A nitrogen-oxygen separation adsorbent and a method for preparing the same

Abstract

The application discloses a nitrogen-oxygen separation adsorbent, characterized in that the adsorbent comprises an inner adsorbent layer and an outer adsorbent layer, the inner adsorbent layer comprises low-silicon X molecular sieve and a binder, and the outer adsorbent layer comprises Y molecular sieve and a binder, cation sites of the low-silicon X molecular sieve are occupied by Li, and cation sites of the Y molecular sieve are occupied by at least one of Na and K. The adsorbent is used for separating nitrogen and oxygen in air through pressure swing adsorption, and is used for preparing oxygen-rich gas, and has good separation performance.

Description

Technical Field

[0001] This invention relates to a nitrogen and oxygen separation adsorbent and its preparation method, specifically, a nitrogen and oxygen separation adsorbent with X molecular sieve as the active component and its preparation method. Background Technology

[0002] Oxygen has wide applications in various industrial fields such as metallurgy, chemical industry, and environmental protection. Pressure swing adsorption (PSA) technology can separate nitrogen from other gases in the air to obtain oxygen-enriched gas with an oxygen concentration exceeding 90%. The active component of the adsorbent in PSA separation is typically X molecular sieve. X molecular sieve is mixed uniformly with clay in a certain proportion, and then spheroidized, dried, and calcined to obtain adsorbent spheres.

[0003] CN1146374A discloses an adsorbent for cyclic pressure swing adsorption (BPSA) processes, wherein the adsorbent contains a framework SiO2 / Al2O3 molar ratio of 2.0–2.4 and contains 60–89% (equivalent) Ca. ++ Cations, 10–40% (equivalent) Na + Cations and 0–10% (equivalent) K + Cation-type X-type zeolite, Ca ++ Na + and K + With a total cation equivalent of at least 90%, this type X zeolite is far more effective as an adsorbent for air separation in pressure swing adsorption processes at 50–20°C and 5–506.5 kPa (0.05–5.0 atm) than the same type X zeolite that exchanges calcium to a greater or lesser extent.

[0004] CN101708456A discloses a molecular sieve adsorbent for pressure swing adsorption (PSA) air separation oxygen production and its preparation method. The active component of the adsorbent is CaO2 / Al2O3 with a ratio of 2.0-2.1. 2+ Exchange-grade low-silica type X molecular sieve, in which Ca 2+ The exchange degree is 80-100%. Because the exchange of calcium-type X molecular sieves with high exchange degree is difficult and costly, calcium chloride solution is used to exchange low-silica X molecular sieves to reduce costs.

[0005] CN1158139C discloses an improved binder zeolite adsorbent, the active component of which is an X molecular sieve with a Si / Al atomic ratio of 1 and deep lithium exchange. High lithium exchange rate and nitrogen adsorption capacity can be obtained by multiple exchanges with lithium chloride solution.

[0006] CN1291907A discloses an improved PSA adsorbent, the active component of which is a LiX zeolite material, the macropore structure of which is improved by using an appropriate amount of aggregated binder which can be converted into zeolite by caustic digestion ("CD") and by adding combustible fibers or particulate material during the molding process, thereby increasing the intrinsic mass transfer rate of the PSA adsorbent.

[0007] CN104138741A discloses a rare earth modified lithium low-silicon molecular sieve adsorbent and a preparation method thereof, which can significantly improve hydrothermal stability and prolong service life by introducing rare earth elements into the cavity structure of the lithium low-silicon molecular sieve.

[0008] In the pressure swing adsorption separation process, carbon dioxide, water vapor and other gases in the air are also adsorbed by the low-silicon X molecular sieve adsorbent, but due to the strong binding ability of carbon dioxide and water vapor with the low-silicon X molecular sieve, these gases are difficult to desorb quickly when the system pressure is reduced, thereby causing a significant decrease in the separation performance of the adsorbent, and even deactivation. SUMMARY

[0009] The purpose of the present application is to provide a nitrogen-oxygen separation adsorbent based on the prior art, which is used for separating nitrogen and oxygen in air by pressure swing adsorption, and is used for preparing high-concentration oxygen, and has high nitrogen and oxygen separation performance.

