Purification method and purification apparatus for nmp

Abstract

The present invention relates to a purification method and purification apparatus for NMP. Specifically, according to one embodiment of the present invention, the purification method for NMP purifies a gas mixture (A) containing NMP, separated out through a sludge separator, before performing an NMP purification step, and thus can improve processability, and the recovery rate and purity of NMP. In addition, a mixture containing sludge, separated out through a sludge separator, is injected into a filtrate recovery device and heat treated such that components having boiling points higher than that of NMP contained in the mixture containing sludge can be effectively removed, and a circulation step using an impurity tank is included to allow the components having boiling points higher than that of recirculated NMP to act as a transfer material of waste NMP, thereby facilitating use in an NMP purification process such that processability can be improved.

Description

Purification method and purification apparatus of NMP

[0001] The present invention relates to a method and apparatus for purifying waste NMP.

[0002] With the recent increase in technological development for portable devices such as mobile phones and cameras, interest in secondary batteries as energy sources has grown. Demand for lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, and low self-discharge rates, has rapidly increased. Research into their recycling is also ongoing.

[0003] N-Methyl-2-pyrrolidone (NMP), an organic solvent, is widely used as a solvent in industries such as petrochemicals, plastics, and pharmaceuticals due to its chemical stability, low volatility, and ability to dissolve various substances, and is also used in the process of manufacturing secondary batteries.

[0004] In particular, lithium ion secondary batteries are composed of a positive electrode manufactured by applying an electrode material including a lithium compound such as lithium cobaltate or lithium manganate, a binder such as polyvinylidene fluoride, and N-methyl-2-pyrrolidone (NMP) as a solvent to a substrate and firing the same, and a negative electrode manufactured by applying an electrode material including a lithium compound including carbon, titanium, etc., a binder such as polyvinylidene fluoride, and water as a solvent to a substrate and firing the same. As such, NMP is not only used as a main material for manufacturing the positive electrode in the electrode manufacturing process, but is also emitted in large quantities for use in cleaning and drying, and therefore research into technologies for effectively recovering it is ongoing.

[0005] For example, Korean Patent No. 10-2050990 discloses a system for separating and recovering NMP from NMP gas by bringing NMP-containing gas containing NMP into gas-liquid contact with water that has absorbed NMP, thereby allowing NMP in the NMP-containing gas to be absorbed into the water.

[0006] [Prior Art Literature]

[0007] [Patent Document]

[0008] (Patent Document 1) Korean Patent No. 2050990

[0009] Accordingly, the present invention aims to provide a method and a purification device for purifying NMP, which can improve the recovery rate of NMP recovered from waste NMP and provide high-purity NMP.

[0010] A method for purifying NMP according to one embodiment of the present invention comprises the steps of: (1) introducing waste NMP from a raw material tank into a sludge separator; (2) discharging a gas mixture (A) containing NMP separated from the sludge separator through the top of the sludge separator and discharging a mixture containing sludge through the bottom of the sludge separator; (3) introducing the discharged gas mixture (A) containing NMP into a first distillation column to perform first purification; (4) discharging an effluent containing water separated through the first purification to the outside of the system through the top of the first distillation column and discharging a first draw-out through the bottom of the first distillation column; (5) introducing the discharged first draw-out into a second distillation column to perform second purification; (6) discharging purified NMP separated through the second purification to the outside of the system through the top of the second distillation column and discharging a second draw-out through the bottom of the second distillation column; (7) a step of introducing a mixture including sludge discharged in the step (2) into a filtrate recovery device and subjecting it to heat treatment; (8) a step of discharging the tertiary effluent separated through the heat treatment to the outside of the system through the lower end of the filtrate recovery device and discharging a gas mixture (B) including NMP through the upper end of the filtrate recovery device; (9) a step of introducing the secondary effluent discharged in the step (6) and the gas mixture (B) including NMP discharged in the step (8) into an impurity tank and mixing them; and (10) a step of circulating the mixture in the impurity tank to the raw material tank.

