Composite li-ca-ce-lsx hydrophobic molecular sieves, methods of making and use thereof

Abstract

This invention discloses a composite Li-Ca-Ce-LSX hydrophobic molecular sieve, its preparation method, and its applications. The method further modifies Li-LSX molecular sieves with Ca and Ce, synthesizing the composite Li-Ca-Ce-LSX hydrophobic molecular sieve via an aqueous solution exchange method. The preparation method of this invention is simple, and the obtained composite Li-Ca-Ce-LSX hydrophobic molecular sieve has a particle size of 0.2~0.4 mm, exhibits good crystallinity and adsorption performance, high polarizability, high adsorption capacity for nitrogen and nitrogen-oxygen separation coefficient, and a certain degree of hydrophobicity. This significantly improves the molecular sieve's environmental sensitivity and extends its service life. It can be used as a high-efficiency catalyst, heavy metal ion adsorbent, and concrete additive, with a wide range of applications.

Description

Technical Field

[0001] This invention belongs to the technical field of pressure swing adsorption molecular sieve materials, and relates to a composite Li-Ca-Ce-LSX hydrophobic molecular sieve, its preparation method and its application. Background Technology

[0002] Pressure Swing Adsorption (PSA) boasts advantages such as flexibility, convenience, low investment, low energy consumption, high performance, simple process flow, and high degree of automation. In recent years, it has been widely applied in small- to medium-scale industrial oxygen enrichment applications, and its application has expanded to industries such as wastewater treatment, papermaking, pharmaceuticals, and home healthcare. The core technology of PSA oxygen generation is the adsorbent. The adsorption and separation performance of the adsorbent directly determines the energy consumption, size, and lifespan of the oxygen generation device. Therefore, researching highly efficient oxygen-generating adsorbents remains a core direction in PSA oxygen generation research.

[0003] According to statistics from the international consulting firm TechNavio, the global market size for molecular sieve adsorbents will reach US$2.01 billion by 2023, representing a compound annual growth rate of 6.08% compared to 2018, showing a steady growth trend. In the industrial oxygen production sector, with the vigorous promotion of energy-saving and consumption-reducing technologies and the continuous improvement of environmental protection requirements, the industrial oxygen market will continue to expand, leading to a significant demand for oxygen-generating molecular sieves and creating greater growth potential for molecular sieve adsorbents. Simultaneously, with the improvement of people's living standards, people are paying more attention to their health, and oxygen therapy and oxygen health care, as new technologies for enhancing physical fitness and preventing diseases, are gradually being accepted and promoted. Supported by a large elderly population, people engaged in high-intensity mental labor, and people living in high-altitude areas, the gradual popularization of medical and home oxygen concentrators will create a huge market space for medical and health care oxygen-generating molecular sieves. Furthermore, there are many patients with respiratory diseases and asthma in society. If they experience breathing difficulties at home, timely use of oxygen concentrators can solve the problem of insufficient oxygen. Therefore, the research and development of oxygen-generating molecular sieves is crucial.

[0004] Currently, the commonly used adsorbents for pressure swing adsorption (PSA) oxygen generation are mainly X-type molecular sieves, such as Li-LSX and Ca-LSX molecular sieves. However, they have the following main problems: (1) low oxygen-nitrogen separation coefficient and high energy consumption for the preparation of oxygen per unit; (2) water and carbon dioxide in the environment have a great impact on the performance of the adsorbent; (3) when applied to small portable oxygen generation equipment, the low bulk density of large particles affects the high efficiency of the oxygen generation equipment and the high oxygen concentration. Summary of the Invention

[0005] The purpose of this invention is to provide a composite Li-Ca-Ce-LSX hydrophobic molecular sieve with strong adsorption capacity and a large separation coefficient, its preparation method, and its applications. This invention uses lithium-exchanged low-silica aluminum X-type zeolite molecular sieve (Li-LSX) as raw material, combining forming technology and lithium exchange technology, further modifying it with Ca and Ce, and synthesizing the composite Li-Ca-Ce-LSX hydrophobic molecular sieve using an aqueous solution exchange method. This molecular sieve has higher polarizability and stronger interaction with nitrogen, thus exhibiting a high adsorption capacity and nitrogen-oxygen separation coefficient for nitrogen. Furthermore, it possesses a certain degree of hydrophobicity, improving the molecular sieve's environmental sensitivity and extending its service life.

