Synthesis method of beta molecular sieve

Abstract

The invention discloses a method for synthesizing a template-free beta molecular sieve, which is characterized by comprising the following steps of: uniformly mixing a silicon source, an aluminum source, an alkali source and a beta molecular sieve seed crystal under the condition of taking water as a medium to form a reaction mixture of a synthesis system, heating to 70-150 DEG C in a closed pressure-resistant container, treating, and standing to form two-phase layering of supernatant liquid and lower gel, and after extracting supernatant liquid, continuously carrying out static or low-speed dynamic hydrothermal crystallization on the lower gel, and recovering a hydrothermal crystallization product to obtain the beta molecular sieve.

Description

Technical Field

[0001] The present invention relates to the field of molecular sieve synthesis, and more specifically to a method for synthesizing beta molecular sieve. Background Art

[0002] β molecular sieve has a three-dimensional twelve-membered ring channel structure and was first synthesized by Mobil Corporation in the United States in 1967 (US3,308,069). Due to its unique topological structure and good thermal and hydrothermal stability, β molecular sieve exhibits excellent catalytic performance in reactions such as hydrocracking, hydroisomerization, hydrocarbon cracking, and alkylation. Currently, β molecular sieve has been industrialized.

[0003] In the prior art, there are two methods for synthesizing β molecular sieves: synthesis with a template and synthesis without a template.

[0004] In the synthesis method with template agent, in addition to the synthesis using tetraethylammonium hydroxide as template agent mentioned in US3308069, US4554145 uses 1,4-diazabicyclo[2,2,2]octane and US4642226 uses methyldibenzylamine, which can achieve the purpose of synthesizing β molecular sieve. The synthesis method with template agent has the problems of high synthesis cost and pollution in production and post-treatment process, which limits the application of β molecular sieve.

[0005] CN101249968A and US8865121 disclose a method for synthesizing beta molecular sieve without template agent, which is the first method to synthesize beta molecular sieve without template agent. Since then, many studies have been conducted on template-free synthesis. However, since there are many problems to be solved in the template-free synthesis system, it has not been industrialized so far. One of the problems is that the utilization rate of silicon source is low under the synthesis system. The yield of synthesizing beta molecular sieve with template agent in industry is usually above 85%, while the yield under the template-free condition is less than 30%. The method disclosed in CN102285667A improves the utilization rate of silicon source by recycling the mother liquor of synthesizing beta molecular sieve without template agent. This method can solve the problem of low utilization rate of silicon source to a certain extent, but its process is still complicated, and new mother liquor will be produced after each kettle crystallization, which is difficult to implement in industry. Summary of the invention

[0006] The purpose of the present invention is to provide a method for synthesizing beta molecular sieve without template, which has the advantages of improving single-pot yield, simple operation and good repeatability, in view of the problem of low yield of existing beta molecular sieve synthesized without template.

[0007] The present invention provides a method for synthesizing a template-free β molecular sieve, which is characterized in that a silicon source, an aluminum source, an alkali source and a β molecular sieve seed are uniformly mixed under the condition of water as a medium to form a synthesis system reaction mixture, and then the mixture is heated to 70-150° C. in a closed pressure-resistant container and allowed to stand to form two-phase separation of an upper clear liquid and a lower gel, and after the upper clear liquid is extracted, the lower gel is continuously subjected to static or low-speed dynamic hydrothermal crystallization, and the hydrothermal crystallization product is recovered to obtain the β molecular sieve.

[0008] In the synthesis method provided by the present invention, the silicon source is selected from solid silicon sources such as solid silica gel and white carbon black, and common solid silicon sources and liquid silicon sources on the market such as silica sol, water glass, and tetraethyl orthosilicate. The aluminum source is one or more of water-soluble compounds such as sodium aluminate, aluminum sulfate, aluminum nitrate, and aluminum chloride. The alkali source is selected from sodium aluminate, water glass, or an alkali metal ion compound whose aqueous solution is alkaline, and the alkali metal ion compound whose aqueous solution is alkaline is NaOH, Na2CO3, or NaHCO3.

[0009] In the synthesis method provided by the present invention, the β molecular sieve seed is of ammonium type and / or hydrogen type, and the molar ratio of silicon oxide to aluminum oxide is 8 to 50, preferably 15 to 30.

