An ethylene oligomerization process

Abstract

The present application relates to a kind of ethylene oligomerization processes, including by the tetramerization reaction of ethylene and the dimerization reaction of ethylene in reaction vessel alternately to prepare alpha-olefin;Wherein, the reaction temperature of the dimerization reaction is 110~130 ℃, the reaction temperature of the tetramerization reaction is 40~80 ℃.The ethylene oligomerization process of one embodiment of the present application, by the combination of low-temperature ethylene tetramerization reaction and high-temperature ethylene dimerization reaction, can eliminate or reduce the influence of byproduct polymer on process, so that ethylene oligomerization process is stably operated for a long period of time;Meanwhile, reaction product can also meet the subsequent use requirements.

Description

Technical Field

[0001] This invention relates to olefin polymerization, and more particularly to an ethylene oligomerization process that can extend the operating cycle. Background Technology

[0002] Linear α-olefins have a wide range of industrial applications. Their oligomers can be used in many fields, including plasticizers, fatty acids, and lubricant additives. Copolymers of linear α-olefins can be used to produce polyolefin elastomers, which are applicable to footwear materials, polymer modification, and photovoltaics.

[0003] Currently, the mainstream polyolefin elastomers on the market are random copolymers of ethylene and 1-butene, and ethylene and 1-octene. With the continuous increase in polyolefin elastomer production capacity, the planned capacity is approaching one million tons. Since the amount of α-olefin used is about 30-35% of the total raw material mass, the demand for 1-butene and 1-octene is also increasing. As one of the mainstream processes for producing low carbon number (C4-C8) linear α-olefins, selective ethylene oligomerization has received extensive research and attention in recent years.

[0004] The polymerization of ethylene tetramers in existing technologies is carried out at medium to low temperatures, during which byproduct polymers gradually accumulate and precipitate in the system, affecting heat and mass transfer. The presence of byproduct polymers significantly shortens the stable operation cycle of the reaction, requiring frequent reactor switching or shutdown for hot washing, thus reducing production efficiency. Although some high-temperature resistant catalytic systems have modified or replaced the catalyst ligands, the actual polymerization activity, temperature resistance, and selectivity are still unsatisfactory. Summary of the Invention

[0005] To overcome at least one of the defects of the prior art, in a first aspect, one embodiment of the present invention provides an ethylene oligomerization process, comprising preparing α-olefins by alternating tetramerization and dimerization of ethylene in a reaction vessel; wherein the reaction temperature of the dimerization reaction is 110–130°C, and the reaction temperature of the tetramerization reaction is 40–80°C.

[0006] Secondly, one embodiment of the present invention provides the application of the above-described ethylene oligomerization process in the preparation of polyolefin elastomers.

[0007] The ethylene oligomerization process of one embodiment of the present invention combines a low-temperature ethylene tetramerization reaction with a high-temperature ethylene dimerization reaction, which can eliminate or reduce the impact of by-product polymers on the process, enabling the ethylene oligomerization process to operate stably for a long period of time; at the same time, it can also make the reaction products better meet the requirements for subsequent use. Detailed Implementation

[0008] Typical embodiments embodying the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different embodiments without departing from the scope of the present invention, and the description herein is for illustrative purposes only and not intended to limit the present invention.

[0009] One embodiment of the present invention provides an ethylene oligomerization process, comprising preparing α-olefins by alternating tetramerization and dimerization of ethylene in the same reaction vessel; wherein the reaction temperature of the dimerization reaction is 110-130°C and the reaction temperature of the tetramerization reaction is 40-80°C.

[0010] In one embodiment, the main process of the ethylene oligomerization process is the tetramerization reaction of ethylene, and the auxiliary process is the dimerization reaction of ethylene.

[0011] In one embodiment of the present invention, the ethylene oligomerization process involves tetramerizing ethylene at a low temperature (40–80°C). When the accumulated byproduct polymer in the system significantly affects heat or mass transfer, the system is temporarily switched to ethylene dimerization at a high temperature (110–130°C). The high temperature allows the polymer to dissolve. After the aforementioned effects are eliminated and the system returns to normal, the system is switched back to tetramerization. This alternating switching allows for online dissolution of the polymer without requiring reactor switching or shutdown operations, achieving multiple objectives such as improving production efficiency, reducing manual operation and production fluctuations, and extending the operating cycle of the equipment.

[0012] In one embodiment, the reaction temperature for the dimerization reaction is 110–130°C, for example, 115°C, 120°C, or 125°C; and the reaction temperature for the tetramerization reaction is 40–80°C, for example, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, or 75°C.

[0013] In one embodiment, the reaction pressure for both the dimerization and tetramerization of ethylene can be 3.0 to 5.0 MPa (gauge pressure), for example 3.5 MPa, 4.0 MPa, and 4.5 MPa.

