Lsx type and a type composite molecular sieve and a seed-free controllable preparation method thereof

Abstract

The application discloses LSX type and A type composite molecular sieves and a controllable preparation method thereof without seeds. The preparation method comprises the following steps: after kaolin is calcined, the kaolin is dispersed into mixed alkali liquor, low-temperature aging and high-temperature crystallization are carried out, and then the LSX type and A type composite molecular sieves are obtained through filtration, washing and drying; wherein, the low-temperature aging and high-temperature crystallization are controlled to be carried out under static, dynamic or static-dynamic combination, so as to control the proportion of the LSX type and A type molecular sieves in the obtained composite molecular sieves. The preparation method has the advantages of simple raw materials, low preparation cost, simple operation, controllable proportion of the LSX type and A type in the obtained composite molecular sieves, adaptability to industrial production, and the like, and can be applied to the fields of adsorption and separation.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve synthesis, specifically to an LSX-type and A-type composite molecular sieve and its seedless, controllable preparation method. Background Technology

[0002] Molecular sieves possess advantages such as large specific surface area, uniform and regular pore structure, uniform pore size, and ease of ion exchange, making them widely used in the adsorption and separation of mixed gases. Both low silica-to-alumina ratio (LSX) type molecular sieves and type A molecular sieves have frameworks formed by SiO4 tetrahedra and AlO4 tetrahedra bridged by oxygen atoms. The difference lies in the connection method between the structural units, sod cages. Sod cages are connected by double four-membered rings, forming a type A zeolite (LTA) structure with an α cage at the center; sod cages are connected by double six-membered rings, forming an octahedral zeolite (FAU) structure with supercages containing 12-membered pores.

[0003] According to existing technology reports, LSX-type and A-type molecular sieves exhibit high adsorption capacity and high selectivity for various non-hydrogen gases, respectively. However, research on LSX-type and A-type composite molecular sieves is limited. The silicon-to-aluminum molar ratio of LSX-type molecular sieves is between 2.0 and 2.2, very close to that of A-type molecular sieves, and both share the same structural units, allowing them to form eutectic composite molecular sieves during crystallization. Composite molecular sieves possess a multi-channel structure, which, compared to single-structure molecular sieves, can produce a synergistic effect on gas adsorption, increasing the types of gases adsorbed and improving adsorption performance, making them valuable for hydrogen purification. However, the synthesis of composite molecular sieves typically involves adding a large amount of molecular sieve powder as seed crystals and introducing a silicon source, resulting in high production costs and hindering large-scale production.

[0004] CN116078346A discloses a method for preparing a composite adsorbent of X-type and A-type molecular sieves. This technology uses the binder in a molded 13X molecular sieve as the aluminum source for synthesis, adds a silicon source and a strong alkali, and then seals the vessel for aging and crystallization to obtain a composite adsorbent of X-type and A-type molecular sieves with good strength and excellent adsorption performance. However, the molded 13X molecular sieve contains a large amount of 13X molecular sieve powder, and the addition of a silicon source results in high raw material costs for the adsorbent, limiting large-scale industrial production and commercialization.

[0005] CN109485058A discloses a method for preparing binderless LSX molecular sieves. Using LSX molecular sieve powder and kaolin as raw materials, the method involves mixing and molding, drying and calcining, treatment with a sodium-potassium mixed alkali solution, sodium ion exchange, and secondary drying and calcining to obtain binderless LSX molecular sieves. However, this binderless LSX molecular sieve adsorbent requires the addition of 85%–90% LSX molecular sieve powder during preparation, resulting in high production costs and hindering industrialization.

[0006] Wang Ju et al. (Guangdong Chemical Industry, 2022, 14(49), 47-49) roasted a mixture of coal-based kaolin and sodium hydroxide and then carried out hydrothermal synthesis and crystallization to obtain 4A molecular sieves. However, this method only yielded type A molecular sieves with poor CO2 adsorption performance.

[0007] Luo Heji et al. (Comprehensive Utilization of Mineral Resources, 2012, 5, 32-34+49) synthesized LSX molecular sieves by using coal-series kaolin and silica sol as raw materials and carrying out gelation and crystallization reactions after long-term vigorous stirring. However, this method only yielded LSX-type molecular sieves, and the addition of an external silicon source made the operation time-consuming.

