Lithium battery NMP waste liquid rectification system and process

Abstract

The invention provides an NMP waste liquid rectification system and process for a lithium battery, and relates to the technical field of NMP waste liquid treatment. The rectification system comprises a dehydrating tower and a product tower which are connected in series, the dehydrating tower is connected with the raw material tank, a condenser 1 is arranged at the top of the dehydrating tower, a reboiler 1 is arranged at the bottom of the dehydrating tower, and the bottom of the dehydrating tower is connected with the product tower; a condenser 2 is connected to the top of the product tower, a reboiler 2 is arranged at the bottom of the product tower, a concentrator is connected to the bottom of the product tower, and a kettle residue discharge outlet is formed in the bottom of the concentrator; a condenser 3 is arranged at a side line extraction opening of the product tower and is connected with a finished product storage tank; and a plurality of layers of tower plates are arranged in the dehydrating tower and the product tower, and are filled with structured packing. The preparation process comprises the following steps: dehydrating and removing amine, extracting a main product from a side line, and recycling a high-boiling residue. According to the invention, double towers are used together, and the product is extracted from a side line and has high quality; and more heat sources are saved, the production cost is low, and operation is easy and safe.

Description

Technical Field

[0001] The present invention relates to the technical field of NMP waste liquid treatment, and particularly relates to a rectification system and process for NMP waste liquid used in lithium batteries. Background Art

[0002] N-Methyl-2-pyrrolidone (NMP) is an organic compound with the chemical formula C5H9NO, which is a colorless to light yellow transparent liquid. With the rapid development of the lithium battery industry, NMP is widely used as an additive for electrolytes or a solvent for positive and negative electrode materials of lithium batteries in the production of lithium batteries.

[0003] In the process of preparing lithium batteries, key processes such as coating and drying will generate NMP waste liquid solvent. Lithium battery enterprises need to recycle this kind of waste liquid to save costs and reduce environmental pollution. For the purified products, if they need to be supplied to battery manufacturing enterprises in a closed loop, in addition to conventional product indicators such as moisture, purity, and chromaticity, higher requirements are also put forward for free amines, particles, metals, etc.

[0004] The currently common and mainstream recovery processes in the industry are rectification and extraction processes, both of which require dehydration of the waste liquid first, and then rectification purification or extraction purification is selected.

[0005] The common extraction process in the industry requires the addition of an extraction agent during purification, and the extraction agent needs to be separated later. There is a risk of pollution caused by the introduction of the extraction agent in the product. At the same time, multiple rectification tower devices need to be used in series. Therefore, the construction investment cost and production cost are very high.

[0006] The most common process in the industry is the rectification process. Relying on fine process parameters and cooperating with a rectification tower, the rectification purification of NMP waste liquid can also be achieved. However, there are also relatively large disadvantages. Generally, a recycling factory will use 3 to 4 sets of rectification tower devices in series, with many process control points, complex operations, and high construction investment and production costs. There are also some recycling factories. Due to the selection of plate rectification towers, the operation control difficulty is large, and it is easy to cause problems such as flooding and tower surging, which affect product quality and production rate. Or although a packed tower is selected, the selection and filling method of the packing, the setting of operation parameters, etc. are unreasonable, resulting in some indicators of the purified product being unqualified, such as free amines, metals, particles, etc., or the production rate cannot meet the requirements. Summary of the Invention

[0007] The present invention provides a rectification system and process for NMP waste liquid used in lithium batteries. By using a dehydration tower and a product tower in series and adopting a process of side-line product extraction, the purified NMP is several times superior to the recycling standard of the lithium battery industry in terms of indicators such as free amines, moisture, and residual metal ions, meeting the ultra-pure requirements of high-end lithium battery production for NMP solvent.

[0008] A rectification system for NMP waste liquid used in lithium batteries, comprising a dehydration tower and a product tower arranged in series,

[0009] The dehydration tower is connected to a raw material tank. A condenser 1 is arranged at the top of the dehydration tower, a reboiler 1 is arranged at the bottom of the dehydration tower, and the bottom of the dehydration tower is connected to the product tower;

[0010] The top of the product tower is connected to a condenser 2, a reboiler 2 is arranged at the bottom of the product tower, the bottom of the product tower is connected to a concentrator, and a bottom residue discharge outlet is arranged at the bottom of the concentrator;

[0011] A condenser 3 is arranged at the side-line extraction outlet of the product tower, and the condenser 3 is connected to a finished product storage tank;

[0012] Multiple layers of trays are arranged inside both the dehydration tower and the product tower, and structured packings are filled. The structured packings are located above the trays.

[0013] The present invention adopts two towers in series (dehydration tower + product tower). Through functional division: dehydration and deamination → product purification, it replaces traditional multiple towers, reduces the number of equipment and operation nodes, and reduces the investment cost by more than 30%; the present invention sets side-line extraction, directly extracts high-purity NMP in the middle section of the product tower, avoiding the problem of entrainment of light and heavy components caused by traditional top or bottom extraction, and breakthroughly realizes ultra-high indexes of free amine < 5 ppm and metal < 5 ppb.

[0014] Conventional NMP distillation towers mostly adopt all packings (easy to block) or all trays (low efficiency), which are difficult to handle waste liquid containing metal particles and polymers, and cannot balance high separation efficiency and anti-blocking performance. The packing method inside the tower of the present invention adopts a segmented combination setting: dehydration tower: structured packing in the upper section, efficient dehydration and deamination, trays in the lower section, anti-blocking treatment of particulate materials; product tower: structured packing in the middle section, precise separation of NMP and light components, trays at the bottom to intercept high-boiling substances; aiming at the functional differences between the dehydration tower and the product tower, through the precise matching of the number of trays and the packing density, it breaks through the limitations of traditional single structures and solves the long-existing contradictions of efficiency - blockage - energy consumption in the industry.

[0015] The present invention combines two towers in series with side-line extraction for NMP waste liquid, and the removal rates of impurities such as free amine and metal are increased by 6 - 10 times, meeting the ultra-pure requirements of high-end lithium battery production for NMP solvent. Two towers in series reduce the equipment investment by 35% compared with the three-tower process, and the floor area is reduced by 40%; and through the optimization of the internal structure of the tower (structured packing + trays), the problems of high pressure drop and easy blockage in the two-tower process are solved. The combination of packing and trays reduces the blockage risk, and the cleaning cycle is extended by 3 times; the tray section effectively intercepts metal particles and polymers, and the continuous operation time of the system > 2000 hours (traditional process < 800 hours); the NMP recovery rate > 99.5%, the decomposition rate < 0.1%, and the emission of VOCs (volatile organic compounds) is reduced by more than 90%.

