A pervaporation membrane for separating 2,2-dimethylbutane from cyclopentane and a method for preparing the same
By grafting pyridine coordinating groups and strong coordination of nanocrystals into the pervaporation membrane, combined with the gradient selectivity layer of the block copolymer, the problem of efficient separation of the near-boiling system of 2,2-dimethylbutane and cyclopentane was solved, achieving high-purity separation and long-term membrane stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANDONG SENZHIHAI NEW MATERIALS CO LTD
- Filing Date
- 2026-03-16
- Publication Date
- 2026-06-05
Smart Images
Figure CN122141483A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of pervaporation membrane technology, specifically to a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane, and its preparation method. Background Technology
[0002] 2,2-Dimethylbutane (neohexane) and cyclopentane are important high-value-added components in the C5 / C6 fractions of petrochemical products. Cyclopentane can be used as a novel environmentally friendly foaming agent, widely applied in polyurethane insulation materials and other fields. 2,2-Dimethylbutane is a high-quality organic solvent and a blending component for gasoline. High-purity separation of these two components is crucial for improving the quality of downstream products. However, their boiling points are 49.74℃ and 49.25℃ respectively, with a boiling point difference of only 0.49℃, classifying them as a typical near-boiling system. Conventional distillation techniques struggle to achieve efficient separation, requiring numerous theoretical plates and extremely high reflux ratios, resulting in significant drawbacks such as high energy consumption, complex equipment, and high separation costs. Even... Improved processes such as azeotropic distillation also face challenges such as cumbersome azeotropic agent recovery, complex process flow, and difficulty in further improving product purity. Pervaporation technology, as a novel membrane separation technology that is efficient, low-energy, and environmentally friendly, is not limited by gas-liquid equilibrium and is particularly suitable for the separation of near-boiling and azeotropic systems. It is an ideal alternative to traditional distillation technology for separating such systems. However, research on pervaporation membranes for the 2,2-dimethylbutane and cyclopentane system is currently scarce. Due to the similar molecular structures and kinetic diameters of the two, conventional membrane materials show very little difference in solubility and diffusion selectivity for them, resulting in low separation factors that cannot meet the high-purity separation requirements of industry. Summary of the Invention
[0003] The purpose of this invention is to provide a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane and its preparation method, so as to solve the technical problems mentioned in the background art.
[0004] To achieve the above objectives, the present invention provides the following technical solution:
[0005] A method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane includes the following steps:
[0006] (1) Hydroxyl polyimide was synthesized using 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 3,5-diaminobenzoic acid and 4,4'-(hexafluoroisopropene)phthalic anhydride as monomers;
[0007] (2) A hydroxyl-containing polyimide was reacted with isonicotinic chloride hydrochloride to prepare a coordination-functionalized polyimide grafted with a pyridine ring;
[0008] (3) In the solution of coordination-functionalized polyimide, 2-aminoterephthalic acid, acetic acid and zirconium tetrachloride are added to carry out in-situ reaction to prepare a hybrid casting solution containing UiO-66-NH2. The hybrid casting solution is coated into a film and dried to obtain a hybrid base film.
[0009] (4) The hybrid base film is reacted with 2-bromoisobutyryl bromide solution to anchor the ATRP initiator on the surface;
[0010] (5) Starting from the base film with anchoring initiator, atom transfer radical polymerization is used to sequentially add isobornyl methacrylate, tridecyl fluorooctyl methacrylate and hydroxyethyl methacrylate for block copolymerization, and graft block copolymers containing terminal hydroxyl groups onto the surface of the base film.
[0011] (6) The grafted base membrane is immersed in a hexamethylene diisocyanate trimer solution for interfacial crosslinking reaction, and then extracted with solvent and dried to obtain the pervaporation membrane.
[0012] In the technical solution of this invention, the prepared pervaporation membrane synergistically improves the separation effect of 2,2-dimethylbutane and cyclopentane in the following aspects: (1) First, through the esterification reaction of phenolic hydroxyl groups and isonicotinyl chloride on the polyimide backbone, pyridine coordination groups are grafted onto the polymer chain to provide uniformly distributed confined nucleation sites for MOF growth, and then, relying on the pyridine ring and Zr 4+The strong coordination effect of UiO-66-NH2 enables monodisperse in-situ growth of UiO-66-NH2 nanocrystals in a polyimide matrix. The nanocrystals and polymer form a defect-free and strongly bonded interface structure through coordination bonds. Relying on the regular and uniform rigid channels of UiO-66-NH2, preferential and rapid diffusion of cyclopentane with a smaller kinetic diameter can be achieved, while steric sieving of 2,2-dimethylbutane with a larger kinetic diameter and higher steric hindrance can be achieved. At the same time, the rigid network constructed by coordination bonds can effectively inhibit the swelling and deformation of the membrane in the alkane system, avoiding the expansion of the membrane channels and the resulting decrease in sieving accuracy. The diffusion selectivity of cyclopentane and 2,2-dimethylbutane is greatly enhanced at the membrane bulk diffusion level, providing a core molecular sieving basis for the efficient separation of the two. (2) The ATRP initiator is directly anchored by the residual hydroxyl groups on the membrane surface, and then PIBOMA-b-PFOMA-b-PHEMA block copolymer is grafted in a directional manner. Taking advantage of the high matching between the solubility parameters of PIBOMA block and cyclopentane, the preferential adsorption and dissolution capacity of cyclopentane on the membrane surface is greatly improved, and the difference in solubility selectivity between cyclopentane and 2,2-dimethylbutane is significantly amplified. The PFOMA block gives the membrane surface low surface energy and excellent anti-swelling properties, reducing non-specific adsorption and membrane structure swelling instability. Finally, through the interfacial crosslinking of the copolymer terminal hydroxyl groups and hexamethylene diisocyanate trimer, a gradient selectivity layer from the membrane body to the surface is constructed, realizing strong covalent bonding between the graft layer and the base membrane, eliminating interfacial mass transfer resistance and concentration polarization, and strengthening the separation selectivity from the dissolution level of the membrane surface. This forms a synergistic effect with the diffusion selectivity of the first aspect mentioned above, and ultimately improves the separation factor and permeate flux of the membrane for the 2,2-dimethylbutane / cyclopentane system, and ensures the long-term stability of the membrane.
