Modified molecular sieve for PSA nitrogen preparation and preparation method and application thereof

Abstract

The invention discloses a modified molecular sieve for PSA nitrogen preparation and a preparation method and application thereof, and belongs to the technical field of gas separation materials. The modified molecular sieve comprises a silicon-aluminum molecular sieve matrix, a transition metal oxide and an organic amine compound; the molar ratio of SiO2 to Al2O3 of the silicon-aluminum molecular sieve matrix is 5-8; the transition metal oxide is a compound of copper oxide and cobalt oxide, the mass ratio of the copper oxide to the cobalt oxide is 2: 1, and the total loading amount of the transition metal oxide is 3%-8% of the mass of the silicon-aluminum molecular sieve matrix; the organic amine compound is ethylenediamine or triethylene tetramine, and the loading capacity of the organic amine compound is 1-5% of the mass of the silicon-aluminum molecular sieve matrix. The modified molecular sieve takes a silicon-aluminum molecular sieve as a matrix, bifunctional modification is performed by loading transition metal oxides (copper oxide and cobalt oxide) and an organic amine compound, and the synergistic effect of the modified molecular sieve and the silicon-aluminum molecular sieve is optimized, so that the limitation of the prior art is broken through, and the sustainable development of the ammonia synthesis industry is promoted.

Description

A modified molecular sieve for PSA nitrogen production, its preparation method and application Technical Field

[0001] This invention belongs to the field of gas separation materials technology, specifically relating to a modified molecular sieve for PSA nitrogen production, its preparation method, and its application. Background Technology

[0002] In the field of industrial nitrogen production, pressure swing adsorption (PSA) technology dominates due to its advantages such as low energy consumption and flexible operation. Its core principle is the selective adsorption of nitrogen and oxygen by an adsorbent to achieve separation. Molecular sieves are key adsorbents in PSA nitrogen production, and their performance directly determines the nitrogen production efficiency, purity, and operating costs. Currently, the mainstream adsorbents for PSA nitrogen production are 13X molecular sieves and carbon molecular sieves, but both have insurmountable technical bottlenecks.

[0003] While traditional 13X molecular sieves possess a high nitrogen adsorption capacity (25-30 mL / g), their oxygen adsorption selectivity is insufficient (separation ratio approximately 5-8). This necessitates frequent switching of the adsorption-desorption cycle during the preparation of high-purity nitrogen (≥99.99%), increasing energy consumption by 15%-20%. Operational data from a chemical company shows that a PSA system using 13X molecular sieves consumes significantly more energy per Nm³ produced. 3 Nitrogen gas with a purity of 99.99% requires 0.85 kWh of electricity, and the molecular sieve's adsorption capacity decreases by 25% after 6000 hours of operation, necessitating replacement earlier. While carbon molecular sieves offer a higher nitrogen / oxygen separation ratio (approximately 10⁻¹²), their adsorption capacity is low (only 10⁻¹⁵ mL / g), requiring a larger adsorption tower volume to ensure sufficient gas production. More importantly, carbon molecular sieves are prone to pore blockage due to water vapor adsorption in environments with humidity >60%. Furthermore, existing improvement schemes have significant limitations: single transition metal modification (such as supported Cu)... 2+ While it can improve oxygen adsorption activity, it leads to a 10%-15% decrease in nitrogen adsorption capacity. Simple organic amine modification (such as ethylenediamine) can optimize the pore structure, but it is prone to volatilization and loss at the high temperatures (40-60℃) of PSA cycling, resulting in insufficient stability. Furthermore, modified molecular sieves prepared by traditional impregnation methods suffer from uneven distribution of active components; approximately 30% of transition metal ions accumulate on the molecular sieve surface and cannot participate in the adsorption process within the pores, leading to resource waste.

