Agca-lsx molecular sieve material, preparation method and application thereof

Abstract

The application discloses an AgCa-LSX molecular sieve material, a preparation method and application thereof. The method uses CaCl2 and AgNO3 as cation exchange agents, modifies Li-LSX molecular sieve by adopting a solution ion exchange method, and obtains the AgCa-LSX molecular sieve by a one-step method. The synthesis process is simple, the hydrogen adsorption performance of the prepared molecular sieve material is excellent, the price is low, under the condition of the same adsorption capacity, the price of the molecular sieve adsorbent is one third of that of PdO, the production cost is reduced, the molecular sieve adsorbent can replace PdO and be applied to all special steel cylinders in all links of LNG (liquefied natural gas) transportation, storage and use, and has a wide market application prospect.

Description

Technical Field

[0001] This invention belongs to the field of adsorbent materials, and relates to an AgCa-LSX molecular sieve material, its preparation method, and its application. Background Technology

[0002] Due to its excellent thermal insulation properties, high-vacuum multilayer insulation has been widely used in cryogenic storage tanks. However, problems such as reduced interlayer vacuum and deteriorated insulation performance caused by leakage and venting seriously affect the service life of cryogenic storage tanks. Therefore, to ensure a stable and good high vacuum in the interlayer, it is necessary to select a suitable adsorbent. Cryogenic insulated storage tanks often use 5A molecular sieves or activated carbon as interlayer adsorbents, which readily adsorb N2 and O2, but their adsorption capacity for hydrogen at liquid nitrogen temperatures is very small, which cannot meet the needs of practical applications. Hydrogen is the main cause of the decrease in interlayer vacuum. PdO powder has a good adsorption capacity for hydrogen and is currently a widely used adsorbent material by domestic LNG cylinder manufacturers. However, its high price and large fluctuations due to market influences severely restrict its large-scale application. Moreover, its adsorption capacity and adsorption rate are not high, and the exothermic reaction process between PdO and H2, which generates sparks and is easily combustible, are also fatal drawbacks. Therefore, it is necessary to find a new material to replace PdO for use in high-vacuum multilayer insulated storage tanks.

[0003] Low silica-to-alumina ratio (LSX) molecular sieves have a low silica-to-alumina ratio and a high number of anions in their framework. Through cation exchange, the pore size, pore volume, and internal electric field of the molecular sieve can be altered, thereby changing its adsorption properties. The ease of cation exchange in molecular sieve materials is mainly determined by both charge intensity and ionic radius; the smaller the charge intensity and ionic radius, the easier the exchange, with charge intensity being the dominant factor. 2+ Although the radius is larger than Li + However, its charge intensity is low, making it easier to exchange. Ag + As a monovalent equilibrium cation, it possesses a 3d empty orbital structure, readily forming π-complexes with adsorbates, thus facilitating gas adsorption. The preparation of molecular sieve materials exhibiting excellent hydrogen adsorption performance under high vacuum conditions via ion exchange is of great practical significance. Summary of the Invention

[0004] The purpose of this invention is to provide an AgCa-LSX molecular sieve material, its preparation method, and its application.

[0005] The technical solution to achieve the purpose of this invention is as follows:

[0006] The preparation method of AgCa-LSX molecular sieve material, with specific steps as follows:

[0007] Step 1: Dissolve NaOH, KOH and Al(OH)3 in water, heat in a water bath to 45±5 ℃, then add Na2SiO3·9H2O under stirring, stir until a sol is formed and then age, then heat to 90±10 ℃, stir evenly and let stand to crystallize, filter after the reaction is complete, wash with water and vacuum dry to obtain LSX powder.

[0008] Step 2: Add the heated and activated LSX powder to a LiCl solution with pH=9±0.5, sonicate to dissolve it, heat in a water bath at 90±10℃ and stir to carry out the exchange reaction. After the reaction is completed, filter, wash the precipitate, add the precipitate to a LiCl solution with pH=9±0.5, repeat the above exchange reaction steps, and vacuum dry to obtain Li-LSX powder.

