Molecular sieve membrane based on nutrient-rich solution as well as preparation method and application of molecular sieve membrane

Abstract

The invention provides a molecular sieve membrane based on a nutrient-rich solution as well as a preparation method and application of the molecular sieve membrane, and belongs to the technical field of inorganic molecular sieve membrane materials and membrane separation. According to the method, a high-nutrition reaction system is constructed, the composition of a silicon source and an alkali source is accurately regulated and controlled, rapid nucleation and efficient growth of molecular sieve crystals are realized in a relatively short time, and the high-crystallinity molecular sieve seed crystal is prepared; then uniformly loading the seed crystal on the surface of the porous support body to form a continuous and compact seed crystal layer; and then carrying out short-time hydrothermal growth by utilizing the eutrophic reaction liquid, and rapidly constructing the molecular sieve membrane with a complete structure and controllable thickness. The preparation method disclosed by the invention is simple and efficient, the preparation period of the molecular sieve membrane is effectively shortened, alternation and dense accumulation among crystals are promoted, and the generation of membrane defects is remarkably reduced. The prepared molecular sieve membrane shows excellent separation performance in pervaporation separation application of water and low-molecular-weight and low-polarity organic solvents (such as acetonitrile, ethanol, acetone, isopropanol, tetrahydrofuran, n-butyl alcohol, tert-butyl alcohol and dimethyl carbonate), and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of inorganic membrane materials and preparation technology, specifically to a molecular sieve membrane based on nutrient-rich solution, its preparation method, and its application in separating water / isopropanol, water / acetone, water / ethanol, water / dimethyl carbonate, water / acetonitrile, water / tetrahydrofuran, water / n-butanol, and water / tert-butanol. Background Technology

[0002] Membrane separation is a technology that separates components based on differences in the transport behavior of substances within a membrane. It typically features low energy consumption, mild operating conditions, compact equipment, and ease of continuous operation, demonstrating promising application potential in chemical production, energy conversion, and environmental treatment. The structural characteristics, pore properties, and chemical stability of membrane materials are key factors affecting membrane separation performance. Compared to polymer membranes, inorganic membranes maintain better structural stability and lifespan even in high-temperature, strong solvent, and corrosive environments. Among these, molecular sieve membranes, with their regular crystal structure and highly uniform pore size, enable precise sieving at the molecular scale, thus gradually becoming an important development direction for high-performance membrane materials.

[0003] T-type molecular sieves are a class of aluminosilicate materials with specific pore structures. Their effective pore size is 0.36 nm × 0.51 nm, making them suitable for the selective separation of water / organic molecules. They have potential applications in organic solvent dehydration and small molecule separation. Furthermore, these molecular sieves typically exhibit some hydrophilicity and good chemical stability, making them applicable in complex systems. However, because T-type molecular sieves are alumina-rich, they are prone to uneven silica-alumina distribution and insufficient grain bonding during crystal growth. This can lead to grain boundary defects or non-selective mass transfer channels in the membrane, thus affecting the membrane's separation selectivity and long-term operational stability.

[0004] Existing methods for preparing T-type molecular sieve membranes mostly employ hydrothermal in-situ synthesis or seed-induced growth processes. However, these methods generally suffer from limitations in the nutrient levels of the reaction system, resulting in slow crystal nucleation and growth rates, long film formation cycles, difficulty in precisely controlling membrane thickness, insufficient surface uniformity, and ineffective defect suppression. Furthermore, some methods rely on mineralizers or require high-temperature post-treatment steps, which not only increase energy consumption and process complexity but also easily lead to structural defects such as membrane cracking and delamination due to excessive crystal growth and thermal stress, affecting the overall integrity and lifespan of the membrane. Therefore, how to achieve rapid construction, controllable thickness growth, and effective defect suppression of T-type molecular sieve membranes while ensuring the integrity of the membrane structure, through controlling the composition of the reaction system and the crystal growth process, remains a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] (a) Technical problems to be solved To address the common problems in the preparation of existing T-type molecular sieve membranes, such as slow film formation rate, long preparation cycle, difficulty in precisely controlling membrane thickness and structure, grain boundary defects, and insufficient process repeatability and stability, this invention proposes a molecular sieve membrane based on nutrient-rich solution and its preparation method.

[0006] This invention constructs a high-nutrient reaction system and coordinates the induced growth of multi-sized, highly active crystal seeds to achieve rapid nucleation and controllable epitaxial growth of T-type molecular sieve crystals within a short hydrothermal time. This solves the problems of slow membrane growth, discontinuous structure, and difficulty in suppressing defects in traditional methods, and enables the preparation of T-type molecular sieve membranes with rapid membrane construction, controllable thickness, dense structure, and stable separation performance.

