Method for preparing CaLi-LSX molecular sieve

Abstract

The invention discloses a method for preparing a CaLi-LSX molecular sieve, which comprises the following steps: (1) carrying out calcium ion exchange on a calcium salt solution and a KNa-LSX molecular sieve, and then separating, washing and drying to obtain a Ca-LSX molecular sieve; (2) the lithium salt solution and the Ca-LSX molecular sieve are subjected to lithium ion exchange, solid-liquid separation is carried out, a solid phase and a liquid phase are obtained, the solid phase is the CaLi-LSX molecular sieve, and the liquid phase is a mixed solution of calcium salt and lithium salt; (3) carrying out calcium removal treatment on the liquid phase to obtain a recycled lithium salt solution; carrying out lithium ion exchange on the recycled lithium salt solution and the solid phase obtained in the previous step, and carrying out solid-liquid separation to obtain a solid phase and a liquid phase; and (4) repeating the step (3), and then washing and drying the solid phase obtained by separation to obtain the CaLi-LSX molecular sieve. According to the method, the lithium salt is recycled while the CaLi-LSX molecular sieve is prepared, so that the utilization rate of the lithium salt is increased, and the production cost is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical fields of molecular sieve preparation and lithium salt recovery and reuse, and specifically relates to a method for preparing CaLi-LSX molecular sieve and a method for simultaneously recovering and reusing lithium salts. Background Art

[0002] In recent years, with the rapid development of society, the demand for oxygen in industries such as industry, medical treatment, and military has been increasing year by year. At present, there are mainly two methods for obtaining high-purity oxygen: cryogenic distillation and pressure swing adsorption. The core technology of the pressure swing adsorption method lies in the preparation of LSX molecular sieve adsorbent. LSX is the abbreviation of low-silica X-type molecular sieve, and its silica-alumina ratio (SiO 2 / Al 2 O 3 ) is generally 2.0 - 2.1. Therefore, it has the most exchangeable cation sites and is often used for the separation of various gases after ion exchange modification.

[0003] Li-LSX molecular sieve is the most used adsorbent in the current pressure swing adsorption oxygen production industry, and has the advantages of large nitrogen adsorption capacity and high nitrogen-oxygen separation coefficient. However, only about 30% of the lithium in the molecular sieve has an adsorption and separation effect, and the utilization rate of lithium ions is low. The CaLi-LSX molecular sieve uses cheap Ca 2+ to replace Li + without adsorption active sites in Li-LSX, ensuring a high nitrogen-oxygen separation activity while reducing the lithium consumption. However, during the ion exchange process, the molecular sieve has a greater selectivity for Ca 2+ than for Li + , and conventional methods require multiple exchanges of calcium sieve with fresh lithium solution, resulting in a large waste of lithium salts.

[0004] CN101289196A proposes a multi-step continuous modification method of first exchanging K + , then exchanging NH 4 + , and finally exchanging Li + , which effectively improves the utilization rate of lithium salts, but it is only applicable to the preparation of lithium sieve and cannot be used to produce CaLi-LSX molecular sieve accordingly. CN103539150A proposes a method of first exchanging part of the Na + in Na-LSX molecular sieve with Li + , and then exchanging the remaining Na + with Ca 2+ to prepare CaLi-LSX molecular sieve, but this method cannot ensure that all Li + is in the adsorption active sites, resulting in a low nitrogen adsorption capacity. CN107486146A proposes first exchanging all the Na + in Na-LSX molecular sieve with Ca 2+, and then a small amount of lithium ions are used to exchange Ca 2+ , this method can effectively control costs, but due to the low degree of lithium ion exchange, the nitrogen-oxygen separation coefficient of the molecular sieve is not high. Therefore, there is an urgent need to develop a preparation method of CaLi-LSX molecular sieve that can simultaneously improve the degree of lithium ion exchange and the utilization rate of lithium salts. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem of low utilization rate of lithium salts in the preparation of CaLi-LSX molecular sieve existing in the prior art, and to provide a method for preparing CaLi-LSX molecular sieve. This method realizes the recycling and reuse of lithium salts while preparing CaLi-LSX molecular sieve, enables all lithium salts to be used for molecular sieve exchange, improves the utilization rate of lithium salts, greatly reduces the production cost, and has a simple process and is easy to operate.

