A method for preparing SAPO-44 microporous molecular sieve by using palygorskite as raw material

Abstract

The application discloses a method for preparing SAPO-44 microporous molecular sieves by using palygorskite as raw material, and comprises the following steps: step A: adding palygorskite into an acid solution, uniformly mixing, placing in a hydrothermal reaction kettle for hydrothermal treatment, cooling, washing, drying, and obtaining a rod-shaped silicon source; step B: mixing an aluminum source, phosphoric acid and deionized water, uniformly stirring at room temperature, and obtaining solution a; step C: mixing the rod-shaped silicon source and tetraethylammonium hydroxide, uniformly stirring at room temperature, and obtaining solution b; step D: under the condition of stirring at room temperature, adding solution a into solution b drop by drop to form a sol-gel system; step E: transferring the sol-gel system obtained in step D into a homogeneous reactor for dynamic hydrothermal reaction; and step F: filtering, washing, drying and calcining the crystallization product to obtain high-purity and high-crystallinity SAPO-44 microporous molecular sieves. The application realizes effective utilization of silicon elements in palygorskite, reduces production cost, shortens a synthesis period, and makes the prepared SAPO-44 microporous molecular sieves high in purity and good in crystallinity, so that the application has a wide application prospect in industry.

Description

[0001] Field of study

[0002] This invention relates to the field of molecular sieve preparation technology, specifically to a method for preparing SAPO-44 microporous molecular sieve using attapulgite as raw material. Background Technology

[0003] SAPO-n molecular sieves are crystals formed by the combination of tetrahedral TO4 (T = Si, Al, P) units, possessing a three-dimensional framework structure. Different n values ​​represent different crystal structures; common types include SAPO-5, SAPO-11, SAPO-18, SAPO-34, and SAPO-44. SAPO-n molecular sieves have a negatively charged framework, a uniform microporous structure, and numerous acidic sites on their surface, allowing for cation exchange. Therefore, they can be widely used in catalysis fields such as petrochemicals, energy, and environmental pollutant treatment.

[0004] SAPO-44 possesses CHA pores and three-dimensional intersecting channels composed of four-membered rings, double six-membered rings, and eight-membered rings, with a maximum pore size of approximately 0.43 nm. Due to its microporous structure, SAPO-44 molecular sieves exhibit excellent shape selectivity. It also possesses excellent hydrothermal stability and is rich in acidity, thus SAPO-44 has broad application prospects in petroleum catalytic cracking and pollution control.

[0005] Attapulgite is abundant in my country and is known as the "King of Soils." Currently, its direct applications are mainly in coatings and food decolorization, resulting in low utilization and relatively low added value. However, due to the presence of silica and aluminum in attapulgite, it can be used to synthesize high-value-added molecular sieves. Furthermore, attapulgite is inexpensive, which can significantly reduce the production cost of SAPO-44 molecular sieves, thus benefiting their industrial applications.

[0006] US Patent 4440871A discloses a hydrothermal synthesis method for SAPO-44. This method uses cyclohexylamine, an organic template agent, as a raw material and reacts it at 200°C for 52 hours to prepare SAPO-44. The resulting product contains impurities in addition to the SAPO-44 molecular sieve, making it impossible to obtain high-purity SAPO-44 molecular sieve. Patent WO99 / 19254 (CN1278780A) also discloses a synthesis method for SAPO-44, which also uses cyclohexylamine as a template agent, and the obtained SAPO-44 similarly contains impurities. To improve the purity of SAPO-44, patents CN201210363833.5 and CN201310499121.0 use a composite template agent and undergo two crystallization processes at different temperatures to synthesize SAPO-44. However, these methods increase the preparation steps, making the preparation process cumbersome. Patent CN104743574A uses a composite template agent to synthesize high-purity SAPO-44 molecular sieve through a single crystallization process, but the synthesis time is 96 hours, which is relatively long. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing SAPO-44 microporous molecular sieves using attapulgite as raw material. This method has low production cost, short synthesis cycle, and is convenient for industrial application of molecular sieves.

[0008] This invention is achieved through the following technical solution:

[0009] A method for preparing SAPO-44 microporous molecular sieve using attapulgite as raw material, characterized by the following steps: Step A: Adding attapulgite to an acid solution, mixing evenly, placing it in a hydrothermal reactor for acid hydrothermal treatment, cooling, filtering, washing, and drying to obtain rod-shaped silicon source; Step B: Mixing aluminum source, phosphoric acid, and deionized water, stirring evenly at room temperature to obtain solution a; Step C: Mixing rod-shaped silicon source and tetraethylammonium hydroxide, stirring evenly at room temperature to obtain solution b; Step D: Adding solution a dropwise to solution b under stirring at room temperature to form a sol-gel system; Step E: Transferring the sol-gel system obtained in step D to a homogeneous reactor for dynamic hydrothermal reaction to obtain a crystallized product; Step F: Filtering, washing, drying, and calcining the crystallized product to obtain the SAPO-44 microporous molecular sieve.

