CN102274743B - High intercrystal poriness zeolite coating material on surface of porous silicon carbide carrier and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of structural catalysts and their applications, and in particular relates to a zeolite coating material with high intercrystalline porosity on the surface of a porous silicon carbide carrier and a preparation method thereof. The porous silicon carbide carrier involved in the material has a macroscopic porous structure, such as a foam structure and a honeycomb structure. Zeolite coatings have high intercrystalline porosity. In this method, the surface of the silicon carbide carrier is modified by a colloidal zeolite directing agent to realize the preferential growth of zeolite crystals on the surface of the silicon carbide carrier; interporosity. The coating material has high intercrystalline porosity, small zeolite crystal size, good molecular diffusion performance, large zeolite loading capacity, adjustable zeolite crystal silicon-aluminum ratio, zeolite coating thickness, and good interface bonding performance between zeolite crystal and silicon carbide carrier. The structured catalyst is conducive to enhancing mass transfer and heat transfer, and will have broad application prospects in the fields of catalysis, adsorption, separation and the like.

Description

High intercrystalline porosity zeolite coating material on the surface of porous silicon carbide carrier and its preparation

technical field

The invention belongs to the technical field of structural catalysts and their applications, and in particular relates to a zeolite coating material with high intercrystalline porosity on the surface of a porous silicon carbide carrier and a preparation method thereof.

Background technique

Zeolite crystals have unique structures and properties, and have been widely used as catalysts, catalyst supports or adsorbents in petrochemical, environmental protection and other fields. Traditional zeolite crystal catalysts are applied in the fixed bed in the form of particles, which not only leads to a waste of energy due to the increase of bed pressure drop, but also produces a large concentration and temperature gradient in the production process, which reduces the catalytic performance of the catalyst. efficiency. At the same time, the separation and recovery of zeolite crystal catalysts are difficult, resulting in catalyst loss and environmental pollution.

Supported zeolites have high mechanical strength, low pressure drop, high catalytic activity and high thermal stability, and have attracted the attention of many catalytic workers. There are two main methods for preparing the loaded zeolite molecular sieve coating: (1) Dip coating. This method is to directly immerse the carrier into the slurry containing zeolite molecular sieve molecular sieve and oxide binder, so that a layer of zeolite molecular sieve is loaded on the surface of the carrier. The prominent advantage of this method is that it is easy to operate and can be applied to carriers of various shapes. But its disadvantage is that the bond between the zeolite coating and the carrier is not strong enough, so the loaded zeolite prepared by this method is not ideal in some reaction processes with severe temperature changes, fast airflow speed and large mechanical shock. (2) In situ synthesis method. That is, the carrier is directly synthesized by immersing the carrier in a solution containing nutrients required for zeolite growth. The remarkable advantage of this method is that the zeolite coating is more firmly combined with the carrier surface. But the disadvantage of this method is that the coating is very dense and there are very few intergranular pores. In order to obtain a larger loading capacity, the usual method is to prepare large zeolite crystals or thicker zeolite membranes on the surface of the carrier. In this way, the diffusion of reactants and reaction products in the zeolite crystal and zeolite coating is limited. As a result, only the inner surface of the zeolite near the outside of the catalyst particle is used, while the inner surface of the micropore center and inside cannot be used. , reducing the utilization of the catalyst. The reaction product cannot be separated from the zeolite crystal in time, which increases the probability of secondary reactions and reduces the selectivity to the target product. At the same time, due to the large zeolite crystal size or the thick zeolite coating, the heat transfer between the zeolite coating and the carrier is limited, which easily causes local overheating in the zeolite coating and deactivates the catalyst.

