Midong Shi

Reaction Equilibrium and Kinetics of Synthesis of Polyoxymethylene Dimethyl Ethers from Formaldehyde and Methanol

Polyoxymethylene dimethyl ethers (PODEn) are environmentally friendly diesel fuel additives. They belong to alkyl ethers that could reduce solid particulate matter formation and emissions of carbon monoxide and nitrogen oxide when added into diesel fuels. This work aimed to researching chemical equilibrium and reaction kinetics of the synthesis of polyoxymethylene dimethyl ethers from formaldehyde and methanol catalyzed by an ion-exchange resin at the reaction temperatures 313, 333, 343 and 353 K. In the reversible reaction, the Kn ≥ 2/K2 ratio was equal to one. The reaction orders of methanol, formaldehyde, water and PODEn were 0.2638, 0.1328, 0.1565 and 0.0048, respectively. At a 10 wt % dosage of H-SIR1 resin, the rate constants of the methylal (dimethoxymethane) formation and depolymerization were 1.04 × 104 and 3.43 × 106 min–1, respectively, and the pre-exponential factor for the PODEn + 1 formation was 2.50 × 103 min–1. Activation energies for the methylal propagation and depolymerization and PODEn > 1 formation were 30.46, 48.40 and 27.10 kJ/mol, respectively. The results indicated that the equilibrium constants of PODEn > 1 formation reactions were consistent. The exothermic reaction of methylal formation was easier than the reverse reaction and more difficult than the formation of PODEn > 1.

Hydrolysis of Methylal Catalyzed by Ion Exchange Resins in Aqueous Media

In the present work, the chemical equilibrium and kinetics of methylal (PODE1) hydrolysis catalyzed by ion–exchange resin in aqueous solutions were investigated. The study covers temperatures between 333.15 and 363.15 K at various starting compositions covering (PODE1 + MeOH)/water molar ratio ranges from 0.5 to 1.5 in a time scale. On the basis of the experimental results, a mole fraction-based model of the chemical equilibrium and a pseudohomogeneous model are proposed to fit data based on true amount of monomeric formaldehyde. It has been demonstrated that the hydrolysis of PODE1 is slightly endothermic with the enthalpy 8.19 kJ/mol and the rate determining step. Finally, a feed–forward artificial neural networks (ANN) model is developed to model the concentration change of methanol in aqueous solutions. The results showed that the predicted data from designed ANN model were in good agreement with the experimental data with the coefficient (R2) of 0.98. Designed ANN provides a reliable method for modeling the hydrolysis reaction of methylal (PODE1).