A method for crystallization and purification of N-methylmorpholine-N-oxide

Abstract

The present invention discloses a method for crystallizing and purifying N-methylmorpholine-N-oxide, and relates to the technical field of N-methylmorpholine-N-oxide purification. The method comprises the following steps: adding a crude N-methylmorpholine-N-oxide product to a recrystallization solvent, heating the product, and then filtering the product while hot to obtain a filtrate; cooling the filtrate for crystallization, filtering the product with suction, and vacuum drying the resulting solid. The present invention, for the first time, uses a suitable ratio of 12-crown ether-4 and a C2-C4 diol having a specific cavity structure as a recrystallization solvent, significantly reducing the content of impurities such as N-methylmorpholine in the crude N-methylmorpholine-N-oxide product, thereby allowing the obtained pure N-methylmorpholine-N-oxide to meet the quality standards for Tencel production. Furthermore, the entire purification process is simple to operate and time-efficient, thus overcoming the shortcomings of the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of N-methylmorpholine-N-oxide purification, in particular to a method for crystallization and purification of N-methylmorpholine-N-oxide. Background Art

[0002] N-Methylmorpholine-N-oxide (NMMO) is an important aliphatic cyclic tertiary amine oxide with extensive applications in fiber spinning, particularly in the production of Tencel (Lyocell) fibers, where NMMO plays an indispensable role as a key solvent. Industrial production of NMMO is typically achieved by reacting hydrogen peroxide with N-methylmorpholine. This method, characterized by its simplicity and readily available raw materials, has led to its widespread application.

[0003] However, during the preparation of NMMO by reacting hydrogen peroxide with N-methylmorpholine, the resulting crude NMMO often contains a certain amount of impurities due to factors such as raw material purity and reaction conditions. These impurities may include incompletely reacted N-methylmorpholine, reaction byproducts, catalyst residues, and impure substances in the solvent. The presence of these impurities not only affects the purity and quality of NMMO but can also adversely affect the subsequent fiber spinning process, reducing the performance and quality of the product.

[0004] To obtain high-purity NMMO products that meet the quality standards for Tencel production, crude NMMO needs to be purified. Currently, commonly used purification methods include distillation, extraction, and crystallization. Among them, crystallization purification methods are highly favored due to their ease of operation and high purification efficiency. However, existing crystallization purification methods often suffer from problems such as long purification time, poor purification results, and complex operations, making them difficult to meet the needs of large-scale industrial production. Summary of the Invention

[0005] To solve the above problems, the present invention provides a method for crystallization and purification of N-methylmorpholine-N-oxide.

[0006] The present invention provides a method for the crystallization and purification of N-methylmorpholine-N-oxide, such as Figure 1 As shown, the method for crystallization and purification of N-methylmorpholine-N-oxide comprises the following steps:

[0007] The crude N-methylmorpholine-N-oxide is added to a recrystallization solvent and heated to a high temperature, and then filtered while hot to obtain a filtrate;

[0008] The filtrate was cooled and crystallized, and then filtered and the obtained solid was vacuum dried to obtain pure N-methylmorpholine-N-oxide;

[0009] The recrystallization solvent is composed of 12-crown ether-4 and C2-C4 diol in a volume ratio of 100:(17-29).

[0010] Furthermore, the volume ratio of the 12-crown ether-4 to the C2-C4 diol is 100:23.

[0011] Furthermore, the C2-C4 diol includes at least one of ethylene glycol, 1,3-propylene glycol and 1,4-butanediol.

[0012] Furthermore, the crude N-methylmorpholine-N-oxide is a crude product prepared by reacting hydrogen peroxide with N-methylmorpholine; the N-methylmorpholine content in the crude N-methylmorpholine-N-oxide is greater than 1000 ppm.

[0013] Furthermore, the weight ratio of the crude N-methylmorpholine-N-oxide to the recrystallization solvent is 1:(4-7).

[0014] Furthermore, the heating step includes: heating from room temperature to 90-94° C. at a heating rate of 2° C. / min, and keeping the temperature for 20-40 minutes.

[0015] Furthermore, the cooling crystallization step includes: cooling to 35-40°C at a cooling rate of 0.5°C / min, pouring out half the weight of the recrystallization solvent; and then continuing to cool to 5-10°C at a cooling rate of 1°C / min.

[0016] Furthermore, in a 50% mass concentration aqueous solution of the pure N-methylmorpholine-N-oxide, the N-methylmorpholine content is less than 50 ppm, the hydrogen peroxide content is less than 20 ppm, and the N-nitrosomorpholine content is less than 5 ppb.

