WO2022242424A1 - N-甲基吗啉-n-氧化物的纯化方法、系统、检测方法及所得n-甲基吗啉-n-氧化物 - Google Patents

N-甲基吗啉-n-氧化物的纯化方法、系统、检测方法及所得n-甲基吗啉-n-氧化物 Download PDF

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WO2022242424A1
WO2022242424A1 PCT/CN2022/088743 CN2022088743W WO2022242424A1 WO 2022242424 A1 WO2022242424 A1 WO 2022242424A1 CN 2022088743 W CN2022088743 W CN 2022088743W WO 2022242424 A1 WO2022242424 A1 WO 2022242424A1
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methylmorpholine
oxide
crystallization
nmmo
impurity
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English (en)
French (fr)
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路万里
马杰
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华茂伟业绿色科技股份有限公司
西安斯派特环保科技有限公司
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Priority to EP22803748.7A priority Critical patent/EP4335842A1/en
Publication of WO2022242424A1 publication Critical patent/WO2022242424A1/zh

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/10—Vacuum distillation
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D295/00—Heterocyclic compounds containing polymethylene-imine rings with at least five ring members, 3-azabicyclo [3.2.2] nonane, piperazine, morpholine or thiomorpholine rings, having only hydrogen atoms directly attached to the ring carbon atoms
    • C07D295/22—Heterocyclic compounds containing polymethylene-imine rings with at least five ring members, 3-azabicyclo [3.2.2] nonane, piperazine, morpholine or thiomorpholine rings, having only hydrogen atoms directly attached to the ring carbon atoms with hetero atoms directly attached to ring nitrogen atoms
    • C07D295/24—Oxygen atoms
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D9/00—Crystallisation
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F2/00—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/86—Signal analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/86—Signal analysis
    • G01N30/8624—Detection of slopes or peaks; baseline correction
    • G01N30/8631—Peaks
    • G01N30/8634—Peak quality criteria
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
    • Y02P70/62—Manufacturing or production processes characterised by the final manufactured product related technologies for production or treatment of textile or flexible materials or products thereof, including footwear

Definitions

  • the present invention relates to the purification method of N-methylmorpholine-N-oxide, the purification system of N-methylmorpholine-N-oxide, the detection method of N-methylmorpholine-N-oxide and the obtained N-Methylmorpholine-N-oxide.
  • N-methylmorpholine-N-oxide methylmorpholine oxide, NMMO
  • NMMO methylmorpholine oxide
  • the Lyocell fiber obtained by silk has excellent fiber performance, and the NMMO solvent is easy to recover in the Lyocell fiber production process, and the recovery rate is over 99.5%. Lyocell fiber has great advantages in environmental protection, energy consumption and fiber performance. Advantages, the development prospects are very broad.
  • NMMO is prepared by reacting hydrogen peroxide (H 2 O 2 ) with N-methylmorpholine.
  • the crude NMMO product usually has a darker color.
  • the NMMO yield of this reaction is more than 99%, the total impurity mass content in the crude product of NMMO reaction is less than 1%, and the impurity contains a certain amount of unreacted N-methylmorpholine, morpholine, hydrogen peroxide and some Impurities generated by side reactions such as strong carcinogen N-nitrosomorpholine, organic peroxides and some unknown impurities, etc., also contain a certain amount of metal cations such as copper and iron ions and anions such as phosphate and nitrate, NMMO
  • the conductivity of the crude product is generally above 500 ⁇ s/cm.
  • the quality standard of the NMMO aqueous solution product with a mass concentration of 50% that can be used in the production of Tencel at present is: the electrical conductivity is less than 10 ⁇ s/cm, the copper ion content is less than 2ppm, the iron ion content is less than 2ppm, the unreacted hydrogen peroxide content is less than 50ppm, N- The content of methylmorpholine is less than 100ppm, the content of morpholine is less than 200ppm, the content of N-nitrosomorpholine is less than 50ppb, and the appearance of the product is a colorless transparent solution.
  • NMMO is an amine-based oxide, and a Cope elimination reaction will occur at a certain temperature to generate the corresponding olefin compound with a double bond at the end group. Due to the presence of a large amount of hydrogen peroxide in the NMMO preparation process, hydrogen peroxide will react with olefins to generate organic peroxides such as organic hydrogen peroxide, peroxyether and organic peroxyacids, so the crude NMMO product inevitably contains a certain amount of organic Peroxide impurities.
  • the cleavage of the cellulose molecular chain in the production of Tencel is mainly caused by the N-methylmorpholine free radical produced by the free radical decomposition reaction of NMMO (Adorjan I., Potthast A., Rosenau T., Sixta H. and Kosma P. 2005.Discoloration of cellulose solutions in N-methylmorpholine-N-oxide(Lyocell).Part 1:Studies on model compounds and pulps.Cellulose 12:51-57)(Rosenau T.,Potthast A.,Adorjan I.,Hofinger A ., Sixta H., Firgo H. and Kosma P. 2002.
  • Peroxides including hydrogen peroxide and other inorganic peroxides and organic peroxides, are a class of excellent free radical initiators, which will decompose to generate free radicals at a certain temperature, thereby inducing the occurrence of NMMO free radical decomposition reactions, resulting in cellulose molecular chains Fracture, tencel fiber strength decreases, and at the same time the final product of NMMO free radical decomposition reaction is morpholine and formaldehyde, there may continue to react between the two to generate methylene morpholine carbanion.
  • NMMO contacts metal equipment, reactors, pipes and containers, etc., causing NMMO to contain some metal ions such as copper and iron ions.
  • metal ions such as copper and iron ions.
  • hydrogen peroxide also contains some metal and non-metal ions. Copper and iron ions will catalyze the decomposition reaction of NMMO. , resulting in the loss of NMMO, and the copper and iron ions in the NMMO cellulose solution in the production of Tencel will also complex with cellulose, resulting in cellulose degradation (Wu Cuiling, Li Xinping, Qin Shengli and Wang Jianyong “New Organic Cellulose Solvent-NMMO Research", Journal of Lanzhou University of Technology, 2005, 31(2), 73-76).
  • copper and iron ions will also complex with propyl gallate added in the production of Tencel, resulting in a darker color, which will affect the color of the final Tencel fiber.
  • copper and iron ions will also catalyze the peroxide oxidation of cellulose in NMMO , accelerate the decomposition of cellulose, and catalyze the Maillard reaction to produce color, and even catalyze the NMMO self-catalyzed free radical decomposition reaction, releasing a lot of heat, which may cause an explosion in severe cases (such as CN 104801354B and US 5556452), so the excessive Copper and iron ions are very harmful to the production of NMMO, so it is required that the content of copper and iron ions in Tencel-grade NMMO products should be as low as possible.
  • the technology of industrialized purification of NMMO is a multi-step purification process, wherein one step uses the ion exchange resin method to remove anions and cations and some organic impurities including pigments in the NMMO crude product (CN 104801354 B), while other purification processes (such as X-ray irradiation and special adsorption resins, etc.) to remove N-nitrosomorpholine and other organic impurities.
  • special catalytic reduction treatment is required to remove peroxides more deeply.
  • the expired ion exchange resin needs to be regenerated before it can be reused.
  • the cation exchange resin usually uses 4-6 times the resin volume of 4-5% hydrochloric acid aqueous solution to continuously wash and regenerate, while the anion exchange resin uses 4-6 times the resin volume of 4-5% NaOH
  • the aqueous solution is continuously rinsed and regenerated.
  • these regeneration waste liquids not only contain about 5% NaCl and other small amounts of metal and non-metal ion salts, but also contain other organic impurities adsorbed by the resin and a small amount of NMMO adsorbed, so the COD content is usually 5000ppm- 20000ppm.
  • this treatment method not only consumes a lot of energy, but also contains high COD in the obtained waste salt, which can only be handed over to qualified environmental protection companies as hazardous waste treatment, and the cost is very high.
  • the COD content in the water obtained by MVR evaporation is usually high, and must be treated by catalytic oxidation or direct incineration.
  • ion exchange resins and special adsorption resins that adsorb organic impurities are not only expensive, but their lifespan is generally only 1-2 years, and the discarded resins are listed as hazardous wastes in accordance with the national hazardous waste classification list and must be disposed of by qualified environmental protection companies. , the cost is also very high.
  • the ion exchange resin and the special resin for adsorbing organic impurities will adsorb NMMO, resulting in a decrease in the yield of NMMO. Therefore, the current industrial purification process for preparing Tencel-grade NMMO not only has serious environmental protection problems of "three wastes", but also has very high energy consumption and purification costs.
  • NMMO can combine with water molecules to form three different Water content crystals
  • 1 NMMO molecule can form monohydrate crystals (NMMO ⁇ H 2 O) with 1 water molecule, the appearance is white crystals, melting point: 76-78°C, NMMO concentration in the crystal is 84.5%, density 1.28g /cm 3
  • 2 NMMO molecules can also form 2.5 hydrate crystals (2NMMO ⁇ 5H 2 O) with 5 water molecules, the appearance is white crystals, the melting point is 36-39°C, the concentration of NMMO in the crystal is 72.2%, and the density is 1.33g/cm cm 3
  • 1 NMMO molecule can also form pentahydrate crystals with 5 water molecules (NMMO ⁇ 5H 2 O), melting point: -20°C, and NM
  • NMMO ⁇ H 2 O and NMMO ⁇ 2.5H 2 O can be obtained by dehydration of NMMO aqueous solution. It mainly investigated and studied the solubility of different hydrate crystals of NMMO to cellulose, and used NMMO ⁇ H 2 O to dissolve cellulose by utilizing the low melting point characteristics of NMMO ⁇ H 2 O and the characteristics of better dissolving cellulose.
  • the main purpose of the present invention is to provide a kind of purification method, system, detection method of N-methylmorpholine-N-oxide compound and the obtained N-methylmorpholine-N-oxide compound, to overcome the N-oxide compound in the prior art - the defects of high energy consumption in the purification process of methylmorpholine-N-oxide, environmental pollution, low yield, and low purity of the obtained N-methylmorpholine-N-oxide.
  • the present invention provides a purification method of N-methylmorpholine-N-oxide, which is prepared from the reaction of N-methylmorpholine and hydrogen peroxide N-methylmorpholine-N-oxide crude product, the mass concentration of N-methylmorpholine-N-oxide in the N-methylmorpholine-N-oxide crude product is 50% ⁇ 60% %, the purification method comprises: cooling and crystallizing the crude N-methylmorpholine-N-oxide product at -20°C to 78°C to obtain N-methylmorpholine-N-oxide crystals.
  • the purification method also includes concentrating the crude product of N-methylmorpholine-N-oxide , so that the mass concentration of N-methylmorpholine-N-oxide in the N-methylmorpholine-N-oxide crude product is 56.5% to 84.5%, and then cooling crystallization is performed.
  • a seed crystal is added during the cooling crystallization process, and the amount of the seed crystal added is the N- 0.1%-1.0% by weight of the crude product of methylmorpholine-N-oxide.
  • the purification method of N-methylmorpholine-N-oxide of the present invention in one embodiment, after concentrated treatment, N-methylmorpholine in the crude product of N-methylmorpholine-N-oxide When the mass concentration of -N-oxide is 56.5% to 72.2%, the temperature of the cooling crystallization is -20 to 39°C; after concentration treatment, N-methylmorpholine-N-oxide crude product When the mass concentration of morpholine-N-oxide is greater than 72.2% and less than or equal to 84.5%, the cooling crystallization temperature is greater than 39°C and less than or equal to 78°C.
  • the purification method of N-methylmorpholine-N-oxide of the present invention in one embodiment, after concentrated treatment, N-methylmorpholine in the crude product of N-methylmorpholine-N-oxide
  • the mass concentration of -N- oxide is 66%-71%, and the temperature of the temperature-dropping crystallization is 25°C-35°C.
  • the purification method of N-methylmorpholine-N-oxide according to the present invention in one embodiment, in the cooling crystallization process, when crystals start to appear to 30°C, the cooling rate is 1-2°C/hour ; Between -20°C and 30°C, the cooling rate is 3-4°C/hour.
  • the cooling crystallization at least includes primary cooling crystallization and secondary cooling crystallization, and the primary cooling crystallization obtains N -Methylmorpholine-N-oxide crystals and crystallization mother liquor, the crystallization mother liquor is subjected to secondary cooling crystallization treatment after being concentrated.
  • the present invention also provides the N-methylmorpholine-N-oxide compound obtained by the purification method of the above-mentioned N-methylmorpholine-N-oxide compound, N-methylmorpholine-N-oxide compound
  • the recovery rate of N-methylmorpholine-N-oxide compound is more than 97%
  • the liquid chromatography detection result of N-methylmorpholine-N-oxide compound is that organic impurity content is 0, and the obtained N-methylmorpholine-N-oxide compound is made into mass concentration It is a 50% aqueous solution, the electrical conductivity of the aqueous solution is 0-10 ⁇ s/cm, and the content of hydrogen peroxide is 0.
  • the present invention further provides a purification method of N-methylmorpholine-N-oxide, which does not use ion exchange resin.
  • the present invention provides a purification system of N-methylmorpholine-N-oxide, which is used for N-methylmorpholine- Purification of N-methylmorpholine-N-oxide in N-oxide crude product, the purification system includes:
  • Crystallization device used for crystallization treatment of N-methylmorpholine-N-oxide crude product
  • the control device is connected with the crystallization device to control the crystallization conditions in the crystallization device.
