Table 5206 Maximum Capacity Of

ACTIVATED CARBON FOR VARIOUS SOLVENTS FROM AIR AT 20°C AND 1 ATM

Adsorbate

Maximum Capacity, kg/kg Carbon

Carbon tetrachloride, CCl4 Butyric acid, C4H8O2 Amyl acetate, C7H14O2 Toluene, C7H8 Putrescene, C4H12N2 Skatole, C9H9N Ethyl mercaptan, C2H6S Eucalyptole, C10H18O Ethyl acetate, C4H5O2 Sulfur dioxide, SO2 Acetaldehyde, C2H4O Methyl chloride, CH3Cl Formaldehyde, HCHO Chlorine, Cl2 Hydrogen sulfide, H2S Ammonia, NH3 Ozone, O3

0.45 0.35 0.34 0.29 0.25 0.25 0.23 0.23 0.19 0.10 0.07 0.05 0.03 0.022 0.014 0.013 decomposes to O2

Source: P.C. Wankat, 1990, Rate-controlled separations (London: Elsevier).

where L and Ps are the bed length and the bulk density of the adsorber, respectively. For new and completely regenerated adsorbents, wo = 0.

The actual breakpoint time t is always less than ts. If the adsorption zone is small compared to the bed length L, most of the adsorbent is used.

In an ideal case of no mass-transfer resistance and no axial dispersion, the adsorption zone becomes zero, i.e., t = ts. However, since mass-transfer resistance always exists, the practical operating capacity is normally 25-50% of the theoretical isotherm value.

FIG. 5.20.13 Zeolite-based adsorption system for solvent vapors. The large wheel in the middle of the unit adsorbs vapors and is simultaneously regenerated.

In a fixed, cylindrical bed adsorber, the adsorption zone shown in Figure 5.20.14 moves down the column at a nearly constant pattern. The shape and velocity of the adsorption zone are influenced by the adsorption isotherm. For Freundich-type adsorption, in which co = awf as expressed in Equation 5.20(15), the following equation gives velocity of the adsorption zone:

and the following equation expresses the height of the adsorption zone:

where K is the overall gas-solid mass-transfer coefficient (s_1) and c is the breakthrough concentration set by the oo

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