[0004] In summary, although molecular sieve adsorbents have made some progress over the years, with the increasing demands of industry for nitrogen purity (such as 99.999% in the electronics industry) and production continuity, there is an urgent need to develop a new type of molecular sieve material that combines high selectivity, high capacity and long lifespan in order to break through the performance bottleneck of existing PSA nitrogen production technology. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to provide a modified molecular sieve for PSA nitrogen production, its preparation method, and its application. The modified molecular sieve uses a silica-alumina molecular sieve as a matrix and is bifunctionally modified by loading transition metal oxides (copper oxide, cobalt oxide) and organic amine compounds. The loading of transition metal oxides is 3%-8% of the molecular sieve mass, and the loading of organic amine compounds is 1%-5%. The synergistic effect between the organic amine compounds and the silica-alumina molecular sieve is optimized, thereby breaking through the limitations of the prior art and promoting the sustainable development of the ammonia synthesis industry.

[0006] To achieve the above objectives, the present invention employs the following technical solution: The present invention provides a modified molecular sieve for PSA nitrogen production, comprising a silica-alumina molecular sieve matrix, transition metal oxides, and organic amine compounds; the SiO2 / Al2O3 molar ratio of the silica-alumina molecular sieve matrix is ​​5-8; the transition metal oxide is a complex of copper oxide and cobalt oxide, wherein the mass ratio of copper oxide to cobalt oxide is 2:1, and the total loading of the transition metal oxide is 3%-8% of the mass of the silica-alumina molecular sieve matrix; the organic amine compound is ethylenediamine or triethylenetetramine, and the loading of the organic amine compound is 1%-5% of the mass of the silica-alumina molecular sieve matrix.

[0007] In one embodiment, the particle size of the silica-alumina molecular sieve matrix is ​​8-10 mesh, and the specific surface area is 600-800 m². 2 / g, with an average pore size of 0.5-0.8nm.

[0008] In one embodiment, the total loading of the transition metal oxides is 5%-6% of the mass of the silica-alumina molecular sieve matrix; the loading of the organic amine compounds is 2%-3% of the mass of the silica-alumina molecular sieve matrix.

[0009] The present invention also provides a method for preparing a modified molecular sieve for PSA nitrogen production, comprising the following steps: S1, adding a silicon-aluminum molecular sieve matrix to a mixed aqueous solution of copper nitrate and cobalt nitrate, stirring and then allowing it to stand to obtain a pre-treated molecular sieve; S2, drying the pre-treated molecular sieve and then calcining and activating it to obtain a calcined and activated molecular sieve; S3, adding the calcined and activated molecular sieve to an aqueous solution of organic amine, stirring, then filtering and drying to obtain a modified molecular sieve for PSA nitrogen production.

[0010] In one embodiment, in S1, the mass ratio of copper nitrate to cobalt nitrate in the mixed aqueous solution is 2:1, the total concentration of the mixed aqueous solution is 0.1-0.3 mol / L, and the solid-liquid ratio of the silica-alumina molecular sieve matrix to the mixed aqueous solution is 1:5; in S3, the mass-volume concentration of the organic amine aqueous solution is 0.5%-1%.

[0011] In one embodiment, in S3, the mass-volume concentration of the organic amine aqueous solution is 0.7%-0.8%.

[0012] In one embodiment, in S1, the stirring temperature is 60-80°C, the stirring time is 2-4 hours, and the settling time is 12 hours.

[0013] In one embodiment, in S2, the drying temperature is 105°C and the time is 6 hours; the calcination activation is carried out in a muffle furnace, and the calcination activation process is to heat up to 400-500°C at a rate of 2°C / min and hold for 3-5 hours.

[0014] In one embodiment, in step S3, the stirring pressure is 0.1-0.2 MPa, the temperature is 40-50°C, and the time is 1-2 hours; the drying temperature is 105°C, and the time is 4 hours.

[0015] This invention also provides an application of a modified molecular sieve for PSA nitrogen production in pressure swing adsorption (PSA) nitrogen production, at an adsorption pressure of 0.6 MPa and a space velocity of 3000 h⁻¹. -1 Under the specified conditions, the purity of nitrogen gas produced by the modified molecular sieve is not less than 99.99%; after the modified molecular sieve operates for 500 hours in an environment with a humidity of 40%-80%, the adsorption capacity decay rate does not exceed 3%.

