Study On Separating Methyl Acetate-Methanol By Salt Extractive Distillation

During the Polyvinyl Alcohol (PVA) producion, the product cannot be polymerized by the monomer directly. Generally, it can be obtained by alcoholysis of poly vinyl acetate in the solution of methanol. According to this process, great deals of methyl acetate will appeare as by product. Nowadays, methyl acetate is reclaimed by hydrolyzed to acetic acid and methanol. Accroding to the literature, the energy consuming of reclaim process was about 50%~60% of total cost of PVA production, while the energy consumption of methyl acetate recycling was about 70% of the energy consuming reclaim process. So, it is an urgent problem for all the PVA manufactures to cut down the energy consumption of methyl acetate reclaimation. In this paper, the processes of methyl acetate recycling were reviewed; the method of separation methyl acetate-methanol by salt effect distillation was proposed.The measurements and analysis methods for measuring VLE for methyl acetate-methanol-water/salt were set up. The modified Othmer recirculation still has been used to determine the relative volatility of methyl acetate-methanol systems under 0.1013 MPa. The relative volatility at azeotrope point with different solvents and salts were determined respectively. The relative volatility could be improved to 6.21 with the solution of acetate potassium as extractive solvent; the ratio of solvent was 1:1(v/v). While the relative volatility could be improved to 2.83 only, when just water was added in as extractive solvent. According to the result, the salt effect extractive distillation was better than ordinary extractive distillation in improving solvent efficiency and saving energy.Isobaric VLE data at 0.1013MPa were determined for the methyl acetate-methanol systems under the conditions of different fixed salt mole fraction. In addition, effects of solvents and salts on VLE for the systems were studied. It showed that different salt effection was brought by different salt, and the salt effection was attributed to the solubility and concentration of the salt in the solvent, it was increased by the solubility and concentration.Using artificial-neural-network (ANN) tools, a model for correlating and predicting VLE data for methyl acetate-methanol-water/salt systems were proposed. The correlation results of these experimental data were better than those of some semi-empirical models (such as Sander model, Macedo model and Kikic model). The common deficiencies of these models are complicated calculations and too many parameters used, while these disadvatages could be avoided by ANN model. Meanwhile, Macedo model was modified respectively, and its correlation results were better than that of the original one. A new salt was used as a salt-effect agent and the continuous distillation was carried out. High concentration methyl acetate was achieved (above 99.5%). According to the experimental results and part of the VLE data measured by the author, energy consumption of separation methyl acetate-methanol 120 thousands t/a were estimated.