Synthesis and Application of a Catalyst for Selective Oligomerization of Ethylene

Abstract

The present invention discloses the synthesis and application of a catalyst for the selective oligomerization of ethylene, and relates to the synthesis and application of a catalyst for ethylene tetramerization, which is composed of a transition metal compound, a ligand compound and an alkylaluminum cocatalyst. When the ethylene oligomerization catalyst system using the silicon-nitrogen-boron compound claimed in the present invention as a ligand catalyzes the ethylene oligomerization reaction, it has strong coordination ability, can form a relatively stable complex with the transition metal; the electrons on the nitrogen atom are fed back to the boron atom center, and the ligand is not prone to electron transfer reactions, the catalyst has high activity, high selectivity for 1-octene, and fewer side reactions; various substituents can be conveniently modified on the silicon atom; it has a novel structure, is easy to prepare, and has good solubility.

Description

Technical Field

[0001] The present invention belongs to the field of ethylene oligomerization, and particularly relates to the synthesis and application of a catalyst for selective ethylene oligomerization. Background Art

[0002] Linear α-olefins (LAOs) are important organic chemical raw materials and intermediates, and are widely used in fields such as high-density polyethylene, linear low-density polyethylene, and polyolefin elastomers. In recent years, with the gradual high-endization of the quality of polyolefin products, the apparent consumption of LAOs has shown an increasing trend year by year. However, the advanced and mature LAO production technologies are mainly in the hands of well-known global enterprises such as Chevron Phillips, Shell, Sasol, Idemitsu, SABIC / Linde, and INEOS. In recent years, large central enterprises represented by Sinopec and PetroChina have achieved industrial breakthroughs in the selective ethylene trimerization to produce 1-hexene, but there is still a large gap compared with foreign countries in the high polymerization of ethylene to produce high-carbon LAOs with 8 or more carbon atoms. Moreover, with the intensification of competition among global chemical enterprises in the polyolefin field, foreign countries have strengthened the technical blockade of the production of high-carbon LAOs, and China cannot introduce mature LAO production processes. Therefore, it is of great significance to independently develop domestic technologies.

[0003] Specifically, in the selective dimerization and trimerization of ethylene, domestic technologies have both broken through foreign technologies and achieved industrialization. However, in the field of selective ethylene tetramerization, only Sasol has achieved industrialization globally, and domestic industrialization has not been realized yet. In the field of higher-carbon selective ethylene, such as the pentamerization of ethylene to produce 1-decene, industrialization has not been achieved globally yet, and relevant technologies need further research.

[0004] In the market, with the increasingly wide application of materials such as linear low-density polyethylene, high-density polyethylene, and polyolefin elastomers, the consumption of linear α-olefin (LAO) monomers such as 1-hexene and 1-octene used to synthesize linear low-density polyethylene has also increased significantly. In 2022, the production capacity of α-olefins with 5 or more carbon atoms in China was 95,000 tons / year, and the output was 45,000 tons, with the main contribution coming from 1-hexene projects. In addition to importing pure α-olefins, China also imports a large number of derivative products of α-olefins every year, such as LLDPE / HDPE, PAO, and POE. Therefore, the equivalent consumption of α-olefins and the degree of foreign dependence are much greater than the above values.

[0005] Among numerous linear α-olefins, 1-octene is particularly important. Compared with LLDPE synthesized using 1-butene and 1-hexene as comonomers, LLDPE synthesized with 1-octene as a comonomer has more excellent tensile properties, better optical properties, etc. due to the increase in the carbon chain of the comonomer. On the other hand, POE synthesized by copolymerizing 1-octene and ethylene can significantly improve the mechanical properties, optical properties, and elasticity of POE. In terms of applications, with the proposal of China's carbon neutrality and carbon emission reduction strategy in the past two years, green power projects represented by photovoltaic have been widely implemented. POE is an indispensable material for producing photovoltaic cells. Therefore, with the continuous development of photovoltaic projects, the global consumption of POE will continue to rise, driving the consumption of 1-octene to increase continuously.

