A method for synthesizing ZSM-5 molecular sieve

Abstract

The invention discloses a method for synthesizing a ZSM-5 molecular sieve: an aluminum sulfate solution is added to a water glass solution in two portions according to a certain proportion, the process temperature is controlled to be less than 35°C, and each addition of aluminum sulfate requires standing and aging for 30 minutes, and the slurry is recorded as A; aluminum sulfate is added to a sodium aluminate solution in a certain proportion, and a certain proportion of ZSM-5 molecular sieve is added after stirring, and the slurry is recorded as B; A and B are mixed evenly, ammonia water and α-alumina powder are added, and filtered and washed; the filter cake is sprayed and granulated after pulping, and the obtained particles are calcined and solidified, and the obtained particles are recorded as C; a certain proportion of water is added to C, liquid alkali is added in batches, the temperature is raised for crystallization, and the product after crystallization is added with a mixed solution of ammonium dihydrogen phosphate and lanthanum chloride for exchange, and the title compound can be obtained by drying after filtering and washing. The obtained catalyst has a high propylene yield.

Description

[0001] Technical field: The present invention relates to a method for synthesizing ZSM-5 molecular sieve, belonging to the field of molecular sieve preparation Background technology:

[0002] ZSM-5 zeolite is a new type of zeolite molecular sieve synthesized by Mobil Corporation in the United States in the late 1960s. 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. It has also been introduced into FCC catalysts to improve gasoline octane number and increase the production of low-carbon olefins.

[0003] There are generally two ways to introduce active components into FCC catalysts: semi-synthesis and total synthesis. The so-called semi-synthesis method is to mix the active components with a matrix and a binder to form a slurry, and then spray-dry and granulate them into microsphere catalysts. The so-called total synthesis is to first spray kaolin into microspheres, and after calcination, grow the molecular sieve active components on the kaolin microspheres by hydrothermal crystallization under appropriate conditions (i.e., in-situ crystallization).

[0004] The all-kaolin catalyst containing Y-type molecular sieve prepared by in-situ crystallization method has been used in China and abroad for a long time.

[0005] In recent years, the growing demand for propylene requires an increase in the content of ZSM-5 selective molecular sieves in FCC catalysts, but the mechanical strength of microsphere catalysts is limited and the molecular sieve content cannot be increased indefinitely. Therefore, in recent years, the in-situ crystallization of ZSM-5 molecular sieve technology has attracted widespread attention from domestic and foreign researchers.

[0006] CN101462740A uses calcined kaolin microspheres and silicon-rich clay microspheres, adds an organic template agent, and synthesizes ZSM-5 molecular sieves by in-situ crystallization, and its relative crystallinity can reach 30-90%. The method also involves adding ZSM-5 seed crystals during the preparation of kaolin microspheres, and synthesizing ZSM-5 by in-situ crystallization without adding an organic template agent.

[0007] CN101332995A discloses a method for in-situ crystallization of ZSM-5 molecular sieve using modified kaolin microspheres. Kaolin and modified components are first mixed and formed, and then calcined at high temperature and mixed with an external silicon aluminum source, a template agent, a crystal seed, and water to synthesize a kaolin-based ZSM-5 molecular sieve by hydrothermal crystallization. The relative crystallinity of the product is 30-80%.

[0008] USP6908603 discloses a method for in-situ synthesis of ZSM-5 molecular sieve on kaolin microspheres without using an organic template or ZSM-5 seed crystals, but requiring the introduction of a Y molecular sieve seed crystal solution. The technical feature of this method is that a seed crystal solution containing a Y molecular sieve is introduced into a mixture system of calcined kaolin microspheres, alkali, and silicate.

[0009] USP5145659 uses clay matrix microspheres and an organic amine template method to synthesize ZSM-5 molecular sieves, and the crystallinity can reach 35%-38%.

[0010] The EP0156595 technology mixes clay, silicon aluminum source and high-silicon molecular sieve seed crystals, calcines them at high temperature, and then mixes them with an alkaline solution to form a mixture that meets the high-silicon molecular sieve production ratio. The mixture is then aged at low temperature and then crystallized at high temperature to obtain an in-situ crystallized product with a high-silicon molecular sieve content of up to 60%, wherein the high-temperature crystallization time is as long as 4 days.

[0011] Problems with current technology:

[0012] (1) The active silica and aluminum in the kaolin microspheres will dissolve into the alkaline medium. It cannot be guaranteed that all of them will be converted into in-situ crystallized molecular sieves. Some of them will be formed by non-in-situ crystallization in the liquid phase. These particles are relatively small and can easily run away during subsequent drying or when entering the catalytic cracking regenerator.

