Modified LSX molecular sieve as well as preparation method and application thereof

Abstract

The invention relates to the field of molecular sieves and discloses a modified LSX molecular sieve as well as a preparation method and application thereof. The method comprises the following steps: (1) carrying out potassium ion exchange on a K-containing LSX molecular sieve by using a potassium salt solution; (2) optionally, carrying out ammonium ion exchange on the solid obtained in the step (1) by using ammonium salt; (3) optionally, mixing the solid obtained in the step (2) with a lithium salt solution for lithium ion exchange; wherein in terms of K2O, the content of K in the K-containing LSX molecular sieve is not less than 8.5 wt%. According to the method disclosed by the invention, the higher lithium salt utilization rate can be obtained while the high lithium ion exchange degree is ensured.

Description

Technical Field

[0001] The present invention relates to the field of molecular sieves, and particularly to a modified LSX molecular sieve, a preparation method thereof, and an application thereof. Background Art

[0002] Low-silica X-type molecular sieve, abbreviated as LSX, has a SiO 2 / Al 2 O 3 molar ratio of 2.0 - 2.1. It has the maximum number of cation sites and has many adsorption centers. Currently, the commercially available air separation oxygen adsorption agent with the best application effect is lithium-modified LSX molecular sieve (LiLSX). This adsorbent has a large nitrogen adsorption capacity and a high nitrogen-oxygen separation coefficient, and is the core component of the pressure swing adsorption oxygen production process. The pressure swing adsorption air separation technology has been widely applied in many fields such as home medical care, metallurgy, steelmaking, carbon black production, fertilizer gasification, chemical oxidation, glass processing, pulp bleaching, aquaculture, sewage treatment, and military. LiLSX molecular sieve shows great market potential.

[0003] The technical key to preparing the LiLSX molecular sieve adsorbent is the exchange of Li + The synthesized X-type molecular sieve usually contains Na + or K + ions. After the exchange of Li + , LiLSX molecular sieve can be obtained. The exchange degree is generally required to be above 88%. The performance will be better with the increase of the exchange degree of Li+. Since the radius of Li + is small and its hydration ability is extremely strong, the existing tank exchange technology is to dissolve the metal salt containing the ion to be exchanged (usually lithium chloride) in water, and then mix and stir the aqueous solution with the zeolite molecular sieve to achieve ion exchange at a certain temperature. The prepared cation solution can replace the original cations in the molecular sieve cage to achieve the purpose of changing the cations in the molecular sieve. In order to achieve a higher exchange degree, intermittent multiple exchanges or continuous exchange methods can be used. Since it is quite difficult to achieve a high exchange degree of lithium ions in an aqueous solution, the amount of lithium required for each exchange is required to be more than 3 - 6 times in excess, the exchange time is quite long and the number of exchanges is more than 5 times, resulting in extremely low lithium utilization rate, long production cycle, and high cost of LiLSX molecular sieve due to the high price of lithium salt.

[0004] CN101289196A introduces a molecular sieve modification method with a higher lithium salt utilization rate. The LSX zeolite raw powder is exchanged into KLSX molecular sieve by a leaching method, and then the potassium ions in the KLSX molecular sieve are replaced with ammonium ions by using an ammonium-containing solution. Finally, Li + exchange is carried out with LiOH solution at low temperature to obtain LiLSX molecular sieve, and at the same time, air is introduced to discharge NH 3In this process, lithium exchange always proceeds in the forward direction without being restricted by equilibrium, resulting in a lithium salt utilization rate higher than 90%. However, during the preparation of this scheme, the potassium exchange degree is about 93 - 95%, and the ammonium exchange degree is about 94 - 96%. The residual potassium and sodium ions in the molecular sieve lead to a final lithium ion exchange degree close to 95%. US5268023 shows that when the lithium exchange degree of LSX molecular sieve increases from 95% to 100%, the nitrogen adsorption capacity and nitrogen-oxygen separation coefficient of the oxygen production adsorbent will increase significantly. Therefore, the activity of the products prepared by the above technology is restricted to a certain extent. In summary, it is still very necessary and significant to find a molecular sieve modification method with both high lithium salt utilization rate and better lithium ion exchange degree to prepare LiLSX products. Summary of the Invention

[0005] The object of the present invention is to overcome the problems existing in the prior art and provide a modified LSX molecular sieve, its preparation method and application.

