A Ni-based catalyst, its preparation method, and its application in ethylene oligomerization.

Abstract

This invention discloses a Ni-based catalyst, its preparation method, and its application in the oligomerization reaction of ethylene, belonging to the field of catalyst synthesis technology. This invention uses ammonium niobate oxalate hydrate as the niobium source and adds an ammonium solution to the reaction system. Under ultrapure water as the solvent, a niobium oxide support with a nanorod morphology is synthesized. A metal nitrate is used as a supporting metal precursor, and the precursor is loaded onto the nanorod niobium oxide support using a wet impregnation method to obtain a catalyst precursor. The catalyst precursor is then heat-treated to obtain a nanorod niobium oxide-supported nickel-based catalyst. The nanorod niobium oxide-supported nickel-based catalyst prepared by this invention exhibits high 1-butene selectivity and ethylene conversion in the ethylene oligomerization reaction.

Description

Technical Field

[0001] This invention belongs to the field of catalyst synthesis technology, specifically relating to a Ni-based catalyst, its preparation method, and its application in ethylene oligomerization. Background Technology

[0002] Linear-chain α-olefins (LAOs), including 1-butene, 1-hexene, and 1-octene, are widely used in the synthesis of ethylene comonomers (C4-6), LLDPE comonomers (C6, C8), and plasticizers (C6, C10). Currently, the main production method for α-olefins is ethylene oligomerization, which uses ethylene derived from naphtha cracking or ethane cracking. This method consumes a significant amount of energy to produce the ethylene feedstock.

[0003] Nickel-based catalysts have proven highly effective in the formation of oligomers. 1-Butene, as a product of ethylene oligomerization, can be used directly as a raw material for the production of butene oxide and polybutene, and also as a comonomer for ethylene to produce high-strength polyethylene. Therefore, developing a method for selectively controlling the oligomerization of ethylene to C4 olefins is of great significance.

[0004] Chinese patent CN119406456A discloses a catalytic system employing a carbon-chromium catalyst, an organoboron additive, and an aluminum-containing activator to achieve selective oligomerization of ethylene, exhibiting high catalytic activity (103.1 g × 10⁻⁶). 6 The main products are ethylene trimer and tetramer (g / (molCr·h)). However, it requires the participation of organoboron additives and aluminum-containing activators, making catalyst recovery difficult and the preparation method cumbersome.

[0005] Chinese patent CN120205161A uses nickel sulfate and nickel nitrate to load ordinary niobium oxide directly to achieve selective control of C4 olefins in ethylene oligomerization under deposition precipitation and initial wet impregnation methods, but the generated C4 olefins are mainly trans-2-butene and cis-2-butene.

[0006] The preparation of C4 olefins by ethylene oligomerization involves using molecular sieves or metal-organic frameworks to support active metals. However, these catalysts are prone to carbon deposition and have poor stability. Furthermore, there is a lack of systematic methods for controlling the C4 olefin products. Therefore, developing a method that can systematically control the selectivity of C4 olefins during ethylene oligomerization is of great significance for the design and preparation of catalysts for ethylene oligomerization. Summary of the Invention

[0007] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0008] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0009] One objective of this invention is to provide a method for preparing a Ni-based catalyst, wherein the synthesized support is inexpensive and readily available, and the preparation is simple, which can achieve high dispersion of active nickel metal and effectively control the selectivity of the catalytic system for ethylene oligomeric C4 olefins.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing a Ni-based catalyst, comprising using ammonium niobate oxalate hydrate as a niobium source, adding an ammonium ion solution to the reaction system, and synthesizing a niobium oxide support with a nanorod morphology under the condition of ultrapure water as a solvent;

[0011] Using metal nitrates as supported metal precursors, catalyst precursors were obtained by loading them onto niobium oxide nanorod supports using the initial wet impregnation method.

[0012] The catalyst precursor was subjected to heat treatment to obtain a nickel-based catalyst supported on niobium nanorods; the nickel content in the nickel-based catalyst was 3-6 wt%.

[0013] In a preferred embodiment of the method for preparing the Ni-based catalyst of the present invention, the ammonium solution comprises one or more of ammonium oxalate solution, ammonium acetate solution, ammonium formate solution, and ammonium carbonate solution.

[0014] In a preferred embodiment of the preparation method of the Ni-based catalyst of the present invention, the concentration of ammonium ions in the ammonium ion solution is 0.2~3 mol / L.

[0015] In a preferred embodiment of the preparation method of the Ni-based catalyst of the present invention, the synthesis temperature of the niobium oxide support is 180~210 °C.

