Composite molecular sieve for nitrogen generator and application thereof

Abstract

This invention discloses a composite molecular sieve for nitrogen generators and its application. It is composed of a large-pore molecular sieve and a small-pore molecular sieve. The average micropore particle size of the large-pore molecular sieve is 0.36-0.45 nm, and the average micropore particle size of the small-pore molecular sieve is 0.28-0.36 nm. It can be used to prepare nitrogen with a purity of 99.999%, which is convenient and safe.

Description

Technical Field

[0001] This invention relates to the field of nitrogen preparation technology, and in particular to a composite molecular sieve for nitrogen generators and its applications. Background Technology

[0002] Air composition: Normal air composition by volume fraction is as follows: nitrogen (N2) approximately 78%, oxygen (O2) approximately 21%, rare gases approximately 0.939% (helium He, neon Ne, argon Ar, krypton Kr, xenon Xe, radon Rn), carbon dioxide (CO2) approximately 0.031%, and other gases and impurities approximately 0.03%, such as ozone (O3), nitric oxide (NO), nitrogen dioxide (NO2), and water vapor (H2O).

[0003] There are three existing methods for preparing nitrogen gas of a certain purity: cryogenic air separation, pressure swing adsorption (PSA), and membrane separation. Cryogenic air separation separates gases based on their boiling points, yielding relatively high purity gas. However, due to its inherent technical limitations, it involves complex equipment, large footprint, high initial infrastructure costs, high operating costs, and slow gas production, making it unsuitable for small- to medium-scale applications such as laboratories. PSA utilizes the differences in the movement of different gases under different pressures and their interaction with porous carbon molecular sieves for separation. This method is relatively mature, can be scaled up or down, is easy to maintain and operate, and has moderate operating costs, making it particularly suitable for small- to medium-scale gas needs. Membrane air separation uses air as a raw material. Under pressure, it utilizes the different volume and motion properties of gas molecules, resulting in different permeation rates within the membrane to purify nitrogen. This method is the cheapest and most stable of the three, but due to its inherent limitations, the highest purity nitrogen produced can only reach 99%. Therefore, the main methods for preparing nitrogen with a purity exceeding 99.99% are cryogenic air method and pressure swing adsorption (PSA).

[0004] For small to medium-sized applications requiring high-purity nitrogen (99.99% and above), the pressure swing adsorption (PSA) method is currently the primary method for nitrogen preparation, with most scenarios requiring a nitrogen concentration of 99.999%. However, some detection schemes and equipment require nitrogen with a purity of 99.999%. For example, the carrier gas in gas chromatography must be high-purity nitrogen with a purity of 99.999%. Some oxygen-sensitive chemical preparation reactions require protection under nitrogen with a purity of 99.999%. Furthermore, the gas used in the glove box for handling reactive metals such as lithium also requires 99.999% nitrogen.

[0005] However, the existing mature technology, Pressure Swing Adsorption (PSA), cannot produce nitrogen gas with a true purity of 99.999%. Therefore, many applications still rely on gas cylinders. This is because the claimed 99.999% high-purity nitrogen produced by PSA is primarily tested using a purity meter, which infers nitrogen content from oxygen levels. Air contains not only oxygen and nitrogen, but also other gases such as carbon dioxide, carbon monoxide, methane, and water. Furthermore, GCMS experiments have revealed that commercially available 99.999% high-purity nitrogen still contains carbon dioxide, carbon monoxide, oxygen, and methane exceeding concentration limits. Therefore, the 99.999% high-purity nitrogen produced by PSA is not truly high-purity nitrogen and does not achieve 99.999% purity.

[0006] To achieve truly high-purity nitrogen, practical applications often employ additional purification methods at the outlet, such as capture wells, purifiers, and heat source catalytic hydrocarbon removal. However, these methods have many drawbacks, including the need for frequent replacements, high costs, and safety hazards posed by high-temperature heat sources. Therefore, a convenient, safe technical solution capable of producing 99.999% high-purity nitrogen is needed. Summary of the Invention

[0007] In view of this, this application provides a composite molecular sieve for nitrogen generators and its application, which can be used to prepare nitrogen gas with a purity of 99.999%, which is convenient and safe.

[0008] To achieve the above technical objectives, this application adopts the following technical solution:

[0009] In a first aspect, this application provides a composite molecular sieve for a nitrogen generator, which is composed of a large-pore molecular sieve and a small-pore molecular sieve. The average micropore particle size of the large-pore molecular sieve is 0.36-0.45 nm, and the average micropore particle size of the small-pore molecular sieve is 0.28-0.36 nm.

[0010] Preferably, the porosity of the large-pore molecular sieve is greater than or equal to 90%, and the sum of the specific surface areas of the micropores of the large-pore molecular sieve is greater than or equal to 1000 m². 2 / g.

[0011] Preferably, the porosity of the small-pore molecular sieve is greater than or equal to 90%, and the sum of the micropore specific surface areas of the small-pore molecular sieve is greater than or equal to 1000 m². 2 / g.