[0007] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: One objective of this invention is to provide a method for preparing a molecular sieve membrane based on a nutrient-rich solution, the specific preparation steps of which are as follows: S1. Preparation of the first reaction solution: Aluminum source, silicon source, first inorganic base, second inorganic base, organic template agent and deionized water are mixed evenly in molar ratio to form a solution, and the solution is continuously aged at room temperature to obtain the first reaction solution; S2. Preparation of molecular sieve seed crystals: The first reaction solution obtained in S1 is transferred to a high-pressure reactor for hydrothermal synthesis reaction. After the reaction is completed, the reactor is cooled, the reaction product is separated by centrifugation, washed with deionized water until neutral, and freeze-dried to obtain the original molecular sieve seed crystals. S3. Template removal and ball milling: The original molecular sieve seed crystals obtained in S2 are placed in a muffle furnace for calcination to obtain first-size seed crystals; the calcined seed crystals are cooled to room temperature and then ball milled to obtain second-size seed crystals with smaller sizes for later use. S4. Preparation of seeded support: The two sizes of molecular sieve seeds obtained in S3 are added to deionized water to prepare a seed solution of the first size and a seed solution of the second size with a concentration of 0.25-1wt%. The two types of seeds are uniformly coated onto the porous support to form a seed layer on the surface of the support, thus obtaining a seeded support. S5. Preparation of molecular sieve membrane: Aluminum source, silicon source, first inorganic base, second inorganic base and deionized water are mixed evenly in molar ratio to obtain a mixed solution. The mixed solution is continuously stirred at room temperature to obtain a nutrient-rich second reaction solution. The second reaction solution and the seeded support prepared in S4 are placed in a reaction vessel and subjected to hydrothermal synthesis reaction in an oven. After the reaction is completed, the reaction vessel is cooled and the membrane is removed, cleaned and dried to obtain the molecular sieve membrane.

[0008] A further embodiment of the present invention: In S1 and S5, the aluminum source is one of sodium aluminate, sodium aluminate, aluminum sulfate octadecyl hydrate, and aluminum isopropoxide; the silicon source is one of silica sol, sodium silicate, and tetraethyl orthosilicate; the first inorganic base is sodium hydroxide; and the second inorganic base is at least one of potassium hydroxide, lithium hydroxide, and aluminum hydroxide.

[0009] A further embodiment of the present invention: In S1, the molar ratio of aluminum source, silicon source, first inorganic base, second inorganic base, organic template agent, and deionized water is 1:(15-21):(3.2-5.2):3:(1.5-3):(163-263), wherein the aluminum source is calculated as Al2O3, the silicon source as SiO2, the first inorganic base as Na2O, and the second inorganic base as OH-. - Organic template agents are calculated as TMAOH.

[0010] A further embodiment of the present invention: In step S5, the molar ratio of aluminum source, silicon source, first inorganic base, second inorganic base, and deionized water is 1:(15-21):(3.2-5.2):3:(163-263), wherein the aluminum source is calculated as Al2O3, the silicon source as SiO2, the first inorganic base as Na2O, and the second inorganic base as OH-. - count.

[0011] A further aspect of the present invention is that the hydrothermal synthesis reaction in S2 is carried out at 80-120°C for 36-60 hours.

[0012] A further aspect of the present invention is as follows: In step S3, the calcination conditions are calcination at 450-650℃ for 4-8 hours; the average size of the first-size seed crystals obtained after calcination is 1.1 μm, and the average size of the second-size seed crystals obtained after ball milling is 0.25 μm; the ball milling conditions are ball milling at 450 r / min for 3 hours.

[0013] A further aspect of the present invention is as follows: In step S4, the concentration of both seed solutions is 0.5 wt%. Silicone plugs are used to seal both ends of the porous support. The porous support with an average pore size of 1-2 μm is immersed in the seed solution for coating by dip coating method, and the coating time is 60 s.

[0014] A further aspect of the present invention is that, in step S5, the hydrothermal synthesis reaction is carried out in an oven at 140-160°C for 2-6 hours.

[0015] A further aspect of the present invention is that, in step S5, the cooling method for the reaction vessel after the reaction is completed is quenching.

[0016] Another object of the present invention is to provide a molecular sieve membrane prepared by the above-described method for preparing a molecular sieve membrane based on a nutrient-rich solution, wherein the prepared molecular sieve seed crystals and molecular sieve membrane have a T-type zeolite structure.

[0017] A further embodiment of the present invention: the molecular sieve membrane has a thickness of 2.3-8.7 μm, the membrane layer is continuous and dense, and has a complete molecular sieve crystal structure.

[0018] Another object of the present invention is to provide the application of the above-mentioned molecular sieve membrane in the separation of water / isopropanol, water / acetone, water / ethanol, water / dimethyl carbonate, water / acetonitrile, water / tetrahydrofuran, water / n-butanol, and water / tert-butanol.

[0019] (III) Beneficial Effects Compared with the prior art, the beneficial effects of the present invention are: (1) Rapid film formation and significantly shortened preparation cycle: By constructing a nutrient-rich reaction system, this invention significantly improves the nucleation rate and growth kinetics of T-type molecular sieve crystals, enabling crystals to complete rapid nucleation and efficient growth in a short time, thereby achieving rapid construction of T-type molecular sieve membranes and greatly shortening the overall preparation cycle of the membrane.

[0020] (2) Crystal growth is controllable and film thickness is easy to adjust: The present invention uses T-type molecular sieve seed crystals with high crystallinity and high activity, and constructs a continuous and dense seed crystal layer on the surface of the support, providing a uniform nucleation interface for the orderly growth of subsequent film layers, thereby significantly improving the controllability and repeatability of film formation.