[0016] In a preferred embodiment of the preparation method of the Ni-based catalyst of the present invention, the metal nitrate includes a nickel nitrate solution or a nickel chloride solution; the molar concentration of the metal nickel in the metal nitrate solution is 0.1~0.4 mol / L.

[0017] As a preferred embodiment of the preparation method of the Ni-based catalyst of the present invention, the initial wet impregnation method is wherein the impregnation temperature is 20~40 ℃, the impregnation process is kept stirred, and the stirring speed is kept at 800~1200 r / min.

[0018] In a preferred embodiment of the method for preparing the Ni-based catalyst of the present invention, the heat treatment atmosphere is air or nitrogen, the temperature is 400~600 ℃, and the time is 4~6 h.

[0019] Another object of the present invention is to provide a Ni-based catalyst obtained by the preparation method described above.

[0020] Another object of the present invention is to provide the application of the Ni-based catalyst as described above in the oligomerization reaction of ethylene, wherein ethylene is oligomerized in a fixed-bed reactor under the action of the Ni-based catalyst to obtain the C4 olefin.

[0021] As a preferred embodiment of the application of the Ni-based catalyst of the present invention in the ethylene oligomerization reaction, the oligomerization reaction is carried out under the following conditions: the pretreatment atmosphere is nitrogen, the pretreatment temperature is 300 °C, the pretreatment time is 2-10 h, the oligomerization reaction temperature is 130 °C, and the pressure is 1-3 MPa; the weight hourly space velocity of the ethylene feed is 3-10 h⁻¹. -1 .

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The niobium oxide nanorod-supported nickel-based catalyst prepared in this invention exhibits different acidity as a catalyst for the oligomerization of ethylene to C4 olefins, and possesses a higher specific surface area and pore size compared to ordinary niobium oxide. It also demonstrates high 1-butene selectivity and ethylene conversion in product selectivity. The oligomerization reaction of this invention is carried out in a fixed-bed reactor, enabling continuous production and making it suitable for large-scale industrial production. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0025] Figure 1 The images shown are HR-TEM and HAADF-TEM images of the nickel-based catalyst Ni / Nb2O5-C2O4-0.2 obtained in Example 1 of this invention.

[0026] Figure 2The nitrogen adsorption-desorption isotherms (a) and pore size distribution (b) of the series of catalysts obtained in Example 1 of this invention are shown. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0028] This invention provides a method for preparing a nickel-based catalyst, comprising the following steps:

[0029] Using ammonium niobate oxalate hydrate as the niobium source, and adding ammonium ions of different forms and molar concentrations to the reaction system, a series of niobium oxide supports with nanorod morphology were synthesized under different reactor temperatures and different molar concentrations of ammonium ions in the reaction system, with ultrapure water as the solvent. The niobium oxide supports were then washed with ultrapure water and anhydrous ethanol, and the catalyst precursors were obtained by loading the synthesized series of nanorod niobium oxide supports using the initial wet impregnation method.

[0030] The catalyst precursor was subjected to heat treatment to obtain the nanorod niobium oxide supported nickel-based catalyst.

[0031] The metal salt solution includes nickel nitrate solution and nickel chloride solution, preferably nickel nitrate solution.

[0032] Unless otherwise specified, the raw materials used in this invention are preferably commercially available products.

[0033] In this invention, the purity of the ammonium oxalate hydrate is preferably 99.9%. In this invention, the synthesis temperature of the catalyst support is preferably 180-210 °C. In this invention, the loading of the active nickel metal is preferably 3%-6%, more preferably 3%. In this invention, the particle size of the nickel-based catalyst used for activity testing is preferably 20-80 mesh, more preferably 20-40 mesh. This invention uses niobium nanorods as the catalyst support. The niobium nanorods provide excellent conditions for high dispersion of the active nickel metal on the support, effectively increasing the dispersion of the loaded metal, preventing carbon buildup and blockage during the reaction, and improving the catalytic stability of the catalyst. Furthermore, the nickel-based catalyst obtained by this invention is a heterogeneous catalyst, which has a larger specific surface area compared to homogeneous catalysts, is easier to recover, and does not require a co-catalyst during the catalytic reaction.

[0034] In this invention, the metal salt solutions are preferably aqueous solutions of nickel nitrate and nickel chloride, specifically preferably aqueous solutions of nickel nitrate hexahydrate. In this invention, the niobium nanorods synthesized under different conditions possess different surface morphologies and different acidities, thus exhibiting different C4 olefin selectivity in the ethylene oligomerization reaction. In this invention, the molar concentration of the nickel salt in the metal salt solution is preferably 0.1~0.4 mol / L, more preferably 0.1 mol / L. In this invention, the preparation method of the metal salt mixture preferably includes: dissolving nickel nitrate hexahydrate in water and subjecting it to ultrasonic treatment to obtain the metal salt solution. In this invention, the water is preferably ultrapure water. In this invention, the frequency of the ultrasonic treatment is preferably 50 Hz, and the time is preferably 5 min. In this invention, the initial wet impregnation method for loading active nickel metal onto the niobium nanorod support can ensure that the nickel is uniformly dispersed on the support and has a small particle size, effectively improving the atomic utilization rate of the active metal.

