| POM, one of the three general engineering plastics in the world today, which is comprehensively fine thermoplastics, has been widely applied in the field of electrical and electronics, household light industry, automobile, agriculture and so on. The production process of copolyoxymethylene which use 37%wt formaldehyde aqueous solution as raw material is a common synthesis process in the POM manufacturers in China. The waste liquor which generated from the side reactions during the POM production contains a large amount of organic components, including methyl formate,methylal, methanol,formic acid, dioxolane and the like. The mixed organic liquid with the components above is highly toxic, which will cause a great adverse effect to environment and also be a waste of resources in the mean time if discharged directly.Based on the vapor-liquid equilibrium data of methyl formate- methanol- methylal through the experiment. This essay demonstrates the possibility to use the distillated methyl formate from the tower as a product after distillation recycling of the waste liquid by Aspen Plus.As the data shows, the vapor-liquid equilibrium(VLE) data of methyl formate-methanol-methylal and the related systems are T-x-y data of methyl formate-methanol system at 101.3k Pa and some T-x data of methanol-methylal system at 101.3k Pa. In this paper, the isothermal VLE data of methyl formate-methylal, methanol-methylal,methyl formate-methanol and methyl formate-methanol-methylal systems had been measured by an improved Rose equilibria Binary method, and the thermodynamic consistency of the experimental data was verified. The experiment results show that only methanol-methylal exists azeotropic mixture at atmospheric pressure and the azeotropic point of methanol-methylal is 41.4℃with the 15.9% of methanol.Three sets of binary system measurements obtained the corresponding model parameters through Wilson, NRTL and UNIQUAC equation Regression. Using these three groups of parameters respectively, VLE data of methyl formate-methanol-methylal ternary system were predicted and compared with experimental data: The temperature’s average relative deviations were respective1.16%,1.21%,1.13%; the average relative deviations of methanol’s vapor composition were respectively 4.77%,4.92%,4.72%; the average relative deviations of methylformate’s vapor composition were respectively 4.43%,4.47%,4.29%; the average relative deviations of methylal’s vapor composition were respectively3.37%,3.86%,3.79%. There is minimum deviation between UNIQUAC equation calculation value and experimental value. Its precision meets the requirements, which can provide the reliable thermodynamic data for liquid waste distillation separation of methyl formate.In this paper, it rectified the waste liquid by using a comprehensive experimental device produced by beiyang laboratory equipment for reactive distillation experiments.It begins to produce methyl formate when the reflux ratio is 3, and the mass fraction of methyl formate separated from the tower is 89%. The reason it cannot obtain high purity products through simple distillation method is not only the closeness of the boiling points of methyl formate(31.6℃) and other components such as methylal(41.67℃) and methanol-methylal’s azeotropic mixture(41.4℃), but also the theoretical plate number of this rectification tower is too low.It uses the Aspen Plus to simulate and optimize the distillation recycling of methyl formate from POM waste liquid. After studying how the factors such as the feed stage, feed temperature, stage number, reflux ratio effect on concentration of product and the energy consumption, the parameters of the optimal methyl formate recovery tower are obtained as follows: feed stage 64,feed temperature 34℃, stage number 80, reflux ratio 3.59, the mass fraction of methyl formate separated from the tower is 99.22%, at the same time, the recovery rate of methyl formate is 96% in the whole distillation process. |
PDF Full Text Request