Method and system for extracting high-quality DMF from DMF waste liquid

Abstract

The invention discloses a method and a system for extracting high-quality DMF (Dimethyl Formamide) from DMF waste liquid, and belongs to the technical field of chemical separation. The method adopts a double-tower combined vacuum rectification combined side extraction process and comprises the following steps: firstly, feeding the DMF waste liquid into a first rectification tower, removing light and heavy components under the conditions that the pressure is 3 + / -0.2 kPa and the tower kettle temperature is 80-90 DEG C, and carrying out side extraction to obtain a DMF semi-finished product; the semi-finished product enters a second rectifying tower after passing through a buffer tank, dimethylamine and residual impurities are deeply removed under the conditions that the pressure is 2 + / -0.2 kPa and the tower kettle temperature is 80-85 DEG C, and a DMF finished product is obtained through side extraction. Key process parameters include that the number of theoretical plates of the two towers is 80 and 100 respectively, specific feeding and side mining positions are adopted, and the reflux ratio is controlled to be 1.5-7. According to the method, hydrolysis of DMF is inhibited through low-pressure and low-temperature operation, efficient removal of dimethylamine and deep separation of impurities are achieved through double-tower division of labor, the base number and the acid value of the product are both lower than 20 ppm, the purity is larger than or equal to 99.5%, the requirements of national standard first-grade products are met, and the method has the advantages of being high in recovery rate, continuous, stable, environmentally friendly and capable of saving energy.

Description

Technical Field

[0001] This invention relates to the field of chemical solvent recovery technology, specifically to a process and system for extracting high-quality DMF from DMF (N,N-dimethylformamide) waste liquid, which is particularly suitable for the resource recovery and purification of DMF waste liquid containing dimethylamine, formic acid derivatives and complex light and heavy components. Background Technology

[0002] DMF (N,N-dimethylformamide) is an important high-boiling-point aprotic polar solvent widely used in SN2 nucleophilic substitution reactions in chemical, pharmaceutical, and pesticide industries. However, DMF is prone to hydrolysis under high temperature or acidic / alkaline conditions, producing formic acid and dimethylamine, leading to a decline in its quality and the generation of off-odors. DMF wastewater generated during industrial use or recycling typically contains light components such as water, alcohols, and esters, as well as polymeric components such as DMF-formic acid complexes, amide condensates, and formic acid derivatives. Its complex composition makes direct reuse difficult.

[0003] Currently, some literature reports on the recovery and treatment of DMF-containing wastewater, mainly employing methods such as distillation, extraction, and adsorption. However, these methods are primarily designed for low-concentration DMF aqueous solutions and are insufficient for directly extracting high-purity DMF that meets industrial first-class standards from high-concentration DMF wastewater with high impurity content. In particular, dimethylamine present in the wastewater has extremely high compatibility with DMF, making effective separation difficult with conventional distillation. This results in a high alkalinity in the recovered product, failing to meet the national standard HG / T 2028-2009 requirement of an alkalinity value ≤20 ppm.

[0004] In addition, traditional recycling processes often use distillation at atmospheric pressure or high temperature, which can easily trigger further hydrolysis of DMF, producing more dimethylamine, creating a vicious cycle that seriously affects recycling efficiency and product quality.

[0005] Therefore, there is an urgent need for a recycling process that can efficiently separate light and heavy components from complex DMF waste liquid, completely remove dimethylamine, and avoid secondary hydrolysis of DMF, so as to produce high-quality DMF products with both alkalinity and acidity meeting the standards. Summary of the Invention

[0006] This invention aims to solve the following technical problems existing in the current DMF waste liquid recovery process: Dimethylamine in DMF waste liquid is highly compatible with DMF, making it difficult to effectively remove through conventional distillation, resulting in excessive alkalinity in the recovered product. Traditional recovery processes are often carried out at high temperatures, which can easily trigger secondary hydrolysis of DMF, generating new dimethylamine and creating a vicious cycle. Incomplete removal of heavy components leads to product acidity failing to meet national standards. Furthermore, there is a lack of continuous, stable, and efficient recovery processes suitable for high-concentration, complex-composition DMF waste liquid. Therefore, this invention provides a method and system for extracting high-quality DMF from DMF waste liquid, aiming to achieve efficient removal of dimethylamine, inhibit DMF hydrolysis, and thoroughly remove light and heavy components, ultimately obtaining a DMF product with an alkalinity and acidity value below 20 ppm, meeting the first-class standard of HG / T 2028-2009, and suitable for continuous industrial production.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for extracting high-quality DMF from DMF waste liquid employs a dual-tower combined vacuum distillation process with side-harvesting. The system structure is as follows: Figure 1 As shown, it includes a first distillation column, a semi-finished product buffer tank, and a second distillation column.