[0012] Preferably, the micropore bulk density of the large-pore molecular sieve is 610 kg / m³. 3 .

[0013] Preferably, the micropore bulk density of the small-pore molecular sieve is 670 kg / m³. 3 .

[0014] Preferably, small-pore molecular sieves account for 75-100% of the mass of the composite molecular sieve.

[0015] Preferably, the mass ratio of small-pore molecular sieve to large-pore molecular sieve is 80.7:19.3, at which point the nitrogen purity can reach 99.999% optimally.

[0016] Secondly, an application of a composite molecular sieve is provided, comprising the following steps: the composite molecular sieve is vibratingly packed into a molecular sieve tower, and nitrogen is obtained by separating nitrogen using air as raw material and pressure swing adsorption.

[0017] Preferably, large-pore molecular sieves are packed at the bottom of small-pore molecular sieves. Considering the differences in the movement speed of different types of gas molecules and their interactions with the corresponding purification molecular sieves, the packing is distributed according to the gas movement speed. For example, large-volume or heavier molecules move much slower than small-volume or lighter, higher-energy molecules. Therefore, molecular sieves designed to remove large molecules should be packed at the bottom of the molecular sieve tower, while those designed to remove large molecules should be packed at the top.

[0018] Preferably, the total molecular sieve amount is 5.7 kg for nitrogen production demand of 0.5-2 L / min, 8.8 kg for nitrogen production demand of 4 L / min, and 9.5 kg for nitrogen production demand of 5 L / min.

[0019] The beneficial effects of this application are as follows: The composite molecular sieve of this scheme can effectively remove oxygen, water and hydrocarbon mixtures from the air, thereby achieving the same concentration of high-purity nitrogen as that in the cylinder. At the same time, the dew point of the nitrogen prepared by this technology can be measured to be -66℃ to -76℃ by a dew point meter. The pressure swing adsorption method can separate air to obtain 99.999% high-purity nitrogen, which is safe and convenient and can be installed in a nitrogen generator. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the composite molecular sieve in this scheme;

[0021] Figure 2 This is a graph showing the impurity response of gases purified by different embodiments. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] As mentioned above, in existing technologies, pressure swing adsorption (PSA) often uses molecular sieves to purify nitrogen, but it often fails to achieve a purity of 99.999%. This is because the purity of the nitrogen obtained is calculated by back-calculating the oxygen content, only considering the nitrogen and oxygen components in the air while ignoring other impurities. Therefore, it is impossible to obtain nitrogen with a purity of 99.999%. Furthermore, the pore size of existing molecular sieves is selected based on the size of nitrogen and oxygen molecules. Molecular sieves with larger pore sizes (greater than or equal to 0.36 nm) are generally not used for the purification of high-purity nitrogen.

[0024] The technical approach of this solution is as follows: This solution selects molecular sieves with different pore sizes for blending. For carbon molecular sieves with smaller pore sizes (average micropore size 0.28-0.36 nm), small molecules in the air can be removed more effectively. For example, oxygen molecules are smaller in volume than nitrogen molecules and have higher kinetic energy. Under certain pressure and resistance, oxygen molecules will preferentially enter the molecular sieve interior. For carbon molecular sieves with larger pore sizes (average micropore size 0.36-0.45 nm), large molecules in the air, such as carbon dioxide, can be removed more effectively. Hydrocarbons, because their volume is larger than that of nitrogen molecules, all molecules enter the molecular sieve pores under certain pressure and resistance. When the pressure is released, smaller molecules leave the molecular sieve pores faster than larger molecules. Therefore, by selecting two molecular sieves with different pore sizes and varying their ratios according to the gas source composition and the final purification goal, it is possible to achieve the true preparation of 99.999% pure nitrogen. In analytical chemistry, 99.998% and 99.999% represent a significant difference in application. The principle diagram is shown below. Figure 1 As shown.

[0025] Based on this, the present invention was created.

[0026] Example 1

[0027] A composite molecular sieve for nitrogen generators is composed of macropore molecular sieves and micropore molecular sieves. The average micropore particle size of the macropore molecular sieve is 0.36-0.45 nm, and the average micropore particle size of the micropore molecular sieve is 0.28-0.36 nm. The porosity of the macropore molecular sieve is greater than or equal to 90%, and the sum of the specific surface areas of the micropores of the macropore molecular sieve is greater than or equal to 1000 m². 2 / g, the porosity of small-pore molecular sieves is greater than or equal to 90%, and the sum of the micropore specific surface areas of large-pore molecular sieves is greater than or equal to 1000m². 2 / g, the micropore bulk density of the large-pore molecular sieve is 610 kg / m³. 3 The micropore bulk density of the small-pore molecular sieve is 670 kg / m³. 3 The mass ratio of small-pore molecular sieve to large-pore molecular sieve is 80.7:19.3, with the large-pore molecular sieve filling the lower part of the small-pore molecular sieve.

