A method for preparing linear alpha-olefins by highly selective polymerization of ethylene

Abstract

The present invention relates to the technical field of ethylene selective polymerization, and specifically discloses a method for preparing linear alpha-olefins by highly selective polymerization of ethylene. The method is that ethylene is selectively polymerized in a system comprising a main catalyst, a composite alkyl aluminum cocatalyst, an inhibitor and an organic solvent to generate linear alpha-olefins at a certain reaction temperature and reaction pressure. The catalytic reaction system of the present invention reduces the generation of by-product polymers while maintaining the activity of polymerization, and the content of polymer components is as low as 0.01% (wt.); in addition, the operating cost is reduced while maintaining high catalytic activity; the content of 1-octene and 1-hexene in the prepared alpha-olefins can reach up to 91.2%, and the catalyst reaction activity is not less than 1000kg / (gCr·h).

Description

Technical Field

[0001] The invention relates to the technical field of ethylene selective oligomerization, and specifically discloses a method for preparing linear alpha-olefins by high-selective ethylene oligomerization. Background Art

[0002] Linear α-olefins (LAOs) refer to monoolefins with a straight molecular chain and a double bond at one end. As an important type of organic chemical raw materials and chemical intermediates, they are widely used in polyα-olefins (PAO), polyolefin elastomers (POE), polyolefin plastomers (POP), surfactants and oil additives. At present, linear α-olefins are one of the products with the greatest value-added potential and the most urgent need in China.

[0003] The production methods of linear α-olefins mainly include alcohol dehydration, Fischer-Tropsch synthesis, cycloolefin isomerization, fatty alcohol dehydrogenation, paraffin cracking, ethylene polymerization, etc. The current mainstream production processes of linear α-olefins in China mainly include Fischer-Tropsch synthesis, ethylene selective polymerization and ethylene non-selective polymerization. The raw materials of Fischer-Tropsch synthesis come from synthesis gas, the products are complex, and the separation energy consumption is high; the raw materials of ethylene selective polymerization and non-selective polymerization are both ethylene, and the traditional non-selective polymerization products are linear α-olefins with a wide carbon number distribution, and there are many separation steps; while the ethylene highly selective polymerization method is to produce linear α-olefins with a specific carbon number, which was first reported by Sasol. The ethylene selective polymerization method has the advantages of high atomic utilization, good economy, high product selectivity and purity, and is the current mainstream process route.

[0004] With the successive implementation of domestic ethylene non-selective oligomerization and ethylene trimerization industrial units, the price and demand of 1-hexene in China have gradually fallen, but the price and market demand of 1-octene are still high. Currently, only Maoming Petrochemical has a 1-octene production capacity of only 8,000 tons / year, which mainly relies on imports. With the localization of POE and POP and the growth of the PAO market, the demand for 1-octene will be huge in the future.

[0005] China's patent application CN111715296A discloses an ethylene tetramerization catalytic system, preparation method and application thereof. The catalytic activity of the catalyst in a 500mL reactor reaches 896kg / gCr·h, of which 1-hexene selectivity is 20.32%, 1-octene selectivity is 65.43%, and the polymer mass fraction is 0.13%. In addition, it contains a large amount of by-products methylcyclopentane (4.86%) and methylenecyclopentane (5.12%). China's patent application CN115028508A discloses an ethylene tetramerization process with reduced PE production. A small-scale ethylene tetramerization experiment in a 300mL reactor found that the activity of the catalyst reached 830kg / gCr·h, of which 1-hexene selectivity is 19.0%, 1-octene selectivity is 67.3%, and the proportion of polymer PE is 0.3%. In addition, the by-products methylcyclopentane and methylenecyclopentane are 1.8% and 1.9%, respectively. Chinese patent application CN 104511311A discloses a highly selective ethylene trimerization and tetramerization catalyst system and its use method. The catalyst evaluation in a 300mL high-pressure reactor obtained an optimal catalyst activity of 824.5kg / gCr·h, and the common selectivity of 1-hexene and 1-octene was 91.3%. Chinese patent application CN117088747A discloses an ethylene oligomerization process, which produces linear α-olefins by alternately performing ethylene tetramerization and ethylene dimerization reactions in a 1L reactor, eliminating or reducing the impact of by-product polymers on the process, and making the ethylene oligomerization process run stably for a long period of time. The ethylene tetramerization catalyst activity reaches 1500kg / gCr·h, with a 1-hexene selectivity of 18.9%, a 1-octene selectivity of 68.7%, and a polymer selectivity of 0.3%.