[0016] Furthermore, the number of trays in the dehydration column is 15 - 25, and the packing density of structured packing is 250 - 300 m 2 / m 3 .

[0017] The 15 - 25 trays are located at the bottom of the column, intercepting more than 90% of the particulate matter. The moisture removal rate in the packing section is > 99.5%, and the free amine removal rate is > 95%. The 15 - 25 trays reduce the reboiler heat load, the steam consumption is reduced by 15%, and the cleaning cycle is extended to 2000 hours. The medium - density packing of 200 - 300 m 2 / m 3 is located in the upper - middle section of the column. While avoiding blockage, it improves the mass transfer efficiency of moisture and amines. Compared with a fully - packed column, the column pressure is reduced by 30%, and the low - pressure - drop design in the packing section reduces the energy consumption of the vacuum pump by 20%.

[0018] Furthermore, the number of trays in the product column is 20 - 30, and the packing density of structured packing is 300 - 500 m 2 / m 3 .

[0019] The 20 - 30 trays are located at the bottom of the column to deal with the deposition of high - boiling substances (such as metal salts, polymers) and prevent the upward movement of high - boiling substances. The high - density packing of 250 - 350 m 2 / m 3 is located in the middle section of the column, accurately separating NMP from trace light components, achieving an NPM purity of > 99.99%, and the metal ions in the side - line product are < 5 ppb (traditional process > 50 ppb), meeting the requirements of lithium - battery - grade solvents; shortening the purification time and reducing the unit - output energy consumption by 25%.

[0020] Furthermore, a collection tank 1 is provided at the outlet of the condenser 1, and a collection tank 2 is provided at the outlet of the condenser 2; a pre - filter is provided between the dehydration column and the raw material tank, and a vacuum pump is provided between the dehydration column and the product column.

[0021] The condenser cools the rising steam into a liquid state, but there may be a small amount of un - condensed gas remaining (such as non - condensable gas or light components). The collection tank achieves a complete separation of gas - liquid two - phases by expanding the volume and reducing the flow rate. As a buffer container, the collection tank stores part of the condensate, adjusts the reflux ratio and the draw - off amount through liquid - level control; through the liquid - level sensor and the regulating valve, dynamically controls the reflux amount to ensure stable mass transfer in the column. The liquid - level sensor selects the UDX - 41 liquid - level regulator, and the regulating valve can be the ZZYP type self - acting regulating valve; buffers the feed fluctuations, avoids flooding or weeping in the column, and improves the anti - interference ability of the system.

[0022] Collection tank 1 (top of the dehydration tower): Separates condensed water, free amines (liquid phase) and residual gases (such as air, trace volatile organic compounds), preventing gas from carrying droplets into the vacuum system and protecting the vacuum pump. Collection tank 2 (top of the product tower): Isolates light components (such as residual water, trace amines) from non-condensable gases, preventing them from mixing into the side-line product or interfering with the system vacuum.

[0023] In addition, the collection tank temporarily stores the condensate for convenient periodic sampling analysis or continuous discharge.

[0024] Collection tank 1: Ensure that the temperature at the top of the dehydration tower is < 40°C to prevent light components (such as amines) from returning to the tower due to insufficient condensation, affecting the dehydration efficiency; collect the wastewater (containing a small amount of NMP and amines) at the top of the dehydration tower, monitor the water and amine content to ensure that the dehydration effect meets the standard. Collection tank 2: Temporarily store the light components (such as trace water and amines) at the top of the product tower, and discharge them from the system through the discharge valve to prevent the light components from accumulating at the top of the tower, avoiding their mixing into the side-line extraction outlet and causing the product indicators to exceed the standard, and preventing their accumulation from affecting the purity of the side-line product. The pre-filter is used to pre-filter the NMP waste liquid to remove suspended particles and metal debris.

[0025] A rectification process applicable to the NMP waste liquid rectification system for lithium batteries described above includes the following steps:

[0026] S100. Filter the NMP waste liquid through the pre-filter and then pump it into the dehydration tower for vacuum distillation. After heat exchange in the reboiler 1, the steam in the raw material enters the first condenser for condensation and reflux. The condensed wastewater enters the collection tank 1 and is taken out, and the tail gas is pumped out by the vacuum pump.

[0027] S200. Pump the material at the bottom of the dehydration tower into the product tower for vacuum distillation. After heat exchange in the second reboiler, the steam in the raw material enters the condenser 2 at the top of the product tower for condensation and reflux. The intermediate product enters the collection tank 2 and is taken out, and the tail gas is pumped out by the above-mentioned vacuum pump; the qualified product collected at the side-line extraction outlet of the product tower is condensed by the condenser 3 and stored in the finished product storage tank.

[0028] S300. The high-boiling substances at the bottom of the product tower enter the concentrator for secondary heating, the residual target components are recovered into the product tower for continuous vacuum distillation, and the kettle residue is discharged through the kettle residue discharge outlet.

[0029] Traditional NMP waste liquid recovery processes mostly adopt single-tower multi-stage separation or a three-tower process (dehydration tower, product tower, refining tower), and there are the following problems: Complex equipment: The series connection of multiple towers leads to high investment costs and many operation nodes; High energy consumption: Repeated heating and condensation increase the consumption of steam and cooling water; Purity bottleneck: The top / bottom extraction is prone to entrain light and heavy components, making it difficult to meet the ultra-high purity requirements of lithium battery grade NMP.

[0030] The present invention adopts a three-step integration process (S100→S200→S300): S100 dehydration and deamination: quickly remove moisture and free amine through vacuum distillation to avoid thermal decomposition of NMP; S200 side-line purification: extract high-purity NMP (free amine < 5 ppm) from the middle section of the product tower, breaking through the purity limitation of traditional top / bottom extraction; S300 high-boiling concentration: reheat the bottom residue to recover residual NMP, with the emission amount only 0.8 - 1.1%, reducing waste. The present invention connects the dehydration tower and the product tower in series, sharing the vacuum system, simplifying the equipment and reducing energy consumption; through the coordinated setting of temperature and vacuum degree, step-by-step purification is achieved; the two-tower series connection replaces the three-tower process, reducing equipment investment by 35% and floor area by 40%. In the distillation process of the present invention, side-line extraction avoids entrainment of light components at the top of the tower and heavy components at the bottom of the tower, and combines the packing-tray combined structure to achieve ultra-precise separation.

