A high-crystallinity ZSM-12 molecular sieve and its preparation method and application

Abstract

The present invention relates to the technical field of molecular sieve catalytic materials, and in particular to a high-crystallinity ZSM-12 molecular sieve and a preparation method and application thereof. The method comprises the following steps: subjecting a reaction mixture to a crystallization treatment, and sequentially subjecting the obtained crystallized product to calcination and an inorganic ammonium salt ion exchange treatment; wherein the reaction mixture comprises an inorganic base, an aluminum source, a boron source, dimethyldiethoxyammonium hydroxide, a silicon source, and water; the method has the advantages of precisely controlling the alkalinity of the synthesis system by using boric acid in conjunction with a weakly alkaline template agent, dimethyldiethoxyammonium hydroxide, effectively inhibiting the formation of impurities and improving the crystallinity of the ZSM-12 molecular sieve, while optimizing the acid strength; the method has a simple process and low cost, and the obtained molecular sieve can reduce cracking side reactions and improve the yield of isomerized hydrocarbons in the isomerization reaction of long-chain alkanes, and has the potential for large-scale industrial application.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieve catalytic materials, and in particular to a high-crystallinity ZSM-12 molecular sieve and a preparation method and application thereof. Background Art

[0002] ZSM-12 molecular sieve (MTW) ​​is a typical one-dimensional straight-channel molecular sieve composed of twelve-membered rings, with a pore size of 0.56 x 0.6 nm. As a typical solid acid catalyst, ZSM-12 has important applications in hydroisomerization / cracking and other petroleum processing processes.

[0003] In the synthesis of molecular sieves, structure-directing agents are an important factor in cost savings and a key factor influencing molecular sieve performance. Gopal used the more economical tetraethylammonium hydroxide (TEAOH) as a structure-directing agent to synthesize ZSM-12 molecular sieves and found that the lower limit of the Si / Al ratio of ZSM-12 synthesized with TEAOH is 50. Because TEAOH can also guide the formation of Beta molecular sieves, ZSM-5 and Beta molecular sieves are easily formed under conditions of lower Si / Al ratios or higher template content. Therefore, the phase range of ZSM-12 molecular sieves synthesized with TEAOH as a structure-directing agent is narrow, which is not conducive to industrial production.

[0004] CN119320148A discloses a hollow-structured ZSM-12 molecular sieve and a preparation method thereof. The ZSM-12 molecular sieve is first contacted with water vapor for treatment, and then washed, separated and dried. The resulting material is then mixed with an inorganic base, an aluminum source, a silicon source and water for reaction. Finally, the ZSM-12 molecular sieve is obtained after washing, separation, drying and roasting. The operation process is relatively complicated.

[0005] CN115959678A discloses a method for preparing a dendritic ZSM-12 molecular sieve using a dual-template method to control the growth of crystal faces and form a dendritic structure. However, the characteristic MFI peaks are clearly observed in the comparative XRD pattern, and the large branches are not conducive to the diffusion and mass transfer of reactant and product molecules.

[0006] CN106966408A discloses a bifunctional template for guiding the synthesis of multi-level porous ZSM-12 zeolite molecular sieves, its preparation, and a molecular sieve based thereon. The bifunctional template is first prepared, and then the bifunctional template is used to prepare a multi-level porous ZSM-12 zeolite with mesoporous-microporous dual pores by a one-step hydrothermal crystallization method.

[0007] Therefore, existing ZSM-12 molecular sieve preparation technologies generally rely on complex templates (such as bifunctional templates) or cumbersome processes (such as step-by-step hydrothermal / alkaline treatment), which have problems such as many synthesis steps, long cycles, and easy production of MFI impurities. In addition, complex templates are expensive, highly polluting, and difficult to mass-produce, which seriously hinder their industrial application. Summary of the Invention

[0008] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a high-crystallinity ZSM-12 molecular sieve, a preparation method thereof, and an application thereof. By using boric acid in conjunction with a weakly alkaline template agent, dimethyldiethoxyammonium hydroxide, the alkalinity of the synthesis system is precisely controlled, the formation of impurities is effectively suppressed, the crystallinity of the ZSM-12 molecular sieve is improved, and the acid strength is optimized at the same time. The method is simple in process and low in cost. The obtained molecular sieve can reduce cracking side reactions and increase the yield of isomerized hydrocarbons in the isomerization reaction of long-chain alkanes, and has the potential for large-scale industrial application.

[0009] The present invention is achieved through the following technical solutions: On the one hand, a method for preparing a high-crystallinity ZSM-12 molecular sieve is provided, wherein a reaction mixture is crystallized, and the obtained crystallized product is sequentially calcined and subjected to an inorganic ammonium salt ion exchange treatment;

[0010] The reaction mixture comprises an inorganic base, an aluminum source, a boron source, dimethyldiethoxyammonium hydroxide, a silicon source and water;

[0011] In molar ratio:

[0012] SiO2 / Al2O3=40-300;

[0013] H2O / SiO2=11-20;

[0014] B2O3 / Al2O3=0.05-1;

[0015] R / SiO2=0.05-0.3;

[0016] MOH / SiO2=0.02-0.2;

[0017] The silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, the boron source is calculated as B2O3, and the inorganic base is calculated as MOH, where M represents an alkali metal cation and R is dimethyldiethoxyammonium hydroxide.

[0018] Through the above technical solution, in the above-mentioned crystallization, calcination, inorganic ammonium salt ion exchange treatment, and preparation of high-crystallinity molecular sieves, the molar ratio of the synthesis process is the key factor, suitable aging conditions, crystallization temperature and time, and the selection of a suitable calcination temperature during calcination ensure that the organic template is completely decomposed while ensuring that the molecular sieve skeleton structure is not destroyed by high-temperature treatment.