[0006] High polymer content is the biggest problem in the industrialization of ethylene selective polymerization production technology, which seriously hinders the stability of the production unit. The second biggest problem is the high cost of the co-catalyst. How to reduce the cost of the co-catalyst while maintaining the catalyst activity and product selectivity, and how to reduce or even eliminate the polymer content as much as possible is worth further exploration. Summary of the invention

[0007] The object of the present invention is to overcome the deficiencies of the prior art and provide a method for preparing linear α-olefins by highly selective oligomerization of ethylene.

[0008] The present invention discloses a method for preparing linear α-olefins by high-selective polymerization of ethylene, which adopts the following technical scheme:

[0009] A method for preparing linear α-olefins by highly selective oligomerization of ethylene, wherein the method comprises the following steps: at a certain reaction temperature and reaction pressure, ethylene is selectively oligomerized in a system comprising a main catalyst, a composite alkyl aluminum co-catalyst, an inhibitor and an organic solvent to produce linear α-olefins.

[0010] Preferably, the inhibitor is one or more of methanol, ethanol, isopropanol and tert-butanol.

[0011] Preferably, the concentration of the inhibitor relative to the organic solvent is 10 to 500 ppm, preferably 50 to 200 ppm.

[0012] Preferably, the reaction temperature is controlled at 30-80° C., and the reaction pressure is controlled at 3.0-6.0 MPa.

[0013] Preferably, the composite alkyl aluminum co-catalyst comprises a first auxiliary agent, and the first auxiliary agent is selected from one or more of trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, trihexylaluminum, and trioctylaluminum.

[0014] Preferably, the composite alkyl aluminum cocatalyst includes a second auxiliary agent, the second auxiliary agent is selected from one or more of methylaluminoxane (MAO), modified methylaluminoxane (MMAO) and isobutylaluminoxane, and the molar ratio of the first auxiliary agent to the second auxiliary agent is 0.5-20.

[0015] Preferably, the main catalyst is a metal salt complex formed by a metal salt and a ligand, the metal salt complex is selected from one or more of tetrahydrofuran chromium trichloride, chromium acetylacetonate, chromium 2-ethylhexanoate, tricarbonyl chromium and hexacarbonyl chromium, and the ligand is selected from one or more of N,N-bis(diphenylphosphino)-1,2-dimethylpropylamine (1,2-DMP-PNP), N,N-bis(diphenylphosphino)-tert-butylamine (tBu-PNP), and N,N-bis(diphenylphosphino)-isopropylamine (iPr-PNP).

[0016] Preferably, the molar ratio of the ligand to the metal salt in the main catalyst is 2.

[0017] Preferably, the organic solvent is one or more of benzene, toluene, ethylbenzene, xylene, 1-hexene, hexane, cyclohexane, methylcyclohexane, 1-octene, and n-heptane, preferably 1-octene and 1-hexene.

[0018] Preferably, the molar ratio of the composite alkyl aluminum co-catalyst to the main catalyst is 10-2000, preferably 100-800.

[0019] Preferably, the molar concentration of the main catalyst relative to the organic solvent is 1 to 50 umol / L, preferably 5 to 20 umol / L.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects:

[0021] (1) The catalytic reaction system of the present invention reduces the generation of by-product polymers while maintaining the polymerization activity, and the polymer component content is as low as 0.01% (wt.).

[0022] (2) In the present invention, the operating cost is reduced while maintaining high catalytic activity. The content of 1-octene and 1-hexene in the prepared α-olefin can reach up to 91.2%, and the catalyst reaction activity is not less than 1000 kg / (gCr·h). DETAILED DESCRIPTION

[0023] The following embodiments further illustrate the technical solutions provided by the present invention, but the present invention is not limited to the listed embodiments, and also includes any other known changes within the scope of the present invention.

[0024] The collected ethylene selective oligomerization liquid phase product is analyzed by gas chromatography, and the solid by-product is separated by suction filtration, dried and then weighed.

[0025] Example 1

[0026] Heat a 5L high-pressure stainless steel reactor to 90°C, evacuate with a vacuum pump for no less than 2h, and replace with 1MPa nitrogen intermittently for no less than 10 times during this period to ensure that there is no water and no oxygen in the reactor. When the temperature is cooled to 30°C, add 1.5L of dehydrated and deoxygenated organic solvent (1-octene: 1-hexene = 2: 1 (wt.)) (containing 100ppm of tert-butyl alcohol), 1mL of modified methylaluminoxane (MMAO-3A) and 2mL of triisobutylaluminum, 20mL (1-octene: 1-hexene = 2: 1 (wt.)) pre-configured main catalyst solution with a concentration of 0.8mmol / L to the reactor. Slowly introduce ethylene to 5.0MPa, and maintain the ethylene pressure at 5.0MPa through the cylinder pressure reducing valve, and react for 60min at a temperature of 40°C and stirring at 500rpm. After the reaction was completed, the ethylene feed valve was closed, the temperature was lowered to below 30°C, the pressure in the reactor was lowered to normal pressure, and the product was transferred to a quenching tank containing excess isopropanol to terminate the reaction and weigh it. The quenched reaction liquid was filtered and the supernatant was taken for chromatographic analysis. The solid product obtained by filtration was dried in a vacuum oven at 85°C for 10 hours and weighed. The results are shown in Table 1.

