PYROLYTIC REACTIONS OF THE PHENYL RADICAL IN THE PR ESENCE OF ACEPYROLYTIC REACTIONS OF THE PHENYL RADICAL IN THE PR ESENCE OF ACETYLENETYLENEA. Comandini1, S. H. Duerrstein2, M. Olzmann2*, K. Brezinsky1*

1University of Illinois at Chicago, USA; 2University Karlsruhe (TH), Germanykenbrez@uic.edu; olzmann@chemie.uni-karlsruhe.de

Institute of Physical Chemistry

Chair of Molecular Physical Chemistry

Kaiserstr.12, 76128 Karlsruhe, Germany

1000 1200 1400 1600

0,0

0,2

0,4

0,6

0,8

1,0

1,2

C6H

5I Pyrolysis

Reaction Time~1.5-2 ms

[C6H

5I] / [

C6H

5I] 0

Reflected Shock Temperature T5/K

■ [C6H5I]0 = 50 ppm, 50 atm ▲ [C6H5I]0 = 300 ppm, 50 atm ● [C6H5I]0 = 850 ppm, 50 atm ∆ [C6H5I]0 = 200 ppm, 25 atm ○ [C6H5I]0 = 300 ppm, 25 atm

1000 1200 1400 1600 1800

0,00

0,04

0,08 C

6H

6

C6H

5C

2H

C10H8

C6H

5I Pyrolysis, 300 ppm, 25 atmReaction Time~1.5-2 ms

Nor

mal

ized

Mol

e F

ract

ion

Reflected Shock Temperature T5/K

1000 1200 1400 1600 1800

0,00

0,04

0,08

0,12

0,16

0,20

0,24

0,28

C2H

2

C4H

2

C6H

5I Pyrolysis, 300 ppm, 25 atm Reaction Time~1.5-2 ms

Nor

mal

ized

Mol

e F

ract

ions

Reflected Shock Temperature T5/K

Pyrolysis of Iodobenzene as Phenyl Radical Precursor

Pyrolytic Reactions of Phenyl Radical in the Presenc e of Acetylene: Experimental Data

• Negligible formation of phenylacetylene

• BUT: considerable formation of naphthalene

• Phenylacetylene profiles conform to phenyl + acetyle ne recombination

• BUT: naphthalene profiles NOT conform to phenylacetyle ne + acetylene recombination

