A saop-11 molecular sieve, a synthesis method and application thereof

Abstract

The application provides a SAPO-11 molecular sieve and a synthesis method and application thereof, wherein the synthesis method comprises the following steps: uniformly mixing an aluminum source, an auxiliary acid, phosphoric acid and water to obtain a phosphorus aluminum precursor; respectively dissolving a template agent and a solid silicon source in deionized water, and then adding the template agent and the solid silicon source into the phosphorus aluminum precursor in a pulse feeding mode to obtain a mixed gel; in the mixed gel, the molar ratio of the aluminum source calculated according to Al2O3, the phosphoric acid calculated according to P2O5, the silicon source calculated according to SiO2, the template agent, the auxiliary acid and water is 1:0.90-1.00:0.40-0.65:0.70-0.85:0.05-0.32:8-15; the mixed gel is first pre-crystallized at 90-150 DEG C. for 0.5-2h, and then crystallized at 190-210 DEG C. for 12-20h; and the obtained crystallization product is subjected to filter washing and drying to obtain the SAPO-11 molecular sieve. The synthesis method can effectively inhibit the generation of impurity crystals and can improve the single-kettle yield.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of SAPO-11 molecular sieve and its synthesis method and application, belong to molecular sieve synthesis technical field. BACKGROUND

[0002] SAPO-11 is a kind of phosphorus aluminosilicate molecular sieve with AEL type topology, which was first synthesized by UCC in the 1980s. Its pore structure is one-dimensional ten-membered ring straight pore, and the size is Due to its special pore structure and mild acidity, it can be used for catalyzing linear alkane hydrogenation isomerization reaction. At present, SAPO-11 is mainly produced by hydrothermal synthesis method in industry. In order to avoid the problem of high solid content, high viscosity and dispersion difficulty in raw material system, the water content of the system is still high, and the single-pot yield is only about 6.5%, which restricts the production efficiency and cost.

[0003] At present, the research reports on the preparation of molecular sieve under the condition of high solid content raw material are as follows:

[0004] CN 103864088A discloses a method for synthesizing molecular sieve by solid phase grinding, which can prepare SAPO-11 molecular sieve with high crystallinity, and the yield and single-pot utilization rate are greatly improved. The specific steps include: weighing the silicon source, aluminum source and self-made template agent, pouring into the mortar, grinding and mixing for 5-10 min, and then loading into the reaction kettle for crystallization reaction. The reaction temperature of crystallization reaction is 180-220℃, and the reaction time is 9h-5d. The silicon source is white carbon black or silica gel, the aluminum source is boehmite or aluminum hydroxide, and the content of boehmite is 70% Al2O3 and 30% H2O. The self-made template agent is di-n-propylamine phosphate or diisopropylamine phosphate. The specific preparation steps of the self-made template agent include: adding phosphoric acid into di-n-propylamine or diisopropylamine, then adding anhydrous ethanol, stirring at 0-80℃ for 2 hours, washing the white solid with a mixture of diethyl ether and ethanol to remove the residual reactants on the white solid, and finally drying the washed white solid to obtain di-n-propylamine phosphate or diisopropylamine phosphate, which is used as self-made template agent.

[0005] The defects of this technology or the deficiencies of the present application include: 1. In the gelation process, it needs to be realized by grinding, which is not conducive to mixing and gelation, and is difficult to realize industrial application; 2. Because the reaction system is solid phase, the mass transfer and heat transfer efficiency is low, so a long crystallization time (mostly 3 to 5 days in the examples) is needed to achieve high crystallinity; 3. The template agent is organic amine phosphate, which needs to be self-made, and the process steps are more and more complex.

[0006] CN106517230A discloses a kind of hierarchical pore SAPO-11 molecular sieve and solid-phase synthesis method, by using double-template method in solid-phase system to realize the synthesis of molecular sieve.Detailed information is as follows: solid silicon source, aluminum source, mesoporous template, microporous template and phosphorus source are mixed and ground, and crystallization reaction is carried out at 200 DEG C.Then, the reaction product is suction filtered, dried and calcined to obtain molecular sieve raw powder.As no solvent and organic template are used, yield is improved, and raw material cost is reduced.

[0007] The defects of this technology or the deficiencies relative to the present application include: 1. In the gelation process, it needs to be achieved by grinding, which is not conducive to mixing and gelation, and is difficult to realize industrial application; 2. The template is di-n-propylamine phosphate and cetyltrimethylammonium bromide. Di-n-propylamine phosphate needs to be self-made, and the process steps are more and more complex. The price of cetyltrimethylammonium bromide is relatively high. The dosage of the two templates accounts for more than 70% of the total mass of the raw materials, and there is a problem of high cost.

[0008] CN106044791A discloses a solid-phase synthesis method of thin-layer SAPO-34, which adds fluoride in the initial gel to solve the problems of low crystallinity and poor stability in solid-phase production, and realizes solid-phase synthesis. The specific steps include: mixing deionized water, silicon source, aluminum source, phosphorus source, fluoride and template in a specific ratio to prepare an initial gel; drying the gel at room temperature to obtain a dry gel; then adding a mixture of water and triethylamine to the bottom of the reaction kettle, crushing the dry gel, placing it in a polytetrafluoroethane beaker, placing the beaker above the liquid in the kettle, and crystallizing to obtain SAPO-34 molecular sieve.

[0009] The defects of this technology or the deficiencies relative to the present application include: 1. The synthesis steps are more, which leads to complex process, affecting yield and cost; 2. Fluoride exists in the product, and there are safety and environmental problems in the post-processing process.

[0010] CN111434611A discloses a method for preparing NaY molecular sieve by solid-phase conversion, which realizes solid-phase crystallization by adjusting the ratio of raw materials and optimizing the guide agent. The specific steps include: according to the ratio requirements of NaY molecular sieve, a certain amount of guide agent is selectively added to solid silicon source and aluminum source, and the mixture is stirred uniformly to become a solid-state reaction mixture, which is then loaded into a reaction kettle for crystallization reaction at a temperature of 90-140 DEG C for 24-120 hours. Finally, after filtration, washing and drying, NaY molecular sieve with a relative crystallinity of more than 60% is obtained. This method is different from the traditional hydrothermal crystallization method for producing NaY molecular sieve, and has the characteristics of high utilization rate of silicon and aluminum sources and high product yield.

[0011] The defects of the technology or the deficiencies of the present application include: the reactant is solid, which adversely affects the mass transfer and heat transfer in the synthesis process, the crystallinity of the molecular sieve is difficult to improve, and industrial production is difficult to achieve.