[0021] (3) Synergistic effect of multi-size crystals to effectively suppress membrane defects: The present invention uses a multi-size seed crystal synergistic deposition method to enable the seed crystals to fully fill the micropores and recessed areas on the surface of the support, avoiding the structural defect problems caused by uneven deposition and excessive gaps of traditional large-size seed crystals, which is conducive to obtaining a molecular sieve membrane layer with a smooth surface and controllable thickness.

[0022] (4) The membrane structure is continuous and dense, and the separation performance is stable and excellent: The molecular sieve membrane prepared by the present invention has a continuous and dense membrane layer, low defect density, and adjustable thickness, which significantly improves the separation selectivity and long-term operation stability of the membrane. It has excellent and stable separation performance in applications such as pervaporation dehydration and gas separation.

[0023] (5) Mild process conditions, excellent repeatability and stability: The process flow of this invention is simple, the operation steps are easy to control, and the membrane layer can be constructed in a short time. It has good process stability and repeatability, is suitable for scale-up production and continuous equipment, and has good engineering adaptability and industrial application potential.

[0024] (6) Wide range of applications: The molecular sieve membrane prepared by this invention is suitable for dehydration of various organic solvents, green separation processes and membrane reactor systems, and has broad application potential in the fields of fine chemicals, biofuel refining and separation. Attached Figure Description

[0025] Figure 1 SEM images of the molecular sieve seeds prepared in Examples 1 and 2 of this invention; Figure 2 The XRD patterns are of the molecular sieve seeds prepared in Examples 1 and 2 of this invention. Figure 3 The images show the surface and cross-sectional SEM images of the molecular sieve membranes prepared in Examples 1 and 2 of this invention. Figure 4 The image shows the XRD pattern of the molecular sieve membrane prepared in Example 1 of this invention. Figure 5 The images show the surface and cross-sectional SEM images of the molecular sieve membranes prepared in Examples 3 and 4 of this invention. Figure 6 The XRD patterns are of the molecular sieve membranes prepared in Examples 3 and 4 of this invention. Figure 7 The images show the surface and cross-sectional SEM images of the molecular sieve membranes prepared in Examples 5 and 6 of this invention. Figure 8 The XRD patterns are of the molecular sieve membranes prepared in Examples 5 and 6 of this invention. Figure 9 The images show the surface and cross-sectional SEM images of the molecular sieve membranes prepared in Examples 7 and 8 of this invention. Figure 10 The images show the surface and cross-sectional SEM images of the molecular sieve membranes prepared in Examples 9 and 10 of this invention. Figure 11 SEM images of the surface and cross-section of the molecular sieve membrane prepared in Comparative Example 1; Figure 12 SEM images of the surface and cross-section of the molecular sieve membrane prepared in Comparative Example 2; Figure 13 SEM images of the surface and cross-section of the molecular sieve membrane prepared in Comparative Example 3; Figure 14 SEM images of the surface and cross-section of the molecular sieve membrane prepared in Comparative Example 4; Figure 15 SEM images of the surface and cross-section of the molecular sieve membrane prepared in Comparative Example 5; Figure 16 The graphs show the separation results of organic solvent pervaporation dehydration of the molecular sieve membranes prepared in the embodiments and comparative examples of the present invention. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0027] Please see Figure 1-16 The present invention provides the following technical solutions.

[0028] Example 1 The preparation steps of the molecular sieve membrane based on nutrient-rich solution are as follows: S1. Preparation of the first reaction solution: Sodium aluminate, silica sol, sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, and deionized water are mixed in the following order: Al₂O₃: SiO₂: Na₂O: OH⁻ - The molar ratio of TMAOH: H2O = 1: 18: 4.2: 3: 1.5: 213 was added to a stirred tank and mixed thoroughly. The solution was aged at room temperature for 24 hours to obtain the first reaction solution. S2, preparation of T-type molecular sieve seed crystals: The first reaction solution obtained by S1 was transferred to a high-pressure reactor lined with polytetrafluoroethylene and hydrothermally synthesized at 100°C for 48 hours; after the reaction was completed, the reactor was quenched, the reaction product was centrifuged and separated, washed with deionized water until neutral, and then freeze-dried to obtain T-type molecular sieve seed crystals; S3, template removal and ball milling: The seed crystals obtained in S2 are placed in a crucible and calcined in a muffle furnace at 550°C for 6 hours to obtain the first-size seed crystals; the calcined seed crystals are ball milled at 450 r / min for 3 hours to obtain the second-size seed crystals with a smaller size, for later use; S4. Preparation of seeded support: The two sizes of T-type molecular sieve seeds obtained in S3 were added to deionized water to prepare a seed solution of the first size and a seed solution of the second size with a concentration of 0.5wt%. The first size seed was uniformly coated onto a porous support with an average pore size of 1-2μm using a dip-coating method. After drying, the second size seed was uniformly coated onto the surface of the support again using a dip-coating method to form a seed layer, thus obtaining a seeded support. S5. Preparation of molecular sieve membrane: Sodium aluminate, silica sol, sodium hydroxide, potassium hydroxide, and deionized water are mixed in the following ratio: Al₂O₃:SiO₂:Na₂O:OH - The molar ratio of H2O = 1:18:4.2:3:213 was added to a stirred tank to obtain a mixed solution. The mixed solution was stirred continuously at room temperature for 24 hours to obtain a nutrient-rich second reaction solution. The second reaction solution and the seeded support prepared by S4 were placed in a reaction vessel and hydrothermally synthesized in an oven at 150℃ for 4 hours. After the reaction was completed, the reaction vessel was quenched, and the membrane was removed, cleaned, and dried to obtain the T-type molecular sieve membrane M1.

