A rectification purification process of NMP

Abstract

The present application belongs to the technical field of organic matter purification, and relates to a rectification purification process of NMP. The present application aims to solve the problem that the existing NMP purification process is difficult to simultaneously and efficiently remove water and organic impurities. The present application obtains overhead NMP by subjecting raw material NMP to normal-pressure initial distillation treatment; obtains refined NMP by subjecting the overhead NMP to adsorption rectification unit treatment; obtains dehydrated NMP by subjecting the refined NMP to azeotropic rectification treatment, and detects the water content of the dehydrated NMP by using a water content detection unit; if the water content is higher than a threshold value, the azeotropic rectification is performed again; if the water content is lower than the threshold value, the dehydrated NMP is introduced into a vacuum distillation unit, and electronic-grade NMP product is finally obtained through a membrane separation unit, and the waste heat is recovered for preheating of the raw material NMP. The rectification purification process proposed in the present application can purify industrial-grade raw material NMP to obtain electronic-grade NMP product, and can recycle and utilize the waste heat in the distillation process.

Description

Technical Field

[0001] This invention belongs to the field of organic purification technology, and relates to a distillation purification process for NMP. Background Technology

[0002] NMP, or N-methylpyrrolidone, is a common organic solvent, belonging to the polar aprotic solvent category. Thanks to its unique chemical structure, NMP exhibits excellent solubility for a wide range of organic and inorganic substances, and is widely used in various industrial fields.

[0003] In the electronics industry, NMP (Natural Metallurgy Processing) has significant applications in electrode manufacturing, circuit board printing, and photoresist stripping. However, various impurities, including water, other organic solvents, and metal ions, can be introduced into NMP during production and transportation. These impurities can degrade the performance of devices and materials or even cause them to fail during the manufacturing process. Therefore, the industry has proposed a series of requirements for electronic-grade NMP, including high purity, low water content, and low metal content, to meet the relevant requirements of the electronics industry. NMP products required by the electronics industry are generally purified from industrial NMP because byproducts, metal ions, and other impurities remaining in traditional preparation processes can significantly affect the quality of battery electrodes or the photolithography process, making them difficult to apply directly in the electronics industry.

[0004] With the development of the electronics industry and increasingly stringent environmental protection requirements, the current NMP purification process needs to be more integrated, efficient, and environmentally friendly in order to adapt to industrial and social development.

[0005] Currently, the existing NMP purification process is unable to efficiently remove both water and organic impurities simultaneously, which remains a significant challenge for the industry.

[0006] Therefore, a distillation purification process for NMP is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a distillation purification process for NMP. This invention involves initial distillation of raw NMP at atmospheric pressure to obtain top NMP; the top NMP is then processed by an adsorption distillation unit to obtain purified NMP; the purified NMP is then subjected to azeotropic distillation to obtain dehydrated NMP. The water content of the dehydrated NMP is detected by a water content detection unit. If the water content is higher than a threshold, azeotropic distillation is performed again; if the water content is lower than the threshold, the dehydrated NMP is passed into a vacuum distillation unit and finally separated by a membrane separation unit to obtain electronic-grade NMP product. Waste heat is recovered for preheating the raw NMP. The distillation purification process proposed in this invention can effectively purify industrial-grade raw NMP to obtain electronic-grade NMP product with extremely low water content and extremely low organic impurity content, and can recover and utilize the waste heat from the distillation process.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A distillation purification process for NMP includes the following steps:

[0010] The raw material NMP is preheated and then fed into the atmospheric pressure primary distillation unit. After primary distillation, the top NMP of the column is obtained.

[0011] The NMP at the top of the column is passed into the adsorption distillation unit, and purified NMP is obtained after adsorption distillation.

[0012] The purified NMP was passed into an azeotropic distillation unit and an azeotropic agent was introduced for azeotropic distillation to obtain dehydrated NMP.

[0013] The dehydrated NMP is passed into the moisture content detection unit to detect whether the moisture content of the dehydrated NMP is higher than the threshold.