[0014] In one embodiment, ethylene dimerization is carried out under the action of a first catalyst, and ethylene tetramerization is carried out under the action of a second catalyst. The switching between dimerization and tetramerization is achieved by adding the first or second catalyst to the reaction vessel and adjusting the reaction conditions (e.g., reaction temperature).

[0015] In one embodiment, the tetramerization of ethylene is carried out under low-temperature conditions using a second catalyst system. When the byproduct polymer in the system accumulates to the point that it affects heat and mass transfer (e.g., the heat exchange efficiency decreases significantly or the temperature difference between different parts of the reactor continues to increase), the system is temporarily switched to high-temperature conditions to carry out the dimerization of ethylene using a first catalyst system. After the system returns to normal, it is switched back to the tetramerization of ethylene, and this cycle is repeated.

[0016] In one embodiment, the dimerization reaction in the reaction vessel is switched to the tetramerization reaction after a time t1, where t1 can be 12 to 60 hours, for example, 15 hours, 20 hours, 24 hours, 30 hours, 35 hours, 40 hours, 45 hours, 50 hours, or 55 hours.

[0017] In one embodiment, the tetramerization reaction in the reaction vessel is switched to the dimerization reaction after a time t2, where t2 is 60 to 240 h, for example 80 h, 100 h, 120 h, 150 h, 180 h, 200 h, or 220 h.

[0018] In one embodiment, the reaction time ratio of dimerization to tetramerization in the reaction vessel can be t1:t2 = (1-5):(5-20), further wherein t1:t2 < 1, for example 2:(5-20), 3:(5-20), 4:(5-20), 2:(10-20), 3:(10-20), 4:(10-20), 2:(6-10), 2:(15-20), 3:(15-20), 4:(15-20). Furthermore, the activity of the tetramerization reaction can be 5-10 times (e.g., 6, 7, 8, 9 times) that of the dimerization reaction. Given that the reaction time and activity of the tetramerization reaction are both greater than those of the dimerization reaction, briefly switching the tetramerization system to the dimerization reaction will not affect the activity and selectivity of the main process ethylene tetramerization.

[0019] In one embodiment, a dimerization reaction is carried out under the action of a first catalyst, the first catalyst comprising a first main catalyst and a first co-catalyst, the first main catalyst comprising a first chromium salt and a first ligand, the first ligand having the following structure:

[0020]

[0021] R1, R2, R3, and R4 are each independently selected from -H, -OCH3, -F, and -CF3.

[0022] In one implementation, R1, R2, R3, and R4 are the same, that is, all are -H, all are -OCH3, all are -F, or all are -CF3.

[0023] The ethylene oligomerization process of one embodiment of the present invention uses a first catalyst including the above-mentioned first ligand to carry out the dimerization reaction of ethylene, which enables the dimerization reaction to be carried out at a higher temperature of 110-130°C. Furthermore, by alternating with the low-temperature tetramerization reaction of ethylene, the continuous operation cycle of the ethylene oligomerization process is extended.

[0024] In one embodiment, the first ligand is selected from the following compounds:

[0025] Ligand A

[0026] Ligand B:

[0027] Ligand C:

[0028] In one implementation, the first ligand is ligand A or ligand C.

[0029] In one embodiment, the first ligand is ligand A, and the reaction temperature for the dimerization reaction is 110–120°C, or more specifically 110–115°C.

[0030] In one embodiment, the first metallic chromium salt comprises one or more of chromium tetrahydrofuran dichloride, chromium acetylacetone, chromium 2-ethylhexanoate, and chromium hexacarbonyl.

[0031] In one embodiment, the molar ratio of the first metallic chromium salt to the first ligand is (0.5 to 5):1, more specifically (1 to 2):1, for example 1.2:1, 1.5:1, 1.8:1, 3:1, or 4:1.

[0032] In one embodiment, the first cocatalyst comprises one or more of trimethylaluminum, triethylaluminum, triisobutylaluminum, trioctylaluminum, methylaluminoxane (MAO), and modified methylaluminoxane (MMAO).

[0033] In one embodiment, the molar ratio of the first co-catalyst to the first main catalyst is (100-1000):1, further (200-500):1, for example 250:1, 300:1, 350:1, 400:1, 450:1, 600:1, 700:1, 800:1, 900:1.

[0034] In one embodiment, the tetramerization of ethylene is carried out under the action of a second catalyst, the second catalyst comprising a second main catalyst and a second co-catalyst, the second main catalyst comprising a second chromium salt and a second ligand.

[0035] In one embodiment, the second metallic chromium salt comprises one or more of chromium tetrahydrofuran dichloride, chromium acetylacetone, chromium 2-ethylhexanoate, and chromium hexacarbonyl.

[0036] In one embodiment, the second ligand includes one or more of (Ph)2PN(iPr)P(Ph)2, (Ph)2PN(t-Bu)P(Ph)2, (oF-Ph)2PN(iPr)P(oF-Ph)2, (Ph)2P(CH3-CH)2P(Ph)2, and (Ph)2P-Ph-P(Ph)2.