[0029] In Example 1, the SEM results of the prepared T-type molecular sieve seed crystals (first-size seed crystals) and the ball-milled T-type molecular sieve seed crystals (second-size seed crystals) are as follows: Figure 1 As shown, the first-sized seed crystals are rice-grain shaped with an average diameter of approximately 1.1 μm, while the second-sized seed crystals have an average diameter of 0.25 μm. The XRD results of the seed crystals are shown below. Figure 2 As shown, the prepared T-type molecular sieve seed crystals and the ball-milled T-type molecular sieve seed crystals are pure phase T crystals.

[0030] Surface and cross-sectional SEM images of the final membrane product prepared in Example 1 – T-type molecular sieve membrane M1, are shown below. Figure 3 As shown in the figure, the surface crystals of the prepared T-type molecular sieve membrane M1 exhibit regular rod-like growth, are relatively dense, and have a membrane thickness of approximately 3.2 mm (1.5 mm greater than its seed layer). The XRD pattern of the T-type molecular sieve membrane M1 is shown below. Figure 4 As shown, the diffraction peaks of the prepared T-type molecular sieve membrane are consistent with the standard peaks, indicating that the prepared T-type molecular sieve membrane is a pure-phase molecular sieve membrane.

[0031] The T-type molecular sieve membrane M1 prepared in Example 1 was subjected to pervaporation separation of a water / isopropanol mixed solution containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0032] Furthermore, the T-type molecular sieve membrane M1 in Example 1 also exhibits excellent separation performance for pervaporation dehydration of other organic solvent systems (such as acetonitrile, ethanol, acetone, tetrahydrofuran, n-butanol, tert-butanol, and dimethyl carbonate), as shown in the separation experimental results. Figure 16 As shown.

[0033] Example 2 Compared with Example 1, the preparation conditions in Example 2 of the present invention differ in that: The molar ratio of sodium aluminate, silica sol, sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, and deionized water in S1 is Al₂O₃ : SiO₂ : Na₂O : OH⁻. - TMAOH: H2O = 1: 18: 4.2: 3: 3: 213; T-type molecular sieve membrane M2 was prepared.

[0034] In Example 2, the SEM results of the prepared T-type molecular sieve seeds are as follows: Figure 1 As shown, its morphology is similar to that of the T-type molecular sieve seeds prepared in Example 1, and the average diameter of the T-type molecular sieve seeds is approximately 0.4-0.7 mm; the XRD results of the seeds are as follows. Figure 2 As shown, the prepared T-type molecular sieve seed crystals are pure-phase T crystals.

[0035] The surface and cross-sectional SEM images of the final membrane product prepared in Example 2—the T-type molecular sieve membrane M2—are shown below. Figure 3 As shown in the figure, the surface rod-shaped crystals of the prepared T-type molecular sieve membrane M2 are arranged in a relatively disordered manner, but through mutual stacking and staggered growth, they effectively cover the surface of the support, and the membrane thickness is about 8.2 mm (6.5 mm longer than its seed layer).

[0036] The T-type molecular sieve membrane M2 prepared in Example 2 was subjected to pervaporation separation of a water / isopropanol mixed solution containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0037] Example 3 Compared with Example 1, the preparation conditions in Example 3 of the present invention differ in that: The T-type molecular sieve membrane M3 was prepared by hydrothermal synthesis in the reactor at 140℃ in S5.

[0038] The surface and cross-sectional SEM images of the final membrane product prepared in Example 3—T-type molecular sieve membrane M3—are shown below. Figure 5 As shown in the figure, the surface of the prepared T-type molecular sieve membrane M3 is dominated by irregular crystalline phases and amorphous structures, with uneven crystal morphology. The membrane thickness is approximately 2.6 mm (0.9 mm longer than its seed layer). The XRD pattern of the T-type molecular sieve membrane M3 is shown in the figure. Figure 6 As shown, the diffraction peaks of the prepared T-type molecular sieve membrane are consistent with the standard peaks, but the diffraction peak intensities are lower, indicating that the prepared membrane is a pure-phase T-type molecular sieve membrane. The T-type molecular sieve membrane M3 prepared in Example 3 was subjected to pervaporation separation of a water / isopropanol mixed solution containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0039] Example 4 Compared with Example 1, the preparation conditions in Example 4 of the present invention differ in that: The T-type molecular sieve membrane M4 was prepared by hydrothermal synthesis in the reactor at 160℃ in S5.

[0040] Surface and cross-sectional SEM images of the final membrane product prepared in Example 4 – T-type molecular sieve membrane M4, are shown below. Figure 5 As shown, the thickness of the prepared T-type molecular sieve membrane is approximately 4.5 mm (an increase of 2.8 mm relative to its seed layer); the XRD pattern of the T-type molecular sieve membrane M4 is shown below. Figure 6 As shown, the diffraction peaks of the prepared T-type molecular sieve membrane are consistent with the standard peaks, indicating that the prepared membrane is a pure-phase T-type molecular sieve membrane.

