Method for crystallizing and purifying N-methylmorpholine-N-oxide

Abstract

The invention discloses a method for crystallization and purification of N-methylmorpholine-N-oxide, and relates to the technical field of purification of N-methylmorpholine-N-oxide, and the method for crystallization and purification of N-methylmorpholine-N-oxide comprises the following steps: adding a crude product of N-methylmorpholine-N-oxide into a recrystallization solvent for heating, then filtering while the solution is hot to obtain filtrate; cooling and crystallizing the filtrate, then carrying out suction filtration, and carrying out vacuum drying on the obtained solid. According to the method, 12-crown ether-4 and C2-C4 dihydric alcohol with a specific cavity structure in a proper proportion are used as recrystallization solvents for the first time, so that the content of impurities such as N-methylmorpholine in the crude product of the N-methylmorpholine-N-oxide is remarkably reduced, and the obtained pure product of the N-methylmorpholine-N-oxide can meet the quality standard of tencel production; and the whole purification process is simple to operate and short in time consumption, and overcomes the defects in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of N-methyl morpholine-N-oxide purification, and particularly to a method for purifying N-methyl morpholine-N-oxide by crystallization. Background Art

[0002] N-methyl morpholine-N-oxide (NMMO) is an important aliphatic cyclic tertiary amine oxide and has wide applications in the field of fiber spinning. Especially in the production of Lyocell fibers, NMMO plays an indispensable role as a key solvent. Industrial production of NMMO is usually prepared by the reaction of hydrogen peroxide with N-methyl morpholine. This method has the advantages of simple process and easy availability of raw materials, so it has been widely used.

[0003] However, in the process of preparing NMMO by the reaction of hydrogen peroxide with N-methyl morpholine, due to factors such as raw material purity and reaction condition control, the obtained crude NMMO often contains a certain amount of impurities. These impurities may include unreacted N-methyl morpholine, reaction by-products, catalyst residues, and impurities in the solvent, etc. The presence of these impurities will not only affect the purity and quality of NMMO, but may also have an adverse impact on the subsequent fiber spinning process, reducing the performance and quality of the product.

[0004] In order to obtain a high-purity NMMO product and meet the quality standards for Lyocell production, it is necessary to purify the crude NMMO. Currently, common purification methods include distillation, extraction, crystallization, etc. Among them, the crystallization purification method is favored due to its simple operation and high purification efficiency. However, existing crystallization purification methods often have problems such as long purification time, poor purification effect, and complex operation, and it is difficult to meet the requirements of large-scale industrial production. Summary of the Invention

[0005] To solve the above problems, the present invention provides a method for purifying N-methyl morpholine-N-oxide by crystallization.

[0006] The present invention provides a method for purifying N-methyl morpholine-N-oxide by crystallization, as Figure 1 shown, the method for purifying N-methyl morpholine-N-oxide by crystallization includes the following steps:

[0007] Adding the crude N-methyl morpholine-N-oxide to a recrystallization solvent, heating and raising the temperature, and then performing hot filtration to obtain a filtrate;

[0008] Cooling the filtrate for crystallization, then performing suction filtration and vacuum drying the obtained solid to obtain pure N-methyl morpholine-N-oxide;

[0009] Among them, the recrystallization solvent is composed of 12-crown-4 and C2-C4 diol with a volume ratio of 100:(17-29).

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

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

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

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

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

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

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

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

[0018] The embodiments of the present invention provide a method for crystallizing and purifying N-methylmorpholine-N-oxide. For the first time, 12-crown-4 with a specific cavity structure and C2-C4 diol in an appropriate ratio are used as the recrystallization solvent, which not only significantly reduces the content of impurities such as N-methylmorpholine in the crude N-methylmorpholine-N-oxide, and the obtained pure N-methylmorpholine-N-oxide can meet the quality standards for Tencel production; moreover, the entire purification process is simple in operation and short in time consumption, making up for the deficiencies of the prior art. Description of the Drawings

[0019] The accompanying drawings here are incorporated into the specification and form a part of this specification, showing embodiments in accordance with the present invention, and are used together with the specification to explain the principles of the present invention.

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 It is a schematic flow chart of a method for the crystallization purification of N-methylmorpholine-N-oxide provided by an embodiment of the present invention. Detailed implementation manners

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0023] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or can be prepared by existing methods.

