A low-silicon nano-sheet SAPO-34 molecular sieve and its preparation method and application

Abstract

The present invention discloses a SAPO-34 molecular sieve with low silicon flake morphology, its preparation and application in methanol to olefins. It belongs to the technical field of molecular sieve preparation. The molecular sieve is prepared by reducing the content of silica sol in the precursor, and adopting low-temperature crystallization, and a hydrothermal synthesis method with continuous and rapid stirring during the crystallization process. The synthesized SAPO-34 product has both low acidity and extremely small-sized nano-flake morphology. The synthesis method of the present invention is simple, efficient and controllable, without the need to add other solvents and surfactants, etc. The molecular sieve shows extremely high selectivity for low-carbon olefins in the methanol to olefins reaction, especially the total yield of ethylene and propylene can reach more than 88%, and the stability performance is excellent, which is very suitable for industrial scale-up application.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieves, and in particular relates to a preparation method of a SAPO-34 molecular sieve with low silicon flake morphology and an application thereof in a methanol to olefin reaction. Background Art

[0002] Among the basic chemical products with the largest production and consumption in the world, ethylene and propylene rank first and second respectively. In industrial production, ethylene and propylene are mainly produced by cracking petroleum products such as light oil, heavy oil, and light diesel. Based on my country's current energy structure of rich coal, poor oil, and little gas, and its increasing dependence on foreign oil, the use of non-petroleum routes to produce low-carbon olefins is one of the feasible ways to solve the problem of energy shortage. The route of methanol to low-carbon olefins (MTO) is considered to be an ideal alternative process. At the same time, combined with the characteristics of my country's relatively rich coal resources and excess methanol production capacity, the MTO conversion route has greater development advantages. At the same time, MTO technology has also promoted the diversification of domestic olefin production technology and sources, providing new opportunities for the structural adjustment of my country's petrochemical industry.

[0003] Among the numerous MTO molecular sieve catalysts, the SAP0-34 molecular sieve with a topological structure exhibits excellent catalytic activity and selectivity for low-carbon olefins in the methanol to olefins reaction due to its suitable acid strength, unique pore structure, good thermal stability and hydrothermal stability. However, due to the narrow pores of the SAPO-34 molecular sieve, it is easy to accumulate carbon during the reaction, thus quickly deactivating. How to overcome the carbon accumulation deactivation caused by the narrow pores and further improve the catalytic performance is the focus of current research.

[0004] The current SAPO-34 molecular sieves are mostly micron-sized and cubic in shape. Their mass transfer paths are long, and the generated target products are prone to side reactions during the diffusion process.

[0005] The current synthesis of nano SAPO-34 molecular sieve mainly includes mixed template method, microwave synthesis method, ultrasonic synthesis method, recrystallization and seed method and xerogel conversion method, and the molecular sieve size obtained by these methods is mainly between 100-500nm, and the silicon content is high, and it is difficult to accurately control the synthesis of low silicon, molecular sieves of different sizes by regulating and controlling variables. The existing report of the method for synthesizing low-acid SAP0-34 molecular sieve is also very few. Therefore, the nano-sheet SAPO-34 molecular sieve with low silicon content is developed, and the research improving its catalytic performance becomes an important research direction in this field. Summary of the invention

[0006] The present invention aims to provide a low-silicon nano-sheet SAPO-34 molecular sieve and a preparation method thereof, and apply it to the methanol to light olefin reaction to solve the problem of easy deactivation of the molecular sieve and improve the conversion rate and selectivity of the catalyst.

[0007] To achieve the above object, the present invention adopts the following technical scheme:

[0008] The present invention provides a low-silicon nano-sheet SAPO-34 molecular sieve, which has both low silicon content and small-size nano-sheet morphology, wherein the silicon content is Si / (Si+A1+P)=0.0015-0.010 in terms of atomic ratio, the average particle size of the molecular sieve is 40-500nm, and the thickness is 10-30nm. The molecular sieve exhibits extremely high selectivity for low-carbon olefins in the methanol to olefins reaction, especially the total yield of ethylene and propylene can reach more than 88%, and has excellent stability.