[0010] In the synthesis method provided by the present invention, the molar ratio of the reaction mixture is SiO2 / Al2O3=16-50, NaOH / SiO2=0.40-0.60, H2O / SiO2=10-35, preferably, the molar ratio of the gel-like substance is SiO2 / Al2O3=16-40, NaOH / SiO2=0.45-0.60, H2O / SiO2=15-25; the amount of β molecular sieve seed added is 5% to 20% of the SiO2 in the silicon source by mass, preferably 7% to 15%.

[0011] In the synthesis method provided by the present invention, the final pH of the synthesis system is greater than 10; the static operation is to keep the temperature constant for more than 1 hour under static conditions and then cool it down to room temperature.

[0012] In the synthesis method provided by the present invention, the aluminum content in the supernatant is ≤500ppm. The operation of extracting the supernatant is generally considered to be an operation of extracting at least about 90% of the supernatant, for example, preferably about 95%-100% in the embodiment, which can achieve the purpose of synthesizing β molecular sieve and improving the single-pot yield.

[0013] In the synthesis method provided by the present invention, the hydrothermal crystallization is static hydrothermal crystallization or low-speed dynamic hydrothermal crystallization under self-pressure in a closed reactor. The low-speed dynamic hydrothermal crystallization has a stirring rate of

[0014] ≤50rpm / min, preferably stirring rate ≤30rpm / min. Hydrothermal crystallization can be one-stage hydrothermal crystallization or two-stage hydrothermal crystallization; the conditions of the one-stage hydrothermal crystallization are: temperature 110-160°C, time 24-150h; the conditions of the two-stage hydrothermal crystallization are: one-stage hydrothermal crystallization temperature 130-160°C, time 15-30h, two-stage hydrothermal crystallization temperature 110-130°C, time 30-50h.

[0015] The molecular sieve obtained by the synthesis method provided by the present invention is a pure phase β molecular sieve with complete crystal form. The method has the characteristics of high silicon source utilization, less wastewater generated by synthesis, simple process, low operation difficulty, and easy industrial production. Compared with the traditional template-free β molecular sieve synthesis technology, the synthesis method provided by the present invention must have a higher single-pot yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is the XRD spectrum of the sample of Example 1.

[0017] Figure 2 This is the SEM spectrum of the sample in Example 1. DETAILED DESCRIPTION

[0018] The present invention will be further described below by way of examples, but the contents of the present invention are not limited thereto.

[0019] In the examples, the X-ray diffraction (XRD) crystal phase diagram was obtained by Philips Panalytical X'pert, and the test conditions were: Cu target, Kα radiation, Ni filter, super energy detector, tube voltage 30KV, tube current 40mA.

[0020] The scanning electron microscope (SEM) images were taken by a Quanta 200F scanning electron microscope from FEI Company. The test conditions were: after drying, vacuum evaporation and gold spraying were used to increase the conductivity, and the electron microscope acceleration voltage was 20 kV.

[0021] The elemental analysis data were obtained by using a Rigaku ZSX Primus II X-ray fluorescence spectrometer under the following test conditions: tungsten target, excitation voltage of 40 kV, and excitation current of 50 mA. The intensity of the characteristic spectral lines of each element was measured by a scintillation counter to perform quantitative or semi-quantitative element analysis.

[0022] Example 1

[0023] Add white carbon black (Shenyang Chemical Industry Group Co., Ltd., silicon dioxide 93.0 wt %), sodium aluminate (sodium oxide 287 g / L, aluminum oxide 159.7 g / L), and β molecular sieve seeds (Sinopec Catalyst Co., Ltd. Changling Branch, SiO2 / Al2O3 (molar ratio) = 22) into deionized water respectively and stir until uniformly dispersed.

[0024] The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3)=25, n(H2O / SiO2)=15, n(Na / SiO2)=0.55, m(seed / SiO2)=0.10. Transfer to a sealed pressure-resistant container, heat to 120°C while stirring, and keep the temperature at this temperature for 3 hours. Cool down and let stand until complete stratification.

[0025] The upper clear liquid was extracted, and the lower gel sample was taken for elemental analysis. The remaining lower gel was transferred to a pressure-resistant stainless steel reactor, heated to 140°C, kept at a constant temperature for 36 hours in a static state, and then cooled. The solid product was separated by filtration, washed, and dried at 80°C for 12 hours to obtain sample A1.