[0037] In one embodiment, the second ligand is (Ph)2PN(iPr)P(Ph)2 or (oF-Ph)2PN(iPr)P(oF-Ph)2.

[0038] In one embodiment, the molar ratio of the second chromium salt to the second ligand is (0.5 to 5):1, more specifically (1 to 2):1, for example 1.2:1, 1.5:1, 1.8:1, 3:1, or 4:1.

[0039] In one embodiment, the second cocatalyst comprises one or more of trimethylaluminum, triethylaluminum, triisobutylaluminum, trioctylaluminum, methylaluminoxane (MAO), and modified methylaluminoxane (MMAO).

[0040] In one embodiment, the molar ratio of the second co-catalyst to the second main catalyst is (100-1000):1, more specifically (200-500):1, for example 250:1, 300:1, 350:1, 400:1, 450:1, 600:1, 700:1, 800:1, or 900:1.

[0041] In one embodiment, the solvents for the first catalyst and the second catalyst may be one or more of n-hexane, n-heptane, cyclohexane, methylcyclohexane, tetrahydrofuran, toluene, and xylene.

[0042] In one embodiment, the solvent in the reaction vessel may be one or more of the following: n-hexane, n-heptane, cyclohexane, methylcyclohexane, tetrahydrofuran, toluene, and xylene.

[0043] In one embodiment, the reaction products of the ethylene oligomerization process include α-olefins. Further, the reaction products include α-olefins with 8 or fewer carbon atoms, such as 1-butene, 1-hexene, and 1-octene.

[0044] In one embodiment, the selectivity of α-olefins with 8 or fewer carbon atoms in the reaction products of the ethylene oligomerization process is over 90%, enabling highly selective co-production of α-olefins with 8 or fewer carbon atoms.

[0045] In one embodiment, the products of the ethylene dimerization reaction include 1-butene, 1-hexene, and 1-octene.

[0046] In one embodiment, the products of the ethylene tetramerization reaction include 1-hexene and 1-octene.

[0047] The ethylene oligomerization process of one embodiment of the present invention can simultaneously produce 1-butene, 1-hexene and 1-octene, meeting the demand for raw materials for polyolefin elastomers.

[0048] Unless otherwise specified, the dimerization process, tetramerization process and apparatus used for the reaction of ethylene in this invention can be existing processes and apparatus.

[0049] One embodiment of the present invention provides the application of the above-described ethylene oligomerization process in the preparation of polyolefin elastomers. The polyolefin elastomer may be, for example, a polyolefin polyol (POP).

[0050] The ethylene oligomerization process of one embodiment of the present invention alleviates the clogging problem caused by the accumulation of by-product polymers in the low-temperature tetramerization reaction, avoids the cumbersome and complex catalyst structure design and synthesis, and can extend the stable operating time of the ethylene oligomerization reaction without sacrificing polymerization activity and selectivity.

[0051] Some existing technologies employ complex ligands to improve the high-temperature resistance of catalysts or reduce the generation of byproduct polymers; however, these ligands are costly and compromise other properties (such as reactivity). An embodiment of the ethylene oligomerization process of the present invention can extend the stable operating time of the ethylene oligomerization reaction while maintaining low cost and high reactivity.

[0052] One embodiment of the ethylene oligomerization process of the present invention involves performing the tetramerization reaction of ethylene at a low temperature. When the polymer in the system accumulates to a certain extent, the process switches to a high temperature for the dimerization reaction of ethylene. After the polymer dissolves in the reaction system, the process switches back to the tetramerization reaction of ethylene. This alternating switching can reduce the frequency of shutdowns caused by the accumulation of by-product polymers, improve production efficiency and operational stability, and significantly extend the continuous operation cycle of the ethylene oligomerization process.

[0053] The ethylene oligomerization process of one embodiment of the present invention realizes online polymer dissolution and reactor cleaning, thereby avoiding frequent shutdowns of production equipment or reactor switching, reducing reaction fluctuations and improving the stable operation cycle of the reaction.

[0054] One embodiment of the ethylene oligomerization process of the present invention, by switching between dimerization and tetramerization reactions of ethylene, extends the reaction process operation time by, for example, 2 to 3 times compared to a standalone ethylene tetramerization process, while maintaining the reaction activity and selectivity largely unaffected, thus improving the operational stability of the reaction and reducing manual operation. Furthermore, it can achieve highly selective co-production of 1-butene, 1-hexene, and 1-octene (with α-olefins below C8 accounting for more than 90%) in a single unit, offering greater target selectivity and cost advantages compared to non-selective oligomerization processes (α-olefins below C8 accounting for less than 60%).

