N-methylmorpholine and its purification method, oxidized methylmorpholine and its preparation method

Abstract

The application discloses N-methylmorpholine and a purification method and an oxidation methylmorpholine and a preparation method thereof, and the purification method comprises the following steps: mixing N-methylmorpholine crude products with water to prepare N-methylmorpholine aqueous solution, and exchanging the N-methylmorpholine aqueous solution with acid cation exchange resin to remove impurities morpholine. The application separates morpholine from N-methylmorpholine by adsorbing morpholine on the resin through acid cation exchange resin containing trace impurities morpholine, so that the purpose of further purifying N-methylmorpholine is achieved. The application uses hierarchical titanium silicalite-1 (TS-1) as a catalyst to catalyze the reaction of N-methylmorpholine and hydrogen peroxide. In the hierarchical titanium silicalite-1, the volume of mesoporous pore size accounts for more than 40% of the total pore size volume, compared with common microporous TS-1 molecular sieve, the catalyst catalytic activity can be improved, and the generation of N-nitrosomorpholine in NMMO can be effectively reduced, and then the content of N-nitrosomorpholine in the product is reduced.

Description

Technical Field

[0001] This invention relates to a method for purifying N-methylmorpholine and the obtained N-methylmorpholine, and also to a method for preparing oxidized methylmorpholine and the obtained oxidized methylmorpholine. Background Technology

[0002] Currently, the primary use of N-methylmorpholine is in the preparation of methylmorpholine oxide (NMMO) aqueous solutions required for Lyocell production. The 50% NMMO aqueous solution required for Lyocell production must contain less than 50 ppb of the potent carcinogen N-nitrosomorpholine. NMMO is prepared by reacting N-methylmorpholine with hydrogen peroxide. Existing technologies (e.g., CN109046475A, CN 106283276) report that morpholine also generates N-nitrosomorpholine under the action of hydrogen peroxide during NMMO formation. Reducing the morpholine impurity content in N-methylmorpholine can effectively reduce the N-nitrosomorpholine content in NMMO. Furthermore, altering the NMMO synthesis reaction conditions can also affect the formation of N-nitrosomorpholine impurities.

[0003] The typical preparation process for N-methylmorpholine involves using morpholine as a raw material and methylating it. The main methylating raw materials are as follows:

[0004] (1) Formic acid and formaldehyde, morpholine reacts with excess formic acid and formaldehyde to prepare N-methylmorpholine (Xing Peng, Wang Yong, Chen Ligong, "Synthetic Study of Morpholine Derivatives", Chemical Industry and Engineering, 2003, 20(6), 347-366). It is reported that 4-5% of morpholine did not react during the reaction and remained in the crude product.

[0005] (2) Formaldehyde or paraformaldehyde, under the action of sodium dihydrogen phosphite as a reducing agent, morpholine reacts with excess formaldehyde or paraformaldehyde to prepare N-methylmorpholine (Zhang Sizhu and Wu Mingshu, “Research on the Synthesis of N-methylmorpholine” Fine Petrochemicals, 2002, (4), 3-5). It is reported that the yield of this reaction is 95%, and the purity of N-methylmorpholine after distillation is 98%.

[0006] (3) N-methylmorpholine was prepared by reacting dimethyl carbonate with morpholine (reported by Yu Hongyan et al., “Research on Green Synthesis of N-Methylmorpholine”, Chemistry and Adhesion, 2007, 29(1): 66-67). It was reported that 4-5% of morpholine did not react during this reaction.

[0007] (4) Chloromethane: Zhang Sizhu, Zhang Jichang and Wu Mingshu reported the process of preparing N-methylmorpholine by reacting morpholine with chloromethane (Synthesis of N-methylmorpholine, Applied Chemistry, 2003, 20(9), 917-918). The reaction yield was about 85%, and the purity of N-methylmorpholine after distillation was greater than 98%.

[0008] (5) Methanol. Chinese patent CN100548477C reported a catalyst prepared by using diethylene glycol, ammonia and methanol as raw materials, Cu and Ni as catalyst active components, γ-alumina as catalyst support, and compounding one of BaO, MgO and CaO. The reaction of diethylene glycol was basically complete (conversion rate 93.2-100%), the yield of morpholine was 43-55%, the yield of N-methylmorpholine was 26-38%, and the total yield of morpholine + N-methylmorpholine was 75-88%. In this patent, the preparation of N-methylmorpholine is actually the reaction of diethylene glycol and ammonia to generate morpholine first, and then the morpholine further reacts with methanol to generate N-methylmorpholine.

[0009] As mentioned above, the preparation methods of N-methylmorpholine either use morpholine as a raw material, resulting in a crude product containing a considerable amount of unreacted morpholine; or the reaction generates a large amount of morpholine simultaneously with the formation of N-methylmorpholine (e.g., the process of preparing N-methylmorpholine from diethylene glycol, ammonia, and methanol). Furthermore, morpholine and N-methylmorpholine have relatively close boiling points, making it difficult to obtain high-purity N-methylmorpholine with ultra-low morpholine impurity content through distillation. Generally, distillation only yields N-methylmorpholine with a morpholine content of around 0.5%. If the morpholine content in N-methylmorpholine is too high, the reaction between morpholine and hydrogen peroxide during NMMO preparation will produce a large amount of the potent carcinogen N-nitrosomorpholine. Tencel-grade NMMO requires an N-nitrosomorpholine content of less than 50 ppb. Therefore, only by sufficiently low morpholine impurity content in N-methylmorpholine and simultaneously optimizing the NMMO synthesis process can the formation of N-nitrosomorpholine be reduced, resulting in a solvent-based NMMO product that meets the requirements for Tencel production.

[0010] Another patent application by the applicant (publication number CN 111111670 A) discloses a method for preparing N-methylmorpholine with a morpholine impurity content of less than 0.02%, and this method has been implemented on a large scale for industrial production. The method involves reacting diethylene glycol with monomethylamine under the action of a specific catalyst to obtain a crude N-methylmorpholine product with a low morpholine impurity content in one step. Since morpholine is neither a raw material nor an intermediate product in the preparation of N-methylmorpholine using this method, the morpholine impurity content in the crude product is very low (less than 0.1%), and the N-methylmorpholine content is above 95%. Therefore, N-methylmorpholine products with a morpholine impurity content of less than 0.02% can be easily obtained through distillation. However, using existing NMMO preparation methods, even NMMO prepared from N-methylmorpholine with a morpholine impurity content of less than 0.02% still has an N-nitrosomorpholine content far exceeding 50 ppb. Although theoretically, increasing the number of trays in the distillation column or continuing multiple distillations can further reduce the morpholine impurity content and improve the purity of N-methylmorpholine, in practice, the distillation separation effect is not very obvious. It is difficult to obtain high-purity N-methylmorpholine with a morpholine impurity content of less than 1 ppm through distillation. Moreover, multiple distillations are labor-intensive, time-consuming, energy-intensive, and have low product yields.

[0011] Ion exchange resins are mainly used to remove various metal ions and other cations and non-metal anions from water. In addition, ion exchange resins are also used to separate and purify acidic or basic pharmaceutical components from complex natural product extracts.

[0012] Ma Jianbiao and He Binglin reported on the separation and purification of amino acids using ion exchange resins ("Application of Ion Exchange Resins in the Extraction and Separation of Natural Products", China Pharmaceutical Industry Magazine, 1993, 28(4), 376-381); "Separation and Extraction of Effective Components of Traditional Chinese Medicine" (Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai Science and Technology Press, 1983, 402-409) mentions the use of strong acid cation exchange resins to separate and purify pumpkin seed amino acids from pumpkin seed extract; Japanese patent (Japan Patent Publication No. 88-115853) invented a method for separating and purifying taurine from oysters. It utilizes the difference in acidity and steric hindrance between taurine and other acids in oyster extracts, and uses a series of cation and anion ion exchange resins such as Dowex-99, Dowex-88, Dowex-66 and Dowex TG-55A to remove alkaloids and other different biological acidic substances from oyster extracts, and separates and purifies taurine from them.

