A Li-SAPO-RHO molecular sieve, its preparation method and application

Abstract

This invention relates to the field of molecular sieve adsorption materials, and more particularly to a Li-SAPO-RHO molecular sieve, its preparation method, and its applications. The crystalline framework of this molecular sieve is a silica-alumina phosphate with an RHO topology. In the molecular sieve framework, the molar ratio of SiO2 to Al2O3 is 0.02-0.5. The advantages of this invention are that the Li-SAPO-RHO molecular sieve has a low Li content of 0.2-2.0%, with the lower Li content located at the pore openings of the molecular sieve framework, forming an alkali metal cation hinge effect, which is beneficial for increasing the adsorption of nitrogen molecules. The low SiO2 / Al2O3 molar ratio in the molecular sieve framework (0.02-0.5) helps the molecular sieve maintain a high crystallinity (over 99%) and a specific surface area of ​​up to 800 m² after high-temperature calcination. 2 / g, can be used as an adsorbent for the production of high-purity nitrogen by pressure swing adsorption.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve adsorption materials technology, and in particular to a Li-SAPO-RHO molecular sieve, its preparation method, and its application. Background Technology

[0002] High-purity nitrogen is one of the most important inert gases in the electronics industry, used in the manufacture of semiconductors, liquid crystal displays, light-emitting diodes, and solar cells. In the production of electronic components, high-purity nitrogen is used to create a pollution-free environment and ensure product quality. For example, in semiconductor manufacturing, high-purity nitrogen is used in processes such as deposition, etching, and cleaning. Furthermore, high-purity nitrogen plays a vital role in the chemical, food, pharmaceutical, metal industries, aerospace, and scientific research fields.

[0003] The molecular dynamic diameter of nitrogen is 0.364 nm, and that of oxygen is 0.346 nm. Although their dynamic diameters are similar, their polarity, quadrupole moment, and interaction with the adsorbent channels differ, allowing them to be separated by adsorption. Pressure swing adsorption (PSA) for nitrogen production generally utilizes the different adsorption capacities of adsorbents for nitrogen and oxygen, achieving nitrogen separation and purification by periodically changing the pressure of the adsorption bed. Commonly used adsorbents include activated carbon, carbon molecular sieves, and molecular sieves. Activated carbon has a highly developed pore structure with varying pore sizes, resulting in low nitrogen-oxygen separation selectivity, and usually requires use in conjunction with other adsorbent materials. Carbon molecular sieves have similar adsorption capacities for nitrogen and oxygen, requiring precise control of pore size through special processing techniques during production to ensure effective nitrogen-oxygen separation.

[0004] Traditional 5A molecular sieves exhibit some adsorption capacity for both nitrogen and oxygen, but their selectivity is low, limiting their use for nitrogen production alone. Low-silicon-to-alumina (Si / A) LiLSX molecular sieves demonstrate excellent nitrogen and oxygen adsorption and separation performance, and are commonly used in pressure swing adsorption (PSA) oxygen production processes. However, the Si / A ratio of low-silicon LSX molecular sieves is already at the lower limit of X-type molecular sieves, making them prone to the formation of A-type impurities during industrial scale-up. Furthermore, two-thirds of the Li in LiLSX molecular sieves does not contribute to adsorption and separation; the Li exchange rate must be above 98% to achieve nitrogen and oxygen separation. Therefore, the preparation of LiLSX molecular sieves requires a large amount of Li, and the limited and expensive nature of Li resources keeps the price of LiLSX molecular sieves high, limiting their application in high-purity nitrogen production.

[0005] Therefore, developing a novel molecular sieve adsorption material with low lithium content, controllable production cost, and excellent nitrogen and oxygen separation performance has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a Li-SAPO-RHO molecular sieve, its preparation method and application. This molecular sieve can be used as an adsorbent for producing high-purity nitrogen by pressure swing adsorption. Furthermore, the Li-SAPO-RHO molecular sieve prepared by this invention using a one-step hydrothermal crystallization method has a low Li content and a high N2 / O2 separation effect.

