Ethylene oligomerization process

Abstract

The invention provides an ethylene oligomerization method which comprises the following steps: premixing feed gas containing ethylene and hydrogen with an organic solvent to obtain a premix; the premix is in contact with a catalyst system a for a pre-reaction, and a pre-reactant is obtained; the catalyst system a is a bridged diphosphine chromium complex; the pre-reactant is in contact with a catalyst system b for a polymerization reaction, and a product containing alpha-olefin is obtained; the catalyst system b is an organic aluminum compound. According to the method disclosed by the invention, the activity and the product selectivity of the catalyst are improved by premixing the gas phase and the liquid phase and pre-activating the catalyst system, so that the utilization efficiency of the catalyst is improved, and the production cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for ethylene polymerization, in particular to a method for ethylene oligomerization with improved reaction activity, and belongs to the technical field of petroleum chemical industry. BACKGROUND

[0002] Alpha-olefins are important substances for co-monomers, detergents, lubricants, plasticizers, etc., and have been widely used in commerce. Commonly used alpha-olefins are usually produced by oligomerization or oligomerization reaction of ethylene. Ethylene oligomerization or oligomerization reaction is carried out by using ethylene as a reactant in the presence of a catalyst, and the oligomerization reaction usually obtains C 2-20 Olefin oligomers.

[0003] Since the 1970s, transition metal complex catalyzed ethylene oligomerization or oligomerization has gradually attracted the attention of scientists, and researchers have begun to strive to develop new catalysts and improve existing catalysts to improve the activity of the catalysts and the selectivity of the catalyzed products. The activity of the transition metal complex catalyst in the process of olefin polymerization or oligomerization and the selectivity of the produced products depend on the structure of the catalyst ligand and the operating conditions.

[0004] US20100137669 discloses a PCCP symmetrical skeleton type catalyst, which is more stable than the PNP system in the ethylene tetramerization reaction, but the total selectivity of 1-hexene and 1-octene is not more than 85%. CN107075009A discloses a method for inhibiting the occurrence of additional side reactions of products by adding a deactivator, which reduces the isomers of 1-hexene and / or 1-octene to some extent, but also increases the reaction cost. In order to improve the reaction activity, patent EP2489431B1 discloses a method for preparing a catalyst composition for ethylene oligomerization reaction and a corresponding catalyst composition pre-forming device, and the catalyst system prepared in a special device can only exist stably for a short time, which is not conducive to long-period operation. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for ethylene polymerization with improved catalyst reaction activity in the reaction, which prepares alpha-olefins from ethylene as raw material in the presence of a bridged diphosphine modified chromium catalyst system, wherein ethylene and hydrogen are pre-mixed with a solvent in the reactor under certain conditions, and then a bridged diphosphine chromium complex and an organic aluminum compound are added for reaction. A reasonable process flow is designed to improve the activity of the organic phosphine modified chromium catalyst system in the reaction process, thereby improving the catalyst use efficiency and reducing the production cost.

[0006] The ethylene oligomerization method provided by the present application comprises:

[0007] S1 raw material gas containing ethylene and hydrogen is pre-mixed with an organic solvent to obtain a pre-mixture;

[0008] S2 the pre-mixture is contacted with catalyst system a to perform pre-reaction to obtain a pre-reaction product; the catalyst system a is a bridged chromium complex of double phosphine;

[0009] S3 the pre-reaction product is contacted with catalyst system b to perform reaction to obtain a product containing α-olefin (preferably 1-hexene and 1-octene); the catalyst system b is an organic aluminum compound.

[0010] According to some embodiments of the present application, the mass ratio of hydrogen, ethylene and solvent is 1:1-10000:1-10.

[0011] According to preferred embodiments of the present application, the mass ratio of hydrogen, ethylene and solvent is 1:100-2000:2-5.

[0012] The mass ratio of hydrogen, ethylene and solvent is selected from any value in 1:200:2, 1:500:2, 1:500:2, 1:2000:2, 1:500:3, 1:2000:3 or a range value between any two of them.

[0013] The pre-mixing conditions include: the pre-mixing temperature is 0-100℃; the pre-mixing pressure P1 is 0-6Mpa; the pre-mixing time is 0.1-30min.

[0014] According to preferred embodiments of the present application, the pre-mixing temperature is 20-80℃.

[0015] According to more preferred embodiments of the present application, the pre-mixing temperature is 20-50℃.

