Preparation process of high-purity NMP (N-Methyl Pyrrolidone) based on ultra-microporous ceramic membrane

Abstract

The invention relates to the technical field of production and preparation of N-methyl pyrrolidone, in particular to a high-purity NMP (N-Methyl Pyrrolidone) preparation process based on an ultra-microporous ceramic membrane. The method overcomes the defects that NMP prepared by an existing high-purity NMP preparation process is high in water content and high in impurity metal ion content. The method comprises the following steps: introducing an N-methyl pyrrolidone raw material into a pretreatment unit, and carrying out filtration, gas treatment and negative pressure stabilization to obtain pretreated NMP; introducing the pretreated NMP into a filler rectification unit, and carrying out preheating and rectification treatment to obtain rectified NMP; the rectified NMP is introduced into a first-stage ultra-microporous ceramic membrane treatment unit to be treated, and then first-stage treated NMP is obtained; treating the primary treated NMP through a reduced pressure distillation unit to obtain distilled NMP; and finally, treating the distilled NMP by a secondary microporous ceramic membrane treatment unit to obtain high-purity NMP, wherein the highest purity of the finally obtained NMP is 99.6%.

Description

Technical Field

[0001] The invention relates to the technical field of production and preparation of N-methylpyrrolidone, in particular to a high-purity NMP preparation process based on an ultra-microporous ceramic membrane. Background Art

[0002] As an excellent organic solvent, N-methylpyrrolidone (NMP) has the characteristics of high solubility, low volatility, strong chemical stability, etc. It is miscible with water and a variety of organic solvents and plays a key role in many fields such as chemical industry, electronics, and medicine. In the electronics industry, it is used for photoresist stripping and electronic component cleaning, which can effectively remove impurities and ensure the performance of electronic products.

[0003] However, due to the limitations of the production process, industrial-grade NMP often contains low-boiling-point impurities such as ethanol, water, solid particles and high-boiling-point impurities. These impurities will seriously affect product quality and performance in the field of high-end electronic chip manufacturing where purity requirements are strict. Therefore, the demand for high-purity NMP is becoming more and more urgent.

[0004] At present, there are various methods for preparing high-purity NMP. The traditional multi-stage distillation method uses the difference in boiling points of different substances to separate impurities, but it consumes a lot of energy and has low efficiency. There are also processes that combine membrane separation technology with specific raw materials for synthesis, such as using ultra-microporous ceramic membranes for fine filtration. Although these processes are effective, there is still room for optimization in each process. Innovative solutions are urgently needed to further remove water molecules and impure metal ions in NMP raw materials, thereby improving the purity of NMP and meeting the needs of high-end industries.

[0005] Therefore, a high-purity NMP preparation process based on ultra-microporous ceramic membrane was proposed. Summary of the invention

[0006] The object of the present invention is to provide a high-purity NMP preparation process based on ultra-microporous ceramic membrane. The present invention is to pass N-methylpyrrolidone raw material into a pretreatment unit, filter, gas treatment, and obtain pretreated NMP after negative pressure stabilization; pass the pretreated NMP into a filler distillation unit, preheat and distill to obtain distilled NMP; pass the distilled NMP into a primary ultra-microporous ceramic membrane treatment unit for treatment to obtain primary treated NMP; the primary ultra-micropores are obtained by surface treatment, composite coating, and coating curing and strengthening of the primary ceramic membrane; the primary treated NMP is treated by a vacuum distillation unit to obtain distilled NMP; finally, the distilled NMP is treated by a secondary microporous ceramic membrane treatment unit to obtain high-purity NMP; the secondary ultra-microporous ceramic membrane is obtained by surface treatment, grafting modification, and cross-linking curing of the secondary ceramic membrane; the purity of the NMP finally obtained is up to 99.6%.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a high-purity NMP preparation process based on ultra-microporous ceramic membrane, and the specific steps include:

[0009] The N-methylpyrrolidone raw material is passed into the pretreatment unit, filtered, gas treated, and negative pressure stabilized to obtain pretreated NMP;

[0010] The pretreated NMP is passed into a packing distillation unit to obtain distilled NMP after preheating and distillation treatment;

[0011] The distilled NMP is passed through a primary ultra-microporous ceramic membrane treatment unit for treatment to obtain primary treated NMP;

[0012] The primary treated NMP is treated by a vacuum distillation unit to obtain distilled NMP;

[0013] The distilled NMP is treated by a two-stage microporous ceramic membrane treatment unit to obtain high-purity NMP.

[0014] Preferably, the operation method of the pretreatment unit is: methylamine gas is introduced into the N-methylpyrrolidone raw material through a pipeline, and stirring is performed continuously. The reaction time is 0.5h. After the reaction is completed, negative pressure is stabilized for 15min to obtain pretreated NMP.

[0015] Preferably, the packed distillation unit comprises a preheating unit and a packed distillation tower;

[0016] The operating conditions of the packing distillation unit are as follows: the pretreated NMP is first filtered through the fine filtering unit and then enters the preheating unit, where it is preheated to 80-120° C. to obtain a preheated liquid, which is then passed through a packing distillation tower for distillation to obtain distilled NMP.

[0017] Preferably, the operating conditions of the packed distillation tower are: tower top pressure 2-8 kPa, tower bottom temperature 140-160° C., and reflux ratio 6-10.

