CN110746468B - Star-shaped pyridine imine nickel-based catalyst and preparation method and application thereof - Google Patents

Star-shaped pyridine imine nickel-based catalyst and preparation method and application thereof Download PDF

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CN110746468B
CN110746468B CN201910995468.1A CN201910995468A CN110746468B CN 110746468 B CN110746468 B CN 110746468B CN 201910995468 A CN201910995468 A CN 201910995468A CN 110746468 B CN110746468 B CN 110746468B
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catalyst
nickel
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pyridine imine
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CN110746468A (en
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张娜
王俊
李翠勤
毛国梁
陈丽铎
王玲
翟岩亮
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Northeast Petroleum University
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
    • C07F15/00—Compounds containing elements of Groups 8, 9, 10 or 18 of the Periodic System
    • C07F15/04—Nickel compounds
    • C07F15/045—Nickel compounds without a metal-carbon linkage
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • B01J31/16—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes
    • B01J31/18—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes containing nitrogen, phosphorus, arsenic or antimony as complexing atoms, e.g. in pyridine ligands, or in resonance therewith, e.g. in isocyanide ligands C=N-R or as complexed central atoms
    • B01J31/1805—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes containing nitrogen, phosphorus, arsenic or antimony as complexing atoms, e.g. in pyridine ligands, or in resonance therewith, e.g. in isocyanide ligands C=N-R or as complexed central atoms the ligands containing nitrogen
    • B01J31/181—Cyclic ligands, including e.g. non-condensed polycyclic ligands, comprising at least one complexing nitrogen atom as ring member, e.g. pyridine
    • B01J31/1815—Cyclic ligands, including e.g. non-condensed polycyclic ligands, comprising at least one complexing nitrogen atom as ring member, e.g. pyridine with more than one complexing nitrogen atom, e.g. bipyridyl, 2-aminopyridine
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2/00—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms
    • C07C2/02—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by addition between unsaturated hydrocarbons
    • C07C2/04—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by addition between unsaturated hydrocarbons by oligomerisation of well-defined unsaturated hydrocarbons without ring formation
    • C07C2/06—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by addition between unsaturated hydrocarbons by oligomerisation of well-defined unsaturated hydrocarbons without ring formation of alkenes, i.e. acyclic hydrocarbons having only one carbon-to-carbon double bond
    • C07C2/08—Catalytic processes
    • C07C2/26—Catalytic processes with hydrides or organic compounds
    • C07C2/32—Catalytic processes with hydrides or organic compounds as complexes, e.g. acetyl-acetonates
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2231/00—Catalytic reactions performed with catalysts classified in B01J31/00
    • B01J2231/20—Olefin oligomerisation or telomerisation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2531/00—Additional information regarding catalytic systems classified in B01J31/00
    • B01J2531/02—Compositional aspects of complexes used, e.g. polynuclearity
    • B01J2531/0238—Complexes comprising multidentate ligands, i.e. more than 2 ionic or coordinative bonds from the central metal to the ligand, the latter having at least two donor atoms, e.g. N, O, S, P
    • B01J2531/0241—Rigid ligands, e.g. extended sp2-carbon frameworks or geminal di- or trisubstitution
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2531/00—Additional information regarding catalytic systems classified in B01J31/00
    • B01J2531/80—Complexes comprising metals of Group VIII as the central metal
    • B01J2531/84—Metals of the iron group
    • B01J2531/847—Nickel
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts

Abstract

The application relates to the technical field of organic synthesis and petrochemical industry, in particular to a star-shaped pyridine imine nickel catalyst, and a preparation method and application thereof. The structural formula (I) of the star-shaped pyridine imine nickel catalyst is as follows:
Figure DDA0002239584270000011
wherein R is selected from H, Br and CH3One kind of (1). The star-shaped pyridine imine nickel catalyst has the characteristics of both a homogeneous catalyst and a heterogeneous catalyst, has good catalytic activity and high-carbon olefin selectivity, and is easy to separate and convenient to recycle.

Description

Star-shaped pyridine imine nickel-based catalyst and preparation method and application thereof
Technical Field
The application relates to the technical field of organic synthesis and petrochemical industry, in particular to a star-shaped pyridine imine nickel catalyst, and a preparation method and application thereof.
Background
Linear alpha-olefins (LAOs) are used as important chemical intermediates, have wide application in the production fields of plasticizers, lubricating oils, detergents, surfactants and the like, and also have very important functions in the field of ethylene polymerization. Alpha-olefin is usually used as an important comonomer to produce a high-performance polyolefin product due to good tear resistance, and the high-performance polyolefin product has good tensile breaking stress, tensile yield stress, tear strength and other properties. There are various methods for producing linear alpha-olefins, including dehydration of primary alcohols, cracking of paraffins, extraction separation, and ethylene polymerization, among which ethylene polymerization is the main one.
The ethylene polymerization catalyst is a key element for synthesizing linear alpha-olefin by using an ethylene polymerization method, and common catalytic systems include transition metal catalysts such as Zr system, Ni system, Ti system, Fe system, Cr system and the like. Some of these catalysts are homogeneous catalysts, which have high catalytic activity, but have the disadvantage of being difficult to separate from the system after the reaction; some are heterogeneous catalysts, which are easily separated from the reaction system, but the catalytic activity is not ideal. Therefore, the existing ethylene polymerization catalyst is difficult to have higher catalytic activity and good separation effect at the same time, and the development of the ethylene polymerization catalyst with a novel structure is actually needed, so that the comprehensive performance of the ethylene polymerization catalyst is more outstanding.
Disclosure of Invention
The application aims to provide a star-shaped pyridine imine nickel catalyst, and a preparation method and application thereof, so as to solve the problems that the existing ethylene polymerization catalyst is difficult to have high catalytic activity and good separation effect at the same time.
In a first aspect, the present application provides a star-shaped pyridine imine nickel-based catalyst, wherein the structural formula (I) of the star-shaped pyridine imine nickel-based catalyst is:
Figure BDA0002239584250000021
wherein R is selected from H, Br and CH3One kind of (1).
In a second aspect, the present application provides a preparation method of a star-shaped pyridine imine nickel-based catalyst, including the following steps:
s1, adding pyridine-2 formaldehyde or a pyridine-2 formaldehyde substituent and a water absorbent into a first organic solvent to form a reaction system, cooling the reaction system to-5 ℃ under the condition of inert gas, adding an organic solution of a compound with a structural formula (II), reacting for 15-60min, stirring and heating to 20-40 ℃, continuously stirring and reacting for 20-40h, and filtering after reaction to obtain a filtrate;
Figure BDA0002239584250000022
s2, reacting the filtrate with an organic solution of nickel chloride hexahydrate under the condition of inert gas at the temperature of 20-40 ℃ for 20-40 hours under stirring to obtain the star-shaped pyridine imine nickel catalyst, wherein the structural formula (I) of the star-shaped pyridine imine nickel catalyst is as follows:
Figure BDA0002239584250000031
wherein R is selected from H, Br and CH3One kind of (1).
