A catalyst system and preparation method for preparing 1-octene and 1-hexene by alternating continuous reaction of ethylene trimerization and tetramerization

Abstract

The invention provides a dual catalyst system and a preparation method for preparing 1-octene and 1-hexene by alternating continuous reaction of ethylene trimerization and tetramerization, wherein the catalyst preparation raw materials used in the tetramerization reaction include PNP ligands, Cr(III)-containing main catalysts and Al-containing co-catalysts; the catalyst preparation raw materials used in the trimerization reaction include N-containing ligands, Cr(III)-containing main catalysts, Al-containing co-catalysts and Cl-containing promoters. The dual catalytic reaction system is alternately used for ethylene trimerization and tetramerization, and can achieve high-temperature cleaning of reaction polymers without stopping the reaction, extending the continuous production cycle to three times that of the original process; and the product selectivity is high.

Description

Technical Field

[0001] The invention belongs to the technical field of continuous production of polyolefins, and in particular relates to a catalyst system and a method for preparing 1-octene and 1-hexene by alternating continuous reaction of ethylene trimerization and tetramerization. Background Art

[0002] Linear α-olefins are an important chemical raw material with huge demand. C4-C10 linear α-olefins are widely used in the preparation of low-density polyethylene, high-density polyethylene, high-end detergents, high-end lubricants, surfactants, POE and high-end straight-chain alcohols. Among them, 1-octene and 1-hexene are particularly important, accounting for more than 55% of the total α-olefin usage, and the amount is increasing year by year.

[0003] There are many methods for producing linear α-olefins. Traditional processes include coal chemical extraction, wax cracking, alkane dehydrogenation, alkane catalytic cracking, fatty alcohol dehydrogenation, olefin dimerization and disproportionation, etc. Some of these production methods have been eliminated due to high costs, low yields, wide product distribution, difficulty in separation, and complex processes. Ethylene oligomerization has become the world's most important production method due to its advantages of concentrated product distribution, good product quality, high degree of linearization, and high economic benefits.

[0004] The existing ethylene selective polymerization catalytic system is mainly based on the PNP-Cr-MAO catalytic system. The activity of this type of catalytic system can reach 600kg / g(Cr).h, and the products are mainly 1-hexene and 1-octene, which can meet the production needs. However, a high content of polymers is generated during the reaction process. During the production process, the polymer solids are easy to adhere to the wall, resulting in uneven mass and heat transfer in the reactor, frequent maintenance of stirring and filtering equipment, and extremely cumbersome operation, which seriously affects the continuous production efficiency.

[0005] In order to solve the problem of polymer removal in the ethylene polymerization method, domestic and foreign teams are also actively conducting research. One team uses a widely distributed iron-based catalytic system for production. The reaction temperature of this system can reach above 130°C. Most polymers are soluble in the reaction solvent at this temperature and flow freely with the reaction liquid, which can extend the continuous reaction time of the reactor. However, the products obtained by this process are widely distributed, the separation energy consumption is high, and the cost is high.

[0006] Another team uses the PNP-Cr-MAO catalytic system as the main production system, and after continuous operation for a period of time, uses a high-boiling point solvent for flushing, and circulates for a period of time without dismantling the reactor, which can also greatly reduce the phenomenon of polymer wall adhesion and equipment pipeline clogging. However, this method needs to be carried out when the reaction is stopped, which greatly affects production efficiency. Summary of the invention

[0007] In view of this, the object of the present invention is to provide a catalyst system and method for preparing 1-octene and 1-hexene by alternating continuous reactions of ethylene trimerization and tetramerization, wherein the catalyst system can achieve high temperature cleaning of the reaction polymer without stopping the reaction, thereby extending the continuous production cycle.

[0008] The present invention provides a catalyst system for producing 1-octene and 1-hexene by alternating continuous reaction of ethylene trimerization and tetramerization. The catalyst preparation raw materials used in the tetramerization reaction include PNP ligands, a main catalyst containing Cr (III) and an Al-containing co-catalyst; the catalyst preparation raw materials used in the trimerization reaction include N-containing ligands, a main catalyst containing Cr (III), an Al-containing co-catalyst and a Cl-containing promoter.

[0009] The PNP ligand has a structure of Formula I:

[0010]

[0011] The R1, R2, R3, R4 and R5 are independently selected from C1-C10 alkyl, C6-C20 aryl and their derivatives;

[0012] The N-containing ligand is a nitrogen-containing five-membered ring, an alkyl-substituted nitrogen-containing five-membered ring, a nitrogen-containing six-membered ring, or an alkyl-substituted nitrogen-containing six-membered ring.

