CN112439320A - Method for separating and refining NMP (N-methyl pyrrolidone) by using pervaporation membrane - Google Patents
Method for separating and refining NMP (N-methyl pyrrolidone) by using pervaporation membrane Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/36—Pervaporation; Membrane distillation; Liquid permeation
- B01D61/362—Pervaporation
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- C07D207/00—Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom
- C07D207/02—Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom with only hydrogen or carbon atoms directly attached to the ring nitrogen atom
- C07D207/18—Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom with only hydrogen or carbon atoms directly attached to the ring nitrogen atom having one double bond between ring members or between a ring member and a non-ring member
- C07D207/22—Heterocyclic compounds containing five-membered rings not condensed with other rings, with one nitrogen atom as the only ring hetero atom with only hydrogen or carbon atoms directly attached to the ring nitrogen atom having one double bond between ring members or between a ring member and a non-ring member with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
- C07D207/24—Oxygen or sulfur atoms
- C07D207/26—2-Pyrrolidones
- C07D207/263—2-Pyrrolidones with only hydrogen atoms or radicals containing only hydrogen and carbon atoms directly attached to other ring carbon atoms
- C07D207/267—2-Pyrrolidones with only hydrogen atoms or radicals containing only hydrogen and carbon atoms directly attached to other ring carbon atoms with only hydrogen atoms or radicals containing only hydrogen and carbon atoms directly attached to the ring nitrogen atom
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Abstract
The invention provides a method for separating and refining NMP by a pervaporation membrane, which comprises the following steps: preheating a water-containing NMP raw material according to batches, then feeding the preheated water-containing NMP raw material into a first storage tank, feeding the buffered raw material into a membrane separation unit for primary dehydration, and feeding a permeate into a permeate treatment unit; and (3) the retentate obtained by the first dehydration enters a second storage tank, is continuously conveyed to the membrane separation unit for second dehydration in a circulating manner, enters the first storage tank, and is conveyed to the rectification unit for purification through the second storage tank when the water content of the retentate is detected to meet the product requirement, so that a high-purity NMP product is produced. Compared with the traditional method for refining NMP by multi-tower rectification, the method for producing high-purity NMP by pervaporation membrane separation has the advantages of high NMP recovery efficiency and greatly reduced operation cost; and the intermittent or continuous dehydration operation mode can be flexibly selected according to the different treatment capacity and the water content of the waste NMP solvent, the switching is flexible, and the operation is convenient.
Description
Technical Field
The invention relates to the field of high-purity NMP production, in particular to a method for separating and refining NMP by a pervaporation membrane.
Background
NMP is an abbreviation for N-methylpyrrolidone. N-methyl pyrrolidone (NMP) is an organic solvent and has the advantages of low toxicity, high boiling point, difficult volatilization, strong solubility, stable chemical property and the like. The high-purity NMP product is widely used in the industries of lithium batteries, carbon nano tube conductive paste, liquid crystal electronics, semiconductors, insulating materials and the like. With the rising and rapid development of the lithium battery industry, the demand of high-purity NMP in the fields of power batteries, energy storage batteries and the like is increasing day by day. In the production process of lithium batteries, high-purity NMP greatly affects the quality and effect of coating and the improvement of energy density of lithium batteries. In the blending stage, the PVDF solution is used as a PVDF solvent and can keep stable slurry in a certain viscosity range; in the coating stage, the coating material is used as a main liquid carrier of the slurry and has very good wettability and fluidity; in the coating and baking stage, the coating and baking liquid is volatilized from the wet film at a stable speed to form a porous microelectrode structure with uniform pore size and distribution.