[0006] Although 1-octene has very high value and is scarce, the current method for producing 1-octene is still mainly non-selective oligomerization. Unlike 1-hexene, which has achieved high-selectivity oligomerization production (the selectivity of 1-hexene products is greater than 90%), the product distribution of ethylene non-selective oligomerization conforms to the Schulz-Flory distribution, and not only 1-octene can be obtained, but also a large amount of C4-C 20 olefin products are produced, and the selectivity of 1-octene is very low, not exceeding 30%. The selectivity of 1-octene in the ethylene oligomerization using a nickel metal catalyst in Shell's US3676523A is 11%. The selectivity of 1-octene in the ethylene polymerization product using a nickel compound catalyst in US Patent US6184428B2 is 19%. The selectivity of 1-octene in the ethylene polymerization product using a zirconium metal catalyst in Japanese Patent JP2002121157A is 15%. Chinese Patent CN101816951B discloses a catalyst of Zr complex, and the highest selectivity of C8 can reach 24.37%; Chinese Patent CN101569865B discloses a catalyst of Zr complex, and the highest selectivity of C8 can reach 27.28%.

[0007] In addition to the above non-selective oligomerization of ethylene, there are also a large number of laboratory studies on the selective oligomerization of ethylene. For example, the patents applied by Sinopec, such as CN102040624B, CN102451759B, CN103100420A, CN105268480B, CN105498840B, CN105562095B, CN105562101B, CN105562102B, CN105562103B, CN105566037B, CN107282128B, the patent CN103285926 A by PetroChina, the patent CN 110801864 A by Merck & Co., Inc., and the patents US10539517, US10538088, US11629533, US11993396 by Sasol, etc. all disclose the use of a chromium compound / ligand / co - catalyst system for the selective oligomerization of ethylene, and the selectivity of 1 - octene in the product can be greater than 70%.

[0008] The applicant has also carried out relevant research on ethylene trimerization and tetramerization. By methods such as synthesizing new ligands and improving the catalyst formulation, the goals of improving the selectivity of the target products 1 - hexene or 1 - octene, reducing the selectivity of polymers, and increasing the catalyst activity have been achieved. The patents applied are as follows: CN112264106A, CN112517080A, CN113880879A, CN113880881A, CN114011469A, CN113996343A, CN114225968A, CN114789067A, 202310556844.3, etc.

[0009] Currently, there are five mature non - selective processes for producing α - olefins globally, namely Shell, Chevron, Gulf, Ethyl, and Linde, with a production capacity of 2.1 million tons per year. The main product range extends from C4 to C20. However, the product distribution of this type of production process is wide, the selectivity for specific products is poor, and a large amount of energy is required to separate high - purity α - olefins, making it difficult to meet the market demand for high - purity LAO.

[0010] Most of the ligands in the ethylene tetramerization catalysts disclosed or reported currently are of the PNP - type structure. The synthesis process is relatively complex, the ligand coordination ability is weak, electron transfer reactions are likely to occur, it is extremely easy to absorb water and cause inactivation, and there are many side reactions. In addition, a small amount of polyethylene by - products are likely to block the pipelines and control valves in the reaction system after accumulation, which is the main reason affecting the long - term operation of the catalytic system. SUMMARY OF THE INVENTION

[0011] The purpose of the present invention is to provide the synthesis and application of a catalyst for the selective oligomerization of ethylene.

[0012] To achieve the above object, the present invention adopts the following technical solutions:

[0013] The ethylene tetramerization catalyst composition consists of an organometallic salt, a ligand, and an alkylaluminum cocatalyst. Among them, the spatial configuration and electron-donating property of the ligand become the key factors affecting the catalytic performance.

[0014] Based on this, under the condition that the two main components of the transition metal compound and the alkylaluminum cocatalyst remain unchanged, the present invention first synthesized a novel silicon-nitrogen-boron ligand, and such ligands have the following structures. That is, the ethylene tetramerization catalyst composition of the present invention is composed of a chromium metal salt, a silicon-nitrogen-boron ligand compound, and an alkylaluminum. Such polydentate ligands have strong coordination ability and can form relatively stable complexes with transition metals; the electrons on the nitrogen atom are fed back to the boron atom center, and the ligand is not prone to electron transfer reactions, and there are fewer side reactions; various substituents can be conveniently modified on the silicon atom; the structure is novel, easy to prepare, and has good solubility.