[0011] According to another embodiment of the present invention, an NMP purification device comprises: a raw material tank for supplying waste NMP; a sludge separator having a sludge filter and a sludge separator therein, and discharging a gas mixture (A) including NMP separated from the supplied waste NMP through an upper portion and a mixture including sludge through a lower portion; a first distillation column for performing a first purification of the gas mixture (A) including NMP, discharging an effluent including water separated through the first purification to the outside of the system through an upper portion, and discharging a first draw-out through a lower portion; a second distillation column for performing a second purification by distilling the first draw-out, discharging purified NMP separated through the second purification to the outside of the system through an upper portion, and discharging a second draw-out through a lower portion; a filtrate recovery device for heat-treating a mixture including sludge discharged from the sludge separator, discharging a third draw-out separated through the heat-treatment to the outside of the system through an lower portion, and discharging a gas mixture (B) including NMP through an upper portion; And it includes an impurity tank for mixing a gas mixture (B) including the secondary effluent discharged from the secondary distillation tower and NMP discharged from the filtrate recovery device and injecting the mixture into the raw material tank.

[0012] A method for purifying NMP according to one embodiment of the present invention can improve the recovery rate of NMP recovered from waste NMP, thereby providing high-purity NMP.

[0013] Specifically, waste NMP recovered after use as a material for lithium secondary batteries may contain a large amount of sludge. This waste NMP containing a large amount of sludge is difficult to transport during the NMP recovery process, potentially blocking the transport pipes and requiring a separate solution for transport.

[0014] A method for purifying NMP according to one embodiment of the present invention can improve the processability as well as the recovery rate and purity of NMP by purifying a gas mixture (A) containing NMP separated through a sludge separator prior to performing the NMP purification step. In particular, the sludge separator includes a sludge filter and a sludge separation plate, so that a large amount of sludge contained in waste NMP can be effectively separated simply without having to specifically control process conditions.

[0015] In addition, by introducing a mixture containing sludge separated through the sludge separator into a filtrate recovery device and subjecting it to heat treatment, components having a boiling point higher than NMP contained in the mixture containing the sludge can be effectively removed.

[0016] In addition, by introducing the gas mixture (B) containing the secondary effluent discharged from the secondary purification stage and the NMP discharged from the filtrate recovery device into the impurity tank and mixing them, and then introducing them back into the raw material tank and circulating them, the recovery rate and purity of NMP can be improved, and since a component having a higher boiling point than the circulated NMP acts as a transport material for the waste NMP, it can be easily utilized in the NMP purification process, thereby improving the processability.

[0017] In addition, when the mixture in the above impurity tank is heat-treated and then introduced into a secondary distillation tower, the recovery rate of NMP can be further improved.

[0018] Figure 1 schematically illustrates a flow chart of an NMP purification method according to one embodiment of the present invention.

[0019] Figure 2 illustrates an example of an NMP purification device according to another embodiment of the present invention.

[0020] The present invention is described in detail below. The present invention is not limited to the details disclosed below and may be modified in various ways without altering the spirit of the invention.

[0021] In this specification, when a part is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0022] All numbers and expressions indicating the amounts of components, reaction conditions, etc. described in this specification should be understood to be modified by the term “about” in all cases unless otherwise specified.

[0023] When it is described in this specification that one component is formed on or under another component, it includes both cases where one component is formed directly on or under the other component, or indirectly through the interposition of another component.

[0024] In this specification, the terms "primary," "secondary," "first," and "secondary" are used to describe various components, and the components are not limited by the terms. The terms are used solely to distinguish one component from another.

[0025]

[0026] NMP purification method

[0027] A method for purifying NMP according to one embodiment of the present invention comprises the steps of: (1) introducing waste NMP from a raw material tank into a sludge separator; (2) discharging a gas mixture (A) containing NMP separated from the sludge separator through the top of the sludge separator and discharging a mixture containing sludge through the bottom of the sludge separator; (3) introducing the discharged gas mixture (A) containing NMP into a first distillation column to perform first purification; (4) discharging an effluent containing water separated through the first purification to the outside of the system through the top of the first distillation column and discharging a first draw-out through the bottom of the first distillation column; (5) introducing the discharged first draw-out into a second distillation column to perform second purification; (6) discharging purified NMP separated through the second purification to the outside of the system through the top of the second distillation column and discharging a second draw-out through the bottom of the second distillation column; (7) a step of introducing a mixture including sludge discharged in the step (2) into a filtrate recovery device and subjecting it to heat treatment; (8) a step of discharging the tertiary effluent separated through the heat treatment to the outside of the system through the lower end of the filtrate recovery device and discharging a gas mixture (B) including NMP through the upper end of the filtrate recovery device; (9) a step of introducing the secondary effluent discharged in the step (6) and the gas mixture (B) including NMP discharged in the step (8) into an impurity tank and mixing them; and (10) a step of circulating the mixture in the impurity tank to the raw material tank.

