Overview in Zeolites Adsorptive Separation

Adsorption is the process whereby molecules of a gas or liquid species adhere to a solid surface. If a certain species A has a greater affinity for the solid surface than another species B in the mixture the preferentially adsorbed species can in principle be separated from the other molecules in the gas or Hquid mixture. If the solid adsorbent is to be reused the adsorbed species must be desorbed from the solid. In gas phase adsorption the adsorbed material is most often removed by changing the temperature and/or the pressure of the system along with a carrier or sweeper gas. For liquid systems a chemical desorbent must be found that preferentially displaces the desired product species from the soHd. The desorbent must itself be easily separated from the product in another separation step, usually distillation. 

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I 5 Overview in Zeolites Adsorptive Separation Table 5.3 Continued... 

An excellent review and detailed coverage on commercial adsorbents and new adsorbent materials has been presented by Yang in his newly published monograph on adsorbents.A very brief overview of existing commercial adsorbents is given here. Commercial sorbents that have been used in large-scale adsorptive separation and purification processes include activated carbon, zeolites, activated alumina, silica gel, and polymeric adsorbents. Although the worldwide sales of sorbent materials are relatively small as compared with other chemical commodities, sorbents and adsorption processes play a very important role in many process industries. The estimated worldwide sales of these sorbents are as follows ... 

In the development of zeolite science, infrared spectroscopy has been one of the major tools for structure and reactivity characterization. However, the field of zeolite Raman spectroscopy is gaining importance. The Raman effect is an intrinsically weak phenomenon, and Raman spectra of zeolites are often obscured by a broad fluorescence. Just like IR spectroscopy, Raman can detect small. X-ray amorphous zeolite particles. Therefore, Raman spectroscopy has been used to examine zeolite synthesis mixtures with ex-situ methods (with separation of solid and liquid) and in-situ methods. In this work we give an overview of the zeolite framework vibrations, zeolite synthesis, adsorption on zeolites and metal substitution and ion exchange in zeolites. 

Zeolites are used as detergent builders, adsorbents, and catalysts. In the past decade, we saw the development of a variety of zeoiite membranes, and a number of investigators reported on the preparation of such membranes and their applications to a variety of separation systems. These research activities are motivated by features common to inorganic membranes, such as thermal resistance and resistance to organic solvents, and features unique to zeolite materials, such as molecular sieving, selective adsorption, and catalytic activity.In this article, the discussion will be restricted to zeolite membranes for use in separation and catalysis. First, an overview is presented on recent progress in zeolite membranes, followed by a discussion of our research activities. 

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