[0013] In the present invention, R1, R2, R3, R4 and R5 are independently selected from methyl, ethyl, n-propyl, isopropyl, tert-butyl, cyclopentyl, cyclohexyl, phenyl or substituted phenyl.

[0014] In the present invention, the parent ring of the N-containing ligand is selected from pyrazole, pyrrole, pyridine or pyrimidine ring;

[0015] The substituent of the N-containing ligand is selected from one or more of methyl, ethyl, n-propyl, isopropyl and tert-butyl.

[0016] In the present invention, the Al-containing co-catalyst is selected from one or more of MAO, MMAO and modified MMAO;

[0017] The Cr(III)-containing main catalyst is selected from one or more of chromium acetylacetonate, chromium isooctanoate and tritetrahydrofuran chromium trichloride;

[0018] The Cl-containing accelerator is selected from one or more of ethyl chloride, ethylene dichloride, chloroform, carbon tetrachloride, tetrachloroethane, hexachloroethane, hexachlorocyclohexane and chlorobenzene.

[0019] In the present invention, the molar ratio of the Cr(III)-containing main catalyst to the Al-containing co-catalyst is 1:200-1000;

[0020] The molar ratio of the Cr(III)-containing main catalyst, the Al-containing co-catalyst and the Cl-containing promoter is 1:3-10:4-20.

[0021] The present invention provides a method for producing 1-octene and 1-hexene by alternating continuous reactions of ethylene trimerization and tetramerization using the catalytic system described in the above technical solution, comprising the following steps:

[0022] In the presence of a PNP ligand, a Cr(III)-containing main catalyst and an Al-containing co-catalyst, ethylene is subjected to a tetramerization reaction in a solvent to obtain 1-octene and 1-hexene; then the catalyst system is switched to a N-containing ligand, a Cr(III)-containing main catalyst, an Al-containing co-catalyst and a Cl-containing promoter to carry out a trimerization reaction to obtain 1-hexene; and this cycle is repeated.

[0023] During the tetramerization reaction, the ethylene pressure is 4.0-7.0 MPa, the reaction temperature is 30-100°C, and the reaction time is 3-30 days;

[0024] During the trimerization reaction, the ethylene pressure is 4.0-7.0 MPa, the reaction temperature is 80-200°C, and the reaction time is 3-15 days.

[0025] In the present invention, the solvent is selected from one or more of methylcyclohexane, n-heptane, cyclohexane and toluene;

[0026] During the tetramerization reaction, the concentration of the Cr(III) main catalyst is 2 to 20 μmol / L;

[0027] During the trimerization reaction, the concentration of the Cr(III) main catalyst is 10 to 100 μmol / L.

[0028] The present invention adopts a dual catalytic reaction system, which is alternately used for ethylene trimerization and tetramerization, and can achieve high-temperature cleaning of reaction polymers without stopping the reaction, extending the continuous production cycle to three times that of the original process; and the product selectivity is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The process flow chart of the catalyst system used in the embodiment of the present invention for the alternating continuous reaction of ethylene trimerization and tetramerization to prepare 1-octene and 1-hexene. DETAILED DESCRIPTION

[0030] The invention provides a catalyst system for preparing 1-octene and 1-hexene through alternating continuous reaction of ethylene trimerization and tetramerization. The raw materials for preparing the catalyst used in the tetramerization reaction include PNP ligands, a main catalyst containing Cr(III) and a co-catalyst containing Al; the raw materials for preparing the catalyst used in the trimerization reaction include N-containing ligands, a main catalyst containing Cr(III), a co-catalyst containing Al and a promoter containing Cl.

[0031] The dual catalytic system alternating reaction adopted in the present invention utilizes the difference in reaction temperature of the two different catalytic systems to treat the polymer generated by the reaction, and at the same time utilizes the phenomenon that the two catalytic systems have little mutual influence, so as to achieve non-stop reaction while reducing the residual polymer in the reactor, thereby extending the working time of the reactor, greatly simplifying the frequent maintenance and overhaul of equipment in industrialization, and improving production efficiency.

[0032] In the present invention, the catalyst preparation raw material used in the tetramerization reaction includes a PNP ligand; the PNP ligand has a structure of formula I:

[0033]

[0034] The R1, R2, R3, R4 and R5 are independently selected from C1-C10 alkyl groups, C6-C20 aryl groups and derivatives thereof.