[0026] The XRD spectrum of sample A1 is shown in Figure 1 , SEM photos see Figure 2 , XRD spectrum and SEM photos have typical characteristics of β molecular sieve.

[0027] The lower gel and the β molecular sieve sample A1 were subjected to elemental analysis, and the data are shown in Table 1. In Table 1, "before crystallization" refers to the gel sample after the upper clear liquid was extracted.

[0028] Example 2

[0029] Water glass (Jinan Mingchuan Chemical Co., Ltd., specific gravity 1.26, modulus 3.30), aluminum sulfate, sodium hydroxide, sodium carbonate, and β molecular sieve seeds were added into deionized water respectively, and stirred until the system was evenly dispersed.

[0030] The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3)=20, n(H2O / SiO2)=20, n(Na / SiO2)=0.60, m(seed / SiO2)=0.08. Transfer to a sealed pressure-resistant container, heat to 100°C under stirring, and keep the temperature at this temperature for 4 hours. Cool down and let stand until complete stratification.

[0031] The upper clear liquid was extracted, and the lower gel sample was taken for elemental analysis. The remaining lower gel was transferred to a pressure-resistant stainless steel reactor, heated to 135°C, kept at a constant temperature for 45 hours in a static state, and then cooled. The solid product was separated by filtration, washed, and dried at 80°C for 12 hours to obtain sample A2.

[0032] Both the XRD spectrum and SEM of sample A2 show the typical characteristics of β molecular sieve.

[0033] The lower gel and β molecular sieve sample A2 were subjected to elemental analysis, and the data are shown in Table 1.

[0034] Example 3

[0035] Silica gel powder (Qingdao Ocean Chemical Co., Ltd., 80-160 mesh, 500m 2 ), water glass, sodium aluminate (sodium oxide 287 g / L, aluminum oxide 159.7 g / L), and β molecular sieve seeds were added into deionized water respectively and stirred until the system was evenly dispersed.

[0036] The mixture of the synthesis system has the following proportions: n(SiO2 / Al2O3)=36, n(H2O / SiO2)=15, n(Na / SiO2)=0.55, m(seed / SiO2)=0.10, and is transferred to a sealed pressure-resistant container, heated to 100°C under stirring, and kept at this temperature for 4 hours. Cool down and let stand until complete stratification.

[0037] The upper clear liquid was extracted, and the lower gel sample was taken for elemental analysis. The remaining lower gel was transferred to a pressure-resistant stainless steel reactor, heated to 120°C, kept at a constant temperature for 120 hours in a static state, and then cooled. The solid product was separated by filtration, washed, and dried at 80°C for 12 hours to obtain sample A3.

[0038] Both the XRD spectrum and SEM of sample A3 show the typical characteristics of β molecular sieve.

[0039] The lower gel and β molecular sieve sample A3 were subjected to elemental analysis, and the data are shown in Table 1.

[0040] Example 4

[0041] Alkaline silica sol (30 wt % silicon dioxide), sodium aluminate (287 g / L sodium oxide, 159.7 g / L aluminum oxide), sodium hydroxide, sodium bicarbonate, and β molecular sieve seeds were added to deionized water respectively, and stirred until the system was evenly dispersed.

[0042] The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3)=25, n(H2O / SiO2)=30, n(Na / SiO2)=0.65, m(seed crystal / SiO2)=0.15. Transfer it to a sealed pressure-resistant container, heat it to 140°C while stirring, and keep it at this temperature for 1 hour.

[0043] The upper clear liquid was extracted, and the lower gel sample was taken for elemental analysis. The remaining lower gel was transferred to a pressure-resistant stainless steel reactor, heated to 120°C, kept at a constant temperature for 120 hours in a static state, and then cooled. The solid product was separated by filtration, washed, and dried at 80°C for 12 hours to obtain sample A4.

[0044] Both the XRD spectrum and SEM of sample A4 show the typical characteristics of β molecular sieve.

[0045] The lower gel and β molecular sieve sample A4 were subjected to elemental analysis, and the data are shown in Table 1.

[0046] Example 5

[0047] White carbon black (Shenyang Chemical Industry Group Co., Ltd., silicon dioxide 93.0 wt %), sodium aluminate (sodium oxide 287 g / L, aluminum oxide 159.7 g / L), β molecular sieve seed (Sinopec Catalyst Co., Ltd. Changling Branch, SiO2 / Al2O3 (molar ratio) = 22, XRD spectra and SEM photos are shown in Table 1. Figure 1 and Figure 2 ) were added into deionized water and stirred until uniformly dispersed.

