Method for purifying by-product methyl acetate generated during production of PVA (polyvinyl acetate)

Abstract

The invention discloses a method for purifying by-product methyl acetate generated during production of PVA (polyvinyl acetate). The method comprises the three unit processes: extractive distillation, purification and drying. The extractive distillation process is that an azeotropic mixture of by-product crude methyl acetate, methanol and water is added from the middle lower part of an extractive distillation column, an extracting agent is added from the upper part of the extractive distillation column, the temperature at the top of the extractive distillation column is controlled to 55 to 65 DEG C; and the azeotropic mixture of methyl acetate and methanol as well as the extracting agent is discharged from the top of the extractive distillation column; and the purification process is that the azeotropic mixture of methyl acetate and methanol as well as the extracting agent, which is discharged from the top of the extractive distillation column, is sent to a purification column for purification, and pure methyl acetate is obtained in a column bottom, and dried to obtain finished methyl acetate. The extracting agent is acetic acid or acetic acid aqueous solution, does not bring new substances to a system, and can be recycled; and methyl acetate with the purity of more than 99.5% and the yield of more than 90% can be obtained under the condition of smaller additive amount of azeotropic mixture of by-product crude methyl acetate, methanol and water as well as the extracting agent.

Description

1. Technical field [0001] The invention relates to a process for purifying by-products, in particular to a method for purifying methyl acetate, a by-product in polyvinyl alcohol (PVA) production. 2. Background technology [0002] Methyl acetate is a colorless, flammable liquid with an aromatic odor, miscible with most organic solvents, and widely used as an industrial solvent. It can be used in paints and coatings, as well as in the manufacture of artificial leather and fragrances, and as an extractant for oils and fats. High-purity methyl acetate is an important organic raw material with a wide range of uses, and can be used to synthesize acetic acid, acetic anhydride, methyl acrylate, vinyl acetate and acetamide. The carbonylation of methyl acetate to produce acetic anhydride is currently the most economical process for producing acetic anhydride. Compared with the traditional ketene process and acetyl oxidation process, this process has significant advantages in reducing...

AI Technical Summary

Problems solved by technology

In order to recycle by-products, most PVA manufacturers decompose methyl acetate through resin to obtain a mixture of dilute acetic acid, methanol and methyl acetate, and then obtain methyl acetate through distillation and separation. In this production process, its disadvantages: ① system Involving acetic acid, methyl acetate, and trace amounts of chloride ions, sulfonate ions, etc., which are extremely corrosive to equipment

②Acetic acid-water is a difficult-to-separate system, and the concentration of dilute acetic acid consumes a lot of energy, which occupies a high proportion of the production cost of PVA

The lack of this process brings a new substance (extractant)-salt into the system, which has a certain impact on the purification of the system

In addition, salt is consumed in the production process, so not only the energy consumption is large, but also the material consumption is relatively large.