Ethylene oligomerization long-period operation method

Abstract

The invention discloses an ethylene oligomerization long-period operation method, which comprises the following steps: mixing a solvent for ethylene polymerization, a cocatalyst and a main catalyst to obtain a liquid phase system, and after the temperature of the liquid phase system reaches the reaction temperature, sequentially introducing hydrogen and ethylene to start reaction to obtain an ethylene oligomerization main product and a byproduct polymer, by controlling the reaction temperature, the hydrogen feeding amount, the Al / Cr dosage ratio in the catalyst system and other parameters, the molecular weight distribution A of the by-product polymer, the weight-average molecular weight B of the polymer and the catalyst activity C in the obtained product meet a certain relational expression range, so that the blockage of a reaction kettle and a pipeline can be avoided, and the long-period operation of ethylene oligomerization is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer preparation, and in particular to a method for long-term operation of ethylene oligomerization. Background Art

[0002] Linear α-olefins have a wide range of industrial uses. Their oligomers can be used in many fields such as plasticizers, fatty acids, and lubricant additives; their copolymers can be used to produce polyolefin elastomers, which are widely used in shoe materials, polymer modification, photovoltaic adhesive films, and automobiles. At the same time, the production technology of α-olefins, which are important raw materials for POE, is a key factor restricting the industrialization of POE. Comparing the raw materials 1-octene and 1-hexene, POE prepared from 1-octene has very obvious advantages. Therefore, the domestic demand for 1-octene is very large.

[0003] At present, the production processes of linear α-olefins are divided into two types: one is non-selective oligomerization, and the other is selective oligomerization. The latter has become the current mainstream production process due to its high atom utilization rate and good economic benefits. At present, for the production of α-olefins by ethylene oligomerization, there are only a few industrialized cases of trimerization in China. Among them, there is no industrialized case for the production of 1-octene by ethylene tetramerization, and there are only literature reports. In the selective tetramerization process, in addition to the main product linear α-olefins, there are also a small amount of by-product polymers. The polymers are prone to wall adhesion on the surface of the reactor or heat exchanger. Long-term operation will cause a decrease in the mass transfer and heat transfer efficiency, and ultimately block the valves or pipelines, forcing the device to stop.

[0004] CN113511949A discloses a production system for co-producing 1-hexene and 1-octene by connecting three loop reactors in series. When a solid blockage occurs in a certain reactor, the reactor in the hot standby state can be switched in time, so that the blocked reactor can be hot washed, thus realizing staggered feeding. CN113233951A reports a process for ethylene oligomerization reaction by heat transfer of ethylene gas phase. On the one hand, it can reduce the blockage risk of the traditional heat transfer method; on the other hand, it can reduce the concentration of light components in the system, improve the selectivity of the product and reduce the high-carbon by-products generated by secondary reactions. However, the continuous operation cycle of the devices used in the ethylene oligomerization processes provided by the above-mentioned prior arts is relatively short, which limits the industrial progress of the ethylene oligomerization process. Summary of the Invention

[0005] In view of this, the main purpose of the present invention is to provide a method for long-term operation of ethylene oligomerization, which can avoid blockages in the reaction kettle and pipelines, and enable the polymerization device or process to operate in a long cycle.

[0006] To achieve the above-mentioned invention purpose, the first aspect of the present invention provides a method for long-term operation of ethylene oligomerization, including the following steps:

[0007] Mix the solvent, cocatalyst, and main catalyst for ethylene polymerization to obtain a liquid-phase system. After the temperature of the liquid-phase system reaches the reaction temperature, introduce 0.4 - 0.8 Mpa of hydrogen and 2 MPa - 7 MPa of ethylene in sequence to start the reaction. The reaction temperature is 35 - 90 °C, and the reaction time is 10 min - 240 min to obtain the main product of ethylene oligomerization and by-product polymer. The cocatalyst includes an alkyl aluminum compound, and the molar ratio of Al / Cr in the cocatalyst to the main catalyst is 200 - 2000:1.

[0008] Further, the reaction temperature is 40 - 70 °C, and the reaction time is 20 min - 100 min.

[0009] Further, the molar ratio of Al / Cr is 300 - 1500:1.