[0019] Molecular sieve crystallization is a very complex chemical reaction process, which requires appropriate alkalinity / water amount / organic template addition amount. Different silicon-aluminum ratio ranges have different requirements for these factors, but there is an optimal range. The molar ratio of the above substances defined in the present invention is the optimal synthesis range obtained through a large number of experimental studies.

[0020] The present invention uses dimethyldiethoxyammonium hydroxide as an organic template. Its kinetic diameter is 0.58-0.62 nm, which is close to the twelve-membered ring pore size of the ZSM-12 molecular sieve (0.56 nm × 0.6 nm), making it a highly compatible with the ZSM-12 molecular sieve. During the crystallization process, the flexibility of the ethoxy group enables the organic template to effectively fill the ZSM-12 molecular sieve pores and stabilize the framework structure, thereby promoting the formation of ZSM-12 molecular sieve crystal nuclei. Furthermore, the electron-withdrawing effect of the ethoxy group makes the organic template relatively weakly alkaline. Combined with the control of alkalinity by boric acid, the alkaline environment required for ZSM-12 molecular sieve crystal nucleation is precisely controlled. Within this alkaline range, the formation of ZSM-5 crystal nuclei can be effectively suppressed, thereby ensuring a high degree of crystallinity in the resulting product.

[0021] Furthermore, the reaction mixture is aged at 30-90° C. for 1-9 hours before crystallization; the crystallization condition is 140-170° C. for 48-120 hours.

[0022] The above technical solution ensures that the silica-alumina sol is more homogenized by aging it at a temperature between 30°C and 90°C for 1-9 hours. The aging time can be appropriately extended at low aging temperatures, and shortened at slightly higher temperatures. The aging step ensures that the silicon and aluminum sources are fully mixed, effectively shortening the crystallization time, reducing energy consumption, and improving the dispersion and crystallinity of the molecular sieve crystals.

[0023] Furthermore, the boron source is boric acid; and the inorganic ammonium salt is ammonium nitrate, ammonium chloride or ammonium sulfate.

[0024] Through the above technical solution, boron compounds can be divided into oxides, hydrides - borane, borohydrides, boron halides, fluoroboric acid, boric acid, polyborates - borax, metal borides, boron heterocyclic compounds and other boron compounds (perborate, boron nitride), etc. Borax and boric acid are the most widely used compounds.

[0025] The boric acid used in this invention is mainly used to precisely control the pH of the system. Among the above substances, only boric acid can play this role. Since the synthetic gel of the molecular sieve is strongly alkaline (pH = 11~12), under such alkaline conditions, boric acid reacts with OH in the system. -The reaction occurs: H3BO3+NaOH=NaBO2+H2O. Only by using boric acid can we ensure that other metals / halogen anions / organic matter will not be introduced into the system, avoid system complexity, and make it easier to control.

[0026] The acidic properties of molecular sieves are mainly derived from the bridging hydroxyl groups of the framework. The framework of the directly synthesized molecular sieve is composed of Na + After high temperature calcination, the organic template decomposes and leaves proton hydrogen, and the molecular sieve has weak acidity. + Still retained in the molecular sieve, Na + The role of inorganic ammonium salt is to react with Na in the molecular sieve framework. + Ion exchange occurs in ammonium salt solution, based on kinetic and thermodynamic effects, NH4 + It will enter the molecular sieve pores and remove the Na + After replacement, an ammonium-type molecular sieve can be obtained. The ammonium-type molecular sieve is calcined at high temperature to decompose the ammonium and diffuse out of the molecular sieve pores, leaving protons. Only then can a high-crystallinity hydrogen-type molecular sieve be obtained.

[0027] Ammonium sulfate, ammonium nitrate, and ammonium chloride can all be used to exchange sodium molecular sieves and produce highly crystalline hydrogen molecular sieves. Ammonium sulfate or ammonium nitrate is generally used in industry because ammonium chloride is highly corrosive and places stringent demands on equipment materials. Furthermore, when heated, ammonium chloride readily decomposes to produce hydrogen chloride and ammonia, forming a white mist. Furthermore, upon cooling, hydrogen chloride and ammonia readily react again to produce crystals, raising significant environmental concerns on site.

[0028] Furthermore, the inorganic base is selected from sodium hydroxide or potassium hydroxide; the aluminum source is selected from at least one of aluminum isopropoxide, sodium metaaluminate, aluminum sulfate 18hydrate, and aluminum nitrate.

[0029] Through the above technical solution, the inorganic base provides the alkalinity necessary for the synthesis of the molecular sieve, which has a stabilizing effect on the silicate sol; at the same time, the alkali metal cations in the inorganic base can balance the negative charge of the molecular sieve framework and also play a role in pore filling; if H + or other cations replacing the alkali metal cations, the sol may be destabilized, resulting in precipitation or solidification.

[0030] Furthermore, the silicon source is selected from at least one of silica sol, silica gel powder, water glass, and white carbon black.

[0031] Through the above technical solution, the molecular sieve synthesized by the present invention is an aluminosilicate, and the silicon source is an essential raw material. In the synthesis system, the silicon in the silicon source can form silicon-oxygen tetrahedrons, which are the basic structural units of the molecular sieve.

[0032] Furthermore, the crystallized product must be washed and dried before calcination; the primary calcination temperature is 550-580° C., and the primary calcination time is 8-9 hours; the secondary calcination temperature is 500-560° C., and the secondary calcination time is 5-6 hours.

[0033] Through the above technical solution, the decomposition of the template requires temperature. If the temperature is too low, the template will not be completely decomposed and will remain in the pores, affecting subsequent ion exchange. However, the higher the temperature, the better. Too high a temperature will damage the skeleton structure of the molecular sieve, so it should be moderate. Selecting this temperature range can ensure that the template is fully decomposed on the one hand, and on the other hand, it can ensure that the skeleton structure of the molecular sieve is not destroyed.

