CN1107645C - Process for synthesizing molecular sieve (MCM-22) with special crystal structure - Google Patents

Abstract

A method for synthesizing MCM-22 molecular sieve, wherein a silicon source, an aluminum source, an alkali source, an organic template agent, and water are formulated into a synthetic colloid according to existing techniques, and then the synthetic colloid is hydrothermally crystallized and the product is recovered. The hydrothermal crystallization is characterized by first hydrothermally crystallizing at 160-200°C for 1-20 hours, and then cooling to 130-155°C for hydrothermal crystallization for 8-100 hours. The method of the present invention can synthesize qualified products under static crystallization conditions and can reduce the amount of organic template agent used.

Description

A kind of synthetic method of MCM-22 molecular sieve

As an effective solid acid catalyst, zeolite molecular sieve has been widely used in petroleum refining, fine chemical industry and adsorption separation and other fields. The outstanding advantage of zeolite molecular sieve is that it can adjust the acidity, and at the same time, it can provide pores and holes of different sizes to play a shape-selective effect. Therefore, molecular sieves with different pore sizes have different shape-selective effects. For example, in catalytic cracking, Y-type (twelve-membered ring) and ZSM-5 (ten-membered ring) molecular sieves are combined to make catalysts to meet the requirements of conversion rate, product distribution and quality at the same time. Therefore, some molecular sieves with both ten-membered and twelve-membered rings have been reported since the 1990s, such as MCM-22, PSH-3, SSZ-25, SSZ-33 and CIT-1. The unique structure of molecular sieves such as MCM-22 indicates that it will be widely used in the field of petrochemical catalysis.

Bayer AG has developed a molecular sieve called PSH-3 (USP4,439,409), which has ten-membered rings and twelve-membered ring channels that are not connected to each other. Source, using hexamethyleneimine as a template, synthesized according to the general hydrothermal synthesis method; later it was proved that the PSH-3 molecular sieve synthesized by this method contained heterocrystals of other molecular sieves such as ZSM-5 or ZSM-12. The reason for the miscellaneous crystals may be that the concentration of sodium ions in the system is too high (using water glass as raw material).

The MCM-22 molecular sieve (USP4,954,325) reported by Mobil Company in 1990 also has ten-membered ring and twelve-membered ring channel system that are not connected to each other. The difference between it and PSH-3 is that it does not contain heterocrystals, so its X There is no miscellaneous crystal peak in the ray diffraction pattern (XRD) (Example 21-23 in USP4,954,325). In USP4,954,325, a conventional hydrothermal crystallization method is adopted to synthesize MCM-22 molecular sieves by using spray-dried precipitated silica, sodium metaaluminate and sodium hydroxide as raw materials and using hexamethyleneimine as a template. Included static and dynamic crystallization method in the description of this patent, but all adopt dynamic crystallization in the example, and the consumption of template agent is bigger (N/Si=0.35～0.50) in the example synthesis; In fact, the applicant's Studies have shown that the synthesis conditions of MCM-22 molecular sieves need to be strictly controlled. If static crystallization is adopted under the conditions adopted in USP4,954,325, the product will definitely produce miscellaneous crystals, and if the amount of template agent is low ( R/SiO ₂ <0.3) When static crystallization is used, the desired product cannot be synthesized (the product is amorphous).

The SSZ-25 molecular sieve (USP4,826,667) developed by Chevron is also a molecular sieve with the same structure as the MCM-22 molecular sieve, except that it uses adamantane quaternary ammonium base as a template during its synthesis.

Corma et al. also reported that if static crystallization is adopted, ferrierite FER can be easily transformed into crystal. And the synthetic condition of MCM-22 molecular sieve needs strict control, if control is bad, can generate ZSM-5 or ZSM-12 miscellaneous crystal (Corma A, Zeolites, 15, 1995, P2-8).

The purpose of the present invention is to provide a kind of improved method of synthesizing MCM-22, make under the condition of static crystallization just can synthesize desired pure molecular sieve product; And the method of the present invention can produce ratio under the condition of dynamic crystallization A product with better performance by the conventional method; meanwhile, the method of the invention can reduce the consumption of the template agent hexamethyleneimine used in the synthesis.

Generally speaking, the crystallization temperature when synthesizing MCM-22 molecular sieves should not be too high, otherwise it is easy to generate miscellaneous crystals or the desired product cannot be synthesized. The present inventors found that when adopting the second-stage crystallization method of high temperature and then low temperature, not only the desired pure molecular sieve product can be synthesized under the condition of static crystallization, but also the template agent hexamethylene used in the synthesis can be made The consumption of base imine reduces, thereby reaches the object of the present invention.