[0013] Preferably, in step (1), the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 3,5-diaminobenzoic acid, and 4,4'-(hexafluoroisopropene)phthalic anhydride is 4:(0.5-1.5):(4-6).
[0014] Preferably, in step (2), the mass ratio of hydroxyl polyimide to isonicotinic acid chloride hydrochloride is 10:(1-2).
[0015] Preferably, in step (3), the amount of 2-aminoterephthalic acid added is 0.5 to 1.0 wt% of the coordination-functionalized polyimide solution.
[0016] Preferably, in step (3), the amount of zirconium tetrachloride added is 1 to 2 wt% of the coordination-functionalized polyimide solution.
[0017] Preferably, in step (4), the concentration of the 2-bromoisobutyryl bromide solution is 0.1 to 0.3 mol / L.
[0018] Preferably, in step (5), glycidyl methacrylate and butyl acrylate are also added to the reaction system.
[0019] In experiments, this invention revealed that the pervaporation membrane body (PI and UiO-66-NH2) constitutes a highly rigid micro-network, while the block copolymer brush grafted on the membrane surface has extremely high flexibility and swelling properties. During long-term separation operation, fluctuations in feed concentration cause the flexible grafted layer to undergo periodic swelling-shrinkage volume changes. This thermodynamic deformation mismatch generates concentrated shear stress at the interface between the rigid MOF particles and the flexible polymer brush, eventually tearing the interface like a lever and generating non-selective nanocracks that reduce separation selectivity. To address this technical problem, this invention introduces butyl acrylate (BA) and glycidyl methacrylate (GMA) monomers into the reaction system in step 5, constructing a synergistic transition layer before main chain copolymerization. The principle is as follows: Firstly, utilizing the extremely low glass transition temperature of BA, a molecular-level elastic damping pad is laid between the rigid substrate and the upper steric hindrance grafted chain. The movement of the flexible polymer segments perfectly absorbs and dissipates the local shear stress generated by periodic swelling. Secondly, GMA utilizes the active epoxy groups on its side chains to undergo an in-situ ring-opening addition reaction with the amino groups on the exposed UiO-66-NH2 on the membrane surface, creating numerous "chemical rivets" at the interface. This directly and firmly covalently anchors the polymer graft layer to the inorganic nanocrystal surface. The synergistic effect of the two, one flexible and one rigid, completely eliminates stress concentration and microcrack risks at extremely low cost, endowing the pervaporation membrane with excellent stability, maintaining zero interfacial defects even under long-term high-load swelling cycles.
[0020] Preferably, in step (5), the molar ratio of isoborneol methacrylate, tridecyl fluorooctyl methacrylate, and hydroxyethyl methacrylate is 4:(3-5):(0.5-1.5).
[0021] Preferably, in step (6), the mass concentration of the hexamethylene diisocyanate trimer solution is 4-6 wt%.
[0022] A pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane is prepared by the method described above.
[0023] Compared with the prior art, the beneficial effects of the present invention are:
[0024] (1) The rigid channels of MOF grown in situ preferentially diffuse cyclopentane and inhibit membrane swelling, thus greatly improving diffusion selectivity from the bulk. (2) The grafted block copolymer preferentially adsorbs and dissolves cyclopentane by utilizing the difference in solubility parameters, thus enhancing solubility selectivity from the surface. (3) The introduction of flexible BA segments absorbs deformation stress, while GMA covalently anchors MOF, completely eliminating interfacial microcracks and ensuring long-term operational stability. Attached Figure Description
[0025] Figure 1 This is a low-magnification SEM image of the surface of the pervaporation membrane prepared in Example 1 of the present invention.
[0026] Figure 2 This is a medium-magnification SEM image of the surface of the pervaporation membrane prepared in Example 1 of the present invention.
[0027] Figure 3 This is a high-magnification SEM image of the surface of the pervaporation membrane prepared in Example 1 of the present invention.
[0028] Figure 4 The XPS test spectrum of the pervaporation membrane prepared in Example 1 of this invention is shown.
[0029] Figure 5 The image shows the XRD pattern of the pervaporation membrane prepared in Example 1 of this invention. Detailed Implementation
[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0031] Example 1
[0032] A method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane includes the following steps:
[0033] (1) In a 250 mL three-necked flask under nitrogen protection and equipped with a water separator and a spherical reflux condenser, add 0.04 mol of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and 0.012 mol of... 3,5-Diaminobenzoic acid was mixed with 80 mL of anhydrous N-methylpyrrolidone and 20 mL of anhydrous toluene in a 0°C ice-water bath and mechanically stirred until the monomer was completely dissolved. Then, 0.055 mol of 4,4'-(hexafluoroisopropene)phthalic anhydride was added in two equimolar batches, with a 30-minute interval between each batch. After the addition was completed, the reaction was carried out at an ice-water bath temperature for 4 hours. Nitrogen bubbling protection was maintained throughout the process, and the temperature was programmed for thermal imidization at 80°C for 2 hours, 120°C for 2 hours, 150°C for 3 hours, and 170°C for 2 hours. Water was removed through a water separator throughout the reaction. After the reaction was completed, the temperature was naturally cooled to 25°C, and toluene was removed by vacuum distillation. The product was slowly poured into 500 mL of anhydrous ethanol for precipitation. The filter cake was collected and extracted with anhydrous ethanol using a Soxhlet extractor for 24 hours. The product was then dried in a vacuum drying oven at 80°C for 24 hours to obtain hydroxyl-containing polyimide.
