A recovery process for NMP-containing cleaning waste
By combining flocculant agglomeration and staged water washing with multi-stage distillation, the problems of equipment blockage and NMP residue caused by solid impurities were solved, achieving efficient and low-consumption recovery of NMP and improving recovery rate and purity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGSU ELECTRONIC TECH ENVIRONMENTAL CO LTD
- Filing Date
- 2026-02-26
- Publication Date
- 2026-06-02
AI Technical Summary
In existing NMP-containing waste recovery technologies, solid impurities can easily cause equipment blockage, and residual NMP in the filter residue is not fully recovered, affecting the recovery rate and purity.
Flocculants are used to agglomerate solid impurities. Combined with staged water washing and multi-stage distillation, water is absorbed through molecular sieves, eliminating the need for coarse distillation and improving NMP recovery rate and purity.
It achieves efficient and low-consumption recovery of NMP, improves recovery rate and purity, and reduces the risk of equipment blockage.
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Abstract
Description
Technical Field
[0001] This application relates to the technical field of waste treatment, and in particular to a recycling process for NMP-containing cleaning waste. Background Technology
[0002] Existing technologies for recovering NMP-containing waste mainly include the following methods: using industrial-grade alum, anionic PAM, or other coagulants to agglomerate tiny particles in the waste, followed by solid-liquid separation and subsequent recovery; preheating the NMP solvent to 80-99℃ and then passing it through a thin-film evaporator to separate the gaseous NMP from the solid residue; forming an NMP-containing extract by contacting the extractant with the NMP-containing wastewater, followed by distillation to separate the extractant from the NMP; and purifying NMP through multiple distillations, such as a two-step distillation process of "vacuum dehydration-degravimetric separation" or "two-stage dehydration-distillation." All of these methods are based on physical or physicochemical separation principles, utilizing the differences in boiling point, solubility, and particle morphology between NMP and impurities to achieve preliminary NMP recovery and reduce hazardous waste emissions. However, solid impurities can easily cause blockage of subsequent equipment, requiring manual slag removal or additional coarse distillation processes. Furthermore, residual NMP in the filter residue after solid-liquid separation is not fully recovered, affecting the NMP recovery rate and purity. Summary of the Invention
[0003] To improve the recovery rate and purity of NMP, this application provides a recycling process for NMP-containing cleaning waste.
[0004] This application provides a recycling process for NMP-containing cleaning waste, which adopts the following technical solution: A recycling process for NMP-containing cleaning waste includes the following steps: Pretreatment: Add flocculant to NMP cleaning waste, flocculate and settle to obtain supernatant and filter residue; Washing: Wash the filter residue with water. Add the washing liquid A from the first wash to the filtrate tank. Then, wash the filter residue with circulating water until the NMP content in the washing liquid does not change significantly. Add the resulting washing liquid B to the filtrate tank. Fine filtration: Add the supernatant to the filtrate tank, and perform fine filtration on the supernatant, washing liquid A, and washing liquid B in the filtrate tank to obtain fine filtrate; Multistage distillation: The filtrate is subjected to multistage distillation, and the resulting fraction is dehydrated by passing it through a molecular sieve to obtain the NMP product.
[0005] By adopting the above technical solution, solid impurities are first efficiently agglomerated using a coagulant, then residual NMP in the filter residue is maximized through segmented water washing, fine filtration eliminates the coarse steaming process, and finally, water is absorbed by multiple distillations and molecular sieves, taking into account both purification efficiency and finished product moisture content control, achieving efficient and low-consumption recovery of NMP, and improving the recovery rate and purity of the final NMP product.
[0006] In one specific implementation, the flocculant comprises an alum solution and an anionic polyacrylamide solution with a mass concentration of 6%-10%.
[0007] By adopting the above technical solution, too little alum will affect the flocculation and sedimentation effect, while too much will result in waste; anionic polyacrylamide plays a coagulation aid role, further improving the flocculation and sedimentation effect.