[0014] If the water content of the dehydrated NMP is higher than the threshold, the dehydrated NMP is passed back into the azeotropic distillation unit for azeotropic distillation.

[0015] If the water content of the dehydrated NMP is lower than the threshold, the dehydrated NMP is passed into a vacuum distillation unit, and high-temperature NMP is obtained after vacuum distillation.

[0016] High-temperature NMP is passed into a membrane separation unit, and after separation, electronic-grade NMP products and waste heat are obtained.

[0017] Waste heat is recovered via a heat exchange network and used for preheating the raw material NMP.

[0018] Preferably, the purity of the raw material NMP is 80-99%; the atmospheric pressure primary distillation unit includes a degassing unit and a balanced distillation column; the primary distillation process is as follows: the raw material NMP is introduced into the degassing unit, degassed for 20-30 minutes, and then introduced into the balanced distillation column. After balanced distillation at 1 atm, the top product of the column is obtained, which is the top NMP.

[0019] Preferably, the operating temperature of the degassing unit is 150-180℃ and the operating pressure is 0.8MPa; the bottom temperature of the equilibrium distillation column is 200-220℃, the top temperature is 90-100℃, and the reflux ratio is 2-2.5.

[0020] Preferably, the adsorption distillation unit includes a pressurization unit and an adsorption distillation column; the adsorption distillation process is as follows: the NMP at the top of the column is pressurized to 1.8-2.0 atm through the pressurization unit and then fed into the adsorption distillation column; the product at the bottom of the column after adsorption distillation is purified NMP; wherein, the packing layer of the adsorption distillation column is filled with an adsorbent, which is an ion exchange resin; the reflux ratio of the adsorption distillation column is 2.0-2.5, the bottom temperature is 210℃, and the top temperature is 95℃.

[0021] Preferably, the azeotropic distillation unit includes: an azeotropic agent premixing unit and an azeotropic distillation column; the azeotropic agent is a mixture of cyclohexane and toluene, wherein the mass ratio of cyclohexane to toluene is 2:1; the azeotropic distillation process is as follows: in the azeotropic agent premixing unit, the azeotropic agent is mixed with purified NMP at a ratio of 2wt%, and pressurized to 2 atm before being fed into the azeotropic distillation column, wherein the bottom temperature of the azeotropic distillation column is 210°C, the top temperature is 90°C, the reflux ratio is 3.0, and the bottom product after azeotropic distillation is dehydrated NMP.

[0022] Preferably, the working process of the moisture content detection unit is as follows: dehydrated NMP is introduced into the moisture content detection unit, and the moisture content is determined by online infrared spectroscopy. When the moisture content of the dehydrated NMP is higher than 100 ppm, the dehydrated NMP is introduced into the azeotropic distillation unit again; when the moisture content of the dehydrated NMP is lower than 100 ppm, the dehydrated NMP is introduced into the vacuum distillation unit.

[0023] Preferably, the vacuum distillation unit is a vacuum distillation column; the vacuum distillation process is as follows: dehydrated NMP is introduced into the vacuum distillation column, wherein the operating pressure of the vacuum distillation column is 0.3-0.5 atm, the bottom temperature is 170-180℃, the top temperature is 80-90℃, the reflux ratio is 1.5, and the top product of the vacuum distillation column is high-temperature NMP.

[0024] Preferably, the membrane separation unit includes a heat exchanger, a nanofiltration unit, and a reverse osmosis unit; the separation process is as follows: high-temperature NMP is introduced into the heat exchanger, cooled to 25°C to obtain residual heat and room-temperature NMP; the room-temperature NMP is then introduced into the nanofiltration unit at an operating pressure of 1.5 MPa and an operating temperature of 25°C, wherein the nanofiltration membrane in the nanofiltration unit has a molecular weight cutoff of 120 Da; the treated room-temperature NMP is further introduced into the reverse osmosis unit, wherein the reverse osmosis unit operates at an operating pressure of 4.5 MPa, an operating temperature of 25°C, and a membrane flux of 25-45 L·m⁻¹. -2 ·h -1 After processing, electronic-grade NMP products are obtained.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. A degassing unit is introduced in the primary distillation process, which effectively removes volatile components dissolved in the raw material NMP before the first rectification separation. The equilibrium distillation process is adopted in the atmospheric pressure primary distillation unit, which improves the separation efficiency of high-boiling-point components. It can stably and efficiently complete the preliminary purification and separation of NMP and reduce the process difficulty of subsequent purification processes.