[0007] The present invention is achieved through the following technical solution: On the one hand, a Li-SAPO-RHO molecular sieve is provided, wherein the crystal framework of the molecular sieve is a silica-aluminophosphate with a RHO topology; in the molecular sieve framework composition, the molar ratio of SiO2 to Al2O3 is 0.02-0.5;

[0008] Li, as a charge-balancing cation in the molecular sieve + Its content, expressed as a percentage of elemental mass, is 0.2-2.0%.

[0009] Furthermore, the molecular sieve has a crystallinity ≥99% and a specific surface area ≥800 m². 2 / g.

[0010] Furthermore, the molecular sieve is prepared by a one-step hydrothermal crystallization method from a reaction mixture containing a lithium source, an aluminum source, a phosphorus source, a silicon source, an organic template agent R, cetyltrimethylammonium bromide CTAB and deionized water.

[0011] In the reaction mixture, the molar ratio of aluminum source (calculated as Al2O3), phosphorus source (calculated as P2O5), silicon source (calculated as SiO2), lithium source (calculated as Li), organic template agent R, CTAB, and H2O is:

[0012] (0.05-2.0)R:1.0Al2O3:(0.6-1.5)P2O5:(0.01-0.6)SiO2:(0.1-1.0)Li:(0.01-0.2)CTAB:(15-60)H2O.

[0013] A method for preparing the above-mentioned Li-SAPO-RHO molecular sieve is also provided. This molecular sieve is prepared based on a one-step hydrothermal crystallization method, and the specific steps are as follows:

[0014] Step 1) Prepare the reaction gel;

[0015] A reaction gel was obtained by mixing lithium source, aluminum source, phosphorus source, silicon source, organic template agent R, hexadecyltrimethylammonium bromide (CTAB), and deionized water; and the molar ratio of each component was:

[0016] (0.05-2.0)R:1.0Al2O3:(0.6-1.5)P2O5:(0.01-0.6)SiO2:(0.1-1.0)Li:(0.01-0.2)CTAB:(15-60)H2O;

[0017] Step 2) Crystallization;

[0018] The reaction gel was aged at room temperature for 1-3 hours and then crystallized at 180-200℃ for 48-72 hours.

[0019] Step 3) Post-processing;

[0020] The crystallized products are subjected to solid-liquid separation, washing, and drying;

[0021] Step 4) Roasting;

[0022] The dried product is calcined to remove the organic template agent R and CTAB, thus obtaining the final product.

[0023] Using the above technical solution, weigh out a measured amount of deionized water, add a lithium source, start stirring, and sequentially add measured amounts of organic template agents diethylamine (DEA) and N,N-dimethylethylenediamine (DMEN). Stir for a certain time under a sealed condition to form an organic lithium solution.

[0024] An aluminum source was added to a mixed solution of deionized water and phosphoric acid and stirred for a certain period of time to form a gel mixture. A silicon source and hexadecyltrimethylammonium bromide were then slowly added to the resulting gel mixture and stirred for 1-2 hours to obtain a gel.

[0025] The obtained organic lithium solution was added to the obtained gel, and the mixture was stirred and aged in a closed state for a certain period of time to form a homogeneous gel mixture. The obtained gel mixture was transferred to a stainless steel autoclave, heated to 180℃-200℃ for a certain period of time, and crystallized at this temperature for 48-72 hours. After naturally cooling to room temperature, the product was obtained by centrifugation or vacuum filtration and washing, and then dried in a constant temperature oven at 100℃ for later use. The dried molecular sieve powder containing the template agent was then placed in a muffle furnace for high-temperature calcination to remove the organic template agent, thereby obtaining Li-SAPO-RHO molecular sieve.

[0026] In the above-mentioned crystallization, centrifugal washing, drying, calcination to remove organic template agent and preparation of high crystallinity molecular sieve, the molar ratio of the synthesis process is the key factor. Appropriate aging conditions, crystallization temperature and time, and the selection of a suitable calcination temperature during calcination ensure that the organic template agent is completely decomposed while ensuring that the molecular sieve framework structure is not damaged by high temperature treatment. For example, aging at room temperature for 1-3 hours can ensure that the prepared sol is more homogeneous, thereby effectively shortening the crystallization time, reducing energy consumption, and improving the dispersion and crystallinity of molecular sieve crystals.

