# On the Formation of PAHs from the Oxidation of Ethylene in a JSR

Philippe Dagaut, Shunsuke Suzuki

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Philippe Dagaut, Shunsuke Suzuki. On the Formation of PAHs from the Oxidation of Ethylene in a JSR. Twenty-Second International Conference on Flow Dynamics, IFS, Tohoku University, Nov 2025, Sendai, Japan. hal-05368803

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<figure><img src="image_1.png" /></figure>

22nd International Conference on Flow Dynamics

Nov. 10-13, 2025

Sendai International Center,
Sendai, Miyagi, Japan

<figure><img src="image_2.png" /></figure>
# On the Formation of PAHs from the Oxidation of Ethylene in a JSR

Philippe Dagaut¹, Shunsuke Suzuki²

¹CNRS, ICARE

1C, Avenue de la recherche scientifique, Orleans, 45071, France

²National Institute of Advanced Industrial Science and Technology, Research Institute for Energy Efficient Technologies
Namiki 1-2-1, Tsukuba 305-8564, Ibaraki, Japan

## ABSTRACT

The oxidation of ethylene was performed in a jet-stirred reactor at 1 bar and high-temperature under fuel-rich conditions. The reacting mixtures were sampled and analyzed using gas chromatography, mass spectrometry, and high-pressure liquid chromatography. Polyaromatic hydrocarbons were measured. The experiments were simulated using several detailed kinetic reaction mechanisms, indicating that improvements are needed.

## 1. Introduction

Polyaromatic hydrocarbons are produced during the oxidation of hydrocarbons. In flames, their formation is considered as an important step towards the production of soot. The prediction of the formation of these pollutants is therefore important to predict soot formation.

The present work aims to better characterize the products of oxidation of ethylene under fuel-rich conditions and extend the knowledge acquired in our previous studies [1, 2]. To this end, the oxidation of ethylene was undertaken in a jet-stirred reactor at 1 bar and high-temperature. The products of oxidation were analyzed by gas chromatography with TCD, FID, and MS detection, and by high-pressure liquid chromatography and UV detection. The experiments were simulated using detailed kinetic reaction mechanisms.

## 2. Method

The experiments (Table 1) were performed in a jet-stirred reactor (JSR) setup introduced previously [3]. The JSR is made of fused silica (30 cm³, 4 nozzles of 1 mm I.D. providing stirring). It is fitted inside a 1.5 kW regulated electric oven (thermally insulated by ceramic wool) which upholds its temperature at chosen working temperatures. The reactor temperature was increased stepwise and gases flow rates were set to operate at constant mean residence time across experimental conditions. Mass flow controllers were used to deliver the fuel-nitrogen mixture. Oxygen diluted by nitrogen was delivered separately to the reactor to prevent oxidation of the fuel before entering the JSR. Mass flow controllers were used to deliver nitrogen and oxygen flows. Temperature homogeneity was checked by moving a Pt-Pt/Rh-10% thermocouple (0.1 mm wires protected by a thin-wall fused-silica tube) along the vertical axis of the spherical reactor. Typical T-gradients of < 1 K/cm were recorded.

A small fused-silica sonic probe was used to stop reactions and collect gas samples (i) in 1L bulbs at 50 mBar for analysis offline by gas chromatography, and (ii) in trapping cartridges filled with Amberlite XAD-2 (Supelco) to collect PAHs. The cartridges were filled with ca. 1.5 g of adsorbent. The XAD-2 resin is a hydrophobic cross linked polystyrene copolymer resin, supplied as 20-60 mesh size white insoluble beads. PAHs were extracted by acetonitrile for liquid chromatography analysis. The

HPLC system from Shimadzu (Shimadzu Corporation, Kyoto, Japan) equipped with a reversed phase, 5 µm C18, 250x4.6 mm column, binary pump PDA (Photodiode Array Detector), and fluorimetric detector was used. The range of wavelength studied ranged from 200 to 800nm. We used a Vydac 201SP54 (C18, 5µm, 90Å, 4.6mmID x 250mmL) column. Water and acetonitrile Chromasolv plus for HPLC were obtained from Sigma Aldrich. PAHs standards (16 EPA TLC Polynuclear Aromatic Hydrocarbons Mix, 2000 µg/mL in methylene chloride:benzene 50:50) were obtained from Supelco. They contained acenaphthene, acenaphthylene, anthracene, benz[a] anthracene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[g,h,i] perylene, benzo[k]fluoranthene, chrysene, dibenz[a,h]anthracene, fluoranthene, fluorene, indeno[1,2,3-c,d]pyrene, naphthalene, phenanthrene, and pyrene.