[0035] In this invention, the parameters of the initial wet impregnation method include: the rotor stirring speed is preferably 400~1000 r / min, specifically preferably 800 r / min; the single impregnation time is preferably 2~12 h, specifically preferably 10 h; the drying temperature is preferably 60~120 ℃, specifically preferably 60 or 70 ℃, the drying is preferably carried out in an oven, and the calcination temperature is preferably 400~800 ℃, specifically preferably 400 ℃.

[0036] After the wet impregnation is completed, the catalyst precursor is subjected to heat treatment to obtain the nanorod niobium oxide supported nickel-based catalyst.

[0037] In this invention, the atmosphere for the heat treatment is preferably air, nitrogen, or oxygen, more preferably air; the temperature is preferably 200~800 ℃, more preferably 400 ℃; the heating rate to the heat treatment temperature is preferably 0.5~5 ℃ / min, more preferably 2 ℃ / min, more preferably 2 ℃ / min; the time is preferably 4~6 h, more preferably 4 h.

[0038] This invention also provides a nanorod niobium oxide-supported nickel-based catalyst prepared by the preparation method described above. In this invention, the catalyst comprises a nanorod niobium oxide support, with an active metallic nickel or nickel salt attached to the nanorod niobium oxide support. In this invention, the metallic salt is preferably nickel nitrate. In this invention, the nickel content in the nanorod niobium oxide-supported nickel-based catalyst is 3 wt% to 6 wt%, preferably 3 wt%.

[0039] The present invention also provides a method for heterogeneous ethylene oligomerization to synthesize carbotetraene, comprising the following steps:

[0040] The ethylene feedstock undergoes a heterogeneous oligomerization reaction under the action of a catalyst to obtain the C4 olefin.

[0041] The catalyst is the nickel-based catalyst described in the above technical solution.

[0042] In this invention, the temperature of the ethylene oligomerization reaction is preferably 130~330℃, specifically 130℃; the pressure is preferably 1~3 MPa, specifically 1 MPa, 2 MPa or 3 MPa.

[0043] In this invention, the weight hourly space velocity of the ethylene is preferably 3 to 10 h. -1 Specifically, it can be 7.5 hours. -1 .

[0044] In this invention, the ethylene oligomerization reaction is preferably carried out in a stainless steel fixed-bed reactor equipped with an electronic back pressure valve.

[0045] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0046] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0047] Unless otherwise specified, all raw materials used in the examples are commercially available.

[0048] Example 1

[0049] Five niobate oxalate aqueous solutions were prepared by placing 9.6 g of ammonium niobate oxalate hydrate in 20 ml of ultrapure water and stirring magnetically for 10 minutes. Subsequently, four ammonium oxalate solutions were prepared with ammonium molar concentrations of 0.2, 1, 2, 3, and 4 mol / L, respectively. These solutions were prepared by placing 0.71 g, 3.55 g, 7.1 g, 10.65 g, and 14.2 g of ammonium oxalate in 50 ml of ultrapure water, respectively, and then heating the ammonium oxalate solutions to 60 °C and stirring magnetically to dissolve the ammonium oxalate in the ultrapure water.

[0050] Five portions of ammonium oxalate solutions with different ammonium concentrations were then mixed with niobium oxalate aqueous solution and placed in a high-pressure reactor. The reaction temperature was set at 200℃ and the holding time was set at 24 hours. After the reaction, the resulting white precipitate was washed by placing it in a centrifuge tube and centrifuging at 8000 r / min for 8 minutes. Under the same conditions, the precipitate was washed three times with ultrapure water, followed by three times with anhydrous ethanol. The resulting white precipitate was then dried in a 70℃ oven for more than 10 hours to obtain dried niobium oxide nanorods.

[0051] 0.297 g of Ni(NO3)3·6H2O was dissolved in 5 mL of deionized water and continuously sonicated at 50 Hz for 10 min in an ultrasonic bath to obtain a nickel nitrate solution with a concentration of 0.1 mol / L. 2 g of dried niobium oxide nanorod support was weighed, and the nickel nitrate solution was slowly added dropwise to the niobium oxide support while continuously stirring at 800 r / min for 10 h. Subsequently, it was placed in an oven to dry at 100 ℃ for 12 h.

