A method for preparing a space division adsorbent

Abstract

A kind of space separation adsorbent, including inner adsorbent layer and outer adsorbent layer, the inner adsorbent layer includes low silicon X molecular sieve and binder, the outer adsorbent layer includes MFI molecular sieve and binder, the cation site of low silicon X molecular sieve is occupied by Li, and the MIF molecular sieve is high silicon MFI molecular sieve or full silicon MFI molecular sieve.The adsorbent is used for separating nitrogen and oxygen in air by pressure swing adsorption, and prepares oxygen-rich gas, with good separation performance.

Description

Technical Field

[0001] The present invention relates to an air separation adsorbent and a preparation method thereof, in particular to an air separation adsorbent with X molecular sieve as an active component and a preparation method thereof. Background Art

[0002] Oxygen is widely used in various industrial fields, including metallurgy, chemical engineering, and environmental protection. Using pressure swing adsorption (PSA) technology to separate nitrogen from other gases in the air, oxygen-enriched gas with an oxygen concentration exceeding 90% can be obtained. The active component of PSA separation adsorbent is typically molecular sieve X. This adsorbent is prepared by mixing molecular sieve X with clay in a specific ratio, rolling, drying, and calcining the resulting adsorbent pellets.

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

[0004] CN101708456A discloses a molecular sieve adsorbent for pressure swing adsorption air separation oxygen production and its preparation method. The active component of the adsorbent is Ca2O3 with SiO2 / Al2O3=2.0-2.1. 2+ Exchanged low silicon X-type molecular sieve, in which Ca 2+ The exchange degree is 80-100%. Since the exchange of calcium-type X molecular sieve with high exchange degree is difficult and costly, calcium chloride solution is used to exchange low-silicon X molecular sieve to reduce costs.

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

[0006] CN1291907A discloses an improved PSA adsorbent whose active component is LiX zeolite material. The intrinsic mass transfer rate of the PSA adsorbent is improved by using an appropriate amount of agglomerated binder that can be converted into zeolite by alkali cooking ("CD") and adding combustible fibers or particulate materials during the molding process to improve the macroporous structure.

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

[0008] During the pressure swing adsorption separation process, carbon dioxide, water vapor, etc. in the air will also be adsorbed by the low-silicon X molecular sieve adsorbent. However, 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, resulting in a significant decrease in the adsorbent separation performance or even deactivation. Summary of the Invention

[0009] The purpose of the present invention is to provide an air separation adsorbent based on the existing technology, which is used for pressure swing adsorption separation of nitrogen and oxygen in the air to produce high-concentration oxygen and has high nitrogen and oxygen separation performance.

[0010] The air separation adsorbent provided by the present invention comprises an inner adsorbent layer and an outer adsorbent layer, wherein the inner adsorbent layer comprises a low-silicon X molecular sieve and a binder, and the outer adsorbent layer comprises an MFI molecular sieve and a binder. The cation sites of the low-silicon X molecular sieve are occupied by Li, and the MIF molecular sieve is a high-silicon MFI molecular sieve or an all-silicon MFI molecular sieve.

[0011] The present invention also provides a method for preparing an air separation adsorbent, comprising the following steps:

[0012] (1) Mix low-silicon X molecular sieve and binder in a mass ratio of 50-79:21-50, place in a turntable and roll while spraying water to aggregate the solid into small balls, which serve as the inner adsorbent layer. Then add powder of MFI molecular sieve and binder in a mass ratio of 10-60:40-90, continue spraying water and rolling to form an outer adsorbent layer, and obtain small balls with a particle size of 300-850 μm after screening;

[0013] (2) Spreading the pellets obtained in step (1) to a bed thickness of less than or equal to 30 mm, and drying them in a flowing air atmosphere at a temperature of 60 to 120° C., preferably 80 to 100° C., for 6 to 12 hours;

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

[0015] The present invention also provides a method for preparing oxygen from air using the nitrogen-oxygen separation adsorbent of the present invention or the nitrogen-oxygen separation adsorbent prepared by the method provided by the present invention.