  • the purification system also includes a concentration device, connected with the crystallization device and the control device, so that the The N-methylmorpholine-N-oxide crude product is concentrated in the concentration device, and then input to the crystallization device; the control device controls the concentration conditions of the concentration device.
  • the present invention provides a kind of detection method of N-methylmorpholine-N-oxide compound again, and described N-methylmorpholine-N-oxide compound is made of N-methylmorpholine and
  • the N-methylmorpholine-N-oxide crude product prepared by hydrogen peroxide reaction is crystallized at lower temperature, and the detection method includes the determination of the residual rate of crystal impurities of N-methylmorpholine-N-oxide, and the N -The determination of the crystal impurity residual rate of methylmorpholine-N-oxide compound comprises the steps:
  • Step 1 carry out liquid chromatography measurement to N-methylmorpholine-N-oxide crude product, measure wavelength is 200nm-220nm, perhaps be 200nm-210nm, carry out all impurity peaks in the obtained liquid chromatography spectrogram Integrate the area to obtain the sum of the area integrals of all impurity peaks, which is recorded as the sum of the area integrals of the first impurity peaks;
  • Step 2 the N-methylmorpholine-N-oxide is subjected to liquid chromatography determination, the measurement conditions are the same as in step 1, and all impurity peaks in the obtained liquid chromatography spectrum are area integrated to obtain all impurity The sum of the area integrals of the peaks is recorded as the sum of the area integrals of the second impurity peaks;
  • Residual rate of the first crystalline impurity the sum of the integrals of the peak areas of the second impurities ⁇ the sum of the integrals of the peak areas of the first impurities.
  • the determination of the crystal impurity residual rate of described N-methylmorpholine-N-oxide also includes the following steps :
  • Step 3 carry out liquid chromatography measurement to N-methylmorpholine-N-oxide crude product, measure wavelength is 230nm-240nm, carry out area integration to all impurity peaks in the obtained liquid chromatography spectrogram, obtain all impurity The sum of the area integrals of the peaks is recorded as the sum of the area integrals of the third impurity peaks;
  • Step 4 the N-methylmorpholine-N-oxide is subjected to liquid chromatography determination, the determination conditions are the same as in step 3, and all impurity peaks in the obtained liquid chromatography spectrogram are area integrated to obtain all impurity The sum of the area integrals of the peaks is recorded as the sum of the area integrals of the fourth impurity peak;
  • the second crystal impurity residual rate the sum of the integrated peak areas of the fourth impurity ⁇ the integrated sum of the peak area of the third impurity.
  • the detection method of N-methylmorpholine-N-oxide of the present invention also comprises the mensuration of N-methylmorpholine and morpholine content; Said N-methylmorpholine
  • the method for determining the content of morpholine and morpholine is as follows: N-methylmorpholine-N-oxide is measured by liquid chromatography, the measurement wavelength is 200nm-210nm, and the measurement time is greater than or equal to 30 minutes.
  • the detection method of N-methylmorpholine-N-oxide of the present invention also comprises the mensuration of N-nitrosomorpholine content; Said N-nitroso
  • the method for measuring the morpholine content is as follows: perform liquid chromatography measurement on N-methylmorpholine-N-oxide, the measurement wavelength is 230nm-240nm, and the measurement time is greater than or equal to 30 minutes.
  • the detection method also includes: at least one of hydrogen peroxide content, electrical conductivity, iron ion content, copper ion content
  • the determination of the item; the determination of the hydrogen peroxide content is carried out according to GB 5009.226-2016; the determination of the iron ion content or copper ion content is determined by an inductively coupled plasma emission spectrometer.
  • the invention provides a high-efficiency, low-cost, and green method for purifying NMMO, which mainly includes crystallization of the crude product.
  • the crystallization operation temperature can be close to normal temperature (25-35°C), and the energy consumption is low; the recovery rate of NMMO is above 97%.
  • the purified NMMO is formulated into an NMMO aqueous solution with a mass concentration of 50%, and its conductivity is less than 10 ⁇ s/cm, even reaching about 1 ⁇ s/cm, and the content of copper and iron ions is less than 1ppb.
  • HPLC cannot detect N-nitroso
  • organic impurities such as morphine
  • the HPLC test results show that the total impurity content does not exceed 2ppm (ie NMMO purity > 99.999%), and the hydrogen peroxide content is also lower than the detectable lower limit of the national standard GB 5009226-2016, and the product quality reaches or exceeds Tencel The NMMO product quality standard of production requirement;
  • NMMO purification method of the present invention does not use ion-exchange resin, thoroughly solves the problem that high-salt high COD waste water and waste ion-exchange resin pollute the environment that the purification process that adopts ion-exchange resin faces at present.
  • Fig. 1 is a schematic diagram of a purification system of N-methylmorpholine-N-oxide according to an embodiment of the present invention.
  • the invention discloses a method for purifying N-methylmorpholine-N-oxide, which is mainly used for the N-methylmorpholine-N-oxide crude product prepared by the reaction of N-methylmorpholine and hydrogen peroxide.
  • -purification of methylmorpholine-N-oxide compound, purification method of the present invention does not comprise ion-exchange resin treatment step, therefore can overcome the problems of polluting the environment and high energy consumption caused when using ion-exchange resin purification, purification method of the present invention has It has the characteristics of high efficiency, low energy consumption, low cost, environmental protection, high yield, and high purity of N-methylmorpholine-N-oxide.
  • the present invention provides a method for purifying N-methylmorpholine-N-oxide, which is derived from the reaction of N-methylmorpholine and hydrogen peroxide
  • the prepared N-methylmorpholine-N-oxide crude product, the mass concentration of N-methylmorpholine-N-oxide in the N-methylmorpholine-N-oxide crude product is 50% ⁇ 60%
  • the purification method comprises: cooling and crystallizing the crude N-methylmorpholine-N-oxide product at -20° C. to 78° C. to obtain N-methylmorpholine-N-oxide crystals.
  • the crystallization purification method is to cool down and use the different solubility of each component in the mixture to make the concentration of the substance to be crystallized and purified in the mother liquor exceed its saturation solubility to form a supersaturated solution.
  • the substance to be crystallized and purified is in the supersaturated solution Crystals are formed and precipitated in the mother liquor, while the impurity components with relatively low content remain in the mother liquor, so as to achieve the effect of separation and purification.
  • the main factors affecting crystal purity are the adsorption of mother liquor on the crystal surface and the occlusion of mother liquor inside the crystal.
  • the present invention washes the crystal with pure N-methylmorpholine-N-oxide saturated solution to remove the mother liquor adsorbed on the crystal surface. Further improve the crystallization process conditions or improve the occlusion of the mother liquor in the crystal by recrystallization.
  • N-methylmorpholine-N-oxide In industry, due to the transportation problems of pure N-methylmorpholine-N-oxide, in addition, the downstream manufacturers who use N-methylmorpholine-N-oxide usually use N-methylmorpholine- Aqueous N-oxide solution is used as raw material, therefore, N-methylmorpholine-N-oxide usually prepared in this field exists in the state of aqueous solution.
  • the present invention utilizes the characteristics of N-methylmorpholine-N-oxide hydrate crystals, and by controlling the temperature-lowering crystallization conditions, N-methylmorpholine-N-oxide and water are combined to form crystals in a specific ratio, thereby achieving the same The purpose of separating impurities in aqueous solution.
  • the present invention obtains N-methylmorpholine-N-oxide hydrate solid by crystallization, and reaches the purpose of purifying N-methylmorpholine-N-oxide, and then N-methylmorpholine-N -Oxide hydrate solids are formulated into aqueous solutions of required concentration to be supplied to downstream manufacturers.
  • the NMMO crude product prepared by the reaction of N-methylmorpholine and hydrogen peroxide is generally brownish yellow in color. According to the concentration of hydrogen peroxide used, the mass concentration of NMMO in the crude reaction product is between 50% and 60%.
  • the present invention does not particularly limit the reaction process of N-methylmorpholine and hydrogen peroxide, and conventional reaction conditions in the field are sufficient.
  • the present invention first concentrates the crude product of N-methylmorpholine-N-oxide to obtain N-methylmorpholine-N-oxide with a mass content between 56.5% and 84.5%. Concentrated solution, and then the concentrated solution is cooled and crystallized, which can improve the crystallization efficiency.
  • the concentration treatment method is evaporation, such as heating evaporation, reduced pressure evaporation, and the like.
  • the present invention concentrates the crude product of N-methylmorpholine-N-oxide, and the mass content of N-methylmorpholine-N-oxide in the obtained concentrate is between 56.5% and 72.2% %, the concentrated solution is cooled and crystallized between -20-39°C, and the NMMO crystal obtained in this way is 2NMMO ⁇ 5H 2 O (ie NMMO ⁇ 2.5H 2 O); in the obtained concentrated solution, N-methylmorpholine- When the mass content of N-oxide is 72.2%-84.5% (excluding 72.2%), the concentrated solution is cooled and crystallized between 39-78°C (excluding 39°C), and the NMMO crystals obtained in this way are NMMO ⁇ H 2 O.
  • the different concentrations of NMMO in the concentrated solution determine the different crystallization temperatures, and thus different NMMO crystals are obtained.
  • the present invention considers the cost of industrialized purification and the convenience of operation, and concentrates the crude product of N-methylmorpholine-N-oxide to a mass concentration of NMMO of 66%-71%. °C normal temperature range for cooling crystallization (final crystallization temperature is 25 °C and above). Under the optimum crystallization conditions, 2NMMO ⁇ 5H 2 O crystals with high purity and a crystallization yield of more than 50% can be obtained through primary crystallization.
  • crystal seeds can be added during the crystallization process, and the amount of seed crystals added is 0.1% to 1.0% of the weight of the crude product of N-methylmorpholine-N-oxide, or the amount of seed crystals added is 0.1% to 1.0% of the weight of the above concentrate. In another embodiment, the amount of seed crystals added is 0.1% to 0.3% of the weight of the crude product of N-methylmorpholine-N-oxide, or the amount of seed crystals added is 0.1% to 0.3% of the weight of the concentrated solution %. In cooling crystallization, adding seed crystals to induce crystallization can very effectively reduce the supersaturation of NMMO in solution, and obtain crystals with higher purity of NMMO.
  • the seed crystals added in the present invention are crushed small particles with uniform particle size as far as possible, high-purity crushed crystals, the particle size is, for example, 0.01-0.1mm, and the amount of seed crystals added is 0.1-1.0% of the weight of the NMMO crude product. %. Larger seed crystal particles and too little addition will lead to a decrease in the purity of NMMO crystals, and the final NMMO crystal particle size distribution will be uneven; too many seed crystal particles will result in smaller crystal particles.
  • the seed crystal should not be added too early, otherwise the solution temperature will be too high, and the concentration of NMMO hydrate in the solution will be lower than its corresponding solubility, resulting in crystal dissolution, and the meaning of adding seed crystal will be lost; if the seed crystal is added too late, the solution temperature will be too low , the supersaturation of the solution is too high at this time, which will reduce the actual effect of adding seed crystals.
  • the timing of adding the seed crystals is generally determined according to the NMMO content in the crude NMMO product or concentrated solution and the initial cooling temperature. In one embodiment, the seed crystals are added when the solution cools down to 30-37°C.
  • the seed crystals of the present invention are soaked in a high-purity NMMO saturated aqueous solution for at least 1 hour before being added to the crystallization system, so as to improve the crystallization effect and ensure that the crystals precipitated in the crystallization system are uniform in size.
  • crystallization begins to appear in the crystallization system until the temperature of the crystallization system drops to 30°C, the cooling rate is controlled at 1-2°C/hour, and after the temperature of the crystallization system is lower than 30°C (such as At -20-30°C), the cooling rate can be controlled at 3-4°C/hour. In this way, crystal purity can be guaranteed. This is because, in cooling crystallization, the cooling rate directly determines the crystallization rate. When the crystallization system is in a higher temperature range, the solubility curve of NMMO hydrate changes greatly. Therefore, in the initial stage of crystallization after crystallization, the cooling rate of the solution system should not be too fast, and the crystal growth rate should be limited, otherwise the solution will be oversaturated. High, affecting crystal purity.
  • the crystallization solution is quickly vacuum-filtered through a Buchner funnel, and the crystallization mother liquor is released from the filter bottle. Rinse with NMMO aqueous solution to obtain NMMO crystals, weigh and analyze the content.
  • the present invention adopts primary crystallization to obtain very high-purity NMMO crystals. Add water to the NMMO crystals obtained from the above-mentioned primary crystallization to form an NMMO aqueous solution with a mass concentration of 50%.
  • the color is colorless and transparent, and the conductivity can reach 4-10 ⁇ s /cm.
  • the cooling crystallization in the present invention includes at least two crystallizations, for example, primary crystallization and secondary crystallization. That is, after the first crystallization, the crystals are obtained and water is added to prepare a certain concentration of NMMO aqueous solution, and the secondary crystallization (recrystallization) is carried out.
  • the temperature-lowering crystallization of the present invention also includes tertiary crystallization, quaternary crystallization, and the like.
  • the crystal obtained by secondary crystallization of the present invention is analyzed and detected by liquid chromatography, and no organic impurities such as N-nitrosomorpholine, N-methylmorpholine, morpholine, peroxide, etc. have been detected, and water is added to prepare the mass content It is 50% NMMO aqueous solution, and its conductivity is 3-6 ⁇ s/cm, even up to about 1 ⁇ s/cm.
