Method for purifying laurolactam

Abstract

The present invention relates to a method for purifying laurolactam, and more particularly to a purification method capable of obtaining high-purity laurolactam containing almost no impurities. The present invention is a method for purifying laurolactam from a reaction product of a laurolactam synthesis process, comprising the steps of: (S1) distilling the reaction product to separate and remove low-boiling substances to obtain a first mixed solid; (S2) removing impurities suspended in a first mixed solution obtained by dissolving the first mixed solid in a good solvent; (S3) adding a poor solvent to the first mixed solution from which the impurities have been removed to obtain a precipitated second mixed solid; and (S4) evaporating the molten product obtained by heating and melting the second mixed solid to obtain gaseous laurolactam, followed by crystallization.

Description

[Technical Field]

[0001] The present invention relates to a method for purifying laurolactam, and more particularly to a purification method by which highly pure laurolactam containing almost no impurities can be obtained. [Background technology]

[0002] Generally, in industrial synthesis of cyclic amide monomers, such as laurolactam, cyclododecanone oxime is synthesized through the Beckmann rearrangement reaction.

[0003] Such polyamide polymeric materials can be synthesized by anionic polymerization, and the purity of the laurolactam monomer is a very important factor since it has a significant effect on the polymerization reaction activity.

[0004] Conventionally, laurolactam monomer produced by the Beckmann rearrangement reaction is purified by distilling off the solvent after the reaction is completed, followed by removing Heavies in the solid and / or liquid phases. However, various impurities such as organic substances and ions remain in the final laurolactam product, which causes a problem of rapidly reducing the activity of the anionic polymerization reaction.

[0005] Therefore, there is a need for a method for purifying high-purity laurolactam by removing various impurities remaining after the Beckmann rearrangement reaction in a simplified process, and for increasing the anionic polymerization activity of laurolactam monomers, etc.

[0006] As one such method, in the previously filed patent application No. 10-2019-0080535, the applicant studied a method of recovering a monomer from which impurities have been removed to some extent by distillation and evaporation.

[0007] However, there is a problem that the sticky material still exists at the interface, and even if recrystallized, it damages the anionic reaction sites during the anionic polymerization of the monomer, making it impossible to increase the degree of polymerization or reducing the conversion rate. Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a purification method that can obtain highly pure laurolactam from the product of the laurolactam synthesis process. [Means for solving the problem]

[0009] The present invention provides a method for purifying laurolactam from a reaction product of a laurolactam synthesis process, comprising the steps of: (S1) distilling the reaction product to separate and remove low-boiling substances to obtain a first mixed solid; (S2) removing impurities floating in a first mixed solution obtained by dissolving the first mixed solid in a good solvent; (S3) adding a poor solvent to the first mixed solution from which the impurities have been removed to obtain a precipitated second mixed solid; and (S4) evaporating the molten product obtained by heating and melting the second mixed solid to obtain gaseous laurolactam, followed by crystallization.

[0010] In the method for purifying laurolactam according to one embodiment of the present invention, the distillation in step (S1) may be performed using a simple distillation apparatus, at a temperature of 90° C. to 200° C. and a vacuum of −0.1 to −1 barg.

[0011] In the method for purifying laurolactam according to one embodiment of the present invention, in step (S2), the first mixed solid:the good solvent may be mixed at a weight ratio of 1:5-10.

[0012] In the method for purifying laurolactam according to one embodiment of the present invention, the temperature of the good solvent in step (S2) may be 40°C to 80°C.

[0013] In the method for purifying laurolactam according to one embodiment of the present invention, in step (S3), the good solvent in step (S2):the poor solvent may be mixed in a weight ratio of 1:0.5 to 2.

[0014] In the method for purifying laurolactam according to one embodiment of the present invention, the good solvent and the poor solvent may be miscible.

[0015] In the method for purifying laurolactam according to one embodiment of the present invention, the step (S3) may utilize the difference in solubility between the catalyst and a good solvent for laurolactam.