[0017] The above technical solution provided by the embodiment of the present invention has at least the following advantages compared with the prior art:

[0018] An embodiment of the present invention provides a method for crystallization and purification of N-methylmorpholine-N-oxide. The present invention, for the first time, uses 12-crown ether-4 having a specific cavity structure and C2-C4 diols in an appropriate ratio as recrystallization solvents. This method not only significantly reduces the content of impurities such as N-methylmorpholine in the crude N-methylmorpholine-N-oxide product, but also allows the obtained pure N-methylmorpholine-N-oxide to meet the quality standards for Tencel production. Moreover, the entire purification process is simple to operate and time-saving, thus overcoming the shortcomings of the existing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0021] Figure 1 The present invention provides a schematic flow chart of a method for crystallization and purification of N-methylmorpholine-N-oxide. DETAILED DESCRIPTION

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0023] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0024] The present invention provides a method for the crystallization and purification of N-methylmorpholine-N-oxide, such as Figure 1 As shown, the method for crystallization and purification of N-methylmorpholine-N-oxide comprises the following steps:

[0025] The crude N-methylmorpholine-N-oxide is added to a recrystallization solvent and heated to a high temperature, and then filtered while hot to obtain a filtrate;

[0026] The filtrate was cooled and crystallized, and then filtered and the obtained solid was vacuum dried to obtain pure N-methylmorpholine-N-oxide;

[0027] The recrystallization solvent is composed of 12-crown ether-4 and C2-C4 diol in a volume ratio of 100:(17-29).

[0028] An embodiment of the present invention provides a method for crystallization and purification of N-methylmorpholine-N-oxide. The present invention, for the first time, uses 12-crown ether-4 having a specific cavity structure and C2-C4 diols in an appropriate ratio as recrystallization solvents. This method not only significantly reduces the content of impurities such as N-methylmorpholine in the crude N-methylmorpholine-N-oxide product, but also allows the obtained pure N-methylmorpholine-N-oxide to meet the quality standards for Tencel production. Moreover, the entire purification process is simple to operate and time-saving, thus overcoming the shortcomings of the existing technology.

[0029] The recrystallization solvent in the present invention is a mixed solvent prepared by adding an appropriate amount of C2-C4 diol to 12-crown ether-4 as the main solvent. The addition of C2-C4 diol can not only regulate the solubility properties of the obtained mixed solvent and improve the removal effect of impurities during the recrystallization process, but also effectively reduce the freezing point of the obtained mixed solvent to below 0°C, effectively avoiding the problem of solvent solidification during the recrystallization process.

[0030] In some specific embodiments, the volume ratio of the 12-crown ether-4 to the C2-C4 diol is 100:23.

[0031] In some specific embodiments, the C2-C4 diol includes at least one of ethylene glycol, 1,3-propylene glycol, and 1,4-butanediol.

[0032] In some specific embodiments, the crude N-methylmorpholine-N-oxide is a crude product prepared by reacting hydrogen peroxide with N-methylmorpholine; and the N-methylmorpholine content in the crude N-methylmorpholine-N-oxide is greater than 1000 ppm.

[0033] In some specific embodiments, the weight ratio of the crude N-methylmorpholine-N-oxide to the recrystallization solvent is 1:(4-7).

[0034] In some specific embodiments, the heating step includes: heating from room temperature to 90-94° C. at a heating rate of 2° C. / min, and keeping the temperature for 20-40 minutes.

[0035] In some specific embodiments, the cooling crystallization step includes: cooling to 35-40°C at a cooling rate of 0.5°C / min, pouring out half the weight of the recrystallization solvent; and then continuing to cool to 5-10°C at a cooling rate of 1°C / min.

[0036] In some specific embodiments, in a 50% mass concentration aqueous solution of pure N-methylmorpholine-N-oxide, the N-methylmorpholine content is less than 50 ppm, the hydrogen peroxide content is less than 20 ppm, and the N-nitrosomorpholine content is less than 5 ppb.

[0037] It should be noted that the components and raw materials involved in the method for crystallization and purification of N-methylmorpholine-N-oxide provided in the embodiment of the present invention, unless otherwise specified or specifically explained, can be directly commercially available products or homemade using existing public preparation methods; at the same time, the steps and parameters involved, unless otherwise specified or specifically explained, can be carried out according to the preparation process disclosed in the prior art or directly using existing equipment with reference to the instructions for use, and the present invention document will not describe them one by one.