  • the crystal obtained by secondary crystallization is added with water to prepare an aqueous solution with a mass concentration of NMMO of 50%, and the conductivity of the NMMO solution (50% mass concentration of NMMO) is about 1 ⁇ s/cm;
  • MS detection the presence of copper ions and iron ions is almost undetectable (thus indicating that the contents of copper ions and iron ions are both less than 0.001ppm); according to the national standard GB 5009.226-2016, the presence of hydrogen peroxide cannot be detected. Therefore, the aqueous solution of 50% NMMO mass concentration prepared by the above-mentioned crystals can fully meet the quality requirements of Tencel production for NMMO, and is far higher than the quality requirements of Tencel production for NMMO.
  • the present invention in order to increase the yield of NMMO, includes at least secondary crystallization, that is, to carry out primary crystallization of the N-methylmorpholine-N-oxide crude product to obtain crystals and crystallization mother liquor, and to obtain primary crystallization
  • the resulting crystallization mother liquor is evaporated by vacuum heating until the mass concentration of NMMO is 69-71% or 69-70.5%, and then cooled to crystallize (secondary crystallization).
  • the crystallization conditions are consistent with the above-mentioned primary crystallization, and the crystallization rate is about 80-85%.
  • the obtained crystals can be recycled and dissolved in the NMMO crude product, and recovered as a primary crystallization raw material liquid to further improve the crystal purity.
  • the crystallization mother liquor obtained by the secondary crystallization can continue to concentrate and crystallize. At this time, the amount of crystallization mother liquor obtained by the secondary crystallization is very small, generally less than 3% of the initial NMMO crude product quality.
  • the purification method of N-methylmorpholine-N-oxide of the present invention includes: heating, evaporating and concentrating under reduced pressure, and concentrating the NMMO crude product generated by the reaction of N-methylmorpholine and hydrogen peroxide to NMMO
  • the mass content is 56.5-84.5%, and high-purity NMMO hydrate crystals can be obtained through cooling and crystallization, and Tencel-grade NMMO products can be obtained without ion exchange resins.
  • the operating temperature of cooling crystallization is -20-78°C.
  • the mass concentration of NMMO in the crude product is best controlled at 66-71%, so that cooling crystallization can be carried out at 25-35°C , and a crystal product with high purity and a crystallization yield of more than 50% can be obtained.
  • the temperature-lowering crystallization method of the present invention is as follows: cool down the NMMO crude product with a NMMO mass concentration of 66.5-70% at a temperature of about 40°C until it does not dissolve after the seed crystal is added, and then add a small amount of seed crystal,
  • the seed crystals are preferably small NMMO ⁇ 2.5H 2 O crushed crystals immersed in a high-purity NMMO saturated solution. These small particle crushed crystals are soaked in the NMMO saturated solution for at least 1 hour, and the amount of seed crystals added is the mass of the crude NMMO product. 0-1%, preferably 0.1-0.3%. After the seed crystal is added, the NMMO crude product is cooled slowly by cooling treatment.
  • the cooling rate is controlled at 1-2 °C/hour between the crystal initiation temperature and 30 °C.
  • the cooling rate can be appropriately accelerated to 3 -4°C/hour, the crystallization termination temperature is 25°C, and crystals with larger particles and uniform particle size distribution are obtained.
  • the crystal solution is quickly filtered, and the mother liquor is collected and weighed after filtration. The crystal is first washed with NMMO crude product.
  • the volume of the crude product rinse liquid is about 30% of the obtained crystal mass, and then the high-purity NMMO aqueous solution with a mass concentration of 59.5 ⁇ 0.5% is used to continue Washing, the amount of washing liquid is about 30% of the crystal mass, to obtain primary crystals, collect primary crystals, weigh and analyze the crystal purity.
  • the primary crystallization is prepared by adding water to an aqueous solution with a mass concentration of NMMO of 50%, and the contents of various impurities, hydrogen peroxide, electrical conductivity and metal ions in the solution are detected.
  • the secondary crystallization is similar to the primary crystallization process condition, the primary crystallization crystal is dissolved in water at 40 °C, and the NMMO mass concentration is prepared into an aqueous solution of 66-70%, and the secondary crystallization is carried out according to the same crystallization process condition, and collected Secondary crystallization crystals were weighed and analyzed for crystal purity.
  • the purification method of NMMO in the present invention is as follows: the NMMO crude product prepared by reacting N-methylmorpholine and hydrogen peroxide is concentrated by vacuum heating until the mass concentration of NMMO is 56.5-84.5%, and crystallized by cooling to obtain High-purity NMMO hydrate crystals, add water to the crystals to prepare an aqueous solution with a mass concentration of NMMO of 50%, the conductivity is even about 1 ⁇ s/cm, copper and iron ions are less than 0.001ppm, and a high-purity NMMO aqueous solution with a mass concentration of 50% product.
  • Crystallization The remaining crystallization mother liquor is subjected to secondary or more stage crystallization, which can recover the NMMO to the greatest extent.
  • the secondary crystallization of the crystallization mother liquor can recover more than 97% of the NMMO in the crude NMMO product. More stages of crystallization will further improve NMMO recovery rate.
  • the present invention provides a method for purifying and preparing NMMO meeting the quality requirements of Lyocell production from methylmorpholine oxide (NMMO) reaction crude product by a crystallization method.
  • the present invention does not use ion exchange resin to remove metal ions and non-metal ions and some organic impurities including pigments, and there is no large amount of high-salt, high-COD wastewater and waste ions generated during ion exchange resin regeneration Exchange resin hazardous waste and other substances that pollute the environment; the NMMO aqueous solution product produced by the method of the present invention can not only reach or even exceed the quality requirements of the current Tencel industry for NMMO products, but also has simple purification process, low purification cost, and high NMMO yield.
  • the invention is an efficient, simple and low-cost green method for purifying NMMO.
  • the present invention also provides a purification system of N-methylmorpholine-N-oxide, which is used for N-methylmorpholine prepared by the reaction of N-methylmorpholine and hydrogen peroxide
  • N-methylmorpholine-N-oxide Purification of N-methylmorpholine-N-oxide in the crude product of -N-oxide, this purification system can be used for the purification of N-methylmorpholine-N-oxide in industrial production, and large-scale automation can be realized control, the purification system includes:
  • Crystallization device used for crystallization treatment of N-methylmorpholine-N-oxide crude product
  • the control device is connected with the crystallization device to control the crystallization conditions in the crystallization device.
  • the purification system also includes a concentrating device, which is connected with the crystallization device and the control device, so that the N-methylmorpholine-N-oxide crude product is in the concentrating device After being concentrated, it is then input into the crystallization device; the control device controls the concentration conditions of the concentration device.
  • the purification system of N-methylmorpholine-N-oxide of the present invention is shown in Figure 1, primary concentration device 1 is communicated with primary crystallization device 2, N-methylmorpholine-N-
  • the crude oxide product 10 is passed into a primary concentration device 1 for concentration treatment, and the primary concentration device 1 is, for example, an evaporation device.
  • the condensed liquid 11 flows out from the top of the primary concentration device 1, and the obtained primary concentrated liquid 12 is passed into the primary crystallization device 2 for crystallization treatment.
  • the crystallization conditions have been described in detail above and will not be repeated here.
  • the primary crystallization device 2 is connected with the primary crystallization separation device 3, and the mixture obtained after the crystallization of the primary crystallization device 2 is passed into the primary crystallization separation device 3 for solid-liquid separation to obtain the primary crystallization crystal 31 and the primary crystallization mother liquor 32 .
  • the primary crystallization separation device 3 is communicated with the secondary concentration device 4, so that the primary crystallization mother liquor 32 is passed into the secondary concentration device 4 for concentration treatment to obtain a secondary concentrated liquid 41 and a condensate 42 ;
  • the secondary concentration device 4 communicates with the secondary crystallization device 5, and the secondary concentrated solution 41 is passed into the secondary crystallization device 5 for secondary crystallization treatment. This can increase the yield of NMMO.
  • the secondary crystallization device 5 is communicated with the secondary crystallization separation device 6, and the mixture obtained after the crystallization of the secondary crystallization device 5 is passed into the secondary crystallization separation device 6 for solid-liquid separation to obtain secondary crystallization crystals 61 and secondary crystallization mother liquor 62 .
  • the secondary crystallization separation device 6 is also communicated with the secondary concentration device 4, so that the secondary crystallization mother liquor 62 can be circulated back to the secondary concentration device 4 for concentration treatment, and then participate in the crystallization process again to further improve the NMMO yield.
  • the secondary crystallization mother liquor 62 can also be directly discharged for treatment.
  • the purification system of N-methylmorpholine-N-oxide of the present invention also includes a dissolving device 7, communicated with the primary crystallization separation device 3 and the secondary crystallization separation device 6 respectively, so that the primary crystallization
  • the crystal 31 and the secondary crystal 61 are transported to the dissolving device 7 and mixed with the input water 71 to obtain a crystal dissolving solution 72 .
  • the dissolving device 7 is connected to the recrystallization device 8, and the recrystallization device 8 is also connected to the recrystallization separation device 9, and the crystal solution 72 is sent to the recrystallization device 8 for recrystallization treatment, so that the purity of NMMO can be further improved.
  • the mixture obtained after crystallization by the recrystallization device 8 is sent to the recrystallization separation device 9 to obtain recrystallization crystals 91 and recrystallization mother liquor 92 .
  • the liquid chromatography analysis and detection of the recrystallized crystal 91 showed that various organic impurities such as N-nitrosomorpholine, N-methylmorpholine, morpholine, and peroxides in the crude NMMO product could not be detected. etc., adding water to the recrystallized crystal 91 to prepare a 50% NMMO aqueous solution with a conductivity of 3-6 ⁇ s/cm.
  • the recrystallization separation device 9 is also communicated with the primary crystallization separation device 3 and the secondary crystallization separation device 6 respectively, so that the recrystallization mother liquor 92 is used for washing the primary crystallization crystal 31 and the secondary crystallization crystal 61 , reduce the mother liquor adsorbed on the surface of the primary crystal 31 and the secondary crystal 61, so as to further remove the impurities contained in the primary crystal 31 and the secondary crystal 61.
  • the purification system of N-methylmorpholine-N-oxide of the present invention is used for industrial production, and the purification system also includes a control device (not shown in the figure), which is connected with the primary concentration device 1 and the primary concentration device 1, respectively.
  • a control device (not shown in the figure), which is connected with the primary concentration device 1 and the primary concentration device 1, respectively.
  • crystallization device 2 primary crystallization separation device 3, secondary concentration device 4, secondary crystallization device 5, secondary crystallization separation device 6, melting device 7, recrystallization device 8, and recrystallization separation device 9 Electrically connected to control process parameters of the crystallization process.
  • the present invention provides a detection method of N-methylmorpholine-N-oxide, said N-methylmorpholine-N-oxide is composed of N-methylmorpholine and hydrogen peroxide
  • the N-methylmorpholine-N-oxide crude product prepared by the reaction is obtained by crystallization, and the detection method includes the determination of the residual rate of crystal impurities of N-methylmorpholine-N-oxide, and the N-methylmorpholine-N-oxide
  • the mensuration of the crystal impurity residual rate of base morpholine-N-oxide compound comprises the steps:
  • Step 1 carry out liquid chromatography measurement to N-methylmorpholine-N-oxide crude product, measure wavelength is 200nm-220nm, for example 200nm-210nm, all impurity peaks are carried out area in the obtained liquid chromatography spectrogram Integrate to obtain the sum of the area integrals of all impurity peaks, which is recorded as the sum of the area integrals of the first impurity peaks;
  • Step 2 the N-methylmorpholine-N-oxide is subjected to liquid chromatography determination, the determination conditions are the same as in step 1, and all impurity peaks in the obtained liquid chromatography spectrum are area integrated to obtain all impurity The sum of the area integrals of the peaks is recorded as the sum of the area integrals of the second impurity peaks;
  • Residual rate of the first crystalline impurity the sum of the integrals of the peak areas of the second impurities ⁇ the sum of the integrals of the peak areas of the first impurities.
  • the determination of the crystal impurity residual rate of N-methylmorpholine-N-oxide also includes the following steps:
  • Step 3 carry out liquid chromatography measurement to N-methylmorpholine-N-oxide crude product, measure wavelength is 230nm-240nm, carry out area integration to all impurity peaks in the obtained liquid chromatography spectrogram, obtain all impurity The sum of the area integrals of the peaks is recorded as the sum of the area integrals of the third impurity peaks;
  • Step 4 the N-methylmorpholine-N-oxide is subjected to liquid chromatography determination, the determination conditions are the same as in step 3, and all impurity peaks in the obtained liquid chromatography spectrogram are area integrated to obtain all impurity The sum of the area integrals of the peaks is recorded as the sum of the area integrals of the fourth impurity peak;
  • the second crystal impurity residual rate the sum of the integrated peak areas of the fourth impurity ⁇ the integrated sum of the peak area of the third impurity.
  • the present invention can detect the residual impurities of the obtained crystal from different aspects by measuring the residual impurities of the first crystal and the residual impurities of the second crystal.
  • the detection method of N-methylmorpholine-N-oxide of the present invention also includes the mensuration of N-methylmorpholine and morpholine content, the mensuration of N-nitrosomorpholine content, hydrogen peroxide content , electrical conductivity, iron ion content, copper ion content at least one of the determination.
  • the determination method of N-methylmorpholine and morpholine content is: N-methylmorpholine-N-oxide is subjected to liquid chromatography determination, the measurement wavelength is 200nm-210nm, and the measurement time is greater than or equal to 30 minutes .