[0016] In the method for purifying laurolactam according to one embodiment of the present invention, after step (S3) and before step (S4), the step (S3-1) of adding a poor solvent again to the residue obtained by separating the second solid mixture to obtain a precipitated second solid mixture can be repeated one or more times to repeatedly obtain the second solid mixture.

[0017] In the method for purifying laurolactam according to one embodiment of the present invention, the step (S3-1) can be repeated 1 to 3 times.

[0018] In the method for purifying laurolactam according to one embodiment of the present invention, the temperature of the anti-solvent in step (S3) may be 50°C to 100°C.

[0019] In the method for purifying laurolactam according to one embodiment of the present invention, the heating in step (S4) can be carried out at a vacuum of -0.1 barg to -1 barg.

[0020] In the method for purifying laurolactam according to one embodiment of the present invention, in the step (S4), 50% to 70% of the total amount of the melt is vaporized to obtain laurolactam.

[0021] In the method for purifying laurolactam according to one embodiment of the present invention, the good solvent may be a C1-C4 hydrocarbon organic solvent containing one or more functional groups selected from the group consisting of a hydroxy group, an amine group, and a thiol group.

[0022] In the method for purifying laurolactam according to one embodiment of the present invention, the anti-solvent may be distilled water or deionized water.

[0023] In a method for purifying laurolactam according to one embodiment of the present invention, the laurolactam synthesis step may be performed through a Beckmann rearrangement of cyclododecanone oxime in the presence of a cyanuric chloride (TCT) catalyst, and the Beckmann rearrangement may be performed by synthesizing cyclododecanone oxime to laurolactam via a cyanuric chloride (TCT) catalyst in a solvent containing isopropylcyclohexane (IPCH).

[0024] The present invention also relates to a laurolactam composition purified by the above purification method.

[0025] In the laurolactam composition according to one embodiment of the present invention, the laurolactam composition may have a laurolactam purity of 99% or more.

[0026] The present invention also provides a method for producing polylaurolactam, which comprises anionically polymerizing the laurolactam composition in the presence of an anionic initiator to produce polylaurolactam.

[0027] In the method for producing polylaurolactam according to one embodiment of the present invention, the degree of polymerization of the polymerized polylaurolactam may be 70% or more. [Effects of the Invention]

[0028] The method for purifying laurolactam according to the present invention can provide highly pure laurolactam.

[0029] Laurolactam purified by such a purification method can have a high degree of polymerization. DETAILED DESCRIPTION OF THE INVENTION

[0030] Unless otherwise defined, the technical and scientific terms used in this specification have the meanings that are commonly understood by a person of ordinary skill in the art to which this invention belongs, and in the following description and accompanying drawings, explanations of notifying functions and configurations that may unnecessarily obscure the gist of the present invention will be omitted.

[0031] Also, as used herein, the singular forms "a," "an," and "the" can be intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0032] Furthermore, units used in this specification unless otherwise specified are based on weight, and as an example, the unit of % or ratio means % by weight or weight ratio, and % by weight means the weight % of any component in the total composition, unless otherwise defined.

[0033] Furthermore, numerical ranges used herein include lower and upper limits and all values ​​within that range, increments logically derived from the shape and width of the defined range, all doubly limited values, and all possible combinations of upper and lower limits of differently limited numerical ranges. Unless otherwise specified in the specification of the present invention, values ​​outside the numerical range that may occur due to experimental error or rounding off are also included in the defined numerical range.

[0034] As used herein, the term "comprising" is an open-ended term equivalent to terms such as "comprising," "containing," "having," or "characterized by," and does not exclude further unrecited elements, materials, or processes.

[0035] Also, as used herein, the term "substantially" means that, along with a particular element, material, or process, other elements, materials, or processes not listed may be present in an amount or degree that does not unacceptably affect at least one basic and novel technical idea of ​​the present invention.

