A pretreatment system and method for N-methylpyrrolidone waste liquid

Abstract

The invention discloses a pretreatment system and method for N-methylpyrrolidone waste liquid, and its system includes NMP waste liquid storage tank, alkali liquid storage tank, microreactor and post-processing mechanism; the microreactor includes an outer wall tube, a membrane tube and an inner wall tube sequentially arranged from the outside to the inside, a dispersed phase cavity is formed between the outer wall tube and the membrane tube, and the membrane tube surface is provided with micropores, and a continuous phase cavity is formed between the membrane tube and the inner wall tube; the alkali liquid storage tank is connected to the dispersed phase cavity of the microreactor by the first conveying mechanism, and the NMP waste liquid storage tank is connected to the continuous phase cavity of the microreactor by the second conveying mechanism, and the outlet end of the microreactor is connected to the post-processing mechanism. The present invention can realize the rapid reaction and efficient filtering of acidic impurities in NMP waste liquid, and the reaction solution flowing out from the microreactor does not need to be put into the tank and is left to stand, and polymers and insoluble impurities can be directly filtered out, and the continuous production can be realized, and the NMP product yield is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical equipment, and in particular relates to a pretreatment system and method for N-methylpyrrolidone waste liquid. Background Art

[0002] N-Methylpyrrolidone (NMP) is an important organic solvent, which is widely used in the fields of chemical industry, medicine, electronics, etc. The new energy industry is developing rapidly. In the production of lithium batteries, NMP is used as a solvent to dissolve adhesive PVDF, positive electrode active materials, conductive agents and other substances, so that the adhesive is fully in contact with other substances and evenly distributed, and is also used to dilute the slurry. A large amount of NMP-containing waste liquid will be generated in the production process of lithium batteries. However, NMP will generate a large amount of waste liquid containing NMP and other impurities (acid, PVDF, etc.) during use. It is necessary to recycle the NMP waste liquid to create economic and social benefits and avoid environmental pollution. Therefore, the recycling and reuse of NMP is of great significance.

[0003] NMP waste liquid in the lithium battery industry is generally acidic, mainly composed of organic acids produced by NMP decomposition and conjugated polyene structure gel impurities produced by HF removal from PVDF ([1] Zhu Yalong. Analysis of NMP hydrolysis products and research on influencing factors [D]. Lanzhou University of Technology, 2017; [2] Li Yongkun, Shao Lidong, Yun Yu, et al. Color change reaction of PVDF membrane in alkaline DMSO [J]. Chemistry and Bioengineering, 2022, 39(02): 10-14; [3] Wu Yusong, Wu Xuqing, Liu Yifan, et al. Study on alkaline corrosion of polyvinylidene fluoride, a lithium battery binder [J]. Plastics Industry, 2021, 49(08): 100-104). NMP waste liquid contains ≤30% water, ≥70% NMP (mass fraction) and other trace impurities, and its pH value is 3.5~6.5. Therefore, neutralization reaction is a key step in NMP recovery pretreatment, which is crucial for controlling the pH value, purity and stability of the product. However, the traditional NMP neutralization reaction preparation method has problems such as long reaction time, low control accuracy, and unstable product quality.

[0004] Chinese patents CN110407729A, CN111675642A and CN116574044A disclose the necessity of neutralization reaction in NMP recovery, by adding a certain concentration of liquid alkali to the NMP waste liquid kettle tank for stirring intermittent reaction, wherein Chinese patents CN110407729A and CN111675642A add liquid alkali to the NMP waste liquid to be treated, adjust the pH value to about 10.5, fully stir for about 1 hour, and then put it into a raw material tank to wait for the next step of distillation treatment. The disclosed technology has a long reaction time, and the impurity removal is performed by static sedimentation in the material tank and is not continuous. At the same time, unreacted alkali and newly generated organic salt insolubles and polymer (conjugated polyolefin color impurities produced by PVDF deterioration) impurities easily enter the distillation system to cause coking and clogging of the device, etc., which are also factors causing unstable operation of the distillation system and unstable decolorization effect. Therefore, the known pretreatment method is a bottleneck process for the continuous distillation recovery process of NMP, and the problem of continuous and stable impurity removal needs to be solved urgently. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a pretreatment system and method for N-methylpyrrolidone waste liquid, which can achieve rapid reaction and efficient filtration of acidic impurities in NMP waste liquid, and the reaction liquid flowing out of the microreactor does not need to be placed in a tank for standing, and polymers and insoluble impurities can be directly filtered out, so that continuous production can be achieved and the yield of NMP products can be improved.