[0016] The air separation adsorbent provided by the present invention adopts a composite layer structure. The outer adsorbent layer comprises a hydrophobic high-silicon MFI molecular sieve or an all-silicon MFI molecular sieve and a binder. During the adsorption process, the high-silicon MFI molecular sieve or the all-silicon MFI molecular sieve can prevent a small amount of water vapor from entering the outer layer of the adsorbent. At the same time, the binder adsorbs carbon dioxide and residual water vapor in the air, thereby preventing the carbon dioxide and water vapor from being adsorbed by the low-silicon X molecular sieve in the inner adsorbent layer, which would otherwise reduce the nitrogen and oxygen separation ability of the adsorbent. Since the binder has a relatively weak adsorption capacity for carbon dioxide and water vapor, the carbon dioxide and water vapor adsorbed by the outer adsorbent layer can be quickly removed during the pressure reduction and purge process, reducing their impact on the low-silicon X molecular sieve, thereby facilitating improved nitrogen and oxygen separation performance of the adsorbent. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of pressure swing adsorption device.

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

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

[0020] The nitrogen-oxygen separation adsorbent provided by the present invention is rolled into two batches. First, a mixture of a low-silicon X molecular sieve with a high nitrogen adsorption capacity and a binder is rolled into small balls to serve as an inner adsorbent layer. Then, a mixture of a high-silicon MFI molecular sieve or a full-silicon MFI molecular sieve and a binder is added and rolled to form an outer adsorbent layer to prepare a composite layer adsorbent. During pressure swing adsorption, as the pressure increases, the high-silicon MFI molecular sieve or all-silicon MFI molecular sieve in the outer adsorbent layer prevents a small amount of water vapor in the air from entering the outer adsorbent layer, while the binder adsorbs carbon dioxide and remaining water vapor in the air, preventing them from entering the inner adsorbent layer. After the remaining air enters the inner adsorbent layer, nitrogen is selectively adsorbed, and the remaining gas passes through the adsorbent bed and is discharged to obtain oxygen-rich gas. During the pressure reduction process, the nitrogen previously adsorbed by the low-silicon X molecular sieve in the inner adsorbent layer is desorbed. At the same time, due to the weak adsorption capacity of the binder in the outer adsorbent layer for water and carbon dioxide, the adsorbed carbon dioxide and water vapor are quickly removed and discharged together with the nitrogen desorbed from the inner adsorbent layer. This effectively solves the problem of reduced nitrogen and oxygen separation performance due to the adsorption of carbon dioxide and water vapor by the low-silicon X molecular sieve, increases the concentration of the obtained oxygen, and thus improves the overall nitrogen and oxygen separation performance of the composite layer adsorbent.

[0021] The air separation adsorbent provided by the present invention comprises an inner adsorbent layer and an outer adsorbent layer, wherein the inner adsorbent layer comprises a low-silicon X molecular sieve and a binder, and the outer adsorbent layer comprises an MFI molecular sieve and a binder. The cation sites of the low-silicon X molecular sieve are occupied by Li, and the MIF molecular sieve is a high-silicon MFI molecular sieve or an all-silicon MFI molecular sieve.

[0022] The air separation adsorbent provided by the present invention comprises an inner adsorbent layer comprising 50 to 79% by mass of a low-silicon X molecular sieve and 21 to 50% by mass of a binder, based on the total amount of the inner adsorbent layer; the outer adsorbent layer comprises 10 to 60% by mass of an MFI molecular sieve and 40 to 90% by mass of a binder; and based on the total amount of the outer adsorbent layer, the inner adsorbent layer accounts for 90 to 96% by mass of the adsorbent.

[0023] In the air separation adsorbent provided by the present invention, the silicon oxide / aluminum oxide molar ratio of the low silicon X molecular sieve is 1.90 to 2.05, the grain size of the low silicon X molecular sieve is 0.4 to 10 microns, and the Li2O content in the low silicon X molecular sieve is greater than or equal to 10% by mass.