[0006] To achieve the above purpose, the present invention provides a method for preparing CaLi-LSX molecular sieve, and the method includes the following steps:

[0007] (1) Carry out calcium ion exchange on a calcium salt solution and KNa-LSX molecular sieve, and then through separation, washing and drying, obtain Ca-LSX molecular sieve;

[0008] (2) Carry out lithium ion exchange on a lithium salt solution and Ca-LSX molecular sieve, and through solid-liquid separation, obtain a solid phase and a liquid phase. Among them, the solid phase is CaLi-LSX molecular sieve, and the liquid phase is a mixed solution of calcium salt and lithium salt;

[0009] (3) Carry out calcium removal treatment on the liquid phase to obtain a recycled lithium salt solution; carry out lithium ion exchange on the recycled lithium salt solution and the solid phase obtained in the previous step, and through solid-liquid separation, obtain a solid phase and a liquid phase;

[0010] (4) Repeat step (3), and then carry out post-treatment on the separated solid phase to obtain CaLi-LSX molecular sieve.

[0011] Through the above technical solution, the beneficial technical effects obtained by the present invention are as follows:

[0012] The method of the present invention realizes the recycling and reuse of lithium salts while preparing CaLi-LSX molecular sieve, enables all lithium salts to be used for molecular sieve exchange, greatly improves the utilization rate of lithium salts in the ion exchange process, reduces the production cost, and has a simple process and is easy to operate, and is suitable for large-scale application and promotion.

[0013] The present invention provides a method for recycling and reusing the exchanged lithium salt solution. Through calcium removal treatment, a recycled lithium salt solution is obtained, and this recycled lithium salt solution is continuously used to complete the next lithium exchange. By repeating this process several times, lossless utilization of the lithium solution is achieved. Moreover, the molecular sieve prepared by this method has a large adsorption capacity and a high nitrogen-oxygen separation coefficient, and CaLi-LSX molecular sieves with any desired degree of lithium exchange can be prepared as required. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The normal temperature N 2 isothermal adsorption curves of the CaLi-LSX molecular sieves prepared in the comparative example and Examples 1-3 of the present invention;

[0015] Figure 2 The normal temperature O 2 isothermal adsorption curves of the CaLi-LSX molecular sieves prepared in the comparative example and Examples 1-3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0017] The present invention provides a method for preparing CaLi-LSX molecular sieves, and the method comprises the following steps:

[0018] (1) Performing calcium ion exchange on a calcium salt solution and a KNa-LSX molecular sieve, and then through separation, washing and drying, a Ca-LSX molecular sieve is obtained;

[0019] (2) Performing lithium ion exchange on a lithium salt solution and the Ca-LSX molecular sieve, and through solid-liquid separation, a solid phase and a liquid phase are obtained, wherein the solid phase is a CaLi-LSX molecular sieve and the liquid phase is a mixed solution of a calcium salt and a lithium salt;

[0020] (3) Performing calcium removal treatment on the liquid phase to obtain a recycled lithium salt solution; performing lithium ion exchange on the recycled lithium salt solution and the solid phase obtained in the previous step, and through solid-liquid separation, a solid phase and a liquid phase are obtained;

[0021] (4) Repeating step (3), and then performing post-treatment on the separated solid phase to obtain a CaLi-LSX molecular sieve.

[0022] The present invention provides a method for recycling and reusing the exchanged lithium salt solution. Through calcium removal treatment, a recycled lithium salt solution is obtained, and this recycled lithium salt solution is continuously used to complete the next lithium exchange. By repeating this process several times, lossless utilization of the lithium solution is achieved. Moreover, the molecular sieve prepared by this method has a large adsorption capacity and a high nitrogen-oxygen separation coefficient, and CaLi-LSX molecular sieves with any desired lithium exchange degree can be prepared as needed.

[0023] The method of the present invention realizes the recycling and reusing of lithium salts while preparing CaLi-LSX molecular sieves, enabling all lithium salts to be used for molecular sieve exchange, greatly improving the utilization rate of lithium salts in the ion exchange process, reducing production costs, and having a simple process, being easy to operate, and suitable for large-scale application and promotion.