[0027] Furthermore, in step 4), the roasting temperature is 570-600℃ and the time is 8-10h.

[0028] Furthermore, the organic template agent R is composed of diethylamine DEA and N,N-dimethylethylenediamine DMEN in a molar ratio of 1:1-3.

[0029] Preferably, the phosphorus source is selected from any one or both of orthophosphoric acid and metaphosphoric acid; and / or,

[0030] The aluminum source is selected from at least one of aluminum isopropoxide, aluminum chloride, aluminum hydroxide, aluminum sulfate octahydrate, aluminum nitrate, boehmite, and SB powder.

[0031] Preferably, the silicon source is selected from at least one of silica sol, silica gel powder, silica fume, and tetraethyl orthosilicate.

[0032] Finally, an application of the above-mentioned Li-SAPO-RHO molecular sieve in the selective adsorption of nitrogen from a mixture of nitrogen and oxygen is provided.

[0033] Furthermore, the Li-SAPO-RHO molecular sieve exhibits an adsorption separation coefficient greater than 7 for nitrogen and oxygen at 25°C and 1 bar, which can be used to prepare nitrogen with a purity of not less than 99.8% by pressure swing adsorption process.

[0034] Beneficial effects:

[0035] The Li-SAPO-RHO molecular sieve prepared by this invention has a Li content as low as 0.2-2.0%. The low Li content is located at the pore openings of the molecular sieve framework, forming an alkali metal cation hinge effect, which is beneficial to increasing the adsorption of nitrogen molecules.

[0036] The SiO2 / Al2O3 molar ratio in the molecular sieve framework is as low as 0.02-0.5. This low Si / Al molar ratio helps the molecular sieve maintain a high crystallinity of over 99% after high-temperature calcination, and a specific surface area as high as 800 m². 2 / g;

[0037] Under static conditions, the N2 / O2 adsorption separation coefficient is >7, and the purity of the outlet nitrogen gas tested by pressure swing adsorption separation process is >99.8%, which meets the requirements for the preparation of high-purity nitrogen gas by pressure swing adsorption and is suitable for large-scale industrial production. Attached Figure Description

[0038] Figure 1 This invention demonstrates the XRD patterns of samples obtained in each embodiment;

[0039] Figure 2 The XRD patterns of the samples obtained in each comparative example are shown in this invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0041] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions, or parts are by weight.

[0042] Unless otherwise specified, the reagents and raw materials used in the embodiments and comparative examples of this invention are commercially available.

[0043] Example 1

[0044] First, 2.14 g of lithium chloride was added to 152.45 g of deionized water, and stirring was started. Then, 36.87 g of organic template agent DEA and 46.40 g of DMEN were added, and the mixture was stirred for 5 hours under sealed conditions to form an organolithium solution. 204.25 g of aluminum isopropoxide was weighed and dissolved in a mixed solution of 355.72 g of deionized water and 92.24 g of phosphoric acid (85 wt%). After stirring for 3 hours, 30 g of silica sol (40 wt%) and 36.81 g of CTAB were added to the mixed gel, and stirring was continued for 1 hour. The organolithium solution was then quickly added, and stirring was continued for 2 hours under sealed conditions until a homogeneous gel was formed. Finally, the gel mixture was transferred to a stainless steel autoclave, heated to 200°C for 6 hours, and crystallized at this temperature for 48 hours. Heating was then stopped and the mixture was allowed to cool naturally to room temperature. After centrifugation or vacuum filtration and washing (water washing + ethanol washing), a white solid product was obtained. The product was dried in a constant temperature oven at 100°C and then transferred to a muffle furnace. After 6 hours, the temperature was raised to 600°C and calcined at this temperature for 8 hours to obtain the target product.

