Preparation method of high-strength and high-roundness molecular sieve pellets

Abstract

The application relates to the technical field of synthesis and molding of molecular sieve materials, in particular to a preparation method of high-strength high-roundness molecular sieve pellets, wherein the raw materials of the high-strength high-roundness molecular sieve pellets comprise sodium silicate, aluminum sulfate, boric acid, cumeng stone and deionized water containing sodium bicarbonate, and the preparation method mainly comprises the following steps: mixing the raw materials to prepare homogeneous gel; drop forming and pre-solidification are carried out through a constant-temperature oil column of liquid paraffin to obtain pre-solidified green bodies; the pre-solidified green bodies are immersed in a composite guiding liquid prepared from 1-butyl-3-methyl imidazole chloride, ammonium fluoride, triethylamine and water for pre-soaking; then, the pre-soaking is carried out together with the guiding liquid through step-by-step static crystallization with temperature programming; finally, the product is obtained through washing, drying and calcination. The method effectively improves the mechanical strength and shape roundness of the molecular sieve pellets, and the product is suitable for the fields of catalysis, adsorption and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of synthesis and molding of molecular sieve materials, and particularly relates to a preparation method of high-strength high-roundness molecular sieve pellets. BACKGROUND

[0002] As a kind of crystal material with regular pore structure, molecular sieve has been widely used in petroleum and chemical industry, natural gas purification, environmental governance, gas separation and other industrial fields due to its excellent adsorption separation performance, catalytic activity and shape selectivity. In industrial devices (such as fixed bed reactors, adsorption towers), spherical molecular sieve is the preferred form of large-scale application due to its good flowability, small bed resistance, good uniformity of filling and other advantages, and its performance directly affects the operation efficiency, energy consumption level and service life of the device. With the development of industrial processes towards high efficiency and long cycle, higher requirements are put forward for the core performance of spherical molecular sieve: on the one hand, the high-pressure operating environment and material flow impact of industrial devices require the molecular sieve pellets to have sufficient compressive strength to avoid breakage and pulverization during use, reduce the problems of increased bed pressure drop and equipment blockage; on the other hand, high-roundness molecular sieve pellets can further optimize the bed filling density, reduce fluid channeling, improve mass / heat transfer efficiency, and reduce inter-particle wear and tear. Patent CN119059531A discloses a full-crystal graded porous ZSM-5 type molecular sieve and its preparation method and application, the obtained silicon-aluminum molecular sieve powder and pectin are mixed in water, and a peristaltic pump is used to extrude the molecular sieve pellets. Patent CN117942929A discloses a 5A molecular sieve adsorbent and its preparation method and application, the powder containing 4A molecular sieve and a binder is subjected to ball forming to obtain pellets, and the pellets are dried and calcined to obtain matrix pellets; the matrix pellets are pre-wetted, and then subjected to crystal transformation to obtain 4A molecular sieve pellets; the 4A molecular sieve pellets are sequentially contacted with inorganic acid and organic acid, then washed with water, and then subjected to calcium exchange to obtain 5A molecular sieve pellets. The existing preparation technology of spherical molecular sieve still has significant bottlenecks: for example, the use of a binder for auxiliary molding can achieve spheroidization, but the introduction of the binder will reduce the effective active sites of the molecular sieve, and interface defects are easily formed after calcination, resulting in reduced compressive strength of the product, which is difficult to adapt to high-pressure working conditions; some binder-free preparation processes can improve the strength, but often have problems such as insufficient spheroidization and uneven particle size distribution. In addition, the directing agent (such as a single amine compound) can only achieve basic guidance of the molecular sieve framework during the crystallization process, and cannot consider the control of the crystal aggregation form, resulting in a balance between the roundness and strength of the product. In the existing technology, the molding and crystallization processes of spherical molecular sieve are often separated, and the morphology control in the pre-solidification stage and the structure construction in the subsequent crystallization process lack coordinated design, which causes the green body to be easily deformed and cracked during the crystallization process, and finally affects the roundness and strength stability of the product.

[0003] Therefore, in view of the contradiction between the strength and the roundness of the spherical molecular sieve in the prior art, it is of important industrial application value and scientific significance to develop a preparation technology of the molecular sieve small ball without relying on a binder, by optimizing components of a reaction system, to realize the synergistic optimization of high strength and high roundness. SUMMARY

[0004] The present application aims at overcoming the deficiencies in the prior art, and provides a preparation method of high-strength and high-roundness molecular sieve small balls, comprising the following steps:

[0005] Step S1. Preparing a homogeneous gel, adding sodium silicate, aluminum sulfate and boric acid into deionized water containing sodium bicarbonate and mixing uniformly, and then adding a luctite and performing stirring and ultrasonic dispersion treatment;

[0006] Step S2. Oil phase forming and pre-solidification, including liquid paraffin pretreatment, building a constant-temperature oil column, dropping the homogeneous gel into the oil column for forming and pre-solidification, and obtaining a pre-solidified green body after cleaning and air-drying;

[0007] Step S3. Preparing a composite guiding liquid, and pre-soaking the pre-solidified green body in the composite guiding liquid;

[0008] Step S4. Placing the pre-solidified green body and the composite guiding liquid into a reaction kettle for step-by-step static crystallization;

[0009] Step S5. Washing, drying and calcining the small balls after crystallization for post-processing, to obtain high-strength and high-roundness molecular sieve small balls.

[0010] Preferably, in step S1, the molar ratio of sodium bicarbonate, sodium silicate, aluminum sulfate, boric acid and luctite is (0.73-4.35) : (10-30) : 0.5 : (0.5-2) : (0.017-0.127).