[0052] After drying, the catalyst was ground and calcined in a muffle furnace under air heat treatment. The calcination temperature was set to 400 °C, the calcination time to 4 h, and the heating rate to 2 °C / min. After calcination, niobium nanorod supported nickel-based catalyst was obtained. It was then ground in a mortar and pressed into tablets and sieved to a particle size of 20-40 mesh to obtain the nickel-based catalyst, which was named Ni / Nb2O5-C2O4-0.2, Ni / Nb2O5-C2O4-1.0, Ni / Nb2O5-C2O4-2.0, Ni / Nb2O5-C2O4-3.0, and Ni / Nb2O5-C2O4-4.0, respectively.

[0053] The HR-TEM and HAADF-TEM images of the obtained nickel-based catalyst Ni / Nb2O5-C2O4-0.2 are as follows: Figure 1 As shown in Table 1, the EDX-mapping elemental statistics of the obtained nickel-based catalyst Ni / Nb2O5-C2O4-0.2 are presented.

[0054] Table 1 Statistics of EDX-mapping elements

[0055]

[0056] Figure 1The HR-TEM image of the catalyst confirms that the synthesized Nb2O5 support possesses a nanorod structure. The successful loading of nickel is confirmed by HAADF-TEM and EXD-Mapping. The elemental statistics of EXD-Mapping show that the actual nickel loading is consistent with the theoretical value of approximately 3%.

[0057] The nitrogen adsorption-desorption isotherms of the above nickel-based catalyst ( Figure 2 a) and aperture distribution map ( Figure 2 b) in the example Figure 2 As shown in Table 2, the specific surface area and average pore size of the above nickel-based catalysts are statistically analyzed.

[0058] Table 2 Statistical analysis of specific surface area and average pore size

[0059]

[0060] pass Figure 2 As shown in Table 2, the synthesized supports have good mesoporous properties. With the increase of ammonium concentration during the synthesis process, the specific surface area of ​​the Nb2O5 support gradually decreases, while the average pore size shows an upward trend. Among them, the Nb2O5-C2O4-0.2 support has the highest specific surface area and the smallest average pore size.

[0061] The nickel-based catalyst was then diluted with quartz sand and placed in a stainless steel fixed-bed reactor. The catalyst bed was fixed in the isothermal section of the reactor using quartz wool. The catalyst was pretreated with nitrogen gas at a temperature of 300°C for 2 hours at a heating rate of 2°C / min, with a weight hourly space velocity of 7.5 h⁻¹. -1 .

[0062] The obtained series of nickel-based catalysts were used to oligomerize ethylene to C4 olefins under the conditions (pressure, temperature) shown in Table 3. The ethylene conversion and C4 olefin selectivity of the obtained nickel-based catalysts are shown in Table 3.

[0063] Table 3. Reaction conditions and test results of the series of catalysts obtained in Example 1

[0064]

[0065] As shown in Table 3, when the temperature is 130 ℃ and the pressure is 2 MPa, the Ni / Nb2O5-C2O4-4.0 catalyst has the highest selectivity for 1-butene, but its ethylene conversion rate decreases significantly. The Ni / Nb2O5-C2O4-0.2 catalyst has the highest selectivity for 2-butene.

[0066] Example 2

[0067] Four niobate oxalate aqueous solutions were prepared. The method involved placing 9.6 g of ammonium niobate oxalate hydrate in 20 ml of ultrapure water and stirring magnetically for 10 minutes. Subsequently, four ammonium formate solutions were prepared with ammonium molar concentrations of 0.2, 1, 2, and 3 mol / L, respectively. The method involved placing 0.63 g, 3.15 g, 6.3 g, and 9.45 g of ammonium oxalate in 50 ml of ultrapure water, respectively, and then heating the ammonium formate solutions to 60°C and stirring magnetically to dissolve the ammonium formate in the ultrapure water.

[0068] Then, four ammonium formate solutions with different ammonium concentrations were mixed with niobium oxalate aqueous solution and placed in a high-pressure reactor. The reaction temperature was set at 200℃ and the holding time was set at 24 hours. After the reaction, the obtained white precipitate was washed by placing the white precipitate in a centrifuge tube and centrifuging at 8000 r / min for 8 minutes. Under the same conditions, the precipitate was washed three times with ultrapure water, followed by three times with anhydrous ethanol. The resulting white precipitate was then dried in a 70℃ oven for more than 10 hours to obtain dried niobium oxide nanorods.