[0045] The molar ratio of the gel composition in the synthesis process is 2.0R: 1.0 Al2O3: 0.8 P2O5: 0.4 SiO2: 0.1Li:0.2 CTAB: 60 H2O, where DEA:DMEN = 1:1.

[0046] The obtained sample was tested by X-ray diffraction, and the results showed that it was a highly crystalline SAPO-RHO molecular sieve. Figure 1 .

[0047] Example 2

[0048] First, weigh 13.93 g of lithium nitrate and add it to 101.15 g of deionized water. Start stirring and add 18.43 g of organic template agent DEA and 23.20 g of DMEN. Stir for 5 hours under sealed conditions. Then, weigh 70.15 g of boehmite and add it to a mixed solution of 236.02 g of deionized water and 92.24 g of phosphoric acid (85 wt%). Stir for 3 hours, then add 15 g of silica sol (40 wt%) and 18.41 g of CTAB to the mixed gel. Continue stirring for 1 hour, then quickly add the organic lithium solution and continue stirring for 2 hours under sealed conditions until a homogeneous gel is formed. Finally, the gel mixture was transferred to a stainless steel autoclave, heated to 180°C for 4 hours, and crystallized at this temperature for 72 hours. Heating was then stopped and the mixture was allowed to cool naturally to room temperature. After centrifugation or vacuum filtration and washing (water washing + ethanol washing), a white solid product was obtained. After drying in a constant temperature oven at 100°C, the product was transferred to a muffle furnace, heated to 590°C for 6 hours, and calcined at this temperature for 9 hours to obtain the target product.

[0049] The molar ratio of the gel composition in the synthesis process is 1.0R: 1.0 Al2O3: 0.8 P2O5: 0.2 SiO2: 0.4Li:0.1 CTAB: 40 H2O, where DEA:DMEN = 1:1.

[0050] The obtained sample was tested by X-ray diffraction, and the results showed that it was a highly crystalline SAPO-RHO molecular sieve. Figure 1 .

[0051] Example 3

[0052] First, 19.99 g of lithium acetate was added to 76.83 g of deionized water, and stirring was started. Then, 9.22 g of organic template agent DEA and 34.79 g of DMEN were added, and the mixture was stirred for 5 h under a sealed environment. Next, 70.15 g of boehmite was added to a mixed solution of 179.26 g of deionized water and 92.24 g of phosphoric acid (85 wt%), and the mixture was stirred for 3 h. Then, 1.58 g of silica gel powder (95 wt%) and 9.20 g of CTAB were added to the mixed gel, and the mixture was stirred for another 1 h. The organic lithium solution was then quickly added, and the mixture was stirred for another 2 h under a sealed environment until a homogeneous gel was formed. Finally, the gel mixture was transferred to a stainless steel autoclave, heated to 180°C for 4 hours, and crystallized at this temperature for 72 hours. Heating was then stopped and the mixture was allowed to cool naturally to room temperature. After centrifugation or vacuum filtration and washing (water washing + ethanol washing), a white solid product was obtained. The product was dried in a constant temperature oven at 100°C and then transferred to a muffle furnace. After 6 hours, the temperature was raised to 580°C and calcined at this temperature for 9 hours to obtain the target product.

[0053] The molar ratio of the gel composition in the synthesis process is 1.0R: 1.0 Al2O3: 0.8 P2O5: 0.05 SiO2: 0.6 Li: 0.05 CTAB: 40 H2O, where DEA: DMEN = 1:3.

[0054] The obtained sample was tested by X-ray diffraction, and the results showed that it was a highly crystalline SAPO-RHO molecular sieve. Figure 1 .

