Binder-free Li-LSX molecular sieve as well as preparation method and application thereof

Abstract

The invention discloses a binderless Li-LSX molecular sieve and a preparation method and application of the binderless Li-LSX molecular sieve in the technical field of adsorption materials for oxygen production, and the preparation method of the binderless Li-LSX molecular sieve comprises the following steps: taking LSX molecular sieve powder and kaolin as raw materials; the binder-free Li-LSX molecular sieve is prepared through mixing molding, drying roasting, material saturation water absorption, sodium-potassium mixed alkali liquor treatment, lithium ion exchange and secondary drying roasting, the N2 adsorption capacity of the binder-free Li-LSX molecular sieve is larger than 28 mL / g at the temperature of 25 DEG C, the pressure swing adsorption capacity of an adsorbent is remarkably improved, and the binder-free Li-LSX molecular sieve has good application prospects and can be used in a PSA / VPSA oxygen production process.

Description

Technical Field

[0001] This invention relates to the field of adsorption materials technology for oxygen production, specifically to a method for preparing and using a binder-free LSX molecular sieve. Background Technology

[0002] Air is the gas surrounding the Earth, layered over its surface. It is transparent, colorless, and odorless, primarily composed of nitrogen and oxygen, and has a significant impact on human survival and production. Currently, air separation technologies mainly include: cryogenic air separation, membrane separation, and pressure swing adsorption (PSA). PSA technology separates specific gases from the air through the principle of physical adsorption. This process typically uses molecular sieves or other adsorbents to alternately adsorb and desorb gases under different pressures. Its main advantages include lower operating costs, smaller equipment footprint, and flexibility in operating conditions. However, the lifespan and performance of the adsorbent are also important factors limiting the further development of PSA technology.

[0003] LSX (silicon oxide to alumina molar ratio of 2) molecular sieve raw powder is mainly synthesized in a mixed alkaline solution of sodium hydroxide and potassium hydroxide. Due to its low silica-to-alumina ratio, it has a large adsorption capacity. The lithium molecular sieve obtained after lithium exchange is a relatively ideal adsorbent with a large nitrogen-oxygen separation coefficient and nitrogen adsorption capacity. However, after granulation with binders such as kaolin and attapulgite, the adsorption capacity of the granular molecular sieve is reduced, which is not conducive to the adsorption and separation of gases such as water, carbon dioxide, and nitrogen.

[0004] By using alkaline solutions such as sodium hydroxide and potassium hydroxide as crystallization solutions, and water glass and activated silicon as silicon sources, active binders such as kaolin in molecular sieves can be converted into binder-free molecular sieves with adsorption properties.

[0005] Chinese patent CN1234782A discloses a method for producing LSX zeolite particles with low inert binder content. This patent utilizes LSX powder and a zeolite-forming binder, which are then shaped, dried, and calcined. The mixture of sodium hydroxide and potassium hydroxide is then crystallized at 95°C for 3-24 hours to prepare a binder-free molecular sieve containing a large amount of type A molecular sieve, with the binder mainly converted into type A molecular sieve.

[0006] Chinese patent CN101524637A discloses a method for preparing a binder-free adsorbent rich in LSX molecular sieves. This patent uses NaLSX as the active component and kaolin-like substances as binders. The process involves adding an alkali source and a silicon source (optional) for molding and calcination. Crystallization is mainly achieved by adding sodium hydroxide alkali solution, which converts the kaolin binder into X-type zeolite. The product has a high silicon-to-alumina ratio.

[0007] Chinese patent CN102513059A discloses a method for preparing binder-free 13X molecular sieves. This patent involves mixing 13X molecular sieve powder with hydrous kaolin and attapulgite clays, granulating, sieving, and high-temperature calcining. The calcined product is then immersed in a sodium hydroxide and silica-sodium silicate mixed solution for crystallization. After washing, drying, and high-temperature calcination, binder-free 13X molecular sieves are obtained. The main method involves adding a silicon source to convert kaolin into an X-type molecular sieve.

[0008] The shortcoming of the existing technology is that, in order to shape the molecular sieves into granules or spheres during preparation, a binder is required. In subsequent use, the material properties of the binder will affect the mesoporous structure, thereby reducing its ability to adsorb nitrogen. Summary of the Invention

[0009] The purpose of this invention is to provide a binder-free Li-LSX molecular sieve, its preparation method and uses. It does not use a binder to assist in molding, and the prepared binder-free Li-LSX molecular sieve has a high nitrogen adsorption capacity.

