Catalyst system for ethylene trimerization and tetramerization with little polymer generation, preparation method and application thereof

Abstract

The application provides an ethylene trimerization and tetramerization catalyst system with little polymer generation, a preparation method and application thereof, and belongs to the technical field of homogeneous catalysis. The ethylene selective trimerization and tetramerization catalyst system comprises: a transition metal complex cation a, which is a metal complex cation of group IVB-VIII; an activator b, which is at least one of an alkyl aluminum compound, an alkoxy aluminum compound, an aryloxy aluminum compound, an alkyl aluminum alkoxide compound and an organic boron compound; and an ionic liquid c, which is composed of a quaternary ammonium salt cation and a tetrafluoroborate anion, a hexafluorophosphate anion, a tetraalkoxy aluminum anion or a tetra-perfluorophenyl boron anion. The catalyst system is mainly used for ethylene oligomerization, and when used for catalyzing ethylene trimerization and tetramerization, has the characteristics of high catalytic activity, high 1-hexene and 1-octene selectivity, little high polymer byproduct generation and low production cost.

Description

Technical Field

[0001] This invention belongs to the field of homogeneous catalysis technology, specifically relating to catalyst systems for ethylene trimerization and tetramerization with minimal polymer formation, their preparation methods, and applications. Background Technology

[0002] Higher linear α-olefins such as 1-hexene and 1-octene are important basic organic chemical raw materials with significant applications in high-performance polyolefins and high-end synthetic lubricants, and their demand continues to grow. Selective oligomerization of ethylene is the main method for producing high-purity higher linear α-olefins such as 1-hexene, 1-octene, 1-decene, and 1-dodecene. Among these methods, the trimerization of ethylene to 1-hexene and the tetramerization of ethylene to 1-octene exhibit high selectivity and good atom economy, aligning with the development trend of green chemistry.

[0003] Many studies have combined transition metals with aromatic heterocyclic ligands containing N, P, S, and O for use in trimerization, tetramerization, and polymerization catalytic systems of olefins, such as WO03 / 053890A1, WO 03 / 053891, WO 04 / 056479A1, WO 04 / 056477A1, WO 04 / 056480A1, WO 04 / 056478A1, WO 05 / 123884A2, WO 05 / 123633A1, CN1741850A (WO2004 / 056478A1), CN1741849A (WO2004 / 056479A1), CN101032 695A, CN101351424A, CN101415494A, CN1651142A, CN101291734A, US2006 / 0128910A1, CN20 Patents include 1880057196.4, CN201780043063.7, CN201780032874.7, CN201380014632.7, CN201080003564.0, CN201080003564.0, CN200880002464.9, CN200880002464.9, and CN200780100280.1. In the aforementioned methods for trimerizing and tetramerizing olefins, neutral transition metal complexes are used as catalysts, requiring the in-situ formation of oligomerization catalytic active centers under the action of one or more activators. However, during this process, a small number of high-polymerization catalytic active centers inevitably form, leading to the unavoidable formation of high-molecular-weight polyethylene and other polymers during the ethylene oligomerization reaction.

[0004] Activators used for olefin oligomerization generally include: organoaluminum compounds, organoaluminoxane compounds, organoboron compounds, organic salts (such as methyllithium and methylmagnesium bromide), and inorganic acids and inorganic salts (such as tetrafluoroborate ethers, silver tetrafluoroborate, and sodium hexafluoroantimonate). Among these, alkylaluminoxanes are commonly used, especially methylaluminoxane (MAO) or modified methylaluminoxane (MMAO). However, due to the high cost of MAO or MMAO activators, industrially, ethylene oligomerization is generally carried out under low activator concentration conditions to ensure economic viability. However, under low initial aluminum concentrations (e.g., <6 mmol / L), the reduced aluminum chain transfer efficiency decreases the oligomerization rate during catalytic ethylene oligomerization. Simultaneously, the high-molecular-weight active centers are used to generate high-molecular-weight polyethylene and other polymers. These polymers, due to their poor solubility, can cause reactor blockage and reduced heat exchanger efficiency, affecting the long-term operation of the production plant.

[0005] The use of organoboron compounds as activators is well-known. David S McGuinness et al. have studied in detail the effects of adding borate or aluminate compounds on catalytic activity, product selectivity, and catalyst degradation pathways in ethylene trimerization and tetramerization catalytic systems. They found that the combination of borate or aluminate with alkylaluminum can induce catalytic activity in Cr / PNP combined trimerization and tetramerization catalysts. The selectivity of the liquid fraction is similar to that when MAO is used as the activator, but the catalytic activity is greatly reduced, and a certain proportion of polymer is still generated. Organometallic 2007, 26, 11:08-11:11; Organometallic 2007, 26, 2561-2569).