[0010] Further, the main catalyst includes a complex formed by a transition metal compound and a ligand.

[0011] Further, the main catalyst is selected from one or more of phosphine chromium complexes.

[0012] Further, the solvent includes any one or a combination of at least two of n-hexane, n-heptane, cyclohexane, methylcyclohexane, tetrahydrofuran, toluene, or xylene.

[0013] Further, the alkyl aluminum compound includes any one or a combination of at least two of trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, or trioctyl aluminum.

[0014] Further, the reaction is carried out under a vacuum state.

[0015] Further, after the reaction, the molecular weight distribution of the by-product polymer is A, the weight-average molecular weight of the polymer is B, and the catalyst activity is C. A, B, and C satisfy the following formula: When 1 < A < 2, 2AC + B / 1000 + C < 125; when A > 4, A + B / 1000 + 1 / 2C 2 <150.

[0016] Further, the preferred ranges of A, B, and C are respectively: A is selected from 1 - 25, B is selected from 500 - 70000, and C is selected from 0 - 10.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] The inventors of the present application have for the first time discovered that, without changing the main process and formula of the ethylene oligomerization reaction, by controlling parameters such as the reaction temperature, the hydrogen feed rate, and the Al / Cr dosage ratio, the molecular weight distribution A of the by-product polymer, the weight-average molecular weight B of the polymer, and the catalyst activity C in the obtained product satisfy the following formulas: when 1 < A < 2, 2AC + B / 1000 + C < 125; when A > 4, A + B / 1000 + 1 / 2C² < 150. When A, B, and C are within the ranges satisfying the above relationships, the by-product polymer can be discharged with the solvent in a dissolved manner, fundamentally avoiding the occurrence of blockages in the reaction kettle and pipelines, and ensuring the long-term operation of ethylene oligomerization.

[0019] Other features and advantages of the present invention will be described in detail in the following specific embodiments. Specific Embodiments

[0020] The following provides a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0021] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0022] I. The raw material information involved in the present invention is as follows:

[0023] The raw materials used in the examples are all conventional raw materials in the art, and the purity specifications used are analytical pure or chemically pure.

[0024] Chromium(III) chloride trifluoride tetrahydrofuran: Beijing Innochem Co., Ltd.

[0025] Chromium(III) acetylacetonate: Beijing Innochem Co., Ltd.

[0026] Methylcyclohexane: Beijing Innochem Co., Ltd.

[0027] MMAO-3a: Nouryon Co., Ltd.

[0028] PCCP-Cr complex a: Shanghai Wuxi AppTec Co., Ltd.

[0029] PCNP-Cr complex b: Shanghai Wuxi AppTec Co., Ltd.

[0030] Ethylene: Mingju Chemical Co., Ltd.

[0031] II. The main testing methods involved in the present invention are as follows:

[0032] The catalyst activity of the oligomerization reaction was analyzed qualitatively and quantitatively for each component in the reaction solution. The conditions of the GC analysis instrument used were as follows:

[0033] Instrument model: Shimadzu GC2010

[0034] Chromatographic column: DB-5 (30m 0.25mm 0.25μm)

[0035] Column temperature program: First, hold at 35°C for 10 min, then increase to 250°C at a rate of 10°C / min, and hold at this temperature for 10 min.

[0036] Detector temperature: 300°C

[0037] Carrier gas: 1 bar

[0038] Air: 0.3 bar

[0039] Fuel gas (H2): 0.3 bar

[0040] The sample mass analysis was carried out using the internal standard method. There should be:

[0041]

[0042] Where m1 is the mass of a certain product, m is the mass of the internal standard, a1 is the peak area detected for the product in the gas chromatography, and a is the peak area of the internal standard. k is a correction factor related to the substance to be measured and the detection conditions.

[0043] Catalyst activity: The mass of the reaction product that can be catalyzed per gram of catalyst, with the unit kgPE / gCr.h.

