Method for detecting decomposition product content of N-methylmorpholine-N-oxide and application thereof

Abstract

The invention discloses a method for detecting the content of decomposition products of N-methylmorpholine-N-oxide and application of the method. The method comprises the following steps: (1) performing a two-step purification method on a sample to be detected containing the N-methylmorpholine-N-oxide and the decomposition products of the N-methylmorpholine-N-oxide to obtain a purified solution; and (2) quantitatively detecting morpholine and methylmorpholine in the purified solution by adopting HPLC (High Performance Liquid Chromatography). The method adopts a two-step purification method to quickly and efficiently separate decomposition products of morpholine and methylmorpholine, ensures high recovery rate of the decomposition products of morpholine and N-methylmorpholine, and has the characteristic of ensuring chemical stability of a substance to be detected. Meanwhile, the purification liquid obtained by the two-step purification method can be used for quickly, simply and conveniently detecting decomposition products of morpholine and N-methylmorpholine through an HPLC (High Performance Liquid Chromatography) detection method, and the detection limit is 0.200 ppm.

Description

Technical Field

[0001] The present invention belongs to the field of analysis and detection, and in particular relates to a method for detecting the content of decomposition products of N-methylmorpholine-N-oxide and an application thereof. Background Art

[0002] Lyocell fiber, hailed as the green fiber of the 21st century, is a regenerated cellulose fiber made from refined pulp dissolved in an aqueous solution of N-methylmorpholine-N-oxide (NMMO) and then spun through wet and dry spinning processes. Lyocell fiber is produced using a closed-loop process, resulting in a short production process and no toxic byproducts. Lyocell fiber exhibits excellent mechanical properties, comfort, and drapeability, and is naturally biodegradable.

[0003] Since NMMO is expensive, in order to improve the economic efficiency of the Lyocell fiber production process, it is necessary to recycle NMMO, concentrate the NMMO solution, and reuse it in the cellulose dissolution process to achieve recycling. During the spinning solution preparation, dissolution spinning, and solvent recovery processes, a small amount of NMMO will undergo decomposition reactions, and the decomposition products are N-methylmorpholine (hereinafter referred to as NMM), morpholine (hereinafter referred to as M), etc. Each production section needs to control the NMMO decomposition within a certain range to ensure that the NMMO solvent quality is good, the cellulose swelling is fully dissolved, and the spinning solution performance is uniform, so that high-quality fiber products can be spun. Therefore, in the Lyocell fiber production process, tracking and testing the changes in the concentration of NMMO decomposition products is of great significance for guiding production.

[0004] Currently, commercially available NMMO aqueous solutions used in Lyocell fiber production have a mass concentration of approximately 50%. The mainstream NMMO production process uses NMM, a byproduct of the morpholine plant, as a raw material, and hydrogen peroxide as an oxidant, over a catalyst to produce NMMO. Commercially available product quality standards have strict requirements for single-pass conversion rate, product yield, and quality control during transportation, with NMM content required to be less than 100 ppm and M content less than 200 ppm. Testing the NMM and M contents in the NMMO product directly evaluates the quality of the NMMO solvent.

[0005] The decomposition product concentrations of NMMO solvents used in the aforementioned recycling process and commercially available NMMO products are generally in the ppm range, ranging from 0.1 to 1000 ppm. Therefore, to evaluate NMMO purity and investigate its decomposition, researchers have sought to develop methods for accurately detecting trace amounts of NMMO and M in NMMO solutions.

[0006] Liquid chromatography is currently the most common method for determining NMMO and M. However, due to the significantly higher concentration of NMMO relative to its decomposition products, conventional liquid chromatography separation techniques are difficult to achieve effective separation. The NMMO peak significantly overlaps the peaks of lower-concentration decomposition products, resulting in very low resolution for decomposition product detection. Limited by the pressure resistance, peak capacity, and selectivity of the detection instrument, the peak capacity of liquid chromatography separation cannot be significantly increased, making it difficult to obtain effective measurement results.

[0007] The article "Study on the Recovery Process and Mechanism of N-methylmorpholine-N-oxide (NMMO) Solvent Used in Lyocell Fiber Production" discusses the quantitative detection of N-methylmorpholine-N-oxide (NMMO) and its main decomposition products N-methylmorpholine (NMM) and morpholine (M) by high performance liquid chromatography (HPLC) under different detection conditions. The minimum detection limits of NMMO, NMM and M in this technology are 50ppm, 20ppm and 20ppm, respectively.