[0008] In one specific implementation scheme, the pretreatment step is as follows: adding alum solution dropwise to NMP cleaning waste while stirring, and after the addition is complete, adding anionic polyacrylamide solution dropwise, stirring, flocculating and settling to obtain supernatant and filter residue.
[0009] In one specific implementation, the pretreatment step further includes a preheating adjustment step, in which the NMP cleaning waste is heated to 43-47°C, stirred at a speed of 200-300 rpm, and then the pH is adjusted to 6.2-6.8 using sodium hydroxide solution.
[0010] By adopting the above technical solution, preheating and stirring are performed before pretreatment to adjust the pH, reduce the viscosity of NMP cleaning waste, and improve flocculation and filtration efficiency.
[0011] In one specific implementation, the washing step involves using a filter press for cleaning. The first wash uses 40°C water at a pressure of 0.3 MPa to rinse the filter residue, yielding washing liquid A. The circulating wash uses 40°C water at a pressure of 0.3 MPa to re-wash the filter residue until the NMP content in the washing liquid shows no significant change and the NMP concentration is below 0.2%. At this point, the circulating wash is stopped, yielding washing liquid B.
[0012] In one specific feasible implementation, the fine filtration step involves first filtering with 1-2 ml of water. 3 The flow rate passes through a 5-micron security filter at a rate of / h, and then at a speed of 0.8-1.5m. 3 A flow rate of / h passes through a 0.5-micron security filter to complete fine filtration.
[0013] In one specific implementation, the multi-stage distillation step is further included before the elution step, in which the filtrate is eluted by passing it through a resin column packed with macroporous adsorption resin at a temperature of 35-45°C.
[0014] By adopting the above technical solution, resin columns are used for elution to further remove impurities from the filtrate, thereby improving the quality and stability of the final product.
[0015] In one specific implementation scheme, the multi-stage distillation step involves evaporating the filtrate in a primary evaporator, followed by dehydration in a secondary dehydration tower, and finally purification in a tertiary purification tower.
[0016] By adopting the above technical solution, the light phase and water phase are first removed by evaporation in a primary evaporator, then dehydrated in a secondary dehydration tower to reduce the water content, and finally purified by a tertiary purification tower to improve the purity of the distilled NMP.
[0017] In one specific implementation scheme, in the multi-stage distillation step, the temperature of the first-stage evaporator is 85-95℃ and the vacuum degree is −0.085-−0.095MPa; the temperature of the second-stage dehydration tower for dehydration is 95-120℃ and the pressure is 30-60kPa; and the temperature of the third-stage purification tower for purification is 110-140℃ and the pressure is 10-25kPa.
[0018] In one specific implementation, during the multi-stage distillation step, when the fraction obtained after dehydration in the secondary dehydration tower is passed through a molecular sieve for water absorption, the pressure is 0.1-0.2 MPa and the temperature is 30-45°C, so that the water content of the fraction is not higher than 0.03%.
[0019] In summary, this application includes at least one of the following beneficial technical effects: The process in this application first achieves efficient agglomeration of solid impurities through a coagulant, then maximizes the recovery of residual NMP in the filter residue through segmented water washing, eliminates the coarse steaming process through fine filtration, and finally achieves efficient and low-consumption recovery of NMP by using multiple distillations and molecular sieve water absorption, taking into account both purification efficiency and finished product moisture content control, thereby improving the recovery rate and purity of the final NMP product. The process in this application involves preheating and stirring before pretreatment to adjust the pH, reduce the viscosity of NMP cleaning waste, and improve flocculation and filtration efficiency. The process described in this application involves elution using a resin column before multi-stage distillation to further remove impurities from the filtrate, thereby improving the quality and stability of the final product. Detailed Implementation
[0020] The present application will be further described in detail below with reference to the embodiments.
