A pressure swing adsorption molecular sieve and its preparation method

Abstract

The present invention relates to a pressure swing adsorption molecular sieve and a preparation method thereof, belonging to the technical field of adsorbents, and comprising the following steps: adding sodium silicate, sodium aluminate, calcium chloride and sodium titanate into an alkaline solution, stirring and mixing to form a uniform synthesis solution, adding a polymer precursor as a carbon source, carrying out hydrothermal reaction, centrifuging the product to separate solids, and then washing with deionized water; drying the washed product and then roasting to activate the molecular sieve to obtain a 5A pressure swing adsorption molecular sieve. The present invention takes silicon as the basic element, and improves the heat resistance and thermal stability of the molecular sieve by doping a certain amount of titanium, aluminum and carbon. Taking the polymer precursor as the carbon source to realize the adjustment of the pore size and adsorption performance of the molecular sieve. At the same time, the heat resistance and its stability under high temperature and high pressure conditions of the present invention are improved.

Description

Technical Field

[0001] The present invention relates to a pressure swing adsorption molecular sieve and a preparation method thereof, belonging to the technical field of adsorbents. Background Art

[0002] Pressure Swing Adsorption (PSA for short) is a technology that uses an adsorbent to selectively adsorb gas components at different pressures for separation. Molecular sieve is a commonly used adsorbent with a regular microporous structure and a high specific surface area, capable of selective adsorption. During the PSA process, the adsorption capacity of the molecular sieve for specific gas components changes with the pressure, thereby realizing the separation and purification of gases.

[0003] During the pressure swing adsorption process, the gas mixture under high pressure passes through the molecular sieve bed for adsorption. During this process, the molecular sieve selectively adsorbs certain gas molecules, while other gas molecules flow out through the bed. Then, the pressure is reduced to achieve desorption, releasing the gas adsorbed on the molecular sieve for the next round of adsorption process. Through the cyclic adsorption and desorption process, continuous separation and purification of gases can be achieved.

[0004] Pressure swing adsorption molecular sieves are widely used in many industrial applications, such as: preparation of nitrogen and oxygen, purification of hydrogen, biogas upgrading, industrial gas separation, etc. Existing pressure swing adsorption molecular sieves still have disadvantages such as insufficient strength, low yield, and insufficient heat resistance. For example, a preparation method of a pressure swing adsorption molecular sieve adsorbent disclosed in Chinese Patent CN114682234A. The method includes: (1) mixing a molecular sieve raw material with a binder and an auxiliary agent for molding; (2) sequentially performing dealumination and ion exchange post-treatment on the molded adsorbent obtained in step (1); (3) treating the adsorbent obtained in step (2) with an azeotrope of water; (4) drying and calcining the adsorbent obtained in step (3) to obtain a finished adsorbent. The inventive method can obtain a molecular sieve adsorbent with high crystallinity, high strength, and high yield. However, its heat resistance and stability have not been improved. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art and provide a pressure swing adsorption molecular sieve with good heat resistance, stability, and high strength, as well as a preparation method thereof.

[0006] The technical solution adopted by the present invention to solve its technical problems is: a preparation method of a pressure swing adsorption molecular sieve, characterized by comprising the following steps:

[0007] a) Sodium silicate, sodium aluminate, calcium chloride and sodium titanate are added to an alkaline solution and stirred and mixed to form a uniform synthesis solution, where the molar ratio of silicon, aluminum, calcium and titanium is 1﹕0.1 - 0.3﹕0.1 - 0.3﹕0.01 - 0.1;

[0008] b) A polymer precursor as a carbon source is further added to the synthesis solution in step 1), and the addition amount of the polymer precursor is 0.1 - 1.0 moles of carbon per mole of aluminum element;

[0009] c) Hydrothermal reaction is carried out at 80°C - 100°C and 0.12 MPa - 0.15 MPa, and the reaction time is 28 h - 34 h;

[0010] d) After the reaction is completed, the product is centrifuged to separate the solid, and then washed with deionized water;

[0011] e) The washed product is dried and then calcined at a temperature of 300°C - 600°C; to remove the residual lattice water and to achieve the decomposition of the carbon source and carbon doping to activate the molecular sieve, thus obtaining the 5A pressure swing adsorption molecular sieve.

