A method for treating DMF waste liquid

Abstract

The application discloses a DMF waste liquid treatment method, and generates high-acidity DMF rectification liquid in the DMF waste liquid treatment process. The treatment method comprises the following steps: controlling the water content in the DMF rectification liquid to be 0.05%-1% and the acidity to be 2%-10%; adding an alkaline substance to the DMF rectification liquid at 20-30 DEG C, uniformly mixing, controlling the pH value of the system to be 7-9, and reacting formate in the DMF rectification liquid with the alkaline substance to generate formate salt; reducing the temperature of the system to 0-10 DEG C, continuously stirring, and crystallizing and separating out the formate salt in the system; solid-liquid separation and separately recovering the formate salt solid and the DMF liquid; post-treatment of the formate salt: drying the formate salt obtained through solid-liquid separation after cleaning with an alcohol substance; and subsequently recovering residual DMF in the alcohol substance through concentration. The DMF waste liquid treatment method of the application obtains DMF material with greatly reduced acidity and highly concentrated formate salt, the DMF material can be further purified and recovered, and the formate salt, after impurity removal and drying through washing, can be sold as raw material.

Description

[0001] This application is a divisional application of the invention patent application with the application number 2023107604497, the application date of June 27, 2023, and the invention name of "Treatment method of high-acidity DMF rectification liquid and treatment method of DMF waste liquid". TECHNICAL FIELD

[0002] The present application belongs to the technical field of DMF waste liquid treatment, and specifically relates to a treatment method of high-acidity DMF rectification liquid and a treatment method of DMF waste liquid including the treatment step of the high-acidity DMF rectification liquid. BACKGROUND

[0003] DMF is a kind of organic solvent commonly used in the textile finishing industry. After being used and treated by waste gas treatment facilities, DMF waste liquid with a concentration of 10%-50% is generated. If this waste liquid is directly discarded, it will cause great resource waste and environmental pollution. The conventional recovery process is to purify and recover such waste liquid by rectification, thereby effectively recovering the DMF contained therein, achieving the purpose of resource recycling and pollutant treatment meeting the discharge standard.

[0004] The existing DMF recovery is carried out by heating and rectification. During the heating and recovery process, DMF decomposition may occur to produce formic acid and dimethylamine, and finally produce DMF rectification liquid containing high-concentration formic acid. To reduce the influence of formic acid in the DMF waste liquid recovery system, the most primitive treatment process is to directly and continuously add an alkaline substance during the DMF heating and rectification process to neutralize the acid and base, reduce the acidity in the system, and then return the neutralized mixture to the DMF solution storage tank for further purification. However, this treatment scheme has many disadvantages, such as: 1. The sodium salt generated during the treatment process remains in the system and is eventually discharged in the form of rectification residue, which requires additional incineration treatment, resulting in high treatment cost; 2. The generated sodium salt may enter the rectification tower during the rectification process, increasing the risk of tower blockage; 3. There is a high risk of safety production; 4. Directly adding an alkaline substance during the DMF heating and rectification process may cause decomposition of DMF, reducing the purity and yield of DMF.

[0005] In view of the above-mentioned disadvantages, the above-mentioned method of directly adding an alkaline substance during the DMF heating and rectification process is now abandoned, and an improved process is adopted: the generated formic acid needs to be treated by pyrolysis to decompose formic acid into carbon dioxide and water. Although this treatment method achieves harmless treatment, it consumes a large amount of electric energy during the treatment process, resulting in high treatment cost, and the decomposed formic acid cannot be recycled.

[0006] The disclosure of the foregoing Background Art is given only for the purpose of facilitating understanding of the inventive concept and technical solutions of the present application and does not necessarily belong to the prior art of the present application. In the absence of explicit evidence that the above-mentioned content has been disclosed before the filing date of the present application, the above-mentioned background art should not be used to evaluate the novelty and inventiveness of the present application. SUMMARY

[0007] Therefore, in order to overcome the defects of the prior art, the purpose of the present application is to provide an improved treatment method for high-acidity DMF rectified liquid, which can realize the separation and recovery of formic acid and DMF in the high-acidity DMF rectified liquid without decomposition of DMF.