[0035] In the present invention, R1, R2, R3, R4 and R5 are independently selected from methyl, ethyl, n-propyl, isopropyl, tert-butyl, cyclopentyl, cyclohexyl, phenyl or substituted phenyl.

[0036] In the present invention, the PNP ligand is specifically selected from (Ph2P)2N(i-C3H7), (Ph2P)2N(i-C5H9)

[0037] The catalyst preparation raw materials used in the trimerization reaction include N-containing ligands, Cr(III)-containing main catalysts, Al-containing cocatalysts and Cl-containing promoters. In the present invention, the N-containing ligands are nitrogen-containing five-membered rings, alkyl-substituted nitrogen-containing five-membered rings, nitrogen-containing six-membered rings or alkyl-substituted nitrogen-containing six-membered rings; the parent ring of the N-containing ligands is selected from pyrazole, pyrrole, pyridine or pyrimidine rings; the substituents of the N-containing ligands are selected from one or more of methyl, ethyl, n-propyl, isopropyl and tert-butyl.

[0038] In the present invention, the Cr(III)-containing main catalyst is selected from one or more of chromium acetylacetonate, chromium isooctanoate and chromium trichloride in tetrahydrofuran; the Al-containing co-catalyst is selected from one or more of MAO, MMAO and modified MMAO.

[0039] In the present invention, in the raw materials for preparing the catalyst used in the trimerization reaction, the molar ratio of the main catalyst containing Cr(III) to the co-catalyst containing Al is 1:30-500, preferably 1:50-200.

[0040] In the raw material for preparing the catalyst used in the tetramerization reaction, the molar ratio of the main catalyst containing Cr(III) to the co-catalyst containing Al is 1:200-1000;

[0041] The molar ratio of the Cr(III)-containing main catalyst, the Al-containing co-catalyst and the Cl-containing promoter is 1:3-10:4-20, preferably 1:5-8:5-10.

[0042] In the present invention, the catalyst system for ethylene tetramerization is prepared according to the following method:

[0043] Under nitrogen protection, the PNP ligand and the Cr(III)-containing main catalyst are dissolved in a solvent, reacted, and then the Al-containing co-catalyst is added to obtain a catalyst system for ethylene tetramerization.

[0044] Alternatively, the PNP ligand and the Cr(III)-containing main catalyst are dissolved in a solvent, and the product after the reaction and the Al-containing co-catalyst are fed separately for use.

[0045] The present invention provides a method for preparing 1-octene and 1-hexene by using the catalytic system described in the above technical solution through alternating continuous reactions of ethylene trimerization and tetramerization, comprising the following steps:

[0046] In the presence of a PNP ligand, a Cr(III)-containing main catalyst and an Al-containing co-catalyst, ethylene is reacted in a solvent to obtain 1-octene and 1-hexene; then the catalyst system is switched to: a N-containing ligand, a Cr(III)-containing main catalyst, an Al-containing co-catalyst and a Cl-containing promoter, and the reaction is performed to obtain 1-hexene; and this cycle is repeated.

[0047] In the present invention, the catalyst system for ethylene trimerization is prepared according to the following method:

[0048] The N-containing ligand, the Cr(III)-containing main catalyst and the Cl-containing promoter are dissolved in a solvent according to a certain molar ratio, and then the Al-containing co-catalyst is added to obtain a catalyst system for ethylene trimerization reaction.

[0049] Alternatively, the N-containing ligand, the Cr(III)-containing main catalyst and the Cl-containing promoter are dissolved in a solvent, and the product after the reaction and the Al-containing co-catalyst are fed separately for use.

[0050] The solvent used for dissolving is selected from one or more of toluene, xylene, cyclohexane, methylcyclohexane, n-heptane, and n-hexane, preferably toluene or n-heptane. The solvent used for trimerization or tetramerization of ethylene is selected from one or more of toluene, xylene, cyclohexane, methylcyclohexane, n-heptane, and n-hexane, preferably toluene or n-heptane. During tetramerization, the concentration of the Cr(III) main catalyst is 2 to 20 μmol / L, preferably 3 to 10 μmol / L; during trimerization, the concentration of the Cr(III) main catalyst is 10 to 100 μmol / L, preferably 15 to 50 μmol / L.