[0027] Example 2

[0028] The steps of Example 1 were followed, except that 1.5 L of a dehydrated and deoxygenated mixed solvent (1-octene: 1-hexene = 1:1 (wt.)) (containing 100 ppm of tert-butanol) and 20 mL of a pre-prepared main catalyst solution (1-octene: 1-hexene = 1:1 (wt.)) with a concentration of 0.8 mmol / L were added to the reactor.

[0029] Example 3

[0030] The steps of Example 1 were followed, except that 1.5 L of a dehydrated and deoxygenated mixed solvent (1-octene: 1-hexene = 1:2 (wt.)) (containing 100 ppm of tert-butanol) and 20 mL of a pre-prepared main catalyst solution (1-octene: 1-hexene = 1:2 (wt.)) with a concentration of 0.8 mmol / L were added to the reactor.

[0031] Example 4

[0032] The steps of Example 1 were followed, except that 1.5 L of dehydrated and deoxygenated 1-octene (containing 100 ppm of tert-butyl alcohol) and 20 mL of a pre-prepared 0.8 mmol / L main catalyst solution (1-octene) were added to the reactor.

[0033] Example 5

[0034] The steps of Example 1 were followed, except that 1.5 L of dehydrated and deoxygenated 1-hexene (containing 100 ppm of tert-butanol) and 20 mL (1-hexene) of a pre-prepared main catalyst solution with a concentration of 0.8 mmol / L were added to the reactor.

[0035] Example 6

[0036] The steps of Example 1 were followed, except that 1.5 L of dehydrated and deoxygenated cyclohexane (containing 100 ppm of tert-butanol) and 20 mL (cyclohexane) of a pre-prepared main catalyst solution with a concentration of 0.8 mmol / L were added to the reactor.

[0037] Example 7

[0038] The steps of Example 1 were followed, except that 20 mL (1-octene: 1-hexene = 2:1 (wt.)) of pre-prepared main catalyst solution with a concentration of 0.8 mmol / L was increased to 1 mmol / L.

[0039] Example 8

[0040] The steps of Example 1 were followed, except that 20 mL (1-octene: 1-hexene = 2:1 (wt.)) of the pre-prepared main catalyst solution with a concentration of 0.8 mmol / L was reduced to 0.6 mmol / L.

[0041] Example 9

[0042] The steps of Example 1 were followed, except that 1.5 L of a dehydrated and deoxygenated mixed solvent (1-octene: 1-hexene = 2:1 (wt.)) (containing 50 ppm of tert-butanol) was added to the reactor.

[0043] Example 10

[0044] The steps of Example 1 were followed, except that 1.5 L of a dehydrated and deoxygenated mixed solvent (1-octene: 1-hexene = 2:1 (wt.)) (containing 150 ppm of tert-butanol) was added to the reactor.

[0045] Comparative Example 1

[0046] The steps of Example 1 were followed, except that 1.5 L of a dehydrated and deoxygenated mixed solvent (1-octene: 1-hexene = 2:1 (wt.)) was added to the reactor (without adding the inhibitor tert-butyl alcohol).

[0047] Comparative Example 2

[0048] The steps of Example 1 were followed, except that 2 mL of triisobutylaluminum was adjusted to 5 mL, and 1 mL of modified methylaluminoxane (MMAO-3A) was not added.

[0049] Comparative Example 3

[0050] The steps of Example 1 were followed, except that 1.5 L of dehydrated and deoxygenated cyclohexane (containing 100 ppm of phenol) was added to the reactor, and 20 mL of cyclohexane was pre-prepared with a concentration of 0.8 mmol / L of the main catalyst solution.

[0051] Comparative Example 4

[0052] The steps of Example 1 were followed, except that 1.5 L of dehydrated and deoxygenated cyclohexane (containing 100 ppm of 4-tert-butylphenol) was added to the reactor, and 20 mL of cyclohexane was pre-configured with a concentration of 0.8 mmol / L of the main catalyst solution.

