X-type zeolite molecular sieve with low silica-alumina ratio as well as preparation method and application of X-type zeolite molecular sieve
By performing in-situ crystallization treatment on X-type zeolite molecular sieves, the problem of binder clogging the pores was solved, and high-performance X-type zeolite molecular sieves with low silicon-to-alumina ratio were prepared for use in CO2 adsorption and purification processes, thus improving the industrial application effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HONEYWELL UOP ENG TECH R&D CO LTD
- Filing Date
- 2024-11-08
- Publication Date
- 2026-05-12
AI Technical Summary
In the existing technology, the use of binders during the molding process of X-type zeolite molecular sieves leads to pore blockage, which reduces its dynamic performance and affects the industrial application effect.
By mixing, molding, drying, and calcining the raw material X-type zeolite molecular sieve with a binder, and then performing in-situ crystallization treatment with an inorganic alkaline solution to transform the binder into a molecular sieve, a low silica-alumina ratio X-type zeolite molecular sieve is prepared, which reduces the non-crystalline phase and improves pore volume and adsorption performance.
The prepared low-silicon-alumina ratio X-type zeolite molecular sieve has high crystallinity and low amorphous phase, which significantly improves the micropore volume and CO2 adsorption capacity. It also exhibits excellent dynamic performance and is suitable for CO2 adsorbents and purification processes.
Smart Images
Figure CN122010136A_ABST
Abstract
Description
Technical Field This invention relates to the field of molecular sieve adsorbents. Specifically, this invention relates to a low silica-to-alumina ratio X-type zeolite molecular sieve, its preparation method, and its applications. Background Technology Molecular sieve materials are crystalline aluminosilicates with ordered pore structures, good hydrothermal stability, and tunable functionality, finding wide applications in industrial catalysis, adsorption separation, and ion exchange. X-type zeolites are silicate crystals with a FAU-type framework structure, their basic structure consisting of SiO4 and AlO4 tetrahedra forming a three-dimensional network structure through shared oxygen atoms, belonging to the octahedral zeolite category. X-type zeolite molecular sieves can be further classified according to the SiO2 / Al2O3 molar ratio into low-silicon X-type (SiO2 / Al2O3 = 2.0-2.2), medium-silicon X-type (SiO2 / Al2O3 = 2.0-2.4), and high-silicon X-type (SiO2 / Al2O3 = 2.4-3.0). Low-silicon-to-alumina ratio zeolites, due to their high-alumina lattice containing a large amount of negative charge and a greater number of balancing cations, exhibit higher adsorption capacity and selective adsorption performance, thus showing great application potential. Current research on reducing the silicon-to-alumina ratio of X-type zeolites has been reported.
[0001] Generally, synthetic X-type zeolites are in powder form and need to be mixed with binders. After molding and activation, they can be used in industrial applications to obtain molecular sieves with a certain strength. In industrial applications, the effective component of the molding material is the molecular sieve, while the binder mainly serves to bind the molecular sieve and impart a certain strength. While the binder imparts strength, it also reduces the effective component of the molding material; it may also block some pores, causing a decrease in the dynamic performance of the molecular sieve, and thus reducing the performance of the molded molecular sieve material in industrial applications. Summary of the Invention In view of the above-mentioned problems of the prior art, the present invention provides a low silica-alumina ratio X-type zeolite molecular sieve, its preparation method and its application. The molecular sieve has excellent micropore volume and adsorption capacity, and is simple to prepare and low in cost, effectively solving or at least alleviating one or more problems existing in the prior art.
[0002] Therefore, according to one aspect of the present invention, a low silica-to-alumina ratio X-type zeolite molecular sieve is provided, comprising, by weight, 70-90 wt% of raw material X-type zeolite molecular sieve, 10-30 wt% of transcrystalline X-type zeolite molecular sieve, and no more than 1.5 wt% of amorphous phase, wherein the low silica-to-alumina ratio X-type zeolite molecular sieve has a SiO2 / Al2O3 molar ratio of 2.0-2.15 and a particle size distribution in the range of 4-6 μm and 400-600 nm.
