A method for resourceful treatment of polyimide-containing NMP waste liquid

Abstract

The application relates to the technical field of waste liquid treatment, and specifically discloses a resourceful treatment method of polyimide-containing NMP waste liquid, which comprises the following steps: S1: uniformly mixing 1000 parts of water, 15-20 parts of polyvinylpyrrolidone and 20-30 parts of fumed nano silicon dioxide at 40-50 DEG C, adjusting the pH of the system to 9.5-10.5 by using an organic alkali solution, uniformly mixing, cooling, and obtaining a crystal seed inducing liquid; S2: adding pretreated waste liquid into a reactor, heating to 40-50 DEG C, adding 15%-20% of the crystal seed inducing liquid based on the mass of the pretreated waste liquid, heating to 90-100 DEG C, refluxing for 4-5 hours, and obtaining a mixed liquid; and S3: after the mixed liquid is subjected to solid-liquid separation, the filtrate is subjected to two-stage vacuum rectification of rough distillation and refining in sequence, and a high-purity NMP product is obtained. The high-purity NMP product prepared by the application has the advantages of high gas chromatography purity and low water content.

Description

Technical Field

[0001] This application relates to the technical field of waste liquid treatment, and more specifically, it relates to a method for the resource-based treatment of NMP waste liquid containing polyimide. Background Technology

[0002] Polyimide (PI) is a high-performance polymer with excellent heat resistance, mechanical strength, insulation, and chemical resistance. It is widely used in the microelectronics and display panel industries and is a core material for integrated circuit packaging, flexible circuit board manufacturing, and display panel alignment layer preparation. N-methylpyrrolidone (NMP), as a strongly polar aprotic solvent, has excellent solubility for PI and its precursor polyamic acid (PAA). It is a dedicated solvent for PI coating and cleaning processes in production equipment. Therefore, a large amount of PI-containing NMP waste liquid is generated during industrial production.

[0003] This type of waste liquid has a high NMP content and extremely high recycling value, but it faces three major industry challenges: First, there are strong hydrogen bonds and polar interactions between PI and NMP molecules, making them tightly bound and difficult to separate efficiently using conventional methods; second, the PI content in the waste liquid fluctuates greatly, and the viscosity is extremely high and the fluidity is poor at low temperatures, and it also contains a large number of solid particulate impurities, making transportation and treatment extremely difficult; third, in traditional distillation processes, as the distillation process progresses, PI in the residual liquid continuously accumulates, and the viscosity increases sharply, which can easily lead to problems such as coking, wall adhesion, and even equipment blockage, seriously threatening production safety, and making it difficult to prepare panel-grade NMP products that meet the requirements of the display panel industry.

[0004] Patent application CN111620398A discloses a method for recovering NMP-containing waste stripping liquid, comprising the following steps: solid-liquid separation, wherein the NMP-containing waste stripping liquid is subjected to solid-liquid separation to obtain waste stripping liquid residue and stripping liquid distillate; and distillation purification, wherein the stripping liquid distillate is subjected to distillation purification to obtain recovered stripping liquid. The distillation purification process conditions are: temperature ≤145℃, pressure 1-2kPa, cooling water temperature 11~13℃, and distillation time 7.5~17h.

[0005] This technical solution is mainly applicable to waste stripping fluid systems containing NMP, where the waste liquid composition is relatively simple and the viscosity is low. However, for NMP waste liquid containing polyimide generated in the display panel industry, due to the strong hydrogen bonding and polar interaction between PI and NMP molecules, the waste liquid has high viscosity and high solid content. When directly treated using the above process, problems such as low membrane separation efficiency, adsorbent clogging, and coking and wall adhesion during the distillation process are likely to occur, making it difficult to achieve efficient separation of PI and NMP and prepare panel-grade NMP products. Summary of the Invention

[0006] In order to achieve efficient separation of PI and NMP and prepare panel-grade NMP products, this application provides a method for the resource-based treatment of NMP waste liquid containing polyimide.

[0007] A method for resource recovery treatment of NMP waste liquid containing polyimide, comprising the following steps by weight: S1: At 40~50℃, mix 1000 parts of water, 15~20 parts of polyvinylpyrrolidone and 20~30 parts of fumed nano silica, adjust the pH of the system to 9.5~10.5 with organic alkali solution, mix well, cool, and obtain seed induction solution. S2: Add the pretreated waste liquid into the reactor, heat it to 40~50℃, add seed induction liquid accounting for 15%~20% of the mass of the pretreated waste liquid, heat it to 90~100℃, reflux for 4~5 hours to obtain a mixed liquid; S3: After solid-liquid separation of the mixed liquid, the filtrate is subjected to two-stage vacuum distillation, namely coarse evaporation and refining, to obtain high-purity NMP product.