[0024] In the air separation adsorbent provided by the present invention, the silicon oxide / aluminum oxide molar ratio of the high-silicon MFI molecular sieve is greater than 200, preferably greater than 500, and more preferably greater than 800, and the crystal particle size of the MFI molecular sieve is 0.1 to 0.8 microns.

[0025] In the air separation adsorbent provided by the present invention, the binder is selected from one of kaolin, halloysite and attapulgite.

[0026] The water content of the air separation adsorbent provided by the present invention is less than or equal to 0.6% by mass.

[0027] The air separation adsorbent provided by the present invention is preferably in the form of small balls, and the average particle size of the small balls is 300 to 850 microns.

[0028] The preparation method of the air separation adsorbent provided by the present invention comprises the following steps:

[0029] (1) Mix low-silicon X molecular sieve and binder in a mass ratio of 50-79:21-50, place in a turntable and roll while spraying water to aggregate the solid into small balls, which serve as the inner adsorbent layer. Then add powder of MFI molecular sieve and binder in a mass ratio of 10-60:40-90, continue spraying water and rolling to form an outer adsorbent layer, and obtain small balls with a particle size of 300-850 μm after screening;

[0030] (2) Spreading the pellets obtained in step (1) to a bed thickness of less than or equal to 30 mm, and drying them in a flowing air atmosphere at a temperature of 60 to 120° C., preferably 80 to 100° C., for 6 to 12 hours;

[0031] (3) The dried pellets obtained in step (2) are spread flat with a bed thickness of less than or equal to 20 mm, and calcined in a flowing air atmosphere in stages, successively at 150-220° C. for 1-3 hours, 250-320° C. for 1-3 hours, 350-420° C. for 1-3 hours, and 450-540° C. for 4-8 hours.

[0032] In step (1), the cation sites of the low-silicon X molecular sieve described are occupied by Li, the cation sites of the Y molecular sieve are occupied by at least one of Na or K, and the mass of the inner adsorbent layer is 90-96% of the mass of the inner adsorbent layer and the outer adsorbent layer; the low-silicon X molecular sieve and the MFI molecular sieve are prepared by conventional methods in the art and will not be described in detail here. The equipment for ball rolling can be a turntable, a sugar coating pan or a drum. During ball rolling, the uniformly mixed solid raw materials are placed in the rotating equipment and water is sprayed while rolling to make the solid powder adhere and agglomerate into small balls. The amount of water added during ball rolling is 5-16% of the total mass of the solid, preferably 8-12%. After rolling into balls, the small balls are sieved to obtain small balls with a particle size of 300-850 microns.

[0033] In the preparation method of the air separation adsorbent provided by the present invention, in step (2), the beads obtained in step (1) are spread flat to form a bed layer with uniform thickness. The thickness of the bed layer is preferably less than or equal to 20 mm. During the drying process, air needs to continuously pass through the bed layer to quickly carry away water vapor. In order to prevent high-temperature water vapor from destroying the molecular sieve in the beads, the residence time of the 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 air separation adsorbent provided by the present invention, in step (3), the pellets obtained in step (2) are spread flat to form a bed layer of uniform thickness, the thickness of the bed layer is preferably less than or equal to 15 mm, and the pellets are calcined in four stages. The calcination temperatures are preferably 160-200°C, 270-300°C, 370-400°C, and 460-500°C, 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°C / min, preferably 1-3°C / min. During the calcination process, air needs to continuously pass through the bed layer to quickly remove water vapor. In order to prevent high-temperature water vapor from destroying the molecular sieve in the pellets, the air residence time in the adsorbent bed layer is less than or equal to 20 seconds, preferably less than or equal to 15 seconds. After the calcination process is completed, the adsorbent pellets are cooled to room temperature under vacuum conditions.

[0035] The adsorbent provided by the present invention is suitable for separating nitrogen and oxygen from air by pressure swing adsorption to produce high-concentration oxygen. The pressure swing adsorption process can be implemented using a dual-column or multi-column system, or with the aid of a rotary valve or solenoid valve assembly. The operating pressure is 0.2-0.5 MPa, and the operating temperature is 5-50°C.