[0008] Chinese patent application CN112362773A discloses a method for quantitatively detecting NMMO and its decomposition products using liquid chromatography. However, the method uses a mass fraction ratio of NMMO to NMM of 4.93 and a mass fraction ratio of NMMO to M of 6.46 in the sample. When the mass fractions differ significantly, the liquid chromatography detection limit makes it impossible to accurately determine the concentrations of NMM and M.

[0009] Chinese patent application publication number CN1165514A discloses the use of high-pressure liquid chromatography to determine the contents of NMMO, NMM, and M. However, this technique employs samples with a mass fraction ratio of NMMO to NMM ranging from 0.70 to 2350, and a mass fraction ratio of NMMO to M ranging from 1.21 to 1032. At higher mass fraction ratios, the detection capability of liquid chromatography is significantly limited.

[0010] As domestic research on Lyocell fiber production technology deepens, strengthening the quality control of NMMO decomposition products has become a top priority in process control. However, the high cost of high-end testing instruments has created tremendous pressure on production investment, making it difficult to meet the needs of the development of the Lyocell fiber industry.

[0011] Therefore, the Lyocell fiber industry urgently needs a detection method with low requirements for detection instruments, simple and fast detection process, and accurate and stable detection results.

[0012] In view of this, the present invention is proposed. Summary of the Invention

[0013] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for detecting the content of decomposition products of N-methylmorpholine-N-oxide and its application. The present invention utilizes a two-step purification method to rapidly and efficiently separate the decomposition products morpholine and methylmorpholine, ensuring a high recovery rate of the decomposition products morpholine and N-methylmorpholine while also ensuring the chemical stability of the substance being tested. Furthermore, the purified solution obtained by the two-step purification method can be rapidly and easily detected by HPLC chromatographic detection, with a detection limit of 0.200 ppm.

[0014] In order to solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0015] The present invention provides a method for detecting the content of decomposition products of N-methylmorpholine-N-oxide, the method comprising:

[0016] (1) A sample containing N-methylmorpholine-N-oxide and its decomposition products is purified by a two-step method to obtain a purified solution;

[0017] (2) HPLC chromatography was used to quantitatively detect morpholine and methylmorpholine in the purified solution.

[0018] The present invention adopts a two-step purification method to quickly and efficiently separate the decomposition products morpholine and methylmorpholine, ensuring the high recovery rate of the decomposition products morpholine and N-methylmorpholine, while having the characteristics of ensuring the chemical stability of the substance to be tested. At the same time, the purified liquid obtained by the two-step purification method can quickly and easily detect the decomposition products morpholine and N-methylmorpholine by the method of HPLC chromatographic detection, with a detection limit of 0.200ppm. The reagents and test conditions used in the present invention are all easily achieved, and N-methylmorpholine-N-oxide and its decomposition products can be separated under conditions of relatively low temperature and short time, effectively reducing the test difficulty and improving test efficiency. The method provided by the present invention has relatively low requirements for detection instruments, and the detection process is simple, accurate and rapid, and is suitable for being put into industrial production as a low-cost assay method.

[0019] In a further embodiment, in step (1), the mass ratio of N-methylmorpholine, morpholine, and N-methylmorpholine-N-oxide in the sample to be tested is 4.0×10 -6 ~1.0×10 -3 :4.0×10 -6 ~1.0×10 -3 :1.

[0020] In a further embodiment, in step (1), the mass fraction of N-methylmorpholine-N-oxide in the sample to be tested is 4%-87%;

[0021] Preferably, the mass fraction of N-methylmorpholine-N-oxide in the sample to be tested is 5%-72%;

[0022] Preferably, the mass fraction of N-methylmorpholine-N-oxide in the sample to be tested is 5%-55%.

[0023] In a further embodiment, in step (1), the sample to be tested is first diluted and then purified, and the mass fraction of N-methylmorpholine-N-oxide in the diluted solution to be tested is 4%-25%;

[0024] Preferably, the mass fraction of N-methylmorpholine-N-oxide in the diluted test solution is 5%-20%;

[0025] Preferably, the mass fraction of N-methylmorpholine-N-oxide in the diluted test solution is 15%-20%.

[0026] In a further embodiment, in step (1), before the two-step purification method is used, a base is added to the test solution to adjust the pH value to 10.0-13.0;

[0027] Preferably, the base is selected from sodium hydroxide and potassium hydroxide.