[0034] (2) Take 10g of the hydroxyl-containing polyimide prepared above and add it to 90g of anhydrous N-methylpyrrolidone. Stir mechanically at 25°C until the polymer is completely dissolved to prepare a polymer solution. Add 1.8g of isonicotinic chloride hydrochloride and 2.5g of triethylamine to the solution in sequence. After purging the system with high-purity nitrogen for 30min, stir at 40°C for 12h. After the reaction is completed, let it cool naturally to 25°C to obtain a polyimide solution with grafted pyridine rings.
[0035] (3) To 100g of the coordination-functionalized polyimide solution prepared above, add 0.9g of 2-aminoterephthalic acid, 8.8g of acetic acid and 20mL of anhydrous N-methylpyrrolidone in sequence, and stir at 25°C for 30min under an anhydrous nitrogen atmosphere until the solid is completely dissolved; in an oxygen-free glove box environment, quickly add a pre-prepared solution of 1.8g of zirconium tetrachloride dissolved in 10mL of anhydrous N-methylpyrrolidone, and stir for 10min with high-purity nitrogen gas to mix evenly. Seal the system and program the temperature to 80°C and react at a constant temperature for 24h. Allow it to cool naturally to obtain the hybrid casting solution; use this hybrid casting solution to... The film solution was placed in a vacuum drying oven at 25°C for 2 hours to remove bubbles. The solution was then uniformly coated onto a clean glass substrate using an adjustable gap scraper with a scraper gap of 500 μm. The substrate was then transferred to a horizontally placed constant temperature oven and dried at 60°C for 4 hours. The temperature was then increased to 120°C and dried for 12 hours. After natural cooling and peeling, the substrate was successively immersed in anhydrous ethanol for 6 hours and in deionized water for 18 hours. Finally, it was dried in a vacuum drying oven at 60°C for 24 hours to obtain the hybrid base film.
[0036] (4) Cut and fix the hybrid base film prepared above, immerse it in a pre-prepared 0.25 mol / L anhydrous cyclohexane solution of 2-bromoisobutyryl bromide, add 0.12 mol / L triethylamine to the solution, seal the system and react at 25°C in the dark for 12 h; after the reaction is completed, take out the base film, rinse the film surface with anhydrous cyclohexane and anhydrous ethanol three times each, and dry it in a vacuum drying oven at 25°C for 12 h to obtain the base film with surface anchored ATRP initiator.
[0037] (5) In an oxygen-free glove box, the base film with the above anchoring initiator was placed in a Schlenk polymerization tube, and 20 mL of a mixed solvent of trifluorotoluene and anisole (volume ratio 4:1), 0.001 mol of butyl acrylate and 0.001 mol of glycidyl methacrylate were added in sequence; then 0.0002 mol of cuprous bromide, 0.0004 mol of pentamethyldiethylenetriamine and 0.0004 mol of L-ascorbic acid were added, and the mixture was quickly sealed and reacted at 60 °C for 1 h; under nitrogen protection, 0.02 mol of isobornyl methacrylate was quickly added to the system and the reaction was continued at 60 °C for 3 h; then 0.022 mol of tridecafluorooctyl methacrylate was added and the reaction was continued for 4 h; finally, 0.006 mol of hydroxyethyl methacrylate was added and the reaction was continued for 1 h; after the reaction was completed, the base film was removed, immersed in pre-cooled methanol to quench the polymerization, the film surface was rinsed with ethanol, and a block copolymer containing terminal hydroxyl groups was grafted onto the surface of the base film.
[0038] (6) The grafted base membrane was immersed in an anhydrous acetonitrile solution of hexamethylene diisocyanate trimer with a mass concentration of 5.5 wt%. Dibutyltin dilaurate catalyst with a mass of 0.5% of the hexamethylene diisocyanate trimer was added to the solution. After purging the air with high-purity nitrogen for 30 min, the system was sealed and the temperature was programmed to rise to 60 °C and reacted at a constant temperature for 6 h. The base membrane was taken out and rinsed with anhydrous acetonitrile three times. It was then placed in a vacuum drying oven at 25 °C and dried for 6 h. The membrane was then placed in a Soxhlet extractor and extracted with chloroform at a constant temperature for 6 h. Then, it was extracted with anhydrous ethanol at a constant temperature for 6 h. After taking it out, it was rinsed with fresh anhydrous ethanol twice and placed in a vacuum drying oven at 40 °C and dried at a constant temperature for 24 h to obtain the pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane.
[0039] Example 2
[0040] A method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane includes the following steps:
[0041] (1) In a 250 mL three-necked flask under nitrogen protection and equipped with a water separator and a spherical reflux condenser, add 0.04 mol of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and 0.008 mol of... 3,5-Diaminobenzoic acid was mixed with 80 mL of anhydrous N-methylpyrrolidone and 20 mL of anhydrous toluene in a 0°C ice-water bath and mechanically stirred until the monomer was completely dissolved. Then, 0.045 mol of 4,4'-(hexafluoroisopropene)phthalic anhydride was added in two equimolar batches, with a 30-minute interval between each batch. After the addition was completed, the reaction was carried out at an ice-water bath temperature for 4 hours. Nitrogen bubbling protection was maintained throughout the process, and the temperature was programmed for thermal imidization at 80°C for 2 hours, 120°C for 2 hours, 150°C for 3 hours, and 170°C for 2 hours. Water was removed through a water separator throughout the reaction. After the reaction was completed, the temperature was naturally cooled to 25°C, and toluene was removed by vacuum distillation. The product was slowly poured into 500 mL of anhydrous ethanol for precipitation. The filter cake was collected and extracted with anhydrous ethanol using a Soxhlet extractor for 24 hours. The product was then dried in a vacuum drying oven at 80°C for 24 hours to obtain hydroxyl-containing polyimide.
[0042] (2) Take 10g of the hydroxyl-containing polyimide prepared above and add it to 90g of anhydrous N-methylpyrrolidone. Stir mechanically at 25℃ until the polymer is completely dissolved to prepare a polymer solution. Add 1.3g of isonicotinic chloride hydrochloride and 2.5g of triethylamine to the solution in sequence. After purging the system with high-purity nitrogen for 30min, stir at 40℃ for 12h. After the reaction is completed, let it cool naturally to 25℃ to obtain a polyimide solution with grafted pyridine rings.
