Method for purifying polar organic solvent containing polyimide precursor

Abstract

The present invention relates to a method for recovering an expensive polar organic solvent from waste liquid containing a polyimide precursor, which is generated during the manufacture of a polyimide film. Specifically, the method comprises: a step of adding and stirring an amine-based organic compound, which prevents the aggregation of the polyimide precursor in the waste liquid, so as to cause a chemical reaction; a primary vacuum distillation step of separating out moisture contained in the waste liquid; and a secondary vacuum distillation step of separating out, on the basis of boiling points, a polar organic solvent contained in the waste liquid. According to the present invention, the imidization of the polyimide precursor in the waste liquid is prevented, and thus blocking or failure of equipment can be prevented and a high-purity polar organic solvent can be recovered at the same time.

Description

Method for purifying a polar organic solvent containing a polyimide precursor

[0001] The present invention relates to a method for purifying a polar organic solvent containing a polyimide precursor, and more particularly, to a method for purifying a polar organic solvent capable of preventing polyimideization of a polyimide precursor, thereby enabling a purification process without damage or clogging of a vacuum distillation facility, and at the same time ensuring a high regeneration recovery rate.

[0002] Polyimide is a material characterized by excellent mechanical strength, chemical resistance, weather resistance, and heat resistance, all based on the chemical stability of the imide ring. Furthermore, it is easy to synthesize, can be formed into thin films, and has outstanding electrical properties, making it a highly functional polymer material. For example, polyimide films are actively used in foldable displays, semiconductor packaging, secondary batteries, and FPCBs, and their applications are expanding.

[0003] A typical method for manufacturing polyimide films involves dissolving a polyimide precursor, such as polyamic acid or polyamic ester, in a polar organic solvent, coating the film on a substrate, removing the solvent through heat treatment, and inducing an imidization reaction. (See Figure 1)

[0004] After manufacturing a polyimide film, the coating equipment is washed or the remaining residual solution is generated as waste liquid, and this waste liquid consists of a polar organic solvent containing a polyimide precursor polymer.

[0005] To purify waste liquids containing polar organic solvents as their main component, vacuum distillation is typically used to remove polymers, metal impurities, and moisture. However, during the heat treatment of waste liquids generated during the polyimide manufacturing process, some polyimide precursors present in the waste liquid undergo an imidization reaction, resulting in the generation of solid polyimide within the waste liquid.

[0006] These solid polyimide impurities have low solubility in polar organic solvents, which can cause them to harden and clog purification equipment or pipes, resulting in equipment damage. For this reason, waste liquid containing polyimide precursors cannot be recycled to recycle the main component, expensive organic solvents like N-methylpyrrolidone (NMP), and can only be used as low-grade waste-derived fuel (WDF).

[0007] Therefore, in order to reuse waste liquid containing polyimide precursors, it is urgently necessary to develop a technology that can recover polar organic solvents without damaging the equipment even after the reduced pressure distillation process by suppressing the imidization reaction of the polyimide precursors.

[0008] In this regard, Korean Patent No. 10-2109401 discloses a method for purifying a waste NMP mixture by adding a basic compound to the waste NMP mixture to simultaneously remove impurities NMS (N-Methylsuccinimide) and GBL (gamma-Butyrolactone, γ-Butyrolactone). However, a method for recovering high-purity NMP from a waste NMP mixture containing a polyimide precursor, as in the present invention, has not been proposed.

[0009] Therefore, the task of the present invention is to develop a purification method capable of smoothly recovering an expensive polar organic solvent through a reduced pressure distillation process by preventing solidification of a polyimide precursor during heat treatment of a waste liquid containing a polyimide precursor.

[0010] In order to solve the above problem, the present invention provides a method for recovering a polar organic solvent from a waste liquid containing a polyimide precursor, comprising: i) a step of adding an amine-based organic compound to the waste liquid to react the polyimide precursor with the amine-based organic compound (S100); ii) a step of removing moisture through a first reduced pressure distillation (S200); and iii) a step of separating the polar organic solvent through a second reduced pressure distillation (S210); wherein the waste liquid contains 10 to 98 wt% of the polar organic solvent, 0.1 to 30 wt% of the polyimide precursor, and 0 to 50 wt% of moisture, and the amine-based organic compound is added in an amount equal to the mass of the polyimide precursor.

[0011] According to one embodiment of the present invention, the polyimide precursor is characterized in that it is polyamic acid or polyamic ester.