[0021] All raw materials used in the examples were commercially available. The anionic polyacrylamide had the CAS number 9003-05-8; the macroporous adsorption resin was Amberlite™ XAD16HP; and the molecular sieve was Zeochem Z3-03(3A). Example
[0022] Example 1 Example 1 provides a recycling process for NMP-containing cleaning waste, comprising the following steps: Pretreatment: A 6% alum solution was added dropwise to the NMP cleaning waste at a rate of 1.0 L / min, while stirring at 350 rpm. After the addition was complete, a 0.2% anionic polyacrylamide solution was added dropwise, and the mixture was stirred at 180 rpm for 10 min. Flocculation and sedimentation were then carried out for 60 min, yielding a supernatant and filter residue. The alum solution comprised 3.1% of the NMP cleaning waste by weight, and the anionic polyacrylamide solution comprised 5% of the NMP cleaning waste by weight. Washing: The filter cake is washed using a filter press. The first wash uses 40°C water at a pressure of 0.3 MPa to rinse the filter cake, obtaining washing liquid A. Then, the filter cake is washed again using 40°C water at a pressure of 0.3 MPa until the NMP content in the washing liquid does not change significantly and the NMP concentration is below 0.2%. The washing liquid is then stopped, obtaining washing liquid B. Washing liquid A from the first wash is added to the filtrate tank, and washing liquid B is also added to the filtrate tank. The mass ratio of water used for the first wash to water used for the circulating wash is 400:600. Fine filtration: Add the supernatant to the filtrate tank, and perform fine filtration on the supernatant, washing solution A, and washing solution B in the filtrate tank, first at 1m... 3 A flow rate of / h passes through a 5-micron security filter, and then at 0.8m 3 The solution is passed through a 0.5-micron security filter at a flow rate of / h to complete fine filtration and obtain fine filtrate; Multi-stage distillation: The filtrate is first evaporated in a primary evaporator, then dehydrated in a secondary dehydration tower, and finally purified in a tertiary purification tower. If the water content of the resulting fraction is higher than 0.03%, it is filtered through a molecular sieve at a pressure of 0.1 MPa and a temperature of 30°C to ensure that the water content of the fraction is no higher than 0.03%, thus obtaining the NMP product. The primary evaporator operates at a temperature of 85°C, a vacuum of −0.085 MPa, and a residence time of 60 s. The secondary dehydration tower operates at a temperature of 95°C, a pressure of 30 kPa, and a reflux ratio of 1.0. The tertiary purification tower operates at a temperature of 110°C, a pressure of 10 kPa, and a reflux ratio of 2.0.
[0023] Example 2 The difference between Example 2 and Example 1 is the pretreatment: an 8% alum solution was added dropwise to the NMP cleaning waste at a rate of 1.0 L / min, while stirring at 350 rpm. After the addition was complete, a 0.2% anionic polyacrylamide solution was added dropwise, and the mixture was stirred at 180 rpm for 10 min. Subsequently, flocculation and sedimentation were carried out for 60 min to obtain the supernatant and filter residue. The alum solution accounted for 3.1% of the NMP cleaning waste by weight, and the anionic polyacrylamide solution accounted for 5% of the NMP cleaning waste by weight. The remaining steps were the same as in Example 1.
[0024] Example 3 The difference between Example 3 and Example 1 is the pretreatment: a 10% alum solution was added dropwise to the NMP cleaning waste at a rate of 1.0 L / min, while stirring at 350 rpm. After the addition was complete, a 0.2% anionic polyacrylamide solution was added dropwise, and the mixture was stirred at 180 rpm for 10 min. Subsequently, flocculation and sedimentation were carried out for 60 min to obtain the supernatant and filter residue. The alum solution accounted for 3.1% of the NMP cleaning waste by weight, and the anionic polyacrylamide solution accounted for 5% of the NMP cleaning waste by weight. The remaining steps were the same as in Example 1.
[0025] Example 4 The difference between Example 4 and Example 1 is the pretreatment: a 4% alum solution was added dropwise to the NMP cleaning waste at a rate of 1.0 L / min, while stirring at 350 rpm. After the addition was complete, a 0.2% anionic polyacrylamide solution was added dropwise, and the mixture was stirred at 180 rpm for 10 min. Subsequently, flocculation and sedimentation were carried out for 60 min to obtain the supernatant and filter residue. The alum solution accounted for 3.1% of the NMP cleaning waste by weight, and the anionic polyacrylamide solution accounted for 5% of the NMP cleaning waste by weight. The remaining steps were the same as in Example 1.