[0010] Furthermore, in step A, the silica content in the attapulgite is as high as 47-70%, and the alumina content is 5-20%.

[0011] Further, in step A, the acid is hydrochloric acid, the mass-to-volume ratio of attapulgite to hydrochloric acid is 1g:10-20ml, and the acid hydrothermal time is 4-10h.

[0012] Furthermore, in step B, the aluminum source is one of boehmite, aluminum hydroxide, aluminum oxide, or sodium aluminate.

[0013] Furthermore, in step B, the molar ratio of phosphoric acid and aluminum source is controlled to be 0.6-1.5:1.

[0014] Furthermore, the molar ratio of the silicon source in step C to the aluminum source in step B is controlled to be 0.1-1:1.

[0015] Furthermore, the molar ratio of the tetraethylammonium hydroxide added in step C to the aluminum source added in step B is controlled to be 1.5-5:1.

[0016] Furthermore, the rotation speed of the dynamic hydrothermal reaction in step E is set to 5-50 rpm / min, and the sol-gel system is dynamically crystallized at 170-220℃ for 6-72 h.

[0017] Furthermore, the washing in step F is performed using deionized water until the pH of the filtrate is 7.0; the drying is performed at 60-120℃ for 6-12 hours; and the calcination is first performed at 200-300℃ for 1-3 hours, and then at 350-700℃ for 3-24 hours.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention realizes the effective utilization of silicon in attapulgite, reduces production costs, and uses inexpensive and widely distributed attapulgite to replace the silicon source and part of the aluminum source in the synthesis of SAPO-44 microporous molecular sieve, thus synthesizing a molecular sieve with high economic value. Furthermore, the use of tetraethylammonium hydroxide template agent shortens the synthesis cycle, resulting in high purity and good crystallinity of the prepared SAPO-44 microporous molecular sieve, thus having broad application prospects. Attached Figure Description

[0019] Figure 1 The XRD patterns of SAPO-44 microporous molecular sieves prepared in Examples 1(A), 2(B), 3(C), 4(D), and 5(E) are shown.

[0020] Figure 2 The infrared spectrum of the SAPO-44 microporous molecular sieve prepared in Example 1;

[0021] Figure 3 Scanning electron microscope image of the SAPO-44 microporous molecular sieve prepared in Example 1;

[0022] Figure 4 The nitrogen adsorption-desorption curves of the SAPO-44 microporous molecular sieves prepared in Examples 1(A), 2(B), 3(C), and 5(E) are shown. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments.

[0024] Example 1

[0025] A method for preparing SAPO-44 microporous molecular sieves using attapulgite as raw material comprises the following steps:

[0026] 2g of attapulgite (with a silica content as high as 57% and an alumina content of 7.3%) was heat-treated with 20ml of hydrochloric acid for 5 hours. After cooling, filtration, and washing until the pH reached approximately 7, the rod-shaped silicon source was obtained after drying. It should be noted that the silica content of the attapulgite is high, ranging from 47% to 70%, and the alumina content is any value between 5% and 20%. This embodiment and subsequent embodiments use attapulgite with a silica content of 57% and an alumina content of 7.3% for illustrative purposes, and will not be repeated here. 3.45g of phosphoric acid was dissolved in water and stirred. 1.56g of boehmite was added, and the mixture was stirred continuously. 0.26g of the rod-shaped silicon source was added to 17.67g of tetraethylammonium hydroxide and stirred evenly at room temperature. The two solutions were mixed and stirred at room temperature. The synthesized sol-gel system was transferred to a polytetrafluoroethylene-lined autoclave and crystallized in a homogeneous reactor heated at 170°C for 48 hours to obtain the crystallized product. The crystallized product was washed with deionized water until the pH of the filtrate was 7.0. It was then dried at 60°C for 12 hours and placed in a muffle furnace. The temperature was raised to 300°C and held for 3 hours. Finally, it was calcined at 700°C for 3 hours to obtain SAPO-44 microporous molecular sieve.