[0031] Further, in step S100, the temperature at the bottom of the dehydration tower is 100 - 130°C, the vacuum degree is selected to be 35 - 60 torr, the temperature at the top of the tower is 25 - 40°C, the temperature in the middle and upper sections of the tower is 90 - 120°C, and the reflux ratio at the top of the tower is controlled at 0.8 - 1.2:1.

[0032] Traditional dehydration towers often adopt single-temperature control, resulting in local overheating (NMP decomposition) or uneven mass transfer (incomplete dehydration) in the tower. The bottom temperature of the dehydration tower in the present invention is 100 - 130°C, ensuring that moisture and free amine are fully vaporized under vacuum conditions (35 - 60 torr); strictly lower than the starting temperature of NMP thermal decomposition to prevent the generation of by-products; the temperature in the middle and upper sections of the dehydration tower is 90 - 120°C: maintain the temperature in the gas-liquid mass transfer zone above the boiling point of light components to forcibly vaporize residual moisture and amines; avoid too high a temperature at the top of the tower (< 40°C) to prevent NMP condensation and reflux.

[0033] Conventional processes adopt a fixed vacuum degree, resulting in high energy consumption or insufficient separation efficiency. The vacuum degree in the present invention is set at 35 - 60 torr: avoid excessive pressure reduction (such as < 30 torr) leading to a sharp increase in equipment costs; ensure stable evaporation of NMP at the bottom temperature of 100 - 130°C, avoiding high-temperature decomposition; cooperate with temperature: when the vacuum degree is 60 torr, the bottom temperature needs to be ≥ 100°C to maintain evaporation; when the vacuum degree drops to 35 torr, the bottom temperature can drop to 110°C (still lower than the decomposition threshold).

[0034] Traditional processes adopt a fixed reflux ratio (such as 1:1) and cannot adapt to raw material fluctuations. The present invention sets the reflux ratio at 0.8 - 1.2:1: reduce reflux when the raw material moisture is low, reducing steam consumption; enhance reflux when the raw material moisture is high to ensure complete dehydration; adjust the reflux ratio in real time by online monitoring of the top components, with an error < 5%

[0035] The temperature, vacuum degree, and top - tower reflux ratio of the present invention act synergistically to significantly improve the dehydration efficiency: the water removal rate > 99.5%; the temperature gradient forces the vaporization of residual water, the vacuum degree reduces the boiling point, and the water content is reduced from 5% - 10% of the raw material to < 0.002%; the free amine removal rate > 95%; precisely controlling the bottom - tower temperature (100 - 130 °C) avoids the thermal decomposition of amines, and combining with a high reflux ratio (1.2:1) strengthens the separation. The NMP decomposition rate < 0.1%; the bottom - tower temperature is strictly limited to below 130 °C, and the vacuum degree avoids local overheating, and the NMP recovery rate > 99.5%. It effectively reduces the generation of by - products such as pyrrolidone and methylamine, and the product purity meets the lithium - battery - grade standard (free amine < 5 ppm); the steam consumption is reduced by 20%; the vacuum degree and temperature act synergistically to reduce the reboiler heat load, and the dynamic adjustment of the reflux ratio saves the condensation energy consumption; avoiding high - temperature and high - pressure conditions reduces coking and corrosion in the tower, and the maintenance period is extended to 2000 hours. In step S100, through the coordinated parameter settings of temperature gradient, vacuum matching, and reflux - ratio regulation, the industry problems of efficiency - energy consumption - stability in the NMP waste - liquid dehydration process are solved.

[0036] Further, in step S200, the bottom - tower temperature of the product tower is 110 - 135 °C, the vacuum degree is selected to be 25 - 50 torr, and the ratio of the top - tower reflux flow rate to the side - line product extraction flow rate is controlled at about 1.8 - 2.2:1.

[0037] In the traditional NMP distillation process, a single vacuum degree or a fixed temperature is often used in the product tower, resulting in: when the temperature is too high, the decomposition of NMP accelerates, generating by - products such as pyrrolidone; when the vacuum degree is insufficient, the temperature needs to be increased to maintain vaporization, increasing the risk of thermal damage.

[0038] The temperature range of the present invention is 110 - 135 °C: at a vacuum degree of 25 - 50 torr, it ensures that the boiling point of NMP (about 100 - 125 °C) is covered, achieving sufficient vaporization, strictly lower than the NMP thermal - decomposition threshold (150 °C), and combining with a short residence time (the concentrator < 30 minutes) to control the decomposition rate < 0.1%; the vacuum - degree range of the present invention is 25 - 50 torr: avoiding excessive pursuit of low pressure (such as < 20 torr) resulting in a sharp increase in the energy consumption of the vacuum pump; ensuring that NMP can still be effectively vaporized when the bottom - tower temperature ≤ 135 °C; the two act synergistically to achieve "low - temperature and high - efficiency separation".

[0039] The ratio of the top - tower reflux flow rate to the side - line product extraction flow rate of the present invention is 1.8 - 2.2:1: ensuring sufficient liquid - phase reflux to separate trace light components (such as water < 0.002%); avoiding energy - consumption waste caused by excessive condensation, and the decomposition rate is controllable (< 0.1%). According to the online - monitored purity of the side - line product (such as a water sensor and an amine detector), the reflux ratio is adjusted in real - time, with an error < 3%.

[0040] In step S200, the temperature-vacuum reflux ratio is linked: high vacuum (25 torr) + low temperature (120 °C): suitable for high-purity raw materials (moisture < 0.005%), reducing the decomposition risk; low vacuum (50 torr) + high temperature (135 °C): suitable for high-impurity raw materials (moisture > 0.01%), enhancing the separation driving force; the ratio of the overhead reflux flow to the side stream product withdrawal flow is dynamically matched: optimized synchronously when the temperature / vacuum is adjusted to maintain the separation efficiency.

[0041] Further, in step S200, the qualified product entering the finished product storage tank is processed through a filter and a filling system to obtain a high-purity product.

[0042] During distillation and storage and transportation, trace particulate matter may be introduced, such as metal particles generated by equipment wear, dust in pipelines, or salts precipitated by crystallization. The core objective of the filter is to intercept these particles to prevent them from affecting downstream applications, such as the uniformity in lithium battery coating. Although NMP itself has antibacterial properties, microorganisms or colloidal impurities may still be mixed in an open environment, and the filter can effectively retain such pollutants.

[0043] The filter can be a microfiltration filter, made of chemically resistant materials such as polypropylene (PP) and polytetrafluoroethylene (PTFE), with a pore size of 0.1 - 1 μm, intercepting tiny particles to ensure the clarity of the NMP liquid.

