Ni-doped ZSM-5 molecular sieve as well as preparation method and application thereof

Abstract

The invention provides a Ni-doped ZSM-5 molecular sieve, which is a spherical aggregate with a size of 0.5-5 [mu] m formed by molecular sieve nanocrystals with a size of not more than 50 nm, the molar ratio of SiO2 / Al2O3 is 20-50, and the doping amount of Ni is 0.2-1.5 wt.% based on the mass of NiO. The invention also provides a preparation method and application of the Ni-doped ZSM-5 molecular sieve. The invention further provides a method for preparing aviation kerosene through low-carbon olefin oligomerization. The Ni-doped ZSM-5 molecular sieve provided by the invention is a micron-sized spherical aggregate formed by nano-sized crystals, is very suitable for being used as a catalyst for low-carbon olefin oligomerization reaction, not only can obtain excellent catalytic performance, but also can reduce carbon deposition and prolong the service life of the catalyst, so that the Ni-doped ZSM-5 molecular sieve has good industrial practicability.

Description

Technical Field

[0001] This invention relates to the field of industrial catalysts, specifically to a Ni-doped ZSM-5 molecular sieve, its preparation method and uses, and also to a method for preparing aviation kerosene by oligomerization of low-carbon olefins. Background Technology

[0002] Sustainable aviation fuel (SAF) is key to achieving net-zero carbon emissions in the global aviation industry. Compared to conventional aviation fuel, SAF can reduce greenhouse gas emissions by 88%. SAF can be blended with conventional aviation fuel and serves as a direct alternative to petroleum-based aviation fuels without requiring any modifications to aircraft technology or fuel infrastructure. The global SAF market is projected to exceed 18 million tons by 2030, valued at tens of billions of US dollars. Currently priced at around 20,000 yuan per ton, it has a very promising market outlook.

[0003] Aviation kerosene is characterized by a distillation range between naphtha and diesel, and a relatively concentrated carbon number (C8-C16). To ensure the safety of aircraft engines, it also has a high freezing point requirement (not exceeding -40°C). Furthermore, it contains 8-20% aromatics. Currently, the main production routes for aviation kerosene include the oil and fat hydrogenation route, the ATJ (Automatic Air Jet) route, and the biomass gasification-Fischer-Tropsch route, all of which have obtained international certification. The aviation kerosene fractions obtained from these synthetic routes are mainly composed of straight-chain / branched alkanes, which do not meet aviation kerosene standards and must be blended with petroleum-based products. In May 2023, Honeywell announced the launch of UOP eFining, a mature solution for producing low-carbon, sustainable aviation fuel. TM The technology involves synthesizing methanol using green hydrogen and carbon dioxide. The methanol is then further converted into C2-C5 low-carbon olefins via a molecular hydrogenation (MTO) process. These low-carbon olefins undergo a simplified cryogenic separation process and are then further converted into various sustainable fuels, including SAF, gasoline, and diesel, through oligomerization. This method received international certification at the end of 2023. The oligomerization of low-carbon olefins is a crucial step, and the catalysts used are generally ZSM-5 molecular sieves or Ni-doped ZSM-5 molecular sieves as the active component. However, due to the acidity of the molecular sieve, these catalysts inevitably experience carbon buildup during use, which clogs the pores and causes deactivation, affecting the catalyst's lifespan. This necessitates carbon burning for regeneration, significantly impacting the process complexity and carbon utilization rate. Carbon buildup is mainly related to the diffusion of reactant and product molecules within the molecular sieve crystal pores; the longer the diffusion path, the easier it is for carbon buildup and deactivation to occur.

[0004] Chinese patent CN 104649295A discloses the preparation and application of hierarchical porous ZSM-5 zeolite molecular sieve aggregates. The characteristic of these molecular sieve aggregates is the addition of seed crystals prepared with tetrapropylammonium hydroxide as a guiding agent to a silica-alumina sol gel synthesized from inorganic aluminum and inorganic silicon sources. The resulting molecular sieve aggregates retain the activity of monodisperse nanoparticles but exhibit an aggregate morphology. However, the basic crystals of the aggregates obtained in this patent only barely maintain a thickness of 50–100 nm, while their length is already at the submicron level, thus failing to fundamentally solve the problem of carbon deposition and deactivation.

[0005] Therefore, there is an urgent need to develop a ZSM-5 molecular sieve catalyst with high catalytic activity and long service life to improve the production efficiency of aviation fuel and expand its production and application. Summary of the Invention

[0006] To overcome the shortcomings of the existing technology, one object of the present invention is to provide a Ni-doped ZSM-5 molecular sieve, which has a special aggregate morphology and can achieve excellent catalytic performance and significantly extend service life when used as a catalyst, thus having good industrial application value.

[0007] Another object of the present invention is to provide a method for preparing the Ni-doped ZSM-5 molecular sieve and its uses.

