JPH0127058B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering dimethylformamide in high yield and purity from acidic waste liquid containing dimethylformamide.

Up to now, methods have been known for recovering dimethylformamide from dimethylformamide used in a spinning solution and aqueous waste liquid of dimethylformamide used for processing polyurethane resins. In all of these methods, the target of recovery is dimethylformamide, which was used simply as a solvent, so the waste liquid does not contain acidic compounds, and recovery of dimethylformamide requires the use of ion exchange resin, solvent extraction, dehydration and drying, Alternatively, it can be easily achieved by a distillation method or the like.

However, recovery of dimethylformamide used as a solvent in chemical reactions from acidic waste liquids has not been carried out until now and has been discarded as waste liquids due to various difficult problems as described below.

Namely: (1) If the acidic waste liquid remains, it is difficult to separate it from water for distillation due to equipment corrosion.

(2) In addition, if the acidic waste liquid is allowed to reach the neutralization point (PH8-10) using an aqueous solution of caustic alkali and then left to stand, it will become acidic again due to hydrolysis, and if it is made alkaline again, it will become even more acidic. Hydrolysis occurs and eventually caustic neutralization is not possible.

(3) Furthermore, if it is strongly alkaline and distilled in a water-containing state, it will decompose and dimethylformamide will not be recovered.

(4) Alkaline earths cannot be used for the same reasons as caustic alkali, and when the acidic waste liquid is neutralized using readily available lime, the calcium chloride produced has an affinity for dimethylformamide, so it is difficult to purify it. Adding an even more troubling problem to the above.

As a result of extensive research into methods for recovering dimethylformamide contained in acidic waste liquids, the present inventors discovered that anhydrous or almost anhydrous dimethylformamide waste liquid (water content of 10% or less) was recovered using anhydrous carbonate. The present invention was completed based on the knowledge that dimethylformamide can be recovered with high purity and high yield by neutralization with sodium.

The acidic waste liquid of dimethylformamide referred to in the present invention refers to liquids ranging from weakly acidic to strongly acidic. Examples include liquids containing compounds that become acidic when hydrolyzed, such as phosphorus trichloride, and acid chlorides of carboxylic acids. transformation,
It is a waste solution resulting from the synthesis of carboxylic acid derivatives, the cyclization reaction in which chemical reactions are carried out using acidic or strongly acidic reagents in dimethylformamide, and the result of dissolving acidic substances with dimethylformamide.
It may contain a solvent that does not react with alkali, such as alcohol.

In the present invention, anhydrous sodium carbonate is used.
This anhydrous sodium carbonate has a dehydrating effect, and the neutralized waste liquid will not become acidic even if it is left to stand or is distilled. Moreover, anhydrous sodium carbonate is almost insoluble in dimethylformamide, and therefore it is easy to separate the acidic waste liquid after neutralization.

It is preferable that the water content in the waste liquid is low, but 0 to 10%.
There is no particular problem as long as it is within a certain range.

There is no particular limitation on the concentration of dimethylformamide in the waste liquid.

Next, the operation of the recovery method of the present invention will be explained.

Powdered anhydrous sodium carbonate is added to the waste liquid in an amount slightly in excess of the amount sufficient to neutralize the acidic substances in the waste liquid, and the mixture is stirred at room temperature. In this case, the time required for neutralization varies depending on the acidity of the waste liquid, the excess amount of anhydrous sodium carbonate used, the temperature during stirring, etc., but since solid anhydrous sodium carbonate is poorly soluble in dimethylformamide, it is stirred for a long time.

After the neutralization reaction is completed and the liquid phase exhibits a pH of 8 to 10, stirring is discontinued and the solid is separated by decanting or filtration.

The recovered dimethylformamide may be used as is or after purification such as distillation or decolorization, depending on the purpose.

The method of the present invention will be explained in detail with reference to Examples below.

Example 1 Anhydrous soda carbonate (powder) in an excess of 20 to 30% of the amount required for neutralization was added to a dimethylformamide waste solution containing hydrogen chloride and exhibiting a pH of 1 to 2, and the mixture was stirred overnight at room temperature. The resulting salt is then filtered out and distilled under reduced pressure to produce pure dimethylformamide (boiling point 91℃/
100 mmHg) was collected.

Using this method, dimethylformamide could be recovered from wastewater containing sulfuric acid, phosphoric acid, or organic acids. The purpose was achieved by using the same cell and using potassium carbonate instead of soda carbonate.

Example 2 To a waste solution containing 13.1 g of phosphorus trichloride in 100 ml of dimethylformamide, 60.6 g of anhydrous soda carbonate was added and stirred for 18 to 20 hours. The salt produced was then filtered out and pure dimethylformamide could be recovered by distillation under reduced pressure. The recovery rate was over 80%.

Claims (1)

[Claims] 1. A method for recovering dimethylformamide, which comprises adding solid anhydrous sodium carbonate to an acidic anhydrous or dimethylformamide-containing solution with a moisture content of 10% or less to perform a neutralization treatment.