[0036] The present invention provides a method for purifying laurolactam from a product of a laurolactam synthesis process, comprising the steps of (S1) distilling the product to separate and remove low-boiling substances to obtain a first mixed solid, (S2) dissolving the first mixed solid in a good solvent to remove impurities floating in a first mixed solution, (S3) adding a poor solvent to the first mixed solution from which the impurities have been removed to obtain a precipitated second mixed solid, and (S4) evaporating the molten product obtained by heating and melting the second mixed solid to obtain gaseous laurolactam, followed by crystallization.

[0037] Previously, research has been conducted on methods to recover monomers from which impurities have been removed to some extent by distillation and evaporation of the product, but there are problems in that sticky substances still remain and recrystallization damages the anionic reaction sites during the anionic polymerization of the monomer, making it impossible to increase the degree of polymerization or resulting in a low conversion rate.

[0038] The purification method of the present invention can obtain high-purity laurolactam from the product produced in the laurolactam synthesis step, and the high-purity laurolactam obtained by the production method of the present invention can have a high degree of polymerization when polymerized.

[0039] In the present invention, the laurolactam synthesis step is carried out via a Beckmann rearrangement of cyclododecanone oxime in the presence of a cyanuric chloride (TCT) catalyst, and the Beckmann rearrangement may be, but is not limited to, a reaction in which cyclododecanone oxime is converted to laurolactam via a cyanuric chloride (TCT) catalyst in a solvent containing isopropylcyclohexane (IPCH).

[0040] The Beckmann rearrangement reaction can proceed at a temperature of 70 to 130°C, preferably 90 to 110°C, and more preferably 95 to 100°C, for 1 to 20 minutes, preferably 5 to 20 minutes, and more preferably 5 to 15 minutes. If the reaction temperature is too high, a large amount of by-products such as polymeric substances (Heavies) is produced. If the reaction temperature is too low, the reaction rate is not fast enough, making it difficult to apply to commercial processes. Furthermore, if the reaction time is less than 1 minute, cyclododecanone oxime cannot be sufficiently rearranged to laurolactam, and if it exceeds 20 minutes, excessive side reactions occur, which is undesirable.

[0041] Meanwhile, the Beckmann rearrangement reaction refers to a reaction in which a ketoxime is converted to an acid amide, and in particular, in the present invention, it can refer to a reaction in which the cyclododecanone oxime is converted to laurolactam.

[0042] The catalyst is cyanuric chloride (TCT). Specifically, the catalyst may be contained in an amount of 0.1 to 10 parts by weight, preferably 0.1 to 5 parts by weight, and more preferably 0.5 to 2 parts by weight, per 100 parts by weight of cyclododecanone oxime. If the catalyst content is too low, the Beckmann rearrangement reaction does not proceed sufficiently. If the catalyst content is too high, a high content of catalyst material remains in the reaction product after completion of the reaction, making it difficult to effectively remove it in a purification step.

[0043] More specifically, the catalyst may contain cyanuric chloride and zinc chloride in a weight ratio of 2:1 to 1:1, preferably 1.5:1 to 1:1, and more preferably 1.3:1 to 1:1, thereby effectively synthesizing laurolactam by suppressing the decrease in conversion rate due to the water content, which is a limitation of the Beckmann rearrangement reaction, and after completion of the reaction, the catalyst remaining in the reaction product can be easily removed by a simplified process.

[0044] The solvent is preferably an organic solvent containing, for example, isopropylcyclohexane (IPCH), which, due to its strong non-polarity, can be used to successfully convert cyclododecanone oxime to laurolactam via the Beckmann rearrangement reaction.