[0003] According to another aspect of the present invention, a method for preparing the above-mentioned low silica-to-alumina ratio X-type zeolite molecular sieve is provided, comprising the following steps: 1) Mix the raw material X-type zeolite molecular sieve with the binder evenly, shape, dry, and calcine; 2) Take the calcined molecular sieve from step 1) and place it in an inorganic alkaline solution for in-situ crystallization treatment; and 3) The shaped molecular sieve material after in-situ crystallization treatment is washed, dried and calcined.
[0004] According to another aspect of the present invention, the above-mentioned low silica-alumina ratio X-type zeolite molecular sieve is provided as a CO2 adsorbent.
[0005] This invention involves mixing, molding, drying, and calcining raw material X-type zeolite molecular sieve with a binder, followed by in-situ crystallization treatment with an inorganic alkaline solution to convert the binder into a molecular sieve. The resulting X-type zeolite molecular sieve exhibits high crystallinity, low amorphous phase impurities (≤1.5 wt%), and a SiO2 / Al2O3 molar ratio as low as the theoretical value of 2.0. It also possesses excellent micropore volume and CO2 adsorption capacity, thus showing great application potential in the CO2 adsorbent market. Furthermore, the raw materials for preparing this low Si / Al ratio X-type zeolite molecular sieve are readily available, the preparation process is simple, and it can be widely applied in industrial manufacturing processes. Attached Figure Description The invention will be described in conjunction with the accompanying drawings to enable those skilled in the art to better understand the various features and advantages of the invention, in which: Figure 1 These are scanning electron microscope images of the spherical parent molecular sieve prepared in Example 3; Figure 2 These are scanning electron microscope images of the target product molecular sieve prepared in Example 3; Figure 3 These are the X-ray diffraction patterns of the target product molecular sieve and the molecular sieve raw powder used in Example 3; Figure 4 This is a scanning electron microscope image of commercially available binder-free X-type molecular sieve adsorbent 1; Figure 5 This is a scanning electron microscope image of the binder-free X-type molecular sieve adsorbent 2 prepared according to existing technology. Detailed Implementation To enable those skilled in the art to further understand the present invention, specific embodiments of the present invention are described in detail below. However, it should be understood that the embodiments of the present invention described herein are merely exemplary, and the present invention is not limited to these embodiments.
[0006] According to one aspect of the present invention, a low silica-to-alumina ratio X-type zeolite molecular sieve is provided, comprising, by weight, 70-90 wt% of raw material X-type zeolite molecular sieve, 10-30 wt% of transcrystalline X-type zeolite molecular sieve, and no more than 1.5 wt% of amorphous phase, wherein the low silica-to-alumina ratio X-type zeolite molecular sieve has a SiO2 / Al2O3 molar ratio of 2.0-2.15 and a particle size distribution in the range of 4-6 μm and 400-600 nm.
[0007] Preferably, the low silica-alumina ratio X-type zeolite molecular sieve comprises 80-90 wt% raw material X-type zeolite molecular sieve, 10-20 wt% transcrystalline X-type zeolite molecular sieve, and no more than 1.0 wt% amorphous phase.
[0008] Preferably, the SiO2 / Al2O3 molar ratio of the low-silicon-aluminum ratio X-type zeolite molecular sieve is 2.0-2.11.
[0009] Preferably, the specific surface area of the low silica-to-alumina ratio X-type zeolite molecular sieve is 720-870 m². 2 / g, micropore area is 666-865m² 2 / g, with a micropore volume of 0.26-0.34cm³. 3 / g.
[0010] Preferably, the specific surface area of the low silica-alumina ratio X-type zeolite molecular sieve is 830-864 m². 2 / g, micropore area is 750-855m² 2 / g, micropore volume is 0.28-0.32cm³ 3 / g.