[0012] In the paper "Rapid synthesis of P-type molecular sieve with high calcium and magnesium ion exchange performance by solid phase method" (Zhang S, Guo H F, Liu X W, et al. Rapid synthesis of P-type molecular sieve with high calcium and magnesium ion exchange performance by solid phase method [J]. Chinese Journal of Inorganic Chemistry, 2019, 35(12): 2323-2330.), P-type molecular sieve crystallization in a high solid content system was achieved by first preparing a silica-alumina dry gel. The specific details are as follows: Na2SiO3·9H2O and Al2(SO4)3·18H2O were dissolved in an appropriate amount of water, heated to 60℃ and stirred thoroughly, mixed uniformly, cooled to room temperature and filtered, washed several times until there was no SO4 2- in the washing liquid, and then placed in a 100℃ constant temperature drying box for 3h to obtain a silica-alumina dry gel. The silica-alumina dry gel was placed in a stainless steel crystallization kettle with a polytetrafluoroethylene liner, and sodium hydroxide and water were added in a certain proportion, stirred thoroughly and mixed uniformly, then statically crystallized at a certain temperature for a period of time, and then removed, filtered, washed with deionized water, and dried to obtain P-type molecular sieve products.

[0013] The defects of the technology or the deficiencies of the present application include: 1. Compared with the conventional method, the solid phase method is achieved by first preparing a silica-alumina dry gel, which is more complex; 2. P-type molecular sieve is the first generation of molecular sieve, which does not require a template during synthesis, so the synthesis phase region is very wide, and the theory and method are not suitable for the synthesis of more complex SAPO-11 molecular sieves.

[0014] In summary, the current existing technology for high solid content production of SAPO-11 molecular sieves mostly uses the method of grinding into gel in a mortar. This method has a small processing capacity and requires self-made templates, making it difficult to scale up the synthesis. In addition, the high solid content synthesis method of other molecular sieves mostly uses the introduction of fluoride mineralizers and the increase of template types or amount, which has the problems of cost increase and environmental emission. Since SAPO-11 is a one-dimensional channel molecular sieve, its crystal structure is metastable and is prone to produce impurities, so it is difficult to develop a high solid content synthesis method.

[0015] Therefore, it has become a technical problem to be solved in the field to provide a new, efficient and stable SAPO-11 molecular sieve and its synthesis method and application. SUMMARY

[0016] In order to solve the above-mentioned shortcomings and deficiencies, one object of the present application is to provide a synthesis method of SAPO-11 molecular sieve.

[0017] Another object of the present application is also to provide a SAPO-11 molecular sieve prepared by the above-mentioned synthesis method of SAPO-11 molecular sieve.

[0018] Still another object of the present application is also to provide the use of the above-mentioned SAPO-11 molecular sieve in catalyzing the hydrogen isomerization reaction of linear alkanes.

[0019] To achieve the above objects, in one aspect, the present application provides a synthesis method of SAPO-11 molecular sieve, wherein the synthesis method of SAPO-11 molecular sieve comprises:

[0020] Step one: uniformly mixing an aluminum source, an auxiliary acid, phosphoric acid and water to obtain a phosphorus-aluminum precursor;

[0021] Step two: adding a template agent and a solid silicon source, which are respectively dissolved in deionized water, into the phosphorus-aluminum precursor in a pulse feeding manner to obtain a mixed gel;

[0022] In the mixed gel, the molar ratio of the aluminum source calculated based on Al2O3, the phosphoric acid calculated based on P2O5, the silicon source calculated based on SiO2, the template agent, the auxiliary acid and water is 1:0.90-1.00:0.40-0.65:0.70-0.85:0.05-0.32:8-15;

[0023] Step three: pre-crystallizing the mixed gel at 90-150℃ for 0.5-2h, and then crystallizing the mixed gel at 190-210℃, preferably at 200℃ for 12-20h, and after the crystallization is completed, filtering and washing the obtained crystallization product and drying the same to obtain the SAPO-11 molecular sieve.

[0024] As a specific embodiment of the above-mentioned synthesis method of the present application, step one specifically comprises: adding water to the aluminum source, and then adding the auxiliary acid and the phosphoric acid, and then keeping the temperature of the system at 40-55℃ by temperature control and stirring for 0.5-3h to obtain the phosphorus-aluminum precursor.

[0025] As a specific embodiment of the above-mentioned synthesis method of the present application, the aluminum source comprises at least one of pseudo-boehmite and aluminum hydroxide.

[0026] As a specific embodiment of the above-mentioned synthesis method of the present application, the auxiliary acid comprises at least one of hydrochloric acid, nitric acid, sulfuric acid, ethanedioic acid, propanedioic acid, terephthalic acid and the like; preferably at least one of ethanedioic acid, propanedioic acid, terephthalic acid and the like. The present application does not specifically require the concentration of hydrochloric acid, nitric acid and sulfuric acid, which can be reasonably adjusted according to the actual operation condition. For example, in some embodiments of the present application, the concentration of hydrochloric acid, nitric acid and sulfuric acid can be 37%, 63-65% and 96%, respectively.

[0027] As a specific embodiment of the above-mentioned synthetic method of the present application, in step two, the template agent and the solid silicon source are respectively dissolved in deionized water and then added to the phosphorus-aluminum precursor in a pulse feeding manner under temperature control and stirring at 40-55°C to obtain a mixed gel.

[0028] As a specific embodiment of the above-mentioned synthetic method of the present application, the solid silicon source comprises at least one of solid silica gel, white carbon black, etc. In some embodiments of the present application, the solid silica gel can be coarse-pore silica gel.

[0029] As a specific embodiment of the above-mentioned synthetic method of the present application, the template agent is an organic amine template agent.

[0030] As a specific embodiment of the above-mentioned synthetic method of the present application, the template agent comprises at least one of di-n-propylamine, diisopropylamine, etc.

[0031] As a specific embodiment of the above-mentioned synthetic method of the present application, the pH value of the mixed gel is 5.5-7.0.

[0032] As a specific embodiment of the above-mentioned synthetic method of the present application, in step two, if the pH value of the mixed gel is not 5.5-7.0, an auxiliary acid is added to the mixed gel to make the pH value thereof 5.5-7.0.

[0033] In the present application, since the addition of acid and template agent in steps one and two will both cause obvious heat release, temperature control is required in these two steps. As a specific embodiment of the above-mentioned synthetic method of the present application, the temperature control is performed in a water bath.

[0034] As a specific embodiment of the above-mentioned synthetic method of the present application, the pulse feeding manner comprises: the feeding speed is 1-3% of the total weight of the template agent solution and the solid silicon source solution per minute, and the feeding points are 2-4.