[0053] Comparative Example 5

[0054] The steps of Example 1 were followed, except that 1.5 L of dehydrated and deoxygenated cyclohexane (containing 100 ppm of 4-isopropylphenol) was added to the reactor, and 20 mL of cyclohexane was pre-configured with a concentration of 0.8 mmol / L of the main catalyst solution.

[0055] Comparative Example 6

[0056] The steps of Example 1 were followed, except that 1.5 L of dehydrated and deoxygenated cyclohexane (containing 100 ppm of 2-naphthol) and 20 mL of cyclohexane were pre-prepared with a main catalyst solution having a concentration of 0.8 mmol / L into the reactor.

[0057] Table 1 Results of ethylene selective oligomerization

[0058]

[0059]

[0060] In the ethylene polymerization reaction, the composite alkyl aluminum co-catalyst has the function of removing impurities from the reaction system and forming active centers. Some alkyl aluminum co-catalysts used in the prior art are expensive and not conducive to practical application. The composite co-catalyst system developed in this reaction system reduces the cost of the co-catalyst while maintaining the catalyst reaction activity and product selectivity. The reaction activity is as high as 2120kg / gCr·h, and the content of 1-octene and 1-hexene in the prepared α-olefin can reach up to 91.2%, and the content of polymer by-products is as low as 0.01wt%.

[0061] In addition, the method reduces the content of by-product polymers by adding inhibitors. Comparison of the test data of Example 1 and Comparative Example 1 shows that by adding inhibitors of methanol, ethanol, isopropanol or tert-butyl alcohol, not only the content of by-product polymers is greatly reduced, but also the catalyst reactivity is improved, so that the efficiency of the polymerization reaction is improved, and energy consumption and production costs are reduced. The use of other inhibitors such as Comparative Examples 3-6, although the content of by-product polymers is reduced to a certain extent, has a negative impact on the reactivity of the catalyst system used in this reaction.

[0062] From the comparison of the detection data of Examples 1-6, it can be seen that using a certain ratio of 1-octene and 1-hexene mixture as the reaction solvent not only reduces the subsequent solvent removal process and improves production efficiency, but also further reduces the polymer ratio.

[0063] From the comparison of the detection data of Example 1 and Examples 7-10, it can be seen that the effects of the concentration of the co-catalyst solution and the concentration of the inhibitor in the reaction system on the catalyst reaction activity, product selectivity and by-product content show a curve change. This method explores that the optimal concentration range of the main catalyst solution is 5-20umol / L, and the optimal concentration range of the inhibitor is 50-200ppm.

[0064] The technical solution provided by the present invention is introduced in detail above. Specific examples are used in this article to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for preparing linear α-olefins by highly selective oligomerization of ethylene, characterized in that: The method comprises the following steps: at a certain reaction temperature and reaction pressure, ethylene is selectively polymerized in a system comprising a main catalyst, a composite alkyl aluminum co-catalyst, an inhibitor and an organic solvent to generate linear α-olefins; The inhibitor is tert-butyl alcohol; The concentration of the inhibitor relative to the organic solvent is 10 to 500 ppm; The main catalyst is a metal salt complex formed by a metal salt and a ligand, the metal salt is selected from tetrahydrofuran chromium trichloride, and the ligand is selected from N,N-bis(diphenylphosphino)-1,2-dimethylpropylamine; The composite alkyl aluminum co-catalyst comprises a first auxiliary agent, wherein the first auxiliary agent is selected from one or more of trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, trihexylaluminum, and trioctylaluminum; The composite alkyl aluminum co-catalyst includes a second auxiliary agent, the second auxiliary agent is selected from one or more of methylaluminoxane, modified methylaluminoxane and isobutylaluminoxane, and the molar ratio of the first auxiliary agent to the second auxiliary agent is 0.5 to 20; The organic solvent is a mixture of 1-octene and 1-hexene in a mass ratio of 2:

1.

2. The method for preparing linear α-olefins by highly selective oligomerization of ethylene as claimed in claim 1, characterized in that: The reaction temperature is controlled at 30-80° C., and the reaction pressure is controlled at 3.0-6.0 MPa.

3. The method for preparing linear α-olefins by highly selective oligomerization of ethylene as claimed in claim 1, characterized in that: The molar ratio of the composite alkyl aluminum co-catalyst to the main catalyst is 10 to 2000.

4. The method for preparing linear α-olefins by highly selective oligomerization of ethylene as claimed in claim 1, characterized in that: The molar concentration of the main catalyst relative to the organic solvent is 1 to 50 umol / L.

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