[0016] According to more preferred embodiments of the present application, the pre-mixing temperature is 30-60℃.

[0017] The pre-mixing temperature is selected from any value in 0℃, 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃ or a range value between any two of them.

[0018] According to preferred embodiments of the present application, the pre-mixing pressure P1 is 2-4MPa.

[0019] The pre-mixing pressure P1 is selected from any value in 0Mpa, 2Mpa, 2.5Mpa, 3Mpa, 3.2Mpa, 4Mpa, 5Mpa, 6Mpa or a range value between any two of them.

[0020] According to preferred embodiments of the present application, the mixing time is 15-25min.

[0021] The pre-mixing time is selected from any value of 0.1 min, 1 min, 10 min, 15 min, 20 min, 25 min, 30 min or a range value between any two of them.

[0022] The pre-reaction conditions include: the pre-reaction temperature is 0-100℃; the pre-reaction pressure P2 is 0-6 MPa; the pre-reaction time is 0.1-30 min.

[0023] According to a preferred embodiment of the present application, the pre-reaction temperature is 20-80℃.

[0024] According to a more preferred embodiment of the present application, the pre-reaction temperature is 20-50℃.

[0025] According to a more preferred embodiment of the present application, the pre-reaction temperature is 30-60℃.

[0026] The pre-reaction temperature is selected from any value of 0℃, 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃ or a range value between any two of them.

[0027] According to a preferred embodiment of the present application, the pre-reaction pressure P2 is 2-4 MPa.

[0028] The pre-reaction pressure P2 is selected from any value of 0 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.2 MPa, 4 MPa, 5 MPa, 6 MPa or a range value between any two of them.

[0029] According to a preferred embodiment of the present application, the pre-reaction time is 1-20 min.

[0030] The pre-reaction time is selected from any value of 0.1 min, 1 min, 2 min, 5 min, 10 min, 20 min, 50 min, 100 min or a range value between any two of them.

[0031] The polymerization reaction conditions include: the polymerization reaction temperature is 0-80℃; the polymerization reaction time is 10-120 min; the polymerization reaction pressure is P3, P3>P1, P3>P2; preferably, P3-P1>0.8 MPa; P3-P2>0.8 MPa; preferably, P3 is 0-10 MPa.

[0032] According to a preferred embodiment of the present application, the polymerization reaction temperature is 20-60℃.

[0033] The temperature of the polymerization reaction is selected from any value or a range between any two values of 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C.

[0034] According to a preferred embodiment of the present application, the reaction time of the polymerization reaction is 20-60 min.

[0035] The time of the polymerization reaction is selected from any value or a range between any two values of 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 100 min, 120 min.

[0036] According to some embodiments of the present application, the pressure P3 of the polymerization reaction is higher than the pressure P1 of the premixing and higher than the pressure P2 of the pre-reaction.

[0037] The present application applies a pressure step to the reaction stage, such that the pressure is increased from the lower pressure of the premixing stage to the higher pressure of the reaction stage. In particular, the pressure of the reaction stage of the process of the present application is controlled to be at least 0.8 MPa higher than the pressure of the premixing stage and higher than the pressure of the pre-reaction stage.

[0038] According to a preferred embodiment of the present application, the pressure P3 of the polymerization reaction is 2.8-6 MPa.

[0039] The pressure P3 of the polymerization reaction is selected from any value or a range between any two values of 0 Mpa, 2 Mpa, 2.8 Mpa, 4 Mpa, 6 Mpa, 8 Mpa, 10 Mpa.

[0040] According to some embodiments of the present application, the bridged diphosphine chromium complex is complexed from an organic chromium compound and a bridged diphosphine ligand, the molar ratio of the organic chromium compound to the bridged diphosphine ligand is 1:0.1-10, preferably 1:0.25-2, and more preferably 1:0.5-2, calculated on the basis of the metal chromium.

[0041] According to a preferred embodiment of the present application, the bridged diphosphine ligand is represented by formula (I):

[0042]

[0043] wherein L is a bridging group selected from ethyl with or without a substituent or N, wherein the substituent on the ethyl is a non-cyclic hydrocarbon substituent. R1, R2, R3 and R4 are each independently selected from hydrogen, halogen, straight-chain or branched-chain alkane, free of O element, and R1 and R2 are the same, and R1 and R2 are the same or different from R3 or R4.