[0013] (2) In order to obtain active silicon or aluminum species, high-temperature calcination treatment is required, which requires special high-temperature calcination equipment and has relatively high energy consumption.

[0014] (3) Most crystallization processes require the addition of an organic template, which is expensive and the wastewater is difficult to treat.

[0015] (4) The appearance of the prefabricated microspheres is easily destroyed in alkaline solutions, and some crystals grow inside the microspheres, which have poor accessibility. They only pursue crystallinity without considering the subsequent use effect. Summary of the invention:

[0016] In order to solve the deficiencies of the above technologies, the present invention provides a method for synthesizing ZSM-5 molecular sieve, and the specific synthesis steps are as follows:

[0017] (1) Aluminum sulfate solution is added to water glass solution in two portions according to a certain ratio, and the process temperature is controlled to be less than 35°C. After each addition of aluminum sulfate, the slurry is allowed to stand and age for 30 minutes. The slurry is recorded as A.

[0018] (2) Aluminum sulfate is added to the sodium aluminate solution in a certain proportion, stirred evenly, and then a certain proportion of ZSM-5 molecular sieve is added, and the mixture is aged for 30 minutes. The slurry is recorded as B;

[0019] (3) A and B are mixed evenly, ammonia water and α-alumina powder are added, and the mixture is filtered and washed;

[0020] (4) beating the filter cake, spray granulating, calcining and solidifying, and the obtained granules are recorded as C;

[0021] (5) Add a certain proportion of water to C, add liquid alkali in batches, raise the temperature for crystallization, add a mixed solution of ammonium dihydrogen phosphate and lanthanum chloride to the product after crystallization for exchange, filter, wash and dry to obtain the title compound.

[0022] In step (1), the mass ratio of the first addition amount of aluminum sulfate solution to water glass in terms of oxide is Al2O3:SiO2=(0.150-0.169):1, and the mass ratio of the second addition amount in terms of oxide to water glass is Al2O3:SiO2=(0.375-0.450):1;

[0023] In step (2), the amount of aluminum sulfate and sodium aluminate added is such that the molar ratio of each substance in the slurry is Na2O:Al2O3:SO4 2- :H2O=(1.25-1.38):1:1.38:57;

[0024] In step (2), the concentration of the sodium aluminate solution is Al2O3=98-102 g / L, and the caustic ratio is 1.45-1.50;

[0025] The concentration of the aluminum sulfate solution used is Al2O3=88-92g / L, and the concentration of the water glass solution is SiO2=120-130g / L;

[0026] During the process, the amount of ZSM-5 molecular sieve and α-alumina powder added is 0.5-3wt% and 5-10wt% of the title compound, and the silicon-aluminum ratio of ZSM-5 molecular sieve is 28-48. It should be synthesized using an organic template;

[0027] In step (4), the calcination temperature is 300-500° C. and the calcination time should be no less than one hour;

[0028] The amount of liquid alkali added in step (5) is such that the molar ratio of each substance in the slurry is OH - :SiO2=(0.12-0.20):1, the added amounts of ammonium dihydrogen phosphate and lanthanum chloride are such that P=3-5wt% and RE2O3=0.3-0.9wt% in the title product on a dry basis.

[0029] The benefits of the present invention are:

[0030] (1) Two materials, one rich in silicon and the other rich in aluminum, are prepared separately and mixed with α-alumina to prevent the release of both silicon and aluminum ions at one point by alkali at the same time, so that the released silicon and aluminum can only crystallize by combining with the surface of the microspheres, avoiding the presence of too much silicon and aluminum in the solution to produce non-in situ crystallized molecular sieves.

[0031] (2) The mixing ratio of A and B can be adjusted. The two materials with different silicon aluminum contents and structures are mixed into microspheres, which is equivalent to adjusting the local silicon aluminum distribution of the microspheres. In addition, the intentionally added inactive α-alumina can control the degree of in-situ crystallization. The material of the present invention does not simply pursue the degree of crystallinity, but more considers the accessibility and actual needs of the molecular sieve.

[0032] (3) In step 2, a certain proportion of ZSM-5 molecular sieve is added and pre-activated under initial alkaline conditions to produce small silicon-aluminum fragments, which can more easily lead to the formation of ZSM-5 molecular sieve.