[0009] Step 3: Add Li-LSX powder to a mixed solution of CaCl2 and AgNO3, sonicate to dissolve, heat in a water bath at 90±10℃ and stir to carry out the exchange reaction. After the reaction is completed, filter, wash the precipitate, vacuum dry, and calcine at 200±10℃ for 1~2 h under a nitrogen atmosphere, then at 400±10℃ for 2~3 h to obtain AgCa-LSX molecular sieve. Alternatively, add the washed precipitate to a mixed solution of CaCl2 and AgNO3, repeat the above exchange reaction step 1~2 times, and then vacuum dry and calcine to obtain AgCa-LSX molecular sieve.

[0010] Preferably, in step 1, the molar ratio of NaOH, KOH, Al(OH)3, and Na2SiO3·9H2O is 1:1:0.7:0.7.

[0011] Preferably, in step 1, the aging time is 24 hours and the crystallization time is 4 hours.

[0012] Preferably, in step 2, the heating activation method of LSX powder is as follows: the dried LSX powder is placed in a tube furnace and heated to 450 °C at a heating rate of 2 °C / min under a nitrogen atmosphere, and activated for 4 h.

[0013] Preferably, in step 2, the mass ratio of LSX powder to LiCl is 1:5~8.

[0014] Preferably, in step 2, the number of repetitions is 5.

[0015] Preferably, in step 3, the mass ratio of Li-LSX powder, CaCl2, and AgNO3 is 1:2.2:1.4.

[0016] Preferably, in steps 1, 2, or 3, the vacuum drying temperature is 50~60 ℃ and the drying time is 6~12 h.

[0017] The present invention also provides AgCa-LSX molecular sieves prepared by the above preparation method.

[0018] Furthermore, the present invention provides the application of the above-mentioned AgCa-LSX molecular sieve as an H2 adsorbent in a high-vacuum multilayer insulated storage tank.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) The synthesis process of this invention is simple and easy to operate. The cost of the AgCa-LSX molecular sieve to adsorb the same volume of hydrogen is less than one-third of the cost of PdO adsorbent, which significantly reduces the cost. It can replace PdO in all special steel cylinders used in the transportation, storage and use of LNG liquefied natural gas, and has broad market application prospects.

[0021] (2) The preparation cost and performance of the AgCa-LSX molecular sieve of the present invention can be customized by adjusting the calcium-silver exchange degree. Attached Figure Description

[0022] Figure 1 This is a picture of an AgCa-LSX molecular sieve.

[0023] Figure 2 These are the hydrogen adsorption-desorption isotherms of PdO molecular sieves.

[0024] Figure 3 This is the hydrogen adsorption-desorption isotherm of the AgCa-LSX molecular sieve synthesized in Example 2.

[0025] Figure 4 These are hydrogen adsorption isotherms of AgCa-LSX molecular sieves at different exchange rates. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0027] Example 1

[0028] Weigh 17.1 g NaOH, 26.6 g KOH and 23.2 g Al(OH)3 and dissolve them in 200 ml deionized water. Stir rapidly for 30 min to form a homogeneous solution. Transfer the solution to a 500 ml three-necked flask and heat it in a water bath to 45 °C. Add 84.7 g Na2SiO3·9H2O under magnetic stirring. After a sol is formed, age it for 24 h, raise the temperature to 90 °C and stir for 2 h. Then, allow it to crystallize at this temperature for 4 h. After the reaction is complete, filter it and wash it with deionized water until the pH is <9. Dry it in a vacuum drying oven at 60 °C for 12 h to obtain LSX powder.