[0027] 2. The pressurized unit and the adsorption distillation column are used together to perform adsorption distillation on the NMP at the top of the column after preliminary purification. While initially removing low-boiling-point components from the NMP, most of the metal ions are adsorbed. The pressurized operation improves the separation efficiency of low-boiling-point components, and at the same time, it can ensure that the NMP at the top of the column can freely pass through the packing layer filled with adsorbent, ensuring the continuity of operation. Moreover, the lower metal ion content is conducive to improving the efficiency of the subsequent distillation process.

[0028] 3. Azeotropic distillation improves the water removal efficiency from NMP, avoiding the problem of incomplete water removal in traditional distillation methods. Simultaneously, a water content detection unit is installed to monitor the products from the azeotropic distillation unit. NMP products with incomplete water removal are re-treated with azeotropic distillation to ensure extremely low water content.

[0029] 4. A vacuum distillation unit is installed after the azeotropic distillation unit to thoroughly remove high-boiling-point components from NMP at a lower operating temperature, while preventing the decomposition and oxidation of NMP due to high temperatures. Simultaneously, excess azeotropic agent introduced in the azeotropic distillation unit is also removed in the vacuum distillation unit, ensuring extremely low organic impurity content in the product.

[0030] 5. By setting up nanofiltration and reverse osmosis units at the end of the process, metal ions and other inorganic ions in the NMP product are thoroughly removed, ensuring extremely low metal ion content in the product. The operating temperature of the membrane separation process is much lower than that of the distillation process. Therefore, a heat exchange unit is set up before membrane separation to recover the waste heat from the high-temperature NMP and use it for waste heat feedstock NMP, realizing the recycling of energy. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the NMP distillation purification process in this invention.

[0032] Figure 2 This is a process flow diagram of the distillation and purification process of NMP in this invention. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below through some embodiments and experimental examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Reference Figure 1 and Figure 2 The schematic diagram and process flow diagram shown illustrate that this invention provides a distillation purification process for NMP, the technical solution of which is as follows:

[0035] Example 1

[0036] Industrial NMP products with a purity of 99% were used as raw NMP.

[0037] The raw material NMP was preheated to 180°C and introduced into the degassing unit for 30 minutes at 0.8 MPa. Then it was introduced into a balanced distillation column with the bottom temperature set at 220°C, the top temperature at 100°C, the reflux ratio at 2.5, and the operating pressure at 1 atm. After distillation, the top product was taken as the top NMP.

[0038] The NMP from the top of the column was pressurized to 2.0 atm by a pressurization unit and then fed into an adsorption distillation column. The column bottom temperature was set at 210℃, the column top temperature at 95℃, and the reflux ratio at 2.5. The product from the column bottom after treatment was purified NMP. The packing layer of the adsorption distillation column was filled with ion exchange resin adsorbent.

[0039] The purified NMP was introduced into the azeotropic agent premixing unit, mixed with 2 wt% of the azeotropic agent, and pressurized to 2 atm before being introduced into the azeotropic distillation column. The bottom temperature of the azeotropic distillation column was 210℃, the top temperature was 90℃, and the reflux ratio was 3.0. The bottom product after azeotropic distillation was dehydrated NMP.

[0040] Dehydrated NMP is introduced into the moisture content detection unit. While maintaining process continuity, dehydrated NMP with a moisture content greater than 100 ppm is sent back to the azeotropic distillation column for azeotropic distillation again, while dehydrated NMP with a moisture content less than 100 ppm is sent into the vacuum distillation unit.

[0041] Dehydrated NMP was introduced into a vacuum distillation column, with the operating pressure set at 0.5 atm, the bottom temperature at 180°C, the top temperature at 90°C, and the reflux ratio at 1.5. The top product after vacuum distillation was taken as high-temperature NMP.