[0034] Furthermore, the preparation process of the reaction mixture comprises the following steps:

[0035] Step 1: Dissolve the inorganic base and aluminum source in deionized water, then add the boron source and stir until clear;

[0036] Step 2: Add dimethyldiethoxyammonium hydroxide to the solution obtained in the first step and stir for 10-20 minutes;

[0037] Step 3: Slowly add silicon source to form silica-alumina gel to obtain the reaction mixture.

[0038] Through the above technical solution, the above process is the basic operation step for synthesizing molecular sieves, and the reaction mixture is an amorphous silica-alumina gel, which is alkaline and has a certain viscosity.

[0039] Furthermore, in the reaction mixture, SiO2 / Al2O3=40-300; B2O3 / Al2O3=0.05-1.

[0040] The above technical solution can ensure that the synthesized product is a ZSM-12 molecular sieve with high crystallinity, does not contain impurities, has suitable acidic properties, and has high catalytic reaction activity and isomerized hydrocarbon yield when used as a catalyst for the hydroisomerization of long-chain alkanes using n-heptane as a probe molecule.

[0041] In addition, a high-crystallinity ZSM-12 molecular sieve prepared by the above method is provided, the XRD pattern of the molecular sieve conforms to the standard spectrum of ZSM-12 and has no impurity crystal peaks, the weak acid content is 0.0584-0.5671mmol / g, and the strong acid content is 0.1169-0.7135mmol / g.

[0042] Using the above technical solution, the spectrum shows a pure phase ZSM-12 molecular sieve with no impurity peaks and high peak intensity, indicating that the synthesized molecular sieve has high crystallinity. The weak and strong acid content of the molecular sieve is positively correlated with the silicon-aluminum ratio. As the silicon-aluminum ratio of the molecular sieve increases, its weak and strong acid content gradually decreases.

[0043] Finally, an application of the high crystallinity ZSM-12 molecular sieve as described above is provided, which is loaded with 0.5 wt.% Pt as a catalyst for the hydroisomerization reaction of long-chain alkanes.

[0044] Through the above technical solution, the ZSM-12 molecular sieve prepared by the present invention has a higher isohydrocarbon yield at a lower catalytic reaction temperature due to its high purity and moderate acidity. Therefore, in actual industrial applications, the operating temperature of the device can be reduced, saving energy consumption; at the same time, the yield of the target product isohydrocarbon is increased, and more products can be obtained under the same catalyst loading amount. From another perspective, the amount of catalyst used to obtain the same amount of isohydrocarbons can be reduced.

[0045] Beneficial effects

[0046] This invention aims to improve the crystallinity of ZSM-12 molecular sieves and impart an appropriate acid strength by adding boron to the system. This approach overcomes the difficulty of forming impurities in existing ZSM-12 molecular sieve synthesis methods. Dimethyldiethoxyammonium hydroxide, due to the electron-withdrawing effect of the ethoxy group, has slightly weaker alkalinity than conventional quaternary ammonium salt organic templates. Combined with the weak acidity of boric acid, it is more suitable for reactions requiring precise alkalinity control, such as ZSM-12 synthesis.

[0047] The present invention utilizes a combination of dimethyldiethoxyammonium hydroxide and boric acid to broaden the ZSM-12 molecular sieve synthesis phase range and improve crystallinity. Furthermore, the preparation method provided by the present invention has a simple process route and does not require special, expensive reagents. The resulting ZSM-12 molecular sieve exhibits moderate acidity, effectively reducing cracking side reactions during the isomerization of long-chain alkanes and improving the yield of isomerized hydrocarbons. This method is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The XRD patterns of the samples obtained in various embodiments of the present invention are shown below;

[0049] Figure 2 The XRD patterns of the samples obtained in the comparative examples of the present invention are shown below;

[0050] Figure 3 This is a SEM image of the sample obtained in Example 1 of the present invention;

[0051] Figure 4This is a SEM image of the sample obtained in Example 2 of the present invention;

[0052] Figure 5 This is a SEM image of the sample obtained in Example 3 of the present invention;

[0053] Figure 6 This is a SEM image of the sample obtained in Example 4 of the present invention;

[0054] Figure 7 This is a SEM image of the sample obtained in Example 5 of the present invention;

[0055] Figure 8 This is a SEM image of the sample obtained in Comparative Example 1 of the present invention;

[0056] Figure 9 This is a SEM image of the sample obtained in Comparative Example 2 of the present invention;

[0057] Figure 10 This is a SEM image of the sample obtained in Comparative Example 3 of the present invention;

[0058] Figure 11 This is a SEM image of the sample obtained in Comparative Example 4 of the present invention;

[0059] Figure 12 This is the SEM image of the comparative example 5 sample of the present invention;

[0060] Figure 13 The present invention embodies the trend of the conversion rate of the samples loaded with Pt as a function of reaction temperature in Examples 2 / 3 / 4 and Comparative Examples 3 / 5;

[0061] Figure 14 The present invention embodies the trend of the selectivity of isomers and cracking products after the samples are loaded with Pt as a function of reaction temperature in Examples 2 / 3 / 4 and Comparative Examples 3 / 5;

[0062] Figure 15 The relationship between the yield of isomers and the reaction temperature after the samples are loaded with Pt in Examples 2 / 3 / 4 and Comparative Examples 3 / 5 of the present invention is shown;

[0063] Figure 16 This is the corresponding relationship between the isomer yield and conversion rate after the samples are loaded with Pt in Examples 2 / 3 / 4 and Comparative Examples 3 / 5 of the present invention. DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solutions 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 intended to limit the present invention.