[0035] In some embodiments of the present application, in step two, the template agent and the solid silicon source are respectively dissolved in deionized water, then the template agent solution and the solid silicon source solution are mixed to obtain a mixed solution, and the mixed solution is added to the phosphorus-aluminum precursor in a pulse feeding manner to obtain a mixed gel. Alternatively, the template agent solution and the solid silicon source solution can be added to the phosphorus-aluminum precursor respectively or simultaneously without mixing, and when they are added respectively, the template agent solution is preferably added first, and then the solid silicon source solution is added.

[0036] As a specific embodiment of the above-mentioned synthetic method of the present application, the step one and step two need to be carried out in a closed reaction kettle or reactor; the step three needs to be carried out in a synthesis kettle.

[0037] As a specific embodiment of the above-mentioned synthetic method of the present application, the temperature of the pre-crystallization is 95-130℃.

[0038] In the step three of the above-mentioned synthetic method of the present application, the filter washing and drying are both conventional operations, and the operation steps and process parameters used in the filter washing and drying can be reasonably adjusted according to the actual operation needs on site.

[0039] In another aspect, the present application also provides a SAPO-11 molecular sieve, wherein the SAPO-11 molecular sieve is prepared by the above-mentioned synthetic method of the SAPO-11 molecular sieve.

[0040] As a specific embodiment of the above-mentioned SAPO-11 molecular sieve of the present application, the SAPO-11 molecular sieve is nanospherical with a particle size of 20-35 nm.

[0041] In still another aspect, the present application also provides the above-mentioned SAPO-11 molecular sieve for use in catalyzing the hydrogenation isomerization reaction of straight-chain alkanes.

[0042] Compared with the prior art, the present application can achieve the following beneficial technical effects:

[0043] (1) The synthesis method of the SAPO-11 molecular sieve provided by the present application can overcome the problems of mass transfer in the gelation process and product heterocrystal existing in the prior art under the condition of high solid content (water / aluminum ratio of 8-15) raw materials, thereby being capable of improving the single-pot yield of the SAPO-11 molecular sieve, and the reasons or mechanisms for producing the beneficial technical effects include the following points: first, temperature control is performed in steps one and two, which promotes the dissolution of the solid aluminum salt and the silicon source, and significantly reduces the system viscosity. Second, the multi-point pulse feeding mode is adopted in step two, which is beneficial to the uniform dispersion of each raw material component in the gelation process. Third: the auxiliary acid is added, and the auxiliary acid added has strong acidity, which can accelerate the dissolution of the aluminum source and promote the phosphoric acid gelation; in addition, when the auxiliary acid is oxalic acid, malonic acid, terephthalic acid or the like, it also has a good directing effect, and it is easier to form a pure-phase SAPO-11 molecular sieve, the reasons may be: part of the organic acid reacts with the organic amine template agent such as di-n-propylamine and diisopropylamine to generate long-chain molecules, and the long-chain molecules have stronger directing effect; another possibility is that the organic acid reacts with other reactions in the reaction system to generate cationic or anionic directing agents with a directing effect. Fourth: in step three, pre-crystallization is first performed at a lower temperature, and then crystallization is performed by increasing the temperature, and the pre-crystallization at a lower temperature can accelerate the depolymerization and dissolution of the solid raw materials, and also effectively inhibit the generation of heterocrystal. As can be seen from the above, through the synergistic effect of the four means of adding auxiliary acid, multi-point pulse feeding, temperature control and two-stage crystallization, the generation of heterocrystal is inhibited, and a pure-phase SAPO-11 molecular sieve is prepared.

[0044] (2) Due to the reduction of water in the raw material system, less template agent can be added to achieve the corresponding template agent concentration, thereby reducing the template agent dosage by more than 15% (calculated in terms of template agent / Al2O3 molar ratio, from 0.95 to 0.85 or less), and on the basis of reducing the template agent dosage, through the synergistic effect of the four means of adding auxiliary acid, multi-point pulse feeding, temperature control and two-stage crystallization, the generation of heterocrystal is inhibited, and a pure-phase SAPO-11 molecular sieve is prepared.

[0045] (3) Since the water / aluminum ratio in the raw material is reduced from 60 to 15 or less, the single-pot yield is significantly improved, which can increase the single-pot yield from 6.5% to more than 25%, and on the basis of reducing the water / aluminum ratio in the raw material, through the synergistic effect of the four means of adding auxiliary acid, multi-point pulse feeding, temperature control and two-stage crystallization, the generation of heterocrystal is inhibited, and a pure-phase SAPO-11 molecular sieve is prepared. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments description will be briefly introduced. Obviously, the accompanying drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 XRD pattern of SAPO-11 molecular sieve provided for Comparative Example 1.

[0048] Figure 2 XRD pattern of SAPO-11 molecular sieve provided for Comparative Example 2.

[0049] Figure 3 XRD pattern of SAPO-11 molecular sieve provided for Comparative Example 3.

[0050] Figure 4 XRD pattern of SAPO-11 molecular sieve provided for Comparative Example 4.

[0051] Figure 5 XRD pattern of SAPO-11 molecular sieve provided for Comparative Example 5.

[0052] Figure 6 XRD pattern of SAPO-11 molecular sieve provided for Embodiment 1 of the present application.

[0053] Figure 7 XRD pattern of SAPO-11 molecular sieve provided for Embodiment 2 of the present application.

[0054] Figure 8 XRD pattern of SAPO-11 molecular sieve provided for Embodiment 3 of the present application.

[0055] Figure 9 XRD pattern of SAPO-11 molecular sieve provided for Embodiment 4 of the present application.

[0056] Figure 10 XRD pattern of SAPO-11 molecular sieve provided for Embodiment 5 of the present application.

[0057] Figure 11 XRD pattern of SAPO-11 molecular sieve provided for Embodiment 6 of the present application.

[0058] Figure 12 XRD pattern of SAPO-11 molecular sieve provided for Embodiment 7 of the present application.

[0059] Figure 13 XRD pattern of SAPO-11 molecular sieve provided for Embodiment 8 of the present application.

[0060] Figure 14The XRD pattern of the SAPO-11 molecular sieve provided for the embodiment 9 of the present application.

[0061] Figure 15 The SEM pattern of the SAPO-11 molecular sieve provided for the embodiment 1 of the present application. DETAILED DESCRIPTION

[0062] It has to be understood that the term "comprising", or variations such as "comprise" or "comprises", as used in the present specification and in the claims, is not intended to exclude that at least one of the stated steps or elements can be present in the process, method, system, product or apparatus. In other words, any feature of the description or claims that is expressed in a positive sense is meant to additionally permit its existence in the negative situation.

