Exchange level

Next, both composite streams are plotted on the same diagram (Fig. 3.7). On this diagram, thermodynamic feasibility of mass exchange is guaranteed when the lean composite stream is always above the waste composite stream. This is equivalent to ensuring that at any mass>exchange level (which comesponds to a horizontal line), the composition of the lean composite stream is located to the left of the waste composite stream, asserting thermodynamic feasibility. Therefore,... 

Sample Metal loading (wt.%) Na exchanged (%) Metal exchange level (%)... 

The larger ionic radius of K further occludes the pore openings into the type A and we effectively slow down or completely block access to the structure. Both CO2 and N2 demonstrate essentially this effect as exchange level is increased towards about 50% of the ions being K. Once we have that level the product is essentially type 3A. 

Extensive studies of the acidity and basicity of zeolites by adsorption calorimetry have been carried out over the past decades, and many reviews have been published [62,64,103,118,120,121,145,146,153,154]. For a given zeolite, different factors can modify its acidity and acid strength the size and strength of the probe molecule, the adsorption temperature, the morphology and crystallinity, the synthesis mode, the effect of pretreatment, the effect of the proton exchange level, the Si/Al ratio and dealumination, the isomorphous substitution, chemical modifications, aging, and coke deposits. 

A binder—free Na-Y zeolite with Si/Al ratio of 2.29 was obtained from Strem Chemical Co., La,Na—Y and Cs,Na-Y zeolites were prepared by exchanging Na-Y zeolite with LaCls and CsCl solution at room temperature. The percentage of metal ion exchanged in a zeolite has been determinated by Inductively-Coupled-Plasma Atomic Emission Spectroscopy and the number is used as prefix for the samples, e.g., Cs exchanged level of 667. is represented as 66Cs,Na-Y sample. 

Within the present expoimaits, ZSM-S was the most active catalyst at aroimd 773 K. In the figure, with Y-type zeolite, the ccmversion of NO exhibited a characteristic correlaticHi with the exchange level. On the basis of the location of Cu2 ions in the zeolite fiamework determined by X-ray diffraction 20, 21 qj- other techniques,22 an increase in the catalytic activity above 30% should be associated with the increase in the occupancy of supercage sites by the Cu2 ions. 

A volume of 100 L of a solution containing 1000 ppm Pb2+ and minor amounts of other ions has to be treated. The desired final concentration is 100 ppm. The available adsorbent is a zeolite with a particle size of 1.3 mm, density of 2 g/cm3, and the REC is QM = 176 mg/g. Suppose that we have efficient agitation and solid diffusion is the controlling mechanism. Solid diffusion is about 6.4 X 10 1° cm2/s. Furthermore, the system obeys a favorable Langmuir isotherm with La = 0.03 and the maximum exchange level is qmm = 106 mg/g. 

Porfirio, B., Dallapiccola, B., Mokini, V., Alimena, G. Gandini, E. (1983) Failure of diepoxybutane to enhance sister chromatid exchange levels in Fanconi s anemia patients and heterozygotes. Hum. Genet., 63, 117-120... 

Morrison [232,233] finds that the free energy of electrons in the bulk phase (Fermi energy) is about the same for different selective and active catalysts. He notes that this value is very near (or just above) the electron exchange level of oxygen and hence makes reduction of oxygen possible. 

A Linde NaY zeolite without binder was ion exchanged in an ammonia-cal solution of PdCl2 which provides exchangeable (Pd(NH3)4)2+ cations. The solution was stirred at room temperature for 24 hr and then filtered. The zeolite was washed with ammonia solution to eliminate Cl ions. The desired exchange level was readily obtained by allowing the zeolite to equilibrate in a solution where a suitable amount of palladium has been introduced. Chemical analysis for palladium and sodium showed the composition of the calcined sample to be Pdtf.sNaiQ.sHn.sAlfieSiiaeCW (10 wt % of Pd proton concentration determined by difference). 

As shown in Figure 5, the infrared frequencies for the Rb+ and Cs+ exchanged forms are only slightly different from that of the parent Na+ form. Furthermore, the maximum exchange levels at room temperature are considerably lower than those of other monovalent cations (69% and... 

The appearance of the hydroxyl bands at 3650 and 3550 cm-1 upon heating the ammonium form accompanies the decrease and disappearance of the NH-stretching bands as ammonia is evolved. The rate of decomposition of the ammonium ions appears to be influenced by the calcination conditions. Ward observed that most of the ammonium ions decomposed between 200° and 350°C, and at 420° only discreet hydroxyl bands were present (148). With extensively exchanged samples (>90% of the exchange sites occupied by ammonium ions), the 3550-cm I band was more intense than that at 3650 cm-1, in contrast to the intensity relationship observed at lower ammonium-exchange levels. Angell and Schaffer also noted the variability of the relative intensities of the two bands with different extents of ammonium ion exchange. 

The volume of solution used per g of zeolite also plays a part in determining the ion exchange level achieved. As pointed out iu a previous section, in 0.01 M Cu(II) solution with v/m =... 

Seff et al. (27) have reported that 20% or greater exchange of Cu2+ in acidic media into A-zeolites results in the breakdown of the crystal structure. Our studies involve an exchange of 0.3% Cu2+ per unit cell for which low exchange level we did not observe significant structural breakdown. At this low exchange level Cu2+ populates only the most preferential sites. 2+... 

In sustained efforts to localize transition metal cations within the zeolite framework, EPR, UV, IR and X-ray diffraction studies were undertaken by several authors (1-5). This localization was thought to help clarify and possibly account for variations of catalytic properties upon various parameters including the exchange level. The overwhelming conclusions of these investigations was the high mobility of the exchanged transition metal... 

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