Simulation Results (LPUV/H. 2. O. 2. ) â NAIX + Dealkalization -. 0.00. 0.50. 1.00. 1.50. 2.00. 2.50. 3.00. 3.50. 4.00. 0.0. 2.0. 4.0. 6.0. 8.0. 10.0. 12.0. 14.0. 16.0. 5.
Rational Design of Advanced Oxidation Processes using Computational Chemistry AOT 16, November 15-18, 2010 San Diego, CA.
Daisuke Minakata1, Ke Li2, John C. Crittenden1, David Hand3 School of Civil and Environmental Engineering Georgia Institute of Technology 2 Faculty of Engineering, University of Georgia 3 Civil and Environmental Engineering Michigan Technological University 1
1
Modeling AOPs 1. 2. 3. 4.
Simplified Pseudo-Steady-State Model AdoxTM – AOP simulation software Conventional Approach for Kinetic Model Computer-based Kinetic Model
2
UV/H2O2 H2O2/O3 Simplified pseudo-steady-state model
kR k12 HO
ss, 0
1. UV/H2O2
2H2O2I0 fH2O2 (1- e ) -A
[HOg]ss,0
3 0
k10 [H2O2 ]0 k11[HCO ] k12 [R]0 k13 [NOM]0
2. H2O2 and O3 are added simultaneously
HO ss, 0
K L a PO3 H O3
k9 HO2 k10 H 2O2 0 k11 HCO3 k12 R 0 k13 NOM 0 0 0
3. H2O2 is added to a water containing O3, i.e. [O3]0 is known.
pH pK H2O2 2k1 H 2O2 0 10 O3 res HO ss, 0 k11 HCO3 k12 R 0 k13 NOM 0 0
3
Flow Models: Ideal flow at steady state (1st order reaction) 1. Plug Flow Reactor (PFR)
C C0e
k
Q C0 V ln k C
2. Completely Mixed Flow Reactor (CMFR)
C
C0 (1 k)
V
Q C0 C r
3. Tank-in-series (TIS)
C
C0 n
1 nk
C 1/ n nQ V 0 1 C k
4
Flow Models: Non-ideal flow
4. Dispersed flow model closed system
1 vL 4a exp CA 2 E C Ao (1 a)2 exp a vL (1 a)2 exp a vL 2 E 2 E
a 1 4k(E / vL) 5
Known reaction rate constants Halflife, min Compound
k HO•
-9
[HO•]=10 M
-1 -1 M s
MtBE
1.6×109
Oxalic acid
1.4×10
Acetate ion
7
7×10
Trichloromethane
5.0×106
1,1,2-Trichloroethane Chloroform Chloroacetic cid Glycolic acid 1,1,1-Trichloroethane Benzene Phenol
6
8
1.1×10 6
5×10
7
4.3×10 8
6×10
7
-10
[HO•]=10
M
-11
[HO•]=10
0.01
0.1
1
8
83
825
0.2
2
17
2
23
231
0.11
1
11
2
23
231
0.3
2.7
27
0.02
0.2
2
0.3
3
29
9
0.001
0.01
0.1
9
0.002
0.02
0.2
4×10
7.8×10 6.6×10
kHCO3- = 8.5×106 M-1s-1 kCO3-- = 3.9×108 M-1s-1 H2CO3* ↔ H+ + HCO3(pKa=6.3) HCO3- ↔ H+ + CO32(pKa=10.3)
M
kNOM =(3.0 ~ 4.5)×108
M-1s-1
7
Hypothesis -GCM
k = Ae
Ea RT
Essence is same as the GCM for the gaseous phase Observed experimental reaction rate constant for a given organic compound is the combined rate of all elementary reactions involving HO•, which can be estimated using Arrhenius kinetic expression. The Ea consists of two parts: (1) Base part from main reaction mechanisms (i.e., H-atom abstraction, HO• addition to alkenes and aromatic compounds and HO• interaction with S, N, or P-atom-containing compounds). (2) Functional group contribution partially from neighboring and/or next nearest neighboring functional group. Minakata, Li, Westerhoff, Crittenden, 2009 ES&T 43, 6220-6227
8
GCM Results -overall 2/21.0E+11
Ideal fit
1.0E+10
kexp/kcal = 0.5 and 2.0
H-atom abstraction (Calibrated)
k cal (M-1s-1)
1.0E+09
HO addition to alkene (Calibrated)
1.0E+08
HO interaction with N,S,P-atomcontaining compounds (Calibrated) HO addition to aromatic compounds (Calibrated)
1.0E+07
H-atom abstraction (Prediction) HO interaction with N, S, P-atomcontaining compounds (Prediction)
1.0E+06
HO addition to aromatic compounds (Prediction)
1.0E+05 1.0E+05 1.0E+06 1.0E+07 1.0E+08 1.0E+09 1.0E+10 1.0E+11 k exp (M-1s-1)
• Over or under prediction for the oxygenated multifunctional group compounds due to solvation effects, and for the halogenated and carboxylic compounds due to larger steric hindrance Minakata, Li, Westerhoff, Crittenden, 2009 ES&T 43, 6220-6227 9
Challenges still remains GCM is limited because: 1. Many datasets are required to calibrate parameters 2. Only deal with molecules for which all required group rate constants and group contribution factors have been calibrated before. 3. Limited number of literature-reported experimental rate constants for other reaction mechanisms than HO• 4. Assumed that a functional group has approximately the same interaction properties under a given molecule, so that the GCM disregards the changes of the functional properties that can arise from the intramolecular environment by electronic push-pull effects, hydrogen bond formation, or by steric effects.
