A method of reducing loss of adsorption capacity of a LiX molecular sieve adsorbent

Abstract

The present application relates to the field of molecular sieve adsorbent, and discloses a method for reducing the adsorption capacity loss of LiX molecular sieve adsorbent.The method for reducing the adsorption capacity loss of LiX molecular sieve adsorbent comprises the following steps: (1) performing one-step pre-drying on a LiX molecular sieve matrix to obtain a pre-dried product, wherein the water content of the pre-dried product is 13-28 mass%; (2) performing activation treatment on the pre-dried product of step (1) by using continuous vacuum calcination to obtain a LiX molecular sieve, wherein the activation treatment is performed under the following conditions: vacuum degree is (-0.05)-(-0.1) MPa, temperature is 400-630 DEG C, and time is 2-8 h.The method uses one-step pre-drying and continuous vacuum calcination in combination to perform calcination and activation on the LiX molecular sieve matrix, and the prepared LiX molecular sieve adsorbent has an adsorption capacity loss of less than 5%, and has good adsorption performance.

Description

Technical Field

[0001] This invention relates to the technical field of molecular sieve adsorbents, and specifically to a method for reducing the adsorption loss of LiX molecular sieve adsorbents. Background Technology

[0002] Zeolite molecular sieves are excellent adsorbents with strong adsorption capacity for polar small molecules, exhibiting selective adsorption for molecules with different critical diameters, polarities, shapes, and degrees of unsaturation. Therefore, zeolite molecular sieves are widely used in many fields, especially in gas separation. LiX zeolite molecular sieves are a representative example, possessing good nitrogen and oxygen adsorption and separation performance. Calcination is a crucial step in molecular sieve production, aiming to remove adsorbed moisture from the pores of the molecular sieve, thereby activating or modifying it. Currently, LiX molecular sieves are mainly calcined under normal pressure. The high-temperature water vapor generated during calcination can damage the structure of the molecular sieve, resulting in a certain degree of impairment in its adsorption performance.

[0003] Patent application No. 201110303560.0 discloses a LiX molecular sieve adsorbent and its preparation method. The adsorbent matrix is ​​prepared by combining X molecular sieve powder, binder and additives. After calcination, alkali boiling and ammonium exchange, lithium salt solution is impregnated onto the molecular sieve adsorbent by impregnation. Then, it is dried at a temperature not exceeding 300°C for 10 minutes to 10 hours, and then calcined and activated at a temperature of 400-750°C for 1-16 hours to obtain the LiX molecular sieve adsorbent.

[0004] Patent application number 202010014725.1 discloses a continuous vacuum drying and calcination method for small-grain 5A molecular sieves. The method uses a vacuum forced suction to remove the high-temperature water vapor generated during the calcination process. The method is applied to the calcination and activation of 5A molecular sieves, and mainly describes the structure of the continuous vacuum calcination furnace. It does not mention the use of vacuum continuous drying and calcination to treat LiX molecular sieves. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems existing in the prior art and provide a method for reducing the adsorption loss of LiX molecular sieve adsorbents. This method uses a combination of one-step pre-drying and continuous vacuum calcination to calcinate and activate the LiX molecular sieve matrix. The resulting LiX molecular sieve adsorbent has an adsorption loss of less than 5% and exhibits good adsorption performance.

[0006] To achieve the above objectives, the present invention provides a method for reducing the adsorption loss of LiX molecular sieve adsorbents, wherein the method includes the following steps:

[0007] (1) The LiX molecular sieve matrix is ​​pre-dried in one step to obtain a pre-dried product, wherein the water content of the pre-dried product is 13-28% by mass.

[0008] (2) The pre-dried product in step (1) is activated by continuous vacuum calcination to obtain LiX molecular sieve. The activation conditions include: vacuum degree of (-0.05)-(-0.1) MPa, temperature of 400-630℃, and time of 2-8h.

[0009] The method provided by this invention combines pre-drying and continuous vacuum calcination. Compared with the existing technology of atmospheric pressure calcination for LiX molecular sieves, this invention can control the moisture content of LiX molecular sieves within the range described in this invention through a one-step pre-drying process, effectively removing moisture from the pores of LiX molecular sieves. At the same time, it can also reduce the impact of moisture on subsequent continuous vacuum calcination and avoid damage to the LiX molecular sieve structure by high-temperature water vapor. The nitrogen adsorption loss of the LiX molecular sieve adsorbent prepared by the method provided by this invention is less than 5%, which is far lower than the 7% loss in the prior art, effectively reducing the loss of nitrogen adsorption capacity of LiX molecular sieve adsorbents. The LiX molecular sieve adsorbent has good adsorption performance.