[0063] The ranges disclosed herein are given using the format "from x to y", in which x and y are real numbers. For a range including x and y, and including x and y, there is no difference. Thus "from x to y" indicates that a range from the lower point of x to any and all upper points of y is continuously and undividedly combined. For another range excluding x and y, and excluding x and y, there is no difference. Thus "from x to y" indicates that a range from any and all lower points of x to any and all upper points of y is continuously and undividedly combined.

[0064] In the present application, unless otherwise specified, the numerical range "a-b" represents a shorthand notation for any real combination of numbers between a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in the present application, and "0-5" is only a shorthand notation for these numerical combinations.

[0065] In the present application, unless otherwise specified, all embodiments and preferred embodiments mentioned in the present application can be combined with each other to form new technical solutions.

[0066] In the present application, unless otherwise specified, all technical features and preferred features mentioned in the present application can be combined with each other to form new technical solutions.

[0067] In the present application, unless otherwise specified, the term "two" used in the present specification means "at least two".

[0068] In the present application, if not otherwise specified, all the steps mentioned herein can be carried out in sequence or randomly, but preferably in sequence. For example, the method comprises steps (a) and (b), indicating that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method mentioned herein can further comprise step (c), indicating that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0069] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in combination with the accompanying tables, drawings and examples. The examples described below are part of the examples of the present application, but not all the examples, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the examples in the present application, all the other examples obtained by those skilled in the art without making creative efforts fall within the scope of protection of the present application. If the specific conditions are not mentioned in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not mentioned by the manufacturer, they are all conventional products that can be purchased on the market.

[0070] The sources of raw materials or equipment in the examples and comparative examples of the present application, including the names, specifications and manufacturers of raw materials, are shown in Table 1 below.

[0071] Table 1

[0072]

[0073]

[0074] Example 1

[0075] The present example provides a SAPO-11 molecular sieve, which is prepared by a synthesis method comprising the following specific steps:

[0076] (1) preparing a phosphorus aluminum precursor: adding phosphoric acid and hydrochloric acid to pseudoboehmite after adding water, and then controlling the temperature, such as water bath, to keep the temperature at 55℃ and stirring for 0.5h to obtain a phosphorus aluminum precursor;

[0077] (2) Gelation process: dissolve the di-n-propylamine and the solid silica gel in deionized water respectively, then mix the obtained solutions to obtain a mixed solution, and then add the mixed solution into the phosphorus aluminum precursor in a pulse feeding manner, the adding speed is 1% (accounting for the total weight of the mixed solution) per minute and 2 adding points are adopted, until the addition of all the mixed solution is completed, during which stirring and temperature control and incubation at 55°C are maintained, finally a mixed gel is obtained, the pH value of which is 7.0, and the mixed gel ratio (molar ratio) is aluminum source (calculated as Al2O3): phosphoric acid (calculated as P2O5): silicon source (calculated as SiO2): template agent: auxiliary acid: water = 1: 1.00: 0.5: 0.85: 0.05: 8;

[0078] (3) Crystallization and out of the kettle process: add the obtained mixed gel into the synthesis kettle, first pre-crystallize at a temperature of 90°C for 2h, and then crystallize at 200°C for 20h; after crystallization is completed, filter washing is performed, and the SAPO-11 molecular sieve product is obtained by drying, and the single-kettle yield is 31.8%.

[0079] Example 2

[0080] The present embodiment provides a SAPO-11 molecular sieve, which is prepared by a synthesis method comprising the following specific steps:

[0081] (1) Preparation of phosphorus aluminum precursor: after adding water to pseudo-boehmite, phosphoric acid and hydrochloric acid are added, and then temperature control is performed, such as water bath at a temperature of 40°C and stirring for 3h, to obtain a phosphorus aluminum precursor;

[0082] (2) Gelation process: dissolve the di-n-propylamine and the solid silica gel in deionized water respectively, then mix the obtained solutions to obtain a mixed solution, and then add the mixed solution into the phosphorus aluminum precursor in a pulse feeding manner, the adding speed is 1% (accounting for the total weight of the mixed solution) per minute and 2 adding points are adopted, until the addition of all the mixed solution is completed, during which stirring and temperature control and incubation at 55°C are maintained, finally a mixed gel is obtained, the pH value of which is 7.0, and the mixed gel ratio (molar ratio) is aluminum source (calculated as Al2O3): phosphoric acid (calculated as P2O5): silicon source (calculated as SiO2): template agent: auxiliary acid: water = 1: 1.00: 0.5: 0.85: 0.05: 8;

[0083] (3) Crystallization and out of the kettle process: add the obtained mixed gel into the synthesis kettle, first pre-crystallize at a temperature of 90°C for 2h, and then crystallize at 200°C for 20h; after crystallization is completed, filter washing is performed, and the SAPO-11 molecular sieve product is obtained by drying, and the single-kettle yield is 31.8%.

[0084] Example 3

[0085] The embodiment provides a SAPO-11 molecular sieve which is prepared by a synthesis method comprising the following specific steps:

[0086] (1) preparing a phosphorus-aluminum precursor: after adding pseudo-boehmite into water, phosphoric acid and hydrochloric acid are added, then temperature control is performed, such as water bath, to keep the temperature at 50 DEG C and stirring is performed for 3h, so that the phosphorus-aluminum precursor is obtained;

[0087] (2) gel forming process: di-n-propylamine and coarse silica gel are respectively dissolved in deionized water, then the obtained solutions are mixed to obtain a mixed solution, the mixed solution is added into the phosphorus-aluminum precursor in a pulse feeding mode, the adding speed is 3% (accounting for the total weight of the mixed solution) per minute and four adding points are adopted, until the addition of all the mixed solution is completed, during which stirring and temperature control and incubation at 55 DEG C are kept, finally the mixed gel is obtained, the pH value of the mixed gel is 5.5, and the mixed gel ratio (molar ratio) is: aluminum source (calculated in terms of Al2O3): phosphoric acid (calculated in terms of P2O5): silicon source (calculated in terms of SiO2): template agent: auxiliary acid: water = 1:0.90:0.65:0.85:0.18:12;

[0088] (3) crystallization and out of the reactor process: the obtained mixed gel is added into a synthesis kettle, pre-crystallization is performed at a temperature of 150 DEG C for 1h, then crystallization is performed at 200 DEG C for 20h; after the crystallization is completed, filtration and washing are performed, and drying is performed to obtain the SAPO-11 molecular sieve product, and the single-kettle yield is 30.0%.

