Bio-based polyamide nanofiltration membrane and application thereof

Abstract

The invention discloses a bio-based polyamide nanofiltration membrane and application thereof, and belongs to the technical field of synthesis of bio-based polyamide nanofiltration membranes and purification of 5-hydroxymethylfurfural and 2, 5-furandicarboxylic acid. According to the invention, 2, 5-dimethyl furandicarboxylate and hexamethylenediamine are used as raw materials, polydimethyl furandicarboxylate hexamethylenediamine prepared by an amine ester exchange method is used as a film-forming polymer, and a solution phase inversion method is further adopted to prepare the bio-based polyamide nanofiltration membrane polydimethyl furandicarboxylate hexamethylenediamine membrane. The method has the advantages that 5-hydroxymethylfurfural and soluble humin can be selectively separated by the aid of the method, impurities in 2, 5-furandicarboxylic acid sodium salt aqueous solution can be separated, and accordingly the high-purity 5-hydroxymethylfurfural and 2, 5-furandicarboxylic acid can be prepared.

Description

Technical Field

[0001] The invention belongs to the technical field of synthesis of bio-based polyamide nanofiltration membrane and purification of 5-hydroxymethylfurfural and 2,5-furandicarboxylic acid, and specifically relates to a bio-based polyamide nanofiltration membrane and application thereof. Background Art

[0002] With the increasing consumption of fossil fuel energy and the prominence of environmental pollution problems, the development of green renewable resources has become a research target.

[0003] 5-Hydroxymethylfurfural (HMF), as a renewable biomass raw material, can be prepared by multiple dehydration of hexoses such as glucose and fructose. The dehydration byproducts are the main obstacles to the expansion of the process scale and the reduction of HMF selectivity and yield. Therefore, the biggest challenge in the industrialization of HMF is the separation and purification of the product. In the synthesis of HMF, polar aprotic solvents, H2O and ionic liquids are mainly used. HMF is unstable in water and is rehydrated to synthesize levulinic acid. In addition, due to the condensation reaction of sugars and the degradation of HMF at high temperatures, humin byproduct is formed. Temperature, catalyst, pH and initial sugar concentration have a great influence on the formation of humin. The colored impurities in the reaction solution or crude product of HMF are soluble in water and most organic solvents, which brings difficulties to the refining of HMF. At present, common purification methods of HMF include extraction, adsorption, column chromatography, crystallization, distillation, etc. Patent CN112279826A discloses a method for preparing and separating HMF, using fructose as raw material. Under the action of acid catalysis, HMF is prepared by low-temperature reaction in choline chloride solvent. This patent extracts HMF from choline chloride solvent by organic solvent, and then separates solvent and HMF by distillation. Since the extraction method does not separate HMF from small molecule byproducts, the final HMF purity is only 90%. Compared with the extraction method, although the distillation method can obtain HMF with higher purity, HMF has poor thermal stability, and further degradation of HMF will occur during the distillation process. Therefore, vacuum distillation is required to reduce the temperature and time, thereby increasing the energy consumption and cost of distillation. Patent CN101720320A discloses a method for purifying HMF using non-functional polymer resins. Although HMF can be separated from by-products and a high-purity product can be obtained, the purification process using two non-functional polymer resins is relatively complicated, and will further cause the loss of HMF, which is not conducive to the industrial production of HMF. Patent CN115073402A provides a method for purifying HMF, which uses a falling film crystallizer and sequentially undergoes pretreatment, melt crystallization, sweating, and melting to achieve a purity of HMF above 99.9%. Unlike traditional distillation and recrystallization processes, this method avoids the introduction of solvents, thereby further reducing the generation of new impurities, and thus can reduce the production cost of HMF.

