A Fundamental investigation of the pyrolysis chemistry of oxymethylene ethers. Part II: Experiments and comprehensive model analysis

Abstract

Oxymethylene ethers (OMEs) form a high-potential family of synthetic chemicals to replace fossil-based fuels. These alternative liquid energy carriers can contribute to a circular carbon economy when synthesized through carbon capture and utilization technology using renewable electricity, so-called e-fuels. Despite the potential to significantly reduce greenhouse gas and particulate matter emissions and their favorable ignition characteristics, the radical decomposition chemistry of long-chain OMEs remains largely unexplored. Pyrolysis of small OMEs is well understood. Still, there is limited data available for long-chain OMEs, such as oxymethylene ether-3 (OME-3), oxymethylene ether-4 (OME-4), and oxymethylene ether-5 (OME-5). In this study, the pyrolysis of these long-chain OMEs is investigated by combined experimental and kinetic modeling work. Six new datasets are acquired from experimental units with tubular and jet-stirred reactors. The thermal decomposition is examined across a broad range of reaction conditions, which enables studying both the primary and secondary decomposition chemistry. At low temperatures, smaller OMEs and formaldehyde are the major decomposition products, whereas at high temperatures H₂, CO, and methane become the dominant products. The yield of species with carbon-carbon bonds remains low. The kinetic model based on first principles from Part I, consisting solely of elementary reaction steps, is validated against the newly acquired experimental datasets. This new model outperforms literature models and predicts experimental trends of important products, on average, within the experimental uncertainty margin without fitting model parameters. Comprehensive model analysis by means of rate of production and sensitivity analyses indicates that formaldehyde elimination reactions, which yield smaller OMEs, dominate the thermal decomposition.