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Formation of highly oxidized multifunctional compounds in alkane autoxidation: relevance to atmospheric and combustion chemistryMani Sarathy1, Zhandong Wang1, Matti P Rissanen2, Mikael Ehn2
1 Clean Combustion Research Center, KAUST2 University of Helskinki (INAR)
• Introduction• Auto-oxidation
• Background• Combustion• Atmosphere
• Questions
Presentation Outline/Timeline
0
20
40
60
80
100
0 5 10 15 20
Interest Level (%
)
Time (min)
nap time comfort
Simulated Attention Span P=1 atm, T=298 K, =1800 s
Prof. Bengt Johansson 3
4
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Fuels/Chemicals Production
Complex Molecules
Chemical Kinetics Modeling
Reacting Flow Experiments
Computer-Aided Engineering Our research interests
and expertise
• Gas-phase autoxidation is a pseudo-unimolecular fast lane to molecular growth and reduction in vapor pressure
• Results in low volatile HOM (=highly oxidized multifunctional compounds)• Condensable low volatile vapors form SOA (=secondary organic aerosol)• HOMs lead to auto-ignition in combustion engines
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Auto-oxidation is important in atmospheric and combustion systems
From: Lehtipalo, K. et al. Nature Comm. 2016
CH3
CH3CH3
CH3CH3 CH3
OO
O
O
CH3
CH3 CH3
O OOH
O
OOH
OOH
O
O
Do common alkanes also lead to HOM formation?
10
COMBUSTION
Zhandong Wang, Sarathy
Dagaut Hansen, Taatjes
Popolan-Vaida, Leone
Kohse-Höinghaus Moshammer
• Jet-Stirred Reactor-Synchrotron Radiation Photoionization Mass Spectrometry
High fidelity experiments to explore auto-oxidation chemistry
Electrical Furnace
JSR
Sampling tube
Thermocouple
GC
Temperature controller
Syringe pump
Fuel
MFC
Multi-gas controller
Pressure valve
Pressure gauge
Thermometer
O2 supply
N2 supply
Vaporizer
• JSR-APCI-Orbitrap mass spectrometer analysis, KAUST Atmospheric pressure chemical ionization (APCI), soft ionization, mono-
charged ions, proton transfer (M+1)
High mass resolution: 100000 to 200000 and Ultra-high detection limit: 1 ppt
Sampling tubeJSR reactor APCI‐Orbitrap MS
High fidelity experiments to explore auto-oxidation chemistry
Wang et al., Combust Flame, 2017
Auto-oxidation intermediates under combustion conditions
O3 species has one –OOH
O5 species has two –OOHs
Wang et al. PNAS (2017), 114, 13102
T= 520 KP= 1 atm= 2 s
Eight hydrocarbons
Five oxygenates
Multiple O2 addition auto-oxidation scheme
Organic compounds autoxidation scheme
Wang et al. PNAS (2017), 114, 13102
2,7-dimethyloctane autoxidation
3rd O2 addition auto-oxidation scheme
3rd O2 addition:intramolecular H-atom abstraction of the C-H not alpha to the -OOH group
2nd O2 addition: intramolecular H-atom abstraction of the C-H alpha to the -OOH group
OOQOOH radicals
Wang et al. PNAS (2017), 114, 13102
OOQOOH
3rd O2 addition autoxidation tendency
Auto-oxidation is structure dependent
Relative ratios of CxHy-2O5 to CxHy-2O3 in eighthydrocarbon autoxidation reactions
α,γ-OOQOOH intramolecular H-abstraction
Blue underlined numbers denote activationenergy, unit is kcal/mol; red italicized numbersdenote entropy change, unit is cal/mol/K.
Wang et al. PNAS (2017), 114, 13102
Multiple O2 additions promote ignition• Effect of 3rd O2 addition reaction scheme on ignition
ST (top-left axes) and RCM(bottom-right axes) auto-ignitiondelay times for stoichiometric n-hexane/air mixtures at 15 atm
• Third O2 addition promotes the ignition of n-hexane at RCM conditions• Engine ignition is advance when third O2 addition is considered• Production of HOM increases advances OH radical production.