• Similar trends observed at a nominal pressure of 25 atm

1000 1200 1400 1600

0

50

100

150

200

Pyrolysis of C6H

5I-C

2H

2 Blends

P~50atm; Reaction Time~1.5-2ms

C6H

5I m

ole

frac

tion/

ppm

Reflected Shock Temperature T5/K

C2H

2=280ppm

C2H

2=60ppm

1000 1200 1400 160040

80

120

160

200

240

280

320

Pyrolysis of C6H

5I-C

2H

2 Blends

P~50atm; Reaction Time~1.5-2ms

C2H

2 mol

e fr

actio

n/pp

m

Reflected Shock Temperature T5/K

C2H

2=280ppm

C2H

2=60ppm

1000 1200 1400 1600

0

10

20

30

40

Pyrolysis of C6H

5I-C

2H

2 Blends

P~50atm; Reaction Time~1.5-2ms

C4H

2 m

ole

frac

tion/

ppm

Reflected Shock Temperature T5/K

C2H

2=280ppm

C2H

2=60ppm

1000 1200 1400 1600

0

5

10

15

20

25

30

35

40

45

Pyrolysis of C6H

5I-C

2H

2 Blends

P~50atm; Reaction Time~1.5-2ms

C6H

6 mol

e fra

ctio

n/pp

m

Reflected Shock Temperature T5/K

C2H

2=280ppm

C2H

2=60ppm

1000 1200 1400 1600

0

10

20

30

40

Pyrolysis of C6H

5I-C

2H

2 Blends

P~50atm; Reaction Time~1.5-2ms

C6H

5C2H

mol

e fr

actio

n/pp

m

Reflected Shock Temperature T5/K

C2H

2=280ppm

C2H

2=60ppm

1000 1200 1400 1600 1800

0

5

10

15

20

25

Pyrolysis of C6H

5I-C

2H

2 Blends

P~50atm; Reaction Time~1.5-2ms

C10

H8 m

ole

frac

tion/

ppm

Reflected Shock Temperature T5/K

C2H

2=280ppm

C2H

2=60ppm

HPST Operating ConditionsTemperatures: 600 - 2500 K

Pressures: 5 - 1000 atmReaction Times: 0.5 - 3.0 ms

Experimental Technique: High-Pressure Shock Tube

100 +/- 2 °C over last 30 inches of tube

Key Steps: Formation of the first aromatic ring (be nzene) a

Formation of the second aromatic ring (naphthalene) a

Formation of polycyclic aromatics (PAH) and subsequ ent growth to PM a,b

Benzene formation – Fairly well characterized c

Naphthalene and multiple ring structures formation – Uncertain pathways c

a. H. Bockhorn, Soot formation in combustion-Mechanisms and Models, Springer Series in Chemical Physics, Volume 59, 1994, 3-9.b. H. Richter, J. B. Howard, Prog. Ener. Combust. Sci., 26, 2000, 565-608.c. J. A. Miller, M. J. Pilling, J. Troe, Proc. Combust. Inst., 30, 2005, 43-88.

Reaction Pathways to PM formation: Role of Aromatic Species

UICUNIVERSITYOF ILLINOISAT CHICAGO

Technical Objective : characterization of the pyrolytic reactions of the p henyl radical in the presence of acetylene over a wide ra nge of pressures (1 - 50 atm) and temperatures (1000 - 1700 K) as possible pathway to the formation of naphthalene

Summary Acknowledgments• Experiments on pyrolytic reactions of the phenyl rad ical in the presence of acetylene conducted over a wide range of pressures (1 - 50 atm) and temperature s (1000 - 1700 K) using two different experimental techniques.

• The experiments conducted at University Karlsruhe ind icate that at low pressure the recombination betwee n phenyl and acetylene does not lead to naphthalene formation.

• The experimental and theoretical work conducted at UIC shows that at high pressure acetylene is involv ed in the formation of the second-ring species, but the HACA mechanism is not the main pathway to naphthalene.

• Possibly alternative pathways to naphthalene format ion at high pressure exist.

SERDP, financial sponsor through contract WP 1575.

DFG, financial support through contract OL85/2-1.

This work reflects the collaborative efforts of UIC and University Karlsruhe, and the authors would additionally like to thank the sponso rs for encouraging this collaboration.

Pyrolytic Reactions of the Phenyl Radical in the Pre sence of Acetylene: ModelingMain Naphthalene Formation Pathways

a Richter, H. ; Mazyar, O. A. ; Sumathi, R. ; Green, W. H. ; Howard, J. B. ; Bozzelli, J. W. J. Phys. Chem. A 2001, 105, 1561-1573.b Frenklach, M.; Wang, H. Proc. Combust. Inst. 1991, 23, 1559.c Estimated.d Wang, H.; Frenklach, M. J. Phys. Chem. 1994, 98, 11465-11489.