The quality of NMP is mainly influenced by key indexes such as purity, moisture and metal ions. Lithium batteries have strict limits on the purity of NMP, especially on the water content, which is required to be less than 0.02% or even lower. At present, the water content of domestic NMP is generally more than 0.03 percent, and the requirements of the lithium battery industry are difficult to meet. After the imported NMP is purified, the index requirements are as follows: the requirement of the color is less than 10, the requirement of the purity is more than 99.9 percent, and the requirement of the moisture content is not more than 0.02 percent. At present, few documents report related purification contents in China, and the purification research of NMP needs to be further strengthened.
Patent CN103351321A discloses a continuous energy-saving production method of NMP, wherein a reaction unit obtains a NMP crude product, partial water and monomethylamine are separated through a normal pressure tower, the obtained NMP crude product enters a negative pressure tower again, residual moisture and low boiling point substances are dehydrated, and finally the obtained dry NMP product without water enters a rectifying tower for vacuum rectification to separate high boiling point substances, so that a refined NMP finished product with purity meeting the requirement is obtained. The method adopts three rectifying towers, NMP product is vaporized for three times in the whole refining process in order to remove water and monomethylamine, and the NMP finished product is obtained finally, but the method has high energy consumption, complex operation and high operation cost. In the process of repeated vaporization and condensation, the NMP product operates at high temperatures for a long time, which has a certain effect on its product stability.
Pervaporation, including vapor permeation, is a novel membrane technology for the separation of gas (liquid) mixtures, where components permeate the membrane layer by diffusion, driven by the pressure difference between the components across the membrane, and vaporize to vapor on the permeate side. The pervaporation membrane has high efficiency, can realize high separation degree in a single stage, has low energy consumption, and can save energy consumption by 1/2-2/3 compared with the rectification process. Meanwhile, the process is simple, excessive matching treatment is not needed, the system is reliable and high in stability, other components are not introduced in the separation process, and the method belongs to an environment-friendly technology.
Disclosure of Invention
The invention aims to solve the problems of high energy consumption and high equipment investment cost in the existing NMP refining process, provides a method for producing high-purity NMP by pervaporation membrane separation, and discloses a set of low-energy-consumption integrated device for separating and refining NMP by pervaporation membrane, which is suitable for the method.
The method for separating and purifying NMP by the pervaporation membrane comprises the following steps:
preheating a water-containing NMP raw material at a mass flow rate of 1200 +/-100 kg/batch, then feeding the preheated water-containing NMP raw material into a first storage tank, feeding the buffered raw material into a membrane separation unit for primary dehydration, and feeding a permeate into a permeate treatment unit; and (3) the retentate obtained by the first dehydration enters a second storage tank, is continuously conveyed to the membrane separation unit for second dehydration in a circulating manner, enters the first storage tank, and is conveyed to the rectification unit for purification through the second storage tank when the water content of the retentate is detected to meet the product requirement, so that a high-purity NMP product is produced.
In order to fully implement the above method for separating and purifying NMP by using pervaporation membrane of the present invention, the present invention further provides a set of apparatus for separating and purifying NMP by using pervaporation membrane, which is suitable for the above method, comprising a raw material processing unit, a membrane separation unit, a permeate processing unit and a rectification unit, wherein: the raw material processing unit comprises first heat exchange equipment, a first storage tank and a second storage tank; wherein the second storage tank is provided with a material inlet and a material outlet; the membrane separation unit is provided with a material inlet, a retentate outlet and a permeate outlet; the material inlet of the second storage tank is connected with the retentate outlet of the membrane separation unit; the material outlet of the second storage tank is connected with the rectification unit; and the permeate outlet of the membrane separation unit is connected with the permeate treatment unit. The method for separating and purifying NMP by using the device and the pervaporation membrane comprises the following steps: an aqueous NMP feed is preheated through a first heat exchange means at a mass flow rate of 1200 ± 100 kg/batch, buffered in a first storage tank, and the buffered feed is passed into a membrane separation unit in vapour or liquid state. And (3) the retentate obtained by the separation of the membrane separation unit enters a second storage tank for buffering, the buffered material enters the membrane separation unit again, the retentate is conveyed to the first storage tank, the steps are circulated until the moisture content of the retentate meets the requirements of a final product, and the retentate is conveyed to a rectification unit for purification, so that a high-purity NMP product is produced. The permeate (namely water vapor) obtained by the separation of the membrane separation unit enters a permeate treatment unit, and is discharged out of the system after condensation and buffering.