  • the method for determining the content of N-nitrosomorpholine is as follows: performing liquid chromatography measurement on N-methylmorpholine-N-oxide, the measurement wavelength is 230nm-240nm, and the measurement time is greater than or equal to 30 minutes. Like this, can obtain N-methylmorpholine and morpholine content according to gained liquid phase chromatogram.
  • the determination of hydrogen peroxide content is carried out in accordance with GB 5009.226-2016; the determination of iron ion content or copper ion content is determined by inductively coupled plasma emission spectrometer. Conductivity measurement can be carried out according to conventional methods in the art, and the present invention is not particularly limited.
  • N-methylmorpholine and morpholine content detection method liquid chromatography, chromatographic column: AichromBond-1, C18, 5 ⁇ m 4.6x150mm; Mobile phase: 0.2% phosphate buffer; Mobile phase flow rate: 1ml/min; column temperature: 35°C; UV detection wavelength: 200nm; injection volume: 20 ⁇ l, detection time: 30 minutes.
  • N-nitrosomorpholine content detection method liquid chromatography, chromatographic column: AichromBond-1, C18, 5 ⁇ m 4.6x150mm; mobile phase: 0.2% phosphate buffer; mobile phase flow rate: 1ml/min; column temperature: 35°C ; UV detection wavelength: 235nm; injection volume: 20 ⁇ l, detection time: 30 minutes.
  • the present invention uses the impurity residual rate to indicate the purity of the obtained NMMO crystals.
  • the detection method of the impurity residual rate is: add water to the NMMO crude product and crystals respectively, prepare an aqueous solution with a NMMO mass concentration of 50%, and perform liquid chromatography The prepared NMMO aqueous solution was measured, and the UV detection wavelengths were 200nm, 220nm and 235nm (respectively measured at three wavelengths).
  • the present invention utilizes the above detection method to measure the NMMO crude product prepared by the reaction of N-methylmorpholine and hydrogen peroxide used in the following examples, and the obtained results are as follows:
  • N-methylmorpholine content 1130ppm
  • This embodiment mainly analyzes the influence of different crystallization ratios of NMMO on the crystallization purity of NMMO.
  • the NMMO crude product was heated and evaporated in vacuum, concentrated to NMMO mass concentrations of 63.5%, 65.2%, 66.5%, 67.9% and 69.2%, respectively, and then cooled and crystallized respectively.
  • the temperature of the solution with a mass concentration of 63.5%, 65.2%, 66.5%, 67.9% and 69.2% was lowered to 31.2°C, 32.1°C, 33.2°C, 34.2°C, 35.1°C respectively, and the seed crystals pre-soaked in NMMO saturated solution were added, The amount of addition is 0.15% of the mass of the NMMO crude product.
  • the crude NMMO product and the obtained crystals were added with water respectively to prepare an aqueous solution with a mass concentration of NMMO of 50%, and analyzed and detected.
  • the detection results are shown in Table 1.
  • crystallization can effectively remove various impurities in the NMMO crude product, and the impurity content and electrical conductivity in the obtained crystals are greatly reduced. change, but the crystallization rate is greater than 65%, and the crystal purity decreases slightly as the crystallization rate increases.
  • This example mainly analyzes the influence of different crystallization rates on the purity of NMMO crystals.
  • the NMMO crude product is heated and evaporated in vacuum, and concentrated to a NMMO mass concentration of 67.9%.
  • NMMO seed crystals the amount of seed crystals added is 0.15% of the mass of the NMMO crude product, the NMMO crude product is divided into 4 parts, and crystallized according to the following different cooling and cooling rates, the crystallization solution is lowered to 25 ° C, and it is suction filtered while it is hot.
  • Example 1 way to deal with the crystal.
  • Cooling rate 1 From 34.2°C to 30°C, the cooling rate is controlled at 1°C/hour; at 30-25°C, the cooling rate is controlled at 4°C/hour.
  • Cooling rate 2 From 34.2°C to 30°C, the cooling rate is controlled at 2°C/hour; at 30-25°C, the cooling rate is controlled at 4°C/hour.
  • Cooling rate 3 From 34.2°C to 30°C, the cooling rate is controlled at 2°C/hour, and at 30-25°C, the cooling rate is controlled at 2°C/hour.
  • Cooling rate 4 From 34.2°C to 30°C, the cooling rate is controlled at 4°C/hour, and at 30-25°C, the cooling rate is controlled at 4°C/hour.
  • NMMO crystals were added with water to prepare an NMMO aqueous solution with a mass concentration of 50%, and then analyzed and detected. The detection results are shown in Table 2.
  • the cooling rate should not be too fast, and it is better to control it at 1-2/hour, otherwise the crystal purity will drop significantly; in the later stage of cooling crystallization, the cooling rate should be Can be properly accelerated.
  • the main reason for the analysis is that the solubility of NMMO crystals changes greatly with temperature in the high temperature region, so too fast cooling will lead to excessive supersaturation of the solution, so that the crystals will contain more mother liquor and reduce the purity of the crystals; the crystallization temperature is lower in the later stage of crystallization , the solubility of NMMO crystals slows down with temperature, so the cooling rate can be appropriately accelerated.
  • This embodiment mainly analyzes the effect of the amount of seed crystals added on the crystal particle size and crystal purity. Evaporate the crude NMMO product under vacuum heating, concentrate until the mass concentration of NMMO is 67.9%, divide the concentrated NMMO crude product into 6 parts, and add the NMMO seed crystals pre-soaked in the NMMO saturated solution when the temperature of the NMMO crude product drops to 34.2°C , the seed crystal addition amount is respectively: 0 (without adding crystal seed), 0.05%, 0.1%, 0.2%, 0.3% and 0.6% (being the percentage of NMMO crude product quality), then crystallize and process by the mode of embodiment 1 crystals.
  • the NMMO crystals were added with water to prepare an aqueous solution with a NMMO mass concentration of 50%, and then detection and analysis were performed.
  • the analysis results are shown in Table 3.
  • the crystallization process is greatly influenced without seed crystals, and the temperature drops to 25° C., but there is still no obvious crystal generation; when the amount of seed crystals added is less (0.05%), the grain size distribution is uneven It shows that the addition of seed crystals is small, the supersaturation of the solution system is relatively large, and small crystal nuclei are spontaneously precipitated, and the purity of the obtained crystals is also slightly lower; increasing the amount of seed crystals added, the distribution of crystal particles becomes uniform, the crystal purity improves, and the crystal The larger the amount of seed added, the smaller the particles; if too many seeds (0.6%) are added, the resulting crystal particles are too small, and the surface of the particles may be contaminated with more mother liquor impurities, resulting in a decrease in crystal purity, while the crystal particle size is too small , will also affect the crystal filtration rate, and the optimum crystal addition is 0.1-0.3% of the mass of the NMMO crude product.
  • This embodiment mainly analyzes the influence of two crystallizations on the purity of NMMO crystals.
  • the crude product of the NMMO reaction was evaporated under vacuum heating, and concentrated to a mass concentration of NMMO of 69.2%, respectively.
  • a seed crystal soaked in a saturated NMMO solution was added in an amount of 0.15% of the mass of the NMMO crude product.
  • the crystal is first washed with a crude product of NMMO with a mass concentration of 60%, and the amount of washing is about 30% of the crystal mass, and then washed with a high-purity NMMO aqueous solution with a mass concentration of 59.5%.
  • the amount is about 30% of the crystal mass, and the collected crystals (primary crystallization) are weighed to calculate the crystallization rate, and the crystal purity (residual impurity rate) is analyzed and detected.
  • the NMMO crystals obtained by primary and secondary crystallization were respectively added with water to prepare an aqueous solution with a mass concentration of NMMO of 50%, and then analyzed and detected.
  • the detection results are shown in Table 4.
  • not detectable means that the content of the above-mentioned substances to be detected is lower than the minimum detectable value of the instrument.
  • the secondary crystallization can further purify NMMO, and the content of various organic impurities is further greatly reduced.
  • concentration of 50% aqueous solution prepared by adding water to NMMO crystals reduces the conductivity to 0.9 ⁇ s/cm, and the copper and iron ions are less than 1ppb. The value is 11.4.
  • the results in Table 4 show that the crystals obtained by the two crystallizations are detected by HPLC, wherein the impurity content is 0.02% of the impurity content in the NMMO crude product (UV detection wavelength: 200nm, 220nm and 235nm), so the total content of impurities in the crystals obtained from the two crystallizations does not exceed 2ppm.
  • This example mainly analyzes the result of recovering NMMO through multi-stage crystallization and the remaining mother liquor after primary crystallization.
  • the mother liquor separated from the primary crystallization of Example 4 was heated, evaporated and concentrated under reduced pressure until the mass concentration of NMMO was 70.1%.
  • Crystallization was carried out according to the crystallization process conditions in Example 4 (seeding was added when the temperature of the mother liquor was 35.2° C.), and the obtained The crystals were added with water to prepare an aqueous solution with a mass concentration of NMMO of 50%, and then analyzed and detected, and the detection results are shown in Table 5.
  • the primary crystallization mother liquor is concentrated again and then crystallized.
  • the crystallization rate reaches 84%, the purity of the obtained crystals is still very high, and the secondary crystallization is equivalent to recovering 96% of the NMMO quality in the NMMO crude product as NMMO crystals , if you want to further increase the yield of NNMO crystallization, you can also concentrate and crystallize the secondary crystallization mother liquor again, or further increase the total crystallization rate of the secondary crystallization.
  • the crystals obtained from the multistage crystallization of the mother liquor can be returned and dissolved in the crude NMMO product as a raw material for primary crystallization.
  • the present invention provides a method for high-efficiency, low-cost, green purification and preparation of high-purity NMMO aqueous solution, including cooling crystallization treatment, the crystallization operating temperature is close to normal temperature (25-35 ° C), and the crude product of NMMO reaction is obtained by the present invention
  • Purification method purification the recovery rate of NMMO is above 96%; the conductivity of the obtained NMMO aqueous solution with a mass concentration of 50% is about 1 ⁇ s/cm, the content of copper and iron ions is less than 1ppb, and the HPLC test results show that the total content of organic impurities does not exceed 2ppm (i.e.
  • the NMMO purification method of the present invention does not use ion exchange resins, so it completely solves the environmental protection problems such as high-salt, high-COD waste water and waste ion exchange resins that the current purification process using ion exchange resins faces.
  • the NMMO purification method provided by the present invention is also applicable to other fields that involve the use and need to purify NMMO, such as the coagulation bath NMMO purification process in the production of lyocell, semiconductor chips containing NMMO etchant waste liquid, and NMMO-containing electronic cleaning liquid waste Liquid recovery and purification process, etc.

