WO2023274038A1 - N-甲基吗啉-n-氧化物的纯化方法、***及得到的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、***及得到的n-甲基吗啉-n-氧化物 Download PDF

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WO2023274038A1
WO2023274038A1 PCT/CN2022/100880 CN2022100880W WO2023274038A1 WO 2023274038 A1 WO2023274038 A1 WO 2023274038A1 CN 2022100880 W CN2022100880 W CN 2022100880W WO 2023274038 A1 WO2023274038 A1 WO 2023274038A1
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crystallization
nanofiltration
methylmorpholine
nmmo
treatment
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PCT/CN2022/100880
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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 EP22830362.4A priority Critical patent/EP4361132A1/en
Publication of WO2023274038A1 publication Critical patent/WO2023274038A1/zh

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    • 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
    • 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
    • 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
    • D01F13/00—Recovery of starting material, waste material or solvents during the manufacture of artificial filaments or the like
    • D01F13/02—Recovery of starting material, waste material or solvents during the manufacture of artificial filaments or the like of cellulose, cellulose derivatives or proteins
    • 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

  • Lyocell (lyocell) fiber is made by directly dissolving cellulose pulp in a mixed solvent of oxidized methylmorpholine (N-methylmorpholine-N-oxide, NMMO) and water for dry spraying and wet spinning. And the obtained man-made cellulose fiber, wherein, the liquid obtained after separating out the lyocell fiber is called the lyocell fiber coagulation bath or the discharge liquid of the lyocell fiber coagulation bath. Lyocell fiber has excellent performance, its raw materials are renewable, the production process is simple, the NMMO solvent used is non-toxic, the product waste is biodegradable, and does not pollute the environment, so it is called "green fiber with good development prospects in the 21st century".
  • 9,845,575 finds that hemicellulose is dissolved in the lyocell spinning bath, and the lyocell fibers spun out can largely relieve the fibrils of lyocell fibers
  • Another patent mentions that chitosan is added in the lyocell spinning bath, and the lyocell fibers spun out have antibacterial and deodorizing functions; if graphene is added in the lyocell spinning bath (US10,351,971 ), kaolin (US10,400,356), pearl powder (US8,633,120) and other inorganic functional powder materials, respectively, can spin functional lyocell fibers with excellent thermal conductivity, flame retardancy and beautiful flash.
  • the above-mentioned Lyocell fiber production process is divided into two parts, one is the dissolving and spinning process of cellulose in NMMO, and the other is the NMMO solvent purification in the lyocell fiber coagulation bath or the effluent of the lyocell fiber coagulation bath after lyocell spinning Recycling process parts.
  • the NMMO solution that dissolves cellulose can also be used to prepare lyocell films and films (US7,938,993), lyocell non-woven fabrics (US8,420,004), cigarette filter materials (US10,306,919), etc. After forming corresponding lyocell products, the NMMO solvent in the lyocell coagulation bath is purified and recovered.
  • cellulose pulp is firstly dissolved in an NMMO aqueous solution with a mass concentration of 85% or more at 100-110°C to make a lyocell spinning bath with a cellulose content of 10-14%, and then dry-sprayed,
  • the wet spinning method is used for spinning or forming and adding water to make corresponding cellulose products, and at the same time, a lyocell fiber coagulation bath with a mass concentration of NMMO of 10-25% is obtained.
  • NMMO and cellulose will undergo a complex chemical decomposition reaction under heating, resulting in a variety of impurities.
  • NMMO In order to recycle NMMO, it is necessary to remove various impurities dissolved in the lyocell coagulation bath. Taking the spinning of lyocell short filament, which is the most widely used at present, as an example, the mass concentration of NMMO in the coagulation bath after lyocell spinning is generally 10-25%, the color is brownish yellow or even soy sauce color, and the pH value is 7.5-9. The dissolution of pulp in NMMO needs to be carried out at a higher temperature. At high temperature, NMMO may be decomposed into impurities such as N-methylmorpholine, morpholine, formaldehyde and compounds containing large ⁇ bond conjugated structures.
  • Highly active free radicals will also be generated during the process, which will cause the cellulose to be oxidized and the cellulose chain to be broken and decomposed.
  • the metal ions in the cellulose solution such as copper ions and iron ions, will catalyze and accelerate the decomposition of NMMO and the breakage of cellulose. And deepen the color of the cellulose solution.
  • the cellulose fragmentation products include oligosaccharides and monosaccharides above disaccharides.
  • sugars will be decomposed to produce more than a dozen impurities such as sugar ketones, sugar acids, furans, furfurals, and phenols.
  • NMMO in the coagulation bath cannot effectively remove these impurities, the accumulation will have a negative impact on spinning, especially the damage to the production of lyocell filaments; in order to prevent NMMO decomposition and cellulose breakage, dissolve the fiber in NMMO
  • PG propyl gallate
  • PG propyl gallate
  • PG propyl gallate
  • the final condensation products have a darker color, and too many of these chromogenic groups remaining in the solution will deepen the color of the lyocell fiber and affect the whiteness of the product.
  • the NMMO purification and recovery process in the coagulation bath mainly uses anion exchange resin and cation exchange resin for purification.
  • anion exchange resin and cation exchange resin for purification.
  • the recovered and purified NMMO still contains many impurities and has low purity.
  • Many impurities contained in the coagulation bath cannot form ions in an acid-base environment, so they cannot be completely removed by ion exchange resins, such as propyl gallate (PG) and its reaction products, sugars and decomposition products, and NMMO are heated Decomposition products and other impurities, so there will still be a lot of impurities in the NMMO purified and recovered only by ion exchange resin.
  • PG propyl gallate
  • the NMMO purified and recovered by this method is likely to affect the production of lyocell filaments.
  • the applicant of the present invention has carried out liquid chromatography comparative analysis on the lyocell coagulation baths before and after the ion exchange resin purification treatment by many domestic lyocell manufacturers, and found that more than ten kinds of impurities including PG oxides in the coagulation bath cannot pass through the lyocell coagulation bath.
  • various impurities such as PG cannot be completely removed by ion exchange resin, so the purity of NMMO after purification by ion exchange resin is not high.
  • Ion exchange resins suitable for NMMO purification in lyocell coagulation baths are expensive, and their lifespan is only 1-2 years.
  • the cost per ton of lyocell fibers is about 500 yuan.
  • Hazardous waste must be handed over to a qualified environmental protection company for treatment, and the cost is also very high, and the treatment cost of high-salt and high-COD wastewater produced by regenerated ion exchange resin is also very high.
  • the main purpose of the present invention is to provide a kind of purification method of N-methylmorpholine-N-oxide compound, system and the obtained N-methylmorpholine-N-oxide compound, to overcome the coagulation bath of lyocell fiber in the prior art Among them, the purification cost of NMMO is high, the purification method is not environmentally friendly, and the purity of NMMO obtained by purification is not high.
  • the invention provides a kind of purification method of N-methylmorpholine-N-oxide, for the purification of N-methylmorpholine-N-oxide in Lyocell fiber coagulation bath, comprising The steps are as follows: the lyocell fiber coagulation bath is cooled between -20° C. and 78° C. for crystallization to obtain N-methylmorpholine-N-oxide hydrate crystals.
  • the method for purifying N-methylmorpholine-N-oxide of the present invention, wherein, the lyocell fiber coagulation bath also includes: removing sugar in the lyocell fiber coagulation bath before cooling crystallization class of substances.
  • the purification method of N-methylmorpholine-N-oxide according to the present invention also includes: performing microfiltration on the lyocell fiber coagulation bath before cooling crystallization At least one of treatment, ultrafiltration treatment and nanofiltration treatment.
  • the method for purifying N-methylmorpholine-N-oxide of the present invention wherein, the lyocell fiber coagulation bath also includes before cooling crystallization: combining the lyocell fiber coagulation bath with coagulation aid
  • the mixed solution is obtained by mixing the reagents for flocculation and sedimentation; and then the mixed solution is subjected to at least one of microfiltration treatment, ultrafiltration treatment and nanofiltration treatment.
  • the purification method of N-methylmorpholine-N-oxide according to the present invention wherein, the lyocell fiber coagulation bath is concentrated before cooling and crystallization, so that the N- The mass concentration of the methylmorpholine-N-oxide is 56.5%-84.5%, and then crystallization is carried out by cooling down.
  • the method for purifying N-methylmorpholine-N-oxide of the present invention wherein, the concentration treatment makes the mass concentration of N-methylmorpholine-N-oxide in the lyocell fiber coagulation bath It is 56.5-72.2%, and the temperature of cooling crystallization is 25-40 °C.
  • the purification method of N-methylmorpholine-N-oxide according to the present invention wherein, in the cooling crystallization process, when crystals begin to appear to 30°C, the cooling rate is 1-2°C/hour; -20°C Between ⁇ 30°C, the cooling rate is 3 ⁇ 4°C/hour.
  • the purification method of N-methylmorpholine-N-oxide of the present invention wherein, add crystal seed in the process of described cooling crystallization, the addition amount of described seed crystal is described lyocell fiber coagulation bath More than 0.01% of the weight of N-methylmorpholine-N-oxide in it.
  • the purification method of N-methylmorpholine-N-oxide according to the present invention wherein, the cooling crystallization at least includes primary cooling crystallization and secondary cooling crystallization, and the primary cooling crystallization obtains N-methylmorpholine A phenoline-N-oxide hydrate crystal and a crystallization mother liquor, wherein the crystallization mother liquor is concentrated and then subjected to secondary temperature-lowering crystallization.
  • the method for purifying N-methylmorpholine-N-oxide of the present invention wherein, the mixed solution is subjected to microfiltration to obtain a microporous filtrate; the microporous filtrate is subjected to the ultrafiltration to obtain ultrafiltration concentrate and ultrafiltration filtrate; the ultrafiltration filtrate undergoes the cooling crystallization;
  • the filtration precision of the microfiltration treatment is 0.5-5 microns; the filtration precision of the ultrafiltration treatment is 1000-100000 molecular weight.
  • the method for purifying N-methylmorpholine-N-oxide of the present invention wherein, the ultrafiltration filtrate is firstly subjected to primary nanofiltration treatment to obtain primary nanofiltration concentrate and primary nanofiltration Supernatant liquid, then make described primary nanofiltration filtrate carry out described cooling crystallization;
  • the filtration precision of the first-stage nanofiltration treatment is 300-1000 molecular weight.
  • the method for purifying N-methylmorpholine-N-oxide according to the present invention wherein, the first-stage nanofiltration filtrate is first subjected to the second-stage nanofiltration treatment to obtain the second-stage nanofiltration concentrate and the second-stage nanofiltration concentrate.
  • Level nanofiltration filtrate, the N-methylmorpholine-N-oxide is trapped in the secondary nanofiltration concentrated solution, and then the secondary nanofiltration concentrated solution is subjected to the cooling crystallization;
  • the filtration precision of the secondary nanofiltration treatment is 100-200 molecular weight.
  • the present invention also provides the N-methylmorpholine-N-oxide hydrate crystal obtained by the above purification method.
  • the control device is connected with the crystallization device to control the crystallization conditions in the crystallization device.
  • the purification system of N-methylmorpholine-N-oxide of the present invention also includes:
  • At least one of the microfiltration device, ultrafiltration treatment device and nanofiltration treatment device is communicated with the crystallization device and the control device, and the lyocell fiber coagulation bath is passed into the microfiltration device, ultrafiltration treatment device, At least one of the nanofiltration treatment devices is processed to obtain a filtrate, and the filtrate is passed into the crystallization device for crystallization treatment.
  • the purification system of N-methylmorpholine-N-oxide of the present invention also includes:
  • a flocculation settling device, the lyocell fiber coagulation bath and coagulation aid are passed into the flocculation settling device to obtain a mixed solution for flocculation and settling treatment;
  • the microfiltration device is communicated with the flocculation and sedimentation device, so that the mixed solution is passed into the microfiltration device to filter solids to obtain a microporous filtrate;
  • the ultrafiltration treatment device is communicated with the microfiltration device, and the microporous filtrate is passed into the ultrafiltration treatment device for ultrafiltration treatment to obtain an ultrafiltration concentrate and an ultrafiltration filtrate;
  • the nanofiltration treatment device is respectively communicated with the ultrafiltration treatment device and the crystallization device, and the ultrafiltration filtrate is passed into the nanofiltration treatment device for nanofiltration treatment to obtain a nanofiltration concentrate and a nanofiltration filtrate,
  • the N-methylmorpholine-N-oxide is trapped in the nanofiltration concentrate, and the nanofiltration concentrate is passed into the crystallization device for crystallization treatment.
  • the nanofiltration treatment device comprises a primary nanofiltration treatment device and a secondary nanofiltration treatment device;
  • the primary nanofiltration treatment device is communicated with the ultrafiltration treatment device, and the ultrafiltration filtrate is passed into the primary nanofiltration treatment device for primary nanofiltration treatment to obtain a primary nanofiltration concentrate and a primary nanofiltration treatment device. grade nanofiltration filtrate;
  • the secondary nanofiltration processing device is respectively communicated with the primary nanofiltration processing device and the crystallization device, and the primary nanofiltration filtrate is passed into the secondary nanofiltration processing device to perform secondary nanofiltration processing to obtain A secondary nanofiltration concentrate and a secondary nanofiltration filtrate, the N-methylmorpholine-N-oxide is trapped in the secondary nanofiltration concentrate, and the secondary nanofiltration concentrate is passed through into the crystallization device for crystallization.
  • the present invention adopts the crystallization process technology, or membrane filtration and crystallization process combination technology to purify and reclaim NMMO in the lyocell fiber coagulation bath, and the method for purifying and reclaiming NMMO in the lyocell fiber coagulation bath by ion exchange resin, the obtained NMMO crystal purity High, even comparable to the purity of new NMMO products, it can be completely reused in lyocell production, and the total recovery rate of NMMO is high, almost no "three wastes" are generated during the recovery and purification process, and the cost of purification and recovery is low.