[0004] 2,5-Furandicarboxylic acid (FDCA), as the only bio-based platform molecule with a conjugated aromatic ring structure, is listed as one of the twelve important bio-based platform chemicals by the U.S. Department of Energy. The structure of FDCA is similar to that of the monomer terephthalic acid (PTA) of the traditional petrochemical product polyethylene terephthalate (PET), and can be used as a substitute to participate in almost all chemical reactions downstream of PTA. There are currently various by-products in the FDCA reaction prepared by HMF catalytic oxidation. If the purity of FDCA is low, it will affect the synthesis of FDCA downstream products. For example, the purity of polyethylene furandicarboxylate (PEF) prepared by the polymerization reaction of FDCA and ethylene glycol has a great influence on the molecular weight and color of PEF polyester. The most reported purification methods of FDCA are oxidation or hydrogenation under high temperature and high pressure conditions. Patent CN115028610A provides a method for purifying 2,5-furandicarboxylic acid. Before hydrogenation, the catalyst in the crude diacid is removed under the action of a metal ion remover and a recrystallization solvent, and then a hydrogenation reaction is carried out in the presence of a hydrogenation catalyst and hydrogen to finally obtain a FDCA product with a higher purity. Patent CN104334537B provides a method for purifying crude FDCA by hydrogenation. HMF is first oxidized to a crude FDCA product containing 5-formylfuran-2-carboxylic acid (FFCA) under the action of a Co / Mn / Br catalytic system, and then the FFCA impurities in the crude FDCA product are removed by hydrogenation. There is a problem in this method that Co and Mn catalysts are easily left in the crude FDCA product, which will affect the effect of the hydrogenation catalyst in removing FFCA, and then affect the purity of the FDCA product. In addition, there are other methods for purifying FDCA, such as oxidation, aged salt, column chromatography, distillation, and crystallization. Patent CN109721578A provides a method for purifying FDCA by crystallization. The purity of FDCA can be further improved by recrystallizing the crude FDCA product using a solvent with a suitable dipole moment.

[0005] In recent years, in order to overcome the above purification problems of HMF and FDCA, researchers have proposed to intercept humin in the dehydration reaction by nanofiltration to achieve the purpose of purifying HMF. Nanofiltration (NF) membrane, as a new type of separation membrane, is a membrane separation process driven by pressure difference, and the molecular weight cutoff is approximately in the range of 100 to 1000. Since humin is inevitably produced during the preparation of HMF, relevant studies have shown that nanofiltration separation can meet the conditions for intercepting humin (small molecule polymer). Patent CN114805255A provides a method for HMF preparation and membrane separation and purification. After HMF and humin are separated in the HMF reaction solution by filtration, microfiltration and nanofiltration, a permeate is obtained, and then the permeate is reduced pressure distilled to obtain a high-purity HMF product. This method uses nanofiltration membrane to purify the product, reducing the separation cost while realizing the continuous production of HMF.

[0006] Based on this, the present invention separates and purifies the crude 5-hydroxymethylfurfural solution or the sodium salt solution of 2,5-furandicarboxylic acid to obtain a high-purity 5-hydroxymethylfurfural or 2,5-furandicarboxylic acid product. The present invention uses poly(dimethyl furandicarboxylate hexamethylenediamine) (PA6F) as a membrane-forming polymer and adopts a solution phase inversion method to prepare a PA6F nanofiltration membrane, which can selectively separate HMF and soluble humin, and can also separate impurities in the sodium salt solution of FDCA, thus providing a new idea for the separation and purification of HMF and FDCA. Summary of the invention

[0007] The purpose of the present invention is to provide a bio-based polyamide nanofiltration membrane to solve the problems of high purification cost, low recovery rate and poor purity of 5-hydroxymethylfurfural and 2,5-furandicarboxylic acid.

[0008] The purpose of the present invention can be achieved through the following technical solutions:

[0009] In a first aspect, a bio-based polyamide nanofiltration membrane is prepared by the following steps:

[0010] S1. Preparation of poly(dimethyl furandicarboxylate) hexamethylenediamine (PA6F):

[0011] Adding dimethyl 2,5-furandicarboxylate (DMFDCA) and hexamethylenediamine into a polymerization reactor at a molar ratio of 1:1 to 1.3, then sequentially adding a titanium catalyst, a phosphorus stabilizer and an antioxidant, heating to 60 to 90° C. for reaction for 1 to 1.5 hours under nitrogen protection, then heating to 120 to 130° C. for reaction for 1 to 1.5 hours, then heating to 210 to 230° C. for reaction at a pressure of 1.2 to 1.6 MPa for 1 to 1.5 hours, then reducing the pressure to ≤200 Pa within 1 to 2 hours, and continuing the reaction for 2 to 4 hours to obtain polydimethyl furandicarboxylate hexamethylenediamine;

[0012] S2. Preparation of poly(dimethyl furandicarboxylate) hexamethylenediamine film:

[0013] Dissolve poly(dimethyl furandicarboxylate) hexamethylenediamine and additives in a solvent, heat and stir, mix evenly to obtain a homogeneous casting liquid; vacuum degas the homogeneous casting liquid and scrape it into a film; immerse the film in a coagulation bath, let it stand to form, and obtain a poly(dimethyl furandicarboxylate) hexamethylenediamine film (PA6F film), take it out from the coagulation bath, soak it in pure water for 22 to 26 hours, remove excess solvent, and store it after drying it with a freeze dryer.