[0008] In this technical solution, water is used as the dispersion medium, and polyvinylpyrrolidone (PVP) is used as a steric hindrance stabilizer. Long-chain molecules adsorb and spread on the surface of fumed silica nano-seeds, forming a steric barrier to prevent agglomeration of the nano-seeds. An organic alkaline solution adjusts the system to a strongly alkaline environment. On one hand, this modifies the surface of the silica nano-seeds with hydroxylation, increasing the surface charge density and creating a double-layer electrostatic stabilization effect. This synergizes with the steric hindrance effect of PPV to achieve long-term stable dispersion of the seed induction solution. On the other hand, the organic alkaline solution provides alkaline active components for the subsequent carboxyl neutralization reaction of PI, enabling the seed induction solution to simultaneously possess the dual functions of supplying heterogeneous nucleation sites and alkaline hydrogen bond breaking. Heating the pretreated waste liquid effectively reduces its viscosity, enhances the kinematic activity of PI molecular chains, and improves the dispersion and mass transfer efficiency of the seed-inducing solution. After the seed-inducing solution is added, its alkaline components neutralize the carboxyl groups on the PI molecular chains, ionizing them and disrupting the strong hydrogen bonds and polar interactions between PI and NMP, thus achieving pre-dissociation of PI and NMP. Simultaneously, fumed silica seeds provide heterogeneous nucleation sites for the dissociated PI molecules, causing them to aggregate and grow directionally on the seed surface, preventing the formation of difficult-to-separate nanocolloids through homogeneous nucleation. Reflux at 90-100°C further strengthens the dissociation and precipitation process of PI, achieving efficient pre-separation of PI and NMP. Through solid-liquid separation and two-stage vacuum distillation, NMP is efficiently purified, stably producing panel-grade high-purity NMP products.

[0009] Furthermore, the specific preparation method of the pretreated waste liquid is as follows: after preheating and cooling the NMP waste liquid containing polyimide to allow it to settle, the upper layer of waste liquid is taken to obtain the pretreated waste liquid.

[0010] Further, in step S3, the crude distillation parameters are: the absolute pressure at the top of the tower is controlled at 15~20 kPa, the heating temperature is 110~120℃, and the condensation temperature is 35~45℃.

[0011] Further, in step S3, the refining parameters are: the absolute pressure at the top of the column is controlled at 10~15 kPa, the heating temperature is 110~120℃, and the condensation temperature is 35~45℃.

[0012] Furthermore, the organic alkaline solution comprises tetramethylammonium hydroxide and water, wherein the mass fraction of tetramethylammonium hydroxide is 25% to 30%.

[0013] Furthermore, the organic alkaline solution also includes triethylamine, with a mass fraction of 7% to 10%.

[0014] In this technical solution, triethylamine and tetramethylammonium hydroxide are combined to form a complex organic base system. Triethylamine can compete with the PI molecular chain for hydrogen bonds, further enhancing the dissociation effect of PI and NMP. At the same time, the boiling point of triethylamine is lower than that of NMP, so it can be removed as a light component in the crude distillation stage without any residual risk.

[0015] Furthermore, the fumed silica nanoparticles are hydrophilic fumed silica nanoparticles with an average particle size of 15-25 nm.

[0016] In this technical solution, the hydrophilic fumed nano silica has a large specific surface area and a high surface hydroxyl content, which can provide sufficient heterogeneous nucleation sites. At the same time, it is easy to disperse uniformly in the aqueous system, has good compatibility with polyvinylpyrrolidone and organic bases, and can stably form a monodisperse seed system.

[0017] Furthermore, in step S1, after adding the fumed nano-silica, the step of adding 5-7 parts by mass of nano-cerium oxide is also included.

[0018] In this technical solution, nano-cerium oxide and fumed nano-silica are combined to form a composite seed system, which increases the density of nucleation sites and enhances the heterogeneous nucleation and precipitation effect of PI.

[0019] Furthermore, the particle size distribution of the nano-cerium oxide is 5~25nm, preferably 10~20nm.

[0020] Furthermore, in step S1, after adding the fumed nano-silica, the following steps are also included: adding 10-12 parts by mass of dopamine hydrochloride and mixing well, adjusting the pH of the system to 8.5-9.0 with an organic alkali solution, and reacting for 2-3 hours.

[0021] In this technical solution, a stepwise pH control process is used to first achieve controllable self-polymerization of dopamine hydrochloride on the surface of the composite seed crystal within a pH range of 8.5 to 9.0, forming a uniform polydopamine coating layer. The polydopamine layer is rich in phenolic hydroxyl and amino groups, which can significantly improve the interfacial bonding force between the seed crystal and PI molecules, enhance the directional nucleation and precipitation effect of PI, and further improve the dispersion stability of the seed crystal in strongly alkaline and NMP systems, avoiding seed crystal agglomeration and deactivation.

[0022] Furthermore, after the dopamine hydrochloride is added, the pH of the seed crystal induction solution is controlled to be no higher than 10.0, preferably no higher than 9.5.

