Page 172 - Materials Chemistry, Second Edition

Vadose Zone Soil Remediation 155

Discussion:
1. The saturated vapor concentration of the weathered gasoline can
be a few times smaller than that of the fresh gasoline. In this
example, it is more than five times smaller.
2. The calculated vapor concentrations are essentially the same as
those listed in Table 5.1.

Example 5.2: Estimate Saturated Vapor Concentrations
of a Binary Mixture
A site is impacted by an industrial solvent. The solvent consists of 50% tol-
uene and 50% xylenes by weight. Soil venting is being considered for site
remediation. Estimate the maximum vapor concentration of the extracted
vapor. The subsurface temperature of the site is 20°C.

Solution:
(a) From Table 2.5, the following physicochemical properties were
obtained:

Molecular weight of toluene = 92.1
Molecular weight of xylenes = 106.2
P vap of toluene = 22 mm-Hg
P vap of xylenes = 10 mm-Hg

(b) The mole fractions of toluene and xylenes in the solvent can be
found as:

Basis: 1,000 g solvent
Moles of toluene = mass/MW = [(50%)(1,000)]
÷ (92.1) = 5.43 moles
Moles of xylenes = mass/MW = [(50%)(1,000)]
÷ (106.2) = 4.71 moles
Mole fraction of toluene = (5.43)/(5.43 + 4.71) = 0.536
Mole fraction of xylenes = 1 − 0.536 = 0.464
(c) The saturated vapor concentration can be found by using
Equation (5.1) as:

x ) (22mm-Hg)(0.536)=
P toluene = P ( vap )( A
= 11.79 mm-Hg = 0.0155 atm