[0011] The X-type zeolite molecular sieve used in this application is a commercially available conventional X-type zeolite. Preferably, the X-type zeolite molecular sieve is selected from sodium-type or sodium-potassium-type X-type zeolite, with a SiO2 / Al2O3 molar ratio of 2.0-2.5 and a particle size range of 4-6 μm.
[0012] In some embodiments, the transformable X-type zeolite molecular sieve is obtained by in-situ crystallization treatment with a binder. The binder is a clay-based binder that can be transformed into a molecular sieve structure, such as selected from kaolin, montmorillonite, dickite, perlite, refractory stone, halloysite, or mixtures thereof, preferably halloysite. All binders are commercially available.
[0013] The non-crystalline phase is the residue after the binder has undergone in-situ crystallization.
[0014] The low silica-to-alumina ratio X-type zeolite molecular sieve of this invention exhibits two characteristic particle size ranges: 4-6 μm and 400-600 nm, respectively. Comparison of scanning electron microscope images of the molecular sieve before and after in-situ crystallization reveals that the molecular sieve particle size on the adsorbent containing the binder is approximately 4-6 μm, with almost no small-diameter molecular sieves. Therefore, it can be determined that the large-diameter molecular sieve is the raw material molecular sieve, while the small-diameter molecular sieve is obtained from the in-situ crystallization of the binder. The small-diameter molecular sieve has a comparable static adsorption capacity to the large-diameter molecular sieve, but its dynamic mass transfer capacity is higher, exhibiting better performance in industrial applications.
[0015] According to another aspect of the present invention, a method for preparing low silica-to-alumina ratio X-type zeolite molecular sieves is provided, comprising the following steps: 1) Mix the raw material X-type zeolite molecular sieve with the binder evenly, shape, dry, and calcine; 2) Take the calcined molecular sieve from step 1) and place it in an inorganic alkaline solution for in-situ crystallization treatment; and 3) The shaped molecular sieve material after in-situ crystallization treatment is washed, dried and calcined.
[0016] In some embodiments, in step 1), the raw material X-type zeolite molecular sieve and the binder are mixed uniformly at a weight ratio of 70:30-90:10, preferably 80:20-90:10. The raw material X-type zeolite molecular sieve and the binder are as described above.
[0017] In step 1), any molding method known to those skilled in the art can be used to mold the homogeneous mixture of raw material X-type zeolite molecular sieve and binder, including but not limited to ball forming and extrusion forming.
[0018] The equipment for ball forming can be a polishing machine, a Natal mixer, or an Ellis mixer. During ball forming, the uniformly mixed and compacted raw materials are placed in a rotating device, and water is sprayed while the materials are rolling to cause them to adhere and agglomerate into small balls. The amount of water added during ball forming is 30-45 wt%, preferably 37-39 wt%, of the total solid weight. The small balls formed by rolling are then dried and calcined to obtain the final product.
[0019] Extrusion molding is performed using a commonly used industrial extrusion molding machine. During extrusion molding, the raw materials are first mixed evenly, and an appropriate amount of water is added to ensure the loss on ignition (LOI) is between 30-45%. The mixed material is then transferred to the extrusion machine, and a suitable extrusion die is selected for extrusion molding. The extruded adsorbent is then dried and calcined to obtain the final product.
[0020] When using spherical molding, the preferred size of the formed molecular sieve is a sphere with a diameter of 1-3 mm. When using extrusion molding, the preferred size of the formed molecular sieve is a strip with a diameter of 1.5-3.5 mm and a length of 2-5 mm.
[0021] In some implementations, in step 1), the drying temperature is 90-270℃ and the drying time is 0.3-12h; the calcination temperature is 300-650℃ and the calcination time is 0.2-4h.
[0022] In some implementations, in step 2), the inorganic base is selected from sodium hydroxide, potassium hydroxide, or a mixture thereof.
[0023] In some embodiments, in step 2), the concentration of the inorganic alkaline solution is 0.4-4 mol / L, preferably 1-4 mol / L, and more preferably 3-4 mol / L.
