A method for synthesizing silicon-aluminum EUO molecular sieve

Abstract

The present invention relates to the technical field of molecular sieves, and in particular to a method for synthesizing a silicon-aluminum EUO molecular sieve, comprising the following steps: step S1, mixing; step S2, flash evaporation; step S3, supplementing an aluminum source; step S4, crystallization; step S5, filtering, washing, drying, and calcining the crystallized product obtained in step S4; wherein in step S2, the precursor powder is amorphous as detected by XRD, and the precursor powder is amorphous as detected by XRD. 27 Al magic angle spinning solid nuclear magnetic resonance detection shows that tetracoordinated and hexacoordinated aluminum species exist at the same time. The present invention first mixes a silicon source, an alkali source and a part of an aluminum source, and then flash evaporation and drying is performed to form chemical bonds between silicon and aluminum species, especially aluminum species, which form tetracoordinated and hexacoordinated species, which are helpful for crystallization, and then introduces an aluminum source with high reactivity for quick de-powdering, and after mixing, crystallization is performed in an extremely concentrated system, and the alkaline auxiliary agent plays a role in maintaining the high alkalinity of the system, so that crystallization is completed in a relatively short time.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieves, and in particular to a method for synthesizing a silicon-aluminum EUO molecular sieve. Background Art

[0002] Silica-alumina EUO molecular sieve, also known as EU-1 molecular sieve, was first successfully developed by Casci et al. in 1981. It has a one-dimensional pore structure, including a ten-membered ring straight channel (0.58nm×0.41nm) along the

[100] direction and a twelve-membered ring side pocket (0.68nm×0.58nm×0.80nm) perpendicular to it along the

[001] direction. The unique pore structure gives it special shape selectivity and isomerization properties, especially in the xylene isomerization reaction, where it exhibits excellent catalytic performance and has great application potential.

[0003] Goergen et al. developed a method for synthesizing EU-1 molecular sieve by dry gel method, which used hexamethonium bromide as template, the synthetic silicon-aluminum ratio range was 40-60, and the crystallization time was 7 days (Microporous and Mesoporous Materials, 2009, 126, 283-290.). T. Dou et al. used hexamethonium bromide as template, and synthesized EU-1 molecular sieve with high silicon-aluminum ratio by adding seed crystals (Journal of Colloid and Interface Science, 2011, 358, 252-260). Patent CN111170333A discloses a method for synthesizing large-grain EU-1 molecular sieve by controlling the hydrolysis and aging conditions of silicon-aluminum sources, and the silicon-aluminum ratio of EU-1 molecular sieve synthesized by this method is 20-30. Patent CN106698454B discloses a method for synthesizing a nano EU-1 molecular sieve, which comprises mixing a raw material mixed gel with macroporous carbon, ultrasonically treating the mixture, then heating and stirring until viscous, drying, and crystallizing to obtain a nano EU-1 molecular sieve. However, viscous materials are difficult to transfer and handle in industrial production, thus restricting the industrial application of this technology. US65144479 discloses a method for hydrothermally synthesizing EUO molecular sieves using ultrasonic technology. There is no report on the application of large-scale ultrasonic equipment in the industrial production of molecular sieves, so the EU-1 synthesis method assisted by ultrasonic technology is difficult to achieve industrial production at this stage. US4537754 discloses a method for synthesizing EU-1 molecular sieves using alkylated derivatives of polymethylene α-ω-diamine ions as templates and under the condition of adding seed crystals. The template is relatively complex and expensive, making it difficult to achieve large-scale production of molecular sieves. Patent CN106946267B reports a method for synthesizing EU-1 using a dual template, and the synthesized EU-1 molecular sieve has an aluminum oxide silicon aluminum molar ratio of 11 to 20. Patent CN108862314B discloses a method for synthesizing EU-1 using a long-chain silane compound as a crystallization aid and a diquaternary ammonium salt of an alkane structure substituted with a double five-membered heterocyclic group as an organic template. In the prior art, the synthesis of silicon-aluminum EUO molecular sieves mainly has the following problems: (1) the synthetic silicon-aluminum ratio range is narrow, and when the silicon-aluminum ratio of the feed is too high, the ZSM-48 molecular sieve impurity phase is likely to appear; (2) it is necessary to add seed crystals to adjust the crystallization system; (3) the crystallization time is long and the synthesis efficiency is low. Researchers mainly develop new methods for synthesizing silicon-aluminum EUO molecular sieves through the following means: (1) using composite templates, special templates or special crystallization aids; (2) using special processes such as ultrasound; (3) adjusting aging and crystallization conditions. However, these methods will bring new problems of cost and process, which restricts the development of its industrial technology. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for synthesizing a silicon-aluminum EUO molecular sieve, by first mixing a silicon source, an alkali source and a portion of an aluminum source, and then flash drying the mixture to form chemical bonds between silicon and aluminum species, especially aluminum species, which form tetracoordinate and hexacoordinate species to facilitate crystallization, and then introducing an aluminum source with high reaction activity to quickly de-powder the mixture. After uniform mixing, crystallization is carried out in an extremely concentrated system, and an alkaline auxiliary agent plays a role in maintaining the high alkalinity of the system, so that crystallization is completed in a relatively short time.