[0028] FIG. 1 schematically illustrates an NMP purification method according to one embodiment of the present invention, and FIG. 2 illustrates an example of an NMP purification device according to another embodiment of the present invention. Specifically, FIG. 2 illustrates an NMP purification device composed of a raw material tank (RT), a sludge separator (W), a first distillation column (D1), a second distillation column (D2), a filtrate recovery device (R), and an impurity tank (PT).

[0029] Hereinafter, a method for purifying NMP according to one embodiment of the present invention will be described with reference to FIGS. 1 and 2.

[0030]

[0031] Step (1) of feeding waste NMP from the raw material tank into the sludge separator

[0032] A method for purifying NMP according to one embodiment of the present invention includes a step of introducing waste NMP from a raw material tank into a sludge separator.

[0033] The above-mentioned waste NMP may be recovered after being used in the process of manufacturing a lithium secondary battery, but is not limited thereto. For example, the above-mentioned waste NMP may be recovered after being used as a material for a lithium secondary battery and may contain a large amount of sludge.

[0034] The above waste NMP may contain NMP in an amount of 70 wt% or more. For example, the content of NMP in the waste NMP may be 72 wt% or more, 75 wt% or more, 78 wt% or more, 80 wt% or more, 85 wt% or more, 90 wt% or more, or 95 wt% or more based on the total weight of the waste NMP.

[0035] Additionally, the waste NMP may contain moisture. For example, the moisture content in the waste NMP may be 30 wt% or less, 25 wt% or less, 20 wt% or less, or 15 wt% or less based on the total weight of the waste NMP.

[0036] The above sludge separator may include a sludge filter and a sludge separator. Specifically, the sludge filter may be in the form of a mesh net located at the upper portion inside the sludge separator. In addition, the sludge separator may be provided at a position lower than the sludge filter, and may be provided at a position where the waste NMP is fed into the sludge separator. The sludge separator serves to block the flow of waste NMP fed into the sludge separator so that the waste NMP does not directly contact the sludge filter, and the shape may be an “L” shape, but is not limited thereto. The sludge separator may primarily filter sludge by blocking the flow of waste NMP fed into the sludge separator, thereby not only removing sludge with high efficiency but also extending the life of the sludge filter.

[0037] The above waste NMP can pass through the sludge separator and the sludge filter, and a gas mixture (A) containing the NMP can be discharged to the top of the sludge separator, and a large amount of sludge contained in the waste NMP can be effectively separated through the sludge separator and the sludge filter.

[0038] The NMP purification method according to one embodiment of the present invention has excellent processability because it can simply separate a large amount of sludge contained in waste NMP without specifically controlling process conditions by using a sludge separator having the above technical characteristics.

[0039] In addition, before introducing the waste NMP into the sludge separator in the step (1), a step (1-1) of preheating the waste NMP to a temperature of 60°C to 100°C may be additionally included. For example, the step (1-1) may be a step of preheating the waste NMP to a temperature of 62°C to 100°C or 65°C to 95°C, and the preheated waste NMP may be introduced into the sludge separator.

[0040]

[0041] Step (2) of discharging a gas mixture (A) containing NMP separated in the sludge separator through the top of the sludge separator and discharging a mixture containing sludge through the bottom of the sludge separator

[0042] A method for purifying NMP according to one embodiment of the present invention includes the steps of discharging a gas mixture (A) containing NMP separated in the sludge separator through the upper portion of the sludge separator and discharging a mixture containing sludge through the lower portion of the sludge separator.

[0043] Specifically, the above step (2) effectively separates a gas mixture (A) containing separated NMP and a mixture containing sludge using a sludge separator, thereby removing a large amount of sludge contained in waste NMP, thereby improving the process for recovering NMP and the recovery rate and purity of NMP.

[0044]

[0045] Step (3) of performing primary purification by introducing the gas mixture (A) containing the discharged NMP into the primary distillation tower

[0046] A method for purifying NMP according to one embodiment of the present invention includes a step of introducing a gas mixture (A) containing the discharged NMP into a first distillation column to perform first purification.

[0047] In the above step (3), the gas mixture (A) containing the discharged NMP may be introduced into the upper portion of the first distillation column. Specifically, it may be preferable for the gas mixture (A) containing the NMP to be introduced into the middle portion of the first distillation column or a portion higher therefrom in order to more efficiently perform the first purification, but the present invention is not limited thereto.