[0024] In some embodiments, the in-situ crystallization process is carried out under static conditions or under stirring. Preferably, the in-situ crystallization process is carried out under stirring.
[0025] In some embodiments, the liquid / solid ratio of the inorganic alkaline solution to the shaped molecular sieve in the in-situ crystallization treatment is 1-6 L / kg, preferably 1-4 L / kg; the treatment temperature is 80-100℃, preferably 88-96℃; and the treatment time is 2-24 h, preferably 4-12 h.
[0026] In some implementations, in step 3), the drying temperature is 120-250℃ and the drying time is 0.4-3h; the calcination temperature is 450-600℃ and the calcination time is 0.2-2h.
[0027] According to another aspect of the present invention, the above-mentioned low silica-alumina ratio X-type zeolite molecular sieve is provided as a CO2 adsorbent.
[0028] The low silica-to-alumina ratio X-type zeolite molecular sieve of the present invention has a 2 torr CO2 adsorption capacity of more than 39.7 mL / g, and even up to 47.4 mL / g, as measured at 25°C.
[0029] The CO2 characteristic diffusion coefficient of the low silica-to-alumina ratio X-type zeolite molecular sieve of this invention is 2.7*10. -6 s -1 -3.39*10 -6 s -1 .
[0030] The molecular sieve provided by this invention achieves its effect by in-situ crystallizing a binder into a small-particle-size, low-silica-alumina ratio X-type molecular sieve, thus avoiding pore blockage and improving the dynamic performance of the adsorbent. Furthermore, for molecular sieves with the same topology, the small-particle-size, low-silica-alumina ratio X-type molecular sieve exhibits superior dynamic performance compared to the large-particle-size molecular sieve, further enhancing the dynamic performance of the molecular sieve and resulting in superior performance in industrial applications such as CO2 adsorption. For example, the low-silica-alumina ratio X-type zeolite molecular sieve of this invention can be used as an adsorbent in CO2 pressure swing / temperature swing adsorption processes or in any other CO2-containing gas purification process.
[0031] The descriptions of various features or implementation schemes in this application can be combined with each other without contradiction, and all fall within the scope of protection claimed in this application.
[0032] As used in this application, "comprising" and "including" include both cases where the application consists only of the included elements and cases where it includes other elements in addition to the included elements.
[0033] In this application specification and claims, figures indicating temperature, quantity, concentration, percentage, etc., should in all cases be understood to be modified by the term "approximately".
[0034] Unless otherwise defined, all scientific and technical terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict between the definitions of terms in this application and their commonly understood meanings by one of ordinary skill in the art, the definitions set forth in this application shall prevail.
[0035] Example The present invention will be further described below with reference to embodiments and accompanying drawings, so that those skilled in the art can fully understand the purpose, features and effects of the present invention. However, the scope of protection of the present invention is not limited to the following embodiments.
[0036] Description of the main raw materials and performance parameter testing equipment in the embodiments: Raw material X-type zeolite molecular sieve: commercial sodium-type X-type zeolite with a SiO2 / Al2O3 molar ratio of 2.06 and a particle size range of 4-6μm; Halloysite: a commercially available product with a SiO2 / Al2O3 molar ratio of 1.84; SiO2 / Al2O3 molar ratio determination: using a PE-8000 ICP-OES instrument from Platinum Elmo; CO2 adsorption capacity determination: A Bel-Max adsorption instrument from Bayer, Japan was used. The determination process was as follows: First, an appropriate amount of adsorbent was weighed and placed in the sample chamber. The sample was heated to 400℃ under vacuum and held for 6 hours. Then, in-situ vacuum activation was performed on the adsorption instrument for 4 hours. After activation, CO2 was introduced at 25℃ and the adsorption isotherm was recorded. The CO2 adsorption capacity can be obtained from the adsorption isotherm.