The amount of the first organic solvent, the amount of the organic solution used in the organic solution of the compound of formula (II), and the amount of the organic solution used in the organic solution of nickel chloride hexahydrate are not limited strictly, and those skilled in the art can select and determine the amount of the first organic solvent according to practical situations, for example, the amount of the first organic solvent can be more than the amount of the first organic solvent used in the reaction and the amount of the second organic solvent used in the post-treatment, and will not be described in detail herein.
It is understood that the temperature reduction to-5 to 5 ℃ in said step of S1 includes any value within this range, for example to-5 ℃, -3 ℃, -1 ℃, 0 ℃, 2 ℃, 4 ℃ or 5 ℃; the reaction time of 15-60min includes any point value in the time range, such as 15min, 20min, 30min, 45min, 50min or 60 min; heating to 20-40 deg.C with stirring, including any point in this temperature range, for example, heating to 20 deg.C, 25 deg.C, 30 deg.C, 35 deg.C, or 40 deg.C with stirring; stirring the reaction for 20-40h includes any point within the time range, for example stirring the reaction for 20h, 24h, 30h, or 40 h. In the S2 step, the reaction temperature is 20-40 ℃ including any point in the temperature range, for example, the reaction temperature is 20 ℃, 25 ℃, 30 ℃, 35 ℃ or 40 ℃; the stirring reaction time is 20-40h and includes any point in the time range, such as 20h, 24h, 30h or 40 h.
In addition, pyridine-2-carbaldehyde, substituted pyridine-2-carbaldehyde, a compound of formula (II), and nickel chloride hexahydrate are well known in the art and are commercially available from a variety of sources and will not be described in detail herein.
Further, the step S1 is: adding pyridine-2-formaldehyde or a pyridine-2-formaldehyde substitute and the water absorbent into the first organic solvent at room temperature to form a reaction system, cooling the reaction system to 0 ℃ under the condition of inert gas, adding the organic solution of the compound of the structural formula (II), reacting for 30min, stirring and heating to 25 ℃, continuously stirring and reacting for 24h, and filtering under negative pressure after the reaction to obtain the filtrate; wherein the molar ratio of the compound of the structural formula (II) to the pyridine-2-carbaldehyde or the substituent of the pyridine-2-carbaldehyde is 1:5-1: 6.
Further, the step S2 is: slowly dropwise adding the organic solution of nickel chloride hexahydrate into the filtrate under the condition of inert gas to form a reaction solution, stirring and reacting for 24 hours at 25 ℃, and carrying out post-treatment on the reaction solution after reaction to obtain the star-shaped pyridine imine nickel catalyst; wherein the molar ratio of the compound shown in the structural formula (II) to the nickel chloride hexahydrate is 1:3-1: 4.
Further, in the step S2, the post-processing is: and adding ether into the reaction solution after the reaction to separate out a green solid, filtering and collecting the green solid, washing the green solid with anhydrous ether, and drying the washed green solid to constant weight under a vacuum condition to obtain the star-shaped pyridine imine nickel catalyst.
Further, in the preparation method, the substitute of pyridine-2-carbaldehyde is selected from 6-methyl-2-pyridinecarbaldehyde or 6-bromo-2-pyridinecarbaldehyde, and the water absorbent is selected from anhydrous sodium sulfate, anhydrous magnesium sulfate or anhydrous calcium chloride; the inert gas is selected from nitrogen, helium or argon; the first organic solvent in the step S1 is one or a mixture of two of methanol and ethanol; the solvent used in the organic solution of the compound of the structural formula (II) and the solvent used in the organic solution of the nickel chloride hexahydrate are both selected from one or a mixture of two of methanol and ethanol.
In the right 7-third aspect, the application provides a use of the star-shaped pyridine imine nickel catalyst in the preparation of alpha-olefin by ethylene oligomerization.
In a fourth aspect of claim 8, the present application provides a process for producing α -olefins, the process comprising: and dissolving the star-shaped pyridine imine nickel catalyst in a second organic solvent, adding a cocatalyst, and introducing ethylene for reaction to obtain the alpha-olefin.
Further, the method comprises the following steps: dissolving the star-shaped pyridine imine nickel catalyst in the second organic solvent, adding a cocatalyst, introducing ethylene to 0.1-1.0MPa, keeping the ethylene pressure constant, and stirring and reacting at 10-50 ℃ to obtain the alpha-olefin; wherein the cocatalyst is methylaluminoxane, and the molar ratio of aluminum element in the methylaluminoxane to nickel element in the star-shaped pyridine imine nickel catalyst is 300:1-1500: 1.
It is understood that in the method for preparing alpha-olefin, the constant pressure reaction time is not particularly required, as long as the activity of the catalyst for catalyzing the ethylene oligomerization and the product selectivity can be ensured, for example, the activity can be calculated by the mass difference before and after the reaction, the product selectivity can be detected by gas chromatography, and a person skilled in the art can select a suitable reaction time according to actual conditions, and the detailed description is omitted.
Further, in the method, the second organic solvent is one or a mixture of toluene, methylcyclohexane or cyclohexane.
Preferably, the method is: dissolving the star-shaped pyridine imine nickel catalyst in toluene, adding methylaluminoxane, introducing ethylene to 1.0MPa, keeping the ethylene pressure constant, and stirring and reacting at 10 ℃ to obtain the alpha-olefin; wherein the molar ratio of the aluminum element in the methylaluminoxane to the nickel element in the star-shaped pyridine imine nickel catalyst is 500: 1.
Compared with the prior art, the beneficial effects of this application are as follows:
firstly, the application provides a nickel catalyst with a novel structure, namely a star-shaped pyridine imine nickel catalyst, and the ligand of the catalyst is star-shaped pyridine imine, so that the catalyst has a unique main structure and a unique microenvironment, and further has unique physical and chemical properties including a wide cavity structure, a nano-scale size and molecular dissolving capacity, so that the catalyst has the characteristics of a homogeneous catalyst and a heterogeneous catalyst, and the problems of difficult separation of the homogeneous catalyst, poor catalytic capacity of the heterogeneous catalyst and the like are well solved.
