CEE 690K ENVIRONMENTAL REACTION KINETICS

Introduction David A. Reckhow

CEE690K Lecture #09 1 Updated: 8 October 2013

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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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