[0005] The present invention is achieved through the following technical solutions: On the one hand, a method for synthesizing a silicon-aluminum EUO molecular sieve is provided, comprising the following steps:

[0006] Step S1, mixing;

[0007] Mixing a silicon source, an aluminum source, an alkali source and deionized water in a certain proportion to obtain a mixed solution;

[0008] Step S2, flash evaporation;

[0009] The mixed solution obtained in step S1 is dried by a flash dryer to obtain a precursor powder;

[0010] Step S3, replenishing aluminum source;

[0011] Adding the second aluminum source to the precursor powder obtained in step S2, mixing and grinding, to obtain a powder mixture;

[0012] Step S4, crystallization;

[0013] Adding the powder mixture obtained in step S3 to a mixed aqueous solution containing a template and an auxiliary agent, sealing, aging, and hydrothermal crystallization to obtain a crystallized product;

[0014] Step S5, filtering, washing, drying and roasting the crystallized product obtained in step S4 to obtain;

[0015] Wherein, in step S2, the precursor powder is amorphous as detected by XRD, 27 Al magic angle spinning solid-state NMR detected the existence of both tetracoordinated and hexacoordinated aluminum species.

[0016] Through the above technical scheme, the silicon source, aluminum source one and alkali source are first fully mixed, and then the precursor powder is obtained by flash drying. In this process, the aluminum species will react with the silicon species to form a four-coordinated and six-coordinated structure, which helps the aluminum species to crystallize into the molecular sieve framework. Then, the highly reactive aluminum source two is added and mixed and ground, and then an aqueous solution containing a template and an auxiliary agent is added for aging and crystallization to finally obtain the product silicon-aluminum EUO molecular sieve.

[0017] Furthermore, in step S1, the molar ratio of the silicon source: the aluminum source: the alkali source is 1:0.0005~0.03:0.1~0.45.

[0018] Furthermore, in step S1, in the mixed solution, the mass ratio of the deionized water:silicon source is 5-30:1.

[0019] Furthermore, the molar ratio of the aluminum source 1:aluminum source 2 is 0.1~1.5:1.

[0020] Furthermore, the silicon source is an inorganic silicon source, selected from at least one of silica sol, white carbon black, silica gel powder, and water glass;

[0021] Alternatively, the aluminum source is selected from at least one of aluminum sulfate, aluminum chloride, aluminum hydroxide, pseudo-boehmite, sodium aluminate, and aluminum nitrate;

[0022] Alternatively, the second aluminum source is rapidly de-powdered.

[0023] Further, in step S2, the inlet temperature of the flash dryer is 150-400°C, the outlet temperature is 90-120°C, the drying temperature is 60-100°C, and the drying time is 1-12h.