[0045] The organic solvent containing IPCH can be used in an amount of 30 to 50 parts by weight per 100 parts by weight of cyclododecanone oxime. When the amount is within this range, the Beckmann rearrangement reaction of cyclododecanone oxime is easy, and the solvent can be easily removed by distilling the reaction product. The steps for purifying the reaction product obtained by the above method to obtain high-purity laurolactam will be described in detail below. Specifically, first, a step (S1) is carried out in which the reaction product is distilled to separate and remove low boiling point substances to obtain a first mixed solid. In the present invention, the first mixed solid may refer to a reaction product from which low boiling point substances have been removed by distillation, where the low boiling point substances may be IPCH and cyclododecanone.

[0046] The distillation in step (S1) can be carried out using a distillation apparatus known in the art, preferably a simple distillation apparatus. When distilling using a simple distillation apparatus, the temperature and vacuum can be appropriately adjusted depending on the boiling point of the low-boiling substance to be separated. Preferably, the temperature is 90°C to 200°C, specifically 120°C to 180°C, more specifically 140°C to 160°C, and the vacuum can be -0.1 to -1 barg. Within these ranges, the removal rate of the low-boiling substance to be removed in this step is high. Specifically, it is possible to efficiently remove isopropyl cyclohexane (IPCH), which was used as a solvent, while also achieving a high removal rate of cyclododecanone (CDON), the intermediate product of the Beckmann rearrangement reaction.

[0047] Next, (S2) a step of removing impurities floating in a first mixed solution obtained by dissolving the first mixed solid in a good solvent is carried out.

[0048] In the present invention, the impurities may be, but are not limited to, particulate catalysts contained in the first mixed solid material, and may be suspended in the first mixed solution and contain substances other than laurolactam. The good solvent may be a C1-C4 hydrocarbon organic solvent, preferably a C1-C4 hydrocarbon organic solvent containing one or more functional groups selected from the group consisting of a hydroxy group, an amine group, and a thiol group, more preferably a C1-C4 hydrocarbon containing a hydroxy group, or a C1-C4 alcohol.

[0049] When the good solvent is mixed, the catalyst can be removed by taking advantage of the difference in solubility between the catalyst and laurolactam in the good solvent. Specifically, the catalyst does not dissolve in the good solvent and precipitates as solid particles, whereas laurolactam has high solubility in the good solvent and may be substantially completely dissolved in the good solvent and not precipitate. The catalyst precipitated as particles can then be easily removed using a filter. If too little good solvent is added, some laurolactam may not dissolve and remain as a solid, which may be removed from the filter along with the remaining catalyst, resulting in a reduced laurolactam yield. Furthermore, some laurolactam that does not dissolve in the good solvent may aggregate with the remaining catalyst and pass through the filter, remaining. Conversely, if too much good solvent is added, recrystallization of laurolactam in the subsequent step (S3) may be difficult. Therefore, the laurolactam synthesized in step a) and the good solvent can be mixed in a weight ratio of 1:5 to 1:10, preferably 1:5 to 1:7, and more preferably 1:6 to 1:7.

[0050] In this case, the temperature of the good solvent is advantageously 40°C to 80°C, specifically 50°C to 60°C in terms of the dissolution rate of laurolactam.

[0051] Meanwhile, in the specification of the present invention, a good solvent means a solvent that has a high affinity for laurolactam and can dissolve it well, and a poor solvent means a solvent that has a low affinity for laurolactam and cannot dissolve it well. Next, in step (S3), a poor solvent is added to the first mixed solution from which impurities have been removed in step (S2) to obtain a precipitated second mixed solid. The poor solvent can be a substance miscible with the good solvent, specifically distilled water or deionized water. When a poor solvent is added, laurolactam can be precipitated by utilizing the difference in solubility between the good solvent and the poor solvent. Specifically, laurolactam has high solubility in good solvents and low solubility in poor solvents. When a poor solvent is added to the good solvent containing dissolved laurolactam in step (S2), the solubility of laurolactam decreases as the concentration of the good solvent decreases, resulting in recrystallization of laurolactam and precipitation as a solid. The precipitated second mixed solid can then be obtained by filtering.

