Beads, zeolitic

The principal adsorbents used in GSC are silica, alumina, graphltlzed carbon blacks, porous polymer beads, zeolites and cyclodextrlns [8,430,431,445]. The bonded phase sorbents discussed in section 2.2.3 could also be considered as modified adsorbents in many respects. 

The base exchange process removes both the temporary and permanent hardness salts from the water by allowing the water to flow through resin beads containing sodium zeolite, Na2Z. 

The effectiveness of zeolites in catalysis and separation can often be improved by the textural and chemical properties of the matrices in which they are imbedded. Chitosan gels issued from renewable resources are already used as supports for the preparation of heterogeneous catalysts in the form of colloids, flakes or gel beads [1, 2], In this study we present several methods for the incorporation of zeolites in chitosan matrices and characterize the synergic effect of the components on the properties of the composite. 

A preformed chitosan-silica composite with 60% weight inorganic part [7] is used as the source of silica for the zeolite synthesis. An alkaline solution of sodium aluminate (Na 2.1 M, Al 1 M) was used in three methods of preparation (A) beads of the chitosan-silica composite were stirred overnight in the aluminate solution, extracted and submitted to a hydrothermal treatment at 80 °C during 48h (B) beads of the chitosan-silica composite were immersed in the aluminate solution and the system underwent a hydrothermal treatment at 80 °C for 48h (C) beads of the chitosan-silica composite were stirred overnight in the aluminate solution, extracted, dried at 80 °C and exposed to water vapour at 80°C during 48h. 

In the X-ray powder diffraction patterns of the composites, the disappearance of the broad band centered at 22 °20, typical of amorphous silica, indicates that the zeolitisation of the mineral fraction of the parent composite was complete. In no diffraction pattern any sign of crystallised chitosan could be found. The two methods in which the silica-polymer beads were extracted from the aluminate solution after impregnation (methods A and C) allowed the formation of the expected zeolite X, with traces of gismondine in the case of the method C. The method B, in which excess aluminate solution was present during the hydrothermal treatment, resulted in the formation of zeolite A. 

Figure 4. (a) Adsorption-desorption isotherms of N2 at -196°C of 80°C-outgassed (empty squares) chitosan, (filled trangles) zeolite X-chitosan composite from in-situ zeolite synthesis and (empty triangles) zeolite Y-chitosan composite from encapsulation of the zeolite in the gelling chitosan. (b) Scanning electron micrographs of a calcined zeolite-chitosan bead prepared by zeolitisation of a silica-chitosan composite. 

Some bead materials possess porous structure and, therefore, have very high surface to volume ratio. The examples include silica-gel, controlled pore glass, and zeolite beads. These inorganic materials are made use of to design gas sensors. Indicators are usually adsorbed on the surface and the beads are then dispersed in a permeation-selective membrane (usually silicone rubbers). Such sensors possess high sensitivity to oxygen and a fast response in the gas phase but can be rather slow in the aqueous phase since the gas contained in the pores needs to be exchanged. Porous polymeric materials are rarer and have not been used so far in optical nanosensors. 

The earliest catalyst was made from clay later, synthetic beads from siUca-alumina were introduced. In the early 1960s, catalysts were introduced that employed up to 10% X or Y zeolite in a silica-alumina matrix. 

Zeolite particles are incorporated into a number of different engineered forms, including smaU spherical parhcles for fluidized bed appHcations and smaU granules for powdered detergents. Larger forms include extruded peUets with various cross-sectional shapes and beads made by bead-forming processes. 

Figure 3.1 Principal mass transfer resistances in a packed bed of zeolite beads [69].

The adsorbent is an alkali exchanged faujasite bound into a bead. Because m-xylene is by far the most basic of the four mixed xylene isomers, the selectivity of the zeolite is tailored for this chemical trait. 

Synthetic inorganic ion exchangers Zeolites Synthetic zeolites (Figure 4.7) are available as powder, pellet, or bead. The greatest advantage of synthetic zeolites against natural zeolites is that they can be manufactured with a wide variety of physicochemical properties. The main disadvantages of synthetic zeolites are... 

Other problems with ion exchangers include coating of the resin beads or zeolite particles with suspended matter from turbid water (pretreatment with a coagulant may be necessary) or algal growths (chlorination of the water may be required). Zeolites may cause significant silica carryover and should not be used to treat boiler water for steam turbines. Finally, although Ca2+ and Mg2+ are objectionable in boiler or laundry operations, they are necessary nutrients in the human diet. Furthermore, excessive consumption of Na+ can contribute to hypertension and other blood circulatory problems. In Canada, for example, the incidence of heart disease and related health problems is lower in areas where the water supply is... 