[0051] The catalyst system used for ethylene tetramerization or trimerization needs to be diluted before use; the solvent used for dilution is selected from one or more of methylcyclohexane, n-heptane, cyclohexane and toluene; preferably cyclohexane or n-heptane.

[0052] In a specific embodiment, Figure 1 As shown, it includes mixed feeding of trimerization catalytic system, mixed feeding of tetramerization catalytic system, flash filtration, pre-separation, solvent recovery, and product distillation; specifically, firstly, the tetramerization catalytic system is used for feeding, the ethylene pressure is 4.0-7.0 MPa, and the Cr / Al are fed into the reactor respectively according to a certain ratio, the initial temperature of the reactor is maintained at 50°C, and the temperature during the reaction is maintained at 50-80°C; the residence time of the catalyst in the reactor is maintained at 0.5-2h; the reaction is carried out continuously, and whenever the liquid level of the reactor reaches 60%, more than 60% of the reaction is The liquid enters the flash filter tower behind, the gas phase ethylene can be reused, the reaction liquid enters the separation tower, the separated solvent can be reused, and then the remaining components enter the purification distillation tower, 1-octene and 1-hexene can be separated; after several days of continuous reaction production under this condition, switch the feed and use the trimerization catalytic system for feeding; at the beginning of trimerization feeding, the reactor temperature should be quickly raised to above 100°C, and the main catalyst and auxiliary catalyst are still fed separately to ensure that the reaction temperature is controlled at 110-150°C, and the subsequent flash filtration, pre-separation, solvent recovery, product distillation and other treatment processes remain unchanged. After several days of reaction production under this condition, feed is then fed according to the reaction conditions of the tetramerization catalytic system, and the reaction is cyclically reacted several times.

[0053] In the present invention, during the tetramerization reaction, the ethylene pressure is 4.0-7.0 MPa, the reaction temperature is 30-100°C, and the reaction time is 3-30 days, preferably 5-15 days; the reaction time is determined according to the specific reaction conditions, and should be switched immediately when uneven mass and heat transfer occurs.

[0054] During trimerization, the ethylene pressure is 4.0-7.0 MPa, the reaction temperature is 80-200°C, and the reaction time is 3-15 days, preferably 5-10 days. The reaction switching time should be determined according to the mass transfer and heat transfer conditions. The reaction should be switched to tetramerization immediately on the second day after the mass transfer and heat transfer are uniform and controllable.

[0055] In the present invention, when the tetramerization reaction is carried out, if the temperature control time exceeds 30 minutes, it indicates that the polymer wall adhesion phenomenon is serious, and the feeding trimerization catalytic system is switched. After operation, if the temperature control time is within 30 minutes, it indicates that the heat conduction is in place in time, and the tetramerization reaction system can be switched.

[0056] Compared with a single tetramerization reaction system, the alternating continuous reaction method of the ethylene trimerization and tetramerization catalytic system provided by the present invention can prolong the tetramerization reaction time.

[0057] Furthermore, the tetramerization catalytic system has little effect on the trimerization catalytic reaction, and the reaction can proceed immediately, but the trimerization reaction has a certain effect on the tetramerization reaction system. Therefore, when switching from the trimerization to the tetramerization reaction system, attention should be paid to the progress of the reaction. This phenomenon can be overcome by increasing the feed amount. Usually, the optimal activity of the tetramerization can be achieved after 2 hours of feeding.

[0058] In the present invention, the C8 content of the product of the tetramerization catalytic system accounts for 55-75%, the C6 content accounts for 30-10%, and the activity is 600-3000 kg / g(Cr).h;

[0059] The product of the trimerization catalytic system has a C6 content of 90-97% and an activity of 100-400 kg / g(Cr).h.

[0060] Figure 1 There are no special requirements for flash filtration, pre-separation, solvent recovery and product distillation and purification compared with the current industrial equipment; further, the filtration equipment should adopt two sets, one for backup and one for use, so that the reaction can be kept uninterrupted when cleaning the filtrate.

[0061] To further illustrate the present invention, a catalyst system and preparation method for producing 1-octene and 1-hexene by alternating continuous reaction of ethylene trimerization and tetramerization provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0062] Example 1

[0063] Cyclohexane is selected as the reaction solvent, n-heptane is selected as the catalyst preparation solvent, and the tetramerization catalytic system selects (Ph2P)2N(i-C3H7) as the ligand, chromium acetylacetonate as the chromium source, and methylaluminoxane as the co-catalyst. The trimerization catalytic system selects the Philips catalytic system, dimethylpyrrole as the ligand, chromium isooctanoate as the chromium source, hexachloroethane as the auxiliary agent, and triethylaluminum as the co-catalyst. The molar ratio of each material in the tetramerization system PNP / Cr / Al is 1.1:1:600, and the molar ratio of each material in the trimerization system Cr / N / Cl / Al is 1:4:5:80. The trimerization and tetramerization catalytic systems prepare the main catalyst according to the above ratio and set it aside.

