Reaction kinetics and equilibrium parameters for the production of oxymethylene dimethyl ethers (OME) from methanol and formaldehyde

A catalyst screening comprising zeolites and ion exchange resins for the synthesis of oligomeric oxymethylene dimethyl ethers (OME) from methanol (MeOH) and formaldehyde (FA) has been carried out. All catalysts led to the same product spectrum and parameters for chemical equilibrium have been determined. The ion exchange resin Dowex50Wx2 showed highest activity and reaction kinetics has been investigated employing this catalyst. The influence of the FA:MeOH ratio and water as well as refeeding of OMEs with undesired chain lengths have been considered in the kinetic model, which is based on a hyperbolic approach. Experiments have been carried out in the temperature range between 40 and 120 °C and variable FA:MeOH ratios from 0.5 to 1.5 g/g have been employed. Regarding water, up to 23 wt.% have been added to the reaction mixtures to investigate its influence on yield and reaction rate. Low water contents lead to high OME selectivities. By varying the FA:MeOH ratio, chain lengths of the OMEs can be influenced. Regarding the most active catalyst Dowex50Wx2, 90% of equilibrium conversion is reached after 5 min at 60 °C employing a catalyst loading of 1 wt.%. A study on the long term performance of the catalyst has been carried out and after 17 days the decrease of activity was below 10% while selectivity remained the same. For different Dowex catalysts a general kinetic model could be developed, which is not limited to Dowex50Wx2.