[0012] The present invention is based on silicon as the basic element, and improves the heat resistance and thermal stability of the molecular sieve by doping a certain amount of titanium, aluminum and carbon. Among them, the polymer precursor is used as the carbon source, and by adjusting the chemical structure and heat treatment conditions of the polymer precursor, the content and distribution of the carbon source can be precisely controlled, thereby regulating the pore size and adsorption performance of the molecular sieve. The polymer precursor has higher thermal stability compared to traditional carbon sources such as glucose. This enables the polymer precursor to maintain a relatively stable structure during the decomposition of the carbon source and the carbon doping process at high temperatures, making it easier to control the release and diffusion rate of the carbon source, contributing to the formation of uniformly dispersed carbon doping, and then changing the pore structure and reducing the thermal expansion coefficient, thereby improving the heat resistance of this molecular sieve and its stability under high temperature and high pressure conditions.

[0013] In the specific preparation process, the present invention first adds sodium silicate, sodium aluminate, calcium chloride and sodium titanate to an alkaline solution and stirs and mixes, and then adds a polymer precursor as a carbon source thereto. Sodium silicate, sodium aluminate, calcium chloride and sodium titanate are first added to an alkaline solution and stirred and mixed to form a uniform solution system. This helps to ensure that the various raw materials are fully mixed, and promotes uniform dispersion between the reactants, improves the uniformity of the reaction, and is conducive to the production of uniformly distributed molecular sieves; then adding a polymer precursor as a carbon source can better control the decomposition and carbon doping process of the carbon source. This is because the addition of the polymer precursor as an independent step can form a clearer interface between the reactants, which helps to control the release rate and diffusion rate of the carbon source, thereby affecting the pore size and surface properties of the final molecular sieve. In addition, adding the polymer precursor as the last feed can reduce its exposure in the early reaction, help protect the integrity and activity of the carbon source, and ensure that it can be effectively carbon-doped in the final product.

[0014] The present invention adjusts the hydrothermal reaction process parameters to promote the growth and formation of crystals so as to control the crystal morphology of the molecular sieve. The suitable hydrothermal conditions of the present invention promote the formation and expansion of pores, increase the adsorption surface area and pore volume of the molecular sieve, and improve the adsorption performance. In the hydrothermal reaction, the carbon source reacts with sodium silicate, sodium aluminate, calcium chloride and sodium titanate to perform carbon doping, and the diffusion degree of the polymer precursor is controlled by adjusting the reaction conditions, thereby adjusting the pore size and surface properties of the molecular sieve. Finally, the residual organic matter and structural template in the molecular sieve are removed by appropriate roasting conditions, the thermal stabilization of the crystal is promoted, and its high temperature resistance is improved. The optimized hydrothermal process and roasting conditions can improve the crystallinity and purity of the molecular sieve.

[0015] Preferably, the molar ratio of silicon, aluminum, calcium and titanium in step a) is 1:0.15~0.25:0.15~0.25:0.04~0.0.06. Under the preferred element ratio, the molecular sieve crystallizes more thoroughly and exhibits better heat resistance and thermal stability.

[0016] Preferably, the alkaline solution described in step a) is a sodium hydroxide solution with a mass concentration of 15% to 25%. Sodium silicate, sodium aluminate, calcium chloride and sodium titanate are mixed into a synthetic solution with a specific concentration of sodium hydroxide to better promote the dissolution and reaction rate of the reactants, and to facilitate the formation and crystallization of the product. This concentration can effectively prevent some of the raw materials in the solution from precipitating or separating out. It helps to maintain the uniformity and stability of the reaction system and promote the uniform formation of molecular sieves.

[0017] Preferably, the addition amount of the polymer precursor described in step b) is 0.3 to 0.5 moles of carbon per mole of aluminum element. The preferred addition amount of the carbon source is to precisely control the content of the carbon source, thereby adjusting the pore size of the molecular sieve and achieving better adsorption performance.