When the method is used for separating and refining the NMP by the pervaporation membrane, the dehydrated NMP meets the requirement of water content and has high dehydration efficiency; removing heavy components from the dehydrated NMP crude product through an NMP refining tower to obtain a high-purity NMP finished product; compared with the traditional method for refining NMP by multi-tower rectification, the method has the advantages that the NMP recovery efficiency is high, and the operation cost is greatly reduced; the membrane separation process is realized by adopting liquid feeding, so that the re-vaporization in the NMP dehydration process is avoided, the energy consumption is greatly reduced, and the problem of product denaturation and deterioration caused by repeated heating of NMP is avoided; and the intermittent or continuous dehydration operation mode can be flexibly selected according to the different treatment capacity and the water content of the waste NMP solvent, the switching is flexible, and the operation is convenient.
Drawings
FIG. 1 is a diagram of an apparatus for purifying NMP by pervaporation membrane separation according to the present invention;
FIG. 2 is a diagram showing an NMP purification apparatus used in a comparative example of the present invention, wherein:
1. a first heat exchange device; 2. a first storage tank; 3. a second storage tank; 4. a first fluid delivery device; 5. a second heat exchange device; 6. a first membrane separation module; 7. a second membrane separation module; 8. a permeate processing apparatus; 9. a third storage tank; 10. a second fluid delivery device; 11. a third fluid delivery apparatus; 12. a first separation column; 13. a fourth heat exchange device; 14. a fifth heat exchange device; 15. a second separation column; 16. a sixth heat exchange device; 17. a seventh heat exchange device.
Detailed Description
The following detailed description of the embodiments of the present invention is provided in conjunction with the accompanying drawings and the accompanying drawings of which 1 is illustrated.
The invention provides a method for refining NMP by pervaporation membrane separation, which comprises the steps of preheating a water-containing NMP raw material at a mass flow rate of 1200 +/-100 kg/batch, then feeding the preheated water-containing NMP raw material into a first storage tank, feeding the buffered raw material into a membrane separation unit for primary dehydration, and feeding a permeate into a permeate treatment unit; and (3) the retentate obtained by the first dehydration enters a second storage tank, is continuously conveyed to the membrane separation unit for second dehydration in a circulating manner, enters the first storage tank, and is conveyed to the rectification unit for purification through the second storage tank when the water content of the retentate is detected to meet the product requirement, so that a high-purity NMP product is produced. In order to ensure the product quality, in the method for producing high-purity NMP by pervaporation membrane separation, the water content in the raw material containing water NMP is 1-20% by mass. The preheating temperature of the raw materials is preferably 120 +/-10 ℃.
In the prior art, a rectifying tower is mostly adopted to prepare a high-purity NMP product, and the purity of the NMP product prepared by using a common rectifying method is still not high. In order to obtain an NMP product with purity meeting the requirement, a plurality of rectifying towers are often needed, and although an NMP finished product is finally obtained, the energy consumption is high, the operation is complex, and the operation cost is high. By using the method of the invention, the NMP is dehydrated by the molecular sieve membrane, and then the NMP product obtained by refining the NMP through the rectifying tower has high purity, and the energy consumption is greatly saved.
