A method for preparing and application of a multi-level pore zeolite membrane formed by MFI and MEL symbiosis

Abstract

This invention belongs to the field of inorganic membrane separation technology, specifically relating to a method for preparing a hierarchical porous zeolite membrane formed by the symbiosis of MFI and MEL, and its application. Symbiotic seed crystals are prepared using raw materials including SiO2, TBAOH, and water. These seed crystals are dispersed in anhydrous ethanol to obtain a seed crystal suspension. A preheated carrier is immersed in the seed crystal suspension for coating, calcined and solidified, and then immersed in a synthesis mother liquor formed by a mixture of SiO2, TBAOH, and water. A hydrothermal reaction is then performed to synthesize a zeolite membrane, which is dried, calcined, and cooled to obtain the hierarchical porous zeolite membrane. This hierarchical porous zeolite membrane can be used as a preferential pervaporation membrane for biomass ethanol under relatively low temperature conditions. Experimental results show that 2-5 nm mesopores are successfully introduced into the microporous zeolite membrane. The increased porosity reduces the mass transport path and transport resistance. When applied to the pervaporation separation of biomass ethanol, the membrane exhibits a significantly reduced decrease in long-term pervaporation flux.

Description

Technical Field

[0001] This invention belongs to the field of inorganic membrane separation technology, and relates to a method for preparing a multi-level porous zeolite membrane formed by the symbiosis of MFI and MEL and its application. Background Technology

[0002] Biomass ethanol is obtained through fermentation of grains, straw, and grass. The fermentation broth contains not only small molecules like ethanol and water, but also a large amount of carbon-containing macromolecules. Therefore, to obtain the desired ethanol, it needs to be separated and purified. Traditional MFI zeolite membranes (silicate-1) have a uniform microporous structure, do not contain Al in their crystal structure, and are highly hydrophobic. However, the presence of non-volatile byproducts such as succinic acid in the fermentation broth leads to membrane fouling, thus reducing flux and selectivity. Patent CN1096635044A discloses a method for preparing a bioethanol permeation membrane on an Al2O3 support, using silicalite-1 / ZSM-5 (seed-loaded) (MFI type) for bioethanol permeation, with a flux of only 1 kg / (m³). 2 h); Patent CN109433022A discloses a method for preparing an alcohol-permeable membrane material, which uses a combination of silicalite-1 seeds and a carrier to prepare an MFI-type zeolite membrane for alcohol permeation, with a flux of only 1-1.6 kg / (m²). 2 h), it can be seen that the permeation flux of these membranes is too small, which affects the amount of fermentation broth that can be processed in industry. Summary of the Invention

[0003] To address the issue of low membrane permeation flux, this invention provides a novel method for preparing a hierarchical porous zeolite membrane. The membrane comprises MFI and MEL type structures, which, through repeated branching and rotational co-existence, form micropores and mesopores between the layers. This membrane is used for pervaporation of fermentation broth to purify ethanol, reducing the impact of membrane fouling on the flux of pervaporation separation of biomass ethanol. A preferential permeation membrane for biomass ethanol separation is developed under relatively low temperature conditions. By introducing mesopores into conventional microporous zeolite, the external surface area increases, and the micropore diffusion length decreases, thereby improving the mass transfer rate of macromolecules and further enhancing its pervaporation deethanolination performance.

[0004] The above-mentioned technical objective provided by this invention is achieved through the following technical solutions:

[0005] The present invention provides a method for preparing a hierarchical porous zeolite membrane, comprising the following steps:

[0006] S1. Prepare symbiotic seed crystals using raw materials including silicon dioxide, tetrabutylammonium hydroxide and water;

[0007] S2. The seed solution is coated onto the carrier using the dip-coating method, and then dried and calcined.

[0008] S3. Place the seed carrier and crystallization mother liquor obtained in step S2 into a reaction vessel and carry out a hydrothermal synthesis reaction. After the reaction is completed, clean and dry to obtain the multi-level porous zeolite membrane.

[0009] Furthermore, the carrier in step S2 is a macroporous ceramic tube or a ceramic sheet.

[0010] Furthermore, the molar ratio of seed material in step S1 is SiO2:TBAOH:H2O = 1:(0.2~2.0):20.