[0044] Reduce the particle (0.5 μm) content to < 10 particles / mL (required by the lithium battery industry); avoid particles causing coating defects or battery micro-shorts in subsequent processes.

[0045] Functions of the filling system:

[0046] Adsorb residual organic matter: Remove trace unevaporated free amines, aldehydes, or other organic impurities by filling adsorbents (such as activated carbon, molecular sieve); ion exchange to remove metals: Use ion exchange resin to selectively adsorb residual metal ions (such as Li+, Co 2+ ), ensuring that the metal content < 5 ppb; adjust product properties: Some filling systems may add desiccants (such as molecular sieve) to further reduce the moisture to < 0.002%.

[0047] Types of filling systems include:

[0048] Materials of the activated carbon adsorption column: coconut shell activated carbon, coal-based activated carbon; functions: adsorb free amines, pigments, trace VOCs; processing capacity: 1 kg of activated carbon can process 1 - 2 tons of NMP.

[0049] Ion exchange resin column: type: chelating resin (such as iminodiacetic acid type); functions: selectively adsorb Li+, Fe 3+Metal ions such as...; Regeneration method: Regenerate after pickling (e.g., with HCl).

[0050] Pore size of the molecular sieve drying column: (Only allows water molecules to pass through); Function: Deep dehydration to ensure water content < 0.001%.

[0051] The filling system can purify organic substances, further reducing the free amine content from < 5 ppm to < 1 ppm; it can deeply remove metal ions, optimizing the metal ion concentration from < 5 ppb to < 1 ppb; it can effectively control moisture, with the moisture content stably maintained at < 0.001%, avoiding the deterioration of the lithium battery electrolyte.

[0052] Rectification can remove most of the water and free amines, but has limited removal of nanoscale particles, trace metals, and some polar organic substances (such as aldehydes); physical filtration and chemical adsorption are used to make up for the deficiencies of distillation to achieve full-dimensional purification. The filters and filling system after the finished product storage tank are the "last line of defense" in the NMP high-purification process, controlling impurities from the ppm level to the ppb level to meet the ultra-pure requirements of lithium batteries, semiconductors, etc.; intercepting trace pollutants that cannot be removed by distillation to ensure the reliability of the end product; forming a complete technical chain with the front-end rectification to achieve the full-life cycle management of impurities.

[0053] Furthermore, in step S300, the heating temperature of the concentrator is 140 - 160 °C, the residence time of the bottom residue is 10 - 30 minutes, and the vacuum degree is controlled at 20 - 50 torr.

[0054] Under vacuum conditions (20 - 50 torr), the boiling point of NMP is reduced to about 100 - 130 °C. This temperature range ensures the full evaporation of the residual NMP while avoiding the decomposition risk caused by high temperature (> 160 °C) under normal pressure; the residence time of the bottom residue (10 - 30 minutes): Short-term high-temperature exposure (combined with vacuum) can not only recover NMP but also avoid long-term thermal damage; the 20 - 50 torr vacuum condition and temperature are synergistically controlled to achieve low-temperature and high-efficiency evaporation.

[0055] Step S300 solves the industry problem of difficult coexistence of high recovery rate and low decomposition rate in the NMP waste liquid concentration process through the three-dimensional coordinated control of temperature - vacuum degree - time. Double improvement in recovery rate and purity: NMP recovery rate > 98.5%, impurities < 5 ppm; Double reduction in energy consumption and cost: 30% energy saving, 40% reduction in maintenance cost; Double optimization of environmental protection and efficiency: 60% reduction in waste, 66% increase in production capacity.

[0056] Furthermore, in step S300, the bottom residue discharge amount is 0.95 - 1.05% of the system throughput.

[0057] The residue discharge of the conventional NMP recovery process is usually 1.5% - 3%. In this solution, the heating temperature of the concentrator is optimized to 140 - 160°C to fully evaporate the residual NMP and reduce the residue of the target components in the residue; the vacuum degree is 20 - 50 torr: reducing the actual heating temperature of NMP and inhibiting the generation of decomposition by-products; the residence time is 10 - 30 minutes to balance the evaporation efficiency and the risk of thermal damage, forming a process closed-loop, reducing the residue discharge to 0.95 - 1.05%, and reducing waste by 30% - 50%. Calculated based on an annual processing volume of 10,000 tons, the annual reduction of residue discharge is about 40 - 70 tons, saving about 200,000 - 350,000 yuan in hazardous waste treatment costs (calculated at a treatment fee of 5,000 yuan / ton).

[0058] The dehydration tower (S100) and the product tower (S200) efficiently remove moisture, amines, and metal ions, reducing the generation amount of high-boiling substances and reducing the residue treatment load at the source; the side-line extraction process: the extraction of high-purity NMP (moisture < 0.002%, metal < 5 ppb) reduces the entry of impurities into the concentrator and avoids residue pollution. The annual comprehensive cost is saved by about 2.5 - 3.5 million yuan (including waste treatment, raw material recovery, and maintenance costs); the reduction of hazardous waste is more than 40%, and the carbon emission is reduced by 15%; the equipment life is extended by 30%, and the production continuity is improved.

[0059] The vacuum degrees of the dehydration tower and the product tower are achieved by steam jet pumps or mechanical vacuum pumps.

[0060] Advantages of the Invention

[0061] In the present invention, the tandem connection of two towers and side-line extraction are combined for the purification of NMP waste liquid, so that the removal rates of impurities such as free amines, moisture, and metals in the NMP waste liquid are increased by 6 - 10 times compared with the conventional distillation process; in the NMP side-line extraction process of the present invention, the high-purity NMP section is accurately intercepted, avoiding the light components at the top of the tower and the heavy components at the bottom of the tower. In the distillation process of the present invention, the side-line extraction avoids the entrainment of light components at the top of the tower and heavy components at the bottom of the tower, and combines with the packing-tray combined structure to achieve ultra-precise separation. The product quality can reach: moisture < 0.002%, free amines < 5 ppm, metals < 5 ppb, particles (0.5 um) < 10, meeting the ultra-pure requirements of NMP solvents for high-end lithium battery production. Description of the Drawings

[0062] Figure 1 It is the device flow chart of the present invention;

[0063] Figure 2 It is the simple flow chart of the present invention. Detailed Embodiments

[0064] Example 1

[0065] As Figure 1As shown in the figure, a rectification system for NMP waste liquid used in lithium batteries includes a dehydration tower and a product tower arranged in series. The dehydration tower is connected to a raw material tank. A condenser 1 is provided at the top of the dehydration tower, and a reboiler 1 is provided at the bottom of the dehydration tower. The bottom of the dehydration tower is connected to the product tower through a vacuum pump. The top of the product tower is connected to a condenser 2, and a reboiler 2 is provided at the bottom of the product tower. The bottom of the product tower is connected to a concentrator, and a bottom residue discharge outlet is provided at the bottom of the concentrator. A condenser 3 is provided at the side line extraction outlet of the product tower, and the condenser 3 is connected to a finished product storage tank. Inside the dehydration tower and the product tower, there are multiple layers of trays and structured packings are filled. The structured packings are located above the trays and in the upper middle section of the tower.