[0010] The method provided by this invention can control the moisture content within the range of this invention with only one pre-drying step, providing a good foundation for subsequent continuous vacuum calcination. It can effectively reduce the loss of nitrogen adsorption by LiX molecular sieve adsorbent and save energy, thus having good process value. Detailed Implementation

[0011] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0012] This invention provides a method for reducing the adsorption loss of LiX molecular sieves, wherein the method includes the following steps:

[0013] (1) The LiX molecular sieve matrix is ​​pre-dried in one step to obtain a pre-dried product, wherein the water content of the pre-dried product is 13-28% by mass.

[0014] (2) The pre-dried product in step (1) is activated by continuous vacuum calcination to obtain LiX molecular sieve. The activation conditions include: vacuum degree of (-0.05)-(-0.1) MPa, temperature of 400-630℃, and time of 2-8h.

[0015] The method provided by this invention combines pre-drying and continuous vacuum calcination. Compared with the existing technology of atmospheric pressure calcination for LiX molecular sieves, this invention can control the moisture content of LiX molecular sieves within the range described in this invention through a one-step pre-drying process, effectively removing moisture from the pores of LiX molecular sieves. At the same time, it can also reduce the impact of moisture on subsequent continuous vacuum calcination and avoid damage to the LiX molecular sieve structure by high-temperature water vapor. The nitrogen adsorption loss of the LiX molecular sieve adsorbent prepared by the method provided by this invention is less than 5%, which is far lower than the 7% loss in the prior art, effectively reducing the loss of nitrogen adsorption capacity of LiX molecular sieve adsorbents. The LiX molecular sieve adsorbent has good adsorption performance.

[0016] The method provided by this invention can control the moisture content within the range of this invention with only one drying step, providing a good foundation for subsequent continuous vacuum calcination. It can effectively reduce the loss of nitrogen adsorption by LiX molecular sieve adsorbent and save energy, thus having good process value.

[0017] Vacuum calcination involves timely extraction of water vapor generated during the high-temperature calcination and activation of molecular sieves via vacuum suction, preventing damage to the pore structure of the molecular sieves from the high-temperature water vapor. In this invention, a one-step pre-drying process controls the water content in the LiX molecular sieve matrix within the range described herein, effectively preventing damage to the LiX molecular sieve adsorbent structure from moisture during subsequent continuous vacuum calcination, reducing the loss of adsorption capacity, and improving the adsorption performance of the LiX molecular sieve adsorbent. When the water content in the feed is too high, the instantaneous water vapor generation in the vacuum furnace remains high and cannot be extracted in time, even with guaranteed throughput, resulting in insufficient vacuum and damage to the pore structure of the molecular sieve. When the water content in the feed is too low, it indicates that the moisture inside the molecular sieve pores evaporates under normal pressure, leading to a decrease in the adsorption capacity of the molecular sieve. In this invention, a one-step pre-drying process controls the water content in the LiX molecular sieve matrix within the range described herein, effectively preventing damage to the LiX molecular sieve structure from moisture during subsequent continuous vacuum calcination, reducing the loss of adsorption capacity, and improving the adsorption performance of LiX. Preferably, in step (1), the moisture content of the dried product is 17-22% by mass.

[0018] In this invention, the moisture content refers to the weight lost by the sample after calcining at 550°C for 1 hour, also known as the loss on ignition at 550°C.

[0019] In this invention, the pre-drying conditions are not particularly limited, as long as they meet the moisture content requirements of the pre-dried product. Preferably, in step (1), the pre-drying conditions include: a temperature of 120-250℃ and a time of 0.5-6h; more preferably, in step (1), the pre-drying conditions include: a temperature of 180-200℃ and a time of 2-3h. This invention, by using only one pre-drying step and controlling the pre-drying conditions, has the advantage of ensuring the throughput while reducing the loss of adsorption performance of the molecular sieve adsorbent.