[0055] An embodiment of the ethylene oligomerization process of the present invention allows most of the products to be used in the preparation of polyolefin elastomers. Specifically, the tetramerization product includes a high content of 1-octene and a low content of 1-hexene, while the dimerization product includes a high content of 1-butene, a small amount of 1-octene, and a low content of 1-hexene. Both 1-butene and 1-octene are raw materials required for the preparation of polyolefin elastomers. In other polymerization reactions of ethylene, such as trimerization, the main product is 1-hexene, but 1-hexene is not a mainstream raw material required for the preparation of polyolefin elastomers. If the ethylene oligomerization process alternates between trimerization and tetramerization, most of the trimerization product cannot be used to prepare commercially available polyolefin elastomers. Therefore, the ethylene oligomerization process of one embodiment of the present invention, which alternates between dimerization and tetramerization, can largely cover the demand for polyolefin elastomer raw materials in the market.

[0056] The following describes an embodiment of the ethylene oligomerization process of the present invention in further detail with reference to specific examples. The raw materials and testing methods used are as follows:

[0057] 1. Raw materials

[0058] Chromium acetylacetone: 98%, purchased from Beijing Bailingwei Technology Co., Ltd.

[0059] Tetrahydrofuran chromium dichloride: 98%, purchased from Sigma-Aldrich;

[0060] (Ph)2PN(iPr)P(Ph)2: 98%, purchased from Jiangsu Xinnoco Catalyst Co., Ltd.;

[0061] (oF-Ph)2PN(iPr)P(oF-Ph)2: 98%, purchased from Solvay Chemicals Ltd.;

[0062] (Ph)2P-Ph-P(Ph)2: 98%, purchased from Jiangsu Xinnuoke Catalyst Co., Ltd.;

[0063] Dimeric pyridyl PNP ligands: 98%, purchased from Jiangsu Xinnuoke Catalyst Co., Ltd.;

[0064] Methylcyclohexane (MCH): 99%, purchased from Aladdin Biochemical Technology Co., Ltd.;

[0065] n-Heptane: 99%, purchased from Shanghai Titan Technology Co., Ltd.;

[0066] Triisobutylaluminum (TIBA): 1.0 mol / L, purchased from Panjin Yanfeng Technology Co., Ltd.; Modified methylaluminoxane (MMAO-3A): 7% solution, purchased from AkzoNobel; 2-Ethyl-1-hexanol: 99%, purchased from Aladdin Biochemical Technology Co., Ltd.

[0067] The structure of the dimer pyridyl PNP ligand is as follows:

[0068] Ligand A:

[0069] Ligand B:

[0070] Ligand C:

[0071] 2. Testing Methods

[0072] Liquid products are characterized by gas chromatography to obtain the mass of each liquid product, while solid products are separated, dried, and weighed. The analytical conditions for gas chromatography are as follows:

[0073] The sample injection temperature was 250℃, and the column oven temperature was 35℃.

[0074] The heating process includes: maintaining the temperature at 35°C for 10 minutes, then increasing the temperature to 250°C at a rate of 10°C / min, maintaining the temperature at 250°C for 10 minutes, and then cooling down to room temperature.

[0075] The detector temperature is 250℃, the carrier gas pressure is 1.0MPa, the air pressure is 0.03MPa, and the hydrogen pressure is 0.03MPa.

[0076] The product was characterized using n-nonane as an internal standard, and the calculation method is as follows:

[0077]

[0078] In the formula, m1 represents the mass of a certain analyte, m is the mass of nonane, a1 is the peak area of ​​this analyte measured in GC, a is the peak area of ​​n-nonane measured in GC, and k is the correction coefficient.

[0079] Reactivity (Kg / gCr) refers to the mass of product that can be catalyzed by a unit weight of chromium atoms. Selectivity refers to the mass percentage of a specific component in the total product.

[0080] Example 1

[0081] Tetramerization of ethylene

[0082] A 1L high-pressure stainless steel reactor (full reactor operation, bottom inlet, top outlet) was heated to 120℃ and evacuated for 3 hours, during which it was purged with nitrogen three times. Then, it was evacuated again and purged with hydrogen three times. After cooling to room temperature, hydrogen was introduced into the reactor to bring the pressure to 0.2MPa. A plunger pump was used to inject into the reactor a solution containing 950mL of dehydrated and deoxygenated n-heptane, 2.0mL of MMAO-3A (second co-catalyst), and 8.0mL of a pre-prepared n-heptane solution with a molar concentration of 1.0µmol / mL for the second main catalyst, PNP ligand (Ph)₂PN(iPr)P(Ph)₂ / chromium acetylacetone (molar ratio 1.2:1). Ethylene was introduced into the reactor to maintain the reaction pressure at 4.5MPa, and the reaction was initiated at an initial temperature of 45℃ and a rotation speed of 600rpm.

[0083] When the system temperature rises above 50°C, n-heptane, the aforementioned second main catalyst, and the second co-catalyst are continuously introduced into the reactor through a high-pressure solvent plunger pump to maintain the system's second main catalyst (Cr / PNP) solution concentration at 8 μmol / L, Al / Cr ratio at 500, and residence time at 60 min. The reactor is connected to a pressure equalization product buffer tank containing excess quencher 2-ethyl-1-hexanol via a side line. The reaction liquid product is continuously discharged, and the reaction heat is removed by an external circulation cooler and jacket, controlling the reactor temperature between 45 and 50°C.