[0006] Therefore, for the ethylene oligomerization (including trimerization and tetramerization) reaction process, in order to reduce production costs and ensure the long-term operation of the production equipment, a catalyst system is proposed that can solve the following problems, including: ① improving the activity of the catalyst; ② reducing the amount of MAO or MMAO used or finding low-cost alternatives; ③ reducing the formation of polymers by-products, etc., which are long-term research directions for researchers. Summary of the Invention

[0007] This invention provides a catalyst system for ethylene trimerization and tetramerization with minimal polymer formation, its preparation method, and its application. The catalyst system involved has the characteristics of high catalytic activity, high selectivity for 1-hexene and 1-octene, and minimal formation of polymer byproducts when used to catalyze ethylene trimerization and tetramerization.

[0008] This invention proposes a catalyst system for selective trimerization and tetramerization of ethylene, comprising:

[0009] Transition metal complex cation a is a metal complex cation of group IVB~VIII, and has the structure shown in formula (I);

[0010] Activator b is at least one of alkylaluminum compounds, alkoxyaluminum compounds, aryloxyaluminum compounds, alkylaluminoxane compounds, and organoboron compounds;

[0011] Ionic liquid c is composed of quaternary ammonium salt cations and tetrafluoroborate anions, hexafluorophosphate anions, tetraalkoxyaluminum anions, or tetraperfluorophenylboron anions.

[0012] Formula (I);

[0013] In formula (I),

[0014] A and C are independently selected from nitrogen, phosphorus, sulfur, and oxygen atoms, respectively.

[0015] B is a linker consisting of multiple atoms or a single atom;

[0016] R 1 R 2 R 3 R 4 R 5 Each group is independently selected from alkyl, aryl, or dialkylamino groups;

[0017] R 6 R 7 R 8 Each is independently selected from alkyl, aryl, or halogen groups;

[0018] M is selected from metals of groups IVB to VIII.

[0019] Furthermore, when B is a single atom, B is selected from nitrogen, phosphorus, silicon, boron, or germanium atoms;

[0020] Preferably, when B is a linker formed by multiple atoms, B is selected from a linker group formed by two or more carbon atoms, an aryl group, or a bridging group formed by chemical bonds of heteroatoms; wherein the heteroatoms are at least one of silicon, tin, boron, phosphorus, nitrogen, oxygen, or sulfur.

[0021] More preferably, B is selected from nitrogen, phosphorus, ethyl, propyl, vinyl, propenyl or phenyl.

[0022] Furthermore, the alkyl group is C1-C. 10 Alkyl groups;

[0023] Preferably, the alkyl group is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, cyclopentyl, or cyclohexyl;

[0024] More preferably, the alkyl group is selected from methyl, ethyl, isopropyl, isobutyl, isopentyl, or cyclopentyl.

[0025] Furthermore, the aryl group is C6-C. 20 Aryl and aryl derivatives;

[0026] Preferably, the aryl group comprises substituted phenyl or unsubstituted phenyl.

[0027] Furthermore, M is selected from chromium, molybdenum, tungsten, cobalt, titanium, tantalum, vanadium, zirconium, iron, nickel, or palladium.

[0028] Furthermore, in activator b, the alkylaluminum compound is a trialkylaluminum compound;

[0029] Preferably, the alkylaluminum compound includes at least one of trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, or tri-n-octylaluminum.

[0030] Further, the ionic liquid c includes at least one of 1,3-dimethylimidazolium tetrafluoroborate, 1,3-di-(1-methylimidazolyl)-2-propanol tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1,3-dimethylimidazolium hexafluorophosphate, 1,3-dimethylimidazolium hexafluoroantimonate, bis(octadecylmethylamine)tetrafluorophenylborate, and bis(octadecylbenzylamine)tetrafluorophenylborate.

[0031] Furthermore, the molar ratio of the transition metal complex cation a, activator b, and ionic liquid c is 1:0.5~5000:0.1~100.

[0032] The present invention also proposes a method for preparing any of the above-described catalyst systems, comprising the following steps:

[0033] Transition metal complex cation a, activator b, and ionic liquid c are premixed or directly added to the reaction system for in-situ synthesis.

[0034] The present invention also proposes a method for ethylene oligomerization, wherein the ethylene oligomerization reaction is carried out in the presence of any of the catalyst systems described above.

[0035] This invention has the following advantages:

[0036] The catalyst system proposed in this invention comprises a transition metal complex cation a formed by a ligand and a metal active center. Under the action of an activator b and an ionic liquid c, the transition metal complex cation a coordinates with the activator b and the ionic liquid c to form a bidentate complex active center. This active center is activated by the R-phase in the transition metal complex cation a. 1 R 2 R 3 R 4 R5 R 6 R 7 R 8 The adjustment of the steric hindrance and electronic properties of the functional groups, along with the synergistic effect of activator c, can effectively regulate the chemical environment of the active center of the transition metal complex cation a. In particular, the introduction of ionic liquid c inhibits the isomerization of the transition metal complex cation a and the formation of the polymer active center, greatly solving the problem of polymer by-product generation. This effectively addresses the issue of long-term operation of production equipment affected by by-product polymer blockage of pipelines and reactors. Furthermore, it exhibits high selectivity for 1-hexene and 1-octene, as well as high catalytic activity. Moreover, when activator b is a lower-cost alkylaluminum compound, the catalyst activity and selectivity for 1-hexene and 1-octene remain good, completely resolving the high production cost caused by the expensive activator in ethylene trimerization and tetramerization catalytic systems. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. In the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0038] The catalyst system of the present invention will be described below.