[0018] Preferably, the reaction temperature of the hydrothermal reaction described in step c) is 85°C to 90°C, and the reaction time is 30 h to 32 h. Under the preferred process conditions of the hydrothermal reaction, the crystal morphology of the molecular sieve can be better controlled, and its adsorption performance is improved.

[0019] Preferably, the centrifugation and washing described in step d) are repeated 2 to 3 times.

[0020] Preferably, the drying temperature in step e) is 80°C to 120°C, and the drying time is 6 h to 12 h. The preferred drying process can better control the precipitation rate of water, prevent the formation of large water vapor channels during drying, and thus ensure the strength of the molecular sieve.

[0021] Preferably, the calcination temperature in step e) is 450°C to 500°C, and the calcination time is 2 h to 6 h. The preferred calcination conditions can better remove the residual organic matter and structure templates in the molecular sieve, control the decomposition rate of the carbon source, form a suitable pore size, better promote the thermal stabilization of the molecular sieve crystals while ensuring the adsorption capacity of the molecular sieve.

[0022] Preferably, the polymer precursor is polymethyl acrylate (PMMA) and polystyrene (PS). The present invention preferably uses PMMA and PS as the carbon sources for realizing carbon doping of the pressure swing adsorption molecular sieve because PMMA and PS have high thermal stability as carbon sources, enabling them to better maintain the carbonized structure and morphology during high-temperature calcination, and are not prone to decomposition or loss of carbon elements. PMMA and PS have relatively low volatility compared to other polymer precursors, reducing the content of organic impurities in the molecular sieve after use, and obtaining a higher purity of the pressure swing adsorption molecular sieve. PMMA and PS can be more effectively carbonized at the calcination temperature of the present invention, generating carbonaceous substances with a high carbon content, which can increase the carbon content and the number of surface carbon functional groups of the molecular sieve, improving the adsorption performance and selectivity.

[0023] The pressure swing adsorption molecular sieve prepared by the above preparation method. This molecular sieve has good heat resistance and stability, high strength, and strong adsorption force.

[0024] Compared with the prior art, a pressure swing adsorption molecular sieve of the present invention and its preparation method have the following beneficial effects: The present invention uses silicon as the basic element, and improves the heat resistance and thermal stability of the molecular sieve by doping a certain amount of titanium, aluminum, and carbon. Using a polymer precursor as the carbon source to achieve the adjustment of the pore size and adsorption performance of the molecular sieve. At the same time, the heat resistance of the present invention and its stability under high temperature and high pressure conditions are improved. The preparation method can ensure the uniformity of the reaction, control the release rate and diffusion rate of the carbon source, and effectively carry out carbon doping. The appropriate hydrothermal conditions of the present invention promote the formation and expansion of the pores, increase the adsorption surface area and pore volume of the molecular sieve, and improve the adsorption performance. The hydrothermal process and calcination conditions improve the crystallinity and purity of the molecular sieve. Detailed Embodiment

[0025] The object of the present invention is to prepare a 5A pressure swing adsorption molecular sieve containing titanium doping and carbon doping. The following is the preparation method.

[0026] a) Prepare a synthesis solution: Mix sodium silicate, sodium titanate, sodium aluminate, calcium chloride, and an alkaline solution in a certain proportion. Usually, the molar ratio of silicon, aluminum, calcium, and titanium can be adjusted according to actual needs and performance requirements. The molar ratio can be Si﹕Al﹕Ca﹕Ti = 1﹕0.1~0.3﹕0.1~0.3﹕0.01~0.1; the concentration of the alkaline solution (sodium hydroxide) also needs to be adjusted according to actual needs;

[0027] Add a polymer precursor (methyl polyacrylate or polystyrene) as the carbon source to the synthesis solution. The addition amount of the polymer precursor can be adjusted according to actual needs and performance requirements, usually 0.1~1.0 moles of carbon per mole of aluminum element.