[0006] The present invention provides the following technical solutions:

[0007] In a first aspect, a pretreatment system for N-methylpyrrolidone waste liquid is provided, comprising an NMP waste liquid storage tank, an alkali liquid storage tank, a microreactor and a post-treatment mechanism;

[0008] The microreactor comprises an outer wall tube, a membrane tube and an inner wall tube arranged in sequence from the outside to the inside, a dispersed phase cavity is formed between the outer wall tube and the membrane tube, micropores are arranged on the surface of the membrane tube, and a continuous phase cavity is formed between the membrane tube and the inner wall tube;

[0009] The alkali solution storage tank is connected to the dispersed phase cavity of the microreactor through a first conveying mechanism, the NMP waste liquid storage tank is connected to the continuous phase cavity of the microreactor through a second conveying mechanism, and the outlet end of the microreactor is connected to a post-processing mechanism.

[0010] Furthermore, the outer wall tube is provided with a dispersed phase inlet, the two ends of the membrane tube are respectively provided with a mobile phase inlet and a reaction liquid outlet, and the two ends of the inner wall tube are respectively provided with a heat medium inlet and a heat medium outlet.

[0011] Furthermore, the outer wall tube material of the microreactor is 304 stainless steel or 316L stainless steel, preferably 316L stainless steel; the membrane tube material is one of 304 stainless steel, 316L stainless steel, and PTFE, preferably 316L stainless steel.

[0012] Furthermore, the diameter of the micropores on the surface of the membrane tube is 1-5 μm.

[0013] Furthermore, the microreactor heats the heat medium by controlling the temperature of the TCU.

[0014] Furthermore, a plurality of vortex baffles are provided between the membrane tube and the inner wall tube.

[0015] Vortex baffles can produce alternating vortices in the fluid, which can increase the contact area and turbulence between the fluid and the membrane surface, thereby promoting material transfer and heat exchange; vortex motion helps to mix between different fluid layers, allowing the reactants to reach molecular level contact more quickly, thereby accelerating the chemical reaction; in the membrane dispersion process, concentration polarization is a common problem, which will lead to a decrease in membrane flux. The use of vortex baffles can help reduce concentration polarization on the membrane surface and maintain a higher membrane flux; vortex motion can also help reduce the formation of deposits on the membrane surface, thereby delaying the membrane fouling process and extending the service life of the membrane; vortex baffles can improve the distribution of fluid in the membrane tube, reduce flow dead zones, and allow the fluid to pass through the membrane tube more evenly; vortex motion can help stabilize the flow state of the fluid, reduce flow velocity fluctuations and pressure fluctuations, and improve the stability of the entire reaction system.

[0016] Furthermore, the vortex baffle body is made of 304 stainless steel or 316L stainless steel, preferably 316L stainless steel.

[0017] Furthermore, the cross-sectional shape of the vortex baffle body is one of circular, square and triangular, preferably circular.

[0018] Furthermore, the first conveying mechanism includes a first filter connected to the alkali solution storage tank and a first feed pump connected to the first filter; the second conveying mechanism includes a second filter connected to the NMP waste liquid storage tank and a second feed pump connected to the second filter.

[0019] Furthermore, the shell material of the first filter and the second filter is 304 stainless steel or 316L stainless steel, preferably 316L stainless steel.

[0020] Furthermore, the post-processing mechanism includes a sand filter, a membrane filter, a buffer tank and a distillation mechanism connected in sequence, and the inlet end of the sand filter is connected to the outlet of the reaction liquid.

[0021] Furthermore, the number of the sand filters is at least 2 and they are arranged in parallel, and the sand filter material used in the sand filter is quartz sand with a particle size of 0.1-0.25 mm;

[0022] The number of the membrane filters is at least 2 and they are arranged in parallel. The pore size of the filter element membrane of the membrane filter is 0.1-5 μm, preferably 0.2-1 μm, and more preferably 0.5-1 μm.

[0023] Furthermore, the filter element material of the membrane filter is PTFE, and the skeleton material is PP.