[0008] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0009] A treatment method for high-acidity DMF rectified liquid, comprising the following steps:

[0010] The water content in the DMF rectified liquid is controlled to be 0.05%-1%, and the acidity is controlled to be 2%-10%;

[0011] At room temperature, an alkaline substance is added to the DMF rectified liquid, and the mixture is uniformly mixed, and the pH value of the system is controlled to be 7-9, and the formate is generated by the reaction of formic acid in the DMF rectified liquid and the alkaline substance;

[0012] The temperature of the system is reduced to 0-10℃, and the stirring is continued, and the formate in the system is crystallized and separated out;

[0013] The formate solid and the DMF liquid are separated and recovered respectively.

[0014] The acidity in the present application refers to the content of formic acid in the DMF rectified liquid, which is obtained by the method specified in the national standard "HG / T 2028-2009 Industrial Dimethylformamide". Low acidity will result in low content of generated formate and low removal rate, and high acidity is relatively more beneficial, but excessive increase of acidity (more than 10%) will cause serious corrosion to the reaction kettle equipment.

[0015] The treatment method for DMF rectified liquid of the present application adds sodium hydroxide, potassium hydroxide or sodium bicarbonate, combines sodium or potassium with formic acid to generate formate, and uses the difference in solubility to make it crystallize and separate out, without introducing substances affecting purity. This method avoids using thermal decomposition method to harmless treatment of formic acid, and avoids decomposition of DMF; at the same time, the generated formate can be used as a chemical raw material, greatly reducing the treatment cost.

[0016] According to some preferred embodiments of the present application, the basic substance is a solid or a basic solution with a mass fraction greater than or equal to 50%, preferably a solid powder. The addition of solid or high-concentration alkali solution is to reduce the introduced water content, thereby reducing the dissolution of the generated formate salt, increasing the crystallization yield of the formate salt, and thus improving the removal rate of the formate salt.

[0017] According to some preferred embodiments of the present application, the basic substance is one or more of sodium hydroxide, potassium hydroxide, and sodium bicarbonate.

[0018] According to some preferred embodiments of the present application, the addition time of the basic substance is controlled within 10-20 min. The relatively slow addition of the basic substance avoids the local over-high alkalinity and the local sudden increase in temperature caused by the decomposition of DMF.

[0019] According to some preferred embodiments of the present application, the room temperature is 20-30℃. That is, the temperature of the high-acidity DMF distillation liquid when the basic substance is added is maintained at 20-30℃, avoiding the decomposition of DMF caused by high temperature.

[0020] According to some preferred embodiments of the present application, the temperature of the system during the reaction is maintained at 20-30℃. Normal temperature operation can ensure the acid-base reaction rate while avoiding the decomposition of DMF.

[0021] According to some preferred embodiments of the present application, after the addition of the basic substance to the DMF distillation liquid, the reaction is continuously stirred for 30-60 min, and the stirring rate is 60-120 r / min.

[0022] According to some preferred embodiments of the present application, during crystallization, the stirring time is 10-30 min, and the stirring rate is 15-30 r / min.

[0023] According to some preferred embodiments of the present application, the step includes post-treatment of the formate salt: the filtered formate salt is washed with an alcohol substance and then dried.

[0024] According to some preferred embodiments of the present application, the acidity of the recovered DMF liquid after separation is less than or equal to 0.01%.

[0025] The present application also provides a DMF waste liquid treatment method comprising the treatment steps of the high-acidity DMF distillation liquid as described above.

[0026] Compared with the prior art, the method for treating the high-acidity DMF rectification liquid has the advantages that: the method uses the alkali material as the reactant, utilizes the low water content in the DMF rectification liquid, makes the formic acid react with the alkali material to generate the formate, and separates the formate through the cooling crystallization and the precipitation, so that the DMF material with greatly reduced acidity and the formate with high purity are obtained; the DMF material can be returned to the recovery system for further purification and recovery, and the formate can be used or sold as the raw material after the impurities are removed through washing and drying; and the decomposition of the DMF is avoided through the control of the conditions. DETAILED DESCRIPTION

[0027] In order for those skilled in the art to better understand the technical solutions of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the protection scope of the present application.