In order to better implement the method of the present invention, in a specific embodiment of the present invention, there is provided an apparatus for separating and purifying NMP by a pervaporation membrane, which is used exclusively for the method, and the method is implemented using the apparatus. The NMP device for pervaporation membrane separation and purification comprises a raw material processing unit, a membrane separation unit, a retentate processing unit and a rectification unit, wherein: the raw material processing unit comprises a first heat exchange device 1, a first storage tank 2 and a second storage tank 3; wherein the second storage tank 3 is provided with a material inlet and a material outlet; the membrane separation unit is provided with a material inlet, a retentate outlet and a permeate outlet; the material inlet of the second storage tank 3 is connected with the retentate outlet of the membrane separation unit; the material outlet of the second storage tank 3 is connected with the rectification unit; and the permeate outlet of the membrane separation unit is connected with the permeate treatment unit. The raw material of the water-containing NMP to be treated enters the membrane separation unit through the raw material treatment unit, and the membrane separation process is carried out. Water molecules penetrate through the molecular sieve membrane to form permeate, and the permeate is discharged out of the system by the permeate treatment unit. NMP with larger molecular size is intercepted by a molecular sieve membrane to form finished NMP with ultralow water content, and the finished NMP is conveyed to a rectification unit for purification and collection to form a product.
In a specific embodiment, the device comprises a raw material processing unit, a membrane separation unit, a permeate processing unit and a rectification unit, wherein: the raw material processing unit comprises a first heat exchange device 1, a first storage tank 2 and a second storage tank 3; the membrane separation unit comprises a first membrane separation assembly 6 and a second membrane separation assembly 7; a first fluid conveying device 4 and a second heat exchange device 5 are also arranged between the raw material processing unit and the membrane separation unit; the permeate processing unit comprises a permeate processing device 8, a third storage tank 9 and a second fluid conveying device 10; the rectifying unit is provided with a first separation tower 12, the top of the first separation tower 12 is connected with a fourth heat exchange device 13, and the bottom of the first separation tower 12 is connected with a fifth heat exchange device 14; wherein, the second storage tank 3 is provided with a material inlet and a material outlet; the membrane separation unit is provided with a material inlet, a retentate outlet and a permeate outlet; the material inlet of the second storage tank 3 is connected with the retentate outlet of the membrane separation unit; the material outlet of the second storage tank 3 is connected with the rectification unit, and a third fluid conveying device 11 is arranged between the material outlet and the rectification unit; the permeate outlet of the membrane separation unit is connected with the permeate treatment unit; the material outlet of the second storage tank 3 is also connected with a first fluid conveying device 4.
In the apparatus for purifying NMP by pervaporation membrane separation according to the present invention described above:
the first heat exchange device 1 provides a site for preheating the feedstock. According to the process requirements, the first heat exchange device 1 can be selected from, but not limited to, a fixed tube-plate type tube-and-tube heat exchanger, a floating head type tube-and-tube heat exchanger, a U-shaped tube-and-tube heat exchanger, a spiral plate type heat exchanger, a spiral tube wound heat exchanger and a plate type heat exchanger.
The first storage tank 2 is used for buffer storage of the water-containing NMP raw material.
The second reservoir 3 is used for retentate buffer storage.
The first fluid transfer means 4 is adapted to transfer the aqueous feed to a membrane separation unit, which may be selected from, but is not limited to, a centrifugal pump, a positive displacement pump.
The second heat exchange means 5 is adapted to receive and heat exchange the aqueous NMP feedstock from the feedstock treatment unit. The second heat exchanger 5 can be selected from, but not limited to, a fixed tube-plate type tube-and-tube heat exchanger, a floating head type tube-and-tube heat exchanger, a U-shaped tube-and-tube heat exchanger, a spiral plate type heat exchanger, a spiral tube wound heat exchanger, and a plate type heat exchanger.