[0089] Embodiment 4

[0090] The embodiment provides a SAPO-11 molecular sieve which is prepared by a synthesis method comprising the following specific steps:

[0091] (1) preparing a phosphorus-aluminum precursor: after adding pseudo-boehmite into water, phosphoric acid and hydrochloric acid are added, then temperature control is performed, such as water bath, to keep the temperature at 50 DEG C and stirring is performed for 3h, so that the phosphorus-aluminum precursor is obtained;

[0092] (2) gel forming process: di-n-propylamine and coarse silica gel are respectively dissolved in deionized water, then the obtained solutions are mixed to obtain a mixed solution, the mixed solution is added into the phosphorus-aluminum precursor in a pulse feeding mode, the adding speed is 3% (accounting for the total weight of the mixed solution) per minute and four adding points are adopted, until the addition of all the mixed solution is completed, during which stirring and temperature control and incubation at 55 DEG C are kept, finally the mixed gel is obtained, the pH value of the mixed gel is 5.5, and the mixed gel ratio (molar ratio) is: aluminum source (calculated in terms of Al2O3): phosphoric acid (calculated in terms of P2O5): silicon source (calculated in terms of SiO2): template agent: auxiliary acid: water = 1:0.90:0.65:0.85:0.18:12;

[0093] (3) Crystallization and out of the kettle process: the resulting mixed gel is added to the synthesis kettle, first pre-crystallization, the temperature is 150 ℃, the time is 2 h, then crystallization at 210 ℃ for 18 hours; after crystallization, filter washing, drying to obtain SAPO-11 molecular sieve product, single kettle yield is 29.9%.

[0094] Example 5

[0095] The present embodiment provides a SAPO-11 molecular sieve, which is prepared by a synthesis method comprising the following specific steps:

[0096] (1) Preparation of phosphorus aluminum precursor: after adding water to aluminum hydroxide, then add phosphoric acid and hydrochloric acid, then control the temperature, such as water bath, keep the temperature at 55 ℃ and stir for 3 h, get the phosphorus aluminum precursor;

[0097] (2) Gelation process: the di-n-propylamine and diisopropylamine, solid silica gel are respectively dissolved with deionized water, then the obtained solution is mixed to obtain a mixed solution, then the mixed solution is added to the phosphorus aluminum precursor in a pulse feeding manner, the adding speed is 1% (accounting for the total weight of the mixed solution) per minute and 4 adding points are adopted, until the addition of all the mixed solution is completed, during which the stirring and temperature control are kept at 45 ℃, finally the mixed gel is obtained, the pH value is 6.8, the mixed gel ratio (molar ratio) is, aluminum source (calculated as Al2O3): phosphoric acid (calculated as P2O5): silicon source (calculated as SiO2): template: auxiliary acid: water = 1:0.96:0.55:0.85:0.10:8;

[0098] (3) Crystallization and out of the kettle process: the resulting mixed gel is added to the synthesis kettle, first pre-crystallization, the temperature is 120 ℃, the time is 2 h, then crystallization at 190 ℃ for 12 hours; after crystallization, filter washing, drying to obtain SAPO-11 molecular sieve product, single kettle yield is 26.7%.

[0099] Example 6

[0100] The present embodiment provides a SAPO-11 molecular sieve, which is prepared by a synthesis method comprising the following specific steps:

[0101] (1) Preparation of phosphorus aluminum precursor: after adding water to pseudo-boehmite, then add phosphoric acid and hydrochloric acid, then control the temperature, such as water bath, keep the temperature at 40 ℃ and stir for 3 h, get the phosphorus aluminum precursor;

[0102] (2) Gelation process: dissolve the di-n-propylamine and the white carbon black in deionized water respectively, then mix the obtained solutions to obtain a mixed solution, and then add the mixed solution into the phosphorus aluminum precursor in a pulse feeding manner, the adding speed is 2% (accounting for the total weight of the mixed solution) per minute and 3 adding points are adopted until the addition of all the mixed solution is completed, during which the stirring and temperature control and heat preservation at 40°C are maintained, finally a mixed gel is obtained, the pH value of the mixed gel is 5.5, and the mixed gel ratio (molar ratio) is aluminum source (calculated as Al2O3): phosphoric acid (calculated as P2O5): silicon source (calculated as SiO2): template agent: auxiliary acid: water = 1:0.95:0.57:0.82:0.13:12;

[0103] (3) Crystallization and out of the kettle process: add the obtained mixed gel into the synthesis kettle, first pre-crystallize at a temperature of 150°C for 0.5h, and then crystallize at 200°C for 20h; after crystallization is completed, filter washing is performed, and drying is performed to obtain a SAPO-11 molecular sieve product, and the single-kettle yield is 30.3%.

[0104] Example 7

[0105] The present embodiment provides a SAPO-11 molecular sieve, which is prepared by a synthesis method comprising the following specific steps:

[0106] (1) Preparation of phosphorus aluminum precursor: after adding water to pseudo-boehmite, phosphoric acid and oxalic acid are added, and then temperature control is performed, such as water bath to keep the temperature at 40°C and stirring for 3h, to obtain a phosphorus aluminum precursor;

[0107] (2) Gelation process: dissolve the di-n-propylamine and the white carbon black in deionized water respectively, then mix the obtained solutions to obtain a mixed solution, and then add the mixed solution into the phosphorus aluminum precursor in a pulse feeding manner, the adding speed is 2% (accounting for the total weight of the mixed solution) per minute and 3 adding points are adopted until the addition of all the mixed solution is completed, during which the stirring and temperature control and heat preservation at 40°C are maintained, finally a mixed gel is obtained, the pH value of the mixed gel is 5.5, and the mixed gel ratio (molar ratio) is aluminum source (calculated as Al2O3): phosphoric acid (calculated as P2O5): silicon source (calculated as SiO2): template agent: auxiliary acid: water = 1:0.95:0.57:0.82:0.13:12;

[0108] (3) Crystallization and out of the kettle process: add the obtained mixed gel into the synthesis kettle, first pre-crystallize at a temperature of 150°C for 0.5h, and then crystallize at 200°C for 20h; after crystallization is completed, filter washing is performed, and drying is performed to obtain a SAPO-11 molecular sieve product, and the single-kettle yield is 30.3%.