[0038] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the invention. The experimental methods in the following examples where specific conditions are not specified are generally measured in accordance with national standards. If there are no corresponding national standards, then the methods are carried out in accordance with general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0039] The crude N-methylmorpholine-N-oxide described in the following examples and comparative examples is a crude product prepared by reacting hydrogen peroxide with N-methylmorpholine. Testing showed that the crude N-methylmorpholine-N-oxide had an N-methylmorpholine content of 1085 ppm and an electrical conductivity of 694 μs / cm.

[0040] Example 1

[0041] This example provides a method for purifying N-methylmorpholine-N-oxide crystals, which comprises the following steps:

[0042] The crude N-methylmorpholine-N-oxide is added to a recrystallization solvent and heated to a high temperature, and then filtered while hot to obtain a filtrate;

[0043] The filtrate was cooled and crystallized, and then filtered and the obtained solid was vacuum dried to constant weight to obtain pure N-methylmorpholine-N-oxide;

[0044] Wherein, the recrystallization solvent is composed of 12-crown ether-4 and C2-C4 diol in a volume ratio of 100:23, and the C2-C4 diol is 1,3-propylene glycol;

[0045] The weight ratio of the crude N-methylmorpholine-N-oxide to the recrystallization solvent is 1:5;

[0046] The heating step includes: heating from room temperature to 92°C at a heating rate of 2°C / min and keeping the temperature for 30 minutes;

[0047] The cooling and crystallization step comprises: cooling to 38°C at a cooling rate of 0.5°C / min, pouring out half the weight of the recrystallization solvent; and then continuing to cool to 7°C at a cooling rate of 1°C / min.

[0048] The pure N-methylmorpholine-N-oxide obtained in this example was prepared into an aqueous solution with a mass concentration of 50%. Testing showed that its N-methylmorpholine content was 13 ppm, its hydrogen peroxide content was 3.5 ppm, and its N-nitrosomorpholine content was 1.2 ppb, which met the quality standards for Tencel production. In addition, its electrical conductivity was 1.8 μs / cm, indicating that its content of cations such as copper and iron ions and anions such as phosphate and nitrate was extremely low.

[0049] Example 2

[0050] This example provides a method for purifying N-methylmorpholine-N-oxide crystals, which comprises the following steps:

[0051] The crude N-methylmorpholine-N-oxide is added to a recrystallization solvent and heated to a high temperature, and then filtered while hot to obtain a filtrate;

[0052] The filtrate was cooled and crystallized, and then filtered and the obtained solid was vacuum dried to constant weight to obtain pure N-methylmorpholine-N-oxide;

[0053] Wherein, the recrystallization solvent is composed of 12-crown ether-4 and C2-C4 diol in a volume ratio of 100:17, and the C2-C4 diol is ethylene glycol;

[0054] The weight ratio of the crude N-methylmorpholine-N-oxide to the recrystallization solvent is 1:7;

[0055] The heating step comprises: heating from room temperature to 90°C at a heating rate of 2°C / min and keeping the temperature for 40 minutes;

[0056] The cooling and crystallization step comprises: cooling to 35°C at a cooling rate of 0.5°C / min, pouring out half the weight of the recrystallization solvent; and then continuing to cool to 10°C at a cooling rate of 1°C / min.

[0057] The pure N-methylmorpholine-N-oxide obtained in this example was prepared into an aqueous solution with a mass concentration of 50%. Testing showed that its N-methylmorpholine content was 46 ppm, its hydrogen peroxide content was 17.2 ppm, and its N-nitrosomorpholine content was 4.3 ppb, which met the quality standards for Tencel production. In addition, its electrical conductivity was 3.1 μs / cm, indicating that its content of cations such as copper and iron ions and anions such as phosphate and nitrate was extremely low.

[0058] Example 3

[0059] This example provides a method for purifying N-methylmorpholine-N-oxide crystals, which comprises the following steps:

[0060] The crude N-methylmorpholine-N-oxide is added to a recrystallization solvent and heated to a high temperature, and then filtered while hot to obtain a filtrate;

[0061] The filtrate was cooled and crystallized, and then filtered and the obtained solid was vacuum dried to constant weight to obtain pure N-methylmorpholine-N-oxide;

[0062] Wherein, the recrystallization solvent is composed of 12-crown ether-4 and C2-C4 diol in a volume ratio of 100:29, and the C2-C4 diol is 1,4-butanediol;

[0063] The weight ratio of the crude N-methylmorpholine-N-oxide to the recrystallization solvent is 1:4;

[0064] The heating step comprises: heating from room temperature to 94°C at a heating rate of 2°C / min and keeping the temperature for 20 minutes;

[0065] The cooling and crystallization step comprises: cooling to 40°C at a cooling rate of 0.5°C / min, pouring out half the weight of the recrystallization solvent; and then continuing to cool to 5°C at a cooling rate of 1°C / min.