[0044] The present invention provides a method for long-term operation of ethylene oligomerization, including the following steps:

[0045] Mix the solvent, cocatalyst, and main catalyst used in the ethylene polymerization system to obtain a liquid-phase system. After the temperature of the liquid-phase system reaches the reaction temperature, hydrogen at 0.4 - 2 Mpa and ethylene at 2 MPa - 7 MPa are sequentially introduced to start the reaction. The reaction temperature is 35 - 90°C, and the reaction time is 10 min - 240 min to obtain the main product of ethylene oligomerization and by-product polymers; the cocatalyst includes an alkylaluminum compound, and the molar ratio of Al / Cr in the cocatalyst to the main catalyst is 200 - 2000:1.

[0046] In some embodiments, the hydrogen pressure is 0.4 Mpa, 0.6 Mpa, 0.8 Mpa, 1.0 Mpa, 1.2 Mpa, 1.5 Mpa, or 2.0 Mpa, etc.

[0047] In some embodiments, the ethylene pressure is 2 Mpa, 2.5 Mpa, 3 Mpa, 3.5 Mpa, 4 Mpa, 4.5 Mpa, 5 Mpa, 5.5 Mpa, 6 Mpa, 6.5 Mpa or 7 Mpa, etc.

[0048] In some embodiments, the reaction temperature is 40 - 70 °C, such as 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C or 70 °C, etc.; the reaction time is 20 min - 100 min, such as 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min or 100 min, etc.

[0049] In some embodiments, the Al / Cr molar ratio is 300 - 1500:1, such as 300:1, 400:1, 500:1, 800:1, 1000:1, 1200:1, 1400:1, 1500:1, etc.

[0050] In some embodiments, the main catalyst comprises a complex formed by a transition metal compound and a ligand.

[0051] In some embodiments, the main catalyst is selected from one or more of phosphine chromium complexes.

[0052] In some embodiments, the solvent comprises any one or a combination of at least two of n - hexane, n - heptane, cyclohexane, methylcyclohexane, tetrahydrofuran, toluene or xylene.

[0053] In some embodiments, the alkylaluminum compound comprises any one or a combination of at least two of trimethylaluminum, triethylaluminum, triisobutylaluminum or trioctylaluminum.

[0054] In some embodiments, the reaction is carried out under a vacuum state.

[0055] In some embodiments, after the reaction, the molecular weight distribution of the by - product polymer is A, the weight - average molecular weight of the polymer is B, and the catalyst activity is C. A, B and C satisfy the following formula: when 1 < A < 2, 2AC + B / 1000 + C < 125; when A > 2, A + B / 1000 + 1 / 2C 2 <150.

[0056] The catalyst activity (polymer) is the catalyst activity corresponding to the polymer selectivity, and its unit is kgPE / gCr·h.

[0057] Preferably, the preferred ranges of A, B and C are respectively: A is selected from 1 - 25, B is selected from 500 - 70000, and C is selected from 0 - 10.

[0058] The present invention will be further described in conjunction with the following embodiments:

[0059] Example 1

[0060] Before the reaction, a 300 ml reaction kettle was heated to 150 °C, evacuated for 3 h, and purged with nitrogen three times. After the temperature was cooled to room temperature, it was purged with ethylene twice. First, 100 ml of dehydrated and deoxygenated solvent methylcyclohexane and 1.05 mmol of (Al / Cr = 500) MMAO-3a (7 wt% Al, n-heptane) were added, and then 3.5 μmol of PCCP-Cr complex a was added. When the temperature was constant at 70 °C, 0.4 Mpa of hydrogen and 2 MPa of ethylene were sequentially introduced to start the reaction. The reaction temperature was 70 °C, and the reaction time was 100 min. After the reaction was completed, the ethylene inlet valve was closed, and it was quickly cooled to below 5 °C with an ice-water bath or, and the pressure was slowly released, and the reaction kettle was unloaded to obtain the ethylene oligomerization product.

[0061]

[0062] The product was analyzed by GC and GPC. The catalyst activity was 10 kgPE / gCr·h, the polymer PDI = 2, Mw = 70003, and the continuous operation time was greater than 600 h.