[0066] The dehydration tower has 20 layers of trays, and the feeding position is on the 8th layer (from top to bottom). The structured packing is selected as metal perforated plate corrugated packing, and the packing density of the structured packing is 270 m 2 / m 3 .

[0067] The product tower has 25 layers of trays, and the feeding position is on the 12th layer (from top to bottom). The structured packing is selected as wire mesh corrugated packing, and the packing density of the structured packing is 400 m 2 / m 3 .

[0068] A collection tank 1 is provided at the outlet of the condenser 1, and a collection tank 2 is provided at the outlet of the second condenser. A pre-filter is provided between the dehydration tower and the raw material tank, and a vacuum pump is provided between the dehydration tower and the product tower.

[0069] The NMP wastewater in the raw material tank enters the dehydration tower after being filtered by the pre-filter, starts the bottom pump for self-circulation, and the reboiler 1 is input with steam heat source. The raw material and steam exchange heat in the reboiler 1. As the temperature rises, the water in the raw material is evaporated, continuously rises and then enters the condenser 1 to exchange heat with circulating water. The condensed wastewater is continuously concentrated and then extracted. The material at the bottom of the tower contains basically no water and most of the free amines are removed, and is pumped into the product tower for further rectification and purification.

[0070] After the material enters the product tower, start the bottom pump for self-circulation, and the reboiler 2 is input with steam heat source. The material and steam exchange heat in the reboiler 2. As the temperature rises, the product components are evaporated, continuously rise and then enter the condenser 2 to exchange heat with circulating water. The condensed target components are mixed with a small amount of water or light components and continuously reflux and concentrate. The qualified product is collected from the side line of the product tower, exchanges heat with circulating water through the condenser 3, and is pumped into the finished product storage tank after cooling.

[0071] The high-boiling substances at the bottom of the product tower enter the concentrator and are heated again by the steam heat source to recover the remaining target components, and the bottom residue after continuous concentration is discharged.

[0072] Example 2

[0073] A rectification system for NMP waste liquid used in lithium batteries, with the structure and connection relationship being the same as in Example 1. The number of trays in the dehydration tower is 15 layers, and the feeding position is on the 6th layer (from top to bottom). The structured packing is selected as metal perforated plate corrugated packing, and the packing density of the structured packing is 300 m 2 / m 3 。The number of trays in the product tower is 30 layers, and the feeding position is on the 14th layer (from top to bottom). The structured packing is selected as wire mesh corrugated packing, and the packing density of the structured packing is 500 m 2 / m 3 。

[0074] Example 3

[0075] A rectification system for NMP waste liquid used in lithium batteries, with the structure and connection relationship being the same as in Example 1. The number of trays in the dehydration tower is 25 layers, and the feeding position is on the 12th layer (from top to bottom). The structured packing is selected as metal perforated plate corrugated packing, and the packing density of the structured packing is 250 m 2 / m 3 。The number of trays in the product tower is 20 layers, and the feeding position is on the 8th layer (from top to bottom). The structured packing is selected as wire mesh corrugated packing, and the packing density of the structured packing is 300 m 2 / m 3 。

[0076] Example 4

[0077] As Figure 2 shown, a rectification process applicable to the rectification system for NMP waste liquid used in lithium batteries includes the following steps:

[0078] S100. Pump 1 ton of NMP waste liquid into the dehydration tower for vacuum distillation after filtering through a pre-filter. After heat exchange in the reboiler 1, the steam in the raw material enters the condenser 1 for condensation and reflux. The condensed wastewater enters the collection tank 1 and is taken out, and the tail gas is extracted by the vacuum pump; the temperature at the bottom of the dehydration tower is 110 °C, the vacuum degree is selected as 50 torr, the temperature at the top of the tower is 32 °C, the temperature in the middle and upper sections of the tower is 105 °C, and the reflux ratio at the top of the tower is controlled at 1:1; the temperature of the circulating condensed water is 30 °C.

[0079] S200. Pump the material at the bottom of the dehydration tower into the product tower for vacuum distillation. After heat exchange in the reboiler 2, the steam in the raw material enters the condenser 2 at the top of the product tower for condensation and reflux. The intermediate product enters the collection tank 2 and is taken out, and the tail gas is extracted by the above-mentioned vacuum pump; the qualified product collected at the side line extraction port of the product tower is condensed by the condenser 3 and stored in the finished product storage tank; the temperature at the bottom of the product tower is 120 °C, the vacuum degree is selected as 38 torr, the ratio of the reflux flow at the top of the tower to the extraction flow of the side line product is 2:1, and the temperature of the circulating condensed water is 5 °C.

[0080] The high-boiling substances at the bottom of the product column of the S300 enter the concentrator for secondary heating, and the residual target components are recycled into the product column for continued vacuum distillation. The still residue is discharged through the still residue discharge outlet; the heating temperature of the concentrator is 150 °C, the residence time of the still residue is 20 minutes, and the vacuum degree is controlled at 35 torr; the discharge amount of the still residue is 1% of the system processing capacity.

[0081] The rectification systems of Examples 1-3 were respectively applied, and the rectification process of Example 4 was used to purify the NMP wastewater. The parameter data of the obtained NMP solution are shown in Table 1, item numbers 1-4, 2-4, and 3-4 respectively.

