Efficient purification system and process for N-methyl pyrrolidone waste liquid

Abstract

The invention belongs to the technical field of lithium battery manufacturing waste liquid treatment, and particularly discloses an efficient purification system and process for N-methyl pyrrolidone waste liquid, the purification system comprises a rectification dehydration unit, a falling film evaporation unit, a rectification heavy component removal unit, a cooling unit and a heat recovery unit, the rectification dehydration unit comprises a light component removal tower, a reflux pump and a reflux tank; the falling film evaporation unit comprises a falling film evaporator and a compressor; the rectification de-heavy unit comprises a de-heavy tower, a finished product intermediate tank and a finished product delivery pump; the cooling unit comprises a finished product cooler and a residual liquid cooler; and the heat recovery unit comprises a raw material preheater. According to the invention, dehydration and heavy component removal are independently completed by the light component removal tower and the heavy component removal tower respectively; the evaporation temperature in the purification process is reduced by adopting reduced pressure distillation, the process of self-polymerization of NMP due to high temperature is reduced, the loss rate is reduced, and the recovery amount of NMP is increased; meanwhile, the steam recompression technology is utilized, heat is repeatedly utilized, and the operation energy consumption in the separation and purification process is greatly reduced; the raw material preheater is used for recovering heat, and the overall energy consumption of the system is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery manufacturing waste liquid treatment, and particularly relates to a high-efficiency purification system and process for N-methyl pyrrolidone. BACKGROUND

[0002] N-methyl pyrrolidone (NMP) is an excellent solvent, which has the advantages of strong selectivity and good chemical stability, and is widely used in high-precision electronics, circuit boards, lithium batteries and the like. In the manufacturing of lithium ion secondary batteries, electrode materials comprising active materials such as lithium compounds, binders such as polyvinylidene fluoride and NMP as a solvent are coated on a metal foil substrate, and the coated substrate is fired to produce an electrode. At present, NMP generated as a gas in the firing process is recovered by a zeolite adsorption method or a water absorption method.

[0003] The existing NMP waste liquid purification in China mainly adopts a two-tower or three-tower rectification process, which is respectively used for removing water and high-boiling-point impurities. However, this process has a significant problem of energy consumption: a large amount of steam heat energy needs to be consumed in the conventional evaporation link, and a large-scale cooling water system needs to be matched for the condensation of the tower top steam. The heat carried by the cooling water is finally discharged into the atmosphere through a cooling tower and the like, resulting in the triple waste of steam, cooling water and electric energy (for driving the circulating pump). At the process control level, the rectification system in series connection of multiple towers has inherent operation defects. In order to achieve high-purity products, more than ten parameters such as the temperature gradient and the reflux ratio of each tower need to be accurately controlled. Due to the strong coupling relationship between the two-tower / three-tower system, the parameters significantly influence each other, for example, the pressure fluctuation of the dehydration tower will directly cause the change of the feed state of the refining tower. This complex dynamic balance makes it difficult to achieve long-term stable operation of the system, and in actual production, the purity fluctuation often exceeds the process window. How to break through the energy efficiency bottleneck of the multi-tower rectification and establish a more intelligent process control system has become a technical problem to be solved in the field of NMP waste liquid purification. SUMMARY

[0004] The purpose of the present application is to overcome the defects in the prior art and provide a high-efficiency purification system and process for N-methyl pyrrolidone waste liquid.

[0005] In order to achieve the above purpose, the technical scheme of the present application is as follows:

[0006] A high-efficiency purification system for N-methyl pyrrolidone waste liquid, comprising a rectification dehydration unit, a falling film evaporation unit, a rectification heavy component removal unit, a cooling unit and a heat recovery unit, wherein the rectification dehydration unit comprises a light component removal tower, a reflux pump and a reflux tank; the falling film evaporation unit comprises a falling film evaporator and a compressor; the rectification heavy component removal unit comprises a heavy component removal tower, an intermediate tank for finished products and a finished product delivery pump; the cooling unit comprises a finished product cooler and a residual liquid cooler; and the heat recovery unit comprises a raw material preheater.