[0011] Furthermore, in the preparation of the seed crystals in S1, pre-crystallization is carried out at 60–100℃ for 24–48 hours, and hydrothermal synthesis is carried out at 100–150℃ for 24–48 hours.

[0012] Furthermore, the seed crystals in step S1 are hierarchical porous zeolite molecular sieves with a particle size of 1–3 μm and a seed solution concentration of 1–3 wt%.

[0013] Furthermore, the carrier prepared in step S2 is immersed in the seed solution for 5–30 seconds, dried at 80–200°C for 1–3 hours, and then placed in a muffle furnace for calcination at 500–600°C for 3–6 hours to solidify the seed crystal.

[0014] Furthermore, in step S3, the mother liquor is synthesized using silicon dioxide, tetrabutylammonium hydroxide and deionized water as raw materials, with a molar ratio of SiO2:TBAOH:H2O = 1:0.2:(20-50).

[0015] Furthermore, in step S3, the pre-crystallization temperature of the hierarchical porous zeolite membrane is 60–100℃, and the time is 24–48 h; the hydrothermal synthesis temperature is 100–150℃, and the time is 24–48 h. Temperatures that are too high or too low will result in membranes with pores that are too large or too small, leading to poor separation of the ethanol / water system. Similarly, if the time is too long or too short, it will cause changes in the membrane's surface morphology; too long a time results in a too dense membrane, while too short a time results in defective membranes and decreased separation performance.

[0016] Furthermore, after the hydrothermal synthesis of the zeolite membrane, the calcination and cooling processes employ programmed temperature control. Specifically, the heating rate is first controlled at 5–0.5 °C / min, raising the temperature to 500–600 °C and holding it for 6–12 hours. Then, the cooling rate is controlled at 5–0.5 °C / min until the temperature drops to room temperature. Excessive heating or cooling rates can lead to excessive temperature differences on the membrane surface, causing thermal stress and potentially causing the membrane to crack.

[0017] The second objective of this invention is to provide a method for separating biomass ethanol by pervaporation, using the aforementioned multi-level porous zeolite membrane as the separation membrane.

[0018] The above-mentioned technical objective of the present invention is achieved by the following technical solution:

[0019] A method for applying a hierarchical porous zeolite membrane is disclosed, which uses the membrane for pervaporation separation of biomass ethanol de-alcoholization. By introducing mesopores into the microporous MFI zeolite membrane, the pore volume is increased, the transport path and resistance of the material are reduced, thereby reducing the degree of decrease in the membrane's long-term pervaporation flux.

[0020] In summary, the present invention has the following beneficial effects:

[0021] This invention provides a method for preparing a hierarchical porous zeolite membrane. The membrane interior is formed by repeated branching and rotational symbiosis, resulting in micropores and mesopores between the layers. Its high external surface area and reduced micropore diffusion length enhance the transport channels, improve the mass transfer rate of macromolecules, significantly improve the utilization efficiency of zeolite materials, and consume minimal energy, time, and raw materials. This reduces the decrease in pervaporation flux and improves separation performance. Attached Figure Description

[0022] Figure 1 SEM images of the zeolite membranes prepared in Examples 1 (ab), 2 (cd), and 1 (ef);

[0023] Figure 2 The XRD patterns are of the synthesized products of Example 1, Example 2, and Comparative Example 1.

[0024] Figure 3 Nitrogen adsorption-desorption and pore size distribution of zeolite in Examples 1, 2, and 1 (Comparative Example 1);

[0025] Figure 4 This is a schematic diagram illustrating the formation principle of the multi-level porous zeolite membrane of the present invention. Detailed Implementation

[0026] This invention is not limited to the specific embodiments listed below. Those skilled in the art can implement this invention using various other specific embodiments based on the content disclosed herein. Any modifications or alterations made to the design structure and concept of this invention fall within the protection scope of this invention. It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0027] The present invention will be further described in detail below with reference to the embodiments:

[0028] This invention provides a method for preparing a hierarchical porous zeolite membrane, comprising the following steps:

[0029] (1) The hydrothermal synthesis of symbiotic seed crystals, namely hierarchical porous zeolite molecular sieves, includes the use of silicon dioxide, tetrabutylammonium hydroxide and water as raw materials, with a molar ratio of SiO2:TBAOH:H2O=1:(0.2~2.0):20, pre-crystallization at 60~100℃ for 24~48h, hydrothermal synthesis at 100~150℃ for 24~48h, after the synthesis is completed, the membrane is washed with deionized water until neutral, and dried at 80℃ to obtain symbiotic seed crystals.