[0008] Wang Yu et al. (Guangzhou Chemical Industry, 2015, 43(15), 114-115+136) used industrial-grade water glass, sodium aluminate and other raw materials to form a gel by stirring and then statically synthesized LSX zeolite molecular sieves in two steps of hydrothermal synthesis. However, this method uses chemical reagents for synthesis, which is costly and causes serious pollution during post-processing, and does not conform to the concept of green chemistry.

[0009] To address the problems of existing technologies that involve adding a large amount of molecular sieve powder as seed crystals and external silicon sources during the synthesis of molecular sieves using kaolin as raw material, resulting in complex raw materials and high preparation costs; and the difficulty in controlling the molecular sieve crystal form when preparing a single-crystal molecular sieve, leading to uncontrollable adsorption performance and long operation time, this invention provides a method for controllable preparation of LSX-type and A-type composite molecular sieves without the need for external seed crystals. Summary of the Invention

[0010] The purpose of this invention is to provide an LSX-type and A-type composite molecular sieve and its seedless controllable preparation method. This preparation method uses simple raw materials, does not require the addition of molecular sieve powder as a seed, has low preparation cost, is easy to operate, and can control the ratio of LSX-type and A-type in the obtained composite molecular sieve. It is suitable for industrial production and can be used in the fields of adsorption and separation.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] This invention provides a seedless and controllable preparation method for LSX-type and A-type composite molecular sieves, wherein the seedless and controllable preparation method includes:

[0013] Kaolin was calcined and dispersed in a mixed alkaline solution for low-temperature aging and high-temperature crystallization. Then it was filtered, washed and dried to obtain LSX-type and A-type composite molecular sieves.

[0014] The ratio of LSX-type and A-type molecular sieves in the resulting composite molecular sieve is controlled by adjusting the low-temperature aging and high-temperature crystallization under static, dynamic, or combined static and dynamic conditions.

[0015] Compared with existing technologies for synthesizing composite molecular sieves, the preparation method using kaolin as raw material in this invention does not require the addition of a large amount of molecular sieves as seed crystals, significantly reducing production costs. Furthermore, the proportion of composite molecular sieves can be controlled through static and dynamic aging (crystallization) methods. Specifically, dynamic aging and crystallization processes tend to synthesize more LSX-type molecular sieves, while static aging and crystallization processes tend to synthesize more A-type molecular sieves.

[0016] According to the seedless controllable preparation method of the present invention, preferably, the silicon-aluminum molar ratio of the kaolin is (1.8-2.2):1.

[0017] According to the seedless controllable preparation method of the present invention, preferably, the calcination temperature of the kaolin is 650-800°C and the calcination time is 1-3 hours.

[0018] According to the seedless controllable preparation method of the present invention, preferably, the mixed alkaline solution is a mixed alkaline solution of sodium hydroxide and potassium hydroxide.

[0019] More preferably, the amount of kaolin is calculated based on silicon dioxide, and the amount of the mixed alkaline solution is calculated based on the sum of sodium oxide and potassium oxide. In the mixed alkaline solution, the molar ratio of water to the sum of sodium oxide and potassium oxide is (15-20):1, and the molar ratio of potassium oxide to the sum of sodium oxide and potassium oxide is (0.1-0.4):1. In the addition ratio of the mixed alkaline solution and kaolin, the molar ratio of the sum of sodium oxide and potassium oxide to silicon dioxide is (2.0-4.0):1.

[0020] According to the seedless controllable preparation method of the present invention, preferably, the aging temperature of the low-temperature aging is 40-70°C, more preferably 50-60°C, and the aging time is 3-18 hours.

[0021] According to the seedless controllable preparation method of the present invention, preferably, the crystallization temperature of the high-temperature crystallization is 80-100°C, more preferably 90-95°C, and the crystallization time is 2-15 hours.

[0022] According to the seedless controllable preparation method of the present invention, preferably, the sum of the aging time of the low-temperature aging and the crystallization time of the high-temperature crystallization is 15-20 hours.

[0023] According to the seedless controllable preparation method of the present invention, preferably, static aging or static crystallization involves placing the reaction raw materials in a polytetrafluoroethylene liner, sealing the reaction vessel, and then placing it in a forced-air drying oven for aging or crystallization reaction.