[0052] The good solvent and the poor solvent can be added in a weight ratio of, for example, 1:0.5 to 1:2, preferably 1:0.8 to 1:1.5. Adding an excess amount of the good solvent relative to the poor solvent is undesirable because a portion of the laurolactam may not precipitate as a solid but may remain dissolved in the good solvent, which may result in a reduced yield of purified laurolactam.

[0053] The temperature of the poor solvent in step (S3) is, but is not limited to, 50° C. to 100° C., specifically 60° C. to 70° C. However, when a poor solvent having a temperature in this range is used, the concentration of chloride ions remaining in the second solid mixture is reduced, and laurolactam with higher purity can be obtained.

[0054] In one embodiment of the present invention, after step (S3), but before step (S3), a step (S3-1) of adding a poor solvent again to the residue from which the second solid mixture is separated to obtain a precipitated second solid mixture can be included. This step can be repeated one or more times to repeatedly obtain the second solid mixture from the first solution. Such a step can increase the recovery rate of laurolactam and further increase the yield of laurolactam. Specifically, from the viewpoint of process efficiency, it is preferable to repeat step (S3-1) less than 10 times, specifically 1 to 3 times. Next, (S4) the second mixed solid is heated and melted, and the resulting melt is evaporated to obtain gaseous laurolactam, which is then crystallized.

[0055] The heating in step (S4) is not limited as long as it can melt the second solid mixture, and can be performed at a temperature equal to or higher than the melting temperature of laurolactam, specifically 150°C to 220°C, more specifically 150°C to 170°C, but is not limited thereto. Heating can be performed at a vacuum of -0.1 to -1 barg. When heating is performed under reduced pressure within this range, oxidation by oxygen during the heating process can be prevented, and laurolactam with higher purity can be obtained. The evaporation in step (S4) can be carried out using an evaporation or distillation apparatus known in the art, and the crystallization can be carried out using a crystallization apparatus known in the art.

[0056] Specifically, evaporation can be carried out at a temperature of 150°C to 220°C, specifically 160°C to 200°C, but is not limited thereto. At this time, the degree of vacuum is not limited as long as it is less than 0.1 bar, and evaporation can be carried out for 30 minutes to 1 hour. In step (S4), it is preferable to evaporate the second mixed solid after it has completely melted. If it is evaporated in an incompletely melted state, it may be difficult to obtain high-purity laurolactam due to the Heavies' popping phenomenon contained in the melt.

[0057] In one embodiment of the present invention, in step (S4), laurolactam can be obtained by vaporizing only 30% to 90%, specifically 50% to 70%, of the total amount of the melt. If laurolactam is obtained by vaporizing all at once and then crystallizing, Heavies' popping phenomenon occurs, resulting in laurolactam contaminated with Heavies' popping. As a specific example, 50% to 70% of the total amount of the melt is evaporated and then crystallized to obtain laurolactam, and the remaining 50% to 70% is evaporated again and then crystallized to obtain laurolactam, and this process can be repeated. In contrast to this, in the case of a continuous process, laurolactam can be obtained by evaporating and crystallizing only 50% to 70% of the total amount of the molten material, and the molten material in the amount evaporated is continuously supplied, and laurolactam can be continuously obtained by evaporation and crystallization. The present invention relates to a laurolactam composition purified by the above-mentioned purification method, and is a highly pure laurolactam composition containing almost no impurities due to the purification by the above-mentioned method. Specifically, the laurolactam composition of the present invention has a laurolactam purity of 99%, preferably 99.5% or more, and is therefore very pure. The laurolactam composition may contain a catalyst used in the Beckmann rearrangement reaction in an amount of 3 wt % or less, preferably less than 2 wt %, more preferably 0.1 wt % or less, based on the total weight of the laurolactam composition. If the catalyst content exceeds this range, the activity of the anionic initiator used in the anionic polymerization is significantly reduced, making it difficult for the polymerization reaction to proceed.