[0016] Compared with existing technologies, this invention has the following advantages: This invention provides a modified molecular sieve for PSA nitrogen production, using aluminosilicate molecular sieve as the modified support framework. Its structural characteristics provide the necessary conditions for bifunctional modification. The high specific surface area of ​​this matrix provides sufficient loading sites for transition metal oxides and organic amine compounds, avoiding the aggregation of active components and solving the problem that about 30% of transition metal ions cannot participate in the adsorption of internal pores in the traditional impregnation method. The specific particle size ensures the flowability of gas flow in the PSA nitrogen production process, and the appropriate average pore size creates a structural basis for the subsequent adsorption and separation of gas molecules. At the same time, the polarity of the aluminosilicate molecular sieve provides an auxiliary role in the initial separation of nitrogen and oxygen. The electrostatic field formed by its framework structure can produce differentiated adsorption tendencies for nitrogen and oxygen molecules of different polarities, laying the foundation for the enhanced separation effect of subsequent bifunctional modification. The transition metal oxide is a mixture of copper oxide and cobalt oxide in a mass ratio of 2:1, with a total loading of 3%-8% (preferably 5%-6%) of the mass of the aluminosilicate molecular sieve matrix, which is a key component for improving the selectivity of oxygen adsorption. According to the instructions, this component enhances the chemical adsorption capacity for oxygen by adjusting the electron cloud density on the molecular sieve surface. Compared to traditional 13X molecular sieves that rely solely on physical adsorption for nitrogen and oxygen separation, the introduction of transition metal oxides significantly improves the adsorption specificity for oxygen, compensating for the insufficient oxygen adsorption selectivity of traditional molecular sieves. The test results of Comparative Example 2 show that the nitrogen / oxygen separation ratio of the molecular sieve modified with a single transition metal can reach 10.2, higher than the 7.8 of the traditional 13X molecular sieve, confirming the enhancing effect of transition metal oxides on separation selectivity. Furthermore, this compound component also possesses a certain degree of resistance to humidity interference. The organic amine compound selected is ethylenediamine or triethylenetetramine, with a loading of 1%-5% (preferably 2%-3%) of the silica-alumina molecular sieve matrix. Its core function is to modify the molecular sieve pore structure, improving the physical adsorption selectivity for nitrogen. Its molecular chains can modify the pores, and combined with its loading characteristics, it can optimize the microenvironment of the molecular sieve pores, making the pore structure more suitable for the adsorption requirements of nitrogen molecules, thereby increasing the nitrogen adsorption capacity. The test data from Comparative Example 3 show that the nitrogen adsorption capacity of the molecular sieve modified with a single organic amine is 29 mL / g, which is higher than the 25 mL / g of the molecular sieve modified with a single transition metal, demonstrating the effect of organic amine compounds on improving nitrogen adsorption capacity. Furthermore, in step 3, the organic amine aqueous solution is contacted with the molecular sieve under a pressure of 0.1-0.2 MPa. This pressure-assisted process allows the organic amine to penetrate deeper into the molecular sieve channels, reducing its volatilization and loss under the high-temperature environment of PSA cycling, and improving the structural stability of the molecular sieve.

[0017] This invention constructs a dual-function synergistic separation system through the combined design of "silica-alumina molecular sieve matrix, transition metal oxides, and organic amine compounds." Its core breakthrough lies in: using silica-alumina molecular sieves as a stable carrier, transition metal oxides to enhance oxygen adsorption selectivity, and organic amine compounds to optimize nitrogen adsorption capacity and pore stability. The three form a complementary and synergistic mechanism, ultimately solving the technical bottlenecks of traditional molecular sieves, such as the inability to simultaneously achieve selectivity and capacity, poor stability, high energy consumption, and weak environmental adaptability. It achieves a comprehensive improvement in nitrogen / oxygen separation ratio, adsorption capacity, operating life, and environmental adaptability, meeting the needs of the electronics, food, and chemical industries for high-purity nitrogen preparation.

