Updated: 4 September 2013 CEE 697K Lecture #2 1 Print version CEE 697K ENVIRONMENTAL REACTION KINETICS Lecture #2 Rate Expressions: Bromide + Chlorine case study & lab project Kumar & Margerum paper Introduction David A. Reckhow
Reactions with Chlorine 2 Oxidized NOM The Precursors! and inorganic chloride •Aldehydes HOCl + natural organics Chlorinated Organics (NOM) •TOX •THMs •HAAs The THMs Br Br Br Cl H C Cl C H H C Br C H Br Cl Cl Br Cl Cl Chloroform Bromodichloromethane Chlorodibromomethane Bromoform CEE 697K Lecture #2 David A. Reckhow
The Haloacetic Acids 3 Br Br Br Cl COOH C Cl C COOH COOH Br COOH C C Br Cl Cl Br Cl Cl Trichloroacetic Bromodichloroacetic Chlorodibromoacetic Tribromoacetic Acid Acid Acid Acid (TCAA) Br Br Cl H C COOH COOH C H C COOH H Cl Br Cl Dichloroacetic Bromochloroacetic Dibromoacetic Acid Acid Acid (DCAA) CEE 697K Lecture #2 David A. Reckhow
Distribution: Variability within a single system 4 Example: New Haven Service Area DS model CEE 697K Lecture #2 David A. Reckhow
New Haven Distribution System 3,400 pipes 2,500 junctions Sept 11, 1997 5 22:00 chlorine 8.7 MG Millrock Basins West River WTP Lake Gaillard WTP Maltby Tank 3 MG Lake Saltonstall WTP 2.0 mg/L DOC (Treated) pH 7 1.8 mg/L chlorine dose CEE 697K Lecture #2 David A. Reckhow
Sept 11, 1997 6 22:00 TTHM CEE 697K Lecture #2 David A. Reckhow
7 Sept 11, 1997 22:00 HAA6 CEE 697K Lecture #2 David A. Reckhow
Work of Michael Plewa Genotoxicity Univ. of Illinois 8 Tribromopyrrole EMS +Control DBP Chemical Class Dibromoacetamide Trihloroacetamide Bromate Chloroacetamide Bromoacetamide Iodoacetamide MX Other DBPs 3,3-Bromochloro-4-oxopentanoic Acid 3,3-Dibromo-4-oxopentanoic Acid Bromochloroacetonitrile 2-Iodo-3-bromopropenoic Acid Trichloroacetonitrile Dibromoacetonitrile Dichloroacetonitrile Haloacetamides Chloroacetonitrile 2,3-Dibromopropenoic Acid Bromoacetonitrile 2-Bromobutenedioic Acid Iodoacetonitrile BDCNM DBCNM DBNM TBNM TCNM BCNM DCNM Haloacetonitriles CNM BNM Halonitromethanes CDBAA DBAA BCAA TBAA DIAA Halo Acids BIAA BAA CAA IAA Haloacetic Acids 10 -6 10 -5 10 -4 10 -3 10 -2 Single Cell Gel Electrophoresis Genotoxicity Potency Log Molar Concentration (4 h Exposure) Not Genotoxic: DCAA, TCAA, BDCAA, Dichloroacetamide, CEE 697K Lecture #2 David A. Reckhow 3,3-Dibromopropenoic Acid, 3-Iodo-3-bromopropenoic Acid, 2,3,3,Tribromopropenoic Acid July 2006
Bromide: THM Formation 9 100 Data from: Minear & Bird, 1980 96 hours, pH 7.0 5 mg/L Chlorine Dose 80 CHCl 3 1 mg/L Humic Acid Percent of TTHM CHBr 3 60 CHBr 2 Cl 40 CHBrCl 2 20 0 0.0 0.4 0.8 1.2 1.6 2.0 CEE 697K Lecture #2 David A. Reckhow Bromide Concentration (mg/L)