[0011] The luctite, as a layered silicate mineral, has a uniform sheet structure which is uniformly embedded in the molecular sieve gel under the action of ultrasonic dispersion, forming a homogeneous gel composite system. On the one hand, the interlayer hydroxyl groups of the luctite form hydrogen bond with the silicate and aluminate species, providing anchoring sites for crystal growth and inhibiting particle agglomeration and deformation in the crystallization process. On the other hand, the boron atoms in the boric acid can partially replace the aluminum atoms in the silicate-aluminate framework, forming B-O-Si bonds and improving the cross-linking density of the framework. Meanwhile, the introduction of boron elements can adjust the pH value and viscosity of the gel system, creating a suitable environment for the uniform dispersion of luctite. The synergistic effect of luctite and boric acid not only solves the problem of uneven strength caused by the easy agglomeration of the reinforcing phase, but also strengthens the stability of the crystal structure by framework doping, so that the compressive strength is improved.

[0012] Preferably, in step S1, after adding the alietite, mechanical stirring is performed first, followed by ultrasonic dispersion, the mechanical stirring time is 20 minutes, the ultrasonic dispersion frequency is 20-30 kHz, and the time is 15-20 minutes.

[0013] Preferably, in step S2, the liquid paraffin pretreatment method is vacuum dehydration, the constant-temperature oil column is formed by heating and keeping the pretreated liquid paraffin, and the pre-solidification is the shrinkage molding of the gel droplets in the oil column.

[0014] Preferably, the temperature of the constant-temperature oil column is 80-100℃, and the height is 50-80 cm.

[0015] Preferably, in step S3, the raw materials of the composite directing agent include 1-butyl-3-methylimidazolium chloride, ammonium fluoride, triethylamine and water, and the molar ratio is 1:(0.5-0.8):2:(30-100).

[0016] Triethylamine, as an amine directing agent, dominates the construction of the basic framework of the molecular sieve, ensuring the formation of a regular channel structure; the ionic liquid can be adsorbed on the crystal growth surface due to its unique cation hydrophobic chain and anion coordination ability, thereby inhibiting the anisotropic growth of the crystal and guiding the uniform development of the crystal along the radial direction, thereby improving the sphericity; F - in the ammonium fluoride can form stable Si-F complexes with silicon species, adjust the crystal growth rate, and avoid the morphology distortion caused by local overgrowth; meanwhile, the introduction of F - can reduce the formation of defects during crystallization, further strengthening the framework strength.

[0017] Preferably, in step S3, the mass ratio of the pre-solidified green body to the composite directing agent is 1:(20-50), and slight stirring is performed regularly during the soaking.

[0018] Preferably, in step S3, the pre-soaking temperature is 40-60℃, and the time is 6-24 hours.

[0019] Preferably, the specific procedure of the step-by-step static crystallization is as follows: 1. increasing the temperature to 60℃ at a rate of 1℃ / min and keeping the temperature constant for 8-12 hours; 2. increasing the temperature to 90℃ at a rate of 0.5℃ / min and keeping the temperature constant for 18-24 hours; 3. increasing the temperature to 160℃ at a rate of 0.1℃ / min and keeping the temperature constant for 36-48 hours; and the cooling rate after the crystallization is completed is ≤2℃ / min.

[0020] During the 160℃ high-temperature stage, 1-butyl-3-methylimidazolium chloride penetrates into the interlayer of alietite, promoting the interlayer crystal growth, the alkaline environment controlled by triethylamine accelerates the crystal crosslinking, the rigid framework of alietite limits the excessive expansion of the crystal, and the spherical profile is maintained.

[0021] Preferably, in step S5, the process of roasting is 2℃ / min to 550℃, constant temperature roasting for 4 hours, and then cooling to room temperature with the furnace.

[0022] 2℃ / min slow heating, to avoid thermal stress caused by crystal shedding or ball cracking, the thermal conductivity of the palygorskite makes the internal temperature of the ball evenly distributed, to ensure the gradual decomposition of 1-butyl-3-methylimidazolium chloride, triethylamine, to avoid the gas impact of violent decomposition to destroy the crystal structure.

[0023] Beneficial effects:

[0024] The present application will contain sodium silicate, aluminum sulfate, boric acid and palygorskite homogeneous gel pre-cured green body, the green body is immersed in the composite guiding liquid, through the program crystallization and post-processing, high strength high roundness molecular sieve pellets are prepared, the composite guiding liquid includes 1-butyl-3-methylimidazolium chloride, ammonium fluoride, triethylamine, the triethylamine molecule is embedded between the silicon aluminum oxygen tetrahedron, through the coordination of N atom and skeleton oxygen, guide the crystal to form regular pore structure, the cation hydrophobic chain of 1-butyl-3-methylimidazolium chloride gathers together, and a layer of flexible coating layer is formed on the crystal surface, and the steric hindrance effect inhibits the excessive growth of the crystal along the specific crystal surface, and the anion Cl - forms electrostatic adsorption with the Al 3+ of the crystal surface, and guides the crystal to uniformly expand along the radial direction, and finally forms a spherical growth mode. The presence of triethylamine can accelerate the formation of crystal nucleus (strong coordination ability of amino group), and F - in the ammonium fluoride forms stable [SiF6] 2- complex with silicon species, reduces the polymerization rate of aluminosilicate, and makes the crystal growth rate stable, F - adsorption on the crystal surface has selectivity, preferentially adsorbs on the high-energy crystal surface which grows too fast, further inhibits the growth of the low-energy crystal surface, so that the crystal grows synchronously along the radial direction under the constraint of 1-butyl-3-methylimidazolium chloride, avoids the decrease of sphericity caused by local protrusion. The interlayer hydroxyl group of palygorskite and the Si-OH of molecular sieve skeleton are condensed by hydrogen bond to form a palygorskite-molecular sieve composite skeleton, and the presence of F - avoids the agglomeration of palygorskite layers, so that the reinforcing phase is uniformly dispersed. As a natural layered mineral, palygorskite limits the irregular flow of the gel when the green body is formed, and its interlayer structure can bind active ions such as silicon, aluminum and boron in the reaction system, avoiding the disorder of crystal growth caused by local high concentration. The imidazole ring structure of 1-butyl-3-methylimidazolium chloride is combined with the palygorskite layer by π-π interaction, and its cation guides the arrangement of silicon, aluminum and boron ions according to a specific topological structure. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is the product picture of the molecular sieve pellets obtained in Example 1.

