Heterogeneous separations filter

This section describes catalytic systems made by a heterogeneous catalyst (e.g., a supported metal, dispersed metals, immobilized organometaUic complexes, supported acid-base catalysts, modified zeolites) that is immobilized in a hydrophilic or ionic liquid catalyst-philic phase, and in the presence of a second liquid phase—immiscible in the first phase—made, for example, by an organic solvent. The rationale for this multiphasic system is usually ease in product separation, since it can be removed with the organic phase, and ease in catalyst recovery and reuse because the latter remains immobilized in the catalyst-philic phase, it can be filtered away, and it does not contaminate the product. These systems often show improved rates as well as selectivities, along with catalyst stabilization. 

First, the solute transport in a porous filter (membrane) separating two solutions at different concentrations or electric potentials is likely to be dominated by electro-osmotic circulation as compared to molecular electrodiffusion in the pores. An accurate calculation of the circulation seems desirable. In particular, the observations upon the highly performing composite heterogeneous ion-exchange membrane [13], formed by casting a thin... 

Suitable light sources for exciting the sensitizer include halogen or mercury lamps equipped with a 400 nm cut-off filter to transmit visible light. The sensitizers methylene blue (MB), meso-tetraphenylporphine (TPP), sulfonated aluminum phtha-locyanine, and Rose Bengal (RB) are widely used in homogeneous solutions. The main appeal of heterogeneous sensitizers is that they are easy to separate from... 

The molecular-sieving effect on proteins has been very clearly demonstrated by Pedersen (1962). Bovine serum albumin, obtained by fractionated ammonium sulfate precipitation, was filtered through a column of cross-linked dextran of water regain 15 gm/gm (Sephadex G-200). Monomer and dimer forms were easily separated from each other and from other components of larger sedimentation constants (Fig. 8). Heterogeneity in the monomer as well as in the dimer preparation was indicated... 

The immobilization of the enzyme, the redox catalyst, and sometimes also the cofactor can also take place at a solid support different from the electrode so that the components can be recovered within a solid-bed reactor (a column filled with the enzyme-containing particles) or by a filter plate or membrane. The immobilization of enzymes at solid supports or by the foraiation of cross-linked enzyme crystals can sometimes also enhance the enzyme stability. This concept has the advantage of the ease of separation but the disadvantage of diffusional limitations due to the heterogeneity of the reactions between the enzyme and the substrate and the cofactor or the redox catalyst. Additionally, the number of available redox centers is usually limited. 

Heterogeneous mixtures composed of solids and liquids are easily separated by filtration. Filtration is a technique that uses a porous barrier to separate a solid from a liquid. As Figure 3-15 shows, the mixture is poured through a piece of filter paper that has been folded into a cone shape. The liquid passes through, leaving the solids trapped in the filter paper. 

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