Environmental Engineering Reference
In-Depth Information
10
0
Benzene
10
-1
Tetrachloroethylene
10
-2
n
-decane
Aniline
10
-3
Phenol
10
-4
Naphthalene
10
-5
Lindane
10
-6
Phenanthrene
10
-7
Anthracene
10
-8
10
-9
Benzanthracene
10
-10
10
-11
10
-10
10
-9
10
-8
10
-7
10
-6
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
Calculated vapor pressure / kPa
FIGURE 3.3
A parity plot of the experimental and predicted vapor pressure of selected liquid
and solid organic molecules. (From Schwarzenbach, R.P., Gschwend, P.M., and Imboden, D.M.
1993.
Environmental Organic Chemistry
. NewYork: Wiley.)
For solids, the vapor pressure
P
i
is related to the sub-cooled liquid vapor pressure,
P
s(l)
, as follows (Prausnitz et al., 1980; Mackay, 1991):
ln
P
i
P
s
(l)
6.8
T
m
1
.
=−
T
−
(3.41)
Figure 3.3 is a comparison of experimental vapor pressures plotted against the
predicted values using the equations above for some of the compounds.
E
XAMPLE
3.9 V
APOR
P
RESSURE
E
STIMATION
Estimate the vapor pressure of benzene (a liquid) and naphthalene (a solid) at room
temperature (25
◦
C).
For benzene, which is a liquid (
T
b
=
353 K), ln
P
i
=
19
(
1
−
353
/
298
)
+
8.5 ln
(
353
/
298
)
=−
3.50
+
1.44
=−
2.06. Hence vapor pressure is 0.12 atm.
For naphthalene, which is a solid (
T
m
=
353 K,
T
b
=
491 K), ln (
P
i
/
P
s(l)
)
=
−
6.8
(
353
/
298
−
1
)
=−
1.255. For
T <T
b
,ln
P
s(l)
=
19
(
1
−
491
/
298
)
+
8.5 ln
(
491
/
298
)
=−
8.06.
P
s(l)
=
3.1
×
10
−
4
atm. Hence
P
i
=
8.8
×
10
−
5
atm.
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