[0084] Dimerization of ethylene

[0085] After 180 hours of operation of the ethylene tetramerization reaction, a decrease in heat transfer efficiency and poor liquid flow from the overflow pipeline occurred. The valves / pipelines were then switched to the first main catalyst (1 μmol / L, chromium dichloride in tetrahydrofuran at a molar ratio of 1:1 to ligand A) and the first co-catalyst (triisobutylaluminum, 1 mol / L hexane solution) for ethylene dimerization. The co-catalysts were continuously added to the reactor according to their respective flow rates for ethylene tetramerization. The heat of reaction was removed using the internal coil and jacket, and the reaction temperature was controlled at 110–115°C. After 48 hours of ethylene dimerization, the byproduct polymer in the reactor gradually dissolved. Once the system stabilized, the reactor was switched back to ethylene tetramerization. The ethylene tetramerization and dimerization reactions were cyclically switched according to the above process. The total operating cycle of the ethylene oligomerization process was 480 hours after the reactions were completed.

[0086] Every hour, the reaction solution after termination was collected and filtered. The supernatant was analyzed by GC. The solid product was dried in a vacuum oven at 80°C for 12 hours and weighed. The activity and selectivity of the product were then calculated. Based on comprehensive calculations, the catalytic activity for ethylene tetramerization was approximately 1500 kg / gCr·h, with a selectivity of 18.9% for 1-hexene, 68.7% for 1-octene, and 0.3% for PE (polyethylene). The catalytic activity for ethylene dimerization was 15.7 kg / gCr·h, with a selectivity of 58.3% for 1-butene, 25.2% for 1-hexene, 10.6% for 1-octene, and 0.01% for PE.

[0087] Example 1-1

[0088] Tetramerization of ethylene

[0089] The tetramerization reaction of ethylene was carried out using the same raw materials and process as in Example 1.

[0090] Dimerization of ethylene

[0091] The dimerization reaction of ethylene was carried out using essentially the same raw materials and process as in Example 1, with the only difference being that ligand B was used instead of ligand A, and the reaction temperature was 115–120°C. After 36 hours of reaction, the byproduct polymer in the reactor gradually dissolved. Once the system stabilized, the reaction was switched back to tetramerization. After multiple cycles of switching, the reaction was completed. The total operating cycle of the ethylene oligomerization process was 360 hours.

[0092] Based on comprehensive calculations, the catalytic activity of ethylene tetramerization is approximately 1500 kg / gCr·h, with a selectivity of 18.9% for 1-hexene, 68.7% for 1-octene, and 0.3% for PE; the catalytic activity of ethylene dimerization is 18 kg / gCr·h, with a selectivity of 56% for 1-butene, 28% for 1-hexene, 7% for 1-octene, and 0.02% for PE.

[0093] Examples 1-2

[0094] Tetramerization of ethylene

[0095] The tetramerization reaction of ethylene was carried out using the same raw materials and process as in Example 1.

[0096] Dimerization of ethylene

[0097] The dimerization of ethylene was carried out using essentially the same raw materials and process as in Example 1, with the only difference being that ligand C was used instead of ligand A, and the reaction temperature was 125–130°C. After 24 hours of reaction, the by-product polymer in the reactor gradually dissolved. Once the system stabilized, the process was switched back to tetramerization. After multiple cycles of switching, the reaction was completed. The total operating cycle of the ethylene oligomerization process was 400 hours.

[0098] Based on comprehensive calculations, the catalytic activity of ethylene tetramerization is approximately 1500 kg / gCr·h, with a selectivity of 18.9% for 1-hexene, 68.7% for 1-octene, and 0.3% for PE; the catalytic activity of ethylene dimerization is 23 kg / gCr·h, with a selectivity of 58% for 1-butene, 21% for 1-hexene, 14% for 1-octene, and 0.03% for PE.

[0099] Examples 1-3

[0100] Tetramerization of ethylene

[0101] The tetramerization reaction of ethylene was carried out using the same raw materials and process as in Example 1.

[0102] Dimerization of ethylene

[0103] The dimerization reaction of ethylene was carried out using essentially the same raw materials and process as in Example 1, with the only difference being that the reaction temperature was 125–130°C. After 30 hours of reaction, the by-product polymer in the reactor gradually dissolved. Once the system stabilized, the reaction was switched back to tetramerization. After multiple cycles of switching, the reaction was completed. The total operating cycle of the ethylene oligomerization process was 380 hours.

[0104] Based on comprehensive calculations, the catalytic activity of ethylene tetramerization is approximately 1500 kg / gCr·h, with a selectivity of 18.9% for 1-hexene, 68.7% for 1-octene, and 0.3% for PE; the catalytic activity of ethylene dimerization is 16 kg / gCr·h, with a selectivity of 52% for 1-butene, 25% for 1-hexene, 14% for 1-octene, and 0.02% for PE.