[0055] Example 4

[0056] First, weigh 4.84 g of lithium hydroxide and add it to 67.23 g of deionized water. Start stirring and add 7.37 g of organic template agent DEA and 18.56 g of DMEN. Stir for 5 hours under sealed conditions. Then, dissolve 70.15 g of boehmite in a mixed solution of 156.88 g of deionized water and 119.91 g of phosphoric acid (85 wt%). After stirring for 3 hours, add 1.5 g of silica sol (40 wt%) and 1.84 g of CTAB to the above mixed gel. Continue stirring for 1 hour, then quickly add the organic lithium solution and continue stirring for 2 hours under sealed conditions until a homogeneous gel is formed. Finally, the gel mixture was transferred to a stainless steel autoclave, heated to 200°C for 6 hours, and crystallized at this temperature for 48 hours. Heating was then stopped and the mixture was allowed to cool naturally to room temperature. After centrifugation or vacuum filtration and washing (water washing + ethanol washing), a white solid product was obtained. The product was dried in a constant temperature oven at 100°C and then transferred to a muffle furnace. After 6 hours, the temperature was raised to 580°C and calcined at this temperature for 8 hours to obtain the target product.

[0057] The molar ratio of the gel composition in the synthesis process is 0.6 R: 1.0 Al2O3: 1.04 P2O5: 0.02 SiO2:0.4 Li:0.01 CTAB: 27 H2O, where DEA:DMEN = 1:2.

[0058] The obtained sample was tested by X-ray diffraction, and the results showed that it was a highly crystalline SAPO-RHO molecular sieve. Figure 1 .

[0059] Comparative Example 1

[0060] SAPO-RHO molecular sieves containing organic template agents were prepared according to Example 2 of patent CN106276945B. Specifically, aluminum isopropoxide, phosphoric acid (85wt%), tetraethyl orthosilicate, triethylamine, and water were mixed evenly to obtain mixture I. Then, CTAB was added to mixture I to obtain mixture II, with a molar ratio of Al:P:Si:R:S:H2O = 1.0:0.8:0.6:1.5:0.1:30. Mixture II was transferred to a stainless steel high-pressure reactor and crystallized at 200°C for 24 h. After crystallization, the solid product was centrifuged, washed, and dried in air at 100°C to obtain SAPO-RHO molecular sieves containing organic template agents.

[0061] The dried sample was placed in a muffle furnace and heated to 600°C for 6 hours, and then calcined at this temperature for 8 hours to remove the organic template agent, thus obtaining SAPO-RHO raw powder.

[0062] The obtained sample was tested by X-ray diffraction and the results showed that it was a SAPO-RHO molecular sieve, but the crystallinity decreased significantly after calcination. Figure 2 .

[0063] Comparative Example 2

[0064] First, SAPO-RHO molecular sieves containing organic template agents were prepared according to Example 2 of patent CN106276945B. Specifically, aluminum isopropoxide, phosphoric acid (85wt%), tetraethyl orthosilicate, triethylamine, and water were mixed evenly to obtain mixture I. Then, CTAB was added to mixture I to obtain mixture II, with a molar ratio of Al:P:Si:R:S:H2O = 1.0:0.8:0.6:1.5:0.1:30. Mixture II was transferred to a stainless steel high-pressure reactor and crystallized at 200°C for 24 h. After crystallization, the solid product was centrifuged, washed, and dried in air at 100°C to obtain SAPO-RHO molecular sieves containing organic template agents.

[0065] The dried sample was placed in a muffle furnace and calcined at 600℃ for 8 hours to remove the organic template agent. The calcined SAPO-RHO powder, after removing the organic template agent, was mixed with a LiCl solution (0.5 mol / L) at a solid-liquid ratio of 1:50 (S / L = 1:50). The mixture was stirred in a water bath at 60℃ for 4 hours, then filtered, washed, and dried at 100℃. This process was repeated to obtain Li-SAPO-RHO containing Li ions.

[0066] The obtained sample was tested by X-ray diffraction and the results showed that it was a SAPO-RHO molecular sieve. The crystallinity was slightly improved after the exchange process. Figure 2 .