[0018] Preferably, the primary ultra-microporous ceramic membrane treatment unit comprises a primary ultra-microporous ceramic membrane;

[0019] The preparation method of the first-level ultra-microporous ceramic membrane is as follows: the first-level ceramic membrane is subjected to surface treatment, composite coating, and coating curing and strengthening to obtain the first-level ultra-microporous ceramic membrane;

[0020] The surface treatment method is as follows: firstly, the first-level ceramic membrane with a pore size of 100 nm is alkaline-washed in a sodium hydroxide solution for 1.5 hours, then rinsed with deionized water, and then pickled in a hydrochloric acid solution for 0.5 hours to obtain a surface-treated first-level ceramic membrane;

[0021] The composite coating method is as follows: immersing the surface treated primary ceramic membrane in a dopamine hydrochloride solution for 6-8 hours of oscillation immersion time, and then immersing it in a pretreated multi-walled carbon nanotube dispersion for a second oscillation immersion time of 3-4 hours to obtain a primary composite modified ceramic membrane;

[0022] The coating curing enhancement method is as follows: immersing the primary composite modified ceramic membrane in a 3-aminopropyltriethoxysilane solution for 1 hour, and then drying it under vacuum conditions for 1 hour to obtain a primary ultra-microporous ceramic membrane.

[0023] Preferably, the preparation method of the dopamine hydrochloride solution is: dissolving dopamine hydrochloride in a Tris-HCl buffer solution having a pH value of 8.5 to prepare a dopamine hydrochloride solution having a concentration of 2-4 g / L;

[0024] The preparation method of the pretreated multi-walled carbon nanotube dispersion is as follows: adding the multi-walled carbon nanotubes to a mixed solution of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:3 and treating them under ultrasound for 3 hours, then washing and drying to obtain the pretreated multi-walled carbon nanotubes; adding the pretreated multi-walled carbon nanotubes to anhydrous ethanol and ultrasonically dispersing them to obtain a pretreated multi-walled carbon nanotube dispersion with a concentration of 0.5-1g / L.

[0025] The preparation method of the 3-aminopropyltriethoxysilane solution is as follows: 3-aminopropyltriethoxysilane is dissolved in anhydrous ethanol to prepare a 3-aminopropyltriethoxysilane solution with a volume fraction of 3%.

[0026] Preferably, the vacuum distillation unit is a vacuum distillation tower; the operating conditions of the vacuum distillation tower are a vacuum distillation tower pressure of 20-40 kPa, a tower bottom temperature of 70-80°C, and a tower top temperature of 65-75°C.

[0027] Preferably, the secondary ultra-microporous ceramic membrane treatment unit comprises a secondary ultra-microporous ceramic membrane;

[0028] The preparation method of the secondary ultra-microporous ceramic membrane is as follows: the secondary ceramic membrane is subjected to surface treatment, grafting modification, and cross-linking and curing to obtain the secondary ultra-microporous ceramic membrane;

[0029] The surface treatment method is as follows: firstly wash the secondary ceramic membrane with a pore size of 50 nm in a sodium hydroxide solution for 1 hour, then rinse it with deionized water, and then wash it in a hydrochloric acid solution for 0.2 hours to obtain a surface-treated secondary ceramic membrane;

[0030] The grafting modification method is as follows: placing the surface treated secondary ceramic membrane into a composite modification solution, adding an initiator, and performing a grafting reaction at a temperature of 60° C. for 4-6 hours to obtain a secondary grafted ceramic membrane;

[0031] The cross-linking curing method is: after the grafting reaction time is completed, N, N'-methylenebisacrylamide is added to the composite modified solution, and the curing reaction is carried out at a curing temperature of 80°C for 1-2 hours; after the cross-linking curing reaction is completed, the secondary grafted ceramic membrane is cleaned and dried to obtain a secondary ultra-microporous ceramic membrane.

[0032] Preferably, the composite modified solution is prepared from a monomer mixture with a concentration of 8-12 g / L; the monomer mixture is a mixture of glycidyl methacrylate and disodium ethylenediaminetetraacetate in a mass ratio of 3:1;

[0033] The initiator is azobisisobutyronitrile.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. In the present invention, the N-methylpyrrolidone raw material is first treated by a pretreatment unit, and the gas treatment is carried out by methylamine, which can effectively remove the γ-butyrolactone impurity in the N-methylpyrrolidone raw material. By changing the aperture of the nozzle, the reaction is made more complete. After the reaction is completed, it is subjected to negative pressure treatment. On the one hand, it can replace the step of letting the methylamine escape automatically by standing, so that the tiny bubbles of methylamine gas in the N-methylpyrrolidone can escape as soon as possible, thereby maintaining the uniformity of the substances in the pretreatment liquid and facilitating subsequent treatment; on the other hand, it can prevent the residual methylamine in the pretreated NMP from being excessively aminated under the high temperature condition of the packing distillation unit, or from generating new impurities with other impurity components, thereby affecting the purity of the final NMP.

[0036] 2. In the present invention, a packing distillation operation process is adopted. On the one hand, the by-products generated when methylamine is introduced and the original heavy components in the raw materials can be removed, so as to reduce the pressure of the subsequent first-level ultra-microporous ceramic membrane unit and increase the service life of the first-level ultra-microporous ceramic membrane; at the same time, azeotropes of water molecules and NMP will be produced in the distillation stage. The distillation operation is set at the front end of the first-level ultra-microporous ceramic membrane, so that the azeotropes can be removed in the next stage.

[0037] 3. In the present invention, during the modification process of the primary ceramic membrane, the number of hydroxyl groups on the membrane surface increases after the surface cleaning treatment. Water molecules, as polar molecules, are easy to form hydrogen bonds with the hydroxyl groups on the membrane surface. The phenolic hydroxyl groups and amine groups in the introduced polydopamine molecules can also form hydrogen bonds with water molecules to further capture water molecules. The rich phenolic hydroxyl and amine functional groups of the polydopamine molecules can be tightly combined with the newly added hydroxyl groups on the membrane surface after acid washing and the original siloxane groups through hydrogen bonds, covalent bonds and other interactions, forming a uniform and highly adhesive polydopamine layer molecular filter on the membrane surface, filling the tiny pores on the membrane surface, adjusting the roughness of the membrane surface, and intercepting light component impurities, thereby improving the final NMP purity. At the same time, after the primary ceramic membrane is modified, the primary ultra-microporous ceramic membrane can be matched with a distillation unit to improve the service life of the primary ultra-microporous ceramic membrane.

