Zeolites, as adsorbents

Alefeld, G., P. Maier-Laxhuber, and M. Rothmeyer, 1981. Thermochemical heat storage and heat transformation with zeolites as adsorbents, In Proceedings of the IEA Conference on New Energy Conservation Technologies and their Commercialization, 6-10 April 1981, Vol. 1,, J.P. Millhone E.H. Willis, Springer Verlag, Berlin,, pp. 796-819. 

The study of zeolites as adsorbent materials began in 1938, when Barrer published a series of papers on the adsorptive properties of zeolites [97], In the last 50 years, zeolites, both natural and synthetic, have become one of the most important materials in modern technology [97-107], Today, the production and application of zeolites for industrial processes is a multimillion dollar industry. 

The study of zeolites as adsorbent materials began in 1938 when Professor Barrer published a series of papers on the adsorptive properties of zeolites [28], In the last 50 years, zeolites, natural and synthetic, have turned out to be one of the most significant materials in modem technology [27-37], Zeolites have been shown to be good adsorbents for H20, NH3, H2S, NO, N02, S02, C02, linear and branched hydrocarbons, aromatic hydrocarbons, alcohols, ketones, and other molecules [2,31,34], Adsorption is not only an industrial application of zeolites but also a powerful means of characterizing these materials [1-11], since the adsorption of a specific molecule gives information about the microporous volume, the mesoporous area and volume, the size of the pores, the energetics of adsorption, and molecular transport. 

Using a 5A zeolite as adsorbent and a total cycle time of 10 seconds (compared to conventional PSA cycles of 60-240 seconds), the RPSA process could produce a 27.5% O2 enriched gas stream with an O2 recovery of 64.1% from feed air at a pressure of 2.22 atm [3]. The O2 productivity rate was 2300 sft /ft /hr which was an order of magnitude higher than that of a conventional PSA. The process was found to be suitable for producing 23-40% O2 from air for enhanced combustion applications in cupolas, metalluigical furnaces, etc. [10]. 

Simulation data on mixture adsorption can be used to screen zeolites as adsorbents, but experimental data are necessary to validate the simulations and to accurately design the separation process. The first step of the process design is to obtain such data. However, the experimental assessment of multi-component adsorption equilibria and kinetics is not straightforward and is highly time-consuming. As a result, some theories have been developed that predict adsorption behaviour for a mixture based on the pure component equilibria [1,3]. The isotherm data have to be correlated before their use in a design model... 

The product gas and the exhaust gas were measured for dichloromethane-laden air feed by PSA system using a resin adsorbent and a high silica zeolite as adsorbent. The PSA method for solvent recovery with each adsorbent seems to be technically feasible. The high silica zeolite gave better performance than the resin adsorbent, as expected from their isotherms. 

Using active carbons and some other carbonic adsorbents, several processes have been elaborated to output commercial products (sulphuric acid, sulphur, and sulphur dioxide), Reinluft (FRG), Hitashi (Japan), and Westvaco (USA). However, because of the deficit and high cost of adsorbents, these processes may be recommended only for purification of small volumes of ejected gases. Recently, the methods using natural acid-stable clinoptilolite- and mordenite-type zeolites as adsorbents have been introduced into industry. It is safe to say, however that general drawback of all granular physical adsorbents is their low sorption activity at a sufficiently low concentration of SO2 n g comparatively high aerodynamic resistance. 

According to the Langmuir model (Eq.2) the adsorption capacity qm for Cd is 2.5 times grater than for Zn and adsorption capacity qm for Pb is 2 times grater than Zn when granular activated carbon is used. When natural zeolite is used as adsorbent, the adsorption capacity qm for Zn is 5 times lower than Cd and Pb. So, qm varied in the order Cd (II)> Pb(II) >Zn(II) for GAC, and Pb(II) = Cd(II)>Zn(II) for the natural zeolite as adsorbent. Ricordel et al (2001) and Tsoi and Zhao (2004) reported a similar relationship when different adsorbents were used. This can be explained on the basis of their ionic radii, hydration energy, ionic mobility and diffusion coefficient. The explanations of different authors were given on the basis of the surface covered by the adsorbed metal ions or on the basis of metal surface complexation constants and thermodynamic parameters values. 

Very recently, adsorption of dihydrogen as an IR probe was extended by Kazansky and coworkers to cation-containing zeolites as adsorbents [609-612]. The main aim of their studies was to locaHze the adsorption sites in these materials, especially the cations. This is especially difficult to achieve by other methods in the case of the catalytically important zeolites loaded with low amounts of transition metal cations. In the context of the pertinent investigations by Kazansky and coworkers, the dissociative adsorption of dihydrogen (and light paraffins) in cation-containing zeoHtes was dealt with, too. 

Barthomeuf D Zeolites as adsorbents and catalysts. The Interactive system encaged molecule/zeolite framework. In... 

We review several PSA processes for production of oxygen-enriched and nitrogen-enriched product gases using zeolites as adsorbents. Comparative process performances will be given when appropriate. 

The main uses of natural zeolite as adsorbent are as drying agents, deodorants, adsorbents for air separation, ion exchangers for water purification especially for removing ammonium ion and heavy metal ions and for water softening, soil upgrading and so on. 

Gytlr6k LL, Li H, Belosevic M, Finch GR (1999) Ozone inactivation kinetics of Cryptosporidium in phosphate buffer. J Environ Eng ASCE 125(10) 913-924 Han R, Zou L, Zhao X, Xu Y, Xu F, Li Y, Wang Y (2009) Cheuacterization and properties of iron oxide-coated zeolite as adsorbent for removed of copper(II) from solution in fixed bed column. Chem Eng J 149(1-3) 123-131... 

Sorbex configuration) utilizes a 5A zeolite adsorbent and light naphtha as desorbent for the separation of linear and branched chain paraffins. Olefins may be separated from saturated hydrocarbon isomers by the Olex process using CaX zeolite as adsorbent and heavy naphtha as desorbent. Separation of fructose from glucose is achieved in the Sarex process using CaY zeolite as adsorbent and water as desorbent. All of these processes are summarized in Table 5.1. 

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