[0048] The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3)=30, n(H2O / SiO2)=30, n(Na / SiO2)=0.60, m(seed crystal / SiO2)=0.08.

[0049] Transfer to a sealed pressure-resistant container, raise the temperature to 100°C while stirring, and keep it at this temperature for 4 hours. Cool down and let it stand until the layers are completely separated.

[0050] The upper clear liquid was extracted, and the lower gel sample was taken for elemental analysis. The remaining lower gel was transferred to a pressure-resistant stainless steel reactor, heated to 120°C, kept at a constant temperature for 120 hours in a static state, and then cooled. The solid product was separated by filtration, washed, and dried at 80°C for 12 hours to obtain sample A5.

[0051] Both the XRD spectrum and SEM of sample A5 show the typical characteristics of β molecular sieve.

[0052] The lower gel and β molecular sieve sample A5 were subjected to elemental analysis, and the data are shown in Table 1.

[0053] Example 6

[0054] Silica gel powder (Qingdao Ocean Chemical Co., Ltd., 80-160 mesh, 500m 2 ), aluminum sulfate, sodium carbonate, sulfuric acid, and β molecular sieve seed crystals are added into deionized water respectively, and stirred until it becomes viscous and the solid is evenly dispersed.

[0055] The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3)=36, n(H2O / SiO2)=15, n(Na / SiO2)=0.50, m(seed crystal / SiO2)=0.15.

[0056] Transfer to a sealed pressure-resistant container, raise the temperature to 100°C while stirring, and keep it at this temperature for 4 hours. Cool down and let it stand until the layers are completely separated.

[0057] The upper clear liquid was extracted, and the lower gel sample was taken for elemental analysis. The remaining lower gel was transferred to a pressure-resistant stainless steel reactor, heated to 120°C, kept at a constant temperature for 120 hours in a static state, and then cooled. The solid product was separated by filtration, washed, and dried at 80°C for 12 hours to obtain sample A6.

[0058] Both the XRD spectrum and SEM of sample A6 show the typical characteristics of β molecular sieve.

[0059] The lower gel and β molecular sieve sample A6 were subjected to elemental analysis, and the data are shown in Table 1.

[0060] Comparative Example 1

[0061] This comparative example synthesizes β molecular sieve according to the method of Example 1, except that the process of heating and stratification and extracting the supernatant after cooling is omitted.

[0062] Add white carbon black, sodium aluminate (sodium oxide 287 g / L, aluminum oxide 159.7 g / L) and β molecular sieve crystals into deionized water and stir until they are evenly dispersed.

[0063] The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3)=25, n(H2O / SiO2)=15, n(Na / SiO2)=0.55, m(seed crystal / SiO2)=0.10.

[0064] The obtained reaction mixture gel was transferred to a pressure-resistant stainless steel reactor, heated to 140°C, kept at a constant temperature for 36 hours in a static state, and then cooled. The solid product was separated by filtration, washed, and dried at 80°C for 12 hours to obtain a β molecular sieve comparison product DA1. The sample was subjected to elemental analysis, and the analysis data are shown in Table 1.

[0065] Comparative Example 2

[0066] In this comparative example, beta molecular sieve was synthesized according to the method of Example 3, except that the steps of heating and stratification and extracting the supernatant after cooling were omitted.

[0067] Silica gel powder (Qingdao Ocean Chemical Co., Ltd., 80-160 mesh, 500m 2), water glass, sodium aluminate (sodium oxide 287 g / L, aluminum oxide 159.7 g / L), and β molecular sieve seeds were added into deionized water respectively and stirred until the system was evenly dispersed.

[0068] The mixture ratio of the synthesis system is as follows: n(SiO2 / Al2O3)=36, n(H2O / SiO2)=15, n(Na / SiO2)=0.55, m(seed crystal / SiO2)=0.10.

[0069] The obtained reaction mixture was transferred to a pressure-resistant stainless steel reactor, heated to 140°C, kept at a constant temperature for 36 hours in a static state, and then cooled. The solid product was separated by filtration, washed, and dried at 80°C for 12 hours to obtain the β molecular sieve product DA3. The sample was subjected to elemental analysis. The analysis data are shown in Table 1.