[0013] In addition, NMMO is prepared by reacting N-methylmorpholine with hydrogen peroxide. It has been reported that catalysts can effectively promote the reaction, and reaction conditions such as pH value and reaction temperature also have a certain influence on the yield and reaction rate of NMMO.

[0014] Xu Junhui, Liu Yijun, Feng Yunfang, and Xu Jiong reported ("Research on the Synthesis of Methylmorpholine Oxide", Journal of Zhejiang Sci-Tech University, 2008, 25(4), 402-405) that the reaction temperature, pH value of the reaction system, and the ratio of N-methylmorpholine to hydrogen peroxide have an impact on the reaction results. Among them, the optimal reaction results were obtained when the reaction temperature was 70℃, the pH value was 7.8, and the molar ratio of N-methylmorpholine to hydrogen peroxide was 1:1.1. Excessive hydrogen peroxide addition will lead to an increase in side reactions and reduce the yield of NMMO. In addition, a series of catalysts were screened, including manganese dioxide, copper oxide, quaternary ammonium salt, organic acid B, and the authors' self-made composite catalyst. The authors' self-made composite catalyst showed the best catalytic effect on the NMMO reaction. The amount of catalyst added was 1% of the amount of N-methylmorpholine added. Under the action of the authors' self-made catalyst, the reaction temperature was 70℃, the ratio of N-methylmorpholine to hydrogen peroxide was 1:1.1, and the reaction time was 6 hours, with an NMMO yield of 94%.

[0015] Sun Yingjuan ("Research on the Synthesis of N-Methylmorpholine (NMMO)", Journal of North China Institute of Science and Technology, 2007, 4(2), 33-35) and Zhang Jibo, Zhang Qizhong and Song Yan ("Research on the Synthesis of N-Methylmorpholine (NMMO)", Second Annual Meeting of Science and Technology of Jilin Province, 484-486) ​​screened a series of NMMO reaction catalysts, including strong base ion exchange resins, sodium carbonate, potassium carbonate, sodium tripolyphosphate, sodium pyrophosphate, etc. They all found that strong base ion exchange resins showed the best catalytic activity.

[0016] Chinese patent application CN110283145A discloses a method for preparing NMMO by using nano zinc oxide as a catalyst to catalyze the reaction of hydrogen peroxide with N-methylmorpholine. The amount of nano zinc oxide added is approximately 0.5% of N-methylmorpholine, and the optimal reaction temperature is 40℃.

[0017] Chinese patent application CN110483443A discloses a method for preparing NMMO by catalyzing the reaction of hydrogen peroxide with N-methylmorpholine using titanium dioxide as a catalyst. The amount of titanium dioxide added is equivalent to 0.23-0.9% of N-methylmorpholine, and the optimal reaction temperature is 40℃.

[0018] Xie Fei, Ren Xiyu, Zhang Chunli, Qi Meizhou and Li Wenjiang reported ("New Catalyst Titanium-Silicon Hollow Microsphere Catalysis for the Oxidation of N-Methylmorpholine", Molecular Catalysis, 2010, 24(2), 142-146) that hollow microsphere titanium-silicon molecular sieve (TS-1) can effectively catalyze the reaction of hydrogen peroxide with N-methylmorpholine to prepare NMMO, with an optimal reaction temperature of 70℃ and a reaction time of 6 hours.

[0019] However, the existing methods for preparing NMMO described above cannot meet the requirements for the production of Tencel. That is, the content of the potent carcinogen N-nitrosomorpholine impurity in the 50% NMMO aqueous solution product obtained by the above preparation method is still difficult to reach the standard of less than 50 ppb. Summary of the Invention

[0020] The main objective of this invention is to provide N-methylmorpholine and its purification method, as well as oxidized methylmorpholine and its preparation method, to overcome the shortcomings of existing technologies where N-methylmorpholine has a high content of impurity morpholine and oxidized methylmorpholine has a high content of impurity N-nitrosomorpholine, which cannot meet the requirements of Tencel production.

[0021] To achieve the above objectives, the present invention provides a purification method for N-methylmorpholine, the purification method comprising: mixing crude N-methylmorpholine with water to prepare an aqueous solution of N-methylmorpholine, and exchanging the aqueous solution of N-methylmorpholine with an acidic cation exchange resin to remove impurity morpholine.

[0022] The purification method for N-methylmorpholine according to the present invention further includes: distilling and dehydrating the exchanged N-methylmorpholine aqueous solution, wherein the distillation and dehydration includes a first distillation, a second distillation, and a third distillation; the first distillation involves directly distilling the exchanged N-methylmorpholine aqueous solution to remove some impurity morpholine and some water, obtaining an azeotrope of N-methylmorpholine and water; the second distillation involves mixing the azeotrope of N-methylmorpholine and water with an organic solvent and distilling it azeotropically to remove most of the water, obtaining a mixture of N-methylmorpholine and an organic solvent; the third distillation involves distilling the mixture of N-methylmorpholine and the organic solvent and collecting the fraction at 114-116℃.

[0023] The purification method for N-methylmorpholine according to the present invention, wherein the method for exchanging the N-methylmorpholine aqueous solution with an acidic cation exchange resin is as follows: the N-methylmorpholine aqueous solution flows through an acidic cation exchange resin column, the volume of acidic cation exchange resin packed in the acidic cation exchange resin column is V1, and the volume of N-methylmorpholine in the N-methylmorpholine aqueous solution flowing through the acidic cation exchange resin column per hour is V2, where V2≤2V1.

[0024] The purification method for N-methylmorpholine according to the present invention, wherein the acidic cation exchange resin is a weakly acidic cation exchange resin; and / or the acidic cation exchange resin is a gel-type resin.

[0025] The purification method for N-methylmorpholine according to the present invention, wherein the mass content of impurity morpholine in the crude N-methylmorpholine product is ≤0.02%; and the organic solvent is cyclohexane or benzene.

[0026] The purification method for N-methylmorpholine according to the present invention, wherein the volume of N-methylmorpholine in the aqueous solution of N-methylmorpholine flowing through the acidic cation exchange resin column is V3, and V3≤88V1.

[0027] To achieve the above objectives, the present invention also provides N-methylmorpholine obtained by the purification method of the above-mentioned N-methylmorpholine.

[0028] The N-methylmorpholine of the present invention, wherein the content of impurity morpholine in the N-methylmorpholine is less than or equal to 1 ppm.

[0029] To achieve the above objectives, the present invention further provides a method for preparing methylmorpholine oxide, the method comprising: reacting N-methylmorpholine and hydrogen peroxide under the action of a catalyst, wherein the catalyst is a hierarchical porous titanium silicate molecular sieve TS-1, the hierarchical porous titanium silicate molecular sieve TS-1 includes mesopores, and the volume of the mesopores accounts for more than 40% of the total pore volume of the hierarchical porous titanium silicate molecular sieve TS-1.

[0030] The method for preparing oxidized methylmorpholine according to the present invention, wherein the mass ratio of the catalyst to the N-methylmorpholine is 0.5%-5.0%; and the mass content of titanium in the hierarchical porous titanium silicate molecular sieve TS-1 is 1.0%-5.0%.