[0026] Example 5 Example 5 provides a recycling process for NMP-containing cleaning waste, comprising the following steps: Pretreatment: An 8% (w / w) alum solution was added dropwise to the NMP cleaning waste at a rate of 1.0 L / min, while stirring at 350 rpm. After the addition was complete, a 0.2% (w / w) anionic polyacrylamide solution was added dropwise, and the mixture was stirred at 180 rpm for 10 min. Flocculation and sedimentation were then carried out for 60 min, yielding a supernatant and filter residue. The alum solution comprised 3.1% of the NMP cleaning waste by weight, and the anionic polyacrylamide solution comprised 5% of the NMP cleaning waste by weight. Washing: The filter cake is washed using a filter press. The first wash uses 40°C water at a pressure of 0.3 MPa to rinse the filter cake, obtaining washing liquid A. Then, the filter cake is washed again using 40°C water at a pressure of 0.3 MPa until the NMP content in the washing liquid does not change significantly and the NMP concentration is below 0.2%. The washing liquid is then stopped, obtaining washing liquid B. Washing liquid A from the first wash is added to the filtrate tank, and washing liquid B is also added to the filtrate tank. The mass ratio of water used for the first wash to water used for the circulating wash is 400:600. Fine filtration: Add the supernatant to the filtrate tank, and perform fine filtration on the supernatant, washing solution A, and washing solution B in the filtrate tank, first at 1.5m... 3 A flow rate of / h passes through a 5-micron security filter, and then at 1.2m... 3 The solution is passed through a 0.5-micron security filter at a flow rate of / h to complete fine filtration and obtain fine filtrate; Multi-stage distillation: The filtrate is first evaporated in a primary evaporator, then dehydrated in a secondary dehydration tower, and finally purified in a tertiary purification tower. If the water content of the resulting fraction is higher than 0.03%, it is filtered through a molecular sieve at a pressure of 0.15 MPa and a temperature of 38°C to ensure that the water content of the fraction is no higher than 0.03%, thus obtaining the NMP product. The primary evaporator operates at a temperature of 90°C, a vacuum of −0.09 MPa, and a residence time of 60 s. The secondary dehydration tower operates at a temperature of 108°C, a pressure of 45 kPa, and a reflux ratio of 1.0. The tertiary purification tower operates at a temperature of 125°C, a pressure of 18 kPa, and a reflux ratio of 2.0.
[0027] Example 6 Example 6 provides a recycling process for NMP-containing cleaning waste, comprising the following steps: Pretreatment: An 8% (w / w) alum solution was added dropwise to the NMP cleaning waste at a rate of 1.0 L / min, while stirring at 350 rpm. After the addition was complete, a 0.2% (w / w) anionic polyacrylamide solution was added dropwise, and the mixture was stirred at 180 rpm for 10 min. Flocculation and sedimentation were then carried out for 60 min, yielding a supernatant and filter residue. The alum solution comprised 3.1% of the NMP cleaning waste by weight, and the anionic polyacrylamide solution comprised 5% of the NMP cleaning waste by weight. Washing: The filter cake is washed using a filter press. The first wash uses 40°C water at a pressure of 0.3 MPa to rinse the filter cake, obtaining washing liquid A. Then, the filter cake is washed again using 40°C water at a pressure of 0.3 MPa until the NMP content in the washing liquid does not change significantly and the NMP concentration is below 0.2%. The washing liquid is then stopped, obtaining washing liquid B. Washing liquid A from the first wash is added to the filtrate tank, and washing liquid B is also added to the filtrate tank. The mass ratio of water used for the first wash to water used for the circulating wash is 400:600. Fine filtration: Add the supernatant to the filtrate tank, and perform fine filtration on the supernatant, washing solution A, and washing solution B in the filtrate tank, first at 2m... 3 A flow rate of / h passes through a 5-micron security filter, and then at 1.5m... 3 The solution is passed through a 0.5-micron security filter at a flow rate of / h to complete fine filtration and obtain fine filtrate; Multi-stage distillation: The filtrate is first evaporated in a primary evaporator, then dehydrated in a secondary dehydration tower, and finally purified in a tertiary purification tower. If the water content of the resulting fraction is higher than 0.03%, it is filtered through a molecular sieve at a pressure of 0.2 MPa and a temperature of 45°C to ensure that the water content of the fraction is no higher than 0.03%, thus obtaining the NMP product. The primary evaporator operates at a temperature of 95°C, a vacuum of −0.095 MPa, and a residence time of 60 s. The secondary dehydration tower operates at a temperature of 120°C, a pressure of 60 kPa, and a reflux ratio of 1.0. The tertiary purification tower operates at a temperature of 140°C, a pressure of 25 kPa, and a reflux ratio of 2.0.