[0039] It should be noted that the "selectivity of 1-hexene and 1-octene" in the text refers to the proportion of 1-hexene or 1-octene in the total products (all linear α-olefins and byproducts).

[0040] This invention provides a catalyst system for the selective trimerization and tetramerization of ethylene, comprising:

[0041] Transition metal complex cation a is a metal complex cation of group IVB~VIII, and has the structure shown in formula (I);

[0042] Activator b is at least one of alkylaluminum compounds, alkoxyaluminum compounds, aryloxyaluminum compounds, alkylaluminoxane compounds, and organoboron compounds;

[0043] Ionic liquid c is composed of quaternary ammonium salt cations and tetrafluoroborate anions, hexafluorophosphate anions, tetraalkoxyaluminum anions, or tetraperfluorophenylboron anions.

[0044] Formula (I);

[0045] In formula (I),

[0046] A and C are independently selected from nitrogen, phosphorus, sulfur, and oxygen atoms, respectively;

[0047] B is a linker consisting of multiple atoms or a single atom;

[0048] R 1 R 2 R 3 R 4 R 5 Each group is independently selected from alkyl, aryl, or dialkylamino groups;

[0049] R 6 R 7 R 8 Each is independently selected from alkyl, aryl, or halogen groups;

[0050] M is selected from metals of groups IVB to VIII.

[0051] The catalyst system proposed in this invention comprises a transition metal complex cation a formed by a ligand and a metal active center. Under the action of activator b and ionic liquid c, the transition metal complex cation a coordinates with activator b and ionic liquid c to form a bidentate complex active center. This active center is formed by the R-phase in the transition metal complex cation a. 1 R 2 R 3 R 4 R 5 R 6 R 7 R 8 The adjustment of the steric hindrance and electronic properties of the group, as well as the synergistic effect of activator c, can effectively regulate the chemical environment of the active center of the transition metal complex cation a. In particular, the introduction of ionic liquid c inhibits the formation of transition metal complex cation a isomers and polymer active centers. A small amount of polymer will be generated in the catalytic system, but it will not have too much impact on the resulting product. This greatly solves the problem of polymer by-product formation. As a result, the catalyst system of this invention is used for the selective oligomerization of ethylene and has the characteristics of high selectivity for 1-hexene and 1-octene and high catalytic activity.

[0052] The catalyst system proposed in this invention mainly includes a transition metal complex cation a, an activator b, and an ionic liquid c.

[0053] Regarding the transition metal complex cation a in the catalyst system, it is a metal complex cation of group IVB~VIII with the structure shown in formula (I) above, as follows:

[0054] In a preferred embodiment of the present invention, A and C are each independently selected from phosphorus atoms. The two phosphorus atoms form coordination with the transition metal, facilitating the subsequent stable catalytic activity of the metal active center. The transition metal complex cation a can be a bisphosphine complex cation of the PNP, PCCP, PNSiP, PCNP, or PCCCP type. The substituents on the two phosphorus atoms of these complex cations can be symmetrical or asymmetrical. Under the action of activator b and ionic liquid c, the transition metal complex cation a coordinates with activator b and ionic liquid c to form a bidentate complex active center. By adjusting R... 1 R 2 R 3 R 4 R 5 R 6 R 7 R 8 The steric hindrance and electronic properties of the functional groups can effectively regulate the chemical environment of the active center of the transition metal complex cation a, thereby affecting the selective oligomerization reaction of ethylene.

[0055] It should be noted that, in the embodiments of the present invention, when A and C are independently selected from oxidized nitrogen, phosphorus, or sulfur atoms, the valence states of A and C allow for this oxidation. Furthermore, when A or C is oxygen or sulfur, R... 2 R 5 It can be non-existent.

[0056] In one embodiment of the present invention, when B is a single atom, B is selected from nitrogen, phosphorus, silicon, boron or germanium atoms.

[0057] In one embodiment of the present invention, when B is a linker composed of multiple atoms, B is selected from linking groups formed by two or more carbon atoms, aryl groups, or bridging groups formed by chemical bonds between heteroatoms. The heteroatom is at least one of silicon, tin, boron, phosphorus, nitrogen, oxygen, or sulfur. That is, the heteroatom is one, two, or a combination of two or more of silicon, tin, boron, phosphorus, nitrogen, oxygen, or sulfur. For example, the linking group formed by two or more carbon atoms is a linking group formed by single, double, or triple bonds between two or more carbon atoms.