[0042] High-temperature NMP was passed through a heat exchanger to cool it to 25°C, and the residual heat was recovered through a heat exchange network. Room-temperature NMP was then passed through a nanofiltration unit, treated at an operating pressure of 1.5 MPa and an operating temperature of 25°C, and then passed through a reverse osmosis unit. After reverse osmosis treatment at an operating pressure of 4.5 MPa and an operating temperature of 25°C, electronic-grade NMP was obtained. The nanofiltration membrane in the nanofiltration unit had a molecular weight cutoff of 120 Da, and the membrane flux of the reverse osmosis unit was 25-45 L·m⁻¹. -2 ·h -1 .

[0043] The difference between Examples 2-10 and Example 1 is that some operating parameters are changed, but the overall process is the same. The changes in parameters are summarized in Tables 1 and 2.

[0044] Examples 11-15 use NMP with 80% purity as the raw material, but with the parameters changed. The overall process remains the same. The parameter changes are summarized in Tables 1 and 2.

[0045] Examples 16-20 use industrial NMP with a purity of 95% instead of NMP as the raw material, with the same overall process. The parameter changes are summarized in Tables 1 and 2.

[0046] Examples 21-25 use NMP with 85% purity as the raw material, but with the parameters changed. The overall process remains the same. The parameter changes are summarized in Tables 1 and 2.

[0047] Table 1. Parameter variations in Examples 1-25 (Part 1)

[0048]

[0049]

[0050] Table 2. Parameter variations in Examples 1-25 (II)

[0051]

[0052]

[0053] Comparative Example 1

[0054] Unlike Example 1, a degassing unit was not used; the preheated raw material NMP was directly fed into the equilibrium distillation column, while all other process steps remained the same.

[0055] Comparative Example 2

[0056] Unlike Example 1, equilibrium distillation was performed first, followed by degassing; all other process steps were the same.

[0057] Comparative Example 3

[0058] Unlike Example 5, no pressurization unit was used. Instead, the atmospheric pressure NMP from the top of the column was directly fed into the adsorption distillation column for adsorption distillation. All other process steps were the same.

[0059] Comparative Example 4

[0060] Unlike Example 5, the packing layer of the adsorption distillation column was not filled with ion exchange resin adsorbent, but all other process steps were the same.

[0061] Comparative Example 5

[0062] Unlike Example 11, the moisture content detection unit was removed, and only one round of azeotropic distillation was performed, while the other process steps remained the same.

[0063] Comparative Example 6

[0064] Unlike Example 11, only cyclohexane was used as an azeotropic agent, while all other process steps were the same.

[0065] Comparative Example 7

[0066] Unlike Example 11, only toluene was used as an azeotropic agent, while all other process steps were the same.

[0067] Comparative Example 8

[0068] Unlike Example 16, the vacuum distillation unit is removed, but all other process steps are the same.

[0069] Comparative Example 9

[0070] Unlike Example 16, the operating pressure of the vacuum distillation unit was adjusted to 1 atm, the bottom temperature was adjusted to 220°C, and the top temperature was adjusted to 100°C. All other process steps remained the same.

[0071] Comparative Example 10

[0072] The difference from Example 20 is the order of the reverse osmosis unit and the nanofiltration unit; all other process steps are the same.

[0073] Comparative Example 11

[0074] Unlike Example 20, the heat exchanger is removed, the high-temperature NMP is not cooled, and it is directly introduced into the nanofiltration unit. All other process steps are the same.

[0075] Comparative Example 12

[0076] Unlike Example 20, the nanofiltration unit is removed, but all other process steps are the same.

[0077] Comparative Example 13

[0078] Unlike Example 20, the reverse osmosis unit is removed, but all other process steps are the same.

[0079] Example 26

[0080] The physical parameters of the distillation products obtained in Examples 1-4 and Comparative Examples 1-2 at 25°C were compared, and the relevant parameters are summarized in Table 3.