[0064] Raise the reactor temperature to 50°C, ethylene pressure to 5.0Mpa, start feeding the tetramerization catalytic system, and ensure that the concentration of the main catalyst in the reactor is 5μmol / L. When the main catalyst, auxiliary catalyst and ethylene are mixed in the reactor, the reaction occurs immediately. Adjust the feed rate so that the residence time of the catalyst in the reactor is stable at about 1h, and the reaction temperature is controlled at 50-80°C. Whenever the reactor liquid level is higher than 60%, it will flow into the flash filter tower, according to Figure 1 Carry out separation and purification.

[0065] After 172 hours of continuous operation, it was found that it took 30 minutes or even longer to control the temperature from 50°C to 60°C, indicating that the polymer wall hanging phenomenon was serious. At this time, the feed trimerization catalytic system was switched immediately. After 75 hours of operation, it was found that the temperature control time from 120°C to 130°C was less than 30 minutes, indicating that heat conduction was in place in time. At this time, it can be switched to the tetramerization reaction system, and the reaction can be operated alternately and continuously according to the above method. When the reaction ran for 2284 hours, the temperature control was seriously delayed, and the trimerization reaction could still be carried out, but there was no improvement after 72 hours of operation. At this time, the feed should be stopped and the equipment should be maintained.

[0066] The products collected during the reaction were subjected to comprehensive calculation, test and analysis. The catalytic activity of ethylene tetramerization was about 1342 kg / g(Cr).h, the selectivity of 1-hexene was 13.172%, the selectivity of 1-octene was 69.525%, and the PE was 0.31%; the catalytic activity of ethylene trimerization was 462 kg / g(Cr).h, the selectivity of 1-hexene was 94.285%, and the selectivity of C 10 Olefin is 0.322% and PE is 0.06%.

[0067] Example 2

[0068] Select n-heptane as the reaction solvent, and other conditions are the same as in Example 1.

[0069] The total reaction time can reach 2324 hours. During the reaction, the collected products are subjected to comprehensive calculation, test and analysis. The catalytic activity of ethylene tetramerization is about 1450kg / g(Cr).h, the selectivity of 1-hexene is 12.032%, the selectivity of 1-octene is 69.884%, and the PE is 0.23%; the catalytic activity of ethylene trimerization is 528kg / g(Cr).h, the selectivity of 1-hexene is 95.114%, and the selectivity of C 10 Olefin is 0.319% and PE is 0.05%.

[0070] Example 3

[0071] The tetramerization catalytic ligand selected was (Ph2P)2N(i-C5H9), and the other conditions were the same as those in Example 1.

[0072] The total reaction time can reach 2081 hours. During the reaction, the collected products are subjected to comprehensive calculation, test and analysis. The catalytic activity of ethylene tetramerization is about 1621kg / g(Cr).h, the selectivity of 1-hexene is 15.667%, the selectivity of 1-octene is 65.324%, and the PE is 0.33%; the catalytic activity of ethylene trimerization is 457kg / g(Cr).h, the selectivity of 1-hexene is 94.541%, and the selectivity of C 10 Olefin is 0.254% and PE is 0.05%.

[0073] Example 4

[0074] The trimerization catalytic ligand selected was tripyrazole methane, and other conditions were the same as those in Example 1.

[0075] The total reaction time can reach 810 hours. The catalytic activity of ethylene tetramerization is about 1326kg / g(Cr).h, the selectivity of 1-hexene is 15.11%, the selectivity of 1-octene is 69.107%, and the PE is 0.31%; the catalytic activity of ethylene trimerization is 262kg / g(Cr).h, the selectivity of 1-hexene is 95.507%, and the selectivity of C 10 Olefin is 0.288% and PE is 0.05%.

[0076] Example 5

[0077] Tetrachloroethane was selected as the trimerization catalyst promoter, and other conditions were the same as those in Example 1.