[0014] Furthermore, the titanium catalyst is one or more of titanium isopropoxide, titanium citrate, and butyl titanate; the amount of the titanium catalyst added is 0.5 to 2 wt% of the amount of dimethyl 2,5-furandicarboxylate;

[0015] And / or, the phosphorus stabilizer is any one or more of triphenyl phosphate, triphenyl phosphite, ethyl phosphate, phosphoric acid, trimethyl phosphate, trimethyl phosphite, and polyphosphoric acid; the amount of the phosphorus stabilizer added is 0.05 to 0.2 wt % of the amount of dimethyl 2,5-furandicarboxylate.

[0016] Further, the antioxidant is any one or more of an amine antioxidant, a phenolic antioxidant, and a phosphorus-containing compound; preferably, the antioxidant is one or more of antioxidant 1010, antioxidant 1178, antioxidant 1076, antioxidant 618, antioxidant 425, antioxidant 330, antioxidant 626, and antioxidant 168;

[0017] And / or, the amount of antioxidant added is 0.01 to 0.1 wt % of the amount of dimethyl 2,5-furandicarboxylate used.

[0018] Further, the additive is inorganic particles LiCl, NH4Cl, Al2O3, SiO2, TiO2, Fe3O4, NaNO3, H3PO4; high molecular weight organic matter PEG (polyethylene glycol), PVP (polyvinyl pyrrolidone) and one of organic small molecules acetone, butanone, tetrahydrofuran;

[0019] And / or, the solvent is one of DMAc (dimethylacetamide), DMF (N,N-dimethylformamide), NMP (N-methylpyrrolidone), and DMSO (dimethyl sulfoxide).

[0020] Furthermore, in the homogeneous casting solution, the mass percentage of poly(hexamethylenediamine)dimethyl furandicarboxylate is 10-20wt%, the mass percentage of the additive is 1-8wt%, and the balance is the solvent.

[0021] Furthermore, the coagulation bath is one of water, an organic solvent, and a water / organic solvent mixture; the organic solvent includes but is not limited to one of DMAc (dimethylacetamide), DMF (N,N-dimethylformamide), NMP (N-methylpyrrolidone), DMSO (dimethyl sulfoxide), ethylene glycol, methanol, ethanol, propanol, and octanol.

[0022] In a second aspect, the present invention provides an application of the bio-based polyamide nanofiltration membrane for separation and purification of 5-hydroxymethylfurfural or 2,5-furandicarboxylic acid.

[0023] Furthermore, the application of the bio-based polyamide nanofiltration membrane for separation and purification of 5-hydroxymethylfurfural comprises the following steps:

[0024] The crude 5-hydroxymethylfurfural solution is fed into a device equipped with the nanofiltration membrane, the membrane separation pressure is controlled to be 0.5-4 MPa, and a permeate containing 5-hydroxymethylfurfural and a residual liquid containing humin are obtained by nanofiltration; the residual liquid containing humin is diluted with a solvent, and nanofiltered again after impurities are removed; the permeates are combined, and the solvent and 5-hydroxymethylfurfural are obtained by reduced pressure distillation.

[0025] Furthermore, the solvent in the crude 5-hydroxymethylfurfural solution is at least one of methyl isobutyl ketone, acetone, dimethyltetrahydrofuran, tetrahydrofuran, dimethyl carbonate, 1,4-dioxane, isopropanol and acetonitrile.

[0026] It should be noted that the synthesis method of 5-hydroxymethylfurfural is a preparation method disclosed in the art, that is, a sugar raw material is converted into 5-hydroxymethylfurfural in the presence of a reaction solvent and a catalyst; the crude 5-hydroxymethylfurfural solution is a solution with a purity of 85-90% obtained after the reaction solution is treated by conventional impurity removal means such as adsorption and filtration.

[0027] The residual liquid containing humin obtained after nanofiltration is treated with activated carbon adsorption to remove humin, and the obtained liquid can be further recycled for nanofiltration separation; in addition, the solvent obtained after the permeate is subjected to reduced pressure distillation can be recycled.

[0028] Furthermore, the application of the bio-based polyamide nanofiltration membrane for separation and purification of 2,5-furandicarboxylic acid comprises the following steps:

[0029] The sodium salt solution of 2,5-furandicarboxylic acid is sent into a device equipped with the nanofiltration membrane, and the membrane separation pressure is controlled to be 0.5-4 MPa. A permeate and a residual liquid containing 2,5-furandicarboxylic acid are obtained by nanofiltration. Hydrochloric acid is added to the permeate to acidify and adjust the pH value to less than 1, and then a solid is precipitated, which is filtered and dried to obtain 2,5-furandicarboxylic acid.

