A small-pore zeolite molecular sieve, a preparation method, a catalyst and a molecular sieve zeolite membrane

Abstract

This application relates to a small-pore zeolite molecular sieve, its preparation method, catalyst, and zeolite membrane. The raw materials for the small-pore zeolite molecular sieve include a silicon source, an aluminum source, a potassium source, and a metal source M. The silicon source, aluminum source, potassium source, and metal source M are arranged in a molar ratio of SiO2:Al2O3:K2O:M. x The O:H₂O mixture is prepared in a ratio of (1-20):(0.3-5):(0.5-3.1):(0-0.5):(160-1856), wherein M is selected from any one or more alkaline earth metals, alkali metals, and transition metals, and x is 0.5-2. In this application, by adding any one or more alkaline earth metals, alkali metals, and transition metals to the raw materials, and by preparing the silicon source, aluminum source, potassium source, and M metal source according to a specified molar ratio, the silicon-to-aluminum ratio can be increased, thereby improving the stability of the small-pore zeolite molecular sieve.

Description

Technical Field

[0001] This application belongs to the field of molecular sieves, specifically relating to a small-pore zeolite molecular sieve, its preparation method, catalyst, and molecular sieve zeolite membrane. Background Technology

[0002] Studies have shown that nitrogen oxide emissions from diesel vehicles cause serious environmental problems, such as acid rain, ozone layer depletion, photochemical smog, and haze. Since diesel vehicles primarily operate in densely populated areas, their exhaust emissions pose a direct threat to human health. Currently, ammonia selective catalytic reduction (NH3-SCR) is considered one of the more effective technologies for removing nitrogen oxide emissions from diesel vehicles, and the core of this technology is the catalyst. To limit nitrogen oxide emissions, my country's current National VI emission standard imposes stringent requirements on the catalytic activity and high stability of selective catalytic reduction (SCR) catalyst units.

[0003] Molecular sieve-based SCR catalysts exhibit better high-temperature stability than traditional vanadium-based catalysts. Compared to mesoporous (ten-membered ring) or macroporous (twelve-membered ring) molecular sieves, small-pore molecular sieves (eight-membered ring) show higher high-temperature stability. In recent years, Cu-based small-pore molecular sieve catalysts, represented by Cu-SSZ-13, have attracted much attention due to their excellent NH3-SCR activity, N2 selectivity, and high-temperature stability. Among them, the catalyst support molecular sieve is a small-pore eight-membered ring molecular sieve with a chalcogenide structure.

[0004] Taking SSZ-13 molecular sieve as an example, the synthesis methods of small-pore zeolite molecular sieves can be divided into organic template methods and inorganic template methods according to the template agent used. Generally, the organic template agent used in the organic template method is relatively expensive, resulting in a higher price for the synthesized small-pore zeolite. Inorganic template methods, on the other hand, are a green and inexpensive synthesis method, which does not require expensive organic template agents and does not cause waste gas pollution. Generally, inorganic template methods include direct crystallization, crystal transformation, and seed crystal methods. For example, KG molecular sieves with a CHA structure have been synthesized, which are the earliest artificially synthesized small-pore zeolite molecular sieves, with a Si / Al ratio between 1.2 and 2.1. Na is also used in some cases. +To synthesize molecular sieve R with a CHA structure using inorganic template agents, molecular sieve R with a CHA structure was obtained via direct crystallization, with a Si / Al ratio between 1.72 and 1.82. Although the direct crystallization method is simple and convenient, the Si / Al ratio of the product is below 3, and such molecular sieves typically exhibit poor high-temperature hydrothermal stability, requiring further exploration of synthesis conditions to improve the Si / Al ratio. Another study used a crystallization method, reacting specific NaY in a potassium hydroxide solution to obtain a small-pore zeolite molecular sieve with a Si / Al ratio of 2.27, with a yield of 83%. However, the crystallization method is lengthy, requiring the initial synthesis of NaY, followed by ion exchange to obtain NaY with a specific Na ion content, and finally crystallization to obtain the small-pore zeolite molecular sieve. The seed crystal method is currently the most commonly used method for template-free molecular sieve preparation: by adding seed crystals to a sol, silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra grow along the seed crystal topology, ultimately obtaining the target molecular sieve. While the current seed crystal method for synthesizing small-pore zeolite molecular sieves boasts a high silica-to-alumina ratio, its yield is relatively low. Further research is needed on the synthesis solution ratio and to explore synthesis conditions that improve yield. Therefore, the direct crystallization method is simple but has a low silica-to-alumina ratio; the transcrystalline method involves multiple steps but also has a low silica-to-alumina ratio; and the seed crystal method involves multiple steps and has a high silica-to-alumina ratio but a low yield. Thus, obtaining small-pore zeolite membranes with high yield and good stability is a pressing issue for the industry. Summary of the Invention

[0005] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a small-pore zeolite molecular sieve, a preparation method, a catalyst, and a molecular sieve zeolite membrane. This small-pore zeolite molecular sieve has low synthesis cost, high stability, and high synthesis yield.