[0008] Preliminary separation in the first distillation column: DMF waste liquid is continuously fed into the first distillation column for distillation under reduced pressure. The pressure inside the column is controlled at 2.8-3.2 kPa(A), the bottom temperature at 80-90℃, and the top temperature at 35-65℃. Light components (water, alcohols, esters, etc.) are collected from the top of the column through reflux condensation, heavy components (DMF-formic acid complex, polymers, etc.) are collected from the bottom, and DMF semi-finished product is collected from the side outlet in the middle of the column.

[0009] Intermediate buffer and regulation: The DMF semi-finished product collected from the first tower enters the semi-finished product buffer tank, which plays a role in flow balancing and material temporary storage, ensuring the continuous and stable operation of the system.

[0010] Deep deamination and purification in the second distillation column: The DMF semi-finished product is fed into the second distillation column for distillation at a lower pressure. The pressure inside the column is controlled at 1.8-2.2 kPa(A), the bottom temperature at 80-85℃, and the top temperature at 60-66℃. The light component containing dimethylamine is collected from the top of the column, the residual heavy component is collected from the bottom, and the high-quality DMF finished product is collected from the side outlet in the middle of the column.

[0011] System structural characteristics: The first distillation column has 80 theoretical plates, with the feed inlet located on the 40th-45th theoretical plate and the side outlet located on the 25th-30th theoretical plate. The reflux ratio is 1.5-3. The second distillation column has 100 theoretical plates, with the feed inlet located on theoretical plates 50-55 and the side outlet located on theoretical plates 30-35. The reflux ratio is 3-7. A semi-finished product buffer tank is installed between the two towers to achieve a smooth transition of materials and system balance.

[0012] The present invention has the following beneficial effects: By using a second distillation column for deep distillation under low pressure (2±0.2 kPa), combined with optimized tray number and reflux ratio, efficient separation of dimethylamine was achieved, resulting in a stable DMF base value below 20 ppm in the finished product. This completely solved the core problem of excessive alkalinity in traditional recovery processes.

[0013] The entire process is carried out under reduced pressure, which significantly reduces the distillation temperature (bottom temperature ≤ 90℃), effectively suppresses the hydrolysis tendency of DMF during the recovery process, avoids secondary decomposition and dimethylamine formation caused by high temperature, and ensures the chemical stability of the product.

[0014] Through the division of labor and cooperation between the two towers, the first tower removes most of the light and heavy components, while the second tower further refines the product, so that the acid value in the product is also below 20ppm, fully meeting the first-class product standard of HG / T 2028-2009.

[0015] The dual-tower design, along with a semi-finished product buffer tank, enables a smooth material transition and system balance, enhancing operational flexibility and continuity, making it suitable for large-scale, continuous industrial production.

[0016] By optimizing the ratio of side extraction to extraction, the DMF recovery rate is high. At the same time, the closed-loop operation of the system reduces the emission of volatile organic compounds, realizing the resource utilization of waste liquid and clean production, which has both economic and environmental benefits.

[0017] By precisely matching key parameters such as theoretical plate number, feed location, and reflux ratio, it provides clear and replicable operating guidelines, making it highly adaptable to the process and easy to implement and control. Attached Figure Description

[0018] Figure 1 This is a flowchart of the system structure of the present invention. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the implementation of the present invention is not limited thereto.

[0020] The present invention will be further described in detail below with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0021] like Figure 1As shown, the system for extracting high-quality DMF from DMF waste liquid provided by the present invention mainly includes a first distillation column, a second distillation column, a semi-finished product buffer tank 13, and a finished product tank. The first distillation column is provided with a feed inlet 1, a condenser 2, a top outlet 3, a side outlet 4, a reboiler 5, and a bottom outlet 6; the second distillation column is provided with a feed inlet 7, a condenser 8, a top outlet 9, a side outlet 10, a reboiler 11, and a bottom outlet 12; the semi-finished product buffer tank 13 is connected between the side outlet 4 of the first distillation column and the feed inlet 7 of the second distillation column, and is used to temporarily store and regulate the material flow rate; the finished product tank is connected to the side outlet 10 of the second distillation column and is used to receive the final product.

[0022] In one specific embodiment of the present invention, DMF waste liquid is first continuously fed into the first distillation column through inlet 1. Under the action of reboiler 5, the material vaporizes and rises in the column, and after partial condensation by condenser 2, it forms reflux. The absolute pressure in the column is controlled at 3±0.2 kPa, the bottom temperature at 80–90℃, the top temperature at 35–65℃, the number of theoretical plates at 80, the inlet at the 40th–45th theoretical plate, the side outlet at the 25th–30th theoretical plate, and the reflux ratio at 1.5–3, preferably 2. Based on a feed rate of 1000 kg / h, 90–110 kg / h of light components are collected from the top of the column, 90–110 kg / h of heavy components are collected from the bottom of the column, and 780–820 kg / h of DMF semi-finished product is obtained from the side outlet. The top product mainly includes light components such as water, methanol, ethanol, methyl tert-butyl ether, and ethyl acetate, while the bottom product mainly includes DMF-formic acid complex, amide condensates, and formic acid-derived polymers. The DMF semi-finished product obtained from the side product enters the semi-finished product buffer tank 13.