[0041] The T-type molecular sieve membrane M4 prepared in Example 4 was subjected to pervaporation separation of a water / isopropanol mixed solution containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0042] Example 5 Compared with Example 1, the preparation conditions in Example 5 of the present invention differ in that: Hydrothermal synthesis in S5 for 2 hours; T-type molecular sieve membrane M5 was obtained.

[0043] Surface and cross-sectional SEM images of the final membrane product prepared in Example 5 – T-type molecular sieve membrane M5, are shown below. Figure 7 As shown in the figure, the surface of the prepared T-type molecular sieve membrane M5 mainly exhibits a gel-like morphology, with no obvious regular rod-shaped crystal features. The membrane thickness is approximately 2.3 mm (0.6 mm longer than its seed layer). The XRD pattern of the T-type molecular sieve membrane M5 is shown in the figure. Figure 8 As shown, the diffraction peaks of the prepared T-type molecular sieve membrane are consistent with the standard peaks, but the diffraction peak intensities are lower, indicating that the prepared membrane is a pure-phase T-type molecular sieve membrane.

[0044] The T-type molecular sieve membrane M5 prepared in Example 5 was subjected to pervaporation separation of a water / isopropanol mixed solution containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0045] Example 6 Compared with Example 1, the preparation conditions in Example 6 of the present invention differ in that: Hydrothermal synthesis was carried out in S5 for 6 hours to prepare T-type molecular sieve membrane M6.

[0046] Surface and cross-sectional SEM images of the final membrane product prepared in Example 6 – the T-type molecular sieve membrane M6 – are shown below. Figure 7 As shown, the thickness of the prepared T-type molecular sieve membrane is approximately 3.7 mm (2.0 mm thick relative to its seed layer); the XRD pattern of the T-type molecular sieve membrane M6 is shown below. Figure 8 As shown, the diffraction peaks of the prepared T-type molecular sieve membrane are consistent with the standard peaks, indicating that the prepared membrane is a pure-phase T-type molecular sieve membrane.

[0047] The T-type molecular sieve membrane M6 prepared in Example 6 was subjected to pervaporation separation of a water / isopropanol mixed solution containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0048] Example 7 Compared with Example 1, the preparation conditions in Example 7 of the present invention differ in that: In S5, the molar ratio of sodium aluminate, silica sol, sodium hydroxide, potassium hydroxide, and deionized water is Al₂O₃ : SiO₂ : Na₂O : OH⁻. - The second reaction solution was obtained by mixing H2O in a molar ratio of 1:15:4.2:3:213; and a T-type molecular sieve membrane M7 was prepared.

[0049] The surface and cross-sectional SEM images of the final membrane product prepared in Example 7—the T-type molecular sieve membrane M7—are shown below. Figure 9 As shown in the figure, the surface of the prepared T-type molecular sieve membrane M7 is mainly composed of alternating stacked sheet-like and irregular crystals with overlapping between them. The membrane thickness is about 2.4 mm (0.7 mm longer than its seed layer).

[0050] The T-type molecular sieve membrane M7 prepared in Example 7 was subjected to pervaporation separation of a water / isopropanol mixed solution containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0051] Example 8 Compared with Example 1, the preparation conditions in Example 8 of the present invention differ in that: In S5, the molar ratio of sodium aluminate, silica sol, sodium hydroxide, potassium hydroxide, and deionized water is Al₂O₃ : SiO₂ : Na₂O : OH⁻. - The second reaction solution was obtained by mixing H2O in a molar ratio of 1:21:4.2:3:213; and a T-type molecular sieve membrane M8 was prepared.

[0052] Surface and cross-sectional SEM images of the final membrane product prepared in Example 8 – the T-type molecular sieve membrane M8 – are shown below. Figure 9 As shown in the figure, the prepared T-type molecular sieve membrane M8 has certain spherical crystals on its surface, the crystal size distribution is relatively dispersed, the membrane surface morphology is relatively rough, and the membrane thickness is about 4.6 mm (2.9 mm longer than its seed layer). The T-type molecular sieve membrane M8 prepared in Example 8 was subjected to pervaporation separation of a water / isopropanol mixed solution containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0053] Example 9 Compared with Example 1, the preparation conditions in Example 9 of the present invention differ in that: In S5, the molar ratio of sodium aluminate, silica sol, sodium hydroxide, potassium hydroxide, and deionized water is Al₂O₃ : SiO₂ : Na₂O : OH⁻. -The second reaction solution was obtained by mixing H2O in a molar ratio of 1:18:3.2:3:213; and a T-type molecular sieve membrane M9 was prepared.

[0054] Surface and cross-sectional SEM images of the final membrane product prepared in Example 9 – the T-type molecular sieve membrane M9 – are shown below. Figure 10 As shown in the figure, the surface of the prepared T-type molecular sieve membrane M9 is mainly composed of fine plate-like and irregular granular crystals, and the membrane thickness is about 2.6 mm (which is 0.9 mm longer than its seed layer). The T-type molecular sieve membrane M9 prepared in Example 9 was subjected to pervaporation separation of a water / isopropanol mixed solution containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0055] Example 10 Compared with Example 1, the preparation conditions in Example 10 of the present invention differ in that: In S5, the molar ratio of sodium aluminate, silica sol, sodium hydroxide, potassium hydroxide, and deionized water is Al₂O₃ : SiO₂ : Na₂O : OH⁻. - The second reaction solution was obtained by mixing H2O in a molar ratio of 1:18:5.2:3:213; and a T-type molecular sieve membrane M10 was prepared.