[0023] In summary, this application has the following beneficial effects: This application achieves efficient dissociation and directional precipitation separation of polyimide and NMP in NMP waste liquid containing polyimide by preparing a seed induction liquid with dual functions of alkaline hydrogen bond breaking and heterogeneous nucleation. Optionally, by constructing a composite seed system and optimizing the seed modification scheme with stepwise pH control, the precipitation separation effect of polyimide can be further enhanced, the dispersion stability of the seed system can be improved, and the product purity and process operation stability can be improved simultaneously. Attached Figure Description

[0024] Figure 1 This is the high-performance gas chromatogram of the high-purity NMP product in Example 3; Figure 2 This is a high-performance gas chromatogram of the high-purity NMP product in Example 4. Detailed Implementation

[0025] The present application will be further described in detail below with reference to the embodiments.

[0026] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0027] The waste liquid containing polyimide (PI) from the display panel industry was used. The NMP content was approximately 88.0% by mass, the polyamic acid / polyimide (PI) resin content was 4.5% by mass, and the moisture and trace heavy metal impurities content was 7.5% by mass. Preheating-cooling sedimentation pretreatment was carried out: preheating in a constant temperature chamber at 50℃ for 7 days, cooling to below 20℃, and physical sedimentation for 30 days. After sedimentation, the state of the raw material waste liquid in the ton container was screened before production. The top 30% to 60% of the waste liquid in the ton container with good fluidity and viscosity η < 10 Pa·s was transferred to the system tower for later use, thus obtaining the pretreated waste liquid.

[0028] Fumed silica nanoparticles, hydrophilic, with a particle size of 15~25nm and a purity better than 99.8%; Nano-sized cerium oxide, with a particle size of 10-20 nm and a purity better than 99.5%; Tetramethylammonium hydroxide aqueous solution, electronic grade, mass concentration 25%; Polyvinylpyrrolidone, industrial grade, weight average molecular weight approximately 40,000; Triethylamine, analytical grade, with a purity better than 99.5%.

[0029] Example 1 The resource recovery treatment method for NMP waste liquid containing polyimide in this embodiment includes the following steps: S1: Add 1000g of deionized water to a mixing tank equipped with a mechanical stirrer, turn on the stirrer to 400rpm, add 18g of polyvinylpyrrolidone in 5 portions to the mixing tank, heat to 45℃, and continue stirring and mixing for 30min after the addition is complete. Slowly add the fumed silica dispersion (prepared by ultrasonically dispersing 25g of fumed silica powder in 50g of deionized water), and simultaneously turn on the ultrasonic disperser, setting the ultrasonic frequency to 40kHz and the power density to 0.5W / cm³. 3 The mixture was ultrasonically treated for 45 minutes, cooled to room temperature, and the pH of the system was adjusted to 9.5 using a 25% tetramethylammonium hydroxide aqueous solution to obtain the seed crystal induction solution. S2: Pump 0.8 kg of pretreated waste liquid into a three-necked flask equipped with a reflux condenser. Control the waste liquid temperature at 45°C, start the stirrer, set the speed to 150 rpm, and simultaneously turn on the external variable frequency ultrasonic generator, setting the ultrasonic frequency to 28 kHz and the power density to 0.35 W / cm³. 3 The seed crystal induction solution was uniformly and continuously sprayed and added to the surface of the waste liquid at a rate of 20 g / min. The amount of seed crystal induction solution was 17% of the mass of the pretreated waste liquid. After the addition was completed, the ultrasonic treatment was turned off, and the mixture was stirred at 150 rpm and heated to 95°C for a preheating reflux reaction for 4.5 h. During the reflux process, the alkaline component in the seed crystal induction solution reacted with PI to neutralize the carboxyl groups: R-COOH + OH- - →R-COO - +H2O ionizes the carboxyl groups in the PI molecular chain, destroying the hydrogen bonds, polar interactions, and intermolecular forces between PI and NMP; at the same time, the nanocrystals in the seed induction solution provide heterogeneous nucleation sites for PI, causing the ionized PI to aggregate and grow on the seed surface, forming a light yellow PI-seed composite precipitate, resulting in a mixed solution.

[0030] S3: The mixed liquid is separated into solid and liquid components using a plate and frame filter press. The filtered clear liquid is transferred to a storage stirred tank of the batch distillation system for two-stage vacuum distillation: rough distillation and refining. (1) Coarse steaming process: Start the heating and vaporization system of the stirring tank, control the absolute pressure of the tower top to 15 kPa, the heating temperature of the tower bottom to 115℃, the condensation temperature of the tower top to 40℃, set the reflux ratio to 3.0, and carry out coarse steaming through heating, vaporization, condensation, reflux and collection processes; in the later stage of coarse steaming, when it is observed that the residual liquid in the tower bottom shows a viscous trend, stop collection in time and discharge the residual liquid in the tower bottom to avoid the residual liquid sticking to the wall and clogging the equipment, and collect the NMP intermediate product obtained from coarse steaming; (2) Refining process: The NMP intermediate product obtained from crude distillation is pumped into a secondary distillation column. The absolute pressure at the top of the column is controlled at 10 kPa, the bottom heating temperature is 115°C, the top condensation temperature is 40°C, and the reflux ratio is set to 4.0. The reduced pressure distillation is then carried out to further remove moisture, triethylamine and trace amounts of high-boiling-point oligomers. The gaseous NMP solvent is collected after being fully condensed at the top of the column to obtain a colorless and transparent high-purity NMP product. Trace amounts of high-boiling-point impurities are retained at the bottom of the column and are periodically discharged and sent to the hazardous waste treatment system for harmless disposal.