[0028] Example 2

[0029] A composite molecular sieve for a nitrogen generator is the same as in Example 1, except that the mass ratio of small-pore molecular sieve to large-pore molecular sieve is 75:25.

[0030] Example 3

[0031] A composite molecular sieve for a nitrogen generator is the same as in Example 1, except that the mass ratio of small-pore molecular sieve to large-pore molecular sieve is 90:10.

[0032] Example 4

[0033] A composite molecular sieve for a nitrogen generator is otherwise identical to that in Example 1, except that a large-pore molecular sieve is packed on top of a small-pore molecular sieve.

[0034] Comparative Example 1

[0035] A molecular sieve for a nitrogen generator comprises a macropore molecular sieve with an average micropore size of 0.36-0.45 nm.

[0036] Comparative Example 2

[0037] A molecular sieve for a nitrogen generator comprises a small-pore molecular sieve with an average micropore size of 0.28-0.36 nm.

[0038] Comparative Example 3

[0039] A molecular sieve for a nitrogen generator comprises a macropore molecular sieve with an average micropore size of 0.48-0.55 nm.

[0040] Comparative Example 4

[0041] A composite molecular sieve for a nitrogen generator is the same as in Example 1, except that the mass ratio of small-pore molecular sieve to large-pore molecular sieve is 1:1.

[0042] Comparative Example 5

[0043] A composite molecular sieve for a nitrogen generator is the same as in Example 1, except that the mass ratio of small-pore molecular sieve to large-pore molecular sieve is 25:75.

[0044] Applications and Testing

[0045] The molecular sieves used in Examples 1-4 and Comparative Examples 1-5 were vibratory-packed with a packing density of 560-620 kg / m³. 3The total loading weight was 5.7 kg. The molecular sieve tower parameters used were φ102, inlet flow rate was 40 L / min, outlet flow rate was 2 L / min, and nitrogen production flow rate was 1 L / min. GCMS was used to test and calculate the obtained nitrogen purity and other impurity responses. Figure 2 As shown, the nitrogen purity in different embodiments is relatively high, and the specific quantification results are shown in Table 1.

[0046] Table 1. Test results of each molecular sieve

[0047]

[0048] The results show that the nitrogen obtained by this method has high purity, especially in Example 1, where nitrogen with a purity of 99.999% can be obtained. The composite molecular sieve in Example 1 was analyzed for composition, with air, cylinder gas, and membrane nitrogen generation as comparisons. The tested components included oxygen, water, alkanes, alkenes, aromatics, alkynes, alcohols, phenols, ethers, aldehydes, ketones, esters, carboxylic acids, amines, oxygen-containing compounds, and halogenated compounds. Characteristic mass spectrometry fragments were used as the testing basis, with m / z values ​​of 16, 18, 29, 32, 41, 43, 44, 50, 56, 75, and 91. The testing tool was an Agilent GCMS; the chromatographic column used was a GS-GASPRO 30M 0.32MM; the injection method was manual injection (after three repeated extractions); and the injection volume was 1000 μL. Test results show that the composite molecular sieve using this method can effectively remove oxygen, water, and hydrocarbon mixtures from the air, thereby achieving the same high-purity nitrogen gas concentration as the gas in the cylinder. At the same time, the dew point of the nitrogen gas prepared by this technology can reach -66℃ to -76℃, as measured by a dew point meter.

[0049] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite molecular sieve for use in a nitrogen generator, characterized in that, It is composed of large-pore molecular sieves and small-pore molecular sieves, wherein the average micropore particle size of the large-pore molecular sieve is 0.36-0.45 nm, and the average micropore particle size of the small-pore molecular sieve is 0.28-0.36 nm; the mass ratio of the small-pore molecular sieve to the large-pore molecular sieve is 80.7:19.

3. The porosity of the macropore molecular sieve is greater than or equal to 90%, and the sum of the micropore specific surface areas of the macropore molecular sieve is greater than or equal to 1000 m². 2 / g; The porosity of the small-pore molecular sieve is greater than or equal to 90%, and the sum of the micropore specific surface areas of the small-pore molecular sieve is greater than or equal to 1000 m². 2 / g; The micropore bulk density of the macropore molecular sieve is 610 kg / m³. 3 ; The micropore bulk density of the small-pore molecular sieve is 670 kg / m³. 3 ; The large-pore molecular sieve is filled in the lower part of the small-pore molecular sieve.

2. An application of the composite molecular sieve as described in claim 1, characterized in that, The process includes the following steps: the composite molecular sieve is vibratingly packed into a molecular sieve tower, and nitrogen is obtained by separating nitrogen using air as raw material and pressure swing adsorption.

3. The application according to claim 2, characterized in that, For nitrogen production requirements of 0.5-2 L / min, a total molecular sieve weight of 5.7 kg is used; for nitrogen production requirements of 4 L / min, a total molecular sieve weight of 8.8 kg is used; and for nitrogen production requirements of 5 L / min, a total molecular sieve weight of 9.5 kg is used.

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