Embed Size (px)
Citation preview
Direct measurement of vinoxy radicals from ozonolysis of 2-butenes using
Cavity Ring-Down Spectroscopy
Mixtli Campos-PinedaGroup Meeting
Winter 2017
OutlineMotivation
OzonolysisCriegee intermediates (CIs)Vinoxy radicals
Experimental SetupCRDSMeasurement of ∙CH2CHO and HCHO
Resultstrans-2-butenecis-2-butene
Summary
Motivation
One of the most important reaction pathways of Volatile Organic Carbons (VOCs) in the atmosphere is oxidation.
One of the main oxidation reactions of unsaturated VOCs is ozonolysis.
O 2
R, alkyl radical
RH, hydrocarbon
HONO +hn OH
OH NO
RO 2
RO
HO 2NO 2
ROONO 2
RONO 2
RO 2carbonyl+
alcohol
ROOH
NO 2
O3
O2
hn
OH Alkenes
OH productionmechanism inalkene + O3 reactions
Carbonyl oxides, also know as Criegee Intermediates (CIs), are produced by ozonolysis through the breaking of a primary ozonide (POZ).
The ozonolysis reaction is highly exothermic. The primary ozonide is formed with high internal energy.
Olzmann, M., Kraka, E., Cremer, D., Gutbrod, R. & Andersson, S. The Journal of Physical Chemistry A 101, 9421–9429 (1997).
CIs are formed with a broad energy distribution.
Olzmann, M., Kraka, E., Cremer, D., Gutbrod, R. & Andersson, S. The Journal of Physical Chemistry A 101, 9421–9429 (1997).
“hot” CI
“stabilized” CI
“vinoxy” radicalVinyl hydroperoxide (VHP)
Vinoxy radical
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.
Dye Laser PMT
To pump
Purge Purge
03 gen
FM
N2 inFMSO2/HFA in
FMTME in
FM
CRDS:
Suitable for atmospheric measurements due to:Long sample path (high sensitivity).Real time measurements.Portability (in situ measurements).
1 2 3 4 5 76 8 109P
To pump
Purge N2
Purge N2
Blue: Ozone inletGreen: Alkene inlet(+ Oxygen during oxygen experiments)
Blue: plugged port (ultratorr+cap)
Multi-inlet flow cell/CRDS cavity
1 P
To pump
Purge N2
Purge N2
Green: Alkene + Ozone inlet(+ Oxygen during oxygen experiments)
Blue: plugged port (ultratorr+cap)
Single-inlet flow cell/CRDS cavity
Measurement of ∙CH2CHO and HCHO:
346.8 347.2 347.6 348.0 348.4
0.050
0.055
0.060
0.065
0.070
0.075
0.080
[
]
Experiment Fit
)(11
0
fNNLdc
formformvinoxyvinoxy
∙CH2CHO feature at ~347 nm
HCHO feature at ~348 nm
Simulation of the reaction in a flow reactor.
The system of ODEs is solved using an approximation method by the kinetic simulator KINTECUS.
OO
+
O3
OCH2CO CH3OH
SOZ
OH
O O
H H
O
O++H2O
P
P
P
P
P
O O +
H H
O
+
P
H H
O
+ 2O2 P
SOZ
P
H H
O
OH
OH + CO
OH
O2
H2OO3
OH
wall
decomp
wall
O
O
CH2OHCH3OH2O
OH
O2
H H
O
+ HO2
OHOH
HO2 + O2P
P
trans-2-butene ozonolysis mechanism used in KINTECUS (12/04/2016)
2 +H2O+H2C2
1.00 0.1 0.4 0.05 0.07
0.950.05
0.850.15
1.1E-12
2.6E-14
3.6E-15
1.7E-16
7.5E-13
1.9E-16
6.4E-11 1.6E-12
4E-18
166 s-1
1E-15
1E-12
1.2E-14
3.8E-14
5E-14
1E-11
9.1E-12
1E-11
10 s-1
10 s-1
1E-11 HCHO + OH HCO + H2O
7.5E-13
trans-2-butene: Single-inlet cavity
Results
Formaldehyde production accurately described by the model, whereas CH2CHO is overestimated by a factor of 2