[0105] Examples 1-4

[0106] Tetramerization of ethylene

[0107] The tetramerization reaction of ethylene was carried out using the same raw materials and process as in Example 1.

[0108] Dimerization of ethylene

[0109] The dimerization reaction of ethylene was carried out using essentially the same raw materials and process as in Example 1, except that ligand C was used instead of ligand A. After 48 hours of reaction, the by-product polymer in the reactor gradually dissolved. Once the system stabilized, it was switched back to tetramerization. After multiple cycles of switching, the reaction was completed. The total operating cycle of the ethylene oligomerization process was 400 hours.

[0110] Based on comprehensive calculations, the catalytic activity of ethylene tetramerization is approximately 1500 kg / gCr·h, with a selectivity of 18.9% for 1-hexene, 68.7% for 1-octene, and 0.3% for PE; the catalytic activity of ethylene dimerization is 18 kg / gCr·h, with a selectivity of 55% for 1-butene, 23% for 1-hexene, 14% for 1-octene, and 0.02% for PE.

[0111] Example 2-1

[0112] Tetramerization of ethylene

[0113] The tetramerization of ethylene was carried out using essentially the same raw materials and processes as in Example 1, with the only difference being that the reaction temperature was maintained at around 55–60°C.

[0114] Dimerization of ethylene

[0115] The dimerization reaction of ethylene was carried out using the same raw materials and process as in Example 1. The only difference was that after the tetramerization reaction of ethylene was run for 150 hours, the heat transfer efficiency decreased and the liquid discharge from the overflow pipeline was obstructed. The process was then switched to the dimerization reaction of ethylene. After the system stabilized, the process was switched back to the tetramerization reaction. The reaction was completed after multiple cycles of switching. The total operating cycle of the ethylene oligomerization process was 360 hours.

[0116] Based on comprehensive calculations, the catalytic activity of ethylene tetramerization is approximately 1800 kg / gCr·h, with a selectivity of 27.3% for 1-hexene, 60.9% for 1-octene, and 0.5% for PE; the catalytic activity of ethylene dimerization is 15.7 kg / gCr·h, with a selectivity of 58.3% for 1-butene, 25.2% for 1-hexene, 10.6% for 1-octene, and 0.01% for PE.

[0117] Example 2-2

[0118] Tetramerization of ethylene

[0119] The tetramerization reaction of ethylene was carried out using the same raw materials and process as in Example 1, except that the F-PNP ligand (oF-Ph)2PN(iPr)P(oF-Ph)2 was used instead of the PNP ligand, the reaction started at 80°C, and the reaction temperature was maintained at 75-80°C.

[0120] Dimerization of ethylene

[0121] The dimerization reaction of ethylene was carried out using essentially the same raw materials and process as in Example 1, with the only difference being that: after the tetramerization reaction of ethylene was run for 90 hours, the heat transfer efficiency decreased and the overflow pipeline was obstructed, so the process was switched to the dimerization reaction of ethylene; ligand C was used to replace ligand A, and the molar ratio of tetrahydrofuran chromium dichloride to ligand C was 1:1.2; the reaction temperature was 125-130°C, and after 24 hours of reaction, the by-product polymer in the reactor gradually dissolved. After the system stabilized, the process was switched back to the tetramerization reaction. After multiple cycles of switching, the reaction was completed, and the total operating cycle of the ethylene oligomerization process was 320 hours.

[0122] Based on comprehensive calculations, the catalytic activity of ethylene tetramerization is approximately 1200 kg / gCr·h, with a selectivity of 42.1% for 1-hexene, 46.7% for 1-octene, and 0.4% for PE; the catalytic activity of ethylene dimerization is 23 kg / gCr·h, with a selectivity of 58% for 1-butene, 21% for 1-hexene, 14% for 1-octene, and 0.03% for PE.

[0123] Comparative Example 1: Tetramerization of Ethylene

[0124] The tetramerization reaction of ethylene was carried out using essentially the same raw materials and process as in Example 1, with the only difference being that: a complex of PCCP ligand (Ph)2P-Ph-P(Ph)2 and tetrahydrofuran chromium trichloride was used as the second main catalyst, with a molar ratio of 1:1; the initial reaction temperature was 100°C, and the reaction temperature was maintained at 95-100°C.

[0125] Dimerization of ethylene

[0126] The dimerization reaction of ethylene was carried out using essentially the same raw materials and processes as in Example 1, with the only difference being that: after the tetramerization reaction of ethylene had run for 60 hours, the heat transfer efficiency decreased and the overflow line was obstructed, so the process was switched to the dimerization reaction of ethylene; ligand C was used instead of ligand A, and the molar ratio of tetrahydrofuran chromium dichloride to ligand C was 1:1.2; the reaction temperature was 125-130°C, and after 18 hours of reaction, the by-product polymer in the reactor gradually dissolved. After the system stabilized, the process was switched back to the tetramerization reaction. After multiple cycles of switching, the reaction was completed, and the total operating cycle of the ethylene oligomerization process was 200 hours.

