Page 94 - Adsorbents fundamentals and applications

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ACTIVATED CARBON

Activated carbon is the most widely used sorbent. Its manufacture and use date
back to the 19th century (Jankowska et al., 1991). Its usefulness derives mainly
from its large micropore and mesopore volumes and the resulting high surface
area. The pore size distribution of a typical activated carbon is given in Figure 5.1,
compared with several other sorbents. Comprehensive reviews on activated car-
bon are available elsewhere (Mattson and Mark, 1971; Cheremisinoff and Eller-
busch, 1980; Bansal et al., 1988; Jankowska et al., 1991; Rouquerol et al., 1999).

5.1. FORMATION AND MANUFACTURE OF ACTIVATED CARBON
The modern manufacturing processes basically involve the following steps: raw
material preparation, low-temperature carbonization, and activation. The condi-
tions are carefully controlled to achieve the desired pore structure and mechanical
strength. The raw materials for activated carbon are carbonaceous matters such as
wood, peat, coals, petroleum coke, bones, coconut shell, and fruit nuts. Anthracite
and bituminous coals have been the major sources. Starting with the initial pores
present in the raw material, more pores, with desired size distributions, are created
by the so-called activation process. Two standard activation methods are used: gas
and chemical. After initial treatment and pelletizing, gas activation first involves
◦
carbonization at 400–500 C to eliminate the bulk of the volatile matter, and then
◦
partial gasification at 800–1000 C to develop the porosity and surface area. A
mild oxidizing gas such as CO 2 and steam, or flue gas, is used in the gasification
step because the intrinsic surface reaction rate is much slower than the pore diffu-
sion rate, thereby ensuring the uniform development of pores throughout the pel-
let. The activation process is usually performed in fixed beds, but in recent years
fluidized beds have also been used. The activated carbon created by the activation

Adsorbents: Fundamentals and Applications, Edited By Ralph T. Yang
ISBN 0-471-29741-0 Copyright  2003 John Wiley & Sons, Inc.

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