Application of computational chemistry (quantum mechanical calculations) for predicting reaction rate constants in aqueous phase Looking at reaction energies (transition states) 10
Modeling AOPs 1. 2. 3. 4.
Simplified Pseudo-Steady-State Model AdoxTM – AOP simulation software Conventional Approach for Kinetic Model Computer-based Kinetic Model
11
AdOxTM, AOPs Simulation Software • AdOxTM is a part of the Environmental Technologies Design Option Tools (ETDOTTM). It contains mechanism-based models that can be used to evaluate and design advanced oxidation processes. • The final version of AdOx will include the following models: – H2O2/UV model (available in version 1.0) – H2O2/O3 model – UV/O3 model • A comprehensive database is also included in AdOxTM to provide powerful support to the above models as well as ease-of-use features for the user. 12
Crittenden et al., 1999. Wat. Res. 33, 2315-2328
Features of Current Version AdOxTM 1.0 for UV/H2O2 H2O2 + hν → 2HO•
H2O2 = quantum yield of H2O2 (=0.5)
I0 = incident light intensity, einstein cm-2 sec-1 A=2.303b(εH2O2CH2O2+εRCR + εSCS + εHO2-CHO2-) b=pathlength, cm fH2O2= 2.303 b (εH2O2CH2O2 + εHO2-CHO2-)/A H2O2/HO2- + HO H2O/OH- + HO2 H2O2 + HO2/O2- HO + H2O/OH- + O2
2.7×107, 7.5×109 3.0, 0.13
HO + HO H2O2 HO + HO2/O2- H2O/OH- + O2 HO2 + HO2/O2- H2O2/HO2- + O2
5.5×109 6.6×109, 7.0×109 8.3×105, 9.7×107
R + hv Products R + HO Products
kMtBE=1.6×109, ktBA=6.0×108
HO + CO32-/HCO3- CO3- + OH-/H2O HO + NOM Products NOM + hv Products
3.9×108, 8.5×106 2.4×104 (mgC/L)-1s-1 14
Features of Current Version AdOxTM 1.0 • Reactor Options – Completely mixed reactor (CMBR) – Completely flow type reactor (CMFR) w/o TIS – Plug flow reactor – Non-ideal Mixing • Main Process Operational Variables : – Initial hydrogen peroxide concentration – Incident UV-light intensity • Water quality parameters: – TOC concentration – pH – Concentrations of target compounds – Byproducts can be included if they are known 15
Concern about residual H2O2 • H2O2 has low UV light absorption • Need to increase H2O2 concentration to lower EE/O • High residual H2O2 will require treatment to reduce H2O2 such as chlorine
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Simulation Results (LPUV/H2O2) – NAIX + Dealkalization MtBE
tBA
16.0
4.00
14.0
3.50
12.0
3.00
10.0
2.50
8.0
2.00
6.0
1.50
4.0
1.00
2.0
0.50
0.0
0.00 5
10
15
EEO (kWh/kgal-order)
H2 O2 residual conc. (mg/L)
Residual of H2O2
20
H2 O2 Dosage (mg/L)
• 10 mg/L of H2O2 dosage would be the better choice although the optimum dosage of H2O2 is over 20 mg/L. This is because the cost required for over 20 mg/L of H2O2 dose overweigh the energy cost. • At 10 mg/H2O2 dosage, UV dose was calculated as 2,100 mJ/cm2. Li; Hokanson; Crittenden; Trussell; Minakata. Wat. Res. 2008, 43, 5045-5053
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References that were used for model validation
Glaze, W. H.; Lay, Y.; Kang J. W. Advanced oxidation processes. A kinetic model for the oxidation of 1,2-dibromo-3 chloropropane in water by the combination of hydrogen peroxide and UV radiation. Ind. Eng. Chem. Res. 1995, 34, 2314-2323. Li, Ke.; Stefan, M.I.; Crittenden, J.C. UV photolysis of trichloroethylene: Product study and kinetic modeling. Environ. Sci. & Technol. 2004, 38, 6685-6693. Li, Ke.; Stefan, M.I.; Crittenden, J.C. Trichloroethylene degradation by UV/H2O2 advanced oxidation process: Product study and kinetic modeling. Environ. Sci. & Technol. 2007, 41(5), 1696-1703. Li, Ke.; Hokanson, D.R.; Crittenden, J.C.; Trussell, R.R.; Minakata, D. Evaluating UV/H2O2 processes for methyl tertbutyl ether and tertiary butyl alcohol removal: Effect of pretreatment options and light sources 18
AdOxTM 2 Simulation Software for O3, O3/H2O2, and mitigation of bromate and THM formation
19
Concern about bromate • Formation of bromate (BrO3-) during ozonation in the presence of bromide ion (Br-) • A nationwide survey of Br- in drinking water sources: approximately 80 μg/L (Amy et al., 1994) • Br- in costal area is expected higher • 10 μg/L of BrO3- standard of MCL associated with cancer risk, Stage 1 of the Disinfectant/Disinfection By-Product (D/DBP) Rule (EPA, 1998) • When ozone is applied to disinfection, tradeoffs between inactivation of cryptosporidium and bromate formation should be evaluated. 20
Mechanisms of bromate formation Simplified reaction scheme for bromate formation during ozonation Disproportionation
Haag and Hoigné, 1983 von Gunten and Hoigné, 1994
pKa = 8.8 Ozone involving pathway
k (M-1 s-1)
HO• involving pathway
O3 + Br - → OBr- + O2 OBr- + O3 → 2O2 + Br OBr- + O3 → O2 + BrO2 HOBr + O3 → O2 + BrO2 - + H+ BrO2 - + O3 → BrO3 - + O2 O3 + Br• → BrO• + O2
160 330 100
HO• + HOBr → BrO• + H2O
