Formation kinetics of polyoxymethylene dimethyl ethers from methylal and trioxane with little water

Abstract

Polyoxymethylene dimethyl ethers (CH3-O-(CH2O)n-CH3, PODEn, n > 1) can be added to diesel to reduce air pollution caused by incomplete combustion. Driven by this need, a cost-effective and efficient synthetic route is presented and investigated by this work for the production of PODEn, which are formed from methylal and trioxane with low water content (< 10 %(mass)) over HZSM-5 catalyst in a batch slurry autoclave at the temperature from 353.15 K to 393.15 K. The reaction rate laws including the PODEn and byproducts of polyoxymethylene hemiformals (HFn), polyoxymethylene glycols (MG), methanol (MeOH) and methyl formate (MF) are developed. The rate constants of propagation step (k6) and depolymerization step (k−6) are assumed independent on polymerization degree of PODEn. The rate of reaction is proportional to the content of the catalyst (Wcat) for the catalytic reaction within the scope of the study. All kinetic parameters were estimated by combining genetic algorithm and least square regression to fit experimental data well. This work is valuable for process optimization and reactor design.