Research On Synthesis Process Of Propylene Glycol Monomethyl Ether Acetate Via Reaction Distillation

Propylene glycol monomethyl ether acetate (PMA) is a colorless transparent liquid with aromatic flavorit is an important industrial solvent and extensively employed in ink, coatings, printing, dyeing, pesticides and other fields, due to its kindly environmental performance, excellent thermostability, little viscosity variations with temperature and low toxicity. Therefore, the demand for PMA is gradually increasing and the production of PMA grows greatly. At present, the major method to synthesis of PMA is direct esterification reaction of propylene glycol monomethyl ether with acetic acid under the catalysis of sulfuric acid; but there are some mian drawbacks of this method, such as serious corrosion on equipment, serious pollution, subsequent processing complex and high acid value of product. A new synthesis process for PMA, the transesterification of PM and Methyl acetate (MeAc) to form PMA and Methanol (MeOH) is investigated in this work, the reaction rectification process were studied. The main contents are as follows:(1) This article measured the two substances under different temperature of saturated vapor pressure in a modified Othmer still, and corresponding Antoine constant via origin, and apply the Clausius-Clapeyron equation to calculate the molar heat of vaporization of the PM and PMA during the measured temperature range. At the same time, isobaric vapor-liquid equilibrium (VLE) data for four binary systems (PM+PMA, MeAc+PM, MeOH+PMA and MeAc+PMA) and a quaternary system (MeAc+MeOH+PM+PMA) at 101.3 kPa were measured in a double circulating still of modified Othmer type. All binary experimental data were correlated by NRTL and Wilson models, and the binary interaction parameters of both models have been obtained by simplex method. Combining with the binary interaction parameters calculated from this work and other binary systems (MeAc+MeOH, MeOH+PM) from literature, these six binary interaction parameters were used to predict the quaternary vapor-liquid equilibrium. The result showed that the prediction results are in good agreement with the experimental values. The Wilson model prediction effect is better.(2) The kinetics for synthesis of PMA was investigated with PM and MeAc over sodium methoxide catalyst in a batch stired-tank reactor. The effects of reaction temperature, reactant molar ratio and catalyst amount on reaction rate were investigated, and a homogeneous kinetics model was established according to a possible reaction mechanism. The reaction rate constants activation energy and other optimal kinetic parameters were obtained by using the MatLab programming. Comparing the model values with the experimental values, the results indicated that the deviations are small. Account for that the kinetic model can characterize the reaction process well.(3) The reactive distillation equipment was self-designed, and the experiments of transesterification synthesis of PMA with PM and MeAc over sodium methoxide catalyst were carried out in the reactive distillation column. The operation factors, catalyst amount, reactant molar ratio and the reaction time on PMA conversion were investigated. Under the conditions of the quality of sodium methoxide catalysts for 0.4% of the total mass of reactants, the MeAc/PM molar ratio of 7:1, at first total reflux when the top of the tower has a back up, then tower material produced with R=2 for 2 h, if the temperature of the top of the tower is too high require a period of total reflux, then reflux ratio must be increased to R=3 before production, reaction time was 5 h, the conversion of PM reached as high as 89%.