2.5x1015 3.0x1015 3.5x1015 4.0x1015 4.5x1015 5.0x10152x1014
3x1014
4x1014
5x1014
6x1014
Experiment Model
HC
HO
Ozone2.5x1015 3.0x1015 3.5x1015 4.0x1015 4.5x1015 5.0x1015
1.0x1012
1.1x1012
1.2x1012
1.3x1012
1.4x1012
1.5x1012
CH2CHO Experiment CH2CHO Model
Ozone
1.4x1012
1.6x1012
1.8x1012
2.0x1012
2.2x1012
2.4x1012
2.6x1012
2.8x1012
Oxygen decreases already low CH2CHO, but the change in HCHO is not significant
4.0x1015 6.0x1015 8.0x1015 1.0x1016 1.2x1016 1.4x10163.8x1014
4.0x1014
4.2x1014
4.4x1014
4.6x1014
4.8x1014
5.0x1014
5.2x1014
Experiment Model
HC
HO
Oxygen6.0x1015 8.0x1015 1.0x1016 1.2x1016 1.4x1016
9.0x1011
1.0x1012
1.1x1012
1.2x1012
1.3x1012
1.4x1012
1.5x1012
CH2CHO Experiment CH2CHO Model
Oxygen
5.0x1011
1.0x1012
1.5x1012
2.0x1012
2.5x1012
3.0x1012
0.0 2.0x1015 4.0x1015 6.0x1015 8.0x1015 1.0x10166.0x1011
7.0x1011
8.0x1011
9.0x1011
1.0x1012
1.1x1012
1.2x1012
CH2CHO Experiment CH2CHO Model
Oxygen
4.0x1011
6.0x1011
8.0x1011
1.0x1012
1.2x1012
1.4x1012
1.6x1012
1.8x1012
2.0x1012
trans-2-butene: Multi-inlet cavity
CH2CHO decrease in the multi-inlet reactor more pronounced due to segmented nature of multi-inlet flow cellHCHO not significantly changed under high oxygen conditions
0.0 2.0x1015 4.0x1015 6.0x1015 8.0x1015 1.0x10166.0x1013
8.0x1013
1.0x1014
1.2x1014
1.4x1014
1.6x1014
1.8x1014
2.0x1014
Experiment Model
HC
HO
Oxygen
trans-2-butene: Pressure dependence
346.5 347.0 347.5 348.0 348.5 349.00.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
10 15 20 30 40 50
5 10 15 20 25 30 35 40 45 50 55
8.0x1011
9.0x1011
1.0x1012
1.1x1012
1.2x1012
1.3x1012
CH
2CH
O
P (torr)5 10 15 20 25 30 35 40 45 50 55
1.0E+14
1.5E+14
2.0E+14
2.5E+14
3.0E+14
3.5E+14
4.0E+14
HC
HO
P (torr)
cis-2-butene
5.0x1015 1.0x1016 1.5x1016 2.0x1016 2.5x1016 3.0x10161x1011
2x1011
3x1011
4x1011
5x1011
6x1011
7x1011
CH2CHO Experiment CH2CHO Model
Oxygen
0.0
4.0x1011
8.0x1011
1.2x1012
1.6x1012
2.0x1012
5.0x1015 1.0x1016 1.5x1016 2.0x1016 2.5x1016 3.0x1016
8.00x1013
8.50x1013
9.00x1013
9.50x1013
1.00x1014
1.05x1014
1.10x1014
HCHO Experiment HCHO Model
Oxygen
346.5 347.0 347.5 348.0 348.5 349.0
0.01
0.02
0.03
0.04
0.05
0.06
30 20 10 40 30
cis-2-butene: Pressure dependence
10 15 20 25 30 35 40
6.0x1011
7.0x1011
8.0x1011
9.0x1011
1.0x1012
1.1x1012
CH
2CH
O
P (torr)10 15 20 25 30 35 40
1.0x1014
1.5x1014
2.0x1014
2.5x1014
3.0x1014
HC
HO
P
SummaryDirect measurement of vinoxy radicals were possible from ozonolysis of cis- and trans-2-butene using multi- and single-inlet flow reactors.
Vinoxy radical reaction with oxygen the main channel for glyoxal and formaldehyde formation for 2-butene ozonolysis.
Decrease in OH radical and HCHO yields for cis-2-butene ozonolysis most likely caused by the decreased vinoxy radical yield.
Segmented addition of reactants along the multi-inlet flow cell allows
AcknowledgementsProf. Jingsong ZhangPaul JonesMike LucasGe SunJian Chen
UCMEXUS Fellowship