[0008] Another object of the present invention is to provide a method for preparing aviation kerosene by oligomerization of low-carbon olefins.

[0009] The first aspect of the present invention provides a Ni-doped ZSM-5 molecular sieve, which is a spherical aggregate with a size of 0.5 to 5 μm formed from molecular sieve nanocrystals with a size not exceeding 50 nm, a SiO2 / Al2O3 molar ratio of 20 to 50, and a Ni doping amount of 0.2 to 1.5 wt.% based on the mass of NiO.

[0010] like Figure 1 and Figure 2 As shown, the Ni-doped ZSM-5 molecular sieve provided by this invention is a micron-sized spherical aggregate formed from nanoscale molecular sieve crystals. The molecular sieve crystals have a three-dimensional size not exceeding 50 nm, significantly shortening the diffusion path of substances within the crystal channels, thus reducing the likelihood of clogging and deactivation. Furthermore, the micron-sized macroscopic structure of the Ni-doped ZSM-5 molecular sieve provided by this invention overcomes the difficulty in separating nanoscale crystals. When used in the oligomerization reaction of low-carbon olefins, the Ni-doped ZSM-5 molecular sieve provided by this invention achieves excellent catalytic performance, significantly improving both feed conversion rate and target product selectivity, and also greatly extending its service life.

[0011] The "size" mentioned in this invention refers to "three-dimensional size", including length, width and height.

[0012] In some preferred embodiments, the Ni-doped ZSM-5 molecular sieve provided by the present invention can be further formed into spherical aggregates with a size of 1 to 3 μm from molecular sieve nanocrystals with a size of 20 to 50 nm.

[0013] In some preferred embodiments, the molar ratio of SiO2 / Al2O3 in the Ni-doped ZSM-5 molecular sieve provided by the present invention can be 25 to 35, and the doping amount of Ni can be 0.8 to 1.2 wt.% based on the mass of NiO (the doping amount mentioned in the present invention refers to the mass percentage relative to the total mass of the Ni-doped ZSM-5 molecular sieve).

[0014] A second aspect of the present invention provides a method for preparing Ni-doped ZSM-5 molecular sieves according to any one of the above-described technical solutions, comprising the following steps:

[0015] S1: An inducing agent is prepared by mixing an aqueous solution of a neutral silica sol with a pH of 6.5–7.5 and a quaternary ammonium base template agent and then subjecting the mixture to hydrothermal crystallization; and

[0016] S2: In the presence of polyethylene glycol and the aforementioned inducing agent, Ni-doped ZSM-5 molecular sieves are prepared via a hydrothermal method using silicon, nickel, and aluminum sources as raw materials, wherein the silicon source is silica with a specific surface area of ​​150–250 m² / g. 2 / g (for example, it can be 180-220m) 2 / g), with an average particle size of 6–15 nm (for example, it can be 10–12 nm).

[0017] As mentioned above, the method described in Chinese Patent CN 104649295A cannot obtain nano-sized crystals in all three dimensions. By selecting specific silicon materials (including silicon materials used in the preparation of inducing agents and silicon materials used in the preparation of molecular sieves), the inventors are able to prepare molecular sieve crystals in all three dimensions. The addition of the surfactant polyethylene glycol can also promote the formation of molecular sieve aggregates, thereby obtaining the molecular sieve aggregates with the special morphology described in this invention.

[0018] In the preparation method provided by this invention, the neutral silica sol used can be of a type commonly found in the art. In some preferred embodiments, the neutral silica sol used has a SiO2 content of 25–35 wt.% (e.g., 30 wt.%), a pH value of approximately 7, and a Na2O content of ≤0.1 wt.%.

[0019] In the preparation method provided by this invention, the quaternary ammonium base template agent used can be of a type commonly found in the art, such as tetraalkylammonium hydroxide, including but not limited to one or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide. In some preferred embodiments, the quaternary ammonium base template agent used can be tetrapropylammonium hydroxide.

[0020] In the preparation method provided by the present invention, the content of the template agent in the aqueous solution of the quaternary ammonium base template agent can be 20-30 wt.% (for example, 25 wt.%).

[0021] In the preparation method provided by this invention, the mass ratio of the neutral silica sol to the quaternary ammonium base template agent, based on the mass of SiO2, can be 1:0.1 to 0.5, for example, about 1:0.1, about 1:0.15, about 1:0.2, about 1:0.25, about 1:0.3, about 1:0.35, about 1:0.4, about 1:0.45, about 1:0.5, or any mass ratio range. In some preferred embodiments, the mass ratio of the neutral silica sol to the quaternary ammonium base template agent can be 1:0.2 to 0.35.