[0078] The total reaction time can reach 2207 hours. The catalytic activity of ethylene tetramerization is about 1380kg / g(Cr).h, the selectivity of 1-hexene is 15.677%, the selectivity of 1-octene is 69.121%, and the PE is 0.31%; the catalytic activity of ethylene trimerization is 409kg / g(Cr).h, the selectivity of 1-hexene is 94.631%, and the selectivity of C 10 Olefin is 0.281% and PE is 0.06%.

[0079] Comparative Example 1

[0080] Only the tetramerization catalytic system was used for the reaction without alternating switching, and the other process conditions were the same as those in Example 1. The reaction operation time was 208 hours, at which time the discharge pipeline was obviously blocked, the temperature control in the reactor failed, and the pressure increased. After disassembling the pipeline and the reactor, it was found that a lot of polymers were deposited in the reactor, blocking the discharge valve and pipeline. The cleaning of the device and pipeline took about a week. The catalytic activity and selectivity were parallel to the data in Example 1. The catalytic activity of ethylene tetramerization was about 1420kg / g(Cr).h, the selectivity of 1-hexene was 16.532%, the selectivity of 1-octene was 68.221%, and PE was 0.32%.

[0081] Comparative Example 2

[0082] Only the trimerization catalytic system was used for the reaction without alternating switching. The other process conditions were the same as those in Example 1. The reaction operation time was about 4508 hours. At this time, the discharge pipe was obviously blocked, the temperature control in the reactor failed, the pressure increased, and the feeding was stopped for maintenance. The trimerization catalytic system did not produce 1-octene. The catalytic activity and selectivity were in line with the data in Example 1. The catalytic activity of ethylene trimerization was 421 kg / g(Cr).h, the selectivity of 1-hexene was 94.668%, and C 10 Olefin is 0.292% and PE is 0.07%.

[0083] As can be seen from the above examples, the present invention adopts a dual catalytic reaction system, which is alternately used for ethylene trimerization and tetramerization, and can achieve high-temperature cleaning of the reaction polymer without stopping the reaction, extending the continuous production cycle to three times that of the original process; and the product selectivity is high. In addition, the method provided by the present invention is simple and feasible, and the flash filtration, pre-separation, solvent recovery and product distillation purification sections of the post-treatment part can be put into operation without special modification, and industrial technical transformation does not require excessive capital investment.

[0084] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing 1-octene and 1-hexene by alternating continuous reaction of ethylene trimerization and tetramerization using a dual catalytic system, comprising the following steps: In the presence of a PNP ligand, a Cr(III)-containing main catalyst and an Al-containing co-catalyst, ethylene is dissolved in a solvent for tetramerization to obtain 1-octene and 1-hexene; then the catalyst system is switched to a N-containing ligand, a Cr(III)-containing main catalyst, an Al-containing co-catalyst and a Cl-containing promoter to perform trimerization to obtain 1-hexene; and this cycle is repeated; The solvent is selected from one or more of methylcyclohexane, n-heptane, cyclohexane and toluene; the PNP ligand is selected from (Ph2P)2N(i-C3H7) or (Ph2P)2N(i-C5H9); The N-containing ligand is selected from dimethylpyrrole or tripyrazole methane; The Al-containing co-catalyst is selected from one or more of MAO, MMAO and modified MMAO; The Cr(III)-containing main catalyst is selected from chromium acetylacetonate; during tetramerization, the concentration of the Cr(III)-containing main catalyst is 2-20 μmol / L; during trimerization, the concentration of the Cr(III)-containing main catalyst is 10-100 μmol / L; the Cl-containing promoter is selected from one or more of ethyl chloride, ethylene dichloride, chloroform, hexachloroethane, hexachlorocyclohexane and chlorobenzene; The molar ratio of the Cr(III) main catalyst to the Al co-catalyst in the trimerization reaction is 1:50~200; The molar ratio of the Cr(III) main catalyst to the Al co-catalyst in the tetramerization reaction is 1:200-1000; During tetramerization, the ethylene pressure is 4.0~7.0MPa and the reaction temperature is 50℃~60℃; During trimerization, the ethylene pressure is 4.0~7.0MPa and the reaction temperature is 120℃~130℃; During the tetramerization reaction, if the time required to control the reaction temperature between 50℃ and 60℃ exceeds 30 minutes, it indicates that the polymer wall adhesion phenomenon is serious, and the feed trimerization catalytic system should be switched. After running, if the time required to control the reaction temperature between 120℃ and 130℃ is within 30 minutes, it indicates that the heat conduction is in place in time and the system should be switched to the tetramerization reaction system.

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