[0009] The present invention provides a method for preparing the above-mentioned low-silicon nano-sheet SAP0-34 molecular sieve, comprising the following steps:

[0010] 1) adding the aluminum source to the mixed system of the template and water, stirring at 20-40° C. for 1-4 hours to obtain a uniform mixture solution;

[0011] 2) adding a phosphorus source to the above mixture solution, stirring at 40-65° C. for 4-6 hours, then adding a silicon source, and continuing stirring for 2-4 hours to obtain an initial gel mixture of SAPO-34 molecular sieve;

[0012] 3) placing the gel mixture obtained in step 2) into a polytetrafluoroethylene reactor, and then fixing it in a rotary oven for low-temperature crystallization;

[0013] 4) After the crystallization is completed, the hydrothermal autoclave is cooled rapidly, the solid product is separated by centrifugation, the solid product is washed with deionized water until it is neutral, and then dried at 80-120° C. to obtain SAPO-34 molecular sieve raw powder;

[0014] 5) The SAP0-34 molecular sieve raw powder is calcined at high temperature to remove the template contained in the raw powder, thereby obtaining a SAPO-34 molecular sieve with low silicon and nano-sized flake morphology.

[0015] Furthermore, in the above technical scheme, in steps 1)-2), the molar ratio of the oxide, template and water components in the initial gel mixture is SiO2:Al2O3:P2O5:template:H2O=0.01-0.2:1:0.8-1.2:1.5-2.5:20-60; in the initial gel mixture, the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the phosphorus source is calculated as P2O5.

[0016] Furthermore, in the above technical scheme, in steps 1)-2), the silicon source is at least one of silica sol, tetraethyl orthosilicate, sodium silicate, white carbon black, and activated silica; the aluminum source is at least one of aluminum oxide, pseudo-boehmite, aluminum isopropoxide, and aluminum hydroxide; the template is at least one of tetraethylammonium hydroxide (TEAOH) aqueous solution, triethylamine (TEA), and morpholine (MOR); and the phosphorus source is selected from at least one of phosphoric acid, phosphate, phosphite, and tributyl phosphate.

[0017] Furthermore, in the above technical solution, in step 3), the rotation speed of the reactor is set to 30-60 r / min, the crystallization temperature is set to 100-115° C., and the crystallization time is set to 60-120 h.

[0018] Furthermore, in the above technical solution, in step 5), the calcination temperature is 500-650° C., and the calcination time is 6-12 hours.

[0019] The present invention provides the use of the low-silicon nano-sheet SAP0-34 molecular sieve prepared by the above preparation method in the methanol to light olefin reaction.

[0020] Furthermore, in the above application scheme, the reaction pressure is 0.1-0.4MPa, and the air velocity is 1-3h -1 , the reaction temperature is 400-550℃.

[0021] Beneficial Effects

[0022] Compared with the prior art, the beneficial effects achieved by the technical solution of the present invention are:

[0023] 1 The present invention reduces the content of silica sol in the precursor, and adopts a hydrothermal synthesis method of low temperature crystallization and continuous rapid stirring during the crystallization process to prepare a product with low acidity.

[0024] Si / (Si+A1+P)=0.0015-0.010 and extremely small size (average particle size of 40-500nm, thickness of 10-30nm) nanosheet SAPO-34 molecular sieve,

[0025] 2 In the present invention, without affecting the catalytic activity, SAPO-34 with a low silicon content can reduce carbon deposits and improve the stability of the catalyst; the smaller size and flaky morphology enable the molecular sieve to have a shorter mass transfer path, improve the selectivity of light olefins, and improve the conversion rate and stability. The performance of the catalyst of the present invention remains stable after 1000 minutes of reaction, and the stability is significantly improved.

[0026] 3 The SAPO-34 molecular sieve prepared by the present invention exhibits excellent catalytic performance in the methanol to light olefins reaction, wherein the total yield of ethylene and propylene can reach more than 88%. DETAILED DESCRIPTION

[0027] Example 1

[0028] 16 g of aluminum isopropoxide was added to a mixture of 25 g of TEAOH and 10 g of water, and stirred at 40°C for 2 hours to obtain a uniform mixture solution; 10.9 g of phosphoric acid was added to the mixture solution, and stirred at 65°C for 4 hours, and then 0.77 g of silica sol was added, and stirring was continued for 2 hours to obtain an initial gel mixture of SAPO-34 molecular sieve; the molar ratio of each component in the gel mixture was

[0029] SiO2:Al2O3:P2O5:TEAOH:H2O=0.13:1:1.2:1.8:40; the gel mixture was loaded into a polytetrafluoroethylene reactor, and then fixed in a rotary oven and crystallized at 115°C for 80 hours; after the crystallization, the hydrothermal reactor was quickly cooled down, the solid product was separated by centrifugation, the solid product was washed with deionized water until neutral, and then dried at 80°C to obtain SAPO-34 molecular sieve raw powder; the SAP0-34 molecular sieve raw powder was calcined at 650°C for 10 hours to remove the template contained in the raw powder, and Si / (Si+A1+P)=0.005, the average particle size is 40-500nm, and the thickness is 10-30nm. Nano-sheet SAPO-34 molecular sieve.