The membrane separation unit is used for realizing efficient separation of NMP and water. For realizing the purpose, the membrane separation unit is preferably an inorganic molecular sieve membrane separation unit and consists of n (n is a positive integer) molecular sieve membrane assemblies. The membrane assembly can be a single tube pass or a plurality of tube passes, and the area of the single membrane assembly can be controlled between 5 square meters and 300 square meters. The number n of membrane modules arranged in each set is determined according to the separation purpose; when n is greater than 1, the membrane modules can be connected in series or in parallel according to the material condition, the separation target and the like. On the other hand, from the component structure, the present invention can adopt, but is not limited to, specific forms such as a thermostatic membrane component or a baffle-type membrane component. In the embodiment of the present invention, the molecular sieve membrane module may be specifically exemplified by, but not limited to, a plate-type, tubular-type, hollow fiber-type or spiral plate-type molecular sieve membrane module, preferably a tubular-type molecular sieve membrane module. Suitable types of molecular sieves include LTA, SOD, FAU, MOR, FER, MFI, PHI, BEA, CHA, ERI, and mixed crystal molecular sieve membranes thereof, preferably type A molecular sieve membranes.
The permeate processing means 8 is arranged to receive the permeate from the membrane separation unit and to further process it. The permeate processing equipment 8 can be selected from, but is not limited to, a vacuum unit with steam condensation recovery.
The third storage tank 9 is a permeate buffer tank, and is output by the second fluid conveying device 10 after being buffered. The second fluid transfer device 10 may be exemplified by, but not limited to, a centrifugal pump, a positive displacement pump.
The third fluid conveying device 11 is used for conveying the finished NMP with the water content meeting the requirement from the second storage tank 3 to a rectification unit for further purification, and specifically, a centrifugal pump and a positive displacement pump can be selected and not limited.
The first separation column 12 is used for refining and purifying NMP by rectification. The first separation column 12 may be selected from, but not limited to, a tray column, a packed column.
The fourth heat exchange means 13 is adapted to receive the overhead vapor from the first separation column 12 and exchange heat therewith to obtain a high purity NMP product. The fourth heat exchange device 13 can be selected from, but is not limited to, a fixed tube-plate type tube-and-tube heat exchanger, a floating head type tube-and-tube heat exchanger, a U-shaped tube-and-tube heat exchanger, a spiral plate type heat exchanger, a spiral tube wound heat exchanger, and a plate type heat exchanger.
The fifth heat exchange device 14 is used for receiving the high-boiling impurities in the bottom material from the first separation tower 12 and further processing the high-boiling impurities to discharge the high-boiling impurities out of the system. The fifth heat exchange device 14 may be selected from, but is not limited to, a fixed tube and plate type tube and tube heat exchanger, a floating head type tube and tube heat exchanger, a U-shaped tube and tube heat exchanger, a spiral plate type heat exchanger, a spiral tube wound heat exchanger, and a plate type heat exchanger.
In the structural description of the above-mentioned device, the components that can be determined by those skilled in the art through the prior art in this field are not described, and these components can be exemplified but not limited to: the pipeline is used for connecting each device, and the valve is used for controlling the material to enter and exit. In addition, in combination with the above description, those skilled in the art can determine the most appropriate device selection and type according to the design requirements and requirements under the guidance of the prior art, and it is needless to describe this.
In combination with the apparatus for separating and purifying NMP by pervaporation membrane in the above embodiment, the method for separating and purifying NMP by pervaporation membrane according to the present invention can be further described as including the following steps:
(1) an NMP raw material with the water content of 1-20% is preheated to 120 +/-10 ℃ through a first heat exchange device 1 at the mass flow rate of 1200 +/-100 kg/batch, enters a first storage tank 2 for buffering, is conveyed to a first membrane separation assembly 6 and a second membrane separation assembly 7 through a first fluid conveying device 4 and a second heat exchange device 5 at the temperature of 120 +/-2 ℃ for primary dehydration, and enters a third storage tank 9 after passing through a permeate treatment device 8, and is discharged out of the system through the second fluid conveying device 10;
(2) conveying the retentate after primary dehydration to a second storage tank 3, and continuously circularly conveying the retentate to a membrane separation unit by a first fluid conveying device 4 for secondary dehydration; transferring the retentate after the secondary dehydration to a first storage tank 2, and circulating the steps; the cumulative mass flow rate of permeate was 180 ± 15 kg/batch with a total water content of greater than 99.5%;
(3) when the water content of the retentate is detected to meet the product requirement, the retentate is conveyed to the first separation tower 12 through the second storage tank 3 by the third fluid conveying device 11 for further purification, the theoretical plate number of the first separation tower 12 is 25 +/-5, ascending steam is provided by the fifth heat exchange device 14 at the tower bottom, the operating temperature of the fifth heat exchange device 14 is 160 +/-10 ℃, the tower top is connected with the fourth heat exchange device 13, the operating temperature of the fourth heat exchange device 13 is 120 ℃, a high-purity NMP product is extracted at the tower top, and high-boiling impurities are extracted at the tower bottom.