[0010] The nitrogen-oxygen separation adsorbent provided by the present application comprises an inner adsorbent layer and an outer adsorbent layer, the inner adsorbent layer comprises a low-silicon X molecular sieve and a binder, the outer adsorbent layer comprises a Y molecular sieve and a binder, the cation site of the low-silicon X molecular sieve is occupied by Li, and the cation site of the Y molecular sieve is occupied by at least one of Na or K.

[0011] The present application also provides a preparation method of a nitrogen-oxygen separation adsorbent, comprising the following steps:

[0012] (1) uniformly mixing a low-silicon X molecular sieve and a binder at a mass ratio of 50-79:21-50, putting into a rotating disc, spraying water while rolling, and making the solid aggregate into small balls as an inner adsorbent layer, then adding powder of Y molecular sieve and binder mixed at a mass ratio of 50-79:21-50, continuing to spray water and roll to form an outer adsorbent layer, and sieving to obtain small balls with a particle size of 300-850 microns;

[0013] (2) laying the small balls prepared in step (1) flat, the bed layer thickness being less than or equal to 30 mm, drying in a flowing air atmosphere, the drying temperature being 60-120 DEG C, preferably 80-100 DEG C, and the time being 6-12 hours;

[0014] (3) The dried small pellets prepared in step (2) are laid flat with a bed layer thickness of less than or equal to 20 mm, and are fired in a flowing air atmosphere in stages, successively at 150-220°C for 1-3 hours, at 250-320°C for 1-3 hours, at 350-420°C for 1-3 hours, and at 450-540°C for 4-8 hours.

[0015] The present application also provides a method for producing oxygen from air using the nitrogen-oxygen separation adsorbent described in the present application or the nitrogen-oxygen separation adsorbent prepared by the method provided in the present application.

[0016] The nitrogen-oxygen separation adsorbent provided in the present application adopts a composite layer structure, and the outer adsorbent layer adsorbs carbon dioxide and water vapor in adsorbable air during the adsorption process, thereby avoiding the influence of the carbon dioxide and water vapor on the separation performance of the low-silicon X molecular sieve for nitrogen and oxygen. Since the adsorption capacity of the outer adsorbent layer for carbon dioxide and water vapor is weak, the carbon dioxide and water vapor adsorbed by the outer adsorbent layer can be quickly removed during pressure reduction and purging, reducing the influence on the low-silicon X molecular sieve, thereby improving the nitrogen-oxygen separation performance of the adsorbent. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a schematic diagram of a pressure swing adsorption device.

[0018] Figure 2 is a scanning electron microscope (SEM) photograph of the low-silicon X molecular sieve in Example 1.

[0019] Figure 3 is a scanning electron microscope (SEM) photograph of the Y molecular sieve in Example 1. DETAILED DESCRIPTION

[0020] The nitrogen-oxygen separation adsorbent provided by the application is divided into two batches for rolling forming, the mixture of low-silicon X molecular sieve with high adsorption capacity for nitrogen and a binder is first rolled into small balls as an inner adsorbent layer, and then the mixture of Y molecular sieve and a binder is added to form an outer adsorbent layer, thereby preparing a composite layer adsorbent. During pressure swing adsorption, in the process of pressure increase, the Y molecular sieve of the outer adsorbent layer first adsorbs carbon dioxide and water vapor in the air to avoid entering the inner adsorbent layer, and then the remaining air enters the inner adsorbent layer, nitrogen is selectively adsorbed, and the remaining gas is discharged through the adsorbent bed, thereby obtaining oxygen-rich gas; in the process of pressure decrease, the nitrogen previously adsorbed by the low-silicon X molecular sieve of the inner adsorbent layer is desorbed, and at the same time, due to the high molar ratio of silicon oxide / alumina of the Y molecular sieve of the outer adsorbent layer, the adsorption of carbon dioxide and water vapor is relatively weak, and the adsorbed carbon dioxide and water vapor can be quickly removed and discharged together with the desorbed nitrogen of the inner adsorbent layer. The adsorbent provided by the application effectively solves the problem that the low-silicon X molecular sieve causes the nitrogen and oxygen separation performance to decrease due to the adsorption of carbon dioxide and water vapor, improves the concentration of the obtained oxygen, and thereby improves the overall nitrogen and oxygen separation performance of the composite layer adsorbent.