[0037] CO2 characteristic diffusion coefficient determination: The BSD DVS adsorbent from Beijing Bestech was used. The determination process is as follows: First, an appropriate amount of adsorbent was weighed and placed in the sample chamber of the equipment. The sample was heated to 300℃ in a flowing nitrogen atmosphere and kept at that temperature for 6 hours. Then, a CO2 / N2 mixed gas with a CO2 concentration of 2000ppm was introduced. The change curve of sample weight over time was recorded. Based on this curve, the diffusion coefficient can be calculated by selecting an appropriate model equation.
[0038] BET specific surface area, micropore area, and micropore volume were determined using a 3Flex adsorption analyzer from Mack (USA). The procedure was as follows: First, an appropriate amount of adsorbent was weighed and placed in the sample chamber. The sample was heated to 400℃ under vacuum and held for 6 hours. Then, in-situ vacuum activation was performed on the adsorption analyzer for 4 hours. After activation, N2 was introduced at -196℃ and the adsorption isotherm was recorded. The BET specific surface area, micropore area, and micropore volume were calculated based on the adsorption isotherm and model equations.
[0039] Preparation Example 1 1) Weigh appropriate amounts of raw material X-type zeolite molecular sieve and halloysite at a weight ratio of 85:15, and then transfer them to a mixer for thorough mixing. Transfer the uniformly mixed mixture to a rolling mill, and add an appropriate amount of water while stirring and rolling. Once the material has been rolled into a dough-like state, transfer the mixture to an extruder for extrusion. Collect the strip extrudate, dry it at 150℃ for 45 min, and calcine it at 600℃ for 20 min to obtain strip-shaped parent molecular sieve.
[0040] Characterization analysis showed that the adsorption capacity of the strip-shaped molecular sieve at 25℃ was 34.4 mL / g with a 2 torr CO2 concentration; the BET specific surface area was 757 m² / g. 2 / g, micropore area is 735m² 2 / g, micropore volume is 0.28cm³ 3 / g.
[0041] 2) Weigh 8g of strip-shaped molecular sieve, place it in 48mL of 0.9mol / L NaOH solution, and keep it at 90℃ for 14h for in-situ crystallization treatment; 3) Wash the in-situ crystallized molecular sieve with deionized water until the washing solution is neutral. Dry the washed molecular sieve at 200℃ for 30 min and calcine it at 550℃ for 30 min to obtain the target product molecular sieve.
[0042] Characterization analysis revealed that the SiO2 / Al2O3 molar ratio of the target product molecular sieve was 2.0; the 2-torr CO2 adsorption capacity of the target product molecular sieve at 25℃ was 42.4 mL / g, an increase of 23.3% compared to the strip-shaped parent molecular sieve; and the BET specific surface area was 855 m². 2 / g, micropore area is 848m² 2 / g, micropore volume is 0.31cm³ 3 / g, representing increases of 12.9%, 15.4%, and 10.7% respectively compared to strip-shaped molecular sieves.
[0043] Preparation Example 2 The preparation was carried out according to the method of Example 1, except that the concentration of NaOH solution was 3.6 mol / L.
[0044] Characterization analysis showed that the SiO2 / Al2O3 molar ratio of the target product molecular sieve was 2.06; the CO2 adsorption capacity of the target product molecular sieve at 25℃ was 45.1 mL / g, which was 31.1% higher than that of the strip-shaped parent molecular sieve.
[0045] Preparation Example 3 The preparation was carried out according to the method of Example 2, except that the molecular sieve was prepared by rolling spheres, that is, a spherical parent molecular sieve.
[0046] Figure 1 The scanning electron microscope image of the spherical parent molecular sieve is shown, which shows that its size is relatively uniform, ranging from 4 to 6 μm.
[0047] Characterization analysis showed that the spherical parent molecular sieve had a 2-torr CO2 adsorption capacity of 34.8 mL / g at 25℃; and a BET specific surface area of 763 m². 2 / g, micropore area is 748m² 2 / g, micropore volume is 0.28cm³ 3 / g.