Specifically, due to the synthesis of the star-shaped pyridine imine ligand structure, the nickel-based catalyst has a highly branched three-dimensional structure and a wide cavity structure, and has at least two advantages. On one hand, although the catalyst is a heterogeneous catalyst on the macroscopic scale and is insoluble in a reaction system, the star-shaped pyridine imine ligand structure enables the nickel-based catalyst to reach the nanoscale size and the dissolving capacity of nano molecules, and the characteristics of the nano material can ensure that the nickel-based catalyst has better dispersibility in the catalytic reaction system, is more fully contacted with catalytic reaction materials, embodies better catalytic activity, and is equivalent to a homogeneous catalyst. That is, the nickel-based catalyst has the characteristics that when the catalytic reaction is carried out, the dispersibility is good due to the nanometer characteristic, and the nickel-based catalyst can be used as a homogeneous catalyst to be fully contacted with reaction materials and shows higher catalytic activity; after the reaction is finished, the nickel catalyst is insoluble in a reaction system, embodies the characteristics of a heterogeneous catalyst, can be conveniently separated from the reaction system, and is high in cyclic utilization rate and long in service life.
Secondly, the nickel-based catalyst realizes high selectivity to alpha-olefin by designing a specific star-shaped pyridine imine cavity structure. Specifically, the star-shaped pyridine imine structure of the nickel-based catalyst has the characteristic of a flexible molecular chain, and does not contain a plurality of benzene ring structures, so that the size of a cavity of a nickel-based catalyst molecule can be adjusted by combining further exploration on the reaction condition of ethylene oligomerization catalysis on the basis of the flexible nickel-based catalyst, and the purposes of narrow distribution and high selectivity of ethylene oligomerization products are achieved. Tests prove that when the star-shaped pyridine imine nickel catalyst is used for catalyzing ethylene oligomerization, the catalyst has higher selectivity on high-carbon alpha-olefin and high catalytic activity. High catalytic activity up to 4.39X 105g/(mol Ni. h), high value-added olefin C8To C18Higher olefin content, higher C in the product8-C18The mass percentage content is more than 31 percent, and the high-purity C can be obtained by simple separation8-C18An olefin.
Finally, the star-shaped pyridine imine nickel catalyst has the advantages of easily obtained preparation raw materials, simple preparation steps and mild reaction conditions, so that the preparation method has low cost, strong practicability and wide applicability.
Drawings
FIG. 1 is an infrared spectrum of a star-shaped pyridine imine nickel catalyst in the embodiment of the present application.
FIG. 2 is an ESI-MS spectrum of a star-shaped pyridine imine nickel catalyst in the example of the present application.
FIG. 3 is an infrared spectrum of the tri-star type nickel pyridine imine catalyst in the embodiment of the present application.
FIG. 4 is an ESI-MS spectrum of a starburst nickel pyridinimine catalyst according to the example of the present application.
FIG. 5 is an infrared spectrum of a penta-form nickel pyridinimine catalyst according to example of the present application.
FIG. 6 is an ESI-MS spectrum of a pentastar type nickel pyridinimine catalyst according to the examples of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be described clearly and completely below, and it should be apparent that the described embodiments are only a part of the embodiments of the present application, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
It should be noted that the terms "comprises" and "comprising," and any variations thereof, in the embodiments of this application, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
In addition, the reaction raw materials used in the examples of the present application are all commercially available.
Example one
This example provides a star-type pyridine imine nickel catalyst, which has the structural formula (I):
Figure BDA0002239584250000071
wherein R represents H.
The embodiment also provides a preparation method of the star-shaped pyridine imine nickel catalyst, which comprises the following steps: s1, adding pyridine-2-formaldehyde and anhydrous sodium sulfate into methanol at room temperature to form a reaction system, cooling the reaction system to 0 ℃ under the condition of nitrogen, adding an organic solution of a compound shown in a structural formula (II), wherein the organic solvent in the organic solution is methanol, reacting for 30min, stirring and heating to 25 ℃, continuously stirring and reacting for 24h, and filtering under negative pressure after the reaction is finished to obtain a filtrate; wherein the molar ratio of the compound shown in the structural formula (II) to the pyridine-2-carbaldehyde is 1:5, and the mass of the anhydrous sodium sulfate is 3.0 g.
Figure BDA0002239584250000081
S2, slowly dropwise adding an organic solution of nickel chloride hexahydrate into the filtrate obtained in the step S1 under the condition of nitrogen to form a reaction solution, wherein an organic solvent adopted in the organic solution of nickel chloride hexahydrate is methanol, and the molar ratio of the compound in the structural formula (II) to the nickel chloride hexahydrate is 1: 3.5; stirring and reacting for 24h at 25 ℃, adding 100mL of diethyl ether into the reaction solution after the reaction is finished for post-treatment to separate out a green solid, filtering and collecting the green solid, repeatedly washing the green solid for 3 times by using anhydrous diethyl ether, and drying the washed green solid to constant weight under a vacuum condition to obtain the star-shaped pyridine imine nickel catalyst of the embodiment. The yield of the star-shaped pyridinimine nickel-based catalyst of this example was calculated to be 72.19%.
The star-shaped pyridine imine nickel-based catalyst of the present example was subjected to structural analysis, and as shown in FIG. 1, it was observed at 3228cm in an infrared spectrum-1And 3069cm-1Near the absorption peaks of N-H on amido bond and C-H telescopic vibration characteristic absorption peaks on pyridine ring respectively appear at 1608cm-1A stretching vibration characteristic absorption peak of-C-N-appears nearby, which shows that the terminal primary amine of the compound with the structural formula (II) and pyridine-2-formaldehyde have Schiff base reaction;
as shown in FIG. 2, an excimer ion peak [ M ] of a starburst nickel pyridinimide compound at M/z 1016 was observed in the ESI-MS spectrum]+(ii) a M/z 803 is a fragment ion peak [ M-6Cl ] formed by 6Cl loss during compound cleavage]+(ii) a Further cracking to lose 3Ni formed fragment ion peak [ M-6Cl-3Ni]+Appearing at m/z 626. The ESI-MS is electrospray ionization mass spectrometry, and is called electrophoresis ionization mass spectrometry for short.
Example two
This example provides a star-type pyridine imine nickel catalyst, which has the structural formula (I):
Figure BDA0002239584250000091
wherein R represents H.
The embodiment also provides a preparation method of the star-shaped pyridine imine nickel catalyst, which comprises the following steps:
s1, adding pyridine-2-formaldehyde and anhydrous sodium sulfate into ethanol at room temperature to form a reaction system, cooling the reaction system to 0 ℃ under the condition of nitrogen, adding an organic solution of a compound shown in a structural formula (II), wherein the organic solvent in the organic solution is ethanol, reacting for 30min, stirring and heating to 35 ℃, continuously stirring and reacting for 24h, and filtering under negative pressure after the reaction is finished to obtain a filtrate; wherein the molar ratio of the compound shown in the structural formula (II) to the pyridine-2-carbaldehyde is 1:6, and the mass of the anhydrous sodium sulfate is 3.0 g.