[0030] Example 2

[0031] 7.2 g of pseudo-boehmite was added to a mixture of 46.8 g of TEAOH and 11 g of water, and stirred at 40°C for 2 hours to obtain a uniform mixture solution; 13 g of phosphoric acid was added to the mixture solution, and stirred at 65°C for 4 hours, and then 1.7 g of silica sol was added, and stirring was continued for 2 hours to obtain an initial gel mixture of SAPO-34 molecular sieve; the molar ratio of each component in the gel mixture was

[0032] SiO2:Al2O3:P2O5:TEAOH:H2O=0.15:0.8:1:2.0:50; the gel mixture was loaded into a polytetrafluoroethylene reactor, and then fixed in a rotary oven and crystallized at 115°C for 80 hours; after the crystallization, the hydrothermal reactor was quickly cooled down, the solid product was separated by centrifugation, the solid product was washed with deionized water until neutral, and then dried at 80°C to obtain SAPO-34 molecular sieve raw powder; the SAP0-34 molecular sieve raw powder was calcined at 650°C for 10 hours to remove the template contained in the raw powder, and Si / (Si+A1+P)=0.007, the average particle size is 40-500nm, and the thickness is 10-30nm. Nano-sheet SAPO-34 molecular sieve.

[0033] Example 3

[0034] 8.4 g of aluminum hydroxide was added to a mixture of 46.8 g of TEAOH and 10 g of water, and stirred at 40°C for 2 hours to obtain a uniform mixture solution; 13 g of phosphoric acid was added to the mixture solution, and stirred at 65°C for 4 hours, and then 1.7 g of silica sol was added, and stirring was continued for 2 hours to obtain an initial gel mixture of SAPO-34 molecular sieve; the molar ratio of each component in the gel mixture was

[0035] SiO2:Al2O3:P2O5:TEAOH:H2O=0.15:0.8:1:2.0:50; the gel mixture was loaded into a polytetrafluoroethylene reactor, and then fixed in a rotary oven and crystallized at 115°C for 80 hours; after the crystallization, the hydrothermal reactor was quickly cooled down, the solid product was separated by centrifugation, the solid product was washed with deionized water until neutral, and then dried at 80°C to obtain SAPO-34 molecular sieve raw powder; the SAP0-34 molecular sieve raw powder was calcined at 650°C for 10 hours to remove the template contained in the raw powder, and Si / (Si+A1+P)=0.003, the average particle size is 40-500nm, and the thickness is 10-30nm. Nano-sheet SAPO-34 molecular sieve.

[0036] Example 4

[0037] 7.2 g of pseudo-boehmite was added to a mixture of 46.8 g of TEAOH and 11 g of water, and stirred at 40° C. for 2 hours to obtain a uniform mixture solution; 13 g of phosphoric acid was added to the mixture solution, and stirred at 65° C. for 4 hours, and then 2.4 g of TEOS was added, and stirring was continued for 2 hours to obtain an initial gel mixture of SAPO-34 molecular sieve; the molar ratio of each component in the gel mixture was

[0038] SiO2:Al2O3:P2O5:TEAOH:H2O=0.15:0.8:1:2.0:50; the gel mixture was loaded into a polytetrafluoroethylene reactor, and then fixed in a rotary oven and crystallized at 115°C for 80 hours; after the crystallization, the hydrothermal reactor was quickly cooled down, the solid product was separated by centrifugation, the solid product was washed with deionized water until neutral, and then dried at 80°C to obtain SAPO-34 molecular sieve raw powder; the SAP0-34 molecular sieve raw powder was calcined at 650°C for 10 hours to remove the template contained in the raw powder, and Si / (Si+A1+P)=0.01, the average particle size is 40-500nm, and the thickness is 10-30nm. Nano-sheet SAPO-34 molecular sieve.

[0039] Example 5

[0040] 7.2 g of pseudo-boehmite was added to a mixture of 46.8 g of TEAOH and 11 g of water, and stirred at 40° C. for 2 hours to obtain a uniform mixture solution; 13 g of phosphoric acid was added to the mixture solution, and stirred at 65° C. for 4 hours, and then 0.5 g of white carbon black was added, and stirring was continued for 2 hours to obtain an initial gel mixture of SAPO-34 molecular sieve; the molar ratio of each component in the gel mixture was

[0041] SiO2:Al2O3:P2O5:TEAOH:H2O=0.15:0.8:1:2.0:50; the gel mixture was loaded into a polytetrafluoroethylene reactor, and then fixed in a rotary oven and crystallized at 115°C for 80 hours; after the crystallization, the hydrothermal reactor was quickly cooled down, the solid product was separated by centrifugation, the solid product was washed with deionized water until neutral, and then dried at 80°C to obtain SAPO-34 molecular sieve raw powder; the SAP0-34 molecular sieve raw powder was calcined at 650°C for 10 hours to remove the template contained in the raw powder, and Si / (Si+A1+P)=0.002, the average particle size is 40-500nm, and the thickness is 10-30nm. Nano-sheet SAPO-34 molecular sieve.