[0028] In a further scheme, in step (1), the two-step purification method includes performing a first-step distillation and a second-step distillation on the sample to be tested, obtaining a first-step purified liquid and a first-step distillation concentrated liquid after the first-step distillation, performing a second-step distillation on the first-step distillation concentrated liquid to obtain a two-step purified liquid; after mixing the first-step purified liquid and the second-step purified liquid, the volume is constant by mass.

[0029] Preferably, pure water is added to the one-step distillation concentrate and then a two-step distillation is performed, and the mass ratio of the pure water to the sample to be tested is 0.5 to 2.0:1.

[0030] Preferably, when performing mass determination, the mass of the constant volume is the sum of the mass of the sample to be distilled and the mass of pure water added to the one-step distillation concentrate.

[0031] It should be noted that the purified liquid mentioned in the present invention refers to the liquid obtained by condensing after the sample is heated and evaporated; the distilled concentrated liquid refers to the concentrated liquid remaining after the sample is heated and evaporated.

[0032] The present invention provides a method for detecting trace amounts of N-methylmorpholine and morpholine in an N-methylmorpholine-N-oxide solution. The method comprises the following steps: diluting the N-methylmorpholine-N-oxide solution to a required concentration range; adding a base (such as sodium hydroxide) to the diluted solution to adjust the pH value; performing a first step distillation on the pH-adjusted solution to obtain a first step purified solution mainly containing N-methylmorpholine and morpholine and a concentrated solution mainly containing N-methylmorpholine-N-oxide; adding pure water to the concentrated solution for dilution again; and performing a second step distillation to obtain a second step purified solution mainly containing N-methylmorpholine and morpholine and a concentrated solution mainly containing N-methylmorpholine-N-oxide. The two purified solutions are uniformly mixed, and the volume is constant to obtain an aqueous phase test sample mainly containing N-methylmorpholine and morpholine, which is then tested using HPLC.

[0033] Specifically, the first step of distillation uses a laboratory assembled distillation apparatus or a rotary evaporator.

[0034] Preferably, the first step of distillation uses a laboratory assembled distillation apparatus.

[0035] In a further embodiment, the conditions for the first step of distillation include: evaporation pressure 3.0-15.0 kPa, evaporation temperature 40.0-70.0° C., cooling water temperature 20.0-32.0° C., and distillation time 0.5-2.0 h.

[0036] Specifically, the second step of distillation adopts a laboratory assembled distillation apparatus or a rotary evaporator.

[0037] Preferably, the second step of distillation uses a laboratory assembled distillation apparatus.

[0038] In a further embodiment, the conditions for the second step of distillation include: evaporation pressure 3.0-15.0 kPa, evaporation temperature 40.0-70.0° C., cooling water temperature 20.0-32.0° C., and distillation time 0.5-2.0 h.

[0039] In a further solution, the mass ratio m of the purified liquid mixture after the two-step purification to the mass of the sample to be distilled and tested is 1.5 to 3.0:1.

[0040] It should be noted that the mass of the sample to be distilled and tested refers to the mass of the sample before the first step of distillation.

[0041] In a further embodiment, in step (2), the method for quantitatively detecting morpholine and methylmorpholine in the purified solution using HPLC chromatography comprises:

[0042] The conditions for detection using HPLC chromatography include:

[0043] The chromatographic column RCX-30 (150 mm × 4.6 mm × 7 μm) was used, and the mobile phase was water containing sodium hexametaphosphate for isocratic elution;

[0044] Preferably, in the water containing sodium hexametaphosphate, the concentration of sodium hexametaphosphate is 0.040 to 0.060 M;

[0045] Preferably, the flow rate is 1.0 mL / min, the injection volume is 20 μL, and the column oven temperature is 32°C;

[0046] Conductivity detector, acquisition time is 30min.

[0047] Specifically, in the HPLC test, the mass concentrations of NMMO, NMM, and M were calculated using the external standard method, and the standard curve calculation formula was:

[0048] NMMO: y = 0.025x + 0.011

[0049] NMM: y = 0.0227x + 0.002

[0050] M:y=0.0278x-0.015

[0051] y is the peak area in the liquid phase test results, and x is the liquid phase content of the test sample, ppm.