[0007] The gas phase pipe provides heat to the lightness removal tower, so that the distillation of the lightness removal tower has the driving force for gas-liquid separation; the pressure pipe allows the non-condensable gas to be extracted to ensure the negative pressure of the falling film evaporator.

[0008] In a preferred embodiment of the present invention, the light-removing tower is provided with a top condenser, which is connected to a reflux tank, and the reflux pump is arranged above the reflux tank and is connected to the reflux tank, the top of the light-removing tower and the light component storage tank through a pipeline; a side sampling port and a gas phase pipe inlet are arranged in the middle and lower part of the light-removing tower, the tube side of the falling film evaporator is connected to the side sampling port and the gas phase pipe inlet of the light-removing tower through a liquid side sampling pipe and a gas phase pipe respectively, and the shell side of the falling film evaporator is connected to the light-removing tower through an air pressure balance pipe; the falling film evaporator is located between the light-removing tower and the weight-removing tower; the compressor is connected to the steam outlet of the weight-removing tower, and the falling film evaporator is connected to the finished product intermediate tank; the raw material preheater is connected to the light-removing tower, the finished product cooler and the finished product delivery pump, and the finished product cooler is arranged below the residual liquid cooler.

[0009] In a preferred embodiment of the present invention, the falling film evaporator is connected to a forced circulation pump to partially discharge the evaporation residual liquid containing heavy components during operation; the residual liquid cooler is connected to the forced circulation pump and the reboiled product storage tank.

[0010] In a preferred embodiment of the present invention, the N-methylpyrrolidone waste liquid efficient purification system also includes a control system, which is distributed in various devices (such as light removal tower pressure sensor, compressor inverter) through sensors and valves to achieve independent parameter adjustment.

[0011] In a preferred embodiment of the present invention, the raw material preheater, tower top condenser, finished product cooler and residual liquid cooler are one of spiral wound tube heat exchangers, shell and tube heat exchangers, spiral plate heat exchangers or plate heat exchangers.

[0012] In a preferred embodiment of the present invention, the light removal tower and the heavy removal tower are both filled with structured packing, and the compressor is an oil-free compressor, which can be a centrifugal compressor, a dry compressor or a screw compressor, and the compression ratio of the compressor is 2-6.

[0013] In a preferred embodiment of the present invention, the falling film evaporator is a one-way type, the upper part of the guide tube is a cylinder with spiral grooves, the liquid falls in the form of a film along the inner wall of the heating tube through the teeth, and the lower part of the guide tube is a cone.

[0014] The overhead condenser condenses the vapor at the top of the tower and separates the light components; the reflux tank and reflux pump control the reflux ratio and stabilize the distillation process. The reflux pump is connected to the reflux tank and is used to return part of the condensate to the light component removal tower and discharge part of the condensate to the light component storage tank. After the gas-liquid mixture is separated in the weight removal tower, the gas phase enters the compressor, and the liquid phase is forced to circulate and discharge the residual liquid. The compressor compresses the gas phase of the weight removal tower into high-temperature and high-pressure steam and then enters the falling film evaporator, exchanging heat with the liquid in the falling film evaporator. After condensation, the part is used as the finished product, and the uncondensed gas phase returns to the light component removal tower. The raw material preheater of the heat recovery system recovers the heat of the evaporation residual liquid and preheats the raw material. The pressure equalization pipe connects the falling film evaporator and the light component removal tower to recover the uncondensed solvent gas phase; the pressure equalization pipe maintains the evaporator pressure stable to reduce solvent loss. The control system independently adjusts the parameters of the light component removal tower and falling film evaporator (such as pressure, temperature, etc.).