[0070] Table 1

[0071]

[0072] It can be seen from the data in Table 1 that the elemental analysis results of the gel after the upper clear liquid is extracted are close to those of the final β molecular sieve product obtained. For example, the SiO2 weight % and Al2O3 weight % of the lower gel in Example 1 are 77.9 and 14.0, respectively, while the SiO2 weight % and Al2O3 weight % of the synthesized β molecular sieve sample A are 76.2 and 15.9, respectively, indicating that the β molecular sieve can be crystallized and synthesized by relying solely on the lower gel after the clear liquid is extracted, and the silicon-aluminum ratio of the synthesized β molecular sieve is close to that of the gel before crystallization, indicating that the degree of crystallization is good and the utilization rate of the silicon source and the aluminum source is high. Compared with the comparative examples, for example, Example 1 and Comparative Example 1, Example 3 and Comparative Example 2, the weights of silicon oxide and aluminum oxide in the synthesized β molecular sieve of the present invention are substantially equivalent, indicating that the extraction of the upper clear liquid has no significant effect on the elemental composition of the finished β molecular sieve.

Claims

1. A method for synthesizing a template-free β molecular sieve, characterized in that: After the silicon source, aluminum source, alkali source and β molecular sieve seed crystals are uniformly mixed under the condition of water as a medium to form a synthetic system reaction mixture, the temperature is raised to 70-150°C in a closed pressure-resistant container and allowed to stand to form two-phase separation of an upper clear liquid and a lower gel. After the upper clear liquid is extracted, the lower gel is continuously subjected to static or low-speed dynamic hydrothermal crystallization, and the hydrothermal crystallization product is recovered to obtain a β molecular sieve.

2. The synthesis method according to claim 1, characterized in that: The molar ratio of the reaction mixture of the synthesis system is SiO2 / Al2O3=16-50, NaOH / SiO2=0.40-0.60, H2O / SiO2=10-35. Preferably, the molar ratio of the reaction mixture of the synthesis system is SiO2 / Al2O3=16~40、NaOH / SiO2=0.45~0.60、H2O / SiO2=15~25;β molecular sieve The amount of seed crystal added is 5% to 20% by mass, preferably 7% to 15% by mass of SiO2 in the silicon source.

3. The synthesis method according to claim 1, characterized in that: The silicon source is selected from one or more of solid silica gel, white carbon black, silica sol, water glass, and ethyl orthosilicate.

4. The synthesis method according to claim 1, characterized in that: The aluminum source is selected from one or more of sodium aluminate, aluminum sulfate, aluminum nitrate, and aluminum chloride.

5. The synthesis method according to claim 1, characterized in that: The alkali source is selected from sodium aluminate, water glass, or an alkali metal ion compound whose aqueous solution is alkaline.

6. The synthesis method according to claim 1, characterized in that: The alkali metal ion compound whose aqueous solution is alkaline is NaOH, Na2CO3 or NaHCO3.

7. The synthesis method according to claim 6, characterized in that: The pH of the reaction mixture of the synthesis system is greater than 10.

8. The synthesis method according to claim 1, characterized in that: The static operation is a process of keeping the temperature constant for more than 1 hour under static conditions and then cooling to room temperature.

9. The synthesis method according to claim 1 or 2, characterized in that: The beta molecular sieve seed crystal is of ammonium type and / or hydrogen type, and the molar ratio of silicon oxide to aluminum oxide is 8-50.

10. The synthesis method according to claim 1, characterized in that: The aluminum content in the supernatant is ≤500ppm.

11. The synthesis method according to claim 1, characterized in that: The low-speed dynamic hydrothermal crystallization has a stirring rate of ≤50 rpm / min, preferably a stirring rate of ≤30 rpm / min.

12. The synthesis method according to claim 1, characterized in that: The hydrothermal crystallization is one-stage hydrothermal crystallization or two-stage hydrothermal crystallization; the conditions of the one-stage hydrothermal crystallization are: temperature 110-160°C, time 24-150h; the conditions of the two-stage hydrothermal crystallization are: one-stage hydrothermal crystallization temperature 130-160℃, time 15-30h, second stage hydrothermal crystallization temperature 110~130℃, time 30-50h.

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