[0022] In the preparation method provided by the present invention, the hydrothermal crystallization temperature in step S1 can be 80–120°C, and the hydrothermal crystallization time can be 10–40 h. In some preferred embodiments, the hydrothermal crystallization temperature in step S1 can be 95–110°C, and the hydrothermal crystallization time can be 20–30 h.

[0023] In the preparation method provided by the present invention, step S2 may further include the following steps:

[0024] S201: Prepare an aqueous solution by mixing the silicon source, nickel source, aluminum source, polyethylene glycol and inducing agent, and perform hydrothermal crystallization at 100-200°C for 20-60 hours to obtain a wet molecular sieve material;

[0025] S202: Ion exchange of the wet molecular sieve material with sulfuric acid solution; and

[0026] S203: The Ni-doped ZSM-5 molecular sieve is obtained by drying and calcining the ion-exchanged material.

[0027] In the preparation method provided by the present invention, the aluminum source can be one or more of sodium aluminate and aluminum isopropoxide.

[0028] In the preparation method provided by this invention, the nickel source can be one or more of nickel nitrate, nickel acetate, nickel sulfate, and their respective hydrates. In some preferred embodiments, the nickel source can be a hydrate of nickel nitrate.

[0029] In the preparation method provided by this invention, the average molecular weight of the polyethylene glycol can be 200-2000. In some preferred embodiments, the polyethylene glycol can be one or more of PEG400, PEG800, and PEG2000.

[0030] In the preparation method provided by the present invention, the content of the inducing agent in the aqueous solution of step S201 can be 1 to 10 wt.%, for example, it can be about 1 wt.%, about 2 wt.%, about 3 wt.%, about 4 wt.%, about 5 wt.%, about 6 wt.%, about 7 wt.%, about 8 wt.%, about 9 wt.%, about 10 wt.%, or any mass percentage range.

[0031] In the preparation method provided by the present invention, the content of polyethylene glycol in the aqueous solution of step S201 can be 1 to 10 wt.%, for example, it can be about 1 wt.%, about 2 wt.%, about 3 wt.%, about 4 wt.%, about 5 wt.%, about 6 wt.%, about 7 wt.%, about 8 wt.%, about 9 wt.%, about 10 wt.%, or any mass percentage range.

[0032] In the preparation method provided by the present invention, the content of the silicon source in the aqueous solution of step S201 can be 15-25 wt.%, for example, it can be about 15 wt.%, about 16 wt.%, about 17 wt.%, about 18 wt.%, about 19 wt.%, about 20 wt.%, about 21 wt.%, about 22 wt.%, about 23 wt.%, about 24 wt.%, about 25 wt.%, or any mass percentage range.

[0033] In the preparation method provided by this invention, the ratio of the silicon source, nickel source, and aluminum source can be adjusted according to the desired silicon-to-aluminum ratio, nickel doping amount, and other conditions of the target product. For example, the mass ratio of the silicon source, nickel source, and aluminum source can be 1:0.01–0.08:0.01–0.12. In some preferred embodiments, the mass ratio of the silicon source, nickel source, and aluminum source can be 1:0.02–0.05:0.06–0.1.

[0034] In the preparation method provided by the present invention, the concentration of the sulfuric acid solution can be 1 to 10 wt.%, for example, 3 to 6 wt.%.

[0035] In the preparation method provided by the present invention, the temperature of the ion exchange can be 60-100℃, for example, 80-90℃.

[0036] In the preparation method provided by this invention, the drying temperature can be 100–150°C, and the drying time can be 1–10 h. In some preferred embodiments, the drying temperature can be 100–120°C, and the drying time can be 1–4 h.

[0037] In the preparation method provided by this invention, the calcination temperature can be 500–650°C, and the calcination time can be 1–10 h. In some preferred embodiments, the calcination temperature can be 500–600°C, and the calcination time can be 2–5 h.

[0038] In the preparation method provided by the present invention, the desired material can be obtained through a separation step, such as separating the wet molecular sieve material after hydrothermal crystallization. The separation equipment or method can be common in the field, including but not limited to natural sedimentation, (atmospheric pressure or vacuum) filtration, centrifugation and other common equipment.

[0039] In the preparation method provided by this invention, the washing step refers to washing the material with distilled water or deionized water until the surface of the material is close to or neutral. The number of washing times can be adjusted according to the actual situation, for example, it can be 2 to 5 times, and usually it can be 3 times.

[0040] In the preparation method provided by this invention, room temperature refers to 25±5℃.

[0041] A third aspect of the present invention provides the use of the Ni-doped ZSM-5 molecular sieve described in any of the above-mentioned technical solutions as a catalyst.

[0042] The Ni-doped ZSM-5 molecular sieve provided by this invention can significantly reduce carbon deposition in the molecular sieve, thereby improving catalyst lifetime. Therefore, it is very suitable for catalyzing the oligomerization reaction of C3-C6 low-carbon olefins (such as one or more of propylene, butene, and pentene) to prepare aviation kerosene.