[0024] In some embodiments of the present invention, the calcium removal treatment specifically includes: using a precipitating agent to precipitate calcium ions from the mixed solution of calcium salt and lithium salt. After removing the precipitate, the pH value of the solution is adjusted with an alkali solution so that the difference from the pH value of the lithium salt solution is not more than 1, preferably not more than 0.5. After removing the precipitate again, a recycled lithium salt solution is obtained.

[0025] In the present invention, the precipitate can be removed by filtration or centrifugation.

[0026] In some embodiments of the present invention, the pH value of the lithium salt solution is 6 - 10, preferably 7 - 8.

[0027] In some embodiments of the present invention, the precipitating agent is selected from acids or salts that can form a precipitate with calcium ions.

[0028] In some preferred embodiments of the present invention, the precipitating agent is selected from one or more of anhydrous oxalic acid, lithium oxalate, and lithium sulfate.

[0029] In the present invention, the specific addition amount of the precipitating agent is determined by the calcium salt content in the solution; then, after removing the precipitate by filtration or centrifugation, a recycled lithium salt solution can be obtained.

[0030] In some embodiments of the present invention, the alkali in the alkali solution is selected from one or more of ammonia water, sodium hydroxide, and lithium hydroxide.

[0031] In some embodiments of the present invention, the alkali concentration in the alkali solution is 0.5 - 3 mol / L.

[0032] In some embodiments of the present invention, the calcium salt in the calcium salt solution is selected from one or more of anhydrous calcium chloride, calcium chloride dihydrate, calcium sulfate, and calcium nitrate.

[0033] In some embodiments of the present invention, the calcium ion concentration in the calcium salt solution is 0.1 - 1 mol / L.

[0034] In some embodiments of the present invention, the volume ratio of the calcium salt solution to the mass of the KNa-LSX molecular sieve is 10 - 40 mL / g.

[0035] In some embodiments of the present invention, the temperature for calcium ion exchange is 10 - 100 °C, the time is 2 - 6 h, and the number of exchange times is 3 - 6 times.

[0036] In step (1) of the present invention, the drying temperature is 10 - 100 °C, and the time is 2 - 48 h.

[0037] In some embodiments of the present invention, the lithium salt in the lithium salt solution is selected from one or more of lithium nitrate, lithium sulfate, and lithium chloride.

[0038] In some embodiments of the present invention, the lithium ion concentration in the lithium salt solution is 1 - 3 mol / L.

[0039] In some embodiments of the present invention, the volume ratio of the lithium salt solution to the mass of the Ca-LSX molecular sieve is 10 - 40 mL / g.

[0040] In some embodiments of the present invention, the temperature for lithium ion exchange is 10 - 100 °C, and the time is 2 - 6 h.

[0041] In some embodiments of the present invention, in step (4), the post-treatment includes washing, drying, and activation.

[0042] In some embodiments of the present invention, the drying temperature is 10 - 100 °C, and the time is 2 - 48 h.

[0043] In some embodiments of the present invention, the activation temperature is 300 - 400 °C, and the time is 4 - 7 h.

[0044] In the present invention, the activation is high-temperature activation, and preferably vacuum degassing is carried out with a vacuum degree not lower than 20 Pa.

[0045] According to a particularly preferred embodiment of the present invention, a method for recycling lithium salt to prepare CaLi-LSX molecular sieve is as follows:

[0046] S1. Prepare Ca-LSX molecular sieve:

[0047] S11. Add deionized water to the calcium salt to completely dissolve it, and prepare a calcium salt solution with a certain concentration. Preferably, the calcium ion concentration is 0.1 - 1 mol / L;

[0048] S12. Add a certain amount of KNa-LSX zeolite to the calcium salt solution obtained in step S11 and stir evenly. Preferably, the ratio of the volume (mL) of the calcium salt solution to the mass (g) of the KNa-LSX zeolite is maintained at 10 - 40 mL / g;

[0049] S13. Stir the slurry obtained in step S12 at a certain temperature for ion exchange several times; preferably, the temperature of the ion exchange is 10 - 100 °C, the exchange time is 2 - 6 h, and the number of exchanges is 3 - 6 times;

[0050] S14. After the exchange, obtain a solid sample by filtration or centrifugation, wash it, and dry it. Preferably, the drying temperature is 10 - 100 °C, and the drying time is 2 - 48 h, thus obtaining Ca-LSX zeolite.

