Pyrolysis of diethyl carbonate: Shock-tube and flow-reactor measurements and modeling

Abstract

Shock-tube and flow-reactor experiments were used to study the thermal decomposition of diethyl carbonate (C2H5OC(O)OC2H5; DEC). The formation of CO2, C2H4, and C2H5OH was measured with gas chromatography/mass spectrometry (GC/MS) and high-repetition-rate time-of-flight mass spectrometry (HRR-TOF-MS) behind reflected shock waves. The same products were also detected by GC/MS in flow reactor experiments. All experiments combined span a temperature range of 663–1203 K at pressures between 1.0 and 2.0 bar. Time-resolved species concentration profiles from HRR-TOF-MS and product compositions from GC/MS measurements were simulated applying a detailed reaction mechanism for DEC combustion. A master-equation analysis was conducted based on computed energies from G4 calculations. Quantum chemical calculations confirm that DEC primarily decomposes by six-center elimination, C2H5OC(O)OC2H5 → C2H4 + C2H5OC(O)OH (1a), followed by rapid decomposition of the alkoxy acid, C2H5OC(O)OH → C2H5OH + CO2(1b). Measured DEC decomposition rate constants k(T) at p ≈ 1.5 bar can be represented by the Arrhenius equation k(T) = 1013.64±0.12 exp(−204.24±1.95 kJ/mol/RT) s − 1. Theoretical predictions for k1a were in good agreement with experimentally derived values. The theoretical analysis also included dipropyl carbonate (C3H7OC(O)OC3H7; DPC) decomposition and the reactivities of DEC and DPC are compared and discussed in the context of reactivity of dialkyl carbonates under pyrolytic conditions.