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Abstract

本发明公开了一种N-甲基吗啉-N-氧化物的纯化方法、系统、检测方法及得到的N-甲基吗啉-N-氧化物，该N-甲基吗啉-N-氧化物来源于N-甲基吗啉与双氧水反应制备的N-甲基吗啉-N-氧化物粗产物，所述N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的质量浓度为50％～60％，该纯化方法包括：将所述N-甲基吗啉-N-氧化物粗产物在-20℃～78℃之间进行降温结晶，得到N-甲基吗啉-N-氧化物晶体。本发明NMMO提纯方法成本低，所得NMMO产品纯度高，几乎无"三废"生成。与目前NMMO提纯工艺不同，本发明提纯方法不需要离子交换树脂，因此彻底解决了离子交换树脂再生所带来的大量高盐高COD废水和废离子交换树脂等环保问题。

Description

N-甲基吗啉-N-氧化物的纯化方法、系统、检测方法及所得N-甲基吗啉-N-氧化物 技术领域
本发明涉及N-甲基吗啉-N-氧化物的纯化方法、N-甲基吗啉-N-氧化物的纯化系统、N-甲基吗啉-N-氧化物的检测方法及得到的N-甲基吗啉-N-氧化物。
背景技术
N-甲基吗啉-N-氧化物(氧化甲基吗啉，NMMO)是一种对纤维素有极强溶解性的优良溶剂。目前可溶解纤维素的溶剂中，可以真正实现工业化生产且前景可观的只有NMMO一种溶剂，NMMO能够很好溶解纤维素，可以得到成纤、成膜性能良好的纤维素溶液，这种溶液纺丝得到的天丝(Lyocell)纤维具有优异的纤维性能，而且Lyocell纤维生产过程中NMMO溶剂易回收，回收率达99.5％以上，Lyocell纤维在环保、能耗和纤维性能等各方面都具有很大的优势，发展前景十分广阔。
工业化NMMO是通过双氧水(H 2O 2)与N-甲基吗啉反应制备而成，反应得到的NMMO粗产物通常有较深颜色，根据申请人(华茂伟业绿色科技股份有限公司)工业化制备NMMO的实践，该反应的NMMO收率在99％以上，NMMO反应粗产物中总杂质质量含量不到1％，杂质中含有一定量未反应的N-甲基吗啉、吗啉、双氧水和一些副反应生成的杂质如强致癌物N-亚硝基吗啉、有机过氧化物以及一些不明杂质等，同时也含有一定量的金属阳离子如铜铁离子等和磷酸根、硝酸根等阴离子，NMMO粗产物电导率一般在500μs/cm以上。
目前可用于天丝生产的质量浓度为50％的NMMO水溶液产品的质量标准为：电导率小于10μs/cm，铜离子含量小于2ppm，铁离子含量小于2ppm，未反应的双氧水含量小于50ppm，N-甲基吗啉含量小于100ppm，吗啉含量小于200ppm，N-亚硝基吗啉含量小于50ppb，产品外观色度为无色透明溶液。对天丝生产而言，上述这些杂质在NMMO浓度50％水溶液产品中含量越低越好，但进一步降低这些杂质含量，需要比目前NMMO提纯工艺更加繁复苛刻的提纯步骤和提纯工艺条件，提纯成本会大幅上升。
另外，NMMO为胺基氧化物，在一定温度下会发生Cope消除反应，生成相应的双键在端基的烯烃化合物。由于NMMO制备过程中存在大量双氧水，双氧水会与烯烃反应，生成相应的有机过氧化氢、过氧化醚和有机过氧酸等有机过氧化物，因此NMMO粗产物中不可避免地含有一定量的有机过氧化物杂质。
天丝生产中纤维素分子链的断裂主要为NMMO的自由基分解反应产生的N-甲基吗啉自由基引发的(Adorjan I.,Potthast A.,Rosenau T.,Sixta H.and Kosma P.2005.Discoloration of cellulose solutions in N-methylmorpholine-N-oxide(Lyocell).Part 1:Studies on model compounds and pulps.Cellulose 12:51-57)(Rosenau T.,Potthast A.,Adorjan I.,Hofinger A.,Sixta H.,Firgo H.and Kosma P.2002.Cellulose solutions in N-methylmorpholime-N-oxide(NMMO)-Degradation processes and stabilizers.Cellulose 9:283-291)。过氧化物包括双氧水等无机过氧化物和有机过氧化物是一类优良的自由基引发剂，在一定温度下会分解产生自由基，从而诱导NMMO自由基分解反应的发生，造成纤维素分子链断裂，天丝纤维强度降低，同时NMMO自由基分解反应的最终产物是吗啉和甲醛，二者之间还有可能继续反应，生成亚甲基吗啉正碳离子，如果纤维素和NMMO形成的纺丝液中亚甲基吗啉正碳离子浓度过高，会大量诱发放热剧烈的NMMO自催化分解反应，导致不可控爆炸(US 5556452)，因此过氧化物对天丝生产危害很大。目前越来越多的天丝厂家已经意识到NMMO产品中有机过氧化物对天丝生产可能带来的危害，对NMMO中除双氧水以外的有机过氧化物杂质含量开始进行规范，尽管目前还没有出台进一步相关标准，但要求其中NMMO中过氧化物含量越低越好。
NMMO在生产过程中接触金属设备、反应器、管道和容器等，导致NMMO含有一些金属离子如铜、铁等离子，另外双氧水中也带有一些金属和非金属离子，铜铁离子会催化NMMO分解反应，造成NMMO的损耗，天丝生产中NMMO纤维素溶液里面的铜铁离子还会与纤维素发生络合，导致纤维素降解(吴翠玲、李新平、秦胜利和王建勇《新型有机纤维素溶剂-NMMO的研究》，兰州理工大学学报，2005，31(2)，73-76)。另外铜铁离子也会与天丝生产中加入的没食子酸丙酯络合，产生较深的颜色，影响最终天丝纤维的色度，同时铜铁离子还会催化NMMO中过氧化物氧化纤维素，加速纤维素分解，以及 催化美拉德反应，产生颜色，甚至会催化NMMO自催化自由基分解反应，放出大量热，严重时有可能产生爆炸(如CN 104801354B和US 5556452)，因此过高的铜铁离子对NMMO生产危害很大，故要求天丝级NMMO产品中铜铁离子含量越低越好。
目前工业化提纯NMMO的工艺都是多步提纯工艺，其中一步使用离子交换树脂法去除NMMO粗产物中的阴阳离子和包括色素在内的部分有机杂质(CN 104801354 B)，同时采用其它提纯工艺(如X光照射和特种吸附树脂等)除去其中的N-亚硝基吗啉和其它有机杂质，为了得到更高品质的NMMO产品，还需要经过特殊催化还原处理，以便更深度除去其中的过氧化物(包括双氧水、有机过氧化氢、过氧化醚和有机过氧酸等)，如果仅采用离子交换树脂纯化的NMMO，无法完全去除其中含有的包括过氧化物在内的非离子型有机杂质。
失效的离子交换树脂需要再生才能重复使用，阳离子交换树脂通常使用4-6倍树脂体积的4-5％盐酸水溶液连续冲洗再生，而阴离子交换树脂使用4-6倍树脂体积的4-5％NaOH水溶液连续冲洗再生。这些再生废液经过酸碱中和后，不仅含有5％左右的NaCl和其它少量金属、非金属离子盐，而且还含有树脂吸附的其它有机杂质以及吸附的少量NMMO，故COD含量通常在5000ppm-20000ppm。一般生产1吨50％NMMO水溶液产品，就要产生1-2吨高COD高盐废水，由于含盐量高，该废水无法通过催化氧化方法处理，因为钠离子和氯离子会导致催化剂Pt中毒，也不能通过有机废液焚烧炉(TO)直接焚烧，因为高盐不仅会严重腐蚀焚烧炉材质，而且大量残留在焚烧炉内的废盐还会严重影响焚烧炉的运行，故通常只能采用多效蒸发(MVR)浓缩得到半固体废盐，将含COD废水中的盐份分离出来。但该处理方式不仅能耗高，而且得到的废盐中含很高的COD，只能交给有资质的环保公司作为危废处理，费用非常高。MVR蒸发得到的水中COD含量通常也很高，必须经过催化氧化或直接焚烧处理。另外离子交换树脂和吸附有机杂质的特种吸附树脂不但售价高，寿命一般仅1-2年，而且报废的树脂按照国家危废分类名录被列为危险废物，必须交由有资质的环保公司处理，费用同样非常高。同时由于离子交换树脂和吸附有机杂质的特种树脂会吸附NMMO，造成NMMO收率的降低。因此目前工业化提纯制备天丝级NMMO的工艺，不仅存在严重的“三废”环 保问题，而且能耗及提纯成本也非常高。
《新型有机纤维素溶剂-NMMO的研究》(吴翠玲、李新平、秦胜利和王建勇，兰州理工大学学报，2005，31(2)，73-76)中公开，NMMO可以与水分子结合形成3种不同含水量的晶体，1个NMMO分子可以与1个水分子形成单水化合物晶体(NMMO·H 2O)，外观为白色晶体，熔点：76-78℃，晶体中NMMO浓度84.5％，密度1.28g/cm 3；2个NMMO分子也可以与5个水分子形成2.5水化合物晶体(2NMMO·5H 2O)，外观为白色晶体，熔点36-39℃，晶体中NMMO浓度72.2％，密度1.33g/cm 3；1个NMMO分子还可以与5个水分子(NMMO·5H 2O)形成五水化合物晶体，熔点：-20℃，晶体中NMMO浓度56.5％。NMMO·H 2O和NMMO·2.5H 2O可通过NMMO水溶液脱水得到。其主要考察研究了NMMO不同水合物晶体对纤维素的溶解性，利用NMMO·H 2O的低熔点特性以及较好地溶解纤维素的特性，将NMMO·H 2O用于溶解纤维素。
发明内容
本发明的主要目的在于提供一种N-甲基吗啉-N-氧化物的纯化方法、系统、检测方法及得到的N-甲基吗啉-N-氧化物，以克服现有技术中N-甲基吗啉-N-氧化物纯化过程能耗高，污染环境，收率低，以及所得N-甲基吗啉-N-氧化物纯度低的缺陷。
为了达到上述目的，本发明提供了一种N-甲基吗啉-N-氧化物的纯化方法，该N-甲基吗啉-N-氧化物来源于N-甲基吗啉与双氧水反应制备的N-甲基吗啉-N-氧化物粗产物，所述N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的质量浓度为50％～60％，该纯化方法包括：将所述N-甲基吗啉-N-氧化物粗产物在-20℃～78℃之间进行降温结晶，得到N-甲基吗啉-N-氧化物晶体。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，在一实施方式中，该纯化方法还包括将所述N-甲基吗啉-N-氧化物粗产物进行浓缩处理，使N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的质量浓度为56.5％～84.5％，然后再进行降温结晶。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，在一实施方式中，在所述降温结晶的过程中加入晶种，所述晶种的加入量为所述N-甲基吗啉-N-氧化 物粗产物重量的0.1％～1.0％。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，在一实施方式中，浓缩处理后，N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的质量浓度为56.5％～72.2％时，所述降温结晶的温度为-20～39℃；浓缩处理后，N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的质量浓度为大于72.2％且小于或等于84.5％时，所述降温结晶的温度为大于39℃且小于或等于78℃。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，在一实施方式中，浓缩处理后，N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的质量浓度为66％～71％，所述降温结晶的温度为25℃～35℃。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，在一实施方式中，所述降温结晶过程中，在开始出现晶体至30℃，降温速率为1～2℃/小时；-20℃～30℃之间，降温速率为3～4℃/小时。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，在一实施方式中，所述降温结晶至少包括一级降温结晶和二级降温结晶，所述一级降温结晶得到N-甲基吗啉-N-氧化物晶体和结晶母液，所述结晶母液经浓缩后进行二级降温结晶处理。
为了达到上述目的，本发明还提供了上述N-甲基吗啉-N-氧化物的纯化方法得到的N-甲基吗啉-N-氧化物，N-甲基吗啉-N-氧化物的回收率为97％以上，N-甲基吗啉-N-氧化物的液相色谱检测结果为有机杂质含量为0，所得到的N-甲基吗啉-N-氧化物配成质量浓度为50％的水溶液，所述水溶液的电导率为0～10μs/cm，双氧水含量为0。
为了达到上述目的，本发明更提供了一种N-甲基吗啉-N-氧化物的纯化方法，该纯化方法不使用离子交换树脂。
为了达到上述目的，本发明又提供了一种N-甲基吗啉-N-氧化物的纯化系统，该纯化系统用于N-甲基吗啉与双氧水反应制备的N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的纯化，该纯化系统包括：
结晶装置，用于N-甲基吗啉-N-氧化物粗产物的结晶处理；
控制装置，与所述结晶装置连接，以控制结晶装置中的结晶条件。
本发明所述的N-甲基吗啉-N-氧化物的纯化系统，在一实施方式中，该纯化系统还包括浓缩装置，与所述结晶装置和所述控制装置连接，以使所述N- 甲基吗啉-N-氧化物粗产物在所述浓缩装置中进行浓缩后，再输入所述结晶装置；所述控制装置控制所述浓缩装置的浓缩条件。