[0026] Figure 2 A photograph of the molecular sieve pellet product obtained in Example 2.

[0027] Figure 3 A photograph of the molecular sieve pellet product obtained in Comparative Example 1.

[0028] Figure 4 XRD patterns of the molecular sieve pellets obtained in each of the examples and comparative examples. DETAILED DESCRIPTION

[0029] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with specific examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0030] The sodium silicate, aluminum sulfate, boric acid and deionized water containing sodium bicarbonate were weighed and added (the pH of the system was adjusted to 8-9), and stirred at 300-500 r / min at room temperature for 30-60 minutes until the system was uniform and transparent; the attapulgite was added, first mechanically stirred for 20 minutes, and then ultrasonically dispersed for 15-20 minutes at 20-30 kHz to obtain a homogeneous gel. The molar ratio of sodium bicarbonate, sodium silicate, aluminum sulfate, boric acid and attapulgite was (0.73-4.35) : (10-30) : 0.5 : (0.5-2) : (0.017-0.127).

[0031] The liquid paraffin was pretreated (100℃ vacuum dehydration for 2 hours to remove trace amounts of water), then poured into a vertical cylindrical container, heated and kept at 80-100℃ to form a constant temperature oil column 50-80 cm high (0.1% Span-80 hydrophobic emulsifier was added to improve the stability of the oil-water interface); the homogeneous gel was transferred into a separatory funnel and dropped vertically into the oil column through a gravity dropping tube with a diameter of 0.8-1.2 mm (dropping speed 1-2 drops per second), the gel droplets were shrunk into spherical shape in the oil column by interfacial tension and freely settled, and at the same time, pre-curing was completed in the 80-100℃ oil phase environment; the bottom formed pellets were collected, washed with 80-90℃ deionized water for 3-5 times (each time soaked for 10-15 minutes) to completely remove the surface liquid paraffin oil film, and dried at room temperature for 30 minutes to obtain the pre-cured green body.

[0032] 1-Butyl-3-methylimidazolium chloride, ammonium fluoride, triethylamine and water were sequentially added to a beaker, stirred at 200-300 r / min at room temperature for 30-60 minutes until completely dissolved, the pH of the composite guiding liquid was adjusted to 8.5-10.0, and stood for 10 minutes for standby use. The molar ratio of 1-butyl-3-methylimidazolium chloride, ammonium fluoride, triethylamine and water was 1: (0.5-0.8) : 2: (30-100).

[0033] The pre-cured green body is immersed in the composite directing liquid, and is placed in a constant-temperature water bath at 40-60℃ for 6-24 hours, and is slightly stirred for 5 minutes (rotation speed: 50 r / min) every 2 hours during the period. The mass ratio of the pre-cured green body to the composite directing liquid is 1:(20-50).

[0034] The pre-cured green body and the composite directing liquid are placed in a sealed reaction kettle, and are subjected to static crystallization according to the following procedure: 1. temperature is raised to 60℃ at a rate of 1℃ / min, and is kept constant for 8-12 hours; 2. temperature is raised to 90℃ at a rate of 0.5℃ / min, and is kept constant for 18-24 hours; 3. temperature is raised to 160℃ at a rate of 0.1℃ / min, and is kept constant for 36-48 hours. After the crystallization is completed, the heating device is turned off, and the temperature is naturally lowered to room temperature at a rate of ≤2℃ / min. The reaction kettle is opened, and the crystallized small spheres are taken out.

[0035] The crystallized small spheres are repeatedly washed with 80-90℃ deionized water, each time for 10-15 minutes, and the washing water is replaced for 3-5 times, until the pH of the washing liquid is 6.5-7.5. The washed small spheres are placed in a forced air drying oven, and are dried at a constant temperature of 80-100℃ for 12-24 hours until the mass of the small spheres is constant. The dried small spheres are transferred into a muffle furnace, and are heated to 550℃ at a rate of 2℃ / min in an air atmosphere, and are kept constant for 4 hours. Then, the temperature is lowered to room temperature along with the furnace, and high-strength high-roundness molecular sieve small spheres are obtained.

[0036] All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative labor fall within the scope of protection of the present application. The experimental methods in the following examples, for which specific conditions are not indicated, are generally carried out according to conventional conditions or according to the conditions recommended by the manufacturers. Unless otherwise specified, all percentages, ratios, proportions or parts are by weight.

[0037] The reagents and raw materials used in the examples and comparative examples of the present application can be obtained through commercial channels unless otherwise specified.

[0038] Example 1

[0039] The preparation method of the high-strength high-roundness molecular sieve small spheres comprises the following steps:

[0040] Sodium silicate, aluminum sulfate and boric acid are weighed, and are added into deionized water containing sodium bicarbonate (to adjust the pH of the system to 8.5). The system is stirred at 400 r / min at room temperature for 40 minutes until it is uniform and transparent. Lectorite is added, and is mechanically stirred for 20 minutes, and then is ultrasonically dispersed for 18 minutes at 25 kHz to obtain a homogeneous gel. The molar ratio of sodium bicarbonate, sodium silicate, aluminum sulfate, boric acid and lectorite is 2.45:20:0.5:1:0.05.

[0041] The liquid paraffin was pretreated (vacuum dehydration at 100°C for 2 hours to remove trace amount of water) and then poured into a vertical cylindrical container, heated and kept at 90°C to form a constant temperature oil column with a height of 60 cm (0.1% Span-80 hydrophobic emulsifier was added to improve the stability of the oil-water interface); the homogeneous gel was transferred into a separatory funnel and dropped vertically into the oil column through a gravity dropping tube with a diameter of 1.0 mm (dropping speed: 1 drop per second), the gel droplets were shrunk into spherical shape in the oil column by interfacial tension and freely settled, and at the same time, pre-solidification was completed in the 90°C oil phase environment; the bottom formed small balls were collected, washed with 85°C deionized water for 4 times (each time for 10 minutes), and completely removed the surface liquid paraffin oil film, and then dried at room temperature for 30 minutes to obtain the pre-solidified green body.