[0063] Example 2

[0064] Before the reaction, a 300 ml reaction kettle was heated to 150 °C, evacuated for 3 h, and purged with nitrogen three times. After the temperature was cooled to room temperature, it was purged with ethylene twice. First, 100 ml of dehydrated and deoxygenated solvent methylcyclohexane and 3.5 mmol of (Al / Cr = 1000) MMAO-3a (7 wt% Al, n-heptane) were added, and then 3.5 μmol of PCNP-Cr complex b was added. When the temperature was constant at 70 °C, 2 Mpa of hydrogen and 7 MPa of ethylene were sequentially introduced to start the reaction. The reaction temperature was 70 °C, and the reaction time was 20 min. After the reaction was completed, the ethylene inlet valve was closed, and it was quickly cooled to below 5 °C with an ice-water bath or, and the pressure was slowly released, and the reaction kettle was unloaded to obtain the ethylene oligomerization product.

[0065]

[0066] The product was analyzed by GC and GPC. The catalyst activity was 8 kgPE / gCr·h, the polymer PDI = 25, Mw = 61587, and the continuous operation time was greater than 600 h.

[0067] Example 3

[0068] Before the reaction, heat a 300 ml reaction kettle to 150 °C, evacuate for 3 h, and displace with nitrogen three times. After the temperature cools to room temperature, displace with ethylene twice. First, add 100 ml of dehydrated and deoxygenated solvent methylcyclohexane and 5.25 mmol of (Al / Cr = 1500) MMAO-3a (7 wt% Al, n-heptane), then add 3.5 μmol of PCCP-Cr complex a. When the temperature is constant at 70 °C, sequentially introduce 2 MPa of hydrogen and 2 MPa of ethylene to start the reaction. The reaction temperature is 40 °C and the reaction time is 30 min. After the reaction is completed, close the ethylene inlet valve, quickly cool to below 5 °C with an ice-water bath or, and slowly relieve the pressure. Unload the kettle to obtain the ethylene oligomerization product.

[0069] The products were analyzed by GC and GPC. The catalyst activity was 0.3 kg PE / g Cr·h, the polymer PDI = 1.2, Mw = 506, and the continuous operation time was greater than 600 h.

[0070] Example 4

[0071] Before the reaction, heat a 300 ml reaction kettle to 150 °C, evacuate for 3 h, and displace with nitrogen three times. After the temperature cools to room temperature, displace with ethylene twice. First, add 100 ml of dehydrated and deoxygenated solvent methylcyclohexane and 3.15 mmol of (Al / Cr = 900) MMAO-3a (7 wt% Al, n-heptane), then add 3.5 μmol of PCNP-Cr complex b. When the temperature is constant at 50 °C, sequentially introduce 1.5 MPa of hydrogen and 3 MPa of ethylene to start the reaction. The reaction temperature is 50 °C and the reaction time is 40 min. After the reaction is completed, close the ethylene inlet valve, quickly cool to below 5 °C with an ice-water bath or, and slowly relieve the pressure. Unload the kettle to obtain the ethylene oligomerization product.

[0072] The products were analyzed by GC and GPC. The catalyst activity was 0.7 kg PE / g Cr·h, the polymer PDI = 2.1, Mw = 28500, and the continuous operation time was greater than 600 h.

[0073] Comparative Example 1

[0074] Before the reaction, heat a 300 ml reaction kettle to 150 °C, evacuate for 3 h, and displace with nitrogen three times. After the temperature cools to room temperature, displace with ethylene twice. First, add 100 ml of dehydrated and deoxygenated solvent methylcyclohexane and 0.35 mmol of (Al / Cr = 100) MMAO-3a (7 wt% Al, n-heptane), then add 3.5 μmol of PCCP-Cr complex a. When the temperature is constant at 70 °C, sequentially introduce 2.5 MPa of hydrogen and 7 MPa of ethylene to start the reaction. The reaction temperature is 70 °C and the reaction time is 100 min. After the reaction is completed, close the ethylene inlet valve, quickly cool to below 5 °C with an ice-water bath or, and slowly relieve the pressure. Unload the kettle to obtain the ethylene oligomerization product.

[0075] The products were analyzed by GC and GPC. The catalyst activity was 8 kg PE / g Cr·h, the polymer PDI = 1.3, Mw = 110800, and the continuous operation time was about 25 h.