[0006] The inventors of the present invention have found through research that by performing potassium ion exchange on a K-containing LSX molecular sieve with a specific K content using a potassium salt solution, the potassium ion exchange degree during potassium ion exchange can be significantly improved, and further the lithium ion exchange degree during lithium ion exchange can be improved. Therefore, in order to achieve the above object, the first aspect of the present invention provides a method for modifying an LSX molecular sieve, the method comprising:

[0007] (1) Performing potassium ion exchange on the K-containing LSX molecular sieve with a potassium salt solution;

[0008] (2) Performing ammonium ion exchange on the solid obtained in step (1) with an ammonium salt;

[0009] (3) Mixing the solid obtained in step (2) with a lithium salt solution for lithium ion exchange;

[0010] Wherein, based on K 2 O, the K content in the K-containing LSX molecular sieve is not less than 8.5% by weight.

[0011] The second aspect of the present invention provides a modified LSX molecular sieve prepared by the above method.

[0012] The third aspect of the present invention provides the application of the above modified LSX molecular sieve in pressure swing adsorption for oxygen production

[0013] The present invention has at least the following beneficial effects:

[0014] (1) While ensuring a high lithium ion exchange degree, the present invention obtains a higher lithium salt utilization rate and generates better air separation activity.

[0015] (2) The LiLSX molecular sieve is prepared by the method of the present invention. The potassium exchange and ammonium exchange steps are preferably modified by elution, which shortens the contact time between the material and the hydrothermal solution, reduces the damage to the molecular sieve framework structure during the exchange process, and is beneficial to improving the activity of the lithium sieve.

[0016] (3) Preferably, when the LiLSX molecular sieve adsorbent is prepared by the method of the present invention, since the amount of lithium hydroxide used is at most 1.1 times the theoretically required amount, the one-way lithium ion utilization rate is greater than 90%. After the exchange, the lithium solution is collected and added to the theoretical lithium salt dosage for the next round of molecular sieve exchange, and high-quality lithium sieve can still be continuously prepared, achieving a 100% lithium salt utilization rate throughout the process, effectively preventing lithium ion waste and reducing the production cost of the adsorbent.

[0017] (4) When the LiLSX molecular sieve adsorbent is prepared by the method of the present invention, Li of LiOH + enters the molecular sieve to exchange out NH 4+ ions, and NH 4+ ions will react with OH - to produce ammonia water, which is discharged from the system in the form of NH 3 under the action of bubbling and stirring. The chemical reaction always proceeds in the forward direction, getting rid of the limitation of chemical equilibrium on the exchange process. Therefore, even if not many lithium ions are introduced during the preparation process, the obtained LiLSX molecular sieve still has a high lithium ion exchange degree.

[0018] (5) The method of the present invention is simple and easy to implement, convenient for industrial preparation, suitable for in-line elution exchange, conducive to large-scale production, has great application potential, and provides the possibility for preparing high-quality and inexpensive oxygen adsorption agents. Detailed Embodiments

[0019] In the ranges disclosed herein, the endpoints and any values are not limited to the exact 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 each range, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values 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.

[0020] The first aspect of the present invention provides a method for modifying an LSX molecular sieve, the method comprising:

[0021] (1) performing potassium ion exchange on the K-containing LSX molecular sieve with a potassium salt solution;

[0022] (2) performing ammonium ion exchange on the solid obtained in step (1) with an ammonium salt;

[0023] (3) mixing the solid obtained in step (2) with a lithium salt solution for lithium ion exchange;

[0024] Among them, in terms of K 2 O, the K content in the K-containing LSX molecular sieve is not less than 8.5% by weight.

[0025] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, in terms of K 2 O, the K content in the K-containing LSX molecular sieve is 9-12% by weight, and it can be 9% by weight, 9.5% by weight, 10% by weight, 10.5% by weight, 11% by weight, 11.5% by weight, 12% by weight or any range formed by any two of the above values and the values within the range.

[0026] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, the concentration of K + in the potassium salt solution is 0.2-5 mol / L, and it can be 0.2 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L or any range formed by any two of the above values and the values within the range.

[0027] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, relative to 1 g of the molecular sieve, the dosage of the potassium salt solution is 5-360 mL, and it can be 5 mL, 10 mL, 50 mL, 60 mL, 70 mL, 80, 90 mL, 100 mL, 120 mL, 140 mL, 160 mL, 180 mL, 200 mL, 240 mL, 260 mL, 280 mL, 300 mL, 320 mL, 340 mL, 360 mL or any range formed by any two of the above values and the values within the range.

[0028] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, the potassium ion exchange method is to wash and filter the K-containing LSX molecular sieve with the potassium salt solution. There is no limitation on the filtering method, and solid-liquid separation can be carried out. Vacuum filtration is preferably used. The washing can be carried out multiple times, such as 2-5 times.