[0010] To achieve the above objectives, the present invention provides a method for preparing binder-free Li-LSX molecular sieves, comprising the following steps:

[0011] (1) Ingredients: Kaolin and LSX molecular sieve powder are mixed; the LSX molecular sieve is NaKLSX molecular sieve with a silicon-aluminum molar ratio of 1.0; the mixing ratio is that the LSX molecular sieve powder accounts for 85-90% of the total weight of the mixture and the kaolin accounts for 10-15% of the total weight of the mixture.

[0012] (2) Shaping: Use a sugar coating machine to form spherical shapes of 0.4-3mm;

[0013] (3) One-time drying and roasting: The shaped material is dried at low temperature and then roasted at high temperature;

[0014] (4) Material saturates with water: After roasting, the material is placed in the air to saturate with water; this avoids the rapid water absorption and cracking caused by placing it directly in the alkaline solution.

[0015] (5) Alkali treatment: The material after water absorption is put into a mixed alkaline solution of sodium hydroxide and potassium hydroxide, and first undergoes low-temperature aging treatment, followed by high-temperature crystallization treatment; in the mixed alkaline solution, the molar ratio of sodium ions to total sodium and potassium ions is 0.72-0.78; the ratio of the total number of moles of water to the total number of moles of sodium and potassium ions is 15.5-18.5; the ratio of the total number of moles of sodium and potassium ions to the number of moles of silicon oxide in kaolin is 3.5-5;

[0016] (6) Lithium ion exchange and secondary drying and calcination: After washing the alkalized product, lithium ion exchange is performed using lithium salt to replace sodium potassium ions, and then secondary drying and calcination is performed to obtain the target product, binder-free Li-LSX molecular sieve.

[0017] Furthermore, in steps (3) and (6), the first drying and calcination and the second drying and calcination are performed by drying the molecular sieve at 100-150℃ and then calcining it at 600-650℃ for 2-5 hours.

[0018] Furthermore, in step (5), the aging temperature is 40-70℃, the aging time is 6-20h, the crystallization temperature is 70-95℃, and the crystallization time is 1-4h.

[0019] Furthermore, lithium-ion exchange is performed using an aqueous solution of lithium salt, with a lithium-ion concentration of 2-2.5 mol / L, an exchange temperature of 80-90℃, a liquid-to-solid ratio of 10:1, and an exchange time of 8-12 hours. The preferred lithium salt is lithium chloride.

[0020] The binder-free Li-LSX molecular sieve prepared by the above method can be used as an adsorbent in the oxygen production field. The prepared lithium-exchange-treated binder-free Li-LSX molecular sieve product exhibits a water adsorption capacity of 32-33.5% at 25℃ and 50% relative humidity, and a nitrogen adsorption capacity >28 mL / g at 25℃. The advantages of this invention are: compared with conventional technologies, this invention uses sodium-potassium alkali solution to convert kaolin into a high-purity, high-capacity binder-free Li-LSX molecular sieve, avoiding the adverse effects of binders. Before conversion, kaolin itself can act as a binder; after conversion, kaolin is transformed into LSX molecular sieve, thus achieving the technical effect of being binder-free. In particular, after lithium-ion exchange, the Li-LSX molecular sieve maintains a spherical morphology and can be used as an N2 adsorbent with a nitrogen adsorption capacity >28 mL / g, significantly reducing oxygen production costs. Attached Figure Description

[0021] Figure 1 XRD pattern of NaKLSX molecular sieve raw powder and kaolin after conversion into LSX type molecular sieve.

[0022] Figure 2 The nitrogen adsorption capacity of converted Li-LSX molecular sieves at 25℃ and different pressures. Detailed Implementation

[0023] In this embodiment, the nitrogen adsorption capacity of the sample was detected using a Mc3020 adsorption instrument; the water absorption capacity of the molecular sieve was detected according to the national standard GB / T-6287.