[0031] The method for preparing methylmorpholine oxide according to the present invention includes the following: in the hierarchical porous titanium silica molecular sieve TS-1, the volume of mesopores accounts for more than 50% of the total pore volume; in the hierarchical porous titanium silica molecular sieve TS-1, the mesopore size is 2-50 nm; and the mass content of titanium in the hierarchical porous titanium silica molecular sieve TS-1 is 2.5%-3.0%.

[0032] The method for preparing methylmorpholine oxide according to the present invention, wherein the mass concentration of hydrogen peroxide is 20%-50%, and the molar ratio of N-methylmorpholine to hydrogen peroxide is 0.8-1.2:0.8-1.2, based on the molar ratio of hydrogen peroxide in hydrogen peroxide.

[0033] The method for preparing methylmorpholine oxide according to the present invention includes a reaction carried out under inert gas protection; after mixing the N-methylmorpholine and the catalyst, hydrogen peroxide is added dropwise, and the dropping rate of the hydrogen peroxide is such that the reaction temperature is maintained at 50-80°C.

[0034] The method for preparing oxidized methylmorpholine according to the present invention, wherein the content of impurity morpholine in the N-methylmorpholine is less than or equal to 1 ppm; the reaction time is 6-12 hours; the reaction is carried out under the synergistic effect of heating and cooling to maintain the reaction temperature at 50-80℃.

[0035] The method for preparing oxidized methylmorpholine according to the present invention, wherein the N-methylmorpholine is obtained by the purification method of N-methylmorpholine according to any one of claims 1-6.

[0036] To achieve the above objectives, the present invention further provides methylmorpholine oxide obtained by the above-mentioned method for preparing methylmorpholine oxide.

[0037] The methylmorpholine oxide of the present invention is prepared into a 50% by mass aqueous solution of methylmorpholine oxide, wherein the content of the impurity N-nitrosomorpholine in the 50% by mass aqueous solution of methylmorpholine oxide is less than 50 ppb.

[0038] The beneficial effects of this invention are:

[0039] (1) The present invention uses an acidic cation exchange resin to pass N-methylmorpholine containing trace amounts of impurity morpholine, so that morpholine is adsorbed onto the resin, thereby separating morpholine from N-methylmorpholine, and thus achieving the purpose of further purifying N-methylmorpholine.

[0040] The purification method of this invention can reduce the content of impurity morpholine in N-methylmorpholine to less than 1 ppm.

[0041] (2) This invention uses hierarchical porous titanium silicate molecular sieve TS-1 as a catalyst to catalyze the reaction of N-methylmorpholine and hydrogen peroxide. In the hierarchical porous titanium silicate molecular sieve TS-1 of this invention, the volume of mesopores accounts for more than 40% of the total pore volume. Compared with ordinary microporous TS-1 molecular sieves, it can not only significantly improve the catalytic activity of the catalyst, but also effectively reduce the formation of N-nitrosomorpholine in NMMO, thereby reducing the N-nitrosomorpholine content in the product and meeting the requirements of Tencel production.

[0042] The content of the impurity N-nitrosomorpholine in the 50% mass content aqueous solution of methyl morpholine prepared by the method of the present invention is less than 50 ppb. Detailed Implementation

[0043] The following provides a detailed description of the embodiments of the present invention. These embodiments are implemented based on the technical solution of the present invention and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0044] The present invention provides a purification method for N-methylmorpholine, the purification method comprising: mixing crude N-methylmorpholine product with water to prepare an aqueous solution of N-methylmorpholine, and exchanging the aqueous solution of N-methylmorpholine with an acidic cation exchange resin to remove impurity morpholine.

[0045] Compared to N-methylmorpholine, morpholine is more basic and has less steric hindrance. This invention exchanges an aqueous solution of N-methylmorpholine with an acidic cation exchange resin, allowing morpholine to be selectively adsorbed onto the acidic cation exchange resin, thereby removing trace amounts of morpholine contained in N-methylmorpholine and obtaining a high-purity N-methylmorpholine product.

[0046] In one embodiment, the purification method of the present invention includes: packing an acidic cation exchange resin to form an acidic cation exchange resin column, passing an aqueous solution of N-methylmorpholine through the acidic cation exchange resin column, wherein morpholine is selectively adsorbed onto the resin, and N-methylmorpholine flows out of the acidic cation exchange resin column with the liquid phase.

[0047] In another embodiment, the purification method of the present invention includes: preparing an aqueous solution containing a certain amount of deionized water from crude N-methylmorpholine containing trace amounts of morpholine, and then slowly passing it through an acidic cation exchange resin column. Morpholine is selectively adsorbed by the acidic cation exchange resin. The N-methylmorpholine aqueous solution flowing out of the acidic cation exchange resin column is collected, and the morpholine content in the N-methylmorpholine effluent (the instantaneous effluent flowing out of the acidic cation exchange resin column) is continuously monitored. Initially, the morpholine content in the effluent is 0. As the amount of effluent increases, the morpholine content gradually increases. When the morpholine content in the effluent reaches or exceeds 1 ppm, the morpholine content in the effluent increases rapidly. When the morpholine content in the effluent reaches 2 ppm, the effluent is transferred to another container to continue collecting the effluent until the morpholine content in the effluent is close to the morpholine content in the aqueous solution of the crude N-methylmorpholine product. At this point, collection is stopped, and the ion exchange resin is regenerated. The N-methylmorpholine effluent with a higher morpholine content collected in the other container can be used as raw material for the next separation. The total effluent obtained by mixing all effluents with a morpholine content of less than 2 ppm contains less than 1 ppm of morpholine. If an even lower morpholine content of N-methylmorpholine is required, the receiving process can be stopped earlier. Therefore, the purification method of this invention can obtain N-methylmorpholine with a morpholine content of less than 1 ppm, or even less than 0.5 ppm.

[0048] In this process, an N-methylmorpholine aqueous solution passes through an acidic cation exchange resin column at a certain velocity. The faster the N-methylmorpholine aqueous solution passes through the acidic cation exchange resin, the worse the separation effect. In one embodiment, the volume of acidic cation exchange resin packed in the acidic cation exchange resin column is V1, and the volume of N-methylmorpholine in the N-methylmorpholine aqueous solution flowing through the acidic cation exchange resin column per hour is V2, where V2 ≤ 2V1. This allows morpholine to be fully adsorbed onto the resin column, thereby ensuring the separation effect between morpholine and N-methylmorpholine. In another embodiment, V2 = (1-2)V1, thus balancing separation effect and production efficiency.

[0049] In one embodiment, the volume of N-methylmorpholine in the N-methylmorpholine aqueous solution flowing through the acidic cation exchange resin column is V3, where V3 ≤ 88V1. This ensures that the morpholine content in the total effluent flowing through the acidic cation exchange resin column is less than 1 ppm.

[0050] In one embodiment, the mass content of impurity morpholine in the crude N-methylmorpholine product is ≤0.02%, which allows the acidic cation exchange resin column to have a large processing capacity and also allows the purified N-methylmorpholine to have a lower morpholine content.

[0051] Before treatment with acidic cation exchange resin, the crude N-methylmorpholine product must be dissolved in a certain amount of water to prepare an N-methylmorpholine aqueous solution. This allows the morpholine to adsorb onto the carboxylic acid or sulfonic acid active groups within the resin during passage through the acidic cation exchange resin. If the concentration of the N-methylmorpholine aqueous solution is too high, the separation effect between morpholine and N-methylmorpholine will be poor. In one embodiment, the mass concentration of the N-methylmorpholine aqueous solution can be 1%-99%; considering the separation effect, the concentration should be less than 70%; comprehensively considering the separation effect and subsequent dehydration treatment, the mass concentration of the N-methylmorpholine aqueous solution is 50%-70%.