[0048] The primary purification of the above step (1) can be performed at a temperature of 50°C to 100°C and a pressure of 100 torr to 130 torr. For example, the primary purification can be performed at a temperature of 52°C to 85°C or 55°C to 75°C and a pressure of 105 torr to 130 torr or 110 torr to 125 torr. By satisfying the temperature and pressure conditions of the primary purification within the above ranges, moisture contained in the gas mixture (A) containing NMP can be effectively removed.

[0049]

[0050] Step (4) of discharging the effluent containing water separated through the first purification to the outside of the system through the top of the first distillation tower, and discharging the first draw-off liquid through the bottom of the first distillation tower

[0051] A method for purifying NMP according to one embodiment of the present invention includes a step of discharging an effluent containing water separated through the primary purification to the outside of the system through the top of the primary distillation column, and discharging the primary draw-off liquid through the bottom of the primary distillation column.

[0052] Specifically, the step (4) can improve the purity of NMP by separating the effluent containing water from the gas mixture (A) containing NMP through the primary purification of the step (3) and discharging it to the outside of the system, thereby reducing the moisture content.

[0053] The moisture content in the primary effluent may be 0.01% or less. For example, the moisture content in the primary effluent may be 0.008% or less, 0.006% or less, or 0.005% or less.

[0054] In addition, the primary effluent may contain NMP in an amount of 99.9 wt% or more. For example, the content of NMP in the primary effluent may be 99.92 wt% or more, 99.94 wt% or more, or 99.95 wt% or more, based on the total weight of the primary effluent. By effectively removing most of the moisture in the waste NMP through the primary purification, the purity of NMP in the primary effluent can be further improved.

[0055]

[0056] Step (5) of performing secondary purification by putting the discharged primary effluent into a secondary distillation tower

[0057] The NMP purification method according to one embodiment of the present invention includes a step of performing secondary purification by introducing the discharged primary effluent into a secondary distillation tower.

[0058] The purity of NMP can be improved through the above secondary purification. Specifically, the waste NMP may contain components with a higher boiling point than the NMP along with the NMP. By performing a secondary purification in step (5) on the first effluent from which moisture has been removed through the first purification, components with a boiling point higher than the NMP can be effectively removed, thereby further improving the purity of the NMP.

[0059] In the above step (5), the first distillate may be injected into the middle or lower portion of the second distillation column. Specifically, it may be preferable for the first distillate to be injected into the middle or lower portion of the second distillation column to more efficiently perform the second distillation, but the present invention is not limited thereto.

[0060] The secondary purification can be performed at a temperature of 120°C to 150°C and a pressure of 50 torr to 90 torr. For example, the secondary purification can be performed at a temperature of 122°C to 148°C or 126°C to 145°C and a pressure of 55 torr to 85 torr or 65 torr to 80 torr. By satisfying the temperature and pressure conditions of the secondary purification within the above ranges, components having a boiling point higher than NMP contained in the primary extractant can be effectively removed.

[0061]

[0062] Step (6) of discharging purified NMP separated through the above secondary purification to the outside of the system through the top of the above secondary distillation tower, and discharging the secondary draw-off liquid through the bottom of the above secondary distillation tower.

[0063] A method for purifying NMP according to one embodiment of the present invention includes a step of discharging purified NMP separated through the secondary purification to the outside of the system through the top of the secondary distillation column, and discharging the secondary draw-off liquid through the bottom of the secondary distillation column.

[0064] Specifically, the step (6) can obtain purified NMP by discharging the second extract containing a component having a boiling point higher than NMP from the first extract through the second purification of the step (5).

[0065] The secondary extract may contain a component having a boiling point higher than NMP in an amount of 1.0 wt% or less. For example, the content of the component having a boiling point higher than NMP in the secondary extract may be 0.8 wt% or less, 0.6 wt% or less, or 0.4 wt% or less, based on the total weight of the secondary extract.

[0066] The secondary extract may contain NMP in an amount of 99 wt% or more. For example, the content of NMP in the secondary extract may be 99.2 wt% or more, 99.4 wt% or more, 99.5 wt% or more, or 99.6 wt% or more, based on the total weight of the secondary extract.