[0018] This invention achieves synergistic performance enhancement through bifunctional modification of transition metal oxides and organic amines, increasing the nitrogen / oxygen separation ratio by over 30% and adsorption capacity by 20%, successfully resolving the contradiction of "selectivity and capacity being mutually exclusive" in traditional molecular sieves. Simultaneously, the organic amines penetrate deep into the pores under pressure assistance, improving their high-temperature stability by 50%, ensuring that the performance degradation rate of the modified molecular sieve remains <5% after 8000 hours of operation, extending its service life by 30%. Under the same nitrogen purity, this modified molecular sieve also extends the adsorption-desorption cycle of the PSA system by 25%, reducing the unit nitrogen energy consumption to 0.65-0.7 kWh / Nm³. 3 Annual operating costs are reduced by 15%-20%; in addition, its tolerance to humidity fluctuations is significantly improved, and its performance is stable within a humidity range of 40%-80%, effectively reducing purity fluctuations caused by environmental changes. Detailed Implementation

[0019] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0020] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0021] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0022] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0023] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0024] This invention provides a modified molecular sieve for PSA nitrogen production, its preparation method, and its application.

[0025] One aspect provides a modified molecular sieve for use in the PSA nitrogen production process, comprising a silica-alumina molecular sieve matrix, transition metal oxides, and organic amine compounds; the silica-alumina molecular sieve matrix has a SiO2 / Al2O3 molar ratio of 5-8, a particle size of 8-10 mesh, and a specific surface area of ​​600-800 m². 2 / g, with an average pore size of 0.5-0.8nm; the transition metal oxide is a complex of copper oxide and cobalt oxide, with a mass ratio of copper oxide to cobalt oxide of 2:1, and the total loading is 3%-8% of the mass of the silica-alumina molecular sieve matrix; the organic amine compound is ethylenediamine or triethylenetetramine, with a loading of 1%-5% of the mass of the silica-alumina molecular sieve matrix.

[0026] Furthermore, the total loading of the transition metal oxides is 5%-6% of the mass of the silica-alumina molecular sieve matrix, and the loading of the organic amine compounds is 2%-3% of the mass of the silica-alumina molecular sieve matrix.

[0027] On the other hand, a method for preparing the modified molecular sieve for PSA nitrogen production is also provided, comprising the following steps: Step 1: Transition metal ion impregnation, adding the silicon-aluminum molecular sieve matrix to a mixed aqueous solution of copper nitrate and cobalt nitrate, wherein the mass ratio of copper nitrate to cobalt nitrate in the mixed aqueous solution corresponds to the mass ratio of copper oxide to cobalt oxide in the transition metal oxide, the total concentration of the mixed aqueous solution is 0.1-0.3 mol / L, the solid-liquid ratio of the silicon-aluminum molecular sieve matrix to the mixed aqueous solution is 1:5, stirring at 60-80℃ for 2-4 hours, and standing for 12 hours; preferably, the stirring temperature in step 1 is 70℃, and the stirring time is 3 hours.

[0028] Step 2: Calcination and activation. The molecular sieve treated in Step 1 is dried at 105°C for 6 hours, and then placed in a muffle furnace and heated to 400-500°C at a rate of 2°C / min, and held for 3-5 hours. Preferably, the calcination temperature in Step 2 is 450°C and the holding time is 4 hours.

[0029] Step 3: Secondary modification with organic amine. The molecular sieve treated in Step 2 is added to an organic amine aqueous solution with a concentration of 5%-10%. The mixture is stirred for 1-2 hours at a pressure of 0.1-0.2 MPa and a temperature of 40-50°C. After filtration, the mixture is dried at 105°C for 4 hours. The solid-liquid ratio of the molecular sieve treated in Step 2 to the organic amine aqueous solution is 1:5 to 1:8. Preferably, the concentration of the organic amine aqueous solution in Step 3 is 7%-8%, the solid-liquid ratio of the molecular sieve treated in Step 2 to the organic amine aqueous solution is 1:5, the pressure is 0.15 MPa, the temperature is 45°C, and the stirring time is 1.5 hours.

[0030] Furthermore, the application of the modified molecular sieve for PSA nitrogen production is also provided. The modified molecular sieve is used in the PSA nitrogen production process to separate nitrogen and oxygen at an adsorption pressure of 0.6 MPa and a space velocity of 3000 h⁻¹. -1 Under the specified conditions, the purity of the nitrogen produced is not less than 99.99%. After operating for 500 hours in an environment with a humidity of 40%-80%, the adsorption capacity decay rate of the modified molecular sieve does not exceed 3%. The PSA nitrogen production system using the modified molecular sieve has a unit nitrogen energy consumption of 0.65-0.7 kWh / Nm³. 3 .