Figure BDA0002239584250000092
S2, slowly dropwise adding an organic solution of nickel chloride hexahydrate into the filtrate obtained in the step S1 under the condition of nitrogen to form a reaction solution, wherein an organic solvent adopted in the organic solution of nickel chloride hexahydrate is ethanol, and the molar ratio of the compound in the structural formula (II) to the nickel chloride hexahydrate is 1: 4; stirring and reacting for 24h at 25 ℃, adding 100mL of diethyl ether into the reaction solution after the reaction is finished for post-treatment to separate out a green solid, filtering and collecting the green solid, repeatedly washing the green solid for 3 times by using anhydrous diethyl ether, and drying the washed green solid to constant weight under a vacuum condition to obtain the star-shaped pyridine imine nickel catalyst of the embodiment.
The infrared spectrum and ESI-MS spectrum of this example are the same as those of the first example, and are not provided and described herein.
EXAMPLE III
This example provides a star-type pyridine imine nickel catalyst, which has the structural formula (I):
Figure BDA0002239584250000101
wherein R represents CH3。
The embodiment also provides a preparation method of the star-shaped pyridine imine nickel catalyst, which comprises the following steps:
s1, adding 6-methyl-2-pyridinecarboxaldehyde and anhydrous sodium sulfate into methanol at room temperature to form a reaction system, cooling the reaction system to 0 ℃ under the condition of nitrogen, adding an organic solution of a compound shown in a structural formula (II), wherein an organic solvent in the organic solution is methanol, reacting for 30min, stirring and heating to 25 ℃, continuously stirring and reacting for 24h, and filtering under negative pressure after the reaction is finished to obtain a filtrate; wherein the molar ratio of the compound shown in the structural formula (II) to 6-methyl-2-pyridinecarbaldehyde is 1:5, and the mass of the anhydrous sodium sulfate is 3.0 g.
Figure BDA0002239584250000111
S2, slowly dropwise adding an organic solution of nickel chloride hexahydrate into the filtrate obtained in the step S1 under the condition of nitrogen to form a reaction solution, wherein an organic solvent adopted in the organic solution of nickel chloride hexahydrate is methanol, and the molar ratio of the compound in the structural formula (II) to the nickel chloride hexahydrate is 1: 3.5; stirring and reacting for 24h at 25 ℃, adding 100mL of diethyl ether into the reaction solution after the reaction is finished for post-treatment to separate out a green solid, filtering and collecting the green solid, repeatedly washing the green solid for 3 times by using anhydrous diethyl ether, and drying the washed green solid to constant weight under a vacuum condition to obtain the star-shaped pyridine imine nickel catalyst of the embodiment.
The structure of the star-shaped pyridinimine nickel-based catalyst of this example was analyzed, and as shown in FIG. 3, it was observed at 3228cm in an infrared spectrum-1And 3069cm-1Near the absorption peaks of N-H on amido bond and C-H telescopic vibration characteristic absorption peaks on pyridine ring respectively appear at 1608cm-1A stretching vibration characteristic absorption peak of-C-N-appears nearby, which shows that the terminal primary amine of the compound with the structural formula (II) and pyridine-2-formaldehyde have Schiff base reaction;
as shown in FIG. 4, starlike pyrazine at m/z 1058 was observed in ESI-MS spectrumExcimer ion peak [ M ] of nickel pyridinimide compound]+(ii) a M/z 845 is the fragment ion peak [ M-6Cl ] formed by 6Cl loss during compound cleavage]+(ii) a Further cracking to lose 3Ni formed fragment ion peak [ M-6Cl-3Ni]+Appearing at m/z 668.
Example four
This example provides a star-type pyridine imine nickel catalyst, which has the structural formula (I):
Figure BDA0002239584250000121
wherein R represents CH3。
The embodiment also provides a preparation method of the star-shaped pyridine imine nickel catalyst, which comprises the following steps:
s1, adding 6-methyl-2-pyridinecarboxaldehyde and anhydrous sodium sulfate into ethanol at room temperature to form a reaction system, cooling the reaction system to 0 ℃ under the condition of nitrogen, adding an organic solution of a compound shown in a structural formula (II), wherein the organic solvent in the organic solution is ethanol, reacting for 30min, stirring and heating to 35 ℃, continuously stirring and reacting for 24h, and filtering under negative pressure after the reaction is finished to obtain a filtrate; wherein the molar ratio of the compound shown in the structural formula (II) to 6-methyl-2-pyridinecarbaldehyde is 1:6, and the mass of the anhydrous sodium sulfate is 3.0 g.
Figure BDA0002239584250000122
S2, slowly dropwise adding an organic solution of nickel chloride hexahydrate into the filtrate obtained in the step S1 under the condition of nitrogen to form a reaction solution, wherein an organic solvent adopted in the organic solution of nickel chloride hexahydrate is ethanol, and the molar ratio of the compound in the structural formula (II) to the nickel chloride hexahydrate is 1: 4; stirring and reacting for 24h at 25 ℃, adding 100mL of diethyl ether into the reaction solution after the reaction is finished for post-treatment to separate out a green solid, filtering and collecting the green solid, repeatedly washing the green solid for 3 times by using anhydrous diethyl ether, and drying the washed green solid to constant weight under a vacuum condition to obtain the star-shaped pyridine imine nickel catalyst of the embodiment.
The infrared spectrum and ESI-MS spectrum of this example are the same as those of the example, and are not provided and described herein.
EXAMPLE five
This example provides a star-type pyridine imine nickel catalyst, which has the structural formula (I):
Figure BDA0002239584250000131
wherein R represents Br.
The embodiment also provides a preparation method of the star-shaped pyridine imine nickel catalyst, which comprises the following steps:
s1, adding 6-bromo-2-pyridinecarboxaldehyde and anhydrous sodium sulfate into methanol at room temperature to form a reaction system, cooling the reaction system to 0 ℃ under the condition of nitrogen, adding an organic solution of a compound shown in a structural formula (II), wherein an organic solvent in the organic solution is methanol, reacting for 30min, stirring and heating to 25 ℃, continuously stirring and reacting for 24h, and filtering under negative pressure after the reaction is finished to obtain a filtrate; wherein the molar ratio of the compound shown in the structural formula (II) to 6-methyl-2-pyridinecarbaldehyde is 1:5, and the mass of the anhydrous sodium sulfate is 3.0 g.