[0006] According to a first aspect of the embodiments of this application, a small-pore zeolite molecular sieve is provided. The raw materials of the small-pore zeolite molecular sieve include a silicon source, an aluminum source, a potassium source, and a metal M source. The silicon source, aluminum source, potassium source, and metal M source are arranged in a molar ratio of SiO2:Al2O3:K2O:M. x The mixture is prepared in the ratio of O:H2O = (1~20):(0.3~5):(0.5~3.1):(0~0.5):(160~1856), wherein M is selected from any one or more of alkaline earth metals, alkali metals and transition metals, and x is 0.5-2.

[0007] According to the embodiments of this application, the small-pore zeolite molecular sieve is a molecular sieve with an eight-membered ring channel and a pore size range of 0.36nm to 0.43nm. The small-pore zeolite molecular sieve has at least the following beneficial effects: by adding any one or more of alkaline earth metals, alkali metals and transition metals to the raw material, the silicon-to-aluminum ratio can be increased, and the stability of the small-pore zeolite molecular sieve can be improved.

[0008] It should be noted that the silica-alumina molecular sieve is composed of [SiO4] tetrahedra and [AlO4] tetrahedra arranged in a specific structural arrangement through shared oxygen vertices. The [SiO4] tetrahedra are electrically neutral, while the [AlO4] tetrahedra carry a negative charge. Therefore, the molecular sieve framework exhibits negatively charged sites, requiring cation balance. To ensure that the [SiO4] and [AlO4] tetrahedra can arrange themselves in a specific structural arrangement, a structure-directing agent is needed. Therefore, in organic template-free synthesis systems, cations play a crucial role: balancing charges on one hand and acting as structure-directing agents on the other. The sol formed from the synthetic raw materials of this application contains the metal cation K. + The presence of any one or more alkaline earth metals, alkali metals, and transition metals significantly influences the stability of the resulting small-pore zeolite molecular sieve. Furthermore, the composition of the sol during synthesis, particularly the silicon-to-aluminum ratio and basicity, affects the configuration of the molecular sieve and significantly impacts its crystallinity. In this application, the silicon source, aluminum source, potassium source, and M metal source are arranged in a molar ratio of SiO2:Al2O3:K2O:M. x The ratio of O:H2O = (1-20):(0.3-5):(0.5-3.1):(0-0.5):(160-1856) has an important influence on the successful synthesis of small-pore zeolite molecular sieves and the acquisition of products with high yield and stability.

[0009] It is understood that the alkaline earth metal includes any one or more of Ca, Sr, and Ba. It should be noted that metal cations in the molecular sieve channels can balance charges, support the channels, and provide structural guidance. Typically, divalent metal ions can connect to a hydroxyl group to form a monovalent state, increasing the volume and thus reducing the number of ions in a single molecular sieve unit cell, thereby increasing the silicon-to-aluminum ratio. Furthermore, divalent metal ions can connect two secondary structural units, significantly improving the utilization efficiency of the structural units and thus enhancing product stability.

[0010] It is understood that the alkali metal includes any one or more of Na, Rb, and Cs. The CHA structure consists of two six-membered rings connected by four circular rings. The alkali metal promotes the formation of four-membered rings and can also promote the connection of two six-membered rings, ultimately promoting the formation of CHA structure microporous zeolite molecular sieves.

[0011] It is understood that the transition metal comprises Y and / or La. 3+ and La 3+ Ions have a larger ionic radius, and if they enter the molecular sieve framework, they can better support the molecular sieve pore structure, making it easier to obtain molecular sieves with a high silica-to-alumina ratio.

[0012] According to some embodiments of this application, the silicon source, aluminum source, potassium source, and M metal source are configured in a molar ratio of SiO2:Al2O3:K2O:M. x The O:H2O ratio is (5-20): (0.3-2): (0.5-3.1): (0.001-0.5): (160-500).

[0013] It is understood that, according to some embodiments of this application, the silicon source, aluminum source, potassium source, and M metal source are configured in a molar ratio of SiO2:Al2O3:K2O:M. x The O:H2O mixture should be prepared in a ratio of (5-13):(0.5-1.5):(1-3):(0.05-0.3):(160-500). Using this ratio, a higher silicon-to-aluminum ratio, higher yield, and better high-temperature stability can be achieved.