[0006] The technical solution for achieving the objective of this invention is as follows:

[0007] The preparation method of the composite Li-Ca-Ce-LSX hydrophobic molecular sieve is as follows:

[0008] Step 1, Preparation of Li-Ca-Ce-LSX molecular sieve: According to the molar ratio of Ca, Ce ions to lithium ions 1:1:3~4, CaCl2 solution, CeCl2 solution and Li-LSX molecular sieve powder are mixed evenly, and stirred at a constant temperature of 60~90℃ to carry out ion exchange reaction. After the reaction is completed, the mixture is filtered, washed with water, dried at room temperature, and then the solid is calcined at 350±50℃ for 2~3h to activate and obtain Li-Ca-Ce-LSX molecular sieve.

[0009] Step 2, hydrophobic modification: Li-Ca-Ce-LSX molecular sieve and polydimethylsiloxane were mixed at a mass ratio of 1:1 to 4 using vapor deposition and reacted at 200±25℃ for 4 to 7 hours. After the reaction was completed, the mixture was cooled to room temperature, the product was taken out and dried to obtain Li-Ca-Ce-LSX molecular sieve with a hydrophobic surface.

[0010] Step 3, Preparation of composite Li-Ca-Ce-LSX hydrophobic molecular sieve: The surface hydrophobic Li-Ca-Ce-LSX molecular sieve and attapulgite clay are mixed evenly at a mass ratio of 3 to 5:1, placed in a mechanical pelletizer to form spheres with a particle size of 0.2 to 0.4 mm, dried, and activated at 100 to 150 °C to obtain composite Li-Ca-Ce-LSX hydrophobic molecular sieve.

[0011] Preferably, in step 1, the concentration of the CaCl2 solution or the CeCl2 solution is 0.4 mol / L.

[0012] Preferably, in step 1, the ion exchange reaction is performed 3 times, and the reaction time for each ion exchange reaction is 3 hours.

[0013] Preferably, in step 3, the drying temperature is 100℃ and the drying time is 2-4 hours.

[0014] Preferably, in step 1, the molar ratio of Ca, Ce ions to lithium ions is 1:1:3; in step 2, the mass ratio of Li-Ca-Ce-LSX molecular sieve to polydimethylsiloxane is 1:3; and in step 3, the mass ratio of hydrophobic Li-Ca-Ce-LSX molecular sieve to attapulgite is 3:1.

[0015] In step 1, the Li-LSX molecular sieve is prepared using existing methods, specifically:

[0016] (1) Preparation of LSX molecular sieve: Sodium hydroxide, aluminum hydroxide and deionized water were mixed evenly at a low temperature of 50-100℃, water glass solution was added and stirred for 1-2 hours. After it became a viscous solution, aluminum dioxide, aluminum oxide, sodium phosphate, elemental silicon and elemental sodium were added and stirred at high speed for 2-4 hours. After stirring was stopped, it was allowed to stand and age at 50-70℃ for 6-8 hours, and then crystallized at 80-100℃ for 6-8 hours. The product was filtered, washed and dried at 80-100℃ to obtain LSX molecular sieve, wherein the molar ratio of SiO2:Al2O3 = 5.0-10.0:1 and NaK:Na:Si = 5-10:4-9:1-5;

[0017] (2) Preparation of Li-LSX hydrophobic molecular sieve: The LSX molecular sieve was placed in a muffle furnace and heated to 100℃ in a step of 10℃ / min and held at that temperature for 1-2 h. The temperature was then increased to 400℃ in a step of 10℃ / min and held at that temperature for 1-2 h. The activated LSX molecular sieve was added to an aqueous solution of Li2SO4 at a ratio of 1:10-30. The pH of the solution was then adjusted to 9 using LiOH. The ion exchange reaction was carried out at 80-100℃ for 1-5 h to obtain Li-LSX molecular sieve.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The present invention uses the aqueous solution exchange method to synthesize composite Li-Ca-Ce-LSX hydrophobic molecular sieves. The prepared product has high purity and no impurity phase is generated in the product. Moreover, the process is relatively simple, and the synthesis process is low-cost, short-cycle, and easy to prepare, which improves production efficiency and reduces synthesis energy consumption.