[0015] Structure of the silicon-nitrogen-boron ligand compound: ; where X is selected from any one of hydrogen, chlorine, and alkanes; Y is selected from any one of chlorine, bromine, and alkanes.

[0016] To solve the above technical problems, the present invention discloses the synthesis and application of an ethylene selective oligomerization catalyst. The present invention relates to the synthesis and application of a catalyst composed of a transition metal compound a, a ligand compound b, and an alkylaluminum cocatalyst c for ethylene tetramerization. When the ethylene oligomerization catalyst system using the silicon-nitrogen-boron compound claimed by the present invention as a ligand catalyzes the ethylene oligomerization reaction, it has strong coordination ability, can form relatively stable complexes with transition metals; the electrons on the nitrogen atom are fed back to the boron atom center, the ligand is not prone to electron transfer reactions, the catalyst activity is high, the selectivity for 1-octene is high, and there are fewer side reactions; various substituents can be conveniently modified on the silicon atom; the structure is novel, easy to prepare, and has good solubility.

[0017] The present invention claims to protect an ethylene selective oligomerization catalyst, which is a composition containing the following components, and the application of this catalyst composition in catalyzing the ethylene oligomerization reaction:

[0018] Transition metal compound a: The transition metal compound is selected from at least one of chromium compounds, molybdenum compounds, iron compounds, titanium compounds, zirconium compounds, and nickel compounds, preferably at least one of chromium acetylacetonate, chromium isooctanoate, tris(tetrahydrofuran)chromium trichloride, and bis(tetrahydrofuran)chromium dichloride;

[0019] The structure of ligand b is: , where X is selected from any one of hydrogen, chlorine, and alkanes; Y is selected from any one of chlorine, bromine, and alkanes;

[0020] Co - catalyst c: one of methylaluminoxane, modified methylaluminoxane, dried methylaluminoxane, triethylaluminum, trimethylaluminum;

[0021] Further, the molar ratio of the alkylaluminum cocatalyst to the metal in the transition metal compound is 100:1 - 1000:1;

[0022] Further, the molar ratio of the ligand compound to the metal in the transition metal compound is 0.01:1 - 100:1; preferably 0.1:1 - 10:1;

[0023] Further, the application of the ethylene tetramerization catalyst: The ethylene tetramerization reaction is mainly carried out in an inert solvent. The catalyst is prepared according to the ratio, and is injected successively in the form of a homogeneous catalyst or premixed evenly and then injected into the reaction system. Subsequently, the ethylene pressure is increased to make it fully contact with the catalyst for ethylene tetramerization. The reaction conditions are: temperature 30 - 150 o °C, pressure 0.5 - 20 MPa, time 0.1 - 2 h;

[0024] Further, the solvent includes alkanes or aromatics;

[0025] Further, the solvent includes benzene, toluene, cyclohexane, methylcyclohexane, n - heptane, n - hexane.

[0026] Further, the preparation and application of the catalyst composition for ethylene tetramerization to prepare 1 - octene specifically include the following steps:

[0027] (1) Catalyst preparation: Weigh a certain amount of chromium salt, ligand and alkylaluminum reagent respectively and dissolve them in a solvent treated by water removal to prepare three solutions for standby;

[0028] (2) Before the reaction, place the reactor body and the liner in an oven at 120 o °C and dry overnight, connect to the evaluation system, seal, heat to 105 o °C and keep it at a constant temperature for 1 h (the tail gas valve is closed) to remove residual water, oxygen and oxygen - containing impurities. Then set the temperature to the reaction temperature, let it cool naturally, and at the same time fill with nitrogen. Subsequently, evacuate, repeat three times to ensure that the air has been replaced completely. Then use a vacuum pump to pump away the nitrogen and fill with ethylene, repeat three times to ensure that the reactor body is full of ethylene.

