CEE 690K ENVIRONMENTAL REACTION KINETICS Lecture #17 Case Study: - - PDF document

4/12/2008 1

CEE690K Lecture #17 1

Updated: 12 April 2008

Print version

CEE 690K

ENVIRONMENTAL REACTION KINETICS Lecture #17

Introduction

David A. Reckhow

Case Study: DCAN & DCAD research

Primary Literature as noted

DHAN

K i di

C N C H Cl Cl C C H Cl Cl N OH H NH C C H Cl Cl N OCl H NCl

H2O

fast fast k2 k1 k4

DCAN OCl OH

Key intermediate Concentrations are

well known

C C Cl Cl OH C C H Cl Cl NH2 O C C H Cl Cl NHCl O H2O

Cl(+II) S (+IV)

C C Cl Cl O

pKa = 3.7

fast k1-2 k1-1

DCAD HOCl OH OH N-Cl-DCAD N-Cl-DCAD anion

C C H Cl Cl O OH NHCl2 NH3 C C H Cl Cl NHCl OCl OH C C H Cl Cl NH2 OH O fast fast

DCAA David A. Reckhow

2 CEE690K Lecture #17

4/12/2008 2

Hydrolysis and oxidation

Proposed Rate Law for DCAN

3

Hydrolysis and oxidation k1 = 1.78 x10-7 ±0.35 x10-7 (s-1)

dC dt k k OH k Cl I C = − + + +

−

{ [ ] [ ( )]}

1 2 3

k2 = 3.42 ±0.31 (M-1s-1) k3 = 1.30 x 10-1 ±0.08 x 10-1 (M-1s-1)

David A. Reckhow

CEE690K Lecture #17

DCAN half-life based on pH & HOCl

• At 20 C

100 1 Hour

4

• From Reckhow,

Platt, MacNeill & McClellan, 2001

Aqua 50:1:1-13

• Degradation in DS
• bserved to

increase with increasing pH

ICR data:

rine Residual (mg/L)

1 10

OCl-

10 Minutes 1 Hour 8 Hours 1 Day 3 Days 1 Week

Obolensky & Frey, 2002

pH

6 7 8 9 10 11

Chlor

0.1

OH- H2O

3 Weeks

David A. Reckhow

CEE690K Lecture #17

4/12/2008 3

Halamides

Compounds

5

Compounds Monohaloacetamides

Chloroacetamide, Bromoacetamide

Dihaloacetamides

Dichloroacetamide (DCAD) Bromochloracetamide (BCAD) Dibromoacetamide (DBAD)

T ih l

t id

Trihaloacetamides

trichloroacetamide & analogues

Chlorination byproducts Probably a bit less prevalent with chloramines Pre-oxidation will probably reduce subsequent formation

David A. Reckhow

CEE690K Lecture #17

DCAD degradation

In presence of chlorine

residual

Rate limiting step is

hypochlorous acid attack in N- chloro-DCAD

But since we usually measure

DCAD , then

[ ] [ ][ ]

DCAD Cl N HOCl k dt DCAD d

t

− − − =

−2 1

DCADt, then

Where, k1-2 ~ 800 M-1s-1

[ ] [ ] [ ]

t t

DCAD H H HOCl k dt DCAD d ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + − =

+ − + −

] [ 10 ] [

7 . 3 2 1

4/12/2008 4

ual (mg/L)

10 100 DCAD Halflife 1 Hour 8 Hours 1 Day 10 Minutes

DCAD Stability

7

Chlorine Residu

0.1 1 3 Weeks 1 Day 3 Days 1 Week

HOCl

6 7 8 9 10 11

pH

6 7 8 9 10 11

OH-

3 Weeks 1 Hour 8 Hours 1 Day 3 Days 1 Week Reducing Conditions

David A. Reckhow

CEE690K Lecture #17

Amino Acids and Proteins

Simple Amino Acids

f M d AN

8

H2C C H COOH NH2

NH 2

some form THMs and HANs Highest reactivity for activated

AAs

Tyrosine & Tryptophan: activated

aromatic

Cysteine: sulfhydryl group Proteins

Alanine Alanine

HO C H2 C H COOH

Tyrosine Tyrosine

many linked AAs; relatively

unreactive polypeptide bonds

Reactions with proteins occurs

most readily on AA side chains

David A. Reckhow

CEE690K Lecture #17

4/12/2008 5

N

C R1 H R4 R3 R2

N

C R1 X R4 R3 R2

N

C X X R4 R3 R2 R1=H X+ Nu X+ Nu

Degradation pathways

9 R2=H or COOH R4=H HX (CO2) R2=H or COOH

C

N R3 X R4

I II III IV C

N R3 R1 R4 NH2X R1=H X+ Nu HX (CO2) General scheme for carbonyl

and cyano formation from chlorination of amines and amino acids

C

O R4 R3

R1NH2 C

N R3

V VI

NH2X HX

Monohalamine Pathway Dihalamine Pathway

amino acids

• (adapted from Nweke and

Scully, 1989, and Armesto et al., 1998).

David A. Reckhow

CEE690K Lecture #17

HOCl & AAs

Pathways

Isoleucine Isoleucine

y

Rapid formation of

nitriles and aldehydes from chlorine, slower and more complex behavior with chloramines

Aldehyde Aldehyde

Froese, Kenneth L., Wolanski, Alina, and Hrudey, Steve E. “Factors Governing Odorous Aldehyde Formation as Disinfection By-Products in Drinking Water”. Water Research 33[6], 1355-1364. 1999.

Nitrile Nitrile

4/12/2008 6

Formation of

aldehydes

Froese, Kenneth L., Wolanski, Alina, and Hrudey, Steve E. “Factors Governing Odorous Aldehyde Formation as Disinfection By-Products in Drinking Water”. Water Research 33[6], 1355-1364. 1999.

12

To next lecture

David A. Reckhow

CEE690K Lecture #17