  • the purification process of the present invention is simple, suitable for industrial production, and is an efficient, simple and low-cost green NMMO purification method.
  • Fig. 1 is a schematic diagram of membrane treatment device in the purification system of N-methylmorpholine-N-oxide compound according to an embodiment of the present invention
  • Fig. 2 is the crystallization device schematic diagram in the purification system of the N-methylmorpholine-N-oxide compound of one embodiment of the present invention
  • Fig. 3 is the liquid chromatography spectrogram of the microporous filtrate of embodiment 2 of the present invention.
  • Fig. 4 is the liquid phase chromatogram of the ultrafiltration concentrated solution of the embodiment of the present invention 2;
  • Fig. 5 is the liquid phase chromatogram spectrogram of ultrafiltration filtrate of the embodiment of the present invention 2;
  • Fig. 6 is the liquid chromatogram spectrogram of embodiment 2 of the present invention primary nanofiltration filtrate
  • Fig. 7 is a liquid chromatogram of the first-stage nanofiltration concentrate of Example 2 of the present invention.
  • the invention provides a purification method of N-methylmorpholine-N-oxide, which is used for the purification of N-methylmorpholine-N-oxide in a lyocell fiber coagulation bath, comprising the following steps: The coagulation bath of Purcell fiber is cooled to crystallize between -20°C and 78°C to obtain the hydrate crystal of N-methylmorpholine-N-oxide.
  • 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.
  • N-methylmorpholine-N-oxide is usually used in the production of lyocell fiber as N-methylmorpholine -N-oxide aqueous solution is used as raw material, therefore, the N-methylmorpholine-N-oxide usually prepared in this field exists in the state of aqueous solution.
  • the present invention utilizes the crystal characteristics of NMMO hydrate, and by controlling the temperature-lowering crystallization conditions, N-methylmorpholine-N-oxide and water are combined in a specific ratio to form crystals, thereby achieving the purpose of separating impurities from the 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 for re-use in lyocell fiber production.
  • the lyocell fiber coagulation bath containing the above impurities can directly purify and recover NMMO by crystallization method, but due to the presence of sugar substances in the lyocell fiber coagulation bath, the viscosity of the crystallization liquid will be high, which will affect the crystallization process of NMMO hydrate and the crystallization of NMMO hydrate It is difficult to obtain NMMO hydrate crystals with high purity and high yield. Moreover, these impurities, especially sugar compounds, will all remain in the crystallization mother liquor, causing the crystallization mother liquor to have a high viscosity and difficult flow, and it is impossible to recrystallize the crystallization mother liquor to further recover the NMMO therein. Therefore, before crystallizing and purifying NMMO in the lyocell fiber coagulation bath, it is best to remove most of the sugar impurities and macromolecular impurities such as PAM in advance.
  • the present invention firstly removes sugar substances in the lyocell fiber coagulation bath, and at the same time removes molecules with larger molecular weights in the lyocell fiber coagulation bath, and then conducts cooling crystallization treatment.
  • the present invention uses membrane treatment (at least one of microfiltration, ultrafiltration and nanofiltration) to remove cellulose, hemicellulose, oligosaccharides, disaccharides and disaccharides in the lyocell fiber coagulation bath The above polysaccharides and some monosaccharides and other impurities.
  • this membrane treatment method can also remove all impurities such as the flocculant PAM, some small molecules with large molecular weights such as the reactants of PG and formaldehyde, and inorganic salts with divalent or higher valence.
  • the lyocell fiber coagulation bath is cooled and crystallized between -20°C and 78°C, which can avoid the influence of sugars and other impurities in the lyocell fiber coagulation bath on crystallization, and further improve the purity and purity of NMMO hydrate crystals. yield.
  • the lyocell fiber coagulation bath of the present invention is mixed with a coagulation aid to obtain a mixed solution for flocculation and sedimentation; then the mixed solution is subjected to at least one of microfiltration, ultrafiltration and nanofiltration.
  • Flocculation and sedimentation treatment can flocculate insoluble solids and colloids, and further separate solids through membrane treatment.
  • the mixed solution is first subjected to microfiltration to filter solids to obtain a microporous filtrate; the microporous filtrate is then subjected to ultrafiltration to obtain an ultrafiltration concentrate and an ultrafiltration filtrate.
  • the filtration precision of the microfiltration treatment is 0.5-5 microns, and the filtration precision of the ultrafiltration treatment is 1000-100000 molecular weight. In this way, microfiltration treatment can remove solids in the mixed solution, and ultrafiltration treatment can remove macromolecular soluble substances in the mixed solution, which can be carried out step by step, which can improve the efficiency of impurity removal and reduce the load of ultrafiltration treatment.
  • the content of NMMO in the ultrafiltration concentrate of the present invention and the ultrafiltration filtrate are basically the same, for example, 150-250 g/L.
  • the ultrafiltration concentrated liquid of the present invention is circulated back to the lyocell fiber coagulation bath for flocculation and sedimentation again.
  • the ultrafiltration filtrate is subjected to nanofiltration treatment to obtain a nanofiltration concentrate and a nanofiltration filtrate, and N-methylmorpholine-N-oxide is trapped in the nanofiltration concentrate.
  • the nanofiltration treatment includes primary nanofiltration treatment and secondary nanofiltration treatment, and the ultrafiltration filtrate is subjected to primary nanofiltration treatment to obtain a primary nanofiltration concentrate and a primary nanofiltration filtrate
  • the filtration accuracy of the primary nanofiltration treatment is, for example, 300-1000 molecular weight, that is, the primary nanofiltration treatment can intercept substances with a molecular weight greater than or equal to 300-1000, such as those with a molecular weight greater than or equal to 300, 400, 500, 700, 900, etc.
  • Substances such a first-level nanofiltration membrane traps polyvalent ions, pigments, metal complexes, polysaccharides and other sugars in the first-level nanofiltration concentrate, and the target recovery NMMO and monovalent salt enter the first-level nanofiltration filtration solution, so that NMMO can be further purified.
  • the primary nanofiltration filtrate is subjected to secondary nanofiltration treatment to obtain the secondary nanofiltration concentrate and the secondary nanofiltration filtrate, and N-methylmorpholine-N-oxide is trapped in the secondary nanofiltration concentrate Middle;
  • the filtration accuracy of the secondary nanofiltration treatment is 100-200 molecular weight, that is, the secondary nanofiltration treatment can intercept substances with a molecular weight greater than or equal to 100-200, such as substances with a molecular weight cutoff greater than or equal to 100, 150, 200, etc.
  • the target recovered NMMO is trapped in the secondary nanofiltration concentrate, and the monovalent salt and solvent water enter the secondary nanofiltration filtrate, so that the NMMO is further purified and initially concentrated.
  • the content of N-methylmorpholine-N-oxide in the primary nanofiltration concentrated liquid and the primary nanofiltration filtrate is basically the same, for example, 150-250 g/L.
  • the primary dialysis treatment When the content of NMMO in the primary nanofiltration concentrate after dialysis is reduced to an acceptable range, such as the primary nanofiltration concentrate After the primary dialysis treatment, the content of N-methylmorpholine-N-oxide is 0-10 g/L, the primary dialysis treatment can be stopped, and the concentrated liquid of the primary nanofiltration is discharged. At this time, all the obtained primary nanofiltration dialysates are mixed, wherein the content of N-methylmorpholine-N-oxide is generally 10-100 g/L. All the obtained primary nanofiltration dialyzate can be subjected to secondary nanofiltration treatment together with the primary nanofiltration filtrate.
  • the content of N-methylmorpholine-N-oxide in the secondary nanofiltration concentrated solution is, for example, 150 to 250 g/L, and the conductivity is 2 to 500us.
  • N-methylmorpholine In the secondary nanofiltration filtrate, N-methylmorpholine
  • the content of -N-oxide is, for example, 0-5 g/L, and the electrical conductivity is 2-300 us. At this time, there are still some monovalent salts in the secondary nanofiltration concentrated solution.
  • the secondary nanofiltration treatment can also use water to perform secondary dialysis treatment on the secondary nanofiltration concentrated solution to obtain Secondary nanofiltration dialysate; wherein, the number of secondary dialysis treatment is at least one time, for example, it can be 2 times, 4 times, 6 times, 8 times, etc.
  • the number of secondary dialysis treatments is mainly determined by the content of monovalent salts in the secondary nanofiltration concentrate, for example, the content of N-methylmorpholine-N-oxide in the secondary nanofiltration concentrate after secondary dialysis treatment is 150 ⁇ 250 g/L, the conductivity is 1 ⁇ 5us, the content of N-methylmorpholine-N-oxide in the secondary nanofiltration dialysate is 0 ⁇ 5 g/L, and the conductivity is 1 ⁇ 1000us, that is Secondary dialysis treatment may be discontinued.
  • the secondary nanofiltration filtrate and the secondary nanofiltration dialyzate can be subjected to reverse osmosis treatment to obtain a reverse osmosis concentrate and a reverse osmosis filtrate containing monovalent salt impurities, and the reverse osmosis filtrate is used as the above-mentioned primary
  • the dialysis treatment and the secondary dialysis treatment use water to save water resources and reduce waste water generation; the reverse osmosis concentrated liquid is discharged or further treated.
  • the present invention judges the concentration ratio of the reverse osmosis treatment according to the conductivity of the reverse osmosis filtrate, for example, the conductivity of the reverse osmosis filtrate is less than 1 us.
  • the secondary nanofiltration concentrate obtained through secondary nanofiltration treatment various low molecular weight impurities including PG and PG oxides still exist, and the HPLC analysis results show that there are still impurities in the secondary nanofiltration concentrate.
  • impurities such as PG and PG oxidation products and more than a dozen other unknown impurities, which need further purification before they can be better used in lyocell fiber production. Therefore, the second-stage nanofiltration concentrate of the present invention needs further crystallization treatment.
  • the secondary nanofiltration concentrate of the present invention is subjected to crystallization without secondary dialysis treatment
  • the present invention does not specifically limit that the crystallization process can only be carried out after the mixed solution has been subjected to all the steps of microfiltration, ultrafiltration, primary nanofiltration and secondary nanofiltration.
  • the microfiltration filtrate is cooled and crystallized
  • the ultrafiltration filtrate is cooled and crystallized
  • the nanofiltration concentrated solution is about to be cooled and crystallized; it is also possible to make the mixed solution go through microfiltration treatment, ultrafiltration treatment, first-level nanofiltration treatment, and second-level nanofiltration treatment.
  • Grade nanofiltration concentrated liquid is cooled and crystallized.
  • the liquid to be crystallized (such as lyocell fiber coagulation bath, microfiltration filtrate, ultrafiltration filtrate, primary nanofiltration concentrate or secondary nanofiltration concentration liquid) to be concentrated, so that the mass concentration of N-methylmorpholine-N-oxide in the liquid to be crystallized is 56.5% to 84.5%, so that the crystallization efficiency can be improved.
  • the concentration treatment method is evaporation, such as vacuum evaporation, vacuum evaporation, atmospheric pressure evaporation, and the like.
  • the present invention concentrates the liquid to be crystallized, and when the mass content of N-methylmorpholine-N-oxide in the obtained concentrated solution is 56.5%-72.2%, the concentrated solution is -20- Cool down and crystallize at 39°C, and the NMMO hydrate crystal obtained in this way is 2NMMO ⁇ 5H 2 O (ie NMMO ⁇ 2.5H 2 O); the mass content of N-methylmorpholine-N-oxide in the obtained concentrated solution At 72.2%-84.5% (excluding 72.2%), the concentrated solution is cooled and crystallized at 39-78°C (excluding 39°C), and the NMMO crystals thus obtained are NMMO ⁇ H 2 O.
  • the different concentrations of NMMO in the concentrated solution determine the different crystallization temperatures, and thus different NMMO hydrate crystals are obtained.
  • the present invention considers the cost of industrial purification and the convenience of operation, concentrates the liquid to be crystallized to a NMMO mass concentration of 56.5-72.2% or 66.5-72%, and concentrates the liquid at 25-40°C or 25-36 Temperature drop crystallization in °C range (final crystallization temperature is 25 °C and above). Under the optimal crystallization conditions, 2NMMO ⁇ 5H 2 O crystals with high purity and a crystallization yield of more than 60% can be obtained through primary crystallization; the higher the concentration of NMMO in the liquid before crystallization, the lower the crystallization termination temperature. The higher the crystallization rate of NMMO obtained.
  • Optimum crystallization conditions are used for crystallization. Different crystallization process conditions such as crystallization rate, cooling rate, and seed addition will affect the metastable supersaturation in the crystallization process, so it will affect the purity of NMMO in the crystal.
  • crystal seeds can be added during the crystallization process, and the amount of seed crystals added is more than 0.01% of the weight of N-methylmorpholine-N-oxide in the liquid to be crystallized, preferably 0.1-0.3 %between.
  • 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 of high-purity crushed crystals with uniform particle size as far as possible, and the particle size is, for example, 0.01-0.1 mm. Larger seed crystal particles or 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 crystal is generally determined according to the NMMO content in the liquid to be crystallized and the initial cooling temperature. In one embodiment, the seed crystal is added when the temperature of the solution is cooled to between 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, and the crystals are washed with a high-purity NMMO aqueous solution with a concentration of 59.5% to obtain NMMO crystals. Weigh and analyze content.
  • the primary crystallization can obtain very high-purity NMMO hydrate crystals, and add water to make an NMMO aqueous solution with a mass concentration of 19.8%.
  • the color is colorless and transparent, and the conductivity can reach 14.9 ⁇ s/cm.