[0028] The method of the present application uses the alkali material (sodium hydroxide, potassium hydroxide or sodium bicarbonate) as the reactant, utilizes the low water content in the DMF rectification liquid, makes the formic acid react with the alkali material to generate the formate, and separates the formate through the cooling crystallization and the precipitation, so that the DMF material with greatly reduced acidity and the formate with high purity are obtained; the DMF material can be returned to the recovery system for further purification and recovery, and the formate can be used or sold as the raw material after the impurities are removed through washing and drying. At the same time, the decomposition of the DMF in the treatment process is avoided through the control of the conditions, and the effective content of the DMF in the final system is improved. The reaction principle in the present application is as follows:

[0029] HCOOH + NaOH + → NaCOOH + H2O -

[0030] In the prior art, the DMF waste liquid also needs to be treated in some fields, such as adding the strong alkali to the DMF waste liquid for the alkaline hydrolysis of the DMF. The DMF alkaline hydrolysis (NaOH) reaction can generate dimethylamine and sodium formate. The principle is as follows:

[0031] HCON(CH3)2 + OH - → HCOO - + NH(CH3)2

[0032] ​However, in the DMF alkaline hydrolysis process, the added alkaline substance is needed to promote the decomposition of DMF, and at the same time, it is usually necessary to control the pH value of the system to be greater than 10, and heating is needed to promote the decomposition of DMF. Therefore, the existing alkaline hydrolysis process is not suitable for the case and purpose in the present application.

[0033] In order to achieve the above purpose, the DMF rectified liquid treatment method in the embodiment includes the following steps:

[0034] Step one, control the water content in the DMF rectified liquid to be 0.05%-1%, and the acidity to be 2%-10%.

[0035] The water content in the DMF rectified liquid is detected and confirmed. When the water content is too low, it will affect the ionization decomposition and reaction rate after the addition of the medicament. When the water content is relatively high, the dehydration time can be adjusted to reduce the water content. If the system acidity is much lower than 2%, the rectification can be continued. The acidity in the tower kettle gradually accumulates, and when it reaches a relatively high concentration (2%-10%), it can be concentrated and discharged for the deacidification treatment in the present application. However, when the acidity is too high (more than 10%), it will cause serious corrosion to the reaction kettle equipment.

[0036] Step two, at room temperature 20-30℃, add alkaline substance to the DMF rectified liquid at room temperature, mix uniformly, and control the amount of alkaline substance added by pH online monitor, so that the pH of the system is 7-9.

[0037] The alkaline substance is sodium hydroxide, potassium hydroxide and / or sodium bicarbonate, and is a solid or an alkaline solution with a mass fraction greater than or equal to 50%; preferably a solid powder. The addition time of the alkaline substance is controlled within 10-20 min to avoid local high alkalinity and local rapid increase of temperature caused by DMF decomposition.

[0038] Step three, stir for 30-60 min, and the stirring rate is 60-120 r / min.

[0039] During the reaction, the temperature of the system is maintained at 20-30℃. If the temperature is too high and the alkalinity is too high, there will be DMF decomposition. By controlling the reaction pH to be acidic to slightly alkaline and the reaction temperature to be room temperature, the decomposition of DMF can be avoided or reduced.

[0040] Step four, reduce the temperature of the system to 0-10℃, continue to stir for 10-30 min to crystallize, and the stirring rate is 15-30 r / min; after filtration, recover the formate solid and DMF liquid respectively. The acidity of the recovered DMF liquid after filtration is less than or equal to 0.01%.

[0041] When crystallizing, the material crystalline growth can further improve the crystallization rate, at this time, slow stirring is needed, while mixing the material, reducing the breakage of the crystalline, improving the crystallization rate.

[0042] Step five, post-treatment of formate salt.

[0043] The filtered formate salt is washed with an alcohol such as methanol or ethanol and then dried.