[0031] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0032] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0033] Example 1: Raw material formulation: 100g of silica-alumina molecular sieve (SiO2 / Al2O3=6), copper nitrate (Cu(NO3)2) 5.2g of cobalt nitrate (Co(NO3)2) 3.8g of 6H2O and 4g of ethylenediamine.

[0034] Step 1: Transition metal ion impregnation. The silica-alumina molecular sieve matrix is ​​added to a mixed aqueous solution of copper nitrate and cobalt nitrate. The total concentration of the mixed aqueous solution is 0.2 mol / L, and the solid-liquid ratio of the silica-alumina molecular sieve matrix to the mixed aqueous solution is 1:5. The mixture is stirred at 70°C for 3 hours and then allowed to stand for 12 hours. Step 2: Calcination and activation. The molecular sieve treated in Step 1 is dried at 105°C for 6 hours, and then placed in a muffle furnace. The temperature is increased to 450°C at a rate of 2°C / min and held for 4 hours. Step 3: Secondary modification with organic amine. The molecular sieve treated in Step 2 is added to an organic amine aqueous solution with a mass-volume concentration of 0.8 g / 100 mL. The mixture is stirred at 0.15 MPa pressure and 45°C for 1-2 hours, filtered, and then dried at 105°C for 4 hours.

[0035] Performance testing: Nitrogen adsorption capacity 32 mL / g (25℃, 0.1 MPa), nitrogen / oxygen separation ratio 12.5; in a PSA system (adsorption pressure 0.6 MPa, space velocity 3000 h⁻¹), the adsorption capacity was 32 mL / g (25℃, 0.1 MPa), and the nitrogen / oxygen separation ratio was 12.5. -1 The nitrogen purity is stable at 99.995%, and the capacity decay rate is less than 3% after 1000 hours of operation.

[0036] Example 2: Raw material formula: 100g of silicon-aluminum molecular sieve (SiO2 / Al2O3=8), 3.5g of copper nitrate, 2.2g of cobalt nitrate, and 3g of triethylenetetramine.

[0037] Step 1: Transition metal ion impregnation. The silica-alumina molecular sieve matrix is ​​added to a mixed aqueous solution of copper nitrate and cobalt nitrate. The total concentration of the mixed aqueous solution is 0.1 mol / L, and the solid-liquid ratio of the silica-alumina molecular sieve matrix to the mixed aqueous solution is 1:5. The mixture is stirred at 60°C for 4 hours and then allowed to stand for 12 hours. Step 2: Calcination and activation. The molecular sieve treated in Step 1 is dried at 105°C for 6 hours, and then placed in a muffle furnace. The temperature is increased to 500°C at a rate of 2°C / min and held for 3 hours. Step 3: Secondary modification with organic amine. The molecular sieve treated in Step 2 is added to an organic amine aqueous solution with a mass-volume concentration of 0.6 g / 100 mL. The mixture is stirred at 0.2 MPa pressure and 50°C for 1-2 hours, filtered, and then dried at 105°C for 4 hours.

[0038] Performance testing: Nitrogen adsorption capacity 30 mL / g, nitrogen / oxygen separation ratio 11.8; nitrogen purity in the PSA system 99.992%, energy consumption reduced to 0.68 kWh / Nm³. 3 It reduces costs by 20% compared to traditional molecular sieves.

[0039] Example 3: Raw material formula: 100g of silicon-aluminum molecular sieve (SiO2 / Al2O3=5), 6.8g of copper nitrate, 3.4g of cobalt nitrate, and 5g of ethylenediamine.

[0040] Step 1: Transition metal ion impregnation. The silica-alumina molecular sieve matrix is ​​added to a mixed aqueous solution of copper nitrate and cobalt nitrate. The total concentration of the mixed aqueous solution is 0.3 mol / L, and the solid-liquid ratio of the silica-alumina molecular sieve matrix to the mixed aqueous solution is 1:5. The mixture is stirred at 80°C for 2 hours and then allowed to stand for 12 hours. Step 2: Calcination and activation. The molecular sieve treated in Step 1 is dried at 105°C for 6 hours, and then placed in a muffle furnace. The temperature is increased to 400°C at a rate of 2°C / min and held for 5 hours. Step 3: Secondary modification with organic amine. The molecular sieve treated in Step 2 is added to an organic amine aqueous solution with a mass-volume concentration of 1.0 g / 100 mL. The mixture is stirred at 0.1 MPa pressure and 40°C for 1-2 hours, filtered, and then dried at 105°C for 4 hours.