[0067] Comparative Example 3

[0068] 70.15 g of boehmite was added to a mixed solution of 346.08 g of deionized water and 92.24 g of phosphoric acid (85 wt%). After stirring for 3 h, 1.58 g of silica gel powder (95 wt%) and 9.20 g of CTAB were added to the mixed gel, and stirring was continued for 1 h. Then, 9.21 g of DEA and 34.79 g of DMEN were quickly added, and stirring was continued for 2 h in a sealed environment until a homogeneous gel was formed. Finally, the gel mixture was transferred to a stainless steel autoclave, heated to 180 °C for 4 h, and crystallized at this temperature for 72 h. Heating was stopped, and the mixture was allowed to cool naturally to room temperature. After centrifugation or vacuum filtration and washing (water washing + ethanol washing), a white solid product was obtained. After drying in a constant temperature oven at 100 °C, the product was transferred to a muffle furnace, heated to 580 °C for 6 h, and calcined at this temperature for 9 h. The calcined raw powder was mixed with LiCl solution (0.5 mol / L) at a solid-liquid ratio of 1:50 (S / L=1:50), stirred for 4 h in a water bath at 60 ℃, filtered, washed, and dried at 100 ℃. The above operation was repeated to obtain Li-SAPO-RHO containing Li ions.

[0069] The molar ratio of the gel composition in the synthesis process is 1.0R:1.0Al2O3:0.8P2O5:0.05SiO2:0.05CTAB:40H2O, where DEA:DMEN = 1:3.

[0070] The obtained sample was tested by X-ray diffraction and the results showed that it was a SAPO-RHO molecular sieve. Figure 2 .

[0071] Comparative Example 4

[0072] First, weigh 4.84 g of lithium hydroxide and add it to 40.50 g of deionized water. Start stirring and add 7.37 g of organic template agent DEA and 18.56 g of DMEN. Stir for 5 hours under sealed conditions. Then, dissolve 70.15 g of boehmite in a mixed solution of 94.51 g of deionized water and 119.91 g of phosphoric acid (85 wt%). After stirring for 3 hours, add 150 g of silica sol (40 wt%) and 1.84 g of CTAB to the above mixed gel. Continue stirring for 1 hour, then quickly add the organic lithium solution and continue stirring for 2 hours under sealed conditions until a homogeneous gel is formed. Finally, the gel mixture was transferred to a stainless steel autoclave, heated to 200°C for 6 hours, and crystallized at this temperature for 48 hours. Heating was then stopped and the mixture was allowed to cool naturally to room temperature. After centrifugation or vacuum filtration and washing (water washing + ethanol washing), a white solid product was obtained. The product was dried in a constant temperature oven at 100°C and then transferred to a muffle furnace. After 6 hours, the temperature was raised to 580°C and calcined at this temperature for 8 hours to obtain the target product.

[0073] The molar ratio of the gel composition in the synthesis process is 0.6 R: 1.0 Al2O3: 1.04 P2O5: 2 SiO2: 0.4 Li: 0.01 CTAB: 27 H2O, where DEA:DMEN = 1:2.

[0074] The obtained sample was tested by X-ray diffraction and the results showed that it was a SAPO-RHO molecular sieve, but the crystallinity decreased significantly after calcination. Figure 2 .

[0075] Comparative Example 5

[0076] First, 21.41 g of lithium chloride was added to 152.44 g of deionized water, and stirring was started. Then, 36.87 g of organic template agent DEA and 46.39 g of DMEN were added, and the mixture was stirred for 5 hours under sealed conditions to form an organolithium solution. 204.25 g of aluminum isopropoxide was weighed and dissolved in a mixed solution of 355.72 g of deionized water and 92.24 g of phosphoric acid (85 wt%). After stirring for 3 hours, 30 g of silica sol (40 wt%) and 36.81 g of CTAB were added to the mixed gel, and stirring was continued for 1 hour. The organolithium solution was then quickly added, and stirring was continued for 2 hours under sealed conditions until a homogeneous gel was formed. Finally, the gel mixture was transferred to a stainless steel autoclave, heated to 200°C for 6 hours, and crystallized at this temperature for 48 hours. Heating was then stopped and the mixture was allowed to cool naturally to room temperature. After centrifugation or vacuum filtration and washing (water washing + ethanol washing), a white solid product was obtained. The product was dried in a constant temperature oven at 100°C and then transferred to a muffle furnace. After 6 hours, the temperature was raised to 600°C and calcined at this temperature for 8 hours to obtain the target product.

