NMP distillation device

Abstract

The present invention relates to an NMP distillation device and, more specifically, to an NMP distillation device including a separate side drum for extracting N-methyl-2-pyrrolidone (NMP) as steam, the device recovering and then purifying NMP, which is used as a solvent in the process of manufacturing lithium secondary battery electrodes, to reuse same as a high-purity product.

Description

NMP distillation unit

[0001] The present invention relates to an NMP distillation apparatus, and more particularly, to an NMP distillation apparatus combined with a separate side drum for extracting NMP as vapor in order to recover NMP (N-methyl-2-pyrrolidone), which is used as a solvent in the process of manufacturing an electrode of a lithium secondary battery, and then purify it and reuse it as a high-purity product.

[0002] Recently, energy storage devices are being used to efficiently utilize renewable energy, and the growing share of eco-friendly electric vehicles has led to a surge in demand for secondary batteries. Consequently, the use of NMP, used in the production of lithium secondary battery cathodes, is also increasing.

[0003] NMP is a type of volatile organic compound that battery manufacturers use when mixing cathode materials, binders, and powdered conductive materials into a slurry. Because it is a very expensive and hazardous substance, most of it is recovered and recycled or reused.

[0004] NMP solvent has a boiling point of 202°C, requiring heating to a very high temperature to vaporize and remove it. However, this requires a high amount of heat energy, which is expensive. Furthermore, instead of combustion, it is often recovered and reused using methods such as refrigeration condensation or absorption.

[0005] Currently, most lithium-ion battery manufacturers utilize a method to recover and reuse NMP from the exhaust air during the drying process. In Korea, the primary method employed is absorption, which utilizes NMP's hydrophilicity to recover it in an absorption tower. However, because this method relies on water, the purity of the recovered NMP is only around 80%. Furthermore, the high moisture content of the treated air makes reuse impossible, so 100% of the air is typically discharged into the atmosphere. This necessitates the installation of separate equipment to manage the exhaust air.

[0006] Another method involves transporting the recovered NMP to a chemical plant for further processing to refine it into a high-purity product, with the remaining solution containing less than 80% NMP being purified. At these plants, the recovered NMP is purified to a purity of 99.9% or higher using known distillation methods. However, this method has the disadvantage of requiring additional transportation costs and pretreatment processes, such as concentration adjustment.

[0007] Furthermore, the distillation and purification of NMP requires highly skilled technology, making it difficult to become familiar with outside chemical plants. Specifically, NMP recovered from the battery manufacturing process contains low-boiling components with boiling points intermediate between those of water and NMP, as well as high-boiling components derived from NMP. This necessitates a precise two-stage distillation process. In particular, when high-boiling components are present, the difference in boiling points is not significant, making it difficult to remove impurities through a simple purification process. Furthermore, the moisture content (NMP concentration) in NMP fluctuates depending on seasonal or manufacturing process fluctuations, leading to fluctuations in throughput, making normal operation difficult.

[0008] In addition, since it has the function of sequentially performing depressurization operation and circulation operation in the distillation column as an automatic processing capability while simultaneously extracting high-purity NMP by the side cutting method from the middle section (220) of the distillation column, a method has also been proposed that can simply and safely purify NMP on-site by automatic operation without requiring a high level of skilled technology. However, a separate control means is required to independently maintain the liquid level at the bottom of the column regardless of fluctuations in the extraction amount of side cutting vapor.

[0009] Therefore, there is a need for the development of an improved NMP recovery, purification, and distillation device that can actively respond to changes in the types and contents of impurities contained in NMP recovered from the battery manufacturing process.

[0010] [Prior Art Literature]

[0011] [Patent Document]

[0012] (Patent Document 1) Domestic Patent No. 10-1565033 (Registration Date: October 27, 2015)

[0013] (Patent Document 2) Domestic Publication No. 10-2018-0069284 (Published on June 25, 2018)

[0014] (Patent Document 3) Domestic Patent No. 10-1709101 (Registration Date: February 16, 2017)

[0015] (Patent Document 4) Japanese Patent Publication JP 5776231 B2 (registration date: July 17, 2015)

[0016] (Patent Document 5) Japanese Patent Publication JP 6898567 B2 (registration date: June 15, 2021)

[0017] [Non-patent literature]

[0018] (Non-patent document 1) Hwang Sun-ho et al., "A Study on the Development of a Hybrid NMP Recovery System for Recovering NMP Used in the Lithium-ion Battery Cathode Manufacturing Process," Trans. Korean Soc. Mech. Eng. B, Vol. 40, No. 5, pp. 289-296, 2016.

[0019]

[0020] The present invention has been devised to solve the above problems, and aims to provide a side-cutting distillation device capable of improving the purity and recovery rate of NMP recovered from a lithium-ion secondary battery manufacturing process.

[0021] In addition, we aim to provide an NMP distillation device that can easily and safely purify NMP regardless of the processing amount or moisture concentration fluctuations of the raw material NMP.

[0022] In order to solve the above technical problem, the present invention provides an NMP distillation device for recovering NMP (N-methyl-2-pyrrolidone), which is used as a solvent in the process of manufacturing an electrode of a lithium secondary battery, and repurifying it to reuse it as a high-purity product, the device comprising: a raw material tank (100) in which a treated raw material is stored; a distillation tower (200) for distilling the treated raw material supplied from the raw material tank into high-purity NMP; a side cut passage (310) for extracting side cutting vapor from a middle section (220) of the distillation tower; a side drum (320) to which the side cutting vapor extracted along the side cut passage is supplied; a condenser (400) to which NMP vapor passing through the side drum is supplied; a first flow rate control valve (510) installed in a supply passage above the middle section of the tower to which the treated raw material of the raw material tank is supplied, and a second flow rate control valve (520) installed at the rear end of the condenser so as to maintain a constant liquid level in the condenser; It includes a first check drum (610) and a second check drum (620) for recovering high-purity NMP obtained from the distillation tower and collecting it as a sample for analysis; a product tank (700) for storing high-purity NMP recovered in the check drums as a product; and a waste liquid tank (800) for storing high-concentration NMP waste liquid containing high-boiling-point components recovered from the bottom of the distillation tower.

[0023] The above side drum (320) is characterized by performing a function of removing NMP impurities in NMP vapor introduced through a side cut path through a reflux process using high-purity NMP.

[0024] The above first flow control valve detects the signal of the liquid level gauge installed at the bottom of the distillation column with a level control (LC) sensor and a flow control (FC) sensor in a flow path from the raw material tank to the distillation column (above the middle part of the column) and controls the liquid level height to be maintained constant by a cascade control device, and the above second flow control valve is characterized in that it controls the amount of NMP discharged from the condenser by using a temperature control (TC) sensor of the distillation column, a level control (LC) sensor of the condenser, and a flow control (FC) sensor in the lower flow path of the condenser.

[0025] According to the present invention, by combining a separate side drum for extracting NMP as vapor, high-concentration NMP having a purity of 99.9% or higher and a recovery rate of 90% or higher can be purified.

[0026] In addition, by configuring the first and second flow control valves that can independently control the liquid level at the bottom of the distillation column and the liquid level of the condenser, NMP can be purified easily and safely without requiring highly skilled operating skills.

[0027] Figure 1 is a process diagram showing the main configuration of an NMP distillation device according to the present invention.

[0028] FIG. 2 is a drawing of a reflux process performed in a side drum of an NMP distillation apparatus according to the present invention.

[0029] FIG. 3 is a drawing of a first flow control valve (dotted line area B1) and a second flow control valve (dotted line area B2) connected to each sensor in an NMP distillation apparatus according to the present invention.

[0030] Hereinafter, the NMP distillation apparatus of the present invention will be described with reference to the attached drawings.

[0031] Before proceeding with a detailed description of the present invention, it should be noted that the terms and words used in this specification and claims described below should not be construed as limited to their conventional or dictionary meanings. Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in their common sense by those of ordinary skill in the art to which the present invention pertains.

[0032] In addition, it should be understood that the embodiments described in this specification and the configurations illustrated in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention, and therefore, there may be various equivalents and modified examples that can replace them at the time of filing this application.

[0033] Here, in the entire drawings for explaining the embodiment of the present invention, parts having the same function are given the same reference numerals, and detailed descriptions thereof are omitted.

[0034] Figure 1 illustrates the main configuration and process flow of an NMP distillation apparatus according to the present invention. In particular, this apparatus is characterized by adopting a distillation column method of a side-cutting method, so that side-cutting vapor extracted along a side-cut path can be purified into high-purity NMP through a reflux process within a side drum.

[0035] In this specification, NMP refers to N-methyl-2-pyrrolidone and an aqueous solution containing it as a main component. In addition, the term "sidecut (or side cut)" refers to a fluid (including vapor) extracted from the middle of a distillation column during a continuous distillation process. The term "reflux (or reflux)" refers to returning a portion of the condensed vapor back to the column of the distillation column to increase the efficiency of evaporation.

[0036] The NMP to be purified in the present invention contains impurities such as water, formic acid, polyvinylidene fluoride (PVDF), etc., which have relatively low boiling points (low boiling point components), and high boiling point components such as NMS (N-methylsuccinimide), NM3P (N-methyl-3-pyrrolin-2-one), gamma-butyrolactone, etc.

[0037] The present invention comprises: a raw material tank (100) in which a treatment raw material is stored; a distillation tower (200) for distilling the treatment raw material supplied from the raw material tank into high-purity NMP; a side cut passage (310) for extracting side cutting vapor from a middle section (220) of the distillation tower; a side drum (320) to which the side cutting vapor extracted along the side cut passage is supplied; a condenser (400) to which NMP vapor passing through the side drum is supplied; a first flow rate control valve (510) installed in a supply passage above the middle section of the tower to which the treatment raw material from the raw material tank is supplied and a second flow rate control valve (520) provided at the rear end of the condenser so as to maintain a constant liquid level in the condenser; a first check drum (610) and a second check drum (620) for recovering high-purity NMP obtained from the distillation tower and collecting it as a sample for analysis; a product tank (700) for storing the high-purity NMP recovered in the check drums as a product; It is characterized by including a waste liquid tank (800) for storing high-concentration NMP waste liquid containing high boiling point components recovered from the bottom of the distillation tower.

[0038] The above raw material tank (100) is a container for storing raw material NMP having a concentration of 80% or less recovered from the battery manufacturing process, and is provided to continuously and efficiently perform distillation treatment. The treated raw material in the raw material tank (100) is supplied to the distillation tower (200) by a raw material supply pump, and a first flow rate control valve (510) is installed in this supply path to control the flow rate.

[0039] The distillation apparatus of the present invention is most preferably used to separate and purify a treatment raw material having a concentration of 80% NMP and 20% water. However, depending on the field situation, the concentration of NMP fed into the distillation apparatus may vary from 50 to 90%, and when the concentration of NMP falls below 70%, there is a disadvantage in that the purification performance is somewhat reduced. Therefore, by detecting the liquid surface height with a level control sensor at the bottom of the tower to maintain a constant amount of NMP in the distillation tower, and connecting a flow control sensor of the NMP aqueous solution fed from the raw material tank together to perform cascade control, more sensitive control than the conventional NMP purification method can be achieved.

[0040] The distillation tower (200) above is a side-cutting distillation tower for distilling and purifying supplied raw material NMP, and is composed of a tower top (210) for separating high-concentration NMP having a concentration of 99 wt% or more and water containing low-boiling-point components; a tower bottom (230) for separating high-purity NMP having a concentration of 99.9 wt% or more and high-concentration NMP containing high-boiling-point components; and a tower middle portion (220) for enabling extraction of high-purity NMP as side-cut vapor along a side-cut path.

[0041] The distillation tower (200) described above is a known packed tower filled with packing material, and a tower type having a height of 25 m or more is sufficient. Specifically, the packed tower has a perforated plate or grid-shaped support tray fixed to the tower body, and packing material is filled in layers of an appropriate height thereon to form a packing bed, and a liquid distributor is typically positioned between the packing beds. At this time, the packing material is a solid with a large surface area and good ventilation, and gas-liquid contact occurs within the packed bed, and a distillation operation is performed. Materials for the packing material include ceramics, graphite, and metal.

[0042] In addition, the collector tray is a device widely known in the art that collects liquid for liquid distribution for the purpose of side-draw and can be applied thereto.

[0043] The side cut channel (310) connected to the middle section (220) of the distillation column may be located between a collector that collects high-concentration NMP obtained by separation from the top of the column and a tray that stores the NMP in the liquid collected by the collector. Specifically, the side cut channel may extend to the center of the middle section of the distillation column to extract NMP vapor contained in the space between the collector and the tray in the distillation column, so in some cases, a separate cover may not be provided on the side cut channel to prevent the inflow of liquid into the space between the collector and the tray.

[0044] The side drum (320), which is a main feature of the present invention, can perform the function of removing NMP impurities in NMP vapor introduced through the side cut path through a reflux process using high-purity NMP.

[0045] This device is advantageous in terms of installation space and ease of operation compared to a conventional two-stage distillation tower, and also has excellent advantages in terms of product purity and recovery rate.

[0046] Figure 2 is an enlarged view of area A of the dotted line in Figure 1. As the NMP vapor (arrow flow F1) introduced through the side cut path and the high-purity NMP (arrow flow F2) cooled and refluxed and re-introduced come into contact within the side drum, the high-boiling-point components included in the NMP gas can be condensed and removed once more, thereby further increasing the purity and recovery rate of the NMP.

[0047] That is, by applying the above side drum (320), the NMP recovery rate can be increased to 90% or more.

[0048] The above condenser (400) functions to condense high-purity NMP extracted as side-cutting vapor. Refrigerant flows through multiple heat transfer tubes forming multiple paths, thereby cooling and condensing the condensable vapor. Generally, it is preferable to use a multi-tube condenser to mitigate liquid level fluctuations.

[0049] In addition, in the distillation apparatus of the present invention, since the amount of high-purity NMP extracted as side cutting vapor fluctuates depending on the change in the NMP concentration or moisture content of the treated raw liquid, a flow control means is installed to control the amount of NMP solution introduced from the raw material tank toward the distillation tower (above the middle part of the tower) so as to maintain the liquid level within a certain range for stable distillation. Specifically, a first flow control valve (510) is selected as the flow control means, which detects the signal of the liquid level gauge installed at the bottom of the distillation tower with a level control (LC) sensor and a flow control (FC) sensor of a flow path from the raw material tank toward the distillation tower (above the middle part of the tower), and can control the liquid level to be maintained constant by a cascade control device (see B1 of FIG. 3). Since the high-purity NMP condensed by the reflux process described below is reintroduced into the distillation tower, it is necessary to independently control the liquid level at the bottom of the tower.

[0050] Meanwhile, a second flow control valve (520) may be selected as a flow control means installed in the lower passage of the condenser (400) independently of the first flow control valve to maintain a constant liquid level within the condenser. Specifically, the amount of NMP discharged from the condenser is controlled using a temperature control (TC) sensor of the distillation column, a level control (LC) sensor of the condenser, and a flow control (FC) sensor of the lower passage of the condenser (see B2 of FIG. 3).

[0051] Since this is to control the amount of discharge from the condenser that has passed through the side drum, it can be said that it is unrelated to controlling the change in the amount of discharge of side cutting steam discharged along the side cut path.

[0052] That is, the first flow control valve (510) is a flow control means for controlling the amount of NMP solution introduced from the raw material tank to the distillation tower (above the middle part of the tower) so as to support the liquid level of the lower part (bottom part) of the distillation tower within a certain range based on the liquid level at the lower part of the distillation tower, and the second flow control valve (520) is a flow control means for controlling the discharge amount of the high-purity NMP solution from the condenser to the product tank so as to support the liquid level of the condenser within a certain range based on the liquid level of the condenser that condenses the high-purity NMP.

[0053] The present invention is characterized in that each flow control valve can be independently controlled so that the user can arbitrarily set the flow control setting values ​​of the first and second flow control valves based on preset design values, and the liquid level height at the bottom of the distillation column and the liquid level height of the condenser can be individually controlled.

[0054] Steam is introduced through the upper passage of the condenser and high-purity NMP in liquid form is discharged through the lower passage, which is connected to the first check drum (610) and the second check drum (620). That is, the high-purity NMP liquefied in the condenser is received through the passages in the first check drum (610) and the second check drum (620), and its purity is analyzed to determine whether it is suitable as a product, and it is sent to the product tank (700) for storage.

[0055] In addition, a path for refluxing the high-purity NMP in the first and second check drums to the side drum is branched and installed. That is, by operating a reflux pump in the branched path to inject high-purity NMP into the side drum, high-boiling-point components contained in the NMP vapor introduced through the side cut path can be removed more efficiently.

[0056] In addition, a reboiler is installed at the bottom of the tower of the present invention to re-heat and evaporate the high-concentration NMP containing high-boiling-point components separated by distillation. A multi-tube heat exchanger having multiple paths formed by multiple heat transfer tubes can be used as the reboiler.

[0057] In addition, a branched flow path is installed to discharge the concentrated high-concentration NMP from the bottom of the distillation column as waste liquid to a waste liquid tank (800). That is, the high-concentration NMP can be controlled by the first flow control valve based on the flow rate of raw NMP supplied to the distillation column, and is discharged as waste liquid through the branched flow path. At this time, in order to suppress the concentration of peroxide, it is preferable to extract about 10 wt% of the flow rate supplied to the distillation column as waste liquid.

[0058] Normally, NMP produces peroxides when exposed to oxygen, and even more so under the heating conditions of distillation, posing a risk of explosion and other hazards. Furthermore, the formation of a slurry can hinder fluid circulation, potentially leading to partial heating of the NMP and the subsequent production of additional peroxides, creating a vicious cycle. Therefore, it is desirable to purify NMP by suppressing the formation of peroxides.

[0059] An operating method for operating a distillation column according to one embodiment of the present invention will be described.

[0060] The operating method of a conventional distillation device that goes through depressurization, circulation, and continuous processing steps can be applied as is to the present invention, but the following is a review focusing on the reflux process step combined with a side drum and the two flow rate control valve control steps.