[0028] Example 7 Example 7 provides a recycling process for NMP-containing cleaning waste, comprising the following steps: Preheating and conditioning: Heat the NMP cleaning waste to 45°C and stir at 250 rpm for 10 min. Then adjust the pH to 6.5 using a 10% sodium hydroxide solution. Pretreatment: An 8% alum solution was added dropwise to the preheated and conditioned NMP cleaning waste at a rate of 1.0 L / min, while stirring at 350 rpm. After the addition was complete, a 0.2% anionic polyacrylamide solution was added dropwise, and the mixture was stirred at 180 rpm for 10 min. Flocculation and sedimentation were then carried out for 60 min, yielding a supernatant and filter residue. The alum solution comprised 3.1% of the NMP cleaning waste by weight, and the anionic polyacrylamide solution comprised 5% of the NMP cleaning waste by weight. Washing: The filter cake is washed using a filter press. The first wash uses 40°C water at a pressure of 0.3 MPa to rinse the filter cake, obtaining washing liquid A. Then, the filter cake is washed again using 40°C water at a pressure of 0.3 MPa until the NMP content in the washing liquid does not change significantly and the NMP concentration is below 0.2%. The washing liquid is then stopped, obtaining washing liquid B. Washing liquid A from the first wash is added to the filtrate tank, and washing liquid B is also added to the filtrate tank. The mass ratio of water used for the first wash to water used for the circulating wash is 400:600. Fine filtration: Add the supernatant to the filtrate tank, and perform fine filtration on the supernatant, washing solution A, and washing solution B in the filtrate tank, first at 1.5m... 3 A flow rate of / h passes through a 5-micron security filter, and then at 1.2m... 3 The solution is passed through a 0.5-micron security filter at a flow rate of / h to complete fine filtration and obtain fine filtrate; Multi-stage distillation: The filtrate is first evaporated in a primary evaporator, then dehydrated in a secondary dehydration tower, and finally purified in a tertiary purification tower. If the water content of the resulting fraction is higher than 0.03%, it is filtered through a molecular sieve at a pressure of 0.15 MPa and a temperature of 38°C to ensure that the water content of the fraction is no higher than 0.03%, thus obtaining the NMP product. The primary evaporator operates at a temperature of 90°C, a vacuum of −0.09 MPa, and a residence time of 60 s. The secondary dehydration tower operates at a temperature of 108°C, a pressure of 45 kPa, and a reflux ratio of 1.0. The tertiary purification tower operates at a temperature of 125°C, a pressure of 18 kPa, and a reflux ratio of 2.0.
