Table 6.8 lists combined hydrolysis and dehydrochlorination rate constants k at
neutral and basic pH values for chlorinated methanes, ethanes, and ethylenes at
25
C (Jeffers et al. 1989). Hydrolysis and dehydrochlorination rates are very slow
under most environmental conditions.
COCs reduction by iron particles is a heterogeneous reaction. However, as to
evaluate kinetic degradation, homogeneous equations are frequently used as a first
approximation.
Homogeneous Approach
Pseudo-orders with respect to the pollutant can be determined by using a great excess
of iron particles, in order to consider a constant concentration in reactant. The
concentration can thus be included in the rate constant:
k obs ¼ k à C
β
ZVI
ð6:38Þ
where k obs is the observed rate constant, k the rate constant, C ZVI the concentration in
reactant (mol L
À1 ), and β the order of reaction with respect to the reactant. The units
of k obs and k depend on the global reaction order: mol L
À1 s
À1 for order zero, s
À1 for
first order, and L mol
À1 s
À1 for second order.
In batch experiments, the rate equation can be written as:
Table 6.8 Combined hydrolysis and dehydrochlorination rate constants k at neutral and alkaline
pH values of chlorinated methanes, ethanes, and ethylenes at 25
C (from Jeffers et al. 1989)
Compounds
Neutral hydrolysis +
dehydrochlorination
Alkaline hydrolysis +
dehydrochlorination
k (min
À1
)
Ea (kJ mol
À1
)
k (min
À1
)
Ea (kJ mol
À1 )
CT
3.26 Â 10
À8
114.5 Æ 5.0
0.00
–
CF
1.91 Â 10
À10
122.9 Æ 13
5.22 Â 10
À10
104.6 Æ 8.0
HCA
0.00
–
7.18 Â 10
À16
109.8 Æ 20
PCA
4.93 Â 10
À8
94.9 Æ 2.9
1.31 Â 10
À4
80.8 Æ 10
1,1,1,2-TeCA 2.60 Â 10
À8
94.9 Æ 15
2.15 Â 10
À9
100.3 Æ 1.7
1,1,2,2-TeCA 9.70 Â 10
À9
92.4 Æ 3.2
3.02 Â 10
À6
78.1 Æ 1.0
1,1,1-TCA
1.24 Â 10
À6
116.1 Æ 2.0
0.00
–
1,1,2-TCA
5.19 Â 10
À11
121.2 Æ 5.9
9.42 Â 10
À9
88.2 Æ 7.5
1,1-DCA
2.15 Â 10
À8
109.5 Æ 3.3
7.20 Â 10
À14
114.8 Æ 2.0
1,2-DCA
1.83 Â 10
À8
103.7 Æ 10
1.04 Â 10
À11
121.6 Æ 6.1
PCE
0.00
–
1.37 Â 10
À15
123.1 Æ 9.4
TCE
0.00
–
1.07 Â 10
À12
126.6 Æ 4.7
1,1-DCE
0.00
–
6.32 Â 10
À17
130.2 Æ 20
1,2-DCE
0.00
–
1.09 Â 10
À14
130.3 Æ 3.9
Ea represents the activation energy of the reaction
316
R. Rodrigues et al.
neutral and basic pH values for chlorinated methanes, ethanes, and ethylenes at
25
C (Jeffers et al. 1989). Hydrolysis and dehydrochlorination rates are very slow
under most environmental conditions.
COCs reduction by iron particles is a heterogeneous reaction. However, as to
evaluate kinetic degradation, homogeneous equations are frequently used as a first
approximation.
Homogeneous Approach
Pseudo-orders with respect to the pollutant can be determined by using a great excess
of iron particles, in order to consider a constant concentration in reactant. The
concentration can thus be included in the rate constant:
k obs ¼ k à C
β
ZVI
ð6:38Þ
where k obs is the observed rate constant, k the rate constant, C ZVI the concentration in
reactant (mol L
À1 ), and β the order of reaction with respect to the reactant. The units
of k obs and k depend on the global reaction order: mol L
À1 s
À1 for order zero, s
À1 for
first order, and L mol
À1 s
À1 for second order.
In batch experiments, the rate equation can be written as:
Table 6.8 Combined hydrolysis and dehydrochlorination rate constants k at neutral and alkaline
pH values of chlorinated methanes, ethanes, and ethylenes at 25
C (from Jeffers et al. 1989)
Compounds
Neutral hydrolysis +
dehydrochlorination
Alkaline hydrolysis +
dehydrochlorination
k (min
À1
)
Ea (kJ mol
À1
)
k (min
À1
)
Ea (kJ mol
À1 )
CT
3.26 Â 10
À8
114.5 Æ 5.0
0.00
–
CF
1.91 Â 10
À10
122.9 Æ 13
5.22 Â 10
À10
104.6 Æ 8.0
HCA
0.00
–
7.18 Â 10
À16
109.8 Æ 20
PCA
4.93 Â 10
À8
94.9 Æ 2.9
1.31 Â 10
À4
80.8 Æ 10
1,1,1,2-TeCA 2.60 Â 10
À8
94.9 Æ 15
2.15 Â 10
À9
100.3 Æ 1.7
1,1,2,2-TeCA 9.70 Â 10
À9
92.4 Æ 3.2
3.02 Â 10
À6
78.1 Æ 1.0
1,1,1-TCA
1.24 Â 10
À6
116.1 Æ 2.0
0.00
–
1,1,2-TCA
5.19 Â 10
À11
121.2 Æ 5.9
9.42 Â 10
À9
88.2 Æ 7.5
1,1-DCA
2.15 Â 10
À8
109.5 Æ 3.3
7.20 Â 10
À14
114.8 Æ 2.0
1,2-DCA
1.83 Â 10
À8
103.7 Æ 10
1.04 Â 10
À11
121.6 Æ 6.1
PCE
0.00
–
1.37 Â 10
À15
123.1 Æ 9.4
TCE
0.00
–
1.07 Â 10
À12
126.6 Æ 4.7
1,1-DCE
0.00
–
6.32 Â 10
À17
130.2 Æ 20
1,2-DCE
0.00
–
1.09 Â 10
À14
130.3 Æ 3.9
Ea represents the activation energy of the reaction
316
R. Rodrigues et al.