CEE 690K ENVIRONMENTAL REACTION KINETICS Introduction David A. Reckhow CEE690K Lecture #09 1 Updated: 8 October 2013 Print version Lecture #9 Reaction Mechanisms: Acid Catalysis Brezonik, Chapter 4
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CEE 690K ENVIRONMENTAL REACTION KINETICS
Introduction David A. Reckhow
CEE690K Lecture #09 1 Updated: 8 October 2013
Print version
Lecture #9 Reaction Mechanisms: Acid Catalysis Brezonik, Chapter 4
Mechanisms: Haloform Reaction
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Chlorine + acetone Morris & Baum, 1978 Brezonik, 1994 Pg 240-241
Haloform reaction: initial step
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Three potential pathways to enolate Reaction with water (KO), hydroxide (KOH), and proton (KH) kf=KO+KOH[OH-]+KH[H+] For acetone, the OH pathway dominates above pH 5.5
What is kr? ][]][[
HAAH
kk
Kr
fa
−+
==
Haloform: Doré’s diagram
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Doré (1989)
RLS is the first one
Loss of intermediates in lab water
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21C, ultrapure water (Nikolaou et al.,
2001)
Profile of TCP in water systems
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1,1,1-Trichloropropanone concentrations compared to the corresponding TTHM concentration for all samples
Chloroform (g/L)
0 20 40 60 80 100 120 140
1,1,
1- tr
ichl
orop
ropa
none
(g/
L)
0
1
2
3
4
5San Francisco Jan(Cl2/NH4Cl)Charleston(ClO2/ NH4Cl)San Francisco Apr (Cl2/NH4Cl)Ann Arbor(O3/NH4Cl)East Bay( Cl2/NH4Cl)Cincinnati(Cl2) Minneapolis (NH4Cl/NH4Cl)Monroe(O3/Cl2)Wyoming( Cl2/Cl2)Pinellas County(Cl2/Cl2) Pinellas County(Cl2/NH4Cl)Knoxville(ClO2/Cl2)
Monroe
Pinellas Co.
Knoxville
Loss in water heaters
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Liu et al., 2013 In review
Reaction Time (hr)
0 20 40 60 80 100 120
CP
( g/
L)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
No heating6 hrs incubation+heating24 hrs incubation+heating48 hrs incubation+heating72 hrs incubation+heating96 hrs incubation+heating
Reaction Time (hr)
0 20 40 60 80 100 120
TCP
( g/
L)
0.0
2.0
4.0
6.0
8.0No heating6 hrs incubation+heating24 hrs incubation+heating48 hrs incubation+heating72 hrs incubation+heating96 hrs incubation+heating
Reaction Time (hr)
0 20 40 60 80 100 120
DC
AN
( g/
L)
0.0
0.5
1.0
1.5
2.0
2.5
No heating6 hrs incubation+heating24 hrs incubation+heating48 hrs incubation+heating72 hrs incubation+heating96 hrs incubation+heating
Reaction Time (hr)
0 20 40 60 80 100 120
1,1-
DC
P (
g/L)
0.0
0.5
1.0
1.5
2.0
2.5
3.0No heating6 hrs incubation+heating24 hrs incubation+heating48 hrs incubation+heating72 hrs incubation+heating96 hrs incubation+heating
a b
c d
Case Study: TCP
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Reckhow & Singer, 1985 “Mechanisms of Organic Halide Formation During Fulvic Acid Chlorination and Implications with Respect to Preozonation”, In Jolley et al., Water Chlorination; Chemistry, Environmental Impact and Health Effect, Volume 5, Lewis.
Observed loss of 1,1,1-trichloropropanone in distribution systems Lab studies show that
chloroform is the product Logically presumed to be
a simple hydrolysis
Note: both TCP and TCAC refer to the 1,1,1-trichloropropanone
TCP (cont.)
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IkH 4.181.4ln −−=
[ ]TT HOClk 32024.0 +=
IkH 6.008.2log −−=
Ionic strength effects
Rate with chlorine Increases greatly
High intercept
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Gurol & Suffet showed 10x higher rate constants
Phosphate?
Disagreement with prior study
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Putting it together
Catalysis
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Homogeneous Catalysis Definition Liquid-phase substances which react with the main reactants or
intermediates thereby providing an alternative pathway to products with a lower activation energy or a higher frequency factor. Catalysts are often regenerated over the course of the reaction.
32 22 ++++ +→+ BABA termolecular reaction? – be skeptical
33
322
22
++++
++++
++++
+→+
+→+
+→+
BCBCCACACACA
32 22 ++++ +→+ BABA
What really happens:
“C” serves as a sort of charge-transfer facilitator, since “B” does not exist in a divalent state
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Summary
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To next lecture
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