[0051] S2. Preparation of CaLi-LSX zeolite and recycling of the lithium salt solution:

[0052] S21. Add deionized water to the lithium salt to completely dissolve it and prepare a lithium salt solution with a certain concentration. Preferably, the lithium ion concentration is 1 - 3 mol / L, and measure its pH value under normal temperature conditions;

[0053] S22. Add a certain amount of Ca-LSX zeolite to the solution obtained in step S21 and stir evenly; preferably, the ratio of the volume (mL) of the lithium salt solution to the mass (g) of the Ca-LSX zeolite is maintained at 10 - 40 mL / g;

[0054] S23. Stir the slurry obtained in step S22 at a certain temperature for ion exchange; preferably, the temperature of the ion exchange is 10 - 100 °C, and the exchange time is 2 - 6 h;

[0055] S24. After the first exchange, separate the solid and liquid of the mixed slurry by filtration or centrifugation. At this time, the solid is CaLi-LSX zeolite with a certain lithium exchange degree, and the liquid is a mixed solution of calcium salt and lithium salt. Measure the contents of calcium salt and lithium salt in the solution;

[0056] S25. Add a precipitant to the liquid separated in step S24. Preferably, the precipitant is an acid or salt such as anhydrous oxalic acid, lithium oxalate, lithium sulfate, etc. that can precipitate calcium ions. The specific addition amount is determined by the calcium salt content in the solution; then, after removing the precipitate by filtration or centrifugation, a lithium salt solution is obtained;

[0057] S26. Add an alkali solution to the solution obtained in step S25 at normal temperature to adjust the pH value to be no more than 1 different from the pH value of the lithium salt solution in step S21, and remove the precipitate again to obtain a processed lithium salt solution;

[0058] S27. Stir and mix the solid separated in step S24 with the solution obtained in step S26 evenly, repeat steps S23 to S26 for exchange and recovery, repeat several times as needed, then separate to obtain a solid product, wash, dry and activate at high temperature. Preferably, the drying temperature is 10 - 100 °C, the drying time is 2 - 48 h, the activation temperature is preferably 300 - 400 °C, the pressure is 20 Pa, and the activation time is 4 - 7 h, then CaLi-LSX molecular sieves with different lithium exchange degrees can be obtained.

[0059] The CaLi-LSX molecular sieve prepared by the aforementioned method can be used as a selective adsorbent for N 2 and O 2 in the PSA oxygen production or VPSA oxygen production process.

[0060] The recycling method of the present invention is simple and convenient, with low cost, greatly improving the utilization rate of lithium salts in the ion exchange process, and is suitable for large-scale application and promotion.

[0061] According to the present invention, the exchange degree represents the number of cations in the non-framework. The calcium ion exchange degree refers to the percentage of the calcium ion charge number in the total charge number among the non-framework cations; the lithium ion exchange degree refers to the percentage of the lithium ion charge number in the total charge number among the non-framework cations.

[0062] According to the present invention, the detection method for the lithium ion exchange degree and the calcium ion exchange degree: Take 0.04 g of molecular sieve, add 10 mL of nitric acid with a mass concentration of about 23%, microwave digest at 200 °C and 10 MPa for 30 min, dilute the digested liquid with nitric acid with a mass fraction of 1% for ICP testing, and obtain the exchange degrees of lithium ions and calcium ions from the test results.

[0063] According to the present invention, use the method specified in GB-T 35109-2017 to test the normal temperature nitrogen and oxygen adsorption capacity of the obtained CaLi-LSX molecular sieve, and obtain the nitrogen adsorption capacity, oxygen adsorption capacity and nitrogen-oxygen separation coefficient.

[0064] The present invention will be described in detail below through preparation examples and implementation examples, but the protection scope of the present invention is not limited to the following description.

[0065] For those not specified in the following preparation examples, implementation examples and comparative examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial channels.

[0066] Preparation Example

[0067] Take 22.42 g of anhydrous calcium chloride, add deionized water to make up the volume to 200 ml to obtain a calcium salt solution for ion exchange; take 10.0 g of KNa-LSX molecular sieve and disperse it evenly in the calcium salt solution. The above system is stirred at room temperature for ion exchange 6 times, 6 hours each time, and the calcium salt solutions used are of the same concentration and volume. After the exchange, it is filtered and washed with 1000 mL of deionized water, and placed in a dry and ventilated indoor environment for drying for 24 h to obtain Ca-LSX molecular sieve.