[0029] (3) Open the tail gas valve. Under stirring conditions, inject the solvent and the additional alkylaluminum cocatalyst successively using a syringe. After the temperature stabilizes to the reaction temperature, inject the dehydrated solvent, alkylaluminum reagent, ligand solution, and chromium salt solution successively using a syringe. Close the tail gas valve, adjust the pressure reducing valve. After the pressure rises to the predetermined pressure value, start timing and record the data of the mass flowmeter. After reacting for a certain period of time, close the ethylene gas, stop the reaction, close the inlet valve, remove the reactor body, and soak it in an ice-water bath to cool the reactor to 10 o °C or below.

[0030] (4) After opening the tail gas valve to relieve pressure, inject 5 ml of 10 wt% HCl / ethanol solution under stirring conditions to quench the alkylaluminum cocatalyst, and then record the weight. Take a small amount of the liquid product and analyze the product using GC-MS. Filter the remaining sample. Weigh the filter paper in advance and record the mass. Then scrape the polymer on the stirring paddle with a spoon, wash it with the solvent into a beaker, place the obtained polymer in a vacuum oven and dry it at 60 o °C overnight, weigh it respectively, and calculate the mass of the polymer obtained. The types of components can be calibrated according to MS. According to the GC results, combined with the mass of the liquid product and the mass of the polymer, the selectivity of each product and the catalyst activity can be calculated.

[0031] The advantages of the present invention are as follows:

[0032] (1) For the first time, a silicon-nitrogen-boron compound is used as a ligand in an ethylene oligomerization catalyst system;

[0033] (2) The silicon-nitrogen-boron multidentate ligand has strong coordination ability and can form a relatively stable complex with a transition metal;

[0034] (3) The electrons on the nitrogen atom are fed back to the boron atom center, and the ligand is not prone to electron transfer reactions, and there are fewer side reactions;

[0035] (4) It is convenient to modify various substituents on the silicon atom;

[0036] (5) The ligand has a novel structure, is easy to prepare, and has good solubility. Description of the Drawings

[0037] Figure 1 is the 1H NMR spectrum of the intermediate lithium salt;

[0038] Figure 2 is the 11B NMR spectrum of the intermediate lithium salt;

[0039] Figure 3 is the 1H NMR spectrum of the silicon-nitrogen-boron ligand 1;

[0040] Figure 4 is the 11B NMR spectrum of the silicon-nitrogen-boron ligand 1;

[0041] Figure 5 1H NMR spectrum of silicon-nitrogen-boron ligand 2

[0042] Figure 6 11B NMR spectrum of silicon-nitrogen-boron ligand 2 Detailed implementation mode

[0043] To make the above features and advantages of the present invention more obvious and understandable, the following specific examples are given for detailed description. Unless otherwise specified, the methods of the present invention are all conventional methods in the art

[0044] Example 1. Preparation of intermediate lithium salt

[0045]

[0046] −78 o At -78 °C, 12 mL of n-butyllithium (2.4 M, 26.0 mmol) was slowly added dropwise to 2,6-diisopropylaniline (4.4 g, 25.0 mmol) in 50 mL of tetrahydrofuran. After the addition was complete, the temperature was slowly raised to room temperature and the reaction was carried out for 2 h. Then, at 0 o °C, isopropanol pinacol borate (4.9 g, 25.0 mmol) dissolved in 20 mL of tetrahydrofuran was introduced into the above system. After reacting for 5 min, the solvent was dried under reduced pressure, extracted with 100 mL of hexane, and placed in a -40 o °C refrigerator overnight to obtain 4.1 g of white solid intermediate lithium salt with a yield of 40%. The 1H NMR and 11B NMR spectra are as follows Figure 1 and Figure 2 shown, which are completely consistent with the structure of the target product intermediate lithium salt, proving the successful preparation of the compound

[0047] 1 1H NMR (400 MHz, C6D6): δ 1.16 (s, 12H, CMe3), 1.18 - 1.22 (m, 4H, OCH2CH2), 1.37 (d, J = 4.0 Hz, 12H, CH(CH3)2), 3.00 - 3.06 (m, 4H, OCH2CH2), 3.75 - 3.84 (m, 2H, CH(CH3)2), 6.93 - 6.98 7.13 - 7.15 (m, 3H).