[0082] Table 1 Parameter data of the purified NMP solution obtained by applying the rectification systems of Examples 1-3 and the rectification process of Example 4

[0083] Group Moisture Residue (%) Metal Ions (ppb) Free Amine (ppm) Particles (0.5μm, number / mL) Product Purity (%) 1-4 0.0009 1.2 2.5 3 99.9 2-4 0.0012 3 2.1 7 99.8 3-4 0.0015 1.8 4 5 99.9

[0084] As shown in Table 1, in item 1-4, after using the rectification system of Example 1 and the rectification process of Example 4 to purify the NMP wastewater, the NMP solution obtained in the finished product storage tank has a water content of 0.0009%, a metal ion content of 1.2 ppb, a free amine content of 2.5 ppm, and 3 particles with a particle size ≥ 0.5 μm per milliliter of NMP. In item 2-4, after using the rectification system of Example 2 and the rectification process of Example 4 to purify the NMP wastewater, the NMP obtained in the finished product storage tank has a water content of 0.0012%, a metal ion content of 3 ppb, a free amine content of 2.1 ppm, and 7 particles with a particle size ≥ 0.5 μm per milliliter of NMP. In item 3-4, after using the rectification system of Example 3 and the rectification process of Example 4 to purify the NMP wastewater, the NMP solution obtained in the finished product storage tank has a water content of 0.0015%, a metal ion content of 1.8 ppb, a free amine content of 4 ppm, and 5 particles with a particle size ≥ 0.5 μm per milliliter of NMP; the product purity can reach 99.9%.

[0085] It can be seen from the data in Table 1 that after using the rectification system of Example 1 and the rectification process of Example 4 to purify the NMP wastewater, the NMP solution obtained in the finished product storage tank has the highest purity.

[0086] Example 5

[0087] A rectification process, applying the NMP waste liquid rectification system for lithium batteries of Example 1, includes the following steps:

[0088] S100. Filter 1 ton of NMP waste liquid through a pre-filter and then pump it into a dehydration tower for vacuum distillation. After heat exchange in reboiler 1, the steam in the raw material enters condenser 1 for condensation and reflux. The condensed wastewater enters collection tank 1 and is drawn out. The tail gas is drawn out by a vacuum pump. The temperature at the bottom of the dehydration tower is 100°C, the vacuum degree is selected as 35 torr, the temperature at the top of the tower is 25°C, the temperature in the middle and upper parts of the tower is 90°C, the reflux ratio at the top of the tower is controlled at 0.8:1, and the temperature of the circulating condensed water is 25°C.

[0089] S200. Pump the material at the bottom of the dehydration tower into a product tower for vacuum distillation. After heat exchange in reboiler 2, the steam in the raw material enters the second condenser at the top of the product tower for condensation and reflux. The intermediate product enters collection tank 2 and is drawn out. The tail gas is drawn out by the above-mentioned vacuum pump. The qualified product collected at the side draw outlet of the product tower is condensed by condenser 3 and then stored in the finished product storage tank. The temperature at the bottom of the product tower is 110°C, the vacuum degree is selected as 25 torr, the ratio of the reflux flow at the top of the tower to the side product draw flow is 1.8:1, and the temperature of the circulating condensed water is 8°C.

[0090] S300. The high-boiling substances at the bottom of the product tower enter a concentrator for secondary heating. The residual target components are recovered into the product tower for continued vacuum distillation. The kettle residue is discharged through the kettle residue discharge outlet. The heating temperature of the concentrator is 14°C, the residence time of the kettle residue is 10 minutes, and the vacuum degree is controlled at 20 torr. The discharge amount of the kettle residue is 0.95% of the system processing capacity.

[0091] Example 6

[0092] A rectification process, applying the NMP waste liquid rectification system for lithium batteries in Example 1, includes the following steps:

[0093] S100. Filter 1 ton of NMP waste liquid through a pre-filter and then pump it into a dehydration tower for vacuum distillation. After heat exchange in reboiler 1, the steam in the raw material enters condenser 1 for condensation and reflux. The condensed wastewater enters collection tank 1 and is drawn out. The tail gas is drawn out by a vacuum pump. The temperature at the bottom of the dehydration tower is 130°C, the vacuum degree is selected as 60 torr, the temperature at the top of the tower is 40°C, the temperature in the middle and upper parts of the tower is 120°C, the reflux ratio at the top of the tower is controlled at 1.2:1, and the temperature of the circulating condensed water is 35°C.

[0094] S200. Pump the material at the bottom of the dehydration tower into a product tower for vacuum distillation. After heat exchange in reboiler 2, the steam in the raw material enters the second condenser at the top of the product tower for condensation and reflux. The intermediate product enters collection tank 2 and is drawn out. The tail gas is drawn out by the above-mentioned vacuum pump. The qualified product collected at the side draw outlet of the product tower is condensed by condenser 3 and then stored in the finished product storage tank. The temperature at the bottom of the product tower is 135°C, the vacuum degree is selected as 50 torr, the ratio of the reflux flow at the top of the tower to the side product draw flow is 2.2:1, and the temperature of the circulating condensed water is 10°C.

[0095]

[0095] The high-boiling substances at the bottom of the product tower enter the concentrator for secondary heating, and the residual target components are recycled into the product tower for continued vacuum distillation. The still residue is discharged through the still residue discharge outlet; the heating temperature of the concentrator is 160 °C, the residence time of the still residue is 30 minutes, and the vacuum degree is controlled at 50 torr; the discharge amount of the still residue is 1.05% of the system throughput.

[0096] Comparative Example 1

[0097]

[0097] The distillation system: A three-tower series arrangement of a dehydration tower, a product tower, and a refining tower is adopted: The dehydration tower uses valve trays with 30 trays, and the feed position is the 18th tray from top to bottom. A falling-film reboiler is provided at the bottom of the tower; the product tower uses sieve trays with 45 feed trays, and the position is the 26th tray from top to bottom. A thermosyphon reboiler is provided at the bottom of the tower; the refining tower uses bubble-cap trays with 10 trays, and the position is the 9th tray from top to bottom. A thermosyphon reboiler is provided at the bottom of the tower; The three towers share a steam jet pump set; A liquid level sensor (UDX-41 type) + a pneumatic control valve (ZJHP type) are used to achieve automatic control of the reflux ratio.

[0098] The product extraction method is top extraction.

[0099] The distillation process includes the following steps:

[0100] 1. Raw material pretreatment: Suspended particles and metal debris are removed through an 8 μm filter; Dilute sulfuric acid is added to adjust the pH to 6.5 to neutralize free amine substances.

[0101] 2. Top extraction of light components: 1 ton of pretreated NMP waste liquid is pumped into the dehydration tower for vacuum distillation. The vacuum degree at the top of the tower is 70 torr, the temperature at the top of the tower is 45 °C, and the temperature at the bottom of the tower is 120 °C; After heat exchange through the falling-film reboiler, the steam in the raw material enters the top condenser for condensation and reflux, and the temperature of the circulating condensed water is 40 °C; The reflux ratio is controlled at 1.8:1, and the condensed light components (water, dimethylamine, etc.) are discharged after condensation by the condenser.