The synthetic method of MCM-22 molecular sieve provided by the present invention is to prepare synthetic colloid according to the method of prior art with silicon source, aluminum source, alkali source, organic templating agent and water, then this synthetic colloid is hydrothermally crystallized and recovered The product is characterized in that the hydrothermal crystallization is carried out at 160-200°C and autogenous pressure for 1-20 hours, and then cooled to 130-155°C for 8-100 hours under autogenous pressure. It is preferred to perform hydrothermal crystallization at 165-190° C. and autogenous pressure for 3-12 hours, and then lower the temperature to 135-150° C. and perform hydrothermal crystallization under autogenous pressure for 16-80 hours.

Silicon source, aluminum source, alkali source, organic template agent (R) etc. adopted in the synthetic method of MCM-22 molecular sieve provided by the present invention are determined according to prior art, and the present invention has no special limitation to it; But this The preferred raw material of the invention is to use solid silica gel as the silicon source, or to use solid silica-alumina gel as the silicon source and part of the aluminum source; to use sodium metaaluminate as all or part of the aluminum source; the alkali source can be sodium hydroxide; the organic template can be is hexamethyleneimine or adamantane quaternary ammonium base, among which hexamethyleneimine is preferred.

The molar composition of said synthetic colloid in the synthesis method of MCM-22 molecular sieve provided by the present invention is OH ⁻ : Al ₂ O ₃ : SiO ₂ : R: H ₂ O=(0.1～0.6):(0.01～0.1): 1:(0.05～0.5):(5～100), preferably OH ^- :Al ₂ O _{3 :} SiO ₂ :R:H ₂ O=(0.15～0.5):(0.015～0.05):1:(0.1～ 0.35): (8-50). Regarding the amount of organic template (R), when the amount is high, the synthesis conditions are easy to control, and it is not easy to produce miscellaneous crystals, the product quality is good, but the synthesis cost is greatly improved; under the conditions of the present invention, when R/SiO ₂ <0.3, Even in the case of R/SiO ₂ <0.2, qualified products can be synthesized without generating miscellaneous crystals, which is impossible in the prior art.

In the synthesis method of MCM-22 molecular sieve provided by the present invention, the hydrothermal crystallization can be carried out under the conditions of dynamic stirring or static non-stirring. Dynamic stirring conditions can stabilize the quality of the synthesized product, but it requires higher equipment and increases the cost of synthesis. The invention can synthesize qualified products under the condition of static without stirring, which is difficult to achieve in the prior art.

Fig. 1 is the X-ray diffraction (XRD) crystal phase diagram of the product obtained in Comparative Example 1, wherein a is the product without roasting, and b is the product after roasting.

Fig. 2 is the X-ray diffraction (XRD) crystal phase diagram of the product obtained in Example 3 after roasting.

The following examples will further illustrate the present invention. In the following examples and comparative examples, the crystallinity of the synthesized molecular sieve is characterized by the strongest diffraction peak height of the X-ray diffraction of MCM-22 molecular sieve, wherein the relative crystallinity is based on the uncalcined MCM obtained in Comparative Example 1 -22 molecular sieve is 100% basis.

Example 1

This example illustrates the preparation of solid silica-alumina colloidal microspheres as a raw material for synthesizing MCM-22 molecular sieves with NaY mother liquor.

The NaY mother liquor (taken from the molecular sieve workshop of the Catalyst Factory of Changling Oil Refinery and Chemical Plant, SiO ₂ content is 47 grams/liter, Na ₂ O content is 25 grams/liter), is that the dilute sulfuric acid of concentration 40% by weight is adjusted pH to 5～ 6. Precipitate the silicon and aluminum in the mother liquor in the form of silica-alumina gel. After filtering, add water to the filter cake and make a slurry with a solid content of 10% by weight. Spray-dry the slurry to obtain silica-alumina gel microspheres. More than 60% of the particle diameters are 40-80 microns, and then the spray-dried microspheres are slurried and washed with 3% by weight of ammonium sulfate solution until the _Na2O content is less than 0.1% by weight. After drying, the obtained silica-alumina Glue microspheres are used in the subsequent synthesis of MCM-22 molecular sieves. Analysis showed that its SiO ₂ content was 92.0% by weight, its Al ₂ O ₃ content was 3.16% by weight, its dry basis on ignition content was 85.2% by weight, and its BET surface area was 501 m ² /g.