Crank angle dependenttemperature profiles and net heatrelease rate (HRR) per crankangle for n-hexane/air mixtures inan HCCI engine
Wang and Sarathy, Combust Flame (2016)
18
ATMOSPHERE
Monge-Palacios Sarathy
Rissanen, Ehn
Zhandong Wang
19
High fidelity experiments to explore auto-oxidation chemistry
Reagent (R) Flow
Sample Flow
Pump
Ion Source
Electrostatic Lenses
R ions
Ion Molecule Interaction Region
CI-APi-ToF – Chemical Ionization Atmospheric Pressure interface Time-of-Flight Mass Spectrometer
Ion production region Sheath flow
Mass spectrometer entrance
Sample flow
0 V
‐135 V
‐115 V
0 V
Inlet flows and electric fields
NO3‐ ionization as
usually for HOM(e.g. Ehn et al. Nature 2014)
TME + O3 OH + other products• Ozone around 100 ppb• TME varied 50, 100, 250, 500 ppb
20
Simple simulation for [RO2]:1. TME + O3 OH + TME_RO22. VOC + OH RO23. TME + OH TME2_RO2
[OH] and [RO2] at 3 seconds for butylcyclo-hexane:
0 100 200 300 400 5000
2
4
6
8
10
OH RO2
[OH
] / 1
09 cm
-3
TME (ppb)
1 m Quartz 2.4 cm i.d. Reactor, High [VOC] ≈ 10 ppm, Residence time ~3s, Room T and p
MSVOC+O3+TME +Air
Experiments under atmospheric conditions
Alkane autoxidationModel compounds
Branched• 2,7-dimethyl octane
Straight chain C, H• n-hexane• n-dodecane
Branched and cyclic• Methyl cyclohexene, butyl
cyclohexene
Straight chain C, H, O• Heptanal• Decanal, Decanol, 2-decanone
CH3 OHCH3
CH3
CH3
CH3
CH3 O
Cyclic• Cyclohexane• Decalin
CH3 CH3
CH3
CH3
CH3CH3
CH3CH3
O
CH3
O
21
H
H
H
H
Cyclohexane (C6H12)+TME+O3
C9H16O7
Monomers DimersC6H11O6
The dominant RO2 radical: C6H11O6
C6H10O5
C6H12O5
C6H10O6
C6H11O6
C6H12O6
C6H10O7
C6H11O7
C6H12O7
C12H22O8
C12H22O9
C12H22O10
Auto-oxidation happens !
cycloalkane vs aldehyde
Monomers MonomersC7H12O4
C7H12O5
C7H14O5
C7H12O6
C7H13O6C7H14O6
C7H12O7
C7H13O7
C7H14O7
C7H12O5
C7H14O5
C7H12O6
C7H13O6C7H14O6
C7H12O7
C7H13O7
C7H14O7
C7H12O8
C7H13O8
C7H14O8
C7H13O6
C7H13O6
Both the dominant RO2 radical: C7H13O6
cycloalkane vs aldehyde +D2O
C7H13O6
C7H13O6
In both cases C7H13O6 radcials has two acid H atoms
C7H15O6
+D2O +D2O
C7H15O6
Cycloalkane auto-oxidation may be initiated by the formation of aldehyde function group
OO
OOH
OO
OHO
OO
OOH
O
H-shift-OH
+ RO2
OO
OOH
+ O2
OO
OHO
H-shift-OH
OO
OH
25
OO
O
OOH
H-shift-OH
H-scrambling?+ RO2
OO
OH
O
- CO2
+ O2
OOH
OO
H-shift
OO
OH
OH
OO
+ O2
H-shift+ O2
OO
O
OOH
H-shift+ O2
Cyclohexane oxidation going for that prompt RO6 radical!
Can you escape this carbonyl forming reaction?
H-shift
+ O2
RO8
RO6
Need to escape all potential termination reactions!
Escape both, carbonyl formation and H‐shift?
Can H‐scrambling avoid decomposition?(e.g. Knap, H. C. et al JPCA 2017)
OO
OHOH O
O
H-shift
+ O2
H-shift
+ O2
OO
OH
OH OOH
OO
*RO intermediate needed to break the ring, right?**Leads to odd oxygen RO2 (i.e., RO3) So then we need two times RO2 + RO2 to get to RO6(...also RO2 + HO2)
Does this need to decompose?
OO
OH
OOH
OO
RO6
• Auto-oxidation under combustion and atmospheric conditions shares many similarities
• Experimental and theoretical techniques/skills from both fields complement each other
• Alkanes auto-oxidation leads to HOM formation in both environments, albeit the underlying chemistry is different.
• RO2+RO2 : atmosphere, RO2=QOOH : combustion
26
Summary
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