeolite with heavy hydrocarbons. 

The rate of adsorption from dilute aqueous solutions by solid adsorbents (zeolites) is a highly significant factor for applications of this process for water quality control. 

The necessity of forming zeolite powders into larger particles or other structures stems from a combination of pressure drop, reactor/adsorber design and mass transfer considerahons. For an adsorption or catalytic process to be productive, the molecules of interest need to diffuse to adsorption/catalytic sites as quickly as possible, while some trade-off may be necessary in cases of shape- or size-selective reactions. A schematic diagram of the principal resistances to mass transfer in a packed-bed zeolite adsorbent or catalyst system is shown in Figure 3.1 [69]. 

A proven solution to the binder problem is to use water insoluble organic polymer binders instead of clay. For example cellulose acetates and cellulose ethers binders are successfully employed to make commercial zeolitic adsorbents for sugar separation in aqueous solutions [154, 205, 218-223, 225-226, 231-232, 238]. This technique allows the use of zeoHte adsorbents in aqueous separation processes. 

McCulloch, B. and Gatter, M.G. (1991) Process for extracting meta-dichlorobenzene from isomer mixtures with mixed alkali metal exchanged X zeolite adsorbents. U.S. Patent 4,995,380. 

Zinnen, H.A. and Issa, K.C. (1992) Separation of dichlorophenol isomers with zeolite adsorbents. U.S. Patent 5,118,876. 

Barder, T. (1991) Separation of 2,7 diisopropylnaphthalene from a feed mixture comprising various diisopropylnaphthalene isomers with a zeolite adsorbent. U.S. Patent 5,012,039. 

Exxon Research and Engineering Co. (1977) Zeolite adsorbent for separating hydrocarbon mixtures. Neth. Patent 7502348. 

Plee, D. and Methivier, A. (2002) Agglomerated zeolite adsorbents, process for their preparation, and their use for adsorbing paraxylene from aromatic C8 fractions. U.S. Patent 5,410,815. 

Liquid phase zeoHtic separation includes two main events adsorption and desorption. Adsorption of an adsorbate (liquid component being adsorbed by solid) onto zeolitic adsorbent is dictated by the characteristics of the adsorbate-adsorbent interaction. A zeolitic adsorbent is a crystalline porous solid having particular characteristics (see Chapter 2). When immersed in a liquid mixture, the porous... 

To desorb the adsorbate from the zeolitic adsorbent, a desorbent is added. A desorbent is a suitable liquid that is capable of displacing or desorbing the adsorbate from the selective pores of the adsorbent. The process of recovering or desorbing the adsorbate from the adsorbent is known as the desorption step. 

One of the parameters in the broad class of liquid adsorption mechanisms is the interaction between the acidic and basic sites of the adsorbent and the adsorbate. The acidity of zeolitic adsorbent is normally affected by the zeolite Si02/Al203 molar ratio, the ionic radii and the valence of the cations exchanged into the zeolite. In this contribution, Sanderson s model of intermediate electronegativity of zeolitic adsorbent acidity (SjJ can be calculated as a representation of the strength of the adsorbent acidity based on the following equation ... 

Acid-base interactions between zeolitic adsorbents and adsorbates do not always correctly predict the trend of adsorbent selectivity. This is illustrated by the adsorptive separation of durene from isodurene. Pulse test experiments indicated that the adsorbent selectivity for durene/isodurene increases from KX < NaX < LiX, shown in Table 6.6 [32], Because isodurene is a stronger base than durene (Table 6.5), one would expect that the results for adsorbent selectivity... 

Adsorbed water molecules on a zeolite adsorbent are polarizable due to a strong electrostatic field between the exchanged cations and alumina framework [26]. 

Figure 6.10 Fructose/glucose separation on zeolite adsorbents.

Ion exchange involves the formation and breakage of bonds between ions in solution and exchange sites in a zeolitic adsorbent. The reaction equilibrium of the ion exchange process depends most significantly on contact time, operating temperature and ionic concentration. 

Shimura, M., Wakamatsu, S., and Shirato, Y. (1996) Separation of p-xylene by using zeolitic adsorbents. Japanese Patent 08,217,700. 

The two adsorbent chambers contain the zeolitic adsorbent, the liquid xylenes and p-diethylbenzene desorbent. Proper loading of the adsorbent into the large diameter vessels in industrial production plants is of critical importance to maximize adsorbent mass in the fixed vessel volume and not generate low and high density areas within the adsorbent bed. Density inconsistencies could adversely affect liquid flow distribution and thereby have a detrimental effect on the performance of the process. Adsorbent loading methods are a matter of proprietary know how of the technology licensors. However, Seko has published a paper on the practical matters involved in an actual problem case [20]. 

Process for the separation of ethylbenzene by selective adsorption on a zeolitic adsorbent. US Patent 3,943,182. 

Though not a general adsorption equilibrium model the Kelvin equation does provide the relationship between the depression of the vapor pressure of a condensable sorbate and the radius (r) of the pores into which it is condensing. This equation is useful for characterization of pore size distribution by N2 adsorption at or near its dew point. The same equation can also describe the onset of capillary condensation the enhancement of sorption capacity in meso- and macro-pores of formed zeolite adsorbents. 

Zeolites have an enormous impact on our daily lives, both directly and indirectly. For example, upstream hydrocarbons such as aromatics and olefins are produced using zeolite catalysts. The aromatics or olefins are then separated from the reaction mixtures using zeolite adsorbents. The purified components produced by these zeolite-based methods are then used in downstream processes to produce products that we use daily, such as clothes, furniture, foods, construchon materials and materials to build roads, automobile parts, fuels, gasoline, etc. In addihon to the indirect impacts mentioned above, zeolites also have a direct impact on our daily lives. For example, zeolites are used as builders in detergent formulations. 

Let us consider a zeolite adsorbent for selective separation in an important oil refinery stream that contains aromatic compounds. 

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