[0014] According to a second aspect of this application, a method for preparing a small-pore zeolite molecular sieve is provided. The small-pore zeolite molecular sieve is prepared using an inorganic template method, the preparation method comprising:

[0015] Deionized water was used as the solvent for the synthesis solution, and silicon, aluminum, potassium, and M metal sources were added to prepare the synthesis sol. The molar ratio of the synthesis sol was SiO2:Al2O3:K2O:M x O: H2O=(1~20): (0.3~5): (0.5~3.1): (0~0.5): (160~1856);

[0016] The synthetic sol was placed in a reaction vessel, and then the reaction vessel was transferred to an oven and stirred at 0℃~50℃ for 0~48 hours to allow for full aging.

[0017] Then, the temperature is linearly increased to the crystallization temperature at a heating rate of 1–30 °C / min;

[0018] Crystallize at 100–200℃ for 6–96 hours;

[0019] After crystallization, the product is collected by centrifugation and washing, and then dried to obtain the final product.

[0020] According to the preparation method described in this application, by adding any one or more of alkaline earth metals, alkali metals, and transition metals to the raw materials, and by preparing the silicon source, aluminum source, potassium source, and M metal source according to the above molar ratio, this method, combined with the above preparation method, is of significant importance for preparing high-yield and stable small-pore zeolite molecular sieves. The aging process has a significant impact on the formation of the sol, especially the primary and secondary structural units, ultimately affecting the resulting product phase. The crystallization temperature affects both the autogenous pressure inside the reactor and the crystallization process and product structure of the molecular sieve. Using the preparation method described in this application, small-pore zeolite molecular sieves with low cost, a yield as high as 75%, and a silicon-to-aluminum ratio greater than 3 can be obtained. Compared with related technologies, the technical solution of this application does not require the use of seed crystals, eliminating the complex seed crystal synthesis process. Furthermore, the preparation method of this application does not require the use of expensive organic template agents, which effectively reduces production costs and avoids the generation of polluting gases such as organic waste gas, carbon dioxide, and nitrogen oxides during the decomposition of organic template agents. Compared with the traditional direct crystallization synthesis of small-pore zeolite molecular sieves, the small-pore zeolite molecular sieves prepared in this application have a higher silicon-to-aluminum ratio and better high-temperature stability, making it a green and inexpensive method for synthesizing small-pore zeolite molecular sieves.

[0021] According to some embodiments of this application, the crystallization temperature is 130–190°C. Within this temperature range, crystallization can be promoted, the crystallization time shortened, and the formation of impurity phases suppressed.

[0022] It is understood that silicon sources include, but are not limited to, silica sol, wherein the components of silica sol may include colloidal silica and water; furthermore, aluminum sources include, but are not limited to, aluminum hydroxide, boehmite, aluminum powder, and alumina; potassium sources include, but are not limited to, potassium hydroxide, potassium acetate, and potassium chloride; and magnesium sources include, but are not limited to, magnesium acetate, magnesium chloride, magnesium nitrate, and magnesium sulfate.

[0023] According to some embodiments of this application, M includes any one or more of alkaline earth metals, alkali metals, and transition metals.

[0024] It is understood that the alkaline earth metals include any one or more of Ca, Sr, and Ba.

[0025] According to a third aspect of this application, a catalyst is provided, wherein the catalyst support comprises the above-described small-pore zeolite molecular sieve or the small-pore zeolite molecular sieve prepared by the above-described preparation method.

[0026] It should be noted that the above catalysts include denitrification and / or methanol-to-olefins catalysts, including but not limited to Cu-SSZ-13. Denitrification test results show that the prepared Cu-SSZ-13 catalyst exhibits good activity and stability.

[0027] According to some embodiments of this application, the small-pore zeolite molecular sieve obtained by the above preparation method is placed in an ammonium chloride solution, stirred, centrifuged, washed, and dried. The above process is repeated to obtain NH4-SSZ-13. Then, NH4-SSZ-13 is placed in a copper acetate solution, stirred, centrifuged, washed, and dried. Finally, it is calcined to obtain Cu-SSZ-13, which is then used for denitrification performance testing.

[0028] According to a fourth aspect of this application, a molecular sieve zeolite membrane is provided, comprising the small-pore zeolite molecular sieve as described above or the small-pore zeolite molecular sieve prepared by the above preparation method.

[0029] Understandably, using the aforementioned small-pore zeolite molecular sieve as seed crystals, the synthesized small-pore zeolite membrane exhibits excellent alcohol-water separation performance.