[0065] A method for preparing high-crystallinity ZSM-12 molecular sieve comprises the following steps:

[0066] 1) Add the inorganic base and aluminum source to deionized water in sequence to dissolve and clarify, then add the boron source and stir to dissolve and clarify;

[0067] 2) Add the organic template to step 1) while stirring, and stir for 10-20 minutes;

[0068] 3) slowly adding the silicon source into step 2) to obtain a silica-alumina gel, i.e., a reaction mixture;

[0069] 4) The reaction mixture is aged at a certain temperature for a period of time, and then crystallized at a certain temperature.

[0070] 5) After the crystallization is completed, the crystallized product is filtered and washed, dried, and then calcined once to remove the organic template.

[0071] 6) The sample after calcination to remove the template is exchanged with an inorganic ammonium salt and then calcined a second time to decompose the ammonium to obtain a highly crystalline hydrogen-type sample.

[0072] In step 1), the inorganic base is selected from sodium hydroxide or potassium hydroxide, preferably sodium hydroxide; the aluminum source is selected from at least one of aluminum isopropoxide, sodium metaaluminate, aluminum sulfate 18hydrate, and aluminum nitrate.

[0073] In step 2), the organic template is dimethyldiethoxyammonium hydroxide.

[0074] In step 3), the silicon source is selected from at least one of silica sol, silica gel powder, water glass, and white carbon black.

[0075] In the above preparation method, the reaction mixture obtained in step 3) comprises an inorganic base, an aluminum source, a boron source, dimethyldiethoxyammonium hydroxide, a silicon source and water;

[0076] In molar ratio:

[0077] SiO2 / Al2O3=40-300;

[0078] H2O / SiO2=11-20;

[0079] MOH / SiO2=0.02-0.2;

[0080] B2O3 / Al2O3=0.05-1;

[0081] R / SiO2=0.05-0.3;

[0082] The silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, the boron source is calculated as B2O3, the inorganic base is calculated as MOH, M represents an alkali metal cation, and R represents dimethyldiethoxyammonium hydroxide.

[0083] In step 4), the aging temperature is 30-90° C., preferably 50-70° C., and the aging time is 1-9 hours, preferably 3-6 hours.

[0084] In step 4), the crystallization temperature is 140-170° C., preferably 145-160° C., and the crystallization time is 48 h-120 h, preferably 48-96 h; the crystallization treatment is preferably a dynamic crystallization treatment.

[0085] In steps 5) and 6), the primary and secondary calcinations are performed at a temperature of 500-600°C and for a time of 5-10 hours. Preferably, the primary calcination temperature is 550-580°C and for a time of 8-9 hours; and the secondary calcination temperature is 500-560°C and for a time of 5-6 hours.

[0086] All other embodiments obtained by persons of ordinary skill in the art based on the embodiments herein without inventive effort are intended to fall within the scope of protection of the present invention. Experimental methods in the following examples, where specific conditions are not specified, were generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise indicated, all percentages, ratios, proportions, and parts are by weight.

[0087] 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.

[0088] Example 1

[0089] Add 164.5g of deionized water to the reactor, start stirring, and add 16.7g of sodium hydroxide, 31.1g of aluminum sulfate 18hydrate, 6.2g of boric acid, and 241.9g of dimethyldiethoxyammonium hydroxide aqueous solution in sequence. Stir for 10 minutes after each material is added before adding the next material to ensure that each material is in a dissolved state. Then slowly add 300g of silica sol while stirring, seal the feed port of the reactor, turn on the heating, set the temperature to 70°C, and age for 3h under stirring. After the aging is completed, set the heating temperature to 145°C. After the temperature is reached, continue to keep warm and crystallize for 120h. After the crystallization is completed, the temperature drops below 80°C and the reactor is opened. The slurry is centrifuged and washed and dried.

[0090] Among them, the composition of silica-alumina gel is SiO2 / Al2O3=40, NaOH / SiO2=0.2, B2O3 / Al2O3=1, H2O / SiO2=15, R / SiO2=0.2.

[0091] The washed and dried powder was calcined once in a muffle furnace to remove the organic template, and the conditions for the first calcination were 580°C for 8 hours; the powder after the first calcination was then exchanged in a 0.5 mol / L ammonium sulfate solution, and after the exchange, it was filtered, washed and dried and then placed in a muffle furnace for a second calcination, and the conditions for the second calcination were 550°C for 5 hours to obtain a hydrogen sample.

[0092] The obtained sample was tested by X-ray diffractometer, and the results showed that it was pure phase ZSM-12 molecular sieve. Figure 1 The crystal morphology of the obtained product is shown in Figure 3 , which are highly dispersible nanoparticles with a size of about 800nm.

[0093] Example 2

[0094] Add 358.5g of deionized water to the reactor, start stirring, and add 17.5g of potassium hydroxide, 10.2g of aluminum isopropoxide, 2.3g of boric acid, and 241.9g of dimethyldiethoxyammonium hydroxide aqueous solution in sequence. Stir for 10 minutes after adding each material before adding the next material to ensure that each material is in a dissolved state. Then slowly add 300g of silica sol while stirring, seal the reactor feed port, turn on the heating, set the temperature to 30°C, and age for 6h while stirring. After the aging is completed, set the heating temperature to 150°C. After the temperature is reached, continue to keep warm and crystallize for 96h. After the crystallization is completed, the temperature drops below 80°C and the reactor is opened, and the slurry is centrifuged, washed, and dried.

[0095] Among them, the composition of silica-alumina gel is SiO2 / Al2O3=80, KOH / SiO2=0.15, B2O3 / Al2O3=0.75, H2O / SiO2=20, R / SiO2=0.2.

[0096] The washed and dried powder was calcined once in a muffle furnace to remove the organic template, and the conditions for the first calcination were 580°C for 8 hours; the powder after the first calcination was then exchanged in a 0.5 mol / L ammonium sulfate solution, and after the exchange, it was filtered, washed and dried and then placed in a muffle furnace for a second calcination, and the conditions for the second calcination were 550°C for 5 hours to obtain a hydrogen sample.