[0030] (2) The multi-level porous zeolite molecular sieve is ultrasonically dispersed in anhydrous ethanol to form a seed solution, wherein the ultrasonic dispersion time is 10-60 min, the particle size of the multi-level porous zeolite molecular sieve is 1-3 μm, and the concentration of the seed solution is 1-3 wt%.

[0031] (3) After coating the seed solution in step (2) onto the carrier, dry it. The carrier used is a macroporous carrier tube or sheet (porosity > 35%). The seed solution is coated onto the carrier by dip-coating method, the dip time is 5 to 30 seconds, and after removal, it is dried at 80 to 200°C for 1 to 3 hours.

[0032] (4) Place the carrier coated with the seed layer in step (3) into a muffle furnace for calcination at a temperature of 500-600°C for 3-6 hours.

[0033] (5) A multi-level porous zeolite membrane was synthesized on the seed carrier in step (4) using a hydrothermal method. The mother liquor consisted of silicon dioxide, tetrabutylammonium hydroxide and deionized water as raw materials, with a molar ratio of SiO2:TBAOH:H2O = 1:0.2:(20-50). The mother liquor was added to the reactor, and the seed carrier was sealed and placed in the reactor. The synthesis was carried out at 100-150℃ for 24-48 hours. After the synthesis was completed, the membrane was washed with deionized water until neutral and dried at 80℃ to obtain a continuous and dense multi-level porous zeolite membrane.

[0034] This specific embodiment also provides an application of the multi-level porous zeolite membrane prepared by the above method, namely, using the membrane as a pervaporation membrane for the pervaporation treatment of biomass ethanol de-alcoholization.

[0035] Example 1:

[0036] A method for preparing a hierarchical porous zeolite membrane includes the following steps:

[0037] S1. The symbiotic seed crystals were synthesized by hydrothermal method with a molar ratio of 1SiO2:0.2TBAOH:20H2O. The seed crystals were pre-crystallized at 80℃ for 48h and then hydrothermally synthesized at 120℃ for 48h.

[0038] S2. Co-existing seed crystals of approximately 1 μm in size were ultrasonically dispersed in anhydrous ethanol at a seed solution concentration of 1 wt%. The seed crystals were then coated onto a macroporous α-Al₂O₃ carrier tube (porosity >35%, pore size 1-2 μm) using a dip-coating method. The dip-coating time was 25 seconds at room temperature. After removal, the tube was placed in a forced-air oven at 80°C for 3 hours to dry. Finally, the tube was placed in a muffle furnace at 500°C for 3 hours to solidify the seed crystals.

[0039] S3. A hierarchical porous zeolite membrane was synthesized using a hydrothermal method. Tetrabutylammonium hydroxide and water were mixed in a molar ratio of 1 SiO2:0.2 TBAOH:20H2O and stirred at room temperature for 10 min. After the mixture was homogeneous, silica sol was slowly added to the beaker and stirred vigorously at room temperature until it became clear and transparent. The mixture was then transferred to a sealed single-necked flask and stirred in an oil bath at 80°C for 48 h to form a synthesis mother liquor. The seed tube from step S2 was placed in a reaction vessel and the mother liquor was added. The mixture was synthesized at 120°C for 48 h. After the synthesis was completed, the membrane was washed with deionized water until neutral and then dried at 80°C to obtain the hierarchical porous zeolite membrane.

[0040] A method for applying a hierarchical porous zeolite membrane: The prepared hierarchical porous zeolite membrane was used for pervaporation separation of a fermentation broth solution containing 5 wt% ethanol. The feed solution was heated to 60℃, and a vacuum (<400 Pa) was applied to the permeate side. After 1 hour of testing, the permeate was collected, yielding a permeate flux of 16 kg·m³. -2 ·h -1 The ethanol concentration on the permeate side is 25 wt%.

