Section 3 VOC Controls - US Environmental Protection Agency

potential and polarizability.[8] In this Manual, the modified D-R equation is referred to as the
Calgon fifth-order polynomial. The data displayed in the Calgon graphs [6] has been fit to the
Freundlich equation. The resulting Freundlich parameters are shown in Table 1.1 for a limited
number of chemicals. The adsorbates listed include aromatics (e.g., benzene, toluene), chlorinated
aliphatics (dichloroethane), and one ketone (acetone). However, the list is far from all-inclusive.
Notice that a range of partial pressures is listed with each set of parameters, k and m.
(Note: In one case (m-xylene) the isotherm was so curvilinear that it had to be split into two parts,
each with a different set of parameters.) This is the range to which the parameters apply.
Extrapolation beyond this range—especially at the high end—can introduce inaccuracy to the
calculated adsorptivity.
But high-end extrapolation may not be necessary, as the following will show. In most air
pollution control applications, the system pressure is approximately one atmosphere (14.696 psia).
The upper end of the partial pressure ranges in Table 1.1 goes from 0.04 to 0.05 psia. According
to Dalton’s Law, at a total system pressure of one atmosphere this corresponds to an adsorbate
concentration in the waste gas of 2,720 to 3,400 ppmv. Now, as discussed in Section 1.1.2, the
adsorbate concentration is usually kept at 25% of the lower explosive limit (LEL). 2 For many
VOCs, the LEL ranges from 1 to 1.5 volume %, so that 25% of the LEL would be 0.25 to
2
Equilibrium Adsorptivity (lb adsorbate/lb adsorbent)
(Note: T1