Pathway exploration in low-temperature oxidation of a new-generation bio-hybrid fuel 1,3-dioxane

Abstract

The joint and flexible utilization of renewable electricity, ligno-cellulosic biomass, and/or CO2 point sources to produce so-called bio-hybrid fuels is a promising solution to achieve carbon neutrality while still meeting the energy demand of the transportation sector. One of the new-generation bio-hybrid fuels is 1,3-dioxane. It has a special chemical structure with two oxygen atoms in a six-membered ring. In this work, the low-temperature oxidation of 1,3-dioxane was studied theoretically and experimentally. Potential energy surfaces of the products of the O2 recombination with the three radicals formed from the H-atom abstraction of 1,3-dioxane were calculated at the DLPNO-CCSD(T)/CBS//B2PLYP-D3/cc-pVTZ level. The reaction rate coefficients were calculated with the RRKM/master equation method (T = 500–2000 K, p = 0.01–100 atm). To validate the proposed pathways, low-temperature oxidation experiments of 1,3-dioxane were performed in a jet stirred reactor (JSR) coupled with a synchrotron photon ionization time of flight molecular beam mass spectrometer (T = 590 K, p = 1 bar). Key intermediates in the investigated pathways were captured and identified by the combination of measured photon ionization efficiency curves and calculated ionization energies. Compared to cyclohexane, which has no oxygen in the six-membered ring, 1,3-dioxane has much weaker C-H bonds for the carbon between the two oxygen atoms, thus enabling faster internal H-atom migration from ROO to QOOH. Furthermore, oxidation of 1,3-dioxane tends to favor cyclic ethers + OH (chain propagation) instead of alkenes + HO2 (chain termination), explaining its high reactivity in the low-temperature regime.