The optimization of the overall solution according to the invention should take into account the influence of the combination of technical features on the overall solution in addition to the application of the above-mentioned preferred technical features. The present invention provides a specific example of the above-mentioned method for purifying NMP by pervaporation membrane separation to specifically explain the mode and effect of the present invention. In this example, the method described herein uses a pervaporation membrane separation and purification apparatus for NMP as schematically shown in fig. 1, and the selection of the respective devices in the apparatus is as follows:
the first heat exchange device 1 is a fixed tube-plate type tubular heat exchanger.
The first storage tank 2 is a first buffer tank.
The second storage tank 3 is a second buffer tank.
The first fluid conveying device 4 is a centrifugal pump.
The second heat exchange device 5 is a fixed tube-plate type tubular heat exchanger.
The first membrane separation component 6 is a tubular molecular sieve membrane component; the molecular sieve membrane is an A-type molecular sieve membrane.
The second membrane separation component 7 is a tubular molecular sieve membrane component; the molecular sieve membrane is an A-type molecular sieve membrane.
The permeate treatment device 8 adopts a vacuum unit with steam condensation and recovery.
The third storage tank 9 is a permeate buffer tank.
The second fluid transfer device 10 is a centrifugal pump.
The third fluid delivery device 11 is a centrifugal pump.
The first separation tower 12 is a packed tower.
The fourth heat exchange device 13 is a fixed tube-plate type tubular heat exchanger.
The fifth heat exchange device 14 is a fixed tube-plate type tubular heat exchanger.
The method for separating and purifying NMP by the pervaporation membrane, which is implemented by combining the device, comprises the following steps:
(1) the waste solvent NMP raw material from the coating section of a lithium battery production workshop, which contains 15% of water and a small amount of alkanone high-boiling point impurities, is preheated to 120 ℃ through a fixed tube plate type tube and tube heat exchanger 1 at a mass flow rate of 1200 kg/batch, enters a first buffer tank 2 for buffering, is conveyed to enter a tubular molecular sieve membrane assembly 6 and a tubular molecular sieve membrane assembly 7 through a centrifugal pump 4 and a fixed tube plate type tube and tube heat exchanger 5 at a temperature of 120 ℃ (the total membrane area of selected molecular sieve membranes is 72m2) Performing primary dehydration, treating the permeate by a vacuum unit 8 with steam condensation recovery, then entering a permeate buffer tank 9, and discharging the permeate from the system by a centrifugal pump 10;
(2) conveying the retentate after primary dehydration to a second buffer tank 3, continuously and circularly conveying the retentate to a membrane separation unit by a centrifugal pump 4 for secondary dehydration, and conveying the retentate after secondary dehydration into a first buffer tank 2 for circulating the steps; the cumulative mass flow rate of permeate was 180 kg/batch with a total water content of greater than 99.5%;
(3) when the water content of the retentate is detected to be less than 200ppm, the retentate is conveyed to a packed tower 12 through a second buffer tank 3 by a centrifugal pump 11 and is further purified under negative pressure, the theoretical plate number of the packed tower 12 is 25, ascending steam is provided by a fixed tube plate type tube-column heat exchanger 14 at the tower bottom, the operating temperature of the fixed tube plate type tube-column heat exchanger 14 is 160 ℃, a fixed tube plate type tube-column heat exchanger 13 is arranged at the tower top, the operating temperature of the fixed tube plate type tube-column heat exchanger 13 is 120 ℃, a high-purity NMP product is extracted from the tower top, the water content of the NMP product is less than 200ppm, the NMP purity is higher than 99.9%, and high-.