[0081] Table 3. Physical parameters of the products obtained in Examples 1-4 and Comparative Examples 1-2

[0082]

[0083]

[0084] As shown in Table 3, the physical parameters of Examples 1-4, although different in their operating parameters, remain largely unaffected, achieving high purity, low water content, and low metal ion content in all cases. In Comparative Example 1, the absence of a degassing unit prevented the removal of volatile components from the raw NMP before equilibrium distillation, thus reducing the separation efficiency of subsequent stages and impacting the final product purity. For electronic-grade NMP, a purity of 99.45% is unacceptable. In Comparative Example 2, the process of removing volatile components via equilibrium distillation still relies on equilibrium distillation itself. Furthermore, the overhead product from equilibrium distillation contains the vast majority of volatile components, failing to achieve effective separation. Degassing the overhead product improves purity, but still does not meet the requirements for electronic-grade NMP. Therefore, the combined use of a degassing unit and equilibrium distillation can efficiently remove most volatile components from the raw NMP and improve the processing efficiency of subsequent stages, thereby increasing the purity of the final electronic-grade NMP.

[0085] Example 27

[0086] The physical parameters of the distillation products obtained in Examples 5-10 and Comparative Examples 3-4 at 25°C were compared, and the relevant parameters are summarized in Table 4.

[0087] Table 4. Physical parameters of the products obtained in Examples 5-10 and Comparative Examples 3-4

[0088]

[0089] As shown in Table 4, although the operating parameters of Examples 5-10 differ, the parameters of the products are basically the same and meet the requirements of high purity, low water content, and low metal ion content. This means that the process provided by this invention has excellent purification effect on 99% pure NMP raw materials. For Comparative Example 3, the lack of a pressurization unit resulted in insufficient processing pressure in the adsorption distillation column, preventing the mobile phase from fully contacting the packing layer and reducing the continuity of the adsorption distillation process. This not only failed to effectively remove metal ions but also reduced the processing effect of subsequent stages, leading to a significant decrease in product purity. For Comparative Example 4, the lack of ion exchange resin adsorbent prevented the adsorption distillation unit from removing metal ions. This can be considered as performing only one additional distillation stage. The purity of the obtained product basically met the requirements, but the metal ion concentration was high, failing to meet the requirements of electronic-grade NMP. Therefore, the combined use of a pressurization unit and adsorption distillation can effectively remove metal ions while ensuring sufficient contact between the mobile phase and the packing layer, so that the purity and metal ion content of the final product simultaneously meet the requirements.

[0090] Example 28

[0091] The physical parameters of the distillation products obtained in Examples 11-15 and Comparative Examples 5-7 at 25°C were compared, and the relevant parameters are summarized in Table 5. The addition ratio of the azeotropic agent was controlled by a flow meter, and different feed rates were selected according to the density of different azeotropic agents to ensure that the amount of azeotropic agent used was 2 wt% of the purified NMP.

[0092] Table 5. Physical parameters of the products obtained in Examples 11-15 and Comparative Examples 5-7

[0093]

[0094] As shown in Table 5, although the operating parameters of Examples 11-15 differed and the purified raw material NMP was at a low concentration of 80%, the resulting NMP products still possessed high purity, low water content, and low metal ion content, meeting the requirements for electronic grade. For Comparative Example 5, performing only one azeotropic distillation process might result in incomplete water removal, leading to an increase in water content in the product. For electronic grade NMP, a water content exceeding 100 ppm can have significant negative impacts on chip etching and other fields; therefore, performing only one azeotropic distillation process is insufficient to guarantee product quality requirements. For Comparative Examples 6-7, if only toluene or cyclohexane is chosen as the azeotropic agent, the dehydration effect will be relatively poor, and the number of azeotropic distillation processes will be excessive, introducing too many azeotropic agent impurities and causing a decrease in the purity of the final product. Therefore, the inclusion of a water content detection unit and the addition of the azeotropic agent together ensure efficient water removal without excessive azeotropic distillation processes, reducing energy waste and guaranteeing high purity and low water content of the product.

