An ethylene trimerization catalyst composition and its application

Abstract

The invention discloses an ethylene trimerization catalyst composition and application thereof. The ethylene trimerization catalyst composition consists of a chromium compound, a pyridine compound, an alkyl aluminum auxiliary agent and an electron donor. The invention uses a pyridine compound as a ligand in an ethylene trimerization catalyst system for the first time, that is, the chromium metal salt, the pyridine compound, the alkyl aluminum and the organic chloride together form the ethylene trimerization catalyst composition. The 1-hexene selectivity in the reaction product is high. Compared with the disclosed catalyst (pyrrole and its derivatives as ligands), the byproduct polyethylene content is extremely small and the catalyst has higher activity. In industrialization, the ethylene trimerization reaction can be carried out by in-situ polymerization without prepolymerization.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and in particular relates to an ethylene trimerization catalyst composition and application thereof. Background Art

[0002] Linear low-density polyethylene (LLDPE) copolymerized with linear α-olefins and ethylene has excellent tear resistance and impact strength, and its service life is greatly improved. Therefore, this type of resin is also widely used in packaging films, greenhouse films and ground films. In terms of comonomers, the performance of LLDPE copolymerized with 1-hexene or 1-octene and ethylene is far better than that of LLDPE copolymerized with 1-butene and ethylene. Therefore, researchers have conducted extensive research on the preparation of long-chain linear α-olefins. Among the many technologies for preparing linear α-olefins, chromium-based catalysts are the most widely used. Phillips (US5856257) is the most prominent. The company's four-component catalytic system consisting of chromium salts, nitrogen-containing ligands, and two co-catalysts shows excellent performance in the selective polymerization of ethylene, among which the selectivity of 1-hexene can reach more than 90%. The company has successfully achieved industrialization based on this catalyst. Subsequently, major companies conducted extensive research on ethylene selective polymerization and achieved good results. CNPC and Sinopec are the most prominent in China. CNPC's independently developed catalytic system has built 5kt / a and 2wt / a 1-hexene production units in Daqing Petrochemical and Dushanzi Petrochemical respectively, and Sinopec's independently developed catalytic system has built a 5wt / a 1-hexene production unit in Yanshan Petrochemical.

[0003] In 1999, Phillips applied for patent US5856257, which used chromium catalyst to catalyze the selective trimerization of ethylene to produce 1-hexene with a selectivity of up to 95%. This device process is currently the most advanced 1-hexene process technology in the world. Sinopec disclosed a method for synthesizing non-toxic or low-toxic sulfur-nitrogen heteroatom ligands in patent CN103787935B. This method uses R1SR2X to react with ammonia under alkaline conditions to obtain (R1SR2)2NH. The chromium trichloride (bis(2-phenylthio-ethyl)-amine) prepared by this ligand is used as a catalyst to catalyze the trimerization of ethylene, and the selectivity of 1-hexene is as high as 99.8%.

[0004] PetroChina's patent CN108686706B protects a dehydrogenated pyridine annulene-type ligand with a 1-hexene selectivity of 97.65%. Tianjin University of Science and Technology's patent CN107597191A discloses a catalyst for preparing 1-hexene by ethylene trimerization, in which the P-containing compound is a diphosphine ligand with a biphenyl or binaphthyl skeleton. The selectivity of the catalyst for preparing 1-hexene by ethylene trimerization is close to 100%, avoiding the subsequent separation process and reducing industrial costs.

[0005] It can be seen that in the ethylene selective trimerization catalytic system, people have focused on the synthesis of new ligands in order to obtain higher 1-hexene selectivity and reduce the selectivity of by-products. Summary of the invention

[0006] The prior art still has the problems of low catalyst activity, high raw material cost, low selectivity for 1-hexene, and a small amount of polymer generated during the polymerization process, which affects the continuous operation of the device. To solve the above problems, the present invention provides an ethylene trimerization catalyst composition and its application. On the basis of keeping the metal chromium salt, alkyl aluminum, and organic chlorine components unchanged, a pyridine compound is used as a ligand to form a catalyst system. The ligand has low cost, high catalyst activity, high selectivity for 1-hexene, and very little polymer generated, which is conducive to long-term operation.