[0058] In a preferred embodiment of the present invention, B is selected from nitrogen (N), phosphorus (P), ethyl (-CC-), propyl (-CCC-), vinyl (-C=C-), propenyl (-C=CC-), or phenyl.

[0059] In this embodiment of the invention, R 1 R 2 R 3 R 4 R 5 They can be the same or different. When R 1 R2 R 3 R 4 R 5 At different times, R 1 R 2 R 3 R 4 R 5 At least one of them is selected from alkyl groups.

[0060] In this embodiment of the invention, R is determined according to different coordination conditions. 6 R 7 It can exist or not exist. For example, when M is chromium, R 6 Or R 7 One of the two may not exist.

[0061] In one embodiment of the present invention, the alkyl group is C1-C. 10 The alkyl group is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, cyclopentyl, or cyclohexyl. More preferably, the alkyl group is selected from methyl, ethyl, isopropyl, isobutyl, isopentyl, or cyclopentyl.

[0062] In one embodiment of the present invention, the aryl group is C6-C. 20 The aryl group and its derivatives. Preferably, the aryl group is selected from substituted phenyl or unsubstituted phenyl groups. More preferably, the substituted phenyl group includes 2-methylphenyl, 2-chlorophenyl, 2-fluorophenyl, 2-methoxyphenyl, 3-methylphenyl, 4-fluorophenyl, 4-chlorophenyl, 4-methoxyphenyl, trifluoromethylphenyl, p-tolyl, 3,5-di(trifluoromethyl)phenyl, or 3,5-dimethyl-4-methoxyphenyl, etc. Preferably, the aryl derivative is selected from naphthyl, substituted naphthyl, or fluorene, etc.

[0063] In one embodiment of the present invention, the dialkylamine group includes dimethylamino, diethylamino, dipropylamino, etc.

[0064] In one embodiment of the present invention, the halogen includes chlorine (Cl), bromine (Br), and iodine (I). Preferably, the halogen is chlorine (Cl).

[0065] In one embodiment of the present invention, M is selected from chromium, molybdenum, tungsten, cobalt, titanium, tantalum, vanadium, zirconium, iron, nickel, or palladium. Preferably, M is selected from chromium, cobalt, or nickel. More preferably, M is selected from chromium.

[0066] In one embodiment of the present invention, the method for preparing transition metal complex cation a includes:

[0067] Under inert gas protection, ligand L and a transition metal source are added to an organic solvent, followed by the addition of an alkylating agent. The first reaction yields an alkylchromium complex.

[0068] Adding ionic liquid further leads to a second reaction, yielding a solution of transition metal complex cation a.

[0069] The specific reaction formula is as follows:

[0070]

[0071] Specifically, ligand L has the structure shown in equation a:

[0072] Formula a;

[0073] In formula a, A and C are independently selected from nitrogen, phosphorus, sulfur, and oxygen atoms, respectively;

[0074] B is a linker consisting of multiple atoms or a single atom;

[0075] R 1 R 2 R 3 R 4 R 5 Each group is independently selected from alkyl, aryl, or dialkylamino groups.

[0076] It should be noted that A, B, C, and R 1 R 2 R 3 R 4 R 5 The structural formula (I) of the above transition metal complex cation a contains A, B, C, and R. 1 R 2 R 3 R 4 R 5 same.

[0077] Specifically, the alkylating agent is selected from alkyl metal compounds. These alkyl metal compounds include alkyl aluminum compounds, alkyl zinc compounds, alkyl lithium compounds, and alkyl magnesium compounds. For example, alkyl aluminum compounds can be triethylaluminum, triisobutylaluminum, etc.

[0078] Specifically, transition metal sources include chromium sources, molybdenum sources, tungsten sources, cobalt sources, titanium sources, tantalum sources, vanadium sources, zirconium sources, iron sources, nickel sources, or palladium sources. More specifically, the transition metal source is a chromium source. For example, a chromium source has the general formula CrR. n The chromium compound shown, where R n It is an organic anion or a neutral molecule. Specifically, R n Chromium typically contains 1 to 10 carbon atoms, where n is an integer from 0 to 6, and the valence state of chromium is 0 to 6. More specifically, R nThe functional group is an organic compound or its functional group containing a carboxyl group, a β-diketone group, or a hydrocarbon group. From the perspective of ease of solubility and handling, more suitable chromium compounds include one of the following: chromium acetate, chromium isooctanoate, chromium n-octanoate, chromium acetylacetonate, dicyclopentadiene chromium, diphenyl chromium, CrCl3(THF)3, CrCl2(THF)2, (phenyl)tricarbonyl chromium, and hexacarbonyl chromium.

