A seed, molecular sieve and preparation method for preparing small-grain ZSM-5 molecular sieve

Abstract

The invention discloses a seed, a molecular sieve and a preparation method for preparing a small-grain ZSM-5 molecular sieve, wherein the raw materials include sodium aluminate, sodium silicate and sodium hydroxide, the molar ratio of silicon dioxide to aluminum oxide in the raw materials is 15.5-16.5:1, the molar ratio of sodium oxide to silicon dioxide in the raw materials is 0.75-0.79:1, and the molar ratio of water molecules to silicon dioxide in the raw materials is 13.5-13.9:1. The prepared seed has high density and strong induction ability, and more crystal nuclei are induced by the seed, thereby obtaining more crystal grains, making the crystal grains smaller. The prepared small-grain ZSM-5 molecular sieve (φ500nm) has low production cost, relatively simple process, environmental friendliness (no ammonia nitrogen compounds are produced), high crystallinity (more than 95%), large specific surface area (400 m 2 / g), large mesoporous surface area (50 m 2 / g), high adsorption, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieves, and in particular to a seed, a molecular sieve and a preparation method for preparing a small-grain ZSM-5 molecular sieve. Background Art

[0002] ZSM-5 zeolite is a new type of zeolite molecular sieve containing organic amine cations. Due to its unique chemical composition, crystal structure and physicochemical properties, it has shown excellent catalytic performance in many organic catalytic reactions and has been increasingly widely used in industry, becoming a promising new catalyst in petrochemical industry.

[0003] In recent years, with the rapid development of nanotechnology, people have a deeper understanding of nanomaterials, and the research on the nanotechnology of molecular sieves has also aroused great interest among researchers. As a new material, small-grain nano-molecular sieves have achieved vigorous development in the fields of catalysis, adsorption, and separation. With the reduction of the size of molecular sieve grains, the surface area increases, the pores shorten, and the number of exposed pores increases, the product molecules can diffuse out in time, so the selectivity of the catalyst for certain specific products and the ability to resist carbon deposition and deactivation can be significantly improved. Generally, most of the small-grain ZSM-5 (grains less than 1000nm) are produced using organic amines as templates. The general process is: sodium aluminate and tetrapropylammonium bromide are added to sodium hydroxide, and then silica sol is added for crystallization, and then separated, washed and dried to obtain the original powder, and then the original powder is subjected to subsequent treatment to obtain different types of molecular sieve active ingredients.

[0004] Among the above-mentioned organic amine systems, organic amines are relatively expensive and highly toxic, and the preparation process is complicated, and a large amount of nitrogen oxides that are not environmentally friendly are produced (need to be subsequently treated). In addition to the organic amine system, there are also a variety of methods such as the loading method, hydrothermal synthesis process and microwave synthesis process.

[0005] In view of the wide application of small-grain ZSM-5 molecular sieves, there is an urgent need for a production method that is low in cost, simple in production process, stable in product and environmentally friendly. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a seed for preparing small-grain ZSM-5 molecular sieve.

[0007] The technical solution adopted by the present invention to solve the technical problem is:

[0008] A seed for preparing a small-grain ZSM-5 molecular sieve. The raw materials include sodium aluminate, sodium silicate and sodium hydroxide. The molar ratio of silicon dioxide to aluminum oxide in the raw materials is 15.5-16.5:1, the molar ratio of sodium oxide to silicon dioxide in the raw materials is 0.75-0.79:1, and the molar ratio of water molecules to silicon dioxide in the raw materials is 13.5-13.9:1.

[0009] Further: the molar ratio of silicon dioxide and aluminum oxide in the raw material is 16:1, the molar ratio of sodium oxide and silicon dioxide in the raw material is 0.78:1, and the molar ratio of water molecules and silicon dioxide in the raw material is 13.75:1.

[0010] Furthermore: the concentration of the sodium aluminate solution is 18.5%, the concentration of the sodium silicate solution is 27%, and the concentration of the sodium hydroxide solution is 50%.

[0011] An object of the present invention is to provide a method for preparing a small-grain ZSM-5 molecular sieve, comprising the following steps:

[0012] Add seed crystals, type C silica gel, sodium silicate, aluminum sulfate, and distilled water into the autoclave and stir for 0.8-2 hours;

[0013] The temperature in the autoclave is raised to 150-170 degrees Celsius and stirring is continued for 8-15 hours;

[0014] The temperature in the autoclave is lowered to 30-50 degrees Celsius, and the filter cake is obtained after decompression using a Buchner funnel;

[0015] The filter cake is placed in distilled water and sulfuric acid, stirred for 1-20 minutes, filtered under reduced pressure using a Buchner funnel, rinsed with water and dried to obtain the finished molecular sieve.