Contents of the invention

The purpose of the present invention is to provide a zeolite coating material with high intercrystalline porosity on the surface of a porous silicon carbide carrier and a preparation method thereof, so as to solve the problems of unsatisfactory loaded zeolite coating in the prior art. The porous silicon carbide carrier involved in the material has a macroscopic porous structure, such as a foam structure and a honeycomb structure. The zeolite coating has high intercrystalline porosity, and the intercrystalline pores are formed by overlapping ZSM-5 or Silicalite-1 zeolite crystals of 0.5-10 microns. In this method, the colloidal zeolite directing agent is grown in situ on the surface of the silicon carbide carrier, and the alkalinity, nutrient concentration, and alkali metal ion addition of the secondary growth solution are controlled to realize the preferential growth of zeolite crystals on the surface of the silicon carbide carrier and to control the crystallinity. interporosity. The coating material has high intercrystalline porosity, small zeolite crystal size, and good molecular diffusion performance; large zeolite loading capacity, zeolite crystal silicon-aluminum ratio, and zeolite coating thickness can be adjusted; zeolite crystal and silicon carbide carrier The interface bonding performance is good .

Technical scheme of the present invention is:

A zeolite coating material with high intercrystalline porosity on the surface of a porous silicon carbide carrier and a preparation method thereof. The method uses silicon carbide with a foam structure or a honeycomb structure as a carrier, and grows zeolite crystals with high intercrystalline porosity on the surface. There are pores of 2-3000 nanometers between the zeolite crystals, which is beneficial to improving the mass transfer capacity of reactants and reaction products in the zeolite coating. The colloidal seed crystal directing agent is used to modify the porous silicon carbide carrier to realize the preferential nucleation and preferential growth of zeolite crystals on the surface of the carrier. Control the alkalinity, nutrient concentration and alkali metal ion addition of the secondary growth solution to realize the preferential growth of zeolite crystals on the surface of the silicon carbide carrier and control the intercrystalline porosity. By adjusting the added amount of aluminum ions, the silicon-aluminum ratio of the zeolite coating is regulated. By changing the ratio of the solution to the porous silicon carbide carrier and the synthesis times, the loading capacity of the zeolite crystal is regulated.

In the present invention, the coating material has a high intercrystalline porosity, the intercrystalline pore size is 2-3000 nanometers, the loading capacity of zeolite crystals on the surface of porous silicon carbide carrier is large, and the loading capacity of zeolite crystals is 0-60% by mass fraction (preferably 10-30%) adjustable within the range. The silicon carbide carrier has a macroporous structure, and the silicon carbide carrier has a foam structure or a honeycomb structure.

In the present invention, the zeolite crystal is ZSM-5 or silicalite-1 type zeolite, and the zeolite crystal size is 0.5-10 microns.

In the present invention, the preparation method of the zeolite coating material with high intercrystalline porosity on the surface of the porous silicon carbide carrier uses a colloidal zeolite directing agent to modify the silicon carbide carrier to control the preferential nucleation and preferential growth of zeolite crystals on the surface of the silicon carbide carrier ; Control the alkalinity of the secondary growth solution, the concentration of nutrients and the amount of alkali metal ions added, and regulate the intercrystalline porosity and loading capacity of the coating.

The preparation of the colloidal zeolite directing agent uses ethyl orthosilicate as the silicon source, tetrapropylammonium hydroxide as the template, and is synthesized in situ in deionized water. The preparation process is as follows:

1) Solution preparation

Mix ethyl orthosilicate, tetrapropylammonium hydroxide, and deionized water in proportion, and the molar ratio between ethyl orthosilicate, tetrapropylammonium hydroxide, and deionized water is 1:0.1～1.0:10 ~100; the preferred molar ratio is 1:0.2~0.4:20~50;

2) Hydrothermal synthesis

After the tetraethyl orthosilicate is completely hydrolyzed, put the above solution and porous silicon carbide carrier in a reaction kettle for hydrothermal synthesis; the temperature of hydrothermal synthesis is 100-170°C, and the reaction time is 0-12 (preferably 1-6) hours , the pressure is the autogenous pressure of the solution.

