Conventional wet ion exchange

Conventional wet ion exchange is used in all types of fields to exchange metal ions into different kinds of zeolites. Normally, a zeolite material in its proton or ammonia form is... 

The latest projects to eliminate the production of waste treatment sludges were undertaken in the wet process metal plating production area. The projects, completed in March 1989, involved the installation of separate cadmium, chrome, copper and nickel recovery systems. All of the recovery systems utilized redundant conventional ion exchange columns for initial metal waste recovery and concentration. 

Figure 9 NOx reduction efficiency of overexchanged Fe-MFI catalysts prepared by using ( ) a conventional ion exchange in an aqueous slurry(9,0,M) ci sublimation technique and (A,A) a solid-state ion exchange. The feed gas composition for (A,9,0,M) was NO, 2,000 ppm i-C4Hio, 2,000 ppm O2, 3% H2O 0 or 10% GHSV = 42,000 k, and that composition for (A, A) was NO, 1,000 ppm i-C Hu), 1,000 ppm O2,3% H2O 0 or 0.7% GHSV = 30,000 k. (Closed symbols) in the dry feed stream (open symbols) in the wet feed stream (adopted from refs. 55,136 and 139)...

High Pressure Ion Chromatography is a relatively recent (1975) and immensely significant development of conventional ion exchange chromatography by Small and co-workers of The Dow Chemical Company. This technique has revolutionized instrumental wet chemical analysis in that micro-amounts of an ion or mixtures of ions may be separated and assessed quantitatively in a matter of minutes compared with hours using traditional techniques. Accurate volumetric dispensing methods means that a quantitative analysis of ions may be achieved whatever their initial concentration. 

Plant CRMs Co After irradiation, wet ash by conventional or microwave methods with HNO3/HCIO4/ HF/H2O2 [WDC WDMCV] Radiochemical separation by ion exchange and extraction chromatography [SEP/ CONC-RNAA] [WDC-SEP/ CONC-RNAA WDMCV-SEP/ CONC-RNAA] Danko et al. (2000)... 

Catalytic membranes can be prepared by deposition of a catalytically active phase (e.g., a metal) in the inert porous membranes through various techniques commonly used for conventional catalyst preparation - such as wet impregnation, monolayer metal complexation, and ion exchange -followed by heat treatment (activation) [17], The conventional activation steps can also be avoided by direct deposition of solvated metal microclusters [21], The structural characteristics of the porous substrate, and in particular the relative laminar and Knudsen contributions to permeation, have a strong influence on the membrane performance [22], They make use of the membrane structure to optimize the access of disfavored reactants, or to control and rule the residence time and contact of species in the active zone. Furthermore, the porous membrane is required to present a rather homogeneous structure to avoid heterogeneities in the reactant-to-catalyst contact, and also to facilitate CMR operation control. 

Roessner et al. [134] found that Zn,H-ZSM-5 or Zn-ZSM-5 obtained via SSIE possessed catalytic activities in n-hexane isomerization similar to those exhibited by Zn,H-ZSM-5 catalysts that had been prepared by conventional methods, i. e., either through ion exchange in aqueous solutions of ZnfNOjlj or by the incipient-wetness technique. The latter method seemed to be in between exchange in aqueous solution and a solid-state reaction (cf. Sect 6.1). Also, Zn-ZSM-5 produced via SSIE proved to be almost as equally active in ethane arom-atization as conventionally modified Zn-ZSM-5 prepared by exchange in aqueous Zn(N03)2 solution [135]. Finally, as was shown by Rojasova et al. [143], incorporation of zinc into NH4-Y by solid-state reaction with, e.g., ZnO yielded catalysts active in n-hexane aromatization. Under equal conditions, ZnO alone did not catalyze this reaction. 

Weckhuysen and Schoonheydt [100, 199] conducted systematic studies of the preparation of Cr-containing zeohtes. These authors employed diffuse reflectance UV spectroscopy (DRS) and ESR spectroscopy. For a comparative investigation, they loaded various zeolites (X, Y, [Ga]Y and MOR-type zeolites) not only by conventional ion exchange or impregnation-incipient wetness techniques but also via soHd-state ion exchange with CrClj 6H2O. After calcination of differently prepared samples at 823 K, similar DRS spectra were obtained (cf. Fig. 58). 

An interesting result of the studies reported by these authors was that Cr,H-Y obtained through SSIE showed the lowest reducibility compared to samples prepared via conventional ion exchange or the impregnation-incipient wetness technique. This behavior was attributed to residual acidity of Cr-containing Y-zeolite produced by solid-state reaction between CrClj OHjO and NH4-Y. 

Conventional pore size analysis techniques require the use of dried materials but many materials undergo drastic structural rearrangement during drying (i.e., before analysis). The use of low-field NMR spin-lattice relaxation measurements is demonstrated for pore structure analysis for a number of wet solids including silica gels and ion exchange resins. 

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