[0109] Example 8

[0110] The embodiment provides a SAPO-11 molecular sieve which is prepared by a synthesis method comprising the following specific steps:

[0111] (1) preparing a phosphorus aluminum precursor: after adding water to pseudo-boehmite, phosphoric acid and malonic acid are added, then temperature control is performed, such as water bath, to keep the temperature at 40 DEG C and stirring is performed for 3h, so that the phosphorus aluminum precursor is obtained;

[0112] (2) gelation process: di-n-propylamine and white carbon black are respectively dissolved in deionized water, then the obtained solutions are mixed to obtain a mixed solution, the mixed solution is added to the phosphorus aluminum precursor in a pulse feeding mode, the adding speed is 1% (accounting for the total weight of the mixed solution) per minute and 4 adding points are adopted, until the addition of all the mixed solution is completed, during which stirring and temperature control and incubation at 40 DEG C are kept, finally a mixed gel is obtained, the pH value of the mixed gel is 6.4, and the mixed gel ratio (molar ratio) is: aluminum source (calculated in terms of Al2O3): phosphoric acid (calculated in terms of P2O5): silicon source (calculated in terms of SiO2): template agent: auxiliary acid: water = 1:0.95:0.57:0.79:0.24:12;

[0113] (3) crystallization and out of the kettle process: the obtained mixed gel is added to a synthesis kettle, pre-crystallization is performed first, the temperature is 150 DEG C, the time is 0.5h, then crystallization is performed at 190 DEG C for 20 hours; after the crystallization is completed, filtration and washing are performed, and drying is performed to obtain a SAPO-11 molecular sieve product, the single-kettle yield is 26.1%.

[0114] Example 9

[0115] The embodiment provides a SAPO-11 molecular sieve which is prepared by a synthesis method comprising the following specific steps:

[0116] (1) preparing a phosphorus aluminum precursor: after adding water to pseudo-boehmite, phosphoric acid, terephthalic acid and hydrochloric acid are added, then temperature control is performed, such as water bath, to keep the temperature at 40 DEG C and stirring is performed for 3h, so that the phosphorus aluminum precursor is obtained;

[0117] (2) gelation process: di-n-propylamine and white carbon black are respectively dissolved in deionized water, then the obtained solutions are mixed to obtain a mixed solution, the mixed solution is added to the phosphorus aluminum precursor in a pulse feeding mode, the adding speed is 1% (accounting for the total weight of the mixed solution) per minute and 4 adding points are adopted, until the addition of all the mixed solution is completed, during which stirring and temperature control and incubation at 40 DEG C are kept, finally a mixed gel is obtained, the pH value of the mixed gel is 6.2, and the mixed gel ratio (molar ratio) is: aluminum source (calculated in terms of Al2O3): phosphoric acid (calculated in terms of P2O5): silicon source (calculated in terms of SiO2): template agent: auxiliary acid: water = 1:0.95:0.57:0.72:0.28 (terephthalic acid is 0.20, and hydrochloric acid is 0.08):12;

[0118] (3) Crystallization and out of reactor process: the obtained mixed gel was added into the synthesis reactor, pre-crystallization was carried out at a temperature of 150°C for 0.5h, and then crystallization was carried out at 210°C for 20h; after the crystallization was completed, filter washing was carried out, and the SAPO-11 molecular sieve product was obtained by drying, and the single reactor yield was 26.4%.

[0119] Comparative Example 1

[0120] The present comparative example provides a SAPO-11 molecular sieve which is prepared by a conventional synthesis method comprising the following specific steps:

[0121] Pseudo-boehmite (aluminum source), phosphoric acid, di-n-propylamine (template agent), silica sol (silicon source), and deionized water were added into a reaction kettle for stirring to prepare a gel, and the ratio (molar ratio) was as follows: aluminum source (Al2O3): phosphoric acid (P2O5): silicon source (SiO2): template agent: water = 1:1.05:0.47:0.93:60, and then crystallization was carried out at a temperature of 200°C for 30h; after the crystallization was completed, the crystallization product was dried and calcined to obtain a SAPO-11 molecular sieve product, and the single reactor yield was 6.5%.

[0122] Comparative Example 2 (high solid content, no auxiliary acid added)

[0123] The present comparative example provides a SAPO-11 molecular sieve which is prepared by a synthesis method comprising the following specific steps:

[0124] (1) Preparation of phosphorus aluminum precursor: after pseudo-boehmite was added with water, phosphoric acid was added, and then the system temperature was kept at 50°C by temperature control and stirring for 3h to obtain a phosphorus aluminum precursor;

[0125] (2) Gelation process: di-n-propylamine and solid silica gel were respectively dissolved with deionized water, and then the obtained solutions were mixed to obtain a mixed solution, and the mixed solution was added into the phosphorus aluminum precursor in a pulse feeding manner, the adding speed was 1% (based on the total weight of the mixed solution) per minute and two adding points were adopted, until the addition of all the mixed solution was completed, and during the period, the stirring and temperature control and keeping at 55°C were maintained, and finally a mixed gel was obtained, and the pH value was 7.0, and the mixed gel ratio (molar ratio) was as follows: aluminum source (calculated as Al2O3): phosphoric acid (calculated as P2O5): silicon source (calculated as SiO2): template agent: water = 1:1.00:0.65:0.85:15;

[0126] (3) Crystallization and out of reactor process: the obtained mixed gel was added into the synthesis reactor, pre-crystallization was carried out at a temperature of 150°C for 0.5h, and then crystallization was carried out at 200°C for 20h; after the crystallization was completed, filter washing and drying were carried out, and the SAPO-11 molecular sieve product was obtained, and the single reactor yield was 26.6%.

[0127] Comparative Example 3 (high solid content, preparation of phosphorus aluminum precursor and no temperature control and insulation during gelation process)

[0128] This comparative example provides a SAPO-11 molecular sieve which is prepared by a synthesis method comprising the following specific steps:

[0129] (1) Preparation of phosphorus aluminum precursor: after adding water to pseudoboehmite, phosphoric acid and hydrochloric acid are added, and then stirred for 3 h to obtain a phosphorus aluminum precursor;

[0130] (2) Gelation process: di-n-propylamine and white carbon black are respectively dissolved in deionized water, and then the obtained solutions are mixed to obtain a mixed solution, and the mixed solution is added to the phosphorus aluminum precursor in a pulse feeding manner, the adding speed is 1% (based on the total weight of the mixed solution) per minute and 3 adding points are adopted until the addition of all the mixed solution is completed, and stirring is maintained during the addition, and finally a mixed gel is obtained, the pH value of the mixed gel is controlled at 6.3, and the ratio (molar ratio) of the mixed gel is aluminum source (calculated as Al2O3): phosphoric acid (calculated as P2O5): silicon source (calculated as SiO2): template: auxiliary acid: water = 1:0.90:0.45:0.80:0.15:15;

[0131] (3) Crystallization and out of the kettle process: the obtained mixed gel is added to a synthesis kettle, pre-crystallization is carried out at a temperature of 150°C for 0.5 h, and then crystallization is carried out at a temperature of 200°C for 20 h; after the crystallization is completed, filter washing and drying are carried out to obtain a SAPO-11 molecular sieve product, and the single-kettle yield is 21.3%.