[0024] Example 1

[0025] 1.2 kg of kaolin (SiO2 content 34%) and 8.8 kg of NaKLSX molecular sieve powder were mixed evenly. The molar ratio of silicon to aluminum in the NaKLSX molecular sieve was 1.0 (i.e., the molar ratio of SiO2 / Al2O3 was 2). The mixture was pelletized into 0.4-3 mm spherical shapes using a sugar coating machine. The pellets were dried at 120℃ for 8-12 h, calcined at 650℃ for 2 h, and exposed to air for 36-48 h to absorb water. The purpose of saturation water absorption was to prevent the spherical material from being placed directly in the alkaline solution, which would cause the spherical shape to absorb water rapidly and crack. This ensured that the final product was a well-formed granular material. Subsequently, a mixed solution was prepared by mixing 1.5 kg of sodium hydroxide, 0.81 kg of potassium hydroxide, and 8.18 L of water and cooled to room temperature. 10 kg of NaKLSX molecular sieve beads, saturated with water, were added to the mixed solution. At this point, the silica and aluminum content in the kaolin of the mixed solution and the NaKLSX molecular sieve beads met the following conditions: After calcination, the total mixed solution of silica, sodium hydroxide alkali solution, and potassium hydroxide alkali solution in the kaolin met the following conditions: n(Na + ) / n(Na + +K + ) is 0.72; n(H2O) / n(Na + +K + ) is 17.5; n(Na + +K + The SiO2 / n ratio is 3.8. After aging at 50℃ for 15 hours and crystallizing at 90℃ for 4 hours, followed by washing and drying, sample 1-1 was obtained. Sample 1-1 showed a water adsorption capacity of 32% at 25℃ and 50% relative humidity. Sample 1-2 was obtained after one exchange with 2.1 mol / L lithium chloride solution at a liquid-to-solid ratio of 10 and exchange conditions of 90℃ / 8 hours. Sample 1-2 showed a water adsorption capacity of 33.7% at 25℃ and 50% relative humidity; and a nitrogen adsorption capacity of 28.2-28.7 mL / g at 25℃ and 1 bar pressure.

[0026] Based on Example 1 above, only the amounts of LSX molecular sieve powder and kaolin were changed, and the target product sample was tested. The results are as follows:

[0027]

[0028] As shown in the table above, the mixing ratio is 85-90% LSX molecular sieve powder and 10-15% kaolin. When the LSX molecular sieve content is below 85%, the target product has a low N2 adsorption capacity. When the LSX molecular sieve content exceeds 90%, it is in powder form and cannot become a granular adsorbent. Although it has a certain adsorption capacity for N2, it cannot flow well in the adsorption device (the airflow carries away the powder, causing loss), making it difficult to install in the adsorption device.

[0029] Based on Example 1 above, only the molar ratio of water to total sodium and potassium ions was changed, and the target product sample was tested. The results are as follows:

[0030] <![CDATA[n(H2O) / n(Na + +K + )]]> Topological structure 15 LSX+SOD impurities 15.5 LSX Pure Phase 16.5 LSX Pure Phase 17.5 LSX Pure Phase 18.5 LSX Pure Phase 19 LSX+A type hetero crystals

[0031] As shown in the table above, when the molar ratio of water to total sodium and potassium ions is 15.5-18.5, the product is the pure LSX phase; when the molar ratio of water to total sodium and potassium ions is below 15.5, the target product contains SOD impurities. When the molar ratio of water to total sodium and potassium ions is above 18.5, the target product contains type A impurities.

[0032] Based on Example 1 above, only the molar ratio of total sodium and potassium ions to silica in kaolin was changed, and the target product sample was tested. The results are as follows:

[0033] <![CDATA[n(Na + +K + ) / n(SiO2)]]> Topological structure 3 LSX+A type hetero crystals 3.5 LSX Pure Phase 3.8 LSX Pure Phase 4.5 LSX Pure Phase 5 LSX Pure Phase 5.5 LSX+SOD impurities

[0034] As shown in the table above, when the molar ratio of total sodium and potassium ions to silica in kaolin is 3.5-5, the product is the pure LSX phase; when the molar ratio of total sodium and potassium ions to silica in kaolin is less than 3.5, the target product contains type A impurities. When the molar ratio of water to total sodium and potassium ions is greater than 5, the target product contains SOD impurities.