[0127] Based on comprehensive calculations, the catalytic activity of ethylene tetramerization is approximately 1000 kg / gCr·h, with a selectivity of 46.5% for 1-hexene, 38.7% for 1-octene, and 0.5% for PE; the catalytic activity of ethylene dimerization is 23 kg / gCr·h, with a selectivity of 58% for 1-butene, 21% for 1-hexene, 14% for 1-octene, and 0.03% for PE.

[0128] Comparative Example 2

[0129] Tetramerization of ethylene

[0130] The tetramerization reaction of ethylene was carried out using the same raw materials and process as in Example 1.

[0131] Dimerization of ethylene

[0132] The dimerization of ethylene was carried out using essentially the same raw materials and process as in Example 1, with the only difference being that the main catalyst used was tetrabutyl titanate, the co-catalyst was triethylaluminum, and the reaction temperature was 115–120°C. After 180 hours of operation of the tetramerization reaction of ethylene, a decrease in heat transfer efficiency and poor liquid discharge from the overflow pipeline occurred. The process was then switched to ethylene dimerization at 115–120°C. After 48 hours of reaction, the by-product polymer in the reactor gradually dissolved. Once the system stabilized, the process was switched back to tetramerization. After multiple cycles of switching, the reaction was completed. The total operating cycle of the ethylene oligomerization process was 240 hours.

[0133] Based on comprehensive calculations, the catalytic activity of ethylene tetramerization is approximately 1500 kg / gCr·h, with a selectivity of 18.9% for 1-hexene, 68.7% for 1-octene, and 0.3% for PE; the catalytic activity of ethylene dimerization is 8 kg / gCr·h, with a selectivity of 75% for 1-butene and 0.5% for PE.

[0134] As can be seen from Example 1, the tetramerization reaction of ethylene experienced a decrease in heat transfer efficiency and poor liquid discharge from the overflow pipeline after 180 hours of operation, which affected the subsequent reaction. However, by switching the system to dimerization, the byproduct polymers that caused the above phenomena could be gradually dissolved, and the tetramerization reaction could continue. Therefore, compared with tetramerization alone, alternating between tetramerization and dimerization can improve the overall stable operation cycle of the process.

[0135] Referring to Examples 1-2, 2-2, and Comparative Example 1, the main differences between Examples 1-2 and Examples 2-2 and Comparative Example 1 lie in the catalyst ligands and reaction temperatures of the tetramerization reaction. The tetramerization reaction temperature in Examples 1-2 was 45–50°C, while the tetramerization reaction temperatures in Examples 2-2 and Comparative Example 1 were 75–80°C and 95–100°C, respectively. Under essentially the same conditions, the total operating cycle of Examples 1-2 was 400 hours, that of Examples 2-2 was 320 hours, and that of Comparative Example 1 was 200 hours. Therefore, using a tetramerization reaction temperature of 40–80°C, compared to a reaction temperature of 95–100°C, can extend the total operating cycle of the ethylene oligomerization process.

[0136] Furthermore, the selectivity and catalytic activity of the tetramerization of 1-octene in Examples 2-2 (46.7%, 1200 kg / g Cr·h) are greater than those in Comparative Example 1 (38.7%, 1000 kg / g Cr·h), and the selectivity and catalytic activity of the tetramerization of 1-octene in Examples 1-2 (68.7%, 1500 kg / g Cr·h) are even greater than those in Examples 2-2. Therefore, the preferred catalyst ligands for the tetramerization reaction are (Ph)₂PN(iPr)P(Ph)₂ of Examples 1-2 and (oF-Ph)₂PN(iPr)P(oF-Ph)₂ of Example 2-2, and more preferably (Ph)₂PN(iPr)P(Ph)₂.

[0137] Overall, by carrying out the tetramerization reaction of ethylene at a temperature of 40–80 °C and selecting specific catalyst ligands, it is not only beneficial to improve the overall operating cycle of the ethylene oligomerization process, but also to maintain high catalytic activity and better product selectivity.

[0138] The difference between Examples 1 to 1-4 and Comparative Example 2 lies in the catalyst and reaction temperature of the dimerization reaction. Their reaction temperatures are all in the range of 110–130°C, while Examples 1 to 1-4 use a main catalyst composed of a first chromium salt and a first ligand, while the main catalyst of Comparative Example 2 is tetrabutyl titanate, a conventional low-temperature catalyst with an applicable temperature of 50–60°C. According to the test results, the catalytic activity and stable operating cycle of Comparative Example 2 are both shorter than those of Examples 1 to 1-4. Therefore, the embodiments of the present invention, by using a specific catalyst to carry out the dimerization reaction of ethylene at a temperature of 110–130°C, can maintain high catalytic activity while extending the total operating cycle of the ethylene oligomerization process.