[0030] It should be noted that the synthesis method of 2,5-furandicarboxylic acid is a preparation method disclosed in the art, that is, 5-hydroxymethylfurfural is converted into 2,5-furandicarboxylic acid in the presence of water, alkali, catalyst and oxygen source; the 2,5-furandicarboxylic acid sodium salt aqueous solution is a solution with a purity of 90-96% obtained by treating the oxidation reaction liquid with conventional impurity removal means such as adsorption and filtration.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The present invention uses 2,5-furandicarboxylic acid dimethyl ester and hexamethylenediamine as raw materials, and further prepares bio-based polyamide nanofiltration membranes using polyfurandicarboxylic acid dimethyl hexamethylenediamine prepared by amine ester exchange method. Compared with FDCA as a reaction raw material, DMFDCA can effectively avoid decarboxylation and N-methylation reactions at high temperatures. The bio-based polyamide nanofiltration membrane PA6F membrane is prepared by solution phase inversion method. In order to improve the structure and performance of the membrane, a certain amount of additives is added to the casting liquid. For example, adding additive LiCl can regulate the membrane structure and performance. The addition of LiCl can increase the viscosity and thermodynamic stability of the casting liquid, thereby inhibiting the formation of macropores during phase separation. In addition, since the PA6F molecular chain contains a large number of amide groups, there is a hydrogen bonding force between the molecular chains, which can also inhibit the formation of macropores during the phase inversion process, making it easier to prepare nanofiltration membranes.

[0033] 2. The prepared bio-based polyamide nanofiltration membrane PA6F membrane is used to separate and purify HMF or FDCA. Since the PA6F membrane has excellent retention performance for impurities, high-purity HMF and FDCA products can be obtained in the end. The purification method of HMF and FDCA provided by the present invention is simple, efficient, green and environmentally friendly, and has important significance for the separation and purification of HMF and FDCA. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be further described below in conjunction with the accompanying drawings.

[0035] Figure 1 This is a SEM (scanning electron microscope) test image of the cross section of the PA6F film prepared in Example 1 of the present invention;

[0036] Figure 2 This is a SEM (scanning electron microscope) test image of the surface of the PA6F membrane prepared in Example 1 of the present invention;

[0037] Figure 3 This is an XRD (X-ray diffraction) test diagram of the PA6F film prepared in Example 1 of the present invention;

[0038] Figure 4 This is a DSC (differential scanning calorimetry) test diagram of the PA6F film prepared in Example 1 of the present invention;

[0039] Figure 5 This is a TGA (thermogravimetric analysis) test chart of the PA6F film prepared in Example 1 of the present invention;

[0040] Figure 6 This is a physical picture of the PA6F membrane prepared in Example 1 of the present invention;

[0041] Figure 7 Schematic diagram of the process flow of using the PA6F membrane prepared in Example 1 of the present invention in HMF separation and purification;

[0042] Figure 8 It is a schematic diagram of the process flow of using the PA6F membrane prepared in Example 1 of the present invention in FDCA separation and purification. DETAILED DESCRIPTION

[0043] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] It should be noted that the heating temperature rise rate and cooling rate parameters of the reaction device in the present invention are adjusted automatically according to the temperature set in the reactor used; in addition, parameters such as the stirring speed are not particularly limited as long as they meet industry standards.

[0045] Example 1

[0046] A bio-based polyamide nanofiltration membrane is prepared by the following steps:

[0047] S1. Preparation of PA6F:

[0048] DMFDCA (18.59 g) and hexamethylenediamine (11.72 g) were added to a polymerization kettle at a molar ratio of 1:1, and 0.186 g of butyl titanate, 0.019 g of phosphoric acid and 0.019 g of antioxidant 1010 were added in sequence. Under nitrogen protection, the temperature was raised to 80°C for reaction for 1.5 h, then raised to 125°C for reaction for 1 h, and then continued to rise to 220°C. After the reaction was carried out at a pressure of 1.4 MPa for 1.5 h, the pressure was reduced to ≤200 Pa within 1 h, and the reaction was continued for 3 h. After the reaction was completed, PA6F was obtained after purification. The product molecular weight Mw was measured to be 22465.

[0049] S2. Preparation of PA6F membrane:

[0050] PA6F, LiCl and DMAc were mixed according to weight percentages of 12wt%, 3wt% and 85wt%, heated at 130°C with stirring, and fully dissolved and mixed to obtain a homogeneous casting liquid; the homogeneous casting liquid was vacuum-insulated and degassed, then poured onto a dry, smooth glass plate, and then scraped with a film scraper to form a film with a thickness of 250um, then immersed in a water bath at room temperature (25-30°C), and allowed to stand for 0.5h to allow the polyamide to solidify and form, and then the obtained PA6F film was post-treated, taken out of the water bath, immersed in pure water for 24h to remove excess solvent, and then dried with a freeze dryer and stored for use.