[0095] Example 29

[0096] The physical parameters of the distillation products obtained in Examples 16-19 and Comparative Examples 8-9 at 25°C were compared, and the relevant parameters are summarized in Table 6.

[0097] Table 6. Physical parameters of the products obtained in Examples 16-19 and Comparative Examples 8-9

[0098]

[0099] As shown in Table 6, the operating parameters of Examples 16-19 differ. The purified raw material NMP has a concentration of 95%, and the resulting NMP product has high purity, low water content, and low metal ion content, meeting the requirements for electronic grade. For Comparative Example 8, the lack of vacuum distillation significantly worsened the removal of high-boiling-point components, resulting in a significant decrease in product purity, clearly failing to meet the requirements for high-purity solvents. For Comparative Example 9, the vacuum distillation operating conditions were changed to atmospheric distillation, which could not effectively remove high-boiling-point components and made it difficult to prevent the decomposition of NMP at high temperatures. Therefore, placing the vacuum distillation unit after the azeotropic distillation unit can significantly improve product purity and, to some extent, remove the azeotropic agent introduced by the azeotropic distillation unit, creating a better synergistic effect. Furthermore, vacuum distillation lowers both the operating pressure and temperature, effectively preventing NMP decomposition caused by continuous high-temperature distillation, resulting in a higher purity NMP product obtained from the entire process.

[0100] Example 30

[0101] The physical parameters of the distillation products obtained in Examples 20-25 and Comparative Examples 10-13 at 25°C were compared, and the relevant parameters are summarized in Table 7.

[0102] Table 7 Physical parameters of the products obtained in Examples 20-25 and Comparative Examples 10-13

[0103]

[0104]

[0105] As shown in Table 7, although the operating parameters of Examples 20-25 differed and the purified raw material NMP was at a low concentration of 85%, the resulting NMP products still possessed high purity, low water content, and low metal ion content, meeting the requirements for electronic grade. In Comparative Example 10, the reverse osmosis unit preceded the nanofiltration unit, reducing the processing efficiency of the reverse osmosis unit. The nanofiltration unit could not remove particulate matter and other impurities from the NMP before the reverse osmosis unit, affecting the ion removal effect of the reverse osmosis unit and resulting in substandard metal ion content in the product. In Comparative Example 11, the direct entry of high-temperature NMP into the membrane separation unit prevented both the nanofiltration and reverse osmosis membranes from operating at their optimal temperatures. This resulted in heat waste and reduced purification efficiency, leading to decreased product purity and increased metal ion content, making it impossible to obtain a qualified product. In Comparative Examples 12 and 13, the absence of a nanofiltration membrane caused the reverse osmosis membrane to be affected by particulate matter, preventing it from achieving optimal operating efficiency, thus impacting both product purity and metal ion content. The absence of a reverse osmosis membrane had a smaller impact on product purity, but significantly increased metal ion content. Therefore, the combined effect and sequence of nanofiltration and reverse osmosis membranes play an important role in ensuring the purity and metal ion content of NMP products. Furthermore, the recovery of waste heat can not only reduce process energy consumption, but also ensure the appropriate processing temperature of the membrane separation process, avoiding the adverse effects of high temperature on the membrane.