[0030] It should be noted that the aforementioned molecular sieve zeolite membrane can be applied to the field of deep dehydration of electronic-grade organic matter. Attached Figure Description

[0031] The present application will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0032] Figure 1 X-ray diffraction results of various alkaline earth metal synthesized small-pore zeolites in one embodiment of this application;

[0033] Figure 2 X-ray diffraction results of small-pore zeolite obtained by processing at different crystallization times in one embodiment of this application;

[0034] Figure 3 X-ray diffraction results of small-pore zeolite obtained by processing at different crystallization temperatures in one embodiment of this application;

[0035] Figure 4 This is a graph showing the denitrification activity test results of the Cu-SSZ-13 catalyst before and after aging in one embodiment of this application;

[0036] Figure 5 The images show the X-ray diffraction results of comparative examples 1, 2, and 3 in one embodiment of this application. Detailed Implementation

[0037] The following will clearly and completely describe the concept and technical effects of this application in conjunction with embodiments, so as to fully understand the purpose, features and effects of this application. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are all within the scope of protection of this application. Unless otherwise specified, the materials and raw materials mentioned in this specification are all common commercially available commodities.

[0038] In the description of this application, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] The specific embodiments of this application are described in detail below.

[0040] Example 1

[0041] Effects of alkaline earth metal ions on the synthesis of small-pore zeolite molecular sieves

[0042] First, 6.06 g of KOH and 0.43 g of magnesium acetate were added to 106 g of water and stirred until homogeneous. Then, 3.12 g of aluminum hydroxide was added to the solution and stirred for 30 minutes. Next, 40 g of silica sol (30 wt%) was added to the solution and stirred for 5 hours to obtain a homogeneous sol with the composition 2.3K₂O:1Al₂O₃:10SiO₂:0.1MgO:400H₂O. The sol was then transferred to a 300 mL reactor and placed in a 170 °C oven for crystallization for 3000 minutes. Finally, the molecular sieve powder (Mg-Z) was collected by centrifugation, washing, and drying.

[0043] Using the above synthesis method, magnesium acetate was replaced with calcium nitrate, strontium acetate, and barium hydroxide, respectively, to obtain a homogeneous sol with the composition 2.3K2O:1Al2O3:10SiO2:0.1MO (M being Ca, Sr, and Ba, respectively):400H2O). Molecular sieve powders Ca-Z, Sr-Z, and Ba-Z were obtained by crystallization.

[0044] The X-ray diffraction results for each substance are as follows: Figure 1As shown in the figure, sample Mg-Z is an amorphous substance and did not form a small-pore zeolite molecular sieve, serving as a comparative example. Ca-Z is a mixture of small-pore zeolite molecular sieve and amorphous substance, while samples Sr-Z and Ba-Z are small-pore zeolite molecular sieves without any impurity phases. The Si / Al ratios of the samples were determined by X-ray fluorescence spectrometry. The Si / Al ratios for samples Mg-Z, Ca-Z, Sr-Z, and Ba-Z were 5.0, 4.6, 3.8, and 3.8, respectively; the yields for samples Mg-Z, Ca-Z, Sr-Z, and Ba-Z were 95%, 90%, 76%, and 76%, respectively. It should be noted that in the Mg-Z system, due to the formation of amorphous substance, almost all silicon and aluminum in the system precipitated. Although the measured Si-Aluminum ratio and yield were high, the target product, the small-pore zeolite membrane, was not actually formed. The Ca-Z, Sr-Z, and Ba-Z systems all formed small-pore zeolite molecular sieves, and the silica-alumina ratio and yield are specific data for small-pore zeolite molecular sieves.

[0045] Example 2

[0046] Effects of crystallization time and temperature on the synthesis of small-pore zeolite molecular sieves

[0047] 4.98 g of KOH and 0.86 g of strontium acetate were added to 206 g of water and stirred until homogeneous. Then, 3.12 g of aluminum hydroxide was added to the solution and stirred for 30 minutes. Next, 50 g of silica sol (30 wt%) was added to the above solution and stirred for 5 hours to obtain a homogeneous sol with the composition 1.9 K₂O:1 Al₂O₃:12.5 SiO₂:0.2 SrO:800 H₂O. The sol was aged at room temperature for 24 hours, and then transferred to 300 mL of reaction solution. The reaction vessel was then placed in a 170°C oven for crystallization for 60, 180, 360, 600, 1440, 3000, 5760, and 7500 minutes respectively. Finally, the molecular sieve powder was collected by centrifugation, washing, and drying and labeled as tZ-60, tZ-180, tZ-360, tZ-600, tZ-1440, tZ-3000, tZ-5760, and tZ-7500 respectively (t represents the crystallization time).

