JPH055556B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) 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 spinning, synthetic leather manufacturing, etc. . However, while the high stability of dimethylformamide is an advantage, it also leads to difficulties in post-use treatment, and is one of the reasons 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.
This poses a new challenge: dealing with the large amounts of ammonia generated during decomposition. 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 is profitable with this purification and recovery method is said to be 30% or more, the concentration in wastewater that is generally discharged 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 enormous costs, and even these treatment companies are unable to carry out effective treatment. There is little chance of this happening, and this poses an environmental health problem. 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 have conducted various experimental studies, and have found that dimethylformamide, which is considered to be an extremely stable substance, can be oxidized very quickly by acids and alkalis. We obtained the knowledge that it is hydrolyzed into 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 creation of this invention. That is, in the method for treating dimethylformamide according to claim 1 of the present invention, an alkali is added and mixed to wastewater containing dimethylformamide to produce dimethylamine and alkali formate, and air is blown into this liquid to produce the above-mentioned dimethylformamide. It is characterized by transferring the amine into the gas phase. The invention of claim 2 is a method of burning the dimethylamine transferred into the gas phase in the method of claim 1 and decomposing it into nitrogen gas and carbon dioxide, and the invention of claim 3 is a method of decomposing the same dimethylamine into an acidic substance. This is a method of absorbing it into the body. Furthermore, the invention according to claim 4 is a method of decomposing the alkali formate produced as a by-product in the methods according to claims 1 to 3 above, by an activated sludge method, with neutralization by addition of acid. (Detailed configuration and operation of the invention) When a wastewater alkali containing dimethylformamide is added and mixed, the reaction is such that when sodium hydroxide is used as the alkali, it is isolated by hydrolysis as shown in the following formula (). This results in the production of dimethylamine and sodium formate. (CH ₃ ) ₂ NCOH+NaOH → (CH ₃ ) ₂ NH+HCOONa …() Here, since dimethylamine is alkaline and has a very low boiling point of about 7°C,
It can be vaporized and separated from the processing 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. Become. Therefore, the rate of transfer of dimethylamine into the gas phase can be taken as the apparent rate of decomposition of dimethylformamide. Note that this apparent decomposition rate is approximately approximated by a linear equation, and the temperature (10
It has been confirmed that the increase in temperature (doubles every time the temperature rises) is proportional to the amount of air blown. As mentioned above, since the decomposition rate can be regarded as 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. In case of hydrolysis with acid, as shown in the following formula (): (CH ₃ ) ₂ NCOH + H ₂ SO ₄ + H ₂ O → [(CH ₃ ) ₂ NH]H・HSO ₄ +HCOOH …() Since dimethylamine, which cannot be removed, is alkaline, it is produced as a salt by-product, but this salt cannot be separated from the liquid alone. 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 (). Thus, the produced dimethylamine salt can be used for appropriate purposes such as raw materials for chemicals. 2(CH ₃ ) ₂ NH+H ₂ SO ₄ → [(CH ₃ ) ₂ NH]H·HSO ₄ …() Furthermore, as the above combustion method, a low-temperature combustion method using a catalyst can be adopted. In this case, since the heat of combustion of dimethylamine is 416 Kcal/mol, if the concentration of dimethylformamide in the wastewater is 2% by weight or more, the dimethylamine that migrates into the gas phase during continuous treatment will not be assisted by the combustion supporting gas. It has been confirmed that it reaches a sufficient natural concentration. This combustion reaction is expressed by the following formula () or (). 4(CH ₃ ) ₂ NH+15O ₂ →2N ₂ +14H ₂ O+8CO ₂ …() 4(CH ₃ ) ₂ NH+17O ₂ →4NO+14H ₂ O+8CO ₂ …() Here, combustion can be terminated by the reaction in equation () above. Ideally, if nitrogen oxides are generated as shown in equation (), the nitrogen oxides can be decomposed as shown in equation () 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 ₃ +O ₂ →4N ₂ +6H ₂ O () On the other hand, alkali formate produced as a by-product by hydrolysis as shown in formula () 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. This decomposition of alkali formate and neutralization of alkali carbonate are expressed by the following formulas () to (). 2HCOONa+O ₂ →H ₂ O+2CO ₂ +Na ₂ O…() Na ₂ O+CO ₂ →Na ₂ CO ₃ …() Na ₂ CO ₃ +2HCl →2NaCl+H ₂ O+CO ₂ …() As described 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 either made useful by absorption into acidic substances after being transferred to the gas phase, or converted into carbon dioxide gas by combustion. It decomposes into water and nitrogen gas and becomes completely harmless, and alkali formate also decomposes into water, carbon dioxide gas, salt, etc. and becomes harmless. (Example) Hereinafter, the method of the present invention will be explained with reference to Examples. (A) Hydrolysis of dimethylformamide 5% dimethylformamide aqueous solution 1
A flask with a capacity of 1 containing 1 is placed in a constant temperature water bath, an aqueous NaOH solution equivalent to 1.2 times that of dimethylformamide is added to the flask, and air is blown into the solution at a constant rate. The relationship between the decomposition rate of dimethylformamide, the decomposition temperature, and the amount of air blown was investigated.
The results are shown in Table 1 below. However, the amount of dimethylformamide decomposed is
The gas discharged from the flask was introduced into an aqueous sulfuric acid solution, and by-produced dimethylamine was absorbed into the sulfuric acid, and the amount of reduction in sulfuric acid was determined as a standard. Although there is a possibility that monotylamine and ammonia may be generated together with dimethylamine as by-products, the amount of these other amines generated is equivalent to that of dimethylformamide and is 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 In addition, 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.

