JPH0418983A - Treatment of dimethylformamide - Google Patents

Abstract

PURPOSE:To make DMF in waste water simply and surely harmless or useful at a low cost by mixing the waste water with alkali, forming dimethylamine and alkali formate and blowing air into the water. CONSTITUTION:Waste water contg. DMF is mixed with alkali. In the case where sodium hydroxide is used as the alkali, liberated dimethylamine and sodium formate are formed by hydrolysis. Since this reaction is an equilibrium reaction, the formed dimethylamine is expelled into a vapor phase by blowing air into the water in the same way as ammonia in water is expelled. By this method, DMF in waste water is decomposed into dimethylamine and alkali formate and the dimethylamine is transferred to a vapor phase and made useful by absorption in an acidic substance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a treatment method for decomposing dimethylformamide, which is widely used as an excellent organic solvent, to render it harmless or useful.

(Prior art and its problems) Dimethylformamide is highly stable and has extremely excellent properties as a solvent for polymeric substances such as acrylonitrile, so it is widely used in chemical fiber textiles, synthetic leather manufacturing, etc.

However, although this high stability of dimethylformamide is an advantage, it leads to difficulties in post-use treatment, and is the reason why a complete treatment method for wastewater containing this drug has not been established at present.

For example, the activated sludge method, which is considered an effective treatment method for organic wastewater, suffers from the toxicity of dimethylformamide, which requires the use of a large amount of dilution water and a large volume aeration tank to suppress this toxicity. A new challenge will be faced: how to deal with the large amounts of ammonia that will be generated. In other words, if this ammonia is discharged as it is, it will cause the problem of eutrophication, but treating it with nitrification and denitrification requires a huge amount of equipment, so it is not practical as a wastewater treatment method from a cost standpoint. I can't say that.

Furthermore, as a processing method that takes advantage of the stability of dimethylformamide, a purification and recovery method using multistage distillation is considered to be promising. However, while the concentration of dimethylformamide that can be collected by such purification and recovery methods is 30% or more, the concentration in wastewater discharged from boat fishing is usually around 2.5 to 7%. Therefore, this method cannot be applied in most cases.

Therefore, at present, the treatment of wastewater containing dimethylformamide is often outsourced to industrial waste treatment companies, which incurs significant costs, and it is difficult for these treatment companies to carry out effective treatment. It has little sex and is fraught with environmental health problems.

In light of the above-mentioned circumstances, the present invention aims to provide an extremely practical treatment method that can easily and reliably render harmless or make useful dimethylformamide contained in wastewater at low cost.

(Means for Solving the Problems) In order to achieve the above object, the present inventors conducted various experimental studies and found that dimethylformamide, which is considered to be an extremely stable substance, can be hydrated fairly quickly with acids and alkalis. We have obtained the knowledge that it is decomposed. Based on this knowledge, more detailed research revealed that while acid hydrolysis poses new problems in the treatment of the product, alkaline hydrolysis makes it much easier to extract and decompose the product. The present inventors have discovered that a sufficient decomposition rate and decomposition efficiency can be obtained for wastewater treatment, and that the treatment cost is low, leading to the completion of this invention.

That is, the method for treating dimethylformamide according to claim (1) of the present invention involves adding and mixing an alkali to wastewater containing dimethylformamide to generate dimethylamine and alkali formate, and blowing air into this liquid to carry out the above-mentioned treatment. This method is characterized by transferring dimethylamine into the gas phase.

The invention of claim (2) is a method of burning dimethylamine transferred into the gas phase in the method of claim (1) to decompose it into nitrogen gas and carbon dioxide gas, and the invention of claim (3) is the same. This method involves absorbing dimethylamine into an acidic substance.

Furthermore, the invention of claim (4) covers the above claims (1) to (3).
In this method, the alkali formate produced as a by-product in the method is decomposed by the activated sludge method while being neutralized by addition of #1.

(Detailed structure and operation of the invention) When a wastewater alkali containing dimethylformamide is added and mixed, the reaction is that when sodium hydroxide is used as the alkali, it is isolated by hydrolysis as shown in the following formula (1). This results in the production of dimethylamine and sodium formate.