[0016] Furthermore: the amount of the seed crystals is 1-2% of the total weight of the feed.

[0017] Further: the water washing is performed with 2 times the volume of water, and the filter cake taken out after the water washing is dried at 130 degrees Celsius.

[0018] Furthermore: the molar ratio of silicon dioxide and aluminum oxide in the material added in the preparation method is 28-31:1, the molar ratio of sodium oxide and silicon dioxide in the material added in the preparation method is 0.09-0.11:1, and the molar ratio of water molecules and silicon dioxide in the material added in the preparation method is 15-16:1.

[0019] Furthermore: the molar ratio of sodium oxide to silicon dioxide in the material added in the preparation method is 0.1:1.

[0020] Further: The BET specific surface area of ​​the molecular sieve is 395-405 m 2 / g, and the mesoporous specific surface area of ​​the molecular sieve is 48-52 m 2 / g, the cleanliness of the molecular sieve is 96-98%, and the XRF silicon aluminum of the molecular sieve is 25.6-26.1.

[0021] Another object of the present invention is to provide a small-grain ZSM-5 molecular sieve prepared by the above preparation method.

[0022] The technical effects achieved by the present invention are:

[0023] In the present invention, firstly, high-efficiency seed crystals are prepared, which have high seed density and strong induction ability, and more crystal nuclei are induced by the seed crystals, thereby obtaining more crystal grains, making the crystal grains smaller. The prepared small-grain ZSM-5 molecular sieve (φ500nm) has the advantages of low production cost, relatively simple process, environmental friendliness (no ammonia nitrogen compounds are produced), high crystallinity (more than 95%), large specific surface area (400m 2 / g), large mesoporous surface area (50m 2 / g), high adsorption, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a scanning electron microscope image of Example 1 of the present invention;

[0025] Figure 2 This is a scanning electron microscope image of Example 2 of the present invention;

[0026] Figure 3 This is a scanning electron microscope image of Example 3 of the present invention;

[0027] Figure 4 This is a scanning electron microscope image of Example 4 of the present invention. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0029] A seed for preparing a small-grain ZSM-5 molecular sieve. The raw materials include sodium aluminate, sodium silicate and sodium hydroxide. The molar ratio of silicon dioxide to aluminum oxide in the raw materials is 15.5-16.5:1, the molar ratio of sodium oxide to silicon dioxide in the raw materials is 0.75-0.79:1, and the molar ratio of water molecules to silicon dioxide in the raw materials is 13.5-13.9:1.

[0030] The preferred solution is that the molar ratio of silicon dioxide to aluminum oxide in the raw material is 16:1, the molar ratio of sodium oxide to silicon dioxide in the raw material is 0.78:1, and the molar ratio of water molecules to silicon dioxide in the raw material is 13.75:1.

[0031] The concentration of the sodium aluminate solution is 18.5%, the concentration of the sodium silicate solution is 27%, and the concentration of the sodium hydroxide solution is 50%.

[0032] The preparation method of the above-mentioned seed crystals includes the following steps: adding sodium aluminate solution (concentration of 18.5%) to sodium hydroxide solution (concentration of 50%) and stirring evenly; adding sodium silicate solution (concentration of 27%) dropwise and stirring evenly; placing the above-mentioned mixture in a constant temperature box at 27 degrees Celsius for 1 week to obtain milky white liquid seed crystals.

[0033] A small-grain ZSM-5 molecular sieve based on the above-mentioned seed crystals is prepared by mixing the seed crystals with type C silica gel, sodium silicate, aluminum sulfate and distilled water for reaction. After a period of time, the temperature is increased and stirred continuously. After a period of time, the temperature is lowered. After filtering, the filter cake is washed with water, exchanged with sulfuric acid, filtered, washed with water and dried to obtain a finished molecular sieve.

[0034] The preparation method of the above-mentioned small-grain ZSM-5 molecular sieve comprises the following steps:

[0035] Add seed crystals (the amount of seed crystals is 1-2% of the total weight of the feed), type C silica gel (solid content is 92%), sodium silicate (concentration is 20%), aluminum sulfate (concentration is 7%) and distilled water into the autoclave and stir for 0.8-2 hours;

[0036] The temperature in the autoclave is raised to 150-170 degrees Celsius (preferably 160 degrees Celsius), and stirring is continued for 8-15 hours (preferably 10 hours);

[0037] The temperature in the autoclave is lowered to 30-50 degrees Celsius (preferably 40 degrees Celsius), and the filter cake is obtained after decompression using a Buchner funnel;

[0038] The filter cake was placed in distilled water and sulfuric acid (concentration of 30%), stirred for 1-20 minutes (preferably 10 minutes), filtered under reduced pressure using a Buchner funnel, and rinsed with 2 times the volume of water. The filter cake taken out after rinsing was dried at 130 degrees Celsius to obtain the finished molecular sieve.