[0038] 4. In the present invention, a secondary ultra-microporous ceramic membrane is used for filtration. During the preparation process of the secondary ultra-microporous ceramic membrane, the free radicals generated by the decomposition of the initiator azobisisobutyronitrile initiate the polymerization of the azobisisobutyronitrile monomer. The free radicals quickly capture the double bond electron cloud in the glycidyl methacrylate monomer molecule, converting the monomer into an active free radical. The active free radicals continuously add to each other to form a polymer chain. The active epoxy groups on these polymer chains can react with the active sites such as hydroxyl groups exposed after the pretreatment of the membrane surface to undergo nucleophilic addition reactions, firmly fixing the polymer chains on the membrane surface. The disodium ethylenediaminetetraacetic acid carried by the polymer chain grafted on the membrane surface has multiple carboxyl groups and amino groups coordinated around the central metal ion to form a stable chelate ring. When the vacuum distillate containing metal ions flows through the membrane surface, a stable chelate is formed by coordination bonds, thereby separating the metal ions from the solution and achieving efficient removal. At the same time, after the secondary ceramic membrane is modified, the secondary ultra-microporous ceramic membrane can be matched with a vacuum distillation unit to increase the service life of the secondary ultra-microporous ceramic membrane.

[0039] 5. In the present invention, by optimizing the reaction conditions of each reaction stage, the preparation time of high-purity NMP can be shortened, and the continuity and efficiency of the preparation can be greatly improved; the N-methylpyrrolidone raw material generally adopts industrial grade N-methylpyrrolidone, and the residual γ-butyrolactone in the N-methylpyrrolidone raw material can be effectively removed by the pretreatment unit, and at the same time, the pretreatment unit and the filler distillation unit can synergistically reduce the by-products of excessive amination; the water molecules in NMP are further removed by the filler distillation unit and the first-level ultra-microporous ceramic membrane treatment unit; by using reduced pressure distillation as a pre-process for the second-level ultra-microporous ceramic membrane, the filtration pressure of the second-level ultra-microporous ceramic membrane can be reduced, and the combination of the two can deeply remove the metal ions in NMP, and the sequential arrangement of the first-level ultra-microporous ceramic membrane unit and the second-level ultra-microporous ceramic membrane unit can gradually remove the water molecules and impurity metal ions in the NMP raw material. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a process flow chart of the preparation of high-purity NMP of the present invention. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] See also Figure 1 The present invention provides a high-purity NMP preparation process based on ultra-microporous ceramic membrane, and the technical scheme is as follows:

[0043] Figure 1 In the process, the N-methylpyrrolidone raw material is passed into a pretreatment unit, gas-treated with methylamine gas, and then negative pressure is stabilized for 5 minutes to obtain pretreated NMP; the pretreated NMP is passed into a packing distillation unit, first filtered by a fine treatment unit, then preheated by a preheating unit, and finally distilled by a packing distillation tower to obtain distilled NMP; the distilled NMP is passed into a primary ultra-microporous ceramic membrane treatment unit to obtain primary treated NMP; the primary treated NMP is treated by a vacuum distillation unit to obtain distilled NMP; the distilled NMP is treated by a secondary microporous ceramic membrane treatment unit to finally obtain the desired high-purity NMP.

[0044] Example 1

[0045] Preparation of primary ultra-microporous ceramic membrane:

[0046] First-level ultra-microporous ceramic membrane material: tubular membrane made of α-aluminum oxide, with a pore size of 100nm, an outer diameter of φ30mm, a length of 1016mm, a number of holes of 19, and an effective membrane area of ​​0.24m 2 、Flow rate 2000L / m 2 ·h, applicable pH=1-14, working pressure 0.3-0.6MPa, backwash pressure difference 0.1-0.3MPa.

[0047] First-stage ultra-microporous ceramic membrane modification:

[0048] Surface pretreatment: Alkaline washing uses 0.7mol / L sodium hydroxide solution, and the tubular ceramic membrane assembly is immersed in it, the temperature is controlled at 55℃, and the immersion time is 1.5-2h. After the alkali washing is completed, rinse with pure water until neutral for acid washing, and then immerse the ceramic membrane in 0.5mol / L hydrochloric acid solution at room temperature for 0.5h;

[0049] Introducing carbon nanotube-polydopamine composite coating:

[0050] Pretreatment of multi-walled carbon nanotubes: Take an appropriate amount of multi-walled carbon nanotubes with an average length of 5 nm, add them to a mixture of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:3, ultrasonically treat for 2 hours for acidification, then repeatedly rinse with a large amount of deionized water until neutral, and dry for use.

[0051] Preparation of polydopamine solution: Weigh an appropriate amount of dopamine hydrochloride, dissolve it in Tris-HCl buffer solution, pH 8.5, concentration 0.05 mol / L, to prepare a solution with a concentration of 3 g / L, and stir it magnetically until it is completely dissolved.