[0079] Specifically, the ionic liquid is an ionic liquid composed of a quaternary ammonium salt cation and tetrafluoroborate anions, hexafluorophosphate anions, tetraalkoxyaluminum anions, or tetraperfluorophenylboron anions. For example, the ionic liquid may include at least one of 1,3-dimethylimidazolium tetrafluoroborate, 1,3-di-(1-methylimidazolyl)-2-propanol tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1,3-dimethylimidazolium hexafluorophosphate, 1,3-dimethylimidazolium hexafluoroantimonate, dioctadecylmethylamine tetraperfluorophenylborate, and dioctadecylbenzylamine tetraperfluorophenylborate.

[0080] Specifically, the time for the first reaction is 0.2 to 1 hour; the time for the second reaction is 0.8 to 1.5 hours.

[0081] Specifically, the molar ratio of ligand L to transition metal source is 1:0.8~1.2. The molar ratio of ionic liquid c to transition metal source is 1:0.8~1.2.

[0082] Regarding the catalyst system, activator b is at least one of alkylaluminum compounds, alkoxyaluminum compounds, alkylaluminoxane compounds, aryloxyaluminum compounds, or organoboron compounds, as detailed below:

[0083] Specifically, alkylaluminum compounds can be various trialkylaluminum compounds, and alkylaluminum compounds can also be alkylaluminum halides, alkylaluminum hydrides, or alkylaluminum sesquichlorides, such as diethylaluminum chloride (AlEt2Cl) and triethylaluminum chloride (Al2Et3Cl3).

[0084] In a preferred embodiment of the present invention, the alkylaluminum compound includes at least one selected from trimethylaluminum (TMA), triethylaluminum (TEA), triisobutylaluminum (TIBA), tri-n-butylaluminum, tri-n-hexylaluminum, or tri-n-octylaluminum (TNOA). In this embodiment, the activator b is an alkylaluminum compound, which directly avoids the use of expensive alkylaluminoxanes, thereby significantly reducing the cost of the catalyst system and possessing extremely important industrial value. Those skilled in the art know that the most commonly used alkylaluminoxane, methylaluminoxane (MAO), has a 15% concentration solution costing approximately 300,000 RMB / ton, while modified methylaluminoxane (MMAO) costs approximately 300,000-700,000 RMB / ton. In contrast, pure alkylaluminum compounds such as triethylaluminum cost only 30,000-50,000 RMB / ton. Therefore, it can be seen that using an alkylaluminum compound as an activator can significantly reduce the cost of the catalyst system.

[0085] Specifically, aluminum alkoxy and aluminum aryloxy compounds can be tri-n-propoxyaluminum, tri-n-octyloxyaluminum, tri-n-octadecyloxyaluminum, Al(OC6F5)3, [(Et2O)2H][Al(OC6F5)4], (Et2O)Al{OCH(C6F5)2}3, (Et2O)-Al{OC(CF3)3}3, [Ph3C][Al{OC(CF3)3}4], [Ph3C][AlF{OC(CF3)3}3], [Ph3C][{(F3C)3CO}3Al-F-Al{OC(CF3)3}3], etc.

[0086] Specifically, organoboron compounds can be selected from ionic forms such as ammonium borate, B(C6F5)3, and [(C 18 H 37 [2MeNH]][B(PhF5)4, N,N-dimethylphenylammonium tetra(heptafluoronaphthyl)borate, N,N-dimethylcyclohexylammonium tetra(pentafluorophenyl)borate, N,N-diethylbenzylammonium tetra(pentafluorophenyl)borate, phenylbis(octadecylammonium)(hydroxyphenyl)tri(pentafluorophenyl)borate, (pentafluorophenyl)bis(octadecylammonium)tetra(pentafluorophenyl)borate, tetra(heptafluoronaphthyl) 2 (Borbid) borates, triphenylcarbontetra(pentafluorophenyl) borates, etc.

[0087] Specifically, the alkylaluminoxane compound can be selected from methylaluminoxane (MAO), modified methylaluminoxane (MMAO), ethylaluminoxane, isobutylaluminoxane, modified aluminum oxane, and methylaluminoxane (DMAO) with volatile components removed, etc. Activator b can be a mixture of an alkylaluminum compound and an alkylaluminoxane with volatile components removed, wherein the alkylaluminum compound can be TEA, and the alkylaluminoxane compound can be DMAO. Preferably, the molar ratio of TEA to DMAO is 0.01~100, more preferably 0.1~10. In this invention, TEA has a relatively weak alkylation ability, making it more suitable for oligomerization catalyst systems. Meanwhile, DMAO can shield the influence of volatile components such as toluene on the catalyst complexation process, thereby improving the activity of the catalyst system. The mixture of the two can further reduce the amount of activator used.