[0020] (2) The composite Li-Ca-Ce-LSX hydrophobic molecular sieve of the present invention has a regular pore structure, a large internal volume, good hydrothermal stability, and a balanced cation charge, and can be applied to various fields. For example, it can be used to prepare high-efficiency catalysts in adsorption and separation; to prepare environmentally friendly catalysts in catalysis, which can simplify the subsequent purification process of the product and achieve zero pollution and zero emissions; in agriculture, it can be used to capture heavy metal ions in the soil, improve the soil, treat agricultural water shortage, and deodorize organic fertilizers; in the building materials industry, adding molecular sieves as an additive to concrete can improve the density and durability of the concrete structure and improve its microstructure.

[0021] (3) This invention increases the adsorption performance of molecular sieves through secondary ion exchange. At the same time, the molecular sieves obtained have hydrophobic properties, small particle size, and large specific surface area, which avoids the molecular sieve from failing due to rapid water absorption during use and greatly extends the service life of the adsorbent. Attached Figure Description

[0022] Figure 1 The TG-DTA curves are for the composite Li-Ca-Ce-LSX hydrophobic molecular sieve.

[0023] Figure 2 The N2 and O2 adsorption isotherms of the composite Li-Ca-Ce-LSX hydrophobic molecular sieve are shown at 25℃ and 1 atm. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings.

[0025] In the following examples, the Li-LSX molecular sieve was prepared by the following steps:

[0026] (1) Preparation of LSX molecular sieve: Sodium hydroxide, aluminum hydroxide, and deionized water were mixed evenly at a low temperature of 80℃, and water glass (30% SiO2, 70% H2O) solution was added and stirred for 2 hours. After becoming a viscous solution, aluminum dioxide, aluminum oxide, sodium phosphate, elemental silicon, and elemental sodium were added, and the mixture was stirred at high speed for 3 hours. After stirring was stopped, the mixture was allowed to age at 60℃ for 6 hours and then crystallized at 80℃ for 6 hours. The product was filtered, washed, and dried at 80℃ to obtain raw LSX molecular sieve powder. The molar ratio was SiO2:Al2O3 = 6.0:1; NaK:Na:Si = 5:4:3.

[0027] (2) Preparation of Li-LSX molecular sieve: The LSX molecular sieve prepared above was placed in a muffle furnace, and the temperature of the muffle furnace was increased to 100℃ in steps of 10℃ / min and held at that temperature for 1-2 hours. Then, the temperature was increased to 400℃ in steps of 10℃ / min and held at that temperature for 1-2 hours. The activated LSX molecular sieve was added to an aqueous solution of Li2SO4, and the pH of the solution was adjusted to 9 using LiOH. The exchange reaction time was 1-5 hours, the reaction temperature was 80-100℃, and the ratio of the mass of the LSX molecular sieve to the volume of the Li2SO4 solution, i.e., the solid-liquid ratio, was selected as 1:10-30 to obtain the Li-LSX molecular sieve.

[0028] Example 1

[0029] (1) Preparation of Li-Ca-Ce-LSX molecular sieve: According to the molar ratio of Ca, Ce ions to lithium ions 1:1:4, 0.4 mol / L CaCl2 solution, 0.4 mol / L CeCl2 solution and Li-LSX molecular sieve powder were mixed evenly and stirred at 80℃. The ion exchange time was 3h each time and the number of exchanges was 3 times. After the reaction was completed, the mixture was filtered, washed with water, dried at room temperature, and then the solid was calcined at 350±50℃ for 3h to activate and obtain Li-Ca-Ce-LSX molecular sieve.