[0012] In addition, the polar organic solvent is characterized in that it is one selected from among N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), m-cresol, Dimethyl sulfoxide (DMSO), or N,N-dimethylpropionamide (DMPA).

[0013] In addition, the above amine organic compound is characterized by being an amine low molecular weight compound, an amine alcohol, or an amine acid.

[0014] In addition, the amine-based low molecular weight compound is characterized by being one selected from among methylamine, dimethylamine, triethylamine, tributylamine, N-Methylformamide, Isopropylamine, Ethylenediamine, propylamine, N,N-dimethylformamide, Butylamine, sec-Butylamine, tert-Butylamine, Isobutylamine, Diaminopropane, N,N-Dimethylacetamide, and 1,4-Diaminobutane.

[0015] In addition, the amine alcohol is characterized in that it is one selected from among Ethanolamine, propanolamine, 3-Amino-1-propanol, 2-Amino-2-methyl-1-propanol, 2-(Butylamino)ethanol, 2-(Dibutylamino)ethanol, N-Butyldiethanolamine, N-Acetylethanolamine, N-Methylethanolamine, N-Methyldiethanolamine, 2-(2-Aminoethoxy)ethanol, 2-[2-(2-Aminoethoxy)ethoxy]ethanol, 2-[2-(Dimethylamino)ethoxy]ethanol, Dimethylethanolamine (DMEA), Diethanolamine, and Triethanolamine (TEA).

[0016] In addition, the above amine acid is characterized in that it is one selected from among Succinic acid, Aspartic Acid, Malic acid, Alanine, Glycine, N-Acetylglycine, Methionine, and Valine.

[0017] In addition, the step of reacting the polyimide precursor and the amine organic compound is characterized in that it is carried out under temperature conditions of 25 to 60°C and stirring for 1 to 120 minutes.

[0018] In addition, the above-mentioned reduced pressure distillation step is characterized by distilling the waste liquid in which the reaction is completed under reduced pressure at 50 to 200°C and 200 torr or less to separate the organic solvent, and then cooling and recovering the organic solvent.

[0019] In addition, the above-mentioned reduced pressure distillation step is characterized in that it is first carried out at 70 to 100°C and secondly carried out at 100 to 180°C.

[0020] In addition, the recovered polar organic solvent is characterized by having a purity of 95 wt% or more and a metal impurity content of 1 ppm or less.

[0021] In addition, the recovered polar organic solvent is characterized in that it contains 0.01 wt% or less of an added amine-based organic compound.

[0022] By adding an amine-based organic compound to a waste liquid containing a polar organic solvent generated during the production of a polyimide film through the purification method of the present invention, agglomeration of a polyimide precursor contained in the waste liquid is prevented, thereby preventing damage or clogging of equipment, and high-purity purification of a polar organic solvent is enabled through a reduced pressure distillation process.

[0023] Figure 1 is a drawing showing an example of polyamic acid being converted into polyimide through an imidization reaction.

[0024] Figure 2 is a drawing showing an example of a reaction between polyamic acid and DMEA.

[0025] Figure 3 is a schematic diagram showing the purification process of the present invention.

[0026] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0111165, filed August 24, 2023, the entire contents of which are incorporated herein by reference.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Furthermore, the nomenclature used herein is well known and commonly used in the art.

[0028] Hereinafter, the present invention will be described in detail through examples and the like.

[0029] First, a waste liquid generated in a polyimide manufacturing process, to which the purification method of the present invention is applied, is prepared. In general, a method using an amide compound such as N-methylpyrrolidone (NMP) as a solvent in a polyimide film manufacturing process is widely known industrially.

[0030] NMP is a colorless, non-toxic, low-viscosity organic solvent with excellent heat resistance. It is also chemically stable and highly polar, making it highly useful in various chemical reactions requiring an inert medium.

[0031] Meanwhile, it is generally known that polyamic acid (PAA) or polyamic ester (PAE) is used as a polyimide precursor for manufacturing polyimide.

[0032] In this way, after manufacturing a polyimide using a polyimide precursor such as polyamic acid or polyamic ester, the remaining unreacted substances such as PAA are removed by washing with NMP or water, and the waste liquid of the present invention is a waste liquid collected after the polyimide manufacturing process and contains 10 to 98 wt% of a polar organic solvent, 0.1 to 30 wt% of a polyimide precursor, and 0 to 50 wt% of moisture.