[0021] The nitrogen-oxygen separation adsorbent provided by the application includes an inner adsorbent layer and an outer adsorbent layer, the inner adsorbent layer includes low-silicon X molecular sieve and a binder, the outer adsorbent layer includes Y molecular sieve and a binder, the cation sites of the low-silicon X molecular sieve are occupied by Li, and the cation sites of the Y molecular sieve are occupied by at least one of Na or K.

[0022] The nitrogen-oxygen separation adsorbent provided by the application includes 50-79 mass% of low-silicon X molecular sieve and 21-50 mass% of a binder in the inner adsorbent layer, and 50-79 mass% of Y molecular sieve and 21-50 mass% of a binder in the outer adsorbent layer, based on the total amount of the inner adsorbent layer and the outer adsorbent layer.

[0023] In the nitrogen-oxygen separation adsorbent provided by the application, the molar ratio of silicon oxide / alumina of the low-silicon X molecular sieve is 1.90-2.05, the content of the low-silicon X molecular sieve accounts for 90-96 mass% of the total amount of molecular sieve in the adsorbent, the grain size of the low-silicon X molecular sieve is 0.4-10 microns, and the content of Li2O in the low-silicon X molecular sieve is greater than or equal to 10 mass%.

[0024] In the nitrogen-oxygen separation adsorbent provided by the application, the molar ratio of silicon oxide / alumina of the Y molecular sieve is 3.2-5.5, and the grain size of the Y molecular sieve is 0.1-0.8 microns.

[0025] In the nitrogen-oxygen separation adsorbent provided by the application, the binder is selected from one of kaolin, halloysite and attapulgite.

[0026] The nitrogen-oxygen separation adsorbent provided by the application has a water content of less than or equal to 0.6% by mass.

[0027] The nitrogen-oxygen separation adsorbent provided by the application is preferably in the form of small spheres, and the average particle size of the small spheres is 300-850 microns.

[0028] The preparation method of the nitrogen-oxygen separation adsorbent provided by the application comprises the following steps:

[0029] (1) uniformly mixing low-silicon X molecular sieves and a binder at a mass ratio of 50-79:21-50, placing the mixture in a rotating disc, spraying water while rotating to make the solids aggregate into small spheres, and using the small spheres as an inner adsorbent layer, then adding powder of Y molecular sieves and a binder mixed at a mass ratio of 50-79:21-50, continuing to spray water and rotate to form an outer adsorbent layer, and sieving to obtain small spheres with a particle size of 300-850 microns;

[0030] (2) laying the small spheres obtained in step (1) flat to form a bed layer with a thickness of less than or equal to 30 mm, and drying the small spheres in a flowing air atmosphere, wherein the drying temperature is 60-120°C, preferably 80-100°C, and the drying time is 6-12 hours;

[0031] (3) laying the dried small spheres obtained in step (2) flat to form a bed layer with a thickness of less than or equal to 20 mm, and sequentially calcining the small spheres in a flowing air atmosphere at 150-220°C for 1-3 hours, at 250-320°C for 1-3 hours, at 350-420°C for 1-3 hours, and at 450-540°C for 4-8 hours.