[0030] (2) Hydrophobic modification: Li-Ca-Ce-LSX molecular sieve and polydimethylsiloxane were mixed at a mass ratio of 1:1 by vapor deposition and reacted at 200±25℃ for 6h. After the reaction was completed, the mixture was cooled to room temperature, the product was taken out and dried to obtain hydrophobic Li-Ca-Ce-LSX molecular sieve.

[0031] (3) Preparation of composite Li-Ca-Ce-LSX hydrophobic molecular sieve: The hydrophobic Li-Ca-Ce-LSX molecular sieve and attapulgite clay are mixed evenly at a mass ratio of 5:1 and placed in a mechanical pelletizer to form spheres with a particle size of 0.2-0.4 mm. The spheres are then dried at 100°C for 4 h and activated at 100°C to obtain industrial Li-Ca-Ce-LSX molecular sieve.

[0032] Example 2

[0033] (1) Preparation of Li-Ca-Ce-LSX molecular sieve: According to the molar ratio of Ca, Ce ions to lithium ions 1:1:4, 0.4 mol / L CaCl2 solution, 0.4 mol / L CeCl2 solution and Li-LSX molecular sieve powder were mixed evenly and stirred at 80℃. The ion exchange time was 3h each time and the number of exchanges was 3 times. After the reaction was completed, the mixture was filtered, washed with water, dried at room temperature, and then the solid was calcined at 350±50℃ for 3h to activate and obtain Li-Ca-Ce-LSX molecular sieve.

[0034] (2) Hydrophobic modification: Li-Ca-Ce-LSX molecular sieve and polydimethylsiloxane were mixed at a mass ratio of 1:4 by vapor deposition and reacted at 200±25℃ for 6h. After the reaction was completed, the mixture was cooled to room temperature, the product was taken out and dried to obtain hydrophobic Li-Ca-Ce-LSX molecular sieve.

[0035] (3) Preparation of composite Li-Ca-Ce-LSX hydrophobic molecular sieve: The hydrophobic Li-Ca-Ce-LSX molecular sieve and attapulgite clay are mixed evenly at a mass ratio of 3:1 and placed in a mechanical pelletizer to form spheres with a particle size of 0.2-0.4 mm. The spheres are then dried at 100°C for 4 h and activated at 100°C to obtain industrial Li-Ca-Ce-LSX molecular sieve.

[0036] Example 3

[0037] (1) Preparation of Li-Ca-Ce-LSX molecular sieve: According to the molar ratio of Ca, Ce ions to lithium ions 1:1:3, 0.4 mol / L CaCl2 solution, 0.4 mol / L CeCl2 solution and Li-LSX molecular sieve powder were mixed evenly and stirred at 80℃. The ion exchange time was 3h each time and the number of exchanges was 3 times. After the reaction was completed, the mixture was filtered, washed with water, dried at room temperature, and then calcined at 350±50℃ for 3h to activate and obtain Li-Ca-Ce-LSX molecular sieve.

[0038] (2) Hydrophobic modification: Li-Ca-Ce-LSX molecular sieve and polydimethylsiloxane were mixed at a mass ratio of 1:3 by vapor deposition and reacted at 200±25℃ for 6h. After the reaction was completed, the mixture was cooled to room temperature, the product was taken out and dried to obtain hydrophobic Li-Ca-Ce-LSX molecular sieve.

[0039] (3) Preparation of composite Li-Ca-Ce-LSX hydrophobic molecular sieve: The hydrophobic Li-Ca-Ce-LSX molecular sieve and attapulgite clay are mixed evenly at a mass ratio of 3:1 and placed in a mechanical pelletizer to form spheres with a particle size of 0.2-0.4 mm. The spheres are then dried at 100°C for 4 h and activated at 100°C to obtain industrial Li-Ca-Ce-LSX molecular sieve.