[0056] Surface and cross-sectional SEM images of the final membrane product prepared in Example 10 – the T-type molecular sieve membrane M10 – are shown below. Figure 10 As shown in the figure, the prepared T-type molecular sieve membrane M10 exhibits a dense and continuous capping layer structure on its surface, with blurred crystal boundaries and a membrane thickness of approximately 5.3 mm (3.6 mm greater than its seed layer). The T-type molecular sieve membrane M10 prepared in Example 10 was subjected to pervaporation separation of a water / isopropanol mixed solution containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0057] Comparative Example 1 Compared with Example 1, the preparation conditions in Comparative Example 1 are different in that: In S4, the seed crystals used for both dip coatings are unmilled T-type molecular sieve seed crystals (first-size seed crystals) to obtain a seeded support; thus, a T-type molecular sieve membrane DBL-1 is obtained.

[0058] Surface and cross-sectional SEM images of the final membrane product prepared in Comparative Example 1—T-type molecular sieve membrane DBL-1—are shown below. Figure 11 As shown, the thickness of the prepared T-type molecular sieve membrane is approximately 4.1 mm (2.4 mm greater than its seed layer). The T-type molecular sieve membrane DBL-1 prepared in Comparative Example 1 was subjected to pervaporation separation of a water / isopropanol mixture containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0059] Comparative Example 2 Compared with Example 1, the preparation conditions in Comparative Example 2 are different in that: In S4, the seed crystals used for both dip coatings are the ball-milled T-type molecular sieve seed crystals (second-size seed crystals), resulting in a seeded support; and a T-type molecular sieve membrane DBL-2 is obtained.

[0060] SEM images of the surface and cross-section of the final membrane product prepared in Comparative Example 2—T-type molecular sieve membrane DBL-2—are shown below. Figure 12 As shown, the thickness of the prepared T-type molecular sieve membrane is approximately 7.1 mm (5.4 mm greater than its seed layer).

[0061] The T-type molecular sieve membrane DBL-2 prepared in Comparative Example 2 was subjected to pervaporation separation of a water / isopropanol mixed solution containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0062] Comparative Example 3 Compared with Example 1, the preparation conditions in Comparative Example 3 are different in that: Long-term hydrothermal synthesis in S5 for 8 hours; T-type molecular sieve membrane DBL-3 was obtained.

[0063] Surface and cross-sectional SEM images of the final membrane product prepared in Comparative Example 3—T-type molecular sieve membrane DBL-3—are shown below. Figure 13 As shown, the thickness of the prepared T-type molecular sieve membrane is approximately 8.3 mm (6.6 mm greater than its seed layer).

[0064] The T-type molecular sieve membrane DBL-3 prepared in Comparative Example 3 was subjected to pervaporation separation of a water / isopropanol mixture containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0065] Comparative Example 4 Compared with Example 1, the preparation conditions in Comparative Example 4 are different in that: In S5, sodium aluminate, silica sol, sodium hydroxide, potassium hydroxide, and deionized water are arranged in the ratio Al₂O₃: SiO₂: Na₂O: OH⁻. - A dilute second reaction solution was obtained by using a molar ratio of H2O = 1: 18: 4.2: 3: 700; a T-type molecular sieve membrane DBL-4 was then prepared.

[0066] SEM images of the surface and cross-section of the final membrane product prepared in Comparative Example 4—the T-type molecular sieve membrane DBL-4—are shown below. Figure 14 As shown, the thickness of the prepared T-type molecular sieve membrane is approximately 2.3 mm (0.6 mm greater than its seed layer).

[0067] The T-type molecular sieve membrane DBL-4 prepared in Comparative Example 4 was subjected to pervaporation separation of a water / isopropanol mixture containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0068] Comparative Example 5 Compared with Example 1, the preparation conditions in Comparative Example 5 are different in that: After the reaction in S5 is completed, the reactor is allowed to cool naturally; the T-type molecular sieve membrane DBL-5 is obtained.

[0069] Surface and cross-sectional SEM images of the final membrane product prepared in Comparative Example 5—T-type molecular sieve membrane DBL-5—are shown below. Figure 15 As shown, the thickness of the prepared T-type molecular sieve membrane is approximately 3.6 mm (1.9 mm thick relative to its seed layer). The T-type molecular sieve membrane DBL-5 prepared in Comparative Example 5 was subjected to pervaporation separation of a water / isopropanol mixture containing 10 wt% water at 75 °C. The separation results are as follows: Figure 16 As shown.

[0070] It should be noted that we cannot list all the embodiments, and the specific implementation of the present invention is only for illustrative purposes.

[0071] Depend on Figure 16 (Examples 1 and 2) show that increasing the amount of organic template agent in step S1 significantly reduces the seed crystal size, significantly accelerates the membrane growth rate, and transforms the regular rod-shaped crystals on the membrane surface from regular growth to disordered stacking growth, thereby increasing the membrane permeation flux. However, excessively rapid crystal growth and a thicker membrane layer also lead to an increase in defects in the membrane layer, causing a significant decrease in the separation factor. The results indicate that an appropriate content of organic template agent is beneficial for achieving a balance between flux and separation factor.