[0043] (3) To 100g of the coordination-functionalized polyimide solution prepared above, add 0.6g of 2-aminoterephthalic acid, 8.8g of acetic acid and 20mL of anhydrous N-methylpyrrolidone in sequence, and stir at 25°C for 30min under an anhydrous nitrogen atmosphere until the solid is completely dissolved; in an oxygen-free glove box environment, quickly add a pre-prepared solution of 1.2g of zirconium tetrachloride dissolved in 10mL of anhydrous N-methylpyrrolidone, and stir for 10min with high-purity nitrogen gas to mix evenly. Seal the system and program the temperature to 80°C and react at a constant temperature for 24h. Allow it to cool naturally to obtain the hybrid casting solution; use this hybrid casting solution to... The film solution was placed in a vacuum drying oven at 25°C for 2 hours to remove bubbles. The solution was then uniformly coated onto a clean glass substrate using an adjustable gap scraper with a scraper gap of 500 μm. The substrate was then transferred to a horizontally placed constant temperature oven and dried at 60°C for 4 hours. The temperature was then increased to 120°C and dried for 12 hours. After natural cooling and peeling, the substrate was successively immersed in anhydrous ethanol for 6 hours and in deionized water for 18 hours. Finally, it was dried in a vacuum drying oven at 60°C for 24 hours to obtain the hybrid base film.
[0044] (4) Cut and fix the hybrid base film prepared above, immerse it in a pre-prepared 0.15 mol / L anhydrous cyclohexane solution of 2-bromoisobutyryl bromide, add 0.12 mol / L triethylamine to the solution, seal the system and react at 25°C in the dark for 12 h; after the reaction is completed, take out the base film, rinse the film surface with anhydrous cyclohexane and anhydrous ethanol three times each, and dry it in a vacuum drying oven at 25°C for 12 h to obtain the base film with surface anchored ATRP initiator.
[0045] (5) In an oxygen-free glove box, the base film with the above anchoring initiator was placed in a Schlenk polymerization tube, and 20 mL of a mixed solvent of trifluorotoluene and anisole (volume ratio 4:1), 0.001 mol of butyl acrylate and 0.001 mol of glycidyl methacrylate were added in sequence; then 0.0002 mol of cuprous bromide, 0.0004 mol of pentamethyldiethylenetriamine and 0.0004 mol of L-ascorbic acid were added, and the mixture was quickly sealed and reacted at 60 °C for 1 h; under nitrogen protection, 0.02 mol of isobornyl methacrylate was quickly added to the system and the reaction was continued at 60 °C for 3 h; then 0.018 mol of tridecafluorooctyl methacrylate was added and the reaction was continued for 4 h; finally, 0.0035 mol of hydroxyethyl methacrylate was added and the reaction was continued for 1 h; after the reaction was completed, the base film was removed, immersed in pre-cooled methanol to quench the polymerization, the film surface was rinsed with ethanol, and a block copolymer containing terminal hydroxyl groups was grafted onto the surface of the base film.
[0046] (6) The grafted base membrane was immersed in an anhydrous acetonitrile solution of hexamethylene diisocyanate trimer with a mass concentration of 4.5 wt%. Dibutyltin dilaurate catalyst with a mass of 0.5% of the hexamethylene diisocyanate trimer was added to the solution. After purging the air with high-purity nitrogen for 30 min, the system was sealed and the temperature was programmed to rise to 60 °C and reacted at a constant temperature for 6 h. The base membrane was taken out and rinsed with anhydrous acetonitrile three times. It was then placed in a vacuum drying oven at 25 °C and dried for 6 h. The membrane was then placed in a Soxhlet extractor and extracted with chloroform at a constant temperature for 6 h. Then, it was extracted with anhydrous ethanol at a constant temperature for 6 h. After taking it out, it was rinsed with fresh anhydrous ethanol twice and placed in a vacuum drying oven at 40 °C and dried at a constant temperature for 24 h to obtain the pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane.
[0047] Example 3
[0048] A method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane includes the following steps:
[0049] (1) In a 250 mL three-necked flask under nitrogen protection and equipped with a water separator and a spherical reflux condenser, add 0.04 mol of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and 0.01 mol of... 3,5-Diaminobenzoic acid was mixed with 80 mL of anhydrous N-methylpyrrolidone and 20 mL of anhydrous toluene in a 0°C ice-water bath and mechanically stirred until the monomer was completely dissolved. Then, 0.05 mol of 4,4'-(hexafluoroisopropene)phthalic anhydride was added in two equimolar batches, with a 30-minute interval between each batch. After the addition was completed, the reaction was carried out at an ice-water bath temperature for 4 hours. Nitrogen bubbling protection was maintained throughout the process, and the temperature was programmed for thermal imidization at 80°C for 2 hours, 120°C for 2 hours, 150°C for 3 hours, and 170°C for 2 hours. Water was removed through a water separator throughout the reaction. After the reaction was completed, the temperature was naturally cooled to 25°C, and toluene was removed by vacuum distillation. The product was slowly poured into 500 mL of anhydrous ethanol for precipitation. The filter cake was collected and extracted with anhydrous ethanol using a Soxhlet extractor for 24 hours. The product was then dried in a vacuum drying oven at 80°C for 24 hours to obtain hydroxyl-containing polyimide.
[0050] (2) Take 10g of the hydroxyl-containing polyimide prepared above and add it to 90g of anhydrous N-methylpyrrolidone. Stir mechanically at 25℃ until the polymer is completely dissolved to prepare a polymer solution. Add 1.5g of isonicotinic chloride hydrochloride and 2.5g of triethylamine to the solution in sequence. After purging the system with high-purity nitrogen for 30min, stir at 40℃ for 12h. After the reaction is completed, let it cool naturally to 25℃ to obtain a polyimide solution with grafted pyridine rings.