The preparation of the secondary growth solution adopts ethyl orthosilicate as a silicon source, tetrapropyl ammonium hydroxide as a template, sodium metaaluminate, aluminum nitrate, aluminum sulfate or aluminum isopropoxide as an aluminum source, adding alkali metal ions ( Sodium chloride or potassium chloride) to balance the charge of the skeleton, synthesized in situ in deionized water, the preparation process is as follows:

1) Solution preparation

Mix ethyl orthosilicate, tetrapropylammonium hydroxide, aluminum source, alkali metal salt, deionized water in proportion, ethyl orthosilicate, tetrapropylammonium hydroxide, aluminum source, alkali metal salt, deionized water The molar ratio between water is 1:0.05～0.50:0～0.1:0.1～0.35:100～500; the preferred molar ratio is 1:0.085～0.38:0～0.08:0.15～0.30:150～380;

2) Hydrothermal synthesis

Put the silicon carbide carrier into the above solution, the weight ratio of the silicon carbide ceramics to the reaction solution is 1: (5-50); the temperature of the hydrothermal synthesis is 130-200°C, the reaction time is 3-72 hours, and the pressure is the self-generated solution pressure;

3) Roasting

First, clean and dry the hydrothermally synthesized sample; then, under the air atmosphere, bake at 500-600°C for 3-12 hours to remove the template agent and obtain a high intercrystalline porosity zeolite coating on the surface of the porous silicon carbide carrier. layer material.

In the present invention, the surface of the porous silicon carbide ceramic has a porous layer formed by overlapping silicon carbide particles, and the formation of the porous layer depends on adding an appropriate amount of silicon powder or silicon oxide powder as a pore-forming agent during the preparation of the silicon carbide carrier.

In the present invention, the foamed silicon carbide ceramic material can use a high-strength and dense foamed silicon carbide ceramic material and its preparation method mentioned in the Chinese invention patent application (publication number: CN1600742A). Cut the foam plastic, immerse it in the slurry, take it out, remove the excess slurry, semi-cure, and then cure at high temperature and high pressure; pyrolyze the cured foam to obtain the same shape as the original foam made of silicon carbide and heat Foamy carbon skeleton composed of decarburization; grind the central hole of the carbon skeleton, inject silicon carbide slurry into the central hole of the carbon skeleton by pressure injection method and fill the central hole, and then pyrolyze; after the siliconizing process, the carbon skeleton The carbon in the silicon reacts with gas phase or liquid phase silicon to form silicon carbide, which is combined with the original silicon carbide particles in the foam skeleton to obtain high-strength and dense silicon carbide foam ceramics. The ceramic bar of the invention has high density and high uniform microstructure strength. The preparation of honeycomb silicon carbide ceramics uses carbon powder and silicon carbide powder as raw materials, epoxy resin as a binder, and is formed by extrusion. After molding, through the siliconizing process, carbon reacts with gas phase or liquid phase silicon to form silicon carbide, which is combined with the original silicon carbide particles in the foam skeleton to obtain high-strength and dense silicon carbide foam ceramics.

In the present invention, the main component range and technical parameters of the ZSM-5 type zeolite coating are as follows: the molecular sieve crystal size is (2～10)×(1.0～5.0)×(0.5～3.0) microns, and the loading capacity is 0～60wt% The thickness of the coating is 2-100 microns, the specific surface area of the composite material composed of the obtained zeolite coating and the porous silicon carbide ceramic carrier is 2-200m ² /g, and the silicon-aluminum atomic ratio is 11-∞.

In the present invention, the main component range and technical parameters of the silicalite-1 type zeolite coating are as follows: the molecular sieve crystal size is (2～10)×(1.5～6.0)×(0.5～4.0) microns, and the loading capacity is 0～60wt% The thickness of the coating is 2-120 microns, and the specific surface area of the composite material composed of the obtained molecular sieve coating and porous silicon carbide ceramic carrier is 2-240m ² /g.

The present invention has following beneficial effect:

First, the zeolite crystal size is small. Zeolite with small crystal grains has large external area, high surface energy, increased number of acid sites on the external surface, and strong adsorption capacity, especially for the adsorption of macromolecules, which is beyond the reach of conventional zeolites. These properties will be beneficial to the activation of macromolecules and the modulation and modification of the outer surface of zeolite. After the particle size of zeolite becomes smaller, its pores are short and regular, which is conducive to the diffusion of molecules and reduces the occurrence of carbon deposition. In addition, the zeolite crystal becomes smaller, which is beneficial to improve the dispersibility and loading capacity of the loaded metal component.