[0035] Based on Example 1 above, only the molar ratio of sodium ions to total sodium-potassium ions was changed, and the target product sample was tested. The results are as follows:

[0036] <![CDATA[n(Na + ) / n(In + +K + )]]> Topological structure 0.65 LSX+SOD impurities+NaP impurities 0.7 LSX+SOD impurities 0.72 LSX Pure Phase 0.75 LSX Pure Phase 0.78 LSX Pure Phase 0.8 LSX+A type hetero crystals 0.85 LSX+A type hetero crystals

[0037] As shown in the table above, when the molar ratio of sodium ions to total sodium-potassium ions is 0.72-0.78, the product is the pure LSX phase; when the molar ratio of sodium ions to total sodium-potassium ions is below 0.72, the target product contains SOD and NaP impurities. When the molar ratio of sodium ions to total sodium-potassium ions is above 0.78, the target product contains type A impurities.

[0038] Example 2

[0039] 1.2 kg of kaolin (SiO2 content 34%) and 8.8 kg of NaKLSX molecular sieve powder (silicon-to-aluminum molar ratio 1.0) were mixed evenly, and then pelletized into 0.4-3 mm spheres using a sugar-coating machine. The pellets were dried at 120℃ for 8-12 hours, calcined at 600℃ for 3 hours, and then exposed to air for 36-48 hours to absorb water. A mixed solution was prepared by mixing 1.65 kg of sodium hydroxide, 0.81 kg of potassium hydroxide, and 8.78 L of water and cooled to room temperature. 10 kg of the saturated NaKLSX molecular sieve pellets were added to the mixed solution. At this point, the silicon and aluminum content of the kaolin in the mixed solution and the NaKLSX molecular sieve pellets met the following conditions: the silicon and aluminum oxide content of the kaolin after calcination, and the total mixed solution of sodium hydroxide and potassium hydroxide solutions met the following conditions: n(Na + ) / n(Na + +K + ) is 0.74; n(H2O) / n(Na + +K + ) is 17.5; n(Na + +K + The SiO2 / n ratio is 4.1. After aging at 40℃ for 20 h and crystallizing at 90℃ for 4 h, followed by washing and drying, sample 2-1 was obtained. Sample 2-1 showed a water adsorption capacity of 31.5% at 25℃ and 50% relative humidity. Sample 2-2 was obtained after one exchange with 2.1 mol / L lithium chloride solution at a liquid-to-solid ratio of 10 and exchange conditions of 90℃ / 8 h. Sample 2-2 showed a water adsorption capacity of 33.2% at 25℃ and 50% relative humidity; and a nitrogen adsorption capacity of 28.1-28.5 mL / g at 25℃ and 1 bar pressure.

[0040] Example 3

[0041] 1.2 kg of kaolin (SiO2 content 34%) and 8.8 kg of NaKLSX molecular sieve (silicon-to-aluminum molar ratio 1.0) powder were mixed evenly, and then pelletized into 0.4-3 mm spheres using a sugar-coating machine. The pellets were dried at 120℃ for 8-12 hours, calcined at 630℃ for 2.5 hours, and then exposed to air for 36-48 hours to absorb saturated water. A mixed solution was prepared by mixing 1.84 kg of sodium hydroxide, 0.81 kg of potassium hydroxide, and 9.52 L of water and cooled to room temperature. 100 g of the saturated NaKLSX molecular sieve pellets were added to the mixed solution. At this point, the silicon and aluminum content in the kaolin of the mixed solution and the NaKLSX molecular sieve pellets met the following conditions: the silicon and aluminum oxide content in the kaolin after calcination, and the total mixed solution of sodium hydroxide and potassium hydroxide alkaline solutions met the following conditions: n(Na + ) / n(Na + +K +) is 0.76; n(H2O) / n(Na + +K + ) is 17.5; n(Na + +K + The SiO2 / n ratio is 4.4. After aging at 60℃ for 12 hours and crystallizing at 90℃ for 4 hours, followed by washing and drying, sample 3-1 was obtained. Sample 3-1 showed a water adsorption capacity of 31% at 25℃ and 50% relative humidity. Sample 3-2 was obtained after one exchange with 2.1 mol / L lithium chloride solution at a liquid-to-solid ratio of 10 and exchange conditions of 90℃ / 8 hours. Sample 3-2 showed a water adsorption capacity of 33% at 25℃ and 50% relative humidity; and a nitrogen adsorption capacity of 28.0-28.4 mL / g at 25℃ and 1 bar pressure.