Impact of Bromide on DHAA Formation 10 100 pH 7, 25 o C, 7 days CHCl 2 COOH 25 mg/L chlorine dose 80 2.9 mg/L TOC Concentration ( µ g/L as Cl - ) 60 CHClBrCOOH CHBr 2 COOH 40 20 0 0 1 2 3 4 5 From Pourmoghaddas, 1990 Bromide Concentration (mg/L) CEE 697K Lecture #2 David A. Reckhow
Formation of Brominated THMs 11 H HOCl HOCl HOCl A B C Cl C Cl Cl H HOCl HOCl Cl C Br E D Cl H HOCl Br C Br F Cl H − − + → + k Br C Br HOCl Br HOBr Cl CEE 697K Lecture #2 David A. Reckhow Br
Bromo speciation 12 1.2 Full-scale data (small symbols) (All 12 plants) from Weinberg et al., 2002 Lab data (large symbols) 1.0 from Hua & Reckhow, 2004 THM Mole Fraction (THM4 only) Lines are geometric model 0.8 CHCl3 CHBrCl2 0.6 CHBr2Cl CHBr3 CHCl3 Lab tests 0.4 CHBrCl2 Lab tests CHBr2Cl Lab tests CHBr3 Lab tests 0.2 0.0 0.0 0.2 0.4 0.6 0.8 1.0 CEE 697K Lecture #2 David A. Reckhow THM Br/(Cl+Br)
Case study: chlorine + bromide 13 Observed reaction + − → + − k 2 HOCl Br HOBr Cl Nucleophilic attack of bromide on oxygen in hypochlorous acid k 2 = 2.95 x10 3 M -1 s -1 at 25ºC Note that HOCl deprotonates at elevated pHs From Farkas et al., 1949 Transfer of Cl + to form intermediate (BrCl) − − + + → + + k HA HOCl Br A H O BrCl 3 2 − − + ← → + fast − − + ← → BrCl Br Br Cl fast Br Br Br 2 2 3 From: Kumar & Margerum, 1987 CEE 697K Lecture #2 David A. Reckhow
Background 14 Absorbance for monitoring reaction Known equilibria CEE 697K Lecture #2 David A. Reckhow
Alkaline Experiments 15 Pseudo-1 st order Bromide in great excess Slow reactions Could be monitored directly by conventional UV spectrophotometer 292 nm peak for hypochlorite (OCl - ) Followed for 4 half-lives Complete from: 1.1 sec – 4 hr Plot ln(A t -A ∞ ) vs time Slope is k obs CEE 697K Lecture #2 David A. Reckhow
K obs is a linear function of Bromide 16 CEE 697K Lecture #2 David A. Reckhow
pH dependency 17 CEE 697K Lecture #2 David A. Reckhow
Overall pH dependence 18 How to explain pH effect on 2 nd order rate constant? See also, Brezonik, pg 230; figure 4-20 CEE 697K Lecture #2 David A. Reckhow
Buffer Tests 19 Low pH High pH CEE 697K Lecture #2 David A. Reckhow
Buffer Effect 20 Proposed dependence on HA = ± − − 2 1 k HA 8 . 9 1 . 3 M s ( ) + + = + − HPO 4 -2 [ ] [ ] [ ] k k k H k HA Br obs 0 H HA + 1 [ H ] C = α = = T [ HA ] C C HCO 3 - + + + 0 T T K 1 [ ] K H a + a [ H ] = ± − − 2 2 1 k HA ( 1 . 25 0 . 15 ) x 10 M s k − k obs − 0 [ Br ] [ buffer ] = + T k k + + + H HA [ ] [ ] H K H a CEE 697K Lecture #2 David A. Reckhow
21 High pH only ( ) + + = + − [ ] [ ] [ ] k k k H k HA Br obs 0 H HA − ( ) d [ OCl ] − = + + + − − k k [ H ] k [ HA ] [ OCl ][ Br ] 0 H HA dt More generally + ( ) d [ Cl ( I )] − − − − = + + k [ OCl ] k [ HOCl ] k [ HA ][ OCl ] [ Br ] 0 HOCl HA dt CEE 697K Lecture #2 David A. Reckhow