[0051] Performance test of PA6F membrane:

[0052] (1) SEM test: Figure 1 and Figure 2 As shown, Figure 1 The cross-sectional SEM morphology of the PA6F membrane shows that the PA6F membrane has a dense cortex-finger-like macropores-sponge-like pores structure. Figure 2 From left to right are the morphologies of the lower and upper surfaces of the PA6F membrane. It can be seen that there are many holes on the surface of the PA6F membrane.

[0053] (2) XRD test: Figure 3 As shown, the PA6F film has a characteristic diffraction peak of polyamide near 21.5°, which is a characteristic diffraction peak of polyamide γ crystal.

[0054] (3)DSC test: Figure 4 As shown, the melting point of PA6F film is 117.33°C.

[0055] (4) TGA test: Figure 5 As shown, the decomposition temperature of PA6F membrane is above 400°C, showing good thermal stability.

[0056] (5) BET test: The test results show that the pore size of PA6F membrane is 1.98975nm and the specific surface area is 20.8696m 2 / g, pore volume / pore volume is 0.010372cm 3 / g.

[0057] (6) Actual picture of PA6F membrane Figure 6 shown.

[0058] Application Example 1-1

[0059] Application of a bio-based polyamide nanofiltration membrane for HMF separation and purification, please refer to Figure 7 , including the following steps:

[0060] The crude HMF solution (HMF purity of 85-90%) was fed into a nanofiltration device equipped with the PA6F membrane prepared in Example 1, and the membrane separation pressure was controlled to be 2 MPa. After the nanofiltration step, a light yellow permeate containing HMF and a residual liquid containing humin were obtained; the residual liquid containing humin was diluted with THF, and nanofiltration was performed again after impurities were removed by activated carbon adsorption; all the permeates were combined and distilled under reduced pressure to obtain THF and HMF products.

[0061] Application Example 1-2

[0062] Application of a bio-based polyamide nanofiltration membrane for FDCA separation and purification, please refer to Figure 8 , including the following steps:

[0063] A sodium 2,5-furandicarboxylic acid salt aqueous solution (FDCA purity of 90-96%) was fed into a nanofiltration device equipped with the PA6F membrane prepared in Example 1, and the membrane separation pressure was controlled to be 2 MPa. A permeate and a residual liquid containing FDCA were obtained by nanofiltration. Hydrochloric acid was added to the permeate to acidify and adjust the pH to <1, and then a solid was precipitated, which was filtered and dried to obtain a FDCA solid product.

[0064] Example 2

[0065] A bio-based polyamide nanofiltration membrane is prepared by the following steps:

[0066] S1. Preparation of PA6F:

[0067] DMFDCA (18.59 g) and hexamethylenediamine (11.72 g) were added to a polymerization kettle at a molar ratio of 1:1, and 0.186 g of butyl titanate, 0.019 g of triphenyl phosphate and 0.019 g of antioxidant 1010 were added in sequence. Under nitrogen protection, the temperature was raised to 80°C for reaction for 1 hour, then raised to 120°C for reaction for 1 hour, and then continued to rise to 210°C. After the reaction was carried out at a pressure of 1.4 MPa for 1 hour, the pressure was reduced to ≤200 Pa within 1 hour, and the reaction was continued for 3 hours. After the reaction was completed, PA6F was obtained after purification; the product molecular weight Mw was measured to be 20971;

[0068] S2. Preparation of PA6F membrane: same as Example 1.

[0069] Application Example 2-1

[0070] A bio-based polyamide nanofiltration membrane is used for separation and purification of HMF. The purification method is the same as that of Application Example 1-1, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 2.

[0071] Application Example 2-2

[0072] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that of Application Example 1-2, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 2.

[0073] Example 3

[0074] A bio-based polyamide nanofiltration membrane, which is different from Example 1 in that, in S1, the molar ratio of DMFDCA to hexamethylenediamine is 1:1.2, and the molecular weight Mw of the PA6F obtained by purification after the reaction is completed is 22465;

[0075] The remaining preparation steps and parameters remained the same.

[0076] Application Example 3-1

[0077] A bio-based polyamide nanofiltration membrane is used for separation and purification of HMF. The purification method is the same as that of Application Example 1-1, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 3.