[0031] Testing revealed that the high-purity NMP product had a gas chromatographic purity of 99.85%, moisture content ≤200ppm, and color ≤10. The crude distillation process yielded approximately 62.0% of the NMP intermediate product (based on 0.8kg of pretreatment waste liquid). The refining process yielded approximately 80.5% of the high-purity NMP product (based on the NMP intermediate product), resulting in an overall yield of 49.9%.

[0032] Example 2 The resource recovery treatment method for NMP waste liquid containing polyimide in this embodiment includes the following steps: S1: Add 1000g of deionized water to a mixing tank equipped with a mechanical stirrer, turn on the stirrer to 400rpm, add 15g of polyvinylpyrrolidone in 5 portions to the mixing tank, heat to 40℃, and continue stirring and mixing for 30min after the addition is complete. Slowly add the fumed silica dispersion (prepared by ultrasonically dispersing 20g of fumed silica powder in 50g of deionized water), and simultaneously turn on the ultrasonic disperser, setting the ultrasonic frequency to 40kHz and the power density to 0.5W / cm³. 3 The mixture was ultrasonically treated for 45 minutes, cooled to room temperature, and the pH of the system was adjusted to 9.5 using a mixed aqueous solution (the mass concentration of tetramethylammonium hydroxide in the mixed solution was 25%, and the mass concentration of triethylamine was 7%) to obtain the seed crystal induction solution. S2: Pump 0.8 kg of pretreated waste liquid into a three-necked flask equipped with a reflux condenser, control the waste liquid temperature at 40℃, start stirring, set the speed to 150 rpm, and simultaneously turn on the external variable frequency ultrasonic generator, setting the ultrasonic frequency to 28 kHz and the power density to 0.35 W / cm³. 3The seed crystal induction solution was uniformly and continuously sprayed and dripped onto the surface of the waste liquid at a rate of 20 g / min. The amount of seed crystal induction solution was 20% of the mass of the pretreated waste liquid. After the dripping was completed, the ultrasonic treatment was turned off, and the mixture was stirred at 150 rpm and heated to 90°C for a preheating reflux reaction for 5 hours. During the reflux process, the alkaline component in the seed crystal induction solution reacted with PI to neutralize the carboxyl groups: R-COOH + OH- - →R-COO - +H2O ionizes the carboxyl groups in the PI molecular chain, destroying the hydrogen bonds, polar interactions, and intermolecular forces between PI and NMP; at the same time, the nanocrystals in the seed induction solution provide heterogeneous nucleation sites for PI, causing the ionized PI to aggregate and grow on the seed surface, forming a light yellow PI-seed composite precipitate, resulting in a mixed solution.

[0033] S3: The mixed liquid is separated into solid and liquid components using a plate and frame filter press. The filtered clear liquid is transferred to a storage stirred tank of the batch distillation system for two-stage vacuum distillation: rough distillation and refining. (1) Coarse steaming process: Start the heating and vaporization system of the stirring tank, control the absolute pressure of the tower top to 20 kPa, the heating temperature of the tower bottom to 110℃, the condensation temperature of the tower top to 35℃, set the reflux ratio to 3.0, and carry out coarse steaming through heating, vaporization, condensation, reflux and collection processes; in the later stage of coarse steaming, when it is observed that the residual liquid in the tower bottom shows a viscous trend, stop collection in time and discharge the residual liquid in the tower bottom to avoid the residual liquid sticking to the wall and clogging the equipment, and collect the NMP intermediate product obtained from coarse steaming; (2) Refining process: The NMP intermediate product obtained from crude distillation is pumped into a secondary distillation column. The absolute pressure at the top of the column is controlled at 15 kPa, the bottom heating temperature is 110°C, the top condensation temperature is 35°C, and the reflux ratio is set to 4.0. The reduced pressure distillation is then carried out to further remove moisture, triethylamine and trace amounts of high-boiling-point oligomers. The gaseous NMP solvent is collected after being fully condensed at the top of the column to obtain a colorless and transparent high-purity NMP product. Trace amounts of high-boiling-point impurities are retained at the bottom of the column and are periodically discharged and sent to the hazardous waste treatment system for harmless disposal.