[0033] (4) After crystallization, ammonium dihydrogen phosphate is used for exchange. A portion of the phosphate is used to modify the molecular sieve phosphorus to improve its hydrothermal stability and selectivity, and the other portion is adsorbed between the microsphere particles and decomposed step by step after heating. It can combine with the aluminum on the particles to stabilize the microspheres.

[0034] (5) When the microspheres are crystallized, the alkaline solution is added in batches to control the alkalinity of the system, which can control the dissolution rate of the active silica-alumina without excessively destroying the appearance of the microspheres.

[0035] (6) Materials A and B have unique structures and pore size distributions that are controllable, making the final microsphere product more suitable for FCC catalysis. Description of the drawings:

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, without paying any creative work, other related drawings can be obtained based on these drawings and they also belong to the protection scope of the present application.

[0037] Figure 1 This is a photo of the pore size distribution of the molecular sieve Z-1 prepared in Example 1;

[0038] Figure 2 This is a photo of the pore size distribution of the molecular sieve Z-2 prepared in Example 2;

[0039] Figure 3 This is a full XRD picture of the molecular sieve Z-1 prepared in Example 1;

[0040] Figure 4 This is a full XRD picture of the molecular sieve Z-2 prepared in Example 2. Specific implementation method:

[0041] The present invention is further described below with reference to examples, but the present invention is not limited to these examples.

[0042] The specifications of the raw materials used in the examples are as follows:

[0043] The following materials are all taken from the production workshop of Qingdao Huicheng Environmental Protection Technology Group Co., Ltd.

[0044] Aluminum sulfate solution: 90.2 g / L based on alumina;

[0045] Water glass solution: 125 g / L in terms of silicon oxide;

[0046] Sodium aluminate solution: 100.5 g / L based on alumina;

[0047] α-alumina: D50 = 1.8 μm;

[0048] ZSM-5 molecular sieve: silicon-aluminum ratio 30, ignition loss 15wt%;

[0049] Lye: OH - 200g / L;

[0050] Ammonium dihydrogen phosphate solution: P = 5wt%;

[0051] Lanthanum chloride solution: 20.3 wt% based on lanthanum trioxide.

[0052] Embodiment 1:

[0053] (1) 4 L of water glass solution was measured and put into a reactor. 859 mL of aluminum sulfate solution was slowly added for the first time, stirred evenly, and allowed to stand for 30 minutes. 2217 mL of aluminum sulfate solution was added for the second time, stirred evenly, and allowed to stand for 30 minutes. The process temperature should be controlled to be less than 35°C. The slurry was recorded as A.

[0054] (2) 2.41 L of water was slowly added to 2.2 L of sodium aluminate solution. The addition speed should be controlled and the solution should be stirred vigorously. Then 4.17 L of aluminum sulfate solution was added. After the addition, 50 g of ZSM-5 molecular sieve was added. After all the materials were added and stirred evenly, they were allowed to stand and age for 30 minutes. The slurry was recorded as B.

[0055] (3) Mix all A and B evenly, add ammonia water to control the pH value of the slurry to 7-8, then add 101.5 g of α-alumina powder, filter and wash;

[0056] (4) The filter cake is slurried and then spray granulated, and then calcined at 450° C. to obtain granules, which are denoted as C;

[0057] (5) A certain proportion of water was added to C, 375 mL of liquid alkali was added three times, the temperature was raised for crystallization, 1184 g of ammonium dihydrogen phosphate and 41.7 g of lanthanum chloride mixed solution were added to the product after crystallization for exchange, filtered, washed and dried, and the obtained molecular sieve was marked as Z-1. Example 2:

[0058] (1) 4 L of water glass solution was measured and put into a reactor. 915 mL of aluminum sulfate solution was slowly added for the first time, stirred evenly, and allowed to stand for 30 minutes. 2411 mL of aluminum sulfate solution was added for the second time, stirred evenly, and allowed to stand for 30 minutes. The process temperature should be controlled to be less than 35°C. The slurry was recorded as A.

[0059] (2) 2.54 L of water was slowly added to 2.73 L of sodium aluminate solution. The addition speed should be controlled and the solution should be stirred vigorously. Then 4.72 L of aluminum sulfate solution was added. After the addition, 40.7 g of ZSM-5 molecular sieve was added. After all the materials were added and stirred evenly, they were allowed to stand and age for 30 minutes. The slurry was recorded as B.