[0029] Example 8 Example 8 provides a recycling process for NMP-containing cleaning waste, comprising the following steps: Preheating and conditioning: Heat the NMP cleaning waste to 45°C and stir at 250 rpm for 10 min. Then adjust the pH to 6.5 using a 10% sodium hydroxide solution. Pretreatment: An 8% alum solution was added dropwise to the preheated and conditioned NMP cleaning waste at a rate of 1.0 L / min, while stirring at 350 rpm. After the addition was complete, a 0.2% anionic polyacrylamide solution was added dropwise, and the mixture was stirred at 180 rpm for 10 min. Flocculation and sedimentation were then carried out for 60 min, yielding a supernatant and filter residue. The alum solution comprised 3.1% of the NMP cleaning waste by weight, and the anionic polyacrylamide solution comprised 5% of the NMP cleaning waste by weight. Washing: The filter cake is washed using a filter press. The first wash uses 40°C water at a pressure of 0.3 MPa to rinse the filter cake, obtaining washing liquid A. Then, the filter cake is washed again using 40°C water at a pressure of 0.3 MPa until the NMP content in the washing liquid does not change significantly and the NMP concentration is below 0.2%. The washing liquid is then stopped, obtaining washing liquid B. Washing liquid A from the first wash is added to the filtrate tank, and washing liquid B is also added to the filtrate tank. The mass ratio of water used for the first wash to water used for the circulating wash is 400:600. Fine filtration: Add the supernatant to the filtrate tank, and perform fine filtration on the supernatant, washing solution A, and washing solution B in the filtrate tank, first at 1.5m... 3 A flow rate of / h passes through a 5-micron security filter, and then at 1.2m... 3 The solution is passed through a 0.5-micron security filter at a flow rate of / h to complete fine filtration and obtain fine filtrate; Elution: The filtrate was eluted by passing it through a resin column packed with macroporous adsorption resin at a temperature of 40°C and a flow rate of 1.0 BV / h. Multi-stage distillation: The eluted filtrate is first evaporated in a primary evaporator, then dehydrated in a secondary dehydration tower, and finally purified in a tertiary purification tower. If the water content of the resulting fraction is higher than 0.03%, it is filtered through a molecular sieve at a pressure of 0.15 MPa and a temperature of 38°C to ensure that the water content of the fraction is no higher than 0.03%, thus obtaining the NMP product. The primary evaporator operates at a temperature of 90°C, a vacuum of −0.09 MPa, and a residence time of 60 s. The secondary dehydration tower operates at a temperature of 108°C, a pressure of 45 kPa, and a reflux ratio of 1.0. The tertiary purification tower operates at a temperature of 125°C, a pressure of 18 kPa, and a reflux ratio of 2.0. Comparative Example
[0030] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the filter cake is washed with water using a filter press. The first wash uses water at 40°C and a pressure of 0.3 MPa to rinse the filter cake, resulting in washing liquid A. Then, the filter cake is rinsed again with water at 40°C and a pressure of 0.3 MPa to obtain washing liquid B. The washing liquid A from the first wash is added to the filtrate tank, and the washing liquid B is also added to the filtrate tank. The mass ratio of the water used for the first wash to the water used for the second wash is 400:600. The remaining steps are the same as in Example 1. Performance testing experiment
[0031] Recovery rate: Recovery rate = (mass of NMP in the finished NMP product / mass of NMP in the waste) * 100%.
[0032] Purity: Purity = (Mass of NMP in the finished NMP product / Mass of the finished NMP product) * 100%.
[0033] Table 1 Performance test results of waste recycling
[0034] Combining Example 1 and Comparative Example 1, the recovery rate and purity of NMP in the recovery process of Example 1 are both high. It can be seen that by using the recovery process in this application, solid impurities are first efficiently agglomerated through a coagulant, and then the residual NMP in the filter residue is maximized through segmented water washing. Fine filtration eliminates the coarse steaming process. Finally, water is absorbed by multiple distillations and molecular sieves, which takes into account both purification efficiency and finished product moisture content control, achieving efficient and low-consumption recovery of NMP and improving the purity of the final NMP product.
[0035] Based on Examples 1-4, it can be seen that when using alum solution for flocculation and sedimentation, a mass concentration of alum solution below 6% will affect the flocculation and sedimentation effect, thereby affecting the recovery of NMP.
[0036] Combining Examples 2, 5, and 6, the recovery rate and purity of NMP were highest in the recovery process of Example 5, indicating that the recovery parameters in Example 5 were optimal.
[0037] Combining Examples 5 and 7, the NMP recovery rate in the recycling process of Example 7 is relatively high. This shows that by preheating and stirring the waste material before pretreatment, adjusting the pH, reducing the viscosity of the NMP cleaning waste material, and improving flocculation and filtration efficiency, the NMP recovery rate is improved.