[0052] The present invention realizes effective separation of NMMO from NMM and M through a two-step purification method, and realizes quantitative detection of trace NMMO decomposition products only by ion chromatography detection, avoiding the use of expensive high-end detection instruments.

[0053] The present invention also provides an application of the above-mentioned method for detecting the content of decomposition products of N-methylmorpholine-N-oxide in quality control during the production or use of N-methylmorpholine-N-oxide solvents;

[0054] Preferably, the invention is used in detecting the content of decomposition products of N-methylmorpholine-N-oxide, a solvent used in Lyocell fiber production.

[0055] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0056] 1. The present invention achieves the purpose of effectively separating NMMO from NMM and M by adopting a two-step purification method, thereby purifying the test sample containing NMM and M, ensuring that subsequent quantitative analysis can be performed only by HPLC. The analysis results have high sensitivity, high discrimination, and high accuracy, with a detection limit of 0.200 ppm.

[0057] 2. The detection method of the present invention is simple and fast, with high analytical sensitivity, reliable and accurate results, and good reproducibility. It provides a fast, stable, and highly sensitive measurement method for controlling changes in solvent components in NMMO, NMM, and M research, especially in lyocell industrial production.

[0058] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an undue limitation of the present invention. Obviously, the drawings described below are only some embodiments. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without inventive effort. In the accompanying drawings:

[0060] Figure 1 Schematic diagram of the steps for detecting the content of decomposition products of N-methylmorpholine-N-oxide, a solvent for Lyocell fibers, according to the present invention;

[0061] Figure 2 This is a schematic diagram of the apparatus assembled in the laboratory for distilling N-methylmorpholine-N-oxide solution;

[0062] Among them, 1 is a water bath, 2 is a capillary, 3 is a thermometer, 4 is a cooling water outlet, 5 is a cooling water inlet, and 6 is a vacuum pump.

[0063] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but rather to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0065] The method for detecting by HPLC in Examples 1-5 includes:

[0066] Preparation of Reference Solution: Accurately weigh an appropriate amount of NMM reference sample and mix with pure water to a concentration of 50 ppm. This is the NMM reference solution. Accurately weigh an appropriate amount of M reference sample and mix with pure water to a concentration of 20 ppm. This is the M reference solution. Accurately weigh an appropriate amount of NMMO reference sample and mix with pure water to a concentration of 50% by mass. This is the NMMO reference solution.

[0067] The instrument conditions were as follows: a chromatographic column RCX-30 (150 mm × 4.6 mm × 7 μm) was used, the mobile phase was water containing sodium hexametaphosphate, the concentration of sodium hexametaphosphate was 0.050 M, the flow rate was constant at 1.0 mL / min, the injection volume was 20 μL, the column oven temperature was 32°C, the conductivity detector was used, and the acquisition time was 30 min.

[0068] Specifically, in the HPLC test, the mass concentrations of NMMO, NMM, and M were calculated using the external standard method, and the standard curve calculation formula was:

[0069] NMMO: y = 0.025x + 0.011

[0070] NMM: y = 0.0227x + 0.002

[0071] M:y=0.0278x-0.015

[0072] y is the peak area in the liquid phase test results, and x is the liquid phase content of the test sample, ppm.

[0073] Example 1

[0074] Take NMM and M reference samples and prepare 1000 mL of a stock solution (test solution 1) with a 50 ppm NMM concentration and a 25 ppm M concentration using pure water. Take NMMO reference sample and prepare 1000 mL of a stock solution (test solution 2) with a 50% NMMO mass fraction using pure water. Add 500 g of test solution 1 to 500 g of test solution 2 to prepare an NMMO dilution solution containing NMM and M (test solution 3). Sodium hydroxide is added to the solution until the pH is 10.80 (test solution 4). Add 50 g of test solution 4 to a laboratory-assembled distillation apparatus and perform a first distillation step under conditions of 6.0 kPa pressure, 50.0°C temperature, and 25.0°C cooling water temperature for 1.0 h to obtain a first-step concentrated solution (test solution 5) and a first-step purified solution (test solution 6). 50 g of pure water was added to test solution 5, and a second distillation step was performed under the conditions of a pressure of 6.0 kPa, a temperature of 50.0° C., and a cooling water temperature of 25.0° C. for 1.0 h to obtain a two-step concentrated solution (test solution 7) and a two-step purified solution (test solution 8). Test solutions 6 and 8 were mixed and the volume was constant to 100 g to obtain a constant-volume purified solution (test solution 9). The contents of NMM and M in test solution 9 were tested by HPLC. The recoveries of NMM and M were 96.4% and 95.2%, respectively.