[0048] Figure 2 The image shows a scanning electron microscope (SEM) image of the final target product molecular sieve. It can be seen that small particles with a particle size range of 400-600 nm are attached to the original spherical parent molecular sieve, i.e., the molecular sieve is generated by in-situ crystallization of the binder.
[0049] Characterization analysis revealed that the SiO2 / Al2O3 molar ratio of the target product molecular sieve was 2.11; the 2-torr CO2 adsorption capacity of the target product molecular sieve at 25℃ was 45.5 mL / g, an increase of 30.7% compared to the spherical parent molecular sieve; and the BET specific surface area was 864 m². 2 / g, micropore area is 855m² 2 / g, micropore volume is 0.32cm³ 3 / g, representing increases of 13.2%, 14.3%, and 14.3% respectively compared to spherical parent molecular sieves.
[0050] The CO2 characteristic diffusion coefficients of the spherical parent molecular sieve and the target product molecular sieve were further characterized, and were 2.26*10⁻⁶ respectively. -6 s -1 and 3.39*10 -6 s -1 The CO2 characteristic diffusion coefficient of the target product molecular sieve was increased by 50% compared with that of the spherical parent molecular sieve.
[0051] Figure 3 The X-ray diffraction patterns are for the product and raw material molecular sieve of Example 3. Figure 3 As can be seen, the molecular sieve after in-situ crystallization has high crystallinity and contains almost no amorphous phase; after in-situ crystallization, no other impurity peaks appeared on the spectrum of Example 3, indicating that halloysite was successfully converted into X-type molecular sieve.
[0052] Preparation Example 4 The preparation was carried out according to the method of Example 3, except that the in-situ crystallization treatment was carried out under stirring.
[0053] Characterization analysis showed that the SiO2 / Al2O3 molar ratio of the target product molecular sieve was 2.02; the CO2 adsorption capacity of the target product molecular sieve at 25℃ was 46.5 mL / g, which was 33.6% higher than that of the spherical parent molecular sieve.
[0054] Comparative Example 1 Comparative Example 1 is a commercially available binder-free X-type molecular sieve adsorbent. Figure 4 This is a scanning electron microscope (SEM) image of the molecular sieve adsorbent in Comparative Example 1. From... Figure 4 As can be seen, the molecular sieve adsorbent of Comparative Example 1 is mainly composed of large crystals with a particle size of 5-10 μm, which is significantly different from the bimodal distribution molecular sieve of the Examples. Furthermore, characterization analysis showed that the SiO2 / Al2O3 molar ratio of the molecular sieve adsorbent of Comparative Example 1 was 2.17.
[0055] Comparative Example 2 Comparative Example 2 is a binder-free X-type molecular sieve adsorbent prepared according to existing technology. The molecular sieve adsorbent of Comparative Example 2 was prepared according to the method disclosed in CN107159105A, namely, using 13X-type molecular sieve, kaolin, molding aid, and pore-forming agent for molding, followed by activation, alkaline aging, alkaline crystallization, and activation. Characterization analysis showed that its CO2 adsorption capacity at 25℃ was 41.5 mL / g (2 torr), which is lower than the CO2 adsorption capacity of the sample in the present invention. Figure 5 This is a scanning electron microscope (SEM) image of the molecular sieve adsorbent in Comparative Example 2. From... Figure 5 As can be seen, the molecular sieve adsorbent of Comparative Example 2 mainly consists of large particles with a diameter of 4-8 μm and some small particles with insufficient crystallinity. Compared with Example 3, the relative crystallinity of the molecular sieve adsorbent of Comparative Example 2 is 95%, which indicates that there is more amorphous phase in Comparative Example 2.