[0097] The obtained sample was tested by X-ray diffractometer, and the results showed that it was pure phase ZSM-12 molecular sieve. Figure 1 The crystal morphology of the obtained product is shown in Figure 4 , which are highly dispersible nanoparticles with a size of about 800nm.

[0098] Example 3

[0099] Add 457.6g of deionized water to the reactor, start stirring, and add 7.3g of sodium hydroxide, 3.1g of sodium aluminate, 0.9g of boric acid, and 66.9g of dimethyldiethoxyammonium hydroxide aqueous solution in sequence. Stir for 10 minutes after each material is added before adding the next material to ensure that each material is in a dissolved state. Then slowly add 138.9g of silica gel powder while stirring, seal the reactor feed port, turn on the heating, set the temperature to 90°C, and age for 1h while stirring. After the aging is completed, set the heating temperature to 160°C. After the temperature is reached, continue to keep warm and crystallize for 96h. After the crystallization is completed, the temperature drops below 80°C and the reactor is opened. The slurry is centrifuged and washed and dried.

[0100] Among them, the composition of silica-alumina gel is SiO2 / Al2O3=150, NaOH / SiO2=0.1, B2O3 / Al2O3=0.5, H2O / SiO2=13, R / SiO2=0.05.

[0101] The washed and dried powder was calcined once in a muffle furnace to remove the organic template, and the conditions for the first calcination were 580°C for 8 hours; the powder after the first calcination was then exchanged in a 0.5 mol / L ammonium sulfate solution, and after the exchange, it was filtered, washed and dried and then placed in a muffle furnace for a second calcination, and the conditions for the second calcination were 550°C for 5 hours to obtain a hydrogen sample.

[0102] The obtained sample was tested by X-ray diffractometer, and the results showed that it was pure phase ZSM-12 molecular sieve. Figure 1 The crystal morphology of the obtained product is shown in Figure 5 , which are highly dispersible nanoparticles with a size of about 800nm.

[0103] Example 4

[0104] Add 113.7g of deionized water to the reactor, start stirring, and add 4.2g of sodium hydroxide, 8.3g of aluminum sulfate 18hydrate, 0.08g of boric acid, and 362.9g of dimethyldiethoxyammonium hydroxide aqueous solution in sequence. Stir for 10 minutes after each material is added before adding the next material to ensure that each material is in a dissolved state. Then slowly add 126.3g of silica gel powder while stirring, seal the reactor feed port, turn on the heating, set the temperature to 90°C, and age for 1h while stirring. After the aging is completed, set the heating temperature to 160°C. After the temperature is reached, continue to keep warm and crystallize for 48h. After the crystallization is completed, the temperature drops below 80°C and the reactor is opened. The slurry is centrifuged, washed, and dried.

[0105] Among them, the composition of silica-alumina gel is SiO2 / Al2O3=150, NaOH / SiO2=0.05, B2O3 / Al2O3=0.05, H2O / SiO2=11, R / SiO2=0.3.

[0106] The washed and dried powder was calcined once in a muffle furnace to remove the organic template, and the conditions for the first calcination were 580°C for 8 hours; the powder after the first calcination was then exchanged in a 0.5 mol / L ammonium sulfate solution, and after the exchange, it was filtered, washed and dried and then placed in a muffle furnace for a second calcination, and the conditions for the second calcination were 550°C for 5 hours to obtain a hydrogen sample.

[0107] The obtained sample was tested by X-ray diffractometer, and the results showed that it was pure phase ZSM-12 molecular sieve. Figure 1 The crystal morphology of the obtained product is shown in Figure 6 , which are highly dispersible nanoparticles with a size of about 800nm.

[0108] Example 5

[0109] Add 108.9g of deionized water to the reactor, start stirring, and add 2.3g of potassium hydroxide, 2.5g of aluminum nitrate, 0.04g of boric acid, and 362.9g of dimethyldiethoxyammonium hydroxide aqueous solution in sequence. Stir for 10 minutes after each material is added before adding the next material to ensure that each material is in a dissolved state. Then, use a peristaltic pump to slowly add 497.1g of sodium silicate solution under stirring, seal the reactor feed port, turn on the heating, set the temperature to 60°C, and age for 4h under stirring. After the aging is completed, set the heating temperature to 160°C. After the temperature is reached, continue to keep warm and crystallize for 48h. After the crystallization is completed, the temperature drops below 80°C and the reactor is opened. The slurry is centrifuged and washed and dried.

[0110] Among them, the composition of silica-alumina gel is SiO2 / Al2O3=300, KOH / SiO2=0.02, B2O3 / Al2O3=0.05, H2O / SiO2=20, R / SiO2=0.3.

[0111] The washed and dried powder was calcined once in a muffle furnace to remove the organic template, and the conditions for the first calcination were 580°C for 8 hours; the powder after the first calcination was then exchanged in a 0.5 mol / L ammonium sulfate solution, and after the exchange, it was filtered, washed and dried and then placed in a muffle furnace for a second calcination, and the conditions for the second calcination were 550°C for 5 hours to obtain a hydrogen sample.

[0112] The obtained sample was tested by X-ray diffractometer, and the results showed that it was pure phase ZSM-12 molecular sieve. Figure 1 The crystal morphology of the obtained product is shown in Figure 7 , which are highly dispersible nanoparticles with a size of about 800nm.

[0113] Comparative Example 1

[0114] Add 169.2g of deionized water to the reactor and start stirring. Then add 16.7g of sodium hydroxide, 31.1g of aluminum sulfate 18hydrate, 6.2g of boric acid, and 235.6g of tetraethylammonium hydroxide (TEAOH) aqueous solution in sequence. Stir for 10 minutes after each material is added before adding the next material to ensure that each material is dissolved. Then, use a peristaltic pump to slowly add 300g of silica sol while stirring. Seal the reactor feed port, turn on the heating, set the temperature to 70°C, and age for 3 hours while stirring. After the aging is completed, set the heating temperature to 145°C. After reaching the temperature, continue to keep warm and crystallize for 120 hours. After the crystallization is completed, the temperature drops below 80°C and the reactor is opened. The slurry is centrifuged, washed, and dried.