[0020] In this invention, the source of the LiX molecular sieve matrix is ​​not particularly limited; for example, it can be prepared by methods conventionally defined in the art. In this invention, the preparation method of the LiX molecular sieve matrix is ​​not particularly limited. Preferably, the preparation method of the LiX molecular sieve matrix includes the following steps:

[0021] S1. Mix NaX molecular sieve raw powder, binder and additives to form a mold, and then calcine, treat with alkali and exchange with ammonium;

[0022] S2. Impregnate the product obtained in step S1 with the lithium precursor using an impregnation method to obtain the LiX molecular sieve matrix.

[0023] In this invention, the properties of the NaX molecular sieve are not particularly limited, and it can be any X-type molecular sieve conventionally defined in the art. Preferably, in step S1, the silicon-to-aluminum atomic ratio of the NaX molecular sieve is 1.1-1.4.

[0024] In this invention, there is no particular limitation on the type of binder; binders conventionally defined in the art are all applicable to this invention. Preferably, in step S1, the binder is selected from at least one of attapulgite, halloysite, kaolin, retardonite, and bentonite.

[0025] In this invention, there is no particular limitation on the type of adjuvant; any adjuvant conventionally defined in the art can be applied to this invention. Preferably, in step S1, the adjuvant is selected from at least one of guar gum powder, cellulose, and starch.

[0026] In this invention, preferably, in step S1, the mass ratio of the NaX molecular sieve raw powder, the binder on a dry basis, and the additives on a dry basis is 1:0.01-0.2:0.01-0.1.

[0027] In this invention, there are no particular limitations on the molding method in step S1, and molding methods conventionally defined in the art are applicable to this invention.

[0028] In this invention, the selection range for the roasting conditions in step S1 is relatively wide. Preferably, the roasting conditions in step S1 include: a temperature of 400-600℃ and a time of 2-8 hours.

[0029] In this invention, preferably, the alkali treatment is carried out in the presence of an alkaline compound.

[0030] In this invention, there is no particular limitation on the type of alkaline compound; any alkaline compound conventionally defined in the art is applicable to this invention. Preferably, in step S1, the alkaline compound is sodium hydroxide and / or potassium hydroxide.

[0031] In this invention, preferably, in step S1, the alkaline compound is provided by a solution containing the alkaline compound, and preferably the concentration of the solution containing the alkaline compound is 0.1-2 mol / L.

[0032] In this invention, there is no particular limitation on the amount of the solution containing the alkaline compound. Preferably, in step S1, the amount of the solution containing the alkaline compound is 0.5-5 L compared to 1 kg of molecular sieve powder.

[0033] In this invention, the selection range of alkali treatment conditions is relatively wide. Preferably, in step S1, the alkali treatment conditions include: a temperature of 85-100℃ and a time of 1-8 hours.

[0034] In this invention, preferably, the method for preparing the LiX molecular sieve matrix further includes washing the product after alkali treatment. The type of detergent used for alkali treatment washing is not particularly limited in this invention; for example, water can be used. Similarly, the number of washing cycles is not particularly limited in this invention; those skilled in the art can adjust it according to actual needs. Preferably, the number of washing cycles is such that the pH is ≤10.

[0035] In this invention, preferably, in step S1, the ammonium exchange is carried out in the presence of an ammonium salt.

[0036] In this invention, there is no particular limitation on the specific type of ammonium salt, and any ammonium salt conventionally defined in the art can be applied to this invention. Preferably, in step S1, the ammonium salt is selected from at least one of ammonium acetate, ammonium sulfate, ammonium bisulfate, ammonium nitrate, ammonium chloride, and ammonium carbonate.

[0037] In this invention, preferably, in step S1, the ammonium salt is provided by an aqueous solution of ammonium salt, and preferably the concentration of the aqueous solution of ammonium salt is 0.1-2 mol / L.

[0038] In this invention, the selection range for ammonium exchange conditions is relatively wide. Preferably, the ammonium exchange conditions include: a temperature of 85-100℃ and a liquid-to-solid volume ratio of 1-6:1.

[0039] In this invention, the number of ammonium exchange cycles is not particularly limited, and those skilled in the art can select the appropriate number based on actual needs. Preferably, the number of ammonium exchange cycles results in the sodium oxide content in the ammonium exchange product being less than 0.1% by mass.

[0040] In this invention, preferably, the method for preparing the LiX molecular sieve matrix further includes washing the product after ammonium exchange. This invention does not particularly limit the type of detergent used in the ammonium exchange process; for example, water can be used. This invention also does not particularly limit the number of washes; those skilled in the art can adjust them according to actual needs.