  • the crystals obtained by the primary crystallization were added with water to prepare a certain concentration of NMMO aqueous solution, and then secondary crystallization (recrystallization) was carried out.
  • the crystals obtained by the secondary crystallization were analyzed and detected by liquid chromatography, and it was found that almost The various organic impurities existing in the original lyocell fiber coagulation bath cannot be detected, and the NMMO aqueous solution with a mass content of 50% is prepared by adding water, and its conductivity can be reduced to below 12.5 ⁇ s/cm. Analysis of the total sugar content in the crystallization mother liquor shows that the sugar content is very low, indicating that the lyocell fiber coagulation bath can remove most of the sugar impurities in it after membrane treatment.
  • the membrane-treated lyocell fiber coagulation bath removes macromolecular impurities such as oligosaccharides that affect the viscosity of the coagulation bath, greatly reduces the viscosity of the crystallization mother liquor, and enables the crystallization mother liquor to achieve multi-stage concentrated crystallization.
  • the mother liquor produced by the primary crystallization is evaporated by vacuum heating until the mass concentration of NMMO is 69-72%, and then the temperature is lowered to crystallize, and the crystallization rate is 80-85% using the optimal crystallization conditions, and the secondary crystallization crystallization rate is 80-85%.
  • the purity is slightly lower than that of primary crystallization, which can be returned and dissolved in the raw material of coagulation bath.
  • the total recovery rate of NMMO of primary crystallization and secondary crystallization can reach 96%. Increased total recovery of NMMO.
  • the crystallization method of the present invention includes: a lyocell fiber coagulation bath treated with a film with a NMMO mass concentration of 66.5-72% at a temperature of about 40° C., and cooling until the seed crystals are added and will not dissolve (this temperature is called the crystallization temperature), and then add a small amount of seed crystals, preferably small particle NMMO ⁇ 2.5H 2 O crushed crystals soaked in high-purity NMMO saturated solution in advance, these small particle crushed crystals in NMMO saturated solution Soak in water for at least 1 hour.
  • the amount of seed crystals added is 0-1% of the weight of NMMO in the coagulation bath, preferably 0.1-0.3%. After adding the seeds, continue to cool down slowly.
  • the cooling rate can be appropriately accelerated to 3-4°C/hour, and the crystallization termination temperature is 25°C.
  • the crystal particles obtained under this crystallization condition are larger, with uniform particle size distribution and low impurity content.
  • the crystal solution was quickly filtered, the mother liquor was collected and weighed, and the crystal was washed with a high-purity NMMO aqueous solution with a mass concentration of 59%.
  • the obtained crystal was a first-grade crystal.
  • the collected crystal was weighed and the crystal purity was analyzed. % aqueous solution, detect the total sugar content, the total amount of impurities, electrical conductivity and the content of copper and iron metal ions.
  • the present invention provides a method for purifying NMMO in Lyocell fiber coagulation bath by crystallization method.
  • membrane treatment is used to remove most of the sugar substances, PAM and other macromolecules that affect the coagulation bath viscosity in Lyocell fiber coagulation bath. Impurities, eliminate the adverse effects of these macromolecular impurities on crystallization, and improve the recovery rate of NMMO.
  • the membrane-treated lyocell fiber coagulation bath is reduced to 56.5-84.5% of the NMMO mass content by heating under reduced pressure, evaporating and concentrating, and high-purity NMMO hydrate crystals are obtained through crystallization.
  • the corresponding cooling crystallization operating temperature is -20-78°C.
  • the NMMO mass concentration in the coagulation bath after concentration is preferably controlled at 66.5-72%. Crystallization and purification can be carried out in a very suitable temperature range of 25-35° C., and 2NMMO ⁇ 5H 2 O crystals with high purity (72.2% NMMO content in crystals) and a crystallization yield of more than 60% can be obtained.
  • the present invention also provides a purification system of N-methylmorpholine-N-oxide, which is used for the purification of N-methylmorpholine-N-oxide in the lyocell fiber coagulation bath, comprising:
  • Crystallization device used for crystallization treatment of lyocell fiber coagulation bath
  • the control device is connected with the crystallization device to control the crystallization conditions in the crystallization device.
  • the purification system of N-methylmorpholine-N-oxide of the present invention also includes:
  • At least one of the microfiltration device, ultrafiltration treatment device and nanofiltration treatment device is communicated with the crystallization device and the control device, and the lyocell fiber coagulation bath is passed into the microfiltration device, ultrafiltration treatment device, and nanofiltration treatment device At least one of them is processed to obtain a filtrate, and the filtrate is passed into a crystallization device for crystallization treatment.
  • the purification system of N-methylmorpholine-N-oxide of the present invention also includes:
  • Flocculation settling device, lyocell fiber coagulation bath and coagulant aid are passed into the flocculation settling device to obtain mixed liquid for flocculation settling treatment;
  • the microfiltration device is communicated with the flocculation and sedimentation device, so that the mixed liquid is passed into the microfiltration device to filter solids and obtain microporous filtrate;
  • the ultrafiltration treatment device is communicated with the microfiltration device, and the microporous filtrate is passed into the ultrafiltration treatment device for ultrafiltration treatment to obtain an ultrafiltration concentrate and an ultrafiltration filtrate;
  • the nanofiltration treatment device is communicated with the ultrafiltration treatment device and the crystallization device respectively, and the ultrafiltration filtrate is passed into the nanofiltration treatment device for nanofiltration treatment to obtain a nanofiltration concentrate and a nanofiltration filtrate, N-methylmorpholine- N-oxides are trapped in the nanofiltration concentrate, and the nanofiltration concentrate is passed into a crystallization device for crystallization treatment.
  • the nanofiltration treatment device includes a primary nanofiltration treatment device and a secondary nanofiltration treatment device;
  • the primary nanofiltration processing device is connected with the ultrafiltration processing device, and the ultrafiltration filtrate is passed into the primary nanofiltration processing device for primary nanofiltration processing to obtain a primary nanofiltration concentrate and a primary nanofiltration filtrate;
  • the secondary nanofiltration treatment device is connected with the primary nanofiltration treatment device and the crystallization device respectively, and the primary nanofiltration filtrate is passed into the secondary nanofiltration treatment device for secondary nanofiltration treatment to obtain the secondary nanofiltration concentrated liquid and the secondary nanofiltration treatment device.
  • the first-stage nanofiltration filtrate, N-methylmorpholine-N-oxide is intercepted in the second-stage nanofiltration concentrate, and the second-stage nanofiltration concentrate is passed into a crystallization device for crystallization treatment.
  • the membrane treatment device in the purification system of N-methylmorpholine-N-oxide of the present invention is shown in Figure 1, and the lyocell fiber coagulation bath 101 and coagulation aid 102 are passed into the flocculation sedimentation In the device A, the mixed liquid is mixed for flocculation and sedimentation treatment; the microfiltration device B is connected with the flocculation and sedimentation device A, and the mixed liquid is passed into the microfiltration device B for microfiltration treatment to filter the solid 105 to obtain the microporous filtrate 106
  • the ultrafiltration treatment device C is communicated with the microfiltration treatment unit B, and the microporous filtrate 106 is passed into the ultrafiltration treatment unit C for ultrafiltration treatment to obtain the ultrafiltration concentrated solution 103 and the ultrafiltration filtrate 104.
  • the ultrafiltration concentrated liquid 103 of the present invention can be circulated back to the flocculation settling device A, mixed with the lyocell fiber coagulation bath 101, and flocculated and settled
  • the primary nanofiltration treatment device D is communicated with the ultrafiltration treatment device C, so that the ultrafiltration filtrate 104 is delivered to the primary nanofiltration treatment device D for primary nanofiltration treatment to obtain a primary nanofiltration concentrate 107 and a primary nanofiltration treatment device.
  • the nanofiltration filtrate 108; the secondary nanofiltration treatment device E communicates with the primary nanofiltration treatment device D, so that the primary nanofiltration filtrate 108 is delivered to the secondary nanofiltration treatment device E for secondary nanofiltration treatment , to obtain the secondary nanofiltration concentrate 109 and the secondary nanofiltration filtrate 110.
  • the reverse osmosis device F communicates with the secondary nanofiltration treatment device E, so as to transport the secondary nanofiltration filtrate 110 to the reverse osmosis device F for reverse osmosis treatment to obtain a reverse osmosis concentrate 111 containing monovalent salt impurities And reverse osmosis filtrate 112.
  • the reverse osmosis filtrate 112 can be recycled back to the first-level nanofiltration treatment device D and the second-level nanofiltration treatment device E, as water for the first-level dialysis treatment and the second-level dialysis treatment, so as to save water resources and reduce waste water production; reverse osmosis concentration Liquid 111 is discharged or further processed.
  • the present invention does not specifically limit the membrane treatment device in the purification system of N-methylmorpholine-N-oxide compound to include the above-mentioned units.
  • the membrane treatment device may not include the above-mentioned microfiltration device B; in another In an embodiment, the membrane treatment device may not include the above-mentioned primary nanofiltration treatment device D and secondary nanofiltration treatment device E, and may be adjusted as required.
  • the crystallization device in the purification system of N-methylmorpholine-N-oxide compound of the present invention is as shown in Figure 2, and the primary concentration device 1 can be combined with the secondary nanofiltration treatment device E and the primary crystallization device.
  • the device 2 is connected, and the secondary nanofiltration concentrated liquid 109 (or lyocell fiber coagulation bath 101) is passed into the primary concentration device 1 for concentration treatment.
  • 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 recrystallized crystal 91 was analyzed and detected by liquid chromatography, and the results showed that various organic impurities in the original lyocell fiber coagulation bath could hardly be detected in the NMMO crystal, and the NMMO aqueous solution with a mass content of 50% was prepared by adding water. Can be reduced to below 2.5 ⁇ 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.
  • Total sugar content detection The total sugar analysis method reported in Chen Huiru's Donghua University doctoral thesis "Research on lyocell fiber spun from cheap high hemicellulose content pulp”.
  • NMMO crystal purity detection (impurity residual rate): the purity of the obtained NMMO hydrate crystal is represented by the impurity residual rate, and the determination method is: adjusting the NMMO mass concentration in the lyocell fiber coagulation bath raw material to 19.8%, to obtain the lyocell fiber coagulation bath raw material solution; Add water to the NMMO hydrate crystal obtained by crystallization to prepare an aqueous solution with a mass concentration of NMMO of 19.8% to obtain a crystal solution; use HPLC to measure the spectrograms of the lyocell fiber coagulation bath raw material solution and the crystal solution, and the UV detection wavelengths are 200nm and 220nm respectively.
  • the ratio of the sum of the integrated area of all impurity peaks in the crystal solution spectrum to the sum of the integrated area of all impurity peaks in the raw material solution spectrum of the lyocell fiber coagulation bath is calculated respectively to obtain the residual crystal impurity rate at each UV detection wavelength.
  • Residual rate of crystal impurities (sum of integral area of all impurity peaks in NMMO crystal solution spectrum) ⁇ (sum of integral area of all impurity peaks in raw material solution spectrum of lyocell fiber coagulation bath)
  • the performance of the lyocell fiber coagulation bath without membrane combination desugar pretreatment is as follows:
  • the above-mentioned lyocell fiber coagulation bath stock solution was heated and evaporated under reduced pressure, concentrated to NMMO mass concentration of 68.0% and 69.9%, and then cooled and crystallized respectively.
  • the concentrated solution of the coagulation bath stock solution of each concentration was cooled to 37°C, and the NMMO concentration was 68.0% and 69.9%.
  • the amount added is 0.15% of the weight of NMMO in the coagulation bath, after adding the seed crystal, control the cooling rate at 1-2°C/hour , until the temperature drops to 30°C, then speed up the cooling rate to 3-4°C/hour, the temperature drops to 25°C, and stop crystallization.
  • the obtained crystals and crystallization mother liquor were added with water respectively to prepare an aqueous solution with a mass concentration of NMMO of 19.8%, and then various analyzes and tests were performed. It was found that crystallization can very effectively remove various organic impurities contained in the coagulation bath, and the obtained NMMO crystal The purity is very high. In addition, the crystallization can also remove the metal and non-metal ions contained in the coagulation bath, which greatly reduces the conductivity of the NMMO crystal. Therefore, the crystallization can be used as a method and means for purifying and recovering NMMO from the lyocell coagulation bath, but it has not been removed by membrane combination.
  • the sugar pretreated lyocell coagulation bath contains too much sugar, so the crystallization mother liquor has a very high viscosity and can hardly flow.
  • the crystallization rate is high, it is difficult to separate the crystal from the crystallization mother liquor, and the crystallization mother liquor cannot be crystallized again.
  • Table 1 below shows the data of NMMO crystallization and purification in coagulation bath of lyocell fiber without membrane combination pretreatment.
  • crystallization can obtain NMMO hydrate crystals with high purity, which can be separated from various impurities contained in the lyocell fiber coagulation bath. Crystallization is difficult, and the crystal particles are small, but the impurity content in the obtained crystal is very low. The main reason may be that the impurity structure in the coagulation bath is very different from that of NMMO, which makes it difficult for these impurities to enter or occlude into the NMMO crystal. In addition, the electrical conductivity of the NMMO concentration 19.8% aqueous solution prepared by crystallization is also greatly reduced, but with the increase of the crystallization rate, the crystal purity decreases slightly.
  • this example shows that after concentration and crystallization in the lyocell coagulation bath without membrane combination treatment, the viscosity of the crystallization mother liquor is very high, it is difficult to separate the crystal from the crystallization mother liquor, the crystallization mother liquor cannot be concentrated and crystallized again, and the recovery rate of NMMO is low.