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

[0025] Adding the crude N-methylmorpholine-N-oxide to a recrystallization solvent, heating and raising the temperature, and then performing hot filtration to obtain a filtrate;

[0026] Cooling the filtrate for crystallization, then performing suction filtration and vacuum drying the obtained solid to obtain pure N-methylmorpholine-N-oxide;

[0027] Among them, the recrystallization solvent is composed of 12-crown-4 and C2-C4 diol with a volume ratio of 100:(17-29).

[0028] An embodiment of the present invention provides a method for the crystallization purification of N-methylmorpholine-N-oxide. For the first time, 12-crown-4 with a specific cavity structure and a C2-C4 diol in an appropriate ratio are used as the recrystallization solvent, which not only significantly reduces the content of impurities such as N-methylmorpholine in the crude N-methylmorpholine-N-oxide, and the obtained pure N-methylmorpholine-N-oxide can meet the quality standards for the production of Tencel; moreover, the entire purification process is simple to operate and time-consuming, making up for the deficiencies of the prior art.

[0029] In the present invention, the recrystallization solvent is a mixed solvent prepared by mixing an appropriate amount of C2-C4 diol on the basis of 12-crown-4. The addition of C2-C4 diol can not only regulate the dissolution properties of the obtained mixed solvent and improve its impurity removal effect during recrystallization; but also can effectively reduce the freezing point of the obtained mixed solvent to below 0 °C, effectively avoiding the problem of solvent solidification during recrystallization.

[0030] In some specific embodiments, the volume ratio of the 12-crown-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-propanediol, 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; the content of N-methylmorpholine in the crude N-methylmorpholine-N-oxide is > 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 step of heating and raising the temperature includes: raising the temperature from room temperature to 90-94 °C at a rate of 2 °C / min and holding for 20-40 minutes.

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

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

[0037] It should be noted that for the component raw materials involved in the method for the crystallization purification of N-methylmorpholine-N-oxide provided in the embodiments of the present invention, if there is no special limitation or specific description, commercially available products can be directly used or self-made by using existing publicly disclosed preparation methods; at the same time, for the steps and parameters involved, if there is no special limitation or specific description, they can be carried out according to the preparation processes disclosed in the prior art or directly used with reference to the usage instructions of existing equipment, and the present invention document will not elaborate one by one.

[0038] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are usually determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0039] The crude N-methylmorpholine-N-oxide mentioned in the following examples and comparative examples is the crude product prepared by reacting hydrogen peroxide with N-methylmorpholine; after detection, the content of N-methylmorpholine in the crude N-methylmorpholine-N-oxide is 1085 ppm, and the conductivity is 694 μs / cm.

[0040] Example 1

[0041] This example provides a method for the crystallization purification of N-methylmorpholine-N-oxide, and the method for the crystallization purification of N-methylmorpholine-N-oxide includes the following steps:

[0042] Add the crude N-methylmorpholine-N-oxide to a recrystallization solvent, heat it up, and then filter it while it is hot to obtain a filtrate;

[0043] Cool the filtrate for crystallization, then carry out suction filtration and vacuum-dry the obtained solid to constant weight to obtain pure N-methylmorpholine-N-oxide;

[0044] Among them, the recrystallization solvent is composed of 12-crown-4 and C2-C4 diol with a volume ratio of 100:23, and the C2-C4 diol is 1,3-propanediol;

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

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

[0047] The steps of cooling and crystallization include: when the temperature is decreased at a rate of 0.5 °C / min to 38 °C, half of the weight of the recrystallization solvent is poured out; then the temperature is continuously decreased at a rate of 1 °C / min to 7 °C.

[0048] In this example, the obtained pure N-methylmorpholine-N-oxide is formulated into an aqueous solution with a mass concentration of 50%. After testing, its N-methylmorpholine content is 13 ppm, its hydrogen peroxide content is 3.5 ppm, and its N-nitrosomorpholine content is 1.2 ppb, meeting the quality standards for Tencel production; moreover, its conductivity is 1.8 μs / cm, indicating that the contents of cations such as copper and iron ions and anions such as phosphate and nitrate ions are extremely low.

[0049] Example 2

[0050] This example provides a method for the crystallization and purification of N-methylmorpholine-N-oxide. The method for the crystallization and purification of N-methylmorpholine-N-oxide includes the following steps:

[0051] The crude N-methylmorpholine-N-oxide is added to the recrystallization solvent and heated to a higher temperature, and then hot filtration is carried out to obtain a filtrate;

[0052] The filtrate is cooled and crystallized, and then suction filtration is carried out and the obtained solid is vacuum dried to a constant weight to obtain pure N-methylmorpholine-N-oxide;

[0053] Among them, the recrystallization solvent is composed of 12-crown-4 and C2-C4 diol with 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 steps of heating to a higher temperature include: heating from room temperature to 90 °C at a rate of 2 °C / min and holding for 40 minutes;

[0056] The steps of cooling and crystallization include: when the temperature is decreased at a rate of 0.5 °C / min to 35 °C, half of the weight of the recrystallization solvent is poured out; then the temperature is continuously decreased at a rate of 1 °C / min to 10 °C.