[0052] Preparation of composite coating: Immerse the pretreated tubular membrane in the above polydopamine solution at room temperature for 7 hours, and change the solution every 1 hour to evenly coat the membrane surface with a layer of polydopamine. Take out the membrane tube, rinse it with deionized water, and immediately immerse it in the pretreated multi-walled carbon nanotube dispersion. The multi-walled carbon nanotubes are ultrasonically dispersed with a small amount of anhydrous ethanol to a concentration of about 0.75g / L. Soak at room temperature for 3.5 hours, and finally rinse the membrane tube with deionized water and dry it in a 70℃ vacuum drying oven for 2 hours.

[0053] Introducing silane coupling agent to enhance adhesion layer:

[0054] Dissolve 3-aminopropyltriethoxysilane in anhydrous ethanol to prepare a solution with a concentration of 3%. After the tubular membrane treated in the previous two steps is cooled to room temperature, it is immersed in the 3-aminopropyltriethoxysilane solution for 30 minutes. During this period, the container is gently shaken to allow the membrane surface to fully contact the solution. After the immersion is completed, the membrane tube is removed with stainless steel tweezers, and vertically hung at 70°C for vacuum drying for about 1 hour. After the 3-aminopropyltriethoxysilane modification is completed, it is rinsed with deionized water and dried in a vacuum drying oven at 70°C for 1 hour to obtain a primary ultra-microporous ceramic membrane.

[0055] Preparation of secondary ultra-microporous ceramic membrane:

[0056] Secondary ultra-microporous ceramic membrane material: using dense multi-channel membrane, the membrane material is Al2O3, ZrO2, TiO2, the membrane pore size is 50nm, the outer diameter is φ40mm, the length is 1016mm, the number of channels is 37, and the effective membrane area is 0.449m 2 , Flux 1200L / m 2 ·h, applicable pH=1-14, working pressure 0.1-0.3MPa, backwash pressure difference 0.1-0.3MPa.

[0057] Surface preparation:

[0058] Alkali washing: Use 0.4 mol / L sodium hydroxide solution to soak the dense multi-channel ceramic membrane assembly in it, the temperature is controlled at 40°C, and the soaking time is 1 hour.

[0059] Acid washing: After alkaline washing, rinse the ceramic membrane with pure water until it is neutral, and then soak it in 0.3 mol / L hydrochloric acid solution at room temperature for 30 minutes.

[0060] Chelating functional group grafting modification:

[0061] Preparation of monomer solution: Mix glycidyl methacrylate monomer and disodium ethylenediaminetetraacetate monomer in a mass ratio of 3:1, dissolve in an appropriate amount of deionized water to prepare a solution with a concentration of 10 g / L, and then add initiator azobisisobutyronitrile in an amount of 0.6% of the total mass of the monomers.

[0062] Graft polymerization reaction: Place the pretreated ceramic membrane assembly into a closed reaction vessel with a stirring device, pour in the prepared monomer solution, pass nitrogen to remove the air in the container for 10 minutes, then heat the container to 60°C and react for 5 hours.

[0063] Cross-linking curing treatment:

[0064] Addition of cross-linking agent: After the grafting reaction is completed, add the cross-linking agent N,N'-methylenebisacrylamide to the reaction system in an amount of 0.3% of the total weight of the monomers.

[0065] Curing reaction: Raise the system temperature to 80°C and allow the curing reaction to proceed for 1.5 hours to allow the cross-linking reaction to proceed fully.

[0066] After the cross-linking and curing reaction is completed, the ceramic membrane assembly is taken out and rinsed with a large amount of pure water to remove the unreacted monomers, cross-linking agents and polymer fragments remaining on the surface, and then vacuum dried at 50°C for 4 hours to obtain a secondary ultra-microporous ceramic membrane.

[0067] Process steps:

[0068] Industrial grade N-methylpyrrolidone with a purity of 99% was preliminarily filtered through a fine filter with a pore size of 5 μm, and then introduced into the reactor. The temperature of the reactor was controlled at 35°C. Methylamine gas was continuously introduced into the industrial grade N-methylpyrrolidone through a pipeline at the bottom of the reactor at a flow rate of 5 L / min at a stirring rate of 150 rpm. The feed ratio was 3:1 according to the mass ratio of methylamine gas: industrial grade NMP, and the temperature was maintained for 1.5 hours. After the reaction was completed, negative pressure was evacuated in the reactor and the negative pressure was kept stable for 15 minutes to obtain pretreated NMP.

[0069] The pretreated NMP is passed into the preheater and preheated to 110°C. The preheated NMP liquid is passed into the packed distillation tower. The packed distillation tower: stainless steel θ ring packing is selected; a full condenser is set at the top of the tower, a shell and tube heat exchanger is used, and the cooling medium is cooling water; a reboiler is configured at the bottom of the tower, a thermosyphon reboiler is selected, and steam or heat transfer oil is used as the heating medium. The top pressure of the tower is controlled at 5kPa, the bottom temperature of the tower is maintained at 150°C, the reflux ratio is set to 8, and the NMP extracted from the top of the tower is the distilled NMP.

[0070] The distilled NMP product is passed through a primary ultra-microporous ceramic membrane, and the pressure difference is set to 0.6 MPa.

[0071] The primary treated NMP after the primary membrane treatment is sent to the vacuum distillation tower, and the pressure of the vacuum distillation tower is adjusted to 30 kPa, the bottom temperature is 75° C., and the top temperature is 70° C. The NMP extracted from the bottom of the tower is the distilled NMP.

[0072] The distilled NMP is finely processed through a secondary ultra-microporous ceramic membrane, the filtration pump is started, the liquid is pushed into the secondary ceramic membrane module, the pressure difference is set to 0.3MPa, and finally high-purity NMP is obtained.