[0023] Next, the DMF semi-finished product is fed from the buffer tank 13 into the second distillation column through the feed inlet 7. Distillation continues under the action of the reboiler 11, with the absolute pressure inside the column controlled at 2±0.2 kPa, the bottom temperature at 80–85℃, the top temperature at 60–66℃, the theoretical plate number at 100, the feed inlet located at the 50th–55th theoretical plate, the side-collection port located at the 30th–35th theoretical plate, and the reflux ratio at 3–7, preferably 5–6. Based on a feed rate of 800 kg / h, the top product yields 10–20 kg / h of material containing dimethylamine and a small amount of light components, the bottom product yields 10–20 kg / h of material containing heavy components and a small amount of DMF, and the side-collection yields 760–780 kg / h of DMF finished product. Under low pressure and suitable temperature conditions, dimethylamine is effectively removed from the liquid phase due to its increased volatility and discharged from the top of the column. The remaining heavy components are discharged from the bottom of the column, and the high-purity DMF product obtained from the side sampling enters the finished product tank.

[0024] The obtained DMF product was tested and found that its alkalinity and acidity were both less than 20 ppm, and its purity was not less than 99.5%, which meets the first-class product index of "HG / T 2028-2009 Industrial N,N-dimethylformamide".

[0025] The following specific embodiment further illustrates the implementation process of the present invention: In the first distillation column, the controlled pressure is 3.0 kPa, the reboiler temperature is 85℃, the top temperature is 50℃, the reflux ratio is 2, the feed rate is 1000 kg / h, the top product is 100 kg / h, the reboiler product is 100 kg / h, and the side product is 800 kg / h; In the second distillation column, the controlled pressure is 2.0 kPa, the reboiler temperature is 83℃, the top temperature is 63℃, the reflux ratio is 5.5, the feed rate is 800 kg / h, the top product is 15 kg / h, the reboiler product is 15 kg / h, and the side product is 770 kg / h. Testing shows that the final DMF product has a purity of 99.6%, an alkalinity of 18 ppm, and an acidity of 15 ppm, all meeting the national first-class product standard.

[0026] The key design advantages of this invention are: low-pressure operation (≤3 kPa throughout) significantly reduces the distillation temperature, fundamentally inhibiting the hydrolysis of DMF; the dual-tower division of labor, with the first tower removing light and heavy components and the second tower focusing on dimethylamine removal, results in high separation efficiency; the side sampling combined with a buffer tank ensures smooth material transfer, providing good system operational flexibility and suitability for continuous production; and the synergistic optimization of parameters such as the number of trays, feed and side sampling positions, and reflux ratio ensures high product purity and low impurity content.

[0027] Example 1: Using DMF waste liquid generated by a chemical enterprise as raw material, its composition includes about 10% light components (water, methanol, ethanol, methyl tert-butyl ether, ethyl acetate, etc.) and about 10% heavy components (DMF-formic acid complex, amide condensate, etc.), with the remainder being DMF and trace amounts of dimethylamine.

[0028] Adopting such Figure 1 The dual-tower combined vacuum distillation system shown is used for recovery. The specific operating steps are as follows: First distillation column operation: The DMF waste liquid is continuously fed into the first distillation column from inlet 1 at a flow rate of 1000 kg / h.

[0029] The absolute pressure inside the control tower is 3.0 kPa, the temperature at the bottom of the tower is 85℃, and the temperature at the top of the tower is 50℃.

[0030] The tower has 80 theoretical trays, with the feed inlet located on the 42nd theoretical tray and the side outlet located on the 28th theoretical tray. The reflux ratio is controlled at 2.

[0031] Light components are collected from the top of the tower at a flow rate of 100 kg / h, heavy components are collected from the bottom of the tower at a flow rate of 100 kg / h, and DMF semi-finished product is collected from the side outlet 4 at a flow rate of 800 kg / h and collected in the semi-finished product buffer tank 13.

[0032] Second distillation column operation: The aforementioned DMF semi-finished product is fed into the second distillation column from inlet 7 at a flow rate of 800 kg / h.

[0033] The absolute pressure inside the control tower is 2.0 kPa, the temperature at the bottom of the tower is 83℃, and the temperature at the top of the tower is 63℃.