[0039] The molar ratio of silicon dioxide to aluminum oxide in the materials added in the preparation method is 28-31:1, the molar ratio of sodium oxide to silicon dioxide in the materials added in the preparation method is 0.09-0.11:1, and the molar ratio of water molecules to silicon dioxide in the materials added in the preparation method is 15-16:1. The preferred solution is that the molar ratio of sodium oxide to silicon dioxide in the materials added in the preparation method is 0.1:1. The above materials refer to C-type silica gel, sodium silicate, aluminum sulfate and distilled water.

[0040] After testing, the BET specific surface area of ​​the sample was 395-405 m 2 / g, and the mesoporous specific surface area of ​​the molecular sieve is 48-52 m 2 / g, the cleanliness of the molecular sieve is 96-98%, and the XRF silicon aluminum of the molecular sieve is 25.6-26.1.

[0041] Example 1

[0042] Take 22.5g of seed crystals, 88.5g of type C silica gel, 392.6g of distilled water, 116.6g of aluminum sulfate and 525.7g of sodium silicate and add them into a pressure autoclave (with a pressure resistance of 30 atmospheres and a temperature resistance of 300 degrees Celsius), stir for 1 hour and heat to 160 degrees Celsius, maintain this temperature and stir, cool to 40°C after 10 hours, and filter to obtain the filter cake.

[0043] Add 500g of distilled water and 150g of sulfuric acid and stir for 10 minutes, filter, rinse with water, and dry to obtain the finished product.

[0044] Test results: BET specific surface area 400 m 2 / g, mesopore specific surface area 52 m 2 / g, XRD crystallinity 98%, XRF silicon-aluminum ratio 25.6, scanning electron microscope photo is shown in Figure 1, diameter 500nm.

[0045] The molar ratios of the feed materials in the above experiment are: the molar ratio of silicon dioxide to aluminum oxide is 28:1, the molar ratio of sodium oxide to silicon dioxide is 0.1:1, the molar ratio of water to silicon dioxide is 16:1, and the seed crystal feeding amount is 2% of the total weight.

[0046] Example 2

[0047] Take 12g of seed crystals, 88.5g of type C silica gel, 392.6g of distilled water, 116.6g of aluminum sulfate and 525.7g of sodium silicate and add them into a pressure autoclave (with a pressure resistance of 30 atmospheres and a temperature resistance of 300 degrees Celsius), stir for 1 hour and heat to 160 degrees Celsius, maintain this temperature and stir, cool to 40°C after 10 hours, and filter to obtain the filter cake.

[0048] Add 500g of distilled water and 150g of sulfuric acid and stir for 10 minutes, filter, rinse with water, and dry to obtain the finished product.

[0049] Test results: BET specific surface area 402 m 2 / g, mesopore surface area 48 m 2 / g, XRD crystallinity 96%, XRF silicon-aluminum ratio 25.9, and the scanning electron microscope photograph is shown in Figure 2.

[0050] The molar ratio of the feed in the above experiment is the same as that in Example 1, and the amount of seed crystals fed is 1% of the total weight.

[0051] Example 3

[0052] Take 22.5g of seed crystals, 91g of type C silica gel, 392.6g of distilled water, 116.6g of aluminum sulfate and 578g of sodium silicate and add them into a pressure autoclave (with a pressure resistance of 30 atmospheres and a temperature resistance of 300 degrees Celsius), stir for 1 hour and heat to 160 degrees Celsius, maintain this temperature and stir, cool to 40°C after 10 hours, and filter to obtain the filter cake.

[0053] Add 500g of distilled water and 150g of sulfuric acid and stir for 10 minutes, filter, rinse with water, and dry to obtain the finished product.

[0054] Test results: BET specific surface area 400 m 2 / g, mesopore surface area 50 m 2 / g, XRD crystallinity 97%, XRF silicon-aluminum ratio 26.3, and the scanning electron microscope photograph is shown in Figure 3.

[0055] The molar ratios of the feed materials in the above experiment are: the molar ratio of silicon dioxide to aluminum oxide is 31:1, the molar ratio of sodium oxide to silicon dioxide is 0.1:1, the molar ratio of water to silicon dioxide is 15:1, and the seed crystal feeding amount is 2% of the total weight.