[0024] In a second aspect, a method for pretreating N-methylpyrrolidone waste liquid is provided, using the pretreatment system for N-methylpyrrolidone waste liquid described in the first aspect, the method comprising the following steps:

[0025] The tetramethylammonium hydroxide aqueous solution in the alkali liquid storage tank is transported as a dispersed phase to the dispersed phase cavity of the microreactor through a first transport mechanism, and the NMP waste liquid in the NMP waste liquid storage tank is transported as a continuous phase to the continuous phase cavity of the microreactor through a second transport mechanism;

[0026] The tetramethylammonium hydroxide aqueous solution in the dispersed phase cavity enters the continuous phase cavity vertically through the micropores on the membrane tube and is dispersed in the NMP waste liquid;

[0027] By controlling the flow rates of the tetramethylammonium hydroxide aqueous solution and the NMP waste liquid, the reaction liquid at the outlet of the microreactor meets the preset pH value, and then is processed by a post-processing mechanism to obtain a finished NMP product.

[0028] Furthermore, the temperature of the tetramethylammonium hydroxide aqueous solution and the NMP waste liquid is controlled to be 15-35° C. before entering the microreactor.

[0029] Furthermore, the mass fraction of the tetramethylammonium hydroxide aqueous solution is 5% to 50%, preferably 8% to 40%, and more preferably 10% to 30%.

[0030] Further, the flow rate of the NMP waste liquid is 1 to 100 mL / min, preferably 10 to 50 mL / min, and more preferably 20 to 30 mL / min; the flow rate of the tetramethylammonium hydroxide aqueous solution is 0.001 to 1 mL / min, preferably 0.02 to 0.5 mL / min, and more preferably 0.03 to 0.3 mL / min.

[0031] Furthermore, the flow rate ratio of the NMP waste liquid to the tetramethylammonium hydroxide aqueous solution is 70-1000:1, preferably 100-500:1.

[0032] Furthermore, the preset pH value is 7-8.

[0033] Furthermore, the reaction temperature of the tetramethylammonium hydroxide aqueous solution and the NMP waste liquid is 10-60°C, preferably 15-40°C, and more preferably 15-35°C.

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

[0035] (1) The present invention adopts a microreactor as the main pretreatment site for NMP waste liquid, and uses alkali solution as the dispersed phase to be transported to the dispersed phase cavity of the microreactor through the first transport mechanism, and NMP waste liquid is transported to the continuous phase cavity of the microreactor as the continuous phase through the second transport mechanism. The alkali solution in the dispersed phase cavity enters the continuous phase cavity vertically through the micropores on the membrane tube and is dispersed in the NMP waste liquid. The dispersion uniformity is high, which is beneficial to improving the reaction conversion rate and shortening the reaction time, and realizes the rapid reaction and efficient filtration of acidic impurities in the NMP waste liquid, so that the time consumption of this process is shortened to less than 5 minutes. In addition, the reaction liquid flowing out of the microreactor does not need to be placed in a tank for standing, and can be directly filtered out of polymers and insoluble impurities by the post-treatment mechanism, thereby realizing continuous production, large NMP waste liquid treatment capacity, low energy consumption, and suitable for industrial production;

[0036] (2) The present invention uses an organic base tetramethylammonium hydroxide (TMAH) as the base used in the neutralization reaction. By combining with a microreactor, it can fully contact and react with the NMP waste liquid, further improving the production efficiency by more than 94% and the yield by about 2%. In addition, the present invention controls the flow rate of the tetramethylammonium hydroxide aqueous solution and the NMP waste liquid so that the reaction liquid at the outlet of the microreactor meets the preset pH value, and ensures the stability of NMP during the recovery process by stably adjusting and controlling the pH end point. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of a pretreatment system for N-methylpyrrolidone waste liquid in an embodiment of the present invention;

[0038] Figure 2 is a schematic structural diagram of a microreactor in an embodiment of the present invention;

[0039] Figure 3 Schematic diagram of the layered structure of the microreactor in an embodiment of the present invention;

[0040] Figure 4 Schematic diagram of the cross-sectional structure of a microreactor in an embodiment of the present invention;

[0041] Markings in the figure are: 1, microreactor; 2, first filter; 3, second filter; 4, first feed pump; 5, second feed pump; 6, first sand filter; 7, second sand filter; 8, first membrane filter; 9, second membrane filter; 10, buffer tank; 11, outer wall tube; 12, membrane tube; 13, inner wall tube; 14, vortex resistance body; 15, mobile phase inlet; 16, dispersed phase inlet; 17, reaction liquid outlet; 18, heat medium inlet; 19, heat medium outlet; 20, NMP waste liquid storage tank; 21, alkali liquid storage tank. DETAILED DESCRIPTION

[0042] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0043] Example 1

[0044] like Figure 1~Figure 4 As shown, this embodiment provides a pretreatment system for N-methylpyrrolidone waste liquid, including an NMP waste liquid storage tank 20, an alkali liquid storage tank 21, a microreactor 1 and a post-treatment mechanism.