[0069] 0.297 g of Ni(NO3)3·6H2O was dissolved in 5 mL of deionized water and continuously sonicated at 50 Hz for 10 min in an ultrasonic bath to obtain a nickel nitrate solution with a concentration of 0.1 mol / L. 2 g of dried niobium oxide nanorod support was weighed, and the nickel nitrate solution was slowly added dropwise to the niobium oxide support while continuously stirring at 800 r / min for 10 h. Subsequently, it was placed in an oven to dry at 100 ℃ for 12 h.

[0070] After drying, the catalyst was ground and calcined in a muffle furnace under air heat treatment. The calcination temperature was set to 400 °C, the calcination time to 4 h, and the heating rate to 2 °C / min. After calcination, niobium nanorod supported nickel-based catalysts were obtained. These catalysts were then ground in a mortar and pressed into tablets and sieved to a particle size of 20-40 mesh to obtain the nickel-based catalysts. They were named Ni / Nb2O5-HCO2-0.2, Ni / Nb2O5-HCO2-1.0, Ni / Nb2O5-HCO2-2.0, and Ni / Nb2O5-HCO2-3.0, respectively.

[0071] The nickel-based catalyst was then diluted with quartz sand and placed in a stainless steel fixed-bed reactor. The catalyst bed was fixed in the isothermal section of the reactor using quartz wool. The catalyst was pretreated with nitrogen gas at a temperature of 300°C for 2 hours at a heating rate of 2°C / min, with a weight hourly space velocity of 7.5 h⁻¹. -1 .

[0072] The obtained series of nanorod-supported niobium oxide nickel-based catalysts were subjected to oligomerization of ethylene to C4 olefins under the conditions (pressure, temperature) shown in Table 4. The ethylene conversion and C4 olefin selectivity of the obtained nickel-based catalysts are shown in Table 4.

[0073] Table 4. Reaction conditions and test results of the series of catalysts obtained in Example 2

[0074]

[0075] As shown in Table 4, when the temperature is 130 °C and the pressure is 2 MPa, the Ni / Nb2O5-HCO2-3.0 catalyst has the highest selectivity for 1-butene, while the Ni / Nb2O5-HCO2-0.2 catalyst has the highest selectivity for 2-butene. The overall ethylene conversion rate is slightly lower than that in Example 1.

[0076] Example 3

[0077] Four portions of niobate oxalate aqueous solution were prepared. The method was to place 9.6 g of ammonium niobate oxalate hydrate in 20 ml of ultrapure water and stir magnetically for 10 minutes. Subsequently, four portions of ammonium acetate solution were prepared with ammonium molar concentrations of 0.2, 1, 2, and 3 mol / L, respectively. The method was to place 0.77 g, 3.85 g, 7.7 g, and 11.55 g of ammonium acetate in 50 ml of ultrapure water, respectively, and then heat the ammonium acetate solution to 60 °C and stir magnetically to dissolve the ammonium acetate in the ultrapure water.

[0078] Then, four portions of ammonium acetate with different ammonium concentrations were dissolved and mixed with niobium oxalate aqueous solution and placed in a high-pressure reactor. The reaction temperature was set at 200℃ and the holding time was set at 24 hours. After the reaction, the obtained white precipitate was washed by placing the white precipitate in a centrifuge tube and centrifuging at 8000 r / min for 8 minutes. Under the same conditions, the precipitate was washed three times with ultrapure water, followed by three times with anhydrous ethanol. The resulting white precipitate was then dried in a 70℃ oven for more than 10 hours to obtain dried niobium oxide nanorods.

[0079] 0.297 g of Ni(NO3)3·6H2O was dissolved in 5 mL of deionized water and continuously sonicated at 50 Hz for 10 min in an ultrasonic bath to obtain a nickel nitrate solution with a concentration of 0.1 mol / L. 2 g of dried niobium oxide nanorod support was weighed, and the nickel nitrate solution was slowly added dropwise to the niobium oxide support while continuously stirring at 800 r / min for 10 h. Subsequently, it was placed in an oven to dry at 100 ℃ for 12 h.

[0080] After drying, the catalyst was ground and calcined in a muffle furnace under air heat treatment. The calcination temperature was set to 400 °C, the calcination time to 4 h, and the heating rate to 2 °C / min. After calcination, niobium nanorod supported nickel-based catalysts were obtained. These catalysts were then ground in a mortar and pressed into tablets and sieved to a particle size of 20-40 mesh. The nickel-based catalysts were named Ni / Nb2O5-CH3CO2-0.2, Ni / Nb2O5-CH3CO2-1.0, Ni / Nb2O5-CH3CO2-2.0, and Ni / Nb2O5-CH3CO2-3.0, respectively.

