Study on oxidation and pyrolysis of carbonate esters using a micro flow reactor with a controlled temperature profile. Part II: Chemical kinetic modeling of ethyl methyl carbonate

Abstract

Little is known on reactivity of ethyl methyl carbonate (EMC), which is widely used as an electrolyte solvent in lithium-ion batteries (LIB). A better understanding on the reactivity of EMC and its chemical kinetics are required to assess the fire risks of LIB. The reactivity of a stoichiometric EMC/air mixture was investigated with a weak flame in a micro flow reactor with a controlled temperature profile (MFR) at atmospheric pressure and a maximum wall temperature (Tw,max) of 1300 K. To investigate species evolution formed in EMC oxidation (equivalence ratios of 0.5, 1.0 and 1.5) and pyrolysis, species measurements were performed in MFR at atmospheric pressure and Tw,max range of 700–1300 K. These experimental insights were used for modeling and validation of a chemical kinetic mechanism for EMC. The first chemical kinetic mechanism of EMC was developed based on reactions of dimethyl carbonate (DMC) and diethyl carbonate (DEC), and literature data.The present EMC mechanism reproduced measured species profiles well. Both experiments and computations showed two-stage increases in CO2 mole fraction: initial fuel decomposition producing CO2 at Tw,max = 850 K and subsequent CO oxidation to CO2 at Tw,max = 1050 K. In the first CO2 increase region, a series of decomposition reaction of EMC produced CO2, C2H4 and CH3OH via methyl formic acid. The oxidation of CH3OH and C2H4 proceeded in the region corresponding to second CO2 increase. The present EMC mechanism also reproduced experimental weak flame position of EMC well. Computational weak flame structure of EMC indicated a three-stage reaction: EMC decomposition, oxidation of decomposition products to CO and oxidation of CO to CO2. The three-stage reaction initiated by fuel decomposition reaction is distinct from the one initiated by low-temperature oxidation of ordinary hydrocarbons. This novel three-stage reaction was also observed for DEC, which has two ethyl groups.