[0067] The purity of the above purified NMP may be 99.9% or higher. For example, the purity of the above purified NMP may be 99.92% or higher, 99.94% or higher, or 99.95% or higher.

[0068]

[0069] Step (7) of heat-treating the mixture containing the sludge discharged in the above step (2) by putting it into a filtrate recovery device.

[0070] A method for purifying NMP according to one embodiment of the present invention includes a step of introducing a mixture containing sludge discharged in step (2) into a filtrate recovery device and subjecting it to heat treatment.

[0071] Specifically, since the mixture containing the sludge separated through the sludge separator may also contain NMP, the mixture containing the sludge may be introduced into a filtrate recovery device and subjected to heat treatment, thereby separating the NMP contained in the mixture containing the sludge in a gaseous form and recycling it.

[0072] In the above step (7), the heat treatment can be performed at a temperature of 110°C to 140°C and a pressure of 60 torr to 100 torr while stirring at 20 rpm to 80 rpm. For example, the heat treatment can be performed at a temperature of 115°C to 140°C, 125°C to 138°C, or 128°C to 135°C, and a pressure of 65 torr to 95 torr, or 75 torr to 85 torr while stirring at 25 rpm to 70 rpm, or 30 rpm to 60 rpm. When the process conditions of the heat treatment satisfy the above ranges, the recovery rate of NMP can be further improved.

[0073] Additionally, the pressure of the filtrate recovery device can be controlled through a vacuum pump connected to the filtrate recovery device, more specifically, a vacuum pump connected to a cooler connected to the filtrate recovery device. Since controlling the pressure of the filtrate recovery device is important to achieve the desired effects of the present invention, the pressure of the filtrate recovery device can be controlled through a vacuum pump.

[0074]

[0075] Step (8) of discharging the separated third effluent separated through the above heat treatment to the outside of the system through the bottom of the filtrate recovery device, and discharging the gas mixture (B) containing NMP through the top of the filtrate recovery device.

[0076] A method for purifying NMP according to one embodiment of the present invention includes a step of discharging the separated third effluent separated through the heat treatment to the outside of the system through the lower end of the filtrate recovery device, and discharging a gas mixture (B) containing NMP through the upper end of the filtrate recovery device.

[0077] Specifically, the step (8) can separate the gas mixture (B) containing the tertiary effluent and NMP through heat treatment in the step (7), and the gas mixture (B) containing NMP can be circulated and used, thereby improving the fairness and the recovery rate of NMP.

[0078] The gas mixture (B) containing the NMP may contain a component having a boiling point higher than that of NMP in an amount of 1.5 wt% or less. For example, the content of the component having a boiling point higher than that of NMP in the gas mixture (B) containing the NMP may be 1.2 wt% or less, 1.0 wt% or less, 0.8 wt% or less, 0.6 wt% or less, or 0.5 wt% or less, based on the total weight of the gas mixture (B) containing the NMP.

[0079]

[0080] Step (9) of mixing the gas mixture (B) containing the secondary discharged liquid from the above step (6) and the NMP discharged from the above step (8) by introducing them into an impurity tank.

[0081] A method for purifying NMP according to one embodiment of the present invention includes a step of introducing a gas mixture (B) containing the secondary effluent discharged in step (6) and the NMP discharged in step (8) into an impurity tank and mixing them.

[0082] The mixture in the impurity tank may contain a component having a boiling point higher than NMP in an amount of 1.5 wt% or less. For example, the content of the component having a boiling point higher than NMP in the mixture in the impurity tank may be 1.0 wt% or less, 0.8 wt% or less, 0.6 wt% or less, or 0.5 wt% or less, based on the total weight of the mixture in the impurity tank.

[0083] According to another embodiment of the present invention, a step (9-1) of cooling the gas mixture (B) containing NMP discharged in the step (9) to 45°C or lower before introducing it into the impurity tank may be additionally included.

[0084] The gas mixture (B) containing NMP discharged in the above step (9) may be circulated by being fed into an impurity tank without separate treatment, but in order to facilitate mixing with the secondary discharged liquid discharged in the above step (6), a step (9-1) of cooling it to 42°C or lower, 40°C or lower, or 35°C or lower using a cooler may be additionally performed before being fed into the impurity tank.

[0085]

[0086] Step (10) of circulating the mixture of the impurity tank to the raw material tank

[0087] A method for purifying NMP according to one embodiment of the present invention includes a step of circulating a mixture in the impurity tank to the raw material tank.

