Biomedical Engineering Reference
In-Depth Information
The Henry's Law constant (dimensionless) represents the ratio of a
contaminant's concentration in the air to its concentration in the water at
equilibrium at a specific temperature and pressure (usually 1 atm). A
compound with a Henry's Law constant
<
0.05 would partition strongly
from the gas phase into the water phase when contaminated air is
brought into contact with clean water (Zogorski et al., 1997). The value
of the Henry's Law constant for methanol given in Table 2.3 is
1.09
10
4
]at25
C. Table 2.3 provides this value and other
physical and chemical properties of methanol, gasoline, and benzene
for comparison. Since Henry's Law constant for methanol is quite low,
and much less than the 0.05 noted earlier, atmospheric methanol would
partition readily into water droplets. Concomitantly, methanol in water
bodies is likely to remain in the aqueous phase. Therefore, once in
water, methanol would be difficult to remove by volatilization—either
passively or actively (e.g., air stripping).
[
TABLE 2.3 A Summary of Physical and Chemical Properties of
Methanol, Gasoline (BTEX), and Benzene
Physical and
Chemical Properties
Methanol
Gasoline
Benzene
100
c
78.11
c
Molecular weight (g/mol)
32.04
Elemental composition by weight
% Oxygen
50%
(Mix of C4-C14
hydrocarbons)
0%
% Carbon
37.5%
92%
% Hydrogen
12.5%
8%
0.72-0.78
c
0.88
c
Specific gravity
0.7915 at
60
F
e
Boiling point (
C)
27-225
b
80.1
c
64.7
100-200
c
Water solubility (mg/l)
Miscible
1780
Vapor pressure
(mm Hg) (at 25
C)
76, 95
c
126
—
(psi) (at 100
F)
d
4.63
7-15
—
Heat of combustion (kJ/kg)
b
19,930
43,030
—
10
6
5.43
10
3c
4.55
Henry's Law constant
(atm m
3
/g mol)
—
10
6c
4.42
(continued )