[0058] The present invention also provides a method for producing polylaurolactam by anionically polymerizing such a laurolactam composition in the presence of an anionic initiator, and by polymerizing using such a laurolactam composition, it is possible to produce polylaurolactam having a high degree of polymerization of 70% or more, more preferably 75% or more.

[0059] Polymerization of purified laurolactam and any novel monomer (comonomer) can be carried out for 10 to 60 minutes at 200 to 350° C. Specifically, the polymerization reaction can be carried out at 200 to 300° C., preferably 220 to 250° C., for 10 to 60 minutes, preferably 10 to 50 minutes, more preferably 20 to 40 minutes.

[0060] The polymerized polylaurolactam can be a laurolactam-containing polymer, such as a copolyamide or a polyether block amide, preferably polyamide 12 (nylon 12).

[0061] The anionic initiator may specifically include one or more selected from the group consisting of NaH, LiH, KH, and n-BuLi. The catalytic material used in the Beckmann rearrangement reaction according to one embodiment of the present invention is known to significantly kill the activity of the anionic initiator. However, the method for producing laurolactam according to one embodiment of the present invention and the laurolactam composition produced thereby can effectively remove the catalytic material, thereby enabling anionic polymerization of laurolactam monomers with a high degree of polymerization in the presence of the anionic initiator. The anionic polymerization can be carried out in a batch reactor or a continuous reactor (CSTR, PFR, or PBR), preferably in a continuous reactor, although the present invention is not limited thereto.

[0062] Example 1 A 100ml round flask was charged with 3g of cyclododecanone oxime, 12g of isopropylcyclohexane, and 0.045g of cyanuric chloride. The temperature was adjusted to 95°C using a heating mantle and the mixture was stirred at 200 rpm or higher to produce the reaction product. The reaction was completed in 5 minutes, with a conversion rate of cyclododecanone oxime of over 99% and a selectivity to laurolactam of over 99%. 100 g of the reaction product prepared above was poured into a simple distillation apparatus and distilled at a temperature of 150° C. and a vacuum of −0.9 barg to remove IPCH and CDON from the top of the simple distillation apparatus. Thereafter, the residual CDON content and LL purity were measured, and the results are shown in Table 1. The residual CDON content and LL purity were both measured using a gas chromatograph. The measuring instrument was an HP-6890N and the column used was an HP-5 column.

[0063] Next, 700g of 60°C ethanol was poured into the resulting brown solid and dissolved in a flask. The floating solid (catalyst) was removed using a 0.22μm filter, and 700g of 60°C distilled water was poured into the laurolactam (LL) dissolved in ethanol to precipitate the LL solid. The precipitated LL was separated using a filter. 700g of distilled water was poured again into the laurolactam dissolved in ethanol from which the solid was first separated to reprecipitate the LL solid. This process was repeated a total of three times to precipitate the LL solid.

[0064] The residual chloride ion concentration was then measured and is shown in Table 2 below. The measuring instrument was a Mitsubishi AQF-2100H, and the column used was a Shodex IC anion column. Elution was performed with a mixed solution of 1 mM sodium carbonate (Na2CO3) and 4 mM sodium bicarbonate (NaHCO3).

[0065] Next, the LL solid was poured into a heater at a vacuum of -0.9 barg and completely melted at 155°C. Then, using a film evaporator, only 60% of the melt volume was evaporated, the Heavies were removed from the bottom, and the LL was separated from the top. Then, only 60% of the remaining melt volume was evaporated, the Heavies were removed again, and the LL was separated. The residual Heavies concentration and the yield of inorganic matter (ash) and LL were measured and are listed in Table 3 below. The inorganic matter was measured by TGA thermal analysis. There was no adhesion between the interfaces during the crystallization, and no solids were not separated. Next, 50 g of the produced LL and a catalyst were placed in a 100 ml round flask in a weight ratio of LL:NaH:EBS (ethylene bis stearamide):TEOS (tetraethyl orthosilicate):CO2 = 100:0.6:0.36:0.15:0.15, and an anionic polymerization reaction was carried out at 240°C for 30 minutes to produce PA 12 (polyamide 12). The degree of polymerization of PA 12 is shown in Table 4 below.