[0042] Example 6

[0043] 7.2 g of pseudo-boehmite was added to a mixture of 23.4 g of TEAOH and 35 g of TEA, and stirred at 40°C for 2 hours to obtain a uniform mixture solution; 13 g of phosphoric acid was added to the mixture solution, and stirred at 65°C for 4 hours, and then 1.7 g of silica sol was added, and stirring was continued for 2 hours to obtain an initial gel mixture of SAPO-34 molecular sieve; the molar ratio of each component in the gel mixture was

[0044] SiO2:Al2O3:P2O5:(TEAOH+TEA):H2O=0.15:0.8:1:(1+1):50; the gel mixture was loaded into a polytetrafluoroethylene reactor, and then fixed in a rotary oven and crystallized at 115°C for 80h; after the crystallization, the hydrothermal reactor was cooled rapidly, the solid product was separated by centrifugation, the solid product was washed with deionized water until neutral, and then dried at 80°C to obtain SAPO-34 molecular sieve raw powder; the SAP0-34 molecular sieve raw powder was calcined at 650°C for 10h to remove the template contained in the raw powder, and a nano-sheet SAPO-34 molecular sieve with Si / (Si+A1+P)=0.007, an average particle size of 40-500nm, and a thickness of 10-30nm was obtained.

[0045] Comparative Example 1

[0046] 7.2 g of pseudo-boehmite was added to a mixture of 46.8 g of TEAOH and 11 g of water, and stirred at 40° C. for 2 hours to obtain a uniform mixture solution; 13 g of phosphoric acid was added to the mixture solution, and stirred at 65° C. for 4 hours, and then 2.4 g of TEOS was added, and stirring was continued for 2 hours to obtain an initial gel mixture of SAPO-34 molecular sieve; the molar ratio of each component in the gel mixture was

[0047] SiO2:Al2O3:P2O5:TEAOH:H2O=0.15:0.8:1:2.0:50; the gel mixture was loaded into a polytetrafluoroethylene reactor, and then fixed in a rotary oven, and crystallized at 150°C for 60 hours; after the crystallization, the hydrothermal reactor was quickly cooled down, and the solid product was separated by centrifugation, and the solid product was washed with deionized water until neutral, and then dried at 80°C to obtain SAPO-34 molecular sieve raw powder; the SAP0-34 molecular sieve raw powder was calcined at 650°C for 10 hours to remove the template contained in the raw powder, and Si / (Si+A1+P)=0.02, the average particle size is 40-500nm, and the thickness is 10-30nm. Nano-sheet SAPO-34 molecular sieve.

[0048] Comparative Example 2

[0049] 7.2 g of pseudo-boehmite was added to a mixture of 46.8 g of TEAOH and 11 g of water, and stirred at 40° C. for 2 hours to obtain a uniform mixture solution; 13 g of phosphoric acid was added to the mixture solution, and stirred at 65° C. for 4 hours, and then 2.4 g of TEOS was added, and stirring was continued for 2 hours to obtain an initial gel mixture of SAPO-34 molecular sieve; the molar ratio of each component in the gel mixture was

[0050] SiO2:Al2O3:P2O5:TEAOH:H2O=0.15:0.8:1:2.0:50; the gel mixture was loaded into a polytetrafluoroethylene reactor, and then fixed in a rotary oven and crystallized at 180°C for 30 hours; after the crystallization, the hydrothermal reactor was quickly cooled down, the solid product was separated by centrifugation, the solid product was washed with deionized water until neutral, and then dried at 80°C to obtain SAPO-34 molecular sieve raw powder; the SAP0-34 molecular sieve raw powder was calcined at 650°C for 10 hours to remove the template contained in the raw powder, and Si / (Si+A1+P)=0.03, the average particle size is 40-500nm, and the thickness is 10-30nm. Nano-sheet SAPO-34 molecular sieve.

[0051] Example 7

[0052] We conducted elemental analysis and nitrogen adsorption test on the eight samples obtained from Examples 1 to 6 and Comparative Examples 1 to 2, and the results are shown in Table 1. It can be seen from Table 1 that the eight samples all have a relatively high specific surface area.