[0052] In one embodiment, the acidic cation exchange resin of the present invention is a weakly acidic cation exchange resin, which has a better separation effect compared with a strong acidic cation exchange resin. In another embodiment, the acidic cation exchange resin of the present invention is a gel-type resin, which can handle a greater amount of N-methylmorpholine compared with a macroporous cation exchange resin. In yet another embodiment, the acidic cation exchange resin of the present invention is a gel-type weakly acidic cation exchange resin.

[0053] In one embodiment, the purification method of the present invention further includes: distilling the exchanged N-methylmorpholine aqueous solution for dehydration, the distillation dehydration including a first distillation, a second distillation and a third distillation; the first distillation is to directly distill the exchanged N-methylmorpholine aqueous solution to remove some impurity morpholine and some water, to obtain an azeotrope of N-methylmorpholine and water; the second distillation is to mix the azeotrope of N-methylmorpholine and water with an organic solvent and distill it azeotropically to remove most of the water, to obtain a mixture of N-methylmorpholine and organic solvent; the third distillation is to distill the mixture of N-methylmorpholine and organic solvent and collect the fraction at 114-116℃.

[0054] In detail, the first distillation involves directly distilling the exchanged N-methylmorpholine aqueous solution. The top product of the continuous distillation column is an azeotrope of N-methylmorpholine and water (N-methylmorpholine mass content 70-77%, water mass content 23-30%), and the bottom product is water and trace amounts of morpholine. The second distillation uses cyclohexane or benzene as a dehydrating agent to perform azeotropic distillation of the N-methylmorpholine and water azeotrope with the dehydrating agent to remove water from the N-methylmorpholine and water azeotrope obtained from the first distillation. The bottom product is N-methylmorpholine, containing trace amounts of water and cyclohexane or benzene. The third distillation further distills the N-methylmorpholine from the bottom of the second distillation, collecting the fraction with a boiling point of 114-116°C at the top of the column to obtain high-purity anhydrous N-methylmorpholine. In one embodiment, the content of impurity morpholine in the high-purity anhydrous N-methylmorpholine obtained by this invention is less than or equal to 1 ppm.

[0055] The present invention also provides a method for preparing oxidized methylmorpholine, the method comprising: reacting N-methylmorpholine and hydrogen peroxide in the presence of a catalyst, wherein the catalyst is a hierarchical porous titanium silicate molecular sieve TS-1, the hierarchical porous titanium silicate molecular sieve TS-1 includes mesopores, and the volume of the mesopores accounts for more than 40% of the total pore volume of the hierarchical porous titanium silicate molecular sieve TS-1.

[0056] During the reaction of N-methylmorpholine and hydrogen peroxide to form methylmorpholine oxide (NMMO), a side reaction occurs where morpholine reacts with hydrogen peroxide to form N-nitrosomorpholine. The formation of N-nitrosomorpholine is related to the concentration of hydrogen peroxide in the reaction system. Therefore, adding a highly efficient catalyst to the reaction system can not only accelerate the reaction of hydrogen peroxide with N-methylmorpholine to form NMMO, but also rapidly and significantly reduce the concentration of hydrogen peroxide in the reaction system, thereby effectively inhibiting the formation of N-nitrosomorpholine impurities.

[0057] The catalyst of this invention is a hierarchical TS-1 molecular sieve rich in mesopores. Compared with ordinary microporous TS-1 molecular sieves, the presence of mesopores can not only greatly improve the transfer efficiency of reactants and products in the molecular sieve channels, thereby increasing the reaction rate, but also reduce the formation of N-nitrosomorpholine in NMMO, thereby reducing the N-nitrosomorpholine content in the product.

[0058] In one embodiment, the mass ratio of the catalyst to N-methylmorpholine is 0.5%-5.0%; the molar ratio of N-methylmorpholine to hydrogen peroxide is 0.8-1.2:0.8-1.2, for example, 1:1. In this invention, the mass concentration of hydrogen peroxide is 20%-50%, for example, 30%.

[0059] In hierarchical TS-1 molecular sieves, the higher the proportion of mesopore volume to the total pore volume (mesopores + micropores), the better the catalytic activity, the faster the NMMO synthesis rate, and the lower the N-nitrosomorpholine content in the crude product. When the proportion of mesopore volume in the total pore volume of TS-1 molecular sieve reaches 50%, the N-nitrosomorpholine content in the crude product is the lowest, and the reaction rate is the fastest. Further increasing the proportion of mesopore volume does not significantly decrease the N-nitrosomorpholine content in the crude product, nor does it significantly increase the reaction rate. Therefore, TS-1 molecular sieves with a mesopore volume proportion of more than 50% of the total pore volume are considered the optimal hierarchical TS-1 molecular sieves. Because the pore diameter of traditional microporous TS-1 molecular sieves is 0.55 nm, the movement of N-methylmorpholine and NMMO molecules within the pores is restricted. Increasing the number of mesopores (mesopore diameter between 2-50 nm) can significantly improve the mass transfer of hydrogen peroxide, N-methylmorpholine, and NMMO in the catalyst, accelerating the NMMO synthesis rate. Simultaneously, due to the rapid consumption of hydrogen peroxide, the side reaction of N-nitrosomorpholine formation can be effectively suppressed, thereby reducing the N-nitrosomorpholine content in the product. In one embodiment, in the hierarchical porous titanium-silicon molecular sieve TS-1 of the present invention, the volume of mesopores accounts for more than 50% of the total pore volume (mesopores + micropores). The mesopore diameter of the hierarchical porous titanium-silicon molecular sieve TS-1 of the present invention is, for example, 2-50 nm.

[0060] The mechanism of TS-1 molecular sieve catalyzing the hydrogen peroxide reaction involves the adsorption and activation of hydrogen peroxide molecules by titanium atoms in the molecular sieve lattice. Too low a titanium content results in poor catalyst activity; too high a titanium content accelerates hydrogen peroxide decomposition, leading to hydrogen peroxide loss, and may also cause side reactions, reducing NMMO yield and increasing the difficulty of subsequent NMMO product purification. TS-1 molecular sieves with a titanium content of 1.0%-5.0%, and even more specifically 2.5%-3.0%, have been found to not only improve the NMMO reaction rate and yield but also significantly reduce the content of N-nitrosomorpholine in the NMMO product.

[0061] In one embodiment, the multi-level porous TS-1 molecular sieve catalyst particles are larger than 300 mesh, which makes it easy to filter and separate the catalyst solid from the liquid NMMO crude product for reuse.

[0062] In one embodiment, the preparation method of N-methylmorpholine oxide of the present invention includes: under the protection of an inert gas (N2 or CO2, etc.), hydrogen peroxide is added dropwise to a reactor containing N-methylmorpholine and hierarchical porous titanium silicate molecular sieve TS-1. The reaction temperature is controlled by the coordinated use of a heating system and a cooling system, and the reaction temperature is maintained by controlling the rate of hydrogen peroxide addition. In one embodiment, the reaction temperature is maintained at 50-80°C. When the content of unreacted N-methylmorpholine in the reaction product is less than 500 ppm, the reaction is stopped by cooling and vacuum distillation is performed to remove most of the unreacted N-methylmorpholine and some water. Then, various metal ions and anions in NMMO are removed by ion exchange resin combination. Water is added to adjust the solution to obtain an NMMO aqueous solution with a mass content of 50%.

[0063] In another embodiment, the reaction temperature of this invention is 65-70℃. The higher the reaction temperature, the faster the reaction rate, but the content of by-products also increases accordingly, as does the content of N-nitrosomorpholine. When the reaction temperature is above 70℃, the decomposition side reaction of NMMO is significantly accelerated, and the by-products increase rapidly.