[0024] Furthermore, in step S4, the template agent is hexamethonium hydroxide; and the concentration of the template agent is 0.2-1.2 mol / L.

[0025] Furthermore, the molar ratio of the auxiliary agent to the silicon source is 0.01-0.3:1; and the auxiliary agent is an alkaline auxiliary agent selected from at least one of ammonium carbonate, hydroxylamine, urea, and ammonia water.

[0026] Furthermore, in step S4, the liquid-to-solid mass ratio of the mixed aqueous solution to the powder mixture is 1-10:1.

[0027] Further, in step S4, the aging is dynamic aging, the aging temperature is 40-90°C, the aging time is 0.5-8h, and the stirring speed is 10-50rpm;

[0028] Alternatively, the crystallization is static crystallization, the crystallization temperature is 160-210° C., and the crystallization time is 6-24 hours.

[0029] Beneficial Effects

[0030] 1) Low template dosage, extremely concentrated system, and high single-pot yield;

[0031] 2) Ability to synthesize EUO molecular sieves with a wide range of Si / Al ratios;

[0032] 3) No need to add seed crystals, short crystallization time, high product crystallinity and high yield;

[0033] 4) By mixing the silicon source, alkali source and part of the aluminum source, and flash drying them, the silicon and aluminum species form chemical bonds, especially the aluminum species, which form tetracoordinated and hexacoordinated species, which is helpful for crystallization. Then, the aluminum source with high reaction activity is introduced to quickly de-powder. After mixing evenly, crystallization is carried out in an extremely concentrated system. The alkaline additive plays a role in maintaining the high alkalinity of the system, so that the crystallization is completed in a shorter time. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is the precursor powder in Examples 1 to 4 27 The Al magic angle spinning solid-state NMR test results confirmed the presence of both tetracoordinated and hexacoordinated aluminum species;

[0035] Figure 2 These are the XRD results of the crystallized products of Examples 1-4 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] A method for synthesizing a silicon-aluminum EUO molecular sieve comprises the following steps: (1) mixing and stirring a silicon source, an aluminum source, an alkali source, and deionized water to obtain a mixed solution; (2) passing the mixed solution through a flash dryer to obtain a precursor powder, and drying the mixture; (3) adding an aluminum source to the dried mixed powder, mixing and grinding to obtain a raw material mixture; (4) adding the powder mixture obtained in step 3 to a mixed aqueous solution containing a template and an auxiliary agent, sealing, aging, and hydrothermal crystallization; and (5) filtering, washing, drying, and calcining the crystallized product to obtain a silicon-aluminum EUO molecular sieve.

[0038] The silicon source is an inorganic silicon source, preferably at least one of silica sol, white carbon black, silica gel powder, and water glass; the first aluminum source is at least one of aluminum sulfate, aluminum chloride, aluminum hydroxide, pseudo-boehmite, sodium aluminate, and aluminum nitrate, preferably aluminum sulfate, sodium aluminate, and pseudo-boehmite; the alkali source is an inorganic alkali, preferably at least one of sodium hydroxide and potassium hydroxide; the second aluminum source is a quick de-powdering agent; the template agent is hexamethonium hydroxide; the auxiliary agent is an alkaline auxiliary agent, which is at least one of ammonium carbonate, hydroxylamine, urea, and ammonia water, preferably ammonium carbonate and urea.

[0039] The silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the alkali source is calculated as M2O, and the following relationship should be satisfied: (1) In the synthesis step (1), the silicon source, the aluminum source 1, and the alkali source are mixed in a molar ratio of 1:0.0005~0.03:0.1~0.45, and the mass ratio of H2O to the silicon source in the mixed solution is 5~30:1; (2) The molar ratio of the aluminum source 1 to the aluminum source 2 is 0.1~1.5:1, preferably 0.25~1:1; (3) In the synthesis step (4), the template concentration in the mixed aqueous solution is 0.2~1.2 mol / L, and the liquid-solid mass ratio of the mixed aqueous solution to the raw material mixture is 1~10:1, wherein the molar ratio of the auxiliary agent to the silicon source is 0.01~0.3:1.