[0045] The microreactor 1 comprises an outer wall tube 11, a membrane tube 12 and an inner wall tube 13 which are arranged in sequence from the outside to the inside. A dispersed phase cavity is formed between the outer wall tube 11 and the membrane tube 12. Micropores are provided on the surface of the membrane tube 12. The pore size of the micropores is 1-5 μm. A continuous phase cavity is formed between the membrane tube 12 and the inner wall tube 13 and a plurality of vortex baffle bodies 14 are provided. A dispersed phase inlet 16 is provided on the outer wall tube 11. A mobile phase inlet 15 and a reaction liquid outlet 17 are provided at both ends of the membrane tube 12. A heat medium inlet 18 and a heat medium outlet 19 are provided at both ends of the inner wall tube 13. The microreactor 1 heats the heat medium by temperature control through a TCU.

[0046] The outer wall tube 11 of the microreactor 1 is made of 304 stainless steel or 316L stainless steel, preferably 316L stainless steel; the membrane tube 12 is made of one of 304 stainless steel, 316L stainless steel, and PTFE, preferably 316L stainless steel. The vortex baffle body 14 is made of 304 stainless steel or 316L stainless steel, preferably 316L stainless steel. The cross-sectional shape of the vortex baffle body 14 is one of circular, square, and triangular, preferably circular. In this embodiment, the vortex baffle body 14 is cylindrical.

[0047] The alkali liquid storage tank 21 is connected to the dispersed phase cavity of the microreactor 1 through a first conveying mechanism, the NMP waste liquid storage tank 20 is connected to the continuous phase cavity of the microreactor 1 through a second conveying mechanism, and the outlet end of the microreactor 1 is connected to a post-processing mechanism.

[0048] Specifically, the first conveying mechanism includes a first filter 2 connected to the alkali liquid storage tank 21 and a first feed pump 4 connected to the first filter 2; the second conveying mechanism includes a second filter 3 connected to the NMP waste liquid storage tank 20 and a second feed pump 5 connected to the second filter 3. The shell material of the first filter 2 and the second filter 3 is 304 stainless steel or 316L stainless steel, preferably 316L stainless steel.

[0049] The post-processing mechanism comprises a sand filter, a membrane filter, a buffer tank 10 and a distillation mechanism which are connected in sequence, and the inlet end of the sand filter is connected to the reaction liquid outlet 17 .

[0050] Specifically, the number of sand filters is at least 2 and they are arranged in parallel. The sand filter material used by the sand filter is quartz sand with a particle size of 0.1~0.25mm. In this embodiment, the number of sand filters is 2, namely the first sand filter 6 and the second sand filter 7, which are used alternately.

[0051] Specifically, the number of membrane filters is at least 2 and they are arranged in parallel, and the filter element membrane pore size of the membrane filter is 0.1-5 μm, preferably 0.2-1 μm. The filter element material of the membrane filter is PTFE, and the skeleton material is PP. In this embodiment, the number of membrane filters is 2, namely the first membrane filter 8 and the second membrane filter 9, which are used alternately.

[0052] The distillation mechanism can adopt a distillation system with separation and purification functions in the prior art, which will not be described in detail here.

[0053] Example 2

[0054] (1) Equipment preparation:

[0055] The pretreatment system for N-methylpyrrolidone waste liquid provided in Example 1 is used, wherein the membrane tube material of the microreactor is 316L stainless steel, the pore size of the micropores on the surface of the membrane tube is 5 μm, the sand filter material used in the sand filter is high-purity quartz sand with a particle size of 0.1~0.25 mm, and the filter element membrane pore size of the membrane filter is 0.5 μm.

