Thermodynamic analysis and experimental verification of a new route for direct diethyl oxalate synthesis

The synthesis of high quality diethyl oxalate (DEO) via transesterification of dimethyl oxalate (DMO) and ethanol (EtOH) was reported. The thermodynamic data of each substance involved in the reaction were estimated by Benson and Joback's group contribution method and Watson formula, and the enthalpy change, entropy change, Gibbs free energy and equilibrium constant of each step of DEO synthesis were calculated by classical thermodynamic formula under atmospheric pressure and in the temperature range of 323−368 K. The DMO conversion, product composition and reaction equilibrium constant at different temperatures and raw material ratios were measured by experiments and compared with the theoretical data. It is found that the error between the measured DMO conversion and the estimated value is less than 1%, and the measured equilibrium constant is basically consistent with the estimated value. After strict experimental verification, it is proved that the thermodynamic data estimated by thermodynamic analysis are reliable. The actual catalytic distillation conditions were simulated, and the composition of the initial raw materials and the final products at 353 K was calculated with the hypothesis of 99.9% DEO purity at the bottom. When the content of EtOH in the bottom was higher than 2.59% and the molar ratio of initial EtOH to DMO was higher than 2.10, the purity of DEO could reach the target, and the overall process energy consumption was significantly reduced. It would be an efficient and green route for DEO synthesis.