[0078] Application Example 3-2

[0079] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that of Application Example 1-2, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 3.

[0080] Example 4

[0081] A method for preparing a bio-based polyamide nanofiltration membrane, which is different from Example 1 in that the homogeneous casting solution in S2 is composed of a mixture of 10wt% PA6F, 3wt% LiCl and 87wt% DMAc, and the other steps and parameters remain the same.

[0082] Application Example 4-1

[0083] A bio-based polyamide nanofiltration membrane is used for separation and purification of HMF. The purification method is the same as that of Application Example 1-1, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 4.

[0084] Application Example 4-2

[0085] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that of Application Example 1-2, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 4.

[0086] Example 5

[0087] A method for preparing a bio-based polyamide nanofiltration membrane, which differs from Example 1 in that the homogeneous casting solution in S2 is composed of a mixture of 15wt% PA6F, 3wt% LiCl and 82wt% DMAc, and the other preparation steps and parameters remain the same.

[0088] Application Example 5-1

[0089] A bio-based polyamide nanofiltration membrane is used for separation and purification of HMF. The purification method is the same as that of Application Example 1-1, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 5.

[0090] Application Example 5-2

[0091] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that of Application Example 1-2, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 5.

[0092] Example 6

[0093] A method for preparing a bio-based polyamide nanofiltration membrane, which differs from Example 1 in that the homogeneous casting solution in S2 is composed of a mixture of 20wt% PA6F, 3wt% LiCl and 77wt% DMAc, and the other preparation steps and parameters remain the same.

[0094] Application Example 6-1

[0095] A bio-based polyamide nanofiltration membrane is used for separation and purification of HMF. The purification method is the same as that of Application Example 1-1, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 6.

[0096] Application Example 6-2

[0097] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that of Application Example 1-2, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 6.

[0098] Example 7

[0099] A method for preparing a bio-based polyamide nanofiltration membrane, which differs from Example 1 in that the homogeneous casting solution in S2 is composed of a mixture of 12wt% PA6F, 2wt% LiCl and 86wt% DMAc, and the other preparation steps and parameters remain the same.

[0100] Application Example 7-1

[0101] A bio-based polyamide nanofiltration membrane is used for HMF separation and purification. The purification method is the same as that of Application Example 1-1, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 7.

[0102] Application Example 7-2

[0103] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that of Application Example 1-2, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 7.

[0104] Example 8

[0105] A method for preparing a bio-based polyamide nanofiltration membrane, which differs from Example 1 in that the homogeneous casting solution in S2 is composed of a mixture of 12wt% PA6F, 5wt% LiCl and 83wt% DMAc, and the other preparation steps and parameters remain the same.

[0106] Application Example 8-1

[0107] A bio-based polyamide nanofiltration membrane is used for HMF separation and purification. The purification method is the same as that of Application Example 1-1, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 8.

[0108] Application Example 8-2

[0109] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that of Application Example 1-2, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 8.

[0110] Example 9

[0111] A method for preparing a bio-based polyamide nanofiltration membrane, which differs from Example 1 in that the homogeneous casting solution in S2 is composed of a mixture of 12wt% PA6F, 7wt% LiCl and 81wt% DMAc, and the other preparation steps and parameters remain the same.

[0112] Application Example 9-1

[0113] A bio-based polyamide nanofiltration membrane is used for separation and purification of HMF. The purification method is the same as that of Application Example 1-1, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 9.

[0114] Application Example 9-2

[0115] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that of Application Example 1-2, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 9.

[0116] Example 10

[0117] A method for preparing a bio-based polyamide nanofiltration membrane, which differs from Example 1 in that LiCl is replaced by PEG-600, and the other preparation steps and parameters remain the same.

[0118] Application Example 10-1

[0119] A bio-based polyamide nanofiltration membrane is used for HMF separation and purification. The purification method is the same as that of Application Example 1-1, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 10.

[0120] Application Example 10-2

[0121] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that of Application Example 1-2, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 10.

[0122] Embodiment 11

[0123] A method for preparing a bio-based polyamide nanofiltration membrane, which differs from Example 1 in that LiCl is replaced by PVP-K30, and the other preparation steps and parameters remain the same.

[0124] Application Example 11-1

[0125] A bio-based polyamide nanofiltration membrane is used for separation and purification of HMF. The purification method is the same as that of Application Example 1-1, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 11.

[0126] Application Example 11-2

[0127] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that of Application Example 1-2, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 11.

[0128] Example 12

[0129] A method for preparing a bio-based polyamide nanofiltration membrane, which differs from Example 1 in that DMAc is replaced by DMF, and the other preparation steps and parameters remain the same.