[0088] Specifically, by introducing the mixture from the impurity tank into the raw material tank and circulating it, the recovery rate and purity of NMP can be improved. In particular, through this circulation, components with a boiling point higher than NMP can serve as transport materials for waste NMP, thereby facilitating their use in the NMP purification process, thereby improving processability.

[0089] According to another embodiment of the present invention, a step (11) of heat-treating the mixture in the impurity tank and then introducing it into the secondary distillation tower may be additionally included. Specifically, the mixture in the impurity tank may be introduced into the raw material tank and circulated, and after heat treatment, introduced into the secondary distillation tower and circulated, thereby further improving the recovery rate of NMP.

[0090] In the above step (11), the heat treatment can be performed at a temperature of 100°C to 130°C. For example, in the above step (11), the heat treatment can be performed at a temperature of 105°C to 130°C or 115°C to 130°C.

[0091] Additionally, the mixture of the impurity tank heat-treated in the above step (11) may be introduced into the middle or lower portion of the secondary distillation column. Specifically, it may be preferable for the gas mixture to be introduced into the middle or lower portion of the secondary distillation column to perform more effective purification, but the present invention is not limited thereto.

[0092] More specifically, the position at which the mixture of the heat-treated impurity tank in the step (11) is introduced into the secondary distillation column may be the same as or lower than the position at which the first draw-out liquid is introduced into the secondary distillation column in the step (5). Since the position at which the mixture of the heat-treated impurity tank in the step (11) is introduced is the same as or lower than the position at which the first draw-out liquid is introduced in the step (5), NMP can be purified more effectively. In particular, since the final product, high-purity NMP, is discharged to the outside of the system through the top of the secondary distillation column, the mixture of the first draw-out liquid and the heat-treated impurity tank must be introduced into the middle and lower parts of the secondary distillation column to increase the efficiency of NMP purification, and by setting the introduction position of the mixture of the heat-treated impurity tank having a low NMP content relatively lower than the introduction position of the first draw-out liquid, more efficient purification can be performed.

[0093]

[0094] NMP purification unit

[0095] According to another embodiment of the present invention, an NMP purification device comprises: a raw material tank for supplying waste NMP; a sludge separator having a sludge filter and a sludge separator therein, and discharging a gas mixture (A) including NMP separated from the supplied waste NMP through an upper portion and a mixture including sludge through a lower portion; a first distillation column for performing a first purification of the gas mixture (A) including NMP, discharging an effluent including water separated through the first purification to the outside of the system through an upper portion, and discharging a first draw-out through a lower portion; a second distillation column for performing a second purification by distilling the first draw-out, discharging purified NMP separated through the second purification to the outside of the system through an upper portion, and discharging a second draw-out through a lower portion; a filtrate recovery device for heat-treating a mixture including sludge discharged from the sludge separator, discharging a third draw-out separated through the heat-treatment to the outside of the system through an lower portion, and discharging a gas mixture (B) including NMP through an upper portion; And it includes an impurity tank for mixing a gas mixture (B) including the secondary effluent discharged from the secondary distillation tower and NMP discharged from the filtrate recovery device and injecting the mixture into the raw material tank.

[0096] Fig. 2 illustrates an example of an NMP purification device according to another embodiment of the present invention. Specifically, Fig. 2 illustrates an NMP purification device comprising a raw material tank (RT), a sludge separator (W), a primary distillation tower (D1), a secondary distillation tower (D2), a filtrate recovery device (R), and an impurity tank (PT).

[0097] First, waste NMP is supplied to the sludge separator (W) (X-1) through the raw material tank (RT). The supply can be performed through the primary pump (P1), and at this time, the waste NMP can be preheated through the preheater (B1).

[0098] The sludge separator (W) may include a sludge filter (W1) provided on the upper part of the interior and a sludge separator plate (W2) provided on the upper side of the interior at a lower position than the sludge filter.

[0099] The above sludge separator (W) separates waste NMP or preheated waste NMP through the sludge filter (W1) and the sludge separator (W2), and the gas mixture (A) containing NMP is discharged through the upper part of the sludge separator (T-1) and is fed into the primary distillation column (D1) through the tertiary pump (P3) (X-2), and the mixture containing sludge is discharged through the lower part of the sludge separator (Y-1). The discharged mixture containing sludge can be transferred to the filtrate recovery device (R) through the secondary pump (P2) (X-3) and can be circulated back to the sludge separator (W) (S-1). At this time, the mixture containing sludge can be preheated through the heater (B2) for the sludge separator before being fed back into the sludge separator (W).