[0076] Comparative Example 2

[0077] Before the reaction, a 300 ml reaction kettle was heated to 150 °C, evacuated for 3 h, and purged with nitrogen three times. After the temperature was cooled to room temperature, it was purged with ethylene twice. First, 100 ml of dehydrated and deoxygenated solvent methylcyclohexane and 1.75 mmol of (Al / Cr = 500) MMAO-3a (7 wt% Al, n-heptane) were added, and then 3.5 μmol of PCCP-Cr complex a was added. When the temperature was constant at 40 °C, 0.1 Mpa of hydrogen and 5 MPa of ethylene were introduced in sequence to start the reaction. The reaction temperature was 120 °C and the reaction time was 30 min. After the reaction, the ethylene inlet valve was closed, and the temperature was quickly cooled to below 5 °C with an ice-water bath, and the pressure was slowly released. The reaction kettle was unloaded to obtain the ethylene oligomerization product.

[0078] The products were analyzed by GC and GPC. The catalyst activity was 15 kg PE / g Cr·h, the polymer PDI = 22, Mw = 19825, and the continuous operation time was about 14 h.

[0079] It can be seen from the comparison between Comparative Examples 1-2 and this example that the dynamic changes of process parameters such as hydrogen pressure, aluminum-chromium ratio in the catalyst system, ethylene pressure, and reaction temperature cause the change in the selectivity of the catalyst for the polymer. For example, the obvious increase in the polymer molecular weight, etc., makes the by-product polymer no longer satisfy the relationship of the present invention, resulting in the inability of ethylene oligomerization to operate in a long cycle.

[0080] Obviously, the above-mentioned examples of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to enumerate all the implementation manners here. All obvious changes or modifications derived from the technical solutions of the present invention are within the spirit scope covered by the present invention.

Claims

1. A method for long-term operation of ethylene oligomerization, characterized in that, The method comprises the following steps: Mix a solvent for ethylene polymerization, a cocatalyst and a main catalyst to obtain a liquid-phase system. After the temperature of the liquid-phase system reaches the reaction temperature, introduce hydrogen at 0.4 - 2 Mpa and ethylene at 2 Mpa - 7 Mpa in sequence to start the reaction. The reaction temperature is 35 - 90 °C, and the reaction time is 10 min - 240 min to obtain the main product of ethylene oligomerization and by-product polymers; the cocatalyst includes an alkylaluminum compound, and the molar ratio of Al / Cr in the cocatalyst to the main catalyst is 200 - 2000:

1.

2. The method for long-term operation of ethylene oligomerization according to claim 1, wherein The reaction temperature is 40 - 70 °C, and the reaction time is 20 min - 100 min.

3. The method for long-term operation of ethylene oligomerization according to claim 1, characterized in that, The molar ratio of Al / Cr is 300 - 1500:

1.

4. The method for long-term operation of ethylene oligomerization according to claim 1, characterized in that, The main catalyst includes a complex formed by a transition metal compound and a ligand.

5. The method for long-term operation of ethylene oligomerization according to claim 4, characterized in that, The main catalyst is selected from one or more of phosphine chromium complexes.

6. The method for long-term operation of ethylene oligomerization according to claim 1, wherein The solvent includes any one or a combination of at least two of n-hexane, n-heptane, cyclohexane, methylcyclohexane, tetrahydrofuran, toluene or xylene.

7. The method for long-term operation of ethylene oligomerization according to claim 1, characterized in that, The alkylaluminum compound includes any one or a combination of at least two of trimethylaluminum, triethylaluminum, triisobutylaluminum or trioctylaluminum.

8. The method for long-term operation of ethylene oligomerization according to claim 1, characterized in that, The reaction is carried out under a vacuum state.

9. The method for long-term operation of ethylene oligomerization according to any one of claims 1-8, characterized in that, After the reaction ends, the molecular weight distribution of the by-product polymer is A, the weight-average molecular weight of the polymer is B, and the catalyst activity is C. A, B, and C satisfy the following formula: when 1 < A < 2, 2AC + B / 1000 + C < 125; when A > 4, A + B / 1000 + 1 / 2C 2 <150.

10. The method for long-term operation of ethylene oligomerization according to claim 9, wherein The preferred ranges of A, B and C are respectively: A is selected from 1 - 25, B is selected from 500 - 70000, and C is selected from 0 - 10.

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