Superactive carbons

Activated charcoal was originally regarded as a relatively inexpensive adsorbent with an assortment of pores of ill-defined size and shape. However, in recent years considerable progress has been made in the development of tailor-made porous carbons such as molecular sieves, activated carbon fibres and carbon composites (Marsh et al., 1997). Superactive carbons are now made on a commercial scale with BET areas of around 3000 m2g-1. Activated carbons can be manufactured as fine particles or granules or in the form of a cloth, felt or consolidated membrane. The properties of some of these special types of activated carbon are discussed in Chapter 12. 

Nitrogen isotherms on some activated carbons and the corresponding as-plots and Dubinin-Radushkevich (DR) plots are shown in Figure 9.11. The isotherms on Carbosieve and the carbon cloth JF005 are of well-defined Type I in the IUPAC classification, but the isotherms on the carbon cloth JF517 and the superactive carbon AX21 are evidently more complex. 

A novel method of chemical activation for producing some of the most active adsorbents so far developed was disclosed by AMOCO (Standard Oil Company) scientists in 1978 (Wennerberg and O Grady, 1978). These superactive carbons were prepared by the high-temperature heat treatment of petroleum coke or coal mixed with excess amounts of potassium hydroxide. After removal of the remaining KOH and other soluble material, the products were reported to have BET areas of over 2300 m2 g 1. 

Adsorption isotherms of nitrogen (at 77 K), toluene (at 293 K) and water vapour (at 294 K) on a sample of AMOCO superactive carbon, PX21, are shown in Figure... 

The first commercial plant for the production of the AMOCO superactive carbons was constructed by the Anderson Development Company, Michigan. Their products were claimed to have BET areas in the range 2800-3500 m2 g i and total pore volumes of 1.4-2.0 cm3 g1. The properties of one batch of the Anderson superactive carbon, designated AX-21 (BET area, 2960 m2 g 1 micropore volume, 1.4 cm3 g ), have been investigated in some detail (Carrott et al., 1987, 1988, 1989b). More... 

Figure 123 Integral molar energies of adsorpuon given by (he immersion of carbon cloth AM4 (1) and superactive PX21 (2) m organic liquids plotted against carbon number (Atkinson et al, 1984)...

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