[0100] The first distillation tower (D1) performs the first purification by distilling the gas mixture (A) containing the introduced NMP, and the effluent containing water separated through the first purification is discharged to the outside of the system through the top of the first distillation tower (D1) (T-2), and the first draw-out liquid is discharged through the bottom of the first distillation tower (D1) (Y-2). The discharged first draw-out liquid can be transferred to the second distillation tower (D2) through the fourth pump (P4) (X-3), and can be circulated back to the first distillation tower (D1) (S-2). At this time, the first draw-out liquid can be preheated through the first reboiler (B3) before being re-introduced into the first distillation tower (D1).

[0101] The secondary distillation tower (D2) performs secondary purification by distilling the supplied primary drawdown, and the purified NMP separated through the secondary purification is discharged to the outside of the system through the top of the secondary distillation tower (D2) (T-3), and the secondary drawdown is discharged to the outside of the system through the bottom of the secondary distillation tower (D2) (Y-3). The purified NMP discharged to the outside of the system can be stored in a storage tank (ST). In addition, the discharged secondary drawdown can be transferred to an impurity tank (PT) through a fifth pump (P5) (X-4) and can be circulated back to the secondary distillation tower (D2) (S-3). At this time, the secondary drawdown can be preheated through a secondary reboiler (B4) before being fed back into the secondary distillation tower (D2).

[0102] The sludge recovery device (R) heat-treats a mixture containing the introduced sludge, and at this time, the pressure can be controlled through a vacuum pump (A). The tertiary effluent separated through the heat treatment is discharged outside the system through the lower end of the sludge recovery device (Y-4), and the gas mixture (B) containing NMP is discharged through the upper end of the sludge recovery device (T-5) and fed into the impurity tank (PT) through the 6th pump (P6) (X-5). At this time, the discharged gas mixture (B) containing NMP can be cooled through a cooler (C1) and then fed into the impurity tank (PT).

[0103] The impurity tank (PT) mixes and mixes the secondary effluent discharged from the secondary distillation tower (D2) with the gas mixture (B) containing NMP discharged from the filtrate recovery device (R), and then circulates the mixture to the raw material tank (RT) (S-5). At this time, a heat treatment device may be additionally provided so that the mixture in the impurity tank can be heat-treated and fed to the secondary distillation tower (D2) (S-4).

[0104]

[0105] [Explanation of symbols]

[0106] D1, D2: First and second distillation columns

[0107] P1~P6: 1st~6th pumps

[0108] B1: Preheater

[0109] B2: Heater for sludge separator

[0110] B3: Primary reboiler

[0111] B4: Secondary reboiler

[0112] W: Sludge separator

[0113] W1: Sludge filter

[0114] W2: Sludge separator

[0115] R: Liquid recovery device

[0116] RT: Raw material tank

[0117] PT: Impurity Tank

[0118] ST: Storage Tank

[0119] T-1~T-5, Y-1~Y-4: Emission stage

[0120] S-1~S-5: Cycle phase

[0121] X-1~X-5: Deployment phase

[0122] A: Vacuum pump

Claims

1. (1) Step of feeding waste NMP from the raw material tank into the sludge separator; (2) A step of discharging a gas mixture (A) containing NMP separated in the sludge separator through the top of the sludge separator, and discharging a mixture containing sludge through the bottom of the sludge separator; (3) A step of performing primary purification by introducing a gas mixture (A) containing the discharged NMP into a primary distillation tower; (4) A step of discharging the effluent containing water separated through the first purification to the outside of the system through the top of the first distillation tower, and discharging the first draw-off liquid through the bottom of the first distillation tower; (5) A step of performing secondary purification by putting the discharged primary effluent into a secondary distillation tower; (6) A step of discharging purified NMP separated through the secondary purification to the outside of the system through the top of the secondary distillation tower, and discharging the secondary draw-off liquid through the bottom of the secondary distillation tower; (7) A step of heat-treating a mixture containing the sludge discharged in the above step (2) by putting it into a sludge recovery device; (8) A step of discharging the tertiary effluent separated through the above heat treatment to the outside through the bottom of the above liquid recovery device, and discharging the gas mixture (B) containing NMP through the top of the above liquid recovery device; (9) a step of mixing the gas mixture (B) containing the secondary discharged liquid from the step (6) and the NMP discharged from the step (8) by introducing them into an impurity tank; and (10) A method for purifying NMP, comprising: a step of circulating a mixture of the impurity tank to the raw material tank.