[0029] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, the conditions for potassium ion exchange include: the temperature is 30-120 °C, and it can be 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C, 110 °C, 120 °C, 130 °C or any range formed by any two of the above values and the values within the range, and the time is 3-45 min, and it can be 1 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min or any range formed by any two of the above values and the values within the range.

[0030] In the present invention, the potassium salt is not limited and can provide K + That's all. It is preferably selected from at least one of potassium sulfate, potassium nitrate, and potassium chloride.

[0031] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, the pH of the potassium salt solution is not lower than 8, preferably 8 - 9.

[0032] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, in the ammonium salt solution, the concentration of NH 4+ is 0.2 - 7 mol / L, and it can be 0.2 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L, 6.5 mol / L, 7 mol / L, or any value within the range formed by any two of the above values.

[0033] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, relative to 1 g of molecular sieve, the dosage of the ammonium salt solution is 5 - 360 mL, and it can be 5 mL, 10 mL, 50 mL, 60 mL, 70 mL, 80, 90 mL, 100 mL, 120 mL, 140 mL, 160 mL, 180 mL, 200 mL, 240 mL, 260 mL, 280 mL, 300 mL, 320 mL, 340 mL, 360 mL, or any value within the range formed by any two of the above values.

[0034] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, the ammonium ion exchange method is to wash and filter the solid obtained in step (1) with the ammonium salt solution. The filtration method is not limited, and solid - liquid separation can be carried out. Vacuum filtration is preferred. The washing can be carried out multiple times, such as 2 - 5 times.

[0035] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, the conditions for ammonium ion exchange include: the temperature is 30 - 120 °C, and it can be 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, or any value within the range formed by any two of the above values; the time is 3 - 45 min, and it can be 1 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, or any value within the range formed by any two of the above values.

[0036] In the present invention, the ammonium salt is not limited as long as it can provide NH 4+ and is preferably at least one selected from ammonium sulfate, ammonium nitrate, and ammonium chloride.

[0037] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, the pH of the potassium salt solution is not lower than 8, preferably 8 - 9.

[0038] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, the concentration of the lithium salt in the lithium salt solution is 1 - 10% by weight, and can be 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, or any range formed by any two of the above values and the values within the range.

[0039] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, the conditions for mixing include: the temperature is 30 - 100 °C, and the time is 30 - 360 min;

[0040] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, the molar ratio of Li + to the cations in the solid obtained in step (2) is not higher than 1.1.

[0041] In the present invention, the inventors found that when the lithium salt is preferably selected from lithium hydroxide, Li in LiOH + enters the molecular sieve to exchange out NH 4+ ions, and the NH 4+ ions will react with OH - to generate ammonia water, and under the action of bubbling and stirring, it is discharged from the system in the form of NH 3 , and the chemical reaction always proceeds in the forward direction, which is beneficial to getting rid of the limitation of chemical equilibrium on the exchange process and helps to obtain a higher lithium ion exchange degree and lithium salt utilization rate.

[0042] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, the pH of the mixing system is 11 - 11.5.

[0043] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, the LSX molecular sieve containing K in step (1) is mixed with water and subjected to the first pulping and filtration before potassium ion exchange; preferably, the thickness of the filter cake obtained from the first pulping and filtration is 1 - 10 mm, and can be 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, or any range formed by any two of the above values and the values within the range, and more preferably 6 - 10 mm.

[0044] In the present invention, the solid obtained in step (1) is washed before ammonium ion exchange, and the solid obtained in step (2) is washed before lithium ion exchange.

[0045] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, the solid obtained in step (1) in step (2) is mixed with water and subjected to secondary pulping and filtration before ammonium ion exchange; preferably, the thickness of the filter cake obtained by the secondary pulping and filtration is 1-10 mm, which can be 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm or any range formed by any two values above and the values within the range, and more preferably 6-10 mm.

[0046] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, and to obtain a modified LSX molecular sieve with a higher degree of uniformity of crystal cluster size, a lower content of miscellaneous crystals, a higher crystallinity, and better adsorption performance, the method further includes: preparing a K-containing LSX molecular sieve in the following manner. The preparation method of the K-containing LSX molecular sieve includes preparing by a method for regulating the crystal cluster size of the LSX molecular sieve (see the patent application with the application number 202211394114.X, which is incorporated herein by reference), specifically: 1) The first silicon source, aluminum source, sodium source, and the first water are subjected to first contact and first aging in sequence to obtain a crystal cluster size regulator;

[0047] 2) The second silicon source, aluminum source, sodium source, potassium source, and the second water are subjected to second contact to obtain a gel;

[0048] 3) The crystal cluster size regulator is subjected to third contact with the gel, and the product of the third contact is subjected to second aging and crystallization treatment in sequence to obtain an LSX molecular sieve,

[0049] wherein, the second silicon source is water glass and / or sodium silicate,

[0050] The relationship between the target average particle size of the LSX molecular sieve crystal cluster and the dosage of the crystal cluster size regulator in step 3) satisfies the following formula:

[0051] y = 1.6517×(100x)-0.274,

[0052] wherein, y is the target average particle size of the LSX molecular sieve crystal cluster, with the unit of μm, and the value range is 1-5.8; x is the weight ratio of the crystal cluster size regulator in step 3) to the gel.