[0042] 1-butyl-3-methylimidazolium chloride, ammonium fluoride, triethylamine and water were sequentially added into a beaker, stirred at 250 r / min at room temperature for 40 minutes until completely dissolved, the pH of the composite guiding liquid was adjusted to 9.0, and then stood for 10 minutes for standby. The molar ratio of 1-butyl-3-methylimidazolium chloride, ammonium fluoride, triethylamine and water was 1:0.6:2:50.

[0043] The pre-solidified green body was immersed in the composite guiding liquid, and stood for immersion in a 50°C constant temperature water bath for 12 hours, and during the period, the pre-solidified green body was slightly stirred for 5 minutes every 2 hours (rotation speed: 50 r / min). The mass ratio of the pre-solidified green body to the composite guiding liquid was 1:30.

[0044] The pre-solidified green body and the composite guiding liquid were placed in a sealed reaction kettle, and the static crystallization was carried out according to the following procedure: 1. heated to 60°C at a rate of 1°C / min, and kept at 60°C for 10 hours; 2. heated to 90°C at a rate of 0.5°C / min, and kept at 90°C for 20 hours; 3. heated to 160°C at a rate of 0.1°C / min, and kept at 160°C for 40 hours; after the crystallization was completed, the heating device was turned off, and the reaction kettle was naturally cooled to room temperature at a rate of ≤2°C / min, and then the crystallized small balls were taken out.

[0045] The crystallized small balls were repeatedly washed with 85°C deionized water, each time for 12 minutes, and the washing water was replaced for 4 times until the pH of the washing liquid was 7.0; the washed small balls were placed in a forced air drying oven, dried at 90°C for 20 hours until the mass of the small balls was constant; the dried small balls were transferred into a muffle furnace, heated to 550°C at a rate of 2°C / min under air atmosphere, kept at 550°C for 4 hours, and then cooled to room temperature with the furnace to obtain high-strength high-roundness molecular sieve small balls, as shown in Figure 1 and Figure 4 The sphericity was 0.97, the compressive strength was 62 N / pellet, the attrition rate was 0.8%, and the specific surface area was 425 m 2 / g.

[0046] Example 2

[0047] A method for preparing high-strength and high-roundness molecular sieve pellets, comprising the following steps:

[0048] Weigh sodium silicate, aluminum sulfate, boric acid, and add them to deionized water containing sodium bicarbonate (adjust the pH of the system to 8), stir at 300 r / min at room temperature for 30 minutes until the system is uniform and transparent; add the rectorite, first mechanically stir for 20 minutes, then ultrasonically disperse for 15 minutes at 20 kHz to obtain a homogeneous gel. The molar ratio of sodium bicarbonate, sodium silicate, aluminum sulfate, boric acid, and rectorite is 0.73:10:0.5:0.5:0.017.

[0049] Pretreat the liquid paraffin (vacuum dehydration at 100°C for 2 hours to remove trace amounts of water), then pour it into a vertical cylindrical container, heat and keep it at 80°C to form a constant-temperature oil column 50 cm high (add 0.1% Span-80 hydrophobic emulsifier to improve the stability of the oil-water interface); transfer the homogeneous gel into a separatory funnel, and drop it vertically into the oil column through a gravity dropping tube with a 0.8 mm diameter (dropping speed of 2 drops per second), the gel droplets shrink into spherical shape in the oil column due to interfacial tension and freely settle, and at the same time, pre-solidification is completed in the 80°C oil phase environment; collect the bottom-formed pellets, rinse them with 80°C deionized water for 3 times (each time for 10 minutes), completely remove the surface liquid paraffin oil film, and air dry at room temperature for 30 minutes to obtain the pre-solidified green body.

[0050] Add 1-butyl-3-methylimidazolium chloride, ammonium fluoride, triethylamine, and water into a beaker in sequence, stir at 200 r / min at room temperature for 30 minutes until completely dissolved, adjust the pH of the composite directing liquid to 8.5, and stand for 10 minutes for standby use. The molar ratio of 1-butyl-3-methylimidazolium chloride, ammonium fluoride, triethylamine, and water is 1:0.5:2:30.

[0051] Immerse the pre-solidified green body into the composite directing liquid, and stand for immersion in a 40°C constant-temperature water bath for 6 hours, with slight stirring for 5 minutes (rotation speed of 50 r / min) every 2 hours during the process. The mass ratio of the pre-solidified green body to the composite directing liquid is 1:20.

[0052] Put the above pre-solidified green body and the composite directing liquid into a sealed reaction kettle together, and perform static crystallization according to the following procedure: 1. increase the temperature to 60°C at a rate of 1°C / min, and keep it constant for 8 hours; 2. increase the temperature to 90°C at a rate of 0.5°C / min, and keep it constant for 18 hours; 3. increase the temperature to 160°C at a rate of 0.1°C / min, and keep it constant for 36 hours; after crystallization, turn off the heating device, and naturally cool it to room temperature at a rate of ≤2°C / min, then open the reaction kettle to take out the crystallized pellets.

[0053] The crystallized beads are repeatedly washed with 80°C deionized water, each time for 10 minutes, and the washing water is replaced for 3 times until the washing liquid pH = 6.5; the washed beads are placed into a forced air drying oven, and dried at 80°C for 12 hours until the mass of the beads is constant; the dried beads are transferred into a muffle furnace, and heated to 550°C at 2°C / min under air atmosphere, and kept at 550°C for 4 hours, and then cooled to room temperature in the furnace, to obtain high-strength high-roundness molecular sieve beads, as shown in Figure 2 and Figure 4 .

