Investigations on an efficient and environmentally benign poly(oxymethylene) dimethyl ether (OME3-5) fuel synthesis

Poly(oxymethylene dimethyl ethers) (OMEn, CH3O˗(CH2O)n˗CH3) with the appropriate chain length n = 3–5 are discussed as alternative diesel fuels due to their applicability for direct blending with diesel fuel in slightly modified diesel engines. This group of oxygenates have regained much interest as they significantly reduce soot formation during combustion, which is reflected in their large-scale pilot plant production. This work focuses on a favorable route for an efficient synthesis of OME3-5 from dimethoxymethane and trioxane at ambient pressure under mild reaction conditions. A detailed study was conducted on the catalytic performance of both methanesulfonic acid and the commercial solid acid Deloxan® as environmentally benign catalysts and promising replacements for sulfuric acid. For this, special focus on the influences of different reaction parameters (e.g. temperature, molar educt ratio, reaction time and pressure) was investigated herein. Hence, methanesulfonic acid (3.5 wt%) and Deloxan® (1.7 wt%) were found to be suitable catalysts for the anhydrous synthesis of OME with an OME3-5 selectivity of 32.7 wt% and 30.0 wt%, respectively. Furthermore, synthesis of OMEs catalyzed by either methanesulfonic acid or Deloxan® was found to follow Schulz-Flory distribution denoting a sequential OME chain-propagation.