[0044] According to a preferred embodiment of the present application, the organic aluminum compound is at least one of an alkyl aluminum compound, an aluminoxane compound and a chlorinated alkyl aluminum compound, preferably methyl aluminoxane.

[0045] According to some embodiments of the present application, the organic solvent is selected from at least one of aldehydes, ketones, benzene, substituted benzene, alkanes and substituted alkanes.

[0046] According to a preferred embodiment of the present application, the organic solvent is at least one of toluene, xylene, chlorobenzene, heptane, cyclohexane or methylcyclohexane.

[0047] According to a preferred embodiment of the present application, the organic solvent is selected from cyclohexane and / or methylcyclohexane.

[0048] According to some embodiments of the present application, the amount of the organic solvent is such that the concentration of the catalyst system a, calculated as the metal chromium element, is 0.1-20 μmol / L.

[0049] According to some embodiments of the present application, the molar ratio of the catalyst system a to the catalyst system b, calculated as chromium and aluminum atoms, is 1:(100-3000) (mol).

[0050] According to some embodiments of the present application, the total selectivity of 1-hexene, 1-octene in the product is >90%, preferably >95%.

[0051] According to some embodiments of the present application, the activity of the catalyst system a is >1.5 x 10 8 g·mol(Cr) -1 ·h -1 , preferably >4.4 x 10 8 g·mol(Cr) -1 ·h -1 .

[0052] The present application has the following advantages: the present application can be premixed in gas phase and liquid phase, and the catalyst system is pre-activated, thus improving the activity of the catalyst and the utilization efficiency of the catalyst, significantly improving the selectivity of the target product, inhibiting the production of by-product polymers, increasing the economic benefits and reducing the production cost. DETAILED DESCRIPTION

[0053] The present application is further described below by way of examples, which in no way limit the scope of the present application.

[0054] In the following examples and comparative examples,

[0055] chromium acetylacetonate, purchased from Beijing Bailingwei Chemical Reagent Co., Ltd;

[0056] Methylcyclohexane, purchased from Beijing Bailingwei Chemical Reagent Co., Ltd.

[0057] Modified methylaluminoxane (MMAO), purchased from Akzo Nobel;

[0058] Bridged bisphosphine ligand, prepared by the method of Preparation Example 3 in Chinese Invention Application Publication CN111434669A.

[0059] The reaction activity is calculated according to the following formula:

[0060]

[0061] The reaction activity refers to the reaction activity of the total reaction system, and the catalyst system a and the catalyst system b jointly constitute the total reaction system.

[0062] The total selectivity of 1-hexene, 1-octene is calculated according to the following formula:

[0063]

[0064] Wherein, m 总产物 refers to the mass of all products obtained by reaction;

[0065] n Cr refers to the molar amount of catalyst calculated as chromium metal;

[0066] h refers to the time of polymerization reaction;

[0067] m 1-己烯 refers to the mass of 1-hexene obtained by reaction;

[0068] m 1-辛烯 refers to the mass of 1-octene obtained by reaction.

[0069] Example 1

[0070] The polymerization reaction device uses a 300ml stainless steel high-pressure reaction kettle. In the glove box under inert atmosphere, 0.5μmol of acetylacetone chromium and 0.75μmol of bridged bisphosphine ligand are mixed and dissolved in 2ml of methylcyclohexane to obtain a uniform mixed solution, which is added to the feed bottle of the reaction kettle for standby.

[0071] Step (1) pre-mixing

[0072] The reaction kettle is heated to 80℃, vacuumed and replaced with nitrogen, then filled with ethylene for replacement, and then the temperature in the reaction kettle is reduced to 40℃ (pre-mixing temperature). Methylcyclohexane (solvent) is added to the reaction kettle, the pressure is set to 3.2MPa (pre-mixing pressure), and then ethylene and hydrogen (mass ratio H2: ethylene: solvent = 1:200:2) are introduced into the reaction kettle, and the pre-mixing stirring is carried out for 20min (pre-mixing time).

[0073] Step (2) Pre-reaction

[0074] Under pressure of 3.2 MPa and temperature of 40 °C, the injection device was opened, and the mixed solution of chromium acetylacetone and bridged bisphosphine ligand in the feed bottle was completely added to the reaction vessel. Then, the injection device was closed and stirring was continued for 5 min (pre-reaction time).