Figure BDA0002239584250000141
S2, slowly dropwise adding an organic solution of nickel chloride hexahydrate into the filtrate obtained in the step S1 under the condition of nitrogen to form a reaction solution, wherein an organic solvent adopted in the organic solution of nickel chloride hexahydrate is methanol, and the molar ratio of the compound in the structural formula (II) to the nickel chloride hexahydrate is 1: 3.5; stirring and reacting for 24h at 25 ℃, adding 100mL of diethyl ether into the reaction solution after the reaction is finished for post-treatment to separate out a green solid, filtering and collecting the green solid, repeatedly washing the green solid for 3 times by using anhydrous diethyl ether, and drying the washed green solid to constant weight under a vacuum condition to obtain the star-shaped pyridine imine nickel catalyst of the embodiment.
Book checkingStructural analysis of the star-shaped pyridinimine nickel-based catalyst of the example was carried out, and as shown in FIG. 5, it was observed at 3228cm in an infrared spectrum-1And 3069cm-1Near the absorption peaks of N-H on amido bond and C-H telescopic vibration characteristic absorption peaks on pyridine ring respectively appear at 1608cm-1A stretching vibration characteristic absorption peak of-C-N-appears nearby, which shows that the terminal primary amine of the compound with the structural formula (II) and pyridine-2-formaldehyde have Schiff base reaction;
as shown in FIG. 6, an excimer ion peak [ M ] of a starburst nickel pyridinimide compound at M/z 1253 was observed in the ESI-MS spectrum]+(ii) a At M/z 1040 is the fragment ion peak [ M-6Cl ] formed by 6Cl loss during compound cleavage]+(ii) a Further cracking to lose 3Ni formed fragment ion peak [ M-6Cl-3Ni]+At m/z 863.
EXAMPLE six
This example provides a star-type pyridine imine nickel catalyst, which has the structural formula (I):
Figure BDA0002239584250000151
wherein R represents Br.
The embodiment also provides a preparation method of the star-shaped pyridine imine nickel catalyst, which comprises the following steps:
s1, adding 6-bromo-2-pyridinecarboxaldehyde and anhydrous sodium sulfate into ethanol at room temperature to form a reaction system, cooling the reaction system to 0 ℃ under the condition of nitrogen, adding an organic solution of a compound shown in a structural formula (II), wherein an organic solvent in the organic solution is ethanol, reacting for 30min, stirring and heating to 35 ℃, continuously stirring and reacting for 24h, and filtering under negative pressure after the reaction is finished to obtain a filtrate; wherein the molar ratio of the compound shown in the structural formula (II) to 6-methyl-2-pyridinecarbaldehyde is 1:6, and the mass of the anhydrous sodium sulfate is 3.0 g.
Figure BDA0002239584250000152
S2, slowly dropwise adding an organic solution of nickel chloride hexahydrate into the filtrate obtained in the step S1 under the condition of nitrogen to form a reaction solution, wherein an organic solvent adopted in the organic solution of nickel chloride hexahydrate is ethanol, and the molar ratio of the compound in the structural formula (II) to the nickel chloride hexahydrate is 1: 4; stirring and reacting for 24h at 25 ℃, adding 100mL of diethyl ether into the reaction solution after the reaction is finished for post-treatment to separate out a green solid, filtering and collecting the green solid, repeatedly washing the green solid for 3 times by using anhydrous diethyl ether, and drying the washed green solid to constant weight under a vacuum condition to obtain the star-shaped pyridine imine nickel catalyst of the embodiment.
The infrared spectrum and ESI-MS spectrum of this example are the same as those of example V, and are not provided and described herein.
The star-shaped pyridine imine nickel-based catalyst obtained in the first to sixth embodiments of the application has a wide cavity structure and a nano-scale size, so that the nickel-based catalyst has the characteristics of a homogeneous catalyst and a heterogeneous catalyst. On one hand, the catalyst presents the characteristics of nano particles through a star-shaped structure, so that after the star-shaped pyridine imine nickel catalyst is put into a catalytic reaction system, the star-shaped pyridine imine nickel catalyst can be fully contacted with reaction materials by virtue of the nano-scale size of the star-shaped pyridine imine nickel catalyst, good molecular dissolving capacity is realized, catalytic reaction activity is improved, and the characteristics of a homogeneous catalyst are embodied. On the other hand, the nickel-based catalyst is not dissolved in the reaction system, so that the nickel-based catalyst can be separated from the reaction system by conventional means such as centrifugation after the reaction is finished, and can be recycled, so that the nickel-based catalyst has a long service life, and the problems that the homogeneous catalyst is difficult to separate or the separation loss rate is high cannot occur.
Moreover, the structural characteristics of the star-shaped pyridine imine nickel catalyst can also show that the ligand structure of the catalyst has no more benzene ring structures, the tail end of the whole structure is provided with a small amount of ring structures, but the middle of the structure is provided with a longer flexible molecular chain, and the star-shaped structures with more flexible molecular chains ensure that the rigidity of the nickel catalyst is not too strong, and when the catalyst is used for catalyzing ethylene oligomerization, the adjustment of the molecular cavity size of the nickel catalyst can be further realized by exploring reaction conditions, so that the purposes of narrowing the product distribution and obtaining high-selectivity olefin products are achieved. Based on the method, the application also explores better conditions for preparing alpha-olefin by using the star-shaped pyridine imine nickel catalyst.
Preparation example 1
The preparation example provides application of the star-type pyridine imine nickel catalyst in preparation of alpha-olefin by ethylene oligomerization, and specifically relates to preparation of alpha-olefin by using the star-type pyridine imine nickel catalyst in the embodiment of the application.
The method for preparing alpha-olefin is as follows: vacuumizing a reaction system with a drying function and a stirring function, replacing the reaction system with ethylene for three times, adding the star-shaped pyridine imine nickel catalyst, toluene serving as a second organic solvent and methylaluminoxane serving as a cocatalyst, introducing ethylene to the reaction system until the pressure is 0.5MPa, keeping the ethylene pressure constant, stirring the mixture at 10 ℃ for reaction for 30min, and emptying the reaction system to normal pressure to obtain alpha-olefin; wherein the molar ratio of the aluminum element in the methylaluminoxane to the nickel element in the star-shaped pyridine imine nickel catalyst is 500: 1.
Wherein the structural formula of the star-shaped pyridine imine nickel catalyst is as follows:
Figure BDA0002239584250000171
wherein R is H.
Preparation example two
The present preparation example differs from the first preparation example only in the catalyst used in the present preparation example. The structural formula of the star-shaped pyridine imine nickel catalyst used in the preparation example is as follows:
Figure BDA0002239584250000181
wherein R is CH3。
The method for preparing alpha-olefin is as follows: vacuumizing a reaction system with a drying function and a stirring function, replacing the reaction system with ethylene for three times, adding the star-shaped pyridine imine nickel catalyst, toluene serving as a second organic solvent and methylaluminoxane serving as a cocatalyst, introducing ethylene to the reaction system until the pressure is 0.5MPa, keeping the ethylene pressure constant, stirring the mixture at 10 ℃ for reaction for 30min, and emptying the reaction system to normal pressure to obtain alpha-olefin; wherein the molar ratio of the aluminum element in the methylaluminoxane to the nickel element in the star-shaped pyridine imine nickel catalyst is 500: 1.
