Effect of formaldehyde precursor and water inhibition in dimethoxymethane synthesis from methanol over acidic ion exchange resins: mechanism and kinetics

Abstract

AbstractA systematic comparison of the use of trioxane and depolymerized paraformaldehyde as formaldehyde precursors for the acetalization of methanol to dimethoxymethane was performed, using the acidic ion exchange resin, Amberlyst 15, as catalyst. Experiments were carried out under isothermal conditions in batch and continuous fixed‐bed reactors. The influence of the main operating parameters, temperature (80–120 °C), space time (2.7–6.2 kg h m−3), and feed concentration (12–22 wt% of trioxane/formaldehyde, 2.5 wt% of water on methanol) on reaction rate and product selectivity were evaluated. When using trioxane as reactant, dimethoxymethane is the main reaction product, with more than 90% selectivity. The catalyst was found to be stable during all the experiments (more than 30 h on stream). However, water caused a reversible inhibitory effect on reaction rate, which can be accounted for by using a competitive adsorption model. A mechanistic kinetic model was proposed and validated using the experimental results. When trioxane is used as reactant, its decomposition to formaldehyde was found to be the rate‐limiting step of the reaction mechanism (activation energy 73.1 kJ mol−1). This was confirmed with additional experiments, in which trioxane was replaced by depolymerized formaldehyde. In this case, reaction rate considerably increased. © 2021 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd.