A method for reducing free amines in NMP

Abstract

This invention belongs to the field of NMP production technology, specifically relating to a method for reducing free amines in NMP, comprising the following steps: N-methylpyrrolidone requiring purification is pumped into a distillation column for distillation. The liquid enters the column and contacts rising vapor, evaporating the purified N-methylpyrrolidone. The evaporated N-methylpyrrolidone then contacts an adsorption unit for further impurity removal. Simultaneously, the activated carbon layer within the adsorption unit is automatically replaced. The distillate from the top of the distillation column is sent to a primary heat exchanger for condensation and conditioning. This solution addresses the problem of insufficient utilization of the packing layer.

Description

Technical Field

[0001] This invention belongs to the field of NMP production technology, specifically relating to a method for reducing free amines in NMP. Background Technology

[0002] The new energy industry is developing rapidly, and the core of this industry, new energy batteries, is also making great strides. Whether used as a binder in PVDF or as the main material for the negative electrode, graphite, and conductive agents, NMP (n-methylpyrrolidone) plays an indispensable role. Due to its production process, NMP contains a small amount of free amines. However, amines can polymerize during charging and discharging, reducing the conductivity of the electrolyte. Furthermore, these substances react with LiPF6 to generate HF, affecting battery life. Therefore, free amines are considered impurities in the finished product, and the battery industry typically requires their content to be below 10 ppm. Currently, domestically produced NMP generally contains between 10-15 ppm of free amines, and some even higher. It is difficult to reduce the free amine content to below 10 ppm using only a distillation system.

[0003] Currently, a method for reducing free amines in NMP (Non-Metallic Acid) with announcement number CN116239514A is available on the market. This method involves feeding the prepared crude NMP product into a first dehydration tower for dehydration. The material collected from the first dehydration tower is neutralized with acid to bring the pH value between 6.5 and 7.5. The neutralized material is then fed into a second dehydration tower for further dehydration and separation. The light components collected from the second dehydration tower are returned to the first dehydration tower, while the heavy components are sent to a purification tower for further purification. The purified NMP is collected at the top of the purification tower, while the neutralized amine salts and the heavy components from the raw material remain at the bottom and are sent to a residue tank, thus separating the neutralized amine salts from the NMP to obtain purified NMP. This invention directly reduces free amines in NMP through a distillation process, which is simple, easy to operate, and suitable for industrial production.

[0004] However, a problem exists: while this method uses boiling point differences to dehydrate and distill NMP, and adjusts the pH to make NMP easier to separate by distillation, the purity is still not high, and some free amines will always remain. Therefore, a packing layer for adsorbing free amines needs to be added to the distillation column.

[0005] Currently, a distillation column with a packed layer, with the announcement number CN210963997U, is available on the market. It includes a support frame, with a column body at the top of the support frame. The column body is characterized by: a liquid inlet pipe at the top, a liquid outlet pipe at the bottom, an inlet pipe on one side of the lower part of the column body, an outlet pipe on one side of the upper part of the column body, a packed layer inside the column body, a transverse gas guide ring surrounding the packed layer, a longitudinal gas guide ring surrounding the transverse gas guide ring, the transverse and longitudinal gas guide rings being connected through through holes, and the longitudinal gas guide ring being fixedly connected to the inner wall of the column body. A first nozzle is located at the bottom of the liquid inlet pipe, directly above the packed layer. A liquid distributor is located below the packed layer, with its top connected to the bottom of the transverse gas guide ring. A second nozzle is located at the center of the bottom of the liquid distributor. The packed layer consists of three sets. Compared to traditional distillation columns, this invention significantly improves the gas-liquid reaction effect and distillation quality.

[0006] However, there is also a problem: if the packing layer is too thick, the outer layer will be absorbed before the inner layer has absorbed anything, resulting in wasted packing layer. If the packing layer is too thin, it will quickly become saturated. Moreover, a saturated packing layer is prone to clogging the distillation column, leading to unstable internal pressure. Summary of the Invention

[0007] This invention provides a method for reducing free amines in NMP to solve the problem of insufficient utilization of the filler layer.

[0008] This solution provides a method for reducing free amines in NMP, comprising the following steps: Step S10: The operator places the first activated carbon layer of the adsorption mechanism on the limit piece that will open when the set value is exceeded, checks whether the steel wire between the activated carbon layers is fixed, and places the remaining activated carbon layers behind the baffle. Step S20: The N-methylpyrrolidone requiring purification is pumped into a distillation column for distillation. The liquid enters the column and contacts the rising vapor, evaporating the purified N-methylpyrrolidone. The evaporated N-methylpyrrolidone then contacts an adsorption unit for further purification. Simultaneously, the activated carbon layer within the adsorption unit is automatically replaced. The distillate from the top of the distillation column is sent to a primary heat exchanger for condensation. Step S30: Open the first control valve. The gaseous product after condensation in the first heat exchanger is sent to the second heat exchanger for condensation through the second pipeline. The liquid product after condensation in the first heat exchanger is sent to the first reflux tank through the fifth pipeline. The gaseous product after condensation in the second heat exchanger is discharged. Step S40: Adjust the third control valve to reflux the liquid phase product condensed in the secondary heat exchanger back to the distillation column; Step S50: Adjust the second control valve so that part of the product in the first-stage reflux tank is returned to the distillation column through the third pipeline, while part of it is collected as N-methylpyrrolidone product through the seventh pipeline and sent to the finished product tank. Step S60: Adjust the fourth control valve to open continuously or intermittently to discharge the high-boiling-point residue from the reactor.

[0009] The principle of this scheme is as follows: N-methylpyrrolidone requiring purification is pumped into a distillation column for distillation. The N-methylpyrrolidone liquid is pumped into the distillation column, where it evaporates, generating impurities and some unseparated free amine gas. Previously, activated carbon or ion exchange resins were used for absorption. This scheme uses multiple activated carbon layers. Initially, the first activated carbon layer rests on a limiting element, horizontally blocking the distillation column, while the remaining layers are held vertically against the column wall by baffles. When the horizontally placed activated carbon absorbs too much free amine, it becomes heavy, causing the first activated carbon layer to fall beyond the limiting element's capacity and rest against the column wall due to gravity. A steel wire pulls the second activated carbon layer through the baffles onto the limiting element, and so on. The distillate from the top of the distillation column is sent to a primary heat exchanger for condensation. Then, the first control valve is opened, and the gaseous product condensed in the first-stage heat exchanger is sent to the second-stage heat exchanger for further condensation through the second pipeline. The liquid product condensed in the first-stage heat exchanger is sent to the first-stage reflux tank through the fifth pipeline, and the gaseous product condensed in the second-stage heat exchanger is discharged. Then adjust the third control valve, and the liquid product condensed in the secondary heat exchanger will be refluxed back to the distillation column; Adjusting the second control valve again, part of the product in the first-stage reflux tank is returned to the distillation column through the third pipeline, while part of it is collected as N-methylpyrrolidone product through the seventh pipeline and sent to the finished product tank. The fourth control valve is then adjusted to open continuously or intermittently to discharge the high-boiling-point residue. During the refining process, the pressure at the top of the distillation column is 1.3~10 kPa, the top temperature is 92~128°C, and the bottom temperature is 94~150°C; the temperature of the first-stage heat exchanger is controlled at 47~118°C with a vapor fraction of 2.1%~50%, the temperature of the second-stage heat exchanger is controlled at 20~46°C, and the ratio of outflow to reflux in the first-stage reflux tank is 1:0.1~2.0.

[0010] The beneficial effects of this scheme are as follows: 1. This scheme uses the activated carbon layer in the adsorption mechanism to automatically replace itself through gravity absorption, thereby improving the utilization rate of multi-layer activated carbon. 2. After absorption, the activated carbon layer will automatically fall against the wall and will not clog the distillation column.

[0011] Furthermore, the automatic replacement in step S10 involves the activated carbon layer falling onto a limiting member, which is a support plate with a return spring. When the activated carbon layer absorbs enough free amine, its weight increases, causing the support plate to flip, the first piece to fall, the support plate to return to its original position, and a steel wire pulls the second piece onto the support plate for replacement. When the weight limit is exceeded, the support plate will flip again, causing the upper activated carbon layer to fall, and then return to its original position under the action of the return spring, supporting the next activated carbon layer. This mechanism effectively achieves automatic replacement and has a simple structure.

[0012] Furthermore, the automatic replacement in step S10 involves the activated carbon layer falling onto a limiting element, which is an airbag containing a non-Newtonian body. When the activated carbon layer absorbs sufficient free amine, its weight increases, compressing the airbag, causing the first piece to fall. The airbag then resets, and a steel wire pulls the second piece onto the support plate. Due to the inertial force of the steel wire, the non-Newtonian body counteracts this inertia, allowing for replacement. Because the activated carbon layer experiences inertia when pulled down by the steel wire, it may be forced past the limiting element, falling before being used. However, non-Newtonian fluids harden and buffer upon impact. When the activated carbon layer quickly falls onto the airbag, the impact is absorbed. As the activated carbon layer becomes heavier, the non-Newtonian body deforms, allowing the activated carbon layer to pass through and fall. This structure differs from a support plate with a reset spring in that: 1. This mechanism effectively counteracts the harmful effects of inertia, preventing the activated carbon layer from being forced past the limiting element due to inertia and falling before adsorption. 2. This structure can buffer the impact between the activated carbon layer and the limiting component, preventing damage to the activated carbon layer due to impact with the limiting component.

[0013] Furthermore, the non-Newtonian material in step S10 is high-temperature resistant nylon 6. Nylon 6 is a non-Newtonian material that maintains its performance at high temperatures. Its melting point is 220°C, while the highest temperature inside the distillation column is between 140-150°C, making it very suitable for use in distillation columns.

[0014] Furthermore, the distillation column is equipped with a pressure gauge. The pressure gauge can monitor the pressure inside the distillation column at all times, preventing pressure instability. Attached Figure Description

[0015] Figure 1 This is a system diagram of a method for reducing free amines in NMP. Figure 2 Example 2 shows the adsorption state diagram of the adsorption mechanism in the distillation column of a method for reducing free amines in NMP. Figure 3 Example 2 shows the falling state of the adsorption mechanism in the distillation column as part of a method for reducing free amines in NMP. Detailed Implementation

[0016] The reference numerals in the accompanying drawings include: 1. Distillation column; 2. Reboiler; 3. Primary heat exchanger; 4. Secondary heat exchanger; 5. Primary reflux tank; 6. Secondary reflux tank; 7. Finished product tank; 8. Inlet pump; 9. Downcomer; 10. Tray; 11. Liquid phase outlet; 12. Steam inlet; 13. Adsorption mechanism; 14. Gas phase outlet; 15. Baffle; 16. Activated carbon layer; 17. Steel wire; 18. Hinge point; 19. Non-Newtonian body; 20. Fourth control valve; 21. Second control valve; 22. Third control valve; 23. First control valve.

[0017] The basics are as follows: Figure 1 As shown: This solution provides an apparatus for reducing free amines in NMP, comprising a distillation column 1, a reboiler 2, a primary heat exchanger 3, a secondary heat exchanger 4, a primary reflux tank 5, a secondary reflux tank 6, a finished product tank 7, and a feed pump 8. The distillation column 1 has a liquid outlet 11, a steam inlet 12, a feed inlet, and a vapor outlet 14. The steam inlet 12 is connected to the reboiler 2, which reboils the liquid and provides rising steam to the distillation column 1. The liquid outlet 11 is connected to the reboiler 2, and unwanted waste from the distillation column 1 is discharged from the liquid outlet 11, while a portion flows into the reboiler 2 for liquid reboiling. NMP liquid is fed into the reboiler 8 through the feed inlet. The obtained gas exits from the vapor outlet 14 and enters the primary heat exchanger 3, which heats the gas, cooling the NMP liquid, which then enters the primary reflux tank 5. The primary reflux tank 5 returns a portion of the liquid to the distillation column 1 and sends the remainder to the finished product tank 7. The gas from the primary reflux tank 5 then enters the secondary reflux tank 6, where it is condensed again. The NMP liquid flows into the secondary reflux tank 6, which then returns the liquid to the distillation column 1 for distillation.

[0018] This solution provides a method for reducing free amines in NMP, comprising the following steps: Step S10: The N-methylpyrrolidone to be purified is fed into the distillation column 1 for distillation via a transfer pump. The distillation column 1 includes a tray 10 and an adsorption mechanism 13. A downcomer 9 is provided on the tray 10, and the adsorption mechanism 13 is located above the tray 10. The adsorption mechanism 13 includes a baffle 15, an activated carbon layer 16, a steel wire 17, a hinge point 18, and a limiting member. Multiple activated carbon layers 16 are provided. One end of the activated carbon layer 16 is rotatably connected to the hinge point 18, and the other end of the activated carbon layers 16 are fixedly connected to each other by the steel wire 17. The hinge point 18 is fixedly connected to the distillation column 1. One end of the baffle 15 is rotatably connected to the distillation column 1, and the other end cooperates with the activated carbon layer 16. The limiting member is fixedly connected to the distillation column 1 and cooperates with the activated carbon layer 16. The limiting member is a non-Newtonian body 19, which is made of high-temperature resistant nylon 6. The N-methylpyrrolidone liquid that needs to be purified is fed into the distillation column 1 via the inlet pump 8.

[0019] Distillation column 1 evaporates N-methylpyrrolidone liquid, generating numerous impurities and some unseparated free amine gas. Traditionally, activated carbon or ion exchange resins are used for absorption. This method employs multiple activated carbon layers 16. Initially, the first activated carbon layer 16 rests on a limiting element, laterally blocking distillation column 1, while the remaining layers are vertically supported against the column wall by baffles 15. When the horizontally positioned activated carbon absorbs excessive free amine, it becomes heavy, causing the first activated carbon layer 16 to fall beyond the limiting element's capacity and rest against the column wall due to gravity. A steel wire 17 pulls the second activated carbon layer 16 through baffles 15 onto the limiting element, and so on. This method yields high-purity NMP. The top distillate from distillation column 1 is sent to the primary heat exchanger 3 for condensation. Step S20: Open the first control valve 23. The gaseous product condensed by the first-stage heat exchanger 3 is sent to the second-stage heat exchanger 4 for condensation through the second pipeline. The liquid product condensed by the first-stage heat exchanger 3 is sent to the first-stage reflux tank 5 through the fifth pipeline. The gaseous product condensed by the second-stage heat exchanger 4 is discharged. Step S30: Adjust the third control valve 22, and the liquid phase product condensed in the secondary heat exchanger 4 is refluxed to the distillation column 1; Step S40: Adjust the second control valve 21. Part of the product in the first-stage reflux tank 5 is returned to the distillation column 1 through the third pipeline, while part of it is collected as N-methylpyrrolidone product through the seventh pipeline and sent to the finished product tank 7. Step S50: Adjust the fourth control valve 20 to open continuously or intermittently to discharge the high-boiling-point residue. During the refining process, the pressure at the top of distillation column 1 is 1.3~10 kPa, the top temperature is 92~128°C, and the bottom temperature is 94~150°C; the temperature of the first-stage heat exchanger 3 is controlled at 47~118°C with a gas phase fraction of 2.1%~50%; the temperature of the second-stage heat exchanger 4 is controlled at 20~46°C; and the ratio of outflow to reflux in the first-stage reflux tank 5 is 1:0.1~2.0.

[0020] The quality indicators of the N-methylpyrrolidone product obtained by purification using this invention are: purity ≥ 99.9% (wt%), free amine ≤ 5 ppm, and light impurities ≤ 0.1 ppm.

[0021] Example 2 The limiting member 20 is an airbag containing a non-Newtonian body 19, and the rest is the same as in Example 1.

[0022] like Figure 2 , Figure 3 As shown: During the purification process in distillation column 1, many impurities and free amine gases are generated. Previously, activated carbon or ion exchange resins were used for absorption. This design employs multiple activated carbon layers 16. Initially, the first activated carbon layer 16 rests on a non-Newtonian body 19 (nylon 6). The non-Newtonian body 19 absorbs the impact of the falling activated carbon and laterally blocks the distillation column 1. The remaining layers are held vertically against the wall of distillation column 1 by the baffle 15. When the horizontally placed activated carbon absorbs too much free amine, it becomes heavy. The first activated carbon layer 16 then exceeds the bearing capacity of the non-Newtonian body 19 and falls, resting against the wall of distillation column 1 under gravity. The steel wire 17 pulls the second activated carbon layer 16 through the baffle 15 onto the non-Newtonian body 19, and so on.

[0023] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for reducing free amines in NMP, characterized in that, Includes the following steps: Step S10: The operator places the first activated carbon layer of the adsorption mechanism on the limit piece that will open when the set value is exceeded, checks whether the steel wire between the activated carbon layers is fixed, and places the remaining activated carbon layers behind the baffle. Step S20: The N-methylpyrrolidone to be purified is fed into a distillation column via a transfer pump for distillation. The liquid enters the column and comes into contact with the rising vapor, evaporating the pure N-methylpyrrolidone. The evaporated N-methylpyrrolidone comes into contact with the adsorption mechanism to remove impurities from the N-methylpyrrolidone again. At the same time, the activated carbon layer in the adsorption mechanism can be automatically replaced. The distillate from the top of the distillation column is sent to the first-stage heat exchanger for condensation. Step S30: Open the first control valve. The gaseous product after condensation in the first heat exchanger is sent to the second heat exchanger for condensation through the second pipeline. The liquid product after condensation in the first heat exchanger is sent to the first reflux tank through the fifth pipeline. The gaseous product after condensation in the second heat exchanger is discharged. Step S40: Adjust the third control valve to reflux the liquid phase product condensed in the secondary heat exchanger back to the distillation column; Step S50: Adjust the second control valve so that part of the product in the first-stage reflux tank is returned to the distillation column through the third pipeline, while part of it is collected as N-methylpyrrolidone product through the seventh pipeline and sent to the finished product tank. Step S60: Adjust the fourth control valve to open continuously or intermittently to discharge the high-boiling-point residual liquid in the reactor; The automatic replacement in step S20 involves the activated carbon layer falling onto the limiting member. Multiple activated carbon layers are provided, with one end rotatably connected to a hinge point and the other end of each layer fixedly connected to the others via steel wire. The hinge point is fixedly connected to the distillation column. One end of a baffle is rotatably connected to the distillation column, and the other end engages with the activated carbon layer. The limiting member, a gasbag containing a non-Newtonian body, is fixedly connected to the distillation column. When the activated carbon layer absorbs enough free amine, its weight increases, the gasbag is compressed, the first piece falls, the gasbag resets, and the steel wire pulls the second piece onto the support plate. Due to the inertial force of the steel wire, the non-Newtonian body can counteract the inertia and replace the activated carbon layer. The non-Newtonian body is made of high-temperature resistant nylon 6.

2. A method for reducing free amines in NMP according to claim 1, characterized in that, The distillation column is equipped with a pressure gauge.

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