[0038] Combining Examples 7 and 8, the recovery rate and purity of NMP in the recovery process of Example 8 are both high. It can be seen that before multi-stage distillation, elution with a resin column and further removal of impurities from the filtrate can improve the final recovery rate and purity of NMP.
[0039] 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 recycling process for NMP-containing cleaning waste, characterized in that: Includes the following steps: Pretreatment: Add flocculant to NMP cleaning waste, flocculate and settle to obtain supernatant and filter residue; Washing: Wash the filter residue with water. Add the washing liquid A from the first wash to the filtrate tank. Then, wash the filter residue with circulating water until the NMP content in the washing liquid does not change significantly. Add the resulting washing liquid B to the filtrate tank. Fine filtration: Add the supernatant to the filtrate tank, and perform fine filtration on the supernatant, washing liquid A, and washing liquid B in the filtrate tank to obtain fine filtrate; Multistage distillation: The filtrate is subjected to multistage distillation, and the resulting fraction is dehydrated by passing it through a molecular sieve to obtain the NMP product.
2. The recycling process for NMP-containing cleaning waste according to claim 1, characterized in that: The flocculant comprises an alum solution and an anionic polyacrylamide solution with a mass concentration of 6%-10%.
3. The recycling process for NMP-containing cleaning waste according to claim 2, characterized in that: The pretreatment steps are as follows: add alum solution dropwise to NMP cleaning waste while stirring. After the addition is complete, add anionic polyacrylamide solution dropwise, stir, and allow flocculation and sedimentation to obtain supernatant and filter residue.
4. The recycling process for NMP-containing cleaning waste according to claim 3, characterized in that: The pretreatment step includes a preheating adjustment step, in which the NMP cleaning waste is heated to 43-47°C and stirred at a speed of 200-300 rpm, and then the pH is adjusted to 6.2-6.8 using sodium hydroxide solution.
5. The recycling process for NMP-containing cleaning waste according to claim 1, characterized in that: In the washing step, a filter press is used for cleaning. The first washing uses 40°C water at a pressure of 0.3 MPa to rinse the filter residue, resulting in washing liquid A. The circulating water washing uses 40°C water at a pressure of 0.3 MPa to re-wash the filter residue until the NMP content in the washing liquid does not change significantly and the NMP concentration is below 0.2%. Then the circulating water washing is stopped, resulting in washing liquid B.
6. The recycling process for NMP-containing cleaning waste according to claim 1, characterized in that: In the fine filtration step, the fine filtration first involves using a 1-2m filter. 3 The flow rate passes through a 5-micron security filter at a rate of / h, and then at a speed of 0.8-1.5m. 3 A flow rate of / h passes through a 0.5-micron security filter to complete fine filtration.
7. The recycling process for NMP-containing cleaning waste according to claim 1, characterized in that: The multi-stage distillation step is preceded by an elution step, in which the filtrate is eluted by passing it through a resin column packed with macroporous adsorption resin at a temperature of 35-45°C.
8. The recycling process for NMP-containing cleaning waste according to claim 1, characterized in that: In the multi-stage distillation process, the filtrate is first evaporated in a primary evaporator, then dehydrated in a secondary dehydration tower, and finally purified in a tertiary purification tower.
9. The recycling process for NMP-containing cleaning waste according to claim 8, characterized in that: In the multi-stage distillation process, the temperature of the first-stage evaporator is 85-95℃ and the vacuum degree is −0.085-−0.095MPa; the temperature of the second-stage dehydration tower is 95-120℃ and the pressure is 30-60kPa; and the temperature of the third-stage purification tower is 110-140℃ and the pressure is 10-25kPa.
10. The recycling process for NMP-containing cleaning waste according to claim 8, characterized in that: In the multi-stage distillation process, when the fraction obtained after dehydration in the secondary dehydration tower is passed through a molecular sieve for water absorption, the pressure is 0.1-0.2 MPa and the temperature is 30-45℃, so that the water content of the fraction is not higher than 0.03%.