[0043] A fourth aspect of the present invention provides a method for preparing aviation kerosene by oligomerization of low-carbon olefins. The method involves carrying out an oligomerization reaction of low-carbon olefins (such as one or more of propylene, butene, and pentene) from C3 to C6 in the presence of a catalyst, thereby obtaining aviation kerosene. The catalyst is Ni-doped ZSM-5 molecular sieve as described in any of the above technical solutions.

[0044] The technical solution provided by this invention has the following advantages:

[0045] (1) The Ni-doped ZSM-5 molecular sieve provided by the present invention has a special morphology, which is a micron-sized spherical aggregate formed by nano-sized crystals. It is very suitable as a catalyst for the oligomerization reaction of low-carbon olefins. It can not only achieve excellent catalytic performance, but also significantly reduce carbon deposition and extend the service life of the catalyst.

[0046] (2) Compared with dispersed nanocrystals, the Ni-doped ZSM-5 molecular sieve provided by the present invention is easier to separate from the reaction system as a micron-sized aggregate, which helps to reduce the process difficulty of the catalytic reaction and improve production efficiency.

[0047] (3) The Ni-doped ZSM-5 molecular sieve preparation process provided by the present invention is simple and highly operable, and does not require expensive reagents. Compared with the mode of directly adding template agents to the molecular sieve synthesis system, the "inducer" mode of the present invention can effectively reduce the amount of template agents used, thus having good industrial applicability and being suitable for large-scale production and application.

[0048] (4) The method for preparing aviation kerosene by low-carbon olefin oligomerization provided by the present invention has ideal raw material conversion rate and target product yield, thus it can significantly improve the production efficiency of aviation kerosene and reduce its production cost, providing a good foundation for expanding the production and application of sustainable aviation fuel. Attached Figure Description

[0049] Figure 1 Here is a SEM image of the molecular sieve material prepared in Example 1;

[0050] Figure 2 Here is a magnified SEM image of the molecular sieve material prepared in Example 1;

[0051] Figure 3 SEM image of the molecular sieve material prepared in Comparative Example 1;

[0052] Figure 4 SEM image of the molecular sieve material prepared in Comparative Example 2;

[0053] Figure 5 SEM image of the molecular sieve material prepared in Comparative Example 3;

[0054] Figure 6 SEM image of the molecular sieve material prepared in Comparative Example 4;

[0055] Figure 7 SEM image of the molecular sieve material prepared in Comparative Example 5;

[0056] Figure 8 The image shows the SEM image of the molecular sieve material prepared in Comparative Example 6. Detailed Implementation

[0057] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0058] Unless otherwise specified, all raw materials or reagents used in the embodiments and comparative examples of this invention are commercially available products, and all percentages used are mass percentages unless otherwise specified.

[0059] In the embodiments and comparative examples of the present invention, the crystal morphology of the molecular sieve was analyzed by scanning electron microscopy (purchased from FEI, model Nova Nano SEM 450); the composition of the catalyst was determined by Rigaku ZSXPrimus II X-ray fluorescence spectrometer (XRF).

[0060] Example 1

[0061] (1) Preparation of inducing agents

[0062] 30g of neutral silica sol (SiO2 content 30wt.%, pH=7, Na2O content ≤0.1%) and 10g of tetrapropylammonium hydroxide solution (concentration 25wt.%) were added to a beaker and stirred at room temperature for 1h to form a homogeneous sol. The obtained sol was then placed in a sealed reaction vessel and crystallized at 100℃ for 24h. After cooling, the sol was transferred to a beaker to obtain an inducing agent for later use.

[0063] (2) Preparation of molecular sieves

[0064] 30g of silica (average particle size 12nm, specific surface area 200m²) was used. 2 1.2g Ni(NO3)2˙6H2O, 2.5g sodium aluminate, 5g polyethylene glycol 400, and 100g deionized water were added to a beaker and stirred at room temperature for 1 hour to form a homogeneous sol. 4.2g of inducing agent was added to the sol, and stirring was continued for 2 hours. The resulting sol was then placed in a sealed reactor and crystallized at 180°C for 48 hours. The crystallized mixture was filtered, and the resulting solid was washed with deionized water at room temperature to obtain a wet molecular sieve. The wet molecular sieve was mixed with 300g of 5wt.% dilute sulfuric acid and stirred at 80°C for 1 hour for ion exchange. The resulting material was then filtered, washed, dried at 120°C for 2 hours, and then calcined at 550°C for 3 hours to obtain the molecular sieve material.