[0081] The nickel-based catalyst was then diluted with quartz sand and placed in a stainless steel fixed-bed reactor. The catalyst bed was fixed in the isothermal section of the reactor using quartz wool. The catalyst was pretreated with nitrogen gas at a temperature of 300°C for 2 hours at a heating rate of 2°C / min, with a weight hourly space velocity of 7.5 h⁻¹. -1 .

[0082] The obtained series of nanorod-supported niobium oxide nickel-based catalysts were used to oligomerize ethylene to C4 olefins under the conditions (pressure, temperature) shown in Table 5. The ethylene conversion and C4 olefin selectivity of the obtained nickel-based catalysts are shown in Table 5.

[0083] Table 5. Reaction conditions and test results of the series of catalysts obtained in Example 3

[0084]

[0085] Table 5 shows that the Ni / Nb2O5-CH3CO2-2.0 catalyst exhibits the highest selectivity for 1-butene at a temperature of 130 ℃ and a pressure of 2 MPa. Increasing the ammonium molar concentration to 3 mol / L improves the selectivity for 1-butene, but slightly reduces the ethylene conversion rate.

[0086] Example 4

[0087] Four niobate oxalate aqueous solutions were prepared by placing 9.6 g of ammonium niobate oxalate hydrate in 20 ml of ultrapure water and stirring magnetically for 10 minutes. Subsequently, four ammonium carbonate solutions were prepared with ammonium molar concentrations of 0.2, 1, 2, and 3 mol / L, respectively. These solutions were prepared by placing 0.48 g, 2.4 g, 4.8 g, and 7.2 g of ammonium carbonate in 50 ml of ultrapure water, respectively, and then heating the ammonium carbonate solutions to 60°C and stirring magnetically to dissolve the ammonium carbonate in the ultrapure water.

[0088] Then, four ammonium carbonate solutions with different ammonium concentrations were mixed with niobium oxalate aqueous solution and placed in a high-pressure reactor. The reaction temperature was set at 200℃ and the holding time was set at 24 hours. After the reaction, the obtained white precipitate was washed by placing the white precipitate in a centrifuge tube and centrifuging at 8000 r / min for 8 minutes. Under the same conditions, the precipitate was washed three times with ultrapure water, followed by three times with anhydrous ethanol. The resulting white precipitate was then dried in a 70℃ oven for more than 10 hours to obtain dried niobium oxide nanorods.

[0089] 0.297 g of Ni(NO3)3·6H2O was dissolved in 5 mL of deionized water and continuously sonicated at 50 Hz for 10 min in an ultrasonic bath to obtain a nickel nitrate solution with a concentration of 0.1 mol / L. 2 g of dried niobium oxide nanorod support was weighed, and the nickel nitrate solution was slowly added dropwise to the niobium oxide support while continuously stirring at 800 r / min for 10 h. Subsequently, it was placed in an oven to dry at 100 ℃ for 12 h.

[0090] After drying, the catalyst was ground and calcined in a muffle furnace under air heat treatment. The calcination temperature was set to 400 °C, the calcination time to 4 h, and the heating rate to 2 °C / min. After calcination, niobium oxide nanorod-supported nickel-based catalysts were obtained. These catalysts were then ground in a mortar and pressed into tablets and sieved to a particle size of 20-40 mesh to obtain the nickel-based catalysts, which were named Ni / Nb2O5-CO3-0.2, Ni / Nb2O5-CO3-1.0, Ni / Nb2O5-CO3-2.0, and Ni / Nb2O5-CO3-3.0, respectively.

[0091] The nickel-based catalyst was then diluted with quartz sand and placed in a stainless steel fixed-bed reactor. The catalyst bed was fixed in the isothermal section of the reactor using quartz wool. The catalyst was pretreated with nitrogen gas at a temperature of 300°C for 2 hours at a heating rate of 2°C / min, with a weight hourly space velocity of 7.5 h⁻¹. -1 .

[0092] The obtained series of nanorod-supported niobium oxide nickel-based catalysts were subjected to oligomerization of ethylene to C4 olefins under the conditions (pressure, temperature) shown in Table 6. The ethylene conversion and C4 olefin selectivity of the obtained nickel-based catalysts are shown in Table 6.

[0093] Table 6. Reaction conditions and test results of the series of catalysts obtained in Example 4

[0094]

[0095] As can be seen from Table 6, when the temperature is 130 °C and the pressure is 2 MPa, the Ni / Nb2O5-CO3-3.0 catalyst has the highest selectivity for 1-butene, while the Ni / Nb2O5-CO3-0.2 catalyst has the highest selectivity for 2-butene. The overall ethylene conversion rate is higher than that of Examples 2 and 3.

