Surface-active properties refining

Occurs in nature in abundance the principal forms are bauxites and lat-erites. The mineral corundum is used to produce precious gems, such as ruhy and sapphire. Activated aluminas are used extensively as adsorbents because of their affinity for water and other polar molecules and as catalysts because of their large surface area and appropriate pore sturcture. As adsorbents, they are used for drying gases and liquids and in adsorption chromatography. Catalytic properties may be attributed to the presence of surface active sites (primarily OFT, 02, and AF+ ions). Such catalytic applications include sulfur recovery from H2S (Clauss catalysis) dehydration of alcohols, isomerization of olefins and as a catalyst support in petroleum refining. 

The study of the textural properties of catalyst supports is of primary importance in terms of understanding the catalytic phenomena involved in petrochemical and refining industry processes. In fact, characteristics, such as the specific surface area, pore size or total porous volume will be useful in various stages of a catalyst s existence its preparation (deposition of active phases), its use in catalysis and its regeneration. They directly influence the physicochemical properties of the solid as well as surface reactivity, shape selectivity and hydrodynamic properties. 

The fabrication of the super alloys of today and those of the future requires improved molds, cores, and binders. Chemical processes and oil refining require catalysts with improved activity, selectivity, and mechanical properties. Classic ceramics and the new ceramics for electronic microcircuits (microelectronics) require purer and more reliable precursors and processes. Chromatographic processes require substrates with improved physical, mechanical, and surface properties. And there is an ever-increasing need of better absorbents, binders, and pigments. 

Immersion calorimetry using polar liquids gives another insight to the characterization of the solid surfaces. Here, specific interactions between the liquid molecules and active centers at the solid surface play a major role. The comparison between enthalpies of immersion of liquids with different polarity provides a refined picture of the surface properties of the solid. This point can be illustrated by the following example. Stoeckli et al. (1983, 1998) measured the enthalpies of immersion of two non-porous illites, with different BET surface areas (N2 77 K) into benzene and water. Whereas the area enthalpy of immersion into benzene was similar for both samples, about 73mJm , the area enthalpies of immersion into water were quite different, 371 and 782 mJ m respectively, Stoeckli et al. (1998). Clearly, the compositions of these illite surfaces differ. 

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