[0106] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A distillation purification process for NMP, characterized in that: The distillation and purification process is as follows: The raw material NMP is preheated and then fed into an atmospheric pressure primary distillation unit. After primary distillation, the top NMP is obtained. The atmospheric pressure primary distillation unit includes a degassing unit and a balance distillation column. The primary distillation process is as follows: the raw material NMP is fed into the degassing unit and degassed for 20-30 minutes. Then, it is fed into the balance distillation column and balanced distilled at 1 atm to obtain the top product, which is the top NMP. The NMP at the top of the column is passed into an adsorption distillation unit, and purified NMP is obtained after adsorption distillation. The adsorption distillation unit includes a pressurization unit and an adsorption distillation column. The packing layer of the adsorption distillation column is filled with an adsorbent, which is an ion exchange resin. The refined NMP is passed into an azeotropic distillation unit and an azeotropic agent is introduced for azeotropic distillation treatment to obtain dehydrated NMP. The dehydrated NMP is passed into a moisture content detection unit to detect whether the moisture content of the dehydrated NMP is higher than a threshold. If the water content of the dehydrated NMP is higher than the threshold, the dehydrated NMP is passed back into the azeotropic distillation unit for azeotropic distillation treatment. If the water content of the dehydrated NMP is lower than a threshold, the dehydrated NMP is passed into a vacuum distillation unit, and high-temperature NMP is obtained after vacuum distillation. The vacuum distillation unit is a vacuum rectification column. The vacuum distillation process is as follows: the dehydrated NMP is passed into the vacuum rectification column, wherein the operating pressure of the vacuum rectification column is 0.3-0.5 atm, the bottom temperature is 170-180℃, the top temperature is 80-90℃, the reflux ratio is 1.5, and the top product of the vacuum rectification column is the high-temperature NMP. The high-temperature NMP is passed into a membrane separation unit, and after separation, electronic-grade NMP product and waste heat are obtained. The membrane separation unit includes a heat exchanger, a nanofiltration unit, and a reverse osmosis unit. The separation process is as follows: the high-temperature NMP is passed into the heat exchanger, cooled to 25°C, and waste heat and room-temperature NMP are obtained. The room-temperature NMP is then passed into the nanofiltration unit at an operating pressure of 1.5 MPa and an operating temperature of 25°C. The processed room-temperature NMP is then passed into the reverse osmosis unit, and after further processing, the electronic-grade NMP product is obtained. The waste heat is recovered via a heat exchange network and used for preheating the raw material NMP.

2. The NMP distillation purification process according to claim 1, characterized in that: The purity of the raw material NMP is 80-99%.

3. The NMP distillation purification process according to claim 1, characterized in that: The degassing unit operates at a temperature of 150-180℃ and a pressure of 0.8MPa; the equilibrium distillation column has a bottom temperature of 200-220℃, a top temperature of 90-100℃, and a reflux ratio of 2-2.

5.

4. The NMP distillation purification process according to claim 1, characterized in that: The adsorption distillation process is as follows: the NMP at the top of the column is pressurized to 1.8-2.0 atm through the pressurization unit and then fed into the adsorption distillation column. The product at the bottom of the column after adsorption distillation is the purified NMP. The reflux ratio of the adsorption distillation column is 2.0-2.5, the bottom temperature is 210℃, and the top temperature is 95℃.

5. The NMP distillation purification process according to claim 1, characterized in that: The azeotropic distillation unit includes an azeotropic agent premixing unit and an azeotropic distillation column; the azeotropic agent is a mixture of cyclohexane and toluene, wherein the mass ratio of cyclohexane to toluene is 2:1; the azeotropic distillation process is as follows: in the azeotropic agent premixing unit, the azeotropic agent is mixed with the purified NMP at a ratio of 2wt%, and pressurized to 2 atm before being introduced into the azeotropic distillation column, wherein the bottom temperature of the azeotropic distillation column is 210°C, the top temperature is 90°C, the reflux ratio is 3.0, and the bottom product after azeotropic distillation is the dehydrated NMP.

6. The NMP distillation purification process according to claim 1, characterized in that: The working process of the moisture content detection unit is as follows: the dehydrated NMP is introduced into the moisture content detection unit, and the moisture content is determined by online infrared spectroscopy, wherein the threshold is 100 ppm; when the moisture content of the dehydrated NMP is higher than the threshold, the dehydrated NMP is introduced into the azeotropic distillation unit again; when the moisture content of the dehydrated NMP is lower than the threshold, the dehydrated NMP is introduced into the vacuum distillation unit.

7. The NMP distillation purification process according to claim 1, characterized in that: The nanofiltration membrane in the nanofiltration unit has a molecular weight cutoff of 120 Da, and the reverse osmosis unit operates at a pressure of 4.5 MPa, an operating temperature of 25°C, and a membrane flux of 25-45 L·m⁻¹. -2 ·h -1 .

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