[0096] Example 5

[0097] Four portions of niobate oxalate aqueous solution were prepared. The method was to place 9.6 g of ammonium niobate oxalate hydrate in 20 ml of ultrapure water and stir magnetically for 10 minutes. Subsequently, four portions of ammonium oxalate solution with an ammonium molar concentration of 3 mol / L were prepared. The method was to place 10.65 g of ammonium oxalate in 50 ml of ultrapure water, heat the ammonium oxalate solution to 60 °C and stir magnetically to dissolve the ammonium oxalate in the ultrapure water.

[0098] Then, four ammonium oxalate solutions with different ammonium concentrations were mixed with niobium oxalate aqueous solution and placed in a high-pressure reactor. The reaction temperatures were set at 180, 190, 200, and 210 °C, respectively, and the holding time was set to 24 hours. After the reaction, the obtained white precipitate was washed by placing it in a centrifuge tube and centrifuging at 8000 r / min for 8 minutes. Under the same conditions, the precipitate was washed three times with ultrapure water, followed by three times with anhydrous ethanol. The resulting white precipitate was then dried in a 70 °C oven for more than 10 hours to obtain dried niobium oxide nanorods.

[0099] 0.297 g of Ni(NO3)3·6H2O was dissolved in 5 mL of deionized water and continuously sonicated at 50 Hz for 10 min in an ultrasonic bath to obtain a nickel nitrate solution with a concentration of 0.1 mol / L. 2 g of dried niobium oxide nanorod support was weighed, and the nickel nitrate solution was slowly added dropwise to the niobium oxide support while continuously stirring at 800 r / min for 10 h. Subsequently, it was placed in an oven to dry at 100 ℃ for 12 h.

[0100] After drying, the catalyst was ground and calcined in a muffle furnace under air heat treatment. The calcination temperature was set to 400 °C, the calcination time to 4 h, and the heating rate to 2 °C / min. After calcination, niobium oxide nanorod-supported nickel-based catalysts were obtained. These catalysts were then ground in a mortar and pressed into tablets and sieved to a particle size of 20-40 mesh. The nickel-based catalysts were named Ni / Nb2O5-C2O4-T180, Ni / Nb2O5-C2O4-T190, Ni / Nb2O5-C2O4-T200, and Ni / Nb2O5-C2O4-T210, respectively.

[0101] The nickel-based catalyst was then diluted with quartz sand and placed in a stainless steel fixed-bed reactor. The catalyst bed was fixed in the isothermal section of the reactor using quartz wool. The catalyst was pretreated with nitrogen gas at a temperature of 300°C for 2 hours at a heating rate of 2°C / min, with a weight hourly space velocity of 7.5 h⁻¹. -1 .

[0102] The obtained series of nickel-based catalysts were used to oligomerize ethylene to C4 olefins under the conditions (pressure, temperature) shown in Table 7. The ethylene conversion and C4 olefin selectivity of the obtained nickel-based catalysts are shown in Table 7.

[0103] Table 7. Reaction conditions and test results of the series of catalysts obtained in Example 5

[0104]

[0105] As can be seen from Table 7, as the synthesis temperature of the nanorod niobium oxide support increases from 180℃ to 210℃, the ethylene conversion rate of the obtained nanorod niobium oxide supported nickel-based catalyst shows a trend of first increasing and then decreasing, among which the Ni / Nb2O5-C2O4-T200 catalyst obtained the highest ethylene conversion rate.

[0106] Example 6

[0107] Two niobate oxalate aqueous solutions were prepared separately. The method was to place 9.6 g of ammonium niobate oxalate hydrate in 20 ml of ultrapure water and stir magnetically for 10 minutes. Then, one ammonium oxalate solution and one ammonium formate solution were prepared with an ammonium molar concentration of 3 mol / L. The method was to place 10.65 g of ammonium oxalate and 9.45 g of ammonium formate in 50 ml of ultrapure water respectively, and then heat the ammonium oxalate solution and ammonium formate solution to 60 °C and stir magnetically to dissolve the ammonium oxalate in the ultrapure water.

[0108] Then, ammonium oxalate solution, ammonium formate solution, and niobium oxalate aqueous solution were mixed and placed in a high-pressure reactor. The reaction temperature was set at 200℃ and the holding time was set at 24 hours. After the reaction, the obtained white precipitate was washed by placing the white precipitate in a centrifuge tube and centrifuging at 8000 r / min for 8 minutes. Under the same conditions, the precipitate was washed three times with ultrapure water, followed by three times with anhydrous ethanol. The resulting white precipitate was then dried in a 70℃ oven for more than 10 hours to obtain dried niobium oxide nanorods.