[0057] In this example, the obtained pure N-methylmorpholine-N-oxide is formulated into an aqueous solution with a mass concentration of 50%. After testing, its N-methylmorpholine content is 46 ppm, its hydrogen peroxide content is 17.2 ppm, and its N-nitrosomorpholine content is 4.3 ppb, meeting the quality standards for Tencel production; moreover, its conductivity is 3.1 μs / cm, indicating that the contents of cations such as copper and iron ions and anions such as phosphate and nitrate ions are extremely low.

[0058] Example 3

[0059] This example provides a method for the crystallization purification of N-methylmorpholine-N-oxide. The method for the crystallization purification of N-methylmorpholine-N-oxide includes the following steps:

[0060] Add the crude N-methylmorpholine-N-oxide to a recrystallization solvent, heat it up, and then perform hot filtration to obtain a filtrate;

[0061] Cool the filtrate for crystallization, then perform suction filtration and vacuum dry the obtained solid to constant weight to obtain pure N-methylmorpholine-N-oxide;

[0062] Among them, the recrystallization solvent is composed of 12-crown-4 and C2-C4 diol with 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 step of heating and raising the temperature includes: raising the temperature from room temperature to 94°C at a heating rate of 2°C / min and holding for 20 minutes;

[0065] The step of cooling and crystallizing includes: when cooling to 40°C at a cooling rate of 0.5°C / min, pour out half of the weight of the recrystallization solvent; then continue to cool to 5°C at a cooling rate of 1°C / min.

[0066] The pure N-methylmorpholine-N-oxide obtained in this example is formulated into an aqueous solution with a mass concentration of 50%. After testing, its N-methylmorpholine content is 28 ppm, hydrogen peroxide content is 8.9 ppm, and N-nitrosomorpholine content is 2.7 ppb, meeting the quality standards for Tencel production; moreover, its conductivity is 2.4 μs / cm, indicating that the contents of cations such as copper and iron ions and anions such as phosphate and nitrate ions are extremely low.

[0067] Comparative Example 1

[0068] This example provides a method for the crystallization purification of N-methylmorpholine-N-oxide, which is only different from Example 1 in that 12-crown-4 is adjusted to 15-crown-5; the remaining steps and parameters are the same.

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

[0070] Comparative Example 2

[0071] This example provides a method for the crystallization purification of N-methylmorpholine-N-oxide, which is only different from Example 1 in that: the volume ratio of 12-crown-4 to 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 is formulated into an aqueous solution with a mass concentration of 50%. After testing, the content of N-methylmorpholine in it is 448 ppm (greater than 100 ppm), which cannot meet the quality standard for Tencel production.

[0073] In summary, the embodiments of the present invention provide a method for the crystallization purification of N-methylmorpholine-N-oxide. For the first time, the present invention uses 12-crown-4 with a specific cavity structure and C2-C4 diol in an appropriate ratio as the recrystallization solvent, which not only significantly reduces the content of impurities such as N-methylmorpholine in the crude N-methylmorpholine-N-oxide, and the obtained pure N-methylmorpholine-N-oxide can meet the quality standard for Tencel production; moreover, the entire purification process is simple to operate and time-consuming, making up for the deficiencies of the prior art.

[0074] The various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present invention; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges 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., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, which applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0075] The above description is only the specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the broadest 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 crystallization and purification of N-methylmorpholine-N-oxide 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 is cooled and crystallized, and then filtered and the obtained solid is 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:(17-29).

2. The method for crystallization and purification of N-methylmorpholine-N-oxide according to claim 1, characterized in that: The volume ratio of the 12-crown ether-4 to the C2-C4 diol is 100:

23.

3. The method for crystallization and purification of N-methylmorpholine-N-oxide according to claim 1, characterized in that: The C2-C4 diol includes at least one of ethylene glycol, 1,3-propylene glycol and 1,4-butanediol.

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

5. 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).

6. 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.

7. The method for crystallization and purification of N-methylmorpholine-N-oxide according to claim 1, characterized in that: The step of cooling and crystallizing 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.

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

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