[0064] In addition, other special purification steps can be used to further remove other impurities in NMMO that affect Tencel production and quality (such as peroxides and residual hydrogen peroxide, etc. These peroxide impurities can induce free radical decomposition reactions during Tencel production, trigger Maillard reactions and cellulose breakage, and consume the stabilizers propyl gallate and hydroxylamine required for Tencel production, thereby affecting the silk quality and whiteness of Tencel fibers, and even inducing dangerous Polonowski reactions and NMMO autocatalytic reactions, causing violent explosions), thus obtaining NMMO aqueous solution products with higher product quality.

[0065] In one embodiment, the content of impurity morpholine in the raw material N-methylmorpholine is less than or equal to 1 ppm, and the reaction time is 6-12 hours. In another embodiment, the raw material N-methylmorpholine is obtained by the above-described purification method for N-methylmorpholine, thus, compared with the prior art, the N-methylmorpholine obtained by the above purification method has a lower content of impurity morpholine.

[0066] In one embodiment, the content of the impurity N-nitrosomorpholine in the oxidized methylmorpholine prepared by the above method of the present invention is less than 50 ppb.

[0067] The technical solution of the present invention will be further described below through specific embodiments.

[0068] Example 1

[0069] This embodiment tests the ability of different types of cation exchange resins to purify N-methylmorpholine.

[0070] Three crude N-methylmorpholine products with different morpholine contents were selected, and the morpholine content in these three crude N-methylmorpholine products was 0.019%, 0.21%, and 0.43%, respectively.

[0071] The crude N-methylmorpholine product was dissolved in water, and the crude N-methylmorpholine product with a morpholine content of 0.019% was prepared into aqueous solutions with N-methylmorpholine contents of 10 wt%, 30 wt%, 50 wt%, 70 wt%, and 85 wt%; the crude N-methylmorpholine products with morpholine contents of 0.21% and 0.43% were prepared only into an aqueous solution with an N-methylmorpholine content of 50 wt%.

[0072] Among them, crude N-methylmorpholine with a morpholine content of 0.019% was dissolved in water to prepare an N-methylmorpholine aqueous solution with a morpholine content of 50wt%, which was then passed through columns packed with 100ml of gel-type strong acid cation exchange resin, macroporous strong acid cation exchange resin, gel-type weak acid cation exchange resin, and macroporous weak acid cation exchange resin, respectively; other N-methylmorpholine aqueous solutions with morpholine contents of 0.21% and 0.43% were passed through gel-type weak acid cation exchange resin only.

[0073] The flow rate of the N-methylmorpholine aqueous solution through the cation exchange resin column is controlled so that the volume of N-methylmorpholine in the aqueous solution flowing through the column per hour is 1-2 times the volume of the cation exchange resin. The morpholine impurity content in the instantaneous N-methylmorpholine receiving solution flowing out of the cation exchange resin is continuously monitored. When the morpholine content reaches 2 ppm, the container is replaced and receiving continues until the morpholine content is close to the morpholine impurity content in the raw material aqueous solution. Receiving is then stopped, and the cation exchange resin can be reused after regeneration. All receiving solutions with a morpholine content less than 2 ppm are mixed, and those with a morpholine content less than 1 ppm are sent to the next process for distillation and dehydration purification. N-methylmorpholine aqueous solutions with relatively high morpholine impurity content can be further processed through the regenerated cation exchange resin.

[0074] The receiving liquid of N-methylmorpholine aqueous solution with a morpholine impurity content of less than 1 ppm is purified by three-step distillation. In the first distillation, an azeotrope of N-methylmorpholine and water containing 70-77% N-methylmorpholine is obtained at the top of the column, while the bottom product is water and trace amounts of morpholine. In the second distillation, cyclohexane is added to the azeotrope of 70-77% N-methylmorpholine and water obtained in the previous step. Cyclohexane reacts with water to remove water from the N-methylmorpholine, and the top product is a water-cyclohexane azeotrope. After water separation, the cyclohexane is returned to the distillation vessel for further dehydration, and the bottom product is N-methylmorpholine containing trace amounts of water and cyclohexane. In the third distillation, the bottom product from the previous step is further purified by distillation to obtain the final N-methylmorpholine product with a morpholine impurity content of less than 1 ppm (morpholine impurity content is generally between 0.6-1.0 ppm).

[0075] Used cation exchange resin needs to be regenerated with a 4-5% (w / w) hydrochloric acid aqueous solution, which is five times the volume of the cation exchange resin. Specifically, the hydrochloric acid aqueous solution is passed through the exhausted resin column, with the volume of hydrochloric acid flowing through the cation exchange resin per hour equal to the volume of the cation exchange resin. The hydrochloric acid remaining after the first hour can be neutralized with NaOH to a pH ≥ 7, and then distilled to obtain the morpholine adsorbed on the resin. Subsequent hydrochloric acid remaining after passing through the cation exchange resin column can be stored in separate tanks for the next regeneration of exhausted cation exchange resin. The regenerated resin can be reused.

[0076] Gas chromatography was used to determine the contents of morpholine and N-methylmorpholine. The capillary column was SE-54, 60 m long; the column oven temperature was 65℃; the injection volume was 1 μL; the injection chamber temperature was 200℃; the detector was FID; the detector temperature was 200℃; and the split ratio was 5:1. The normalization method and the internal standard method were used to determine the contents of trace morpholine in N-methylmorpholine and the contents of N-methylmorpholine in aqueous solution, respectively. The internal standard was N-ethylmorpholine.

[0077] Table 1 shows the results of treating 50% N-methylmorpholine aqueous solutions with 100 ml of different types of cation exchange resins. The crude N-methylmorpholine product used contained 0.019% morpholine impurities. Table 2 shows the effect of different concentrations of N-methylmorpholine aqueous solutions on the morpholine separation ability of gel-type weak acid cation exchange resins. The crude N-methylmorpholine product used contained 0.019% morpholine impurities. Table 3 shows the results of treating 50 wt% N-methylmorpholine aqueous solutions with different morpholine contents with 100 ml of gel-type weak acid cation exchange resins.

[0078] Table 1. Results of treating 50% N-methylmorpholine aqueous solution with different types of cation exchange resins in 100 ml of water.

[0079]

[0080] In this invention, the N-methylmorpholine treatment volume refers to the total volume of N-methylmorpholine in the receiving solution obtained after passing an N-methylmorpholine aqueous solution through a cation exchange resin column until the morpholine content in the instantaneous receiving solution is less than 2 ppm. The morpholine content in N-methylmorpholine refers to the morpholine content in the obtained total receiving solution, based on N-methylmorpholine.

[0081] As shown in Table 1, the separation effect of weak acid cation exchange resin is significantly better than that of strong acid cation exchange resin, and the treatment capacity of gel-type cation exchange resin is stronger than that of macroporous cation exchange resin. The main reason is that weak acid cation exchange resin has a better ability to differentiate and adsorb different alkaline substances than strong acid cation exchange resin. Furthermore, the pore-expanding process during the preparation of macroporous resin results in a lower specific surface area compared to gel-type resin, thus leading to a slightly lower total adsorbed morpholine amount. Although all four types of cation exchange resins have the ability to adsorb and remove trace amounts of morpholine in N-methylmorpholine, gel-type weak acid cation exchange resin exhibits the best separation effect. 100 mL of gel-type weak acid cation exchange resin can treat N-methylmorpholine with a morpholine content of 0.019% to obtain 88 times the volume of cation exchange resin containing less than 1 ppm of N-methylmorpholine (e.g., 0.90 ppm). Because macroporous cation exchange resins have larger pore sizes than gel-type cation exchange resins, it is more conducive to the transfer of morpholine and N-methylmorpholine within the resin. Therefore, the morpholine impurity content in the obtained N-methylmorpholine is slightly lower than that in the gel type.