[0053] In the present invention, in order to obtain a higher lithium ion exchange degree and lithium salt utilization rate, the method for modifying the LSX molecular sieve further includes: performing solid-liquid separation on the mixed product; preferably, drying the solid obtained by the solid-liquid separation; preferably, using the liquid obtained by the solid-liquid separation as the lithium salt solution in step (3) and mixing it with the solid obtained in step (2).

[0054] In the present invention, the solid obtained in step (3) is washed, dried, and activated, and the temperature of the drying is 30-200 °C.

[0055] In the present invention, the activation conditions are not limited and are common activation conditions in the art. The activation conditions can be vacuum calcination or flowing hot air calcination. For example, during vacuum calcination, the temperature is 200-450 °C, the time is 2-8 h, and the pressure is 2-7 Pa; during flowing hot air calcination, the temperature is 450-700 °C, and the time is 1-5 h.

[0056] The second aspect of the present invention provides a modified LSX molecular sieve prepared by the above method.

[0057] The third aspect of the present invention provides the application of the above modified LSX molecular sieve in pressure swing adsorption for oxygen production

[0058] The present invention will be described in detail below through examples.

[0059] (1) In the following examples, the exchange degree of potassium ions refers to the ratio of the number of moles of potassium ions to the sum of the number of moles of potassium ions and sodium ions in the KLSX molecular sieve, that is, the potassium ion exchange degree = (number of moles of potassium ions) / (number of moles of potassium ions + number of moles of sodium ions). This parameter can be obtained by X-ray fluorescence spectrometry (XRF).

[0060] (2) The potassium oxide content in the NH 4 LSX molecular sieve can also be obtained by testing XRF on the dried sample.

[0061] (3) The exchange degree of lithium ions refers to the ratio of the number of moles of lithium ions to the total number of moles of all cations in the LiLSX molecular sieve (all cations in the system are monovalent), that is, the lithium ion exchange degree = (number of moles of lithium ions) / (number of moles of all cations); the lithium ion exchange degree of Comparative Example 2 can be obtained by inductively coupled plasma analysis (ICP). In the remaining examples, the cations other than lithium are ammonium ions, and ICP cannot identify them. Therefore, the lithium ion exchange degree cannot be directly obtained and needs to be indirectly reflected by comparing the adsorption activity (nitrogen adsorption capacity and nitrogen-oxygen separation coefficient) of the oxygen-producing lithium sieve prepared by the can exchange method described in Comparative Example 2:

[0062] According to the solution described in Comparative Example 2, the concentration of the lithium chloride solution and the number of exchanges were changed to obtain a series of oxygen-producing lithium sieve adsorbents with an exchange degree of 70%-99.4%. The adsorption activity (nitrogen adsorption capacity and nitrogen-oxygen separation coefficient) of the prepared lithium sieve was measured. Regardless of the preparation method used, as long as the molecular sieve structure was not damaged, when the exchange degree of the prepared oxygen-producing lithium sieve adsorbent was the same, its adsorption activity (nitrogen adsorption capacity and nitrogen-oxygen separation coefficient) was also the same. Therefore, if the adsorption activity of the oxygen-producing lithium sieve adsorbent prepared by the tank exchange method was close to that of the oxygen-producing lithium sieve adsorbent prepared by the following elution method with an undamaged molecular sieve structure, the exchange degrees of the adsorbents prepared by the two methods were also close.

[0063] (4) The nitrogen adsorption capacity test and the nitrogen-oxygen separation coefficient were tested by the method specified in the national standard (GB / T35109-2017). The better the adsorption activity of the lithium sieve, the higher the lithium ion exchange degree.

[0064] (5) Single-pass utilization rate of lithium salt: lithium content in the molecular sieve product / amount of lithium added. The content of metal elements in the molecular sieve product was measured by ICP.

[0065] (I) Preparation of KNaLSX molecular sieve (with a K content of 10.1 wt% based on K 2 O):

[0066] Prepare the crystal cluster size regulator according to the method in the preparation example of the patent application with the application number 202211394114.X.