[0077] The molar ratio of the gel composition in the synthesis process is 2.0R: 1.0 Al2O3: 0.8 P2O5: 0.4 SiO2: 1Li:0.2 CTAB: 60 H2O, where DEA:DMEN = 1:1.

[0078] The obtained sample was tested by X-ray diffraction, and the results showed that it was a highly crystalline SAPO-RHO molecular sieve. Figure 2 .

[0079] Effect Example

[0080] The following tests were performed on Examples 1-4 and Comparative Examples 1-5:

[0081] 1) XRD test of samples obtained from each embodiment and comparative example: The crystal structure of the calcined powder samples was tested using an X-ray diffractometer.

[0082] 2) Test of silicon-to-aluminum ratio (SiO2 / Al2O3) of samples obtained from each embodiment and comparative example: All samples were tested on a fluorescence spectrometer using the fusion method.

[0083] 3) Testing of Li content in samples obtained from each embodiment and comparative example: All samples were dissolved in hydrofluoric acid and then tested on a flame photometer to calculate the Li content.

[0084] 4) N2 / O2 separation coefficient test of samples obtained from each embodiment and comparative example: After activation treatment at the degassing station, all samples were tested for adsorption isotherms of N2 and O2 using a physical adsorption instrument, and the separation coefficient was calculated.

[0085] The purity of N2 at the outlet of the samples obtained in each embodiment and comparative example was tested on a pressure swing adsorption nitrogen generator.

[0086] Table 1. Basic information of samples obtained from each embodiment and comparative example.

[0087]

[0088] Based on Example 3, the relative crystallinity of each example and comparative example was calculated. Figure 1 and Figure 2 As shown in Table 1, the relative crystallinity of the samples obtained in each embodiment is above 99.8%, mainly because the samples obtained in each embodiment have a lower SiO2 / Al2O3 molar ratio, thus exhibiting higher crystallinity. The relatively lower crystallinity of the sample obtained in Comparative Example 1 is mainly due to the high SiO2 / Al2O3 molar ratio in the SAPO-RHO molecular sieve, which, after high-temperature calcination, caused partial structural collapse of the framework, further exchanging Li... +Subsequently, the presence of metal cations led to a certain degree of restoration of the framework structure, resulting in a significant increase in relative crystallinity. The results obtained in Comparative Example 3 were similar to those in Comparative Example 2, but both were lower than those in the examples. The excessively high SiO2 / Al2O3 molar ratio in the sample obtained in Comparative Example 4 was the main reason for its low relative crystallinity.

[0089] Table 2. N2 / O2 separation performance of samples obtained from each example and comparative example.

[0090]

[0091] Table 2 shows that the N2 / O2 separation coefficients of the samples obtained in each embodiment, tested on the physical adsorption analyzer, ranged from 7.1 to 7.5, corresponding to an outlet N2 concentration of over 99.8% when tested on the pressure swing adsorption nitrogen generator. The sample obtained in Comparative Example 1, due to its lower crystallinity and lack of Li, showed a different result. + Therefore, it does not possess N2 / O2 separation performance. Comparative Examples 2 and 3 introduce Li through multiple ion exchanges. + It requires a higher Li + The content and effect are also not as good as the one-step crystallization in-situ synthesis that directly introduces Li. + The N2 / O2 separation coefficient tested under static conditions and the outlet N2 concentration tested under dynamic conditions were both low. The sample obtained in Comparative Example 5 contained a large amount of Li. + The N2 / O2 separation effect achieved is similar to that of the samples obtained in the four examples, indicating that only a small amount of Li needs to be introduced through one-step crystallization. + This can achieve excellent N2 / O2 separation effect.