[0056] (2) Waste liquid treatment:

[0057] Prepare a 30% TMAH aqueous solution (T=15°C) in an alkali liquid storage tank, temporarily store the NMP waste liquid to be treated in the NMP waste liquid storage tank, and sample the NMP waste liquid to be treated (water content of about 15%, T=15°C), and measure GC99.51% (minus water), pH value of 4.11. Titrate the NMP waste liquid with the aforementioned TMAH aqueous solution to a pH value of 7.25, and calculate the amount of TMAH aqueous solution consumed per unit weight of NMP waste liquid to be 0.33%.

[0058] The TMAH aqueous solution was transported as the dispersed phase to the dispersed phase cavity of the microreactor through the first filter and the first feed pump at a flow rate of 0.05 mL / min; the NMP waste liquid was transported as the continuous phase to the continuous phase cavity of the microreactor through the second filter and the second feed pump at a flow rate of 15 mL / min. The reaction temperature was controlled by TCU, and the reaction was carried out at 15°C for 5 minutes. The reaction liquid flowed out of the microreactor after the reaction, and the pH value was measured by sampling to be 7.23. Subsequently, the impurities (polymers and insolubles, etc.) were filtered and removed through a sand filter and a membrane filter, and the product was continuously passed into a continuous distillation tower for subsequent distillation, separation and purification steps to obtain a high-purity NMP product with a yield of 98.6%. The GC was measured by sampling to be 99.91% and the pH value was 7.15.

[0059] Example 3

[0060] According to the method of Example 2, under the condition that the concentration of TMAH aqueous solution is 30%, the pretreatment reaction temperature is changed to 25°C. Specifically, a 30% TMAH aqueous solution is continuously injected into the dispersed phase cavity of the microreactor at a flow rate of 0.05 mL / min, and the above-mentioned NMP waste liquid is continuously injected into the mobile phase cavity at a flow rate of 15 mL / min. The reaction is carried out at 25°C for 3 minutes, and the pH value of the reaction liquid flowing out of the microreactor is sampled and detected to be 10.05. After adsorption filtration and rectification separation, the NMP finished product is finally obtained with a yield of 98.4%. The GC is 99.90% and the pH value is 7.21.

[0061] Example 4

[0062] According to the method of Example 2, the concentration of the TMAH aqueous solution was changed to 20%. At a temperature of 15° C., a 20% TMAH aqueous solution was continuously injected into the dispersed phase cavity of the microreactor at a flow rate of 0.08 mL / min, and the above-mentioned NMP waste liquid was continuously injected into the mobile phase cavity at a flow rate of 15 mL / min. The reaction was carried out at 15° C. for 3 min. The pH value of the reaction liquid flowing out of the microreactor was sampled and detected to be 10.05. After adsorption filtration and rectification separation, the NMP product was finally obtained with a yield of 98.6%. The GC was 99.91% and the pH value was 7.42.

[0063] Example 5

[0064] According to the method of Example 2, under the condition that the concentration of TMAH aqueous solution is 20%, the pretreatment reaction temperature is changed to 35°C, and a 20% TMAH aqueous solution is continuously injected into the dispersed phase cavity of the microreactor at a flow rate of 0.07 mL / min. The above-mentioned NMP waste liquid is continuously injected into the mobile phase cavity at a flow rate of 15 mL / min. The reaction is carried out at 35°C for 2 minutes. The pH value of the reaction liquid is sampled and detected to be 9.93. After adsorption filtration and rectification separation, the NMP finished product is finally obtained with a yield of 98.4%. The GC is 99.92% and the pH value is 7.32.

[0065] Example 6 (Microreactor-TMAH base)

[0066] According to the method of Example 2, under the conditions of pretreatment temperature of 25°C and TMAH aqueous solution concentration of 20%, a 20% TMAH aqueous solution was continuously injected into the dispersed phase cavity of the microreactor at a flow rate of 0.08 mL / min, and the above-mentioned NMP waste liquid was continuously injected into the mobile phase cavity at a flow rate of 15 mL / min. The reaction was carried out at 25°C for 3 minutes, and the pH value of the reaction solution was sampled and detected to be 10.05. After adsorption filtration and rectification separation, the final yield of NMP finished product was 98.3%, and the GC was sampled and measured to be 99.92% and the pH value was 7.39.