[0032] In step (1), the cation sites of the low-silicon X molecular sieves are occupied by Li, the cation sites of the Y molecular sieves are occupied by at least one of Na or K, and the content of the low-silicon X molecular sieves is 90-96% by mass based on the total amount of the low-silicon X molecular sieves and the Y molecular sieves. The low-silicon X molecular sieves and the Y molecular sieves are prepared by conventional methods in the art, and will not be described here again. The equipment for rolling the small spheres can be a rotating disc, a sugar-coating pot or a roller. When rolling the small spheres, the uniformly mixed solid raw materials are placed in the rotating equipment, and water is sprayed while rotating to make the solid powders adhere and aggregate into small spheres. The amount of water added during rolling is 5-16% of the total mass of the solids, preferably 8-12%. After rolling into small spheres, the small spheres are sieved to obtain small spheres with a particle size of 300-850 microns.

[0033] In the preparation method of the nitrogen-oxygen separation adsorbent provided by the application, the small spheres obtained in step (1) are laid flat to form a bed layer with a uniform thickness, and the bed layer thickness is preferably less than or equal to 20 mm. During the drying process, air needs to continuously pass through the bed layer to quickly remove water vapor. In order to avoid damage to the molecular sieves in the small spheres caused by high-temperature water vapor, the residence time of air in the adsorbent bed layer is less than or equal to 20 seconds, preferably less than or equal to 15 seconds.

[0034] In the preparation method of the nitrogen-oxygen separation adsorbent provided by the present application, the pellets obtained in step (2) are laid flat to form a bed layer with uniform thickness, the thickness of the bed layer is preferably less than or equal to 15 mm, the calcination is carried out in four stages, the calcination temperatures in the four stages are preferably 160-200℃, 270-300℃, 370-400℃ and 460-500℃, respectively, the constant-temperature calcination time in each stage is preferably 2-3 hours, 2-3 hours, 2-3 hours and 5-6 hours, respectively, the heating rate is 0.5-5℃ / min, preferably 1-3℃ / min, and during the calcination process, air needs to be continuously passed through the bed layer to quickly remove water vapor. In order to avoid that high-temperature water vapor destroys the molecular sieve in the pellets, the residence time of air in the adsorbent bed layer is less than or equal to 20 seconds, preferably less than or equal to 15 seconds. After the completion of the calcination process, the adsorbent pellets are cooled to room temperature under vacuum.

[0035] The adsorbent provided by the present application is suitable for the pressure swing adsorption separation of nitrogen and oxygen in air to produce high-concentration oxygen. The pressure swing adsorption can be carried out in a double-column or multi-column mode, or by means of a rotary valve or an electromagnetic valve group to realize the pressure swing adsorption process. The operating pressure is 0.2-0.5 MPa, and the operating temperature is 5-50℃.

[0036] The performance of the adsorbent is evaluated by using a double-column pressure swing adsorption device, and a schematic diagram of the pressure swing adsorption device is shown in Figure 1 The device is composed of a pressure gauge, adsorption columns, electromagnetic valves and the like. The opening or closing of electromagnetic valves V1, V2, V3, V5, V6, V7 and V8 realizes the four steps of pressure increase, adsorption, pressure reduction and purging to continuously produce oxygen-rich gas. About 370 mL of adsorbent is loaded in each of adsorption columns A and B, the adsorption time is set to 3 seconds, the pressure reduction, purging and pressure increase time is 3 seconds in total, the maximum pressure of the adsorption columns is 0.25 MPa, the operating temperature is 35℃, and the oxygen-rich gas production rate is 4.5 L / h. After 50 cycles of continuous operation, the oxygen volume concentration in the product is analyzed by using an oxygen concentration analyzer.

[0037] The determination method of the water content of the adsorbent is as follows: the adsorbent with a mass of m1 is placed in a crucible, and is calcined at 600℃ for 2 hours. After the completion of the calcination, the crucible is quickly taken out and placed in a desiccator to cool to room temperature. The mass of the adsorbent after calcination is m2, and the water content C of the adsorbent is (m1-m2) / m1.

