Poly(oxymethylene) dimethyl ether synthesis – a combined chemical equilibrium investigation towards an increasingly efficient and potentially sustainable synthetic route

Abstract

Polyoxymethylene dimethyl ethers (denoted hereon as OME) are potential sustainable fuels (e.g. as a diesel substitute). In this paper, the fundamental analysis of a potentially, sustainable synthetic OME system is presented (i.e. based on CH₃OH synthesised from H₂ and recycled CO₂). In this context, a multicomponent thermodynamic vapour–liquid equilibrium model, based on CH₃OH as the educt and source of H₂CO for OME synthesis, is described. A thermodynamic equilibrium mathematical model for this complex (i.e. a 29 reaction network) CH₃OH–H₂CO equilibrium system is presented, capable of solving the sequential chemical and phase equilibrium, importantly considering all components in the reaction system including poly(oxymethylene) hemiformals and poly(oxymethylene) glycols. A theoretical efficiency evaluation indicates that the proposed anhydrous route is potentially more attractive than the conventional synthesis (i.e. based on dimethoxymethane and trioxane). To substantiate these theoretical investigations, a complimentary experimental batch OME synthesis is also presented, providing validation for the presented thermodynamic model. An initial kinetic analysis of the OME synthesis over different commercial catalysts is also highlighted. Our presented findings reliably describe the synthesis equilibrium with respect to our experimentally obtained results. The presented work supports further an operating OME synthesis framework based on CH₃OH and H₂CO and highlights the requirement for innovative process design regarding feed preparation, reactor technology, and product separation/fractions recycling.