[0102] 3. Top extraction of the main product: The dehydrated NMP in step 1 is pumped into the product tower for vacuum distillation. The vacuum degree at the top of the tower is 40 torr; The temperature at the top of the tower is 95 °C, and the temperature at the bottom of the tower is 135 °C; After heat exchange through the thermosyphon reboiler, the steam in the raw material enters the top condenser for condensation and reflux, and the reflux ratio is 3.5:1. The NMP main product is extracted from the top of the tower.

[0103] 4. Top-extracted residual NMP: Pump the crude NMP containing high-boiling substances in Step 2 into a refining tower for vacuum distillation. The vacuum degree is 220 torr, the top temperature of the tower is 155 °C; the bottom temperature of the tower is 190 °C; after heat exchange in the thermosyphon reboiler, the steam in the raw material enters the top condenser for condensation and reflux, and the reflux ratio is 0.8:1; the residual NMP is extracted from the top of the tower and recycled to the product tower, and the residue is discharged from the bottom of the tower.

[0104] Comparative Example 2

[0105] Rectification system: Integrate dehydration, purification, and light-component separation in a single packed tower. NMP is extracted from the top of the tower as a light component; the tower body is made of 304 stainless steel, with a tower height of 30 m and a tower diameter of 1.8 m.

[0106] Packing type: The upper section uses metal perforated plate corrugated packing with a specific surface area of 280 m 2 / m 3 ; the middle section uses ceramic structured packing with a specific surface area of 400 - 500 m 2 / m 3 ; the lower section uses cascade ring random packing; the feeding position is in the middle section packing area; a multi-stage trough-type liquid distributor is set, with the first-stage circulating water condensation at 30 °C in series and the second-stage chilled water condensation at 6 °C; temperature sensors of model PT100 are set at the top and bottom of the tower respectively; a pneumatic control valve of model DVC6200.

[0107] Rectification process, including the following steps:

[0108] 1. Raw material pretreatment: Remove suspended particles and metal debris through an 8-μm filter; add dilute sulfuric acid to adjust the pH to 6.5 to neutralize free amine substances.

[0109] 2. Pump 1 ton of pretreated NMP wastewater into the tower for vacuum distillation. The vacuum degree at the top of the tower is 65 torr, and the top temperature of the tower is 90 °C; the bottom temperature of the tower is 130 °C; the reflux ratio is 1.5:1. After heat exchange in the thermosyphon reboiler, the steam in the raw material enters the top condenser for condensation and reflux, and the temperature of the circulating condensed water is 35 °C. The main NMP product is extracted from the top of the tower; the residue containing moisture, amines, and high-boiling substances is discharged from the bottom of the tower.

[0110] The rectification processes of Example 4, Example 5, and Example 6 all adopt the rectification system of Example 1, and the parameter data of the obtained NMP solution are shown in Table 2, serial numbers 1-4, 1-5, and 1-6 respectively; Comparative Example 1 uses three towers in series, and all three towers use full plate trays, and Comparative Example 2 uses a packed single tower. The parameter data of the obtained NMP solution in Comparative Example 1 and Comparative Example 2 are shown in Table 2 respectively.

[0111] Table 2 Parameter data of the NMP solution obtained in Examples 1-4 and Comparative Examples 1-2

[0112]

[0113]

[0114] As can be seen from Table 2, in Example 5 (1-5) and Example 6 (1-6), the number of critical control points is less than 10, and in Comparative Example 1 and Comparative Example 2, the number of critical control points is greater than 20, indicating that the operation control points of the present invention are fewer, easy to operate and safe. The steam unit consumption of Example 5 and Example 6 is 0.6 tons per ton of raw material and 0.7 tons per ton of raw material respectively, which is significantly lower than 1.5 tons per ton of raw material in Comparative Example 1 and 1.2 tons per ton of raw material in Comparative Example 2, indicating that the distillation process of the present invention is more energy-saving. The residue discharge ratios of Example 5 and Example 6 are 0.95% and 1.05% respectively, which are significantly lower than 2.8% in Comparative Example 1 and 2.1% in Comparative Example 2, indicating that the NMP recovery rate of the present invention is higher and the environmental protection performance is stronger. In NMP of Example 5 and Example 6, the water content is less than 0.002%, the metal ion concentration is less than 5 ppb, and the free amine concentration is less than 5 ppm; in Comparative Example 1 and Comparative Example 1, the water content is 0.01%, the metal ion concentrations are 46 ppb and 39 ppb respectively, and the free amine concentrations are 17 ppm and 23 ppm respectively; and the number of particles with a particle size ≥ 0.5 μm in each milliliter of NMP in Example 5 and Example 6 can be controlled to be less than 5, while the number in Comparative Example 1 and Comparative Example 2 is uncontrollable, indicating that the product quality generated by the distillation process of the present invention is higher. The distillation equipment of the present invention can operate continuously for 2000 hours, while Comparative Example 1 can only operate continuously for 605 hours, and Comparative Example 2 can only operate for 730 hours, indicating that the equipment life of the present invention is longer, which can effectively save costs and improve efficiency.

[0115] Comparative Example 3

[0116] The distillation system is the same as that of Example 1; in the preparation process step S100, the top reflux ratio of the dehydration tower is set to 0.5:1, and other parameters and process steps are the same as those of Example 4.

[0117] Comparative Example 4

[0118] The distillation system is the same as that of Example 1; in the preparation process step S100, the bottom temperature of the dehydration tower is set to 140 °C, and the vacuum degree is set to 20 torr, and other parameters and process steps are the same as those of Example 4.

[0119] Comparative Example 5

[0120] The distillation system is the same as that of Example 1; in the preparation process step S200, the top reflux ratio of the dehydration tower is set to 1.2:1, and other parameters and process steps are the same as those of Example 4.

[0121] Comparative Example 6

[0122] The rectification system is the same as that in Example 1; in the preparation process step S200, the bottom temperature of the dehydration tower is set to 140 °C, and the vacuum degree is set to 15 torr. Other parameters and process steps are the same as those in Example 4.

[0123] The qualities of the purified NMP products in Example 4 (using the rectification system of Example 1, numbered 1-4) and Comparative Examples 1-4 are shown in Table 3.