[0067] Prepare the KNaLSX molecular sieve according to the method in Example 1 of the patent application with the application number 202211394114.X.

[0068] The difference is that water glass, aluminum hydroxide, sodium hydroxide, potassium hydroxide, and deionized water were fed in a molar ratio of SiO 2 :Al 2 O 3 :(Na 2 O + K 2 O): water of 2:1:7.5:127.5, and the molar ratio of Na 2 O to Na 2 O + K 2 O was 0.74:1.

[0069] (II) Preparation of KNaLSX molecular sieve (with a K content of 20 wt% based on K 2 O):

[0070] According to the preparation method in (I), the difference is that SiO 2 :Al 2 O 3:(The molar ratio of (Na2O + K2O): water is 2:1:7.5:127.5) Feed sodium silicate, aluminum hydroxide, sodium hydroxide, potassium hydroxide and deionized water in this ratio, and the molar ratio of Na 2 O to Na 2 O + K 2 O is 0.62:1.

[0071] (III) Preparation of all-sodium molecular sieve (NaLSX): Immerse the KNaLSX molecular sieve prepared in (I) (with a K content of 10.1 wt% based on K2O) in a 2 mol / L sodium chloride solution. The ratio of the solution volume (mL) to the molecular sieve mass (g) is 10. Heat it to 70 °C and keep it at a constant temperature for 1 h for ion exchange, and then achieve solid-liquid separation by suction filtration; Immerse the obtained solid in a 2 mol / L sodium chloride solution again, repeat the above operation, and cycle 3 times in this way; After thoroughly washing the exchange product, dry it overnight at 100 °C to obtain the all-sodium molecular sieve.

[0072] Example 1

[0073] 1) Prepare 20 g of special KNaLSX molecular sieve, with a skeletal potassium content of 10.1 wt% based on K 2 O (XRF test result). Add 20 g of deionized water to make a slurry, and suction filter to form a filter cake about 6 mm thick; Prepare 300 mL of a 1 mol / L K + potassium sulfate solution, heat it to 98 °C, adjust the pH value to 8.5 with a 5 wt‰ potassium hydroxide solution, and perform potassium ion exchange on the filter cake by leaching method with the help of vacuum suction filtration. The treatment time is about 4 min, and then prepare a fresh exchange solution and continue to modify according to the above steps. Exchange a total of 3 times; After completion, wash the molecular sieve with 800 mL of deionized water to obtain KLSX molecular sieve, and the potassium ion exchange degree reaches 99.3%;

[0074] 2) Add 20 g of deionized water to 20 g of KLSX molecular sieve to make a slurry, and suction filter to form a filter cake about 6 mm thick; Prepare 300 mL of a 2 mol / L NH 4 + ammonium sulfate solution, heat it to 98 °C, adjust the pH value to 8.5 with ammonia water, and perform ammonium ion exchange on the filter cake by leaching method with the help of vacuum suction filtration. The treatment time is about 4 min, and then prepare a fresh exchange solution and continue to modify according to the above steps. Exchange a total of 3 times; After completion, wash the molecular sieve with 800 mL of deionized water to obtain NH 4 LSX molecular sieve, and at this time the potassium oxide content drops to 0.13%;

[0075] 3) Put the NH 4 LSX molecular sieve obtained in step (2) into a container, add 80 g of deionized water to get a suspension, and stir and heat to 85 °C; Calculate NH 4The theoretical amount of lithium hydroxide required for the complete cation exchange of LSX molecular sieve with lithium ions is 1.08 times this amount, and a 5% mass fraction solution of LiOH is prepared. Air is bubbled into the suspension and the liquid is stirred at 350 rpm, and then the lithium hydroxide solution is slowly introduced while maintaining the pH value between 11 and 11.5. During this process, the exchanged NH 4 + formed NH 3 can be discharged in a timely manner, and at the same time, the lithium hydroxide solution can be fully mixed;

[0076] 4) After the introduction of the lithium hydroxide solution is completed, the reaction is maintained for a certain period of time until the pH of the liquid in the container remains unchanged, indicating that the exchange is over. The solid and liquid in the container are separated, the liquid sample is collected for later use, the solid sample is washed clean with water, dried overnight at 120 °C, and activated under a vacuum condition of 5 Pa at 350 °C for 5 h.

[0077] Thus, the lithium sieve adsorbent A for oxygen production is obtained.

[0078] The single-pass utilization rate of the lithium salt in the adsorbent preparation process is 91.2%.