[0015] An efficient purification process for N-methylpyrrolidone waste liquid comprises the following steps:

[0016] (1) Negative pressure distillation dehydration: The waste liquid containing NMP is preheated in the raw material preheater and then enters the light component removal tower. The steam at the top of the light component removal tower is condensed in the top condenser and then enters the reflux tank. The reflux pump returns part of the condensate to the light component removal tower and discharges part of it to the light component storage tank.

[0017] (2) Falling film evaporation for de-weighting: The bottom liquid containing NMP and heavy components in the de-weighting tower enters the falling film evaporator through the side sampling port for evaporation; the high-temperature and high-pressure steam transfers heat to the liquid in the tube, and the liquid in the tube absorbs heat and becomes a gas-liquid mixed state. After the gas-liquid mixed liquid is further separated in the de-weighting tower, the gas phase enters the compressor and is compressed into high-temperature and high-pressure NMP steam, and then enters the falling film evaporator to exchange heat with the liquid in the falling film evaporator. After the high-temperature and high-pressure NMP steam releases heat and condenses, part of it forms liquid and enters the finished product intermediate tank; the uncondensed gas phase returns to the de-weighting tower to ensure the negative pressure of the falling film evaporator; the liquid phase containing the heavy components circulates in the falling film evaporator through a forced circulation pump, and discharges part of the evaporation residual liquid;

[0018] (3) Cooling and heat recovery: The finished NMP in the finished product intermediate tank is transported to the raw material preheater through the finished product delivery pump for heat exchange, and then cooled in the finished product cooler and recovered to the finished product storage tank; the evaporation residual liquid is cooled in the residual liquid cooler and recovered to the reboiled material storage tank.

[0019] In a preferred embodiment of the present invention, in step (1), the bottom temperature of the light removal tower is 100-160°C, the top temperature is 30-80°C, the pressure in the tower is 2-50kPa, the bottom temperature of the heavy removal tower is 100-160°C, the top temperature is 80-140°C, the pressure in the tower is 2-50kPa, and the condensing medium is circulating cooling water at 0-33°C.

[0020] In a preferred embodiment of the present application, the evaporation process in step (2) adopts reduced pressure distillation.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] 1、The present application proposes a NMP waste liquid purification system and process coupled with rectification-mechanical steam re-compression, which separates the dehydration (light component separation) and heavy component removal from the light component separation tower and the heavy component removal tower respectively; reduced pressure distillation is adopted to reduce the temperature of the purification process, reduce the hydrolysis and self-polymerization process of NMP; at the same time, the steam re-compression technology is used to reuse the heat, greatly reducing the operating energy consumption of the separation and purification process; the heat is recovered by using the raw material preheater to reduce the overall energy consumption of the system; the light component separation tower and the heavy component removal tower are effectively combined, only initial steam needs to be input during the system startup and heating stage, and the system can realize self-provided steam after normal operation, fully recovering the heat of the system, realizing zero consumption of fresh steam on the premise of ensuring the recovery effect, improving the energy utilization rate, achieving energy saving and emission reduction; the falling film evaporator uses high-temperature and high-pressure NMP steam compressed by a steam compressor as a heat source, the steam heating is uniform, the liquid film type flow evaporation of the material liquid in the pipe can overcome the problem of high viscosity in the evaporation residual liquid, improve the NMP recovery rate, and reduce the NMP content in the pot residue;

[0023] 2、The high-temperature and high-pressure NMP steam product in the present application is condensed into a liquid phase product in the shell side of the falling film evaporator through heat exchange, and part of the uncondensed product enters the light component separation tower through the gas-liquid balance pipe for further heat recovery and utilization;

[0024] 3、The present application adopts reduced pressure distillation, which not only ensures the hygiene requirements and environmental protection requirements of the material, but also greatly reduces the evaporation temperature, reduces the self-polymerization process of NMP due to high temperature, reduces the loss rate, and improves the NMP recovery amount. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Fig. 1 is a schematic diagram of the N-methyl pyrrolidone waste liquid high-efficiency purification system of the present application,