[0048] 11 11B NMR (128.3 MHz, C6D6): δ 22.23.

[0049] Example 2. Preparation of silicon-nitrogen-boron ligand 1

[0050]

[0051] −78 o At -78 °C, trichlorosilane (1.34 g, 10.0 mmol) was slowly added dropwise to the intermediate lithium salt (3.8 g, 10.0 mmol) dissolved in 25 mL of tetrahydrofuran. After the addition was complete, the temperature was slowly raised to room temperature and the reaction was carried out for 2 h. The solvent was evaporated to dryness, and the residue was extracted with 20 mL of hexane and placed in a -40 o °C refrigerator overnight to obtain 3.7 g of white solid silicon-nitrogen-boron ligand 1 [DippN(Bpin)SiHCl2] with a yield of 90%. The 1H NMR and 11B NMR spectra are as follows Figure 3 and Figure 4 shown, which are in complete agreement with the structure of the target silicon-nitrogen-boron ligand 1, proving the successful preparation of this compound.

[0052] 1 1H NMR (400 MHz, C6D6): δ 0.97 (s, 12H, C Me 3), 1.27 - 1.29 (d, J J = 4.0 Hz, 12H, CH(C H 3)2), 3.43 - 3.49 (m, 2H, C H (CH3)2), 7.01 - 7.12 (m, 3H, Ar).

[0053] 11 11B NMR (128.3 MHz, C6D6): δ 25.54.

[0054] Example 3. Preparation of silicon-nitrogen-boron ligand 2

[0055]

[0056] −78 o At -78 °C, silicon tetrachloride (0.88 g, 5.0 mmol) was slowly added dropwise to the intermediate lithium salt (1.90 g, 5.0 mmol) dissolved in 25 mL of tetrahydrofuran. After the addition was complete, the temperature was slowly raised to room temperature and the reaction was carried out for 2 h. The solvent was evaporated to dryness, and the residue was extracted with 20 mL of n-hexane and placed in a -40 o °C refrigerator overnight to obtain 1.80 g of white solid silicon-nitrogen-boron ligand 2 [DippN(Bpin)SiCl3] with a yield of 85%. The 1H NMR and 11B NMR spectra are as follows Figure 5 and Figure 6 shown, which are in complete agreement with the structure of the target silicon-nitrogen-boron ligand 2, proving the successful preparation of this compound.

[0057] 1 H NMR (400 MHz, C6D6): δ 0.95(s, 12H, C Me 3), 1.27 - 1.32(d, J = 4.0 Hz, 12H, CH(C H 3)2), 3.47 - 3.52(m, 2H, C H (CH3)2), 6.71 - 6.80, 7.03 - 7.10(m, 3H, Ar).

[0058] 11 B NMR (128.3 MHz, C6D6): δ 25.12.

[0059] Application Example 1:

[0060] The ethylene oligomerization reaction was carried out in a high-pressure stainless-steel autoclave. Before the reaction, the autoclave body was placed in an oven and dried at 120 o °C overnight, connected to the evaluation system, sealed, and heated to 100 o °C and kept at a constant temperature for 1 h (with the tail gas valve closed) to remove residual water, oxygen, and oxygen-containing impurities. Then the temperature was set to 80 o °C, and it was allowed to cool naturally while being filled with nitrogen. Subsequently, it was evacuated and this was repeated three times to ensure that the air had been completely replaced. Then the nitrogen was pumped out with a vacuum pump and the autoclave was filled with ethylene, which was repeated three times to ensure that the autoclave was filled with ethylene. Subsequently, the solvent methylcyclohexane and the catalyst were added successively. In the catalyst, chromium isooctanoate: silicon nitride boron ligand 1: methylaluminoxane MAO = 1:1.2:1000 (molar ratio). The reaction pressure was controlled at 2 MPa. After the reaction for 1 h, the reaction was stopped, the inlet valve was closed, the autoclave body was removed, and it was immersed in an ice-water bath to cool the autoclave to below 10 o °C. After opening the tail gas valve to relieve the pressure, 5 mL of 10 wt% HCl / ethanol solution was injected under stirring conditions to quench the alkylaluminum. Subsequently, the weight was measured and recorded. A small amount of the liquid-phase product was analyzed by GC-MS for the product. The remaining sample was filtered. The filter paper was weighed in advance and the mass was recorded. Subsequently, the polymer on the stirring paddle was scraped off with a spoon, washed with a solvent into a beaker, and the obtained polymer was placed in a vacuum oven and dried at 60 o °C overnight, weighed separately, and the mass of the polymer was calculated. The types of components can be calibrated according to MS, and based on the GC results combined with the mass of the liquid-phase product and the mass of the polymer, the selectivity of each product and the catalyst activity can be calculated. The data results are shown in Table 1.