[0088] In the catalyst system, ionic liquid c is composed of quaternary ammonium salt cations and tetrafluoroborate anions, hexafluorophosphate anions, tetraalkoxyaluminum anions, or tetrafluorophenylboron anions. In this embodiment of the invention, the introduction of a specially structured ionic liquid can effectively regulate the chemical environment of the active center of the transition metal complex cation a, thereby inhibiting the isomerization of transition metal complex cation a and the formation of polymer active centers, thus solving the problem of polymer byproduct formation and resulting in high selectivity and high catalytic activity for 1-hexene and 1-octene. Specifically:

[0089] In this embodiment of the invention, ionic liquid c can be an ionic liquid composed of quaternary ammonium salt cation and tetrafluoroborate anion; ionic liquid c can also be an ionic liquid composed of quaternary ammonium salt cation and tetrafluorophenylboron anion; it can also be an ionic liquid composed of quaternary ammonium salt cation and hexafluorophosphate anion; or it can be an ionic liquid composed of quaternary ammonium salt cation and tetraalkoxyaluminum anion.

[0090] Preferably, the ionic liquid c includes at least one of 1,3-dimethylimidazolium tetrafluoroborate, 1,3-di-(1-methylimidazolyl)-2-propanol tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1,3-dimethylimidazolium hexafluorophosphate, 1,3-dimethylimidazolium hexafluoroantimonate, bis(octadecylmethylamine)tetrafluorophenylborate, and bis(octadecylbenzylamine)tetrafluorophenylborate.

[0091] In one embodiment of the present invention, the molar ratio of transition metal complex cation a, activator b, and ionic liquid c is 1:0.5~5000:0.1~100. Preferably, the molar ratio of transition metal complex cation a, activator b, and ionic liquid c is 1:0.5~1000:0.1~50. More preferably, the molar ratio of transition metal complex cation a, activator b, and ionic liquid c is 1:0.5~500:0.1~10.

[0092] The preparation method of the catalyst system of the present invention will be further described below.

[0093] In one embodiment of the present invention, the preparation method of the catalyst system may include the following steps:

[0094] In situ synthesis is achieved by pre-mixing or directly adding the transition metal complex cation a, activator b, and ionic liquid c to the reaction system. That is, the catalyst is prepared by pre-mixing the transition metal complex cation a, activator b, and ionic liquid c, or by pre-mixing all or part of two or three of them; alternatively, the transition metal complex cation a, activator b, and ionic liquid c can be directly added to the reaction system for in-situ synthesis.

[0095] It should be noted that the transition metal complex cation a, activator b, and ionic liquid c in the catalyst system can combine in any order to form the active components for the trimerization and tetramerization of ethylene.

[0096] The reaction of transition metal complex cation a, activator b, and ionic liquid c can occur through liquid-phase reactions, such as reactions in the presence of solvents like n-hexane, n-heptane, cyclohexane, methylcyclohexane, toluene, benzene, chlorobenzene, and their derivatives; solid-phase reactions; or in-situ reactions during ethylene oligomerization to generate catalyst active centers. The reaction can involve one, two, or all three of the aforementioned transition metal complex cation a, activator b, and ionic liquid c. This process also includes catalyst aging (pre-activation).

[0097] The application of the catalyst system of the present invention in the ethylene oligomerization reaction method is further explained below.

[0098] The present invention also provides a method for ethylene oligomerization, comprising an ethylene oligomerization reaction carried out in the presence of the above-described catalyst system.

[0099] In one embodiment of the present invention, the reaction is carried out in an inert solvent, which is at least one of alkanes, aromatics, halogenated aromatics, alkenes, or ionic liquids. Typical solvents include, but are not limited to, benzene, toluene, xylene, chlorobenzene, bromobenzene, fluorobenzene, cumene, n-heptane, n-hexane, methylcyclohexane, cyclohexane, 1-hexene, 1-octene, ionic liquids, etc., with methylcyclohexane and chlorobenzene being preferred.

[0100] In one embodiment of the present invention, the reaction temperature is 0℃~200℃. Preferably, the reaction temperature is 45℃~100℃.

[0101] In embodiments of the present invention, the pressure of the ethylene oligomerization reaction can be carried out at a pressure of 0.1 MPa to 50 MPa, preferably 1.0 MPa to 10 MPa.

[0102] In one embodiment of the present invention, the concentration of the catalyst in the reaction system can range from 0.01 μmol metal / L to 1000 μmol metal / L, preferably from 0.1 μmol metal / L to 10 μmol metal / L. It should be noted that the metal here refers to the transition metal in the transition metal complex cation a.