[0075] Step (3) Polymerization reaction

[0076] The pressure was adjusted to 4 MPa, the temperature was maintained at 40℃, and modified methylaluminoxane (MMAO) was added to initiate the polymerization reaction. After 30 minutes (polymerization reaction time), 1 mL of ethanol was added as a terminator to terminate the reaction. During the reaction, the total volume of the reaction solution was 150 mL, and the molar ratio of chromium acetylacetone:bridged bisphosphine ligand:MMAO was 1:1.5:300, meaning that the amount of MMAO added was 150 μmol.

[0077] The temperature inside the reactor was lowered to room temperature (25°C). The gaseous product was collected in a gas metering vessel, and the liquid product was collected in an Erlenmeyer flask. The gaseous and liquid products were metered separately and then analyzed by gas chromatography. The catalyst activity and product composition were calculated, and the results are listed in Table 1.

[0078] Example 2

[0079] The experimental method was the same as in Example 1, except that the premixing pressure in step (1) was changed to 2.5 MPa, and the other experimental conditions remained unchanged. The test results are shown in Table 1.

[0080] Example 3

[0081] The experimental method was the same as in Example 1, except that the premixing pressure in step (1) was changed to 4 MPa, and the other experimental conditions remained unchanged. The test results are shown in Table 1.

[0082] Example 4

[0083] The experimental method was the same as in Example 1, except that the premixing pressure in step (1) was changed to 5.0 MPa, and the other experimental conditions remained unchanged. The test results are shown in Table 1.

[0084] Example 5

[0085] The experimental method was the same as in Example 1, except that the premixing temperature in step (1) was changed to 30°C, the reaction temperature remained at 40°C, and the other experimental conditions remained unchanged. The test results are shown in Table 1.

[0086] Example 6

[0087] The experimental method was the same as in Example 1, except that the premixing temperature in step (1) was changed to 60°C, the reaction temperature remained at 40°C, and the other experimental conditions remained unchanged. The test results are shown in Table 1.

[0088] Example 7

[0089] The experimental method was the same as in Example 1, except that the premixing time in step (1) was changed to 10 min, and the other experimental conditions remained unchanged. The test results are shown in Table 1.

[0090] Example 8

[0091] The experimental method was the same as in Example 1, except that the premixing time in step (1) was changed to 30 min, and the other experimental conditions remained unchanged. The test results are shown in Table 1.

[0092] Example 9

[0093] The experimental method was the same as in Example 1, except that the pre-reaction time in step (2) was changed to 2 min, and the other experimental conditions remained unchanged. The test results are shown in Table 1.

[0094] Example 10

[0095] The experimental method was the same as in Example 1, except that the pre-reaction time in step (2) was changed to 10 min, and the other experimental conditions remained unchanged. The test results are shown in Table 1.

[0096] Example 11

[0097] The experimental method was the same as in Example 1, except that the pre-reaction time in step (2) was changed to 20 min, and the other experimental conditions remained unchanged. The test results are shown in Table 1.

[0098] Comparative Example 1: Polymerization without pre-reaction

[0099] The polymerization apparatus uses a 300ml stainless steel high-pressure reactor. In a glove box under an inert atmosphere, 0.5μmol chromium acetylacetone and 0.75μmol bridged bisphosphine ligand are mixed and dissolved in 2ml of methylcyclohexane to obtain a homogeneous mixed solution, which is then added to the feed bottle of the reactor for later use.

[0100] (1) Heat the reactor to 80°C, evacuate it and replace it with nitrogen, then fill it with ethylene and replace it. Then lower the temperature inside the reactor to 40°C, add methylcyclohexane (solvent) to the reactor, set the premixing pressure to 3.2 MPa, and then introduce ethylene and hydrogen into the reactor (mass ratio H2: ethylene: solvent = 1:200:2). Premix and stir for 20 min.

[0101] (2) Adjust the pressure to 4 MPa and maintain the temperature at 40 °C. Add the modified methylaluminoxane (MMAO) and the mixed solution of chromium acetylacetone and bridged bisphosphine ligand from the feed bottle to the reactor simultaneously for polymerization. After 30 minutes, add 1 mL of ethanol as a terminator to terminate the reaction. After the reaction, a large amount of polymer appears in the reactor. During the reaction, the total volume of the mixture is 150 mL, and the molar ratio of chromium acetylacetone:bridged bisphosphine ligand:MMAO is 1:1.5:300, that is, the amount of MMAO added is 150 μmol.