(CHs)t NCOH+NaOH −(CHi) * NH+ HCOON a −(1
) Here, since dimethylamine is alkaline and has a very low boiling point of about 7°C, it can be vaporized and separated from the treatment liquid. However, since the above reaction is an equilibrium reaction, by blowing air into the liquid, the dimethylamine produced is expelled into the gas phase in the same way as ammonia is expelled from water, and the above reaction proceeds to the right side. .

Therefore, the rate of transfer of dimethylamine into the gas phase can be taken as the apparent rate of decomposition of dimethylformamide. It has been confirmed that this apparent decomposition rate approximates a linear equation and is proportional to the temperature (doubling every 10'C increase) and the amount of air blown.

As mentioned above, since the decomposition rate depends on the rate at which dimethylamine is removed from the liquid, a multi-stage decomposition column system, which is effective in removing volatile components, is suitable for the decomposition apparatus.

Incidentally, in hydrolysis with acid, the following formula (■); (CHff)
X NCOH+H2So, +)+20→((CH,),
NH)H-1(So, +HCOOH...(II) As shown in (II), dimethylamine, which cannot be thrown away as it is, is alkaline and will be produced as a salt by-product, but this salt can be isolated from the liquid alone. Cannot be separated.

However, dimethylamine transferred into the gas phase by the method of the present invention can be easily and reliably treated by means of absorption or combustion.

The above absorption means is to absorb dimethylamine into a salt by absorbing dimethylamine into an acidic substance that is difficult to volatilize, such as sulfuric acid, as shown in the following reaction formula (I[l). Thus, the produced dimethylamine salt can be used for appropriate purposes such as raw materials for chemicals.

2 (CHs)*NH+H2S0a → ((CHz)zNH)H-H5Oa...(II[)
Further, as the above-mentioned combustion means, a low-temperature combustion method using a catalyst can be adopted. In this case, the heat of combustion of dimethylamine is 4
Since the concentration of dimethylformamide in the wastewater is 16 Kcal/mol, if the concentration of dimethylformamide in the wastewater is 2% by weight or more, the dimethylamine that migrates into the gas phase in continuous treatment will reach a concentration that is sufficient to self-combust without the assistance of combustion supporting gas. has been approved as f1. This combustion reaction is expressed by the following formula (■) or (V)
It is indicated by.

4 (CHs)zN H+150z →2N□+14HzO+8COz...(IV)4 (
CHri1N H+170yo14NO+14H,O+8CO,-(V) Here, it is ideal that the combustion ends with the reaction of the above equation (R/), but nitrogen oxides are produced as shown in the equation (V). In this case, the nitrogen oxides can be decomposed as shown in the following formula (Vl) by subsequently employing a low-temperature catalytic denitrification method by adding ammonia. Note that the amount of heat required for this denitrification reaction can be sufficiently covered by the combustion heat of dimethylamine.

4NO+4NH! +O□→4Ng+6 HgO...(
Vl) On the other hand, alkali formate produced as a by-product by hydrolysis as shown in formula (1) above can be easily decomposed by the activated sludge method. However, the concentration of alkali carbonate generated by this decomposition is extremely high, leading to an increase in pH to the extent that microorganisms lose their activity. Therefore, an acid equivalent to the amount of alkali formate decomposed, preferably hydrochloric acid, is added to neutralize it. There is a need to. The decomposition of this alkali formate and the neutralization of the alkali carbonate are as follows (■
) to (IX).

2HCOONa+0゜4HfO+2COZ+Na20-(■)N a zo
+ C01=Nazc Oz−(■)NazCO,
+2HCI! .

→2Na Cff1+HzO+C0z-(IX) As mentioned above, according to the method of the present invention, dimethylformamide contained in wastewater is dispersed in dimethylamine and alkali formate, and the former dimethylamine is converted into an acidic substance after transferring into the gas phase. It is made useful by absorption, or completely rendered harmless by being decomposed into carbon dioxide gas, water, and nitrogen gas by combustion, and alkali formate is also decomposed into water, carbon dioxide gas, salt, etc., and rendered harmless.

(Example) The method of the present invention will be explained below with reference to Examples.