[0044] Preferably, the reaction is carried out in a jacketed porcelain reaction kettle, after the reaction is completed, low-temperature ice water is introduced into the jacket of the reaction kettle for cooling, and the temperature is reduced to 0-10°C. After cooling and crystallization, a semi-flowing mixture of formate salt and DMF is formed in the reaction liquid, which is pumped into a centrifugal filtration device, and the filtrate after filtration is a DMF solution with greatly reduced acidity, and the solid part is formate salt crystals containing a small amount of DMF, which is washed with methanol, ethanol or other alcohol solvents and then dried to be used as a product or sold. And the application adopts normal temperature or low temperature processing technology, compared with the high temperature of the traditional process, the safety factor is increased, and the danger coefficient is lower.

[0045] Example 1

[0046] A solvent recovery company produces high-acidity DMF distillate in the process of treating DMF waste liquid, with an acidity of 8% and a water content of 0.1%. 1L of the sample is taken for the following experiment.

[0047] At 25°C, 70g of sodium hydroxide solid powder is added, and the mixture is stirred at 100r / min for 30min. The pH of the system is 7.5, and the temperature of the system is maintained at 25°C during the reaction. Slow stirring at 30r / min is continued for 10min, and the temperature is cooled to 10°C. A DMF mixture containing sodium formate crystals is obtained, which is separated by filtration. The test shows that the acidity of the DMF liquid is reduced to 0.005%, and the filtered sodium formate is washed with ethanol and dried at a low temperature of 80°C. 150g of crystalline sodium formate solid powder is obtained, which is detected to have a purity of 99.5% and can be used as an industrial raw material.

[0048] The experiment uses 70g of sodium hydroxide to produce 150g of sodium formate crystals, which contain about 32g of crystalline water and impurities, and 118g of pure sodium formate, with a yield of 99.7% (calculated based on 118.3g of sodium formate theoretically generated from 80g of formic acid). After filtration, 0.98L of DMF remains, with a yield of 98%. The residual DMF can be recovered by subsequent concentration in an ethanol solution.

[0049] Example 2

[0050] A coating company produces high-acidity DMF distillate in the process of treating DMF waste liquid, with an acidity of 10% and a water content of 0.08%. 5L of the sample is taken for the following experiment.

[0051] Add 437 g of sodium hydroxide solid powder at 25 °C, mix at 80 r / min for 50 min, the pH of the system is 7.2, keep the system temperature at 25 °C during the reaction. Stir at 30 r / min for another 15 min, cool to 10 °C, get the DMF mixed solution containing sodium formate crystals, after filtration, the acidity of the DMF liquid is reduced to 0.009%, the filtered sodium formate is washed with ethanol and dried at 80 °C, get 930 g of crystalline sodium formate solid powder, after testing, the purity of the crystalline sodium formate reaches 98.5%, which can be used as industrial raw materials.

[0052] The experiment inputs 437 g of sodium hydroxide, produces 930 g of sodium formate crystals, of which about 206 g contains crystal water and impurities, 724 g of pure sodium formate, the yield is 98.0% (calculated based on 739 g of sodium formate theoretically produced from 500 g of formic acid). After filtration, 4.92 L of DMF remains, with a yield of 98.4%. The residual DMF is in an ethanol solution, which can be recovered by subsequent concentration.

[0053] Example 3

[0054] A solvent recovery company produces high-acidity DMF distillation liquid in the process of treating DMF waste liquid, with an acidity of 9% and a water content of 0.09%, take 10 L for the following experiment.

[0055] Add 1580 g of 50% sodium hydroxide solution at 20 °C, mix at 100 r / min for 50 min, the pH of the system is 7.1, keep the system temperature at 20 °C during the reaction. Stir at 30 r / min for another 20 min, cool to 5 °C, get the DMF mixed solution containing sodium formate crystals, after filtration, the acidity of the DMF liquid is reduced to 0.0095%, the filtered sodium formate is washed with ethanol and dried at 80 °C, get 1884 g of crystalline sodium formate solid powder, after testing, the purity of the crystalline sodium formate reaches 98.5%, which can be used as industrial raw materials.

[0056] The experiment inputs 790 g of pure sodium hydroxide, produces 1884 g of crystalline sodium formate solid powder, of which about 671 g contains crystal water and impurities, 1213 g of pure sodium formate, the yield is 91.2% (calculated based on 1330 g of sodium formate theoretically produced from 900 g of formic acid). After filtration, 9.96 L of DMF remains, which is not calculated for DMF yield due to the increase in water content. The residual DMF is in an ethanol solution, which can be recovered by subsequent concentration.