[0041] Example 2

[0042] A method for preparing a hierarchical porous zeolite membrane includes the following steps:

[0043] S1. The symbiotic seed crystals were synthesized by hydrothermal method with a molar ratio of 1SiO2:0.2TBAOH:20H2O. The seed crystals were pre-crystallized at 80℃ for 48h and then hydrothermally synthesized at 120℃ for 48h.

[0044] S2. Co-existing seed crystals of approximately 1 μm in size were ultrasonically dispersed in anhydrous ethanol at a seed solution concentration of 1 wt%. The seed crystals were then coated onto a macroporous α-Al₂O₃ carrier tube (porosity >35%, pore size 1-2 μm) using a dip-coating method. The dip-coating time was 25 seconds at room temperature. After removal, the tube was placed in a forced-air oven at 80°C for 3 hours to dry. Finally, the tube was placed in a muffle furnace at 500°C for 3 hours to solidify the seed crystals.

[0045] S3. A hierarchical porous zeolite membrane was synthesized using a hydrothermal method. Tetrabutylammonium hydroxide and water were mixed in a molar ratio of 1 SiO2:0.2 TBAOH:50H2O and stirred at room temperature for 10 minutes. After thorough mixing, silica sol was slowly added to the beaker and vigorously stirred at room temperature until clear and transparent. The mixture was then transferred to a sealed single-necked flask and stirred in an oil bath at 80°C for 48 hours to form a synthesis mother liquor. The seed tube from step S2 was placed in a reaction vessel, and the mother liquor was added. Synthesis was carried out at 120°C for 48 hours. After synthesis, the membrane was washed with deionized water until neutral and then dried at 80°C to obtain the hierarchical porous zeolite membrane.

[0046] A method for applying a hierarchical porous zeolite membrane: The prepared hierarchical porous zeolite membrane was used for pervaporation separation of fermentation broth containing 5 wt% ethanol. The feed liquid temperature was heated to 60℃, and a vacuum (<400 Pa) was applied to the permeate side. After 1 hour of testing, the permeate was collected, yielding a permeate flux of 20 kg·m³. -2 ·h -1 The ethanol concentration on the permeate side is 36 wt%.

[0047] Example 3

[0048] The preparation method of the hierarchical porous zeolite membrane is the same as in Example 1. A method for applying the hierarchical porous zeolite membrane is as follows: The prepared hierarchical porous zeolite membrane is used for pervaporation separation of a fermentation broth containing 5 wt% ethanol. The feed liquid temperature is heated to 30°C, and a vacuum (<400 Pa) is applied to the permeate side. After 1 hour of testing, the permeate is collected, yielding a permeate flux of 8.61 kg·m³. -2 ·h -1 The ethanol concentration on the permeate side was 39 wt%.

[0049] Comparative Example 1

[0050] A method for preparing an MFI zeolite membrane includes the following steps:

[0051] S1. MFI zeolite seed crystals were synthesized by hydrothermal method with a molar ratio of 1 TEOS: 0.2 TPAOH: 150H2O: 4C2H5OH. The mixture was stirred at room temperature for 6 h and then hydrothermally synthesized at 130℃ for 24 h to obtain the seed crystals.

[0052] S2. MFI zeolite seed crystals of approximately 1 μm in size were ultrasonically dispersed in anhydrous ethanol at a seed solution concentration of 1 wt%. The seed crystals were then coated onto a macroporous α-Al₂O₃ carrier tube (porosity >35%, pore size 1-2 μm) using a dip-coating method. The dip-coating time was 25 seconds at room temperature. After removal, the tube was placed in a forced-air oven at 80°C for 3 hours to dry. Finally, the tube was placed in a muffle furnace at 500°C for 3 hours to solidify the seed crystals.

[0053] S3. MFI zeolite membrane was synthesized by hydrothermal method. The molar ratio of 1 TEOS: 0.2 TPAOH: 100H2O was used. Tetrapropylammonium hydroxide and water were mixed and stirred at room temperature for 10 min. After mixing evenly, TEOS was added dropwise and stirred at room temperature for 6 h to form a synthesis mother liquor. The seed tube from step S2 was placed in the reaction vessel and the mother liquor was added. The synthesis was carried out at 160℃ for 24 h. After the synthesis was completed, the membrane was washed with deionized water until neutral and then dried at 80℃ to obtain the MFI zeolite membrane.