[0028] b) Hydrothermal reaction: Carry out the hydrothermal reaction on the synthesis solution at 80℃~100℃. The specific reaction time can be adjusted according to actual needs and performance requirements, usually 12h~72h, (preferably 28h~34h). The pressure conditions are usually natural pressure or higher than natural pressure.

[0029] c) Separation and washing: Centrifuge the product to separate the solid, and then wash it with deionized water or other appropriate solvents to remove impurities and residual synthesis solution. Usually, it needs to be washed 2-3 times to ensure the purity of the product.

[0030] d) Drying: Dry the washed product at a temperature of 80℃~120℃ to remove excess moisture. The drying time is usually 6h~12h.

[0031] e) Activation and carbon doping: The dried product is calcined at a temperature of 300°C to 600°C to remove residual lattice water and achieve the decomposition of the carbon source and carbon doping. The calcination time is usually 2h to 6h and needs to be adjusted according to actual requirements and performance requirements.

[0032] The present invention will be specifically described below through examples. Unless otherwise specified, the raw materials used are commercially available.

[0033] Example 1:

[0034] a) Sodium silicate, sodium aluminate, calcium chloride and sodium titanate were added to a sodium hydroxide solution with a mass concentration of 20% and stirred and mixed for 2 h to form a uniform synthesis solution, where the molar ratio of silicon, aluminum, calcium and titanium was 1:0.20:0.20:0.05;

[0035] b) Methyl polyacrylate as a carbon source was further added to the synthesis solution in step 1), and the addition amount of the polymer precursor was 0.4 mol of carbon per mol of aluminum element;

[0036] c) Hydrothermal reaction was carried out at 87°C and 0.13 MPa for 31 h;

[0037] d) After the reaction was completed, the product was centrifuged to separate the solid, and then washed with deionized water and repeated 3 times;

[0038] e) The washed product was dried at a drying temperature of 100°C for 9 h and calcined at a temperature of 480°C for 4 h to achieve the activation of the molecular sieve, and 5A pressure swing adsorption molecular sieve was obtained.

[0039] Example 2:

[0040] a) Sodium silicate, sodium aluminate, calcium chloride and sodium titanate were added to a sodium hydroxide solution with a mass concentration of 15% and stirred and mixed for 2 h to form a uniform synthesis solution, where the molar ratio of silicon, aluminum, calcium and titanium was 1:0.15:0.25:0.04;

[0041] b) Polystyrene as a carbon source was further added to the synthesis solution in step 1), and the addition amount of the polymer precursor was 0.5 mol of carbon per mol of aluminum element;

[0042] c) Hydrothermal reaction was carried out at 90°C and 0.14 MPa for 30 h;

[0043] d) After the reaction was completed, the product was centrifuged to separate the solid, and then washed with deionized water and repeated 3 times;

[0044] e) Dry the washed product at a drying temperature of 90 °C for 10 h, and calcine it at a temperature of 500 °C for 3 h to activate the molecular sieve, thus obtaining the 5A pressure swing adsorption molecular sieve.

[0045] Example 3:

[0046] a) Add sodium silicate, sodium aluminate, calcium chloride and sodium titanate to a sodium hydroxide solution with a mass concentration of 25% and stir and mix for 2 h to form a uniform synthesis solution, where the molar ratio of silicon, aluminum, calcium and titanium is 1﹕0.25﹕0.15﹕0.06;

[0047] b) Add polymethyl acrylate as a carbon source to the synthesis solution in step 1), and the addition amount of the polymer precursor is 0.3 mol of carbon per mol of aluminum element;

[0048] c) Conduct a hydrothermal reaction at 85 °C and 0.13 MPa for 32 h;

[0049] d) After the reaction is completed, centrifuge the product to separate the solid, and then wash it with deionized water and repeat 2 times;

[0050] e) Dry the washed product at a drying temperature of 110 °C for 7 h, and calcine it at a temperature of 450 °C for 4 h to activate the molecular sieve, thus obtaining the 5A pressure swing adsorption molecular sieve.