[0061] Application Example 2:

[0062] Same as Application Example 1, except that the reaction temperature is 60 o °C, and the data results are shown in Table 1.

[0063] Application Example 3:

[0064] Same as Application Example 1, except that methylcyclohexane is replaced with cyclohexane, and the data results are shown in Table 1.

[0065] Application Example 4:

[0066] Same as Application Example 2, except that the pressure of 2 MPa is replaced with 4 MPa, and the data results are shown in Table 1.

[0067] Application Example 5:

[0068] Same as Application Example 1, except that the silicon-nitrogen-boron ligand 1 is changed to silicon-nitrogen-boron ligand 2, and the data results are shown in Table 1.

[0069] Application Comparative Example 1:

[0070] Same as Example 1, except that the ligand is changed to PNP (the synthesis of PNP refers to the reference (A. Bollmann, K. Blann, J. T. Dixon, et al, J. Am. Chem. Soc. 126 (2004) 14712–14713)), and the data results are shown in Table 1.

[0071] Table 1 Summary of reaction conditions and reaction performance of the examples and comparative examples of the present invention.

[0072]

[0073] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A selective ethylene oligomerization catalyst, characterized in that, The ethylene selective oligomerization catalyst consists of a transition metal compound, a ligand compound and an alkylaluminum cocatalyst; The transition metal compound is selected from at least one of chromium compounds, molybdenum compounds, iron compounds, titanium compounds, zirconium compounds and nickel compounds; The structure of the ligand compound is as follows: , where X is selected from any one of hydrogen, chlorine, and alkane; Y is selected from any one of chlorine, bromine, and alkane; The alkylaluminum cocatalyst is selected from one of methylaluminoxane, modified methylaluminoxane, triethylaluminum and trimethylaluminum.

2. The ethylene selective oligomerization catalyst according to claim 1, characterized in that, The transition metal compound is at least one of chromium acetylacetonate, chromium octoate, tris(tetrahydrofuran)chromium(III) chloride and bis(tetrahydrofuran)chromium(II) chloride.

3. The ethylene selective oligomerization catalyst according to claim 1, characterized in that: The molar ratio of the alkylaluminum cocatalyst to the metal in the transition metal compound is 100:1 to 1000:

1.

4. The ethylene selective oligomerization catalyst according to claim 1, characterized in that: The molar ratio of the ligand compound to the metal in the transition metal compound is 0.01:1 to 100:

1.

5. Use of the ethylene selective oligomerization catalyst according to claim 1, characterized in that: The ethylene tetramerization reaction is mainly carried out in an inert solvent. The components of the ethylene selective oligomerization catalyst are injected successively in the form of a homogeneous catalyst or premixed evenly and then injected into the reaction system. Subsequently, the ethylene pressure is increased to enable full contact with the catalyst for ethylene tetramerization. The reaction conditions are as follows: temperature 30~150 o °C, pressure 0.5~20 MPa, and time 0.1~2 h.

6. The application according to claim 5, wherein: The solvent includes alkanes or aromatics.

7. The application according to claim 5, wherein: The solvent includes benzene, toluene, cyclohexane, methylcyclohexane, n-heptane and n-hexane.

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