[0041] Performance testing: Nitrogen adsorption capacity 34 mL / g, nitrogen / oxygen separation ratio 13.2; after running for 500 hours in an environment with 70% humidity, the adsorption capacity decay rate is only 2.1%, which is much lower than the 8.5% of traditional molecular sieves.

[0042] Example 4: Raw material formula: 100g of silicon-aluminum molecular sieve (SiO2 / Al2O3=7), 4.6g of copper nitrate, 2.3g of cobalt nitrate, and 2.5g of triethylenetetramine.

[0043] Step 1: Transition metal ion impregnation. The silica-alumina molecular sieve matrix is ​​added to a mixed aqueous solution of copper nitrate and cobalt nitrate. The total concentration of the mixed aqueous solution is 0.15 mol / L, and the solid-liquid ratio of the silica-alumina molecular sieve matrix to the mixed aqueous solution is 1:5. The mixture is stirred at 65°C for 3.5 hours and then allowed to stand for 12 hours. Step 2: Calcination and activation. The molecular sieve treated in Step 1 is dried at 105°C for 6 hours, and then placed in a muffle furnace. The temperature is increased to 480°C at a rate of 2°C / min and held for 3.5 hours. Step 3: Secondary modification with organic amine. The molecular sieve treated in Step 2 is added to an organic amine aqueous solution with a mass-volume concentration of 0.5 g / 100 mL. The mixture is stirred at 0.18 MPa pressure and 48°C for 1-2 hours, filtered, and then dried at 105°C for 4 hours.

[0044] Performance testing: Nitrogen adsorption capacity 31 mL / g (25℃, 0.1 MPa), nitrogen / oxygen separation ratio 12.1; in a PSA system (adsorption pressure 0.5 MPa, space velocity 2500 h⁻¹), the adsorption capacity was 31 mL / g (25℃, 0.1 MPa), and the nitrogen / oxygen separation ratio was 12.1. -1 The nitrogen purity reached 99.994%, and after 1500 hours of continuous operation, the capacity decay rate was only 2.8%. Under these conditions, the energy consumption per unit of nitrogen was 0.69 kWh / Nm³. 3 It operates stably in feed gas containing trace amounts of water vapor (dew point 10℃) with no significant fluctuations in adsorption performance.

[0045] Example 5: Raw material formula: 100g of silicon-aluminum molecular sieve (SiO2 / Al2O3=6.5), 5.8g of copper nitrate, 2.9g of cobalt nitrate, and 3.5g of ethylenediamine.

[0046] Step 1: Transition metal ion impregnation. The silica-alumina molecular sieve matrix is ​​added to a mixed aqueous solution of copper nitrate and cobalt nitrate. The total concentration of the mixed aqueous solution is 0.25 mol / L, and the solid-liquid ratio of the silica-alumina molecular sieve matrix to the mixed aqueous solution is 1:5. The mixture is stirred at 75°C for 2.5 hours and then allowed to stand for 12 hours. Step 2: Calcination and activation. The molecular sieve treated in Step 1 is dried at 105°C for 6 hours, and then placed in a muffle furnace. The temperature is increased to 430°C at a rate of 2°C / min and held for 4.5 hours. Step 3: Secondary modification with organic amine. The molecular sieve treated in Step 2 is added to an organic amine aqueous solution with a mass-volume concentration of 0.7 g / 100 mL. The mixture is stirred at 0.12 MPa pressure and 42°C for 1-2 hours, filtered, and then dried at 105°C for 4 hours.

[0047] Performance testing: Nitrogen adsorption capacity 33 mL / g, nitrogen / oxygen separation ratio 12.8; under high load conditions of the PSA system (space velocity 4000 h⁻¹), -1 Under these conditions, the nitrogen purity remains at 99.993%, a significant improvement over traditional molecular sieves (99.97% purity under the same conditions). After 2000 adsorption-desorption cycles, the separation ratio decreased by only 0.3, demonstrating excellent structural stability and suitability for continuous industrial production.