[0067] Comparative Example 1 (intermittent - inorganic alkali)

[0068] Add 2000mL of the above NMP waste liquid (effective content GC99.51%, water content about 15%) to a 5000mL beaker, add 7.03g of 20% sodium hydroxide aqueous solution, stir and react at 25℃ for 30min, sample and measure the pH value to be 9.40; continue to stir and react at this temperature for 1h and sample, pH value 9.31; continue to stir and react at this temperature for 1h and sample, pH value 8.92, continue to stir and react at this temperature for 1h and sample, pH value 8.77. Add the reaction liquid to the distillation tower for distillation separation to obtain NMP finished product, the yield is 95.4%, sample and measure GC99.89%, pH value 7.22.

[0069] Comparative Example 2 (Batch-TMAH Base)

[0070] Add 2000mL of the above NMP waste liquid (effective content GC99.51%, water content about 15%) to a 5000mL beaker, add 15.62g of 20% TMAH aqueous solution, stir and react at 25℃ for 10min, sample and measure pH value to be 8.52; continue stirring and reacting at this temperature for 1h, sample pH value to be 8.51; continue stirring and reacting at this temperature for 1h, sample pH value to be 8.52. Add the reaction liquid to the distillation tower for distillation separation to obtain NMP finished product, with a yield of 97.2%, sample and measure GC99.90%, pH value to be 7.30.

[0071] Comparative Example 3 (microreactor-inorganic base)

[0072] According to the method of Example 1, under the conditions of pretreatment temperature of 25°C and sodium hydroxide aqueous solution concentration of 20%, a 20% TMAH aqueous solution was continuously injected into the dispersed phase cavity of the microreactor at a flow rate of 0.04 mL / min, and the above-mentioned NMP waste liquid was continuously injected into the mobile phase cavity at a flow rate of 15 mL / min. The reaction was carried out at 25°C for 3 minutes, and the pH value of the reaction solution was sampled and detected to be 10.05. After adsorption filtration and rectification separation, the final NMP product yield was 98.0%, and the GC was sampled and measured to be 99.92% and the pH value was 7.25.

[0073] Performance comparison

[0074] (1) It can be seen from Examples 1 to 6 that the present invention uses a microreactor to continuously pretreat NMP waste liquid. The mass transfer efficiency of the microreactor is very high, and it is a continuous reaction, which can effectively shorten the process time, change intermittent production to continuous production, and improve production efficiency. At the same time, the present invention uses a microreactor and an organic base TMAH to react, and the reactants can be fully contacted, which is beneficial to improve the reaction conversion rate and shorten the reaction time, further improving the production efficiency.

[0075] (2) By comparing Example 6 with Comparative Example 1, it can be seen that the efficiency of continuous pretreatment of NMP waste liquid using a microreactor under organic base TMAH conditions is improved by more than 98% and the yield is increased by about 3.0% (95.4% in Comparative Example 1 → 98.3% in Example 6) compared with intermittent reaction under inorganic base conditions.

[0076] (3) By comparing Example 6 with Comparative Example 2, it can be seen that the efficiency of continuous pretreatment of NMP waste liquid using a microreactor under the organic base TMAH condition is improved by more than 98% and the yield is increased by about 1.1% (97.2% in Comparative Example 2 → 98.3% in Example 6) compared with the batch reaction under the organic base TMAH condition.

[0077] (4) By comparing Example 6 with Comparative Example 3, it can be seen that the yield of the NMP waste liquid continuously pretreated by a microreactor under the organic base TMAH condition is increased by about 0.3% (98.0% in Comparative Example 3 → 98.3% in Example 6) compared with the NMP waste liquid continuously pretreated by a microreactor under the inorganic base condition.

[0078] (5) From the comparison between Comparative Example 1 and Comparative Example 3, it can be seen that the efficiency of continuous pretreatment of NMP waste liquid using a microreactor under the condition of inorganic base NaOH is improved by more than 98% compared with the batch reaction under the condition of inorganic base NaOH, and the yield is increased by about 2.6% (95.4%→98%).

[0079] (6) From the comparison between Comparative Examples 1 and 2, it can be seen that the yield of pretreatment of NMP waste liquid by intermittent stirring reaction under organic base TMAH conditions is increased by about 1.8% (95.4% → 97.2%) compared with intermittent reaction under inorganic base conditions.

[0080] It should be noted that, in the description of the present invention, the directions or positional relationships indicated by terms such as "front", "rear", "left", "right", "up", "down", "inside" and "outside" are based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific direction. Therefore, they should not be understood as limitations on the present invention.