[0034] Testing revealed that the high-purity NMP product had a gas chromatographic purity of 99.90%, moisture content ≤200ppm, and color ≤10. The crude distillation process yielded approximately 61.5% of the NMP intermediate product (based on 0.8kg of pretreatment waste liquid). The refining process yielded approximately 80.2% of the high-purity NMP product (based on the NMP intermediate product). The overall yield was 49.3%.

[0035] Example 3 The resource recovery treatment method for NMP waste liquid containing polyimide in this embodiment includes the following steps: S1: Add 1000g of deionized water to a mixing tank equipped with a mechanical stirrer, turn on the stirrer to 400rpm, add 20g of polyvinylpyrrolidone in 5 portions to the mixing tank, heat to 50℃, and continue stirring and mixing for 30min after the addition is complete. Slowly add the fumed silica dispersion (prepared by ultrasonically dispersing 30g of fumed silica powder in 60g of deionized water), and simultaneously turn on the ultrasonic disperser, setting the ultrasonic frequency to 40kHz and the power density to 0.5W / cm³. 3 The mixture was ultrasonically treated for 45 minutes, cooled to room temperature, and the pH of the system was adjusted to 10.5 using a mixed aqueous solution (the mass concentration of tetramethylammonium hydroxide in the mixed solution was 30%, and the mass concentration of triethylamine was 10%) to obtain the seed crystal induction solution. S2: Pump 0.8 kg of pretreated waste liquid into a three-necked flask equipped with a reflux condenser. Control the waste liquid temperature at 50°C, start the stirrer, set the speed to 150 rpm, and simultaneously turn on the external variable frequency ultrasonic generator, setting the ultrasonic frequency to 28 kHz and the power density to 0.35 W / cm³. 3 The seed crystal induction solution was uniformly and continuously sprayed onto the surface of the waste liquid at a rate of 20 g / min. The amount of seed crystal induction solution was 20% of the mass of the pretreated waste liquid. After the addition was completed, the ultrasonic treatment was turned off, and the mixture was stirred at 150 rpm while the temperature was raised to 100°C for a preheating reflux reaction for 4 hours. During the reflux process, the alkaline component in the seed crystal induction solution reacted with PI to neutralize the carboxyl groups: R-COOH + OH- - →R-COO - +H2O ionizes the carboxyl groups in the PI molecular chain, destroying the hydrogen bonds, polar interactions, and intermolecular forces between PI and NMP; at the same time, the nanocrystals in the seed induction solution provide heterogeneous nucleation sites for PI, causing the ionized PI to aggregate and grow on the seed surface, forming a light yellow PI-seed composite precipitate, resulting in a mixed solution.

[0036] S3: The mixed liquid is separated into solid and liquid components using a plate and frame filter press. The filtered clear liquid is transferred to a storage stirred tank of the batch distillation system for two-stage vacuum distillation: rough distillation and refining. (1) Coarse steaming process: Start the heating and vaporization system of the stirring tank, control the absolute pressure of the tower top to 20 kPa, the heating temperature of the tower bottom to 120℃, the condensation temperature of the tower top to 45℃, set the reflux ratio to 3.0, and carry out coarse steaming through heating, vaporization, condensation, reflux and collection processes; in the later stage of coarse steaming, when it is observed that the residual liquid in the tower bottom shows a viscous trend, stop collection in time and discharge the residual liquid in the tower bottom to avoid the residual liquid sticking to the wall and clogging the equipment, and collect the NMP intermediate product obtained from coarse steaming; (2) Refining process: The NMP intermediate product obtained from crude distillation is pumped into a secondary distillation column. The absolute pressure at the top of the column is controlled at 15 kPa, the bottom heating temperature is 120°C, the top condensation temperature is 45°C, and the reflux ratio is set to 4.0. The reduced pressure distillation is then carried out to further remove moisture, triethylamine and trace amounts of high-boiling-point oligomers. The gaseous NMP solvent is collected after being fully condensed at the top of the column to obtain a colorless and transparent high-purity NMP product. Trace amounts of high-boiling-point impurities are retained at the bottom of the column and are periodically discharged and sent to the hazardous waste treatment system for harmless disposal.

[0037] Testing revealed that the high-purity NMP product had a gas chromatographic purity of 99.93%, moisture content ≤200ppm, and color ≤10. The crude distillation process yielded approximately 61.7% of the NMP intermediate product (based on 0.8kg of pretreatment waste liquid). The refining process yielded approximately 80.0% of the high-purity NMP product (based on the NMP intermediate product), resulting in an overall yield of 49.4%.

