From a Batch to a Continuous Supported Ionic Liquid Phase (SILP) Process: Anhydrous Synthesis of Oxymethylene Dimethyl Ethers

Abstract

AbstractOxymethylene dimethyl ethers (OMEn; CH3(−OCH2)n−OCH3) are promising sustainable synthetic fuels when produced from CO2 and green H2. The synthesis pathway presented here overcomes synthetic problems and includes the reaction of dimethoxymethane (OME1) with molecular gaseous formaldehyde in a novel continuous, anhydrous reaction setup. An initially performed wide batch‐catalyst screening highlighted the salts M[NTf2]x with M=Cu+, Co2+ and Mg2+ as especially interesting catalysts (NTf2=N(SO2CF3)2). Supported ionic liquid phase (SILP)‐catalysts were prepared on this basis and demonstrated the successful synthesis of OMEn in a continuous process. The SILP‐catalysts immobilized in the IL EMIM[BF4] showed a fast and strong deactivation, but those with the IL EMIM[NTf2] showed excellent catalytic performance and stable results in continuous operations exceeding 19 h. The influence of the weight hourly space velocity (WHSV), the reaction temperature as well as the storage conditions of the catalysts (inert vs non‐inert) were investigated. 90 °C was identified as ideal reaction temperature. High feed‐gas flows (WHSV=15.8 h−1) are preferable in terms of product selectivity SOME2‐5>90 mol‐ % with an OME1 conversion XOME1=5.10 mol‐ % at the same time. We also demonstrated that the catalysts can be stored in air for 50 days without loss of activity. The SILP‐catalysts were analyzed by NMR and IR spectroscopy. Furthermore, the thermodynamics of the reaction mechanism of some selected catalysts was calculated by DFT theory to this reaction.