[0073] Comparative Example 1

[0074] Referring to the parameters and conditions of Example 1, the pipeline only uses a single, small-aperture nozzle;

[0075] Comparative Example 2

[0076] Referring to the parameters and conditions of Example 1, the negative pressure stabilization step is arranged after the distillation unit, the distilled NMP is passed into the container for negative pressure stabilization first, and then the negative pressure stabilized NMP is passed into the primary ultra-microporous ceramic membrane treatment unit;

[0077] Comparative Example 3

[0078] Referring to the parameters and conditions of Example 1, no negative pressure stabilization is performed after the methylamine gas reaction is completed.

[0079] Experimental Example 1

[0080] In Example 1 and Comparative Example 1, pretreated NMP was used to test γ-butyrolactone. The test method adopted high performance liquid chromatography (HPLC). The sample was tested three times and the test results were averaged.

[0081] The test results of γ-butyrolactone are as follows: the industrial grade NMP raw material is 1259 ppm, the example 1 is 437 ppm, and the comparative example 1 is 746 ppm.

[0082] As can be seen from Example 1, introducing methylamine gas and evenly distributing the methylamine gas in the industrial-grade NMP raw material can remove most of the γ-butyrolactone in the raw material, which helps to reduce the pressure of subsequent processes and thereby improve the removal rate of light components.

[0083] The final high-purity NMP of Example 1 and Comparative Examples 2-3 was tested for parameters. The samples were taken for 3 tests and the test results were averaged. The results are shown in Table 1.

[0084] Table 1 Test results of Example 1 and Comparative Example 3

[0085]

[0086] Example 1 It can be seen from the combination of Comparative Examples 2-3 that negative pressure stabilization has a greater impact on the final NMP purification content, because methylamine has a strong nucleophilicity. If it is not completely removed, when the reaction conditions are slightly deviated, such as too high temperature, too long reaction time or too high local methylamine concentration, excessive amination reaction is likely to occur. The generated impurities are difficult to separate in subsequent purification steps such as membrane filtration and distillation, which will affect the purity of NMP. At the same time, the impurity components in industrial-grade raw materials are diverse, and trace aldehydes and ketone compounds are common. Methylamine reacts with these impurities in nucleophilic addition to generate complex compounds such as imines and enamines. These newly generated impurities are not only unstable in nature, but also prone to decomposition, polymerization and other reactions in subsequent process links, further polluting the system, and their physical and chemical properties such as boiling point and solubility are quite different from NMP, which brings great challenges to the subsequent purification process, especially the distillation separation link, and interferes with the effective separation of NMP and impurities. Arranging the negative pressure stabilization after the methylamine gas is processed can eliminate the remaining methylamine gas molecules as soon as possible and reduce the impact of subsequent temperature rise.

[0087] Examples 2-5 refer to the parameters and conditions of Example 1, only the operating parameters of the packed distillation unit are changed, the preheating temperature of the preheating unit, the top pressure of the packed distillation tower, and the specific parameter changes are shown in Table 2.

[0088] Table 2 Parameters and conditions of Examples 1-5

[0089] Example No. Preheating temperature / ℃ Reflux ratio Tower top pressure / kPa Tower temperature / ℃ Example 1 110 8 5 150 Example 2 90 6 2 140 Example 3 130 8 8 160 Example 4 130 10 8 160 Example 5 130 8 8 150

[0090] Comparative Example 4

[0091] Referring to the parameters and conditions of Example 5, the pretreated NMP was not preheated before entering the distillation column;

[0092] Comparative Example 5

[0093] Referring to the parameters and conditions of Example 5, the preheating temperature of the pretreated NMP when entering the distillation tower is 60°C;

[0094] Comparative Example 6

[0095] Under the parameter conditions of Example 5, the first-stage ultra-microporous ceramic membrane unit was operated continuously for 1 month;

[0096] Comparative Example 7

[0097] Referring to the parameters and conditions of Example 5, the pretreated NMP first enters the primary ultra-microporous ceramic membrane unit for treatment and then undergoes distillation treatment. The remaining process sequence remains unchanged and the process sequence is maintained for continuous operation for 1 month.

[0098] Experimental Example 2

[0099] The final high-purity NMP of Examples 1-5 and Comparative Examples 4-6 was tested for parameters. The samples were taken for 3 tests and the test results were averaged. The results are shown in Table 3.

[0100] Table 3 Test results of Examples 1-5 and Comparative Examples 4-7

[0101]

[0102]

[0103] When the packed distillation tower is operated under the parameter conditions of Example 5, the final NMP obtained has the highest purity, and the removal efficiency of water molecules, impurity metals, and impurity inorganic ions in the industrial-grade NMP raw materials is the best. However, in combination with Example 5 and Comparative Examples 4-5, if the preheating process in the process is removed, the purity of the final NMP will be greatly affected, because the temperature of the pretreated NMP is increased in the preheating stage, so that the 130°C pretreated NMP only needs a short time of heating after entering the packed tower, and the NMP and heavy components can begin to separate, which greatly improves the separation efficiency. At the same time, the preheating stage can also allow the NMP water molecules in the pretreatment liquid to evaporate in advance, preventing the water molecules from continuing to mix in the NMP system in a closed environment later; at the same time, if the preheating temperature is too low, the NMP separation efficiency is also too low, which will also affect the final NMP purity.

[0104] It can be seen from Comparative Examples 6 and 7 that when the distillation treatment unit is before the first-level ultra-microporous ceramic membrane unit, the process has basically no effect on the purity of NMP after running continuously for 1 month. When the distillation treatment unit is placed after the first-level ultra-microporous ceramic membrane, although the ultra-microporous ceramic membrane can intercept water molecules and heavy components, if the distillation unit is not used to remove the heavy components first, the heavy components will accumulate on the surface of the first-level ultra-microporous ceramic membrane in large quantities, causing the subsequent first-level ultra-microporous ceramic membrane to remove water molecules. The effect becomes worse, affecting the service life of the ceramic membrane, and at the same time, the distillation process will also produce azeotropes of water molecules and NMP at the back end, making it more difficult to remove water molecules, and ultimately affecting the purity of NMP.