[0115] Among them, the composition of silica-alumina gel is SiO2 / Al2O3=40, NaOH / SiO2=0.2, B2O3 / Al2O3=1, H2O / SiO2=15, TEAOH / SiO2=0.2.

[0116] The washed and dried powder was calcined once in a muffle furnace to remove the organic template, and the conditions for the first calcination were 580°C for 8 hours; the powder after the first calcination was then exchanged in a 0.5 mol / L ammonium sulfate solution, and after the exchange, it was filtered, washed and dried and then placed in a muffle furnace for a second calcination, and the conditions for the second calcination were 550°C for 5 hours to obtain a hydrogen sample.

[0117] Comparative Example 1 Compared with Example 1, the organic template was changed to tetraethylammonium hydroxide aqueous solution (TEAOH). After the organic template was changed in Comparative Example 1, the obtained sample was tested by X-ray diffractometer to be ZSM-5 molecular sieve. Figure 2 The crystal morphology is shown in Figure 8 , which is a typical ZSM-5 molecular sieve.

[0118] Comparative Example 2

[0119] Add 120.8g of deionized water to the reactor, start stirring, and add 4.2g of sodium hydroxide, 8.3g of aluminum sulfate 18hydrate, 0.08g of boric acid, and 353.2g of tetraethylammonium hydroxide aqueous solution in sequence. Stir for 10 minutes after each material is added before adding the next material to ensure that each material is in a dissolved state. Then slowly add 126.3g of silica gel powder while stirring, seal the feed port of the reactor, turn on the heating, set the temperature to 90°C, and age for 1h while stirring. After the aging is completed, set the heating temperature to 160°C. After the temperature is reached, continue to keep warm and crystallize for 48h. After the crystallization is completed, the temperature drops below 80°C and the reactor is opened. The slurry is centrifuged, washed, and dried.

[0120] Among them, the composition of silica-alumina gel is SiO2 / Al2O3=150, NaOH / SiO2=0.05, B2O3 / Al2O3=0.05, H2O / SiO2=11, TEAOH / SiO2=0.3.

[0121] The washed and dried powder was calcined once in a muffle furnace to remove the organic template, and the conditions for the first calcination were 580°C for 8 hours; the powder after the first calcination was then exchanged in a 0.5 mol / L ammonium sulfate solution, and after the exchange, it was filtered, washed and dried and then placed in a muffle furnace for a second calcination, and the conditions for the second calcination were 550°C for 5 hours to obtain a hydrogen sample.

[0122] Comparative Example 2 Compared with Example 4, the organic template was changed to tetraethylammonium hydroxide aqueous solution (TEAOH). The obtained sample was tested by X-ray diffractometer and the result was a mixture of ZSM-5 + ZSM-12, not a pure phase ZSM-12 molecular sieve. Figure 2 The crystal morphology of the obtained product is shown in Figure 9 From the figure, we can see the ZSM-12 molecular sieve with the morphology of nanoparticles and the ZSM-5 molecular sieve with blocky morphology.

[0123] Comparative Example 3

[0124] Add 458g of deionized water to the reactor, start stirring, and add 2.7g of sodium hydroxide, 3.1g of sodium aluminate, and 66.5g of dimethyldiethoxyammonium hydroxide aqueous solution in sequence. Stir for 10 minutes after each material is added before adding the next material to ensure that each material is in a dissolved state. Then slowly add 138.9g of silica gel powder while stirring, seal the reactor feed port, turn on the heating, set the temperature to 90°C, and age for 1h while stirring. After the aging is completed, set the heating temperature to 160°C. After the temperature is reached, continue to keep warm and crystallize for 96h. After the crystallization is completed, the temperature drops below 80°C, open the reactor, and centrifuge and wash the slurry and dry it.

[0125] Among them, the composition of silica-alumina gel is SiO2 / Al2O3=150, NaOH / SiO2=0.05, H2O / SiO2=13, R / SiO2=0.05.

[0126] The washed and dried powder was calcined once in a muffle furnace to remove the organic template, and the conditions for the first calcination were 580°C for 8 hours; the powder after the first calcination was then exchanged in a 0.5 mol / L ammonium sulfate solution, and after the exchange, it was filtered, washed and dried and then placed in a muffle furnace for a second calcination, and the conditions for the second calcination were 550°C for 5 hours to obtain a hydrogen sample.

[0127] Comparative Example 3 Compared with Example 3, no boric acid was added. The obtained sample was tested by X-ray diffractometer, and the results showed that the main phase was ZSM-12 molecular sieve, but the crystallinity was low. Figure 10 Some amorphous substances can be observed on the surface of the crystal, see Figure 2 The crystal morphology of the obtained product is shown in Figure 10 As can be seen from the figure, there are some flocculent substances on the edge of the ZSM-12 nanoparticles, which are amorphous silica-alumina gels that have not been completely crystallized.

[0128] Comparative Example 4

[0129] Add 108.9g of deionized water to the reactor, start stirring, and add 2.3g of potassium hydroxide, 2.5g of aluminum nitrate, and 362.9g of dimethyldiethoxyammonium hydroxide aqueous solution in sequence. Stir for 10 minutes after each material is added before adding the next material to ensure that each material is in a dissolved state. Then, use a peristaltic pump to slowly add 497.1g of sodium silicate solution while stirring, seal the reactor feed port, turn on the heating, set the temperature to 60°C, and age for 4h under stirring. After the aging is completed, set the heating temperature to 160°C. After the temperature is reached, continue to keep warm and crystallize for 48h. After the crystallization is completed, the temperature drops below 80°C and the reactor is opened. The slurry is centrifuged and washed and dried.

