Midong Shi,Gaoyin He,Fan Gan,Xuemin Yu,Qingsong Li
In order to reduce the energy consumption of distillation and decomposition of methylal in water, the experimental liquid–liquid equilibria (LLE) data of water + methylal + cyclohexane and water + methylal + n-heptane systems were measured in this work at different temperatures: 303.15 and 313.15 K under atmospheric pressure. The reliability of the tie-line data obtained by this present work was determined using the Othmer–Tobias and Hand equations. Moreover, the LLE data were correlated by nonrandom two-liquid (NRTL) and universal quasi-chemical (UNIQUAC) models with good results in both systems.
Polyoxymethylene dimethyl ethers (PODE n ) are promising diesel blend components with high oxygen content, high cetane number and similar properties to diesel. In this paper, we conducted a series of experiments for synthesizing PODE n over a HZSM-5 catalyst in a batch stirred autoclave using methylal and trioxane as reactants. Our research focused on the water influence on these syntheses by contrasting the differences from experiments with or without water and built reaction pathway and rate laws. The experimental and kinetic results showed that decrease of water amount could not only increase yields of the PODE n but also reduce the influences on formation rates of the desired products and eliminate some side reactions. Therefore, it is necessary to optimize water amount in the raw materials for balancing costs of the feed and operation as well as yields of the products to maximize the economy in a commercial production of PODE n .
Poly(oxymethylene) dimethyl ethers (PODE n=3-5 ), as promising diesel additive, were synthesized by reaction of 1,3,5-Trioxan (TOX) and methylal (PODE 1 ) 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∙ N TOX / N PODE1 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 PODE n (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 PODE n . Through optimizing the Schulz-Flory distribution of PODE n based on the kinetics, the maximal selectivity of TOX to PODE 3-5 of 57.80% will achieve under anhydrous conditions, while this will become 54.60% under 5 wt % water in TOX.
Catalytic reaction of methylal (DMM) with trioxane (TOX) for preparation of polyoxymethylene dimethyl ethers (PODMEn, CH3O(CH2O)nCH3, where n > 1) was investigated in a series of Brønsted acid ionic liquids with alkanesulfonic acid groups. The structures, acidities, and properties of ionic liquids were experimentally characterized and theoretically analyzed. The Brønsted acidity–activity correlation for the ionic liquids was studied. Among all these ionic liquids, 1-(4-sulfonic acid) butylpyridinium hydrogen sulfate ([PY-BS][HSO4–]) exhibited the best catalytic performance, which was ascribed to its strong Brønsted acidity. The influences of ionic liquid dosage, molar ratio of DMM to TOX, and reaction temperature on the catalytic reaction were explored using [PY-BS][HSO4–] as the catalyst. Under the optimal conditions of n(methylal):n(trioxane):n(ILs) = 180:60:1, 170 °C, and 10h, the conversion of trioxane and the selectivity of PODME3–8 were as high as 91.18% and 70.90%, respectively. The ionic liquid [PY-BS][HSO4–] could be reused.
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