[0054] Example 3

[0055] A method for preparing high-strength high-roundness molecular sieve beads comprises the following steps:

[0056] Sodium silicate, aluminum sulfate, boric acid, and deionized water containing sodium bicarbonate (adjusting the system pH = 9) are weighed and added, and the system is stirred at 500 r / min at room temperature for 60 minutes until it is uniform and transparent; the cumengite is added, first mechanically stirred for 20 minutes, and then ultrasonically dispersed for 20 minutes at 30 kHz to obtain a homogeneous gel. The molar ratio of sodium bicarbonate, sodium silicate, aluminum sulfate, boric acid, and cumengite is 4.35:30:0.5:2:0.127.

[0057] The liquid paraffin is pretreated (100°C vacuum dehydration for 2 hours to remove trace amounts of water), then poured into a vertical cylindrical container, heated and kept at 100°C to form a constant temperature oil column 80 cm high (add 0.1% Span-80 hydrophobic emulsifier to improve the stability of the oil-water interface); the homogeneous gel is transferred into a separatory funnel and vertically dripped into the oil column through a gravity dropping tube with a 1.2 mm diameter (dripping speed 1 drop / second), the gel droplets are spherical in the oil column due to interfacial tension and free sedimentation, and pre-solidification is completed in the 100°C oil phase environment; the bottom formed beads are collected, washed with 90°C deionized water for 5 times (each time for 15 minutes), and completely removed from the surface liquid paraffin oil film, and air dried at room temperature for 30 minutes to obtain a pre-solidified green body.

[0058] 1-Butyl-3-methylimidazolium chloride, ammonium fluoride, triethylamine, and water are sequentially added to a beaker, stirred at 300 r / min at room temperature for 60 minutes until completely dissolved, the pH of the composite directing liquid is adjusted to 10.0, and it is left to stand for 10 minutes for standby use. The molar ratio of 1-butyl-3-methylimidazolium chloride, ammonium fluoride, triethylamine, and water is 1:0.8:2:100.

[0059] The pre-solidified green body is immersed in the composite directing liquid, and left to stand in a 60°C constant temperature water bath for 24 hours, with slight stirring for 5 minutes every 2 hours (rotation speed 50 r / min), and the mass ratio of the pre-solidified green body to the composite directing liquid is 1:50.

[0060] Put the pre-cured green body and the composite directing liquid into a sealed reaction kettle and perform static crystallization according to the following procedure: 1. increase the temperature to 60°C at a rate of 1°C / min and keep the temperature constant for 12 hours; 2. increase the temperature to 90°C at a rate of 0.5°C / min and keep the temperature constant for 24 hours; 3. increase the temperature to 160°C at a rate of 0.1°C / min and keep the temperature constant for 48 hours; after the crystallization is completed, turn off the heating device and naturally cool the temperature to room temperature at a rate of ≤2°C / min, and then open the reaction kettle to take out the crystallized small balls.

[0061] Wash the crystallized small balls with 90°C deionized water repeatedly, each time for 15 minutes, and replace the washing water 5 times until the washing liquid has a pH of 7.5; place the washed small balls into a forced air drying oven and keep the temperature constant at 100°C for 24 hours until the mass of the small balls is constant; transfer the dried small balls into a muffle furnace, increase the temperature to 550°C at a rate of 2°C / min under an air atmosphere, keep the temperature constant for 4 hours, and then cool the temperature to room temperature with the furnace, to obtain high-strength high-roundness molecular sieve small balls, as shown in FIG. 1. Figure 4

[0062] Comparative Example 1

[0063] A method for preparing high-strength high-roundness molecular sieve small balls includes the following steps:

[0064] Weigh sodium silicate, aluminum sulfate, boric acid, and add them to deionized water containing sodium bicarbonate (adjust the pH of the system to 8.5), and stir at 400 r / min at room temperature for 40 minutes until the system is uniform and transparent; add rectorite, first mechanically stir for 20 minutes, and then ultrasonically disperse for 18 minutes at 25 kHz to obtain a homogeneous gel. The molar ratio of sodium bicarbonate, sodium silicate, aluminum sulfate, boric acid, and rectorite is 2.45:20:0.5:1:0.05.

[0065] Pretreat the liquid paraffin (dehydrate at 100°C for 2 hours under vacuum to remove trace amounts of water), then pour it into a vertical cylindrical container, heat and keep the temperature constant at 90°C to form a 60 cm high constant temperature oil column (add 0.1% Span-80 hydrophobic emulsifier to improve the stability of the oil-water interface); transfer the homogeneous gel into a separatory funnel, and vertically drop it into the oil column through a gravity dropping tube with a 1.0 mm diameter (dropping speed of 1 drop per second), the gel droplets are spherical in shape due to the interfacial tension in the oil column and freely settle, and at the same time, the pre-curing is completed in the 90°C oil phase environment; collect the formed small balls at the bottom, rinse them with 85°C deionized water 4 times (each time for 10 minutes), completely remove the surface liquid paraffin oil film, and air dry at room temperature for 30 minutes to obtain the pre-cured green body.

[0066] Add triethylamine and water into a beaker in sequence, stir at 250 r / min at room temperature for 40 minutes until completely dissolved, adjust the pH to 9.0, and stand for 10 minutes for standby use. The mass ratio of triethylamine to water is 1:100.

[0067] ​The pre-cured green body is immersed in a triethylamine aqueous solution, and is placed in a constant-temperature water bath at 50°C for 12 hours, with slight stirring for 5 minutes (rotation speed 50 r / min) every 2 hours. The mass ratio of the pre-cured green body to the triethylamine aqueous solution is 1:30.

[0068] The pre-cured green body and the triethylamine aqueous solution are placed in a sealed reaction kettle, and static crystallization is performed according to the following procedure: 1. temperature is raised to 60°C at a rate of 1°C / min, and is kept constant for 10 hours; 2. temperature is raised to 90°C at a rate of 0.5°C / min, and is kept constant for 20 hours; 3. temperature is raised to 160°C at a rate of 0.1°C / min, and is kept constant for 40 hours. After crystallization is completed, the heating device is turned off, and the reaction kettle is opened to take out the crystallized small spheres, with natural cooling to room temperature at a rate of ≤2°C / min.

