Ion-exchange Clays

Clay ion-exchange model May be useful for predicting adsorption of heavy metals. Aqueous-phase-... 

The clay ion-exchange model assumes that the interactions of the various cations in any one clay type can be generalized and that the amount of exchange will be determined by the empirically determined cation-exchange capacity (CEC) of the clays in the injection zone. The aqueous-phase activity coefficients of the cations can be determined from a distribution-of-species code. The clay-phase activity coefficients are derived by assuming that the clay phase behaves as a regular solution and by applying conventional solution theory to the experimental equilibrium data in the literature.1 2 3... 

Ion-exchange models are commonly used to describe radionuclide sorption onto the fixed-charged sites of materials like clays. Ion exchange will be strongly affected by competition with monovalent and divalent ions such as Na" " and Ca, whereas it will be less dependent on pH over the compositional ranges common for natural waters. Many studies of strontium and caesium sorption by aluminosilicates (e.g., Wahlberg and Fishman, 1962 Tamura, 1972) have been carried out within the framework of ion-exchange theory. Early mechanistic smdies... 

Ion exchangers can preferentially absorb some types of ions relative to other ions therefore, the ratio between different counterions on an ion exchanger is usually not the same as the ratio between those ions in solution. For example, consider a clay ion exchanger that is selective for calcium. In a groundwater regime that initially contains sodium as the only cation, the clay... 

Benzo-15-crown-5 has been acetylated efficiently using KIO clays ion-exchanged by Cu, Fe or Zr. The best results were obtained with Fe -KlO. The catalytic properties are not related to the acidity of the solid and it can therefore be admitted that the C-Cl bond is activated by a redox mechanism, as proposed earlier for the alkylation of aromatic compounds by benzyl chloride. 

In the first part of our study, the esterification of glycerol with oleic acid in the presence of different acid solids with a controlled porosity (zeolite, clay, ion-exchange resin) was studied (Table 1). 

Acylation of 2-methoxynaphthalene with acetic anhydride was carried out using different solid acid catalysts such as zeolites, acid activated clays, ion exchange resins and sulphated zirconia. The products of the reaction are precursors of many organic and pharmaceutical intermediates. For example, the para isomer of the reaction product, 6-methoxy-2-naphthalene-a-methyl ketone is useful as a raw material for the manufacture of well-known anti-inflammatory dru called naproxen. The reaction products were isolated and confirmed by their melting points, H-NMR, gas chromatography, etc. 

Acidic clays are widely applied in the dehydration of alcohols [38]. Although similar to zeolites in their capacity to induce the formation of both alkenes and ethers, selective alkene synthesis is possible. Various layered materials (clays, ion-exchanged montmorillonite, pillared layered clays) are very active and, in general, selective in transforming primary, secondary, and tertiary aliphatic alcohols to 1-alkenes [39-43]. Al -exchanged montmorillonite, however, induces ether formation from primary alcohols and 2-propanol [41]. Substituted 1-phenyl-1-ethanols yield the corresponding styrene derivatives at high temperature (653-673 K) [44]. 

In the case of the synthesis of polyimide, the polymerization solvent used for polyamic acid (a precursor of polyimide) is usually dimethyl acetoamide (DMAC). We found that clay ion-exchanged dodecyl ammonium ions could be homogeneously dispersed in DMAC. A solution of this organophilic clay and DMAC was added to a DMAC solution of polyamic acid. The film was cast from a homogeneous mixture of clay and polyamic acid, and was heated at 300 °C to achieve the desired polyimide clay nanocomposite film. Its permeability to water decreased to 50% upon addition of 2.0 wt% clay [13]. It was confirmed that its permeability to carbon dioxide also decreased by half [14]. 

The catalytic performance of montmorillonite clay ion-exchanged with ionic liquids in the cycloaddition of carbon dioxide to allyl glycidyl ether (AGE) was evaluated under a range of CO feed pressures [2]. Under a specific set of conditions (AGE=40imnol, catalyst (TDAC-MMT)=0.2 g, temperature= 100 °C, reaction time=2h), the conversion of AGE was measured to determine the effect of COj. Estimate the reaction order in CO and the rate constant. 

---