[0130] Among them, the composition of silica-alumina gel is SiO2 / Al2O3=300, KOH / SiO2=0.02, H2O / SiO2=20, R / SiO2=0.3.

[0131] The washed and dried powder was calcined once in a muffle furnace to remove the organic template, and the conditions for the first calcination were 580°C for 8 hours; the powder after the first calcination was then exchanged in a 0.5 mol / L ammonium sulfate solution, and after the exchange, it was filtered, washed and dried and then placed in a muffle furnace for a second calcination, and the conditions for the second calcination were 550°C for 5 hours to obtain a hydrogen sample.

[0132] The obtained sample was tested by an X-ray diffractometer, and the results showed that it was a pure phase ZSM-12 molecular sieve.

[0133] Comparative Example 4 is compared with Example 5, in which no boric acid is added. The obtained sample was tested by X-ray diffractometer, and the results showed that only a weak characteristic peak of ZSM-12 was observed, which was mainly an amorphous phase. Figure 2 The crystal morphology of the obtained product is shown in Figure 11. A large amount of flocculent material is mainly amorphous silica-alumina gel that has not been completely crystallized.

[0134] Comparative Example 5

[0135] The high crystallinity ZSM-12 molecular sieve was purchased from a petrochemical company. The XRD pattern is shown in Figure 2 The corresponding crystal morphology is shown in Figure 12 , which are small nanoparticles. The small particles adhere to each other and agglomerate, and the dispersion is not high.

[0136] Effect embodiment

[0137] The following tests were performed on Examples 1 to 5 and Comparative Examples 1 to 5:

[0138] 1) XRD test of samples after synthesis and drying: The crystal structure of the powder sample after washing and drying was tested by X-ray diffractometer.

[0139] Test results see Figure 1 and Figure 2 . Figure 1 The XRD curves of the five samples obtained from Example 1 to Example 5 are included. Figure 1 It can be seen from the curve that the samples obtained from Examples 1 to 5 are all pure phase ZSM-12 molecular sieves. Figure 2 As can be seen from the curve, the product obtained in Comparative Example 1 is a ZSM-5 molecular sieve, the product obtained in Comparative Example 2 contains a large amount of ZSM-5 impurities, the product obtained in Comparative Example 3 is mainly ZSM-12, but the crystallinity is low and there is a certain amount of amorphous. The product obtained in Comparative Example 4 has even worse crystallinity and is basically amorphous. Comparative Example 5 is a pure phase ZSM-12 molecular sieve.

[0140] 2) Morphology test of ZSM-12 molecular sieve: The crystal morphology of the powder sample after washing and drying was tested using a scanning electron microscope.

[0141] Test results see Figures 3 to 12 ;

[0142] Figure 3-Figure 7The SEM images of the samples obtained in Examples 1 to 5 show that the obtained products have a typical morphology of ZSM-12 molecular sieve, with high crystal dispersion, a size of the nanoparticles of about 800 nm, and clear crystal edges, which is consistent with the high crystallinity in the XRD pattern. Figure 8 This is the SEM image of the sample obtained in Comparative Example 1. The rectangular morphology is a common crystal form of ZSM-5 molecular sieve. Figure 9 The SEM image of the product obtained in comparative example 2 shows that the ZSM-12 molecular sieve with nano-particle morphology coexists with the ZSM-5 molecular sieve in bulk. Figure 2 The results of the two curves in the comparative example are consistent. Figure 10 The SEM image of the product obtained in comparative example 3 shows that there are obvious flocculent substances on the edge of the nanoparticles, which are some amorphous silica-alumina gels that have not been completely crystallized. Figure 2 The lower diffraction peaks of the three curves in the comparative example remain consistent. Figure 11 The SEM image of the product obtained in comparative example 4 shows a large amount of flocculent matter, which represents completely crystallized silica-alumina gel. Figure 2 XRD curve of comparative example 4. Figure 12 This is the SEM image of the sample of Comparative Example 5. It can be seen that the sample of a petrochemical company is also nano-sized particles, but the agglomeration between the small particles is relatively serious, and the dispersion is not as good as the samples obtained in Examples 1 to 5.

[0143] 3) Preparation of high-crystallinity samples: The synthesized molecular sieve powder is calcined at high temperature to remove the template, and then ion exchange is performed using a 1 mol / L ammonium nitrate solution at 80°C, with two exchanges, each for 2 hours. After the exchange, the sample is filtered, washed, and dried, and finally calcined at 500°C for 5 hours to obtain a high-crystallinity molecular sieve. This step is a routine operation for preparing high-crystallinity molecular sieves.

[0144] The elemental composition of the high-crystallinity samples was tested using an X-ray fluorescence analyzer, and the silicon-to-aluminum ratio and sodium oxide percentage of the samples are shown in Table 1. As can be seen from Table 1, the present invention can synthesize ZSM-12 molecular sieves with a silicon-to-aluminum ratio ranging from 33 to 209. The Na2O content in all samples is approximately 0.03%, which is at a relatively low level, indicating that the exchange process is relatively thorough.

[0145] 4) Acidity Characterization Analysis of High Crystallinity Samples: The prepared high crystallinity ZSM-12 powder was pressed into tablets in a mold and crushed into small particles of 20×40 mesh. The total acid content of the high crystallinity FER molecular sieve was tested using programmed temperature desorption (TTP) using ammonia as the medium. The desorption amount below 300°C was considered weak acid, while that above 300°C was considered strong acid.

[0146] The test results are shown in Table 1. As can be seen from Table 1, as the silicon-aluminum ratio of the sample increases, the weak acid and strong acid content of the sample gradually decreases, which is consistent with the law that the acid properties of the molecular sieve change with the silicon-aluminum ratio. Although Comparative Example 3 has a silicon-aluminum ratio close to that of Example 4, its strong acid content is significantly lower than that of Example 4, which is mainly related to its low crystallinity. Through the acid property characterization test, samples with a suitable silicon-aluminum ratio range can be screened for catalytic reactions based on the acid content required for the catalytic reaction.