[0079] The adsorption activity of the adsorbent was tested. At 25 °C and a pressure of 760 mmHg, the nitrogen adsorption capacity was 31.31 mL / g, and the nitrogen-oxygen separation coefficient was 6.83, which was close to the activity result when the lithium sieve adsorbent for oxygen production prepared by the method described in Comparative Example 2 of this type of molecular sieve reached a lithium ion exchange degree of 98.5%.

[0080] Example 2

[0081] The method described in Example 1 was followed, except that

[0082] In step 1), a filter cake of about 8 mm was formed by suction filtration for potassium ion exchange, and the treatment time for each time was about 4.5 - 5 min. The potassium ion exchange degree of the obtained KLSX molecular sieve was 99.7%;

[0083] In step 2), a filter cake of about 8 mm was formed by suction filtration for ammonium ion exchange, and the treatment time for each time was about 4.5 - 5 min. The obtained NH 4 The potassium oxide content of the LSX molecular sieve was reduced to 0.06%.

[0084] Thus, the lithium sieve adsorbent B for oxygen production is obtained.

[0085] The single-pass utilization rate of the lithium salt in the adsorbent preparation process is 91.7%.

[0086] The adsorption activity of the adsorbent was tested. At 25°C and 760 mmHg pressure, its nitrogen adsorption capacity was 32.48 mL / g, and the nitrogen-oxygen separation coefficient was 6.91. This was close to the activity result of the lithium sieve adsorbent for oxygen production prepared by the method described in Comparative Example 2 of this type of molecular sieve when reaching 99% lithium ion exchange degree, indicating that increasing the filter cake thickness during leaching and exchange can extend the residence time of the hydrothermal solution in the material, achieve the multi-stage utilization of the exchange salt from the upper layer to the lower layer of the filter cake, and ultimately improve the exchange degree of the molecular sieve.

[0087] Example 3

[0088] It was carried out according to the method described in Example 1, except that

[0089] In step 3), the NH 4 LSX molecular sieve was put into a container, 80 g of the standby filtrate collected in step 4) of Example 1 was added to obtain a suspension, and it was stirred and heated to 85°C; calculate the theoretical amount of lithium hydroxide required for all cations of the NH 4 LSX molecular sieve to be exchanged by lithium ions, and take the LiOH of this amount and the remaining standby filtrate collected in step 4) of Example 1 to prepare a solution; after blowing air into the molecular sieve suspension and applying stirring at 350 rpm to the liquid, the above lithium hydroxide solution was slowly introduced, and the pH value was maintained between 11 - 11.5 for lithium ion exchange;

[0090] Thus, the lithium sieve adsorbent C for oxygen production was obtained.

[0091] In the preparation process of this adsorbent, the recycled lithium solution from the previous cycle was used, and the one-way addition amount of lithium hydroxide was the theoretical value. According to this cycle, the utilization rate of lithium salt throughout the process was 100%.

[0092] The adsorption activity of the adsorbent was tested. At 25°C and 760 mmHg pressure, its nitrogen adsorption capacity was 31.35 mL / g, and the nitrogen-oxygen separation coefficient was 6.82. This was close to the activity result of the adsorbent A obtained in Example 1, indicating that using the recycled lithium solution during lithium exchange would not have an adverse impact on the product performance, and this recycling method could be iterated continuously.

[0093] Example 4

[0094] It was carried out according to the method described in Example 1, except that

[0095] In step 1), suction filtration was carried out to form a filter cake of about 2 mm for potassium ion exchange, and the treatment time for each time was about 1 - 2 min. The potassium ion exchange degree of the obtained KLSX molecular sieve was 98.5%;

[0096] In step 2), suction filtration was carried out to form a filter cake of about 2 mm for ammonium ion exchange, and the treatment time for each time was about 1 - 2 min. The potassium oxide content of the obtained NH 4 LSX molecular sieve decreased to 0.72%.

[0097] Thus, the lithium sieve adsorbent E for oxygen production is obtained.

[0098] In the preparation process of this adsorbent, the single-pass utilization rate of lithium salt is 90%.

[0099] The adsorption activity of the adsorbent was tested. At 25°C and 760 mmHg pressure, the nitrogen adsorption capacity was 29.22 mL / g, and the nitrogen-oxygen separation coefficient was 6.49. The activity results were close to those of the lithium sieve adsorbent for oxygen production prepared by the method described in Comparative Example 2 of this type of molecular sieve when the lithium ion exchange degree reached 97%. This indicates that reducing the filter cake thickness during elution and exchange can further improve the exchange degree of the molecular sieve and the utilization rate of lithium ions within the preferred range. By reducing the filter cake thickness, the residence time of the hydrothermal solution in the material is shortened, which affects the final exchange degree of the molecular sieve.