• Quite accurate simulations of phenyacetylene profile s

• BUT: compared to the experiments, too small amounts of naphthalene predicted

1000 1200 1400 1600

0

50

100

150

Pyrolysis of C6H

5I-C

2H

2 Blends

P~25atm; Reaction Time~1.5-2ms

C6H

5I-C

2H

2 m

ole

frac

tion/

ppm

Reflected Shock Temperature T5/K

C6H5I: ○ experiment; ● simulationC2H2: ∆ experiment; ▲ simulation

C4H2: ○ experiment; ● simulationC6H6: □ experiment; ■ simulation

C6H5C2H: ∆ experiment; ▲ simulationC10H8: □ experiment; ■ simulation

1000 1200 1400 1600

0

5

10

15

20

Pyrolysis of C6H

5I-C

2H

2 Blends

P~25atm; Reaction Time~1.5-2ms

C6H

5C2H

-C10

H8

mol

e fr

actio

n/pp

m

Reflected Shock Temperature T5/K

1000 1200 1400 1600

0

10

20

30

Pyrolysis of C6H

5I-C

2H

2 Blends

P~25atm; Reaction Time~1.5-2ms

C4H

2-C

6H6 m

ole

frac

tion/

ppm

Reflected Shock Temperature T5/K

Problem Statement

• Environmental hazards - haze and poor air quality• Reduced combustor efficiency• Increased combustor wear and tear• Hinders tactical effectiveness• Deterrent - active recruitment and training of milit ary personnel• Health hazard - asthma and cancer (10 mg/m3 increase in fine PM ~6% increase cardiopulmonary mortality and 8% increase in lung c ancer mortality) a

Particulate Matter (PM) Emissions

a. Pope, III C. A.; Burnett, T. R.; Thurston, D. G.; Thun, J. M.; Calle, E.; Krewski, D.; Ito, K., Journal of the American Medical Association 2002, 287, 1132-1141.

Supersonic jet

Mass Spectrometer

Pulsed Electron Impact Ionization

125 kHz

45 eV

Reflectron mode

Experimental Technique: Real-time TOF-Mass Spectrom etry behind Shock Waves

1 mm

Pinhole 30 – 140 µm

Sampling unit

TOF-MS ST Operating ConditionsTemperatures: 800 - 2000 K

Pressures: 0.1 - 2 atmTime Resolution: 15 µµµµs

Bath gas: Ne

Pyrolysis of Iodobenzene as Phenyl Radical Precursor

0.0 0.5 1.0 1.50.0

0.2

0.41553 K; 1.14 bar

[C2H

2]; [

C12

H10

] / a

. u.

t / ms

biphenyl acetylene

150 175 200 225

-0.01

0.00

no 3 ring species 4 ring species

2 ring species

I / V

m / z

75 - 210 µs 1.5 - 1.65 ms

• Iodobenzene and argon: 3400 ppm (each)

• Products observed: C 2H2, C6H6, C8H6, C12H10, C18H12

• Diacetylene superimposed (fragment peaks)

• Only PAH with even number of rings !

0.0 0.5 1.0 1.50

1

[C6H

5I] / [

C6H

5I] 0

t / ms

1247 K 1375 K 1492 K 1593 K

0.0 0.5 1.0 1.50.0

0.1

0.2

0.3

[C8H

6] /

[C6H

5I] 0

t / ms

1593 K 1440 K 1247 K

0.0 0.5 1.0 1.50.0

0.2

0.4

0.6

[C6H

6] /

[C6H

5I] 0

t / ms

1593 K 1375 K 1247 K

150 175 200 225

-0.05

0.00

1558 K; 1.04 bart: 15 - 150 µs4000 ppm C

6H

5I

1.23 % C2H

2

C12

H8? C

12H

10 C14

H10

I / V

m / z

0.0 0.5 1.0 1.50.0

0.5

1.0

1.5

2.0

0.0 0.5 1.0 1.50.00

0.25

0.50

0.75

1.00

1.25

[C6H

6],

[C8H

6] / 1

0-8 m

ole

/ cm

3

t / ms

benzene phenylacetylene benzene phenylacetylene

1553 K; 1.14 bar

[C6H

5I] /

10-8

mol

e cm

-3

t / ms

• Iodobenzene: 3300 or 2000 ppm

• C2D2: C6H5 = 3 or 8.5

• C2D2 to separate naphthalene and HI peaks

• BUT: no naphthalene was observed

• Products: C 6H6, C8H6, C12H10, C14H10

Pyrolytic Reactions of the Phenyl Radical in the Pre sence of Acetylene: Experimental Data

+ C2H2

-H2,+H

+C2H2

-H

a, b

c, b

c

c

+C2H2

a, b

b, d

-H

a, b

+C2H2

b, d