[0040] Example 4

[0041] (1) Preparation of Li-Ca-Ce-LSX molecular sieve: According to the molar ratio of Ca, Ce ions to lithium ions 1:1:4, 0.4 mol / L CaCl2 solution, 0.4 mol / L CeCl2 solution and Li-LSX molecular sieve powder were mixed evenly and placed at 80℃ for constant temperature stirring. The ion exchange time was 3h each time and the number of exchanges was 3 times. After the reaction was completed, the mixture was filtered, washed with water, dried at room temperature, and then the solid was calcined at 350±50℃ for 3h to activate and obtain Li-Ca-Ce-LSX molecular sieve.

[0042] (2) Hydrophobic modification: Li-Ca-Ce-LSX molecular sieve and polydimethylsiloxane were mixed at a mass ratio of 1:2 by vapor deposition and reacted at 200±25℃ for 6h. After the reaction was completed, the mixture was cooled to room temperature, the product was taken out and dried to obtain hydrophobic Li-Ca-Ce-LSX molecular sieve.

[0043] (3) Preparation of composite Li-Ca-Ce-LSX hydrophobic molecular sieve: The hydrophobic Li-Ca-Ce-LSX molecular sieve and attapulgite clay are mixed evenly at a mass ratio of 3:1 and placed in a mechanical pelletizer to form spheres with a particle size of 0.2-0.4 mm. The spheres are then dried at 100°C for 4 h and activated at 100°C to obtain industrial Li-Ca-Ce-LSX molecular sieve.

[0044] Table 1

[0045] Experimental Example <![CDATA[N2 / O2 selectivity]]> Particle size Moisture content Example 1 6.01 0.2-0.4mm 1.2％ Example 2 5.20 0.2-0.4mm 0.96％ Example 3 7.18 0.2-0.4mm 0.95％ Example 4 6.0 0.2-0.4mm 1.0％

[0046] Comparing Examples 1 and 4, it can be seen that increasing the ratio of molecular sieve to attapulgite has little effect on particle size, while decreasing the ratio of molecular sieve to polydimethylsiloxane increases the water content of the molecular sieve. Comparing Examples 2 and 4, it can be seen that increasing the ratio of molecular sieve to polydimethylsiloxane reduces the water content of the molecular sieve and also reduces the N2 / O2 selectivity. After selecting the optimal ratio of molecular sieve to polydimethylsiloxane, the experiment of Example 3 was carried out. Comparing Examples 3 and 4, it can be seen that decreasing the ratio of exchange ions increases the N2 / O2 selectivity.

[0047] In summary, this invention first prepares an LSX molecular sieve, then performs a first Li ion exchange, followed by a second Ca and Ce ion exchange, then applies a hydrophobic coating, and finally controls the spheroid size. By changing the reagent ratios and screening for optimal reaction conditions, a molecular sieve with hydrophobic properties and good performance is prepared. For the most common Li-LSX molecular sieves on the market, this invention further performs a second exchange, using ions with good adsorption properties for exchange modification. Since molecular sieves have a strong polarization effect on water molecules, and increased water molecule content weakens the adsorption performance of the molecular sieve, and water vapor can pulverize the molecular sieve, significantly shortening its lifespan, this invention further hydrophobically treats the molecular sieve to prepare a hydrophobic molecular sieve.

[0048] Through the TG-DTA curve ( Figure 1 As can be seen, the weight loss curves of the composite Li-Ca-Ce-LSX hydrophobic molecular sieves prepared in Examples 1-3 become basically flat after 100℃, with a weight loss rate of 27%. Correspondingly, the DTA curve shows a significant strong exothermic peak at 150℃, indicating structural collapse within the molecular sieve. A weak exothermic peak appears near 450℃, indicating further collapse of the molecular sieve within this temperature range. The experimental results show that the composite Li-Ca-Ce-LSX molecular sieve is not suitable for activation at higher temperatures.

[0049] Depend on Figure 2 It can be seen that, under normal temperature and pressure, the static saturated adsorption capacities of the composite Li-Ca-Ce-LSX hydrophobic molecular sieve for N2 and O2 are 14.00 mL / g and 1.95 mL / g, respectively, with a nitrogen-oxygen separation ratio of 7.18. These data indicate that the nitrogen-oxygen separation ratio can be improved to some extent after secondary exchange and hydrophobic treatment.