[0068] Control example

[0069] Take 31.80 g of lithium chloride monohydrate, add deionized water to make up the volume to 200 mL to obtain a lithium salt solution for ion exchange; take 10.0 g of Ca-LSX molecular sieve prepared in the preparation example and disperse it evenly in the lithium salt solution. Heat the above system to 50 °C and stir for ion exchange. After 6 hours, centrifuge the solid-liquid mixture; perform ion exchange 3 times in total, and a new lithium chloride solution needs to be prepared each time. After the exchange, the sample is filtered and washed with 1000 mL of deionized water, placed in a dry and ventilated indoor environment for drying for 24 h, and degassed under vacuum at 350 °C for 5 h to obtain CaLi-LSX molecular sieve.

[0070] The CaLi-LSX molecular sieve obtained in this control example was tested for the nitrogen and oxygen adsorption capacity at room temperature by the method specified in GB-T 35109-2017. The results were 28.27 cm of nitrogen 3 / g (STP, 760 mmHg), 5.54 cm of oxygen 3 / g (STP, 760 mmHg), and the nitrogen-oxygen separation coefficient was 5.10 (STP, 760 mmHg).

[0071] Example 1

[0072] (1) Take 31.80 g of lithium chloride monohydrate, add deionized water to make up the volume to 200 mL to obtain a lithium salt solution for ion exchange, and measure its pH value at room temperature to be 7.69;

[0073] (2) Take 10.0 g of Ca-LSX molecular sieve prepared in the preparation example and disperse it evenly in the lithium salt solution. Heat the above system to 50 °C and stir for ion exchange. After 6 hours, centrifuge the solid-liquid mixture; add 0.72 g of anhydrous oxalic acid to the centrifuged liquid. After it is completely dissolved, filter to remove the precipitate. The obtained filtrate is adjusted to pH 7.85 with 2.5 mol / L lithium hydroxide solution, and the precipitate is removed by filtration again to obtain the recovered lithium salt solution A;

[0074] (3) The solid obtained after centrifugal separation is evenly dispersed in Solution A, heated to 50 °C and stirred for the second ion exchange. After 6 hours, the solid-liquid mixture is centrifuged. 0.30 g of anhydrous oxalic acid is added to the centrifuged liquid. After it is completely dissolved, the precipitate is removed by suction filtration. The obtained filtrate is adjusted to pH 7.94 with 2.5 mol / L lithium hydroxide solution, and the precipitate is removed by suction filtration again to obtain the recovered lithium salt solution B.

[0075] (4) The solid obtained after centrifugal separation is evenly dispersed in Solution B, heated to 50 °C and stirred for the third ion exchange. After 6 hours, the solid-liquid mixture is centrifuged. The solid is washed by suction filtration with 1000 mL of deionized water, placed in a dry and well-ventilated indoor environment for drying for 24 h, and then degassed under vacuum at 350 °C for 5 h to obtain CaLi-LSX molecular sieve.

[0076] (5) 0.16 g of anhydrous oxalic acid is added to the centrifuged liquid. After it is completely dissolved, the precipitate is removed by suction filtration. The obtained filtrate is adjusted to pH 7.74 with 2.5 mol / L lithium hydroxide solution, and the precipitate is removed by suction filtration again to obtain the recovered lithium salt solution C, which can be directly used for the first exchange of the next batch of CaLi-LSX molecular sieve.

[0077] The CaLi-LSX molecular sieve obtained in this example was tested for the normal-temperature nitrogen-oxygen adsorption capacity by the method specified in GB-T 35109-2017. The results were 27.85 cm 3 / g (STP, 760 mmHg) for nitrogen, 5.32 cm 3 / g (STP, 760 mmHg) for oxygen, and 5.22 (STP, 760 mmHg) for the nitrogen-oxygen separation coefficient.

[0078] Example 2

[0079] Take 10.0 g of the Ca-LSX molecular sieve prepared in the preparation example and disperse it evenly in the lithium salt solution C finally obtained in Example 1. The specific exchange steps and the treatment method for recycling the lithium salt solution are the same as those in Example 1. After three exchanges, CaLi-LSX molecular sieve and the recycled lithium salt solution D are finally obtained.

