Liquid phase immobilization

This relationship between the permeability values of several compounds (p) and the partition coefficient of these compounds between the ionic liquid phase immobilized on the membrane and the feed/receive phase (K) has been examined by several authors [16, 18]. The increase in the K values for the compounds was reflected in an increase in the p values. A mathematical correlation between these parameters has been established by de los Rios et al. [22], given in Eq. 11.2 ... 

Another variant of liquid-liquid extraction takes advantage of a liquid phase immobilized on a solid sorbent such as kieselguhr, Celite, Chro-mosorbW, or ChromosorbP [176]. The immobilized phase may be either aqueous or nonaque-ous. 

In the classical set-up of bulk liquid membranes, the membrane phase is a well-mixed bulk phase instead of an immobilized phase within a pore or film. The principle comprises enantioselective extraction from the feed phase to the carrier phase, and subsequently the carrier releases the enantiomer into the receiving phase. As formation and dissociation of the chiral complex occur at different locations, suitable conditions for absorption and desorption can be established. In order to allow for effective mass transport between the different liquid phases involved, hollow fiber... 

These reactors contain suspended solid particles. A discontinuous gas phase is sparged into the reactor. Coal liquefaction is an example where the solid is consumed by the reaction. The three phases are hydrogen, a hydrocarbon-solvent/ product mixture, and solid coal. Microbial cells immobilized on a particulate substrate are an example of a three-phase system where the slurried phase is catalytic. The liquid phase is water that contains the organic substrate. The gas phase supplies oxygen and removes carbon dioxide. The solid phase consists of microbial cells grown on the surface of a nonconsumable solid such as activated carbon. 

Keywords Asymmetric catalysis Salen Diphasic liquid phase Bis(oxazoline) Immobilization... 

As outlined above, immobilization in a fluorinated liquid phase demands the functionahzation of the ligand with perfluoroalkyl chains and, even then, the solubihty is strongly influenced by the nature of the complex. Ionic hquids of the alkylmethyhmidazolium type (Fig. 4) have been recently developed as alternative solvents for organometallic catalysis and have the practical advantage of using directly the commercially available chiral hgands and complexes. 

This result suggests that the reaction rate observed with the gel-immobilized catalysts is lower owing to the smaller concentration of the substrate inside the catalyst with respect to the liquid phase. This implies that the partition of substrates between the catalyst and the bulk liquid phase is fast. This could not be the case always and deviations... 

Different enzymes - particularly lipases - immobilized in membrane reactors have been studied in the presence of two-liquid phases (Table 5). Organic and aqueous phases containing respectively hydrophobic and hydrophilic reactants are separated by a solid mem-... 

We consider, primarily, events in solids since most e.s.r. studies have been carried out on radicals trapped in solids. Only relatively persistent organometallic radicals have been studied by liquid-phase e.s.r. with in situ radiolysis, because of the technical difficulties involved. In most solid systems at low temperature radical centres are physically trapped in the rigid matrix and hence can be studied by e.s.r. without difficulty. However, although radicals as such may be immobile, this does not necessarily apply to electron-gain or -loss centres, particularly if these are charged, since electron-transfer may be facile. 

Immobilization of catalysts is an important process design feature (see Chapter 9.9). A recent example of catalyst immobilization is the biphasic approach which seems superior to immobilization on solids, as successfully proven in the Ruhrchemie/Rhone Poulenc process for the hydro-formylation of olefins.286 Supported liquid phase catalysis was devised as a method for the immobilization of homogeneous catalysts on solids. When the liquid phase is water, a water-soluble catalyst may be physically bound to the solid. 

Recyclability can be achieved by heterogenization of the reaction mixture, by binding the catalyst and products to different phases. This can be achieved by (i) immobilization of the catalyst on a solid inorganic or polymeric support (solid-liquid protocols) or (ii) partitioning the catalyst and reagents/products in different liquid phases (liquid-liquid protocols) (see Chapter 9.9 for more details on supported catalysts). 

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