A dual-core enhanced ethylene selective tetramerization catalytic system and its application

Abstract

The invention discloses a binuclear enhanced ethylene selective tetramerization catalytic system and its application, belonging to the field of polymerization catalysts. The catalytic system of the present invention includes ligand a, transition metal compound b and activator c, wherein ligand a is composed of three parts: PNP ligand, PNNP ligand and rigid linking group. The present invention adopts a rigid group with a substituted group to connect PNP and PNNP, suppresses the interaction of the catalyst active center, reduces catalyst degradation and inactivation, and simultaneously passes through the large π bond of the linking group and the ligand skeleton through p-π conjugation, effectively transmits the electronic effect of the substituent on the linking group to the ligand, and has little influence on its steric group effect, thereby achieving the purpose of enhancing the thermal stability of the catalyst and maintaining its good 1-octene selectivity.

Description

Technical Field

[0001] The present invention belongs to the field of catalysis, and more specifically, relates to a binuclear enhanced ethylene selective tetramerization catalytic system and application thereof. Background Art

[0002] Selective tetramerization of ethylene is an important method for producing 1-octene, and the development and selection of catalytic systems are key technologies. This catalytic system primarily consists of a ligand, a metal salt, and a co-catalyst. The structure of the ligand has a significant impact on catalyst activity, selectivity, and the amount of polyethylene byproduct produced.

[0003] In the industrial application of ethylene selective tetramerization technology, in addition to catalytic activity and selectivity, the suppression and removal of polyethylene byproducts is also a key concern, directly impacting the long-term operation of production equipment. Catalytic systems composed of alkyl- or aryl-substituted bisphosphine ligands are currently the mainstream ethylene selective tetramerization catalytic systems due to their high 1-octene selectivity (generally between 60-75 wt%). However, during the highly selective ethylene oligomerization process, these systems also produce polyethylene byproducts (generally accounting for 0.1% to 10% of the total product). These polyethylene byproducts are generally divided into two types: low-molecular-weight flocculent polyethylene, which primarily dissolves in the reaction solution (completely soluble at 80-100°C) or remains suspended in the reaction solution in a flocculent form. Long-term accumulation can cause fouling on the inner walls of the equipment, hindering heat transfer; and high-molecular-weight filamentous polyethylene, which entangles internal equipment components, making it difficult to remove and prone to straining, leading to the accumulation of suspended polymers. The former is the majority. Therefore, the industry prefers to operate the reaction at higher temperatures to facilitate the majority of polyethylene byproducts to be discharged from the reaction system with the reaction solution. However, due to the structural properties of the ligands themselves, the optimal reaction temperature for catalyst systems composed of such ligands is generally between 30-60°C. Excessively high reaction temperatures can lead to rapid degradation and inactivation of the catalyst's active components, while also producing large amounts of polyethylene byproducts. An invention patent discloses a catalyst system composed of bisphosphine ligands with fluorophenyl or bulky sterically substituted phenyl groups. Leveraging their strong electron-withdrawing and bulky group effects, these ligands can maintain a certain level of catalytic activity at temperatures between 80-105°C. However, the introduction of these substituents increases the steric hindrance of the entire ligand, leading to a significant decrease in tetramerization selectivity (e.g., 1-octene selectivity <45% at 100°C).

[0004] The technical problem to be solved by the present invention is to further enhance the thermal stability of the catalyst active components at higher reaction temperatures through innovative design of the ligand structure, thereby achieving the goals of high temperature resistance, high activity and high 1-octene selectivity. Summary of the Invention

[0005] The present invention aims to overcome the deficiencies of the prior art and provide a dual-core enhanced ethylene selective tetramerization catalytic system and its application.

[0006] To achieve the above objectives, the present invention first provides a binuclear enhanced ethylene selective tetramerization catalytic system comprising three components: a ligand a, a transition metal compound b, and an activator c. The transition metal compound b is a metal compound of Groups IVB to VIII; the activator c is a compound containing a Group IIIA metal; the ligand a comprises a PNP ligand, a PNNP ligand, and a rigid linking group; and the ligand a has a structure as shown in the general formula I:

[0007]

[0008] Among them, R 1 , R 2 , R 3 , R 4 is a substituent group on a rigid linking group, R 1 , R 2 , R 3 , R 4 Same or different; R 5 , R 6 is the substituent group on the PNP and PNNP ligand part P, R 5 , R 6 The same or different; R is a substituent group on the N portion of the PNNP ligand.