[0103] The following specific examples further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0104] Example 1 A method for selective oligomerization of ethylene, comprising:

[0105] 1. Preparation of transition metal complex cation a

[0106] In equation (I), R 1 Cyclopentyl, R 2 and R 3 Isopropyl, R 4 and R 5 For phenyl, R 7 and R 8 Ethyl, A is phosphorus (P), B is nitrogen (N), C is (P), and M is chromium (Cr);

[0107] The synthesis of the raw material N-cyclopentyl-N-(diisopropylphosphine)-1,1-diphenylphosphineamine was performed in accordance with patent ZL202010718125.3;

[0108] In a stirred 100 mL reactor fully purged with N2, 20 mL of dehydrated methylcyclohexane, 9.8 mg (25.2 μmol), and 9.0 mg (24.0 μmol) of CrCl3•(THF)3 were added. After reacting at room temperature for 5 min, 480 μL (1.0 M hexane solution) of 20 times the amount of triethylaluminum (AlEt3) activator was added, and stirring was continued for 30 min to form a light brown solution. Then, 24 μmol of ionic liquid (1,3-dimethylimidazolium tetrafluoroborate) was slowly added, and after stirring for 1 hour, a light green solution of chromium metal cation complex cation a was formed. The specific reaction formula is as follows:

[0109] ;

[0110] 2. Ethylene oligomerization reaction

[0111] The 100mL reactor was heated to 130°C. oThe mixture was evacuated to a vacuum for 20 minutes at a temperature above 60 °C, then cooled to the reaction temperature. After purging with nitrogen several times, ethylene was introduced. Dehydrated methylcyclohexane (20 mL), a solution of the aforementioned chromium metal complex cation a (2 mL, 2.4 μmol), activator b (triethylaluminum TEA, 2.4 mmol), and ionic liquid c (1,3-dimethylimidazolium tetrafluoroborate, 2.9 μmol) were added sequentially. The ethylene oligomerization reaction was carried out at 60 °C and 3.0 MPa ethylene pressure. After 60 min, the mixture was cooled in an ice bath, depressurized, and the reaction was terminated with 10% (w / w) acidified ethanol. The composition of the liquid product was analyzed by gas chromatography.

[0112] The ethylene oligomerization activity and product distribution are shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0113] Example 2

[0114] Same as Example 1. The difference is that R 2 Ethyl, R 3 The product is ethyl. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0115] Example 3

[0116] Same as Example 1. The difference is that R 2 For phenyl, R 3 It is phenyl. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0117] Example 4

[0118] Same as Example 1. The difference is that R 2 dimethylamino, R 3 It is dimethylamino. The synthesis of the ligand is based on patent ZL202010717943.1. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0119] Example 5

[0120] Same as Example 4. The difference is that B is phenyl. The synthesis method of the ligand is based on patent ZL202110284855.1. The distribution of the oligomer is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0121] Example 6

[0122] Same as Example 1. The difference is that R 7 R 8 The product is chlorine (Cl). The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0123] Example 7

[0124] Same as Example 1. The difference is that the amount of triethylaluminum used is 1.5 mmol, and the ionic liquid c is 1-ethyl-3-methylimidazolium tetrafluoroborate. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0125] Example 8

[0126] Same as Example 1. The difference is that the ionic liquid c is bis(octadecylmethylamine)tetrafluorophenylborate. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0127] Example 9

[0128] Same as Example 1. The difference is that the ionic liquid c is bis(octadecylbenzylamine)tetrafluorophenylborate. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0129] Example 10

[0130] Same as Example 1. The difference is that activator b is trimethylaluminum (TMA). The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0131] Example 11

[0132] Same as Example 1. The difference is that activator b is triisobutylaluminum (TIBA). The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0133] Example 12

[0134] Same as Example 2. The difference is that activator b is tri-n-octylaluminum (TNOA). The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0135] Example 13

[0136] Same as Example 2. The difference is that the ionic liquid c is bis(octadecylmethylamine)tetrafluorophenylborate and the reaction pressure is 5.5 MPa. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0137] Example 14

[0138] Same as Example 13. The difference is that R 1It is isopropyl. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0139] Example 15

[0140] Same as Example 2. The difference is that the solvent for synthesizing the transition metal cation and ethylene oligomerization was changed from methylcyclohexane to toluene. The distribution of the oligomerization products is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0141] Example 16

[0142] Same as Example 2. The difference is that the solvent for synthesizing the transition metal cation and ethylene oligomerization was changed from methylcyclohexane to chlorobenzene. The distribution of the oligomerization products is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0143] Example 17

[0144] Same as Example 1. The difference is that the amount of transition metal complex cation a added is 1.2 μmol. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0145] Example 18

[0146] Same as Example 2. The difference is that the reaction temperature was 50°C. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0147] Example 19

[0148] Same as Example 8. The difference is that the amount of ionic liquid added was 12 μmol. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0149] Example 20

[0150] Same as Example 2. The difference is that 1.2 mmol of activator was added during the preparation of the transition metal cation and during the oligomerization of ethylene. The distribution of the oligomerization products is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0151] Example 21

[0152] Same as Example 2. The difference is that the activator b is MAO. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0153] Comparative Example 1

[0154] Same as Example 2. The difference is that no ionic liquid was added. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0155] Comparative Example 2

[0156] Same as Example 2. The difference is that the type of ionic liquid added was changed to 1-ethyl-3-methylimidazolium tetrachloroaluminate. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0157] Comparative Example 3

[0158] Same as Example 2. The difference is that the type of ionic liquid added was replaced with [Ph3C][B(C6F5)4]. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0159] Comparative Example 4

[0160] Same as Example 2. The difference is that the chromium metal complex cation a was replaced by a ligand and a chromium source, which were added to the reaction system separately to react in situ and form a complex. The distribution of the oligomers is shown in Table 1, and the experimental conditions and catalyst activity are shown in Table 2.