(A) Hydrolysis of dimethylformamide A flask with a capacity of 1ρ containing a dimethylformamide aqueous solution 11 with a concentration of 5% is placed in a constant temperature water bath, and an NaOH aqueous solution having an equivalent of 1.2 times the dimethylformamide is placed in the flask. The relationship between the decomposition rate of dimethylformamide, the decomposition temperature, and the amount of air blown was investigated using a method in which air was blown into the solution at a constant rate.

The results are shown in Table 1 below.

However, the amount of dimethylformamide decomposed was determined based on the amount of sulfuric acid reduced by introducing the gas discharged from the flask into an aqueous sulfuric acid solution and absorbing by-product dimethylamine into the sulfuric acid. Although it is possible that monotylamine and ammonia are generated as by-products along with dimethylamine, these other amines are also generated in an equivalent amount to dimethylformamide and are absorbed by sulfuric acid, so the amount of sulfuric acid reduction mentioned above is There is no problem in estimating the amount of decomposition from the above, and in order to keep the reaction under constant conditions, the blown air was passed through an aqueous NaOH solution in advance to remove carbon dioxide gas.

From the above results, the apparent decomposition rate approaches a linear equation and is approximately proportional to the temperature (doubles for every 10°C increase) and air injection amount, and can be fully adopted as a continuous wastewater treatment. It can be seen that the rate of decomposition is

(B), Biodegradation of alkali formate 500g of commercially available reagent special grade sodium formate is 107! An aqueous solution of sodium formate having a concentration of about 5% was prepared by dissolving it in pure water. The actually measured BOD and COD values of this aqueous solution are as follows.

BOD 8060mg/ffi (16,1χ vs. H
COONa) COD 2090erg/l! (5
, 82 vs. HCOONa) Therefore, we adopted a batch biological treatment method for decomposition, adding activated sludge to a PVC tank with an effective volume of 17E, and gradually increasing the load of 5% sodium formate aqueous solution to decompose the sludge. After acclimatization, the animals were subjected to actual processing. The results are shown in the table below.

As shown in the table above, it is possible to sufficiently treat both BOD and COD up to about 3 kg/pot of sodium formate;
It can be seen that when exceeding g/rrf, the removal rate of both decreases. Process D is an example in which the sodium carbonate that decomposes is not neutralized, and the COD
It can be seen that decomposition hardly progresses due to the accumulation of COD (the value is higher than the COD load because it is based on the data 5 days after hydrochloric acid neutralization was stopped).

(C) According to the low-temperature combustion method using dimethylamine catalyst, which has been established for the combustion decomposition number of dimethylamine, a combustion test was conducted under the following conditions, and the gas after combustion was oxidized under the following conditions by adding ammonia. A nitrogen reduction denitrification test was conducted.

<Dimethylamine combustion test conditions> Dimethylamine concentration 6000mjl! /Nrr
fCarrier gas temperature 50℃Carrier gas wind! 200 I2/min dilution factor 2
．． 4 times combustion temperature 350°C <Gas after combustion> Dimethylamine concentration 20-1/Nrd-
Nitric oxide order amount 1750 haze 1! /Ni <Reduction denitrification test> Reduction temperature 450°C Ammonia addition amount 185 (1+l/Nn (NOx after denitrification 70mj!/Nrrf (effect unique to the invention)) According to the present invention, the amount of ammonia added is An extremely practical treatment method is provided that can easily and reliably decompose dimethylformamide at low cost to render it harmless or useful.

Therefore, in the structure of claim (2), dimethylamine generated in the above treatment can be completely decomposed into harmless gas, and in the structure of claim (3), dimethylamine can also be isolated as a salt, It has the advantage that it can be efficiently and easily made harmless by chemical biodegradation.

Claims (4)

[Claims] (1) is characterized by adding and mixing an alkali to wastewater containing dimethylformamide to produce dimethylamine and alkali formate, and blowing air into this liquid to transfer the dimethylamine into the gas phase. A method for treating dimethylformamide. (2) The method for treating dimethylformamide according to claim (1), wherein the dimethylamine transferred into the gas phase is combusted and decomposed into nitrogen gas and carbon dioxide gas. (3) The method for treating dimethylformamide according to claim (1), wherein the dimethylamine transferred into the gas phase is absorbed into an acidic substance. (4) Claims (1) to (3) in which by-produced alkali formate is decomposed by an activated sludge method with neutralization by addition of acid.
) The method for treating dimethylformamide according to any one of the above.