[0048] The obtained X-ray diffraction results are as follows Figure 2As shown in the figure, the characteristic diffraction peaks of the small-pore zeolite molecular sieve gradually increase with increasing crystallization time. After 1440 minutes of crystallization, the crystallinity of the molecular sieve is close to 100%, and further extending the crystallization time has little effect on the crystallinity. X-ray fluorescence results show that with increasing crystallization time, the Si / Al value first gradually decreases (from 5.0 to 3.7), and after 1440 minutes, further extending the crystallization time keeps the Si / Al value stable (3.7), with the yield of all samples above 75%. However, when the crystallization time exceeds 3000 minutes, diffraction peaks of LTL impurity phases appear at low angles. Therefore, the optimized crystallization time is 360–5760 minutes.

[0049] 6.06 g of KOH and 0.65 g of strontium acetate were added to 53 g of water and stirred until homogeneous. Then, 3.09 g of aluminum hydroxide was added to the solution and stirred for 30 minutes. Next, 32 g of silica sol (40%) was added to the above solution and stirred for 5 hours to obtain a homogeneous sol with the composition 2.3K2O:1Al2O3:8SiO2:0.15SrO:200H2O. The prepared synthetic sol was aged at 40 °C for 36 hours. Then, the sol was transferred to a 300 mL reactor and placed in ovens at 110 °C, 130 °C, 150 °C, 170 °C, and 190 °C for crystallization for 3000 minutes. Finally, the molecular sieve powder TZ-T1 (T1 represents the crystallization temperature) was collected by centrifugation, washing, and drying.

[0050] The obtained X-ray diffraction results are as follows Figure 3 As shown in the figure, after crystallization at 110℃, the product exhibits diffraction peaks characteristic of small-pore zeolite molecular sieves, but most are amorphous. With increasing crystallization temperature, the characteristic diffraction peaks of the small-pore zeolite molecular sieve gradually intensify. The molecular sieve obtained at 170℃ has a crystallinity close to 100%. Further increasing the crystallization temperature has little effect on crystallinity, but LTL diffraction peaks appear at low angles. X-ray fluorescence results show that with increasing crystallization temperature, the Si / Al ratio first gradually decreases (from 5.0 to 3.7). Above 130℃, further increasing the crystallization temperature keeps the Si / Al ratio stable (3.7), and the yield of all samples is above 75%. Therefore, the optimal crystallization temperature is between 130 and 190℃.

[0051] Example 3

[0052] Effects of transition metal ions on the synthesis of small-pore zeolite molecular sieves

[0053] First, 6.06 g of KOH and 0.4 g of yttrium nitrate were added to 106 g of water and stirred until homogeneous. Then, 3.12 g of aluminum hydroxide was added to the solution and stirred for 30 minutes. Next, 40 g of silica sol (30 wt%) was added to the solution and stirred for 5 hours to obtain a solution with the composition 1.9 K₂O:1 Al₂O₃:8 SiO₂:0.07 Y. 2 / 3 A homogeneous sol of O:350H2O was formed. The sol was then transferred to a 300mL reaction vessel, which was then placed in a 170℃ oven for crystallization for 1450 minutes. Finally, the molecular sieve powder (YZ) was collected by centrifugation, washing, and drying.

[0054] Using the above synthesis method, yttrium nitrate was replaced with lanthanum nitrate, cerium nitrate, and neodymium nitrate, respectively, to obtain a composition of 1.9K₂O:1Al₂O₃:8SiO₂:0.07M. 2 / 3 A homogeneous sol of O:350H2O (M represents La, Ce, and Nd respectively) was crystallized to obtain molecular sieve powders La-Z, Ce-Z, and Nd-Z respectively.

[0055] All the obtained samples had a CHA structure, and the yields of YZ, La-Z, Ce-Z, and Nd-Z were 90%, 80%, 73%, and 70%, respectively.

[0056] Example 4

[0057] Preparation of Cu-SSZ-13 catalyst

[0058] The SSZ-13 microporous zeolite molecular sieve obtained in Example 2 by crystallization at 170℃ for 3000 minutes was placed in a 1M ammonium chloride solution and stirred at 80℃ for 6 hours. Then, it was centrifuged, washed, and dried. This process was repeated three times to obtain NH4-SSZ-13. NH4-SSZ-13 was then placed in a 0.05M copper acetate solution and stirred at 80℃ for 6 hours. After centrifugation, washing, and drying, it was finally calcined at 600℃ for 3 hours to obtain Cu-SSZ-13-F for denitrification performance testing. The copper content, as determined by ICP, was 2 wt%.