Second, the zeolite loading capacity is large, the zeolite coating has high intercrystalline porosity, and the interface bonding performance between the zeolite coating and the carrier is good, which is conducive to improving the mass transfer and heat transfer capabilities of the zeolite coating, thereby improving the reaction efficiency and Improve selectivity to target products.

Third, the zeolite coating thickness, silicon-aluminum ratio, and thickness can be adjusted to meet the needs of different reactions.

In order to strengthen the mass transfer in the zeolite coating and increase the loading capacity of the zeolite coating, in the present invention, the colloidal zeolite directing agent is grown in situ on the surface of the silicon carbide carrier, and the alkalinity, nutrient concentration and alkali metal concentration of the secondary growth solution are controlled. The method of adding the amount of ions realizes the preferential growth of zeolite crystals on the surface of silicon carbide carrier and controls the intercrystalline porosity. The coating material has high intercrystalline porosity, small zeolite crystal size, and good molecular diffusion performance; large zeolite loading capacity, zeolite crystal silicon-aluminum ratio, and zeolite coating thickness can be adjusted; zeolite crystal and silicon carbide carrier The interface bonding performance is good . The structured catalyst is conducive to enhancing mass transfer and heat transfer, and will have broad application prospects in the fields of catalysis, adsorption, separation and the like.

Description of drawings

Figure 1 shows the surface and fracture morphology of the ZSM-5 zeolite/foamed silicon carbide composite. Among them, (a) is the surface morphology; (b) is the cross-sectional morphology.

Fig. 2 is a pore size distribution diagram of the ZSM-5 type zeolite/foamed silicon carbide composite material. The specific surface area (BET) of the ZSM-5 ^/ foamed SiC composite is 82.47m ² g ^-1 , the micropore surface area is 42.75m ² g ^-1 , and the external surface area of the composite is 39.72m ² g -1 measured by t-plot method ¹ , the micropore volume is 0.022cm ³ g ^-1 . The pore distribution in the range of 1.7-300nm pore diameter was estimated by the method of Barrett-Joyner-Halenda (BJH), and the volume of the pore diameter in the range of 1.7-300nm was calculated as 0.027cm ³ g ^-1 .

Detailed ways

The present invention is described in detail below by way of examples.

Example 1

In this example, the preparation method of the high intercrystalline porosity zeolite coating material on the surface of the foamed silicon carbide carrier:

First, the surface of the foamed silicon carbide support was modified using a colloidal zeolite seed-directing agent. Mix ethyl orthosilicate, tetrapropylammonium hydroxide, and deionized water in a molar ratio of 1:0.32:29. After the tetraethyl orthosilicate was completely hydrolyzed, the foamed silicon carbide carrier and the above solution were placed in a reaction kettle, and hydrothermally synthesized at 130° C. for 4 hours. A secondary growth solution was prepared, and ethyl orthosilicate, tetrapropylammonium hydroxide, aluminum nitrate, sodium chloride, and deionized water were mixed in a molar ratio of 1:0.15:0.013:0.22:150. The weight ratio of the foamed silicon carbide carrier to the reaction solution is 1:30, and the foamed silicon carbide carrier is fixed at 1 cm away from the bottom of the reactor with a polytetrafluoroethylene support frame; the volume of the solution is 55 milliliters, and the volume of the reactor is 100 milliliters. The temperature used for the hydrothermal reaction is 170° C., the time is 48 hours, and the pressure is the autogenous pressure generated by the vaporization of the solution. After the reaction was completed, the sample was washed several times in deionized water at 100°C, and then cleaned by an ultrasonic cleaner with a frequency of 40 Hz for 20 minutes to remove residual solution and molecular sieve crystals weakly connected to the matrix. Put the cleaned sample into a drying oven and dry it at 100°C for 12 hours. After drying, the sample was baked in a muffle furnace at 550°C for 6 hours (the heating rate was 2°C/min, and cooled with the furnace). The loading capacity of the high intercrystalline porosity zeolite coating material obtained on the surface of ZSM-5/foamed silicon carbide carrier is 13wt%, the coating thickness is 10 microns, the silicon-aluminum atomic ratio is 75, and the specific surface area (BET) is 82.47m ² g ^-1 , the micropore surface area is 42.75m ² g ^-1 , the external area of the composite material measured by t-plot method is 39.72m ² g ^-1 , and the micropore volume is 0.022cm ³ g ^-1 . The method of Barrett-Joyner-Halenda (BJH) was used to estimate the pore distribution in the range of 1.7-300nm pore size, and the volume of the part with pore size in the range of 1.7-300nm was calculated as 0.027cm ³ g ^-1 (see Figure 1-Figure 2) .