[0102] The temperature inside the reactor was lowered to room temperature (25℃). The gaseous product was collected in a gas metering vessel, and the liquid product was collected in an Erlenmeyer flask. After separate metering, the gas and liquid products were analyzed by gas chromatography to calculate the catalyst activity and product composition. The reaction activity was 0.7 × 10⁻⁶. 8 g·mol(Cr) -1 ·h -1 The overall selectivity for 1-hexene and 1-octene in the product was 92.5%.

[0103] As can be seen from the comparative examples, without pre-reaction of the catalyst system, the catalyst system has low reactivity and product selectivity, and polymers will appear.

[0104] Table 1

[0105]

[0106] Any numerical value mentioned in this invention, if there is only a two-unit interval between any minimum and any maximum value, includes all values ​​that increase by one unit each time from the minimum to the maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, or time, is stated as 50-90, in this specification it means specifically listing values ​​such as 51-89, 52-88… and 69-71 and 70-71, etc. For non-integer values, it may be appropriately considered that a unit is 0.1, 0.01, 0.001, or 0.0001. These are merely some specifically specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0107] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for ethylene oligomerization, comprising: S1: pre-mixing a raw gas containing ethylene and hydrogen with an organic solvent to obtain a pre-mixture; S2: contacting the pre-mixture with a catalyst system a to perform a pre-reaction to obtain a pre-reaction product; the catalyst system a is a bridged chromium bis-phosphine complex; S3: contacting the pre-reaction product with a catalyst system b to perform a polymerization reaction to obtain a product containing a-olefins; the catalyst system b is an organic aluminum compound.

2. The method of claim 1, wherein, The mass ratio of the hydrogen, ethylene and organic solvent is 1:(1-10000):(1-10), preferably 1:(100-2000):(2-5).

3. The method according to claim 1 or 2, wherein the pre-mixing conditions comprise: the pre-mixing temperature is 0-100℃, preferably 20-80℃, more preferably 20-50℃; the pre-mixing pressure P1 is 0-6 MPa, preferably 2-4 MPa; the pre-mixing time is 0.1-30 min, preferably 15-25 min.

4. The method according to any one of claims 1-3, wherein the pre-reaction conditions comprise: the pre-reaction temperature is 0-100℃, preferably 20-80℃, more preferably 20-50℃; the pre-reaction pressure P2 is 0-6 MPa, preferably 2-4 MPa; the pre-reaction time is 0.1-100 min, preferably 1-20 min.

5. The method according to any one of claims 1-4, wherein the polymerization reaction conditions comprise: the polymerization reaction temperature is 0-80℃, preferably 20-60℃; the polymerization reaction time is 10-120 min, preferably 20-60 min; the polymerization reaction pressure is P3, P3>P1, P3>P2; preferably, P3-P1>0.8 MPa; P3-P2>0.8 MPa; preferably, P3 is 0-10 MPa, preferably 2.8-6 MPa.

6. The method according to any one of claims 1-5, wherein the bridged chromium bis-phosphine complex is complexed by an organic chromium compound and a bridged bis-phosphine ligand, and the molar ratio of the organic chromium compound to the bridged bis-phosphine ligand is 1:0.1-10, preferably 1:0.25-2, more preferably 1:0.5-2, in terms of metal chromium.

7. The method according to any one of claims 1-6, wherein the organic aluminum compound is selected from at least one of an alkyl aluminum compound, an aluminoxane aluminum compound and a chlorinated alkyl aluminum compound, preferably methyl aluminoxane. the organic solvent is selected from at least one of aldehyde compounds, ketone compounds, benzene, benzene substitutes, alkanes and substituted alkanes; preferably at least one of toluene, xylene, chlorobenzene, heptane, cyclohexane or methylcyclohexane.

9. The method according to any one of claims 1-7, wherein the amount of the organic solvent is such that the concentration of the catalyst system a in terms of metal chromium element is 0.1-20 μmol / L. ​ ​ ​ 8. The method according to any one of claims 1-7, characterized in that, ​ ​ ​ And / or, the molar ratio of the catalyst system a to the catalyst system b, respectively in terms of chromium, aluminum atoms, is 1 : (100-3000).

10. The method according to any one of claims 1 to 9, characterized in that, The activity of the catalyst system a is > 1.5 x 10 8 g mol(Cr) -1 · h -1 , preferably more than 4.4 x 10 8 g mol(Cr) -1 · h -1 .

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