[0065] The microstructure of the molecular sieve material was observed using SEM, such as... Figure 1 and Figure 2 As shown. (Through) Figure 1 and Figure 2 It can be determined that the molecular sieve material is a micron-sized aggregate composed of crystals with a diameter of 30–50 nm. XRF analysis shows that the SiO2 / Al2O3 ratio of the molecular sieve material is 30 (molar ratio), and the NiO content is 1.0 wt.%.

[0066] Example 2

[0067] (1) Preparation of inducing agents

[0068] 30g of neutral silica sol (SiO2 content 30wt.%, pH=7, Na2O content ≤0.1%) and 10g of tetraethylammonium hydroxide solution (concentration 25wt.%) were added to a beaker and stirred at room temperature for 1h to form a homogeneous sol. The obtained sol was then placed in a sealed reaction vessel and crystallized at 80℃ for 40h. After cooling, the sol was transferred to a beaker to obtain an inducing agent for later use.

[0069] (2) Preparation of molecular sieves

[0070] 30g of silica (average particle size 15nm, specific surface area 150m²) was used. 2 1.0 g Ni(CH3COO)2˙4H2O, 6.23 g aluminum isopropoxide, 5 g polyethylene glycol 800, and 100 g deionized water were added to a beaker and stirred at room temperature for 1 h to form a homogeneous sol. 1.5 g of inducing agent was added to the sol, and stirring was continued for 2 h. The resulting sol was then placed in a sealed reactor and crystallized at 100 °C for 60 h. The crystallized mixture was filtered, and the resulting solid was washed with deionized water at room temperature to obtain a wet molecular sieve. The wet molecular sieve was mixed with 300 g of 5 wt.% dilute sulfuric acid and stirred at 60 °C for 1 h for ion exchange. The resulting material was then filtered, washed, dried at 120 °C for 2 h, and then calcined at 650 °C for 1 h to obtain the molecular sieve material.

[0071] The microstructure of the molecular sieve material was observed using SEM. Similar to Example 1, the material consisted of micron-sized aggregates composed of crystals ranging from 30 to 50 nm in size. XRF analysis showed that the SiO2 / Al2O3 ratio of the molecular sieve material was 30 (molar ratio), and the NiO content was 1.0 wt.%.

[0072] Example 3

[0073] (1) Preparation of inducing agents

[0074] 30g of neutral silica sol (SiO2 content 30wt.%, pH=7, Na2O content ≤0.1%) and 10g of tetrabutylammonium hydroxide solution (concentration 25wt.%) were added to a beaker and stirred at room temperature for 1h to form a homogeneous sol. The obtained sol was then placed in a sealed reaction vessel and crystallized at 120℃ for 10h. After cooling, the sol was transferred to a beaker to obtain an inducing agent for later use.

[0075] (2) Preparation of molecular sieves

[0076] 30g of silica (average particle size 6nm, specific surface area 250m²) was used. 20.64 g NiSO4, 6.23 g aluminum isopropoxide, 5 g polyethylene glycol 2000, and 100 g deionized water were added to a beaker and stirred at room temperature for 1 h to form a homogeneous sol. 8.5 g of inducing agent was added to the sol, and stirring was continued for 2 h. The resulting sol was then placed in a sealed reactor and crystallized at 200 °C for 20 h. The crystallized mixture was filtered, and the resulting solid was washed with deionized water at room temperature to obtain a wet molecular sieve. The wet molecular sieve was mixed with 300 g of 5 wt.% dilute sulfuric acid and stirred at 100 °C for 1 h for ion exchange. The resulting material was then filtered, washed, dried at 120 °C for 2 h, and then calcined at 500 °C for 10 h to obtain the molecular sieve material.

[0077] The microstructure of the molecular sieve material was observed using SEM. Similar to Example 1, the material consisted of micron-sized aggregates composed of crystals ranging from 30 to 50 nm in size. XRF analysis showed that the SiO2 / Al2O3 ratio of the molecular sieve material was 30 (molar ratio), and the NiO content was 1.0 wt.%.

[0078] Example 4

[0079] (1) Preparation of inducing agents

[0080] 30g of neutral silica sol (SiO2 content 30wt.%, pH=7, Na2O content ≤0.1%) and 10g of tetrapropylammonium hydroxide solution (concentration 25wt.%) were added to a beaker and stirred at room temperature for 1h to form a homogeneous sol. The obtained sol was then placed in a sealed reaction vessel and crystallized at 100℃ for 24h. After cooling, the sol was transferred to a beaker to obtain an inducing agent for later use.