Through the treatment of the device, the NMP mass concentration in the obtained permeate is less than 0.5%, and the NMP recovery rate in the whole process is more than 99.9%. At the same time, the steam consumption per ton of NMP product was about 0.35 ton.
Comparative example 1
Conventionally, a rectifying column is often used for dehydration in NMP purification, and therefore, an NMP purification apparatus shown in fig. 2 is provided.
Wherein, the membrane separation unit is replaced by a rectification dehydration unit, the second separation tower 15 is a dehydration rectification tower and is used for realizing the dehydration of the NMP raw material, and a packed tower is selected. And the sixth heat exchange equipment and the seventh heat exchange equipment adopt fixed tube plate type tubular heat exchangers. Other device options are the same as those selected in the above embodiment.
The NMP purification method implemented by combining the device comprises the following steps:
(1) the waste solvent NMP raw material from the coating section of a lithium battery production workshop, which contains 15% of water and a small amount of alkanone high-boiling point impurities, is preheated to 120 ℃ through a fixed tube plate type tube-and-tube heat exchanger 1 at a mass flow rate of 1200 kg/batch, enters a first buffer tank 2 for buffering, is conveyed to enter a packed tower 15 for dehydration at a temperature of 120 ℃ through a centrifugal pump 4 and a fixed tube plate type tube-and-tube heat exchanger 5;
(2) the theoretical plate number of the packed tower 15 is 25, the fixed tube-plate type tubular heat exchanger 17 provides ascending steam at the tower bottom, the operating temperature of the fixed tube-plate type tubular heat exchanger 17 is 120 ℃, the fixed tube-plate type tubular heat exchanger 16 is configured at the tower top, the operating temperature of the fixed tube-plate type tubular heat exchanger 16 is 40 ℃, and the dehydrated NMP raw material is extracted at the tower top;
(3) when the water content of the NMP raw material is detected to be less than 200ppm, the NMP raw material is conveyed to a packed tower 12 through a second buffer tank 3 by a centrifugal pump 11 to be further purified under negative pressure, the theoretical plate number of the packed tower 12 is 25, ascending steam is provided by a fixed tube plate type tubular heat exchanger 14 at the tower bottom, the operating temperature of the fixed tube plate type tubular heat exchanger 14 is 160 ℃, a fixed tube plate type tubular heat exchanger 13 is arranged at the tower top, the operating temperature of the fixed tube plate type tubular heat exchanger 13 is 120 ℃, a high-purity NMP product is extracted from the tower top, the water content of the NMP product is less than 200ppm, the NMP purity is higher than 99.9%, and high-boiling impurities.
Through the treatment of the device, the NMP product can also meet the requirements of water content and purity, but the steam energy consumption is 0.85-0.9 ton/ton product, and the energy consumption is far higher than that of the method and the device for separating and refining the NMP by the pervaporation membrane provided by the invention.
Claims (7)
1. A method for separating and purifying NMP by a pervaporation membrane, which is characterized by comprising the following steps: preheating a water-containing NMP raw material at a mass flow rate of 1200 +/-100 kg/batch, then feeding the preheated water-containing NMP raw material into a first storage tank, feeding the buffered raw material into a membrane separation unit for primary dehydration, and feeding a permeate into a permeate treatment unit;
and (3) the retentate obtained by the first dehydration enters a second storage tank, is continuously conveyed to the membrane separation unit for second dehydration in a circulating manner, enters the first storage tank, and is conveyed to the rectification unit for purification through the second storage tank when the water content of the retentate is detected to meet the product requirement, so that a high-purity NMP product is produced.