[0130] Application Example 12-1

[0131] A bio-based polyamide nanofiltration membrane is used for HMF separation and purification. The purification method is the same as that of Application Example 1-1, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 12.

[0132] Application Example 12-2

[0133] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that of Application Example 1-2, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 12.

[0134] Example 13

[0135] A method for preparing a bio-based polyamide nanofiltration membrane, which differs from Example 1 in that DMAc is replaced by NMP, and the other preparation steps and parameters remain the same.

[0136] Application Example 13-1

[0137] A bio-based polyamide nanofiltration membrane is used for HMF separation and purification. The purification method is the same as that of Application Example 1-1, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 13.

[0138] Application Example 13-2

[0139] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that of Application Example 1-2, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 13.

[0140] Embodiment 14

[0141] A method for preparing a bio-based polyamide nanofiltration membrane, which differs from Example 1 in that the water bath is replaced by a water / ethanol (v / v=65:35) bath, and the other preparation steps and parameters remain the same.

[0142] Application Example 14-1

[0143] A bio-based polyamide nanofiltration membrane is used for HMF separation and purification. The purification method is the same as that of Application Example 1-1, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 14.

[0144] Application Example 14-2

[0145] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that of Application Example 1-2, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 14.

[0146] Embodiment 15

[0147] A method for preparing a bio-based polyamide nanofiltration membrane, which differs from Example 1 in that the water bath is replaced by a water / NMP (v / v=4:6) bath, and the other preparation steps and parameters remain the same.

[0148] Application Example 15-1

[0149] A bio-based polyamide nanofiltration membrane is used for HMF separation and purification. The purification method is the same as that of Application Example 1-1, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 15.

[0150] Application Example 15-2

[0151] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that of Application Example 1-2, except that the nanofiltration membrane is replaced by the PA6F membrane prepared in Example 15.

[0152] Application Example 16-1

[0153] A bio-based polyamide nanofiltration membrane is used for HMF separation and purification. The purification method is the same as that in Application Example 1-1, except that the membrane separation pressure is replaced with 0.5 MPa, and the remaining steps and parameters are the same.

[0154] Application Example 16-2

[0155] A bio-based polyamide nanofiltration membrane is used for FDCA separation and purification. The purification method is the same as that in Application Example 1-1, except that the membrane separation pressure is replaced with 0.5 MPa, and the remaining steps and parameters are the same.

[0156] Application Example 17-1

[0157] A bio-based polyamide nanofiltration membrane is used for HMF separation and purification. The purification method is the same as that in Application Example 1-1, except that the membrane separation pressure is replaced with 3 MPa, and the remaining steps and parameters are the same.

[0158] Application Example 17-2

[0159] A bio-based polyamide nanofiltration membrane is used for separation and purification of FDCA. The purification method is the same as that in Application Example 1-1, except that the membrane separation pressure is replaced with 3 MPa, and the remaining steps and parameters are the same.

[0160] The PA6F membranes prepared in various embodiments were used to separate and purify HMF or FDCA, respectively. The purity of the purified HMF or FDCA was tested using HPLC. The test results are shown in Table 1.

[0161] Table 1

[0162]

[0163] It can be seen from the test results of the above embodiments and application examples that the present invention adopts poly(hexamethylenediamine furandicarboxylate) (PA6F) as a film-forming polymer and adopts a solution phase inversion method to prepare a PA6F nanofiltration membrane, which can selectively separate HMF and soluble humin, and can selectively separate impurities in an aqueous solution of FDCA sodium salt, thereby obtaining high-purity HMF and FDCA products, which provides a new idea and direction for obtaining higher-purity HMF and FDCA in the future.

[0164] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0165] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A bio-based polyamide nanofiltration membrane, characterized in that: Prepared by the following steps: S1. Add dimethyl 2,5-furandicarboxylate and hexamethylenediamine into a polymerization reactor at a molar ratio of 1:1 to 1.3, then add a titanium catalyst, a phosphorus stabilizer and an antioxidant in sequence, and under nitrogen protection, heat to 60 to 90° C. for reaction for 1 to 1.5 hours, then heat to 120 to 130° C. for reaction for 1 to 1.5 hours, continue to heat to 210 to 230° C., react at a pressure of 1.2 to 1.6 MPa for 1 to 1.5 hours, reduce the pressure to ≤200 Pa within 1 to 2 hours, and continue to react for 2 to 4 hours to obtain polydimethyl furandicarboxylate hexamethylenediamine; S2. Dissolve poly(hexamethylenediamine dimethyl furandicarboxylate) and additives in a solvent, heat and stir, mix evenly to obtain a homogeneous casting liquid; vacuum degas the homogeneous casting liquid and scrape it into a film; immerse the film in a coagulation bath, let it stand to form, and obtain a poly(hexamethylenediamine dimethyl furandicarboxylate) film, soak it in pure water for 22 to 26 hours, take it out and freeze-dry it for storage.