[0036] A double-column pressure swing adsorption device is used to evaluate the adsorbent performance. The schematic diagram of the pressure swing adsorption device is shown in the figure. Figure 1 As shown in Figure 1, the device consists of a pressure gauge, adsorption columns, and solenoid valves. Opening and closing solenoid valves V1, V2, V3, V5, V6, V7, and V8 enable continuous generation of oxygen-enriched gas through four steps: pressure increase, adsorption, pressure reduction, and purging. Approximately 370 mL of adsorbent were loaded into each of columns A and B. The adsorption cycle was set to last for 3 seconds, followed by a pressure reduction, purging, and pressure increase for a total of 3 seconds. The maximum pressure in the columns was 0.25 MPa, the operating temperature was 35°C, and the oxygen-enriched gas generation rate was 4.5 L / h. After 50 cycles of continuous operation, the oxygen volume concentration in the product was analyzed using an oxygen concentration meter.

[0037] Method for determining the moisture content of the adsorbent: place an adsorbent with a mass of m1 in a crucible and calcine it at 600°C for 2 hours. After calcination, quickly take out the crucible and place it in a desiccator to cool to room temperature. Weigh the mass of the adsorbent after calcination as m2, and the moisture content of the adsorbent C = (m1-m2) / m1.

[0038] The present invention is further described below by way of examples, but the present invention is not limited thereto.

[0039] The following examples are used to prepare the adsorbents described in the present invention.

[0040] The preparation methods of low-silicon X molecular sieve, high-silicon MFI molecular sieve and full-silicon MFI molecular sieve in the examples of the present invention are as follows:

[0041] Low-silicon 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 (11.0% Al2O3 by mass, 15.1% Na2O by mass), and 36.72 kg of water glass were added to a reactor and stirred to form a molecular sieve synthesis system. The total molar ratio of the materials in the molecular sieve synthesis system was: SiO2 / Al2O3 = 2.40, M2O / SiO2 = 2.25, and H2O / SiO2 = 45, where M represents K and Na, and K / (K+Na) = 0.23. The molecular sieve synthesis system was transferred to a reactor, aged at 70°C for 6 hours, hydrothermally crystallized at 95°C for 12 hours, and filtered. The resulting solid was washed with deionized water until the filtrate pH reached 8-9 and dried at 80°C for 12 hours to obtain a low-silicon 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 and the low silicon X molecular sieve were mixed at a liquid-to-solid ratio of 5 L / kg. The mixture was exchanged at 80°C for 1 hour, and the exchange was repeated 7 times. The exchanged low silicon X molecular sieve was dried at 40°C for 10 hours to obtain a low silicon X molecular sieve with lithium cation.

[0043] The molar ratio and Li2O content of the low silicon X molecular sieve can be adjusted by adjusting the molar ratio of SiO2 / Al2O3 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 silicon X molecular sieve.

[0044] High silicon MFI molecular sieve: 70.77kg tetrapropylammonium hydroxide solution, 6.09kg sodium hydroxide, 130.32kg deionized water, 6.39kg aluminum sulfate solution, 290.41kg silica sol and 4.36kg all-silicon MFI molecular sieve were added into the reactor and stirred to form a molecular sieve synthesis system. The total molar ratio of each material in the molecular sieve synthesis system is: SiO2 / Al2O3=0.0025, OH - / SiO2=0.15, H2O / SiO2=15, R / SiO2=0.06, S / SiO2=0.05, where R is tetrapropylammonium hydroxide and S is all-silicon MFI molecular sieve. The above molecular sieve synthesis system was transferred to a reactor and hydrothermally crystallized at 150°C for 48 hours. The resulting solid was washed with deionized water until the filtrate pH was 8-9 and dried at 80°C for 12 hours to obtain a high-silicon MFI molecular sieve.