[0024] According to the seedless controllable preparation method of the present invention, preferably, dynamic aging or dynamic crystallization involves placing the reaction raw materials in a polytetrafluoroethylene liner, sealing the reaction vessel, and then placing it in a homogeneous reactor for aging or crystallization reaction, wherein the rotation speed of the homogeneous reactor is 50-200 r / min.

[0025] According to the seedless controllable preparation method of the present invention, the washing is specifically water washing; preferably, water washing is performed until pH < 9.

[0026] According to the seedless controllable preparation method of the present invention, the drying method can be any conventional drying method, and the present invention does not limit it. For example, drying at 120°C for 2 hours as used in the embodiment can achieve the drying purpose.

[0027] In another aspect, the present invention provides an LSX-type and A-type composite molecular sieve, which is obtained by any of the above-mentioned seedless controllable preparation methods.

[0028] The beneficial effects of this invention include:

[0029] 1) This invention uses kaolin as the sole silicon and aluminum source. Without the addition of a large amount of LSX-type or A-type molecular sieves, silicon source, or aluminum source, LSX-type and A-type composite molecular sieves can be directly prepared from kaolin in a mixed alkaline solution, which greatly reduces production costs and simplifies the preparation process.

[0030] 2) This invention can control the ratio of LSX-type and A-type molecular sieves in composite molecular sieves by combining static and dynamic aging (crystallization). The static crystallization process tends to form A-type molecular sieves with stable crystal structure, tightly connected structural units, and small pore size, while the dynamic crystallization process tends to form LSX-type molecular sieves with loose crystal structure and large pore size. Attached Figure Description

[0031] Figure 1 The images show the XRD patterns of the products from Examples 1 and 2 of this invention. Detailed Implementation

[0032] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0033] All numerical specifications in this invention (e.g., temperature, time, concentration, and weight, including ranges for each) are generally approximate values ​​that may be changed (+) or (-) in increments of 0.1 or 1.0. All numerical specifications are to be understood as being preceded by the term "about".

[0034] Source of raw materials or equipment:

[0035] In this embodiment of the invention, the kaolin was analytical grade, with a silicon-to-aluminum molar ratio of 2.05, and was manufactured by Suzhou Kaolin Co., Ltd., China; the sodium hydroxide was analytical grade (≥96%), and was manufactured by Sinopharm Chemical Reagent Co., Ltd.; the potassium hydroxide was analytical grade (≥85%), and was manufactured by Sinopharm Chemical Reagent Co., Ltd. The X-ray diffractometer was model XPert PRO, manufactured by Panaco, Netherlands.

[0036] Example 1

[0037] This embodiment prepares an LSX-type and A-type composite molecular sieve LSX / A-1, including the following steps:

[0038] Kaolin was calcined at 650℃ for 3 hours and then ground into a fine powder for later use.

[0039] Dissolve 21.0g NaOH and 9.9g KOH in 100mL of water to prepare a mixed alkaline solution, and cool to room temperature.

[0040] 11.8 g of calcined kaolin was added to the mixed alkaline solution and stirred until homogeneous. Under static conditions, it was aged at 60℃ for 13 h, crystallized at 90℃ for 3 h, filtered, washed with water until pH < 9, and dried at 120℃ for 2 h to obtain the LSX / A-1 composite molecular sieve (LSX and A types). XRD pattern is shown below. Figure 1 .

[0041] Example 2

[0042] This embodiment prepares an LSX-type and A-type composite molecular sieve LSX / A-2, including the following steps:

[0043] Kaolin was calcined at 700℃ for 2 hours and then ground into a fine powder for later use.

[0044] Dissolve 17.8g NaOH and 8.4g KOH in 100mL of water to prepare a mixed alkaline solution, and cool to room temperature.

[0045] 10.0 g of calcined kaolin was added to the mixed alkaline solution and stirred until homogeneous. The mixture was aged at 60℃ for 5 h at a constant dynamic rotation speed of 100 r / min, crystallized at 95℃ for 12 h, filtered, washed with water until pH < 9, and dried at 120℃ for 2 h to obtain the LSX / A-2 composite molecular sieve (LSX and A types). XRD patterns are shown below. Figure 1 .