2. A bio-based polyamide nanofiltration membrane according to claim 1, characterized in that: The titanium catalyst is one or more of titanium isopropoxide, titanium citrate, and butyl titanate, and the amount of the titanium catalyst added is 0.5 to 2 wt% of the amount of dimethyl 2,5-furandicarboxylate; And / or, the phosphorus stabilizer is any one or more of triphenyl phosphate, triphenyl phosphite, ethyl phosphate, phosphoric acid, trimethyl phosphate, trimethyl phosphite, and polyphosphoric acid, and the amount of the phosphorus stabilizer added is 0.05 to 0.2 wt % of the amount of dimethyl 2,5-furandicarboxylate.

3. The bio-based polyamide nanofiltration membrane according to claim 1, characterized in that: The antioxidant is any one or more of an amine antioxidant, a phenolic antioxidant, and a phosphorus-containing compound; And / or, the amount of antioxidant added is 0.01 to 0.1 wt % of the amount of dimethyl 2,5-furandicarboxylate used.

4. The bio-based polyamide nanofiltration membrane according to claim 1, characterized in that: The additive is one of LiCl, NH4Cl, Al2O3, SiO2, TiO2, Fe3O4, NaNO3, H3PO4, PEG, PVP, acetone, butanone, and tetrahydrofuran; And / or, the solvent in S2 is one of DMAc, DMF, NMP and DMSO.

5. The bio-based polyamide nanofiltration membrane according to claim 1, characterized in that: In the homogeneous casting solution, the mass percentage of poly(dimethyl furandicarboxylate hexamethylenediamine) is 10-20wt%, the mass percentage of the additive is 1-8wt%, and the balance is solvent.

6. The bio-based polyamide nanofiltration membrane according to claim 1, characterized in that: The coagulation bath is one of water, an organic solvent, and a water / organic solvent mixture; the organic solvent includes but is not limited to DMAc, DMF, NMP, DMSO, ethylene glycol, methanol, ethanol, propanol, and octanol.

7. An application of the bio-based polyamide nanofiltration membrane according to claim 1, characterized in that: Used for separation and purification of 5-hydroxymethylfurfural or 2,5-furandicarboxylic acid.

8. The use of the bio-based polyamide nanofiltration membrane according to claim 7, characterized in that: When used for separation and purification of 5-hydroxymethylfurfural, the method comprises the following steps: The crude 5-hydroxymethylfurfural solution is fed into a device equipped with a bio-based polyamide nanofiltration membrane, and the membrane separation pressure is controlled to be 0.5-4 MPa. A permeate containing 5-hydroxymethylfurfural and a residual liquid containing humin are obtained by nanofiltration; the residual liquid containing humin is diluted with a solvent, and the residual liquid is nanofiltered again after impurities are removed; the permeates are combined, and the solvent and 5-hydroxymethylfurfural are obtained by vacuum distillation; The crude 5-hydroxymethylfurfural solution is a solution with a purity of 85-90% obtained by treating the reaction solution with conventional impurity removal means such as adsorption and filtration.

9. The use of the bio-based polyamide nanofiltration membrane according to claim 7, characterized in that: When used for separation and purification of 2,5-furandicarboxylic acid, the method comprises the following steps: The sodium salt solution of 2,5-furandicarboxylic acid is fed into a device equipped with a bio-based polyamide nanofiltration membrane, and the membrane separation pressure is controlled to be 0.5-4 MPa, and a permeate and a residual liquid containing 2,5-furandicarboxylic acid are obtained by nanofiltration; hydrochloric acid is added to the permeate to acidify and adjust the pH to less than 1, and then a solid is precipitated, which is filtered and dried to obtain 2,5-furandicarboxylic acid; The 2,5-furandicarboxylic acid sodium salt aqueous solution is a solution with a purity of 90-96% obtained by treating the oxidation reaction liquid with conventional impurity removal means such as adsorption and filtration.

10. The use of the bio-based polyamide nanofiltration membrane according to claim 8, characterized in that: The solvent in the crude 5-hydroxymethylfurfural solution is at least one of methyl isobutyl ketone, acetone, dimethyltetrahydrofuran, tetrahydrofuran, dimethyl carbonate, 1,4-dioxane, isopropanol and acetonitrile.

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