Preparation example three
The present preparation example differs from the first preparation example only in the catalyst used in the present preparation example. The structural formula of the star-shaped pyridine imine nickel catalyst used in the preparation example is as follows:
Figure BDA0002239584250000191
wherein R is Br.
The method for preparing alpha-olefin is as follows: vacuumizing a reaction system with a drying function and a stirring function, replacing the reaction system with ethylene for three times, adding the star-shaped pyridine imine nickel catalyst, toluene serving as a second organic solvent and methylaluminoxane serving as a cocatalyst, introducing ethylene to the reaction system until the pressure is 0.5MPa, keeping the ethylene pressure constant, stirring and reacting at 10 ℃ for 30min, and emptying to normal pressure to obtain alpha-olefin; wherein the molar ratio of the aluminum element in the methylaluminoxane to the nickel element in the star-shaped pyridine imine nickel catalyst is 500: 1.
Preparation example four
The present preparation example differs from preparation example three only in that methylcyclohexane is used as the second organic solvent in the present preparation example.
Preparation example five
The present preparation example differs from preparation example three only in that cyclohexane is used as the second organic solvent in the present preparation example.
Preparation example six
The preparation example differs from the third preparation example only in that the temperature of the catalytic reaction in this example is 20 ℃.
Preparation example seven
The preparation example differs from the third preparation example only in that the temperature of the catalytic reaction in this example is 30 ℃.
Preparation example eight
The preparation example differs from the third preparation example only in that the temperature of the catalytic reaction in this example is 40 ℃.
Preparation example nine
The preparation example differs from the third preparation example only in that the temperature of the catalytic reaction in this example is 50 ℃.
Preparation example ten
The difference between the preparation example and the third preparation example is that the molar ratio of the aluminum element in the methylaluminoxane to the nickel element in the star-shaped pyridine imine nickel-based catalyst is 300: 1.
Preparation example eleven
The difference between the preparation example and the third preparation example is that the molar ratio of the aluminum element in the methylaluminoxane to the nickel element in the star-shaped pyridine imine nickel-based catalyst in the preparation example is 700: 1.
Preparation example twelve
The difference between the preparation example and the third preparation example is that the molar ratio of the aluminum element in the methylaluminoxane to the nickel element in the star-shaped pyridine imine nickel-based catalyst is 1000: 1.
Preparation example thirteen
The difference between the preparation example and the third preparation example is that the molar ratio of the aluminum element in the methylaluminoxane to the nickel element in the star-shaped pyridine imine nickel-based catalyst is 1500: 1.
Preparation example fourteen
The difference between the preparation example and the third preparation example is that ethylene was introduced into the reaction vessel to a pressure of 0.1 MPa.
Preparation example fifteen
The difference between the preparation example and the third preparation example is that ethylene was introduced into the reaction vessel to a pressure of 0.3 MPa.
Preparation example sixteen
The difference between the preparation example and the third preparation example is that ethylene was introduced into the reaction vessel to a pressure of 0.7 MPa.
Preparation example seventeen
The difference between the preparation example and the third preparation example is that ethylene was introduced into the reaction vessel to a pressure of 1.0 MPa.
Comparative preparation example 1
The comparative preparation example is different from the third preparation example only in that the catalyst used in the comparative preparation example is a conventional non-star-shaped nickel pyridinimine catalyst.
The method for preparing alpha-olefin is as follows: vacuumizing a reaction system with a drying function and a stirring function, replacing the reaction system with ethylene for three times, adding a non-star-shaped pyridine imine nickel catalyst with the structural formula (III), toluene serving as a second organic solvent and methylaluminoxane serving as a cocatalyst, introducing ethylene to the reaction system until the pressure is 0.5MPa, keeping the ethylene pressure, stirring and reacting for 30min at the temperature of 10 ℃, and discharging the reaction system to normal pressure to obtain alpha-olefin; wherein the molar ratio of the aluminum element in the methylaluminoxane to the nickel element in the non-star-shaped pyridine imine nickel catalyst with the structural formula (III) is 500: 1.
Figure BDA0002239584250000211
Comparative preparation example 2
The comparative preparation example is different from the third preparation example only in that the catalyst used in the comparative preparation example is a conventional non-star-shaped nickel pyridinimine catalyst.
The method for preparing alpha-olefin is as follows: vacuumizing a reaction system with a drying function and a stirring function, replacing the reaction system with ethylene for three times, adding a non-star-shaped pyridine imine nickel catalyst with the structural formula (IV), toluene serving as a second organic solvent and methylaluminoxane serving as a cocatalyst, introducing ethylene to the reaction system until the pressure is 0.5MPa, keeping the ethylene pressure, stirring and reacting the mixture at 10 ℃ for 30min, and discharging the reaction system to normal pressure to obtain alpha-olefin; wherein the molar ratio of the aluminum element in the methylaluminoxane to the nickel element in the non-star-shaped pyridine imine nickel catalyst with the structural formula (IV) is 500: 1.
Figure BDA0002239584250000221
Performance testing
1. Effect of different types of catalysts on catalytic Activity and Selectivity
The results of gas phase analysis of the catalytic activity of the catalysts of preparation example three, comparative preparation example one and comparative preparation example two and the products after the reaction are shown in table 1:
Figure BDA0002239584250000222
table 1: catalytic activity and product analysis results of preparation example three, comparative preparation example one and comparative preparation example two
As can be seen from the results in table 1, the nickel-based catalyst of the present invention has excellent catalytic activity and selectivity to higher olefins. Compared with the existing non-star-shaped pyridine imine nickel catalyst, the star-shaped pyridine imine nickel catalyst in the embodiment of the application has higher catalytic activity, and C in the oligomerization product8-C18The content of the olefin is high and can reach 26.76%, which shows that the nickel-based catalyst can obviously improve the catalytic activity and the selectivity to high-carbon olefin in the application of preparing the alpha olefin.