[0048] Comparative Example 1: Raw material: Commercially available 13X molecular sieve (SiO2 / Al2O3=5).

[0049] Performance testing: Nitrogen adsorption capacity 28 mL / g, nitrogen / oxygen separation ratio 7.8; nitrogen purity in the PSA system reaches a maximum of 99.98%, capacity decays by 25% after 6000 hours of operation, and energy consumption is 0.85 kWh / Nm³. 3 .

[0050] Comparative Example 2: (Single Transition Metal Modification) Raw Material Formulation: 100g of silica-alumina molecular sieve (SiO2 / Al2O3=6), copper nitrate (Cu(NO3)2) 5.2g of cobalt nitrate (Co(NO3)2) 3.8g of 6H2O.

[0051] Step 1: Transition metal ion impregnation. The silica-alumina molecular sieve matrix is ​​added to a mixed aqueous solution of copper nitrate and cobalt nitrate. The total concentration of the mixed aqueous solution is 0.1-0.3 mol / L, and the solid-liquid ratio of the silica-alumina molecular sieve matrix to the mixed aqueous solution is 1:5. The mixture is stirred at 70℃ for 3 hours and then allowed to stand for 12 hours. Step 2: Calcination and activation. The molecular sieve treated in Step 1 is dried at 105℃ for 6 hours, and then placed in a muffle furnace. The temperature is increased to 450℃ at a rate of 2℃ / min and held for 4 hours. Performance test: Nitrogen adsorption capacity is 25 mL / g (decreased by 18%), and the nitrogen / oxygen separation ratio is 10.2. After running for 3000 hours, the separation ratio drops to 8.5 due to pore blockage.

[0052] Comparative Example 3: (Single Organic Amine Modification) Raw Material Formula: 100g of silica-alumina molecular sieve (SiO2 / Al2O3=6), 4g of ethylenediamine.

[0053] Step 1: Calcination and activation: The molecular sieve is dried at 105℃ for 6 hours, then placed in a muffle furnace and heated to 450℃ at a rate of 2℃ / min, and held for 4 hours; Step 2: Secondary modification with organic amine: The molecular sieve treated in Step 2 is added to an organic amine aqueous solution with a concentration of 5%-10%, and stirred for 1-2 hours at 0.15MPa pressure and 45℃. After filtration, it is dried at 105℃ for 4 hours.

[0054] Performance testing: Nitrogen / oxygen separation ratio 9.5, nitrogen adsorption capacity 29 mL / g; however, in PSA cycling above 50°C, the volatilization of organic amines caused the separation ratio to drop to 7.2 after 1000 hours.

[0055] This invention discloses a modified molecular sieve for PSA nitrogen production and its preparation method, belonging to the field of gas separation materials technology. The modified molecular sieve uses a silica-alumina molecular sieve as a matrix and undergoes bifunctional modification by loading transition metal oxides (copper oxide, cobalt oxide) and organic amine compounds. The loading of transition metal oxides is 3%-8% of the molecular sieve mass, and the loading of organic amine compounds is 1%-5%. Specifically, the modified molecular sieve composition includes: a matrix of 8-10 mesh silica-alumina molecular sieve powder (SiO2 / Al2O3 molar ratio 5-8), with an initial specific surface area of ​​600-800 m². 2 / g, with an average pore size of 0.5-0.8 nm. Transition metal oxides: Copper oxide (CuO) and cobalt oxide (Co3O4) are compounded at a mass ratio of 2:1, with a total loading of 3%-8% (preferably 5%-6%) of the molecular sieve mass. The chemical adsorption of oxygen is enhanced by adjusting the surface electron cloud density. Organic amine compounds: Ethylenediamine or triethylenetetramine is selected, with a loading of 1%-5% (preferably 2%-3%). Their molecular chains can modify the molecular sieve channels, improving the physical adsorption selectivity for nitrogen. The above preparation method includes three steps: transition metal ion impregnation, calcination, and secondary modification with organic amines. This invention has the advantages of simple preparation method, easy control of preparation conditions, and excellent adsorption performance. Experiments show that the modified molecular sieve improves the nitrogen / oxygen separation ratio by more than 30%, increases the adsorption capacity by 20%, and has an operating life of more than 8,000 hours at 99.99% nitrogen purity. It significantly reduces the energy consumption and cost of PSA nitrogen production and is suitable for the preparation of high-purity nitrogen in the fields of electronics, food, and chemical industry, with broad application prospects.