  • Step 1 mixing the lyocell fiber coagulation bath with the acrylamide coagulation aid for flocculation and sedimentation;
  • step 2 the mixed solution obtained in step 1 is subjected to microporous filtration, and the microporous filtration accuracy is 0.5 to 5 microns, so as to intercept the solid matter and obtain the microporous filtrate; the liquid chromatogram of the obtained microporous filtrate is shown in Figure 3 Shown, wherein peak 1 is NMMO characteristic peak, all the other are impurity peaks.
  • Step 3 subjecting the microporous filtrate to ultrafiltration, with a molecular weight cut-off of 10,000-30,000 Daltons, to intercept small particle size solids, colloids, and macromolecular impurities, and the obtained ultrafiltration concentrate is 5% of the volume of the microporous filtrate , the ultrafiltration concentrate returns to Step 1 for repeated flocculation.
  • the liquid chromatogram of gained ultrafiltration concentrated solution is as shown in Figure 4, and the liquid chromatogram of ultrafiltration filtrate is as shown in Figure 5, and wherein peak 1 is NMMO characteristic peak, compares Fig. 5 and Fig. 3 as can be seen , the purity of NMMO in the ultrafiltration filtrate was improved.
  • Step 4 the ultrafiltration filtrate is subjected to primary nanofiltration treatment, the molecular weight cut-off is 500-800 Daltons, and N-methylmorpholine-N-oxide and monovalent salt enter the primary nanofiltration filtrate , pigments, polysaccharides, metal complexes, high-valent ions and other middle-molecular impurities are intercepted to obtain a first-level nanofiltration concentrate with a concentration factor of 20 times; then add water 17 times the volume of the first-level nanofiltration concentrate As primary dialysis water, the NMMO in the primary nanofiltration concentrate is dialyzed into the primary nanofiltration dialysate, the NMMO content in the primary nanofiltration concentrate is reduced to below 1 g/L, and the primary nanofiltration concentrate Efflux.
  • the liquid chromatogram of the first-level nanofiltration filtrate of gained is as shown in Figure 6, and the liquid chromatogram of the first-level nanofiltration concentrate after the dialysis treatment is as shown in Figure 7, wherein peak 1 is the NMMO characteristic peak .
  • peak 1 is the NMMO characteristic peak .
  • there is less residual NMMO in the first-stage nanofiltration concentrate so that there will be no waste of NMMO, and the recovery efficiency of NMMO can be improved. Comparing Figure 6 and Figure 5, it can be seen that the purity of NMMO in the primary nanofiltration filtrate is improved, but there are still a few impurities in the primary nanofiltration filtrate.
  • Step 5 the mixed solution of the primary nanofiltration filtrate and the primary nanofiltration dialyzate is subjected to secondary nanofiltration treatment, the molecular weight cut-off is 300 Daltons, and the monovalent salt enters the secondary nanofiltration filtrate, N -Methylmorpholine-N-oxide is intercepted by the nanofiltration membrane; when the secondary nanofiltration concentrate is concentrated to 0.2 times, add water 10 times the volume of the secondary nanofiltration concentrate The monovalent salt in the solution is dialyzed into the secondary nanofiltration dialysate, so that the conductivity of the secondary nanofiltration concentrated solution is reduced to below 10us; at this time, the conductivity of the secondary nanofiltration filtrate mixed with the secondary nanofiltration dialysate The rate is below 1000us.
  • Step 6 mix the secondary nanofiltration filtrate with the secondary nanofiltration dialysate and perform reverse osmosis treatment to ensure that the conductivity of the reverse osmosis filtrate is less than 1us, and the reverse osmosis filtrate can be used as the primary dialysis treatment and the secondary The dialysis water used for dialysis treatment.
  • Table 2 below shows the NMMO content data in each of the above stages.
  • the above-mentioned secondary nanofiltration concentrated solution (without secondary nanofiltration dialysis treatment) was formulated into a solution with a NMMO mass content of 19.8%, and the performance of the solution was determined as follows:
  • N-methylmorpholine content 130ppm
  • Iron ion content 0.001ppm
  • Chroma 180.
  • HPLC analysis shows that there are still more than a dozen impurity peaks with different contents in the lyocell fiber coagulation bath after membrane combination treatment.
  • the following examples of the present invention all use the second-stage nanofiltration concentrate after membrane combination treatment in this example as raw material for crystallization and purification.
  • This embodiment mainly analyzes the influence of NMMO crystallization rate on the purity of NMMO crystals.
  • Example 2 The lyocell coagulation bath treated by membrane combination desugaring was heated and evaporated in vacuum, concentrated to NMMO mass concentrations of 63.5%, 65.2%, 66.5%, 67.9% and 69.2%, and then cooled and crystallized respectively.
  • the concentrated solution starts to cool down at 37°C.
  • the concentration of NMMO is 63.5%, 65.2%, 66.5%, 67.9% and 69.2%
  • the temperature of the solution drops to 31.2°C, 32.1°C, 33.2°C, 34.2°C and 35.1°C respectively, add pre-soaked in NMMO
  • the seed crystal in the saturated solution is added in an amount of 0.15% of the mass of NMMO in the coagulation bath concentrate.
  • NMMO crystals with high purity can be obtained by crystallization, which can be separated from various impurities in the lyocell fiber coagulation bath, and the electrical conductivity is also greatly reduced.
  • the residual impurity rate remains basically unchanged, the crystallization rate is greater than 52%, and the crystal conductivity increases slightly with the increase of the crystallization rate.
  • This embodiment mainly analyzes the influence of crystallization rate on the purity of NMMO crystals.
  • the lyocell coagulation bath pretreated by the membrane combination in Example 2 was heated and evaporated in vacuum, concentrated to a NMMO mass concentration of 69.2%, and when the temperature of the coagulation bath concentrate dropped to 34.2°C, NMMO seed crystals pre-soaked in NMMO saturated solution were added, and the seed crystals were added The amount is 0.15% of the mass of NMMO in the concentrated solution. Divide the concentrated solution into 4 parts. After adding seed crystals (34.2°C), carry out crystallization according to the following cooling and cooling rates respectively. The crystallization solution is lowered to 25°C and suction filtered. According to the embodiment 3 ways to handle crystals.
  • Cooling rate 2 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 4°C/hour.
  • NMMO crystals were added with water to prepare an NMMO aqueous solution with a mass concentration of 19.8%, and then various detection and analysis were performed.
  • Table 4 shows the influence data of the cooling rate on the purity of NMMO crystals.
  • the cooling rate should not be too fast, and it is better to control it at 1-2/hour, otherwise the crystal purity will decrease slightly, and the electrical conductivity will increase slightly;
  • the cooling rate can be appropriately accelerated.
  • the main reason is that the solubility of NMMO crystals changes greatly with temperature in the high temperature area, 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; in the late stage of crystallization, the crystallization temperature is low, The crystal solubility slows down with temperature, so the cooling rate can be appropriately accelerated.
  • This embodiment mainly analyzes the effect of whether or not the seed crystal is added and the amount added on the particle size and crystal purity of NMMO crystals.
  • NMMO seed crystals the percentage of the NMMO mass in the concentrated solution in which the amount of seed crystals added is: 0 (without adding crystal seeds), 0.05%, 0.1%, 0.2%, 0.3% and 0.6%, and then crystallized in the manner of Example 3 and process crystals.
  • NMMO crystals Add water to the obtained NMMO crystals to prepare an aqueous solution with a mass concentration of NMMO of 19.8%, and then perform various detection and analysis.
  • Table 5 shows the effect data of the amount of seed crystals added on the purity and particle size of NMMO crystals.
  • the amount of seed added has a greater impact on the crystal particle size.
  • the grain size distribution is uneven, indicating that the amount of seed is few and the solution
  • the supersaturation of the system is still relatively large, and small crystal nuclei will spontaneously precipitate, and the purity of the resulting crystals is also slightly lower; if the amount of seed crystals added is sufficient, the distribution of crystal particles is relatively uniform, and the purity of the crystals is high.
  • This embodiment mainly analyzes the impact of secondary crystallization (recrystallization) on the purity of NMMO crystals.
  • the lyocell coagulation bath pretreated by the membrane combination of Example 2 was concentrated to an NMMO mass concentration of 69.2%, and then crystallized and purified (primary crystallization), and the crystal obtained by the primary crystallization was prepared by adding water to a concentration of 69.9%.
  • the NMMO aqueous solution is recrystallized according to the process in Example 3, the primary crystallization crystals and the recrystallization crystals are weighed to calculate the crystallization rate, and the crystal purity (residual impurity rate) is analyzed and detected.
  • the crystals obtained by primary crystallization and recrystallization were respectively added with water to prepare an aqueous solution with an NMMO concentration of 19.8%, and then various analysis and detection were performed.
  • Table 6 shows the impact data of recrystallization on the purity of NMMO crystals.
  • recrystallization can further purify NMMO, further reduce the content of organic impurities in NMMO crystals, and reduce the conductivity of NMMO crystals to 12.4 ⁇ s/cm.
  • This example mainly analyzes the effect of recovering NMMO in the remaining mother liquor of primary crystallization through secondary crystallization.
  • Example 6 The mother liquor separated from the primary crystallization of the lyocell coagulation bath concentrated solution in Example 6 was evaporated and concentrated under reduced pressure to a NMMO mass concentration of 70.1%, and crystallized according to the crystallization process conditions in Example 3 (adding seed crystals when the temperature of the mother liquor was 35.3° C. ). Add water to the obtained crystals to prepare an aqueous solution with a mass concentration of NMMO of 19.8%, and then perform various analyzes and tests. Table 7 shows the result data of recrystallization of the primary crystallization mother liquor of the lyocell fiber coagulation bath concentrate.
  • the primary crystallization mother liquor was concentrated again and then crystallized.
  • the crystallization rate reached 84%, the purity of the obtained crystals was still high.
  • the lyocell fiber coagulation bath can recover 96% of the NMMO in the lyocell fiber coagulation bath through secondary crystallization; further, the viscosity of the secondary crystallization mother liquor is still not high. If you want to further increase the recovery rate of NNMO crystallization, you can continue to process the secondary crystallization.
  • the mother liquor is concentrated and crystallized, or the crystallization rate of the primary and secondary crystals is further increased.
  • the present invention provides a method for purifying NMMO in a lyocell fiber coagulation bath.
  • the method adopts a crystallization purification method for purification and recovery, and the crystallization operation temperature is close to normal temperature (25-35° C.).
  • the HPLC analysis and detection results show that through this method
  • the purity of NMMO obtained by the crystallization process method provided by the invention is very high, and more than a dozen organic impurities in the lyocell coagulation bath, including PG, PG oxides, sugars, etc., are almost completely removed, and the purity of recovered and purified NMMO is significantly higher than that usually used at present.
  • the NMMO purified and recovered by the advanced ion exchange resin method has high purity, even similar to the purity of new NMMO products, and all kinds of impurities that cannot be removed by ion exchange resin can be removed, which solves the problem that lyocell cannot be removed by the current ion exchange resin purification coagulation bath process There are many impurities in the spinning system, which lead to long-term accumulation and even affect the quality of lyocell spinning.
  • the combination of membrane treatment and crystallization process can further improve the recovery rate of NMMO, and can make the purification process easier, which is suitable for industrial production.
  • the resulting crystallization mother liquor containing a large amount of impurities can be processed by incineration (TO). Since the recovery and purification method of the present invention does not use ion exchange resins, it also completely solves the current purification process using ion exchange resins. Environmental problems such as high-salt, high-COD waste water and waste ion exchange resins are faced. In addition, the crystallization purification process provided by the present invention can remove almost all impurities contained in the lyocell coagulation bath, and there will be no impurities that cannot be removed in the spinning process.
  • TO incineration
  • the fibrillation problem existing in lyocell fiber is a green, low production cost, and efficient method for recovering and purifying NMMO in lyocell fiber coagulation bath.