[0105] In Examples 6-8, the parameters and conditions of Example 5 were referred to, and the oscillation immersion time, the secondary oscillation immersion time, the concentration of the dopamine hydrochloride solution, and the concentration of the pretreated multi-walled carbon nanotube dispersion were changed during the preparation of the primary ultra-microporous ceramic membrane.

[0106] Table 4 Parameter Conditions of Examples 6-8

[0107]

[0108] Comparative Example 8

[0109] Referring to the parameters and conditions of Example 8, the primary ceramic membrane was not modified;

[0110] Comparative Example 9

[0111] Referring to the parameters and conditions of Example 8, the primary ceramic membrane was not subjected to surface treatment during the modification process, and the primary ultra-microporous ceramic membrane unit without surface treatment was operated continuously for 3 months;

[0112] Comparative Example 10

[0113] Referring to the parameters and conditions of Example 8, the coating curing enhancement was not performed during the modification process of the primary ceramic membrane, and the primary ultra-microporous ceramic membrane unit without coating curing enhancement was operated continuously for 3 months;

[0114] Comparative Example 11

[0115] Referring to the parameters and conditions of Example 8, the primary ultra-microporous ceramic membrane was operated continuously for 3 months.

[0116] Experimental Example 3

[0117] The high-purity NMP finally prepared in Examples 6-8 and Comparative Examples 8-11 was tested, and the test results are shown in Table 5.

[0118] Table 5 Test results of Examples 6-8 and Comparative Examples 8-11

[0119]

[0120] Example 8 and Comparative Example 8 show that after the primary ceramic membrane is modified, the removal effect of the primary ultra-microporous ceramic membrane unit on water molecules can be greatly enhanced. After the surface cleaning treatment, the number of hydroxyl groups on the membrane surface increases, and the hydrophilicity is enhanced. As polar molecules, water molecules are easy to form hydrogen bonds with the hydroxyl groups on the membrane surface. The phenolic hydroxyl groups and amine groups in the introduced polydopamine molecules can also form hydrogen bonds with water molecules to further capture water molecules. Moreover, the composite coating makes the membrane surface rougher, increases the contact area, and provides more adsorption sites for water molecules. For azeotropes, although the composition is complex, the polar groups contained therein are attracted by the hydrophilic sites on the membrane surface and the composite coating. Azeotrope molecules move and collide in the solution. When they are close to the membrane, they are restricted by the microstructure of the membrane and are partially intercepted and adsorbed.

[0121] At the same time, polydopamine molecules contain abundant phenolic hydroxyl and amine functional groups. During the soaking process, these functional groups are tightly combined with the newly added hydroxyl groups and original siloxane groups on the membrane surface after acid washing through hydrogen bonds, covalent bonds and other interactions, forming a uniform and highly adhesive polydopamine layer on the membrane surface. This layer of polydopamine molecular filter fills some tiny pores on the membrane surface, adjusts the roughness of the membrane surface, can intercept light component impurities, and improve the final NMP purity.

[0122] Comparative Example 11, combined with Comparative Examples 9-10, shows that the coating curing enhancement during the preparation process of the primary ultra-microporous ceramic membrane greatly improves the service life of the ultra-microporous ceramic membrane. In the pickling step, the hydrogen ions in the hydrochloric acid react with the residual metal oxides on the surface of the membrane, dissolving some of the substances, and at the same time etching the membrane surface to form more aluminum hydroxyls. The amine group of the polydopamine molecule has a high reactivity and can undergo a dehydration condensation reaction with the aluminum hydroxyl group on the membrane surface to form a covalent bond that is stronger and more stable than a hydrogen bond. The amino group in the 3-aminopropyltriethoxysilane molecule can react chemically with the phenolic hydroxyl group and the amine group on the polydopamine coating. On the one hand, the amino group and the phenolic hydroxyl group can form a hydrogen bond to further strengthen the connection between the two; on the other hand, a condensation reaction can occur between the amino group and the amine group to form a new covalent bond. This double chemical bonding action tightly connects the silane layer and the polydopamine layer, strengthening the overall structure from the substrate to the polydopamine layer and then to the silane layer, ensuring that each layer is tightly bonded to the α-alumina substrate in all directions, and ensuring the stable operation of the ceramic membrane in the high-purity NMP preparation process.

[0123] Examples 9-13 refer to the parameters and conditions of Example 8, change the vacuum distillation tower pressure, tower bottom temperature, tower top temperature, modified secondary ultra-microporous ceramic membrane preparation process grafting reaction time, curing reaction time, composite modified solution concentration, the specific parameters are shown in Table 6.

[0124] Table 6 Parameter Conditions of Examples 9-13

[0125]

[0126] Comparative Example 12

[0127] Referring to the parameters and conditions of Example 13, the composite modified solution in the secondary ceramic membrane modification process was changed to using only glycidyl methacrylate to prepare the solution, and the other components and parameters remained unchanged;

[0128] Comparative Example 13

[0129] Referring to the parameters and conditions of Example 13, during the secondary ceramic membrane modification process, the composite modified solution was changed to use only disodium ethylenediaminetetraacetic acid to prepare the solution, and the other components and parameters remained unchanged;

[0130] Comparative Example 14

[0131] Referring to the parameters and conditions of Example 13, the vacuum distillation tower was removed as a process and the process was operated continuously for 2 months;

[0132] Comparative Example 15

[0133] According to the process conditions of Example 13, the process was run continuously for 2 months;

[0134] Comparative Example 16

[0135] Referring to the parameters and conditions of Example 13, only the order of the primary ultra-microporous ceramic membrane unit and the secondary ultra-microporous ceramic membrane unit was exchanged, and the other steps remained unchanged.