[0069] The crystallized small spheres are repeatedly washed with 85°C deionized water, with each soaking for 12 minutes, and the washing water is replaced 4 times, until the washing liquid has pH=7.0. The washed small spheres are placed in a forced air drying oven, and are dried at 90°C for 20 hours until the mass of the small spheres is constant. The dried small spheres are transferred into a muffle furnace, and are heated to 550°C at a rate of 2°C / min under an air atmosphere, and are kept constant for 4 hours. Subsequently, the furnace is cooled to room temperature, to obtain high-strength high-roundness molecular sieve small spheres, as shown in Figure 3 and Figure 4 .

[0070] Comparative Example 2

[0071] A method for preparing high-strength high-roundness molecular sieve small spheres includes the following steps:

[0072] Sodium silicate, aluminum sulfate, boric acid, and deionized water containing sodium bicarbonate (to adjust the pH of the system to 8) are weighed, and are stirred at 300 r / min at room temperature for 30 minutes until the system is uniform and transparent. Lectorite is added, and is mechanically stirred for 20 minutes, and then is ultrasonically dispersed for 15 minutes at 20 kHz, to obtain a homogeneous gel. The molar ratio of sodium bicarbonate, sodium silicate, aluminum sulfate, boric acid, and lectorite is 0.73:10:0.5:0.5:0.017.

[0073] Liquid paraffin is pretreated (vacuum dehydration at 100°C for 2 hours to remove trace amounts of water), and is then poured into a vertical cylindrical container, and is heated and kept at 80°C to form a constant-temperature oil column 50 cm high (0.1% Span-80 hydrophobic emulsifier is added to improve the stability of the oil-water interface); the homogeneous gel is transferred into a separatory funnel, and is vertically dripped into the oil column through a gravity dropping tube with a 0.8 mm opening (dripping speed 2 drops per second). The gel droplets are spherical in shape due to interfacial tension in the oil column, and are free to settle, and at the same time, pre-curing is completed in the 80°C oil phase environment. The bottom-formed small spheres are collected, and are washed with 80°C deionized water 3 times (each time for 10 minutes), to completely remove the surface liquid paraffin oil film. The small spheres are air-dried at room temperature for 30 minutes, to obtain a pre-cured green body.

[0074] The ammonium fluoride, triethylamine and water were sequentially added into a beaker, stirred at 200 r / min for 30 minutes at room temperature until completely dissolved, the pH of the guiding liquid was adjusted to 8.5, and the mixture was allowed to stand for 10 minutes for standby. The molar ratio of ammonium fluoride, triethylamine and water was 1:4:60.

[0075] The pre-cured green body was immersed in the guiding liquid, and the mixture was allowed to stand for 6 hours in a constant temperature water bath at 40℃, during which the mixture was slightly stirred for 5 minutes every 2 hours (rotation speed 50 r / min). The mass ratio of the pre-cured green body to the guiding liquid was 1:20.

[0076] The pre-cured green body and the guiding liquid were placed in a sealed reaction kettle, and the static crystallization was carried out according to the following procedure: 1. The temperature was raised to 60℃ at a rate of 1℃ / min, and the temperature was kept constant for 8 hours; 2. The temperature was raised to 90℃ at a rate of 0.5℃ / min, and the temperature was kept constant for 18 hours; 3. The temperature was raised to 160℃ at a rate of 0.1℃ / min, and the temperature was kept constant for 36 hours. After the crystallization was completed, the heating device was turned off, and the reaction kettle was opened to take out the crystallized beads.

[0077] The crystallized beads were repeatedly washed with 80℃ deionized water, each time for 10 minutes, and the washing water was replaced for 3 times until the pH of the washing liquid was 6.5. The washed beads were placed in a forced air drying oven, and dried at 80℃ for 12 hours until the mass of the beads was constant. The dried beads were transferred into a muffle furnace, and the temperature was raised to 550℃ at a rate of 2℃ / min under air atmosphere, and the temperature was kept constant for 4 hours. Then the furnace was cooled to room temperature to obtain high-strength high-roundness molecular sieve beads.

[0078] Comparative Example 3

[0079] The preparation method of high-strength high-roundness molecular sieve beads comprises the following steps:

[0080] Sodium silicate, aluminum sulfate, boric acid and deionized water containing sodium bicarbonate (adjusting the pH of the system to 9) were weighed and added into a beaker, and the mixture was stirred at 500 r / min for 60 minutes at room temperature until the system was uniform and transparent. Lectorite was added, and the mixture was mechanically stirred for 20 minutes, and then ultrasonically dispersed for 20 minutes at 30 kHz to obtain a homogeneous gel. The molar ratio of sodium bicarbonate, sodium silicate, aluminum sulfate, boric acid and lectorite was 4.35:30:0.5:2:0.127.

[0081] The liquid paraffin is pretreated (vacuum dehydration at 100℃ for 2 hours to remove trace amount of water) and then poured into a vertical cylindrical container, heated and kept at 100℃ to form a constant temperature oil column of 80 cm high (0.1% Span-80 hydrophobic emulsifier is added to improve the stability of the oil-water interface); the homogeneous gel is transferred into a separatory funnel and dropped vertically into the oil column through a gravity dropping tube with a diameter of 1.2 mm (dropping speed of 1 drop per second), the gel droplets are shrunk into spherical shape by the interfacial tension in the oil column and freely settle, and at the same time, the pre-solidification is completed in the 100℃ oil phase environment; the bottom formed small balls are collected, washed with 90℃ deionized water for 5 times (each time for 15 minutes), the surface liquid paraffin oil film is completely removed, and the pre-solidified green body is obtained after air drying at room temperature for 30 minutes.

[0082] The ammonium fluoride and water are sequentially added into a beaker, stirred at 300 r / min at room temperature for 60 minutes until completely dissolved, the pH is adjusted to 10.0, and then left to stand for 10 minutes for standby. The mass ratio of ammonium fluoride to water is 1:100.

