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

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Interest Level (%

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Time (min)

nap time comfort

Simulated Attention Span P=1 atm, T=298 K, =1800 s 

Prof. Bengt Johansson 3

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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)

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ATMOSPHERE

Monge-Palacios Sarathy

Rissanen, Ehn

Zhandong Wang

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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

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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

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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

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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

شكرا

mani.sarathy@kaust.edu.sa  http://cpc.kaust.edu.sa

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