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  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

本发明公开了一种N-甲基吗啉-N-氧化物的纯化方法、***及得到的N-甲基吗啉-N-氧化物，用于回收提纯莱赛尔纤维凝固浴中NMMO，包括：将莱赛尔纤维凝固浴经过絮凝、微滤、超滤与纳滤膜处理，脱除悬浮物、重金属离子、重金属络合物、多糖类物质等大分子杂质后在-20℃至78℃之间进行降温结晶，得到NMMO水合物晶体。由本发明方法得到的NMMO水合晶体，不含有凝固浴中的PG及PG氧化产物、纤维素分解物如各种糖类、糖酮、糖酸、呋喃类、糠醛类、酚类等和NMMO分解物，也不含有各种金属离子和阴离子，该晶体加水配制成浓度为19.8％的NMMO水溶液，电导率在14.8μs/cm左右，将一级结晶的NMMO晶体加水再次结晶，可得纯度更高的NMMO晶体，加水配制19.8％的NMMO水溶液，电导率降至12.4μs/cm以下。

Description

N-甲基吗啉-N-氧化物的纯化方法、***及得到的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***以及利用上述方法和***得到的N-甲基吗啉-N-氧化物。
背景技术
莱赛尔(lyocell)纤维是通过把纤维素浆粕直接溶解在氧化甲基吗啉(N-甲基吗啉-N-氧化物，NMMO)和水的混合溶剂中，进行干喷、湿纺而制得的一种人造纤维素纤维，其中，析出莱赛尔纤维后所得的液体被称为莱赛尔纤维凝固浴或者莱赛尔纤维凝固浴的排出液。lyocell纤维性能优良，其原料可再生，生产工艺简单，所用的NMMO溶剂无毒，产品废弃物生物可降解，不对环境产生污染，故被称为“21世纪具有良好发展前景的绿色环保纤维”。
目前lyocell纤维企业基本上采用含半纤维素3-5％的针叶林浆粕生产lyocell纤维，另外在溶解纤维素纤维的NMMO纺丝液中添加一些其它特种物质或者用其它特殊浆粕替代针叶林浆粕，可以纺出功能性纤维。美国专利US9,441,318使用竹浆粕可以制备防臭的lyocell纤维；美国专利US9,845,575发现在lyocell纺丝浴中溶入半纤维素，纺出的lyocell纤维可以很大程度上缓解lyocell纤维的原纤化问题，另一篇专利(US8,092,732)提到在lyocell纺丝浴中加入壳聚糖，纺出的lyocell纤维具有抗菌除臭功能；如果在lyocell纺丝浴中添加石墨烯(US10,351,971)、高岭土(US10,400,356)、珍珠粉(US8,633,120)等无机功能粉末材料，分别能够纺出导热性能优良、具有阻燃性能和闪光漂亮的功能性lyocell纤维。
上述Lyocell纤维生产工艺分两个部分，一是纤维素在NMMO中溶解纺丝工艺部分，另一是lyocell纺丝后莱赛尔纤维凝固浴或者莱赛尔纤维凝固浴的排出液中NMMO溶剂纯化回收工艺部分。
另外溶解纤维素的NMMO溶液还能够用来制备lyocell薄膜和胶片(US7,938,993)、lyocell无纺布(US8,420,004)、香烟过滤嘴材料(US10,306,919)等，这些生产工艺也同样会在制成相应的lyocell制品后，对lyocell凝固浴中的NMMO溶剂进行纯化回收。
详细而言，在lyocell生产中，100-110℃下纤维素浆粕首先溶解在质量浓度85％以上的NMMO水溶液，制成纤维素含量为10-14％的lyocell纺丝浴，然后干喷、湿纺法纺丝或成型加水制成相应的纤维素制品，同时得到NMMO质量浓度10-25％的lyocell纤维凝固浴。浆粕溶解在NMMO的过程中，NMMO和纤维素在受热状态下会发生比较复杂的化学分解反应，产生多种杂质，为了循环使用NMMO，需要脱除lyocell凝固浴中溶解的各类杂质。以目前应用最普遍的lyocell纤维短丝的纺丝为例，lyocell纺丝后的凝固浴中NMMO质量浓度一般在10-25％，颜色为棕黄色甚至酱油色，pH值7.5-9。浆粕在NMMO中的溶解需要在较高温度下进行，高温下NMMO有可能会分解成为N-甲基吗啉、吗啉、甲醛和含大π键共轭结构的化合物等杂质，在其分解过程中也会产生高活性的自由基，从而导致纤维素被氧化和纤维素链断裂分解，纤维素溶液中的金属离子如铜离子和铁离子等会催化加速NMMO的分解和纤维素的断裂，并加深纤维素溶液的颜色，纤维素断裂产物包括二糖以上的寡糖和单糖，同时糖类物质会分解生成如糖酮、糖酸、呋喃类、糠醛类、酚类等十几种杂质，加之这些分解产物之间还会进一步反应，据报道可生成多达20多种含显色基团的有机杂质(Rosenua T.,Potthast A.,Milacher W.,Adorjan I.,Hofinger A.and Kosma P.，Discoloration of cellulose solutions in N-methylmorpholine-N-oxide(Lyocell).Part 2:Isolation and identification of chromophores.Cellulose 2005,12:197-208)(郑玉成.Lyocell纤维生产中颜色变化的原因分析.合成纤维，2018，47(8)：17-23)。
如果凝固浴中的NMMO循环使用时不能有效脱除这些杂质，累积起来会对纺丝产生负面影响，尤其是对lyocell长丝生产损害更大；为了阻止NMMO分解和纤维素断裂，在NMMO溶解纤维素过程中需要加入包括没食子酸丙酯(PG)和羟胺等在内的多种复合稳定剂，这些稳定剂以及没食子酸丙酯(PG)中和自由基后被氧化的产物和PG与甲醛反应后的缩合产物都有较深的颜色，溶液中残留过多这些显色基团会使lyocell纤维色度加深，影响产品白度。此外为了脱除凝固浴NMMO中残留的悬浮物质，降低溶液的浊度，lyocell生产中通常加入一定量的絮凝剂聚丙烯酰胺(PAM)进行絮凝沉降，然后再粗滤脱除，但仍然有一定量半纤维素、寡糖等没有被脱除，同时还有少量PAM残留在凝固浴的NMMO溶液中，因此lyocell凝固浴中杂质成分很复杂，在其中 NMMO溶剂回收再循环使用时，必须纯化脱除溶解在凝固浴NMMO溶剂中的上述这些杂质。
目前凝固浴中NMMO纯化回收工艺主要采用阴离子交换树脂和阳离子交换树脂进行纯化，离子交换树脂纯化回收工艺存在不少问题：回收纯化后的NMMO仍然含有较多杂质，纯度较低。凝固浴中含有的不少杂质在酸碱环境下不能形成离子，故无法通过离子交换树脂完全脱除，如没食子酸丙酯(PG)及其反应后的产物、糖类及分解产物和NMMO受热分解产物等杂质，因此仅采用离子交换树脂提纯回收的NMMO中仍然会残留不少杂质，这种方法纯化回收的NMMO很大可能会影响lyocell长丝生产。本发明申请人曾对国内多家lyocell生产商采用离子交换树脂法提纯处理前后的lyocell凝固浴，进行液相色谱对比分析，发现凝固浴中包括PG氧化物在内的十几种杂质无法通过离子交换树脂处理脱除，此外还有多种杂质如PG等不能完全被离子交换树脂脱除，因此仅通过离子交换树脂提纯处理后的NMMO纯度不高。
另外目前绝大多数lyocell生产商仅能使用半纤维素含量很低的针叶林浆粕，而便宜易得的阔叶林浆粕则不能使用，主要是因为阔叶林浆粕含半纤维素较多，半纤维素在lyocell生产过程中更容易分解，产生更多的杂质，并在提纯回收的NMMO中大量积累，严重影响lyocell稳定生产，同样如果在lyocell纺丝浴中加入壳聚糖、半纤维素、高岭土、石墨烯、珍珠粉等易分解物质或无机功能材料，也会因为这些添加材料造成纺丝过程产生更多的杂质，而仅采用离子交换树脂提纯回收NMMO的方法，又无法脱除这些杂质，这些杂质就会在纺丝***中逐渐积累，当浓度积累到一定的量时就可能会严重影响上述lyocell功能纤维的生产。
⑵阴离子交换树脂和阳离子交换树脂处理过程产生的高盐高COD废水量较大，存在“三废”污染问题。失活的离子交换树脂需要再生，阳离子交换树脂需要4-6倍树脂体积的4-6％浓度的盐酸水溶液再生，阴离子交换树脂需要4-6倍树脂体积的4-6％的NaOH水溶液再生，树脂再生废液中不仅含盐量高，而且还含有大量有机物杂质，处理起来成本较高。通常生产1吨lyocell纤维就要产生10-15吨左右的树脂再生废液，尽管与粘胶纤维相比，lyocell纤维产生的废水量只有粘胶纤维的10％，但废水产生量仍然是非常巨大的。
⑶生产成本较高。适于lyocell凝固浴NMMO纯化处理的离子交换树脂 价格昂贵，寿命仅1-2年，分摊到每吨lyocell纤维成本大约在500元，按照国家危废分类名录，失效报废的离子交换树脂被列为危险废物，必须交有资质的环保公司处理，费用同样非常高，再生离子交换树脂产生的高盐高COD废水处理成本也非常高。
因此，面对日益严峻的环保形势和生产成本压力，lyocell生产迫切需要更加清洁环保的、提纯效果更好的、成本更低的凝固浴中NMMO纯化回收方法。
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、***及得到的N-甲基吗啉-N-氧化物，以克服现有技术中lyocell纤维凝固浴中NMMO提纯成本高、提纯方法欠环保，提纯得到NMMO纯度不高等缺陷。
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，用于莱赛尔纤维凝固浴中N-甲基吗啉-N-氧化物的纯化，包括如下步骤：将莱赛尔纤维凝固浴在-20℃～78℃之间进行降温结晶，得到N-甲基吗啉-N-氧化物的水合物晶体。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，其中，所述莱赛尔纤维凝固浴在进行降温结晶前还包括：除去所述莱赛尔纤维凝固浴中的糖类物质。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，其中，所述莱赛尔纤维凝固浴在进行降温结晶前还包括：将所述莱赛尔纤维凝固浴进行微滤处理、超滤处理和纳滤处理中的至少一种。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，其中，所述莱赛尔纤维凝固浴在进行降温结晶前还包括：将所述莱赛尔纤维凝固浴与助凝剂混合得到混合液，以进行絮凝沉降；然后将所述混合液进行微滤处理、超滤处理和纳滤处理中的至少一种。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，其中，所述莱赛尔纤维凝固浴在降温结晶前进行浓缩处理，使所述莱赛尔纤维凝固浴中N-甲基吗啉-N-氧化物的质量浓度为56.5％～84.5％，然后进行降温结晶。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，其中，所述浓缩处理使所述莱赛尔纤维凝固浴中N-甲基吗啉-N-氧化物的质量浓度为56.5-72.2％，降温结晶的温度为25-40℃。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，其中，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，其中，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莱赛尔纤维凝固浴中N-甲基吗啉-N-氧化物重量的0.01％以上。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，其中，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-氧化物水合物晶体和结晶母液，所述结晶母液经浓缩后进行二级降温结晶。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，其中，所述混合液进行微滤处理得到微孔过滤液；所述微孔过滤液进行所述超滤处理，得到超滤浓缩液和超滤滤清液；所述超滤滤清液进行所述降温结晶；
其中，所述微滤处理的过滤精度为0.5～5微米；所述超滤处理的过滤精度为1000～100000分子量。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，其中，所述超滤滤清液先进行一级纳滤处理，得到一级纳滤浓缩液和一级纳滤滤清液，然后使所述一级纳滤滤清液进行所述降温结晶；
其中，所述一级纳滤处理的过滤精度为300-1000分子量。
本发明所述的N-甲基吗啉-N-氧化物的纯化方法，其中，所述一级纳滤滤清液先进行所述二级纳滤处理，得到二级纳滤浓缩液和二级纳滤滤清液，所述N-甲基吗啉-N-氧化物被截留于所述二级纳滤浓缩液中，然后使所述二级纳滤浓缩液进行所述降温结晶；
其中，所述二级纳滤处理的过滤精度为100-200分子量。
为了达到上述目的，本发明还提供了上述的纯化方法得到的N-甲基吗啉-N-氧化物水合物晶体。
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***，用于莱赛尔纤维凝固浴中N-甲基吗啉-N-氧化物的纯化，包括：
结晶装置，用于所述莱赛尔纤维凝固浴的结晶处理；
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***，其中，还包括：
微滤装置、超滤处理装置与纳滤处理装置中的至少一种，与所述结晶装置和控制装置连通，所述莱赛尔纤维凝固浴通入所述微滤装置、超滤处理装置、纳滤处理装置中的至少一种进行处理，得到过滤液，所述过滤液通入所述结晶装置进行结晶处理。
本发明所述的N-甲基吗啉-N-氧化物的纯化***，其中，还包括：
絮凝沉降装置，所述莱赛尔纤维凝固浴与助凝剂通入所述絮凝沉降装置中，得到混合液，以进行絮凝沉降处理；
该微滤装置与所述絮凝沉降装置连通，以将所述混合液通入所述微滤装置，以过滤固形物，得到微孔过滤液；
该超滤处理装置与所述微滤装置连通，所述微孔过滤液通入所述超滤处理装置进行超滤处理，得到超滤浓缩液和超滤滤清液；
