Recovery of Methanol and Acetic Acid in Poly Vinyl Alcohol Production

Recovery of Methanol and Acetic Acid in Poly (Vinyl Alcohol) Production [35], [93] 

In the production of poly(vinyl alcohol), a mother liquor containing methanol and methyl acetate is produced. This mother liquor is converted to acetic acid and methanol in a multistage process these substances are then recycled to the production process. 

In the first stage, the mother liquor is subjected to distillation. An azeotropic mixture of methanol and methyl acetate is obtained as overhead product. The methanol-water mixture, which remains in the distillation bottom, is fed to a second distillation stage, and the methanol distilled off is recycled to the production process. 

The azeotropic mixture is subjected to an extractive distillation (extraction medium wastewater from the methanol distillation). The still bottoms so obtained, a water - methanol mixture, are fed to the methanol distillation. Methyl acetate taken from the top of the column is fed to a reactor where it is hydrolyzed to methanol and acetic acid with the aid of an ion-exchange resin. In the subsequent distillation, acetic acid is removed, and the mixture of methanol and unreacted methyl acetate from the extractive distillation is recycled (Fig. 17). Wastewater from this recovery process is treated in a biological wastewater treatment plant. 

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