[0100] Example 5

[0101] According to the method of Example 3, the difference is that the potassium content in the KNaLSX molecular sieve is 20 wt% in terms of K 2 O.

[0102] Thus, the lithium sieve adsorbent E for oxygen production is obtained.

[0103] In the preparation process of this adsorbent, the single-pass utilization rate of lithium salt is 90%.

[0104] The adsorption activity of the adsorbent was tested. At 25°C and 760 mmHg pressure, the nitrogen adsorption capacity was 29.42 mL / g, and the nitrogen-oxygen separation coefficient was 6.51. The activity results were close to those of the lithium sieve adsorbent for oxygen production prepared by the method described in Comparative Example 2 of this type of molecular sieve when the lithium ion exchange degree reached 97%. This shows that controlling the K content within the preferred range can improve the exchange degree of the molecular sieve and the utilization rate of lithium ions.

[0105] Example 6

[0106] According to the method of Example 1, the difference is that

[0107] In step 1), the pH value was adjusted to 6.5 with a 5‰ potassium hydroxide solution.

[0108] In step 2), the pH value was adjusted to 6.5 with ammonia water.

[0109] Thus, the lithium sieve adsorbent F for oxygen production is obtained.

[0110] In the preparation process of this adsorbent, the single-pass utilization rate of lithium salt is 91.1%.

[0111] The adsorbent was tested for adsorption activity. At 25 °C and 760 mmHg pressure, its nitrogen adsorption capacity was 28.64 mL / g, and the nitrogen-oxygen separation coefficient was 6.31, which was close to the activity result of the oxygen-producing lithium sieve adsorbent prepared by the method described in Comparative Example 2 of this type of molecular sieve when reaching 96% lithium ion exchange degree. It shows that when the pH of the potassium salt solution and the pH of the ammonium salt solution are within the preferred ranges, high exchange degree and high lithium ion utilization rate of the molecular sieve can be ensured to produce relatively high nitrogen-oxygen separation activity (nitrogen adsorption capacity and nitrogen-oxygen separation coefficient).

[0112] Example 7

[0113] According to the method of Example 1, the difference is that

[0114] In step 3), air was bubbled into the suspension and the liquid was stirred at 350 rpm, and then lithium hydroxide solution was slowly introduced while maintaining the pH value between 11.5 and 12.5.

[0115] Thus, the oxygen-producing lithium sieve adsorbent G was obtained.

[0116] The single-pass utilization rate of lithium salt in the adsorbent preparation process was 91.3%.

[0117] The adsorbent was tested for adsorption activity. At 25 °C and 760 mmHg pressure, its nitrogen adsorption capacity was 28.93 mL / g, and the nitrogen-oxygen separation coefficient was 6.32, which was close to the activity result of the oxygen-producing lithium sieve adsorbent prepared by the method described in Comparative Example 2 of this type of molecular sieve when reaching 96% lithium ion exchange degree. It shows that by controlling the pH of the mixed system within the preferred range, the prepared molecular sieve has a high exchange degree and a high lithium ion utilization rate, and can produce relatively high nitrogen-oxygen separation activity (nitrogen adsorption capacity and nitrogen-oxygen separation coefficient).

[0118] Comparative Example 1

[0119] It was carried out according to the method described in Example 1, the difference is that

[0120] In step 1), the molecular sieve used was a fully sodium molecular sieve (NaLSX), and its framework potassium content was less than 0.1% (XRF test result) calculated as K 2 O, and the potassium ion exchange degree of the obtained KLSX molecular sieve was 95.7%;

[0121] In step 2), the potassium oxide content of the obtained NH 4 LSX molecular sieve decreased to 0.12%, and the sodium oxide content was 1.93%.

[0122] Thus, the oxygen-producing lithium sieve adsorbent D was obtained.

[0123] The single-pass utilization rate of lithium salt in the adsorbent preparation process was 88.8%.

[0124] The adsorption activity of the adsorbent was tested. At 25 °C and 760 mmHg pressure, its nitrogen adsorption capacity was 28.35 mL / g, and the nitrogen-oxygen separation coefficient was 6.34. The activity results were close to those of the oxygen-producing lithium sieve adsorbent prepared by the method described in Comparative Example 2 of such molecular sieves when reaching 96% lithium ion exchange degree, indicating that the potassium content in the framework of the initial molecular sieve raw material has a significant impact on the final exchange degree of this ion exchange process.