[0038] The present application is further illustrated by examples below, but the present application is not limited thereto.

[0039] The following examples prepare the adsorbent described in the present application.

[0040] The preparation method of the low-silicon X molecular sieve and the Y molecular sieve in the examples of the present application is as follows:

[0041] Low-silica X molecular sieve: 4.66 kg of sodium hydroxide, 7.23 kg of potassium hydroxide, 35.74 kg of deionized water, 47.57 kg of low-alkalinity sodium metaaluminate solution (Al203 mass fraction of 11.0%, Na20 mass fraction of 15.1%), and 36.72 kg of water glass were added into a reaction kettle, and stirred and mixed uniformly to form a molecular sieve synthesis system. The total molar ratio of the materials in the molecular sieve synthesis system was: Si02 / Al203 = 2.40, M20 / Si02 = 2.25, H20 / Si02 = 45, wherein M was K and Na, and K / (K+Na) = 0.23. The above molecular sieve synthesis system was transferred into a reaction kettle, and was aged at 70°C for 6 hours and hydrothermally crystallized at 95°C for 12 hours. The obtained solid was filtered, washed with deionized water until the pH of the filtrate was 8-9, and dried at 80°C for 12 hours to obtain the low-silica X molecular sieve.

[0042] A 1.5 mol / L lithium chloride solution was prepared, and the pH was adjusted to 8-10 with lithium hydroxide. The lithium chloride solution was mixed with the low-silica X molecular sieve at a liquid-solid ratio of 5 L / kg, and the mixture was exchanged at 80°C for 1 hour. The above process was repeated for 7 times. The exchanged low-silica X molecular sieve was dried at 40°C for 10 hours to obtain a low-silica X molecular sieve with lithium as the cation.

[0043] The molar ratio and Li20 content of the low-silica X molecular sieve can be adjusted by adjusting the molar ratio of Si02 / Al203 in the molecular sieve synthesis system, the concentration of the lithium chloride solution, and the liquid-solid ratio of the lithium chloride solution to the low-silica X molecular sieve.

[0044] Y molecular sieve: 4.02 kg of sodium hydroxide, 10.15 kg of deionized water, 2.97 kg of low-alkalinity sodium metaaluminate solution, and 23.24 kg of water glass were added into a reaction kettle, and stirred and mixed uniformly and aged at 30°C for 20 hours to obtain a directing agent.

[0045] 66.29 kg of deionized water, 8.11 kg of low-alkalinity sodium metaaluminate solution, 4.36 kg of aluminum sulfate solution, 31.53 kg of water glass, and 2.65 kg of the directing agent were added into a reaction kettle, and stirred and mixed uniformly to form a molecular sieve synthesis system. The total molar ratio of the materials in the molecular sieve synthesis system was: Si02 / Al203 = 6.5, Na20 / Si02 = 0.5, H20 / Si02 = 50. The above molecular sieve synthesis system was transferred into a reaction kettle, and was hydrothermally crystallized at 95°C for 12 hours. The obtained solid was filtered, washed with deionized water until the pH of the filtrate was 8-9, and dried at 80°C for 12 hours to obtain the Y molecular sieve.