该纳滤处理装置与所述超滤处理装置和结晶装置分别连通，所述超滤滤清液通入所述纳滤处理装置进行纳滤处理，得到纳滤浓缩液和纳滤滤清液，所述N-甲基吗啉-N-氧化物被截留于所述纳滤浓缩液中，所述纳滤浓缩液通入所述结晶装置进行结晶处理。
本发明所述的N-甲基吗啉-N-氧化物的纯化***，其中，该纳滤处理装置包括一级纳滤处理装置和二级纳滤处理装置；
所述一级纳滤处理装置与所述超滤处理装置连通，所述超滤滤清液通入所述一级纳滤处理装置进行一级纳滤处理，得到一级纳滤浓缩液和一级纳滤滤清液；
所述二级纳滤处理装置与所述一级纳滤处理装置和结晶装置分别连通，所述一级纳滤滤清液通入所述二级纳滤处理装置进行二级纳滤处理，得到二级纳滤浓缩液和二级纳滤滤清液，所述N-甲基吗啉-N-氧化物被截留于所述二级纳滤浓缩液中，所述二级纳滤浓缩液通入所述结晶装置进行结晶处理。
本发明的有益效果：
本发明采用结晶工艺技术，或者膜过滤与结晶工艺相结合技术对lyocell纤维凝固浴中NMMO进行提纯回收，与离子交换树脂提纯回收lyocell纤维凝固浴中NMMO的方法相比，所得到的NMMO晶体纯度高，甚至与NMMO新品纯度相当，完全可以再用于lyocell生产，而且NMMO总回收率高，回收提纯过程几乎无“三废”生成，提纯回收成本低。
另外，本发明提纯工艺简单，适于工业化生产，是一种高效简单低成本的绿色NMMO提纯方法。
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***中膜处理装置示意图；
图2为本发明一实施方式的N-甲基吗啉-N-氧化物的纯化***中结晶装置示意图；
图3为本发明实施例2微孔过滤液的液相色谱谱图；
图4为本发明实施例2超滤浓缩液的液相色谱谱图；
图5为本发明实施例2超滤滤清液的液相色谱谱图；
图6为本发明实施例2一级纳滤滤清液的液相色谱谱图；
图7为本发明实施例2一级纳滤浓缩液的液相色谱谱图。
其中，附图标记：
101莱赛尔纤维凝固浴
102助凝剂
103超滤浓缩液
104超滤滤清液
105固形物
106微孔过滤液
107一级纳滤浓缩液
108一级纳滤滤清液
109二级纳滤浓缩液
110二级纳滤滤清液
111反渗透浓缩液
112反渗透滤清液
A絮凝沉降装置
B微孔过滤装置
C超滤处理装置
D一级纳滤处理装置
E二级纳滤处理装置
F反渗透装置
1一级浓缩装置
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例作详细说明，本实施例在以本发明技术方案为前提下进行实施，给出了详细的实施方式和过程，但本发明的保护范围不限于下述的实施例，下列实施例中未注明具体条件的实验方法，通常按照常规条件。
本发明提供了一种N-甲基吗啉-N-氧化物的纯化方法，用于莱赛尔纤维凝固浴中N-甲基吗啉-N-氧化物的纯化，包括如下步骤：将莱赛尔纤维凝固浴在 -20℃～78℃之间进行降温结晶，得到N-甲基吗啉-N-氧化物的水合物晶体。
lyocell纤维凝固浴中杂质组分比较复杂，其中除了含有质量含量为10-25％的NMMO外，还含较大量的糖类杂质如寡糖、多糖和单糖等，糖类分解产物如糠醛类杂质，少量残留的絮凝剂PAM，一定量的PG、PG氧化物及PG与甲醛反应物等杂质，NMMO分解产物如N-甲基吗啉、吗啉等杂质，另外也含有多种NMMO和糖类分解物反应产生的其它不明杂质。
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。
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，N-甲基吗啉-N-氧化物用于lyocell纤维生产通常也是以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NMMO水合物的晶体特性，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，以再用于lyocell纤维生产。
含有上述杂质的lyocell纤维凝固浴可以直接通过结晶方法提纯回收NMMO，但是由于lyocell纤维凝固浴中糖类物质等的存在，会使得结晶液粘度较高，影响NMMO水合物结晶过程与NMMO水合物结晶的分离，难以高纯度、高收率得到NMMO水合物结晶。而且这些杂质尤其是糖类化合物会全部留在结晶母液中，造成结晶母液粘度很大，流动困难，无法对结晶母液再次进行结晶以进一步回收其中的NMMO。因此，在结晶纯化lyocell纤维凝固浴中NMMO之前，最好预先脱除其中绝大部分的糖类杂质和PAM等大分子杂质。
在一实施方式中，本发明先除去莱赛尔纤维凝固浴中的糖类物质，同时除去莱赛尔纤维凝固浴中分子量较大的分子等，然后再进行降温结晶处理。在另一实施方式中，本发明采用膜处理(微滤、超滤和纳滤中的至少一种)脱除 lyocell纤维凝固浴中的纤维素、半纤维素、寡糖、二糖和二糖以上的多糖以及部分单糖等杂质。同时，该膜处理方法也能够脱除全部的絮凝剂PAM、一些分子量较大的小分子如PG与甲醛的反应物等和二价及二价以上的无机盐等杂质。经过膜处理后的lyocell纤维凝固浴在-20℃～78℃之间进行降温结晶，如此可以避免lyocell纤维凝固浴中糖类物质和其他杂质对结晶的影响，进一步提高NMMO水合物晶体的纯度和收率。
在一实施方式中，本发明莱赛尔纤维凝固浴与助凝剂混合得到混合液，以进行絮凝沉降；然后将混合液进行微滤处理、超滤处理和纳滤处理中的至少一种。
絮凝沉降处理可以使不溶性固形物与胶体絮凝，进一步通过膜处理分离固形物。
在一实施方式中，混合液先进行微滤处理以过滤固形物，得到微孔过滤液；微孔过滤液再进行超滤处理，得到超滤浓缩液和超滤滤清液。在另一实施方式中，微滤处理的过滤精度为0.5～5微米，超滤处理的过滤精度为1000～100000分子量。如此，微滤处理可以除去混合液中的固形物，超滤处理可以除去混合液中的大分子可溶物质，分步进行，能够提高除杂效率，减少超滤处理的负载量。
本发明超滤浓缩液和超滤滤清液中NMMO的含量基本一致，例如为150～250克/升。为了提高NMMO的回收效率，在一实施方式中，本发明超滤浓缩液循环回莱赛尔纤维凝固浴中，再次进行絮凝沉降。
在一实施方式中，超滤滤清液进行纳滤处理，得到纳滤浓缩液和纳滤滤清液，N-甲基吗啉-N-氧化物被截留于所述纳滤浓缩液中。
在另一实施方式中，纳滤处理包括一级纳滤处理和二级纳滤处理，超滤滤清液进行一级纳滤处理，得到一级纳滤浓缩液和一级纳滤滤清液；一级纳滤处理的过滤精度例如为300-1000分子量，即一级纳滤处理能够截留分子量大于或等于300-1000的物质，例如分子量大于或等于300，400，500，700，900等的物质，如此一级纳滤膜将多价离子、色素、金属络合物、多糖等糖类物质截留于一级纳滤浓缩液中，目标回收物NMMO与一价盐进入一级纳滤滤清液中，使得NMMO进一步得以纯化。一级纳滤滤清液进行二级纳滤处理，得到二级纳滤浓缩液和二级纳滤滤清液，N-甲基吗啉-N-氧化物被截留于二级纳滤 浓缩液中；二级纳滤处理的过滤精度为100-200分子量，即，二级纳滤处理能够截留分子量大于或等于100-200的物质，例如截留分子量大于或等于100，150，200等的物质，如此，目标回收物NMMO被截留于二级纳滤浓缩液中，一价盐和溶剂水进入二级纳滤滤清液，使得NMMO进一步被纯化且初步得以浓缩。
其中，一级纳滤浓缩液和一级纳滤滤清液中N-甲基吗啉-N-氧化物的含量基本一致，例如为150～250克/升。
为了提高NMMO的回收效率，减少处理过程中NMMO的浪费，一级纳滤处理还包括使用水对一级纳滤浓缩液进行一级透析处理，得到一级纳滤透析液，其中，一级透析处理的次数为至少一次，例如可以为2次、4次、6次、8次等。一级透析处理的次数主要根据透析后的一级纳滤浓缩液中NMMO的含量决定，当透析后的一级纳滤浓缩液中NMMO的含量降低到可接受范围，例如一级纳滤浓缩液进行一级透析处理后N-甲基吗啉-N-氧化物的含量为0～10克/升，即可停止一级透析处理，将一级纳滤浓缩液外排。此时，将得到的所有一级纳滤透析液混合，其中N-甲基吗啉-N-氧化物的含量一般为10～100克/升。所得到的所有一级纳滤透析液可以和一级纳滤滤清液共同进行二级纳滤处理。
二级纳滤浓缩液中N-甲基吗啉-N-氧化物的含量例如为150～250克/升，电导率为2～500us，二级纳滤滤清液中N-甲基吗啉-N-氧化物的含量例如为0～5克/升，电导率在2～300us。此时，二级纳滤浓缩液中尚存在部分一价盐，为了进一步纯化NMMO，除去NMMO中杂质，二级纳滤处理还可以使用水对二级纳滤浓缩液进行二级透析处理，得到二级纳滤透析液；其中，二级透析处理的次数为至少一次，例如可以为2次、4次、6次、8次等。二级透析处理的次数主要根据二级纳滤浓缩液中一价盐的含量决定，例如二级纳滤浓缩液进行二级透析处理后N-甲基吗啉-N-氧化物的含量为150～250克/升，电导率在1～5us，二级纳滤透析液中N-甲基吗啉-N-氧化物的含量为0～5克/升，电导率在1～1000us时，即可停止二级透析处理。
其中，二级纳滤滤清液和二级纳滤透析液可以进行反渗透处理，得到包含一价盐类杂质的反渗透浓缩液和反渗透滤清液，反渗透滤清液作为上述一级透析处理和所述二级透析处理用水，以节约水资源，并减少废水产生；反渗透浓 缩液外排或进一步处理。
在一实施方式中，本发明根据反渗透滤清液的电导率判断反渗透处理的浓缩倍数，例如使反渗透滤清液的电导率小于1us。
在一实施方式中，经过二级纳滤处理得到的二级纳滤浓缩液中，PG、PG氧化物在内的多种低分子量杂质仍然存在，HPLC分析结果显示二级纳滤浓缩液中仍然存在着相当量的PG和PG氧化产物等杂质以及十几种其它不明杂质，需要进一步提纯处理，才能更好地用于lyocell纤维生产中。因此，本发明二级纳滤浓缩液需要进一步进行结晶处理。在另一实施方式中，本发明二级纳滤浓缩液不经过二级透析处理即进行结晶处理
本发明并不特别限定必须使混合液经过微滤处理、超滤处理、一级纳滤处理和二级纳滤处理所有步骤后，才可以进行结晶处理。例如可以使混合液经过微滤处理后，即将微滤过滤液进行降温结晶；可以使混合液经过微滤处理和超滤处理后，即将超滤滤清液进行降温结晶；可以使混合液经过微滤处理、超滤处理和纳滤处理后，即将纳滤浓缩液进行降温结晶；也可以使混合液经过微滤处理、超滤处理、一级纳滤处理、二级纳滤处理后，将二级纳滤浓缩液进行降温结晶。
在一实施方式中，本发明在进行降温结晶前，对待结晶的液体(例如莱赛尔纤维凝固浴、微滤过滤液、超滤滤清液、一级纳滤浓缩液或二级纳滤浓缩液)进行浓缩处理，使待结晶的液体中N-甲基吗啉-N-氧化物的质量浓度为56.5％～84.5％，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，例如真空蒸发、减压蒸发、常压蒸发等。
在一实施方式中，本发明对即将结晶的液体进行浓缩处理，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水合物晶体为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水合物晶体。
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，将待结晶 的液体浓缩至NMMO质量浓度为56.5-72.2％或者66.5-72％，浓缩液在25-40℃或者25-36℃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60％以上的结晶收率；结晶前液体中NMMO的浓度越高，终止结晶温度越低，得到的NMMO结晶率越高。
采用最佳结晶条件进行结晶，结晶工艺条件如结晶率、降温速度、晶种加入等不同，会影响结晶过程的介稳态过饱和度，故对晶体中NMMO的纯度有影响。
在一实施方式中，在结晶的过程中可以加入晶种，晶种的加入量为即将结晶的液体中N-甲基吗啉-N-氧化物重量的0.01％以上，最好在0.1-0.3％之间。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。晶种颗粒较大或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即将结晶的液体中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，从滤瓶放出结晶母液，晶体用浓度为59.5％高纯度NMMO水溶液冲洗，得到NMMO晶体，称重并分析含量。
一级结晶可以得到纯度非常高的NMMO水合物晶体，加水配成质量浓度19.8％的NMMO水溶液，颜色为无色透明，电导率可达14.9μs/cm。为了得到更高纯度的NMMO，一级结晶得到的晶体加水配制成一定浓度NMMO水溶液，进行二次结晶(重结晶)，二次结晶得到的晶体经过液相色谱分析检测，发现在NMMO晶体中几乎无法检测出原来lyocell纤维凝固浴中存在的各种有机杂质，加水配制成质量含量为50％的NMMO水溶液，其电导率可降至12.5μs/cm以下。分析结晶母液中总含糖量，可得其含糖量很低，表明lyocell纤维凝固浴经过膜处理，可以脱除其中绝大部分糖类杂质。
经过膜处理的lyocell纤维凝固浴，脱除了影响凝固浴粘度的大分子杂质例如寡糖等，极大降低了结晶母液的粘度，使得结晶母液能够实现多级浓缩结晶。在本发明实施例中，将一级结晶产生的母液，通过真空加热蒸发至NMMO质量浓度为69-72％，然后降温结晶，采用最佳结晶条件，结晶率80-85％，二次结晶晶体纯度略低于一级结晶，可返回溶解于凝固浴原料中，一级结晶和二级结晶的NMMO总回收率可达96％，二级结晶母液粘度仍然不高，可以继续浓缩结晶，从而进一步提高NMMO总回收率。
