Production of eco-friendly poly(oxymethylene) dimethyl ethers catalyzed by acidic ionic liquid: A kinetic investigation

Large scale green production of poly(oxymethylene) dimethyl ethers(DMMn) would be crucial if the diesel-DMMn blends were applied to tackle the worldwide formidable air pollution by particulate matter. Kinetics studies are of great significance among the core challenges for understanding the reaction principles and process design. Kinetic model was developed for the production of DMMn from methylal and trioxane with sulfonic acid-functionalized ionic liquid as catalyst. Reversible reactions of propagation-depolymerization were simultaneously considered with non-equal rate constants for complex sequential reactions. The kinetic model proposed showed good accuracy and consistency for both forward and backward reactions. Activation energies E-p were in the range of 35.7 to 39.6 kJ mol(-1) for DMMn propagation reactions and 50.8 to 54.7 kJ mol(-1) for DMMn decomposition, with the difference of -15.1 kJ mol(-1) determined by Arrhenius equation. Entropy of activation, determined by Eyring-Polanyi equation, could make a significant contribution to the Gibbs energy barrier in the DMMn propagation/decomposition. It is interesting that the Schulz-Flory type distribution still could be maintained even the calculated rate constants increased with DMMn chain length.