[0053] At the same time, the 8 samples obtained in Examples 1-6 and Comparative Examples 1-2 were tableted and crushed to 20-40 mesh. 0.3 g of the sample was weighed and loaded into a stainless steel reaction tube with an inner diameter of 8 mm, fixed on a fixed bed reactor, and the reaction temperature and gas flow rate were controlled by a program temperature rising device and a flow rate control device during the reaction to perform MTO evaluation. Nitrogen was activated at 500°C for 2.0 hours, then cooled to 400°C, methanol was carried by nitrogen, the nitrogen flow rate was 15 mL / min, and the methanol mass space velocity was 2.0 h -1 , the reaction pressure is 0.25MPa. The obtained product was analyzed by online gas chromatography (Agilcnt7890), and the results are shown in Table 1. From Table 1, it can be seen that all 6 samples of the embodiment have extremely high catalytic life, and the total yield of ethylene and propylene exceeds 88%. , while the life and total yield of ethylene and propylene of the 2 samples of the comparative example are lower than those of the embodiment. Table 1: Skeleton element composition, specific surface area (BET) and MTO reaction test results of the samples synthesized in each embodiment and comparative example

[0054]

[0055] Note: The selectivity and yield in the table are statistical results before the end of the reaction life and when the conversion rate is 100%.

[0056] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing low-silicon nano-sheet SAPO-34 molecular sieve, characterized in that : The low-silicon nano-sheet SAPO-34 molecular sieve has both low silicon content and small-size nano-sheet morphology, wherein the silicon content is Si / (Si+A1+P)=0.0015-0.010 in terms of atomic ratio, the average particle size of the molecular sieve is 40-500nm, and the thickness is 10-30nm; the molecular sieve exhibits extremely high selectivity for low-carbon olefins in the methanol to olefins reaction, the total yield of ethylene and propylene reaches more than 88%, and the stability is excellent; The preparation method of the low-silicon nano-sheet SAPO-34 molecular sieve comprises the following steps: 1) adding the aluminum source to the mixed system of the template and water, stirring at 20-40° C. for 1-4 hours to obtain a uniform mixture solution; 2) adding a phosphorus source to the above mixture solution, stirring at 40-65° C. for 4-6 hours, then adding a silicon source, and continuing stirring for 2-4 hours to obtain an initial gel mixture of SAPO-34 molecular sieve; 3) placing the gel mixture obtained in step 2) into a polytetrafluoroethylene reactor, and then fixing it in a rotary oven for low-temperature crystallization; the crystallization temperature is 100-115° C.; 4) After the crystallization is completed, the hydrothermal autoclave is cooled rapidly, the solid product is separated by centrifugation, the solid product is washed with deionized water until it is neutral, and then dried at 80-120° C. to obtain SAPO-34 molecular sieve raw powder; 5) The SAPO-34 molecular sieve raw powder is calcined at high temperature to remove the template contained in the raw powder, thereby obtaining a SAPO-34 molecular sieve with low silicon and nano-sized flake morphology.

2. The preparation method according to claim 1, characterized in that : The molar ratio of the oxide, template and water components in the initial gel mixture is SiO2:Al2O3:P2O5:template:H2O=0.01-0.2:1:0.8-1.2:1.5-2.5:20-60; in the initial gel mixture, the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the phosphorus source is calculated as P2O5.

3. The preparation method according to claim 1, characterized in that : The silicon source is at least one of silica sol, tetraethyl orthosilicate, sodium silicate, white carbon black, and activated silica; the aluminum source is at least one of aluminum oxide, pseudo-boehmite, aluminum isopropoxide, and aluminum hydroxide; the template is at least one of tetraethylammonium hydroxide (TEAOH) aqueous solution, triethylamine (TEA), and morpholine (MOR); the phosphorus source is selected from at least one of phosphoric acid, phosphate, phosphite, and tributyl phosphate.

4. The preparation method according to claim 1, characterized in that : In step 3), the rotation speed of the oven is set to 30-60r / min and the crystallization time is set to 60-120h.

5. The preparation method according to claim 1, characterized in that : In step 5), the calcination temperature is 500-650°C and the calcination time is 6-12h.

6. Use of the low-silicon nanosheet SAPO-34 molecular sieve prepared by the preparation method according to any one of claims 1 to 5 in the methanol to light olefin reaction.

7. The use according to claim 6, characterized in that :Reaction pressure is 0.1-0.4MPa, space velocity is 1-3h -1 , the reaction temperature is 400-550℃.

Images