Experimental demonstration of the production of poly(oxymethylene) dimethyl ethers from methanolic formaldehyde solutions in a closed-loop mini-plant

Poly(oxymethylene) dimethyl ethers of chain length 3–5 ( [Formula presented] ) are discussed as synthetic diesel fuels due to their potential to significantly reduce soot emissions while presenting physicochemical properties similar to conventional diesel fuels. A recently developed process to produce [Formula presented] directly from methanol and aqueous formaldehyde is a promising way to avoid expensive intermediates such as trioxane, methylal, or dimethyl ether. The process consists of a reactor, a distillation sequence, and a membrane unit. The first distillation column is particularly challenging due to the reactive character of the separation, the high number of components present, and the limited solubility of formaldehyde. Up to now, the feasibility of this separation has yet to be demonstrated. This work presents closed-loop experiments in a demonstration plant erected at the Campus Straubing of the Technical University of Munich with closing recycle. In the distillation step, [Formula presented] with very small impurities of around 800 ppm of formaldehyde was obtained. The experimental results were compared with simulations based on a reactive equilibrium stage model. The simulations of the temperature and composition profiles for the majority of the components are in line with the experiments. Although the membrane separation exhibited weaker water selectivity than in previous tests, it was sufficient to overcome distillation boundaries. Additionally, this study assesses the potential for solid precipitation, explores trade-offs in product quality, and discusses overall mass balances of the process, demonstrating the overall feasibility of the process.