[0029] The dried LSX powder was activated in a tube furnace under a nitrogen atmosphere at a heating rate of 2 °C / min, and held at 450 °C for 4 h. 24.16 g of LiCl·H₂O was weighed and dissolved in 100 ml of deionized water. A certain amount of LiOH was added to adjust the pH to 9, and the solution was stirred until fully dissolved to prepare a LiCl solution. 4 g of the activated LSX powder was added and sonicated to dissolve. The solution was heated in a water bath to 90 °C and magnetically stirred for 3 h. The solution was then filtered, washed, and the washed sample was added back to the mixed solution. This process was repeated 5 times. The sample was then dried in a vacuum drying oven to obtain Li-LSX powder.

[0030] Weigh 11.1 g CaCl2 and 6.8 g AgNO3 and dissolve them in 100 ml deionized water. Stir until fully dissolved, add 5 g Li-LSX powder and sonicate until dissolved. Heat in a water bath to 90 ℃ and stir magnetically for 2 h. Filter, wash the precipitate, dry in a vacuum drying oven, and then transfer to a tube furnace for activation. Under a nitrogen atmosphere, the heating rate is 2 ℃ / min, and the temperature is maintained at 200 ℃ for 1 h and 400 ℃ for 2 h. After cooling to room temperature, AgCa-LSX-1 molecular sieve is obtained.

[0031] Example 2

[0032] Weigh 17.1 g NaOH, 26.6 g KOH and 23.2 g Al(OH)3 and dissolve them in 200 ml deionized water. Stir rapidly for 30 min to form a homogeneous solution. Transfer the solution to a 500 ml three-necked flask and heat it in a water bath to 45 °C. Add 84.7 g Na2SiO3·9H2O under magnetic stirring. After the sol is formed, age it for 24 h, raise the temperature to 90 °C and stir for 2 h. Then let it stand at this temperature for crystallization for 4 h. After the reaction is complete, filter it and wash it with deionized water until the pH is <9. Dry it in a vacuum drying oven at 60 °C for 12 h to obtain LSX powder.

[0033] The dried LSX powder was activated in a tube furnace under a nitrogen atmosphere at a heating rate of 2 °C / min, and held at 450 °C for 4 h. 24.16 g of LiCl·H₂O was weighed and dissolved in 100 ml of deionized water. A certain amount of LiOH was added to adjust the pH to 9, and the solution was stirred until fully dissolved to prepare a LiCl solution. 4 g of the activated LSX powder was added and sonicated to dissolve. The solution was heated in a water bath to 90 °C and magnetically stirred for 3 h. The solution was then filtered, washed, and the washed sample was added back to the mixed solution. This process was repeated 5 times. The sample was then dried in a vacuum drying oven to obtain Li-LSX powder.

[0034] Weigh 11.1 g CaCl2 and 6.8 g AgNO3 and dissolve them in 100 ml deionized water. Stir until fully dissolved, add 5 g Li-LSX powder and sonicate until dissolved. Heat in a water bath to 90 ℃ and stir magnetically for 2 h. Filter and wash the precipitate. Add the washed sample back to the mixed solution and repeat the above process once. Dry the sample in a vacuum drying oven and then transfer it to a tube furnace for activation. Under a nitrogen atmosphere, the heating rate is 2 ℃ / min. Hold at 200 ℃ for 1 h and at 400 ℃ for 2 h. After cooling to room temperature, AgCa-LSX-2 molecular sieve is obtained.

[0035] Example 3

[0036] Weigh 17.1 g NaOH, 26.6 g KOH and 23.2 g Al(OH)3 and dissolve them in 200 ml deionized water. Stir rapidly for 30 min to form a homogeneous solution. Transfer the solution to a 500 ml three-necked flask and heat it in a water bath to 45 °C. Add 84.7 g Na2SiO3·9H2O under magnetic stirring. After the sol is formed, age it for 24 h, raise the temperature to 90 °C and stir for 2 h. Then let it stand at this temperature for crystallization for 4 h. After the reaction is complete, filter it and wash it with deionized water until the pH is <9. Dry it in a vacuum drying oven at 60 °C for 12 h to obtain LSX powder.