Example 2

In this example, the preparation method of the high intercrystalline porosity zeolite coating material on the surface of the foamed silicon carbide carrier:

The method for modifying the surface of the foamed silicon carbide carrier with the colloidal zeolite seed crystal directing agent is the same as in Example 1. To prepare a secondary growth solution, mix ethyl orthosilicate, tetrapropylammonium hydroxide, and deionized water in a molar ratio of 1:0.15:150. The weight ratio of the foamed silicon carbide carrier to the reaction solution is 1:30, and the foamed silicon carbide carrier is fixed at 1 cm away from the bottom of the reactor with a polytetrafluoroethylene support frame; the volume of the solution is 55 milliliters, and the volume of the reactor is 100 milliliters. The temperature used for the hydrothermal reaction is 170° C., the time is 48 hours, and the pressure is the autogenous pressure generated by the vaporization of the solution. After the reaction was completed, the sample was washed several times in deionized water at 100°C, and then cleaned by an ultrasonic cleaner with a frequency of 40 Hz for 20 minutes to remove residual solution and molecular sieve crystals weakly connected to the matrix. Put the cleaned sample into a drying oven and dry it at 100°C for 12 hours. After drying, the sample was baked in a muffle furnace at 550°C for 6 hours (the heating rate was 2°C/min, and cooled with the furnace). The loading of the silicalite-1/foamed silicon carbide carrier surface high intercrystalline porosity zeolite coating material is 19wt%, the coating thickness is 18 microns, the specific surface area (BET) is 120.35m ² g ^-1 , and the micropore surface area is 62.75m ² g ^-1 , the outer surface area of the composite material is 57.60m ² g ^-1 and the micropore volume is 0.034cm ³ g ^-1 measured by t-plot method. The pore distribution with pore diameters in the range of 1.7-300nm was estimated by the method of Barrett-Joyner-Halenda (BJH), and the volume of the pore diameters in the range of 1.7-300nm was calculated as 0.033cm ³ g ^-1 .

Example 3

In this example, the preparation method of the high intercrystalline porosity zeolite coating material on the surface of the honeycomb silicon carbide carrier:

The method for modifying the surface of the honeycomb silicon carbide carrier with the colloidal zeolite seed crystal directing agent is the same as in Example 1. A secondary growth solution was prepared, and ethyl orthosilicate, tetrapropylammonium hydroxide, aluminum nitrate, sodium chloride, and deionized water were mixed in a molar ratio of 1:0.15:0.0065:0.15:190. The weight ratio of the honeycomb silicon carbide carrier to the reaction solution is 1:25, and the honeycomb silicon carbide ceramics is fixed at 1 cm from the bottom of the reactor with a polytetrafluoroethylene support frame; the volume of the solution is 55 milliliters, and the volume of the reactor is 100 milliliters. The temperature used for the hydrothermal reaction is 170° C., the time is 48 hours, and the pressure is the autogenous pressure generated by the vaporization of the solution. After the reaction was completed, the sample was washed several times in deionized water at 100°C, and then cleaned by an ultrasonic cleaner with a frequency of 40 Hz for 20 minutes to remove residual solution and molecular sieve crystals weakly connected to the matrix. Put the cleaned sample into a drying oven and dry it at 100°C for 12 hours. After drying, the sample was baked in a muffle furnace at 550°C for 6 hours (the heating rate was 2°C/min, and cooled with the furnace). The loading capacity of the high intercrystalline porosity zeolite coating material obtained on the surface of the ZSM-5/honeycomb silicon carbide carrier is 23wt%, the coating thickness is 15 microns, the silicon-aluminum atomic ratio is 150, and the specific surface area (BET) is 150.23m ² g ^-1 , the micropore surface area is 80.75m ² g ^-1 , the external area of the composite material measured by t-plot method is 69.48m ² g ^-1 , and the micropore volume is 0.040cm ³ g ^-1 . The pore distribution with pore diameters in the range of 1.7-300nm was estimated by the method of Barrett-Joyner-Halenda (BJH), and the volume of the pore diameters in the range of 1.7-300nm was calculated as 0.038cm ³ g ^-1 .