[0075] Table 1 Liquid chromatography analysis results of samples

[0076]

[0077] Table 2

[0078]

[0079] Example 2

[0080] Take the NMMO solution for Lyocell fiber production (test solution 1, mass concentration 15.0%), add sodium hydroxide reagent until the pH value is 12.0 (test solution 2), take 80g test solution 2 and add it to the laboratory assembled distillation apparatus, and carry out the first step distillation under the conditions of pressure 11.0kPa, temperature 60℃, and cooling water temperature 30.0℃ for 1.5 hours to obtain a one-step concentrated solution (test solution 3) and a one-step purified solution (test solution 4). Add 40g pure water to test solution 3, and carry out the second step distillation under the conditions of pressure 11.0kPa, temperature 60℃, and cooling water temperature 30.0℃ for 1.5 hours to obtain a two-step concentrated solution (test solution 5) and a two-step purified solution (test solution 6). Test solution 4 and test solution 6 are mixed and the volume is constant to 120g to obtain a constant volume purified solution (test solution 7). The NMM and M contents in test solution 7 are detected by HPLC.

[0081] Results: The obtained NMM content was 0.600 ppm and the M content was 0.645 ppm.

[0082] Example 3

[0083] NMMO concentrate for Lyocell fiber production (test solution 1, 78.0% mass concentration) was diluted 5-fold to a NMMO concentration of 15.6% (test solution 2). Potassium hydroxide was added to test solution 2 until the pH was 10.50 (test solution 3). 100 g of test solution 3 was added to a laboratory-assembled distillation apparatus and subjected to a first distillation step at a pressure of 8.0 kPa, a temperature of 65°C, and a cooling water temperature of 25°C for 2.0 h, yielding a first-step concentrate (test solution 4) and a first-step purified solution (test solution 5). 120 g of pure water was added to test solution 4, and a second-step distillation step was conducted at a pressure of 8.0 kPa, a temperature of 65°C, and a cooling water temperature of 25°C for 2.0 h, yielding a second-step concentrate (test solution 6) and a second-step purified solution (test solution 7). Test solution 5 and test solution 7 were mixed, and the volume was adjusted to 220 g to obtain a purified solution (test solution 8). The contents of NMM and M in test solution 8 were detected by HPLC.

[0084] Results: The obtained NMM content was 20.560 ppm and the M content was 7.880 ppm.

[0085] Example 4

[0086] A commercially available NMMO finished solvent (test solution 1, 50.0% mass concentration) from a certain company was diluted 2.5-fold to a NMMO concentration of 20.0% (test solution 2). Potassium hydroxide was added to test solution 2 until the pH was 12.50 (test solution 3). 50 g of test solution 3 was added to a laboratory-assembled distillation apparatus and subjected to a first distillation step at a pressure of 5.0 kPa, a temperature of 45°C, and a cooling water temperature of 32°C for 1.0 h, yielding a first-step concentrated solution (test solution 4) and a first-step purified solution (test solution 5). 75 g of pure water was added to test solution 4, and a second-step distillation step was conducted at a pressure of 5.0 kPa, a temperature of 45°C, and a cooling water temperature of 32°C for 1.0 h, yielding a second-step concentrated solution (test solution 6) and a second-step purified solution (test solution 7). Test solution 5 and test solution 7 were mixed, and the volume was adjusted to 125 g to obtain a purified solution (test solution 8). The contents of NMM and M in test solution 8 were detected by HPLC.

[0087] Results: The obtained NMM content was 62.280 ppm and the M content was 14.170 ppm.

[0088] Example 5

[0089] Take the commercially available NMMO finished solvent (test solution 1, mass concentration 50.2%) from a certain company 2, dilute it 2.5 times to an NMMO concentration of 20.08% (test solution 2), add sodium hydroxide reagent to test solution 2 until the pH value is 11.80 (test solution 3), take 30g of test solution 3 and add it to a laboratory-assembled distillation apparatus, and carry out the first step distillation under the conditions of pressure of 12.0kPa, temperature of 55°C, and cooling water temperature of 30°C for 1.5 hours to obtain a first-step concentrated solution (test solution 4) and a first-step purified solution (test solution 5). Add 50g of pure water to test solution 4, and carry out the second step distillation under the conditions of pressure of 12.0kPa, temperature of 55°C, and cooling water temperature of 30°C for 1.5 hours to obtain a second-step concentrated solution (test solution 6) and a second-step purified solution (test solution 7). Test solution 5 and test solution 7 were mixed, and the volume was adjusted to 80 g to obtain a purified solution (test solution 8). The contents of NMM and M in test solution 8 were detected by HPLC.