Acidic Experiments 22 Pseudo-1 st order Bromide in great excess Fast reactions Required high-speed setup Stopped-flow spectrophotometer Could monitor 2º product 266 nm peak for tribromide (Br 3 - ) Followed for 4 half-lives Complete from 0.40-0.01 sec Plot ln(A t -A ∞ ) vs time Slope is k obs CEE 697K Lecture #2 David A. Reckhow
Stopped-flow 23 Principle Commercial instruments Limitations ′ k Correct for slow mixing speed (k m ) = 1 [ obs ] ( ) k − ′ obs k obs k For Durrum instrument: k m = 1700 s -1 m CEE 697K Lecture #2 David A. Reckhow
K obs is still linear with Br- 24 No difference in mechanism? CEE 697K Lecture #2 David A. Reckhow
Acidic data: impact of acids 25 General and specific acid CEE 697K Lecture #2 David A. Reckhow
Overall pH dependence 26 Three effective zones See also, Brezonik, pg 230; figure 4-20 HOCl H + + HOCl OCl - CEE 697K Lecture #2 David A. Reckhow
Catalysis: comparison with pKa 27 Bronsted catalysis CH 2 ClCOOH HPO 4 -2 H 2 O CH 3 COOH H 3 O + ( ) α = HCO 3 - k G K HA A a α = α = 0 . 75 0 . 27 Indicates that HA engages in greater donation of proton to OCl - than to HOCl CEE 697K Lecture #2 David A. Reckhow
Mechanisms 28 Proposed mechanism Alternative Less likely CEE 697K Lecture #2 David A. Reckhow
Temperature: Arrhenius Equation 29 Arrhenius Equation Ae − = E / RT k a J Where R is the universal gas constant = R 8.3145 o M K Transforms to: 1 E = − Ln k ( ) Ln A ( ) a Or: R T T E 1 1 − − a = R T T k k e b a Tb Ta Ln(k) 1/T CEE 697K Lecture #2 David A. Reckhow
Pizza Kinetics 30 Leenson, 1999 What are the kinetics of pizza spoilage? Do they conform to Arrhenius? J. Chem Ed., 76:4:504-505 CEE 697K Lecture #2 David A. Reckhow
Pizza II 31 Arrhenius plot t~k CEE 697K Lecture #2 David A. Reckhow
Lab Project Example Data #I 32 0.1 M NaOH 0.35 What is the Abs inf ? 0.30 Absorbance at 292 nm (cm -1 ) 0.25 0.20 0.15 0.10 0.05 0.00 0 20 40 60 80 100 Time (min) CEE 697K Lecture #2 David A. Reckhow
Lab Project Example Data #II 33 0.1 M NaOH -1 -2 Set Abs inf = 0.085 Ln (A 292 -A 292inf ) -3 -4 b[0]-1.5509712892 -5 b[1]-0.0400283854 -6 0 20 40 60 80 Time (min) CEE 697K Lecture #2 David A. Reckhow
Lab Project Example Data #III 34 0.05 M NaOH 0.35 Set Abs inf = ? 0.30 Absorbance at 292 nm (cm -1 ) 0.25 0.20 time vs ln(A-Ainf) 0.15 Plot 1 Regr 0.10 0.05 0.00 0 20 40 60 80 Time (min) CEE 697K Lecture #2 David A. Reckhow
Lab Project Example Data #IV 35 0.05 M NaOH -1 -2 Set Abs inf = 0.094 -3 b[0]-1.4076822953 b[1]-0.0862394216 Ln (A 292 -A 292inf ) -4 Maybe too high ? -5 Downward curvature -6 -7 -8 -9 0 20 40 60 80 Time (min) CEE 697K Lecture #2 David A. Reckhow
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