[0066] The pure N-methylmorpholine-N-oxide obtained in this example was prepared into an aqueous solution with a mass concentration of 50%. Testing showed that its N-methylmorpholine content was 28 ppm, the hydrogen peroxide content was 8.9 ppm, and the N-nitrosomorpholine content was 2.7 ppb, which met the quality standards for Tencel production. In addition, its electrical conductivity was 2.4 μs / cm, indicating that its content of cations such as copper and iron ions and anions such as phosphate and nitrate was extremely low.

[0067] Comparative Example 1

[0068] This example provides a method for crystallization and purification of N-methylmorpholine-N-oxide. The only difference from Example 1 is that 12-crown-4 is replaced with 15-crown-5; the remaining steps and parameters are the same.

[0069] The pure N-methylmorpholine-N-oxide obtained in this example was prepared into an aqueous solution with a mass concentration of 50%. After testing, its N-methylmorpholine content was 301 ppm (greater than 100 ppm), which could not meet the quality standards for Tencel production.

[0070] Comparative Example 2

[0071] This example provides a method for crystallization and purification of N-methylmorpholine-N-oxide. The only difference from Example 1 is that the volume ratio of 12-crown ether-4 and C2-C4 diol is adjusted to 100:53; the remaining steps and parameters are the same.

[0072] The pure N-methylmorpholine-N-oxide obtained in this example was prepared into an aqueous solution with a mass concentration of 50%. After testing, its N-methylmorpholine content was 448 ppm (greater than 100 ppm), which could not meet the quality standards for Tencel production.

[0073] In summary, the embodiments of the present invention provide a method for crystallization and purification of N-methylmorpholine-N-oxide. The present invention, for the first time, uses 12-crown ether-4 having a specific cavity structure and C2-C4 diols in an appropriate ratio as recrystallization solvents. This not only significantly reduces the content of impurities such as N-methylmorpholine in the crude N-methylmorpholine-N-oxide, but also allows the obtained pure N-methylmorpholine-N-oxide to meet the quality standards for Tencel production. Moreover, the entire purification process is simple to operate and time-saving, thereby overcoming the shortcomings of the prior art.

[0074] Various embodiments of the present invention may be presented in the form of a range; it should be understood that the description in a range format is only for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention; therefore, the range description should be considered to have specifically disclosed all possible subranges and single numerical values ​​within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated herein, it is intended to include any cited numeral (fractional or integer) within the indicated range.

[0075] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not intended to be limited to the embodiments shown herein, but is intended to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for crystallization and purification of N-methylmorpholine-N-oxide, characterized in that: The method for purifying N-methylmorpholine-N-oxide crystals comprises the following steps: The crude N-methylmorpholine-N-oxide is added to a recrystallization solvent and heated to a high temperature, and then filtered while hot to obtain a filtrate; The filtrate was cooled and crystallized, and then filtered and the obtained solid was vacuum dried to obtain pure N-methylmorpholine-N-oxide; The recrystallization solvent is composed of 12-crown ether-4 and C2-C4 diol in a volume ratio of 100:23, and the C2-C4 diol is 1,3-propylene glycol.

2. The method for crystallization and purification of N-methylmorpholine-N-oxide according to claim 1, characterized in that: The crude N-methylmorpholine-N-oxide product is a crude product prepared by reacting hydrogen peroxide with N-methylmorpholine; the N-methylmorpholine content in the crude N-methylmorpholine-N-oxide product is greater than 1000 ppm.

3. The method for crystallization and purification of N-methylmorpholine-N-oxide according to claim 1, characterized in that: The weight ratio of the crude N-methylmorpholine-N-oxide to the recrystallization solvent is 1:(4-7).

4. The method for crystallization and purification of N-methylmorpholine-N-oxide according to claim 1, characterized in that: The heating step includes heating from room temperature to 90-94° C. at a heating rate of 2° C. / min, and keeping the temperature for 20-40 minutes.

5. The method for crystallization and purification of N-methylmorpholine-N-oxide according to claim 1, characterized in that: The cooling and crystallization step comprises: cooling to 35-40°C at a cooling rate of 0.5°C / min, pouring out half the weight of the recrystallization solvent; and then continuing to cool to 5-10°C at a cooling rate of 1°C / min.

6. The method for crystallization and purification of N-methylmorpholine-N-oxide according to claim 1, characterized in that: In a 50% mass concentration aqueous solution of the pure N-methylmorpholine-N-oxide, the N-methylmorpholine content is less than 50 ppm, the hydrogen peroxide content is less than 20 ppm, and the N-nitrosomorpholine content is less than 5 ppb.

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