<table><caption>Table 1 Experimental conditions.</caption><thead><tr><td>Parameter</td><td>value</td></tr></thead><tbody><tr><td>Pressure / bar</td><td>1</td></tr><tr><td>Temperature / K</td><td>1290-1490</td></tr><tr><td>Residence time / s</td><td>0.2</td></tr><tr><td>Fuel inlet</td><td>1 %</td></tr><tr><td>Equivalence ratio</td><td>3.5</td></tr></tbody></table>

The experiments were simulated using detailed kinetic reaction mechanisms. PSR/Chemkin II [4] and OpenSMOKE++ [5] were used for the simulations.

## 3. Results and Discussion

Mole fraction profiles as a function of temperature were obtained through low-pressure sonic quartz probe sampling followed by GC analyses involving the use of 4 GCs. One GC operated with nitrogen as carrier gas and TCD detection used to measure hydrogen. The other GCs used helium as carrier gas. A multicolumn and multi-detector GC was used to measure permanent gases and simple species (O₂, CO, CO₂, CH₂O). Another GC equipped with a Al₂O₃ column and an FID detector was used to measure hydrocarbons up to C7 whereas hydrocarbons > C5 products were analyzed using a GC-MS operating with a DB5-ms column.

Figure 1 shows the mole fractions of eight PAHs determined as a function of temperature. As can be seen
from that figure, naphthalene and acenaphthylene are the
most abundant PAHs formed under the present conditions
(< 4 ppm).

<figure><img src="image_3.png" /><figcaption>Fig. 1 PAHs mole fractions measured as a function of temperature in a JSR.</figcaption></figure>

The other PAHs mole fractions are lower than 0.4 ppm.

<figure><img src="image_4.png" /><figcaption>Fig. 2 Experimental versus computed mole fractions of PAHs formed in a JSR.</figcaption></figure>

Several kinetic reaction mechanisms [6-11] were used

to simulate the oxidation of ethylene under the present
conditions Figure 2 compares the experimental and
simulated mole fractions of the PAHs measured in this
work. The simulations were performed using the
mechanism proposed by Suzuki and Matsugi [11]. The
total number of species and reactions included in the
kinetic model are 1408 and 8782, respectively [11]. This
model has been validated against PAH data using
ethylene, normal and branched alkanes, aromatics as
fuels, which were obtained in an atmospheric-pressure
flow reactor. The best agreement between the data and
computations was obtained with that mechanism.

4. Concluding Remarks

The oxidation of ethylene was performed in a jet-
stirred reactor at 1 bar, high-temperature, and fuel-rich
conditions. Mole fractions of the reactants and products
of oxidation were determined and used to test several
previously proposed detailed chemical kinetic reaction
mechanisms. The present simulations show that these
models do not always properly represent the data.

References

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[3] Dagaut, P, Cathonnet, M, Rouan, JP, Foulatier, R, Quilgars, A, Boettner, JC, Gaillard, F, James, H, *J. Phys. E-Scientific Instruments*, **19**, (1986), 207-209.

[4] P. Glarborg, R. J. Kee, J. F. Grcar, J. A. Miller in: *PSR: A FORTRAN program for modeling well-stirred reactors.*, SAND86-8209, Sandia National Laboratories, Livermore, CA, 1986.

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[7] N. M. Marinov, W. J. Pitz, C. K. Westbrook, A. M. Vincitore, M. J. Castaldi, S. M. Senkan, *Combust. Flame*, **114** (1998), 192-213.

[8] V. Dias, J. Vandooren, *Proc. ECM2007* (2007).

[9] K. Mati, A. Ristori, S. Gaïl, G. Pengloan, P. Dagaut, *Proc. Combust. Inst.*, **31**, (2007), 2939-2946.

[10] H. Richter, S. Granata, W.H. Green, J.B. Howard, *Proc. Combust. Inst.*, **30**, (2005), 1397-1405.

[11] S. Suzuki, A. Matsugi, *Combust. Flame*, submitted (2025)

Acknowledgements

Support from the Labex Caprysses (convention ANR-11-LABX-0006-01 is gratefully acknowledged.