[0040] When the mixed material passes through the flash dryer, the inlet temperature of the flash dryer is 150~400℃, and the outlet temperature is 90~120℃; the drying temperature of the precursor powder is 60~100℃, and the drying time is 1~12h; the precursor powder is amorphous according to XRD detection. 27 AlMASNMR detection shows that both tetracoordinated and hexacoordinated aluminum species exist; aging is dynamic aging, the aging temperature is 40-90°C, the aging time is 0.5-8h, and the stirring speed is 10-50rpm; crystallization is static crystallization, the crystallization temperature is 160-210°C, and the crystallization time is 6-24h, preferably 12-24h. Filtration, washing, drying and calcination of the crystallized product are conventional steps for the preparation of molecular sieves.

[0041] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The experimental methods without specific conditions in the following examples are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise specified, all percentages, ratios, proportions or parts are by weight.

[0042] Unless otherwise specified, the reagents and raw materials used in the examples and comparative examples of the present invention can be obtained through commercial channels.

[0043] Example 1

[0044] 15g silica sol (30%), 0.28g aluminum sulfate 18hydrate, and 1.56g NaOH were added to 40g water and stirred to mix evenly; the precursor powder was obtained by flash drying, the flash drying feed temperature was 200°C, and the discharge temperature was 100°C; the precursor powder was placed in a 100°C oven and dried for 6h, and then 0.05g of quick powder was added and mixed and ground; 11.3mL of 1mol / L hexamethylammonium hydroxide aqueous solution was weighed, 0.72g of ammonium carbonate was added thereto, stirred to dissolve, and then the mixed and ground powder mixture was added thereto, aged at 60°C at 30rpm for 4h, and statically crystallized at 180°C for 20h, and the crystallized product was filtered, washed, dried, and calcined to obtain the EUO molecular sieve sample. Figure 1 The precursor powder 27 The AlMASNMR detection results confirmed the existence of both tetracoordinated and hexacoordinated aluminum species. Figure 2 This is the XRD result of its crystallization product, which is confirmed to be a pure phase EUO molecular sieve.

[0045] Example 2

[0046] 3.3g silica gel powder (90%), 0.015g sodium aluminate (49.5% Al2O3), and 0.62g NaOH were added to 74g water and stirred to mix evenly; the precursor powder was obtained by flash drying, the flash drying feed temperature was 150°C, and the discharge temperature was 110°C; the precursor powder was placed in an oven at 80°C and dried for 12h, and then 0.03g of quick powder was added and mixed and ground; 12.5mL of 0.4mol / L hexamethylammonium hydroxide aqueous solution was weighed, 0.6g of urea was added thereto, stirred to dissolve, and then the mixed and ground powder mixture was added thereto, aged at 80°C at 50rpm for 2h, and statically crystallized at 210°C for 10h, and the crystallized product was filtered, washed, dried, and calcined to obtain the EUO molecular sieve sample.

[0047] Example 3

[0048] 3g of white carbon black, 0.064g of pseudo-boehmite (66.0% Al2O3), and 2.38g of KOH were added to 58g of water and stirred to mix evenly; a precursor powder was obtained by flash drying, and the feed temperature of the flash drying was 270°C and the discharge temperature was 120°C; the precursor powder was placed in a 60°C oven and dried for 8h, and then 0.085g of quick powder was added and mixed and ground; 25mL of 0.8mol / L hexamethylammonium hydroxide aqueous solution was weighed, 0.44g of ammonia water was added thereto, and the mixed and ground powder mixture was added thereto, aged at 45°C at 10rpm for 8h, and statically crystallized at 160°C for 24h, and the crystallized product was filtered, washed, dried, and calcined to obtain an EUO molecular sieve sample.