[0080] The CaLi-LSX molecular sieve obtained in this example was tested for the normal-temperature nitrogen-oxygen adsorption capacity by the method specified in the national standard (GB-T 35109-2017). The results were 28.67 cm 3 / g (STP, 760 mmHg) for nitrogen, 5.75 cm 3 / g (STP, 760 mmHg) for oxygen, and 4.99 (STP, 760 mmHg) for the nitrogen-oxygen separation coefficient.

[0081] Example 3

[0082] (1) Take 31.80 g of lithium chloride monohydrate, add deionized water to make up the volume to 200 mL to obtain a lithium salt solution for ion exchange, and measure its pH value at 7.81 under normal temperature conditions;

[0083] (2) Take 10.0 g of the Ca-LSX molecular sieve prepared in the preparation example and disperse it evenly in the calcium salt solution. Heat the above system to 50 °C and stir for ion exchange. After 6 hours, centrifuge the solid-liquid mixture; add 1.25 g of anhydrous oxalic acid to the centrifuged liquid. After it is completely dissolved, filter to remove the precipitate. The obtained filtrate is adjusted to pH 7.64 with 2.5 mol / L lithium hydroxide solution, and then filtered again to remove the precipitate to obtain the recovered lithium salt solution F;

[0084] (3) Disperse the solid obtained after centrifugation evenly in solution F, heat to 50 °C and stir for the second ion exchange. After 6 hours, centrifuge the solid-liquid mixture; add 0.63 g of anhydrous oxalic acid to the centrifuged liquid. After it is completely dissolved, filter to remove the precipitate. The obtained filtrate is adjusted to pH 7.88 with 2.5 mol / L lithium hydroxide solution, and then filtered again to remove the precipitate to obtain the recovered lithium salt solution G;

[0085] (4) Disperse the solid obtained after centrifugation evenly in solution G, heat to 50 °C and stir for the third ion exchange. After 6 hours, centrifuge the solid-liquid mixture. The solid is filtered and washed with 1000 mL of deionized water, placed in a dry and well-ventilated indoor environment for drying for 24 h, and then degassed under vacuum at 350 °C for 5 h to obtain CaLi-LSX molecular sieve.

[0086] The CaLi-LSX molecular sieve obtained in this example was tested for the nitrogen and oxygen adsorption capacity at normal temperature by the method specified in the national standard (GB-T 35109-2017). The results were 24.62 cm 3 / g (STP, 760 mmHg) for nitrogen and 5.58 cm 3 / g (STP, 760 mmHg) for oxygen, and the nitrogen-oxygen separation coefficient was 4.41 (STP, 760 mmHg).

[0087] From the above results, it can be seen that the nitrogen-oxygen separation activity of the CaLi-LSX molecular sieve obtained in Example 1 is comparable to that of the CaLi-LSX molecular sieve obtained in the control example, indicating that the adsorption activity of the CaLi-LSX molecular sieve prepared by recycling lithium salts using the method of the present invention is not negatively affected.

[0088] The nitrogen-oxygen separation activity of the CaLi-LSX molecular sieve obtained in Example 2 is comparable to that of the CaLi-LSX molecular sieve obtained in the control example, indicating that the method of the present invention can recycle lithium salts multiple times to prepare CaLi-LSX molecular sieve and has no negative impact on the adsorption activity.

[0089] The nitrogen-oxygen separation activity of the CaLi-LSX molecular sieve obtained in Example 3 is comparable to that of the CaLi-LSX molecular sieve obtained in the control example, indicating that the lithium salt can be reused multiple times to prepare the CaLi-LSX molecular sieve by using the method of the present invention without negative impact on the adsorption activity.

[0090] Comparing Example 3 with Example 1, it can be seen that the nitrogen-oxygen separation activity of the CaLi-LSX molecular sieve obtained in Example 3 is slightly lower than that of the CaLi-LSX molecular sieve obtained in Example 1. The reason is that the excessive anhydrous oxalic acid added during the treatment of the mother liquor in Example 3 causes the residual oxalate ions in the mother liquor to combine with the calcium ions generated by subsequent ion exchange to form calcium oxalate. This solid cannot be separated after mixing with the molecular sieve, so the adsorption activity of the molecular sieve is reduced. It can be seen that the amount of the precipitant added is not the more the better.