[0046] from Figure 1It can be seen that LSX / A-1 and LSX / A-2 exhibit characteristic diffraction peaks of type X molecular sieve at 2θ values ​​of 6.1°, 10.0°, 11.7°, 15.4°, 18.4°, 20.0°, 23.3°, 26.6°, 30.3°, 30.9°, and 33.5°, and characteristic diffraction peaks of type A molecular sieve at 2θ values ​​of 7.2°, 10.2°, 12.5°, 16.1°, 21.7°, 24.0°, 26.1°, 27.1°, and 29.9°, indicating that the products possess the framework structure of LSX-type and type A molecular sieve crystals. This method successfully synthesizes LSX-type and type A composite molecular sieves.

[0047] Example 3

[0048] This embodiment prepares an LSX-type and A-type composite molecular sieve LSX / A-3, including the following steps:

[0049] Kaolin was calcined at 750℃ for 2 hours and then ground into a fine powder for later use.

[0050] Dissolve 21.0g NaOH and 9.9g KOH in 100mL of water to prepare a mixed alkaline solution, and cool to room temperature.

[0051] 16.5g of calcined kaolin was added to the mixed alkaline solution and stirred until homogeneous. Under static conditions, it was aged at 50℃ for 10h, and then crystallized at 95℃ for 5h at a dynamic speed of 100r / min. After filtration and washing with water until pH < 9, it was dried at 120℃ for 2h to obtain LSX-type and A-type composite molecular sieve LSX / A-3.

[0052] Example 4

[0053] This embodiment prepares an LSX-type and A-type composite molecular sieve, LSX / A-4, including the following steps:

[0054] Kaolin was calcined at 800℃ for 1 hour and then ground into a fine powder for later use.

[0055] Dissolve 19.8g NaOH and 9.4g KOH in 100mL of water to prepare a mixed alkaline solution, and cool to room temperature.

[0056] 11.1g of calcined kaolin was added to the mixed alkaline solution and stirred until homogeneous. The mixture was aged at 70℃ for 3 hours at a dynamic speed of 100r / min, then crystallized at 80℃ for 15 hours under static conditions. After filtration and washing with water until pH < 9, the mixture was dried at 120℃ for 2 hours to obtain LSX / A-4, a composite molecular sieve of type LSX and type A.

[0057] Example 5

[0058] This embodiment prepares an LSX-type and A-type composite molecular sieve, LSX / A-5, including the following steps:

[0059] Kaolin was calcined at 650℃ for 3 hours and then ground into a fine powder for later use.

[0060] Dissolve 21.0g NaOH and 9.9g KOH in 100mL of water to prepare a mixed alkaline solution, and cool to room temperature.

[0061] 11.8g of calcined kaolin was added to the mixed alkaline solution and stirred until homogeneous. The mixture was aged at 60℃ for 13h at a dynamic rotation speed of 50r / min throughout the process, crystallized at 90℃ for 3h, filtered, washed with water until pH < 9, and dried at 120℃ for 2h to obtain LSX / A-5, a composite molecular sieve of type LSX and type A.

[0062] Example 6

[0063] This embodiment prepares an LSX-type and A-type composite molecular sieve LSX / A-6, including the following steps:

[0064] Kaolin was calcined at 700℃ for 2 hours and then ground into a fine powder for later use.

[0065] Dissolve 17.8g NaOH and 8.4g KOH in 100mL of water to prepare a mixed alkaline solution, and cool to room temperature.

[0066] 10.0g of calcined kaolin was added to the mixed alkaline solution and stirred until homogeneous. Under static conditions, the mixture was aged at 60℃ for 5 hours, crystallized at 95℃ for 12 hours, filtered, washed with water until pH < 9, and dried at 120℃ for 2 hours to obtain LSX-type and A-type composite molecular sieve LSX / A-6.

[0067] Example 7

[0068] This embodiment prepares an LSX-type and A-type composite molecular sieve, LSX / A-7, including the following steps:

[0069] Kaolin was calcined at 750℃ for 2 hours and then ground into a fine powder for later use.

[0070] Dissolve 27.8g NaOH and 4.9g KOH in 100mL of water to prepare a mixed alkaline solution, and cool to room temperature.