[0041] In this invention, preferably, the method for preparing the LiX molecular sieve matrix further includes solid-liquid separation and drying of the product after ammonium exchange washing. This invention does not particularly limit the specific operation methods for solid-liquid separation and drying; those skilled in the art can adjust them according to actual needs.

[0042] In this invention, there is no particular limitation on the specific type of lithium precursor, as long as lithium can be provided. Preferably, in step S2, the lithium precursor is a lithium-containing compound, preferably selected from at least one of lithium nitrate, lithium chloride, lithium carbonate, and lithium hydroxide.

[0043] In this invention, there is no particular limitation on the specific method of impregnation in step S2. For example, it can be supersaturated impregnation or equal volume impregnation. Impregnation methods conventionally defined in the art can be applied to this invention, and those skilled in the art can make adjustments according to actual needs.

[0044] In this invention, the range of conditions for impregnation is relatively wide. Preferably, the impregnation conditions include: a temperature of 80-95°C and a time of 0.5-2 hours.

[0045] In this invention, there are no particular limitations on the equipment used for impregnation. Those skilled in the art can choose according to actual needs. For example, a rotary evaporator can be used for rotary saturation impregnation.

[0046] In this invention, there is no particular limitation on the amount of lithium precursor used. Preferably, in step S2, the mass ratio of the NaX molecular sieve powder to the lithium precursor (calculated as elemental lithium) is 1:0.01-0.05.

[0047] In this invention, there is no particular limitation on the feeding rate of the pre-dried product, and those skilled in the art can make a reasonable selection according to different application scenarios. Preferably, in step (2), based on a mass of 1 kg of LiX molecular sieve matrix, the feeding rate of the pre-dried product is 0.2-0.8 L / min. In this invention, controlling the feeding rate of the pre-dried product has the advantage of maximizing output while ensuring timely extraction of water vapor from the furnace.

[0048] In this invention, by controlling the conditions of continuous vacuum calcination in step (2) in coordination with the pre-drying treatment in step (1), the damage of moisture to the LiX molecular sieve structure can be reduced, ensuring that the adsorption loss of the LiX molecular sieve during the calcination activation process is minimized, thereby improving the adsorption performance of the LiX molecular sieve. Preferably, in step (2), the activation treatment conditions include: a vacuum degree of (-0.06)-(-0.09) MPa, a temperature of 450-600℃, and a time of 2-5 h.

[0049] In this invention, preferably, the pre-drying in step (1) and the continuous vacuum calcination in step (2) are carried out in different heating devices. In this invention, there is no particular limitation on the heating device used for the pre-drying in step (1), and those skilled in the art can choose according to actual needs; for example, it can be an oven. Similarly, there is no particular limitation on the heating device used for the continuous vacuum calcination in step (2), and those skilled in the art can choose according to actual needs; for example, it can be an electric calcination furnace. In this invention, the advantage of carrying out the pre-drying in step (1) and the continuous vacuum calcination in step (2) in different heating devices is that it increases the throughput while reducing the adsorption loss during the molecular sieve calcination activation process. The high throughput and high moisture content of the feed prevent the high-temperature water vapor in the furnace from being extracted in time, thus damaging the molecular sieve pore structure.

[0050] The method provided by this invention combines pre-drying and continuous vacuum calcination. Compared with the existing technology of atmospheric pressure calcination for LiX molecular sieves, this invention controls the moisture content of the LiX molecular sieve within the range described in this invention through pre-drying, effectively removing moisture from the pores of the LiX molecular sieve. At the same time, it can also reduce the impact of moisture on subsequent continuous vacuum calcination and avoid damage to the LiX molecular sieve structure by high-temperature water vapor. The LiX molecular sieve obtained by the method provided by this invention has an adsorption capacity loss of less than 5%, which is far lower than the 8% loss in the prior art, effectively reducing the loss of adsorption capacity of LiX molecular sieves. The LiX molecular sieve has good adsorption performance.

[0051] The present invention will be described in detail below through embodiments. Unless otherwise specified, all raw materials used in the following embodiments are commercially available products.

