Polymeric adsorbents applications

Polymeric acyl titanate esters, 25 79 Polymeric adsorbents, properties and applications, l 587t... 

Fruit juices can be deacidified with a weak base anion-exchange resin. Removal of compounds which cause a bitter taste is a more popular application (26,27). It is accomplished with resins that have no ion-exchange fimctionality. In essence, they are similar to the copolymer intermediates used by resin manufacturers in the production of macroporous cation and anion exchangers. These products are called polymeric adsorbents. They are excellent for removal of limonin [1180-71-8] and naringin [1023647-2], the principal compounds responsible for bitterness in orange, lemon, and grapefruit juices. The adsorbents are regenerated with steam or alcohol. Decaffeination of coffee (qv) and tea (qv) is practiced with the same polymeric adsorbents (28). 

Figures 1 3 showed the comparison between the microwave and thermal regeneration. It can be seen that the application of microwave to regenerate the polymeric adsorbents can get higher regeneration efficiency than the application of the thermal regeneration method. For three kinds of the polymeric resins that had adsorbed benzene, the regeneration efficiency obtained by using microwave was up to 90%, while the regeneration efficiency obtained by using microwave was merely about 60-70%.

The application of microwave to regenerate the polymeric adsorbents can not only get higher regeneration efficiency in comparison with the use of conventional heat regeneration, but also make the temperatures of the fixed beds be much lower than that when using the heat regeneration. The weaker the polarity of a polymeric adsorbent, the easier its regeneration was. 

J. Penfold and 19 other authors. Recent Advances in the Study of Chemical Surfaces and Interfaces by Specular Neutron Reflection. J. Chem. Soc.. Faraday Trans. 93 (1997) 3899-3917. (Review describing advances in instrumentation and many applications, including Langmuir monolayers, LB films and polymeric adsorbates at air/liquid, liquld/liquid and solid/liquid interfaces.)... 

Initially, SPE was based on the use of polymeric sorbents, such as XAD resins (polymeric adsorbents), which were packed in small disposable columns for use on drug analysis. The early environmental applications consisted of both XAD resins and bonded-phase sorbents, such as C-18 (McDonald and Bouvier, 1995). These precolumns were used for sample trace enrichment prior to liquid chromatography and were often done on-line, which means at the same time as liquid chromatography. However, these first, steel, on-line precolumns quickly were replaced with an off-line column made of plastic in order to be both inexpensive and disposable. Eventually, the term solid-phase extraction was coined for these low-pressure extraction columns (Zief et al., 1982). Thus, solid-phase extraction is an analogous term to liquid-liquid extraction, and in fact, solid-phase extraction might also be called liquid-solid extraction. However, it is the term solid-phase extraction or the acronym SPE that has become the common name for this procedure. 

Specific classes of adsorbents are described herein, along with some typical applications, although no attempt has been made to be exhanstive. Many varieties (activated aluminas, silica gels, activated carbons, zeolites, and polymeric adsorbents) are practically commodities and are generally available off the shelf. New, cnstomized adsorbents can also be synthesized to have different properties, which may translate into better performance. A new adsorbent may take months or years to perfect hence, a mle of thnmb is that there is never enough time to develop a new adsorbent for a specific application. 

The range of applications is somewhat restricted, since the cost of most polymeric adsorbents is typically about ten times more than that of other common adsorbents. In some instances, polymeric materials are the only choice. In other cases, they compensate for the cost differential by yielding much better performance, especially for high value-added uses. Current applications include recovery and purification of antibiotics and vitamins, decolorization, decaffeination, hemop-erfusion, separation of halogenated light orgaifics from water, and treatment of certain industrial wastes such as aqueous phenolics and VOC recovery from off-gases. 

J.M. Duval, Adsorbent Filled Polymeric Membranes Application to Pcrvaporation, Gas Separation, PhD thesis, Twente University, The Netherlands, 1993. 

A whole series of methods has been developed for the investigation of porous solids such as activated carbons, porous glasses, silica gels, and zeolites. Together with some new suggestions, they aU have been applied to the characterization of the porosity of polymeric adsorbents. We will briefly review these methods related to the porosity parameters and emphasize the problems that may arise on their application to polymers, when the specific properties of the polymeric materials are not taken into account. 

Because of the diversity of applications of modem liquid chromatography, there is no universal column packing material. StiU, a more or less ideal HPLC packing should be inert toward analytes, pH stable, and compatible with both nonpolar and polar organic solvents and even water, and allow fast diffusion of analytes in the interior of the sorbent bead. These conditions are best met by the new, third generation of polymeric adsorbent materials, hypercrosslinked polystyrenes. A rigid open-work-type hypercrosslinked network displays extremely high apparent specific surface area (up to... 

Duval, J. M. (1993). Adsorbent filled polymeric membranes Application to pervaporation and gas separation. Ph.D. Dissertation, University of Twente, The Netherlands. 

Adsorption for gas purification comes under the category of dynamic adsorption. Where a high separation efficiency is required, the adsorption would be stopped when the breakthrough point is reached. The relationship between adsorbate concentration in the gas stream and the solid may be determined experimentally and plotted in the form of isotherms. These are usually determined under static equilibrium conditions but dynamic adsorption conditions operating in gas purification bear little relationship to these results. Isotherms indicate the affinity of the adsorbent for the adsorbate but do not relate the contact time or the amount of adsorbent required to reduce the adsorbate from one concentration to another. Factors which influence the service time of an adsorbent bed include the grain size of the adsorbent depth of adsorbent bed gas velocity temperature of gas and adsorbent pressure of the gas stream concentration of the adsorbates concentration of other gas constituents which may be adsorbed at the same time moisture content of the gas and adsorbent concentration of substances which may polymerize or react with the adsorbent adsorptive capacity of the adsorbent for the adsorbate over the concentration range applicable over the filter or carbon bed efficiency of adsorbate removal required. 

In Sec. 3 our presentation is focused on the most important results obtained by different authors in the framework of the rephca Ornstein-Zernike (ROZ) integral equations and by simulations of simple fluids in microporous matrices. For illustrative purposes, we discuss some original results obtained recently in our laboratory. Those allow us to show the application of the ROZ equations to the structure and thermodynamics of fluids adsorbed in disordered porous media. In particular, we present a solution of the ROZ equations for a hard sphere mixture that is highly asymmetric by size, adsorbed in a matrix of hard spheres. This example is relevant in describing the structure of colloidal dispersions in a disordered microporous medium. On the other hand, we present some of the results for the adsorption of a hard sphere fluid in a disordered medium of spherical permeable membranes. The theory developed for the description of this model agrees well with computer simulation data. Finally, in this section we demonstrate the applications of the ROZ theory and present simulation data for adsorption of a hard sphere fluid in a matrix of short chain molecules. This example serves to show the relevance of the theory of Wertheim to chemical association for a set of problems focused on adsorption of fluids and mixtures in disordered microporous matrices prepared by polymerization of species. 

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