[0061] When the distillation column is in operation, the side cutting vapor continuously withdrawn along the side cut path connected to the middle of the distillation column is liquefied in the condenser, and the condensed NMP is refluxed and reintroduced into the side drum via a pump, which is a reflux process. The condensed liquid NMP is sprayed onto the gaseous NMP, so that they come into gas-liquid contact with each other, thereby separating high-boiling-point components. In addition, the high-purity NMP injection amount can be adjusted by 1 to 3 times as needed to more efficiently separate or remove the components. Therefore, the high-purity NMP concentration can be maintained at 99.9%, and the NMP recovery rate can be increased to 90% or more.

[0062] Meanwhile, it is necessary to suppress turbulence within the condenser by gradually adjusting the opening of the second flow control valve (520) to a predetermined flow rate over a period of approximately 15 minutes, thereby preventing a rapid discharge of the high-purity NMP solution from the condenser to the product tank. To this end, the temperature control of the distillation tower, the level control of the condenser, and the flow control of the lower passage of the condenser must be observed simultaneously.

[0063] In addition, by detecting the temperature of the middle section packed bed of the distillation tower with temperature changes with a thermometer and controlling the steam flow rate of the reboiler in a cascade, the temperature of the middle section packed bed is maintained at 120 to 130°C, thereby making it possible to keep the moisture concentration in the side cutting vapor extracted from the side cut path connected to the middle section constant. This is because optimal heating is required in response to changes in the supply amount and concentration of raw material NMP to the distillation tower, or in other words, changes in the moisture content.

[0064] Meanwhile, in order to detect the liquid level at the bottom of the tower and control the height within a certain range, it is necessary to separately control the opening of the first flow control valve (510). This is a flow control means that controls the amount of NMP solution introduced from the raw material tank to the distillation tower (above the middle part of the tower) to maintain the liquid level within a certain range for stable distillation. This is done by controlling the level of the liquid level gauge installed at the bottom of the distillation tower and the flow of the flow path from the raw material tank to the distillation tower (above the middle part of the tower). If continuous operation is continuously performed, the high-purity NMP condensed by the reflux process flows back into the distillation tower, so it is necessary to independently control the liquid level at the bottom of the tower. In other words, it is necessary to consider that the liquid level at the bottom of the tower fluctuates during operation due to the reflux process.

[0065] By doing so, it is possible to easily and safely respond to changes in the NMP composition of the raw material tank, and to significantly reduce the concentration of moisture and impurities (including high-boiling-point components) in the NMP at each stage during operation, thereby improving separation efficiency.

[0066] Although the exemplary embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts of the present invention defined in the following claims also fall within the scope of the present invention.

Claims

1. In the NMP distillation device that recovers NMP (N-methyl-2-pyrrolidone), which is used as a solvent in the process of manufacturing lithium secondary battery electrodes, and then purifies it and reuses it as a high-purity product, A raw material tank (100) in which a treatment raw material is stored; a distillation tower (200) for distilling the treatment raw material supplied from the raw material tank into high-purity NMP; a side cut passage (310) for extracting side cutting vapor from a middle section (220) of the distillation tower; a side drum (320) to which the side cutting vapor extracted along the side cut passage is supplied; a condenser (400) to which NMP vapor passing through the side drum is supplied; a first flow rate control valve (510) installed in a supply passage above the middle section of the tower to which the treatment raw material from the raw material tank is supplied and a second flow rate control valve (520) provided at the rear end of the condenser so as to maintain a constant liquid level in the condenser; a first check drum (610) and a second check drum (620) for recovering high-purity NMP obtained from the distillation tower and collecting it as a sample for analysis; a product tank (700) for storing the high-purity NMP recovered in the check drums as a product; An NMP distillation apparatus including a waste liquid tank (800) for storing high-concentration NMP waste liquid containing high-boiling-point components recovered from the bottom of a distillation column; 2. In claim 1, The above side drum (320) is an NMP distillation device characterized in that it performs the function of removing NMP impurities in NMP vapor introduced through a side cut path through a reflux process using high-purity NMP.

3. In claim 1, The above first flow control valve detects the signal of the liquid level gauge installed at the bottom of the distillation column with a level control (LC) sensor and a flow control (FC) sensor of a flow path from the raw material tank to the distillation column (above the middle part of the column) and controls the liquid level height to be maintained constant by a cascade control device, and the above second flow control valve is an NMP distillation device characterized in that it controls the amount of NMP discharged from the condenser by using a temperature control (TC) sensor of the distillation column, a level control (LC) sensor of the condenser, and a flow control (FC) sensor of the lower flow path of the condenser.

Images