[0026] In the figure: 1-light component separation tower, 2-reflux pump, 3-reflux tank, 4-falling film evaporator, 5-heavy component removal tower, 6-compressor, 7-forced circulation pump, 8-raw material preheater, 9-product cooler, 10-residual liquid cooler, 11-gas pressure balance pipe, 12-light component storage tank, 13-intermediate product tank, 14-tower top condenser, 15-side tapping port, 16-product storage tank, 17-product delivery pump, 18-reboiler storage tank, 19-vacuum system, 20-raw material storage tank, 21-gas phase pipe inlet, 22-gas phase pipe, 23-liquid phase side tapping pipe. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is described in more detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0028] Example 1

[0029] An efficient purification system for N-methylpyrrolidone waste liquid, such as Figure 1 As shown, the system includes a distillation and dehydration unit, a falling film evaporation unit, a distillation and de-weighting unit, a cooling unit, and a heat recovery unit. The distillation and dehydration unit includes a lightness removal column 1, a reflux pump 2, and a reflux tank 3; the falling film evaporation unit includes a falling film evaporator 4 and a compressor 6; the distillation and de-weighting unit includes a de-weighting column 5, a finished product intermediate tank 13, and a finished product delivery pump 17; the cooling unit includes a finished product cooler 9 and a residual liquid cooler 10; and the heat recovery unit includes a raw material preheater 8. The high-efficiency N-methylpyrrolidone waste liquid purification system also includes a vacuum system 19. The de-lightening tower 1 is provided with a top condenser 14, which is connected to the reflux tank 3 through a pipeline. The reflux pump 2 is arranged above the reflux tank 3 and is connected to the reflux tank 3, the top of the de-lightening tower 1 and the light component storage tank 12 through a pipeline; a side sampling port 15 and a gas phase pipe inlet 21 are provided in the middle and lower part of the de-lightening tower 1, and the tube side of the falling film evaporator 4 is connected to the side sampling port 15 and the gas phase pipe inlet 21 of the de-lightening tower 1 through a liquid phase side sampling pipe 23 and a gas phase pipe 22 respectively, and the shell side of the falling film evaporator 4 is connected to the de-lightening tower 1 through a gas pressure balance pipe 11; the falling film evaporator 4 is located between the de-lightening tower 1 and the de-weighting tower 5; the compressor 6 is connected to the steam outlet of the de-weighting tower 5, and the falling film evaporator 4 is connected to the finished product intermediate tank 13; the raw material preheater 8 is connected to the de-lightening tower 1, the finished product cooler 9, and the finished product delivery pump 17, and the finished product cooler 9 is arranged below the residual liquid cooler 10.

[0030] The raw material preheater 8 exchanges heat between the finished NMP in the finished product intermediate tank 13 and the NMP-containing raw material waste liquid in the raw material storage tank 20. The falling film evaporator 4 is connected to a forced circulation pump 7, partially discharging the evaporation residual liquid containing heavy components during operation. The residual liquid cooler 10 is connected to the forced circulation pump 7 and the reboiler storage tank 18 via pipelines. The finished NMP in the finished product intermediate tank 13 is transported to the raw material preheater 8 via a finished product delivery pump 17 for heat exchange, then cooled in the finished product cooler 9 and recovered into the finished product storage tank 20. The efficient N-methylpyrrolidone waste liquid purification system also includes a control system. This control system utilizes sensors and valves distributed throughout various devices (such as the lightness removal column pressure sensor and the compressor inverter) to enable independent parameter adjustment. The raw material preheater 1, overhead condenser 14, finished product cooler 9, and residual liquid cooler 10 all utilize shell-and-tube heat exchangers. Cooling water flows through the shell side of the finished product cooler, while the tube side cools the high-temperature finished product. Cooling water flows through the shell side of the residual liquid cooler. Both the light-removal column and the heavy-removal column are filled with structured packing. Compressor 6 is an oil-free compressor, which can be a centrifugal compressor, a dry compressor, or a screw compressor. The compression ratio of compressor 6 is 2-6. The falling film evaporator 4 is a single-pass evaporator. The upper portion of the guide tube is a cylindrical body with spiral grooves. The liquid flows through the teeth and descends in a film-like manner along the inner wall of the heating tube. The lower portion of the guide tube is conical.