[0081] In the description of the present invention, it is to be understood that the terms "first", "second", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the feature. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0082] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A pretreatment system for N-methylpyrrolidone waste liquid, characterized in that: It includes NMP waste liquid storage tank, alkali liquid storage tank, microreactor and post-processing mechanism; The microreactor comprises an outer wall tube, a membrane tube and an inner wall tube which are sequentially arranged from the outside to the inside, a dispersed phase cavity is formed between the outer wall tube and the membrane tube, micropores are arranged on the surface of the membrane tube, a continuous phase cavity is formed between the membrane tube and the inner wall tube, and a plurality of vortex baffles are arranged between the membrane tube and the inner wall tube; a dispersed phase inlet is arranged on the outer wall tube, and a mobile phase inlet and a reaction liquid outlet are respectively arranged at both ends of the membrane tube; The alkali liquid storage tank is provided with a tetramethylammonium hydroxide aqueous solution as a dispersed phase, and the NMP waste liquid storage tank is provided with NMP waste liquid as a continuous phase; the alkali liquid storage tank is connected to the dispersed phase cavity of the microreactor through a first conveying mechanism, and the NMP waste liquid storage tank is connected to the continuous phase cavity of the microreactor through a second conveying mechanism; the tetramethylammonium hydroxide aqueous solution in the dispersed phase cavity enters the continuous phase cavity vertically through the micropores on the membrane tube and is dispersed in the NMP waste liquid; The outlet end of the microreactor is connected to a post-processing mechanism, which includes a sand filter, a membrane filter, a buffer tank and a distillation mechanism connected in sequence, and the inlet end of the sand filter is connected to the reaction liquid outlet.

2. The pretreatment system for N-methylpyrrolidone waste liquid according to claim 1, characterized in that: A heat medium inlet and a heat medium outlet are respectively arranged at two ends of the inner wall tube.

3. The pretreatment system for N-methylpyrrolidone waste liquid according to claim 2, characterized in that: The first conveying mechanism includes a first filter connected to the alkali solution storage tank and a first feed pump connected to the first filter; the second conveying mechanism includes a second filter connected to the NMP waste liquid storage tank and a second feed pump connected to the second filter.

4. The pretreatment system for N-methylpyrrolidone waste liquid according to claim 1, characterized in that: The pore size of the micropores on the surface of the membrane tube is 1-5 μm.

5. The pretreatment system for N-methylpyrrolidone waste liquid according to claim 1, characterized in that: The number of the sand filters is at least 2 and they are arranged in parallel, and the sand filter material used in the sand filter is quartz sand with a particle size of 0.1-0.25 mm; The number of the membrane filters is at least 2 and they are arranged in parallel, and the pore size of the filter element membrane of the membrane filter is 0.1-5 μm.

6. A method for pretreating N-methylpyrrolidone waste liquid, characterized in that: Using the pretreatment system for N-methylpyrrolidone waste liquid according to any one of claims 1 to 5, the method comprises the following steps: The tetramethylammonium hydroxide aqueous solution in the alkali liquid storage tank is transported as a dispersed phase to the dispersed phase cavity of the microreactor through a first transport mechanism, and the NMP waste liquid in the NMP waste liquid storage tank is transported as a continuous phase to the continuous phase cavity of the microreactor through a second transport mechanism; The tetramethylammonium hydroxide aqueous solution in the dispersed phase cavity enters the continuous phase cavity vertically through the micropores on the membrane tube and is dispersed in the NMP waste liquid; By controlling the flow rates of the tetramethylammonium hydroxide aqueous solution and the NMP waste liquid, the reaction liquid at the outlet of the microreactor meets the preset pH value, and then is processed by a post-processing mechanism to obtain a finished NMP product.

7. The method for pretreating N-methylpyrrolidone waste liquid according to claim 6, characterized in that: The mass fraction of the tetramethylammonium hydroxide aqueous solution is 5% to 50%.

8. The method for pretreating N-methylpyrrolidone waste liquid according to claim 6, characterized in that: The flow rate of the NMP waste liquid is 1-100 mL / min, the flow rate of the tetramethylammonium hydroxide aqueous solution is 0.001-1 mL / min, the flow rate ratio of the NMP waste liquid to the tetramethylammonium hydroxide aqueous solution is 70-1000:1; and the preset pH value is 7-8.

9. The method for pretreating N-methylpyrrolidone waste liquid according to claim 6, characterized in that: The reaction temperature of the tetramethylammonium hydroxide aqueous solution and the NMP waste liquid is 10-60°C.

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