We assume that the adsorbent mass used in the kinetic test consists of a sphere of radius R. It may be composed of several microsize particles (such as zeolite crystals) bonded together as in a commercial zeolite bead or simply an assemblage of the microparticles. It may also be composed of a noncrystalline material such as gels or aluminas or activated carbons. The resistance to mass transfer may occur at the surface of the sphere or at the surface of each microparticle. The heat transfer inside the adsorbent mass is controlled by its effective thermal conductivity. Each microparticle is at a uniform temperature dependent on time and its position in the sphere. 

In the supported systems the catalyst can be coated on the walls of the reactor, supported on a solid substrate or deposited around the case of the light source. Many are the supported materials used in literature, such as glass beads, and tubes [69], silica-based materials [70], hollow beads, membranes [71], optical fibers, zeolites, activated carbon, organic fibers [72], and so on. 

Let us consider a support composed of grains (beads, extrudates or others) several millimeters in diameter and containing a more or less large amount of zeolite Y (20-70 wt%, for example). After impregnation, question arises as to what is ... 

Sodium softeners are used to treated RO influent water to remove soluble hardness (calcium, magnesium, barium, and strontium) that can form scale on RO membranes. Once known as sodium zeolite softeners, zeolites have been replaced with synthetic plastic resin beads. For sodium softeners, these resin beads are strongly acidic cation (SAC) polystyrene resin in the sodium form. The active group is benzene sulfonic acid, in the sodium, not free acid, form. Figure 8.12 shows styrene-divinylbenzene gel cation resin. Equation 8.4 shows the softening reaction for calcium exchange ... 

Previous studies of our work group demonstrated that isomaltose exhibits a distinct higher affinity towards certain dealuminated p-zeolites as opposed to other carbohydrates like fructose or glucose [94, 109]. Sucrose is not adsorbed at all. As a consequence, a process could be developed which directly removes the isomaltose from the reaction solution by adsorption onto zeolite. For this purpose a fluidized bed reactor has been utilized with a special focus on the separation of the two solid phases (Fig. 14). The biocatalyst containing entrapped dextransucrase is produced by the jet-cutter method [110] the alginate beads have a mean particle size of 0.5 mm. To accomplish an adequate high density of biocatalyst, silica flour (30% w/v) is included. The particle diameter of the second solid phase (zeolite) is adjusted to 10 pm. As a consequence, zeolite is loaded with isomaltose inside the reactor and can then freely exit the reactor together with the product solution, whereas the biocatalyst is retained inside the fluidized bed reactor [92, 94],... 

The sieves which are used are BaX or KBaY zeolites. The zeolite cannot be used without appropriate shaping in order to avoid too high a pressure drop. Beads or granulates with a diameter smaller than 1 mm allow maximum packing, maximum diffusion rates and good mechanical properties. 

Zeolite molecular sieves (sodium and calcium aluminosilicates) of nominal pore size 0.3... 0.5 nm, nonnally used as beads except in cases where the use of powdered molecular sieve is essential (marked wifli an asterisk). 

Desiccants. The ion-exchanged forms of zeolite A are well known as general laboratory and industrial drying agents in the form of extrudates or beads. The success of these... 

The zeolite sample used in the present study is a sodium containing faujasite NaX of Si/Al ratio = 1.3. This sample was supplied by CECA S.A. (ref. G5C02M). The sample was in bead form of diameter 1.6-2.5 mm. 

Ail interpretations based on the assumptions with respect to use of the Nernst-Planck relationships are, however, subject to sizable uncertainty because the constancy attributed to the diffusion coefficients used in these relationships is susceptible to sizable variability. Bead volume variations are ignored. This leads to variations in ion mobilities which dictate changes in the diffusion coefficients of the Nemst-Planck relationships. Sizable divergence of measurements firom prediction can be expected on this basis. Even in rigid ion exchangers such as zeolites the difference in size of the counterions exchanged usually affects their mobility, and so leads to variations of the diffusivities [3]. 

Sorption thermodynamic functions of nitrous oxide, N2O, are described for zeolites NaLSX and CaLSX in shapes cA clay-bound beads. They were determined by the Sorption Isosteric Method (SIM) over complete ranges of sorption-phase concentration and compared with those for carbon dioxide, C(>2. nepo earlier for the same NaLSX sorbent... 

---