Specialized activation treatments procedure

Optimization of the pore size distribution is important for the control of both the equilibria and the dynamics of physisorption (see Ruthven, 1984 Do et al., 1993). Most activated carbons are highly microporous, but for some purposes it is desirable to extend the range of pore size into the mesopore or macropore range - or even eliminate the microporosity. Progress in this direction has been made by the use of special pre-treatment procedures and the careful control of the conditions of carbonization and activation. In this connection, physisorption measurements have an important role to play in characterizing the material at various stages of manufacture. 

Activated carbon adsorbents generally show very little selectivity in the adsorption of molecules of different size. However, by special activation procedures it is possible to prepare carbon adsorbents with a very narrow distribution of micropore size and which therefore behave as molecular sieves. The earliest examples of carbon molecular sieves appear to have been prepared by decomposition of polyvinylidene dichloride (Saran) but more recently a wide variety of starting materials have been used. Most commercial carbon sieves are prepared from anthracite or hard coal by controlled oxidation and subsequent thermal treatment. The pore structure may be modified to some extent by subsequent treatment including controlled cracking of hydrocarbons within the micropore system and partial gasification under carefully regulated conditions. ... 

With special techniques for the activation of the metal—e.g. for removal of the oxide layer, and the preparation of finely dispersed metal—the scope of the Refor-matsky reaction has been broadened, and yields have been markedly improved." The attempted activation of zinc by treatment with iodine or dibromomethane, or washing with dilute hydrochloric acid prior to use, often is only moderately successful. Much more effective is the use of special alloys—e.g. zinc-copper couple, or the reduction of zinc halides using potassium (the so-called Rieke procedure ) or potassium graphite. The application of ultrasound has also been reported. ... 

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