[0109] 0.297 g of Ni(NO3)3·6H2O was dissolved in 5 mL of deionized water and continuously sonicated at 50 Hz for 10 min in an ultrasonic bath to obtain a nickel nitrate solution with a concentration of 0.1 mol / L. 2 g of dried niobium oxide nanorod support was weighed, and the nickel nitrate solution was slowly added dropwise to the niobium oxide support while continuously stirring at 800 r / min for 10 h. Subsequently, it was placed in an oven to dry at 100 ℃ for 12 h.

[0110] After drying, the catalyst was ground and calcined in a muffle furnace under air heat treatment. The calcination temperature was set to 400 °C, the calcination time to 4 h, and the heating rate to 2 °C / min. After calcination, niobium oxide nanorod-supported nickel-based catalyst was obtained. It was then ground in a mortar and pressed into tablets and sieved to a particle size of 20-40 mesh to obtain the nickel-based catalyst, which was named Ni / Nb2O5-C2O4-0.2.

[0111] The nickel-based catalyst was then diluted with quartz sand and placed in a stainless steel fixed-bed reactor. The catalyst bed was fixed in the isothermal section of the reactor using quartz wool. The catalyst was pretreated with nitrogen gas at a temperature of 300°C for 2 hours at a heating rate of 2°C / min, with a weight hourly space velocity of 7.5 h⁻¹. -1 .

[0112] The obtained series of nickel-based catalysts were used to oligomerize ethylene to C4 olefins under the conditions (pressure, temperature) shown in Table 8. The ethylene conversion and C4 olefin selectivity of the obtained nickel-based catalysts are shown in Table 8.

[0113] Table 8. Reaction conditions and test results of the catalyst obtained in Example 6

[0114]

[0115] In summary, as the reaction temperature increased from 130℃ to 300℃, the conversion rate of the obtained nanorod niobium oxide-supported nickel-based catalyst for ethylene oligomerization improved, but the selectivity for 1-butene decreased. Conversely, with increasing reaction pressure, the conversion rate of the obtained nanorod niobium oxide-supported nickel-based catalyst for ethylene oligomerization gradually increased, with less change in product selectivity compared to other examples. The highest conversion rate was 75.4%, obtained with Ni / Nb₂O₅-C₂O₄-3.0 at a reaction pressure of 3 MPa.

[0116] The niobium oxide nanorod-supported nickel-based catalyst prepared in this invention exhibits different acidity as a catalyst for the oligomerization of ethylene to C4 olefins, and possesses a higher specific surface area and pore size compared to ordinary niobium oxide. It also demonstrates high 1-butene selectivity and ethylene conversion in product selectivity. The oligomerization reaction of this invention is carried out in a fixed-bed reactor, enabling continuous production and making it suitable for large-scale industrial production.

[0117] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. The application of a Ni-based catalyst in the oligomerization reaction of ethylene, characterized in that: Ethylene was subjected to oligomerization in a fixed-bed reactor with the aid of a Ni-based catalyst to obtain C4 olefins. The oligomerization reaction is carried out under a nitrogen atmosphere at a temperature of 300 °C for 2–10 h. The oligomerization reaction temperature is 130 °C and the pressure is 1–3 MPa. The weight hourly space velocity (WHSV) of the ethylene feed is 3–10 h⁻¹. -1 ; The method for preparing the Ni-based catalyst includes: using ammonium oxalate hydrate of niobate as a niobium source and adding an ammonium solution to the reaction system, and synthesizing a niobium oxide support with a nanorod morphology under ultrapure water as a solvent; using a metal nitrate as a supported metal precursor, loading it onto the nanorod niobium oxide support using a wet impregnation method to obtain a catalyst precursor; and heat-treating the catalyst precursor to obtain a nanorod niobium oxide supported nickel-based catalyst. The nickel-based catalyst contains 3-6 wt% nickel. The ammonium solution includes one or more of ammonium oxalate solution, ammonium acetate solution, ammonium formate solution, and ammonium carbonate solution; The synthesis temperature of the niobium oxide support is 180~210 ℃; The metal nitrate includes nickel nitrate solution or nickel chloride solution.

2. The application as described in claim 1, characterized in that: The ammonium concentration in the ammonium solution is 0.2~3 mol / L.

3. The application as described in claim 1, characterized in that: The concentration of metallic nickel in the metal nitrate solution is 0.1~0.4 mol / L.

4. The application as described in claim 1, characterized in that: The initial wet impregnation method involves an impregnation temperature of 20-40 ℃, with stirring maintained during the impregnation process at a speed of 800-1200 r / min.

5. The application as described in claim 1, characterized in that: The heat treatment is performed in an atmosphere of air or nitrogen, at a temperature of 400-600 °C, for a time of 4-6 h.

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