[0046] Example 1

[0047] (1) Forming: 75 kg of low-silica X molecular sieve with a particle size of about 0.5 μm (SEM photograph is shown in FIG. 1) was mixed with 0.75 kg of 1.5 mol / L lithium chloride solution (pH = 8-10) at a liquid-solid ratio of 5 L / kg, and the mixture was exchanged at 80°C for 1 hour. The above process was repeated for 7 times. The exchanged low-silica X molecular sieve was dried at 40°C for 10 hours to obtain a low-silica X molecular sieve with lithium as the cation. Figure 2and 25 kg of kaolin clay were mixed uniformly and put into a rotating disc to form a bed of small balls as the inner adsorbent layer by spraying water while rotating the disc. Then 3.95 kg of Y molecular sieve with a particle size of about 0.6 μm (SEM photograph shown in Fig. 1) was added to form an outer adsorbent layer by spraying water while rotating the disc. After sieving, small balls with a particle size of 300-850 μm were obtained. Figure 3 and 1.32 kg of mixed powder of kaolin clay to form an outer adsorbent layer by spraying water while rotating the disc. After sieving, small balls with a particle size of 300-850 μm were obtained.

[0048] (2) Drying: The small balls of step (1) were uniformly spread to form a bed with a thickness of 10 mm and dried at 100°C in a flowing air atmosphere. The residence time of air in the adsorbent bed was 15 seconds. The drying was carried out for 10 hours.

[0049] (3) Calcination: The dried small balls of step (2) were uniformly spread to form a bed with a thickness of 8 mm and calcined in a flowing air atmosphere. The residence time of air in the adsorbent bed was 8 seconds. The calcination was carried out by treating the bed successively at 200°C for 3 hours, at 300°C for 3 hours, at 400°C for 3 hours and at 500°C for 6 hours at a heating rate of 2°C / min. After calcination, the bed was cooled to room temperature under vacuum. Nitrogen-oxygen separation adsorbent A was obtained.

[0050] The water content and separation performance of adsorbent A are shown in Table 1.

[0051] Example 2

[0052] Nitrogen-oxygen separation adsorbent B was prepared according to the method of Example 1, except that in step (2) the bed thickness was 18 mm and the drying temperature was 100°C. In step (3) the bed thickness was 15 mm and the heating rate was 3°C / min.

[0053] The water content and separation performance of adsorbent B are shown in Table 1.

[0054] Example 3

[0055] Nitrogen-oxygen separation adsorbent C was prepared according to the method of Example 1, except that in step (2) the drying was carried out at 100°C for 8 hours. In step (3) the calcination was carried out by treating the bed successively at 180°C for 2 hours, at 280°C for 2 hours, at 380°C for 2 hours and at 470°C for 5 hours.

[0056] The water content and separation performance of adsorbent C are shown in Table 1.

[0057] Example 4

[0058] Adsorbent D was prepared according to the procedure of Example 1 except that in step (1) 60 kg of low-silica X molecular sieves having a particle size of about 0.5 μm and 40 kg of attapulgite were mixed uniformly and placed in a rotating tray, water was sprayed while rotating to cause the solids to agglomerate into small pellets, which were used as the inner adsorbent layer, and 5.22 kg of Y molecular sieves having a particle size of about 0.6 μm and 3.48 kg of attapulgite were added and water was sprayed while rotating to form an outer adsorbent layer. The pellets were sieved to obtain pellets having a particle size of 300-850 μm.

[0059] The water content and separation performance of adsorbent D are shown in Table 1.

[0060] Example 5

[0061] Adsorbent E was prepared according to the procedure of Example 4 except that in step (1) low-silica X molecular sieves having a particle size of about 4 μm (silica / alumina molar ratio of 1.93, Li2O content of 10.7 mass %) and Y molecular sieves having a particle size of about 0.8 μm (silica / alumina molar ratio of 4.62, cations being K) were used.

[0062] The water content and separation performance of adsorbent E are shown in Table 1.

[0063] Comparative Example 1

[0064] Adsorbent F was prepared according to the procedure of Example 1 except that in step (1) 75 kg of low-silica X molecular sieves having a particle size of about 0.5 μm (silica / alumina molar ratio of 2.03, Li2O content of 11.9 mass %) and 25 kg of kaolin were mixed uniformly and placed in a rotating tray, water was sprayed while rotating to cause the solids to agglomerate into small pellets, which were sieved to obtain pellets having a particle size of 300-850 μm.