[0161] Table 1 Comparison of carbon number distribution of oligomerization products

[0162]

[0163] Table 2 Experimental conditions and catalyst activities of the examples and comparative examples

[0164]

[0165] Note: 10 6 g oligomer / mol Cr.h; 1,3-dimethylimidazolium tetrafluoroborate (L1), 1-ethyl-3-methylimidazolium tetrafluoroborate (L2), bis(octadecylmethylamine)tetrafluorophenylborate (L3), bis(octadecylbenzylamine)tetrafluorophenylborate (L4); 1-ethyl-3-methylimidazolium tetrachloroaluminate (L5); trimethylaluminum (TMA), triethylaluminum (TEA), triisobutylaluminum (TIBA), tri-n-octylaluminum (TNOA); ① solvent is toluene; ② solvent is chlorobenzene; ③ N-cyclopentyl-N-(diethylphosphine)-1,1-diphenylphosphineamine (0.90 mg, 2.52 μmol) and CrCl3•(THF)3 (0.90 mg, 2.4 μmol) were added in situ to the reaction system to generate cationic complexes for catalytic ethylene oligomerization.

Claims

1. A catalyst system for selective trimerization and tetramerization of ethylene, characterized in that, include: Transition metal complex cation a is a metal complex cation of group IVB~VIII, and has the structure shown in formula (I); Activator b is at least one of alkylaluminum compounds, alkoxyaluminum compounds, aryloxyaluminum compounds, alkylaluminoxane compounds, and organoboron compounds; Ionic liquid c includes at least one of 1,3-dimethylimidazolium tetrafluoroborate, 1,3-di-(1-methylimidazolyl)-2-propanol tetrafluoroborate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1,3-dimethylimidazolium hexafluorophosphate, 1,3-dimethylimidazolium hexafluoroantimonate, bis(octadecylmethylamine)tetrafluorophenylborate, and bis(octadecylbenzylamine)tetrafluorophenylborate. Equation (I); In formula (I), A and C are independently selected from nitrogen, phosphorus, sulfur, and oxygen atoms, respectively; R 1 R 2 R 3 R 4 R 5 Each group is independently selected from alkyl, aryl, or dialkylamino groups; R 6 R 7 R 8 Each is independently selected from alkyl, aryl, or halogen groups; M is selected from metals of groups IVB to VIII; B is a linker formed by connecting multiple atoms or a single atom; when B is a single atom, B is selected from nitrogen, phosphorus, silicon, boron or germanium atoms; when B is a linker formed by connecting multiple atoms, B is selected from a linker group formed by connecting two or more carbon atoms, an aryl group or a bridging group formed by combining heteroatoms through chemical bonds; wherein, the heteroatom is at least one of silicon, tin, boron, phosphorus, nitrogen, oxygen or sulfur.

2. The catalyst system according to claim 1, characterized in that, B is selected from nitrogen, phosphorus, ethyl, propyl, vinyl, propenyl, or phenyl.

3. The catalyst system according to claim 1, characterized in that, The alkyl group is C1-C. 10 Alkyl groups.

4. The catalyst system according to claim 3, characterized in that, The alkyl group is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, cyclopentyl, or cyclohexyl.

5. The catalyst system according to claim 4, characterized in that, The alkyl group is selected from methyl, ethyl, isopropyl, isobutyl, isopentyl, or cyclopentyl.

6. The catalyst system according to claim 1, characterized in that, The aryl group is C6-C. 20 aryl and aryl derivatives.

7. The catalyst system according to claim 6, characterized in that, The aryl group includes substituted phenyl or unsubstituted phenyl.

8. The catalyst system according to claim 1, characterized in that, M is selected from chromium, molybdenum, tungsten, cobalt, titanium, tantalum, vanadium, zirconium, iron, nickel, or palladium.

9. The catalyst system according to claim 1, characterized in that, In activator b, the alkylaluminum compound is a trialkylaluminum compound.

10. The catalyst system according to claim 9, characterized in that, The alkylaluminum compound includes at least one of trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, or tri-n-octylaluminum.

11. The catalyst system according to claim 1, characterized in that, The molar ratio of the transition metal complex cation a, activator b, and ionic liquid c is 1:0.5~5000:0.1~100.

12. A method for preparing the catalyst system according to any one of claims 1 to 11, characterized in that, Includes the following steps: Transition metal complex cation a, activator b, and ionic liquid c are premixed or directly added to the reaction system for in-situ synthesis.

13. A method for ethylene oligomerization, characterized in that, Ethylene oligomerization reaction carried out in the presence of the catalyst system according to any one of claims 1 to 12.

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