[0056] Example 4

[0057] Take 12g of seed crystals, 91g of type C silica gel, 392.6g of distilled water, 116.6g of aluminum sulfate and 578g of sodium silicate and add them into a pressure autoclave (with a pressure resistance of 30 atmospheres and a temperature resistance of 300 degrees Celsius), stir for 1 hour and heat to 160 degrees Celsius, maintain this temperature and stir, cool to 40°C after 10 hours, and filter to obtain the filter cake.

[0058] Add 500g of distilled water and 150g of sulfuric acid and stir for 10 minutes, filter, rinse with water, and dry to obtain the finished product.

[0059] Test results: BET specific surface area 398m 2 / g, mesopore surface area 49 m 2 / g, XRD crystallinity 98%, XRF silicon-aluminum ratio 26.1, and the scanning electron microscope photograph is shown in Figure 4.

[0060] The molar ratio of the feed in the above experiment is the same as that in Example 3, and the amount of seed crystals fed is 1% of the total weight.

[0061] In each embodiment, the scanning electron microscope photo shows that the grain size is 500-600nm, which is significantly smaller than the ordinary 1000nm grain, and is also consistent with the correlation of the enlarged mesopore. The small-grain ZSM-5 molecular sieve of the present invention is used in propylene production additives, and the activity is 25% higher than that of propylene additives made of ordinary grains.

Claims

1. A seed for preparing small-grain ZSM-5 molecular sieve, characterized in that: The raw materials include sodium aluminate, sodium silicate and sodium hydroxide, the molar ratio of silicon dioxide to aluminum oxide in the raw materials is 15.5-16.5:1, the molar ratio of sodium oxide to silicon dioxide in the raw materials is 0.75-0.79:1, and the molar ratio of water molecules to silicon dioxide in the raw materials is 13.5-13.9:1; The preparation method of the seed crystal comprises the following steps: adding sodium aluminate solution into sodium hydroxide solution and stirring evenly; dropping sodium silicate solution and stirring evenly; placing the mixed substance in a constant temperature box at 27 degrees Celsius and storing it for 1 week to obtain milky white liquid seed crystals; the concentration of the sodium aluminate solution is 18.5%, the concentration of the sodium silicate solution is 27%, and the concentration of the sodium hydroxide solution is 50%.

2. A seed crystal for preparing small-grain ZSM-5 molecular sieve according to claim 1, characterized in that: The molar ratio of silicon dioxide to aluminum oxide in the raw material is 16:1, the molar ratio of sodium oxide to silicon dioxide in the raw material is 0.78:1, and the molar ratio of water molecules to silicon dioxide in the raw material is 13.75:

1.

3. A method for preparing a small-grain ZSM-5 molecular sieve, characterized in that: The following steps are involved: Add the seed crystal of claim 1 or 2, type C silica gel, sodium silicate, aluminum sulfate and distilled water into a pressure autoclave and stir for 0.8-2 hours; The temperature in the autoclave is raised to 150-170 degrees Celsius and stirring is continued for 8-15 hours; The temperature in the autoclave is lowered to 30-50 degrees Celsius, and the filter cake is obtained after decompression using a Buchner funnel; The filter cake is placed in distilled water and sulfuric acid, stirred for 1-20 minutes, filtered under reduced pressure using a Buchner funnel, rinsed with water and dried to obtain the finished molecular sieve.

4. The method for preparing a small-grain ZSM-5 molecular sieve according to claim 3, characterized in that: The amount of the seed crystals used is 1-2% of the total weight of the feed.

5. The method for preparing a small-grain ZSM-5 molecular sieve according to claim 3, characterized in that: The water washing is performed with 2 times the volume of water, and the filter cake taken out after the water washing is dried at 130 degrees Celsius.

6. The method for preparing a small-grain ZSM-5 molecular sieve according to claim 3, characterized in that: The molar ratio of silicon dioxide to aluminum oxide in the material added in the preparation method is 28-31:1, the molar ratio of sodium oxide to silicon dioxide in the material added in the preparation method is 0.09-0.11:1, and the molar ratio of water molecules to silicon dioxide in the material added in the preparation method is 15-16:

1.

7. The method for preparing a small-grain ZSM-5 molecular sieve according to claim 6, characterized in that: The molar ratio of sodium oxide to silicon dioxide in the materials added in the preparation method is 0.1:

1.

8. The method for preparing a small-grain ZSM-5 molecular sieve according to claim 6 or 7, characterized in that: The BET specific surface area of ​​the molecular sieve is 395-405 m 2 / g, and the mesoporous specific surface area of ​​the molecular sieve is 48-52 m 2 / g, the cleanliness of the molecular sieve is 96-98%, and the XRF silicon aluminum of the molecular sieve is 25.6-26.

1.

9. A small-grain ZSM-5 molecular sieve prepared by the preparation method according to claim 8.

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