在一具体实施方式中，本发明的结晶方法包括：将温度40℃左右的NMMO质量浓度在66.5-72％的膜处理过的lyocell纤维凝固浴，冷却降温到晶种加入后不会溶解(此时温度称为起晶温度)，然后加入少量晶种，晶种最好是事先浸泡在高纯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，晶种加入量为凝固浴中NMMO重量的0-1％，最好为0.1-0.3％，加入晶种后继续缓慢降温，从起晶温度到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℃。此结晶条件下得到的晶体颗粒较大，粒度分布均一，杂质含量低。晶体溶液迅速抽滤，母液收集称重，晶体用质量浓度59％高纯度NMMO水溶液继续冲洗晶体，得到的晶体为一级结晶晶体，收集晶体称重并分析晶体纯度，晶体加水配制成NMMO浓度19.8％的水 溶液，检测其中总含糖量、含杂质总量、电导率和铜铁金属离子含量等。如果希望得到纯度更高的NMMO，可以加水溶解一级结晶的晶体后，再次进行结晶(二次结晶)，二次结晶与一级结晶工艺条件相似，收集二次晶体称重并分析晶体纯度。结晶分离可以采用间歇结晶方式，也可以采用连续结晶方式。
由此，本发明提供了一种通过结晶方法纯化Lyocell纤维凝固浴中NMMO的方法，首先采用膜处理，脱除Lyocell纤维凝固浴中绝大部分糖类物质、PAM等影响凝固浴粘度的大分子杂质，消除这些大分子杂质对结晶产生的不良影响，提高NMMO的回收率。然后，通过减压加热蒸发浓缩，将经过膜处理的lyocell纤维凝固浴缩至NMMO质量含量为56.5-84.5％，通过结晶，得到高纯度的NMMO水合物晶体。在上述NMMO质量浓度范围内，对应的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，浓缩后凝固浴中NMMO质量浓度最好控制在66.5-72％，这样就可以在25-35℃非常适宜的温度范围内进行结晶提纯，并且得到纯度很高的2NMMO·5H 2O晶体(晶体中NMMO含量72.2％)和60％以上的结晶收率。
与目前采用离子交换树脂提纯回收NMMO方法不同，本发明由于不使用离子交换树脂，故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环保问题，而且按照本发明提供的结晶方法提纯回收的NMMO纯度非常高，几乎能够脱除lyocell凝固浴中所有的杂质，包括离子交换树脂方法无法脱除的许多非离子型杂质，得到的NMMO纯度远高于目前采用离子交换树脂方法提纯的NMMO，另外提纯工艺简单，提纯成本低，NMMO收率高，是一种高效简单低成本的绿色NMMO提纯方法。
本发明还提供了一种N-甲基吗啉-N-氧化物的纯化***，用于莱赛尔纤维凝固浴中N-甲基吗啉-N-氧化物的纯化，包括：
结晶装置，用于莱赛尔纤维凝固浴的结晶处理；
控制装置，与结晶装置连接，以控制结晶装置中的结晶条件。
在一实施方式中，本发明N-甲基吗啉-N-氧化物的纯化***还包括：
微滤装置、超滤处理装置与纳滤处理装置中的至少一种，与结晶装置和控制装置连通，莱赛尔纤维凝固浴通入所述微滤装置、超滤处理装置、纳滤处理装置中的至少一种进行处理，得到过滤液，过滤液通入结晶装置进行结晶处理。
在另一实施方式中，本发明N-甲基吗啉-N-氧化物的纯化***还包括：
絮凝沉降装置，莱赛尔纤维凝固浴与助凝剂通入絮凝沉降装置中，得到混合液，以进行絮凝沉降处理；
微滤装置与絮凝沉降装置连通，以将混合液通入微滤装置，以过滤固形物，得到微孔过滤液；
超滤处理装置与微滤装置连通，微孔过滤液通入超滤处理装置进行超滤处理，得到超滤浓缩液和超滤滤清液；
纳滤处理装置与超滤处理装置和结晶装置分别连通，超滤滤清液通入纳滤处理装置进行纳滤处理，得到纳滤浓缩液和纳滤滤清液，N-甲基吗啉-N-氧化物被截留于纳滤浓缩液中，纳滤浓缩液通入结晶装置进行结晶处理。
在又一实施方式中，纳滤处理装置包括一级纳滤处理装置和二级纳滤处理装置；
一级纳滤处理装置与超滤处理装置连通，超滤滤清液通入一级纳滤处理装置进行一级纳滤处理，得到一级纳滤浓缩液和一级纳滤滤清液；
二级纳滤处理装置与一级纳滤处理装置和结晶装置分别连通，一级纳滤滤清液通入二级纳滤处理装置进行二级纳滤处理，得到二级纳滤浓缩液和二级纳滤滤清液，N-甲基吗啉-N-氧化物被截留于二级纳滤浓缩液中，二级纳滤浓缩液通入结晶装置进行结晶处理。
在一具体实施方式中，本发明N-甲基吗啉-N-氧化物的纯化***中膜处理装置如图1所示，莱赛尔纤维凝固浴101与助凝剂102通入该絮凝沉降装置A中，混合得到混合液，以进行絮凝沉降处理；微滤装置B与絮凝沉降装置A连通，混合液通入微滤装置B进行微滤处理，以过滤固形物105，得到微孔过滤液106；超滤处理装置C与微滤装置B连通，微孔过滤液106通入超滤处理装置C，进行超滤处理，得到超滤浓缩液103和超滤滤清液104。为了提高NMMO回收效率，本发明超滤浓缩液103可以循环回絮凝沉降装置A，与莱赛尔纤维凝固浴101混合，再次进行絮凝沉降。
一级纳滤处理装置D与超滤处理装置C连通，以将超滤滤清液104输送至一级纳滤处理装置D进行一级纳滤处理，得到一级纳滤浓缩液107和一级纳滤滤清液108；二级纳滤处理装置E与一级纳滤处理装置D连通，以将一级纳滤滤清液108输送至二级纳滤处理装置E，进行二级纳滤处理，得到二级纳滤浓缩液109和二级纳滤滤清液110。
反渗透装置F与二级纳滤处理装置E连通，以将二级纳滤滤清液110输送至所述反渗透装置F进行反渗透处理，得到包含一价盐类杂质的反渗透浓缩液111和反渗透滤清液112。
反渗透滤清液112可以循环回一级纳滤处理装置D和二级纳滤处理装置E，作为一级透析处理和二级透析处理用水，以节约水资源，并减少废水产生；反渗透浓缩液111外排或进一步处理。
本发明并不特别限定N-甲基吗啉-N-氧化物的纯化***中膜处理装置包括上述各个单元，在一实施方式中，膜处理装置可以不包括上述微滤装置B；在另一实施方式中，膜处理装置可以不包括上述一级纳滤处理装置D和二级纳滤处理装置E，可以根据需要进行调整。
在一具体实施方式中，本发明N-甲基吗啉-N-氧化物的纯化***中结晶装置如图2所示，一级浓缩装置1可以与二级纳滤处理装置E和一级结晶装置2连通，二级纳滤浓缩液109(或莱赛尔纤维凝固浴101)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，于此不再赘述。
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***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，结果显示在NMMO晶体中几乎无法检测出原来lyocell纤维凝固浴中存在的各种有机杂质，加水配制成质量含量为50％的NMMO水溶液，其电导率可降至2.5μs/cm以下。
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***用于工业化生产，该纯化***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。
以下将通过具体实施例对本发明技术方案进一步进行详细说明。以下未注明的“％”通常指质量百分比。
本发明检测方法：
铁离子和铜离子含量检测：仪器为赛默飞ICP-MS。
总含糖量检测：采用陈慧茹的东华大学博士学位论文《廉价的高半纤维素含量的浆粕纺制的lyocell纤维的研究》中报道的总糖分析方法。
有机杂质、PG和PG氧化物检测：液相色谱(HPLC)分析，色谱柱：AichromBond-1,C18,5μm 4.6x150mm；流动相：0.2％磷酸缓冲液，pH＝2.9；流动相流速：1ml/min；柱温：35℃；UV检测波长：200nm和220nm，分别检测；进样量：20μl；检测时间：30分钟。
NMMO晶体纯度检测(杂质残余率)：用杂质残余率表示所得NMMO水合物晶体的纯度，测定方法为：将lyocell纤维凝固浴原料中NMMO质量浓度调整为19.8％，得lyocell纤维凝固浴原料溶液；将结晶得到的NMMO水合物晶体加水配制成NMMO质量浓度19.8％水溶液，得晶体溶液；采用HPLC测定lyocell纤维凝固浴原料溶液和晶体溶液谱图，UV检测波长分别为200nm和220nm，在每个测定波长下，分别计算晶体溶液谱图中所有杂质峰积分面积总和与lyocell纤维凝固浴原料溶液谱图中所有杂质峰积分面积总和的比值，即得到每个UV检测波长下晶体杂质残余率。
晶体杂质残余率＝(NMMO晶体溶液谱图中所有杂质峰积分面积总和)÷(lyocell纤维凝固浴原料溶液谱图中所有杂质峰积分面积总和)
本发明以下实施例中所有样品，都按上述方法进行分析检测。
实施例1.
检验未经过膜组合脱糖处理的lyocell纤维凝固浴直接进行降温结晶的纯化效果。
未经过膜组合脱糖预处理的lyocell纤维凝固浴性能如下：
NMMO质量含量：19.8％
总糖含量：502ppm
电导率：381μs/cm
N-甲基吗啉含量：140ppm
吗啉含量：36ppm
铁离子含量：1.89ppm
铜离子含量；1.23ppm
浊度：15 NTU
色度：957
将上述lyocell纤维凝固浴原液减压加热蒸发，浓缩至NMMO质量浓度为68.0％和69.9％，然后分别降温结晶，各浓度的凝固浴原液浓缩液至37℃开始降温，NMMO浓度68.0％和69.9％溶液分别降到34.7℃和35.5℃时，加入预先泡在NMMO饱和溶液中的晶种，加入量为凝固浴中NMMO重量的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3-4℃/小时，温度降至25℃，停止结晶，发现在结晶过程中因结晶 体系粘度非常大，结晶后期搅拌较难进行，结晶结束后整个结晶体系流动性较差，较难通过抽滤将母液与晶体分开，因此很难得到较高的NMMO结晶率。取少量晶体和母液，分别放在布氏漏斗中，用大量质量浓度59％的高纯NMMO溶液浸泡冲洗3次，分析检测晶体纯度(杂质残余率)。
将所得到的晶体和结晶母液分别加水，配制成NMMO质量浓度19.8％的水溶液，然后进行各种分析检测，结果发现结晶可以非常有效脱除凝固浴中含有的各种有机杂质，得到的NMMO晶体纯度很高，另外结晶也能够脱除凝固浴中含有的金属和非金属离子，使NMMO晶体电导率大幅降低，因此结晶可以作为lyocell凝固浴提纯回收NMMO的方法和手段，但未经膜组合脱糖预处理的lyocell凝固浴因为含糖类物质过高，导致结晶母液粘度非常大，几乎无法流动，结晶率较高时晶体和结晶母液分离较为困难，而且结晶母液无法再进行结晶。如下表1为未经膜组合预处理的lyocell纤维凝固浴结晶提纯NMMO数据。
表1.未经膜组合预处理的lyocell纤维凝固浴结晶提纯NMMO的数据
Figure PCTCN2022100880-appb-000001
由表1所示，结晶能够得到纯度很高的NMMO水合物晶体，使其与lyocell纤维凝固浴中含有的各种杂质分离，尽管由于体系中糖类物质含量过高，导致体系粘度很大，结晶较难进行，结晶颗粒较小，但得到的晶体中杂质含量却非常低，主要原因可能是凝固浴中的杂质结构与NMMO相差很大，导致这些杂质不易进入或包藏到NMMO晶体中。另外，结晶配制的NMMO浓度19.8％ 水溶液电导率也大幅降低，但随着结晶率提高，晶体纯度略有下降。
同时，本实施例表明未经膜组合处理的lyocell凝固浴浓缩结晶后，结晶母液粘度很大，晶体与结晶母液分离困难，结晶母液无法再次浓缩结晶，NMMO回收率较低。
实施例2
步骤1，将莱赛尔纤维凝固浴与丙烯酰胺助凝剂混合，进行絮凝沉降；
步骤2，将步骤1所得混合液进行微孔过滤，微孔过滤精度为0.5～5微米，以拦截固形物，得到微孔过滤液；所得微孔过滤液的液相色谱谱图如图3所示，其中峰1为NMMO特征峰，其余为杂质峰。
步骤3，将微孔过滤液进行超滤处理，截留分子量为10000-30000道尔顿，以截留小粒径固体、胶体、大分子杂质，所得超滤浓缩液为微孔过滤液体积的5％，超滤浓缩液返回步骤1进行重复絮凝。所得超滤浓缩液的液相色谱谱图如图4所示，超滤滤清液的液相色谱谱图如图5所示，其中峰1为NMMO特征峰，将图5和图3对比可知，超滤滤清液中NMMO纯度得以提高。
步骤4，将超滤滤清液进行一级纳滤处理，截留分子量为500-800道尔顿，N-甲基吗啉-N-氧化物与一价盐进入一级纳滤滤清液中，色素、多糖类物质、金属络合物、高价离子等中分子杂质被拦截，得到浓缩倍数为20倍的一级纳滤浓缩液；然后加入一级纳滤浓缩液体积的17倍的水作为一级透析水，将一级纳滤浓缩液中的NMMO透析至一级纳滤透析液中，一级纳滤浓缩液中NMMO含量降低到1克/升以下，将一级纳滤浓缩液外排。
所得一级纳滤滤清液的液相色谱谱图如图6所示，经过透析处理后的一级纳滤浓缩液的液相色谱谱图如图7所示，其中峰1为NMMO特征峰。由图7所示，一级纳滤浓缩液中残留NMMO较少，如此不会造成NMMO浪费，进而可提高NMMO回收效率。将图6和图5对比可知，一级纳滤滤清液中NMMO纯度得以提高，但是一级纳滤滤清液中尚存在少许杂质。
步骤5，将一级纳滤滤清液与一级纳滤透析液的混合液进行二级纳滤处理，截留分子量为300道尔顿，一价盐分进入二级纳滤滤清液中，N-甲基吗啉-N-氧化物被纳滤膜拦截；当二级纳滤浓缩液浓缩至0.2倍时，加入二级纳滤浓缩液体积的10倍的水，将二级纳滤浓缩液中的一价盐透析至二级纳滤透析 液中，使二级纳滤浓缩液的电导率降低到10us以下；此时二级纳滤滤清液与二级纳滤透析液混合后的电导率为1000us以下。
步骤6，将二级纳滤滤清液与二级纳滤透析液混合后进行反渗透处理，确保反渗透滤清液电导率小于1us，反渗透滤清液可以作为一级透析处理与二级透析处理的透析水使用。
以下表2为上述各阶段中NMMO含量数据。
表2各阶段中NMMO含量
Figure PCTCN2022100880-appb-000002
将上述二级纳滤浓缩液(未经二级纳滤透析处理)配制成NMMO质量含量为19.8％的溶液，测定该溶液性能如下：
NMMO质量含量：19.8％；
总含糖量：5.5ppm；
电导率：76μs/cm；
N-甲基吗啉含量：130ppm；
吗啉含量：34ppm；
铁离子含量：0.001ppm；
铜离子含量：0.001ppm；
浊度：0NTU；
色度：180。
HPLC分析显示lyocell纤维凝固浴经过膜组合处理后仍然还有十几种不同含量的杂质峰。
本发明以下实施例皆采用该实施例中经过膜组合处理后的二级纳滤浓缩液作为原料进行结晶提纯。