[0072] Depend on Figure 16(Examples 1, 3, and 4) show that as the hydrothermal synthesis temperature in S5 increases, the crystal growth kinetics are significantly improved, the membrane layer gradually becomes denser and continuous, and the degree of intercrystalline fusion increases, resulting in a simultaneous increase in membrane permeation flux and separation factor. However, when the hydrothermal synthesis temperature is further increased, although the membrane layer thickens significantly under accelerated growth, excessively rapid crystal growth can easily lead to increased internal mass transfer resistance, and increased intercrystalline forces may introduce micro-defects or intercrystalline cracks, thereby reducing both flux and separation factor. This indicates that the hydrothermal synthesis temperature has a dual impact on the formation and performance of T-type molecular sieve membranes. The synthesis temperature needs to be controlled within a suitable range to ensure membrane density while maintaining low mass transfer resistance, achieving a synergistic optimization of high flux and high selectivity.

[0073] Depend on Figure 16 (Examples 1, 5, 6 and Comparative Example 3) show that the membrane flux and separation factor exhibit distinct changing patterns with increasing synthesis time in S5. When the hydrothermal synthesis time is short, the membrane crystallization is insufficient, and the surface is mainly gel-like, resulting in low flux and separation factor. As the synthesis time increases, the membrane crystals grow sufficiently and the structure becomes continuous and dense, achieving a high separation factor while maintaining high flux. Furthermore, as the membrane continues to thicken, the flux increases, but the separation factor decreases significantly. Excessive membrane growth generates numerous defects, almost eliminating selectivity. The results indicate that a suitable hydrothermal synthesis time is a key condition for achieving high density, high selectivity, and high flux simultaneously.

[0074] Depend on Figure 16 (Examples 1, 7, 8, 9, and 10) show that the molar ratio of sodium aluminate, silica sol, sodium hydroxide, potassium hydroxide, and deionized water in S5 is Al2O3: SiO2: Na2O: OH. - With the increase of silicon and alkali source content, the membrane thickness gradually increases, and the membrane permeation flux and separation factor both show a trend of first increasing and then decreasing. When the component ratios in the second reaction solution are within a suitable range, the resulting molecular sieve membrane has a dense and continuous structure, thus achieving high separation performance. However, when the silicon and alkali source ratios deviate from the suitable range, the membrane crystal morphology tends to be irregular, the membrane density decreases, and thus the separation performance declines. The results show that by adjusting the composition of the second reaction solution and controlling it within a certain range, the membrane separation performance can be effectively improved.

[0075] Depend on Figure 16(Examples 1, 1, and 2) show that different seeding methods for the S4 support significantly affect the pervaporation performance of the T-type molecular sieve membrane. Constructing a seed layer formed by dip-coating with seed crystals of different sizes allows smaller seed crystals to compensate for defects in the larger seed layer, contributing to the construction of a continuous and dense molecular sieve membrane layer and thus achieving excellent separation performance. However, when only a single-size seed crystal is used for repeated dip-coating during the seeding process, the resulting membrane structure is prone to insufficient density or overgrowth, leading to increased membrane thickness and mass transfer resistance, thereby reducing separation performance. The results indicate that by rationally composing seed crystals of different sizes for seeding treatment, membrane growth can be effectively controlled and the overall separation performance of the molecular sieve membrane can be improved.

[0076] Depend on Figure 16 (As shown in Examples 1 and 4) it is evident that increasing the molar ratio of water in S5 leads to a decrease in the concentration of the second reaction solution, resulting in a reduction in the thickness of the resulting membrane and a decrease in the membrane's separation selectivity. When nutrient-rich conditions are used for membrane growth, continuous and dense epitaxial growth is achieved on the seed layer surface, thus exhibiting good separation selectivity. However, when the concentration of the second reaction solution decreases, membrane growth is restricted, making it difficult to form a complete and dense molecular sieve membrane structure. This results in the permeation process being primarily dominated by defect channels, leading to a significant decrease in the selectivity of the molecular sieve membrane, even to the point of near-loss of selectivity. The results indicate that a suitable reaction solution concentration is a necessary condition for constructing a highly selective T-type molecular sieve membrane.

[0077] Depend on Figure 16 (As shown in Examples 1 and 5) the cooling method after the reaction in S5 has a significant impact on the performance of the T-type molecular sieve membrane. When rapid cooling by quenching is used after the reaction, it helps to promptly terminate the continued growth and recrystallization of crystals, thus maintaining the compactness of the membrane structure and exhibiting excellent separation performance. However, natural cooling of the reactor, with its prolonged residence time under high-temperature conditions, easily triggers the regrowth or local rearrangement of crystals, leading to a loose grain boundary structure and micro-defects, thereby reducing the membrane's separation selectivity. The results indicate that rationally controlling the cooling process after the reaction helps stabilize the molecular sieve membrane structure and improve its separation performance.