[0091] The normal temperature N 2 isothermal adsorption curves of the CaLi-LSX molecular sieves prepared in the control example and Examples 1-3 are as Figure 1 shown; it can be seen from Figure 1 that the nitrogen adsorption amounts of Examples 1-3 and the control example are comparable, but that of Example 3 is slightly lower than that of Example 1. The reason is that the excessive anhydrous oxalic acid added during the treatment of the mother liquor in Example 3. It can be seen that the amount of the precipitant added is not the more the better.

[0092] The normal temperature O 2 isothermal adsorption curves of the CaLi-LSX molecular sieves prepared in the control example and Examples 1-3 are as Figure 2 shown; it can be seen from Figure 2 that the oxygen adsorption amounts of Examples 1-3 and the control example are comparable.

[0093] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing CaLi-LSX molecular sieve, characterized in that, the method comprises the following steps: (1) Performing calcium ion exchange on a calcium salt solution and KNa-LSX molecular sieve, and then through separation, washing and drying, obtaining Ca-LSX molecular sieve; (2) Performing lithium ion exchange on a lithium salt solution and Ca-LSX molecular sieve, through solid-liquid separation, obtaining a solid phase and a liquid phase, wherein the solid phase is CaLi-LSX molecular sieve and the liquid phase is a mixed solution of calcium salt and lithium salt; (3) Performing calcium removal treatment on the liquid phase to obtain a recycled lithium salt solution; performing lithium ion exchange on the recycled lithium salt solution and the solid phase obtained in the previous step, through solid-liquid separation, obtaining a solid phase and a liquid phase; (4) Repeating step (3), and then performing post-treatment on the separated solid phase to obtain CaLi-LSX molecular sieve.

2. The method according to claim 1, wherein, the calcium removal treatment specifically comprises: Using a precipitant to precipitate calcium ions from the mixed solution of calcium salt and lithium salt, after removing the precipitate, adjusting the pH value of the solution with an alkali solution so that the difference from the pH value of the lithium salt solution is not more than 1, and after removing the precipitate again, obtaining a recycled lithium salt solution; Preferably, the pH value of the lithium salt solution is 6-10, preferably 7-8.

3. The method according to claim 2, wherein, the precipitant is selected from acids or salts that can form a precipitate with calcium ions; Preferably, the precipitant is selected from one or more of anhydrous oxalic acid, lithium oxalate and lithium sulfate.

4. The method according to claim 2, wherein, the alkali in the alkali solution is selected from one or more of ammonia water, sodium hydroxide and lithium hydroxide; and / or, the alkali concentration in the alkali solution is 0.5-3 mol / L.

5. The method according to any one of claims 1-4, wherein, the calcium salt in the calcium salt solution is selected from one or more of anhydrous calcium chloride, calcium chloride dihydrate, calcium sulfate and calcium nitrate; and / or, the calcium ion concentration in the calcium salt solution is 0.1-1 mol / L.

6. The method according to any one of claims 1-4, wherein, the mass ratio of the volume of the calcium salt solution to the mass of KNa-LSX molecular sieve is 10-40 mL / g.

7. The method according to any one of claims 1-4, wherein, the lithium salt in the lithium salt solution is selected from one or more of lithium nitrate, lithium sulfate and lithium chloride; and / or, the lithium ion concentration in the lithium salt solution is 1-3 mol / L.

8. The method according to any one of claims 1-4, wherein, the mass ratio of the volume of the lithium salt solution to the mass of Ca-LSX molecular sieve is 10-40 mL / g.

9. The method according to any one of claims 1-4, wherein, the temperature of the calcium ion exchange is 10-100 °C, the time is 2-6 h, and the number of exchange times is 3-6 times; and / or, the temperature of the lithium ion exchange is 10-100 °C, the time is 2-6 h.

10. The method according to any one of claims 1-4, wherein, in step (4), the post-treatment includes washing, drying and activation; Preferably, the temperature of the drying is 10 - 100 °C and the time is 2 - 48 h; Preferably, the temperature of the activation is 300 - 400 °C and the time is 4 - 7 h.

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