[0009] According to a preferred embodiment of the present invention, R 1 , R 2 , R 3 , R 4 A hydrogen group, a fluoro group, a trifluoromethyl group or a tris(trifluoromethyl)silyl group are independently selected.

[0010] According to a preferred embodiment of the present invention, R 5 , R 6 , R are independently selected from alkyl, fluorine-substituted alkyl, phenyl, fluorine-substituted phenyl, alkyl-substituted phenyl, naphthyl, fluorine-substituted naphthyl, alkyl-substituted naphthyl, fluorine-substituted anthracenyl, alkyl-substituted anthracenyl, biphenyl, fluorine-substituted biphenyl, alkyl-substituted biphenyl; further preferably selected from methyl, isopropyl, cyclopentyl, cyclohexyl, phenyl, fluorine-substituted phenyl, alkyl-substituted phenyl, naphthyl, fluorine-substituted naphthyl or alkyl-substituted naphthyl.

[0011] According to a preferred embodiment of the present invention, the ligand a is selected from but not limited to one or more of the following structures:

[0012] 、 、 、 、 .

[0013] According to a preferred embodiment of the present invention, the transition metal in the transition metal compound b is selected from one or two of chromium, molybdenum, tungsten, cobalt, titanium, tantalum, vanadium, zirconium, iron, nickel or palladium, preferably chromium.

[0014] According to a preferred embodiment of the present invention, the activator c is one or a mixture of two or more of an alkyl aluminum compound, an alkyl aluminoxane compound, and an organic boron compound, wherein the alkyl aluminoxane compound comprises an alkyl aluminoxane compound from which volatile components have been removed.

[0015] According to a preferred embodiment of the present invention, the activator c is methylaluminoxane, modified methylaluminoxane or a mixture of the two; the activator c may also be a mixture of an alkyl aluminum and an organic boron compound;

[0016] According to a preferred embodiment of the present invention, the molar ratio of the ligand a to the transition metal compound b is 1:0.1-1, and the molar ratio of the ligand a to the activator c is 1:0.1-5000. Preferably, the molar ratio of the ligand a to the transition metal compound b is 1.05-1.2:1; and the molar ratio of the ligand a to the activator c is 1:200-2000.

[0017] The present invention also provides a method for preparing the catalyst system, which comprises pre-mixing the ligand a, the transition metal compound b, and the activator c or directly adding them into the reaction system for in-situ synthesis.

[0018] The present invention further provides a method for preparing 1-octene by using the catalyst system in ethylene oligomerization: ethylene is charged into a polymerization kettle, and then an inert solvent and the catalyst system are added to carry out ethylene oligomerization reaction, the reaction temperature is 0°C to 150°C, and the reaction pressure is 0.1MPa to 50MPa.

[0019] Preferably, the inert solvent is one or a mixture of two or more of an alkane, an aromatic hydrocarbon, an olefin or an ionic liquid.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention uses a rigid group with a substituted group to connect PNP and PNNP, thereby inhibiting the interaction between the active centers of the catalyst and reducing the degradation and deactivation of the catalyst. At the same time, the large π bond of the connecting group and the ligand skeleton are conjugated through p-π, so that the electronic effect of the substituent on the connecting group is effectively transferred to the ligand, while having little effect on its steric group effect, thereby achieving the purpose of enhancing the thermal stability of the catalyst and maintaining its good 1-octene selectivity. DETAILED DESCRIPTION

[0022] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Instead, these embodiments are provided to make the present invention more thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0023] The binuclear enhanced ethylene selective tetramerization catalytic system designed in the present invention comprises three components: ligand a, transition metal compound b and activator c. The transition metal compound b is a metal compound of Groups IVB to VIII; the activator c is a compound containing a Group IIIA metal.