[0037] The dried LSX powder was activated in a tube furnace under a nitrogen atmosphere at a heating rate of 2 °C / min, and held at 450 °C for 4 h. 24.16 g of LiCl·H₂O was weighed and dissolved in 100 ml of deionized water. A certain amount of LiOH was added to adjust the pH to 9, and the solution was stirred until fully dissolved to prepare a LiCl solution. 4 g of the activated LSX powder was added and sonicated to dissolve. The solution was heated in a water bath to 90 °C and magnetically stirred for 3 h. The solution was then filtered, washed, and the washed sample was added back to the mixed solution. This process was repeated 5 times. The sample was then dried in a vacuum drying oven to obtain Li-LSX powder.

[0038] Weigh 11.1 g CaCl2 and 6.8 g AgNO3 and dissolve them in 100 ml deionized water. Stir until fully dissolved, add 5 g Li-LSX powder and sonicate until dissolved. Heat in a water bath to 90 ℃ and stir magnetically for 2 h. Filter and wash the precipitate. Add the washed sample back to the mixed solution and repeat the above process twice. Dry the sample in a vacuum drying oven and then transfer it to a tube furnace for activation. Under a nitrogen atmosphere, the heating rate is 2 ℃ / min. Hold at 200 ℃ for 1 h and at 400 ℃ for 2 h. After cooling to room temperature, AgCa-LSX-3 molecular sieve is obtained.

[0039] Comparative Example 1

[0040] Weigh 17.1 g NaOH, 26.6 g KOH and 23.2 g Al(OH)3 and dissolve them in 200 ml deionized water. Stir rapidly for 30 min to form a homogeneous solution. Transfer the solution to a 500 ml three-necked flask and heat it in a water bath to 45 °C. Add 84.7 g Na2SiO3·9H2O under magnetic stirring. After the sol is formed, age it for 24 h, raise the temperature to 90 °C and stir for 2 h. Then let it stand at this temperature for crystallization for 4 h. After the reaction is complete, filter it and wash it with deionized water until the pH is <9. Dry it in a vacuum drying oven at 60 °C for 12 h to obtain LSX powder.

[0041] The dried LSX powder was activated in a tube furnace under a nitrogen atmosphere at a heating rate of 2 °C / min, and held at 450 °C for 4 h. 24.16 g of LiCl·H₂O was weighed and dissolved in 100 ml of deionized water. A certain amount of LiOH was added to adjust the pH to 9, and the solution was stirred until fully dissolved to prepare a LiCl solution. 4 g of activated LSX powder was added and sonicated to dissolve the solution. The solution was then heated in a water bath to 90 °C and magnetically stirred for 3 h. After filtration and washing, the washed sample was added back to the mixed solution. This process was repeated 5 times. The sample was then dried in a vacuum drying oven to obtain Li-LSX.

[0042] Table 1

[0043]

[0044] Table 1 corresponds to the above three embodiments and one comparative example. Embodiment 1 shows that when the number of exchanges is 1, the Ag in AgCa-LSX-1 obtained is... + The degree of exchange is 11.9%, Ca 2+ The exchange degree is 12.5%, Li + The exchange degree was 75.6%. Example 2 shows that when the number of exchange cycles was 2, the Ag in the obtained AgCa-LSX-2 was... + The exchangeability is 26.1%, Ca 2+ The exchange degree is 26.2%, Li + The degree of exchange was 47.7%. Example 3 shows that when the number of exchange cycles was 3, the Ag in the obtained AgCa-LSX-3 was... + The degree of exchange is 37.4%, Ca 2+ The exchange degree is 40.3%, Li + The degree of exchange was 22.3%. Comparative Example 1 shows that without Ag... + and Ca + Li in exchanged Li-LSX + The commutativity is 100%.

[0045] Figure 1 is a physical diagram of the AgCa-LSX molecular sieve synthesized in the present invention.

