CEE 690K ENVIRONMENTAL REACTION KINETICS Lecture #9 Reaction - - PDF document

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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

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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?

] [ ] ][ [ HA A H k k K

r f a  

 

Haloform: Doré’s diagram

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 Doré (1989) RLS is the first one

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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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TTHM concentration for all samples

Chloroform (g/L)

20 40 60 80 100 120 140

1,1,1- trichloropropanone (g/L)

1 2 3 4 5 San 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

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Loss in water heaters

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 Liu et al.,

2013

 In review

Reaction Time (hr) 20 40 60 80 100 120 CP (g/L) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 No heating 6 hrs incubation+heating 24 hrs incubation+heating 48 hrs incubation+heating 72 hrs incubation+heating 96 hrs incubation+heating Reaction Time (hr) 20 40 60 80 100 120 TCP (g/L) 0.0 2.0 4.0 6.0 8.0 No heating 6 hrs incubation+heating 24 hrs incubation+heating 48 hrs incubation+heating 72 hrs incubation+heating 96 hrs incubation+heating Reaction Time (hr) 20 40 60 80 100 120 DCAN (g/L) 0.0 0.5 1.0 1.5 2.0 2.5 No heating 6 hrs incubation+heating 24 hrs incubation+heating 48 hrs incubation+heating 72 hrs incubation+heating 96 hrs incubation+heating Reaction Time (hr) 20 40 60 80 100 120 1,1-DCP (g/L)

0.0 0.5 1.0 1.5 2.0 2.5 3.0

No heating 6 hrs incubation+heating 24 hrs incubation+heating 48 hrs incubation+heating 72 hrs incubation+heating 96 hrs incubation+heating

a b c d

Case Study: TCP

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“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

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TCP (cont.)

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I kH 4 . 1 81 . 4 ln     

T T

HOCl k 32 024 .  

I kH 6 . 08 . 2 log   

 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.

3 2

2 2

   

   B A B A termolecular reaction? – be skeptical

3 3 3 2 2 2 2            

         B C B C C A C A C A C A

3 2

2 2

   

   B A B A 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