为了达到上述目的，本发明更又提供了一种N-甲基吗啉-N-氧化物的检测方法，所述N-甲基吗啉-N-氧化物是由N-甲基吗啉与双氧水反应制备的N-甲基吗啉-N-氧化物粗产物进行降温结晶得到的，所述检测方法包括N-甲基吗啉-N-氧化物的晶体杂质残留率的测定，所述N-甲基吗啉-N-氧化物的晶体杂质残留率的测定包括如下步骤：
步骤1，对N-甲基吗啉-N-氧化物粗产物进行液相色谱测定，测定波长为200nm-220nm，或者为200nm-210nm，对所得到的液相色谱谱图中所有杂质峰进行面积积分，得到所有杂质峰的面积积分总和，记为第一杂质峰面积积分总和；
步骤2，对所述N-甲基吗啉-N-氧化物进行液相色谱测定，测定条件与步骤1相同，对所得到的液相色谱谱图中所有杂质峰进行面积积分，得到所有杂质峰的面积积分总和，记为第二杂质峰面积积分总和；
第一晶体杂质残留率＝第二杂质峰面积积分总和÷第一杂质峰面积积分总和。
本发明所述的N-甲基吗啉-N-氧化物的检测方法，在一实施方式中，所述N-甲基吗啉-N-氧化物的晶体杂质残留率的测定还包括如下步骤：
步骤3，对N-甲基吗啉-N-氧化物粗产物进行液相色谱测定，测定波长为230nm-240nm，对所得到的液相色谱谱图中所有杂质峰进行面积积分，得到所有杂质峰的面积积分总和，记为第三杂质峰面积积分总和；
步骤4，对所述N-甲基吗啉-N-氧化物进行液相色谱测定，测定条件与步骤3相同，对所得到的液相色谱谱图中所有杂质峰进行面积积分，得到所有杂质峰的面积积分总和，记为第四杂质峰面积积分总和；
第二晶体杂质残留率＝第四杂质峰面积积分总和÷第三杂质峰面积积分总和。
本发明所述的N-甲基吗啉-N-氧化物的检测方法，在一实施方式中，所述检测方法还包括N-甲基吗啉和吗啉含量的测定；所述N-甲基吗啉和吗啉含量的测定方法为：对N-甲基吗啉-N-氧化物进行液相色谱测定，测定波长为200nm-210nm，测定时间为大于或等于30分钟。
本发明所述的N-甲基吗啉-N-氧化物的检测方法，在一实施方式中，所述检测方法还包括N-亚硝基吗啉含量的测定；所述N-亚硝基吗啉含量的测定方法为：对N-甲基吗啉-N-氧化物进行液相色谱测定，测定波长为230nm-240nm，测定时间为大于或等于30分钟。
本发明所述的N-甲基吗啉-N-氧化物的检测方法，在一实施方式中，所述检测方法还包括：双氧水含量、电导率、铁离子含量、铜离子含量中的至少一项的测定；所述双氧水含量的测定按照GB 5009.226-2016进行；所述铁离子含量或铜离子含量的测定采用电感耦合等离子体发射光谱仪进行测定。
本发明的有益效果：
本发明提供了一种高效、低成本、绿色提纯NMMO的方法，主要包括对粗产物进行结晶处理，结晶操作温度可以接近常温(25-35℃)，能耗低；NMMO回收率在97％以上，将纯化后的NMMO配制成质量浓度为50％的NMMO水溶液，其电导率小于10μs/cm，甚至达到1μs/cm左右，铜铁离子含量均小于1ppb，HPLC无法检测到N-亚硝基吗啉等有机杂质的存在，具体例如，HPLC检测结果显示杂质总含量不超过2ppm(即NMMO纯度＞99.999％)，双氧水含量也低于国标GB 5009226-2016可检测下限，产品质量达到或超过天丝生产要求的NMMO产品质量标准；而且，本发明的NMMO提纯方法不使用离子交换树脂，彻底解决了目前采用离子交换树脂的提纯工艺面临的高盐高COD废水和废离子交换树脂污染环境的问题。
附图说明
图1为本发明一实施方式的N-甲基吗啉-N-氧化物的纯化系统示意图。
其中，附图标记：
1一级浓缩装置
10 N-甲基吗啉-N-氧化物粗产物
11冷凝液
12一级浓缩液
2一级结晶装置
3一级结晶分离装置
31一级结晶晶体
32一级结晶母液
4二级浓缩装置
41二级浓缩液
42冷凝液
5二级结晶装置
6二级结晶分离装置
61二级结晶晶体
62二级结晶母液
7溶解装置
71水
72晶体溶解液
8重结晶装置
9重结晶分离装置
91重结晶晶体
92重结晶母液
具体实施方式
以下对本发明的实施方式作详细说明，本实施例在以本发明技术方案为前提下进行实施，给出了详细的实施过程，但本发明的保护范围不限于下述的实施方式，下列实施方式中未注明具体条件的实验方法，通常按照常规条件。如未特殊说明，本发明中含量是指质量含量，％是指质量％。
本发明公开了一种N-甲基吗啉-N-氧化物的纯化方法，主要用于N-甲基吗啉与双氧水反应制备的N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的纯化，本发明纯化方法不包括离子交换树脂处理步骤，因此可以克服使用离子交换树脂纯化时造成的污染环境、能耗高的问题，本发明纯化方法具有高效、低能耗、低成本、绿色环保、收率高，且N-甲基吗啉-N-氧化物纯度高的特点。
在一实施方式中，本发明提供了一种N-甲基吗啉-N-氧化物的纯化方法，该N-甲基吗啉-N-氧化物来源于N-甲基吗啉与双氧水反应制备的N-甲基吗啉-N-氧化物粗产物，N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的质量浓度为50％～60％，该纯化方法包括：将N-甲基吗啉-N-氧化物粗产物在 -20℃～78℃之间进行降温结晶，得到N-甲基吗啉-N-氧化物晶体。
结晶纯化方法是通过冷却降温，利用混合物中各个组分在溶剂中溶解度的不同，使得母液中所要结晶纯化的物质的浓度超过其饱和溶解度，形成过饱和溶液，所要结晶纯化的物质在过饱和溶液中形成晶体析出，而相对含量低的杂质组分则留在母液中，从而达到分离纯化的效果。影响晶体纯度的主要因素有母液在晶体表面的吸附和晶体内部对母液的包藏，本发明通过纯净的N-甲基吗啉-N-氧化物饱和溶液冲洗晶体以除去晶体表面吸附的母液，通过进一步改进结晶工艺条件或通过重结晶方法改善母液在晶体中的包藏问题。
工业中，由于纯净的N-甲基吗啉-N-氧化物存在运输上的问题，另外，使用N-甲基吗啉-N-氧化物的下游厂家通常也是以N-甲基吗啉-N-氧化物水溶液作为原料，因此，本领域通常制备的N-甲基吗啉-N-氧化物是以水溶液的状态存在。
本发明利用N-甲基吗啉-N-氧化物水合物晶体的特性，通过控制降温结晶条件，使N-甲基吗啉-N-氧化物和水以特定比例结合形成晶体，进而达到与水溶液中杂质分离的目的。换言之，本发明通过结晶得到N-甲基吗啉-N-氧化物水合物固体，达到了纯化N-甲基吗啉-N-氧化物的目的，然后再将N-甲基吗啉-N-氧化物水合物固体配制成所需浓度的水溶液，以供应给下游厂商。
工业上，N-甲基吗啉与双氧水反应制备的NMMO粗产物，颜色一般为棕黄色，根据所用双氧水浓度的不同，反应粗产物中NMMO质量浓度在50％-60％之间。本发明并不特别限定N-甲基吗啉与双氧水的反应过程，本领域常规反应条件即可。
在一实施方式中，本发明首先对N-甲基吗啉-N-氧化物粗产物进行浓缩处理，得到N-甲基吗啉-N-氧化物质量含量在56.5％-84.5％之间的浓缩液，然后再对浓缩液进行降温结晶，如此可以提高结晶效率。在另一实施方式中，浓缩处理方式为蒸发，例如加热蒸发、减压蒸发等。
在一实施方式中，本发明对N-甲基吗啉-N-氧化物粗产物进行浓缩处理，得到的浓缩液中N-甲基吗啉-N-氧化物的质量含量在56.5％-72.2％时，浓缩液在-20-39℃之间进行降温结晶，如此得到的NMMO晶体为2NMMO·5H 2O(即NMMO·2.5H 2O)；得到的浓缩液中N-甲基吗啉-N-氧化物的质量含量在72.2％-84.5％(不包括72.2％)时，浓缩液在39-78℃(不包括39℃)之间进 行降温结晶，如此得到的NMMO晶体为NMMO·H 2O。换言之，浓缩液中NMMO浓度不同，决定了结晶温度的不同，进而得到不同的NMMO晶体。
在一实施方式中，本发明考虑到工业化提纯成本和操作便利性，将N-甲基吗啉-N-氧化物粗产物浓缩至NMMO质量浓度为66％-71％，浓缩液在25-35℃常温范围进行降温结晶(结晶终温在25℃及以上)。在该最佳结晶条件下，经过一级结晶就可以得到纯度很高的2NMMO·5H 2O晶体和50％以上的结晶收率。
在一实施方式中，在结晶的过程中可以加入晶种，晶种的加入量为N-甲基吗啉-N-氧化物粗产物重量的0.1％～1.0％，或者晶种的加入量为上述浓缩液重量的0.1％～1.0％。在另一实施方式中，晶种的加入量为N-甲基吗啉-N-氧化物粗产物重量的0.1％～0.3％，或者晶种的加入量为上述浓缩液重量的0.1％～0.3％。在降温结晶中，加晶种诱导结晶可以非常有效地降低NMMO在溶液中的过饱和度，得到NMMO纯度更高的晶体。
在一实施方式中，本发明加入的晶种为压碎的颗粒度尽量均匀的小颗粒高纯度碎晶，粒径例如为0.01-0.1mm，晶种加入量为NMMO粗产物重量的0.1-1.0％。晶种颗粒较大和加入量过少都会导致NMMO晶体纯度降低，并且最终得到的NMMO晶体颗粒大小分布不均；晶种过多会导致所得到的晶体颗粒偏小。另外，晶种加入不宜过早，否则溶液温度过高，溶液中NMMO水合物浓度低于其对应的溶解度，导致晶体溶解，失去加晶种的意义；而晶种加入过晚，溶液温度过低，此时溶液过饱和度已经过高，会降低加入晶种的实际效果。晶种的加入时机一般根据NMMO粗产物或浓缩液中NMMO含量以及初始降温温度决定，在一实施方式中，晶种于溶液降温至30-37℃之间时加入。
在一实施方式中，本发明晶种在加入结晶体系前，在高纯度的NMMO饱和水溶液中浸泡至少1小时，如此可以提高结晶效果，保证结晶体系中析出的晶体大小均一。
在一实施方式中，本发明降温结晶过程中，从结晶体系中开始出现结晶到结晶体系温度降到30℃，冷却速度控制在1-2℃/小时，结晶体系温度低于30℃后(如在-20-30℃)，冷却速度可以控制在3-4℃/小时。如此，可以保证晶体纯度。这是因为，降温结晶中，冷却速度直接决定了结晶速度。在结晶体系处于较高温度范围时，NMMO水合物溶解度曲线变化很大，故起晶后在结晶 初始阶段，溶液体系冷却速度不宜过快，应该限制晶体增长速度，否则会导致溶液过饱和度过高，影响晶体纯度。
在一实施方式中，降温结晶体系达到结晶终止温度后，将结晶溶液快速通过布氏漏斗真空抽滤，从滤瓶中放出结晶母液，晶体分别用NMMO粗产物和浓度为59.5±0.5％高纯度NMMO水溶液冲洗，得到NMMO晶体，称重并分析含量。
本发明采用一级结晶即可以得到纯度非常高的NMMO晶体，将上述一级结晶得到的NMMO晶体加水配成质量浓度为50％的NMMO水溶液，颜色为无色透明，电导率可达4-10μs/cm。
为了得到更高纯度的NMMO，本发明降温结晶至少包括两次结晶，例如包括一次结晶和二次结晶。即经过一次结晶后得到晶体加水配制一定浓度NMMO水溶液，进行二次结晶(重结晶)。在一实施方式中，本发明降温结晶还包括三次结晶、四次结晶等。
本发明二次结晶得到的晶体进行液相色谱分析检测，已经检测不出有机杂质如N-亚硝基吗啉、N-甲基吗啉、吗啉、过氧化物等，加水配制成质量含量为50％的NMMO水溶液，其电导率为3-6μs/cm，甚至可达1μs/cm左右。
在另一实施方式中，将二次结晶得到的晶体加水配制成NMMO质量浓度为50％的水溶液，NMMO溶液(NMMO质量浓度50％)的电导率为1μs/cm左右；采用赛默飞ICP-MS检测，几乎检测不到铜离子和铁离子存在(由此说明铜离子和铁离子含量均小于0.001ppm)；根据国标GB 5009.226-2016，无法检测出双氧水存在。因此，经过上述处理后得到的晶体配制的NMMO质量浓度为50％的水溶液，已经完全能够满足天丝生产对NMMO的质量要求，且远远高于天丝生产对NMMO的质量要求。
在一实施方式中，为了提高NMMO的收率，本发明至少包括二级结晶，即将N-甲基吗啉-N-氧化物粗产物进行一级结晶，得到晶体和结晶母液，将一级结晶产生的结晶母液通过真空加热蒸发至NMMO质量浓度为69-71％或者69-70.5％，然后降温结晶(二级结晶)，结晶条件与上述一级结晶一致，结晶率在80-85％左右，所得晶体可以循环溶解于NMMO粗产物中，回收作为一级结晶原料液，进一步提高晶体纯度。为了进一步提高NMMO的收率，二级结晶所得的结晶母液可以继续浓缩结晶，此时二级结晶所得的结晶母液量很 少，一般不到初始NMMO粗产物质量的3％。
在一具体实施方式中，本发明N-甲基吗啉-N-氧化物的纯化方法包括：通过减压加热蒸发浓缩，将N-甲基吗啉与双氧水反应生成的NMMO粗产物浓缩至NMMO质量含量为56.5-84.5％，通过降温结晶，得到高纯度的NMMO水合物晶体，无需离子交换树脂就能够得到天丝级NMMO产品。其中，降温结晶操作温度为-20-78℃，考虑到工业化提纯的成本和操作适宜性，粗产物中NMMO质量浓度最好控制在66-71％，如此可以在25-35℃下进行降温结晶，并且可以得到纯度很高的晶体产物和50％以上的结晶收率。
在一具体实施方式中，本发明降温结晶方法为：将温度40℃左右的NMMO质量浓度在66.5-70％的NMMO粗产物，冷却降温到晶种加入后不会溶解，然后加入少量晶种，晶种最好是先浸渍在高纯NMMO饱和溶液中的小颗粒NMMO·2.5H 2O碎晶，这些小颗粒碎晶在NMMO饱和溶液中至少浸泡1小时，晶种加入量为NMMO粗产物质量的0-1％，最好为0.1-0.3％。加入晶种后通过冷却处理使NMMO粗产物缓慢降温，在起晶温度到30℃之间，降温速率控制在1-2℃/小时，当温度降到30℃以下，降温速度可以适当加快到3-4℃/小时，结晶终止温度25℃，得到颗粒较大，粒度分布均一的晶体。晶体溶液迅速抽滤，过滤后母液收集称重，晶体先用NMMO粗产物冲洗，粗产物冲洗液量为所得晶体质量的30％左右，再用质量浓度为59.5±0.5％的高纯度NMMO水溶液继续冲洗，冲洗液量为晶体质量的30％左右，得到一次结晶晶体，收集一次结晶晶体称重并分析晶体纯度。一次结晶晶体加水配制成NMMO质量浓度为50％的水溶液，检测溶液中各种杂质含量、双氧水含量、电导率和金属离子含量。
