Ozonolysis of 2-Butenes

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.