Example 2

This example illustrates the preparation of solid silica gel microspheres as raw materials for the synthesis of MCM-22 molecular sieves using water glass.

Water glass (produced by Zhoucun Catalyst Factory of Qilu Petrochemical Company, d ₄ ²⁰ =1.26 g/ml, SiO ₂ content is 265 g/l, Na ₂ O content is 86.4 g/l) is diluted 1.5 times, and concentration is 40 wt. % dilute sulfuric acid to adjust the pH to 3-8, so that the silicon in the water glass is precipitated in the form of silica gel. After filtering, the filter cake is beaten with water to make a slurry with a solid content of 10% by weight, and the slurry is spray-dried to obtain Silica gel microspheres, wherein more than 60% of the particle diameters are 40-80 microns, and then the spray-dried microspheres are washed with 3% by weight of ammonium sulfate solution until the _Na2O content is <0.1% by weight. After drying, The obtained silica gel microsphere product is used for the subsequent MCM-22 molecular sieve synthesis. Analysis showed that its SiO ₂ content was 97% by weight, its Al ₂ O ₃ content was 1.65% by weight, its dry basis on ignition was 83.5% by weight, and its BET surface area was 610 m ² /g.

Comparative example 1

This comparative example illustrates the synthesis of MCM-22 molecular sieve according to the method reported in USP4,954,325.

2.4 grams of sodium metaaluminate (Shanghai Jiangpu Chemical Products Factory, analytically pure) and 0.44 grams of sodium hydroxide (Beijing Chemical Reagent Company, chemically pure) were dissolved in 205.8 grams of water, and 20 grams of commercially available silica gel microspheres ( Qingdao silica gel factory commodity, 120～200 orders, SiO content is 96% by weight), then add 12.78 grams of _{hexamethyleneimine} (being called for short HMI), after stirring, the molar proportion of gained mixture colloid is: 0.18NaOH: SiO ₂ : 0.033 Al ₂ O ₃ : 0.50HMI: 40H ₂ O. Then the resulting mixture was transferred to a 600 ml sealed autoclave, stirred and crystallized at a speed of 60 revolutions per minute at 150° C. and autogenous pressure for 120 hours, and the product was taken out after cooling, filtered, washed and dried, and the XRD of the obtained product was obtained. The crystal phase diagram is shown in Figure 1a, and the crystal phase diagram of the calcined product is shown in Figure 1b, which indicates that it is an MCM-22 molecular sieve with a BET surface area of 493m ² /g. Its crystallinity was set at 100%.

Example 3

Dissolve 0.84 g of sodium metaaluminate and 1.28 g of sodium hydroxide in 60 g of water, add 19.64 g of the silica-alumina microspheres prepared in Example 1 while stirring, then add 5.1 g of hexamethyleneimine and stir evenly , the molar ratio of the obtained mixture colloid is: 0.18NaOH:SiO ₂ :0.033Al ₂ O ₃ :0.20HMI:12H ₂ O. Then transfer the resulting mixture to a stainless steel sealed reaction kettle, statically crystallize at 180°C and autogenous pressure for 6 hours, then cool down to 145°C for static crystallization for 46 hours, take out the product after cooling, filter, wash and dry, and roast The crystal phase diagram of the final product is shown in Figure 2, which shows that it is an MCM-22 molecular sieve with a BET surface area of 480m ² /g. Its relative crystallinity is 110%.

Comparative example 2

Dissolve 0.84 g of sodium metaaluminate and 1.28 g of sodium hydroxide in 60 g of water, add 19.64 g of the silica-alumina microspheres prepared in Example 1 while stirring, then add 5.1 g of hexamethyleneimine, and stir evenly Finally, the molar ratio of the obtained mixture colloid is: 0.18NaOH:SiO ₂ :0.033Al ₂ O ₃ :0.20HMI:12H ₂ O. Then transfer the resulting mixture to a stainless steel sealed reaction kettle, statically crystallize at 180°C and autogenous pressure for 72 hours, take out the product after cooling, filter, wash and dry, and the crystal phase of the calcined product is amorphous as detected by XRD .