[0065] The water content and separation performance of adsorbent F are shown in Table 1.

[0066] Comparative Example 2

[0067] Adsorbent G was prepared according to the procedure of Example 1 except that in step (2) the bed thickness was 35 mm and the residence time of air in the adsorbent bed was 25 seconds.

[0068] The water content and separation performance of adsorbent G are shown in Table 1.

[0069] Comparative Example 3

[0070] Adsorbent H was prepared according to the procedure of Example 1 except that in step (3) the bed thickness was 35 mm and the residence time of air in the adsorbent bed was 25 seconds.

[0071] The water content and separation performance of adsorbent H are shown in Table 1.

[0072] Comparative Example 4

[0073] Adsorbent I was prepared according to the method of Example 1 except that the temperature ramping rate in step (3) was 10°C / min.

[0074] The water content and separation performance of adsorbent I are shown in Table 1.

[0075] Comparative Example 5

[0076] Adsorbent J was prepared according to the method of Example 1 except that no staged calcination was used in step (3) and the temperature was ramped directly to 500°C and calcination was performed for 6 hours.

[0077] The water content and separation performance of adsorbent J are shown in Table 1.

[0078] Comparative Example 6

[0079] Adsorbent K was prepared according to the method of Example 1 except that in step (3) the adsorbent was treated at 200°C for 1 hour, at 300°C for 1 hour and at 400°C for 1 hour.

[0080] The water content and separation performance of adsorbent K are shown in Table 1.

[0081] Table 1

[0082] Example No. Adsorbent No. Water content, mass % Oxygen volume concentration, % 1 A 0.32 95.1 2 B 0.35 93.5 3 C 0.56 94.2 4 D 0.30 92.3 5 E 0.34 94.5 Comparative Example 1 F 0.33 83.6 Comparative Example 2 G 0.26 78.2 Comparative Example 3 H 0.15 41.3 Comparative Example 4 I 0.25 76.5 Comparative Example 5 J 0.22 66.9 Comparative Example 6 K 3.66 85.5

[0083] As can be seen from Table 1, the volume concentration of oxygen obtained by separating air using the adsorbents described in Comparative Examples 1 to 6 is lower than that obtained using the adsorbents described in Examples 1 to 5.

[0084] The adsorbent described in Comparative Example 1 does not contain an outer adsorbent layer and the carbon dioxide and water vapour in air are adsorbed by the low-silica X molecular sieve, which results in a decrease in the nitrogen / oxygen separation performance of the adsorbent.

[0085] In Comparative Example 2, during the preparation of the adsorbent G, the bed thickness in step (2) is relatively thick and the air stays in the adsorbent bed for a relatively long time, which results in the water vapour contacting the adsorbent for too long a time during the drying process, which destroys the structure of the molecular sieve and decreases the separation performance of the adsorbent. In addition, because the structure of the molecular sieve is destroyed, the water adsorption capacity of the adsorbent decreases, so the water content of the adsorbent is relatively low.

[0086] In Comparative Example 3, during the preparation of the adsorbent H, the bed thickness in step (3) is relatively thick and the air stays in the adsorbent bed for a relatively long time, which results in the water vapour contacting the adsorbent for too long a time during the calcination process, which destroys the structure of the molecular sieve and decreases the separation performance of the adsorbent and the water content.

[0087] In Comparative Example 4, during the preparation of the adsorbent I, the temperature ramping rate in step (3) is too fast, which results in the destruction of the structure of the molecular sieve and a decrease in the separation performance of the adsorbent and the water content.

[0088] Comparative Example 5, when preparing the adsorbent J, the step (3) was not carried out by the staged calcination, which resulted in too fast heating rate, leading to the destruction of the molecular sieve structure, and the separation performance of the adsorbent was decreased, and the water content was reduced.