[0054] The prepared MFI zeolite membrane was used for pervaporation separation of fermentation broth containing 5 wt% ethanol. The feed liquid was heated to 60 °C, and a vacuum (<400 Pa) was applied to the permeate side. After 1 hour of testing, the permeate was collected, yielding a permeate flux of 12 kg·m³. -2 ·h -1 The ethanol concentration on the permeate side is 5 wt%.

[0055] Comparative Example 2

[0056] The MFI zeolite membrane was prepared using the same method as in Comparative Example 1. The prepared MFI zeolite membrane was used for pervaporation separation of a fermentation broth containing 5 wt% ethanol. The feed liquid was heated to 30°C, and a vacuum (<400 Pa) was applied to the permeate side. After 1 hour of testing, the permeate was collected, yielding a permeate flux of 7.25 kg·m³. -2 ·h -1 The ethanol concentration on the permeate side is 40 wt%.

[0057] Table 1

[0058]

[0059] Table 1 shows the permeation flux and permeate-side ethanol concentration of the zeolite membranes prepared in Examples 1-3 and Comparative Examples 1-2. The results show that the flux of the multi-level porous zeolite membrane with MEL and MFI rotational coexistence is significantly increased compared with the MFI zeolite membrane. This indicates that the porosity in the multi-level pores is higher, and the reduction in mass transport resistance leads to faster mass transport.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been shown above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a hierarchical porous zeolite membrane, characterized in that, The following steps are included: S1. Using silicon dioxide, tetrabutylammonium hydroxide and water in a molar ratio of 1:0.2:20 as raw materials, precrystallize at 60~100℃ for 24~48h and then hydrothermally synthesize at 100~150℃ for 24~48h to prepare symbiotic seed crystals; S2. Disperse the symbiotic seed crystals in anhydrous ethanol to form a seed crystal solution; The seed solution was coated onto the carrier using the dip-coating method, and then dried and calcined to obtain the seed carrier. S3. Place the seed carrier and crystallization mother liquor obtained in step S2 into a reaction vessel and carry out a hydrothermal synthesis reaction. After the reaction is completed, clean and dry to obtain the multi-level porous zeolite membrane. The crystallization mother liquor is a solution prepared by mixing silicon dioxide, tetrabutylammonium hydroxide and deionized water in a molar ratio of 1:0.2:20~50.

2. The method for preparing a multi-level porous zeolite membrane as described in claim 1, characterized in that, The carrier in step S2 is a macroporous ceramic tube or a ceramic sheet.

3. The method for preparing a multi-level porous zeolite membrane as described in claim 1, characterized in that, The symbiotic seed crystals in step S1 are hierarchical porous zeolite molecular sieves with a particle size of 1~3μm and a seed crystal solution concentration of 1~3wt%.

4. The method for preparing a hierarchical porous zeolite membrane as described in claim 1, characterized in that: The carrier prepared in step S2 is immersed in the seed solution for 5-30 seconds, dried at 80-200°C for 1-3 hours, and then placed in a muffle furnace for calcination at 500-600°C for 3-6 hours to solidify the seed crystal.

5. The method for preparing a hierarchical porous zeolite membrane as described in claim 1, characterized in that: In step S3, the pre-crystallization temperature of the hierarchical porous zeolite membrane is 60~100℃ and the time is 24~48h, while the hydrothermal synthesis temperature is 100~150℃ and the time is 24~48h.

6. The method for preparing a hierarchical porous zeolite membrane as described in claim 1, characterized in that: After the hydrothermal reaction to synthesize the zeolite membrane, the calcination and cooling processes are carried out using a programmed temperature control method. Specifically, the heating rate is first controlled at 5~0.5℃ / min, raised to 500~600℃ and held for 6~12 hours, and then the cooling rate is controlled at 5~0.5℃ / min to cool down to room temperature.

7. The application of the hierarchical porous zeolite membrane prepared by the method according to any one of claims 1 to 6, characterized in that, The multi-level porous zeolite membrane will be used in the purification of biomass ethanol.

Images