[0083] The pre-solidified green body is immersed in the ammonium fluoride aqueous solution, left to stand for immersion in a 60℃ constant temperature water bath for 24 hours, and slightly stirred for 5 minutes (rotation speed of 50 r / min) every 2 hours during the period. The mass ratio of the pre-solidified green body to the ammonium fluoride aqueous solution is 1:50.

[0084] The pre-solidified green body and the ammonium fluoride aqueous solution are placed in a sealed reaction kettle together, and the static crystallization is carried out according to the following procedure: 1. temperature is raised to 60℃ at a rate of 1℃ / min, and kept constant for 12 hours; 2. temperature is raised to 90℃ at a rate of 0.5℃ / min, and kept constant for 24 hours; 3. temperature is raised to 160℃ at a rate of 0.1℃ / min, and kept constant for 48 hours; after the crystallization is completed, the heating device is turned off, the reaction kettle is opened, and the crystallized small balls are taken out.

[0085] The crystallized small balls are repeatedly washed with 90℃ deionized water, each time for 15 minutes, and the washing water is replaced for 5 times until the washing liquid pH is 7.5; the washed small balls are placed into a forced air drying oven, dried at 100℃ for 24 hours until the mass of the small balls is constant; the dried small balls are transferred into a muffle furnace, heated to 550℃ at a rate of 2℃ / min under air atmosphere, kept constant for 4 hours, and then cooled to room temperature with the furnace to obtain high-strength high-roundness molecular sieve small balls.

[0086] Spheroidicity: According to the method for determining the spheroidicity of molecular sieve, at least 50 finished product molecular sieve pellets were randomly selected, and a high-resolution microscopic imaging system was used to collect the two-dimensional projection images of the particles; the image analysis software was used to extract the long axis (L) and short axis (B) size of the particle projection, and the single particle spheroidicity was calculated according to the formula spheroidicity = B / L. Compressive strength: According to the method for determining the compressive strength of molecular sieve in HG / T 2782-2011, 50 finished product pellets were selected, and the particles with cracks or damage on the surface were removed; a particle compressive strength tester was used to apply axial pressure to a single pellet at a constant rate of 1 mm / min, and the maximum pressure value at which the particle was broken was recorded. Abrasion rate: According to the method for determining the abrasion rate of molecular sieve drying agent for thermal power plants in DL / T 956-2017, 100 g of finished product molecular sieve pellets were weighed and placed in a drum abrasion tester, with a speed of 60 r / min and a time of 30 min; after the abrasion test was completed, the powder under the sieve was collected and weighed using a 0.9 mm standard sieve; the abrasion rate was calculated according to the formula abrasion rate = (mass of powder under the sieve / initial mass of the sample) x 100%. XRD: The pellets were ground in a mortar to prepare a tablet, which was tested for crystal type in an X-ray diffractometer. Si / Al ratio: The Si and Al element contents in the molecular sieve were determined by X-ray fluorescence spectrometer (XRF), and the molar ratio was calculated. Acid property characterization: NH3-TPD was used to characterize the acid properties, wherein the weak acid corresponds to a desorption temperature of 150-250°C, the medium strong acid corresponds to a desorption temperature of 250-400°C, and the strong acid corresponds to a desorption temperature of 400-600°C, and the number of acid sites was quantified by the amount of ammonia desorption (unit: mmol / g). The pore structure was determined by low-temperature nitrogen adsorption-desorption experiment. - Programmed temperature desorption (NH3-TPD) characterization, wherein the weak acid corresponds to a desorption temperature of 150-250°C, the medium strong acid corresponds to a desorption temperature of 250-400°C, and the strong acid corresponds to a desorption temperature of 400-600°C, and the number of acid sites was quantified by the amount of ammonia desorption (unit: mmol / g). Pore structure was determined by low-temperature nitrogen adsorption-desorption experiment.

[0087] Table 1 is the mechanical properties and pore structure indicators of the molecular sieve pellets prepared in the examples and comparative examples

[0088]

[0089] Table 2 is the Si / Al ratio and acid property characterization results of the molecular sieve pellets prepared in the examples and comparative examples

[0090]

[0091] As shown in Table 1, the spheroidicity of Examples 1 to 3 is all ≥0.95, the compressive strength is 53-75 N / pellet, and the abrasion rate is 0.5%-0.9%. The spheroidicity of Comparative Examples 1-3 is ≤0.91, the compressive strength is only 25-40 N / pellet, and the abrasion rate is as high as 3.5%-7.8%. The overall mechanical properties of the examples are better than those of the comparative examples, because the examples use a composite directing liquid of 1-butyl-3-methylimidazolium chloride, ammonium fluoride and triethylamine. The cation of 1-butyl-3-methylimidazolium chloride can be adsorbed on the surface of the gel green body by electrostatic action, inhibiting the irregular growth of crystals and ensuring the spheroidicity. Ammonium fluoride provides F -The adjustable molecular sieve crystallization rate, the interface energy of reducing crystal growth, the reduction of crystal boundary defects, and the improvement of crystal density; triethylamine maintains the pH stability of the crystallization system, promotes the uniform nucleation and slow growth of the crystal, and avoids the crystal fragmentation or morphology distortion caused by local supersaturation. The specific surface area of Comparative Examples 1-3 is 182-268 m

