Title: Quantification of Key Peroxy and Hydroperoxide Intermediates in the Low-Temperature Oxidation of Dimethyl Ether

Abstract

Dimethyl ether (DME) oxidation is a model chemical system with a small number of prototypical reaction intermediates that also has practical importance for low-carbon transportation. Although it has been studied experimentally and theoretically, ambiguity remains in the relative importance of competing DME oxidation pathways in the low-temperature autoignition regime. To focus on the primary reactions in DME autoignition, we measured the time-resolved concentration of five intermediates, CH₃OCH₂OO (ROO), OOCH₂OCH₂OOH (OOQOOH), HOOCH₂OCHO (hydroperoxymethyl formate, HPMF), CH₂O, and CH₃OCHO (methyl formate, MF), from photolytically initiated experiments. We performed these studies at P = 10 bar and T = 450-575 K, using a high-pressure photolysis reactor coupled to a time-of-flight mass spectrometer with tunable vacuum-ultraviolet synchrotron ionization at the Advanced Light Source. Our measurements reveal that the timescale of ROO decay and product formation is much shorter than predicted by current DME combustion models. The models also strongly underpredict the observed yields of CH₂O and MF and do not capture the temperature dependence of OOQOOH and HPMF yields. Adding the ROO + OH $$\rightarrow$$ RO + HO₂ reaction to the chemical mechanism (with a rate coefficient approximated from similar reactions) improves the prediction of MF. Increasing the rate coefficients of ROO ↔ QOOH and QOOH + O₂ ↔ OOQOOH reactions brings the model predictions closer to experimental observations for OOQOOH and HPMF, while increasing the rate coefficient for the QOOH $$\rightarrow$$ ₂CH₂O + OH reaction is needed to improve the predictions of formaldehyde. In conclusion, to aid future quantification of DME oxidation intermediates by photoionization mass spectrometry, we report experimentally determined ionization cross-sections for ROO, OOQOOH, and HPMF.

Authors:

Couch, David E. ^[1]; Mulvihill, Clayton R.  ^[2];

• Search DOE PAGES for author "Mulvihill, Clayton R."
• Search DOE PAGES for ORCID "0000-0002-4256-1311"

Sivaramakrishnan, Raghu  ^[2];

• Search DOE PAGES for author "Sivaramakrishnan, Raghu"
• Search DOE PAGES for ORCID "0000-0002-1867-1254"

Au, Kendrew ^[1]; Taatjes, Craig A.  ^[1];

• Search DOE PAGES for author "Taatjes, Craig A."
• Search DOE PAGES for ORCID "0000-0002-9271-0282"

Sheps, Leonid  ^[1]

• Search DOE PAGES for author "Sheps, Leonid"
• Search DOE PAGES for ORCID "0000-0003-4320-0865"

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+ Show Author Affiliations

1. Sandia National Laboratories (SNL-CA), Livermore, CA (United States)
2. Argonne National Laboratory (ANL), Argonne, IL (United States)

Publication Date:

Thu Dec 08 00:00:00 EST 2022

Research Org.:

Argonne National Laboratory (ANL), Argonne, IL (United States); Sandia National Lab. (SNL-CA), Livermore, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division (CSGB)

OSTI Identifier:

2283537

Grant/Contract Number:  

AC02-06CH11357; AC02-05CH11231; NA0003525

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory

Additional Journal Information:

Journal Volume: 126; Journal Issue: 50; Journal ID: ISSN 1089-5639

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Autoignition; NTC Chemistry