[0056] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A modified molecular sieve for PSA nitrogen production, characterized in that, The composition includes a silica-alumina molecular sieve matrix, transition metal oxides, and organic amine compounds; the SiO2 / Al2O3 molar ratio of the silica-alumina molecular sieve matrix is ​​5-8; the transition metal oxides are a mixture of copper oxide and cobalt oxide, wherein the mass ratio of copper oxide to cobalt oxide is 2:1, and the total loading of the transition metal oxides is 3%-8% of the mass of the silica-alumina molecular sieve matrix; the organic amine compounds are ethylenediamine or triethylenetetramine, and the loading of the organic amine compounds is 1%-5% of the mass of the silica-alumina molecular sieve matrix.

2. The modified molecular sieve for PSA nitrogen production according to claim 1, characterized in that, The silica-alumina molecular sieve matrix has a particle size of 8-10 mesh and a specific surface area of ​​600-800 m². 2 / g, with an average pore size of 0.5-0.8nm.

3. The modified molecular sieve for PSA nitrogen production according to claim 1, characterized in that, The total loading of the transition metal oxides is 5%-6% of the mass of the silica-alumina molecular sieve matrix; the loading of the organic amine compounds is 2%-3% of the mass of the silica-alumina molecular sieve matrix.

4. A method for preparing a modified molecular sieve for PSA nitrogen production as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1, The silica-alumina molecular sieve matrix is ​​added to a mixed aqueous solution of copper nitrate and cobalt nitrate, stirred, and allowed to stand to obtain a pre-treated molecular sieve; S2, The pre-treated molecular sieve is dried and then calcined and activated to obtain a calcined and activated molecular sieve; S3, The calcined and activated molecular sieve is added to an aqueous solution of organic amine, stirred, filtered, and then dried to obtain a modified molecular sieve for PSA nitrogen production.

5. The method for preparing the modified molecular sieve for PSA nitrogen production according to claim 4, characterized in that, In S1, the mass ratio of copper nitrate to cobalt nitrate in the mixed aqueous solution is 2:1, the total concentration of the mixed aqueous solution is 0.1-0.3 mol / L, and the solid-liquid ratio of the silica-alumina molecular sieve matrix to the mixed aqueous solution is 1:5; in S3, the mass-volume concentration of the organic amine aqueous solution is 0.5%-1%.

6. The method for preparing the modified molecular sieve for PSA nitrogen production according to claim 5, characterized in that, In S3, the mass-volume concentration of the organic amine aqueous solution is 0.7%-0.8%.

7. The method for preparing the modified molecular sieve for PSA nitrogen production according to claim 4, characterized in that, In S1, the stirring temperature is 60-80℃, the stirring time is 2-4 hours, and the settling time is 12 hours.

8. The method for preparing the modified molecular sieve for PSA nitrogen production according to claim 4, characterized in that, In S2, the drying temperature is 105℃ and the time is 6 hours; the calcination activation is carried out in a muffle furnace, and the calcination activation process is to raise the temperature to 400-500℃ at a rate of 2℃ / min and hold it for 3-5 hours.

9. The method for preparing the modified molecular sieve for PSA nitrogen production according to claim 4, characterized in that, In step S3, the stirring pressure is 0.1-0.2 MPa, the temperature is 40-50℃, and the time is 1-2 hours; the drying temperature is 105℃, and the time is 4 hours.

10. The application of a modified molecular sieve for PSA nitrogen production as described in any one of claims 1 to 3 in pressure swing adsorption nitrogen production, characterized in that, At an adsorption pressure of 0.6 MPa and a space velocity of 3000 h⁻¹ -1 Under the specified conditions, the purity of nitrogen gas produced by the modified molecular sieve is not less than 99.99%; after the modified molecular sieve operates for 500 hours in an environment with a humidity of 40%-80%, the adsorption capacity decay rate does not exceed 3%.