[0024] Ligand a is a key component of the catalyst of the present invention, which consists of three parts: PNP ligand, PNNP ligand and rigid linking group; Ligand a has a structure as shown in general formula I:

[0025]

[0026] Among them, R 1 , R 2 , R 3 , R 4 is a substituent group on a rigid linking group, R 1 , R 2 , R 3 , R 4 Same or different; R 5 , R 6 is the substituent group on the PNP and PNNP ligand part P, R 5 , R 6 Same or different; R is a substituent group on the N portion of the PNNP ligand. Preferably, R 1 , R 2 , R 3 , R 4 are independently selected from hydrogen, fluorine, trifluoromethyl or tris(trifluoromethyl)silyl. 5 , R 6 , R are independently selected from alkyl, fluorine-substituted alkyl, phenyl, fluorine-substituted phenyl, alkyl-substituted phenyl, naphthyl, fluorine-substituted naphthyl, alkyl-substituted naphthyl, fluorine-substituted anthracenyl, alkyl-substituted anthracenyl, biphenyl, fluorine-substituted biphenyl, alkyl-substituted biphenyl; preferably methyl, isopropyl, cyclopentyl, cyclohexyl, phenyl, fluorine-substituted phenyl, alkyl-substituted phenyl, naphthyl, fluorine-substituted naphthyl or alkyl-substituted naphthyl.

[0027] The present invention designed the above-mentioned ligand based on the discovery during research that ethylene selective tetramerization catalytic systems composed of PNP ligands generally have high 1-octene selectivity, but poor thermal stability. They rapidly degrade and become inactivated at reaction temperatures above 70°C, resulting in a significant decrease in catalytic activity. While the thermal stability can be improved by introducing a large steric group or F substituent into the P substituent of the PNP ligand, the increased steric hindrance of the P substituent significantly reduces 1-octene selectivity. Similar to the PNP ligand, the PNNP ligand has an additional nitrogen atom in the ligand skeleton, which increases its electronegativity. Catalysts composed of these ligands have slightly greater thermal stability than the PNP ligand, but exhibit slightly lower 1-octene selectivity. Based on this, the present invention uses a rigid group with a substituted group to connect the PNP and PNNP, inhibiting the interaction between the active centers of the catalyst and reducing catalyst degradation and deactivation. At the same time, the large π bond of the connecting group and the ligand skeleton are conjugated through p-π, so that the electronic effect of the substituent on the connecting group is effectively transferred to the PNP ligand and the PNNP ligand, while having little effect on their steric group effect, thereby achieving the purpose of enhancing the thermal stability of the catalyst and maintaining its good 1-octene selectivity.

[0028] The present invention discloses a method for preparing a binuclear enhanced ethylene selective tetramerization catalytic system, comprising premixing the ligand a, the transition metal compound b, and the activator c or directly adding them to a reaction system for in-situ synthesis. The molar ratio of the ligand a to the transition metal compound b is 1:0.1-1, and the molar ratio of the ligand a to the activator c is 1:0.1-5000. Preferably, the molar ratio of the ligand a to the transition metal compound b is 1.05-1.2:1, and the molar ratio of the ligand a to the activator c is 1:200-2000.

[0029] In the binuclear enhanced ethylene selective tetramerization catalytic system of the present invention, the structure of ligand a is of interest only. Specifically, the selected ligand a is required to satisfy general formula I. However, the route or synthesis method of ligand a is not specifically limited. Typically, but not limiting, ligand a can be synthesized according to the route shown in formula II below:

[0030]

[0031] All substituents in formula II are as defined above, and R is an alkyl group.

[0032] In an optional embodiment, the synthesis method of ligand a is as follows:

[0033] p-Aminophenylhydrazine (Compound III) and an aldehyde compound (such as acetaldehyde) are measured in a 1:1 molar ratio and dissolved in toluene. The toluene solution of the aldehyde compound is slowly added dropwise to a p-aminophenylhydrazine toluene solution dispersed with anhydrous sodium sulfate (a water absorbent) at room temperature under nitrogen protection and stirring. The reaction is then carried out at room temperature for 12 hours. Intermediate 1 is obtained by filtration and concentration and crystallization. Intermediate 1 and sodium borohydride are added to anhydrous ethanol in a 1:2 molar ratio, stirred at room temperature under nitrogen protection for 12 hours, and the solvent is removed by vacuum extraction. Intermediate 2 is then obtained after extraction with n-hexane.

[0034] Under nitrogen protection, intermediate 2 and triethylamine were dissolved in anhydrous dichloromethane at a molar ratio of 1:3.5. Diphenylphosphonium chloride (molar ratio to intermediate 2 was 3.01:1) was slowly added dropwise to the above solution at -20°C while stirring. The temperature was naturally raised to room temperature, and then stirred at room temperature for 12 hours. The mixture was filtered, the solvent was removed, and the product ligand a was obtained after extraction with n-hexane and concentration and crystallization.