Comparative example 3

Dissolve 0.84 g of sodium metaaluminate and 1.28 g of sodium hydroxide in 60 g of water, add 19.64 g of the silica-alumina microspheres prepared in Example 1 while stirring, then add 5.1 g of hexamethyleneimine, and stir evenly Finally, the molar ratio of the obtained mixture colloid is: 0.18NaOH:SiO ₂ :0.033Al ₂ O ₃ :0.20HMI:12H ₂ O. Then transfer the resulting mixture to a stainless steel sealed reaction kettle, statically crystallize at 150°C and autogenous pressure for 144 hours, take out the product after cooling, filter, wash and dry, and the crystal phase of the roasted product is detected by XRD as amorphous .

The results of comparative example 2 and comparative example 3 show that when using the method of the prior art under the situation of the same charging ratio, under the conditions of such low templating agent consumption and static crystallization, at higher crystallization temperature and MCM-22 molecular sieve products cannot be obtained at lower crystallization temperatures.

Example 4

Dissolve 1.46 grams of sodium metaaluminate and 1.49 grams of sodium hydroxide in 70 grams of water, add 19.0 grams of silica gel microspheres prepared in Example 2 while stirring, and then add 4.8 grams of hexamethyleneimine and stir evenly. The molar ratio of the obtained mixture colloid is: 0.25NaOH:SiO ₂ :0.033Al ₂ O ₃ :0.18HMI:14H ₂ O. Then transfer the resulting mixture to a stainless steel sealed reaction kettle, statically crystallize at 175°C and autogenous pressure for 4 hours, then cool down to 150°C and statically crystallize under autogenous pressure for 54 hours, take out the product after cooling, filter and wash And drying, the crystal phase diagram of the product after calcination is similar to that in Figure 2, indicating that it is MCM-22 molecular sieve, and the BET surface area is 449m ² /g. Its relative crystallinity is 81%.

Example 5

Dissolve 0.29 grams of sodium metaaluminate and 1.30 grams of sodium hydroxide in 75 grams of water, add 19.64 grams of silica gel microspheres prepared in Example 2 while stirring, and then add 4.0 grams of hexamethyleneimine and stir evenly. The molar ratio of the obtained mixture colloid is: 0.15NaOH:SiO ₂ :0.025Al ₂ O ₃ :0.15HMI:15H ₂ O. Then transfer the resulting mixture to a stainless steel sealed reaction kettle, statically crystallize at 170°C and autogenous pressure for 12 hours, then cool down to 143°C and statically crystallize under autogenous pressure for 40 hours, take out the product after cooling, filter and wash And drying, the crystal phase diagram of the product after calcination is similar to that in Figure 2, indicating that it is MCM-22 molecular sieve, and the BET surface area is 467m ² /g. Its relative crystallinity is 97%.

Claims (8)

1, a kind of synthetic method of MCM-22 molecular sieve, this method is that silicon source, aluminium source, alkali source, organic formwork agent and water are mixed with synthetic colloid, should synthesize the colloid hydrothermal crystallizing then and reclaim product, it is characterized in that said hydrothermal crystallizing is first hydrothermal crystallizing 1～20 hour under 160～200 ℃ and autogenous pressure, and then be cooled to 130～155 ℃ of hydrothermal crystallizings 8～100 hours under autogenous pressure.

2, according to the process of claim 1 wherein that said silicon source is solid silicone or solid silicon aluminium glue; Said aluminium source is the aluminium in sodium metaaluminate or sodium metaaluminate and the solid silicon aluminium glue; Said alkali source is a sodium hydroxide; Said organic formwork agent is hexamethylene imine or diamantane quaternary ammonium hydroxide.

3, according to the method for claim 2, wherein said organic formwork agent is a hexamethylene imine.

4, according to the process of claim 1 wherein that said synthetic colloidal mole consists of OH-: Al ₂O ₃: SiO ₂: R: H ₂O=(0.1～0.6): (0.01～0.1): 1: (0.05～0.5): (5～100).

5, according to the method for claim 4, wherein said synthetic colloidal mole consists of OH-: Al ₂O ₃: SiO ₂: R: H ₂O=(0.15～0.5): (0.015～0.05): 1: (0.1～0.35): (8～50).

6, according to the process of claim 1 wherein that said hydrothermal crystallizing is not carry out under the stirring condition in dynamic agitation or static state.

7, according to the method for claim 6, wherein said hydrothermal crystallizing is not carry out under the stirring condition in static state.

8,, and then be cooled to 135～150 ℃ of hydrothermal crystallizings 16～80 hours under autogenous pressure according to the process of claim 1 wherein that said hydrothermal crystallizing is first hydrothermal crystallizing 3～12 hours under 165～190 ℃ and autogenous pressure.

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