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246 4. Adsorption and Ion Exchange

The following are examples (see Table 4.2):

• Alcohols are poorly adsorbed; they are very soluble and highly polar .
,
• Aldehydes are highly polar and as the molecular weight increases, the polarity
decreases and adsorbability increases.
• Amines are similar in structure to ammonia (NH 3 ) except that the nitrogen is bonded
to an organic group. Adsorption is limited by polarity and solubility .
• Chlorinated armoatics and chlorinated aliphatics are low-polarity and lo w-solubility
compounds, which make them generally quite adsorbable.
• -soluble, Glycols are w and are not very adsorbable. ater
• Higher molecular weight organic compounds will generally be more adsorbable owing
to adsorptive attraction relatie to size. v

Largely, the same principles apply for water treatment. Consequently acti , v ated carbon
is suitable for organic molecules that are nonpolar and of high molecular weight.
Trichloroethylene, benzene, ethylbenzene, toluene, and xylene are easily adsorbed in the
gas phase when activated carbon, for instance, is used. On the other hand, adsorption is not
etones, preferably selected in applications in relation to aldehydes, k and alcohols. In a suc-
cessful application, reduction in emissions from 400–2000 ppm to under 50 ppm can be
achieved (EPA, 1999), especially for OCs with boiling points between 20 –and 175 °C. V

Table 4.2
From stronger adsorption to weaker adsorption on acti v ated carbon
Compound Molecular weight Boiling point (°C)
Nitrobenzene 123 211
Tetrachloroethane 166 147
Tetrachloroethylene 165 121
Styrene 104 145
Xylene 106 138
Naphthalene 128 217
Toluene 92 111
Benzene 78 80
10% of carbon capacity
MTBE 88 55
Hexane 86 68
Ethylacrylate 100 57
Dichloroethane 99 99
Methylethylketone 72 80
Methylene chloride 84 40
Acrilonitrile 53 74
1% of carbon capacity
Acetone 58 56
Vinylchloride 62 14
Chloroethane 64 12
Bromotrifluoromethane 149 58
Methane 16 161