[0031] Example 2

[0032] An efficient purification process for N-methylpyrrolidone comprises the following steps:

[0033] (1) Negative pressure distillation dehydration: The waste liquid containing NMP is preheated in the raw material preheater and then enters the light component removal tower. The steam at the top of the light component removal tower is condensed by the top condenser and enters the reflux tank. The reflux pump returns part of the condensate to the light component removal tower and discharges part to the light component storage tank. The tower temperature of the light component removal tower is 135℃, the tower top temperature is 54℃, and the pressure in the tower is 10kPa. The tower temperature of the heavy component removal tower is 145℃, the tower top temperature is 110℃, and the pressure in the tower is 5kPa. The condensing medium is circulating cooling water at 20℃.

[0034] (2) Falling film evaporation for de-weighting: The bottom liquid containing NMP and heavy components in the de-weighting tower enters the falling film evaporator through the side sampling port for evaporation; the high-temperature and high-pressure steam transfers heat to the liquid in the tube, and the liquid in the tube absorbs heat and becomes a gas-liquid mixture. After further gas-liquid separation in the de-weighting tower, the gas phase enters the compressor and is compressed into high-temperature and high-pressure NMP steam, and then enters the falling film evaporator to exchange heat with the liquid in the falling film evaporator. The high-temperature and high-pressure NMP steam releases heat and condenses to form a liquid that enters the finished product intermediate tank; the uncondensed gas phase returns to the de-weighting tower to ensure the negative pressure of the falling film evaporator; the liquid phase containing heavy components circulates in the falling film evaporator through a forced circulation pump, and discharges part of the evaporation residual liquid; the inlet and outlet temperature difference of the evaporator is 20℃, and the evaporation intensity is 5000kg / (m 2 h), compressor speed 15000 rpm;

[0035] (3) Cooling and heat recovery: The finished NMP in the finished product intermediate tank is transported to the raw material preheater through the finished product delivery pump for heat exchange, and then cooled in the finished product cooler and recovered to the finished product storage tank; the evaporation residual liquid is cooled in the residual liquid cooler and recovered to the reboiled material storage tank.

[0036] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An efficient purification system for N-methylpyrrolidone waste liquid, characterized in that: It includes a distillation dehydration unit, a falling film evaporation unit, a distillation weight removal unit, a cooling unit and a heat recovery unit. The distillation dehydration unit includes a light removal tower, a reflux pump and a reflux tank; the falling film evaporation unit includes a falling film evaporator and a compressor; the distillation weight removal unit includes a weight removal tower, a finished product intermediate tank and a finished product delivery pump; the cooling unit includes a finished product cooler and a residual liquid cooler; the heat recovery unit includes a raw material preheater.

2. The N-methylpyrrolidone waste liquid efficient purification system according to claim 1, wherein: The light-removing tower is provided with a top condenser, which is connected to a reflux tank. The reflux pump is provided above the reflux tank and is connected to the reflux tank, the top of the light-removing tower and the light component storage tank through pipelines; a side sampling port and a gas phase pipe inlet are provided at the middle and lower part of the light-removing tower, the tube side of the falling film evaporator is connected to the side sampling port and the gas phase pipe inlet of the light-removing tower through a liquid side sampling pipe and a gas phase pipe respectively, and the shell side of the falling film evaporator is connected to the light-removing tower through an air pressure balance pipe; the falling film evaporator is located between the light-removing tower and the weight-removing tower; the compressor is connected to the steam outlet of the weight-removing tower, and the falling film evaporator is connected to the finished product intermediate tank; the raw material preheater is connected to the light-removing tower, the finished product cooler and the finished product delivery pump, and the finished product cooler is provided below the residual liquid cooler.