[0136] Experimental Example 4

[0137] The high-purity NMP finally prepared in Examples 9-13 and Comparative Examples 12-16 was tested, and the test results are shown in Table 7.

[0138] Table 7 Test results of Examples 9-13 and Comparative Examples 12-16

[0139]

[0140] It can be seen from Example 13 and Comparative Example 14 that reduced pressure distillation as a pre-process for the secondary ultraporous ceramic membrane can greatly improve the service life of the secondary ultraporous ceramic membrane. Since the secondary ultraporous ceramic membrane has a smaller pore size and is more prone to clogging, NMP needs to further process water molecules and some small molecules before entering the secondary ultraporous ceramic membrane unit.

[0141] Example 13 combined with Comparative Examples 12-13 shows the synergistic effect of glycidyl methacrylate and disodium ethylenediaminetetraacetate on the removal of metal ions and water molecules. The glycidyl methacrylate molecule contains carbon-carbon double bonds and epoxy groups. Under the action of the initiator, the carbon-carbon double bonds participate in free radical polymerization, so that glycidyl methacrylate forms a polymer chain attached to the membrane surface. The epoxy group can undergo a nucleophilic addition reaction with the pretreated hydroxyl group on the membrane surface, stabilizing the polymer chain on the membrane and introducing a large number of active sites on the membrane surface. Disodium ethylenediaminetetraacetate is a strong chelating agent with multiple carboxyl and amino groups. When synergistic with glycidyl methacrylate, the polymer chain formed by the grafting of glycidyl methacrylate provides abundant binding sites for disodium ethylenediaminetetraacetate, allowing it to be tightly fixed to the membrane surface through chemical bonds. When encountering metal ions, the central atom forms a stable chelate with the metal ion.

[0142] At the same time, after the grafting polymerization of glycidyl methacrylate, a large number of oxygen-containing functional groups are introduced to the membrane surface, such as the hydroxyl groups formed after the ring opening of the epoxy groups, which greatly increases the hydrophilicity of the membrane. From the perspective of intermolecular forces, water molecules, as polar molecules, easily form hydrogen bonds with the hydroxyl groups on the membrane surface, attracting water molecules to gather on the membrane surface, creating conditions for subsequent retention. The disodium ethylenediaminetetraacetic acid molecule itself contains hydrophilic groups, and the process of chelating metal ions is often accompanied by hydration reactions. When capturing metal ions, the surrounding water molecules participate in the coordination to form a hydration layer, further enhancing the interaction between the membrane surface and the water molecules. The two work together to enhance the removal effect of water molecules.

[0143] It can be seen from Comparative Examples 14 and 15 that the vacuum distillation tower as a pre-process for the secondary ultra-microporous ceramic membrane can remove light components and water molecules in the primary treated NMP, and can also be used as a pre-process for the secondary ultra-microporous ceramic membrane unit. N, N'-methylenebisacrylamide is used as a cross-linking agent, and its molecule contains two double bonds. After the graft polymerization reaction is completed, when the system temperature rises to 70-80°C, the double bonds of the N, N'-methylenebisacrylamide molecules are activated, and can undergo cross-linking reactions with the double bonds on the polymer chains grafted on the membrane surface, connecting many polymer chains together to build a three-dimensional network structure, thereby enhancing the durability of the ultra-microporous ceramic membrane. This three-dimensional network structure greatly enhances the stability of the modified layer on the surface of the ceramic membrane, so that the polymer coating on the membrane surface is no longer a loose, independent accumulation of molecular chains, but becomes a closely connected whole. Even under the influence of complex working conditions such as long-term solution scouring and pressure changes, the coating is not easy to displace or peel off, and is always firmly attached to the membrane substrate.

[0144] It can be seen from Example 13 combined with Comparative Example 16 that exchanging the processing order of the primary ultra-microporous ceramic membrane unit and the secondary ultra-microporous ceramic membrane unit has a great influence on the removal of water molecules and impure metal ions. Although more heavy components can be removed in the distillation unit, the secondary ultra-microporous ceramic membrane is not modified for the removal of water molecules. There will be water molecules and azeotropes formed by water molecules and NMP molecules that are difficult to remove in the secondary ultra-microporous ceramic membrane unit. At the same time, components such as impure metal ions are carried through the membrane, resulting in a simultaneous reduction in removal efficiency. Therefore, arranging the primary ultra-microporous ceramic membrane in the front is to gradually reduce the removal pressure of the impurity metal ions of the secondary ultra-microporous ceramic membrane, which can achieve better deep treatment.

[0145] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high-purity NMP preparation process based on ultra-microporous ceramic membrane, characterized in that: The specific steps include: The N-methylpyrrolidone raw material is passed into the pretreatment unit, and the pretreated NMP is obtained after preliminary filtration, gas treatment, and negative pressure stabilization; The pretreated NMP is passed into a distillation unit to obtain distilled NMP after preheating and distillation treatment; Passing the rectified NMP into a primary ultra-microporous ceramic membrane treatment unit for treatment to obtain primary treated NMP; The primary treated NMP is treated by a vacuum distillation unit to obtain distilled NMP; The distilled NMP is treated by a secondary microporous ceramic membrane treatment unit to obtain the high-purity NMP.