[0059] Example 5

[0060] Denitrification activity test of Cu-SSZ-13 catalyst before and after aging

[0061] The activity of a catalyst (60-80 mesh) was evaluated in a fixed-bed quartz reactor after uniformly mixing 60 mg of Cu-SSZ-13 catalyst (60-80 mesh) and 240 mg of quartz sand (60-80 mesh). Thermocouples were inserted into the reactor bed to test the reaction temperature. Each gas was controlled to enter the mixer using a mass flow meter. All pipelines were heated to above 100°C to prevent water vapor condensation. The simulated reaction conditions were as follows: 500 ppm NO, 500 ppm NH3, 6.1% O2, 6.4 vol.% H2O(g), N2 as the carrier gas, and a volume hourly space velocity (VHSV) of 300,000 h⁻¹. -1 The concentrations of NO, NO2, and N2O, the products of the NH3-SCR reaction, were determined using FT-IR with a 2m gas cell, within a temperature range of 150–500℃. The catalyst was pretreated at 550℃ in a reaction atmosphere for 2 hours before testing, and all data were stabilized for 30 minutes before testing and recording. x The conversion rate is calculated using the following formula:

[0062]

[0063] Hydrothermal aging conditions: The catalyst was aged at 750℃ with 10% H2O / air for 16 hours and labeled as Cu-SSZ-13-A.

[0064] The NH3-SCR activity of Cu-SSZ-13 catalyst before and after aging is as follows: Figure 4 As shown in the figure, the initial NOx conversion rate of the catalyst is greater than 90% between 200 and 500℃, and close to 100% between 250 and 500℃. After aging, the NOx conversion rate is still greater than 90% between 250 and 500℃, indicating that the Cu-SSZ-13 catalyst has excellent activity and stability.

[0065] Example 6

[0066] The effect of template-free synthesis of small-pore zeolite molecular sieve seeds on the synthesis of molecular sieve zeolite membranes

[0067] The small-pore zeolite molecular sieve obtained by crystallization at 170°C for 3000 minutes in Example 2 was used as a seed crystal.

[0068] The support used for synthesizing molecular sieve zeolite membranes is an α-Al₂O₃ ceramic tube, approximately 5 cm in length, 12 mm in outer diameter, 8 mm in inner diameter, with a porosity of approximately 40% and a pore size of approximately 2 μm. The support tube needs to be washed with deionized water to remove impurities from its surface and pores, and then dried in a 100°C oven for later use.

[0069] The seed crystals are introduced into the support as follows: First, the seed crystal powder is dispersed in anhydrous ethanol to prepare a seed crystal suspension with a mass fraction of approximately 3 wt.%. Then, the seed crystal particles are sonicated for more than 180 seconds to ensure uniform dispersion in the anhydrous ethanol system. Next, the seed crystal solution is slowly brushed onto the support tube using a fine, soft brush, and then placed in a 60°C oven to dry for more than 5 hours. The seed crystals need to be brushed twice and then dried again for later use.

[0070] The specific synthesis process is as follows: First, 1.098 g of KOH was weighed and dissolved in 200 g of deionized water. The mixture was stirred until the KOH was completely dissolved. Then, 2.733 g of NaAlO2 was weighed and added to the KOH solution. The mixture was stirred until the solid was completely dissolved and the solution was clear and transparent. Then, 6.667 g of silica was slowly added. The molar ratio of the synthesized gel was 0.15 KOH:0.3 NaAlO2:1 SiO2:100 H2O. The mixture was stirred and aged at room temperature for 90 min.

[0071] The ends of the dried seed crystal support tubes were sealed with custom-made PTFE plastic plugs and placed vertically into a Teflon reactor. Blank support tubes without seed crystal coating were also placed in the reactor as a blank control group. Approximately 30g of the aged reaction solution was slowly added to each reactor until the support tube was completely submerged. The reactors were then sealed and placed in a high-temperature oven for crystallization at 175℃ for 24 hours. After crystallization, the reactors were removed and allowed to cool naturally to room temperature. The support tubes were then removed as soon as possible and rinsed repeatedly with deionized water to remove excess alkali and residues. The sediment at the bottom of the reactor was also removed, washed with deionized water to remove alkali, and separated by high-speed centrifugation. The membrane tubes and bottom sediment were then dried in a 60℃ oven for 5 hours. The synthesized molecular sieve zeolite membrane was used for pervaporation testing.

[0072] In the corresponding embodiments, unless otherwise specified, the alcohol-water separation test was performed according to the method described in Journal of Materials Science, 43(2008)3279-3288, with a pervaporation temperature of 60°C and a water analyzer used to test the pervaporation water content.

[0073] The table shows that the molecular sieve zeolite membrane obtained by the organic template-free seeding method has a water content of 100% on the permeate side when the water content of the raw material is 10%, and a water content of 90% on the permeate side when the water content of the raw material is 0.01%, exhibiting extremely high selectivity. This indicates that the obtained molecular sieve zeolite membrane has extremely high selectivity and is suitable for ethanol dehydration, as well as for the dehydration of electronic-grade organic solvents with extremely high water content requirements.