3. The N-methylpyrrolidone waste liquid efficient purification system according to claim 1, wherein: The falling film evaporator is connected to a forced circulation pump, and the residual liquid cooler is connected to the forced circulation pump and a reboiled material storage tank.

4. The N-methylpyrrolidone waste liquid efficient purification system according to claim 1, wherein: The N-methylpyrrolidone efficient purification system also includes a control system.

5. The N-methylpyrrolidone waste liquid efficient purification system according to claim 1, wherein: The raw material preheater, tower top condenser, finished product cooler and residual liquid cooler adopt one of spiral wound tube heat exchanger, shell and tube heat exchanger, spiral plate heat exchanger or plate heat exchanger.

6. The N-methylpyrrolidone waste liquid efficient purification system according to claim 1, wherein: The light-removal tower and the heavy-removal tower are both filled with structured packing; the compressor is an oil-free compressor, which can be a centrifugal compressor, a dry compressor or a screw compressor, and the compression ratio of the compressor is 2-6.

7. The N-methylpyrrolidone waste liquid efficient purification system according to claim 1, characterized in that: The falling film evaporator is a one-way type. The upper part of the guide tube is a cylinder with spiral grooves. The liquid falls in the form of a film along the inner wall of the heating tube through the tooth gap. The lower part of the guide tube is a cone.

8. A purification process based on the N-methylpyrrolidone waste liquid efficient purification system according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) Negative pressure distillation dehydration: The waste liquid containing NMP is preheated in the raw material preheater and then enters the light component removal tower. The steam at the top of the light component removal tower is condensed in the top condenser and then enters the reflux tank. The reflux pump returns part of the condensate to the light component removal tower and discharges part of it to the light component storage tank. (2) Falling film evaporation and de-weighting: The bottom liquid containing NMP and heavy components in the de-weighting tower enters the falling film evaporator through the side sampling port for evaporation; the high-temperature and high-pressure steam transfers heat to the liquid in the tube, and the liquid in the tube absorbs heat and becomes a gas-liquid mixture. After the gas-liquid mixture is further separated in the de-weighting tower, the gas phase enters the compressor and is compressed into high-temperature and high-pressure NMP steam, and then enters the falling film evaporator to exchange heat with the liquid in the falling film evaporator. After the high-temperature and high-pressure NMP steam releases heat and condenses, part of it forms liquid and enters the finished product intermediate tank; the uncondensed gas phase returns to the de-weighting tower to ensure the negative pressure of the falling film evaporator; the liquid phase containing the heavy components circulates in the falling film evaporator through a forced circulation pump, and discharges part of the evaporation residual liquid; (3) Cooling and heat recovery: The finished NMP in the finished product intermediate tank is transported to the raw material preheater through the finished product delivery pump for heat exchange, and then cooled in the finished product cooler and recovered to the finished product storage tank; the evaporation residual liquid is cooled in the residual liquid cooler and recovered to the reboiled material storage tank.

9. The purification process of the N-methylpyrrolidone waste liquid efficient purification system according to claim 8, characterized in that: In step (1), the temperature of the bottom of the light removal tower is 100-160° C., the temperature of the top of the tower is 30-80° C., and the pressure in the tower is 2-50 kPa; In the step (1), the temperature of the kettle of the deweighting tower is 100-160° C., the temperature of the tower top is 80-140° C., the pressure in the tower is 2-50 kPa, and the condensing medium is circulating cooling water at 0-33° C.

10. The purification process of the N-methylpyrrolidone waste liquid efficient purification system according to claim 8, characterized in that: The evaporation process in step (2) adopts reduced pressure distillation.

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