[0092] The specific surface area of Examples 1-3 is 382-486 m 2 / g, and the pore volume is 0.32-0.45 cm 3 / g, and increases with the increase of the proportion of sodium silicate and the addition amount of rectorite. The specific surface area of Comparative Examples 1-3 is 182-268 m 2 / g, and the pore volume is 0.12-0.21 cm 3 / g, which is only 1 / 2-1 / 3 of the Examples, because the hydrophobic chain of 1-butyl-3-methyl imidazole chloride can self-assemble to form a mesoporous channel template, and the hydrophilic group induces the formation of molecular sieve microporous crystal nucleus, realizing the cooperative construction of multi-level pores; the F - The weakly bonded sites of the molecular sieve framework can be selectively etched to form additional mesopores, and 1-butyl-3-methyl imidazole chloride and ammonium fluoride together increase the specific surface area and pore volume of the molecular sieve. Comparative Examples 1-3 cannot form multi-level pores due to the absence of 1-butyl-3-methyl imidazole chloride, and the pore structure is single and narrow, so the pore volume and specific surface area are significantly low. 1-Butyl-3-methyl imidazole chloride provides a mesoporous template, rectorite provides interlayer mesoporous space, and the etching effect of ammonium fluoride can open up the communication path between different pores to form continuous pores. In Example 3, the composite directing liquid and high molar ratio rectorite work together, and the specific surface area reaches 486 m 2 / g, and the pore volume reaches 0.45 cm 3 / g, which is 2.67 times and 3.75 times that of Comparative Example 3 without composite directing liquid, respectively. The rigid support of the rectorite sheet can prevent the collapse of the pore caused by the removal of the 1-butyl-3-methyl imidazole chloride template, and the triethylamine in the composite directing liquid can promote the uniform deposition of silicon and aluminum species between the rectorite layers, and the etching effect of ammonium fluoride can eliminate the amorphous blockage in the pores, further improving the pore connectivity.

[0093] As can be seen from Table 2, the total amount of medium-strong acid and strong acid sites of Examples 1-3 is much higher than that of Comparative Examples 1-3. The imidazole ring cation of 1-butyl-3-methylimidazolium chloride has a specific spatial configuration and charge density, and can act as a molecular template to form a stable precursor complex with silicon-aluminum species through electrostatic interaction and hydrogen bonding, guiding the growth of the molecular sieve framework according to a specific channel structure. Comparative Example 1 only contains triethylamine, which can provide an alkaline environment, but lacks the template effect of 1-butyl-3-methylimidazolium chloride and the etching optimization of NH4F, resulting in many crystal framework defects, strong acid sites being wrapped by amorphous species, and the proportion being only 25%; Comparative Example 3 only contains NH4F, which is excessively etched and lacks alkalinity balance, resulting in the destruction of strong acid sites, and the proportion being only 28.4%; 1-butyl-3-methylimidazolium chloride in Examples 1-3 provides a template effect, guiding the formation of regular channels by silicon-aluminum species and providing a stable carrier for strong acid sites; NH4F selectively etches amorphous defects to expose more strong acid sites; triethylamine balances the alkalinity of the system to avoid excessive protonation of 1-butyl-3-methylimidazolium chloride and excessive etching of NH4F, thereby increasing the proportion of strong acid sites.

[0094] Finally, it should be noted that the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features, as long as they are within the spirit and principles of the present application. Any modification, equivalent replacement, improvement, etc. made within the scope of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing high-strength, high-sphericity molecular sieve microspheres, characterized in that, Includes the following steps: Step S1. Prepare a homogeneous gel by adding sodium silicate, aluminum sulfate, and boric acid to deionized water containing sodium bicarbonate and mixing them evenly, then adding attapulgite and dispersing it by stirring and ultrasonication. Step S2. Oil phase molding and pre-curing, including liquid paraffin pretreatment, construction of a constant temperature oil column, dripping homogeneous gel into the oil column for molding and pre-curing, and obtaining a pre-cured green body after cleaning and drying; Step S3. Prepare the composite guiding liquid and immerse the pre-cured green body in the composite guiding liquid for pre-soaking; Step S4. Place the pre-cured green body and the composite guiding liquid together into the reactor for stepwise static crystallization; Step S5. The crystallized microspheres are washed, dried, and calcined to obtain high-strength, high-sphericity molecular sieve microspheres. In step S1, the molar ratio of sodium bicarbonate, sodium silicate, aluminum sulfate, boric acid, and attapulgite is (0.73-4.35):(10-30):0.5:(0.5-2):(0.017-0.127); in step S2, the liquid paraffin is pretreated by vacuum dehydration, the constant temperature oil column is formed by heating and maintaining the pretreated liquid paraffin, and the pre-curing is the shrinkage and formation of gel droplets in the oil column; in step S3, the raw materials of the composite guiding liquid include 1-butyl-3-methylimidazolium chloride, ammonium fluoride, triethylamine, and water, with a molar ratio of 1:(0.5-0.8):2:(30-100).

2. The method for preparing high-strength, high-sphericity molecular sieve microspheres according to claim 1, characterized in that, In step S1, after adding attapulgite, mechanical stirring is performed first, followed by ultrasonic dispersion. The mechanical stirring time is 20 minutes, and the ultrasonic dispersion frequency is 20-30 kHz for 15-20 minutes.

3. The method for preparing high-strength, high-sphericity molecular sieve microspheres according to claim 1, characterized in that, The temperature of the constant temperature oil column is 80-100℃ and the height is 50-80cm.

4. The method for preparing high-strength, high-sphericity molecular sieve microspheres according to claim 1, characterized in that, In step S3, the mass ratio of the pre-cured green body to the composite guiding liquid is 1:(20-50), and slight stirring is performed periodically during soaking.

5. The method for preparing high-strength, high-sphericity molecular sieve microspheres according to claim 1, characterized in that, In step S3, the pre-soaking temperature is 40-60℃ and the time is 6-24 hours.

6. The method for preparing high-strength, high-sphericity molecular sieve microspheres according to claim 1, characterized in that, The specific procedure for the stepwise static crystallization is as follows: (1) Heat to 60℃ at 1℃ / min and hold for 8-12 hours; (2) Heat to 90℃ at 0.5℃ / min and hold for 18-24 hours; (3) Heat to 160℃ at 0.1℃ / min and hold for 36-48 hours; The cooling rate after crystallization is ≤2℃ / min.

7. The method for preparing high-strength, high-sphericity molecular sieve microspheres according to claim 1, characterized in that, In step S5, the roasting process involves heating to 550°C at a rate of 2°C / min, roasting at a constant temperature for 4 hours, and then cooling to room temperature in the furnace.

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