2. The process for preparing high-purity NMP based on ultra-microporous ceramic membrane according to claim 1, characterized in that: The pretreatment unit includes a primary filtration unit and a gas treatment unit; the N-methylpyrrolidone raw material is first filtered through a fine filter with a pore size of 5 μm in the primary filtration unit before entering the gas treatment unit; The gas treatment unit is operated as follows: methylamine gas is introduced into the N-methylpyrrolidone raw material through a pipeline, and the mixture is continuously stirred. The reaction time is 1.5 hours. After the reaction is completed, negative pressure is stabilized for 15 minutes to obtain the pretreated NMP.

3. The process for preparing high-purity NMP based on ultra-microporous ceramic membrane according to claim 1, characterized in that: The distillation unit includes a preheating unit and a packed distillation tower; The operating conditions of the packing distillation unit are: the pretreated NMP is passed into the preheating unit, preheated to 80-120° C. to obtain a preheated liquid, and the preheated liquid is passed into the packing distillation tower for distillation to obtain the distilled NMP.

4. The process for preparing high-purity NMP based on ultra-microporous ceramic membrane according to claim 3, characterized in that: The operating conditions of the packed distillation tower are: tower top pressure 2-8kPa, tower bottom temperature 140-160°C, and reflux ratio 6-10.

5. The process for preparing high-purity NMP based on ultra-microporous ceramic membrane according to claim 1, characterized in that: The first-level ultra-microporous ceramic membrane treatment unit includes a first-level ultra-microporous ceramic membrane; The preparation method of the first-level ultra-microporous ceramic membrane is as follows: the first-level ceramic membrane is subjected to surface treatment, composite coating, and coating curing and strengthening to obtain the first-level ultra-microporous ceramic membrane; The surface treatment method is as follows: firstly, a first-level ceramic membrane with a pore size of 100 nm is subjected to alkaline washing in a sodium hydroxide solution for 1.5 hours, then, it is rinsed with deionized water after alkaline washing, and then, it is subjected to acid washing in a hydrochloric acid solution for 0.5 hours, so as to obtain a first-level ceramic membrane with surface treatment; The composite coating method comprises: immersing the surface treated primary ceramic membrane in a dopamine hydrochloride solution for an oscillation immersion time of 6-8 hours, and then immersing it in a pretreated multi-walled carbon nanotube dispersion for a second oscillation immersion time of 3-4 hours to obtain a primary composite modified ceramic membrane; The coating curing enhancement method is: immersing the primary composite modified ceramic membrane in a 3-aminopropyltriethoxysilane solution for 1 hour, and then drying it under vacuum conditions for 1 hour to obtain the primary ultra-microporous ceramic membrane.

6. The process for preparing high-purity NMP based on ultra-microporous ceramic membrane according to claim 5, characterized in that: The preparation method of the dopamine hydrochloride solution is as follows: dissolving dopamine hydrochloride in a Tris-HCl buffer solution with a pH value of 8.5 to prepare the dopamine hydrochloride solution with a concentration of 2-4 g / L; The preparation method of the pretreated multi-walled carbon nanotube dispersion is as follows: multi-walled carbon nanotubes are added to a mixed solution of concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 1:3 and treated under ultrasound for 3 hours, and then washed and dried to obtain pretreated multi-walled carbon nanotubes; the pretreated multi-walled carbon nanotubes are added to anhydrous ethanol and ultrasonically dispersed to obtain the pretreated multi-walled carbon nanotube dispersion with a concentration of 0.5-1 g / L; The preparation method of the 3-aminopropyltriethoxysilane solution is as follows: 3-aminopropyltriethoxysilane is dissolved in anhydrous ethanol to prepare the 3-aminopropyltriethoxysilane solution with a volume fraction of 3%.

7. The process for preparing high-purity NMP based on ultra-microporous ceramic membrane according to claim 1, characterized in that: The vacuum distillation unit is a vacuum distillation tower; the operating conditions of the vacuum distillation tower are a vacuum distillation tower pressure of 20-40 kPa, a tower bottom temperature of 70-80°C, and a tower top temperature of 65-75°C.

8. The process for preparing high-purity NMP based on ultra-microporous ceramic membrane according to claim 1, characterized in that: The secondary ultra-microporous ceramic membrane treatment unit comprises a secondary ultra-microporous ceramic membrane; The preparation method of the secondary ultra-microporous ceramic membrane is as follows: surface treatment, grafting modification, and cross-linking and curing of the secondary ceramic membrane are performed to obtain the secondary ultra-microporous ceramic membrane; The surface treatment method is as follows: firstly, the secondary ceramic membrane with a pore size of 50 nm is alkali-washed in a sodium hydroxide solution for 1 hour, then rinsed with deionized water, and then pickled in a hydrochloric acid solution for 0.2 hours to obtain a surface-treated secondary ceramic membrane; The grafting modification method is as follows: placing the surface treated secondary ceramic membrane into a composite modification solution, adding an initiator, and performing a grafting reaction at a temperature of 60° C. for 4-6 hours to obtain a secondary grafted ceramic membrane; The cross-linking curing method is: after the grafting reaction time is completed, N, N'-methylenebisacrylamide is added to the composite modified solution, and the curing reaction is carried out at a curing temperature of 80°C for 1-2 hours; after the cross-linking curing reaction is completed, the secondary grafted ceramic membrane is cleaned and dried to obtain the secondary ultra-microporous ceramic membrane.

9. The process for preparing high-purity NMP based on ultra-microporous ceramic membrane according to claim 8, characterized in that: The composite modified solution is prepared from a monomer mixture with a concentration of 8-12 g / L; the monomer mixture is a mixture of glycidyl methacrylate and disodium ethylenediaminetetraacetate in a mass ratio of 3:1; The initiator is azobisisobutyronitrile.

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