[0051] (3) To 100g of the coordination-functionalized polyimide solution prepared above, add 0.7g of 2-aminoterephthalic acid, 8.8g of acetic acid and 20mL of anhydrous N-methylpyrrolidone in sequence, and stir at 25°C for 30min under an anhydrous nitrogen atmosphere until the solid is completely dissolved; in an oxygen-free glove box environment, quickly add a pre-prepared solution of 1.5g of zirconium tetrachloride dissolved in 10mL of anhydrous N-methylpyrrolidone, and stir for 10min with high-purity nitrogen gas to mix evenly. Seal the system and program the temperature to 80°C and react at a constant temperature for 24h. Allow it to cool naturally to obtain the hybrid casting solution; use this hybrid casting solution to... The film solution was placed in a vacuum drying oven at 25°C for 2 hours to remove bubbles. The solution was then uniformly coated onto a clean glass substrate using an adjustable gap scraper with a scraper gap of 500 μm. The substrate was then transferred to a horizontally placed constant temperature oven and dried at 60°C for 4 hours. The temperature was then increased to 120°C and dried for 12 hours. After natural cooling and peeling, the substrate was successively immersed in anhydrous ethanol for 6 hours and in deionized water for 18 hours. Finally, it was dried in a vacuum drying oven at 60°C for 24 hours to obtain the hybrid base film.
[0052] (4) Cut and fix the hybrid base film prepared above, immerse it in a pre-prepared 0.2 mol / L anhydrous cyclohexane solution of 2-bromoisobutyryl bromide, add 0.12 mol / L triethylamine to the solution, seal the system and react at 25°C in the dark for 12 h; after the reaction is completed, take out the base film, rinse the film surface with anhydrous cyclohexane and anhydrous ethanol three times each, and dry it in a vacuum drying oven at 25°C for 12 h to obtain the base film with surface anchored ATRP initiator.
[0053] (5) In an oxygen-free glove box, the base film with the above anchoring initiator was placed in a Schlenk polymerization tube, and 20 mL of a mixed solvent of trifluorotoluene and anisole (volume ratio 4:1), 0.001 mol of butyl acrylate and 0.001 mol of glycidyl methacrylate were added in sequence; then 0.0002 mol of cuprous bromide, 0.0004 mol of pentamethyldiethylenetriamine and 0.0004 mol of L-ascorbic acid were added, and the mixture was quickly sealed and reacted at 60 °C for 1 h; under nitrogen protection, 0.02 mol of isobornyl methacrylate was quickly added to the system and the reaction was continued at 60 °C for 3 h; then 0.02 mol of tridecafluorooctyl methacrylate was added and the reaction was continued for 4 h; finally, 0.005 mol of hydroxyethyl methacrylate was added and the reaction was continued for 1 h; after the reaction was completed, the base film was removed, immersed in pre-cooled methanol to quench the polymerization, the film surface was rinsed with ethanol, and a block copolymer containing terminal hydroxyl groups was grafted onto the surface of the base film.
[0054] (6) The grafted base membrane was immersed in an anhydrous acetonitrile solution of hexamethylene diisocyanate trimer with a mass concentration of 5 wt%. Dibutyltin dilaurate catalyst with a mass of 0.5% of the hexamethylene diisocyanate trimer was added to the solution. After purging the air with high-purity nitrogen for 30 min, the system was sealed and the temperature was programmed to rise to 60 °C and reacted at a constant temperature for 6 h. The base membrane was taken out and rinsed with anhydrous acetonitrile three times. It was then placed in a vacuum drying oven at 25 °C and dried for 6 h. The membrane was then placed in a Soxhlet extractor and extracted with chloroform at a constant temperature for 6 h. Then, it was extracted with anhydrous ethanol at a constant temperature for 6 h. After taking it out, it was rinsed with fresh anhydrous ethanol twice and placed in a vacuum drying oven at 40 °C and dried at a constant temperature for 24 h to obtain the pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane.
[0055] Example 4
[0056] A method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane includes the following steps:
[0057] (1) In a 250 mL three-necked flask under nitrogen protection and equipped with a water separator and a spherical reflux condenser, add 0.04 mol of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and 0.015 mol of... 3,5-Diaminobenzoic acid was mixed with 80 mL of anhydrous N-methylpyrrolidone and 20 mL of anhydrous toluene in a 0°C ice-water bath and mechanically stirred until the monomer was completely dissolved. Then, 0.06 mol of 4,4'-(hexafluoroisopropene)phthalic anhydride was added in two equimolar batches, with a 30-minute interval between each batch. After the addition was completed, the reaction was carried out at an ice-water bath temperature for 4 hours. Nitrogen bubbling protection was maintained throughout the process, and the temperature was programmed for thermal imidization at 80°C for 2 hours, 120°C for 2 hours, 150°C for 3 hours, and 170°C for 2 hours. Water was removed through a water separator throughout the reaction. After the reaction was completed, the temperature was naturally cooled to 25°C, and toluene was removed by vacuum distillation. The product was slowly poured into 500 mL of anhydrous ethanol for precipitation. The filter cake was collected and extracted with anhydrous ethanol using a Soxhlet extractor for 24 hours. The product was then dried in a vacuum drying oven at 80°C for 24 hours to obtain hydroxyl-containing polyimide.
[0058] (2) Take 10g of the hydroxyl-containing polyimide prepared above and add it to 90g of anhydrous N-methylpyrrolidone. Stir mechanically at 25℃ until the polymer is completely dissolved to prepare a polymer solution. Add 2g of isonicotinyl chloride hydrochloride and 2.5g of triethylamine to the solution in sequence. After purging the system with high-purity nitrogen for 30min, stir at 40℃ for 12h. After the reaction is completed, let it cool naturally to 25℃ to obtain a polyimide solution with grafted pyridine rings.