[0060] (3) Mix all A and B evenly, add ammonia water to control the pH value of the slurry to 7-8, then add 154g of α-alumina powder, filter and wash;

[0061] (4) The filter cake is slurried and then spray granulated, and then calcined at 450° C. to obtain granules, which are denoted as C;

[0062] (5) A certain proportion of water was added to C, 500 mL of liquid alkali was added three times, the temperature was raised for crystallization, and the product after crystallization was exchanged with a mixed solution of 1729 g of ammonium dihydrogen phosphate and 75.7 g of lanthanum chloride, filtered, washed and dried, and the obtained molecular sieve was marked as Z-2.

[0063] The chemical composition of molecular sieve is as follows:

[0064] <![CDATA[Al2O3,%]]> <![CDATA[SiO2,%]]> P，％ <![CDATA[RE2O3,%]]> <![CDATA[Na2O,%]]> Crystallinity Specific surface area Z-1 64.5 30.2 3.6 0.52 0.35 29.5 187 Z-2 66.9 26.4 4.1 0.82 0.19 34.7 204

[0065] The performance evaluation was performed using an ACE evaluation device. The properties of the raw oil used are shown in Table 1. The catalyst of the present invention was added at a ratio of 10%. The comparison agent was the best catalyst on the domestic market. The main catalyst used was the AIC series catalyst produced by Huicheng Environmental Protection Technology. The comparative evaluation results are shown in Table 2.

[0066] Table 1 Raw oil properties

[0067]

[0068] Table 2 ACE comparative evaluation results

[0069]

[0070]

[0071] It can be seen from the evaluation data that at the same addition ratio, the propylene yield and propylene selectivity of the catalyst of the present invention are significantly higher than those of the comparative agent, and the catalyst has excellent performance.

Claims

1. A method for synthesizing a ZSM-5 molecular sieve, wherein the synthesis steps are as follows: (1) Aluminum sulfate solution is added to water glass solution in two portions according to a certain ratio. The process temperature is controlled to be less than 35°C. After each addition of aluminum sulfate, the slurry is left to age for 30 minutes. The slurry is recorded as A. (2) Aluminum sulfate is added to sodium aluminate solution in a certain proportion, stirred evenly, and then a certain proportion of ZSM-5 molecular sieve is added. The solution is aged for 30 minutes and the slurry is recorded as B. (3) A and B are mixed evenly, ammonia water and α-alumina powder are added, and the mixture is filtered and washed; (4) The filter cake is slurried, spray-granulated, and calcined to solidify. The obtained granules are recorded as C; (5) Add a certain proportion of water to C, add liquid alkali in batches, raise the temperature for crystallization, add a mixed solution of ammonium dihydrogen phosphate and lanthanum chloride to the product after crystallization for exchange, filter, wash and dry to obtain the title compound.

2. The synthesis method according to claim 1, characterized in that In step (1), the mass ratio of the first addition amount of aluminum sulfate solution to water glass in terms of oxide is Al2O3:SiO2=(0.150-0.169):1, and the mass ratio of the second addition amount in terms of oxide to water glass is Al2O3:SiO2=(0.375-0.450):

1.

3. The synthesis method according to claim 1, characterized in that In step (2), the amount of aluminum sulfate and sodium aluminate added is such that the molar ratio of each substance in the slurry is Na2O:Al2O3:SO4 2- :H2O = (1.25-1.38) :1 :1.38 :

57.

4. The synthesis method according to claim 1, characterized in that The concentration of the sodium aluminate solution in step (2) is Al2O3=98-102 g / L, and the caustic ratio is 1.45-1.

50.

5. The synthesis method according to claim 1, characterized in that The concentration of aluminum sulfate solution is Al2O3=88-92g / L, and the concentration of water glass solution is SiO2=120-130g / L.

6. The synthesis method according to claim 1, characterized in that The addition amount of ZSM-5 molecular sieve and α-alumina powder accounts for 0.5-3wt% and 5-10wt% of the title compound on a dry basis. The silicon-aluminum ratio of ZSM-5 molecular sieve is 28-48, and it should be synthesized using an organic template.

7. The synthesis method according to claim 1, characterized in that In step (4), the calcination temperature is 300-500°C and the calcination time should be no less than one hour.

8. The synthesis method according to claim 1, characterized in that The amount of liquid alkali added in step (5) is such that the molar ratio of each substance in the slurry is OH - :SiO2=(0.12-0.20):1, the amount of ammonium dihydrogen phosphate and lanthanum chloride added is such that P=3-5wt% and RE2O3=0.3-0.9wt% in the title product on a dry basis.

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