然后进行二次结晶，二次结晶与一次结晶工艺条件相似，在40℃下将一次结晶晶体加水溶解，配制成NMMO质量浓度为66-70％水溶液，按同样结晶工艺条件进行二次结晶，收集二次结晶晶体称重并分析晶体纯度。
在一具体实施方式中，本发明NMMO的纯化方法为：将N-甲基吗啉与双氧水反应制备的NMMO粗产物，通过真空加热浓缩至NMMO质量浓度为56.5-84.5％，通过降温结晶，得到高纯度的NMMO水合物晶体，将该晶体加水配制成NMMO质量浓度为50％的水溶液，电导率甚至为1μs/cm左右、铜铁离子均小于0.001ppm、高纯度质量浓度为50％的NMMO水溶液产品。结晶 剩余的结晶母液进行二级或更多级结晶，可以最大程度回收其中的NMMO，结晶母液的二级结晶可以回收97％以上的NMMO粗产物中的NMMO，更多级的结晶会进一步提高NMMO的回收率。
由此，本发明提供了一种通过结晶方法从氧化甲基吗啉(NMMO)反应粗产物中提纯制备满足天丝(Lyocell)生产质量要求的NMMO的方法。与现有NMMO提纯方法不同，本发明不使用离子交换树脂去除金属离子和非金属离子以及包括色素在内的一些有机杂质，不存在离子交换树脂再生时产生的大量高盐高COD废水以及废离子交换树脂危险废物等污染环境的物质；按本发明方法生产的NMMO水溶液产品，不仅能够达到甚至超过目前天丝行业对NMMO产品的质量要求，而且提纯工艺简单，提纯成本低，NMMO收率高，本发明是一种高效简单低成本的绿色提纯NMMO方法。
在一实施方式中，本发明还提供了一种N-甲基吗啉-N-氧化物的纯化系统，该纯化系统用于N-甲基吗啉与双氧水反应制备的N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的纯化，该纯化系统可以用于工业生产中N-甲基吗啉-N-氧化物的纯化，即可实现大型自动化控制，该纯化系统包括：
结晶装置，用于N-甲基吗啉-N-氧化物粗产物的结晶处理；
控制装置，与所述结晶装置连接，以控制结晶装置中的结晶条件。
在另一实施方式中，该纯化系统还包括浓缩装置，与所述结晶装置和所述控制装置连接，以使所述N-甲基吗啉-N-氧化物粗产物在所述浓缩装置中进行浓缩后，再输入所述结晶装置；所述控制装置控制所述浓缩装置的浓缩条件。
在一实施方式中，本发明N-甲基吗啉-N-氧化物的纯化系统如图1所示，一级浓缩装置1与一级结晶装置2连通，N-甲基吗啉-N-氧化物粗产物10通入一级浓缩装置1中进行浓缩处理，一级浓缩装置1例如为蒸发装置。冷凝液11从一级浓缩装置1顶部流出，得到的一级浓缩液12通入一级结晶装置2进行结晶处理，结晶条件如上述已进行详细阐述，在此不再赘述。
一级结晶装置2与一级结晶分离装置3连通，一级结晶装置2结晶后得到的混合物通入一级结晶分离装置3中进行固液分离，得到一级结晶晶体31和一级结晶母液32。
在另一实施方式中，一级结晶分离装置3与二级浓缩装置4连通，以将一级结晶母液32通入二级浓缩装置4中进行浓缩处理，得到二级浓缩液41和冷 凝液42；二级浓缩装置4与二级结晶装置5连通，二级浓缩液41通入二级结晶装置5中进行二级结晶处理。如此可以提高NMMO的收率。
二级结晶装置5与二级结晶分离装置6连通，二级结晶装置5结晶后得到的混合物通入二级结晶分离装置6中进行固液分离，得到二级结晶晶体61和二级结晶母液62。在一实施方式中，二级结晶分离装置6还与二级浓缩装置4连通，如此使得二级结晶母液62能够循环回二级浓缩装置4进行浓缩处理，进而再次参与结晶过程，以进一步提高NMMO的收率。鉴于二级结晶母液62中所含的NMMO量较少，因此也可以将二级结晶母液62直接外排处理。
在一实施方式中，本发明N-甲基吗啉-N-氧化物的纯化系统还包括溶解装置7，与一级结晶分离装置3和二级结晶分离装置6分别连通，以将一级结晶晶体31和二级结晶晶体61输送至溶解装置7中，与输入的水71混合，得到晶体溶解液72。
溶解装置7与重结晶装置8连通，重结晶装置8还连通有重结晶分离装置9，晶体溶解液72输送至重结晶装置8中进行重结晶处理，如此可以进一步提高NMMO的纯度。重结晶装置8结晶后得到的混合物输送至重结晶分离装置9中，得到重结晶晶体91和重结晶母液92。对重结晶晶体91进行液相色谱分析检测，结果显示已经无法检测出NMMO粗产物中存在的各种有机杂质如N-亚硝基吗啉、N-甲基吗啉、吗啉、过氧化物等，将重结晶晶体91加水配制成质量含量为50％的NMMO水溶液，其电导率为3-6μs/cm。
在一实施方式中，重结晶分离装置9还与一级结晶分离装置3和二级结晶分离装置6分别连通，以将重结晶母液92用于一级结晶晶体31和二级结晶晶体61的洗涤，减少一级结晶晶体31和二级结晶晶体61表面吸附的母液，以进一步除去一级结晶晶体31和二级结晶晶体61夹杂的杂质。
在一实施方式中，本发明N-甲基吗啉-N-氧化物的纯化系统用于工业化生产，该纯化系统还包括控制装置(图未示)，分别与一级浓缩装置1、一级结晶装置2、一级结晶分离装置3、二级浓缩装置4、二级结晶装置5、二级结晶分离装置6、熔融装置7、重结晶装置8、重结晶分离装置9中的一个或几个电性连接，以控制结晶过程的工艺参数。
在一实施方式中，本发明提供了一种N-甲基吗啉-N-氧化物的检测方法，所述N-甲基吗啉-N-氧化物是由N-甲基吗啉与双氧水反应制备的N-甲基吗啉 -N-氧化物粗产物进行结晶得到的，所述检测方法包括N-甲基吗啉-N-氧化物的晶体杂质残留率的测定，所述N-甲基吗啉-N-氧化物的晶体杂质残留率的测定包括如下步骤：
步骤1，对N-甲基吗啉-N-氧化物粗产物进行液相色谱测定，测定波长为200nm-220nm，例如200nm-210nm，对所得到的液相色谱谱图中所有杂质峰进行面积积分，得到所有杂质峰的面积积分总和，记为第一杂质峰面积积分总和；
步骤2，对所述N-甲基吗啉-N-氧化物进行液相色谱测定，测定条件与步骤1相同，对所得到的液相色谱谱图中所有杂质峰进行面积积分，得到所有杂质峰的面积积分总和，记为第二杂质峰面积积分总和；
第一晶体杂质残留率＝第二杂质峰面积积分总和÷第一杂质峰面积积分总和。
在一实施方式中，N-甲基吗啉-N-氧化物的晶体杂质残留率的测定还包括如下步骤：
步骤3，对N-甲基吗啉-N-氧化物粗产物进行液相色谱测定，测定波长为230nm-240nm，对所得到的液相色谱谱图中所有杂质峰进行面积积分，得到所有杂质峰的面积积分总和，记为第三杂质峰面积积分总和；
步骤4，对所述N-甲基吗啉-N-氧化物进行液相色谱测定，测定条件与步骤3相同，对所得到的液相色谱谱图中所有杂质峰进行面积积分，得到所有杂质峰的面积积分总和，记为第四杂质峰面积积分总和；
第二晶体杂质残留率＝第四杂质峰面积积分总和÷第三杂质峰面积积分总和。
如此，本发明通过第一晶体杂质残留率和第二晶体杂质残留率的测定，可以从不同方面检测所得晶体的杂质残留率。
在一实施方式中，本发明N-甲基吗啉-N-氧化物的检测方法还包括N-甲基吗啉和吗啉含量的测定、N-亚硝基吗啉含量的测定、双氧水含量、电导率、铁离子含量、铜离子含量中的至少一项的测定。
其中，N-甲基吗啉和吗啉含量的测定方法为：对N-甲基吗啉-N-氧化物进行液相色谱测定，测定波长为200nm-210nm，测定时间为大于或等于30分钟。N-亚硝基吗啉含量的测定方法为：对N-甲基吗啉-N-氧化物进行液相色谱测定，测定波长为230nm-240nm，测定时间为大于或等于30分钟。如此，根据 所得液相色谱谱图即可得到N-甲基吗啉和吗啉含量。双氧水含量的测定按照GB 5009.226-2016进行；铁离子含量或铜离子含量的测定采用电感耦合等离子体发射光谱仪进行测定。电导率测定按本领域常规方法进行即可，本发明不作特别限定。
在一具体实施方式中，N-甲基吗啉和吗啉含量检测方法：液相色谱，色谱柱：AichromBond-1，C18，5μm 4.6x150mm；流动相：0.2％磷酸缓冲液；流动相流速：1ml/min；柱温：35℃；UV检测波长：200nm；进样量：20μl，检测时间：30分钟。
N-亚硝基吗啉含量检测方法：液相色谱，色谱柱：AichromBond-1，C18，5μm 4.6x150mm；流动相：0.2％磷酸缓冲液；流动相流速：1ml/min；柱温：35℃；UV检测波长：235nm；进样量：20μl，检测时间：30分钟。
本发明利用杂质残余率表示所得NMMO晶体的纯度，在一具体实施方式中，杂质残余率检测方法为：将NMMO粗产物和晶体分别加水，配制成NMMO质量浓度为50％的水溶液，液相色谱测定配制好的NMMO水溶液，UV检测波长分别为200nm、220nm和235nm(在三个波长下分别测定)。
本发明利用上述检测方法，对以下实施例中所使用的N-甲基吗啉与双氧水反应制备的NMMO粗产物进行测定，所得结果如下：
N-甲基吗啉含量：1130ppm；
吗啉含量：133ppm；
双氧水含量：634ppm；
N-亚硝基吗啉：655ppb，
电导率：732μs/cm；
铁离子含量：11.8ppm；
铜离子含量：4.2ppm；
另外液相色谱分析显示NMMO粗产物中还含有包括大量有机过氧化物在内的其它有机杂质。
以下通过具体实施例对本发明技术方案进一步进行说明。
实施例1
本实施例主要分析NMMO不同结晶率对NMMO结晶纯度的影响。
NMMO粗产物真空加热蒸发，分别浓缩至NMMO质量浓度为63.5％、65.2％、66.5％、67.9％和69.2％，然后分别进行降温结晶，各浓度的NMMO粗产物浓缩液在37℃开始降温，NMMO质量浓度为63.5％、65.2％、66.5％、67.9％和69.2％的溶液温度分别降到31.2℃、32.1℃、33.2℃、34.2℃、35.1℃，加入预先泡在NMMO饱和溶液中的晶种，加入量为NMMO粗产物质量的0.15％，加入晶种后，控制降温速率在1-2℃/小时，直至溶液温度降到30℃，然后加快降温速率至3-4℃/小时，溶液温度降至25℃，停止结晶，快速抽滤，将母液与晶体分开，母液收集，晶体先用NMMO质量浓度为58.2％的粗产物冲洗，冲洗量大约为晶体质量的30％，然后再用高纯度NMMO质量浓度为59％水溶液冲洗，冲洗量大约为晶体质量的30％，收集晶体称重计算结晶率，并分析检测晶体纯度(杂质残余率)。
将NMMO粗产物和所得到的晶体分别加水，配制成NMMO质量浓度为50％的水溶液，进行分析检测，检测结果如表1所示。
表1.不同结晶率对结晶纯度的影响
Figure PCTCN2022088743-appb-000001
由表1所示，结晶能够有效去除NMMO粗产物中的各种杂质，得到的晶体中杂质含量和电导率大幅降低，结晶率小于或等于65％时，随结晶率升高NMMO晶体纯度基本不变，但结晶率大于65％，随结晶率升高晶体纯度略有下降。
实施例2
本实施例主要分析不同结晶速率对NMMO晶体纯度的影响，将NMMO粗产物真空加热蒸发，浓缩至NMMO质量浓度为67.9％，NMMO粗产物温度降至34.2℃时加入预先泡在NMMO饱和溶液中的NMMO晶种，晶种加入量为NMMO粗产物质量的0.15％，将NMMO粗产物分成4份，分别按以下不同的冷却降温速率进行结晶，结晶溶液降至25℃，趁热抽滤，按实施例1方式处理晶体。
冷却降温速率：
降温速率1：34.2℃到30℃，降温速率控制在1℃/小时，30-25℃，降温速率控制在4℃/小时。
降温速率2：34.2℃到30℃，降温速率控制在2℃/小时，30-25℃，降温速率控制在4℃/小时。
降温速率3：34.2℃到30℃，降温速率控制在2℃/小时，30-25℃，降温速率控制在2℃/小时。
降温速率4：34.2℃到30℃，降温速率控制在4℃/小时，30-25℃，降温速率控制在4℃/小时。
将NMMO晶体加水配制成质量浓度为50％的NMMO水溶液，然后进行分析检测，检测结果如表2所示。
表2.不同降温速率对NMMO晶体纯度的影响
Figure PCTCN2022088743-appb-000002
由表2所示，初始结晶阶段(起晶温度到30℃区间)，降温速率不宜过快，控制在1-2/小时为佳，否则晶体纯度会有明显下降；在降温结晶后期，降 温速率可以适当加快。分析原因主要为NMMO晶体溶解度在高温区随温度变化较大，故过快降温会导致溶液过饱和度过高，从而使晶体包藏更多的母液，降低了晶体纯度；在结晶后期结晶温度较低，NMMO晶体溶解度随温度变化趋势减缓，故可以适当加快降温速率。
实施例3
本实施例主要分析晶种加入量对晶体颗粒度和晶体纯度的影响。将NMMO粗产物真空加热蒸发，浓缩至NMMO质量浓度为67.9％，将浓缩后的NMMO粗产物分成6份，NMMO粗产物温度降至34.2℃时分别加入预先泡在NMMO饱和溶液中的NMMO晶种，晶种加入量分别为：0(不加晶种)、0.05％、0.1％、0.2％、0.3％和0.6％(为NMMO粗产物质量的百分比)，然后按实施例1的方式结晶和处理晶体。
将NMMO晶体加水配制成NMMO质量浓度为50％的水溶液，然后进行检测分析，分析结果如表3所示。
表3.不同晶种加入量对晶体纯度和颗粒度的影响
Figure PCTCN2022088743-appb-000003
由表3所示，不加晶种对结晶过程有很大影响，温度降至25℃，仍然没有明显晶体生成；当晶种加入量偏少(0.05％)时，晶粒大小分布不均，说明晶种加入量少，溶液体系过饱和度较大，有小晶核自发析出，所得到的晶体纯度也略低；加大晶种加入量，晶体颗粒分布变得均一，晶体纯度提高，晶种加入量越大，颗粒越小；加入过多晶种(0.6％)，最终所得晶体颗粒过小，颗粒表面有可能沾污更多的母液杂质，造成晶体纯度下降，同时晶体颗粒度太小，也会影响晶体过滤速度，最佳晶体加入量为NMMO粗产物质量的0.1-0.3％。
实施例4.