[0046] Figure 2 is the hydrogen adsorption-desorption isotherm of PdO molecular sieve. In the relative pressure range of 0.5 < p / p0 < 1, the hydrogen adsorption capacity of PdO increases significantly. At normal temperature and pressure, the saturated adsorption capacity of PdO for H2 reaches 134.2 cm 3 / g.

[0047] Figure 3 is the hydrogen adsorption-desorption isotherm of the AgCa-LSX molecular sieve synthesized in Example 2. In the relative pressure range of 0.8 < p / p0 < 1, the hydrogen adsorption capacity of the AgCa-LSX molecular sieve sample increases significantly. At normal temperature and pressure, the saturated adsorption capacity of AgCa-LSX for H2 reaches 103.4 cm 3 / g.

[0048] Figure 4 is hydrogen adsorption isotherms of AgCa-LSX molecular sieves obtained with different exchange times (corresponding to Examples 1, 2, 3 and Comparative Example 1). It can be seen that after Ag + and Ca 2+ cation exchange, the adsorption performance of the Li-LSX samples is improved compared with that of the pure Li-LSX samples. As the number of exchanges increases, the H2 adsorption capacity of the molecular sieve material gradually increases. When the number of exchanges is 2, the adsorption capacity is the maximum and the effect is the best.

Claims

1. The application of AgCa-LSX molecular sieve as an H2 adsorbent in high-vacuum multilayer insulated storage tanks, characterized in that, The preparation method of AgCa-LSX molecular sieve material, with specific steps as follows: Step 1: Dissolve NaOH, KOH, and Al(OH)3 in water, heat in a water bath to 45±5 ℃, then add Na2SiO3·9H2O under stirring, stir until a sol is formed, and then age. Then raise the temperature to 90±10 ℃, stir evenly, and let it stand to crystallize. After the reaction is complete, filter, wash with water, and vacuum dry to obtain LSX powder. The molar ratio of NaOH, KOH, Al(OH)3, and Na2SiO3·9H2O is 1:1:0.7:0.

7. Step 2: Add the heated and activated LSX powder to a LiCl solution with pH=9±0.5, sonicate to dissolve it, heat in a water bath at 90±10℃ and stir to carry out the exchange reaction. After the reaction is completed, filter, wash the precipitate, add the precipitate to a LiCl solution with pH=9±0.5, repeat the above exchange reaction steps, and vacuum dry to obtain Li-LSX powder. Step 3: Add Li-LSX powder to a mixed solution of CaCl2 and AgNO3, sonicate to dissolve, heat in a water bath at 90±10℃ with stirring to carry out the exchange reaction. After the reaction is completed, filter, wash the precipitate, vacuum dry, and calcine at 200±10℃ for 1~2 h under a nitrogen atmosphere, then at 400±10℃ for 2~3 h to obtain AgCa-LSX molecular sieve. Alternatively, add the washed precipitate to a mixed solution of CaCl2 and AgNO3, repeat the above exchange reaction step twice, and then vacuum dry and calcine to obtain AgCa-LSX molecular sieve. The mass ratio of Li-LSX powder, CaCl2 and AgNO3 is 1:2.2:1.

4.

2. The application according to claim 1, characterized in that, In step 1, the aging time is 24 hours and the crystallization time is 4 hours.

3. The application according to claim 1, characterized in that, In step 2, the heating activation method of LSX powder is as follows: the dried LSX powder is placed in a tube furnace and heated to 450 ℃ at a heating rate of 2 ℃ / min under a nitrogen atmosphere, and activated for 4 h.

4. The application according to claim 1, characterized in that, In step 2, the mass ratio of LSX powder to LiCl is 1:5~8.

5. The application according to claim 1, characterized in that, In step 2, the number of repetitions is 5.

6. The application according to claim 1, characterized in that, In steps 1, 2, or 3, the vacuum drying temperature is 50~60℃ and the drying time is 6~12 h.

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