[0038] Example 4 The resource recovery treatment method for NMP waste liquid containing polyimide in this embodiment includes the following steps: S1: Add 1000g of deionized water to a mixing tank equipped with a mechanical stirrer, turn on the stirrer to 400rpm, add 20g of polyvinylpyrrolidone in 5 portions to the mixing tank, heat to 50℃, and continue stirring and mixing for 30min after the addition is complete. Slowly add the fumed silica dispersion (prepared by ultrasonically dispersing 25g of fumed silica powder in 60g of deionized water) and the cerium oxide dispersion (prepared by ultrasonically dispersing 5g of cerium oxide powder in 15g of deionized water), while simultaneously turning on the ultrasonic disperser and setting the ultrasonic frequency to 40kHz and the power density to 0.5W / cm³. 3 The mixture was ultrasonically treated for 45 minutes, cooled to room temperature, and the pH of the system was adjusted to 10.5 using a mixed aqueous solution (the mass concentration of tetramethylammonium hydroxide in the mixed solution was 25%, and the mass concentration of triethylamine was 10%) to obtain the seed crystal induction solution. S2: Pump 0.8 kg of pretreated waste liquid into a three-necked flask equipped with a reflux condenser. Control the waste liquid temperature at 50°C, start the stirrer, set the speed to 150 rpm, and simultaneously turn on the external variable frequency ultrasonic generator, setting the ultrasonic frequency to 28 kHz and the power density to 0.35 W / cm³. 3 The seed crystal induction solution was uniformly and continuously sprayed onto the surface of the waste liquid at a rate of 20 g / min. The amount of seed crystal induction solution was 20% of the mass of the pretreated waste liquid. After the addition was completed, the ultrasonic treatment was turned off, and the mixture was stirred at 150 rpm while the temperature was raised to 95°C for a preheating reflux reaction for 5 hours. During the reflux process, the alkaline component in the seed crystal induction solution reacted with the PI to neutralize the carboxyl groups: R-COOH + OH- - →R-COO -+H2O ionizes the carboxyl groups in the PI molecular chain, destroying the hydrogen bonds, polar interactions, and intermolecular forces between PI and NMP; at the same time, the nanocrystals in the seed induction solution provide heterogeneous nucleation sites for PI, causing the ionized PI to aggregate and grow on the seed surface, forming a light yellow PI-seed composite precipitate, resulting in a mixed solution.

[0039] S3: The mixed liquid is separated into solid and liquid components using a plate and frame filter press. The filtered clear liquid is transferred to a storage stirred tank of the batch distillation system for two-stage vacuum distillation: rough distillation and refining. (1) Coarse steaming process: Start the heating and vaporization system of the stirring tank, control the absolute pressure of the tower top to 20 kPa, the heating temperature of the tower bottom to 115℃, the condensation temperature of the tower top to 45℃, set the reflux ratio to 3.0, and carry out coarse steaming through heating, vaporization, condensation, reflux and collection processes; in the later stage of coarse steaming, when it is observed that the residual liquid in the tower bottom shows a viscous trend, stop collection in time and discharge the residual liquid in the tower bottom to avoid the residual liquid sticking to the wall and clogging the equipment, and collect the NMP intermediate product obtained from coarse steaming; (2) Refining process: The NMP intermediate product obtained from crude distillation is pumped into a secondary distillation column. The absolute pressure at the top of the column is controlled at 15 kPa, the bottom heating temperature is 115°C, the top condensation temperature is 45°C, and the reflux ratio is set to 4.0. The reduced pressure distillation is then carried out to further remove moisture, triethylamine and trace amounts of high-boiling-point oligomers. The gaseous NMP solvent is collected after being fully condensed at the top of the column to obtain a colorless and transparent high-purity NMP product. Trace amounts of high-boiling-point impurities are retained at the bottom of the column and are periodically discharged and sent to the hazardous waste treatment system for harmless disposal.

[0040] Testing revealed that the high-purity NMP product had a gas chromatographic purity of 99.94%, moisture content ≤200ppm, and color ≤10. The crude distillation process yielded approximately 62.0% of the NMP intermediate product (based on 0.8kg of pretreatment waste liquid). The refining process yielded approximately 80.1% of the high-purity NMP product (based on the NMP intermediate product), resulting in an overall yield of 49.7%.

[0041] Example 5 The difference between this embodiment and embodiment 4 is that: S1: Add 1000g of deionized water to a mixing tank equipped with a mechanical stirrer, turn on the stirrer to 400rpm, add 20g of polyvinylpyrrolidone in 5 portions to the mixing tank, heat to 50℃, and continue stirring and mixing for 30min after the addition is complete. Slowly add the fumed silica dispersion (prepared by ultrasonically dispersing 25g of fumed silica powder in 60g of deionized water) and the cerium oxide dispersion (prepared by ultrasonically dispersing 7g of cerium oxide powder in 15g of deionized water), while simultaneously turning on the ultrasonic disperser and setting the ultrasonic frequency to 40kHz and the power density to 0.5W / cm³. 3The mixture was ultrasonically treated for 45 minutes, cooled to room temperature, and the pH of the system was adjusted to 10.5 using a mixed aqueous solution (the mass concentration of tetramethylammonium hydroxide in the mixed solution was 25%, and the mass concentration of triethylamine was 10%) to obtain the seed crystal induction solution. The rest is the same as in Example 4.