[0045] All-silicon MFI molecular sieve: Add 37.91kg of tetrapropylammonium hydroxide solution and 26.67kg of silica sol into the reactor and stir and mix them evenly to form a molecular sieve synthesis system. The total molar ratio of each material in the molecular sieve synthesis system is: OH - / SiO2=0.35, H2O / SiO2=19.6, R / SiO2=0.35, where R is tetrapropylammonium hydroxide. The molecular sieve synthesis system was transferred to a reactor, aged at 100°C for 12 hours, hydrothermally crystallized at 150°C for 48 hours, filtered, and the resulting solid was washed with deionized water until the filtrate pH was 8-9, and dried at 80°C for 12 hours to obtain an all-silica MFI molecular sieve.

[0046] Example 1

[0047] (1) Molding: 75 kg of low silicon X molecular sieve with a particle size of about 0.5 μm (SEM photo see Figure 2 , the silica / alumina molar ratio is 2.03, the Li2O content is 11.9% by mass) and 25kg of kaolin are mixed evenly, put into a turntable and rolled while spraying water to make the solid aggregate into small balls as the core, and then 0.53kg of all-silicon MFI molecular sieve with a particle size of about 0.4μm is added (SEM photos see Figure 3 ) and 4.74 kg of attapulgite powder, continue to spray water and roll to form the outer layer of balls, and after sieving, obtain balls with a particle size of 300 to 850 microns.

[0048] (2) Drying: The pellets prepared in step (1) were evenly spread to a bed thickness of 10 mm and dried at 100°C in a flowing air atmosphere with the air staying in the adsorbent bed for 15 seconds for 10 hours.

[0049] (3) Calcination: The pellets dried in step (2) were evenly spread out to a bed thickness of 8 mm and calcined in a flowing air atmosphere. The air stayed in the adsorbent bed for 8 seconds. The pellets were treated at 200°C for 3 hours, 300°C for 3 hours, 400°C for 3 hours, and 500°C for 6 hours, with a heating rate of 2°C / min. After calcination, the pellets were cooled to room temperature under vacuum to obtain adsorbent A.

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

[0051] Example 2

[0052] Adsorbent B was prepared according to the method of Example 1, except that in step (1), 2.63 kg of a mixed powder of all-silicon MFI molecular sieve with a particle size of about 0.4 μm and 2.63 kg of attapulgite were added, and water spraying and rolling were continued to form the outer layer of the spheres.

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

[0054] Example 3

[0055] Adsorbent C was prepared according to the method of Example 1, except that in step (1), 0.95 kg of a mixed powder of approximately 0.4 μm all-silica MFI molecular sieve and 6.78 kg of attapulgite was added, and water spraying and rolling were continued to form the outer layer of the spheres. The water content and separation performance of Adsorbent C are shown in Table 1.

[0056] Example 4

[0057] Adsorbent D was prepared according to the method of Example 1, except that a high-silicon MFI molecular sieve with a particle size of about 0.5 μm and a silicon oxide / aluminum oxide molar ratio of 282 was used in step (1).

[0058] The water content and separation performance of adsorbent D are shown in Table 1.

[0059] Example 5

[0060] Adsorbent E was prepared according to the method of Example 4, except that a low-silicon X molecular sieve with a particle size of about 4 μm (silicon oxide / aluminum oxide molar ratio of 1.93, Li2O content of 10.7 mass %) was used in step (1).

[0061] The water content and separation performance of adsorbent E are shown in Table 1.

[0062] Example 6

[0063] Adsorbent F was prepared according to the method of Example 1, except that the bed thickness in step (2) was 18 mm and the drying temperature was 100°C. The bed thickness in step (3) was 15 mm and the heating rate was 3°C / min.

[0064] The water content and separation performance of adsorbent F are shown in Table 1.

[0065] Example 7

[0066] Adsorbent G was prepared according to the method of Example 1, except that in step (2), it was dried at 100°C for 8 hours. In step (3), it was treated at 180°C for 2 hours, 280°C for 2 hours, 380°C for 2 hours, and 470°C for 5 hours.