[0033] At this time, polar organic solvents in the waste liquid may include N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), m-cresol, Dimethyl sulfoxide (DMSO), N,N-dimethylpropionamide (DMPA), etc.

[0034] Next, the purification and recovery method of polar organic solvents in waste liquid will be explained in detail step by step.

[0035] The first step of the present invention is a step (S100) of reacting a polyimide precursor contained in waste liquid with an amine-based organic compound, which is a step of adding an amine-based organic compound to the collected waste liquid and reacting the polyimide precursor with the amine-based organic compound.

[0036] As described above, the polyimide precursor in the waste liquid may include polyamic acid or polyamic ester, and the type thereof is not limited as long as it can be used as a precursor of polyimide.

[0037] As the amine organic compound added for the reaction, a low molecular amine, an amine alcohol, or an amine acid can be used.

[0038] Specific examples of amine-based low-molecular-weight compounds include methylamine, dimethylamine, triethylamine, tributylamine, N-Methylformamide, Isopropylamine, Ethylenediamine, propylamine, N,N-dimethylformamide, Butylamine, sec-Butylamine, tert-Butylamine, Isobutylamine, Diaminopropane, N,N-Dimethylacetamide, and 1,4-Diaminobutane, and one or more of these may be selected and used.

[0039] Examples of amine alcohols having an -OH group (alcohol group) as a functional group at the end include Ethanolamine, propanolamine, 3-Amino-1-propanol, 2-Amino-2-methyl-1-propanol, 2-(Butylamino)ethanol, 2-(Dibutylamino)ethanol, N-Butyldiethanolamine, N-Acetylethanolamine, N-Methylethanolamine, N-Methyldiethanolamine, 2-(2-Aminoethoxy)ethanol, 2-[2-(2-Aminoethoxy)ethoxy]ethanol, 2-[2-(Dimethylamino)ethoxy]ethanol, Dimethylethanolamine (DMEA), Diethanolamine, and Triethanolamine (TEA). One or more of these may be selected and used.

[0040] Examples of amine acids having a -COOH group (carboxyl group) as a functional group at the end include one or more selected from among Succinic acid, Aspartic Acid, Malic acid, Alanine, Glycine, N-Acetylglycine, Methionine, and Valine.

[0041] In this step, it is important to adjust the amount of amine-based organic compound to a weight that prevents the unreacted polyimide precursor from undergoing imidization in the waste liquid after the reaction with the polyimide precursor is complete, or to add a slightly larger amount than required. Preferably, the amount of amine-based organic compound added is 1 to 1.5 times the weight of the polyimide precursor remaining in the waste liquid.

[0042] If the amount of amine organic compound added is insufficient, the polyimide precursor may undergo an imidization reaction in the subsequent vacuum distillation step, thereby generating a solid polyimide. If the amount of amine organic compound added is too large, unreacted amine organic compound may be included as an impurity in the purified polar organic solvent during the vacuum distillation process, or it may be undesirable from a cost perspective.

[0043] Meanwhile, the chemical reaction between the polyimide precursor and the amine-based organic compound is preferably carried out at a temperature of 25 to 60°C and with stirring for 1 to 120 minutes. If the reaction temperature is lower than 25°C, the reaction completion time becomes longer, and if the reaction temperature is higher than 60°C, an imidization reaction may occur, so it is preferable to maintain the above temperature range.

[0044] As an example of this step, a formula showing the reaction between polyamic acid and DMEA to produce polyamic acid ammonium salt is shown in Figure 2.

[0045] The second step is a step (S200) of removing moisture in the waste liquid through primary reduced pressure distillation from the waste liquid mixture in which the reaction described above has been completed.

[0046] The distillation time of the first pressure-reduced distillation stage is 30 to 60 minutes, the pressure is maintained at 200 torr or less, and the temperature condition of the first pressure-reduced distillation stage is preferably 50 to 100°C.

[0047] The second step removes the moisture contained in the waste liquid.

[0048] The third step is a step (S210) of separating a polar organic solvent from the waste liquid from which moisture has been removed through secondary reduced pressure distillation.

[0049] Secondary vacuum distillation is conducted for 30 to 60 minutes, with the pressure maintained below 200 torr. The temperature range for secondary vacuum distillation is preferably 100 to 200°C. Compared to the first vacuum distillation step, the only difference is the temperature.

