Ozonolysis of 2,3-dimethyl-2-butene

Group Meeting

Winter 2015

OutlineMotivation

Experimental Setup

Results

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).

CIs are formed with a energy distribution that results in only a fraction undergoing reactions or rearrangements. Resulting in short lifetimes.

Rearrangement, decomposition, or reaction of carbonyl oxides in the atmosphere produces secondary organic aerosols, OH radicals, peroxy radicals, etc.

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

O

OO

+ O3+

Simulation of the reaction in a flow reactor.

The system of ODEs is solved using an approximation method by the kinetic simulator KINTECUS.

# k Reaction Comments

1.13E-15 C6H12+O3==>CH3COCH3+0.85CH3COOCH3+0.15CH3CO2CH3 1

2.50E+05 CH3COOCH3==>CH3+CH3+CO2 18

7.80E+05 CH3COOCH3==>CH3COCH2+OH 19

5.00E+04 CH3COOCH3==>CH3OCOCH3 20

1.70E+05 CH3COOCH3==>CH3O+CH3+CO 21

4.40E+05 CH3COOCH3==>CH3O+CH3CO 22

1.10E+05 CH3COOCH3==>CH3OCO+CH3 23

9.13E-13 CH3+O3==>CH2O+H+O2 2

4.50E-11 CH3+CH3O==>CH2O+CH4 3

1.49E-15 CH3O+O2==>CH2O+HO2 4

2.49E-11 CH3O+CH3O==>CH2O+CH3OH 5

4.98E-11 CH3O+OH==>CH2O+H2O 6

1.19E-10 OH+C6H12==>C6H12OH 7

1.39E-11 OH+CH2O==>H2O+HCO 8

1.49E-13 OH+CO==>CO2+H 9

3.82E-13 H+C6H12==>C6H13 10

2.66E-11 H+O3==>OH+O2 11

5.65E-12 HO2+HO2==>H2O2+O2 12

7.97E-11 HO2+OH==>H2O+O2 13

1.66E-12 HO2+CH3O==>CH3OH+O2 14

4.90E-20 CH3CO2CH3 + C6H12 ==> CH3COCH3+C6H12O 15

1.00E-12 CH3CO2CH3 + O3 ==> CH3COCH3+O2+O2 16

3.00E-11 CH3CO2CH3+CH3==>CH3COCH3+CH3O 17

4.00E-11 CH3CO2CH3 + CH3CO2CH3 ==> CH3COCH3+CH3COCH3+O2 C1

5.00E-12 CH3CO2CH3+HO2==>CH3COOCH3HO2 C2 - DUMMY

5.00E-12 CH3CO2CH3+OH==>CH3COOCH3OH C3 - DUMMY

4.00E-14 CH3CO2CH3+CO==>CH3COCH3+CO2 C4

6.00E-13 CH3CO2CH3+CH3COCH3==>CH3CO2CH3CH3COCH3 C5

fNNNL

dcacacformformozoz

0

11

Results

Difference spectrum

n

iiiacRacCOOCHCOOCH NNNf ,2323

Scavenging with HFA

n

iiiHFARHFAacRacCOOCHCOOCH NNNNf ,,2323

∆[Difference spectra]

Scavenging with SO2

fNNNNL

dcacacSOSOformformozoz

22

0

11

Difference spectrum

n

iiiacRac NNf ,

Why?# k Reaction Comments

1.13E-15 C6H12 + O3 CH3COCH3 + 0.85CH3COOCH3 + 0.15CH3CO2CH3 1

4.90E-20 CH3CO2CH3 + C6H12 CH3COCH3 + C6H12O 15

1.00E-12 CH3CO2CH3 + O3 CH3COCH3 + O2 + O2 16

3.00E-11 CH3CO2CH3 + CH3 CH3COCH3 + CH3O 17

4.00E-11 CH3CO2CH3 + CH3CO2CH3 CH3COCH3 + CH3COCH3 +O2 C1

5.00E-12 CH3CO2CH3 + HO2 Products C2

5.00E-12 CH3CO2CH3 + OH Products C3

4.00E-14 CH3CO2CH3 + CO CH3COCH3 + CO2 C4

6.00E-13 CH3CO2CH3 + CH3COCH3 CH3CO2CH3CH3COCH3 C5

3.50E-11 CH3CO2CH3 + SO2 CH3CO2CH3SO2 C6

C6H12 O3 CH3COCH3 CH3COOCH3 CH3CO2CH3 CH2O CH3CO2CH3CH3COCH3 SO2 CH3CO2CH3SO2

no SO2 2.71E+16 8.26E+13 5.87E+14 5.96E+07 3.45E+10 2.37E+14 6.35E+13 0 0

with SO2 2.71E+16 8.26E+13 6.10E+14 5.87E+07 9.58E+08 2.41E+14 1.83E+12 5.45E+14 8.90E+13

∆1/t change1.21E-03

sCI-SO2 adduct contributes to the signal

Initial SO2 Final SO2 Simulation SOZ

2.90E+14 2.20E+14

4.20E+14 3.50E+14

5.50E+14 3.60E+14

6.60E+14 5.00E+14

7.90E+14 6.00E+14

Measuring SO2

Scavenging with different amounts of SO2

Difference Spectra

Change in difference spectra with different initial SO2

Future WorkFix flow fluctuations of SO2

Try more initial SO2 concentrations

Search for SOZ spectra

Try ethene ozonolysis using SO2 as scavenger