[0051] Example 4:

[0052] a) Add sodium silicate, sodium aluminate, calcium chloride and sodium titanate to a sodium hydroxide solution with a mass concentration of 15% and stir and mix for 2 h to form a uniform synthesis solution, where the molar ratio of silicon, aluminum, calcium and titanium is 1﹕0.1﹕0.3﹕0.01;

[0053] b) Add polymethyl acrylate as a carbon source to the synthesis solution in step 1), and the addition amount of the polymer precursor is 1.0 mol of carbon per mol of aluminum element;

[0054] c) Conduct a hydrothermal reaction at 80 °C and 0.15 MPa for 34 h;

[0055] d) After the reaction is completed, centrifuge the product to separate the solid, and then wash it with deionized water and repeat 2 times;

[0056] e) Dry the washed product at a drying temperature of 80 °C for 12 h, and calcine it at a temperature of 300 °C for 6 h to activate the molecular sieve, thus obtaining the 5A pressure swing adsorption molecular sieve.

[0057] Example 5:

[0058] a) Sodium silicate, sodium aluminate, calcium chloride and sodium titanate were added to a sodium hydroxide solution with a mass concentration of 25% and stirred and mixed for 1.5 h to form a uniform synthesis solution, where the molar ratio of silicon, aluminum, calcium and titanium was 1:0.3:0.1:0.1;

[0059] b) Polystyrene as a carbon source was further added to the synthesis solution in step 1), and the addition amount of the polymer precursor was 0.1 mole of carbon per mole of aluminum element;

[0060] c) Hydrothermal reaction was carried out at 100 °C and 0.12 MPa, and the reaction time was 28 h;

[0061] d) After the reaction was completed, the product was centrifuged to separate the solid, and then washed with deionized water and repeated 3 times;

[0062] e) The washed product was dried at a drying temperature of 120 °C and a drying time of 6 h, and calcined at a temperature of 600 °C for 2 h to activate the molecular sieve, and 5A pressure swing adsorption molecular sieve was obtained.

[0063] Example 6:

[0064] a) Sodium silicate, sodium aluminate, calcium chloride and sodium titanate were added to a sodium hydroxide solution with a mass concentration of 20% and stirred and mixed for 3 h to form a uniform synthesis solution, where the molar ratio of silicon, aluminum, calcium and titanium was 1:0.20:0.20:0.05;

[0065] b) Polyvinyl alcohol as a carbon source was further added to the synthesis solution in step 1), and the addition amount of the polymer precursor was 0.4 mole of carbon per mole of aluminum element;

[0066] c) Hydrothermal reaction was carried out at 87 °C and 0.13 MPa, and the reaction time was 31 h;

[0067] d) After the reaction was completed, the product was centrifuged to separate the solid, and then washed with deionized water and repeated 3 times;

[0068] e) The washed product was dried at a drying temperature of 100 °C and a drying time of 9 h, and calcined at a temperature of 480 °C for 4 h to activate the molecular sieve, and 5A pressure swing adsorption molecular sieve was obtained.

[0069] Comparative Example 1:

[0070] a) Sodium silicate, sodium aluminate, calcium chloride, sodium titanate and polymethyl acrylate were added to a sodium hydroxide solution with a mass concentration of 20% and stirred and mixed for 2 h to form a uniform synthesis solution, where the molar ratio of silicon, aluminum, calcium, titanium and carbon was 1:0.20:0.20:0.05:0.08;

[0071] b) Carry out the hydrothermal reaction at 87 °C and 0.13 MPa for 31 h;

[0072] c) After the reaction is completed, centrifuge the product to separate the solid, and then wash it with deionized water, repeating 3 times;

[0073] d) Dry the washed product at a drying temperature of 100 °C for 9 h, and calcine it at 480 °C for 4 h to activate the molecular sieve, thus obtaining the 5A pressure swing adsorption molecular sieve.