[0027] Its XRD pattern is as follows Figure 1 As shown in (A). Figure 1 (A) indicates that the obtained sample is a pure phase SAPO-44 microporous molecular sieve. The characteristic peaks of SAPO-44 microporous molecular sieve in the spectrum are sharp, reflecting that the sample prepared in this example has a high degree of crystallinity. Figure 3 Scanning electron microscopy images show that the synthesized SAPO-44 microporous molecular sieve has a cubic configuration. Figure 2 The infrared spectrum also confirmed that the synthesized sample was SAPO-44 microporous molecular sieve, 3400 cm⁻¹ -1 It is a spectral band produced by the vibration of water, 1120 cm⁻¹ -1 The vibration is due to the tensile vibration of Si-O-Si. And 700cm -1 The surrounding spectral bands are attributed to Al-O vibrations, 796 cm⁻¹ -1 The spectral bands belong to the Al-O-Si vibrational bands, and the double-ring vibrations in the molecular sieve produced a 635 cm⁻¹ band. -1Spectral bands, 420-500cm -1 The band at that point was identified as a bending vibration of the TO (T represents Al, Si, P) bond. The nitrogen adsorption-desorption curve of the product is shown below. Figure 4 As shown in (A), the molecular sieve is a microporous molecular sieve with a surface area of ​​763.528 m². 2 ·g -1 ...

[0028] Example 2

[0029] A method for preparing SAPO-44 microporous molecular sieves using attapulgite as raw material comprises the following steps:

[0030] 4g of attapulgite (with a silica content as high as 57% and an alumina content of 7.3%) was heat-treated with 48ml of hydrochloric acid for 7h. After filtration and washing until the pH reached approximately 7, rod-shaped silicon source was obtained. 2.3g of phosphoric acid was dissolved in water and stirred. 1.04g of boehmite was added, and the mixture was stirred continuously. 0.12g of the rod-shaped silicon source was added to 10.78g of tetraethylammonium hydroxide and stirred evenly at room temperature. The two solutions were mixed and stirred at room temperature. The synthesized sol-gel system was transferred to a polytetrafluoroethylene-lined autoclave and crystallized in a homogeneous reactor heated at 180℃ for 24h to obtain a crystallized product. The crystallized product was washed with deionized water until the pH of the filtrate reached 7.0. It was dried at 120℃ for 6h, then placed in a muffle furnace, heated to 200℃, held for 3h, and then calcined at 600℃ for 5h to obtain SAPO-44 microporous molecular sieve.

[0031] like Figure 1 The XRD pattern shown in (B) indicates that the obtained sample is a pure-phase SAPO-44 microporous molecular sieve. The figure shows that the obtained sample is a pure-phase SAPO-44 microporous molecular sieve with high crystallinity and no other impurities formed. Figure 4 (B) The nitrogen adsorption-desorption curve shows that the molecular sieve is a microporous molecular sieve containing some mesopores, with a surface area of ​​730.513 m². 2 ·g -1 .

[0032] Example 3

[0033] A method for preparing SAPO-44 microporous molecular sieves using attapulgite as raw material comprises the following steps:

[0034] 5g of attapulgite (with a silica content as high as 57% and an alumina content of 7.3%) was heat-treated with 75ml of hydrochloric acid for 8 hours, filtered, and washed until the pH reached approximately 7 to obtain rod-shaped silicon source. 4.4g of phosphoric acid was dissolved in water and stirred. 1.8g of boehmite was added, and the mixture was stirred continuously. 0.4g of the rod-shaped silicon source was added to 29.8g of tetraethylammonium hydroxide and stirred until homogeneous at room temperature. The two solutions were mixed and stirred at room temperature. The synthesized sol-gel system was transferred to a polytetrafluoroethylene-lined autoclave and crystallized in a homogeneous reactor heated at 170℃ for 43 hours to obtain a crystallized product. The crystallized product was washed with deionized water until the pH of the filtrate reached 7.0, dried at 100℃ for 8 hours, then placed in a muffle furnace, heated to 300℃, held for 3 hours, and then calcined at 650℃ for 6 hours to obtain SAPO-44 microporous molecular sieve.

[0035] Figure 1 The XRD pattern in (C) shows that the obtained sample is free of impurities and is a pure-phase SAPO-44 microporous molecular sieve. Its high peak intensity indicates high crystallinity of the molecular sieve. Figure 4 C) The nitrogen adsorption-desorption curve shows that the molecular sieve is a microporous molecular sieve with a surface area of ​​797.40 m². 2 ·g -1 .