实施例3
本实施例主要分析NMMO结晶率对NMMO晶体纯度的影响。
实施例2膜组合脱糖处理过的lyocell凝固浴真空加热蒸发，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，各浓度的凝固浴浓缩液在37℃开始降温，NMMO浓度63.5％、65.2％、66.5％、67.9％和69.2％溶液温度分别降到31.2℃、32.1℃、33.2℃、34.2℃和35.1℃时，加入预先泡在NMMO饱和溶液中的晶种，加入量为凝固浴浓缩液中NMMO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3-4℃/小时，温度降至25℃，停止结晶，快速通过抽滤，将母液与晶体分开，收集结晶母液，发现母液粘度不大，与实施例1未经过膜组合脱糖处理的lyocell凝固浴结晶母液相比，粘度明显降低，很容易通过抽滤将结晶母液与晶体分开，晶体用大量高纯度NMMO浓度59％水溶液冲洗，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)。
将所得到的晶体分别加水，配制成NMMO质量浓度19.8％的水溶液，然后进行各种分析检测，表3为结晶率对NMMO晶体纯度的影响数据。
表3.结晶率对NMMO晶体纯度的影响数据
Figure PCTCN2022100880-appb-000003
Figure PCTCN2022100880-appb-000004
由表3所示，结晶能够得到纯度很高的NMMO晶体，使其与lyocell纤维凝固浴中的各种杂质分离，电导率也大幅降低，结晶率小于65％时，随结晶率升高NMMO晶体杂质残余率基本不变，结晶率大于52％，随结晶率升高晶体电导率略有上升。
实施例4
本实施例主要分析结晶速率对NMMO晶体纯度的影响。
将实施例2膜组合预处理的lyocell凝固浴真空加热蒸发，浓缩至NMMO质量浓度69.2％，凝固浴浓缩液温度降至34.2℃时加入预先泡在NMMO饱和溶液中的NMMO晶种，晶种加入量为浓缩液中NMMO质量的0.15％，将浓缩液分成4份，加入晶种后(34.2℃)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℃，抽滤，按实施例3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。
将所得NMMO晶体加水配制成质量浓度19.8％的NMMO水溶液，然后进行各种检测分析。表4为降温速率对NMMO晶体纯度的影响数据。
表4.降温速率对NMMO晶体纯度的影响数据
Figure PCTCN2022100880-appb-000005
Figure PCTCN2022100880-appb-000006
由表4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，否则晶体纯度会略有下降，电导率略有升高；在降温结晶后期，降温速率可以适当加快。主要原因是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，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5
本实施例主要分析晶种是否加入及加入量对NMMO晶体颗粒度和晶体纯度的影响。
将实施例2膜组合预处理过的lyocell凝固浴真空减压加热蒸发，浓缩至NMMO浓度69.4％，将浓缩液分成6份，浓缩液温度降至34.2℃时分别加入预先泡在NMMO饱和溶液中的NMMO晶种，晶种加入量占浓缩液中NMMO质量的百分比为：0(不加晶种)、0.05％、0.1％、0.2％、0.3％和0.6％，然后按实施例3的方式结晶和处理晶体。
将所得到的NMMO晶体加水配制成NMMO质量浓度19.8％水溶液，然后进行各种检测分析。表5为晶种加入量对NMMO晶体纯度和晶体颗粒度的影响数据。
表5.晶种加入量对NMMO晶体纯度和颗粒度的影响数据
Figure PCTCN2022100880-appb-000007
Figure PCTCN2022100880-appb-000008
由表5所示，晶种加入量对结晶颗粒度大小有较大影响，当不加晶种或加入量偏少(0.05％)时，晶粒大小分布不均，说明晶种量少，溶液体系过饱和度仍然较大，会有小晶核自发析出，受之影响所得的晶体纯度也略低；晶种加入量足够的话，晶体颗粒分布比较均一，晶体纯度高，晶种加入量越大，颗粒越小；但加入过多晶种(0.6％以上)时，所得晶体颗粒过小，颗粒表面有可能沾污更多的母液杂质，造成晶体纯度略有下降，同时晶体颗粒度太小，也会影响晶体过滤速度，因此最佳晶体加入量为浓缩液中NMMO质量的0.1-0.3％。
实施例6
本实施例主要分析二次结晶(重结晶)对NMMO晶体纯度的影响。
按照实施例3中方法，将实施例2膜组合预处理过的lyocell凝固浴浓缩至NMMO质量浓度69.2％后再结晶纯化(一级结晶)，将一级结晶得到的晶体加水配制成浓度69.9％的NMMO水溶液，按实施例3中工艺进行重结晶，收集一级结晶晶体和重结晶晶体称重计算结晶率，并分析检测晶体纯度(杂质残余率)。将一级结晶和重结晶得到的晶体分别加水，配制成NMMO浓度19.8％的水溶液，然后进行各种分析检测。表6为重结晶对NMMO晶体纯度的影响数据。
表6.重结晶对NMMO晶体纯度影响数据
Figure PCTCN2022100880-appb-000009
由表6所示，重结晶能够进一步纯化NMMO，进一步降低NMMO晶体中有机杂质含量，降低NMMO晶体电导率至12.4μs/cm。
实施例7
本实施例主要分析一级结晶剩余母液，通过二级结晶回收其中NMMO的效果。
将实施例6的lyocell凝固浴浓缩液一级结晶分离出来的母液，减压加热蒸发浓缩至NMMO质量浓度70.1％，按实施例3中结晶工艺条件进行结晶(在母液温度35.3℃时加入晶种)。将所得到的晶体加水，配制成NMMO质量浓度19.8％的水溶液，然后进行各种分析检测，表7为lyocell纤维凝固浴浓缩液一级结晶母液再次进行结晶的结果数据。
表7.lyocell纤维凝固浴浓缩液一级结晶母液再次进行结晶的结果数据
Figure PCTCN2022100880-appb-000010
由表7所示，一级结晶母液再次浓缩后结晶，在结晶率达84％时，所得晶体的纯度仍然较高。lyocell纤维凝固浴经过二级结晶能够回收lyocell纤维凝固浴中96％的NMMO；进一步地，二级结晶母液粘度仍然不高，如果希望进一步提高NNMO结晶回收率，还可以继续对二级结晶产生的母液进行浓缩结晶，或者进一步提高一级和二级结晶的结晶率。
工业应用性
综上所述，本发明提供了一种lyocell纤维凝固浴中NMMO的纯化方法，该方法采用结晶提纯方式纯化回收，结晶操作温度接近常温(25-35℃)，HPLC分析检测结果表明，通过本发明提供的结晶工艺方法得到的NMMO纯度非常高，lyocell凝固浴中存在的十几种有机杂质包括PG、PG氧化物、糖类等，几乎完全被去除，回收提纯的NMMO纯度明显比目前通常采用的离子交换树脂法提纯回收的NMMO纯度高，甚至与NMMO新品纯度相近，离子交换树脂无法脱除的各种杂质都能够得到脱除，解决了由于目前离子交换树脂提纯凝固 浴工艺无法脱除lyocell纺丝体系许多杂质，导致长期积累以至影响lyocell纺丝质量的问题。另外，将膜处理与结晶工艺相结合，能够进一步提高NMMO的回收率，并且能够使提纯工艺更易进行，适于工业生产。
采用本发明提供的结晶提纯工艺，所产生的最终含大量杂质的结晶母液可以通过焚烧处理(TO)，由于本发明回收提纯方法不使用离子交换树脂，也彻底解决了目前采用离子交换树脂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，另外本发明提供的结晶提纯工艺能够脱除几乎所有lyocell凝固浴中所含的杂质，不会有杂质因无法脱除的原因在纺丝体系里产生积累，因此lyocell纤维生产使用含易分解半纤维素高的阔叶林浆粕甚至半纤维素含量更高的纸浆成为了可能，拓宽了lyocell浆粕原料的来源，降低甚至可以解决目前lyocell纤维存在的原纤化问题，是一种绿色、低生产成本、高效的lyocell纤维凝固浴中NMMO回收提纯方法。

Claims (17)

  1. 一种N-甲基吗啉-N-氧化物的纯化方法，用于莱赛尔纤维凝固浴中N-甲基吗啉-N-氧化物的纯化，其特征在于，包括如下步骤：将莱赛尔纤维凝固浴在-20℃～78℃之间进行降温结晶，得到N-甲基吗啉-N-氧化物的水合物晶体。
  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，所述莱赛尔纤维凝固浴在进行降温结晶前还包括：除去所述莱赛尔纤维凝固浴中的糖类物质。
  3. 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，所述莱赛尔纤维凝固浴在进行降温结晶前还包括：将所述莱赛尔纤维凝固浴进行微滤处理、超滤处理和纳滤处理中的至少一种。
  4. 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，所述莱赛尔纤维凝固浴在进行降温结晶前还包括：将所述莱赛尔纤维凝固浴与助凝剂混合得到混合液，以进行絮凝沉降；然后将所述混合液进行微滤处理、超滤处理和纳滤处理中的至少一种。
  5. 根据权利要求1-4任一项所述的N-甲基吗啉-N-氧化物的纯化方法，其特征在于，所述莱赛尔纤维凝固浴在降温结晶前进行浓缩处理，使所述莱赛尔纤维凝固浴中N-甲基吗啉-N-氧化物的质量浓度为56.5％～84.5％，然后进行降温结晶。
  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，所述浓缩处理使所述莱赛尔纤维凝固浴中N-甲基吗啉-N-氧化物的质量浓度为56.5-72.2％，降温结晶的温度为25-40℃。
  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℃之间，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，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莱赛尔纤维凝固浴中N-甲基吗啉-N-氧化物重量的0.1％以上。
  9. 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-氧化物水合物晶体和结晶母液，所述结晶母液经浓缩后进行二级降温结晶。
  10. 根据权利要求4所述的N-甲基吗啉-N-氧化物的纯化方法，其特征在于，所述混合液进行微滤处理得到微孔过滤液；所述微孔过滤液进行所述超滤处理，得到超滤浓缩液和超滤滤清液；所述超滤滤清液进行所述降温结晶；
    其中，所述微滤处理的过滤精度为0.5～5微米；所述超滤处理的过滤精度为1000～100000分子量。
  11. 根据权利要求10所述的N-甲基吗啉-N-氧化物的纯化方法，其特征在于，所述超滤滤清液先进行一级纳滤处理，得到一级纳滤浓缩液和一级纳滤滤清液，然后使所述一级纳滤滤清液进行所述降温结晶；
    其中，所述一级纳滤处理的过滤精度为300-1000分子量。
  12. 根据权利要求11所述的N-甲基吗啉-N-氧化物的纯化方法，其特征在于，所述一级纳滤滤清液先进行所述二级纳滤处理，得到二级纳滤浓缩液和二级纳滤滤清液，所述N-甲基吗啉-N-氧化物被截留于所述二级纳滤浓缩液中，然后使所述二级纳滤浓缩液进行所述降温结晶；
    其中，所述二级纳滤处理的过滤精度为100-200分子量。
  13. 权利要求1-12任一项所述的纯化方法得到的N-甲基吗啉-N-氧化物水合物晶体。
  14. 一种N-甲基吗啉-N-氧化物的纯化***，用于莱赛尔纤维凝固浴中N-甲基吗啉-N-氧化物的纯化，其特征在于，包括：
    结晶装置，用于所述莱赛尔纤维凝固浴的结晶处理；
    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。
  15. 根据权利要求14所述的N-甲基吗啉-N-氧化物的纯化***，其特征在于，还包括：
    微滤装置、超滤处理装置与纳滤处理装置中的至少一种，与所述结晶装置和控制装置连通，所述莱赛尔纤维凝固浴通入所述微滤装置、超滤处理装置、纳滤处理装置中的至少一种进行处理，得到过滤液，所述过滤液通入所述结晶装置进行结晶处理。
  16. 根据权利要求15所述的N-甲基吗啉-N-氧化物的纯化***，其特征在于，还包括：
    絮凝沉降装置，所述莱赛尔纤维凝固浴与助凝剂通入所述絮凝沉降装置中，得到混合液，以进行絮凝沉降处理；
    该微滤装置与所述絮凝沉降装置连通，以将所述混合液通入所述微滤装置，以过滤固形物，得到微孔过滤液；
    该超滤处理装置与所述微滤装置连通，所述微孔过滤液通入所述超滤处理装置进行超滤处理，得到超滤浓缩液和超滤滤清液；
    该纳滤处理装置与所述超滤处理装置和结晶装置分别连通，所述超滤滤清液通入所述纳滤处理装置进行纳滤处理，得到纳滤浓缩液和纳滤滤清液，所述N-甲基吗啉-N-氧化物被截留于所述纳滤浓缩液中，所述纳滤浓缩液通入所述结晶装置进行结晶处理。
  17. 根据权利要求16所述的N-甲基吗啉-N-氧化物的纯化***，其特征在于，该纳滤处理装置包括一级纳滤处理装置和二级纳滤处理装置；
    所述一级纳滤处理装置与所述超滤处理装置连通，所述超滤滤清液通入所述一级纳滤处理装置进行一级纳滤处理，得到一级纳滤浓缩液和一级纳滤滤清液；
    所述二级纳滤处理装置与所述一级纳滤处理装置和结晶装置分别连通，所述一级纳滤滤清液通入所述二级纳滤处理装置进行二级纳滤处理，得到二级纳滤浓缩液和二级纳滤滤清液，所述N-甲基吗啉-N-氧化物被截留于所述二级纳滤浓缩液中，所述二级纳滤浓缩液通入所述结晶装置进行结晶处理。
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