[0035] In the embodiment of the present invention, the following ligands were specifically prepared according to the process of Formula II to evaluate the catalytic performance:

[0036]

[0037]

[0038]

[0039]

[0040]

[0041] The present invention uses the following process to evaluate the performance of the catalyst system:

[0042] The catalyst system comprises: ligand a (selected from ligands a1-a5), transition metal compound b, and activator c, with a molar ratio of (1.05-1.2):1: (500-1500).

[0043] A 500 mL autoclave was heated to a vacuum for 2 hours, replaced with nitrogen three times, and cooled to the desired temperature (60-105°C). Dehydrated methylcyclohexane (200 mL) and the catalyst system were added, and ethylene was then introduced to the desired reaction pressure. The oligomerization reaction was carried out at 60-105°C and 4 MPa. After 30 minutes, the temperature was lowered with condensed water, the pressure was released, and the reaction was terminated with 10% by weight of acidified ethanol. The distribution of the resulting oligomerization products is shown in Table 1.

[0044] Table 1 - Comparison of carbon number distribution of ethylene selective oligomerization products

[0045]

[0046] Example 1

[0047] The ligand selected was ligand a1, and the catalyst system composition was as follows: ligand a1, chromium acetylacetonate, and MMAO were pre-mixed in a molar ratio of 1.05:1:500 and added to the reaction system. The chromium content in the reaction system was 2 μmol. The polymerization reaction temperature was 100° C. and the pressure was 4 MPa.

[0048] Example 2

[0049] The ligand selected was ligand a2, and the catalyst system composition was as follows: ligand a1, chromium acetylacetonate, and MMAO were pre-mixed in a molar ratio of 1.1:1:500 and added to the reaction system. The chromium content in the reaction system was 8 μmol. The polymerization reaction temperature was 90°C and the pressure was 4 MPa.

[0050] Example 3

[0051] The ligand selected was ligand a3, and the catalyst system composition was as follows: ligand a1, chromium acetylacetonate, and MMAO were pre-mixed in a molar ratio of 1.05:1:1000 and added to the reaction system. The chromium content in the reaction system was 4 μmol. The polymerization reaction temperature was 105°C and the pressure was 4 MPa.

[0052] Example 4

[0053] The ligand selected was ligand a4, and the catalyst system composition was as follows: ligand a1, chromium acetylacetonate, and MMAO were pre-mixed in a molar ratio of 1.2:1:500 and added to the reaction system. The chromium content in the reaction system was 2 μmol. The polymerization reaction temperature was 90°C and the pressure was 4 MPa.

[0054] Example 5

[0055] The ligand selected was ligand a5, and the catalyst system composition was as follows: ligand a1, chromium acetylacetonate, and MMAO were pre-mixed in a molar ratio of 1.1:1:1000 and added to the reaction system. The chromium content in the reaction system was 6 μmol. The polymerization reaction temperature was 100° C. and the pressure was 4 MPa.

[0056] Examples 6-10

[0057] Other conditions were the same as those in Example 4, except that the polymerization reaction temperatures in Examples 6 to 10 were selected as 60°C, 70°C, 80°C, 105°C, and 110°C, respectively.

[0058] Examples 11-13

[0059] Other conditions were the same as those in Example 4, except that the amount of ligand a4 was changed. The molar ratios in the catalyst systems of each example were: 1.05:1:500 (Example 11); 1.1:1:500 (Example 12); and 1.15:1:500 (Example 13).

[0060] Examples 14-16

[0061] Other conditions were the same as those in Example 4, except that the amount of MMAO was changed. The molar ratios in the catalyst systems of each example were: 1.2:1:1000 (Example 14); 1.2:1:1500 (Example 15); and 1.2:1:2000 (Example 16).

[0062] Example 17

[0063] The ligand selected was ligand a1, and the catalyst system composition was as follows: ligand a1, tetrahydrofuran chromium trichloride, and MMAO were pre-mixed in a molar ratio of 1.05:1:500 and added to the reaction system. The chromium content in the reaction system was 2 μmol. The polymerization reaction temperature was 100° C. and the pressure was 4 MPa.

[0064] Example 18

[0065] The ligand selected was ligand a2, and the catalyst system composition was as follows: ligand a1, chromium acetylacetonate, and MMAO were pre-mixed in a molar ratio of 1.05:1:500 and added to the reaction system. The chromium content in the reaction system was 2 μmol. The polymerization reaction temperature was 100° C. and the pressure was 4 MPa.