[0081] (2) Preparation of molecular sieves

[0082] 30g of silica (average particle size 12nm, specific surface area 200m²) was used. 2 1.8 g Ni(NO3)2˙6H2O, 3.5 g sodium aluminate, 5 g polyethylene glycol 400, and 100 g deionized water were added to a beaker and stirred at room temperature for 1 h to form a homogeneous sol. 4.2 g of inducing agent was added to the sol, and stirring was continued for 2 h. The resulting sol was then placed in a sealed reactor and crystallized at 180 °C for 48 h. The crystallized mixture was filtered, and the resulting solid was washed with deionized water at room temperature to obtain a wet molecular sieve. The wet molecular sieve was mixed with 300 g of 5 wt.% dilute sulfuric acid and stirred at 80 °C for 1 h for ion exchange. The resulting material was then filtered, washed, dried at 120 °C for 2 h, and then calcined at 550 °C for 3 h to obtain the molecular sieve material.

[0083] The microstructure of the molecular sieve material was observed using SEM. Similar to Example 1, the material consisted of micron-sized aggregates composed of crystals ranging from 30 to 50 nm in size. XRF analysis showed that the SiO2 / Al2O3 ratio of the molecular sieve material was 20 (molar ratio), and the NiO content was 1.5 wt.%.

[0084] Example 5

[0085] (1) Preparation of inducing agents

[0086] 30g of neutral silica sol (SiO2 content 30wt.%, pH=7, Na2O content ≤0.1%) and 10g of tetrapropylammonium hydroxide solution (concentration 25wt.%) were added to a beaker and stirred at room temperature for 1h to form a homogeneous sol. The obtained sol was then placed in a sealed reaction vessel and crystallized at 100℃ for 24h. After cooling, the sol was transferred to a beaker to obtain an inducing agent for later use.

[0087] (2) Preparation of molecular sieves

[0088] 30g of silica (average particle size 12nm, specific surface area 200m²) was used. 2 0.25g Ni(NO3)2˙6H2O, 1.5g sodium aluminate, 5g polyethylene glycol 400, and 100g deionized water were added to a beaker and stirred at room temperature for 1 hour to form a homogeneous sol. 4.2g of inducing agent was added to the sol, and stirring was continued for 2 hours. The resulting sol was then placed in a sealed reactor and crystallized at 180°C for 48 hours. The crystallized mixture was filtered, and the resulting solid was washed with deionized water at room temperature to obtain a wet molecular sieve. The wet molecular sieve was mixed with 300g of 5wt.% dilute sulfuric acid and stirred at 80°C for 1 hour for ion exchange. The resulting material was then filtered, washed, dried at 120°C for 2 hours, and then calcined at 550°C for 3 hours to obtain the molecular sieve material.

[0089] The microstructure of the molecular sieve material was observed using SEM. Similar to Example 1, the material consisted of micron-sized aggregates composed of crystals ranging from 30 to 50 nm in size. XRF analysis showed that the SiO2 / Al2O3 ratio of the molecular sieve material was 50 (molar ratio), and the NiO content was 0.2 wt.%.

[0090] Comparative Example 1

[0091] Except for the absence of an inducing agent, the other steps are the same as in Example 1 to prepare molecular sieve materials.

[0092] The microstructure of the molecular sieve material was observed using SEM, such as... Figure 3 As shown. (Through) Figure 3It can be determined that the molecular sieve material is a micron-sized crystal. XRF analysis shows that the SiO2 / Al2O3 ratio of the molecular sieve material is 30, and the NiO content is 1.0 wt.%.

[0093] Comparative Example 2

[0094] (1) Preparation of inducing agents

[0095] The inducing agent was prepared according to the method described in Chinese Patent CN 104649295A. 31g of tetraethyl orthosilicate and 10g of tetrapropylammonium hydroxide solution (concentration 25wt.%) were added to a beaker and stirred at room temperature for 3 hours to form a homogeneous sol. The resulting sol was then placed in a sealed reaction vessel and crystallized at 100℃ for 24 hours. After cooling, the sol was transferred to a beaker to obtain the inducing agent for later use.

[0096] (2) Preparation of molecular sieves

[0097] 100g of silica sol (SiO2 content 30wt.%, pH=7, Na2O content ≤0.1%), 1.2g of Ni(NO3)2˙6H2O, 6.5g of Al(NO3)3, and 100g of deionized water were added to a beaker and stirred at room temperature for 1h to form a homogeneous sol. 4.2g of inducing agent was added to the sol, and stirring was continued for 2h. The resulting sol was then placed in a sealed reactor and crystallized at 180℃ for 48h. The crystallized mixture was filtered, and the resulting solid was washed with deionized water at room temperature to obtain a wet molecular sieve. The wet molecular sieve was mixed with 300g of 5wt.% dilute sulfuric acid and stirred at 80℃ for 1h for ion exchange. The resulting material was then filtered, washed, dried at 120℃ for 2h, and then calcined at 550℃ for 3h to obtain the molecular sieve material.

[0098] The microstructure of the molecular sieve material was observed using SEM, such as... Figure 4 As shown. (Through) Figure 4 It can be determined that the molecular sieve material is a micron-sized aggregate composed of strip-shaped crystals, with crystal lengths reaching the 500–1000 nm level. XRF analysis shows that the SiO2 / Al2O3 ratio of this molecular sieve material is 30, and the NiO content is 1.0 wt.%.