[0066] (Comparative Example 1) 100 g of the reaction product prepared in Example 1 was poured into a simple distillation apparatus and distilled at a temperature of 80° C. and a vacuum of −0.9 barg. The residual CDON content and LL purity were measured and listed in Table 1 below.

[0067] The solids were then poured into a heater under a vacuum of -0.9 barg and completely melted at 155°C. The melt was then evaporated to 100% volume using a film evaporator, the heavies were removed from the bottom, and the LL was separated from the top. Using the LL, 50 g of the LL and catalyst were added to a 100 ml round flask in a weight ratio of LL:NaH:EBS (ethylene bisstearamide):TEOS (tetraethyl orthosilicate):CO2 = 100:0.6:0.36:0.15:0.15. Anionic polymerization was carried out at 240°C for 30 minutes to produce PA 12 (polyamide 12). The degree of polymerization of PA 12 is listed in Table 4 below.

[0068] (Comparative Example 2) The brown solid produced in Example 1 was dissolved in 700 g of ethanol at 60°C in a flask. The floating solid (catalyst) was removed using a 0.22 μm filter. The residual chloride ion concentration was then measured and is shown in Table 2 below.

[0069] The solids were then poured into a heater under a vacuum of -0.9 barg and completely melted at 155°C. The melt was then evaporated to 100% volume using a film evaporator, the heavies were removed from the bottom, and the LL was separated from the top. Using the LL, 50 g of the LL and catalyst were added to a 100 ml round flask in a weight ratio of LL:NaH:EBS (ethylene bisstearamide):TEOS (tetraethyl orthosilicate):CO2 = 100:0.6:0.36:0.15:0.15. Anionic polymerization was carried out at 240°C for 30 minutes to produce PA 12 (polyamide 12). The degree of polymerization of PA 12 is listed in Table 4 below.

[0070] (Comparative Example 3) The melt prepared in Example 1 was completely vaporized to separate the LL. Subsequently, 50 g of the prepared LL and a catalyst were added to a 100 ml round flask in a weight ratio of LL:NaH:EBS (ethylene bis stearamide):TEOS (tetraethyl orthosilicate):CO2 = 100:0.6:0.36:0.15:0.15, and an anionic polymerization reaction was carried out at 240°C for 30 minutes to prepare PA 12 (polyamide 12). The degree of polymerization of PA 12 is shown in Table 4 below.

[0071] Comparative Example 4 The brown solid produced in Example 1 was dissolved in a flask by adding 700 g of ethanol at 60° C. The floating solid (catalyst) was removed using a 0.22 μm filter. Next, the LL solid was poured into a heater at a vacuum of -0.9 barg and the solid was completely melted at 155°C. After that, only 60% of the volume of the melt was evaporated using a film evaporator, the Heavies were removed from the bottom, and the LL was separated from the top. After that, only 60% of the volume of the remaining melt was evaporated, the Heavies were removed again, and the LL was separated.

[0072] Next, 50 g of the produced LL and a catalyst were added to a 100 ml round flask in a weight ratio of LL:NaH:EBS (ethylene bis stearamide):TEOS (tetraethyl orthosilicate):CO2 = 100:0.6:0.36:0.15:0.15, and an anionic polymerization reaction was carried out at 240°C for 30 minutes to produce PA12 (polyamide 12). The degree of polymerization of PA12 is shown in Table 4 below.

[0073] [Table 1]

[0074] [Table 2]

[0075] [Table 3]

[0076] [Table 4] Referring to Table 1, it was confirmed that CDON was removed and high-purity laurolactam was obtained by distillation using a simple distillation apparatus according to the present invention.