[0057] Comparative Example 1

[0058] A solvent recovery company produces high-acidity DMF distillation liquid in the process of treating DMF waste liquid, with an acidity of 9% and a water content of 0.12%, take 1 L for the following experiment.

[0059] Add 790g 10% sodium hydroxide solution at 20°C, mix at 100r / min for 50min, pH of the system is 7, keep the system temperature at 20°C during the reaction. Then mix at 30r / min for 20min, cool to 5°C, no DMF mixed solution containing sodium formate crystals is generated, test shows that the acidity of the DMF liquid is reduced to 0.01%, but the obtained DMF solution is a liquid with increased water content and increased formate content, which produces a large amount of crystals in the subsequent rectification and dehydration process, blocking the recovery pipeline.

[0060] Comparative Example 2

[0061] A solvent recovery company produces high-acidity DMF rectification liquid in the process of treating DMF waste liquid, with an acidity of 8% and a water content of 0.11%, 1L of which is sampled for the following experiment.

[0062] Add 230g 30% sodium hydroxide solution at 20°C, mix at 100r / min for 50min, pH of the system is 7.3, keep the system temperature at 20°C during the reaction. Then mix at 30r / min for 20min, cool to 10°C, no DMF mixed solution containing sodium formate crystals is generated, test shows that the acidity of the DMF liquid is reduced to 0.007%, but the obtained DMF solution is a liquid with increased water content and increased formate content, which produces a large amount of crystals in the subsequent rectification and dehydration process, blocking the recovery pipeline.

[0063] Comparative Example 3

[0064] A solvent recovery company produces high-acidity DMF rectification liquid in the process of treating DMF waste liquid, with an acidity of 8% and a water content of 0.07%, 1L of which is sampled for the following experiment.

[0065] Add 90g sodium hydroxide solid powder at 25°C, mix at 100r / min for 30min, pH>10, keep the system temperature at 20°C during the reaction. Then mix at 30r / min for 10min, cool to 10°C, obtain DMF mixed solution containing sodium formate crystals, test shows that the acidity of the DMF liquid is reduced to 0, the solution is alkaline, the obtained sodium formate is washed with ethanol and dried at low temperature of 80°C, obtaining 181g of mixed solid powder of crystalline sodium formate and sodium hydroxide, which is detected to have a purity of 95% of crystalline sodium formate and about 5% of sodium hydroxide, and cannot be directly used as industrial raw materials.

[0066] The experiment was carried out with 90 g of sodium hydroxide, and 181 g of sodium formate mixed crystals were produced, of which about 45 g contained crystal water and impurities, and 136 g was pure sodium formate, with a yield of 115% (calculated based on 118.3 g of sodium formate produced from 80 g of formic acid). After filtration, 0.75 L of DMF remained, with a yield of 75%. Due to the influence of the alkaline environment, part of the DMF was decomposed into formic acid and dimethylamine, resulting in an increase in the production of sodium formate. The decomposition of DMF reduced the remaining material, and the residual unreacted sodium hydroxide and sodium formate formed a mixture.

[0067] Comparative Example 4

[0068] A solvent recovery company produced DMF rectified liquid with an acidity of 1% and a water content of 0.08% during the treatment of DMF waste liquid. A sample of 10 L was taken for the following experiment.

[0069] At 25°C, 87 g of solid sodium hydroxide powder was added, and the mixture was stirred at 100 r / min for 30 min. The pH of the system was 7.1, and the temperature of the system was maintained at 25°C during the reaction. The mixture was stirred at 30 r / min for another 10 min to obtain a DMF mixture containing sodium formate crystals. The mixture was cooled to 10°C and filtered to obtain a DMF liquid with an acidity of 0.006%. The filtered sodium formate was washed with ethanol and dried at 80°C to obtain 163 g of crystalline sodium formate solid powder, of which about 38.5 g contained crystal water and impurities, and 124.5 g was pure sodium formate, with a yield of 84.2%. The purity of the crystalline sodium formate was 96.5%. Due to the low concentration of formic acid, the reaction did not completely precipitate sodium formate, resulting in a low yield and low purity.