2. Effect of different functional groups on catalytic Activity and Selectivity
In order to study the influence of functional groups with different structures on catalytic activity and selectivity, the catalytic activity and the products after reaction of the star-type pyridine imine nickel catalysts in the first to third preparation examples are subjected to gas phase analysis, and the results are shown in table 2:
Figure BDA0002239584250000223
Figure BDA0002239584250000231
table 2: catalytic activity and product analysis results of preparation examples one to three
From Table 2The results show that the star-type pyridine imine nickel-based catalyst can indeed show good catalytic activity in the method for preparing alpha-olefin by ethylene oligomerization using the star-type pyridine imine nickel-based catalyst in the embodiment of the application, and particularly when R in the star-type pyridine imine nickel-based catalyst is Br, the catalytic activity can reach 1.34 × 105g/(mol Ni. h)). The structure of the nickel-based catalyst in the embodiment of the present application is analyzed by combining the results in table 1, and the applicant believes that as the electron withdrawing effect of the star-type pyridine imine nickel-based catalyst is enhanced, the electron cloud density of the active metal center is reduced, which is beneficial to activating the cocatalyst to form an active center with an empty orbit for ethylene molecule coordination, so that the number of effective active centers in the system is increased, and ethylene participating in coordination and insertion reactions is increased, so that the catalytic activity is increased.
In addition, the electron-withdrawing effect is beneficial to the chain growth reaction, and C in the oligomerization product is added along with the enhancement of the electron-withdrawing effect8-C18The olefin content is gradually increased, and good selectivity for high-carbon olefin is shown; especially when R in the star-shaped pyridine imine nickel-based catalyst is Br, the catalyst is opposite to C8-C18The selectivity of olefin reaches 26.76 wt%. The star-shaped pyridine imine nickel catalyst has good application prospect and industrial popularization value in the field of petrochemical industry due to the catalytic characteristics.
3. Influence of different organic solvents on catalytic activity and selectivity
In order to study the influence of different organic solvents on the catalytic activity and selectivity in the process of preparing alpha-olefin, the application performs gas phase analysis on the catalytic activity of the three to five star-type pyridine imine nickel catalysts in the preparation examples and the products after reaction, and the results are shown in table 3:
Figure BDA0002239584250000232
table 3: catalytic activity and product analysis results of preparation examples three to five
As can be seen from Table 3, the same star-type nickel pyridinimine catalyst can be used to prepare alpha-olefinsHas better catalytic performance, but different solvents used in the preparation process have certain influence on the catalytic activity and the product distribution of the catalyst. Specifically, when toluene is used as the second organic solvent, the catalyst activity of the star-shaped pyridine imine nickel-based catalyst is the highest, and the catalyst activity is C8-C18The selectivity of olefin is best (C)8-C18High olefins are very important target products), catalytic activity is reduced when methylcyclohexane and cyclohexane are used as the second organic solvent, and C8-C18The olefin selectivity also decreases.
4. Influence of different reaction temperatures on catalytic activity and selectivity
The application analyzes the catalytic activity of the star-shaped pyridine imine nickel catalyst in the third preparation example, the sixth preparation example, the ninth preparation example and the products after reaction in a gas phase manner so as to research the influence of different catalytic reaction temperatures on the catalytic performance in the method for preparing alpha-olefin. The results are shown in Table 4:
Figure BDA0002239584250000241
table 4: catalytic activity and product analysis results of preparation example three and preparation examples six to nine
As can be seen from the above Table 4, although the same star-shaped pyridine imine nickel-based catalyst can be used for preparing the alpha-olefin, the catalyst has a better catalytic performance, but the temperature of the catalytic reaction in the preparation process has a certain influence on the catalytic activity and the product distribution of the catalyst. Specifically, the catalytic activity is maximum at a reaction temperature of 10 ℃ C8-C18The selectivity to olefin is also optimal and as temperature continues to rise, the catalytic activity decreases. The applicant analyzes and believes that the reason is that the ethylene molecule solubility in an oligomerization system is reduced along with the increase of the temperature, the effective ethylene molecular weight participating in the reaction is reduced, the oligomerization reaction rate is reduced, and the catalytic activity is reduced; at the same time, the rate of catalyst deactivation increases with increasing temperature, which is another major cause of reduced catalytic activity. In addition, as the temperature increases, the rate of chain growth decreases and the oligomeric productsC in8-C18The olefin content decreases. In general, the preferred reaction temperature for the preparation of alpha-olefins herein is 10 ℃.
5. Influence of different Al/Ni molar ratios on catalytic activity and selectivity
The application analyzes the catalytic activity of the star-type pyridine imine nickel catalyst in preparation example three and preparation examples ten to thirteen and the gas phase of the product after reaction to research the influence of different Al/Ni molar ratios on the catalytic performance in the method for preparing alpha-olefin. The results are shown in Table 5:
Figure BDA0002239584250000242
Figure BDA0002239584250000251
table 5: catalytic activity and product analysis results of preparation example three, preparation examples ten to thirteen
As can be seen from the above Table 5, although the same star-shaped pyridine imine nickel-based catalyst can be used for preparing the alpha-olefin, the catalyst has a better catalytic performance, but the molar ratio of Al to Ni in the preparation process has a certain influence on the catalytic activity and the product distribution of the catalyst. Specifically, with the increase of the molar ratio of Al/Ni, the catalytic activity of the star-shaped pyridine imine nickel-based catalyst shows the trend of increasing firstly and then decreasing, and for C8-C18The selectivity to olefin then shows a decreasing trend. The analysis reason is that when the molar ratio of Al/Ni is small, part of methylaluminoxane is used for eliminating water and oxygen remained in the reaction system, the remained methylaluminoxane is not enough for activating the catalyst into active species completely, and the number of the activated active species of the catalyst is increased along with the increase of the molar ratio of Al/Ni, so that the catalytic activity is improved; when the molar ratio of Al/Ni is more than 1000:1, an excessive amount of methylaluminoxane accumulates at the metal active site, resulting in deactivation of the catalyst, thereby deteriorating catalytic activity. Furthermore, as the Al/Ni molar ratio increases, the chain transfer rate increases, and C8-C18Reduction of olefin selectivity. The catalytic activity is highest when the molar ratio of Al/Ni is 1000:1, but in this case, for C8-C18The selectivity to olefin is somewhat low; when the molar ratio of Al to Ni is 300:1, for C8-C18The selectivity to olefins is higher but the catalytic activity is slightly lower. In order to comprehensively consider the catalytic activity and the selectivity of the high-carbon olefin, the molar ratio of Al to Ni is preferably 500: 1.