【table】

[Table] From the above results, the apparent decomposition rate approximates a linear equation, and doubles for every 10°C rise in temperature.
It can be seen that the decomposition rate is approximately proportional to the amount of air blown, and that the decomposition rate is sufficient for continuous wastewater treatment. (B) Biodegradation of alkali formate 500g of commercially available reagent special grade sodium formate
An aqueous solution of sodium formate having a concentration of about 5% was prepared by dissolving it in pure water. Actual BOD of this aqueous solution,
The COD values are as follows. BOD 8060mg/ (16.1% vs. HCOONa) COD 2090mg/(5.8% vs. HCOONa) Therefore, a batch biological treatment method was adopted for decomposition, and activated sludge was added to a PVC tank with an effective volume of 17%. After gradually increasing the load of sodium formate aqueous solution and acclimating the sludge,
It was subjected to actual processing. The results are shown in the table below.

[Table] As seen in the table above, sodium formate 3
It can be seen that both BOD and COD can be sufficiently treated up to about Kg/m ³ , but when the amount exceeds 5 Kg/m ³ , the removal rate of both decreases. Process D is an example in which sodium carbonate that is decomposed is not neutralized, and it can be seen that decomposition hardly progresses because COD accumulates over time (the numerical value is higher than the COD load). is high because it is based on data 5 days after stopping hydrochloric acid neutralization). (c) Combustion decomposition of dimethylamine In accordance with the already established low-temperature combustion method using a dimethylamine catalyst, a combustion test was conducted under the following conditions, and the gas after combustion was subjected to nitrogen monoxide decomposition under the following conditions by adding ammonia. A reduction denitrification test was conducted. <Dimethylamine combustion test conditions> Dimethylamine concentration 6000ml/Nm ^3Carrier gas temperature 50℃ Carrier gas flow rate 200/min Dilution factor 2.4 times Combustion temperature 350℃ <Gas after combustion> Dimethylamine concentration 200ml/Nm ^3Nitrogen monoxide generation Amount 1750ml/Nm ³ <Reduction denitrification test> Reduction temperature 450℃ Ammonia addition amount 1850ml/Nm ³ NOx after denitrification 170ml/Nm ³ (Effects unique to the invention) According to the present invention, dimethylformamide contained in wastewater can be reduced by An extremely practical treatment method is provided that can easily, reliably, and at low cost decompose the material 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, which can be treated with chemicals. It becomes possible to provide raw materials, etc. Furthermore, the configuration according to claim 4 has the advantage that alkali formate produced as a by-product in the hydrolysis of dimethylformamide can be efficiently and easily rendered harmless by biodegradation.

Claims (1)

[Claims] 1. Adding and mixing an alkali to wastewater containing dimethylformamide to produce dimethylamine and alkali formate, and at the same time blowing air into this liquid to transfer the dimethylamine into the gas phase. A method for treating dimethylformamide, characterized by: 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 4, wherein by-produced alkali formate is decomposed by an activated sludge method with neutralization by addition of acid.
3. The method for treating dimethylformamide according to any one of 3.