[0059] (3) To 100g of the coordination-functionalized polyimide solution prepared above, add 1.0g of 2-aminoterephthalic acid, 8.8g of acetic acid and 20mL of anhydrous N-methylpyrrolidone in sequence, and stir at 25°C for 30min under an anhydrous nitrogen atmosphere until the solid is completely dissolved; in an oxygen-free glove box environment, quickly add a pre-prepared solution of 2g of zirconium tetrachloride dissolved in 10mL of anhydrous N-methylpyrrolidone, and stir with high-purity nitrogen for 10min to mix evenly. Seal the system and program the temperature to 80°C and react at a constant temperature for 24h. Allow it to cool naturally to obtain the hybrid casting solution; use the hybrid casting solution to... The liquid was placed in a vacuum drying oven at 25°C for 2 hours to remove bubbles. The liquid film was then uniformly coated onto a clean glass substrate using an adjustable gap scraper with a scraper gap of 500 μm. The substrate was then transferred to a horizontally placed constant temperature oven and dried at 60°C for 4 hours. The temperature was then increased to 120°C and dried for 12 hours. After natural cooling and peeling, the substrate was successively immersed in anhydrous ethanol for 6 hours and in deionized water for 18 hours. Finally, it was dried in a vacuum drying oven at 60°C for 24 hours to obtain the hybrid base film.
[0060] (4) Cut and fix the hybrid base film prepared above, immerse it in a pre-prepared 0.3 mol / L anhydrous cyclohexane solution of 2-bromoisobutyryl bromide, add 0.12 mol / L triethylamine to the solution, seal the system and react at 25°C in the dark for 12 h; after the reaction is completed, take out the base film, rinse the film surface with anhydrous cyclohexane and anhydrous ethanol three times each, and dry it in a vacuum drying oven at 25°C for 12 h to obtain the base film with surface anchored ATRP initiator.
[0061] (5) In an oxygen-free glove box, the base film with the above anchoring initiator was placed in a Schlenk polymerization tube, and 20 mL of a mixed solvent of trifluorotoluene and anisole (volume ratio 4:1), 0.001 mol of butyl acrylate and 0.001 mol of glycidyl methacrylate were added in sequence; then 0.0002 mol of cuprous bromide, 0.0004 mol of pentamethyldiethylenetriamine and 0.0004 mol of L-ascorbic acid were added, and the mixture was quickly sealed and reacted at 60 °C for 1 h; under nitrogen protection, 0.02 mol of isobornyl methacrylate was quickly added to the system and the reaction was continued at 60 °C for 3 h; then 0.025 mol of tridecafluorooctyl methacrylate was added and the reaction was continued for 4 h; finally, 0.0075 mol of hydroxyethyl methacrylate was added and the reaction was continued for 1 h; after the reaction was completed, the base film was removed, immersed in pre-cooled methanol to quench the polymerization, the film surface was rinsed with ethanol, and a block copolymer containing terminal hydroxyl groups was grafted onto the surface of the base film.
[0062] (6) The grafted base membrane was immersed in an anhydrous acetonitrile solution of hexamethylene diisocyanate trimer with a mass concentration of 6 wt%. Dibutyltin dilaurate catalyst with a mass of 0.5% of the hexamethylene diisocyanate trimer was added to the solution. After replacing the air with high-purity nitrogen for 30 min, the system was sealed and the temperature was programmed to rise to 60 °C and reacted at a constant temperature for 6 h. The base membrane was taken out and rinsed with anhydrous acetonitrile three times. It was then placed in a vacuum drying oven at 25 °C and dried for 6 h. The membrane was then placed in a Soxhlet extractor and extracted with chloroform at a constant temperature for 6 h. Then, it was extracted with anhydrous ethanol at a constant temperature for 6 h. After taking it out, it was rinsed with fresh anhydrous ethanol twice and placed in a vacuum drying oven at 40 °C and dried at a constant temperature for 24 h to obtain the pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane.
[0063] Example 5
[0064] A method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane includes the following steps:
[0065] (1) In a 250 mL three-necked flask under nitrogen protection and equipped with a water separator and a spherical reflux condenser, add 0.04 mol of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and 0.005 mol of... 3,5-Diaminobenzoic acid was mixed with 80 mL of anhydrous N-methylpyrrolidone and 20 mL of anhydrous toluene in a 0°C ice-water bath and mechanically stirred until the monomer was completely dissolved. Then, 0.04 mol of 4,4'-(hexafluoroisopropene)phthalic anhydride was added in two equimolar batches, with a 30-minute interval between each batch. After the addition was completed, the reaction was carried out at an ice-water bath temperature for 4 hours. Nitrogen bubbling protection was maintained throughout the process, and the temperature was programmed for thermal imidization at 80°C for 2 hours, 120°C for 2 hours, 150°C for 3 hours, and 170°C for 2 hours. Water was removed through a water separator throughout the reaction. After the reaction was completed, the temperature was naturally cooled to 25°C, and toluene was removed by vacuum distillation. The product was slowly poured into 500 mL of anhydrous ethanol for precipitation. The filter cake was collected and extracted with anhydrous ethanol using a Soxhlet extractor for 24 hours. The product was then dried in a vacuum drying oven at 80°C for 24 hours to obtain hydroxyl-containing polyimide.
[0066] (2) Take 10g of the hydroxyl-containing polyimide prepared above and add it to 90g of anhydrous N-methylpyrrolidone. Stir mechanically at 25℃ until the polymer is completely dissolved to prepare a polymer solution. Add 1g of isonicotinyl chloride hydrochloride and 2.5g of triethylamine to the solution in sequence. After purging the system with high-purity nitrogen for 30min, stir at 40℃ for 12h. After the reaction is completed, let it cool naturally to 25℃ to obtain a polyimide solution with grafted pyridine rings.