[0070] Comparative Example 5

[0071] A solvent recovery company produced high-acidity DMF rectified liquid with an acidity of 10% and a water content of 0.06% during the treatment of DMF waste liquid. A sample of 1 L was taken for the following experiment.

[0072] At 25℃, 87g of sodium hydroxide solid powder was added, and the mixture was stirred at 100r / min for 30min. The pH of the reaction system was 7.2, and the temperature of the system was not controlled during the reaction, and the highest reaction temperature rose to 55℃. Then the reaction was stirred at 30r / min for 10min, and a DMF mixture containing sodium formate crystals was obtained. The mixture was cooled to 10℃, and then filtered to obtain a DMF liquid with a pH of 4 and an acidity of 1%. The obtained sodium formate was washed with ethanol and dried at 80℃, and 186.7g of crystalline sodium formate solid powder was obtained, containing about 42.2g of crystalline water and impurities, and 144.5g of pure sodium formate, with a yield of 97.7% (calculated based on 87g of sodium hydroxide theoretically producing 147.9g of sodium formate). The purity of the crystalline sodium formate reached 97.9%. However, due to the high temperature reaction, the decomposition of DMF was serious, and a liquid with high acidity was finally generated.

[0073] The method for treating the DMF rectification liquid of the present application involves adding an alkaline agent to the high-acidity DMF rectification liquid, neutralizing the formic acid in the rectification liquid to form formate, and removing the formic acid from the DMF rectification liquid by low-temperature crystallization and solid-liquid separation. The acid content in the solvent is greatly reduced, and the crystallization does not easily block the pipeline during subsequent rectification. The formate separated by crystallization can be washed with a low-solubility solvent to obtain high-purity industrial-grade formate, which can be sold as a byproduct raw material, reducing the cost of thermal decomposition treatment.

[0074] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the spirit and essence of the present application should be covered within the protection scope of the present application.

Claims

1. A method for treating DMF waste liquid, characterized in that, High-acidity DMF distillate is generated during the treatment of DMF waste liquid. The treatment method includes the following steps: The water content in the DMF distillate should be controlled at 0.05%-1%, and the acidity at 2%-10%. At 20-30℃, an alkaline substance is added to the DMF distillation solution, mixed evenly, and the pH value of the system is controlled to be 7-9. The formic acid in the DMF distillation solution reacts with the alkaline substance to form formate. The temperature of the system was lowered to 0-10℃, and the mixture was stirred continuously, causing the formate to crystallize out. Solid-liquid separation and separate recovery of formate solid and DMF liquid; Post-treatment of formate: The formate obtained from solid-liquid separation is washed with alcohol and then dried; The alkaline substance is sodium hydroxide solid powder or sodium hydroxide solution with a mass fraction greater than or equal to 50%; The temperature of the system was maintained at 20-30℃ during the reaction.

2. The processing method according to claim 1, characterized in that, The acidity is the formic acid content in the DMF distillate, obtained by referring to the method specified in the national standard "HG / T 2028-2009 Industrial Dimethylformamide".

3. The processing method according to claim 1, characterized in that, The alkaline substance is added over a period of 10-20 minutes.

4. The processing method according to claim 1, characterized in that, After adding an alkaline substance to the DMF distillate, the reaction is continuously stirred for 30-60 minutes at a stirring rate of 60-120 r / min; during crystallization, the stirring time is 10-30 minutes at a stirring rate of 15-30 r / min.

5. The processing method according to claim 1, characterized in that, The alcohol is methanol or ethanol.

6. The processing method according to any one of claims 1-5, characterized in that, The reaction is carried out in a jacketed enamel-lined reactor. After the reaction is completed, ice water is introduced into the jacket of the reactor for cooling and temperature reduction to 0-10°C. After cooling and crystallization, a mixture of semi-fluid formate and DMF is formed and pumped into a centrifugal filtration device.

7. The processing method according to any one of claims 1-5, characterized in that, The acidity of the DMF liquid recovered after solid-liquid separation is less than or equal to 0.01%.