[0089] Comparative Example 6, when preparing the adsorbent K, the calcination time was too short, and the highest temperature was too low, leading to the higher water content of the adsorbent, and the separation performance of the adsorbent was decreased.

Claims

1. A nitrogen and oxygen separation adsorbent, characterized in that, The adsorbent comprises an inner adsorbent layer and an outer adsorbent layer. The inner adsorbent layer comprises a low-silica X molecular sieve and a binder, and the outer adsorbent layer comprises a Y molecular sieve and a binder. The cation sites of the low-silica X molecular sieve are occupied by Li, and the cation sites of the Y molecular sieve are occupied by at least one of Na or K. The content of the low-silica X molecular sieve in the adsorbent is 90-96% by mass of the total molecular sieve in the adsorbent, and the content of Li2O in the low-silica X molecular sieve is greater than or equal to 10% by mass.

2. The adsorbent according to claim 1, characterized in that, The inner adsorbent layer comprises 50-79% by mass of low-silica X molecular sieve and 21-50% by mass of binder, based on the total amount of the inner adsorbent layer.

3. The adsorbent according to claim 1, characterized in that, The outer adsorbent layer comprises 50-79% by mass of Y molecular sieve and 21-50% by mass of binder, based on the total amount of the outer adsorbent layer.

4. The adsorbent according to claim 1, characterized in that, The silica / alumina molar ratio of the low-silica X molecular sieve is 1.90~2.05, and the silica / alumina molar ratio of the Y molecular sieve is 3.2~5.

5.

5. The adsorbent according to claim 1, characterized in that, The low-silicon X molecular sieve has a crystal size of 0.4~10 micrometers.

6. The adsorbent according to claim 1, characterized in that, The Y molecular sieve has a crystal size of 0.1~0.8 micrometers.

7. The adsorbent according to claim 1, characterized in that, The binder is selected from one of kaolin, halloysite, and attapulgite.

8. The adsorbent according to claim 1, characterized in that, The water content of the adsorbent is less than or equal to 0.6% by mass.

9. A method for preparing the nitrogen and oxygen separation adsorbent according to claim 1, characterized in that, Includes the following steps: (1) Mix low-silica X molecular sieve and binder at a mass ratio of 50~79:21~50 evenly, put them in a turntable and spray water while rolling to make the solid aggregate into small balls as the inner adsorbent layer. Then add powder of Y molecular sieve and binder mixed at a mass ratio of 50~79:21~50, continue to spray water and roll to form the outer adsorbent layer, and obtain small balls with a particle size of 300~850 micrometers after sieving. (2) The small balls obtained in step (1) are laid flat with a bed thickness of less than or equal to 30 mm and dried in a flowing air atmosphere. The drying temperature is 60~120℃ and the time is 6~12 hours. (3) Spread the dried pellets obtained in step (2) evenly, with a bed thickness of less than or equal to 20 mm, and calcine them in sections in a flowing air atmosphere, successively calcine at 150~220℃ for 1~3 hours, 250~320℃ for 1~3 hours, 350~420℃ for 1~3 hours, and 450~540℃ for 4~8 hours.

10. The method according to claim 9, characterized in that, (2) In step 2, the drying temperature is 80~100℃.

11. The method according to claim 9, characterized in that, (1) In step 1, the total amount of water added to the rolling ball is 5 to 16% of the total mass of the solid powder.

12. The method according to claim 9, characterized in that, In step (2) or (3), the residence time of air in the adsorbent bed is less than or equal to 20 seconds.

13. The method according to claim 9, characterized in that, (3) The segmented calcination described in step 3 has a heating rate of 0.5~5℃ / min.

14. The method according to claim 9, characterized in that, (3) The segmented calcination described in step 3 has a heating rate of 1~3℃ / min.

15. A method for preparing oxygen from air using a nitrogen-oxygen separation adsorbent according to any one of claims 1 to 8 or a nitrogen-oxygen separation adsorbent prepared by any one of claims 9 to 14.

Images