[0082] Table 2. Effects of different concentrations of N-methylmorpholine aqueous solution on the morpholine separation ability of gel-type weak acid cation exchange resin.

[0083]

[0084] As shown in Table 2, when the concentration of N-methylmorpholine aqueous solution is less than 70 wt%, the treatment capacity of N-methylmorpholine is relatively large. However, when the concentration of N-methylmorpholine aqueous solution is too high (e.g., 85 wt%), the treatment capacity of N-methylmorpholine decreases significantly. This may be because an excessively concentrated N-methylmorpholine aqueous solution prevents morpholine and N-methylmorpholine from fully reacting with water molecules, thus leading to ionization into the corresponding morpholinoammonium ions and OH-. - The reduced adsorption capacity of the cation exchange resin decreases its ability to selectively adsorb morpholine impurities from N-methylmorpholine. Considering the economic efficiency of subsequent distillation and dehydration purification processes, the optimal concentration range for the N-methylmorpholine aqueous solution is 50-70 wt%.

[0085] Table 3. Results of treating 50wt% N-methylmorpholine aqueous solutions with different morpholine contents using 100ml of gel-type weak acid cation exchange resin.

[0086]

[0087] As shown in Table 3, the higher the morpholine impurity content in the crude N-methylmorpholine product, the less N-methylmorpholine with a morpholine content of less than 1 ppm can be obtained by cation exchange resin. Compared with the crude N-methylmorpholine products with morpholine contents of 0.21% and 0.43% obtained by traditional distillation, using the crude N-methylmorpholine product with a morpholine impurity content of 0.019% prepared by the method in the applicant's previous patent application CN 111111670A as raw material can greatly increase the N-methylmorpholine processing capacity.

[0088] Example 2

[0089] This example measures the N-nitrosomorpholine impurity content in NMMO generated from N-methylmorpholine reaction with different morpholine impurity contents.

[0090] Under N2 or CO2 protection, N-methylmorpholine with morpholine impurity contents of 1 ppm, 0.019%, and 0.21% were added to a three-necked flask. Hydrogen peroxide with a concentration of approximately 30% was added dropwise under stirring in a 60°C water bath. The reaction was strongly exothermic, and the reaction temperature was maintained between 68±2°C by controlling the rate of hydrogen peroxide addition. After the hydrogen peroxide addition was complete, the reaction was carried out at 68±2°C for 15 hours, and then cooled to room temperature. The NMMO content, N-nitrosomorpholine impurity content, and residual N-methylmorpholine content in the crude NMMO product were determined. The molar ratio of reactants added was N-methylmorpholine:hydrogen peroxide = 1:1.

[0091] The external standard method was used to determine the yield of NMMO and the content of N-nitrosomorpholine in the crude NMMO product by liquid chromatography. The mobile phase was 0.1% TFA (trifluoroacetic acid) deionized water; the column was C18; the column temperature was 40℃; the detectors were infrared detectors (IR), with a UV detector wavelength of 200 nm for detecting NMMO content and a UV detector wavelength of 240 nm for detecting N-nitrosomorpholine content.

[0092] The residual amount of N-methylmorpholine in crude NMMO was determined by gas chromatography using the internal standard method. The internal standard was N-ethylmorpholine. The chromatographic column was SE-54, 60 meters long. The injection volume was 0.5 μL. The column oven temperature was 60℃ for 5 minutes, then increased to 250℃ at a rate of 20℃ / min, and then remained at that temperature for another 5 minutes. The injection chamber temperature was 120℃ for 0-3 minutes, then increased to 260℃ after 3 minutes. The FID detector temperature was 260℃. The split ratio was 5:1.

[0093] Table 4. Content of N-nitrosomorpholine in NMMO prepared from N-methylmorpholine with different morpholine impurities.

[0094]

[0095] As shown in Table 4, the lower the morpholine content in the N-methylmorpholine feedstock, the lower the N-nitrosomorpholine content in the crude NMMO product. When the morpholine impurity content in N-methylmorpholine is 1 ppm, the N-nitrosomorpholine impurity content in the crude NMMO product is 107 ppb, which still exceeds the maximum allowable N-nitrosomorpholine content of 50 ppb required for Tencel production.

[0096] In the catalyst-free NMMO synthesis reaction, despite a reaction time of up to 15 hours, the residual amount of N-methylmorpholine in the crude product was still as high as 1000 ppm, which means that the reaction was not yet complete.

[0097] Example 3

[0098] This example examines the effect of different catalysts on the preparation of NMMO.

[0099] In this embodiment, 1% by weight of N-methylmorpholine catalyst powder was added to the reaction. The catalysts were potassium carbonate, sodium pyrophosphate, manganese dioxide, copper oxide, zinc oxide, anatase titanium dioxide, macroporous strong base anion exchange resin, gel-type strong base anion exchange resin, and hierarchical TS-1 molecular sieve (titanium content 2.7%, mesopore volume accounts for 52% of the total pore volume).

[0100] Under N2 or CO2 protection, N-methylmorpholine (1 ppm morpholine impurity) and 1% N-methylmorpholine catalyst (1% by weight) were added to a three-necked flask. Hydrogen peroxide (approximately 30% concentration) was added dropwise in a 60°C water bath with stirring. The reaction was strongly exothermic, and the reaction temperature was maintained at 68±2°C by controlling the hydrogen peroxide dropping rate. After the hydrogen peroxide addition was complete, the reaction system temperature was maintained at 68±2°C for 15 hours, and then cooled to room temperature. The reactant ratio (molar ratio) was 1:1:N-methylmorpholine:hydrogen peroxide. The solid catalyst and liquid crude NMMO were separated by filtration. The NMMO content in the crude NMMO was determined to ascertain the NMMO yield. Additionally, the N-nitrosomorpholine impurity content and residual N-methylmorpholine content in the crude NMMO were determined.

[0101] The titanium content in the molecular sieve was determined by ICP-OES; the mesopore volume and micropore volume of the TS-1 molecular sieve were determined by the BET method.

[0102] Table 5 Catalytic effects of different catalysts on NMMO synthesis

[0103]

[0104] Note 1: TiO2 is anatase titanium dioxide; Note 2: The titanium content of the hierarchical TS-1 molecular sieve is 2.7%, and the mesopore volume accounts for 52% of the total pore volume.

[0105] As shown in Table 5, compared with the reaction without any catalyst (Table 4), the hierarchical TS-1 molecular sieve exhibits excellent catalytic activity for the NMMO formation reaction, achieving an NMMO yield of up to 96%, a residual N-methylmorpholine content of only 412 ppm, and an N-nitrosomorpholine content of 23 ppb in NMMO (meeting the requirement of less than 50 ppb for Tencel production), significantly lower than the reaction without any catalyst (107 ppb). This demonstrates that the reaction in this embodiment with the addition of the hierarchical TS-1 molecular sieve not only resulted in a more complete reaction but also effectively suppressed various side reactions. The main reason is that the hierarchical TS-1 molecular sieve can effectively catalyze the reaction between N-methylmorpholine and hydrogen peroxide, thereby rapidly consuming the hydrogen peroxide and effectively suppressing various side reactions initiated by hydrogen peroxide (such as the reaction that generates N-nitrosomorpholine).