[0099] Comparative Example 3

[0100] Except for using alkaline silica sol (SiO2 content of 30wt%, pH=9.5, Na2O content ≤0.4%) to replace neutral silica sol in the preparation of the inducing agent, the other steps are the same as in Example 1, and molecular sieve materials are prepared.

[0101] The microstructure of the molecular sieve material was observed using SEM, such as... Figure 5 As shown. (Through) Figure 5The molecular sieve material can be identified as micron-sized aggregates composed of 30–50 nm crystals, as well as large-diameter spherical and strip-shaped impurities. XRF analysis shows that the SiO2 / Al2O3 ratio of this molecular sieve material is 30, and the NiO content is 1.0 wt.%.

[0102] Comparative Example 4

[0103] Except for using acidic silica sol (SiO2 content of 30 wt.%, pH=3, Na2O content ≤0.01%) instead of neutral silica sol to prepare the inducing agent, the other steps are the same as in Example 1, and molecular sieve materials are prepared.

[0104] The microstructure of the molecular sieve material was observed using SEM, such as... Figure 6 As shown. (Through) Figure 6 It can be seen that the intergranular gaps between the nanocrystals constituting the molecular sieve aggregates are not obvious, and the aggregated microspheres are developing towards densification. XRF analysis shows that the SiO2 / Al2O3 ratio of this molecular sieve material is 30, and the NiO content is 1.0 wt.%.

[0105] Comparative Example 5

[0106] Except for using sodium silicate instead of silica to prepare molecular sieves (the amount used is the same based on the SiO2 content), the other steps are the same as in Example 1, and molecular sieve materials are prepared.

[0107] The microstructure of the molecular sieve material was observed using SEM, such as... Figure 7 As shown. (Through) Figure 7 It can be seen that the morphology of this molecular sieve material is irregular and lacks nanocrystalline aggregate structure. XRF analysis shows that the SiO2 / Al2O3 ratio of this molecular sieve material is 30, and the NiO content is 1.0 wt.%.

[0108] Comparative Example 6

[0109] Except for the absence of polyethylene glycol 400, the other steps are the same as in Example 1 to prepare molecular sieve materials.

[0110] The microstructure of the molecular sieve material was observed using SEM, such as... Figure 8 As shown. (Through) Figure 8 It can be seen that the nanocrystals constituting this molecular sieve aggregate are difficult to maintain, resulting in dense, nearly spherical aggregates of small crystals. XRF analysis shows that the SiO2 / Al2O3 ratio of this molecular sieve material is 30, and the NiO content is 1.0 wt.%.

[0111] Test case

[0112] The molecular sieve materials prepared in the examples and comparative examples were used as catalysts to evaluate catalyst performance through olefin oligomerization reactions.

[0113] The olefin oligomerization reaction evaluation device was purchased from Borui (Beijing) Technology Co., Ltd. The test method was as follows: 1g of catalyst was loaded into a stainless steel reaction tube; the reactant was pentene; the reaction temperature was 250℃; the pressure was 3.0MPa; and the weight hourly space velocity (WHSV) was 0.4h. -1 The test results are shown in Table 1.

[0114] Table 1 Evaluation results of olefin oligomerization reaction

[0115]

[0116]

[0117] pass Figures 1 to 8 As can be seen from the evaluation results in Table 1:

[0118] No inducing agent was added during the preparation of Comparative Example 1, resulting in large-particle-size molecular sieves with excessively long pore paths, leading to significantly lower selectivity and catalyst lifetime in olefin oligomerization reactions. Comparative Example 2, prepared using the method described in Chinese Patent CN104649295A with different silicon and aluminum sources, produced molecular sieves composed of aggregates of strip-shaped crystals. Because the molecular sieve crystals constituting these aggregates are nearly micron-sized strips, they cannot effectively reduce the diffusion path in olefin oligomerization reactions, resulting in significantly lower pentene conversion and catalyst lifetime compared to the examples. Comparative Examples 3 and 4 used alkaline silica sol and acidic silica sol, respectively. The preparation of inducing agents using neutral silica sol in Comparative Example 3 showed that the molecular sieve contained a large number of impurities, which affected the catalyst performance. The nanocrystal aggregates prepared in Comparative Example 4 were significantly denser than those in Example 1, failing to take advantage of the short diffusion path of small crystals, resulting in a significant reduction in catalyst lifetime. Comparative Example 5 used common sodium silicate as a silicon source to replace silica. The difference in chemical properties between the two led to a huge difference in the morphology of the synthesized molecular sieve, and the catalyst performance was significantly worse than that of the examples. Comparative Example 6 did not add polyethylene glycol as a surfactant, making it difficult to maintain the morphology of the nanocrystals constituting the aggregates, which also seriously affected the catalytic performance.