[0078] Experimental results show that the structure formation and pervaporation separation performance of T-type molecular sieve membranes are synergistically regulated by multiple factors, including seed crystals, synthesis conditions, and post-processing. This invention achieves systematic optimization in key steps such as seed crystal preparation, support seeding, reaction system construction, and post-processing, enabling controllable epitaxial growth of crystals on the seed layer surface. This results in a continuous, dense, and low-defect molecular sieve membrane layer, while maintaining low mass transfer resistance. This achieves a synergistic improvement in both high throughput and high selectivity, fully demonstrating the technical advantages of this invention in the rapid preparation and performance regulation of T-type molecular sieve membranes.

Claims

1. A method for preparing a molecular sieve membrane based on a nutrient-rich solution, characterized in that, The specific steps are as follows: S1. Preparation of the first reaction solution: Aluminum source, silicon source, first inorganic base, second inorganic base, organic template agent and deionized water are mixed evenly in molar ratio to form a solution, and the solution is continuously aged at room temperature to obtain the first reaction solution; S2. Preparation of molecular sieve seed crystals: The first reaction solution obtained in S1 is transferred to a high-pressure reactor for hydrothermal synthesis reaction. After the reaction is completed, the reactor is cooled, the reaction product is separated by centrifugation, washed with deionized water until neutral, and freeze-dried to obtain the original molecular sieve seed crystals. S3. Template removal and ball milling: The original molecular sieve seed crystals obtained in S2 are placed in a muffle furnace for calcination to obtain first-size seed crystals; the calcined seed crystals are cooled to room temperature and then ball milled to obtain second-size seed crystals with smaller sizes for later use. S4. Preparation of seeded support: The two sizes of molecular sieve seeds obtained in S3 are added to deionized water to prepare a seed solution of the first size and a seed solution of the second size with a concentration of 0.25-1wt%. The two types of seeds are uniformly coated onto the porous support to form a seed layer on the surface of the support, thus obtaining a seeded support. S5. Preparation of molecular sieve membrane: Aluminum source, silicon source, first inorganic base, second inorganic base and deionized water are mixed evenly in molar ratio to obtain a mixed solution. The mixed solution is continuously stirred at room temperature to obtain a nutrient-rich second reaction solution. The second reaction solution and the seeded support prepared in S4 are placed in a reaction vessel and subjected to hydrothermal synthesis reaction in an oven. After the reaction is completed, the reaction vessel is cooled and the membrane is removed, cleaned and dried to obtain the molecular sieve membrane.

2. The method for preparing a nutrient-rich molecular sieve membrane according to claim 1, characterized in that, In S1 and S5, the aluminum source is one of sodium aluminate, sodium aluminate, aluminum sulfate octadecyl hydrate, and aluminum isopropoxide; the silicon source is one of silica sol, sodium silicate, and tetraethyl orthosilicate; the first inorganic base is sodium hydroxide; and the second inorganic base is at least one of potassium hydroxide, lithium hydroxide, and aluminum hydroxide.

3. The method for preparing a nutrient-rich molecular sieve membrane according to claim 2, characterized in that, In S1, the molar ratio of aluminum source, silicon source, first inorganic base, second inorganic base, organic template agent, and deionized water is 1:(15-21):(3.2-5.2):3:(1.5-3):(163-263), where the aluminum source is calculated as Al2O3, the silicon source as SiO2, the first inorganic base as Na2O, and the second inorganic base as OH-. - Organic template agents are calculated as TMAOH.

4. The method for preparing a molecular sieve membrane based on nutrient-rich solution according to claim 2, characterized in that, In S5, the molar ratio of aluminum source, silicon source, first inorganic base, second inorganic base, and deionized water is 1:(15-21):(3.2-5.2):3:(163-263), where the aluminum source is calculated as Al2O3, the silicon source as SiO2, the first inorganic base as Na2O, and the second inorganic base as OH-. - count.

5. The method for preparing a molecular sieve membrane based on nutrient-rich solution according to claim 1, characterized in that, The hydrothermal synthesis reaction in S2 is carried out at 80-120℃ for 36-60 hours.

6. The method for preparing a molecular sieve membrane based on nutrient-rich solution according to claim 1, characterized in that, In S3, the calcination conditions are calcination at 450-650℃ for 4-8 hours; the average size of the first-size seed crystals obtained after calcination is 1.1 μm, and the average size of the second-size seed crystals obtained after ball milling is 0.25 μm; the ball milling conditions are ball milling at 450 r / min for 3 hours.

7. The method for preparing a molecular sieve membrane based on nutrient-rich solution according to claim 1, characterized in that, In step S4, the concentration of both seed solutions is 0.5 wt%. Silicone plugs are used to seal both ends of the porous support. The porous support with an average pore size of 1-2 μm is immersed in the seed solution for coating by dip coating method, and the coating time is 60 s.

8. The method for preparing a nutrient-rich molecular sieve membrane according to claim 1, characterized in that, In S5, the hydrothermal synthesis reaction is carried out in an oven at 140-160℃ for 2-6 hours.

9. A molecular sieve membrane based on nutrient-rich solution, characterized in that, The molecular sieve seed crystals and molecular sieve membranes prepared by any one of claims 1-8 have a T-type zeolite structure.

10. The use of the molecular sieve membrane as described in claim 9 in the separation of water / isopropanol, water / acetone, water / ethanol, water / dimethyl carbonate, water / acetonitrile, water / tetrahydrofuran, water / n-butanol, and water / tert-butanol.

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