[0092] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Li-SAPO-RHO molecular sieve, characterized in that, The crystalline framework of this molecular sieve is a silica-aluminophosphate with an RHO topology; in the molecular sieve framework composition, the molar ratio of SiO2 to Al2O3 is 0.02-0.5; Li2O3 acts as a charge-balancing cation in the molecular sieve. + Its content, expressed as a percentage of elemental mass, is 0.2-2.0%; The Li-SAPO-RHO molecular sieve was prepared by a one-step hydrothermal crystallization method, the specific steps of which are as follows: Step 1) Prepare the reaction gel; A reaction gel was obtained by mixing lithium source, aluminum source, phosphorus source, silicon source, organic template agent R, hexadecyltrimethylammonium bromide (CTAB), and deionized water. The molar ratio of aluminum source (based on Al2O3), phosphorus source (based on P2O5), silicon source (based on SiO2), lithium source (based on Li), organic template agent R, CTAB, and H2O was: (0.05-2.0)R:1.0Al2O3:(0.6-1.5)P2O5:(0.01-0.6)SiO2:(0.1-1.0)Li:(0.01-0.2)CTAB:(15-60)H2O; Step 2) Crystallization; The reaction gel was aged at room temperature for 1-3 hours and then crystallized at 180-200℃ for 48-72 hours. Step 3) Post-processing; The crystallized products are subjected to solid-liquid separation, washing, and drying; Step 4) Roasting; The dried product is calcined to remove the organic template agent R and CTAB, thus obtaining the product. The organic template agent R is composed of diethylamine DEA and N,N-dimethylethylenediamine DMEN in a molar ratio of 1:1-3; in step 4), the calcination temperature is 570-600℃ and the time is 8-10h.

2. The Li-SAPO-RHO molecular sieve according to claim 1, characterized in that, The molecular sieve has a crystallinity of ≥99% and a specific surface area of ​​≥800 m². 2 / g.

3. A method for preparing the Li-SAPO-RHO molecular sieve according to claim 1 or 2, characterized in that, This Li-SAPO-RHO molecular sieve was prepared using a one-step hydrothermal crystallization method, the specific steps of which are as follows: Step 1) Prepare the reaction gel; A reaction gel was obtained by mixing lithium source, aluminum source, phosphorus source, silicon source, organic template agent R, hexadecyltrimethylammonium bromide (CTAB), and deionized water. The molar ratio of aluminum source (based on Al2O3), phosphorus source (based on P2O5), silicon source (based on SiO2), lithium source (based on Li), organic template agent R, CTAB, and H2O was: (0.05-2.0)R:1.0Al2O3:(0.6-1.5)P2O5:(0.01-0.6)SiO2:(0.1-1.0)Li:(0.01-0.2)CTAB:(15-60)H2O; Step 2) Crystallization; The reaction gel was aged at room temperature for 1-3 hours and then crystallized at 180-200℃ for 48-72 hours. Step 3) Post-processing; The crystallized products are subjected to solid-liquid separation, washing, and drying; Step 4) Roasting; The dried product is calcined to remove the organic template agent R and CTAB, thus obtaining the product. The organic template agent R is composed of diethylamine DEA and N,N-dimethylethylenediamine DMEN in a molar ratio of 1:1-3; in step 4), the calcination temperature is 570-600℃ and the time is 8-10h.

4. The method for preparing Li-SAPO-RHO molecular sieve according to claim 3, characterized in that, The phosphorus source is selected from any one or two of orthophosphoric acid and metaphosphoric acid; and / or, the aluminum source is selected from at least one of aluminum isopropoxide, aluminum chloride, aluminum hydroxide, aluminum sulfate octahydrate, aluminum nitrate, and boehmite.

5. The method for preparing Li-SAPO-RHO molecular sieve according to claim 3, characterized in that, The silicon source is selected from at least one of silica sol, silica gel powder, fumed silica, and tetraethyl orthosilicate.

6. The application of a Li-SAPO-RHO molecular sieve according to claim 1 or 2 in the selective adsorption of nitrogen from a mixture of nitrogen and oxygen.

7. The application according to claim 6, characterized in that, The Li-SAPO-RHO molecular sieve exhibits an adsorption separation coefficient greater than 7 for nitrogen and oxygen at 25°C and 1 bar, making it suitable for preparing nitrogen with a purity of not less than 99.8% via pressure swing adsorption.

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