[0119] Unless otherwise specified, the terms used in this invention have the meanings commonly understood by those skilled in the art.

[0120] The embodiments described in this invention are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Those skilled in the art can make various other substitutions, changes and improvements within the scope of this invention. Therefore, this invention is not limited to the above embodiments, but is only defined by the claims.

Claims

1. A Ni-doped ZSM-5 molecular sieve characterized in that, The Ni-doped ZSM-5 molecular sieve is a spherical aggregate with a size of 0.5-5 μm formed by nanocrystals of the molecular sieve with a size of not more than 50 nm, the molar ratio of SiO2 / Al2O3 is 20-50, and the doping amount of Ni is 0.2-1.5 wt.%, based on the mass of NiO.

2. The Ni-doped ZSM-5 molecular sieve of claim 1, wherein, The Ni-doped ZSM-5 molecular sieve is a spherical aggregate with a size of 1-3 μm formed by nanocrystals of the molecular sieve with a size of 20-50 nm; and / or The Ni-doped ZSM-5 molecular sieve has a molar ratio of SiO2 / Al2O3 of 25-35, and a doping amount of Ni of 0.8-1.2 wt.%, based on the mass of NiO.

3. The method of making a Ni-doped ZSM-5 molecular sieve of claim 1 or 2, characterized in that, The method comprises the following steps: S1: mixing a neutral silica sol with a pH value of 6.5-7.5 and an aqueous solution of a quaternary ammonium base template agent, and performing hydrothermal crystallization to obtain an inducing agent; and S2: preparing a Ni-doped ZSM-5 molecular sieve by a hydrothermal method with a silicon source, a nickel source and an aluminum source as raw materials in the presence of polyethylene glycol and the inducing agent, wherein the silicon source is white carbon black with a specific surface area of 150-250 m 2 / g and an average particle size of 6-15 nm.

4. The production method according to claim 3, characterized by, The SiO2 content of the neutral silica sol is 25-35 wt.%; and / or The quaternary ammonium base template agent is one or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide, and the content of the quaternary ammonium base template agent in the aqueous solution is 20-30 wt.%; Preferably, the mass ratio of the neutral silica sol to the quaternary ammonium base template agent is 1:0.1-0.5, based on the mass of SiO2; More preferably, the hydrothermal crystallization temperature in step S1 is 80-120 ℃, and the hydrothermal crystallization time is 10-40 h.

5. The production method according to claim 3 or 4, characterized by, The step S2 comprises the following steps: S201: preparing an aqueous solution of the silicon source, the nickel source, the aluminum source, the polyethylene glycol, and the inducing agent, and performing hydrothermal crystallization at 100-200 ℃ for 20-60 h to obtain a wet molecular sieve; S202: ion exchanging the wet molecular sieve with a sulfuric acid solution; and S203: drying and calcining the ion-exchanged material to obtain the Ni-doped ZSM-5 molecular sieve.

6. The preparation method according to claim 5, characterized in that, The aluminum source is one or both of sodium metaaluminate and aluminum isopropoxide; and / or The nickel source is one or more of nickel nitrate, nickel acetate, nickel sulfate, and their respective hydrates; and / or The average molecular weight of the polyethylene glycol is 200-2000, and preferably, the polyethylene glycol is one or more of PEG400, PEG800, and PEG2000.

7. The production method according to claim 5 or 6, characterized by, The content of the inducing agent in the aqueous solution of step S201 is 1-10 wt.%; and / or The content of the polyethylene glycol is 1-10 wt.%; and / or The content of the silicon source is 15-25 wt.%; and / or Preferably, the mass ratio of the silicon source, the nickel source, and the aluminum source is 1:0.01-0.08:0.01-0.

12.

8. The production method according to any one of claims 5 to 7, characterized by, The concentration of the sulfuric acid solution is 1-10 wt.%; and / or The ion exchange temperature is 60-100 ℃; and / or The calcination temperature is 500-650 ℃, and the calcination time is 1-10 h.

9. Use of the Ni-doped ZSM-5 molecular sieve according to claim 1 or 2 as a catalyst; Preferably, the catalyst is used for catalyzing oligomerization of C3-C6 low-carbon olefins to prepare aviation kerosene; More preferably, the low-carbon olefins are one or more of propylene, butene, and pentene.

10. A method for the production of aviation kerosene by oligomerization of low carbon olefins, characterized in that, The present application discloses a method for preparing aviation kerosene by oligomerization of low carbon olefins (C3-C6) in the presence of a catalyst, wherein the catalyst is a Ni-doped ZSM-5 molecular sieve as claimed in claim 1 or 2. Preferably, the low carbon olefins are one or more of propylene, butylene and pentene.

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