Identification and thermodynamic analysis of reaction pathways of methylal and OME-n formation

Renewable energy from wind and solar sources is affected by fluctuations which do not correspond to the demand for electrical energy. Storage options are therefore required and also other possibilities of utilizing this power in a future energy system. Fuel synthesis using CO2 from industrial waste gases and hydrogen from electrolysis is an attractive approach. Methylal and higher oxymethylene ethers represent one fuel option due to the low-emission combustion of ethers with their characteristic CO bonds. However, conventional synthesis is an elaborate process because of the large number of intermediate steps. The direct synthesis of methylal and higher oxymethylene ethers would considerably simplify the technical implementation. Here we present a method that considers Gibbs energy in order to analyze the possibilities of direct synthesis from CO2-H2. High operating pressures and influence of the critical states of educt and products on the thermodynamic state parameters of enthalpy and entropy mean that the real gas properties can be modeled by an equation of state. Methylal can be formed with high conversion rates at pressures of 100 bar and temperatures below 373 K. Formation of dimethyl ether as a potential by-product must be suppressed by a suitable catalyst since it is thermodynamically favored.