[0147] Evaluation of the catalytic performance of n-heptane hydroisomerization: Pt / HZSM-12 loaded with 0.5 wt.% Pt was used as a bifunctional catalyst at a reaction temperature of 413-613 K and a mass space velocity (WHSV) of 1.0 g n-heptane g cat -1 ·h -1 The catalyst was evaluated for n-heptane hydroisomerization under the conditions of .

[0148] Test results see Figure 13-16 .

[0149] Table 1 Si-Al ratios and acidity characterization results of samples in each embodiment and Comparative Example 3 and Comparative Example 5

[0150]

[0151] In summary, the samples of Example 2, Example 3, Example 4 and Comparative Example 3 and Comparative Example 5 were selected and treated under the same exchange process and platinum-loaded process conditions for the catalytic performance evaluation of n-heptane hydroisomerization. The results showed that the samples of Example 2, Example 3, and Example 4 had the best catalytic performance, and the yield of isomerized hydrocarbons was higher than that of Comparative Example 3 and Comparative Example 5 under suitable reaction temperature conditions (513K-573K).

[0152] through Figure 11 and Figure 14Comprehensive analysis of the results reveals that, compared to a ZSM-12 molecular sieve from a petrochemical company, the samples obtained in Examples 2, 3, and 4 of the present invention, loaded with platinum, exhibited higher catalytic activity and higher isohydrocarbon yields as n-heptane hydroisomerization catalysts within the relatively suitable temperature range of 513K-573K. In particular, Example 2 achieved an isohydrocarbon yield of 68.71% at the low temperature of 513K, significantly exceeding the 19.69% of Comparative Example 5. When the temperature was raised to 533K, the isohydrocarbon yields of Examples 3 and 4, which possessed higher silicon-aluminum ratios, gradually increased to 51.40% and 49.33%, respectively, also exceeding the 41.64% of Comparative Example 5. Examples 3 and 4 achieved their highest isohydrocarbon yields (57.19% and 57.99%), respectively, at the milder temperature of 533K, while Comparative Example 5 also achieved its highest isohydrocarbon yield of 41.64%. As the temperature continued to rise, the isomeric hydrocarbon yields of all samples showed a downward trend due to the intense high-temperature cracking reaction. Throughout the entire reaction period, Comparative Example 3 exhibited poor reactivity and isomeric hydrocarbon yields, which was primarily due to its low strong acid content caused by its low crystallinity.

[0153] 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, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or 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 scope of protection of the present invention.

Claims

1. A method for preparing high crystallinity ZSM-12 molecular sieve, characterized in that: The reaction mixture is crystallized, and the resulting crystallized product is sequentially subjected to primary calcination, inorganic ammonium salt ion exchange treatment, and secondary calcination; The reaction mixture comprises an inorganic base, an aluminum source, a boron source, dimethyldiethoxyammonium hydroxide, a silicon source and water; In molar ratio: SiO2 / Al2O3=40-300; H2O / SiO2=11-20; B2O3 / Al2O3=0.05-1; R / SiO2=0.05-0.3; MOH / SiO2=0.02-0.2; The silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, the boron source is calculated as B2O3, the inorganic base is calculated as MOH, M represents an alkali metal cation, R is dimethyldiethoxyammonium hydroxide, and the boron source is boric acid.

2. The method for preparing a high crystallinity ZSM-12 molecular sieve according to claim 1, wherein Before the crystallization, the reaction mixture is aged at 30-90° C. for 1-9 hours; the crystallization condition is 140-170° C. for 48-120 hours.

3. The method for preparing high crystallinity ZSM-12 molecular sieve according to claim 1, characterized in that: The inorganic ammonium salt is ammonium nitrate, ammonium chloride or ammonium sulfate.

4. The method for preparing a high crystallinity ZSM-12 molecular sieve according to claim 1, wherein The inorganic base is selected from sodium hydroxide or potassium hydroxide; the aluminum source is selected from at least one of aluminum isopropoxide, sodium metaaluminate, aluminum sulfate 18hydrate, and aluminum nitrate.

5. The method for preparing high crystallinity ZSM-12 molecular sieve according to claim 1, characterized in that: The silicon source is selected from at least one of silica sol, silica gel powder, water glass and white carbon black.

6. The method for preparing high crystallinity ZSM-12 molecular sieve according to claim 1, characterized in that: The crystallized product must be washed and dried before calcination; the primary calcination temperature is 550-580° C., and the primary calcination time is 8-9 hours; the secondary calcination temperature is 500-560° C., and the secondary calcination time is 5-6 hours.

7. The method for preparing high crystallinity ZSM-12 molecular sieve according to claim 1, characterized in that: The preparation process of the reaction mixture comprises the following steps: Step 1: Dissolve the inorganic base and aluminum source in deionized water, then add the boron source and stir until clear; Step 2: Add dimethyldiethoxyammonium hydroxide to the solution obtained in the first step and stir for 10-20 minutes; Step 3: Slowly add silicon source to form silica-alumina gel to obtain the reaction mixture.

8. A high crystallinity ZSM-12 molecular sieve prepared by the method according to any one of claims 1 to 7, characterized in that: The XRD spectrum of the molecular sieve conforms to the ZSM-12 standard spectrum and has no impurity crystal peaks. The weak acid content is 0.0584-0.5671 mmol / g, and the strong acid content is 0.1169-0.7135 mmol / g.

9. A use of the high crystallinity ZSM-12 molecular sieve according to claim 8, characterized in that: After loading 0.5wt.% Pt, it is used as a catalyst for the hydroisomerization reaction of long-chain alkanes.

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