[0050] After this step, the polar organic solvent contained in the waste liquid can be separated in a high-temperature gaseous state and recovered through a cooling process. Analysis of the recovered polar organic solvent confirmed that the purity was 95 wt% or higher, the content of metal impurities was 1 ppm or less, and the content of added amine-based organic compounds was confirmed to be 0.01 wt% or less.

[0051] Meanwhile, when the secondary vacuum distillation is performed, polar organic solvents and moisture are removed from the waste liquid, and the remaining waste liquid is separated and recovered and treated as waste.

[0052] In the conventional case, during the first and second reduced pressure distillations, the polyimide precursor in the waste liquid undergoes an imidization reaction into polyimide, causing it to stick or clog within the reactor. However, in the case of the present invention, no additional imidization reaction occurs during the reduced pressure distillation process.

[0053] Hereinafter, the present invention will be described in more detail through examples.

[0054] <Example>

[0055] Dimethylethanolamine (DMEA) was weighed and added to a waste solution containing polyamic acid and NMP (see Table 1), the same mass as that of the polyamic acid. The mixture was then stirred to ensure a smooth reaction between DMEA and the polyamic acid, and the reaction temperature was set to 50°C. The reaction was allowed to proceed for 30 minutes, after which reduced pressure distillation was performed in two stages to recover NMP.

[0056] NMPPGMEAWaterPolyamic AcidPolyimideOther ImpuritiesComposition (wt %)8615521

[0057] The pressure condition of the reactor for the first pressure reduction distillation was set to 200 torr, and the temperature condition was set to 70-100 ℃, and water was removed from the waste liquid during the 30 minutes of first pressure reduction distillation.

[0058] The pressure condition for the secondary reduced pressure distillation was the same as that for the primary reduced pressure distillation, 200 torr, and the temperature condition was set at 100-180℃. NMP, a polar organic solvent, was distilled from the waste liquid for 30 minutes, separated, and recovered after cooling. The residue remaining at the bottom of the reactor after the secondary reduced pressure distillation without being distilled was treated as waste liquid.

[0059] The composition of NMP (purified product) obtained through secondary reduced pressure distillation is as shown in Table 2, and at this time, NMP was able to obtain a purity of 99 wt% or more. In addition, the moisture content of the purified product was 0.01 wt%, the DMEA content was also 0.01 wt% or less, metal impurities were detected at 1 ppm or less, and small amounts of other impurities were detected as the remainder.

[0060] NMPPGMEAWaterPolyamic AcidDMEAMetal Impurity Composition (wt%)9900.0100.01 or less1 ppm or less

[0061] Meanwhile, it was confirmed that the polyimide content in the waste liquid did not change before and after the purification process, which seems to mean that the polyamic acid contained in the waste liquid was not converted into polyimide through the imidization reaction.

[0062] As a result, high-purity NMP could be recovered without producing polyimide due to the addition of DMEA, an amine-based organic compound.

[0063] <Comparative Example>

[0064] The waste liquid used in the examples was used identically, and an experiment was conducted to recover a polar organic solvent without adding DMEA, an amine-based organic compound. Therefore, the comparative example proceeded through steps S200 and S210, which are reduced pressure distillation steps, while omitting the reaction step (S100) of the present invention.

[0065] As in the previous example, the vacuum distillation step was conducted in two stages according to the reaction temperature conditions. The pressure condition of the reactor for the first vacuum distillation was set at 200 torr, and the temperature condition was set at 70-100 ℃, and water was removed from the waste liquid during the 30 minutes of the first vacuum distillation.

[0066] The pressure conditions for the secondary reduced pressure distillation were the same as those for the primary reduced pressure distillation stage, 200 torr, and the temperature conditions were set at 100-180℃. NMP, a polar organic solvent, was distilled from the waste liquid for 30 minutes, separated, and recovered after cooling. The residue remaining at the bottom of the reactor after the secondary reduced pressure distillation without being distilled was treated as waste liquid.

[0067] The composition of NMP (purified product) obtained through the final secondary reduced pressure distillation was as shown in Table 3, with a purity of 96 wt%, moisture of 0.09 wt%, metal impurities of less than 1 ppm, and other impurities detected in small amounts as the remainder.

[0068] NMPPGMEAWaterPolyamic AcidMetal Impurity Composition Ratio (wt%)9600.0901 ppm or less

[0069] Meanwhile, the residue remaining at the bottom of the reactor after the secondary reduced pressure distillation was checked, and it was confirmed that the content of coagulated polyimide increased by more than 250% compared to before the purification process.