[0067] The water content and separation performance of adsorbent G are shown in Table 1.

[0068] Comparative Example 1

[0069] Adsorbent H was prepared according to the procedure of Example 1 except that (1) the molding was performed by mixing 75 kg of low-silica X molecular sieves (silica / alumina molar ratio of 2.03, Li20 content of 11.9 mass%) having a particle size of about 0.5 μm and 25 kg of kaolin, and the solid was gathered into pellets by tumbling in a rotating pan while spraying water, and the pellets having a particle size of 300-850 μm were obtained by sieving.

[0070] The water content and separation performance of adsorbent H are shown in Table 1.

[0071] Comparative Example 2

[0072] Adsorbent I was prepared according to the procedure of Example 1 except that the bed thickness in the step (2) was 35 mm and the residence time of air in the adsorbent bed was 25 seconds.

[0073] The water content and separation performance of adsorbent I are shown in Table 1.

[0074] Comparative Example 3

[0075] Adsorbent J was prepared according to the procedure of Example 1 except that the bed thickness in the step (3) was 35 mm and the residence time of air in the adsorbent bed was 25 seconds.

[0076] The water content and separation performance of adsorbent J are shown in Table 1.

[0077] Comparative Example 4

[0078] Adsorbent K was prepared according to the procedure of Example 1 except that the temperature increase rate in the step (3) was 10°C / min.

[0079] The water content and separation performance of adsorbent K are shown in Table 1.

[0080] Comparative Example 5

[0081] Adsorbent L was prepared according to the procedure of Example 1 except that the step (3) was performed without the staged calcination, and the temperature was directly increased to 500°C and the calcination was performed for 6 hours.

[0082] The water content and separation performance of adsorbent L are shown in Table 1.

[0083] Comparative Example 6

[0084] Adsorbent M was prepared according to the procedure of Example 1 except that the step (3) was performed by sequentially treating at 200°C for 1 hour, at 300°C for 1 hour, and at 400°C for 1 hour.

[0085] The water content and separation performance of adsorbent M are shown in Table 1.

[0086] Table 1

[0087] Instance number Adsorbent No. Water content, mass% Oxygen volume concentration, % 1 A 0.29 95.2 2 B 0.30 95.0 3 C 0.29 94.3 4 D 0.30 94.8 5 E 0.32 94.5 6 F 0.25 94.0 7 G 0.53 95.0 Comparative Example 1 H 0.33 83.6 Comparative Example 2 I 0.25 76.1 Comparative Example 3 J 0.13 39.6 Comparative Example 4 K 0.23 72.8 Comparative Example 5 L 0.20 63.5 Comparative Example 6 M 3.45 85.2

[0088] As shown in Table 1, the oxygen volume concentration obtained by separating air using the adsorbents described in Comparative Examples 1-6 is lower than that obtained by using the adsorbents described in Examples 1-7.

[0089] The adsorbent described in Comparative Example 1 does not contain an outer adsorbent layer, and the carbon dioxide and water vapor in air are adsorbed by the low-silicon X molecular sieve, resulting in a decrease in the nitrogen-oxygen separation performance of the adsorbent.

[0090] In the preparation of the adsorbent I described in Comparative Example 2, the bed thickness is thick in step (2), and the air stays in the adsorbent bed for a long time, resulting in a long contact time between water vapor and the adsorbent during the drying process, which destroys the structure of the molecular sieve and decreases the separation performance of the adsorbent. In addition, the water absorption capacity of the adsorbent decreases due to the destruction of the molecular sieve structure, and thus the water content of the adsorbent is low.

[0091] In the preparation of the adsorbent J described in Comparative Example 3, the bed thickness is thick in step (3), and the air stays in the adsorbent bed for a long time, resulting in a long contact time between water vapor and the adsorbent during the calcination process, which destroys the structure of the molecular sieve and decreases the separation performance and water content of the adsorbent.

[0092] In the preparation of the adsorbent K described in Comparative Example 4, the temperature rising rate is too fast in step (3), which destroys the structure of the molecular sieve and decreases the separation performance and water content of the adsorbent.

