DMF RECYCLING METHOD

Abstract

The invention provides a DMF recycling method, the method comprises: neutralization step, extraction and crystallization step, layering step, evaporation step; a condensate obtained by evaporation of the upper layer liquid phase is recycled into the anti-solvent, a concentrated solution obtained by evaporation of the upper layer liquid phase and a condensate obtained by evaporation of the lower layer liquid phase are mixed to obtain a crude DMF solution for recycling of DMF. The recycling method overcomes the problem that acetic acid in the stock solution corrodes the equipment and produces impurities, so as to improve the recycling purity and reduce the equipment cost.

Description

Claims

1. A DMF recycling method, for recycling DMF, acetic acid and water comprised in DMF stock solution used, is characterized in that, the method comprises the following steps: neutralization step: adding alkaline neutralizer to the DMF stock solution, controlling pH value of a mixture within a preset range, and performing a neutralization reaction to convert acetic acid in the DMF stock solution into acetate;extraction and crystallization step: adding an anti-solvent that is insoluble with the acetate to the neutralized solution, mixing and stirring to extract DMF by the anti-solvent, thereby causing an acetate hydrate to crystallize and precipitate, and filtering the solid to obtain mother liquor containing DMF;layering step: standing and layering the mother liquor containing DMF to obtain an upper layer liquid phase and a lower layer liquid phase;evaporation step: the upper layer liquid phase and the lower layer liquid phase are evaporated and concentrated separately; a condensate obtained by evaporation of the upper layer liquid phase is recycled into the anti-solvent, a concentrated solution obtained by evaporation of the upper layer liquid phase and a condensate obtained by evaporation of the lower layer liquid phase are mixed to obtain a crude DMF solution for recycling of DMF.

2. The DMF recycling method according to claim 1, is characterized in that, in the DMF stock solution: DMF mass content is 75% to 95%, water mass content is 4% to 15%, and acetic acid mass content is 1% to 10% .

3. The DMF recycling method according to claim 1, is characterized in that, the alkaline neutralizer is liquid alkali or solid alkali; the liquid alkali is one of NaOH or KOH aqueous solution, and mass concentration is 1% to 50%; the solid alkali is one of NaHCO3, Na2CO3, KHCO3, K2CO3 or Ca(OH)2, or a mixture of NaHCO3 and Na2CO3, or a mixture of KHCO3 and K2CO3, preferably Ca(OH)2.

4. The DMF recycling method according to claim 3, is characterized in that, the amount of solute in the liquid alkali is 0.8 time to 1 time of the amount of substance of acetic acid, reaction temperature is room temperature, reaction time is 5 min to 15 min, and stirring rate is 100 r/min to 300 r/min.

5. The DMF recycling method according to claim 3, is characterized in that, the amount of the solid alkali is 1 to 3 times of the amount of substance of acetic acid, reaction temperature is 40° C. to 70° C., reaction time is 0.5h to 1.5h, and stirring rate is 200 r/min to 400 r/min.

6. The DMF recycling method according to claim 1, is characterized in that, in the neutralization step, the pH of the mixture is controlled from 7 to 11 by adding an alkaline neutralizing agent.

7. The DMF recycling method according to claim 1, is characterized in that, the anti-solvent is one of ether, anisole, isopropyl ether, benzene, toluene and xylene; preferably the anti-solvent is toluene.

8. The DMF recycling method according to claim 1, is characterized in that, the anti-solvent is added in the amount of: volume ratio of DMF stock solution: anti-solvent = 1: 0.5 to 5; preferably: volume ratio of DMF stock solution: anti-solvent = 1: 1 to 3.

9. The DMF recycling method according to claim 1, is characterized in that, in the extraction and crystallization step, the temperature of anti-solvent extraction and crystallization process is room temperature, the stirring rate is 200 r/min to 400 r/min, and the stirring time is 15 min to 60 min.

10. The DMF recycling method according to claim 1, is characterized in that, the method also comprises the step: adjustment step: adding an acidic regulator to the crude DMF solution to adjust the pH of the crude DMF solution to 6-8, preferably 7, and the adjusted crude DMF solution is used to recycle DMF.

11. The DMF recycling method according to claim 10, is characterized in that, the acid regulator used in the adjustment step is inorganic acid, preferably a mixture of one or more of sulfuric acid, phosphoric acid solution, with a mass concentration of 5% to 50%.

12. The DMF recycling method according to claim 1, is characterized in that, the method also comprises the step: secondary recycling step: recycling acetate hydrate solid precipitated in the extraction and crystallization step and/or acetate hydrate solid obtained by evaporation of the lower layer liquid phase in the evaporation step.