[0090] Results: The obtained NMM content was 5.220 ppm and the M content was 0.930 ppm.

[0091] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the present invention can make slight changes or modifications to equivalent embodiments using the above-mentioned technical contents without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the solution of the present invention.

Claims

1. A method for detecting the content of decomposition products of N-methylmorpholine-N-oxide, characterized in that the method include: (1) A sample containing N-methylmorpholine-N-oxide and its decomposition products is purified by a two-step method to obtain a purified solution; (2) HPLC chromatography was used to quantitatively detect morpholine and methylmorpholine in the purified solution.

2. The method according to claim 1, characterized in that In step (1), the mass ratio of N-methylmorpholine, morpholine, and N-methylmorpholine-N-oxide in the sample to be tested is 4.0×10 -6 ~1.0×10 -3 :4.0×10 -6 ~1.0×10 -3 :

1.

3. The method according to claim 1 or 2, characterized in that In step (1), the mass fraction of N-methylmorpholine-N-oxide in the sample to be tested is 4%-87%; Preferably, the mass fraction of N-methylmorpholine-N-oxide in the sample to be tested is 5%-72%; Preferably, the mass fraction of N-methylmorpholine-N-oxide in the sample to be tested is 5%-55%.

4. The method according to any one of claims 1 to 3, characterized in that In step (1), the sample to be tested is first diluted and then purified, and the mass fraction of N-methylmorpholine-N-oxide in the diluted solution to be tested is 4%-25%; Preferably, the mass fraction of N-methylmorpholine-N-oxide in the diluted test solution is 5%-20%; Preferably, the mass fraction of N-methylmorpholine-N-oxide in the diluted test solution is 15%-20%.

5. The method according to any one of claims 1 to 4, characterized in that In step (1), before the two-step purification method is used, a base is added to the test solution to adjust the pH value to 10.0-13.0; Preferably, the base is selected from sodium hydroxide and potassium hydroxide.

6. The method according to any one of claims 1 to 5, characterized in that In step (1), the two-step purification method includes performing a first-step distillation and a second-step distillation on the sample to be tested, obtaining a first-step purified liquid and a first-step distillation concentrated liquid after the first-step distillation, performing a second-step distillation on the first-step distillation concentrated liquid to obtain a second-step purified liquid; mixing the first-step purified liquid and the second-step purified liquid, and then performing mass determination; Preferably, pure water is added to the one-step distillation concentrate and then a two-step distillation is performed, wherein the mass ratio of the pure water to the sample to be tested is 0.5 to 2.0:1; Preferably, when performing mass determination, the mass of the constant volume is the sum of the mass of the sample to be distilled and the mass of pure water added to the one-step distillation concentrate.

7. The method according to claim 6, characterized in that The conditions for the first step of distillation include: evaporation pressure 3.0-15.0 kPa, evaporation temperature 40.0-70.0° C., cooling water temperature 20.0-32.0° C., and distillation time 0.5-2.0 h.

8. The method according to claim 6, characterized in that The conditions for the second step of distillation include: evaporation pressure 3.0-15.0 kPa, evaporation temperature 40.0-70.0° C., cooling water temperature 20.0-32.0° C., and distillation time 0.5-2.0 h.

9. The method according to any one of claims 1 to 8, characterized in that In step (2), the conditions for detection using HPLC chromatography include: The chromatographic column RCX-30 was used, and the mobile phase was water containing sodium hexametaphosphate for isocratic elution; Preferably, in the water containing sodium hexametaphosphate, the concentration of sodium hexametaphosphate is 0.040 to 0.060 M; Preferably, the flow rate is 1.0 mL / min, the injection volume is 20 μL, and the column oven temperature is 32°C.

10. Use of the method for detecting the content of decomposition products of N-methylmorpholine-N-oxide according to any one of claims 1 to 9 in quality control during the production or use of N-methylmorpholine-N-oxide solvents; Preferably, the invention is used in detecting the content of decomposition products of N-methylmorpholine-N-oxide, a solvent used in Lyocell fiber production.

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