[0077] Furthermore, referring to Table 2, it was confirmed that a large amount of chloride ions were removed by adding ethanol and distilled water.

[0078] Furthermore, Table 3 shows that the Heavies and inorganic removal rates are higher when the melt is vaporized multiple times at a given volume than when it is completely vaporized in a single step.

[0079] Furthermore, it was confirmed from Table 4 that when laurolactam purified by the purification method of the present invention is polymerized, a polyamide having a high degree of polymerization and excellent physical properties can be obtained.

[0080] As described above, the present invention has been described using specific matters and limited examples and drawings, but these are provided to help a more comprehensive understanding of the present invention, and the present invention is not limited to the above examples. Those skilled in the art will appreciate that various modifications and variations can be made from these descriptions. Therefore, the concept of the present invention is not limited to the described embodiments, and all aspects that fall within the scope of the claims described below, as well as equivalent or similar variations to the claims, can be said to fall within the scope of the concept of the present invention.

Claims

1. 1. A method for purifying laurolactam from a reaction product of a laurolactam synthesis step, comprising: (S1) distilling the reaction product to separate and remove low-boiling substances to obtain a first mixed solid; (S2) removing impurities floating in a first mixed solution obtained by dissolving the first mixed solid in a good solvent; (S3) adding a poor solvent to the first mixed solution from which the impurities have been removed to obtain a precipitated second mixed solid; (S4) heating and melting the second solid mixture, evaporating the melt to obtain gaseous laurolactam, and then crystallizing the resulting mixture; The laurolactam synthesis step is carried out in the presence of a cyanuric chloride (TCT) catalyst, the good solvent is ethanol, the anti-solvent is distilled water or deionized water; The step (S2) includes mixing the first mixed solid and the good solvent in a weight ratio of 1:5 to 10; In the step (S3), the good solvent in the step (S2):the poor solvent is mixed in a weight ratio of 1:0.5 to 2; In the step (S4), 30% to 80% of the total amount of the melt is vaporized to obtain laurolactam, The laurolactam synthesis step is carried out via a Beckmann rearrangement of cyclododecanone oxime in the presence of cyanuric chloride (TCT) as a catalyst; The Beckmann rearrangement reaction converts cyclododecanone oxime to laurolactam via a cyanuric chloride (TCT) catalyst in a solvent containing isopropylcyclohexane (IPCH). A method for purifying laurolactam.

2. 2. The method for purifying laurolactam according to claim 1, wherein the distillation in step (S1) is carried out using a simple distillation apparatus, the distillation temperature is 90°C to 200°C, and the degree of vacuum is -0.1 to -1 barg.

3. 2. The method for purifying laurolactam according to claim 1, wherein the temperature of the good solvent in step (S2) is 40°C to 80°C.

4. 2. The method for purifying laurolactam according to claim 1, wherein the good solvent and the poor solvent are miscible with each other.

5. 2. The method for purifying laurolactam according to claim 1, wherein the step (S3) utilizes a difference in solubility between the catalyst and a good solvent for laurolactam.

6. After step (S3), before step (S4) (S3-1) adding a poor solvent again to a residue obtained by separating the second solid mixture to obtain a precipitated second solid mixture.

7. The method for purifying laurolactam according to claim 6, wherein the step (S3-1) is repeated 1 to 3 times.

8. 2. The method for purifying laurolactam according to claim 1, wherein the temperature of the poor solvent in step (S3) is 50°C to 100°C.

9. 2. The method for purifying laurolactam according to claim 1, wherein the heating in the step (S4) is carried out at a vacuum degree of −0.1 barg to −1 barg.

10. The step (S4) 2. The method for purifying laurolactam according to claim 1, wherein 50% to 70% of the total amount of the melt is vaporized to obtain laurolactam.

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