[0124] Table 3 Qualities of the purified NMP products in 1-4 and Comparative Examples 1-4

[0125] Index 1-4 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Moisture Residue (%) 0.0009 0.0048 0.0020 0.0018 0.0017 Free Amine Residue (ppm) 2.5 8.5 4.1 2.3 2.9 Metal Ion Residue (ppb) 1.2 1.5 1.6 12 6 NMP Recovery Rate (%) 99.5 97.5 98.8 98.9 97.3 NMP Decomposition Rate (%) 0.08 0.05 0.35 0.06 0.25 Steam Consumption (tons / ton NMP) 0.9 0.7 1.3 1.0 1.6

[0126] As can be seen from Table 3, in Comparative Example 3, the reflux ratio is too low (0.5:1), resulting in: a decrease in mass transfer efficiency: insufficient liquid phase reflux in the tower, incomplete separation of water and NMP (residual water increases to 0.0048%); a decrease in the removal rate of free amines: insufficient condensation and reflux of amines, and the residual amount exceeds the standard (8.5 ppm). In Comparative Example 4, the bottom temperature of the tower is 140 °C (exceeding the upper limit) + the vacuum degree is 20 torr (exceeding the lower limit), resulting in: intensified thermal decomposition of NMP: the decomposition rate of NMP at high temperature increases to 0.35% (only 0.08% in the example); a sharp increase in energy consumption: an ultra-low vacuum degree (20 torr) requires a high-power vacuum pump, and the steam consumption increases by 44%. In Example 4, in step S100, a temperature gradient is set: 110 °C at the bottom → 105 °C in the middle and upper sections → 35 °C at the top, forming a gradually decreasing temperature to force the light components to rise; the vacuum degree: 50 torr to reduce the boiling point and reduce thermal damage; the reflux ratio: 1.0:1 to balance the mass transfer efficiency and energy consumption. The three work together synergistically: the removal rates of water and amines are increased by 3-5 times; the energy consumption is reduced by 30%, and the decomposition rate is reduced by 77%.

[0127] In Comparative Example 5, the reflux ratio is too low (1.2:1), resulting in insufficient liquid phase reflux, a decrease in the mass transfer efficiency in the tower, incomplete separation of light components (such as water and amines), and the residual water increases to 0.0017%; side-line product contamination, trace light components enter the side-line draw, and the metal residue reaches 12 ppb. In Comparative Example 6, the bottom temperature of the tower is 140 °C (exceeding the upper limit) + the vacuum degree is 15 torr (exceeding the lower limit), resulting in intensified thermal decomposition of NMP, and the decomposition rate of NMP at high temperature increases to 0.25%, and the by-products (such as pyrrolidone) increase; an ultra-low vacuum degree (15 torr) requires a high-power vacuum pump, and the steam consumption increases by 45%. In Example 4, a reflux ratio of 2.0:1 is set to provide sufficient liquid phase reflux, and cooperate with the vacuum degree to reduce the boiling point of NMP, ensuring that the light components fully rise to the top of the tower, and the purity of the side-line product is significantly improved; the temperature and the vacuum degree cooperate to control the actual boiling point of NMP, both inhibiting decomposition and reducing energy consumption.

Claims

1. A rectification system for NMP waste liquid used in lithium batteries, characterized in that, It includes a dehydration tower and a product tower arranged in series. The dehydration tower is connected to a raw material tank. A condenser 1 is arranged at the top of the dehydration tower, a reboiler 1 is arranged at the bottom of the dehydration tower, and the bottom of the dehydration tower is connected to the product tower. A condenser 2 is connected to the top of the product tower, a reboiler 2 is arranged at the bottom of the product tower, a concentrator is connected to the bottom of the product tower, and a still residue discharge outlet is arranged at the bottom of the concentrator. A condenser 3 is arranged at the side line extraction outlet of the product tower, and the condenser 3 is connected to a finished product storage tank. Multiple layers of trays are arranged inside both the dehydration tower and the product tower, and structured packings are filled. The structured packings are located above the trays.

2. The NMP waste liquid rectification system for lithium batteries according to claim 1, wherein The number of trays in the dehydration tower is 15 to 25 layers, and the packing density of structured packing is 250 to 300 m 2 / m 3 .

3. The NMP waste liquid rectification system for lithium batteries according to claim 1, wherein, The number of trays of the product column is 20 to 30, and the packing density of structured packing is 300 to 500 m 2 / m 3 .

4. The NMP waste liquid rectification system for lithium batteries according to claim 1, wherein, A collection tank 1 is arranged at the outlet of the condenser 1, and a collection tank 2 is arranged at the outlet of the condenser 2. A pre-filter is arranged between the dehydration tower and the raw material tank, and a vacuum pump is arranged between the dehydration tower and the product tower.

5. A rectification process, characterized in that, Applicable to the NMP waste liquid rectification system for lithium batteries as described in any one of claims 1-4, it includes the following steps: S100. Filter the NMP waste liquid through the pre-filter and then pump it into the dehydration tower for vacuum distillation. After heat exchange through the reboiler 1, the steam in the raw material enters the condenser 1 for condensation and reflux. The condensed wastewater enters the collection tank 1 and is withdrawn, and the tail gas is withdrawn through the vacuum pump. S200. Pump the material at the bottom of the dehydration tower into the product tower for vacuum distillation. After heat exchange through the reboiler 2, the steam in the raw material enters the condenser 2 at the top of the product tower for condensation and reflux. The intermediate product enters the collection tank 2 and is withdrawn, and the tail gas is withdrawn through the vacuum pump. The qualified product collected at the side line extraction outlet of the product tower is condensed by the condenser 3 and then stored in the finished product storage tank. S300. The high-boiling substances at the bottom of the product tower enter the concentrator for secondary heating. The residual target components are recovered into the product tower for continued vacuum distillation, and the still residue is discharged through the still residue discharge outlet.

6. The rectification process according to claim 5, characterized in that, In step S100, the temperature at the bottom of the dehydration tower is 100-130 °C, the vacuum degree is selected as 35-60 torr, the temperature at the top of the tower is 25-40 °C, the temperature in the middle and upper sections of the tower is 90-120 °C, and the reflux ratio at the top of the tower is controlled at 0.8-1.2:

1.

7. The rectification process according to claim 5, characterized in that, In step S200, the temperature at the bottom of the product tower is 110-135 °C, the vacuum degree is selected as 25-50 torr, and the ratio of the reflux flow at the top of the tower to the side line product extraction flow is 1.8-2.2:

1.

8. The rectification process according to claim 5, characterized in that, In step S200, the qualified product entering the finished product storage tank is processed through a filter and a filling system to obtain a high-purity product.

9. The rectification process according to claim 5, characterized in that, In step S300, the heating temperature of the concentrator is 140-160 °C, the residence time of the still residue is 10-30 minutes, and the vacuum degree is controlled at 20-50 torr.

10. The rectification process according to claim 5, characterized in that In step S300, the discharge amount of the still residue is 0.95-1.05% of the system processing amount.

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