[0067] (3) To 100g of the coordination-functionalized polyimide solution prepared above, add 0.5g of 2-aminoterephthalic acid, 8.8g of acetic acid and 20mL of anhydrous N-methylpyrrolidone in sequence, and stir at 25°C for 30min under an anhydrous nitrogen atmosphere until the solid is completely dissolved; in an oxygen-free glove box environment, quickly add a pre-prepared solution of 1g of zirconium tetrachloride dissolved in 10mL of anhydrous N-methylpyrrolidone, and stir with high-purity nitrogen for 10min to mix evenly. Seal the system and program the temperature to 80°C and react at a constant temperature for 24h. Allow it to cool naturally to obtain the hybrid casting solution; use the hybrid casting solution to... The liquid was placed in a vacuum drying oven at 25°C for 2 hours to remove bubbles. The liquid film was then uniformly coated onto a clean glass substrate using an adjustable gap scraper with a scraper gap of 500 μm. The substrate was then transferred to a horizontally placed constant temperature oven and dried at 60°C for 4 hours. The temperature was then increased to 120°C and dried for 12 hours. After natural cooling and peeling, the substrate was successively immersed in anhydrous ethanol for 6 hours and in deionized water for 18 hours. Finally, it was dried in a vacuum drying oven at 60°C for 24 hours to obtain the hybrid base film.
[0068] (4) Cut and fix the hybrid base film prepared above, immerse it in a pre-prepared 0.1 mol / L anhydrous cyclohexane solution of 2-bromoisobutyryl bromide, add 0.12 mol / L triethylamine to the solution, seal the system and react at 25°C in the dark for 12 h; after the reaction is completed, take out the base film, rinse the film surface with anhydrous cyclohexane and anhydrous ethanol three times each, and dry it in a vacuum drying oven at 25°C for 12 h to obtain the base film with surface anchored ATRP initiator.
[0069] (5) In an oxygen-free glove box, the base film with the above anchoring initiator was placed in a Schlenk polymerization tube, and 20 mL of a mixed solvent of trifluorotoluene and anisole (volume ratio 4:1), 0.001 mol of butyl acrylate and 0.001 mol of glycidyl methacrylate were added in sequence; then 0.0002 mol of cuprous bromide, 0.0004 mol of pentamethyldiethylenetriamine and 0.0004 mol of L-ascorbic acid were added, and the mixture was quickly sealed and reacted at 60 °C for 1 h; under nitrogen protection, 0.02 mol of isobornyl methacrylate was quickly added to the system and the reaction was continued at 60 °C for 3 h; then 0.015 mol of tridecafluorooctyl methacrylate was added and the reaction was continued for 4 h; finally, 0.0025 mol of hydroxyethyl methacrylate was added and the reaction was continued for 1 h; after the reaction was completed, the base film was removed, immersed in pre-cooled methanol to quench the polymerization, the film surface was rinsed with ethanol, and a block copolymer containing terminal hydroxyl groups was grafted onto the surface of the base film.
[0070] (6) The grafted base membrane was immersed in an anhydrous acetonitrile solution of hexamethylene diisocyanate trimer with a mass concentration of 4 wt%. Dibutyltin dilaurate catalyst with a mass of 0.5% of the hexamethylene diisocyanate trimer was added to the solution. After purging the air with high-purity nitrogen for 30 min, the system was sealed and the temperature was programmed to rise to 60 °C and reacted at a constant temperature for 6 h. The base membrane was taken out and rinsed with anhydrous acetonitrile three times. It was then placed in a vacuum drying oven at 25 °C and dried for 6 h. The membrane was then placed in a Soxhlet extractor and extracted with chloroform at a constant temperature for 6 h. Then, it was extracted with anhydrous ethanol at a constant temperature for 6 h. After taking it out, it was rinsed with fresh anhydrous ethanol twice and placed in a vacuum drying oven at 40 °C and dried at a constant temperature for 24 h to obtain the pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane.
[0071] Comparative Example 1: This comparative example prepared a pure polyimide film without any modification. The specific steps were as follows: Hydroxyl polyimide was synthesized in accordance with step (1) of Example 1. 10g of the prepared hydroxyl polyimide was added to 90g of anhydrous N-methylpyrrolidone and stirred at 25°C until completely dissolved to prepare a 10wt% polymer solution. After vacuum degassing of the solution, the film was prepared in accordance with the coating process, gradient temperature drying process, solvent immersion and vacuum drying process of step (3) of Example 1. No subsequent coordination grafting, MOF in situ growth, surface initiator anchoring, block grafting and interface crosslinking modification steps were performed. Finally, a pure polyimide film was obtained.
[0072] Comparative Example 2: This comparative example only completed coordination grafting and MOF in-situ growth modification, without surface functionalization modification. The specific steps are as follows: UiO-66-NH2 hybrid base film was prepared in accordance with steps (1)-(3) of Example 1, without performing the subsequent steps (4)-(6) of surface initiator anchoring, block copolymer grafting, and interfacial crosslinking reaction. The hybrid base film was post-treated by the dual-solvent Soxhlet extraction and vacuum drying process in step (6) of Example 1.
[0073] Comparative Example 3: This comparative example only completed the surface grafting and crosslinking modification of the membrane, without coordination grafting and MOF in-situ growth modification. The specific steps are as follows: Hydroxyl polyimide was synthesized according to step (1) of Example 1, and a 10wt% NMP solution was prepared. Pure polyimide-based membrane was prepared directly according to the process of step (3) of Example 1, without coordination grafting in step (2) and MOF in-situ growth in step (3). Subsequently, the surface initiator anchoring, block copolymer grafting, interface crosslinking and post-treatment were completed completely according to steps (4)-(6) of Example 1 to obtain the pervaporation membrane.
[0074] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that butyl acrylate and glycidyl methacrylate are not added in step 5.