[0066] Example 19

[0067] The ligand selected was ligand a3, and the catalyst system composition was: ligand a1, chromium acetylacetonate, MMAO+triethylaluminum in a molar ratio of 1.05:1:500 (MMAO:triethylaluminum = 4:1), which were pre-mixed and added to the reaction system. The chromium content in the reaction system was 2 μmol; the polymerization reaction temperature was 100°C and the pressure was 4 MPa.

[0068] Example 20

[0069] Other conditions were the same as those in Example 4, except that the ligands selected in Example 20 were: PNP ligand (bis(diphenylphosphine)(isopropyl)amine).

[0070] The carbon number distribution comparison of the ethylene selective oligomerization products of each embodiment is shown in Table 1.

[0071] As can be seen from Table 1, the catalyst of the present invention still has high 1-octene selectivity and catalytic activity (1-octene selectivity>50%, catalytic activity>1×10 6 gpro / g Cr / h).

[0072] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A dual-core enhanced ethylene selective tetramerization catalytic system, characterized in that: It consists of three components: Ligand a; A transition metal compound b, wherein the transition metal compound b is a metal compound of Groups IVB to VIII; Activator c, activator c is a compound containing a Group IIIA metal; Among them, ligand a is composed of three parts: PNP ligand, PNNP ligand and rigid linking group; ligand a has the structure shown in the following formula: ; Among them, R 1 , R 2 , R 3 , R 4 is a substituent group on a rigid linking group, R 1 , R 2 , R 3 , R 4 Same or different; R 5 , R 6 is the substituent group on the PNP and PNNP ligand part P, R 5 , R 6 Same or different; R is a substituent group on the N portion of the PNNP ligand.

2. A dual-core enhanced ethylene selective tetramerization catalytic system according to claim 1, characterized in that: R 1 , R 2 , R 3 , R 4 A hydrogen group, a fluoro group, a trifluoromethyl group or a tris(trifluoromethyl)silyl group are independently selected.

3. The dual-core enhanced ethylene selective tetramerization catalytic system according to claim 1, characterized in that: R 5 , R 6 , R are independently selected from alkyl, fluorine-substituted alkyl, phenyl, fluorine-substituted phenyl, alkyl-substituted phenyl, naphthyl, fluorine-substituted naphthyl, alkyl-substituted naphthyl, fluorine-substituted anthracenyl, alkyl-substituted anthracenyl, biphenyl, fluorine-substituted biphenyl, and alkyl-substituted biphenyl.

4. The dual-core enhanced ethylene selective tetramerization catalytic system according to claim 1, characterized in that: The ligand a is selected from one or more of the following structures: 、 、 、 、 。 5. The dual-core enhanced ethylene selective tetramerization catalytic system according to claim 1, characterized in that: The transition metal in the transition metal compound b is selected from one or two of chromium, molybdenum, tungsten, cobalt, titanium, tantalum, vanadium, zirconium, iron, nickel or palladium.

6. The dual-core enhanced ethylene selective tetramerization catalytic system according to claim 1, characterized in that: The activator c is one or a mixture of two or more of an alkyl aluminum compound, an alkyl aluminumoxane compound, and an organic boron compound.

7. The dual-core enhanced ethylene selective tetramerization catalytic system according to claim 6, characterized in that: The activator C is methylaluminoxane, modified methylaluminoxane or a mixture of the two; or the activator C is a mixture of alkyl aluminum and an organic boron compound.

8. The dual-core enhanced ethylene selective tetramerization catalytic system according to claim 1, characterized in that: The molar ratio of the ligand a to the transition metal compound b is 1:0.1~1, and the molar ratio of the ligand a to the activator c is 1:0.1~5000.

9. A method for preparing an ethylene selective tetramerization catalytic system according to any one of claims 1 to 8, characterized in that: The ligand a, the transition metal compound b, and the activator c are pre-mixed or directly added into the reaction system for in-situ synthesis.

10. A method for preparing 1-octene by ethylene oligomerization based on the ethylene selective tetramerization catalytic system according to any one of claims 1 to 8, characterized in that: An inert solvent and the catalyst system are added to a polymerization kettle, and then ethylene is charged to carry out ethylene polymerization reaction. The reaction temperature is 0°C to 150°C; the reaction pressure is 0.1MPa to 50MPa; the inert solvent is one or a mixture of two or more of alkanes, aromatic hydrocarbons, olefins or ionic liquids.

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