Apparent kinetics and prospective operation on synthesizing Poly(oxymethylene) dimethyl ethers over shaped zeolite BETA in Fixed-bed reactor

Abstract

Poly(oxymethylene) dimethyl ethers (PODEn=3-5), as promising diesel additive, were synthesized by reaction of 1,3,5-Trioxan (TOX) and methylal (PODE1) on the catalyst of zeolite BETA in a fixed-bed reactor and kinetically researched under reaction temperature from 308 to 358 K, initial mole ratio 3∙NTOX/NPODE1 from 0.8 to 1.2, space time from 0.33 to 20.78 min⋅kg⋅l−1 and water content from 0 to 2 wt%. A series of rate laws were formulated for quantifying not only their reaction rates but also the role of water. The obtained activation energies of propagation and decomposition reactions of PODEn (n = 3 ∼ 8) are 22.89 kJ⋅mol−1 and 27.46 kJ⋅mol−1 respectively, and their pre-exponential factors depend on the “n” in PODEn. Through optimizing the Schulz-Flory distribution of PODEn based on the kinetics, the maximal selectivity of TOX to PODE3-5 of 57.80% will achieve under anhydrous conditions, while this will become 54.60% under 5 wt% water in TOX.