2. The method according to claim 1, wherein the water content of the raw material containing water NMP is 1-20% by mass.
3. The method according to claim 1, wherein the permeate side pressure of the membrane separation unit is 0.1-30 kPa.
4. The method of claim 1, wherein the feedstock is preheated to a temperature of 120 ± 10 ℃.
5. The method according to claim 1, wherein the method uses a pervaporation membrane separation purification NMP apparatus comprising a raw material treatment unit, a membrane separation unit, a permeate treatment unit, and a rectification unit, wherein: the raw material processing unit comprises a first heat exchange device (1), a first storage tank (2) and a second storage tank (3);
wherein the second storage tank (3) is provided with a material inlet and a material outlet; the membrane separation unit is provided with a material inlet, a retentate outlet and a permeate outlet; the material inlet of the second storage tank (3) is connected with the retentate outlet of the membrane separation unit; the material outlet of the second storage tank (3) is connected with the rectification unit;
and the permeate outlet of the membrane separation unit is connected with the permeate treatment unit.
6. The method according to claim 5, wherein the apparatus for purifying NMP by pervaporation membrane separation comprises a raw material processing unit, a membrane separation unit, a permeate processing unit and a rectification unit, wherein: the raw material processing unit comprises a first heat exchange device (1), a first storage tank (2) and a second storage tank (3); the membrane separation unit comprises a first membrane separation assembly (6) and a second membrane separation assembly (7); a first fluid conveying device (4) and a second heat exchange device (5) are arranged between the raw material processing unit and the membrane separation unit; the permeate treatment unit comprises a permeate treatment device (8), a third storage tank (9) and a second fluid conveying device (10); the rectification unit is provided with a separation tower (12), the tower top of the separation tower (12) is connected with a fourth heat exchange device (13), and the tower bottom is connected with a fifth heat exchange device (14);
wherein the second storage tank (3) is provided with a material inlet and a material outlet; the membrane separation unit is provided with a material inlet, a retentate outlet and a permeate outlet; the material inlet of the second storage tank (3) is connected with the retentate outlet of the membrane separation unit; a material outlet of the second storage tank (3) is connected with the rectification unit, and a third fluid conveying device (11) is arranged between the material outlet and the rectification unit; the permeate outlet of the membrane separation unit is connected with the permeate treatment unit;
the material outlet of the second storage tank (3) is also connected with a first fluid conveying device (4).
7. The method of claim 6, comprising the steps of:
(1) an NMP raw material with the water content of 1-20% is preheated to 120 +/-10 ℃ through a first heat exchange device (1) at the mass flow rate of 1200 +/-100 kg/batch, enters a first storage tank (2) for buffering, is conveyed to 120 +/-2 ℃ through a first fluid conveying device (4) and a second heat exchange device (5) to enter a first membrane separation module (6) and a second membrane separation module (7) for primary dehydration, and is conveyed to a third storage tank (9) after passing through a permeate treatment device (8) and discharged out of a system through the second fluid conveying device (10);
(2) conveying the retentate after primary dehydration to a second storage tank (3), continuously circularly conveying the retentate to a membrane separation unit by a first fluid conveying device (4) for secondary dehydration, and conveying the retentate after secondary dehydration into a first storage tank (2) to circulate the steps;
(3) when the moisture content of the retentate is detected to meet the product requirement, the retentate is conveyed to a separation tower (12) for further purification through a second storage tank (3) by a third fluid conveying device (11), rising steam is provided at the bottom of the tower by a fifth heat exchange device (14), the top of the tower is connected with a fourth heat exchange device (13), a high-purity NMP product is extracted at the top of the tower, and high-boiling impurities are extracted at the bottom of the tower.
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