[0093] In the preparation of the adsorbent L described in Comparative Example 5, step (3) does not use staged calcination, which results in a too fast temperature rising rate, destroys the structure of the molecular sieve, and decreases the separation performance and water content of the adsorbent.

[0094] In the preparation of the adsorbent M described in Comparative Example 6, the calcination time is too short, and the maximum temperature is too low, which results in a high water content and a decrease in the separation performance of the adsorbent.

Claims

1. A nitrogen and oxygen separation air separation adsorbent, characterized in that: The invention comprises an inner adsorbent layer and an outer adsorbent layer, wherein the inner adsorbent layer comprises a low-silicon X molecular sieve and a binder, and the outer adsorbent layer comprises an MFI molecular sieve and a binder. The cation position of the low-silicon X molecular sieve is occupied by Li, the MFI molecular sieve is a high-silicon MFI molecular sieve or an all-silicon MFI molecular sieve, the silicon oxide / aluminum oxide molar ratio of the low-silicon X molecular sieve is 1.90-2.05, and the inner adsorbent layer accounts for 90-96% by mass of the adsorbent.

2. The adsorbent according to claim 1, characterized in that The inner adsorbent layer comprises 50-79 mass % of low-silicon X molecular sieve and 21-50 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 includes 10 to 60 mass % of the MFI molecular sieve and 40 to 90 mass % of the binder, based on the total amount of the outer adsorbent layer.

4. The adsorbent according to claim 1, characterized in that The silicon oxide / aluminum oxide molar ratio of the high-silicon MFI molecular sieve is greater than 200.

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

6. The adsorbent according to claim 1, characterized in that The Li2O content in the low-silicon X molecular sieve is greater than or equal to 10% by mass.

7. The adsorbent according to claim 1, characterized in that The silicon oxide / aluminum oxide molar ratio of the high-silicon MFI molecular sieve is greater than 500.

8. The adsorbent according to claim 1, characterized in that The particle size of the MFI molecular sieve is 0.1 to 0.8 microns.

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

10. 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.

11. A method for preparing the nitrogen and oxygen separation air separation adsorbent according to claim 1, characterized in that: The following steps are involved: (1) Mix low-silicon X molecular sieve and binder in a mass ratio of 50-79:21-50, place in a turntable and roll while spraying water to aggregate the solid into small balls, which serve as the inner adsorbent layer. Then add powder of MFI molecular sieve and binder in a mass ratio of 10-60:40-90, continue spraying water and rolling to form an outer adsorbent layer, and obtain small balls with a particle size of 300-850 μm after screening; (2) Spreading the pellets obtained in step (1) to a bed thickness of less than or equal to 30 mm, and drying them in a flowing air atmosphere at a temperature of 60 to 120° C. for 6 to 12 hours; (3) The dried pellets obtained in step (2) are spread out in a bed with a thickness of less than or equal to 20 mm, and are calcined in a flowing air atmosphere in stages, in the order of 150-220°C for 1-3 hours, 250-320°C for 1-3 hours, 350-420°C for 1-3 hours, and 450-540°C for 4-8 hours.

12. The method according to claim 11, characterized in that In step (2), the drying temperature is 80~100℃.

13. The method according to claim 11, characterized in that In step (1), the total amount of water added for rolling into balls is 5-16% by mass of the total amount of solid powder.

14. The method according to claim 11, characterized in that The residence time of air in the adsorbent bed in step (2) or (3) is less than or equal to 20 seconds.

15. The method according to claim 11, characterized in that The staged calcination described in step (3) has a heating rate of 0.5~5℃ / min.

16. The method according to claim 11, characterized in that The staged calcination described in step (3) has a heating rate of 1~3℃ / min.

17. A method for producing oxygen from air using the nitrogen-oxygen separation air separation adsorbent according to any one of claims 1 to 10 or the nitrogen-oxygen separation air separation adsorbent prepared by the method according to any one of claims 11 to 16.

Images