[0049] Example 4

[0050] 12.79g of water glass (Na2O110.05g / L, SiO2308.66g / L), 0.234g of Al(OH)3 powder, and 0.693g of KOH were added to 65.39g of water and stirred to mix evenly; the precursor powder was obtained by flash drying, the flash drying feed temperature was 380°C, and the discharge temperature was 120°C; the precursor powder was placed in a 70°C oven and dried for 10h, and then 0.204g of quick powder was added and ground and mixed; 20.8mL of 1.2mol / L hexamethylammonium hydroxide aqueous solution was weighed, 0.106g of hydroxylamine hydrochloride was added thereto, stirred to mix evenly, and then the mixed and ground powder mixture was added thereto; aged at 90°C at 20rpm for 0.5h, crystallized at 170°C for 20h, and the crystallized product was filtered, washed, dried, and calcined to obtain the EUO molecular sieve sample.

[0051] Comparative Example 1

[0052] 0.28g of aluminum sulfate 18hydrate and 1.56g of NaOH were added into water and stirred to mix evenly; 0.05g of quick powder, 11.3mL of 1mol / L hexamethonium hydroxide aqueous solution and 0.72g of ammonium carbonate were added thereto in sequence and stirred evenly to form a gel; the mixture was aged at 60°C at 30rpm for 4h and statically crystallized at 180°C for 20h; after the crystallization, the product was filtered, washed, dried and calcined to obtain a sample.

[0053] Comparative Example 2

[0054] 0.28g of aluminum sulfate 18hydrate and 1.56g of NaOH were added into water and stirred to mix evenly; 0.05g of quick powder and 11.3mL of 1mol / L hexamethonium hydroxide aqueous solution were added thereto in turn and stirred evenly to form a gel; the mixture was aged at 60°C at 30rpm for 4h and statically crystallized at 180°C for 20h; after the crystallization, the product was filtered, washed, dried and calcined to obtain a sample.

[0055] Comparative Example 3

[0056] Deionized water, sodium hydroxide and sodium aluminate are mixed and stirred in sequence until they are completely dissolved, and then the template hexamethylammonium bromide and silica sol are added in sequence and stirred evenly to obtain an initial gel, wherein the molar ratio of each component is SiO2:Al2O3:Na2O:HMBr2:H2O=1:0.01:0.18:0.11:15; the above gel is placed at 140°C for dynamic crystallization for 12 hours, and then the temperature is raised to 180°C for dynamic crystallization for 120 hours; after the crystallization is completed, the product is filtered, washed, dried and calcined to obtain a sample.

[0057] Figure 1 The precursor powder of Examples 1 to 427 AlMASNMR test results, Figure 2 1 to 4 and comparative examples 1 to 3 are the XRD results of the crystallized products. Table 1 below shows the feed silicon-to-aluminum ratio, actual silicon-to-aluminum ratio and product yield of Examples 1 to 4 and comparative example 3.

[0058] Table 1 Feed silicon-aluminum ratio, product silicon-aluminum ratio and yield results of samples

[0059]

[0060] Depend on Figure 1 It can be seen that by adopting the method provided by the present invention, the silicon source, the aluminum source and the alkali source are fully mixed, and then the precursor powder is obtained by flash drying, and both tetracoordinated and hexacoordinated aluminum species exist. The presence of these two aluminum species can promote the crystallization of aluminum species into the molecular sieve framework in the subsequent crystallization process, thereby ensuring the product yield.

[0061] Depend on Figure 2 It can be seen that the method of the present invention can obtain a pure phase EUO molecular sieve with good crystallization. Combined with the results of comparative example 1, it can be seen that if the raw materials are mixed without flash drying, there will be a material concentration gradient in the local synthetic gel during crystallization, which will cause the local crystal nucleation and growth rate of the system to be too fast during crystallization, thereby leading to the formation of impurities. Combined with the results of comparative example 2, it can be seen that the crystallization aid plays a key role in the formation of the EUO phase. In the early stage of crystallization, it will consume OH in the synthetic system. - , which reduces the basicity of the system and leads to the appearance of *MRE phase. The presence of crystallization aid can maintain the high basicity of the system to ensure the formation of EUO phase.

