Impregnation of Porous Supports

Impregnation of Porous Supports with Active Substances by Means of Supercritical Fluids... 

The first experiments reported here lead us to think that the impregnation of porous supports by drugs can be achieved by means of supercritical fluids. This one-step method yields a final product exempt from any residual trace of toxic solvent. The kinetics of the mass transfer is faster, besides the thermodynamics of the adsorption seems more favourable here. The main problem encountered up to now is the weak solubility of many active molecules in pure C02, which induces a limitation of the percentage of deposited product. However, this difficulty can be overcome by the use of few amount of an entrainer. In particular, ethanol which does not show any toxicity, would greatly extend the range of active substances which could be used. 

In addition to the traditional deep bed filtration, other interesting examples of different processes and techniques can be described by the same basic principle (i) the tangential micro-filtration and ultra-filtration where a slow deep filtration produces the clogging of the membrane surface (ii) some processes of impregnation of porous supports with a sol in order to form a gel which, after precipitation, will form a membrane layer. Here the sol penetration inside the support is fundamental for the membrane quality. 

Magnan C, Bazan C, Charbit F, Joachim J, Charbit G. Impregnation of porous supports with active substances by means of supercritical fluids. In Rudolf von Rohr P, Trepp C, eds. High Pressure Chemical Engineering. Zurich, Switzerland Elsevier, 1996 509-514. 

One of the best known methods for producing catalysts is the impregnation of porous support materials with solutions of active components [9,10]. Especially catalysts with expensive active components such as noble metals are employed as supported catalysts. A widely used support is AI2O3. After impregnation the catalyst particles are dried, and the metal salts are decomposed to the corresponding oxides by heating. The process is shown schematically in Scheme 6-2. 

In solution impregnation, a porous support is infiltrated with a solution of the active phase or its precursor. After careful removal of the solvent, a high dispersion of the active phase over the whole support is obtained (if a precursor of the active phase is used, a conversion step after drying is necessary). The basic principle of the process is shown in Figure 10.21. 

Liquid impregnated (or immobilized) in the pores of a thin microporous sohd support is defined as a supported liquid membrane (SLM or ILM). The SLM may be fabricated in different geometries. Flat sheet SLM is useful for research, but the surface area to volume ratio is too low for industrial applications. Spiral-wound and hoUow-fiber SLMs have much higher surface areas of the LM modules (103 and 104 m /m, respectively [23]). The main problem of SLM technology is the stability the chemical stability of the carrier, the mechanical stability of porous support, etc. 

Supported metals are among the most important industrial catalysts. They are usually made from metal salts and porous supports such as metal oxides. Typical preparation routes include impregnation of the support or ion exchange with an aqueous solution of a metal salt, followed by calcination and reduction. The weU-known preparation routes are often efficient and economical, being widely used in technology, but they typically produce highly nonuniform materials. Because of this nonuniformity, it is... 

The first step in preparing Phillips-type catalysts is the impregnation of a support of highly porous silica or aluminosilicate of low alumina content with an aqueous... 

A small-scale PROX system was manufactured in a type of heat exchanger using non-pellet catalyst. Pt-Ru catalyst screened was impregnated on the support sheet. The support sheet was made by coating y-AlaOs on porous SUS-mesh plate (thickness 1.0 mm). The surface area of the catalyst sheet was 96 mVg. The catalyst sheet was applied to a heat exchanger type reactor of PROX as shown in Fig. 2. The PROX reactor was manufactured as a unit module and tested. Fig. 3 is the test-set of the PROX. Air was applied as the coolant. 

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