[0036] Example 4

[0037] A method for preparing SAPO-44 microporous molecular sieves using attapulgite as raw material comprises the following steps:

[0038] 1 g of attapulgite (with a silica content as high as 57% and an alumina content of 7.3%) was heat-treated with 20 ml of hydrochloric acid for 10 h, filtered, and washed until the pH reached approximately 7 to obtain rod-shaped silicon source. 2.4 g of phosphoric acid was dissolved in water and stirred. 1.04 g of boehmite was added, and the mixture was stirred further. 0.17 g of the rod-shaped silicon source was added to 18.72 g of tetraethylammonium hydroxide. The mixture was stirred until homogeneous at room temperature. The two solutions were then mixed and stirred at room temperature. The synthesized sol-gel system was transferred to a polytetrafluoroethylene-lined autoclave and crystallized in a homogeneous reactor heated to 210 °C for 40 h to obtain a crystallized product. The crystallized product was washed with deionized water until the filtrate pH reached 7.0, dried at 60 °C for 12 h, then placed in a muffle furnace, heated to 250 °C, held for 1.5 h, and then calcined at 550 °C for 6 h to obtain SAPO-44 microporous molecular sieve.

[0039] like Figure 1 The XRD pattern shown in (D) indicates that the obtained sample is a pure phase SAPO-44 microporous molecular sieve with high crystallinity and does not contain other phases.

[0040] Example 5

[0041] A method for preparing SAPO-44 microporous molecular sieves using attapulgite as raw material comprises the following steps:

[0042] 2g of attapulgite (with a silica content as high as 57% and an alumina content of 7.3%) was heat-treated with 34ml of hydrochloric acid for 6h. After filtration and washing until the pH reached approximately 7, rod-shaped silicon sources were obtained. 2.3g of phosphoric acid was dissolved in water and stirred. 1.04g of boehmite was added, and the mixture was stirred continuously. 0.23g of the rod-shaped silicon source was added to 11.78g of tetraethylammonium hydroxide. The mixture was stirred evenly at room temperature. The two solutions were mixed and stirred at room temperature. The synthesized sol-gel system was transferred to a polytetrafluoroethylene-lined autoclave and crystallized in a homogeneous reactor heated at 195℃ for 6h to obtain a crystallized product. The crystallized product was washed with deionized water until the pH of the filtrate reached 7.0. It was dried at 120℃ for 6h, then placed in a muffle furnace, heated to 200℃, held for 1h, and then calcined at 700℃ for 6h to obtain SAPO-44 microporous molecular sieve.

[0043] Figure 1 The XRD pattern shown in (E) indicates that the obtained sample is a pure-phase SAPO-44 microporous molecular sieve, free of other impurities. Figure 4 (E) The nitrogen adsorption-desorption curves indicate the presence of mesopores in the molecular sieve, with a surface area of ​​597.048 m². 2 ·g -1 .

[0044] In the description of this specification, the references to terms such as "embodiment," "example," and "specific example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0045] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing SAPO-44 microporous molecular sieves using attapulgite as raw material, characterized in that, Includes the following steps: Step A: Add the attapulgite to the acid solution, mix well, place it in a hydrothermal reactor for acid hydrothermal treatment, cool, filter, wash, and dry to obtain rod-shaped silicon source; Step B: Mix the aluminum source, phosphoric acid, and deionized water, and stir until homogeneous at room temperature to obtain solution a; Step C: Mix the rod-shaped silicon source and tetraethylammonium hydroxide, and stir until homogeneous at room temperature to obtain solution b; Step D: While stirring at room temperature, add solution a dropwise to solution b to form a sol-gel system; Step E: Transfer the sol-gel system obtained in step D to a homogeneous reactor for dynamic hydrothermal reaction to obtain the crystallized product; Step F: The crystallized product is filtered, washed, dried, and calcined to obtain the SAPO-44 microporous molecular sieve. In step A, the acid is hydrochloric acid, the mass-to-volume ratio of attapulgite to hydrochloric acid is 1g:10-20ml, and the hydrothermal time of the acid is 4-10h. In step B, the molar ratio of phosphoric acid and aluminum source is controlled to be 0.6-1.5:1, and the aluminum source is boehmite. The molar ratio of the silicon source in step C to the aluminum source in step B is controlled to be 0.1-1:1, and the molar ratio of the tetraethylammonium hydroxide to the aluminum source in step B is controlled to be 1.5-5:

1. The rotation speed for the dynamic hydrothermal reaction in step E is 5-50 rpm, and the sol-gel system is dynamically crystallized at 170-220℃ for 6-72 h.

2. The method for preparing SAPO-44 microporous molecular sieve using attapulgite as raw material according to claim 1, characterized in that, In step A, the attapulgite contains 47-70% silicon dioxide and 5-20% aluminum oxide.

3. The method for preparing SAPO-44 microporous molecular sieve using attapulgite as raw material according to claim 1, characterized in that, The washing described in step F is washing with deionized water until the pH of the filtrate is 7.

0. The drying is drying at 60-120℃ for 6-12 hours. The calcination is first holding at 200-300℃ for 1-3 hours, and then calcining at 350-700℃ for 3-24 hours.

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