[0139] Furthermore, based on the test results of Examples 1 to 1-4, it is evident that, under the same tetramerization process and a dimerization reaction temperature of 110–130°C, using ligands A and C as the first ligand can extend the overall operating cycle of the ethylene oligomerization process compared to other ligands. More preferably, using ligand A as the first ligand and a dimerization reaction temperature of 110–120°C, more preferably 110–115°C, can further extend the overall operating cycle of the ethylene oligomerization process.

[0140] Unless otherwise specified, the terms used in this invention have the meanings commonly understood by those skilled in the art.

[0141] The embodiments described in this invention are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Those skilled in the art can make various other substitutions, changes and improvements within the scope of this invention. Therefore, this invention is not limited to the above embodiments, but is only defined by the claims.

Claims

1. An ethylene oligomerization process comprising producing an α-olefin by alternately carrying out a tetramerization reaction of ethylene and a dimerization reaction of ethylene in a reaction vessel; wherein, The reaction temperature of the dimerization reaction is 110-130℃, and the reaction temperature of the tetramerization reaction is 40-80℃; The dimerization reaction is carried out under the action of a first catalyst, and the tetramerization reaction is carried out under the action of a second catalyst; the first catalyst comprises a first main catalyst and a first cocatalyst, and the first main catalyst comprises a first metal chromium salt and a first ligand; the second catalyst comprises a second main catalyst and a second cocatalyst, and the second main catalyst comprises a second metal chromium salt and a second ligand; The first ligand is selected from the following compounds:

2. The ethylene oligomerization process of claim 1, wherein, The first ligand is: The reaction temperature of the dimerization reaction is 110-120℃.

3. The ethylene oligomerization process of claim 1, wherein, The first metal chromium salt and the second metal chromium salt each independently comprise one or a combination of two or more of chromium dichloride tetrahydrofuran complex, chromium acetylacetonate, chromium 2-ethylhexanoate, and chromium hexacarbonyl; and / or, The molar ratio of the first metal chromium salt to the first ligand is (0.5-5):1; and / or, The first cocatalyst and the second cocatalyst each independently comprise one or more of trimethylaluminum, triethylaluminum, triisobutylaluminum, trioctylaluminum, methylaluminoxane, and modified methylaluminoxane; and / or, The molar ratio of the first cocatalyst to the first main catalyst is (100-1000):

1.

4. The ethylene oligomerization process of claim 3, wherein, The molar ratio of the first metal chromium salt to the first ligand is (1-2):1; and / or, The molar ratio of the first cocatalyst to the first main catalyst is (200-500):

1.

5. The ethylene oligomerization process of claim 1, wherein, The switching between the dimerization reaction and the tetramerization reaction is achieved by adding the first catalyst or the second catalyst into the reaction container and adjusting the reaction conditions; and / or, The reaction pressure of the dimerization reaction and the tetramerization reaction is 3.0-5.0 MPa.

6. The ethylene oligomerization process of claim 1, wherein, The second ligand comprises one or more of (Ph)2PN(iPr)P(Ph)2, (Ph)2PN(t-Bu)P(Ph)2, (o-F-Ph)2PN(iPr)P(o-F-Ph)2, (Ph)2P(CH3-CH)2P(Ph)2, and (Ph)2P-Ph-P(Ph)2; and / or, The molar ratio of the second metal chromium salt to the second ligand is (0.5-5):1; and / or, The molar ratio of the second cocatalyst to the second main catalyst is (100-1000):

1.

7. The ethylene oligomerization process of claim 6, wherein, The second ligand is (Ph)2PN(iPr)P(Ph)2 or (o-F-Ph)2PN(iPr)P(o-F-Ph)2; and / or, The molar ratio of the second metal chromium salt to the second ligand is (1-2):1; and / or, The molar ratio of the second cocatalyst to the second main catalyst is (200-500):

1.

8. The ethylene oligomerization process of claim 1, wherein, In the reaction product, the content of α-olefins with a carbon atom number less than or equal to 8 is 90 wt% or more; and / or, The product of the dimerization reaction comprises 1-butene and 1-hexene, and the product of the tetramerization reaction comprises 1-hexene and 1-octene.

9. The ethylene oligomerization process of claim 1, wherein, switching the reaction in the reaction vessel to the tetramerization reaction after t1 hours of the dimerization reaction, t1 being from 12 to 60 h; and / or, switching the reaction in the reaction vessel to the dimerization reaction after t2 hours of the tetramerization reaction, t2 being from 60 to 240 h; and / or, the ratio of the reaction times of the dimerization reaction to the tetramerization reaction is t1 :t2 = (1-5):(5-20).

10. Use of the ethylene oligomerization process of any one of claims 1 to 9 for the preparation of a polyolefin elastomer.

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