[0052] Adsorption loss refers to the decrease in adsorption capacity of the molecular sieve adsorbent before and after calcination and activation. The calculation formula is: a = (nitrogen adsorption capacity of the molecular sieve after calcination and activation m1 - nitrogen adsorption capacity of the molecular sieve before pre-drying m2) / nitrogen adsorption capacity of the molecular sieve before pre-drying m2 * 100%. Molecular sieve nitrogen adsorption capacity refers to the mass of nitrogen adsorbed per unit mass of molecular sieve. The determination method is as follows: the sample is first degassed under vacuum at 350℃ for 2 hours, then cooled under vacuum. After cooling, the sample is subjected to high-purity nitrogen as the adsorbate at 25℃ and standard atmospheric pressure, and the amount of nitrogen adsorbed is measured.

[0053] The water content of LiX molecular sieve adsorbent refers to the weight loss of the sample after calcining at 550℃ for 1 hour, also known as the 550℃ ignition loss.

[0054] Preparation Example

[0055] 1 kg of molecular sieve raw powder (silicon-to-aluminum atomic ratio of 1.25) was mixed with kaolin and guar gum powder at a dry basis mass ratio of 1:0.06:0.02. The mixture was then rolled into small balls of about 1 mm. The balls were dried at 120℃ for 2 h and calcined at 550℃ for 2 h to obtain NaX matrix small balls. The NaX matrix small balls were then placed in 5 L of 1 mol / L sodium hydroxide solution at 94℃ for 3 h. After repeated washing with water until the pH ≤ 10, the alkali-treated matrix small balls were subjected to ammonium exchange in 5 L of 1 mol / L ammonium acetate solution at 90℃ for 3 h. The mixture was then washed with water. This process was repeated multiple times until the sodium oxide content in the molecular sieve was less than 0.1% by mass. The ammonium-type molecular sieve was dried at 300℃ for 3 hours. The ammonium-exchanged matrix microspheres were then saturated with 1.9 L of 2.5 mol / L lithium chloride solution in a rotary evaporator at 90℃ for 1 hour to obtain the LiX molecular sieve matrix.

[0056] Example 1

[0057] (1) 1 kg of LiX molecular sieve matrix from the preparation example was selected, pre-dried, and the moisture content of the pre-dried product was controlled to be 20% by mass. The pre-drying conditions were: temperature 180℃ and time 3h. Then, continuous vacuum calcination was carried out. The feed rate of the pre-dried product was 0.4 L / min, the vacuum degree was -0.06 MPa, and the calcination temperature was 600℃. After calcination for 2h, LiX molecular sieve adsorbent was obtained.

[0058] Example 2

[0059] (1) 1 kg of LiX molecular sieve matrix from the preparation example was selected, pre-dried, and the moisture content of the pre-dried product was controlled to be 20% by mass. The pre-drying conditions were: temperature 180℃ and time 3h. Then, continuous vacuum calcination was carried out. During the calcination process, the feed rate of the pre-dried product was 0.3 L / min, the vacuum degree was -0.085 MPa, and the calcination temperature was 450℃. After calcination for 2h, LiX molecular sieve adsorbent was obtained.

[0060] Example 3

[0061] The method is the same as in Example 2, except that the moisture content of the pre-dried product is controlled at 18% by mass, and the pre-drying conditions are: temperature of 200°C, time of 3 hours, vacuum degree of -0.09 MPa, and all other conditions are the same.

[0062] Example 4

[0063] The method of Example 2 is the same, except that the moisture content of the pre-dried product is controlled at 13%, and the pre-drying conditions are: temperature of 250°C, time of 3 hours, vacuum degree of -0.095 MPa, and other conditions are the same.

[0064] Example 5

[0065] The method of Example 3 is the same, except that the feed rate is controlled at 0.4 L / min and the vacuum degree is -0.092 MPa, while all other conditions are the same.

[0066] Comparative Example 1

[0067] The method of Example 2 is followed, except that the moisture content of the pre-dried product is controlled at 30% by mass. The pre-drying conditions are: temperature of 180°C and time of 1 hour, with all other conditions being the same.

[0068] Comparative Example 2

[0069] The method is the same as in Example 2, except that the temperature during the vacuum calcination process is controlled at 650°C, while all other conditions are the same.

[0070] Comparative Example 3

[0071] The method of Example 2 was followed, except that the LiX molecular sieve matrix was calcined under normal pressure, while all other conditions were the same.

[0072] Comparative Example 4

[0073] The method is the same as in Example 2, except that the feed rate is controlled at 0.8 L / min and the vacuum degree is -0.03 MPa, while all other conditions are the same.

