Environmental Engineering Reference
In-Depth Information
TABLE 4.2
Temperature Dependence of K aw
K aw =
exp A
T
1
RT
B
Temperature Range ( C)
Compound
A
B
Benzene
10-30
5.534
3194
Toluene
10-30
5.133
3024
Ethylbenzene
10-30
11.92
4994
o -Xylene
10-30
5.541
3220
Chloroform
10-30
11.41
5030
1,1,1-Trichloroethane
10-30
7.351
3399
Trichloroethylene
10-30
7.845
3702
ct 2
K aw =
a
+
bt
+
Temperature Range ( C)
Compound
a
b
c
Benzene
0-50
0.0763
0.00211
0.000162
Toluene
0-50
0.115
0.00474
0.000466
Ethylbenzene
5-45
0.05
0.00487
0.000250
o -Xylene
15-45
0.0353
0.00444
0.000131
Chloroform
0-60
0.0394
0.00486
-
1,1,1-Trichloroethane
0-35
0.204
0.0182
0.000173
Trichloroethylene
5-45
0.151
0.00597
0.000680
Source: FromAshworth, R.A., Howe, G.B., Mullins, M.E., and Rogers, T.N. 1988. JournalofHazardous
Materials 18, 25-36.
Note: R = 8.205 × 10 5 atm m 3 /K mol, T is in K, and t is in C.
Over a wide range of temperature, K aw is correlated to T using the following
polynomial, K aw (T)
cT 2 , where a , b , and c for several compounds are
=
a
+
bT
+
listed in Table 4.2.
E XAMPLE 4.5 K aw AND T EMPERATURE
Determine K aw for benzene at 30 C using Table 4.2.
Using K aw = ( 1 /( 8.205 × 10 5
× 303 ) exp ( 5.534 ( 3194 / 303 )) = 0.267
Using K aw = 0.0763 + 0.00211 30 + 0.000162 900 = 0.285.
Wastewaters and contaminated waters have varied composition and often contain
other organic solvents that are miscible with water. These solvent
water mixtures
affect the overall solubility of organic solutes thus varying x i in the equation for K aw .
There is evidence in the literature that the effects do not become predominant unless
significant concentrations ( > 10 wt%) of a very soluble co-solvent are present in natu-
ral systems.An important paper in the literature in this regard is the one by Munz and
Roberts (1987), where they evaluated the Henry's constants of three chloromethanes
(chloroform, carbon tetrachloride, and hexachloroethane) often encountered in
wastewaters and atmospheric water. Munz and Roberts (1987) observed no significant
+
 
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