2. In paragraph 1, A method for purifying NMP, wherein the sludge separator comprises a sludge filter and a sludge separator plate.

3. In paragraph 1, A method for purifying NMP, further comprising a step (1-1) of preheating the waste NMP to a temperature of 60°C to 100°C prior to introducing the waste NMP into a sludge separator in the above step (1).

4. In paragraph 1, A method for purifying NMP, wherein the mixture in the impurity tank contains 1.5 wt% or less of a component with a boiling point higher than that of NMP.

5. In paragraph 1, A method for purifying NMP, further comprising the step (11) of heat-treating a mixture in the impurity tank and introducing it into the second distillation tower.

6. In paragraph 5, A method for purifying NMP, wherein the heat treatment in the above step (11) is performed at 100°C to 130°C.

7. In paragraph 5, A method for purifying NMP, wherein the position at which the mixture of the heat-treated impurity tank in the above step (11) is fed into the second distillation tower is the same as or lower than the position at which the first distillate is fed into the second distillation tower in the above step (5).

8. In paragraph 1, A method for purifying NMP, wherein the pressure of the above-described liquid recovery device is controlled through a vacuum pump connected to the above-described liquid recovery device.

9. In paragraph 1, A method for purifying NMP, further comprising a step (9-1) of cooling the gas mixture (B) containing NMP discharged in the above step (9) to 45°C or less before introducing it into the impurity tank.

10. In paragraph 1, A method for purifying NMP, wherein the gas mixture (B) containing the above NMP contains 1.5 wt% or less of a component having a boiling point higher than that of NMP.

11. In paragraph 1, A method for purifying NMP, wherein the above-mentioned NMP contains NMP in an amount of 70 wt% or more.

12. In paragraph 1, A method for purifying NMP, wherein the gas mixture (A) containing the discharged NMP in the above step (3) is injected into the upper part of the first distillation column.

13. In paragraph 1, A method for purifying NMP, wherein the first extraction solution contains NMP in an amount of 99.9 wt% or more.

14. In paragraph 1, A method for purifying NMP, wherein the moisture content in the first extraction solution is 0.01% or less.

15. In paragraph 1, A method for purifying NMP, wherein in the above step (5), the first distillate is injected into the middle and lower portion of the second distillation tower.

16. In paragraph 1, A method for purifying NMP, wherein the secondary extract contains NMP in an amount of 99 wt% or more.

17. In paragraph 1, The first purification of the above step (3) is performed at a temperature of 50°C to 100°C and a pressure of 100 torr to 130 torr, An NMP purification method, wherein the secondary purification of the above step (5) is performed at a temperature of 120°C to 150°C and a pressure of 50 torr to 90 torr.

18. In paragraph 1, A method for purifying NMP, wherein the purity of the purified NMP is 99.9% or higher.

19. Raw material tank supplying waste NMP; A sludge separator having a sludge filter and a sludge separator plate inside, and discharging a gas mixture (A) containing NMP separated from the supplied waste NMP through the top, and discharging a mixture containing sludge through the bottom; A first distillation tower which first purifies a gas mixture (A) containing the above NMP, discharges an effluent containing water separated through the first purification to the outside of the system through the top, and discharges the first draw-off liquid through the bottom; A secondary distillation tower that distills the primary extract to perform secondary purification, discharges purified NMP separated through the secondary purification to the outside of the system through the top, and discharges the secondary extract through the bottom; A sludge recovery device that heat-treats a mixture containing sludge discharged from the above sludge separator, discharges the tertiary effluent separated through the heat treatment to the outside of the system through the bottom, and discharges a gas mixture (B) containing NMP through the top; and An NMP purification device including an impurity tank for mixing a gas mixture (B) containing a secondary extract discharged from the secondary distillation tower and NMP discharged from the filtrate recovery device and introducing the mixture into the raw material tank.

20. In paragraph 19, An NMP purification device further comprising a vacuum pump for controlling the pressure of the above-mentioned liquid recovery device.

21. In paragraph 19, An NMP purification device further comprising a heat treatment device for heat-treating a mixture in the impurity tank and feeding it into the second distillation tower.

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