6. Effect of different ethylene pressures on catalytic Activity and Selectivity
The application analyzes the catalytic activity of the star-shaped pyridine imine nickel catalyst in preparation example III and preparation example fourteen to seventeen and the gas phase of the product after reaction to research the influence of different reaction pressures on the catalytic performance in the method for preparing alpha-olefin. The results are shown in Table 6:
Figure BDA0002239584250000252
table 6: preparation example III, preparation examples fourteen to seventeen catalytic activity and product analysis results
As can be seen from the above Table 6, although the same star-shaped pyridine imine nickel-based catalyst can be used for preparing the alpha-olefin, the catalyst has better catalytic performance, the ethylene pressure condition in the preparation process has certain influence on the catalytic activity and the product distribution of the catalyst. Specifically, with the increase of the ethylene pressure, the catalytic activity of the star-shaped pyridine imine nickel catalyst is gradually increased, and the catalyst is used for treating C8-C18The selectivity to olefin also gradually increases. This phenomenon occurs because the solubility of ethylene molecules in the system increases with increasing pressure, the amount of ethylene reacting with the active sites per unit time increases, and the catalytic activity increases; in addition, as the ethylene pressure increases, the rate of chain extension reaction increases by a greater extent than the rate of chain transfer reaction, so C in the product8-C18The higher olefin selectivity increases with increasing ethylene pressure. When the ethylene pressure is 1.0MPa, the catalytic activity reaches 4.39 multiplied by 105g/(mol Ni. h), for C8-C18The olefin selectivity is 31.93%, so that an ethylene pressure of 1.0MP is preferably used hereina reaction conditions.
In conclusion, the nickel-based catalyst with the star-shaped pyridine imine structure is designed and prepared, and the unique main structure and the unique microenvironment of the nickel-based catalyst are utilized, so that the nickel-based catalyst has the dual advantages of a homogeneous catalyst and a heterogeneous catalyst. In addition, the star-shaped pyridine imine nickel catalyst has the advantages of easily obtained raw materials, simple method steps, mild and mild conditions, and the nickel catalyst has good industrial applicability and wide industrial application prospect.
Further, the application also focuses on researching a method for preparing alpha-olefin by ethylene oligomerization by using the star-shaped pyridine imine nickel catalyst, and the reaction conditions of the method for preparing the alpha-olefin are researched in detail to obtain better catalytic activity and product selectivity, so that the product distribution range is not too wide. Particularly, when the star-shaped pyridine imine nickel-based catalyst is used for ethylene oligomerization, the catalyst shows good selectivity on high-carbon olefin, which is difficult to achieve by nickel-based catalysts with other star-shaped structures or other structures, and the star-shaped structures with more and longer flexible molecular chains can really have good catalytic activity and good product selectivity.
The star-shaped pyridine imine nickel-based catalyst disclosed in the embodiment of the application, the preparation method and the application thereof are described in detail, the principle and the implementation mode of the application are explained by applying specific examples, and the description of the examples is only used for helping to understand the method and the core idea of the application; meanwhile, for a person skilled in the art, according to the idea of the present application, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present application.

Claims (9)

1. The star-shaped pyridine imine nickel catalyst is characterized in that the structural formula (I) of the star-shaped pyridine imine nickel catalyst is as follows:
Figure 416104DEST_PATH_IMAGE001
wherein R is selected from H, Br and CH3One kind of (1).
2. The preparation method of the star-shaped pyridine imine nickel-based catalyst according to claim 1, characterized by comprising the following steps:
s1, adding 2-pyridylaldehyde or a substitute of the 2-pyridylaldehyde and a water absorbent into a first organic solvent to form a reaction system, cooling the reaction system to-5 ℃ under the condition of inert gas, adding an organic solution of a compound of a structural formula (II), reacting for 15-60min, stirring and heating to 20-40 ℃, continuously stirring and reacting for 20-40h, and filtering after reaction to obtain a filtrate;
Figure 802086DEST_PATH_IMAGE002
and S2, reacting the filtrate with an organic solution of nickel chloride hexahydrate under the condition of inert gas at the temperature of 20-40 ℃ for 20-40 hours under stirring to obtain the star-shaped pyridine imine nickel catalyst.
3. The method of claim 2, wherein the step of S1 is: adding 2-pyridylaldehyde or a substitute of the 2-pyridylaldehyde and the water absorbent into the first organic solvent at room temperature to form a reaction system, cooling the reaction system to 0 ℃ under the condition of inert gas, adding the organic solution of the compound of the structural formula (II), reacting for 30min, stirring, heating to 25 ℃, continuously stirring for reacting for 24h, and filtering under negative pressure after the reaction to obtain a filtrate; wherein the molar ratio of the compound of the structural formula (II) to the 2-pyridinecarboxaldehyde or the substituent of the 2-pyridinecarboxaldehyde is 1:5-1: 6.
4. The method of claim 2, wherein the step of S2 is: slowly dropwise adding the organic solution of nickel chloride hexahydrate into the filtrate under the condition of inert gas to form a reaction solution, stirring and reacting for 24 hours at 25 ℃, and carrying out post-treatment on the reaction solution after reaction to obtain the star-shaped pyridine imine nickel catalyst; wherein the molar ratio of the compound shown in the structural formula (II) to the nickel chloride hexahydrate is 1:3-1: 4.
5. The method of claim 4, wherein: in the step S2, the post-processing is: and adding ether into the reaction solution after the reaction to separate out a green solid, filtering and collecting the green solid, washing the green solid with anhydrous ether, and drying the washed green solid to constant weight under a vacuum condition to obtain the star-shaped pyridine imine nickel catalyst.
6. The production method according to any one of claims 2 to 5, characterized in that: in the preparation method, the substitute of the 2-pyridine formaldehyde is selected from 6-methyl-2-pyridine formaldehyde or 6-bromo-2-pyridine formaldehyde, and the water absorbent is selected from anhydrous sodium sulfate, anhydrous magnesium sulfate or anhydrous calcium chloride; the inert gas is selected from nitrogen, helium or argon; the first organic solvent in the step S1 is one or a mixture of two of methanol and ethanol; the solvent used in the organic solution of the compound of the structural formula (II) and the solvent used in the organic solution of the nickel chloride hexahydrate are both selected from one or a mixture of two of methanol and ethanol.
7. The use of the star-type nickel pyridinimine catalyst of claim 1 in the oligomerization of ethylene to produce alpha-olefins.
8. A process for the preparation of α -olefins, said process comprising: dissolving the star-shaped pyridine imine nickel catalyst of claim 1 in a second organic solvent, adding a cocatalyst, introducing ethylene to 0.1-1.0MPa, keeping the ethylene pressure constant, and stirring for reaction at 10-50 ℃ to obtain the alpha-olefin; wherein the cocatalyst is methylaluminoxane, and the molar ratio of aluminum element in the methylaluminoxane to nickel element in the star-shaped pyridine imine nickel catalyst is 300:1-1500: 1; the second organic solvent is one or a mixture of toluene, methylcyclohexane or cyclohexane.
9. The method according to claim 8, characterized in that it is: dissolving the star-shaped pyridine imine nickel catalyst in toluene, adding methylaluminoxane, introducing ethylene to 1.0MPa, keeping the ethylene pressure constant, and stirring and reacting at 10 ℃ to obtain the alpha-olefin; wherein the molar ratio of the aluminum element in the methylaluminoxane to the nickel element in the star-shaped pyridine imine nickel catalyst is 500: 1.
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