[0074] Comparative Example 2:

[0075] a) Add sodium silicate, calcium chloride and sodium titanate to a 20% by mass concentration sodium hydroxide solution, stir and mix for 2 h to form a homogeneous synthesis solution, where the molar ratio of silicon, calcium and titanium is 1:0.40:0.05;

[0076] b) Add polymethyl acrylate as the carbon source to the synthesis solution in step 1), and the addition amount of the polymer precursor is 0.4 moles of carbon per mole of aluminum element;

[0077] c) Carry out the hydrothermal reaction at 87 °C and 0.13 MPa for 31 h;

[0078] d) After the reaction is completed, centrifuge the product to separate the solid, and then wash it with deionized water, repeating 3 times;

[0079] e) Dry the washed product at a drying temperature of 100 °C for 9 h, and calcine it at 480 °C for 4 h to activate the molecular sieve, thus obtaining the 5A pressure swing adsorption molecular sieve.

[0080] Respectively take samples (d is 1.6 mm to 2.5 mm) from the molecular sieves prepared in the examples and comparative examples as samples and conduct partial performance tests in accordance with GBT 13550-2015.

[0081] Mass loss rate: Place the sample in a thermogravimetric analyzer, gradually heat it up to 500 °C. Measure the mass loss of the sample and calculate the mass loss rate.

[0082] The experimental results are shown in Table 1.

[0083] Table 1

[0084] Static n - hexane adsorption (0 ± 1 °C) % Yield % Average point - contact crushing force N Mass loss rate ‰ Example 1 19.7 94.7 38.9 0.08 Example 2 19.2 94.1 38.8 0.11 Example 3 18.4 94.5 38.9 0.09 Example 4 16.7 92.3 37.3 0.15 Example 5 16.5 93.1 37.7 0.17 Example 6 13.1 92.7 37.2 2.34 Comparative Example 1 8.6 87.3 19.7 1.67 Comparative Example 2 10.7 91.6 29.2 0.76

[0085] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention in any other form. Any person skilled in the art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A preparation method of a pressure swing adsorption molecular sieve, characterized in that, It includes the following steps: a) Sodium silicate, sodium aluminate, calcium chloride and sodium titanate are added to an alkaline solution and stirred and mixed to form a uniform synthetic solution, where the molar ratio of silicon, aluminum, calcium and titanium is 1﹕0.1~0.3﹕0.1~0.3﹕0.01~0.1; b) A polymer precursor as a carbon source is further added to the synthetic solution in step a), and the addition amount of the polymer precursor is 0.1~1.0 moles of carbon per mole of aluminum element, where the polymer precursor is methyl polyacrylate or polystyrene; c) Hydrothermal reaction is carried out at 80°C~100°C and 0.12 MPa~0.15 MPa, and the reaction time is 28 h~34 h; d) After the reaction is completed, the product is centrifuged to separate the solid, and then washed with deionized water; e) The washed product is dried and then calcined at a temperature of 300°C~600°C to obtain the 5A pressure swing adsorption molecular sieve.

2. The preparation method of a pressure swing adsorption molecular sieve according to claim 1, wherein the molar ratio of silicon, aluminum, calcium and titanium described in step a) is 1﹕0.15~0.25﹕0.15~0.25﹕0.04~0.

06.

3. The preparation method of a pressure swing adsorption molecular sieve according to claim 1, wherein the alkaline solution described in step a) is a sodium hydroxide solution with a mass concentration of 15%~25%.

4. The preparation method of a pressure swing adsorption molecular sieve according to claim 1, wherein the addition amount of the polymer precursor described in step b) is 0.3~0.5 moles of carbon per mole of aluminum element.

5. The preparation method of a pressure swing adsorption molecular sieve according to claim 1, wherein the reaction temperature of the hydrothermal reaction described in step c) is 85°C~90°C, and the reaction time is 30 h~32 h.

6. The preparation method of a pressure swing adsorption molecular sieve according to claim 1, wherein the centrifugation and washing described in step d) are repeated 2~3 times.

7. The preparation method of a pressure swing adsorption molecular sieve according to claim 1, wherein the drying temperature of the drying described in step e) is 80°C~120°C, and the drying time is 6 h~12 h.

8. The preparation method of a pressure swing adsorption molecular sieve according to claim 1, wherein the calcination temperature described in step e) is 450°C~500°C, and the calcination time is 2 h~6 h.

9. The pressure swing adsorption molecular sieve prepared by any one of claims 1~8.