[0062] It can be seen from the results in Table 1 that the silicon-aluminum EUO molecular sieve product obtained by the method of the present invention has a silicon-aluminum ratio that is basically equivalent to the silicon-aluminum ratio of the feed, and the product yield is high. However, for the silicon-aluminum EUO molecular sieve synthesized by the conventional method, the actual silicon-aluminum ratio of the product is significantly lower than the silicon-aluminum ratio of the feed, indicating that there is a phenomenon of raw material loss, and the silicon-aluminum ratio range of the EUO molecular sieve synthesized by the conventional method is relatively narrow.

[0063] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for synthesizing a silicon-aluminum EUO molecular sieve, characterized in that: The following steps are involved: Step S1, mixing; Mixing a silicon source, an aluminum source, an alkali source and deionized water in a certain proportion to obtain a mixed solution; Step S2, flash evaporation; The mixed solution obtained in step S1 is dried by a flash dryer to obtain a precursor powder; Step S3, replenishing aluminum source; Adding the second aluminum source to the precursor powder obtained in step S2, mixing and grinding, to obtain a powder mixture; Step S4, crystallization; Adding the powder mixture obtained in step S3 to a mixed aqueous solution containing a template and an auxiliary agent, sealing, aging, and hydrothermal crystallization to obtain a crystallized product; Step S5, filtering, washing, drying and roasting the crystallized product obtained in step S4 to obtain; Wherein, the second aluminum source is a fast-de-powdering agent; the molar ratio of the auxiliary agent to the silicon source is 0.01-0.3:1; and the auxiliary agent is an alkaline auxiliary agent; In step S2, the inlet temperature of the flash dryer is 150-400°C, and the outlet temperature is 90-120°C; the precursor powder is amorphous as detected by XRD. 27 Al magic angle spinning solid-state NMR detected the existence of both tetracoordinated and hexacoordinated aluminum species.

2. The method for synthesizing the silicon-aluminum EUO molecular sieve according to claim 1, characterized in that: In step S1, the molar ratio of the silicon source: the aluminum source: the alkali source is 1: 0.0005-0.03: 0.1-0.

45.

3. The method for synthesizing the silicon-aluminum EUO molecular sieve according to claim 2, characterized in that: In step S1, in the mixed solution, the mass ratio of the deionized water: the silicon source is 5-30:

1.

4. The method for synthesizing the silicon-aluminum EUO molecular sieve according to claim 1, characterized in that: The molar ratio of the aluminum source 1: the quick-de-powder is 0.1-1.5:

1.

5. The method for synthesizing the silicon-aluminum EUO molecular sieve according to any one of claims 1 to 4, characterized in that: The silicon source is an inorganic silicon source, selected from at least one of silica sol, white carbon black, silica gel powder and water glass; Alternatively, the aluminum source is selected from at least one of aluminum sulfate, aluminum chloride, aluminum hydroxide, pseudo-boehmite, sodium aluminate, and aluminum nitrate.

6. The method for synthesizing the silicon-aluminum EUO molecular sieve according to claim 1, characterized in that: In step S4, the template agent is hexamethonium hydroxide; the concentration of the template agent is 0.2-1.2 mol / L.

7. The method for synthesizing the silicon-aluminum EUO molecular sieve according to claim 1, characterized in that: The alkaline auxiliary agent is selected from at least one of ammonium carbonate, hydroxylamine, urea and ammonia water.

8. The method for synthesizing the silicon-aluminum EUO molecular sieve according to claim 1, characterized in that: In step S4, the liquid-to-solid mass ratio of the mixed aqueous solution to the powder mixture is 1-10:

1.

9. The method for synthesizing the silicon-aluminum EUO molecular sieve according to claim 1, characterized in that: In step S4, the aging is dynamic aging, the aging temperature is 40-90°C, the aging time is 0.5-8h, and the stirring speed is 10-50rpm; Alternatively, the crystallization is static crystallization, the crystallization temperature is 160-210° C., and the crystallization time is 6-24 hours.

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