[0132] Comparative Example 4 (high solid content, no pulse feeding manner is adopted during the gelation process)

[0133] This comparative example provides a SAPO-11 molecular sieve which is prepared by a synthesis method comprising the following specific steps:

[0134] (1) Preparation of phosphorus aluminum precursor: after adding water to pseudoboehmite, phosphoric acid and hydrochloric acid are added, and then stirred for 3 h to obtain a phosphorus aluminum precursor;

[0135] (2) Gelation process: di-n-propylamine and white carbon black are respectively dissolved in deionized water, and then the obtained solutions are mixed to obtain a mixed solution, and the mixed solution is added to the phosphorus aluminum precursor in a pulse feeding manner, the adding speed is 1% (based on the total weight of the mixed solution) per minute and 3 adding points are adopted until the addition of all the mixed solution is completed, and stirring is maintained during the addition, and finally a mixed gel is obtained, the pH value of the mixed gel is controlled at 6.3, and the ratio (molar ratio) of the mixed gel is aluminum source (calculated as Al2O3): phosphoric acid (calculated as P2O5): silicon source (calculated as SiO2): template: auxiliary acid: water = 1:0.90:0.45:0.80:0.15:15;

[0136] (3) Crystallization and out of the kettle process: the resulting mixed gel is added to the synthesis kettle, first pre-crystallization, the temperature is 110 ℃, the time is 1 h, then crystallization at 200 ℃ for 20 hours; after crystallization, filter washing and drying are carried out to obtain SAPO-11 molecular sieve product, the single kettle yield is 29.1%.

[0137] Comparative Example 5 (high solid content, no pre-crystallization)

[0138] The present comparative example provides a SAPO-11 molecular sieve, which is prepared by a synthesis method comprising the following specific steps:

[0139] (1) Preparation of phosphorus aluminum precursor: after adding water to aluminum hydroxide, phosphoric acid and sulfuric acid are added, then temperature control is performed, such as water bath to maintain the temperature at 50 ℃ and stirring for 3 h, to obtain a phosphorus aluminum precursor;

[0140] (2) Gelation process: di-n-propylamine and white carbon black are respectively dissolved in deionized water, then the obtained solutions are mixed to obtain a mixed solution, and the mixed solution is added to the phosphorus aluminum precursor in a pulse feeding manner, the adding speed is 1% (based on the total weight of the mixed solution) per minute and 4 adding points are adopted until the addition of all the mixed solution is completed, during which stirring and temperature control are maintained at 50 ℃, finally a mixed gel is obtained, the pH value of which is 6.3, and the mixed gel ratio (molar ratio) is aluminum source (calculated as Al2O3): phosphoric acid (calculated as P2O5): silicon source (calculated as SiO2): template: auxiliary acid: water = 1:0.90:0.40:0.70:0.05:10;

[0141] (3) Crystallization and out of the kettle process: the resulting mixed gel is added to the synthesis kettle, crystallization at 200 ℃ for 20 hours; after crystallization, filter washing is carried out, and drying is carried out to obtain SAPO-11 molecular sieve product, the single kettle yield is 32.5%.

[0142] Test Example 1

[0143] The SAPO-11 molecular sieves provided by the comparative examples 1-5 and the examples 1-9 are subjected to crystal type determination, wherein the crystal type determination is carried out by XRD test on a Bruker D2 diffractometer, using Cu target K α light source (λ = 0.15432 nm), tube voltage is 40 kV, tube current is 40 mA, and the scanning speed in the range of 5-40° is 4° / min. Qualitative analysis is carried out using X-ray diffraction card (JCPDS).

[0144] The XRD patterns of the products provided by the comparative examples 1-5 and the examples 1-9 are shown in Figures 1-14 .

[0145] From Figure 1 It can be seen that the product provided by Comparative Example 1 is also a pure-phase SAPO-11 molecular sieve, but the prior synthesis method provided by Comparative Example 1 has the disadvantage that the water content of the raw material is high, which results in a low yield of the product, further affecting the production efficiency and energy consumption;

[0146] From Figure 2 It can be seen that the product provided by Comparative Example 2 is a SAPO-11 molecular sieve, but contains obvious AlPO-C heterocrystal;

[0147] From Figure 3 It can be seen that the product provided by Comparative Example 3 is a SAPO-11 molecular sieve, but also contains obvious AlPO-C heterocrystal;

[0148] From Figure 4 It can be seen that the product provided by Comparative Example 4 is a SAPO-11 molecular sieve, but contains obvious SAPO-31 heterocrystal;

[0149] From Figure 5 It can be seen that the product provided by Comparative Example 5 is a mixed crystal of SAPO-11 and SAPO-31 molecular sieves.

[0150] From Figures 6-14 It can be seen from Table 1 that the products provided by Examples 1-9 of the present application are all pure-phase SAPO-11 molecular sieves without heterocrystal.

[0151] Meanwhile, the relative crystallinity of the SAPO-11 molecular sieve products provided by Examples 1-9 of the present application is calculated based on the XRD relative crystallinity of the SAPO-11 molecular sieve provided by Comparative Example 1, which is 100%, and the data is shown in Table 2. The calculation method of the relative crystallinity includes: first selecting 8 characteristic peaks of 2θ of 8.14°, 9.48°, 15.70°, 21.10°, 22.18°, 22.60°, 22.76° and 23.22° in the XRD spectrum of the SAPO-11 molecular sieve sample provided by Comparative Example 1, calculating the sum of the peak intensities of the 8 characteristic peaks, then taking 8 characteristic peaks of 2θ of 8.14°, 9.48°, 15.70°, 21.10°, 22.18°, 22.60°, 22.76° and 23.22° in the XRD spectrum of the SAPO-11 molecular sieve sample provided by Examples 1-9 of the present application, calculating the sum of the peak intensities of the 8 characteristic peaks, and then comparing the sum of the peak intensities in the examples with the sum of the peak intensities in Comparative Example 1 to obtain the relative crystallinity of each sample, and the results are shown in Table 2.

[0152] Table 2

[0153] Product Relative crystallinity / % Comparative Example 1 100 Example 1 94 Example 2 89 Example 3 92 Example 4 91 Example 5 93 Example 6 92 Example 7 98 Example 8 98 Figure 15 101

[0154] From the above Table 2, it can be seen that, compared with Examples 1-6, the crystallinity of the SAPO-11 molecular sieve product prepared in Examples 7-9 is obviously improved, because the organic acid has a certain structure-directing effect in the crystallization process, and it is easier to synthesize a pure-phase SAPO-11 molecular sieve product after adding the organic acid.