[0042] The prepared Li-LSX was used to produce oxygen from the air and to separate oxygen and nitrogen by adsorbing and removing nitrogen. The separation coefficients of oxygen and nitrogen and the amount of nitrogen adsorbed were verified by varying the lithium ion concentration. The experimental data are shown in the table below:

[0043] Serial Number Lithium ion concentration (mol / L) Lithium exchange rate (%) <![CDATA[N2 adsorption capacity (mL / g)]]> 1 1.0 90.1 23.6 2 1.5 94.32 25.3 3 1.8 97.65 26.5 4 2.0 99.91 28.2 5 2.1 99.94 28.7 6 2.2 99.93 28.6 7 2.3 99.91 28.3 8 2.4 99.85 28.2 9 2.5 99.63 28 10 2.6 98.74 27.5 11 2.7 97.7 26.6 12 2.8 96.5 26 13 3.0 94.38 25.5

[0044] The data in the table above indicate that the lithium-containing standard solution used for lithium exchange has a concentration of 2.0-2.5 mol / L, resulting in a high degree of lithium exchange and an N2 adsorption capacity ≥28 ml / g. Ion exchange is a dynamic and reversible process; if the lithium concentration is too low, the exchange will be incomplete, while if the lithium concentration is too high, the lithium ions will undergo a reversible conversion during exchange. Therefore, the preferred lithium ion concentration in the lithium-containing solution used for lithium exchange is 2.0-2.5 mol / L.

[0045] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. A method for preparing binder-free Li-LSX molecular sieves, characterized in that... Includes the following steps: (1) Ingredients: Kaolin and LSX molecular sieve powder are mixed; the LSX molecular sieve is NaKLSX molecular sieve with a silicon-to-aluminum molar ratio of 1.0; the mixing ratio is that the LSX molecular sieve powder accounts for 85-90% of the total weight of the mixture and the kaolin accounts for 10-15% of the total weight of the mixture. (2) Shaping: Use a sugar coating machine to form spherical shapes of 0.4-3mm; (3) First drying and roasting: The shaped material is dried at low temperature and then roasted at high temperature; (4) Material saturates with water: After roasting, the material is placed in the air to allow it to absorb water to its full capacity; (5) Alkali treatment: The material after water absorption is put into a mixed alkaline solution of sodium hydroxide and potassium hydroxide, and first undergoes low-temperature aging treatment, and then high-temperature crystallization treatment; in the mixed alkaline solution, the molar ratio of sodium ions to total sodium and potassium ions is 0.72-0.78; the ratio of the total number of moles of water to the total number of moles of sodium and potassium ions is 15.5-18.5; the ratio of the total number of moles of sodium and potassium ions to the number of moles of silicon oxide in kaolin is 3.5-5; (6) Lithium ion exchange and secondary drying and calcination: After washing the alkalized product, lithium ion exchange is performed using lithium salt to replace sodium and potassium ions, and then secondary drying and calcination is performed to obtain the target product binder-free Li-LSX molecular sieve.

2. The method for preparing a binderless Li-LSX molecular sieve according to claim 1, characterized in that... In steps (3) and (6), the first drying and calcination and the second drying and calcination are to dry the molecular sieve at 100-150℃ and then calcinate it at 600-650℃ for 2-5 hours.

3. The method for preparing a binderless Li-LSX molecular sieve according to claim 1, characterized in that... In step (5), the aging temperature is 40-70℃, the aging time is 6-20h, the crystallization temperature is 70-95℃, and the crystallization time is 1-4h.

4. The method for preparing a binderless Li-LSX molecular sieve according to claim 1, characterized in that... The lithium-ion exchange is carried out using an aqueous solution of lithium salt, with a lithium-ion concentration of 2-2.5 mol / L, an exchange temperature of 80-90℃, a liquid-to-solid ratio of 10:1, and an exchange time of 8-12 h.

5. The method for preparing a binderless Li-LSX molecular sieve according to claim 4, characterized in that... The lithium salt is lithium chloride.

6. A binder-free Li-LSX molecular sieve prepared by the method according to any one of claims 1-5.

7. The use of the binder-free Li-LSX molecular sieve according to claim 6, characterized in that: It is used as an adsorbent in the field of oxygen production.

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