10/8/2013 Updated: 8 October 2013 CEE690K Lecture #09 1 Print version CEE 690K ENVIRONMENTAL REACTION KINETICS Lecture #9 Reaction Mechanisms: Acid Catalysis Brezonik, Chapter 4 David A. Reckhow Introduction Mechanisms: Haloform Reaction 2 Chlorine + acetone Morris & Baum, 1978 Brezonik, 1994 Pg 240-241 CEE690K Lecture #09 David A. Reckhow 1 10/8/2013 Haloform reaction: initial step 3 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 k f [H ][A ] Ka What is kr? kr [HA] CEE690K Lecture #09 David A. Reckhow Haloform: Doré’s diagram 4 Doré (1989) RLS is the first one CEE690K Lecture #09 David A. Reckhow 2 10/8/2013 Loss of intermediates in lab water 5 21C, ultrapure water (Nikolaou et al., 2001) CEE690K Lecture #09 David A. Reckhow Profile of TCP in water systems 6 1,1,1-Trichloropropanone concentrations compared to the corresponding TTHM concentration for all samples 5 San Francisco Jan(Cl2/NH4Cl) Charleston(ClO2/ NH4Cl) San Francisco Apr (Cl /NH Cl) 4 Monroe 2 4 g/L) Ann Arbor(O3/NH4Cl) East Bay( Cl2/NH4Cl) Cincinnati(Cl2) 3 Minneapolis (NH4Cl/NH4Cl) Monroe(O3/Cl2) Wyoming( Cl2/Cl2) 2 Pinellas Co. Pinellas County(Cl2/Cl2) Pinellas County(Cl /NH Cl) Knoxville 2 4 Knoxville(ClO2/Cl2) 1 1,1,1- trichloropropanone ( trichloropropanone 1,1,1- 0 0 20 40 60 80 100 120 140 ChloroformCEE690K (g/L) Lecture #09 David A. Reckhow 3 10/8/2013 Loss in water heaters 7 0.6 3.0 a No heating b Liu et al., 6 hrs incubation+heating 0.5 2.5 24 hrs incubation+heating 48 hrs incubation+heating 2013 0.4 2.0 72 hrs incubation+heating 96 hrs incubation+heating g/L) g/L) 0.3 1.5 In review CP ( No heating 1,1-DCP ( 0.2 1.0 6 hrs incubation+heating 24 hrs incubation+heating 0.1 48 hrs incubation+heating 0.5 72 hrs incubation+heating 96 hrs incubation+heating 0.0 0.0 0 20406080100120 0 20406080100120 Reaction Time (hr) Reaction Time (hr) 8.0 2.5 c No heating No heating d 6 hrs incubation+heating 6 hrs incubation+heating 24 hrs incubation+heating 2.0 24 hrs incubation+heating 6.0 48 hrs incubation+heating 48 hrs incubation+heating 72 hrs incubation+heating 72 hrs incubation+heating 96 hrs incubation+heating 1.5 96 hrs incubation+heating g/L) g/L) 4.0 TCP ( 1.0 DCAN ( 2.0 0.5 0.0 0.0 0 20 40CEE690K 60 Lecture 80 100 #09 120 0 20406080100120David A. Reckhow Reaction Time (hr) Reaction Time (hr) Case Study: TCP Note: both TCP and TCAC refer to the 1,1,1-trichloropropanone 8 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 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, CEE690K Lecture #09 David A. Reckhow Volume 5, Lewis. 4 10/8/2013 TCP (cont.) 9 Ionic strength effects ln kH 4.811.4 I log kH 2.08 0.6 I Rate with chlorine Increases greatly High intercept kT 0.024 32HOCl T CEE690K Lecture #09 David A. Reckhow Disagreement with prior study 10 Gurol & Suffet showed 10x higher rate constants Phosphate? CEE690K Lecture #09 David A. Reckhow 5 10/8/2013 Putting it together 11 CEE690K Lecture #09 David A. Reckhow Catalysis 12 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. 2A2 B 2A B3 termolecular reaction? – be skeptical 2 2 What A C A C 2 2 3 “C” serves as a sort of charge- really A C A C transfer facilitator, since “B” does happens: C 3 B C B3 not exist in a divalent state 2A2 B 2A B3 CEE690K Lecture #09 David A. Reckhow 6 10/8/2013 13 Summary CEE690K Lecture #09 David A. Reckhow 14 To next lecture CEE690K Lecture #09 David A. Reckhow 7.