[0034] The tower has 100 theoretical trays, with the feed inlet located on the 52nd theoretical tray and the side outlet located on the 32nd theoretical tray. The reflux ratio is controlled at 5.5.

[0035] The light component containing dimethylamine is collected from the top of the column at a flow rate of 15 kg / h, the residual heavy component is collected from the bottom of the column at a flow rate of 15 kg / h, and the DMF product is collected from the side outlet 10 at a flow rate of 770 kg / h and enters the finished product tank.

[0036] Product testing: DMF samples were taken from the finished product cans for analysis. The testing was conducted using the methods specified in the national standard HG / T 2028-2009.

[0037] Test results: DMF purity 99.6%, alkali value 18 ppm, acid value 15 ppm.

[0038] Conclusion: All indicators are better than the requirements of Grade I (base value and acid value ≤20ppm, purity ≥99.5%) in HG / T 2028-2009.

[0039] Example 2: Using the same raw materials and system as in Example 1, some operating parameters were adjusted: First distillation column operation: Feed rate 1000 kg / h, absolute pressure inside the column 3.1 kPa, bottom temperature 88℃, top temperature 55℃, reflux ratio 2.5.

[0040] The extraction rate from the top of the tower is 105 kg / h, the extraction rate from the bottom of the tower is 95 kg / h, and the extraction rate of DMF semi-finished product from the side is 800 kg / h.

[0041] Second distillation column operation: Feed rate: 800 kg / h, absolute pressure inside the column: 1.9 kPa, bottom temperature: 82℃, top temperature: 62℃, reflux ratio: 4.0.

[0042] The rate of DMF product extraction is 12 kg / h from the top of the tower, 18 kg / h from the bottom of the tower, and 770 kg / h from the side.

[0043] Product testing: Test results: DMF purity 99.55%, alkali value 19 ppm, acid value 17 ppm.

[0044] Conclusion: The product specifications still fully meet the national first-class product standards.

[0045] The above embodiments are merely illustrative examples. Without departing from the technical concept of this invention, those skilled in the art can make appropriate adjustments to the parameters according to actual production conditions, and such adjustments should still be considered to fall within the protection scope of this invention.

Claims

1. A method for extracting high-quality DMF from DMF waste liquid, characterized in that, Includes the following steps: (1) The DMF waste liquid is sent to the first distillation column for vacuum distillation, and the operating pressure is controlled at 2.8-3.2 kPa (A), the bottom temperature is 80-90℃, and the top temperature is 35-65℃. (2) Light components are collected from the top of the first distillation column, heavy components are collected from the bottom of the column, and DMF semi-finished product is collected from the side outlet of the column body; (3) The DMF semi-finished product is fed into the second distillation column for vacuum distillation, and the operating pressure is controlled at 1.8-2.2 kPa (A), the bottom temperature is 80-85℃, and the top temperature is 60-66℃. (4) Dimethylamine and light components are collected from the top of the second distillation column, heavy components are collected from the bottom of the column, and DMF product is collected from the side outlet of the column. (5) Wherein, a semi-finished product buffer tank is provided between the first distillation column and the second distillation column to regulate and balance the output of the two columns.

2. The method according to claim 1, characterized in that, The first distillation column has 80 theoretical plates, the feed inlet is located on the 40th-45th theoretical plate, the side outlet is located on the 25th-30th theoretical plate, and the reflux ratio is 1.5-3, preferably 2.

3. The method according to claim 1, characterized in that, The second distillation column has 100 theoretical plates, with the feed inlet located on the 50th-55th theoretical plate and the side outlet located on the 30th-35th theoretical plate. The reflux ratio is 3-7, preferably 5-6.

4. The method according to claim 1, characterized in that, The feed rate of the first distillation column is 1000 kg / h, the top product rate is 90-110 kg / h, the bottom product rate is 90-110 kg / h, and the side product rate is 780-820 kg / h.

5. The method according to claim 1, characterized in that, The feed rate of the second distillation column is 800 kg / h, the top product rate is 10-20 kg / h, the bottom product rate is 10-20 kg / h, and the side product rate is 760-780 kg / h.

6. The method according to claim 1, characterized in that, The base value and acid value of the DMF product are both less than 20 ppm.

7. A dual-tower combined vacuum distillation system for implementing the method according to any one of claims 1-6, characterized in that, It includes a first distillation column, a semi-finished product buffer tank, and a second distillation column connected in sequence. Both the first and second distillation columns are provided with a top outlet, a bottom outlet, and a side outlet, and are equipped with a reboiler and a condenser.

8. The system according to claim 7, characterized in that, The first distillation column has 80 theoretical plates, with the side sampling port located on theoretical plates 25-30; the second distillation column has 100 theoretical plates, with the side sampling port located on theoretical plates 30-35.

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