[0074] In addition, the testing and evaluation of molecular sieve membrane products shall refer to the following definitions:

[0075] 1. Separation factor

[0076] This represents the ratio of the relative contents of two substances in a material before and after molecular sieve membrane separation. It is defined as:

[0077]

[0078] In the formula, α i / j x represents the separation coefficient of the molecular sieve membrane for component i (preferentially permeable membrane) and component j; i,p (x j,p ) represents the mass fraction of component i(j) in the permeate; x i,f (x j,f ) represents the mass fraction of component i(j) in the raw material.

[0079] 2. Permeation flux

[0080] The mass of material passing through a unit membrane area per unit time under specified temperature and pressure. It is defined as:

[0081]

[0082] Where J represents the permeation flux (kg / m³) -2 h -1 W represents the mass of the permeate component (kg); Δt represents the sampling interval (h); A represents the effective area of ​​the membrane surface for separation (m²). 2 ).

[0083] Comparative Example 1

[0084] 8.16 g of KOH and 0.43 g of strontium acetate were added to 206 g of water and stirred until homogeneous. Then, 3.12 g of aluminum hydroxide was added to the solution and stirred for 30 minutes. Next, 50 g of silica sol (30%) was added to the above solution and stirred for 5 hours to obtain a homogeneous sol with the composition 3.2 K₂O:1 Al₂O₃:12.5 SiO₂:0.1 SrO:800 H₂O. The sol was aged at room temperature for 24 hours, and then transferred to a 300 mL reaction vessel. The reaction vessel was then placed in a 170 °C oven for crystallization for 3000 minutes. Finally, the molecular sieve powder was collected by centrifugation, washing, and drying and labeled as Control 1.

[0085] Comparative Example 2

[0086] 6.06 g of KOH and 0.43 g of strontium acetate were added to 206 g of water and stirred until homogeneous. Then, 3.12 g of aluminum hydroxide was added to the solution and stirred for 30 minutes. Next, 200 g of silica sol (30%) was added to the above solution and stirred for 5 hours to obtain a homogeneous sol with the composition 2.3K2O:1Al2O3:25SiO2:0.1SrO:800H2O. The sol was aged at room temperature for 24 hours, and then transferred to a 300 mL reaction vessel. The reaction vessel was then placed in a 170 °C oven for crystallization for 3000 minutes. Finally, the molecular sieve powder was collected by centrifugation, washing, and drying and labeled as control 2.

[0087] Comparative Example 3

[0088] 6.06 g of KOH and 0.43 g of strontium acetate were added to 206 g of water and stirred until homogeneous. Then, 3.12 g of aluminum hydroxide was added to the solution and stirred for 30 minutes. Next, 40 g of silica sol (30%) was added to the above solution and stirred for 5 hours to obtain a homogeneous sol with the composition 2.3K2O:1Al2O3:10SiO2:0.1SrO:800H2O. The sol was transferred directly to a 300 mL reaction vessel without aging at room temperature. The reaction vessel was then placed in a 170 °C oven for crystallization for 3000 minutes. Finally, the molecular sieve powder was collected by centrifugation, washing, and drying and labeled as control 3.

[0089] The X-ray diffraction patterns of samples 1, 2, and 3 are as follows: Figure 5 As shown in the figure, when the content of potassium oxide or silicon oxide is not within the protection scope of the embodiments of this application, the result is that there are impurity phases (Comparison 1) or no substance (Comparison 2); while the sol is within the protection scope of the embodiments of this application, but has not undergone an aging process, there are impurity phases in Comparison 3.

[0090] Comparative Example 4

[0091] The effect of seed crystal synthesis via organic template method on molecular sieve zeolite membranes:

[0092] (I) Synthesis of molecular sieve seed crystals:

[0093] Step (1): Mix a certain mass of sodium hydroxide tablets and aluminum hydroxide powder in deionized water and stir at 95°C for half an hour until completely clear to form a homogeneous aluminate solution;

[0094] Step (2): Mix silica with N,N,N-trimethyl-1-adamantyl ammonium hydroxide solution (TMAdaOH, 25%);

[0095] Pour the solution from step (2) into the solution from step (1) and mix. Add commercial SSZ-13 seed crystals to the mixture and add an appropriate amount of deionized water and stir until homogeneous.

[0096] The final seed gel solution had a molar composition of 0.0078Al₂O₃:SiO₂:0.2NaOH:40H₂O:0.2TMAdaOH. The gel was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and placed in an oven at 160°C for 96 hours. After synthesis, the SSZ-13 crystals were centrifuged to recover the crystals, washed with deionized water, dried overnight at 100°C, and calcined in a muffle furnace at 600°C to remove the template agent. The crystals were then cooled and recovered for later use.