[0106] In addition, both gel-type and macroporous strong-base anion exchange resins can catalyze the NMMO reaction, but macroporous resins show slightly better catalytic performance. Hydrogen peroxide has a certain acidity, and strong-base resins can ionize it into OOH. - This achieves the effect of catalytic reaction, but the catalytic effect is not as good as that of hierarchical TS-1 molecular sieve. The pore size of macroporous resin is larger than that of gel resin, which is conducive to the transfer of substances in the pores. Therefore, macroporous resin has better catalytic activity than the corresponding gel resin.

[0107] TiO2, MnO2, and CuO cause significant decomposition of hydrogen peroxide. With a feed molar ratio of N-methylmorpholine to hydrogen peroxide of 1:1, the excessive consumption of hydrogen peroxide inevitably leads to a hydrogen peroxide shortage, resulting in a high residual amount of N-methylmorpholine. Furthermore, Cu ions have been confirmed to cause significant decomposition of NMMO; therefore, these catalysts are unsuitable for use in the NMMO synthesis reaction.

[0108] ZnO can also cause the decomposition of hydrogen peroxide or NMMO to some extent. Moreover, since NMMO is an alkaline substance and ZnO is an amphoteric compound, it is soluble in both acidic and alkaline aqueous solutions. Experiments have shown that ZnO does have considerable solubility in NMMO aqueous solutions. Therefore, ZnO cannot be used as a catalyst for the NMMO reaction.

[0109] Potassium carbonate and sodium pyrophosphate have almost no catalytic effect on the NMMO reaction. Moreover, since these two compounds can dissolve in NMMO aqueous solution, the conductivity increases significantly, making subsequent purification and deionization much more difficult.

[0110] Example 4

[0111] This embodiment measures the effect of hierarchical porous titanium-silicon molecular sieve TS-1 with different titanium contents on the catalytic NMMO reaction. Both the conventional microporous molecular sieve TS-1 and the hierarchical porous titanium-silicon molecular sieve TS-1 used in this invention can be synthesized using existing techniques or are commercially available products. The performance indicators of the titanium-silicon molecular sieves used in this embodiment are shown in Table 6.

[0112] Table 6. Pore structure parameters of TS-1 molecular sieves with four different titanium contents

[0113]

[0114] Following the NMMO preparation reaction method in Example 3, N-methylmorpholine with a morpholine impurity content of 1 ppm was used as the raw material, and TS-1, TS-1A, TS-1B, and TS-1C molecular sieves were used as catalysts to carry out NMMO preparation reactions. The reaction time was 6 hours, and the reaction progress was measured. Table 7 shows the effect of hierarchical porous titanium-silicon molecular sieves with different titanium contents on the catalytic NMMO reaction.

[0115] Table 7. Effect of hierarchical porous titanium-silicon molecular sieves with different titanium contents on the catalytic NMMO reaction.

[0116]

[0117] As shown in Table 7, with the increase of titanium content in the hierarchical porous titanium-silicon molecular sieve TS-1, the NMMO reaction rate accelerates. Due to the rapid consumption of hydrogen peroxide, the formation reaction of N-nitrosomorpholine is effectively suppressed. When the titanium content is around 2.7% (TS-1B), the NMMO yield reaches 96%, and the N-nitrosomorpholine impurity content is 25 ppb. The reaction effect is better than that of the hierarchical porous molecular sieve with a titanium content of 1% (TS-1A), and also significantly better than that of the traditional microporous titanium-silicon molecular sieve (TS-1) with a titanium content of around 2.7%. When the titanium content continues to increase to around 4.6%, due to the excessively high titanium concentration in the synthesized molecular sieve system, some titanium atoms cannot enter the titanium-silicon molecular sieve lattice to become lattice titanium. Instead, they are deposited as anatase TiO2 on the surface of the molecular sieve pores, causing H2O2 to decompose rapidly into water and oxygen, resulting in a large amount of N-methylmorpholine remaining. Traditional microporous TS-1 molecular sieves have low catalytic activity due to their narrow pores. The reaction was not completed after 6 hours, resulting in a large amount of N-methylmorpholine remaining, and the content of N-nitrosomorpholine impurities was also high.

[0118] Example 5

[0119] This embodiment measures the effect of hierarchical porous titanium-silicon molecular sieve TS-1 with different mesoporous pore structures on the catalytic NMMO reaction. The performance indicators of the titanium-silicon molecular sieve used in this embodiment are shown in Table 8.

[0120] Table 8. Titanium content and pore structure of hierarchical porous TS-1 molecular sieve

[0121]

[0122] Following the NMMO preparation reaction method in Example 3, N-methylmorpholine with a morpholine impurity content of 1 ppm was used as the raw material, and TS-2A, TS-2B, and TS-2C molecular sieves were used as catalysts to carry out the NMMO preparation reaction, with a reaction time of 6 hours. Table 9 shows the effect of hierarchical porous titanium-silicon molecular sieves with different mesoporous pore structures on the catalytic NMMO reaction.

[0123] Table 9. Effects of hierarchical porous titanium-silicon molecular sieves with different mesoporous pore structures on the catalytic NMMO reaction.

[0124]

[0125] As shown in Table 9, the larger the mesopore volume of the catalyst, the higher the catalytic activity of the molecular sieve. When the mesopore volume reaches 50% of the total pore volume (TS-2B), the NMMO yield reaches 96%. Further increasing the mesopore volume does not further improve the catalytic activity (TS-2C), indicating that when the mesopore volume accounts for 50% of the total pore volume, this mesopore structure can meet the mass transfer requirements within the molecular sieve pores for the NMMO reaction. Considering factors such as the cost of molecular sieve synthesis (the larger the mesopore volume, the higher the molecular sieve preparation cost), TS-2B molecular sieve is the optimal catalyst.

[0126] Example 6

[0127] This example determines the effect of the amount of TS-2B catalyst added on the reaction.

[0128] Following the NMMO preparation reaction method in Example 3, N-methylmorpholine with a morpholine impurity content of 1 ppm was used as raw material, and TS-2B molecular sieve was used as catalyst. The amounts added were 0.5%, 0.75%, 1%, and 1.5% of the mass of N-methylmorpholine, respectively. The NMMO preparation reaction was carried out at a reaction temperature of 68±2℃ and a reaction time of 6 hours. The effect of the amount of TS-2B catalyst added on the reaction is shown in Table 10.

[0129] Table 10 Effect of catalyst TS-2B addition amount on NMMO reaction

[0130]

[0131] As shown in Table 10, the reaction proceeded fully under the following conditions: TS-2B catalyst dosage was 0.75% of N-methylmorpholine mass, reaction temperature was 68±2℃, and reaction time was 6 hours. Further increasing the catalyst dosage had little effect on the reaction results. Insufficient TS-2B catalyst dosage (0.5%) not only resulted in a slower reaction rate but also a higher content of N-nitrosomorpholine impurities.

[0132] Example 7

[0133] This example measures the effect of different reaction conditions (reaction time and reaction temperature) on the NMMO reaction catalyzed by TS-2B molecular sieve.

[0134] Following the NMMO preparation reaction method in Example 3, N-methylmorpholine with a morpholine impurity content of 1 ppm was used as raw material, and TS-2B molecular sieve was used as catalyst at a mass of 0.75% of N-methylmorpholine. The reaction temperature was 68±2℃. Samples were taken and analyzed at 4, 6, 9 and 12 hours to determine the effect of reaction time on the reaction. The results are shown in Table 11.