[0074] Table 1

[0075] Adsorption loss (%) Water content (mass%) of LiX molecular sieve adsorbent Example 1 4.2 1 Example 2 1 3.5 Example 3 3.4 2.6 Example 4 4.9 0.8 Example 5 3.2 3.7 Comparative Example 1 7.6 6.9 Comparative Example 2 16.4 0.8 Comparative Example 3 19.3 4.6 Comparative Example 4 3.2 9.5

[0076] Note: LiX molecular sieve adsorbent with a water content of <5% by mass is considered qualified.

[0077] As can be seen from the examples and the results in Table 1, the LiX molecular sieve adsorbent prepared by the method of the present invention has the effects of low adsorption loss, qualified product moisture content, and large processing capacity.

[0078] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for reducing the adsorption capacity loss of LiX molecular sieve adsorbents, characterized in that, The method includes the following steps: (1) The LiX molecular sieve matrix is ​​pre-dried in one step to obtain a pre-dried product, wherein the water content of the pre-dried product is 17-22% by mass. (2) The pre-dried product in step (1) is activated by continuous vacuum calcination to obtain LiX molecular sieve adsorbent. In step (2), the activation conditions include: vacuum degree of (-0.06)-(-0.09) MPa, temperature of 450-600℃, and time of 2-5h. In step (1), the pre-drying conditions include: a temperature of 180-200℃ and a time of 2-3h.

2. The method according to claim 1, wherein, The preparation method of LiX molecular sieve matrix includes the following steps: S1. Mix NaX molecular sieve raw powder, binder and additives to form a mold, and then calcine, treat with alkali and exchange with ammonium; S2. Impregnate the product obtained in step S1 with the lithium precursor using an impregnation method to obtain the LiX molecular sieve matrix.

3. The method according to claim 2, wherein, In step S1, the silicon-to-aluminum atomic ratio of the NaX molecular sieve is 1.1-1.

4.

4. The method according to claim 2 or 3, wherein, In step S1, the binder is selected from at least one of attapulgite, halloysite, kaolin, levitate, and bentonite.

5. The method according to claim 2 or 3, wherein, In step S1, the adjuvant is selected from at least one of guar gum powder, cellulose and starch.

6. The method according to claim 2 or 3, wherein, In step S1, the mass ratio of the NaX molecular sieve raw powder, the binder on a dry basis, and the additives on a dry basis is 1:0.01-0.2:0.01-0.

1.

7. The method according to claim 2 or 3, wherein, In step S1, the calcination conditions include: a temperature of 400-600℃ and a time of 2-8h.

8. The method according to claim 2 or 3, wherein, In step S1, the alkali treatment is carried out in the presence of an alkaline compound.

9. The method according to claim 8, wherein, In step S1, the alkaline compound is sodium hydroxide and / or potassium hydroxide.

10. The method according to claim 2 or 3, wherein, In step S1, the conditions for alkali treatment include: a temperature of 85-100℃ and a time of 1-8h.

11. The method according to claim 2 or 3, wherein, In step S1, the ammonium exchange is carried out in the presence of an ammonium salt.

12. The method according to claim 11, wherein, The ammonium salt is selected from at least one of ammonium acetate, ammonium sulfate, ammonium bisulfate, ammonium nitrate, ammonium chloride, and ammonium carbonate.

13. The method according to claim 2 or 3, wherein, In step S1, the conditions for ammonium exchange include: a temperature of 85-100℃ and a liquid-to-solid volume ratio of 1-6:

1.

14. The method according to claim 2 or 3, wherein, In step S2, the lithium precursor is a lithium-containing compound.

15. The method according to claim 14, wherein, In step S2, the lithium precursor is selected from at least one of lithium nitrate, lithium chloride, lithium carbonate, and lithium hydroxide.

16. The method according to claim 2 or 3, wherein, In step S2, the conditions for the impregnation method include: temperature 80-95℃ and time 0.5-2h.

17. The method according to claim 2 or 3, wherein, In step S2, the mass ratio of the NaX molecular sieve raw powder to the lithium precursor (calculated as lithium element) is 1:0.01-0.

05.

18. The method according to claim 1 or 2, wherein, In step (2), based on a mass of 1 kg of LiX molecular sieve matrix, the feed rate of the pre-dried product is 0.2-0.8 L / min.