Claims

1. A method for preparing composite Li-Ca-Ce-LSX hydrophobic molecular sieves, characterized in that, The specific steps are as follows: Step 1, Preparation of Li-Ca-Ce-LSX molecular sieve: According to the molar ratio of Ca, Ce ions to lithium ions 1:1:3, CaCl2 solution, CeCl2 solution and Li-LSX molecular sieve powder are mixed evenly and stirred at a constant temperature of 60~90℃ to carry out ion exchange reaction. The ion exchange reaction is carried out 3 times, and the reaction time of each ion exchange reaction is 3 h. After the reaction is completed, the mixture is filtered, washed with water, dried at room temperature, and then the solid is calcined at 350±50℃ for 2~3 h to activate and obtain Li-Ca-Ce-LSX molecular sieve. Step 2, hydrophobic modification: Li-Ca-Ce-LSX molecular sieve and polydimethylsiloxane were mixed at a mass ratio of 1:3 by vapor deposition and reacted at 200±25℃ for 4~7 h. After the reaction was completed, the mixture was cooled to room temperature, the product was taken out and dried to obtain Li-Ca-Ce-LSX molecular sieve with hydrophobic surface. Step 3, Preparation of composite Li-Ca-Ce-LSX hydrophobic molecular sieve: The surface hydrophobic Li-Ca-Ce-LSX molecular sieve and attapulgite clay are mixed evenly at a mass ratio of 3:1, placed in a mechanical pelletizer to form spheres with a particle size of 0.2~0.4 mm, dried, and activated at 100~150 ℃ to obtain a composite Li-Ca-Ce-LSX hydrophobic molecular sieve with an N2 / O2 selectivity of 7.18 and a water content of 0.95%. The preparation method of Li-LSX molecular sieve is as follows: (1) Preparation of LSX molecular sieve: At a low temperature of 50~100 ℃, sodium hydroxide, aluminum hydroxide and deionized water are mixed evenly, water glass solution is added, and the mixture is stirred for 1~2 h. After it becomes a viscous solution, aluminum dioxide, aluminum oxide, sodium phosphate, elemental silicon and elemental sodium are added, and the mixture is stirred at high speed for 2~4 h. After stirring is stopped, the mixture is allowed to stand and age at 50~70 ℃ for 6~8 h, and then crystallized at 80~100 ℃ for 6~8 h. The product is filtered, washed, and dried at 80~100 ℃ to obtain LSX molecular sieve, wherein the molar ratio is SiO2:Al2O3=5.0~10.0:1, NaK:Na:Si=5~10:4~9:1~5; (2) Preparation of Li-LSX hydrophobic molecular sieve: The LSX molecular sieve was placed in a muffle furnace and heated to 100 ℃ in a step of 10 ℃ / min and held at that temperature for 1~2 h. The temperature was then increased to 400 ℃ in a step of 10 ℃ / min and held at that temperature for 1~2 h. The activated LSX molecular sieve was added to the aqueous solution of Li2SO4 according to the ratio of LSX molecular sieve mass to Li2SO4 solution volume of 1:10~30. The pH of the solution was then adjusted to 9 using LiOH. The ion exchange reaction was carried out at 80~100 ℃ for 1~5 h to obtain Li-LSX molecular sieve.

2. The preparation method according to claim 1, characterized in that, In step 1, the concentration of the CaCl2 solution or CeCl2 solution is 0.4 mol / L.

3. The preparation method according to claim 1, characterized in that, In step 3, the drying temperature is 100 ℃ and the drying time is 2~4 h.

4. The composite Li-Ca-Ce-LSX hydrophobic molecular sieve prepared by any one of the preparation methods according to claims 1 to 3.

5. The application of the composite Li-Ca-Ce-LSX hydrophobic molecular sieve according to claim 4 in the preparation of adsorption catalysts, heavy metal ion adsorbents, or concrete additives.

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