Oxidation of di-n-propyl ether: Characterization of low-temperature products
Introduction
In the recent years, the interest for alternative biofuels has been growing. Ethers, which can be synthesized via dehydration of alcohols, are among the chemicals of interest. Very recently, the kinetics of oxidation of di-n‑butyl ether and diethyl ether received much attention [1], [2], [3], [4], [5], [6], [7], [8]–9]. For di-n-propyl ether (CAS 111-43-3), only one chemical kinetic study has been reported [10] whereas it easily oxidizes at low temperature, making it a good candidate for further investigating the formation of ketohydroperoxides [11], [12], [13], [14], [15], [16], [17], [18]–19], and recently proposed new oxidation pathways [20,21] leading to highly oxygenated molecules (HOMs). Whereas HOMs are minor combustion products, in the troposphere they are considered of paramount importance for the formation of secondary organic aerosols [22]. In previous studies, chromatographic separation of ketohydroperoxides, formed by oxidation of large hydrocarbons, and detection by UV absorption or mass spectrometry was attempted [11–19], but suffered from instruments limitations. With more powerful techniques such as ultra-high-pressure liquid chromatography and OrbitrapⓇ mass spectrometry, one can expect improving the characterization of low temperature oxidation products. This was initiated in our preliminary investigation [23]. Here, new experiments were performed in a JSR to characterize the DPE low temperature oxidation products. Hydroperoxides, ketohydroperoxides, carboxylic acids, cyclic ethers, highly oxygenated molecules resulting from multiple O2 addition were tracked using soft chemical ionization and high-resolution mass spectrometry. After having verified that our chemical kinetic model for the oxidation of di-n-propyl ether (DPE) [10] could represent experimental results obtained for stable products, we used it to simulate the global formation of ketohydroperoxides.
Section snippets
Experimental
Experiments were performed in a fused silica jet-stirred reactor (JSR) setup already described in details [24] and used in previous studies [25], [26]–27]. As in previous works [9,25] the liquid fuel (>98% pure from TCI) was atomized by a nitrogen flow and vaporized in a heated chamber. The fuel and oxygen were sent separately to the JSR to avoid oxidation before reaching the 4 injectors (nozzles of 1 mm I.D.) providing stirring. Flow rates of the nitrogen diluent and oxygen were controlled by
Kinetic modeling
The computations were performed using the PSR computer code [30] from the Chemkin II package [31]. Our kinetic mechanism presented earlier [10] and consisting of 528 species and 3062 reactions was used. Our mechanism includes both low- and high-temperature chemistry but is limited to 2 additions of O2 to fuel's radicals which yield ketohydroperoxides. The formation of the most likely KHPs at 510 K during the oxidation of 1000 ppm of DPE at 10 atm is presented in Fig. 1. According to our
Results and discussion
The formation of ketohydroperoxides and highly oxygenated compounds resulting from O2 addition on the fuel's radicals (R) was observed. Table 1 gives an overview of the results. More detailed information is provided in Supporting Material S2. Their formation proceeds through a sequence of reactions: R + O2 ⇆ RO2; RO2 ⇆ QOOH; QOOH + O2 ⇆ OOQOOH; OOQOOH ⇆ HOOQ'OOH followed by the formation of the hydroxyl radical and a ketohydroperoxide (C6H12O4): HOOQ'OOH → HOOQ'O + OH. Dihydroperoxides can also
Conclusion and perspectives
The oxidation of di-n-propyl-ether was performed in a jet-stirred reactor at 1 and 10 atm and a constant equivalence ratio of 0.5. Residence times of 1 and 0.7 s were used at 1 and 10 atm, respectively. Mole fractions of the reactants and stable products formed during the oxidation of di-n-propyl-ether were obtained through sonic probe sampling, gas chromatography, and Fourier transform infrared spectrometry.
Hydroperoxides, ketohydroperoxides, carboxylic acids, and highly oxygenated molecules
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors gratefully acknowledge funding from the Labex Caprysses (convention ANR-11-LABX-0006-01) and through the projects PROMESTOCK and APROPOR-E (Région Centre Val de Loire, FEDER and CPER). We thank Dr. Quoc-Tuan Do (Greenpharma S.A.S., Orléans, France) for computing dipole moments.
References (37)
- et al.
Energy
(2012) - et al.
Proc. Combust. Inst.
(2015) - et al.
J. Anal. Appl. Pyrolysis
(2016) - et al.
Proc. Combust. Inst.
(2017) - et al.
Combust. Flame
(2018) Combust. Flame
(2018)- et al.
Proc. Combust. Inst.
(2019) - et al.
Combust. Flame
(2017) - et al.
Combust. Flame
(1998) - et al.
Combust. Flame
(1995)
Combust. Flame
Symp. (Int.) Combust.
Tetrahedron Lett.
J. Phys. Chem. A
Int. J. Chem. Kinet.
Int. J. Chem. Kinet.
Anal. Lett.
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