本实施例主要分析两次结晶对NMMO晶体纯度的影响。
NMMO反应粗产物真空加热蒸发，分别浓缩至NMMO质量浓度为69.2％，在35.1℃时加入预先泡在NMMO饱和溶液中的晶种，加入量为NMMO粗产物质量的0.15％，加入晶种后，控制降温速率在1-2℃/小时，直至温度降到30℃，然后加快降温速率至4℃/小时，温度降至25℃，停止结晶，趁热快速抽滤，将母液与晶体分开，收集母液作为实施例5结晶实验原料，晶体先用质量浓度为60％的NMMO粗产物冲洗，冲洗量大约为晶体质量的30％，然后再用高纯度的质量浓度为59.5％的NMMO水溶液冲洗，冲洗量大约为晶体质量的30％，收集晶体(一次结晶)称重计算结晶率，并分析检测晶体纯度(杂质残余率)。
将上述一次结晶得到的晶体加水配制成质量浓度为68.1％的NMMO水溶液，按上述结晶工艺进行二次结晶，在34.3℃加入晶种，所得晶体用高纯度的质量浓度为59.5％的NMMO水溶液冲洗，用量为晶体质量为30％，收集晶体(二次结晶)称重计算结晶率，并分析检测晶体纯度(杂质残余率)。
将一次和二次结晶得到的NMMO晶体分别加水，配制成NMMO质量浓度为50％的水溶液，然后进行分析检测，检测结果如表4所示。
表4.两次结晶处理对结晶纯度的影响
Figure PCTCN2022088743-appb-000004
注：上述“检测不出”“未检测出”或“无明显杂质峰”表示上述欲检测物质含量已经低于仪器可检测最低值。
由表4所示，二次结晶能够进一步纯化NMMO，各种有机杂质含量进一步大幅降低，NMMO晶体加水配制的浓度50％水溶液，电导率降至0.9μs/cm，铜铁离子均小于1ppb，pH值为11.4。
由于结晶所用的NMMO粗产物中的杂质含量不到1％，表4结果显示两次结晶得到的晶体经HPLC检测，其中杂质含量为NMMO粗产物中杂质含量的0.02％(UV检测波长：200nm、220nm和235nm)，故两次结晶所得晶体中杂质总含量不超过2ppm。
实施例5.
本实施例主要分析一次结晶剩余母液，通过多级结晶回收NMMO的结果。将实施例4的一次结晶分离出来的母液，减压加热蒸发浓缩至NMMO质量浓度为70.1％，按实施例4中结晶工艺条件进行结晶(在母液温度35.2℃时加入晶种)，将所得到的晶体加水，配制成NMMO质量浓度为50％的水溶液，然后进行分析检测，检测结果如表5所示。
表5.一次结晶母液再次进行结晶的结果
Figure PCTCN2022088743-appb-000005
Figure PCTCN2022088743-appb-000006
由表5所示，一次结晶母液再次浓缩后进行结晶，在结晶率达84％时，所得晶体的纯度仍然非常高，二级结晶相当于将NMMO粗产物中NMMO质量的96％回收成为NMMO晶体，如果希望进一步提高NNMO结晶收率，还可以再次对二级结晶母液进行浓缩结晶，或者进一步提高二级结晶的总结晶率。母液多级结晶得到的晶体可以返回溶解到NMMO粗产物中，作为一次结晶的原料。
工业应用性
综上所述，本发明提供了一种高效、低成本、绿色提纯制备高纯度NMMO水溶液的方法，包括降温结晶处理，结晶操作温度接近常温(25-35℃)，NMMO反应粗产物采用本发明提纯方法提纯，NMMO回收率在96％以上；得到的质量浓度为50％的NMMO水溶液的电导率在1μs/cm左右，铜铁离子含量均小于1ppb，HPLC检测结果显示有机杂质总含量不超过2ppm(即NMMO纯度＞99.999％)，HPLC几乎无法检测到N-亚硝基吗啉的存在，双氧水含量也低于国标GB 5009226-2016可检测下限，产品质量达到或超过天丝生产要求的NMMO产品质量标准，同时本发明的NMMO提纯方法不使用离子交换树脂，故彻底解决了目前采用离子交换树脂的提纯工艺面临的高盐高COD废水和废离子交换树脂等环保问题。
本发明提供的NMMO提纯方法，也适用于其它涉及使用并需要提纯NMMO的领域，如天丝(lyocell)生产中凝固浴NMMO提纯工艺、半导体芯片含NMMO蚀刻剂废液、含NMMO电子清洗液废液回收提纯工艺等。
当然，本发明还可有其它多种实施例，在不背离本发明精神及其实质的情况下，熟悉本领域的技术人员可根据本发明作出各种相应的改变和变形，但这些相应的改变和变形都应属于本发明权利要求的保护范围。

Claims (20)

  1. 一种N-甲基吗啉-N-氧化物的纯化方法，用于一包含N-甲基吗啉-N-氧化物的混合物，该纯化方法包括：将所述混合物在-20℃～78℃之间进行降温结晶，得到N-甲基吗啉-N-氧化物晶体。
  2. 根据权利要求1所述的N-甲基吗啉-N-氧化物的纯化方法，其特征在于，该混合物为N-甲基吗啉与双氧水反应制备的N-甲基吗啉-N-氧化物粗产物，所述N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的质量浓度为50％～60％。
  3. 根据权利要求2所述的N-甲基吗啉-N-氧化物的纯化方法，其特征在于，该纯化方法还包括将所述N-甲基吗啉-N-氧化物粗产物进行浓缩处理，使N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的质量浓度为56.5％～84.5％，然后再进行降温结晶。
  4. 根据权利要求2所述的N-甲基吗啉-N-氧化物的纯化方法，其特征在于，在所述降温结晶的过程中加入晶种，所述晶种的加入量为所述N-甲基吗啉-N-氧化物粗产物重量的0.1％～1.0％。
  5. 根据权利要求3所述的N-甲基吗啉-N-氧化物的纯化方法，其特征在于，浓缩处理后，N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的质量浓度为56.5％～72.2％时，所述降温结晶的温度为-20～39℃；浓缩处理后，N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的质量浓度为大于72.2％且小于或等于84.5％时，所述降温结晶的温度为大于39℃且小于或等于78℃。
  6. 根据权利要求5所述的N-甲基吗啉-N-氧化物的纯化方法，其特征在于，浓缩处理后，N-甲基吗啉-N-氧化物粗产物中N-甲基吗啉-N-氧化物的质量浓度为66％～71％，所述降温结晶的温度为25℃～35℃。
  7. 根据权利要求1所述的N-甲基吗啉-N-氧化物的纯化方法，其特征在于，所述降温结晶过程中，在开始出现晶体至30℃，降温速率为1～2℃/小时；-20℃～30℃之间，降温速率为3～4℃/小时。
  8. 根据权利要求1所述的N-甲基吗啉-N-氧化物的纯化方法，其特征在于，所述降温结晶至少包括一级降温结晶和二级降温结晶，所述一级降温结晶得到N-甲基吗啉-N-氧化物晶体和结晶母液，所述结晶母液经浓缩后进行二级 降温结晶处理。
  9. 权利要求1-8任一项所述的N-甲基吗啉-N-氧化物的纯化方法得到的N-甲基吗啉-N-氧化物，其特征在于，所得到的N-甲基吗啉-N-氧化物的液相色谱检测结果为有机杂质含量为0；所得到的N-甲基吗啉-N-氧化物配成质量浓度为50％的水溶液，所述水溶液的电导率为0～10μs/cm，双氧水含量为0。
  10. 权利要求9所述的N-甲基吗啉-N-氧化物在纤维素中的应用。
  11. 一种N-甲基吗啉-N-氧化物的纯化方法，其特征在于，该纯化方法不含离子交换树脂处理步骤。
  12. 一种N-甲基吗啉-N-氧化物的制备方法，包括如下步骤：
    步骤1，N-甲基吗啉与双氧水反应制得N-甲基吗啉-N-氧化物粗产物；
    步骤2，将N-甲基吗啉-N-氧化物粗产物在-20℃～78℃之间进行降温结晶，得到N-甲基吗啉-N-氧化物晶体。
  13. 一种N-甲基吗啉-N-氧化物的纯化系统，其特征在于，该纯化系统用于一包含N-甲基吗啉-N-氧化物的混合物中N-甲基吗啉-N-氧化物的纯化，该纯化系统包括：
    结晶装置，用于所述混合物的结晶处理；
    控制装置，与所述结晶装置连接，以控制结晶装置中的结晶条件。
  14. 根据权利要求13所述的N-甲基吗啉-N-氧化物的纯化系统，其特征在于，该纯化系统还包括浓缩装置，与所述结晶装置和所述控制装置连接，以使所述混合物在所述浓缩装置中进行浓缩后，再输入所述结晶装置；所述控制装置控制所述浓缩装置的浓缩条件。
  15. 根据权利要求13所述的N-甲基吗啉-N-氧化物的纯化系统，其特征在于，所述混合物为N-甲基吗啉与双氧水反应制备的N-甲基吗啉-N-氧化物粗产物；所述纯化系统用于工业生产中N-甲基吗啉-N-氧化物的纯化。
  16. 一种N-甲基吗啉-N-氧化物的检测方法，其特征在于，所述N-甲基吗啉-N-氧化物是由N-甲基吗啉与双氧水反应制备的N-甲基吗啉-N-氧化物粗产物进行降温结晶得到的，所述检测方法包括N-甲基吗啉-N-氧化物的晶体杂质残留率的测定，所述N-甲基吗啉-N-氧化物的晶体杂质残留率的测定包括如下步骤：
    步骤1，对N-甲基吗啉-N-氧化物粗产物进行液相色谱测定，测定波长为 200nm-220nm，对所得到的液相色谱谱图中所有杂质峰进行面积积分，得到所有杂质峰的面积积分总和，记为第一杂质峰面积积分总和；
    步骤2，对所述N-甲基吗啉-N-氧化物进行液相色谱测定，测定条件与步骤1相同，对所得到的液相色谱谱图中所有杂质峰进行面积积分，得到所有杂质峰的面积积分总和，记为第二杂质峰面积积分总和；
    第一晶体杂质残留率＝第二杂质峰面积积分总和÷第一杂质峰面积积分总和。
  17. 根据权利要求16所述的N-甲基吗啉-N-氧化物的检测方法，其特征在于，所述N-甲基吗啉-N-氧化物的晶体杂质残留率的测定还包括如下步骤：
    步骤3，对N-甲基吗啉-N-氧化物粗产物进行液相色谱测定，测定波长为230nm-240nm，对所得到的液相色谱谱图中所有杂质峰进行面积积分，得到所有杂质峰的面积积分总和，记为第三杂质峰面积积分总和；
    步骤4，对所述N-甲基吗啉-N-氧化物进行液相色谱测定，测定条件与步骤3相同，对所得到的液相色谱谱图中所有杂质峰进行面积积分，得到所有杂质峰的面积积分总和，记为第四杂质峰面积积分总和；
    第二晶体杂质残留率＝第四杂质峰面积积分总和÷第三杂质峰面积积分总和。
  18. 根据权利要求16所述的N-甲基吗啉-N-氧化物的检测方法，其特征在于，所述检测方法还包括N-甲基吗啉和吗啉含量的测定；所述N-甲基吗啉和吗啉含量的测定方法为：对N-甲基吗啉-N-氧化物进行液相色谱测定，测定波长为200nm-210nm，测定时间为大于或等于30分钟。
  19. 根据权利要求16所述的N-甲基吗啉-N-氧化物的检测方法，其特征在于，所述检测方法还包括N-亚硝基吗啉含量的测定；所述N-亚硝基吗啉含量的测定方法为：对N-甲基吗啉-N-氧化物进行液相色谱测定，测定波长为230nm-240nm，测定时间为大于或等于30分钟。
  20. 根据权利要求16所述的N-甲基吗啉-N-氧化物的检测方法，其特征在于，所述检测方法还包括：双氧水含量、电导率、铁离子含量、铜离子含量中的至少一项的测定；所述双氧水含量的测定按照GB 5009.226-2016进行；所述铁离子含量或铜离子含量的测定采用电感耦合等离子体发射光谱仪进行测定。
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