Claims
1. A low silica-to-alumina ratio X-type zeolite molecular sieve, characterized in that, The product comprises, by weight, 70-90 wt% of raw material X-type zeolite molecular sieve, 10-30 wt% of transcrystalline X-type zeolite molecular sieve, and no more than 1.5 wt% of amorphous phase. The low silica-alumina ratio X-type zeolite molecular sieve has a SiO2 / Al2O3 molar ratio of 2.0-2.15 and a particle size distribution in the range of 4-6 μm and 400-600 nm.
2. The low silica-to-alumina ratio X-type zeolite molecular sieve according to claim 1, characterized in that, It includes 80-90 wt% of raw material X-type zeolite molecular sieve, 10-20 wt% of transcrystalline X-type zeolite molecular sieve, and no more than 1.0 wt% of non-crystalline phase.
3. The low silica-to-alumina ratio X-type zeolite molecular sieve according to claim 1 or 2, characterized in that, Its SiO2 / Al2O3 molar ratio is 2.0-2.
11.
4. The low silica-to-alumina ratio X-type zeolite molecular sieve according to any one of claims 1-3, characterized in that, Its specific surface area is 720-870 m². 2 / g, micropore area is 666-865m² 2 / g, with a micropore volume of 0.26-0.34cm³. 3 / g.
5. The low silica-to-alumina ratio X-type zeolite molecular sieve according to any one of claims 1-4, characterized in that, Its specific surface area is 830-864 m². 2 / g, micropore area is 750-855m² 2 / g, micropore volume is 0.28-0.32cm³ 3 / g.
6. The low silica-to-alumina ratio X-type zeolite molecular sieve according to any one of claims 1-5, characterized in that, The raw material X-type zeolite molecules are selected from sodium-type or sodium-potassium-type X-type zeolite with a SiO2 / Al2O3 molar ratio of 2.0-2.5 and a particle size range of 4-6μm.
7. The low silica-to-alumina ratio X-type zeolite molecular sieve according to any one of claims 1-6, characterized in that, The X-type zeolite molecular sieve is obtained by in-situ crystallization treatment with a binder. The binder is selected from kaolin, montmorillonite, dickite, perlite, refractory stone, halloysite, or a mixture thereof, with halloysite being preferred.
8. A method for preparing low silica-to-alumina ratio X-type zeolite molecular sieves according to any one of claims 1-7, characterized in that, Includes the following steps: 1) Mix the raw material X-type zeolite molecular sieve with the binder evenly, shape, dry, and calcine; 2) Take the calcined molecular sieve from step 1) and place it in an inorganic alkaline solution for in-situ crystallization treatment; and 3) The shaped molecular sieve material after in-situ crystallization treatment is washed, dried and calcined.
9. The method according to claim 8, characterized in that, In step 1), the raw material X-type zeolite molecular sieve and the binder are mixed in a weight ratio of 70:30-90:10, preferably 80:20-90:10, wherein the raw material X-type zeolite molecular sieve and the binder are as defined in claims 6 and 7, respectively.
10. The method according to claim 8 or 9, characterized in that, In step 1), the drying temperature is 90-270℃ and the drying time is 0.3-12h; the calcination temperature is 300-650℃ and the calcination time is 0.2-4h.
11. The method according to any one of claims 8-10, characterized in that, In step 2), the inorganic base is selected from sodium hydroxide, potassium hydroxide, or a mixture thereof. Preferably, the concentration of the inorganic base solution is 0.4-4 mol / L, more preferably 1-4 mol / L, and even more preferably 3-4 mol / L.
12. The method according to any one of claims 8-11, characterized in that, In step 2), the liquid / solid ratio of the inorganic alkaline solution / molded molecular sieve in the in-situ crystallization treatment is 1-6 L / kg, the treatment temperature is 80-100℃, and the treatment time is 2-24 h.
13. The method according to any one of claims 8-12, characterized in that, In step 3), the drying temperature is 120-250℃ and the drying time is 0.4-3h; the calcination temperature is 450-600℃ and the calcination time is 0.2-2h.
14. Use of the low silica-alumina ratio X-type zeolite molecular sieve according to any one of claims 1-7 as a CO2 adsorbent.