[0135] Table 11 Effect of reaction time on TS-2B-catalyzed NMMO reaction

[0136]

[0137] As shown in Table 11, using TS-2B molecular sieve as catalyst, with an addition amount of 0.75% of N-methylmorpholine, a reaction temperature of 68±2℃, and a reaction time of 6 hours, the reaction was fully carried out, achieving an NMMO yield of 96%, an N-nitrosomorpholine content of 24 ppb, and an N-methylmorpholine residue of less than 500 ppm. The longer the reaction time, the slightly lower the NMMO yield, because prolonged heating leads to an increase in NMMO decomposition side reactions.

[0138] Following the NMMO preparation reaction method in Example 3, N-methylmorpholine with a morpholine impurity content of 1 ppm was used as the raw material, and TS-2B molecular sieve was used as the catalyst at a mass of 0.75% of N-methylmorpholine. The reaction time was 6 hours, and the reaction temperatures were 50±2℃, 60±2℃, 68±2℃, 75±2℃, and 80±2℃, respectively. The effect of reaction temperature on the NMMO synthesis reaction was determined, and the results are shown in Table 12.

[0139] Table 12 Effect of different reaction temperatures on the TS-2B-catalyzed NMMO reaction

[0140]

[0141] As shown in Table 12, the NMMO yield was 96% at a reaction temperature of 68±2℃. With increasing reaction temperature, side reactions accelerated, and the content of byproducts also increased. When the temperature exceeded 70℃, side reactions such as NMMO decomposition significantly increased, leading to a decrease in the NMMO yield. Higher reaction temperatures resulted in higher N-nitrosomorpholine content. This may be because the activation energy for the formation of N-nitrosomorpholine from morpholine under hydrogen peroxide is higher than that for the reaction of N-methylmorpholine with hydrogen peroxide. Therefore, with increasing reaction temperature, the content of N-nitrosomorpholine with higher activation energy in the NMMO reaction products increased.

[0142] Example 8

[0143] This example demonstrates the effectiveness of repeated use of the TS-2B catalyst in the NMMO preparation reaction.

[0144] Following the NMMO preparation reaction method in Example 3, N-methylmorpholine with a morpholine impurity content of 1 ppm was used as the raw material, and TS-2B molecular sieve was used as the catalyst at an addition amount of 0.75% of the mass of N-methylmorpholine. The reaction temperature was 68±2℃, and the reaction time was 6 hours. After the reaction, the solid TS-2B molecular sieve catalyst was separated by filtration. The filtered TS-2B molecular sieve, without any regeneration treatment, was used as the catalyst for the next NMMO preparation reaction, and was reused 12 times. The reuse efficiency of the TS-2B catalyst was determined, and the results are shown in Table 13.

[0145] Table 13 Results of TS-2B catalyst reuse

[0146]

[0147] As shown in Table 13, the TS-2B catalyst is reusable and requires no regeneration after each use. It can be reused as a catalyst with its catalytic activity remaining basically stable.

[0148] In summary, this invention provides a purification method for N-methylmorpholine. The method involves dissolving an initial N-methylmorpholine containing trace amounts of morpholine in water to prepare an aqueous solution, which is then slowly passed through an acidic cation exchange resin column to allow the morpholine to be adsorbed onto the resin. Using N-methylmorpholine with a morpholine content of 0.019% as the initial material, this invention can obtain N-methylmorpholine with a morpholine content of less than 1 ppm in a volume 88 times the volume of the acidic cation exchange resin.

[0149] This invention also provides a method for preparing NMMO, using hierarchical porous titanium silicate molecular sieve TS-1 as a catalyst. The volume of the mesopores in the hierarchical porous titanium silicate molecular sieve TS-1 accounts for more than 40% of the total pore volume, thus giving the catalyst better catalytic activity and reducing the occurrence of the N-nitrosomorpholine side reaction. The N-nitrosomorpholine impurity content in the methylmorpholine oxide prepared by this method is less than 50 ppb.

[0150] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing methylmorpholine oxide, characterized in that, The preparation method includes: reacting N-methylmorpholine and hydrogen peroxide under the action of a catalyst, wherein the catalyst is a hierarchical porous titanium silica molecular sieve TS-1, wherein the hierarchical porous titanium silica molecular sieve TS-1 includes mesopores, and the volume of the mesopores accounts for more than 40% of the total pore volume of the hierarchical porous titanium silica molecular sieve TS-1. The N-methylmorpholine contains morpholine impurities at a concentration of less than or equal to 1 ppm; the multi-level porous titanium-silicon molecular sieve TS-1 contains titanium at a mass content of 1.0%-5.0%.

2. The method for preparing methylmorpholine oxide according to claim 1, characterized in that, The mass ratio of the catalyst to the N-methylmorpholine is 0.5%-5.0%.

3. The method for preparing methylmorpholine oxide according to claim 2, characterized in that, In the hierarchical porous titanium-silicon molecular sieve TS-1, the volume of mesopores accounts for more than 50% of the total pore volume; the mesopore size in the hierarchical porous titanium-silicon molecular sieve TS-1 is 2-50 nm; and the mass content of titanium in the hierarchical porous titanium-silicon molecular sieve TS-1 is 2.5%-3.0%.

4. The method for preparing methylmorpholine oxide according to claim 1, characterized in that, The hydrogen peroxide has a mass concentration of 20%-50%, and the molar ratio of N-methylmorpholine to hydrogen peroxide is 0.8-1.2:0.8-1.2, based on the amount of hydrogen peroxide in the hydrogen peroxide.

5. The method for preparing methylmorpholine oxide according to claim 1, characterized in that, The reaction is carried out under inert gas protection; after the N-methylmorpholine and the catalyst are mixed, hydrogen peroxide is added dropwise, and the dropping rate of hydrogen peroxide is such that the reaction temperature is maintained at 50-80°C.

6. The method for preparing methylmorpholine oxide according to claim 5, characterized in that, The reaction takes 6-12 hours and is carried out under the combined action of heating and cooling to maintain the reaction temperature at 50-80°C.

7. The method for preparing methylmorpholine oxide according to claim 1, characterized in that, The purification method of N-methylmorpholine includes: mixing crude N-methylmorpholine with water to prepare an aqueous solution of N-methylmorpholine, and exchanging the aqueous solution of N-methylmorpholine with an acidic cation exchange resin to remove impurity morpholine.

8. The method for preparing methylmorpholine oxide according to claim 7, characterized in that, The purification method for N-methylmorpholine further includes: distilling the exchanged N-methylmorpholine aqueous solution for dehydration, wherein the distillation dehydration includes a first distillation, a second distillation, and a third distillation; the first distillation involves directly distilling the exchanged N-methylmorpholine aqueous solution to remove some impurity morpholine and some water, obtaining an azeotrope of N-methylmorpholine and water; the second distillation involves mixing the azeotrope of N-methylmorpholine and water with an organic solvent and performing azeotropic distillation to remove most of the water, obtaining a mixture of N-methylmorpholine and an organic solvent; the third distillation involves distilling the mixture of N-methylmorpholine and an organic solvent and collecting the fraction at 114-116℃.

9. The method for preparing methylmorpholine oxide according to claim 7, characterized in that, The acidic cation exchange resin is a weakly acidic cation exchange resin; and / or the acidic cation exchange resin is a gel-type resin.

10. The method for preparing methylmorpholine oxide according to claim 8, characterized in that, The crude N-methylmorpholine product contains ≤0.02% morpholine impurities by mass; the organic solvent is cyclohexane or benzene.

11. The method for preparing methylmorpholine oxide according to claim 7, characterized in that, The volume of acidic cation exchange resin packed in the acidic cation exchange resin column is V1, and the volume of N-methylmorpholine in the N-methylmorpholine aqueous solution flowing through the acidic cation exchange resin column is V3, where V3 ≤ 88V1.

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