[0042] Testing revealed that the high-purity NMP product had a gas chromatographic purity of 99.95%, moisture content ≤200ppm, and color ≤10. The crude distillation process yielded approximately 62.3% of the NMP intermediate product (based on 0.8kg of pretreatment waste liquid). The refining process yielded approximately 80.2% of the high-purity NMP product (based on the NMP intermediate product), resulting in an overall yield of 50.0%.

[0043] Example 6 The difference between this embodiment and embodiment 5 is as follows: S1: Add 1000g of deionized water to a mixing tank equipped with a mechanical stirrer, turn on the stirrer to 400rpm, add 20g of polyvinylpyrrolidone in 5 portions to the mixing tank, heat to 50℃, and continue stirring and mixing for 30min after the addition is complete. Slowly add the fumed silica dispersion (prepared by ultrasonically dispersing 25g of fumed silica powder in 60g of deionized water) and the cerium oxide dispersion (prepared by ultrasonically dispersing 7g of cerium oxide powder in 15g of deionized water), while simultaneously turning on the ultrasonic disperser and setting the ultrasonic frequency to 40kHz and the power density to 0.5W / cm³. 3 The mixture was ultrasonically treated for 45 minutes, then 10 g of dopamine hydrochloride was added and mixed well. The pH of the system was adjusted to 8.5 using a mixed aqueous solution (the mass concentration of tetramethylammonium hydroxide in the mixed solution was 25% and the mass concentration of triethylamine was 10%). The mixture was stirred at 200 rpm for 2 hours and cooled to room temperature. The pH of the system was then adjusted to 9.5 using a mixed aqueous solution (the mass concentration of tetramethylammonium hydroxide in the mixed solution was 25% and the mass concentration of triethylamine was 10%) to obtain the seed crystal induction solution. S2: Pump 0.8 kg of pretreated waste liquid into a three-necked flask equipped with a reflux condenser. Control the waste liquid temperature at 50°C, start the stirrer, set the speed to 150 rpm, and simultaneously turn on the external variable frequency ultrasonic generator, setting the ultrasonic frequency to 28 kHz and the power density to 0.35 W / cm³. 3 The seed crystal induction solution was uniformly and continuously sprayed onto the surface of the waste liquid at a rate of 20 g / min. The amount of seed crystal induction solution was 20% of the mass of the pretreated waste liquid. After the addition was completed, the ultrasonic treatment was turned off, and high-purity nitrogen gas was passed through at a rate of 30 mL / min while stirring at 150 rpm and heating to 95°C for a preheating reflux reaction for 5 hours. During the reflux process, the alkaline component in the seed crystal induction solution reacted with PI through a carboxyl neutralization reaction: R-COOH + OH- -→R-COO - +H2O ionizes the carboxyl groups in the PI molecular chain, destroying the hydrogen bonds, polar interactions, and intermolecular forces between PI and NMP; at the same time, the nanocrystals in the seed induction solution provide heterogeneous nucleation sites for PI, causing the ionized PI to aggregate and grow on the seed surface, forming a light yellow PI-seed composite precipitate, resulting in a mixed solution.

[0044] The rest is the same as in Example 5.

[0045] Testing revealed that the high-purity NMP product had a gas chromatographic purity of 99.96%, moisture content ≤200ppm, and color ≤10. The crude distillation process yielded approximately 61.9% of the NMP intermediate product (based on 0.8kg of pretreatment waste liquid). The refining process yielded approximately 80.0% of the high-purity NMP product (based on the NMP intermediate product), resulting in an overall yield of 49.5%.

[0046] Example 7 The difference between this embodiment and embodiment 6 is that: S1: Add 1000g of deionized water to a mixing tank equipped with a mechanical stirrer, turn on the stirrer to 400rpm, add 20g of polyvinylpyrrolidone in 5 portions to the mixing tank, heat to 50℃, and continue stirring and mixing for 30min after the addition is complete. Slowly add the fumed silica dispersion (prepared by ultrasonically dispersing 25g of fumed silica powder in 60g of deionized water) and the cerium oxide dispersion (prepared by ultrasonically dispersing 7g of cerium oxide powder in 15g of deionized water), while simultaneously turning on the ultrasonic disperser and setting the ultrasonic frequency to 40kHz and the power density to 0.5W / cm³. 3 The mixture was ultrasonically treated for 45 min, and 12 g of dopamine hydrochloride was added and mixed well. The pH of the system was adjusted to 9.0 using a mixed aqueous solution (the mass concentration of tetramethylammonium hydroxide in the mixed solution was 25% and the mass concentration of triethylamine was 10%). The mixture was stirred at 200 rpm for 3 h and cooled to room temperature. The pH of the system was adjusted to 9.5 using a mixed aqueous solution (the mass concentration of tetramethylammonium hydroxide in the mixed solution was 25% and the mass concentration of triethylamine was 10%) to obtain the seed crystal induction solution. The rest is the same as in Example 6.