[0125] Comparative Example 2

[0126] Prepare 150 mL of 2.2 mol / L Li + lithium chloride solution, adjust the pH value to 8.5 with 5 wt‰ lithium hydroxide solution, and put in 10 g of special KNaLSX molecular sieve pellets. The potassium content in its framework is 10.1% (XRF test result) in terms of K 2 O. Heat up to 95 °C and exchange for 2 h in a tank exchange manner. Then filter out the solution, add fresh exchange solution and continue to process according to the above steps for a total of 5 times; after completion, wash the molecular sieve with deionized water, dry it overnight at 120 °C, and activate it under a vacuum condition of 5 Pa at 350 °C for 5 h.

[0127] Thus, the oxygen-producing lithium sieve adsorbent F was obtained.

[0128] The lithium ion exchange degree of this adsorbent was 99.4%.

[0129] The adsorption activity of the adsorbent was tested. At 25 °C and 760 mmHg pressure, its nitrogen adsorption capacity was 32.52 mL / g, and the nitrogen-oxygen separation coefficient was 6.93. After calculation, the single-pass lithium salt utilization rate of this exchange process was less than 5%.

[0130] From the above results, it can be seen that by using the method of the present invention, a higher lithium ion exchange degree and lithium salt utilization rate can be obtained.

[0131] 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 all fall within the protection scope of the present invention.

Claims

1. A method for modifying LSX molecular sieve, characterized in that, the method comprises: (1) performing potassium ion exchange on K-containing LSX molecular sieve with a potassium salt solution; (2) performing ammonium ion exchange on the solid obtained in step (1) with an ammonium salt; (3) mixing the solid obtained in step (2) with a lithium salt solution for lithium ion exchange; Among them, taking K 2 O as a measure, the K content in the K-containing LSX molecular sieve is not less than 8.5% by weight.

2. The method according to claim 1, wherein, Based on K 2 calculation, the K content in the K-containing LSX molecular sieve is 9-12 wt%. and / or, the concentration of K in the potassium salt solution + is 0.2 - 5 mol / L; and / or, relative to 1 g of the molecular sieve, the dosage of the potassium salt solution is 5 - 360 mL; and / or, the conditions for the potassium ion exchange include: temperature is 30 - 120 °C, time is 3 - 45 min; and / or, the potassium salt is selected from at least one of potassium sulfate, potassium nitrate and potassium chloride; and / or, the pH of the potassium salt solution is not less than 8, preferably 8 - 9.

3. The method according to claim 1 or 2, wherein, The concentration of NH 4+ in the ammonium salt solution is 0.2 - 7 mol / L; and / or, relative to 1 g of the molecular sieve, the dosage of the ammonium salt solution is 5 - 360 mL; and / or, the conditions for the ammonium ion exchange include: temperature is 30 - 120 °C, time is 3 - 45 min; and / or, the ammonium salt is selected from at least one of ammonium sulfate, ammonium nitrate and ammonium chloride; and / or, the pH of the ammonium salt solution is not less than 8, preferably 8 - 9.

4. The method according to claim 1 or 2, wherein, the concentration of the lithium salt in the lithium salt solution is 1 - 10 wt%; and / or, the conditions for the mixing include: temperature is 30 - 100 °C, time is 30 - 360 min; and / or, said Li + has a molar ratio to the cations in the solid obtained in step (2) of not more than 1.

1.

5. The method according to claim 1 or 2, wherein, the lithium salt is selected from lithium hydroxide; and / or, the pH of the mixing system is 11 - 11.

5.

6. The method according to claim 1 or 2, wherein, in step (1), the K-containing LSX molecular sieve is mixed with water for the first pulping and filtration before potassium ion exchange; Preferably, the thickness of the filter cake obtained from the first pulping and filtration is 1 - 10 mm, more preferably 6 - 10 mm.

7. The method according to claim 1 or 2, wherein, in step (2), the solid obtained in step (1) is mixed with water for the second pulping and filtration before ammonium ion exchange; Preferably, the thickness of the filter cake obtained from the second pulping and filtration is 1 - 10 mm, more preferably 6 - 10 mm.

8. The method according to claim 1 or 2, wherein, the preparation method of the K-containing LSX molecular sieve includes: preparing by a method of regulating the crystal cluster size of the LSX molecular sieve; and / or, the method for modifying the LSX molecular sieve further includes: performing solid-liquid separation on the mixed product; Preferably, drying the solid obtained from the solid-liquid separation; Preferably, using the liquid obtained from the solid-liquid separation as the lithium salt solution in step (3) to mix with the solid obtained in step (2).

9. A modified LSX molecular sieve prepared by the method according to any one of claims 1 - 8.

10. Application of the modified LSX molecular sieve according to claim 9 in pressure swing adsorption for oxygen production.