[0097] (II) Synthesis of Molecular Sieve Zeolite Membranes

[0098] The support used for synthesizing molecular sieve membranes is an α-Al₂O₃ ceramic tube, approximately 5 cm in length, 12 mm in outer diameter, 8 mm in inner diameter, with a porosity of approximately 40% and a pore size of approximately 2 μm. The support tube needs to be washed with deionized water to remove impurities from its surface and pores, and then dried in a 100°C oven for later use.

[0099] The seed crystals are introduced into the support as follows: First, the seed crystal powder is dispersed in anhydrous ethanol to prepare a seed crystal suspension with a mass fraction of approximately 3 wt.%. Then, the seed crystal particles are sonicated for more than 180 seconds to ensure uniform dispersion in the anhydrous ethanol system. Next, the seed crystal solution is slowly brushed onto the support tube using a fine, soft brush, and then placed in a 60°C oven to dry for more than 5 hours. The seed crystals need to be brushed twice and then dried again for later use.

[0100] The specific synthesis process is as follows: First, 1.098 g of KOH was weighed and dissolved in 200.0 g of deionized water. The mixture was stirred until the KOH was completely dissolved. Then, 2.733 g of NaAlO2 was weighed and added to the KOH solution. The mixture was stirred until the solid was completely dissolved and the solution was clear and transparent. Then, 6.667 g of silica was slowly added. The molar ratio of the synthesized gel was 0.15 KOH:0.3 NaAlO2:1 SiO2:100 H2O. The mixture was stirred and aged at room temperature for 90 min.

[0101] The ends of the dried seed-bearing carrier tubes were sealed with custom-made PTFE plastic plugs and placed vertically into a Teflon reactor. Blank carrier tubes without seed coating were also placed in the reactor as a blank control group using the same method. Approximately 30g of the aged reaction solution was slowly added to each reactor until the carrier tube was completely submerged. The reactors were then sealed and placed in a high-temperature oven for crystallization at 175℃ for 24 hours. After crystallization, the reactors were removed and allowed to cool naturally to room temperature. The carrier tubes were then removed as soon as possible and rinsed repeatedly with deionized water to remove excess alkali and residue from the support surface. Simultaneously, the sediment at the bottom of the reactor was removed, washed with deionized water to remove alkali, and separated into solids using high-speed centrifugation. The membrane tubes and bottom sediment were then dried in a 60℃ oven for 5 hours. The synthesized molecular sieve membrane was used for pervaporation testing.

[0102] The table shows that the molecular sieve zeolite membrane obtained by seeding with organic template agent method: when the water content of the raw material is 10%, the water content on the permeate side is 25%, and a large amount of ethanol permeates, indicating that the molecular sieve zeolite membrane has many defects. When the water content on the raw material side is 0.01%, the water content on the permeate side is also 0.01%, with no selectivity.

[0103]

[0104] The embodiments of this application have been described in detail above with reference to specific implementation methods. However, this application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of this application. Furthermore, unless otherwise specified, the embodiments and features described in the embodiments of this application can be combined with each other.

Claims

1. A method for preparing a small-pore zeolite molecular sieve, characterized in that, The small-pore zeolite molecular sieve is prepared using an inorganic template method, the preparation method comprising: Deionized water was used as the solvent for the synthesis solution, and silicon, aluminum, potassium, and M metal sources were added to prepare the synthesis sol. The molar ratio of the synthesis sol was SiO2:Al2O3:K2O:M x O:H2O = (5-20):(0.3-2):(0.5-3.1):(0.001-0.5):(160-500), where M is selected from any one or more alkaline earth metals and transition metals, and x is 0.5-2; the alkaline earth metal is any one or more of Ca, Sr, and Ba, and when the metal source of M is the alkaline earth metal, the configuration of the small-pore zeolite molecular sieve is SSZ-13; the transition metal is Y and / or La, and when the metal source of M is the transition metal, the configuration of the small-pore zeolite molecular sieve is CHA; The synthetic sol was placed in a reaction vessel, and then the reaction vessel was transferred to an oven and stirred at 0℃~50℃ for 0~48 hours to allow for full aging. Then, the temperature is linearly increased to the crystallization temperature at a heating rate of 1–30 °C / min; Crystallize at 110–200℃ for 6–96 hours; After crystallization, the product is collected by centrifugation and washing, and then dried to obtain the final product.

2. A catalyst, characterized in that, The catalyst support comprises a small-pore zeolite molecular sieve prepared by the preparation method described in claim 1.

3. A molecular sieve zeolite membrane, characterized in that, The raw material for the molecular sieve zeolite membrane includes a small-pore zeolite molecular sieve prepared by the preparation method described in claim 1.

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