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Ozonolysis of 2-methyl 2-butene and 2,3-dimethyl 2-butene
Group Meeting
Fall 2014
OutlineMotivation
Experimental Setup
Results2-methyl 2-butene
2,3-dimethyl 2-butene
Future Work
MotivationOne of the most important processes of Volatile Organic Carbons (VOCs) in the atmosphere is oxidation.
One of the main oxidation reactions of VOCs is ozonolysis.
Carbonyl oxides, also know as Criegee Intermediates (CIs), are produced by ozonolysis through the breaking of a primary ozonide (POZ).
Rearrangement, decomposition, or reaction of carbonyl oxides in the atmosphere produces secondary organic aerosols, OH radicals, peroxy radicals, etc.
CIs are formed with a energy distribution that results in only a fraction undergoing reactions or rearrangements. Resulting in short lifetimes.
Experimental SetupOzonolysis of alkenes is done using a flow reactor:
Reaction products are measured using cavity ring-down spectroscopy (CRDS).
Spectra of the main products is subtracted in order to look for CI features.
CRDS:
Suitable for atmospheric measurements due to:Long sample path (high sensitivity).
Real time measurements.
Portability (in situ measurements).
Spectra analysis:
n
iii N
L
dc
L
dc 0
11
318 320 322 324 3260.15
0.20
0.25
0.30
0.35
0.40
0.45
Exp Synth
)(11
0
fNNNL
dcacacformformozoz
Results2-Methyl-2-Butene
O
O O
O
OO
+ O3
+
+
326 328 330 332 3340.0
0.5
1.0
1.5
2.0
2.5
Exp1 Exp2 Synth
318 320 322 324 3260.0
0.2
0.4
0.6
0.8
1.0
Exp1 Exp2 Synth
acacacetaldacetaldformformozoz NNNNL
dc
0
11
n
iiiacRacCOOCHCOOCHCOOCHCOOCH NNNNf ,232333
Comparison of f(λ).
Why?
n
iiiacRacCOOCHCOOCHCOOCHCOOCHMB NNNNf ,2 232333
n
iiiacRacCOOCHCOOCH NNNf ,2323
12 105.0 sf MB
1121.0 sfTME
COOCHCOOCH NN233
2,3-Dimethyl-2-Butene
O
OO
+ O3+
fNNNL
dcacacformformozoz
0
11
n
iiiacRacCOOCHCOOCH NNNf ,2323
326 328 330 332 3340.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Exp1 Exp2 Synth
318 320 322 324 3260.15
0.20
0.25
0.30
0.35
0.40
0.45
Exp1 Exp2 Synth
Difference spectrum: First attempt
318 319 320 321 322 323 324 325 326 327-0.30
-0.25
-0.20
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
Nbump
~ 2x1011 molecules/cm3
N(CSTR simulation) = 9.84x1011 molecules/cm3
Scavenging with HFA
318 320 322 324 326
0.0
0.2
Residual (no HFA) Residual (with HFA)
318 320 322 324 326
0.0
0.2
Residual (no HFA) Residual (no HFA) Residual (with 1.6e15 HFA)
The choice of Nac and f(λ) greatly effect the difference spectrum.
Nac values need to be constrained:Optimization of the ozonolysis reaction using kinetic simulations.
Comparison of product yields with literature values.
318 320 322 324 3260.15
0.20
0.25
0.30
0.35
0.40
0.45
Exp Synth
318 320 322 324 3260.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
Exp1 Synth
Simulation of the reaction in a flow reactor.
The system of ODEs is solved using an approximation method by the kinetic simulator KINTECUS.
Concentration profiles in the reactor.
0 1 2 3 4 5 6 7 8 9 100.0
5.0x1015
1.0x1016
1.5x1016
2.0x1016
2.5x1016
3.0x1016
0 1 2 3 4 5 6 7 8 9 100.0
5.0x1014
1.0x1015
1.5x1015
2.0x1015
2.5x1015
3.0x1015
0 1 2 3 4 5 6 7 8 9 100.0
2.0x1011
4.0x1011
6.0x1011
8.0x1011
1.0x1012
1.2x1012
0 1 2 3 4 5 6 7 8 9 100.0
5.0x1014
1.0x1015
1.5x1015
2.0x1015
TME
N m
olec
ule/
cm3
Acetone
sCI
N m
olec
ule/
cm3
Segment #
O3
Segment #
Product yields for different reaction conditions
Alkene/ Ozone
O3 reacted/ O3 initial
Baselinef(λ)
O3 meas/ O3 sim
Ac meas/ Ac sim
Ac sim/ O3 sim
Ac meas/ O3 meas
YAc YHCHO
(Exp)YHCHO
(Ref)
16.5 0.6 0.1285 3.2 2.2 10.5 7.2 5 0.53 ~0.40*
6.45 0.47 0.1620 3.8 0.65 8.6 1.4 1.6 0.65 ~0.41*
10.24 0.43 0.1134 4 1.41 8.9 3.1 4 0.8 ~0.40*
30.9 0.75 0.1712 2.31 2.1 14 12.7 4.3 0.55 ~0.38*
14.56 0.67 0.2612 2.97 1.31 13.2 5.8 2.8 0.48 ~0.40*
19.85 0.78 0.2312 2.02 1.73 13.6 11.6 3.3 0.52 ~0.41*
10.33 1 0.3322 0 2.3 13.6 NA 3.4 0.36 0.38 ± 0.04
12.36 1 0.2922 0 2.26 14 NA 3.4 0.42 0.38 ± 0.04
Future WorkImprove the measurement of remaining ozone.
Look into the ozone and acetone reactions:
Re-analyze data of TME with HFA using literature yields for acetone.
Run TME ozonolysis with HFA under optimized conditions.