[0075] Performance testing:
[0076] 1. Pervaporation separation performance test: The pervaporation separation performance test was conducted using a self-made pervaporation membrane evaluation device. Before the test, the membrane to be tested was cut to a size with an effective area of 22 cm². 2Circular samples were sealed in a stainless steel membrane assembly. The feed side consisted of a 1:1 mass ratio solution of 2,2-dimethylbutane and cyclopentane, with the feed temperature maintained at a constant 40°C using a constant temperature water bath system. The feed circulation flow rate was set to 500 mL / min to eliminate the effects of concentration polarization. A two-stage rotary vane vacuum pump was used on the permeate side to maintain a system vacuum of ≤100 Pa. The permeate was collected by condensation using a liquid nitrogen cold trap. Timing began after the system had been running stably for 2 hours, and the permeate was collected continuously for 3 hours. The sample and permeate were analyzed using a gas chromatograph equipped with a flame ionization detector. The composition of the permeate was quantitatively analyzed. Each sample was tested in triplicate, and the average value of the test results was used to calculate the permeate flux and separation factor. The permeate flux is the total mass of permeate passing through a unit effective membrane area per unit time. The separation factor is used to characterize the membrane's selectivity for separating the two components and is calculated using the formula: α = (Ycp / Ydm) / (Xcp / Xdm), where Ycp and Ydm are the mass fractions of cyclopentane and 2,2-dimethylbutane in the permeate, respectively, and Xcp and Xdm are the mass fractions of cyclopentane and 2,2-dimethylbutane in the feed solution, respectively. The test results are shown in Table 1.
[0077] 2. Long-term operational stability test method: The long-term operational stability test of the membrane was conducted using the aforementioned pervaporation membrane evaluation device. The test environment, feed composition, temperature, flow rate, vacuum degree, and other test conditions were completely consistent with those of the pervaporation separation performance test. The membrane sample was subjected to a continuous 100-hour operation test. Permeate was collected every 12 hours and its composition was analyzed using gas chromatography. The permeate flux and separation factor of the membrane were calculated at different operating times. Using the separation factor of the initial 2 hours after system stabilization as a baseline, the membrane separation factor decay rate after 100 hours of continuous operation was calculated to characterize the long-term operational stability of the membrane. The decay rate was calculated using the formula: Separation factor decay rate (%) = (Initial separation factor - Separation factor after 100 hours of continuous operation) / Initial separation factor × 100%. The test results are shown in Table 1.
[0078] 3. Solvent Swelling Resistance Test of Membrane: The solvent swelling resistance of the membrane was tested using a gravimetric method. First, the membrane to be tested was cut into 2cm × 2cm square samples and dried in a 60℃ vacuum drying oven until constant weight. The dry membrane weight W0 was weighed and recorded using an electronic analytical balance with an accuracy of 0.01mg. Then, the dried membrane sample was completely immersed in a 1:1 mass ratio solution of 2,2-dimethylbutane and cyclopentane, and sealed and soaked in a 25℃ constant temperature environment for 24 hours until the membrane reached swelling equilibrium. After removing the membrane sample, the residual solution on the membrane surface was quickly blotted dry with filter paper, and the weight W1 of the membrane after swelling equilibrium was immediately weighed and recorded. Each sample was tested in triplicate, and the average value of the test results was used to calculate the swelling degree, which characterizes the solvent swelling resistance of the membrane. The swelling degree calculation formula is: Swelling degree (%) = (W1 - W0) / W0 × 100%. The test results are shown in Table 1.
[0079] Table 1:
[0080]
[0081] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane, characterized in that, Includes the following steps: (1) Hydroxyl polyimide was synthesized using 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 3,5-diaminobenzoic acid and 4,4'-(hexafluoroisopropene)phthalic anhydride as monomers; (2) A hydroxyl-containing polyimide was reacted with isonicotinic chloride hydrochloride to prepare a coordination-functionalized polyimide grafted with a pyridine ring; (3) In the solution of coordination-functionalized polyimide, 2-aminoterephthalic acid, acetic acid and zirconium tetrachloride are added to carry out in-situ reaction to prepare a hybrid casting solution containing UiO-66-NH2. The hybrid casting solution is coated into a film and dried to obtain a hybrid base film. (4) The hybrid base film is reacted with 2-bromoisobutyryl bromide solution to anchor the ATRP initiator on the surface; (5) Starting from the base film with anchoring initiator, atom transfer radical polymerization is used to sequentially add isobornyl methacrylate, tridecyl fluorooctyl methacrylate and hydroxyethyl methacrylate for block copolymerization, and graft block copolymers containing terminal hydroxyl groups onto the surface of the base film. (6) The grafted base membrane is immersed in a hexamethylene diisocyanate trimer solution for interfacial crosslinking reaction, and then extracted with solvent and dried to obtain the pervaporation membrane.
2. The method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane according to claim 1, characterized in that, In step (1), the molar ratio of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 3,5-diaminobenzoic acid, and 4,4'-(hexafluoroisopropene)phthalic anhydride is 4:(0.5-1.5):(4-6).
3. The method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane according to claim 1, characterized in that, In step (2), the mass ratio of hydroxyl polyimide to isonicotinic chloride hydrochloride is 10:(1-2).
4. The method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane according to claim 1, characterized in that, In step (3), the amount of 2-aminoterephthalic acid added is 0.5 to 1.0 wt% of the coordination-functionalized polyimide solution.
5. The method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane according to claim 1, characterized in that, In step (3), the amount of zirconium tetrachloride added is 1 to 2 wt% of the coordination functionalized polyimide solution.
6. The method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane according to claim 1, characterized in that, In step (4), the concentration of the 2-bromoisobutyryl bromide solution is 0.1–0.3 mol / L.
7. The method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane according to claim 1, characterized in that, In step (5), glycidyl methacrylate and butyl acrylate are also added to the reaction system.
8. The method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane according to claim 1, characterized in that, In step (5), the molar ratio of isobornyl methacrylate, tridecafluorooctyl methacrylate, and hydroxyethyl methacrylate is 4:(3-5):(0.5-1.5).
9. The method for preparing a pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane according to claim 1, characterized in that, In step (6), the mass concentration of the hexamethylene diisocyanate trimer solution is 4-6 wt%.
10. A pervaporation membrane for separating 2,2-dimethylbutane and cyclopentane, characterized in that, It is prepared by the method described in any one of claims 1 to 9 above.