Effect of polarity on the adsorption of dichlorobenzene isomers

The influence of reference vapor polarity on the characterization of microporous carbon adsorbents using the Dubinin equations was investigated. Polarity may be an important parameter for reference vapor selection due to the influence of electrostatic forces on the adsorption of polar vapors. Adsorbate polarity was investigated by evaluating the adsorption isotherms and characteristic curves for the three isomers of dichlorobenzene and the heats of adsorption for the two liquid isomers. The three isomers are very similar in terms of molecular weight, vapor pressure, density, and electronic polarizations. The major difference is the range of dipole moments: 1,2-dichlorobenzene, 2.50 D; 1,3-dichlorobenzene, 1.72 D; and 1,4-dichlorobenzene, 0.00 D. If adsorbate polarity has a major influence on adsorption, the three characteristic curves should have different slopes. The slopes of the three curves were not statistically different at the 95% level, and no difference in the heats of adsorption was observed. It was concluded, therefore, that electrostatic forces do not have a major influence on vapor adsorption when adsorbate polarities are between 0 and 2.50 D. Therefore, a single reference vapor may be adequate for characterization of microporous carbon adsorbents.