[0070] That is, the fact that the content of coagulated polyimide in the residue increased appears to be because the polyamic acid present in the waste liquid before the purification process was converted into solid polyimide through an imidization reaction.

[0071] Although the present invention has been described above with reference to one embodiment, it will be understood by those skilled in the art that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below.

Claims

A method for recovering a polar organic solvent from a waste liquid containing a polyimide precursor, ⅰ) A step (S100) of adding an amine-based organic compound to the waste liquid to react the polyimide precursor with the amine-based organic compound; ⅱ) Step of removing moisture through primary reduced pressure distillation (S200); and ⅲ) a step of separating a polar organic solvent through secondary reduced pressure distillation (S210); The above waste liquid contains 10 to 98 wt% of polar organic solvent, 0.1 to 30 wt% of polyimide precursor, and 0 to 50 wt% of moisture. The above amine organic compound is characterized in that it is added in an amount equal to the mass of the polyimide precursor. A method for recovering a polar organic solvent from a waste liquid containing a polyimide precursor. In the first paragraph, The polyimide precursor is characterized in that it is polyamic acid or polyamic ester. A method for recovering a polar organic solvent from a waste liquid containing a polyimide precursor. In the first paragraph, The polar organic solvent is characterized in that it is one selected from among N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), m-cresol, Dimethyl sulfoxide (DMSO), or N,N-dimethylpropionamide (DMPA). A method for recovering a polar organic solvent from a waste liquid containing a polyimide precursor. In the first paragraph, The above amine organic compound is characterized in that it is an amine low molecular weight compound, an amine alcohol or an amine acid. A method for recovering a polar organic solvent from a waste liquid containing a polyimide precursor. In paragraph 4, The above amine-based low molecular weight compound is characterized in that it is at least one selected from among methylamine, dimethylamine, triethylamine, tributylamine, N-Methylformamide, Isopropylamine, Ethylenediamine, propylamine, N,N-dimethylformamide, Butylamine, sec-Butylamine, tert-Butylamine, Isobutylamine, Diaminopropane, N,N-Dimethylacetamide, and 1,4-Diaminobutane. A method for recovering a polar organic solvent from a waste liquid containing a polyimide precursor. In paragraph 4, The above amine alcohol is characterized in that it is at least one selected from Ethanolamine, propanolamine, 3-Amino-1-propanol, 2-Amino-2-methyl-1-propanol, 2-(Butylamino)ethanol, 2-(Dibutylamino)ethanol, N-Butyldiethanolamine, N-Acetylethanolamine, N-Methylethanolamine, N-Methyldiethanolamine, 2-(2-Aminoethoxy)ethanol, 2-[2-(2-Aminoethoxy)ethoxy]ethanol, 2-[2-(Dimethylamino)ethoxy]ethanol, Dimethylethanolamine (DMEA), Diethanolamine (DEA), Triethanolamine (TEA). A method for recovering a polar organic solvent from a waste liquid containing a polyimide precursor. In paragraph 4, The above amine acid is characterized in that it is at least one selected from Succinic acid, Aspartic Acid, Malic acid, Alanine, Glycine, N-Acetylglycine, Methionine, and Valine. A method for recovering a polar organic solvent from a waste liquid containing a polyimide precursor. In the first paragraph, The above step i) is characterized in that it is carried out under temperature conditions of 25 to 60°C and stirring for 1 to 120 minutes for the chemical reaction of the polyimide precursor and the amine organic compound. A method for recovering a polar organic solvent from a waste liquid containing a polyimide precursor. In the first paragraph, The above steps ⅱ) and ⅲ) are characterized in that the waste liquid is distilled under reduced pressure at 50 to 200°C and 200 torr or less to separate the polar organic solvent, and then cooled and recovered. A method for recovering a polar organic solvent from a waste liquid containing a polyimide precursor. In paragraph 9, The above step ⅱ) is performed at 70 to 100°C, and the above step ⅲ) is performed at 100 to 180°C. A method for recovering a polar organic solvent from a waste liquid containing a polyimide precursor. In the first paragraph, The recovered polar organic solvent is characterized in that it has a purity of 95 wt% or more and a metal impurity content of 1 ppm or less. A method for recovering a polar organic solvent from a waste liquid containing a polyimide precursor. In the first paragraph, The recovered polar organic solvent is characterized in that it contains 0.01 wt% or less of the added amine organic compound. A method for recovering a polar organic solvent from a waste liquid containing a polyimide precursor.

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