[0071] 11.7g of calcined kaolin was added to the mixed alkaline solution and stirred until homogeneous. Under static conditions, the mixture was aged at 40℃ for 18h, crystallized at 100℃ for 2h, filtered, washed with water until pH < 9, and dried at 120℃ for 2h to obtain LSX / A-7, a composite molecular sieve of type LSX and type A.

[0072] Example 8

[0073] This embodiment prepares an LSX-type and A-type composite molecular sieve LSX / A-8, including the following steps:

[0074] Kaolin was calcined at 700℃ for 2 hours and then ground into a fine powder for later use.

[0075] Dissolve 16.3g NaOH and 17.2g KOH in 100mL of water to prepare a mixed alkaline solution, and cool to room temperature.

[0076] 20.6g of calcined kaolin was added to the mixed alkaline solution and stirred until homogeneous. The mixture was aged at 40℃ for 18h at a dynamic rotation speed of 200r / min throughout the process, crystallized at 100℃ for 2h, filtered, washed with water until pH < 9, and dried at 120℃ for 2h to obtain LSX-type and A-type composite molecular sieve LSX / A-8.

[0077] The specific synthesis conditions of LSX-type and A-type composite molecular sieves and the proportions of the two molecular sieves in Examples 1-8 above are shown in Table 1.

[0078] Table 1 Synthesis conditions and molecular sieve ratios of LSX-type and A-type composite molecular sieves

[0079]

[0080] As can be seen from Examples 1 and 5, Examples 2 and 6, Examples 7 and 8, the dynamic aging and crystallization process tends to synthesize more LSX-type molecular sieves, while the static aging and crystallization process tends to synthesize A-type molecular sieves.

[0081] The experimental results above show that, using kaolin as the sole silicon and aluminum source, LSX-type and A-type composite molecular sieves can be directly crystallized without the addition of molecular sieves, silicon sources, or aluminum sources. This significantly reduces raw material costs, simplifies the preparation process, and is suitable for large-scale industrial production.

[0082] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A seedless and controllable preparation method for LSX-type and A-type composite molecular sieves, wherein, The seedless controllable preparation method includes: Kaolin was calcined and dispersed in a mixed alkaline solution for low-temperature aging and high-temperature crystallization. Then it was filtered, washed and dried to obtain LSX-type and A-type composite molecular sieves. Among them, the ratio of LSX type and A type molecular sieves in the obtained composite molecular sieve is adjusted by controlling low-temperature aging and high-temperature crystallization under static, dynamic or dynamic-static conditions. The low-temperature aging temperature is 40~70℃, and the aging time is 3~18 h; The crystallization temperature for high-temperature crystallization is 80~100℃, and the crystallization time is 2~15 h; The mixed alkaline solution is a mixture of sodium hydroxide and potassium hydroxide; The amount of kaolin used is calculated based on silicon dioxide, and the amount of the mixed alkaline solution is calculated based on the sum of sodium oxide and potassium oxide. In the mixed alkaline solution, the molar ratio of water to the sum of sodium oxide and potassium oxide is (15~20):1, and the molar ratio of potassium oxide to the sum of sodium oxide and potassium oxide is (0.1~0.4):

1. In the addition ratio of the mixed alkaline solution and kaolin, the molar ratio of the sum of sodium oxide and potassium oxide to silicon dioxide is (2.0~4.0):

1.

2. The seedless controllable preparation method according to claim 1, wherein, The kaolin is calcined at a temperature of 650~800℃ for 1~3 hours.

3. The seedless controllable preparation method according to claim 1, wherein, The sum of the aging time for low-temperature aging and the crystallization time for high-temperature crystallization is 15~20 h.

4. The seedless controllable preparation method according to claim 3, wherein, Static aging or static crystallization involves placing the reaction raw materials in a polytetrafluoroethylene liner, sealing the reaction vessel, and then placing it in a forced-air drying oven for aging or crystallization reaction.

5. The seedless controllable preparation method according to claim 3, wherein, Dynamic aging or dynamic crystallization involves placing the reaction raw materials in a polytetrafluoroethylene liner, sealing the reaction vessel, and then placing it in a homogeneous reactor for aging or crystallization reactions. The rotation speed of the homogeneous reactor is 50~200 r / min.

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