[0155] Test Example 2

[0156] In this test example, the product provided in Example 1 was subjected to morphology analysis by a JSM-7610F Plus type emission scanning electron microscope, with a working voltage of 5-20 kV and a magnification of 1 000-50 000 times. The SEM image of the SAPO-11 provided in Example 1 is shown in FIG. 1. Figure 15 As can be seen from FIG. 1, the morphology of the SAPO-11 provided in Example 1 is a nanoscale small ball, with a particle size of 20-35 nm. ​

[0157] In summary, the synthesis method of the SAPO-11 molecular sieve provided in the examples of the present application can overcome the problems of mass transfer in the gelation process and product impurities in the prior art under the condition of high solid content (water to aluminum ratio of 8-15) raw materials, thereby improving the single-pot yield of the SAPO-11 molecular sieve. The reasons or mechanisms for this beneficial technical effect include the following: first, temperature control is performed in steps one and two, which promotes the dissolution of the solid aluminum salt and the silicon source, and significantly reduces the viscosity of the system. Second, a multi-point pulse feeding method is used in step two, which is beneficial to the uniform dispersion of each raw material component in the gelation process. Third, an auxiliary acid is added, which has strong acidity and can accelerate the dissolution of the aluminum source to promote phosphoric acid gelation. In addition, when the auxiliary acid is an organic acid such as oxalic acid, malonic acid, terephthalic acid, etc., it also has a good directing effect, making it easier to form a pure-phase SAPO-11 molecular sieve. The reasons may be as follows: some organic acids undergo amide reaction with organic amine templates such as di-n-propylamine and diisopropylamine to generate long-chain molecules, which have a stronger directing effect. Another possibility is that the organic acid undergoes other reactions in the reaction system to generate cationic or anionic directing agents with a directing effect. Fourth, pre-crystallization is performed at a lower temperature in step three, followed by crystallization at a higher temperature. Pre-crystallization at a lower temperature can accelerate the depolymerization and dissolution of the solid raw materials, while also effectively inhibiting the formation of impurities. In summary, through the synergistic effect of the addition of an auxiliary acid, multi-point pulse feeding, temperature control, and two-stage crystallization, the formation of impurities is inhibited, and a pure-phase SAPO-11 molecular sieve is prepared.

[0158] ​In the embodiment of the present application, because the water content in the raw material system is reduced, the addition of less template agent can achieve the corresponding template agent concentration, thereby the template agent dosage can be reduced by more than 15% (calculated by the template agent / Al2O3 molar ratio, from 0.95 to 0.85 or less), and on the basis of reducing the template agent dosage, through the synergistic effect of the four means of adding auxiliary acid, multi-point pulse feeding, temperature control and two-stage crystallization, the generation of impurity crystals is inhibited, and the pure phase SAPO-11 molecular sieve is prepared.

[0159] In the embodiment of the present application, because the water / aluminum ratio in the raw material is reduced from the original 60 to 15 or less, the single-pot yield is significantly improved, and the single-pot yield can be increased from 6.5% to more than 25%, and on the basis of reducing the water / aluminum ratio in the raw material, through the synergistic effect of the four means of adding auxiliary acid, multi-point pulse feeding, temperature control and two-stage crystallization, the generation of impurity crystals is inhibited, and the pure phase SAPO-11 molecular sieve is prepared.

[0160] The above is only a specific embodiment of the present application, which cannot limit the scope of the application, so the replacement of equivalent components or equivalent changes and modifications made within the scope of the present application should still belong to the scope covered by the present patent. In addition, the technical features in the present application can be freely combined with each other, between technical features, between technical features and technical inventions, and between technical inventions.

Claims

1. A method for synthesizing SAPO-11 molecular sieve, characterized in that, The method for synthesizing the SAPO-11 molecular sieve includes: Step 1: After adding water to the aluminum source, add auxiliary acid and phosphoric acid, and then maintain the system temperature at 40-55℃ and stir for 0.5-3 hours to obtain the aluminum phosphorus precursor; wherein, the auxiliary acid includes at least one of hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, malonic acid and terephthalic acid. Step 2: Under temperature control and stirring conditions of 40-55℃, the template agent and solid silicon source are dissolved in deionized water and then added to the aluminum phosphate precursor by pulse feeding to obtain a mixed gel. In the mixed gel, the molar ratio of aluminum source (calculated as Al2O3), phosphoric acid (calculated as P2O5), silicon source (calculated as SiO2), template agent, auxiliary acid, and water is 1:0.90-1.00:0.40-0.65:0.70-0.85:0.05-0.32:8-15. Step 3: The mixed gel is pre-crystallized at 90-150℃ for 0.5-2h, then crystallized at 190-210℃ for 12-20h. The resulting crystallized product is then filtered, washed, and dried to obtain the SAPO-11 molecular sieve.

2. The synthesis method according to claim 1, characterized in that, The aluminum source includes at least one of boehmite and aluminum hydroxide.

3. The synthesis method according to claim 1, characterized in that, The auxiliary acid includes at least one of oxalic acid, malonic acid, and terephthalic acid.

4. The synthesis method according to claim 1, characterized in that, The solid silicon source includes at least one of solid silica gel and precipitated silica.

5. The synthesis method according to claim 1, characterized in that, The template agent includes at least one of di-n-propylamine and diisopropylamine.

6. The synthesis method according to claim 1, characterized in that, The pH value of the mixed gel is 5.5-7.

0.

7. The synthesis method according to claim 6, characterized in that, In step two, if the pH value of the mixed gel is not 5.5-7.0, an auxiliary acid is added to the mixed gel to make its pH value 5.5-7.

0.

8. The synthesis method according to claim 1, characterized in that, The pulse feeding method includes: the feeding rate is 1-3% of the total weight of the template agent solution and solid silicon source solution per minute, and the feeding points are 2-4.

9. The synthesis method according to claim 1, characterized in that, The pre-crystallization temperature is 95-130℃.

10. A SAPO-11 molecular sieve, characterized in that, The SAPO-11 molecular sieve is prepared by the synthesis method of the SAPO-11 molecular sieve according to any one of claims 1-9.

11. The SAPO-11 molecular sieve according to claim 10, characterized in that, The SAPO-11 molecular sieve is in the form of nanospheres with a particle size of 20-35 nm.

12. The application of the SAPO-11 molecular sieve according to claim 10 or 11 in the catalytic hydrogenation isomerization reaction of straight-chain alkanes.

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