[0047] Testing revealed that the high-purity NMP product had a gas chromatographic purity of 99.96%, moisture content ≤200ppm, and color ≤10. The crude distillation process yielded approximately 62.2% of the NMP intermediate product (based on 0.8kg of pretreatment waste liquid). The refining process yielded approximately 80.3% of the high-purity NMP product (based on the NMP intermediate product), resulting in an overall yield of 49.9%.

[0048] Table 1. High-performance gas chromatogram data of high-purity NMP products in Example 3

[0049] Table 2. High-performance gas chromatogram data of high-purity NMP products in Example 4

[0050] Combination Figures 1-2 As can be seen from Tables 1 and 2 and the analysis of the test data: In Examples 1-3, polyvinylpyrrolidone, fumed silica nanoparticles, and organic alkali solution were used as the core components of the seed crystal induction solution, achieving effective dissociation of PI and heterogeneous nucleation precipitation. In Example 2, triethylamine was introduced as a composite organic alkali component, which improved product purity but slightly decreased the overall yield. In Example 3, by adjusting the ratio of tetramethylammonium hydroxide to triethylamine, the yield recovered compared to Example 2, and the purity was further improved.

[0051] In Examples 4 and 5, nano-cerium oxide was introduced as the second inorganic seed crystal component to form a composite seed crystal system with fumed nano-silica, which increased the nucleation site density and facilitated the heterogeneous nucleation and precipitation of PI. The crude evaporation yield and the overall yield were both improved, and the product purity continued to increase.

[0052] In Examples 6 and 7, dopamine hydrochloride was introduced into the composite inorganic seed crystals. Polydopamine was generated in situ in the seed crystal induction solution by adjusting the pH stepwise, thus constructing an organic-inorganic hybrid seed crystal system. The purity was slightly improved. By adjusting the amount of dopamine and the reaction time, the overall yield was improved in Example 7 while maintaining the product purity.

[0053] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for the resource-based treatment of NMP waste liquid containing polyimide, characterized in that, By weight, the steps include: S1: At 40~50℃, mix 1000 parts of water, 15~20 parts of polyvinylpyrrolidone and 20~30 parts of fumed nano silica, adjust the pH of the system to 9.5~10.5 with organic alkali solution, mix well, cool, and obtain seed induction solution. S2: Add the pretreated waste liquid into the reactor, heat it to 40~50℃, add seed induction liquid accounting for 15%~20% of the mass of the pretreated waste liquid, heat it to 90~100℃, reflux for 4~5 hours to obtain a mixed liquid; S3: After solid-liquid separation of the mixed liquid, the filtrate is subjected to two-stage vacuum distillation, namely coarse evaporation and refining, to obtain high-purity NMP product.

2. The method for resource recovery treatment of NMP waste liquid containing polyimide according to claim 1, characterized in that, The specific preparation method of the pretreated waste liquid is as follows: after preheating and cooling the NMP waste liquid containing polyimide to allow it to settle, the upper layer of waste liquid is taken to obtain the pretreated waste liquid.

3. The method for resource recovery treatment of NMP waste liquid containing polyimide according to claim 1, characterized in that, The organic alkaline solution comprises tetramethylammonium hydroxide and water, wherein the mass fraction of tetramethylammonium hydroxide is 25% to 30%.

4. The method for resource recovery treatment of NMP waste liquid containing polyimide according to claim 3, characterized in that, The organic alkaline solution also includes triethylamine, with a mass fraction of 7% to 10%.

5. The method for resource recovery treatment of NMP waste liquid containing polyimide according to claim 4, characterized in that, In step S3, the crude distillation parameters are: the absolute pressure at the top of the tower is controlled at 15~20 kPa, the heating temperature is 110~120℃, and the condensation temperature is 35~45℃.

6. The method for resource recovery treatment of NMP waste liquid containing polyimide according to claim 4, characterized in that, In step S3, the refining parameters are: the absolute pressure at the top of the tower is controlled at 10~15 kPa, the heating temperature is 110~120℃, and the condensation temperature is 35~45℃.

7. The method for resource recovery treatment of NMP waste liquid containing polyimide according to claim 1, characterized in that, The fumed silica nanoparticles are hydrophilic fumed silica nanoparticles with an average particle size of 15-25 nm.

8. The method for resource recovery treatment of NMP waste liquid containing polyimide according to claim 1, characterized in that, In step S1, after adding the fumed nano-silica, the step further includes adding 5-7 parts by mass of nano-cerium oxide.

9. The method for resource recovery treatment of NMP waste liquid containing polyimide according to claim 1, characterized in that, In step S1, after adding the fumed nano-silica, the following steps are also included: adding 10-12 parts by mass of dopamine hydrochloride and mixing well, adjusting the pH of the system to 8.5-9.0 with organic alkali solution, and reacting for 2-3 hours.

10. The method for resource recovery treatment of NMP waste liquid containing polyimide according to claim 9, characterized in that, After the dopamine hydrochloride is added, the pH of the seed crystal induction solution is controlled to be no higher than 10.0, preferably no higher than 9.5.

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