Vapor-liquid equilibrium and distillation of mixtures containing formaldehdye and poly(oxymethylene) dimethyl ethers

Poly(oxymethylene) dimethyl ethers (OME, H3C-O-(CH2O)n-CH3) are promising synthetic diesel fuels. For designing OME production processes, a model for describing the vapor-liquid equilibrium (VLE) in mixtures of (formaldehyde + water + methanol + methylal + OME + trioxane) is needed. Building on previous work of our group, a physico-chemical model for the VLE in these mixtures is developed in the present work. For the development and the testing of the model, experiments of different types were carried out: VLE measurements in a thin film evaporator, batch evaporation experiments in an open still, and continuous distillation experiments in a laboratory column. The model predicts the results of the distillation experiments well. It is shown that OME with n ≥ 3 can be separated as bottom product from mixtures of formaldehyde, water, methanol, methylal, and OME with n ≥ 2. This separation is a critical step in a novel OME production process that increases the sustainability of OME production.