The results of the examples show that the colloidal seed crystal directing agent is used to modify the porous silicon carbide carrier to achieve preferential nucleation and preferential growth of zeolite crystals on the surface of the carrier. Control the alkalinity, nutrient concentration and alkali metal ion addition of the secondary growth solution to realize the preferential growth of zeolite crystals on the surface of the silicon carbide carrier and control the intercrystalline porosity. By adjusting the added amount of aluminum ions, the silicon-aluminum ratio of the zeolite coating is regulated.

In the present invention, the structural catalyst uses foamed silicon carbide or honeycomb structure silicon carbide as a carrier, and a zeolite coating with high intercrystalline porosity grows evenly on the surface of the silicon carbide carrier. The coating material has high intercrystalline porosity, small zeolite crystal size, and good molecular diffusion performance; large zeolite loading capacity, zeolite crystal silicon-aluminum ratio, and zeolite coating thickness can be adjusted; zeolite crystal and silicon carbide carrier The interface bonding performance is good . The structured catalyst is conducive to enhancing mass transfer and heat transfer, and will have broad application prospects in the fields of catalysis, adsorption, separation and the like.

Claims (1)

1. A preparation method for a high intercrystalline porosity zeolite coating material on the surface of a porous silicon carbide carrier, characterized in that the silicon carbide carrier is modified by a colloidal zeolite directing agent to control the preferential formation of zeolite crystals on the surface of the silicon carbide carrier Nucleation and preferential growth; control the alkalinity, nutrient concentration and alkali metal ion addition of the secondary growth solution, and regulate the intercrystalline porosity and loading capacity of the coating; The preparation of the colloidal zeolite directing agent uses ethyl orthosilicate as the silicon source, tetrapropylammonium hydroxide as the template, and is synthesized in situ in deionized water. The preparation process is as follows: 1) Solution preparation Mix ethyl orthosilicate, tetrapropylammonium hydroxide, and deionized water in proportion, and the molar ratio between ethyl orthosilicate, tetrapropylammonium hydroxide, and deionized water is 1:0.1～1.0:10 ~100; 2) Hydrothermal synthesis After the tetraethyl orthosilicate is completely hydrolyzed, put the above solution and the porous silicon carbide carrier in a reaction kettle for hydrothermal synthesis; the temperature of the hydrothermal synthesis is 100-170°C, the reaction time is 4-12 hours, and the pressure is the autogenous pressure of the solution. A modified silicon carbide carrier is obtained; The preparation of the secondary growth solution uses ethyl orthosilicate as the silicon source, tetrapropylammonium hydroxide as the template agent, sodium metaaluminate, aluminum nitrate, aluminum sulfate or aluminum isopropoxide as the aluminum source, and alkali metal ions are added to balance the Skeleton charge, synthesized in situ in deionized water, the preparation process is as follows: 1) Preparation of secondary growth solution Mix ethyl orthosilicate, tetrapropylammonium hydroxide, aluminum source, alkali metal salt, deionized water in proportion, ethyl orthosilicate, tetrapropylammonium hydroxide, aluminum source, alkali metal salt, deionized water The molar ratio between water is 1:0.05～0.50:0.013～0.1:0.1～0.35:100～500; 2) Hydrothermal synthesis Put the modified silicon carbide carrier into the secondary growth solution, the weight ratio of the modified silicon carbide carrier to the secondary growth solution is 1: (5-50); the temperature of the hydrothermal synthesis is 130-200 °C, and the reaction time is 3 to 72 hours, the pressure is the self-generated pressure of the solution; 3) Roasting First, clean and dry the sample after hydrothermal synthesis; then, under air atmosphere, bake at 500-600°C for 3-12 hours to remove the template agent and obtain a high intercrystalline porosity zeolite coating on the surface of the porous silicon carbide carrier Material.

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