[0007] To achieve the above object, the technical solution of the present invention is:

[0008] An ethylene trimerization catalyst composition comprises the following components:

[0009] (1) Chromium compounds: chromium 2-ethylhexanoate, chromium acetylacetonate or chromium chloride in tetrahydrofuran;

[0010] (2) Pyridine compounds: The structural formula is as follows:

[0011] , wherein R1, R2, R3, R4 and R5 are the same or different and are selected from hydrogen, alkyl, alkoxy, cycloalkyl or halogen;

[0012] (3) Alkyl aluminum additives: triethyl aluminum, methyl aluminoxane, trimethyl aluminum or isobutyl aluminum;

[0013] (4) Electron donor: tetrachloroethane or hexachloroethane.

[0014] Furthermore, the molar ratio of the chromium compound, the pyridine compound, the alkyl aluminum auxiliary agent and the electron donor is: 1:0.1~100:1~1000:1~1000; preferably 1:0.1~10:1~500:1~50; more preferably 1:1~8:1~100:1~10.

[0015] Application of the above-mentioned ethylene trimerization catalyst composition: The components of the ethylene trimerization catalyst composition are dissolved in an inert solvent respectively, and injected into the ethylene trimerization reaction system in sequence or mixed uniformly in advance in the form of a homogeneous catalyst, and then the ethylene pressure is increased to fully contact with the catalyst to carry out ethylene trimerization reaction to obtain 1-hexene.

[0016] Furthermore, the conditions for the ethylene trimerization reaction are: temperature of 30-250° C., pressure of 0.5-20 MPa, and time of 0.1-2 h; the inert solvent includes benzene, toluene, cyclohexane, methylcyclohexane, n-heptane or n-hexane.

[0017] Furthermore, the use of the ethylene trimerization catalyst composition of the present invention in catalyzing ethylene trimerization reaction specifically comprises the following steps:

[0018] (1) Preparation of ethylene trimerization catalyst composition: Dissolve the components of the ethylene trimerization catalyst composition in an inert solvent that has been treated to remove water to prepare a chromium compound solution, a pyridine compound solution, an alkyl aluminum auxiliary solution, and an electron donor solution for use;

[0019] (2) Before the reaction, place the reactor body and lining in an oven at 120 °C and dry overnight. Install it on the reactor and seal it. Heat it to 105 °C for 1 h under vacuum to remove residual water, oxygen and oxygen-containing impurities. Then set the temperature to the reaction temperature and let it cool down naturally. Fill it with nitrogen and then evacuate it. Repeat this three times to ensure that the air is completely replaced. Then use a vacuum pump to remove the nitrogen and fill it with ethylene. Repeat this three times to ensure that the reactor body is filled with ethylene.

[0020] (3) Under stirring conditions, inject the alkyl aluminum auxiliary solution prepared in step (1) using a syringe. After the temperature stabilizes to the reaction temperature, inject the chromium compound solution, the pyridine compound solution, and the electron donor solution in sequence using a syringe. Close the tail gas valve, adjust the pressure reducing valve, and start timing after the pressure rises to a predetermined pressure value, and record the mass flow meter data. After the reaction is completed, turn off the ethylene gas, stop the reaction, close the air inlet valve, remove the reactor body, and immerse it in an ice water bath to cool the reactor to below 10°C.

[0021] After opening the tail gas valve to release the pressure, inject a certain amount of 5 ml of 10% HCl / ethanol solution under stirring conditions to quench the alkyl aluminum auxiliary agent, and then weigh and record the weight. Take a small amount of liquid phase product and use GC-MS to analyze the product. Filter the remaining sample, weigh the filter paper in advance and record the mass, then scrape the polymer on the stirring paddle with a spoon, wash it with a solvent into a beaker, place the obtained polymer in a vacuum oven at 60°C and dry it overnight, weigh it separately, and calculate the mass of the polymer. According to the MS, the component types can be calibrated, and the selectivity of each product and the catalyst activity can be calculated based on the GC results combined with the mass of the liquid phase product and the mass of the polymer.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) The present invention is the first to use a pyridine compound as a ligand in an ethylene trimerization catalyst system, that is, the present invention comprises a chromium metal salt, a pyridine compound, an alkyl aluminum and an organic chloride to form an ethylene trimerization composition, and the selectivity for 1-hexene in the reaction product is high. Compared with the disclosed catalyst (pyrrole as a ligand), the by-product polyethylene content is extremely small, and the catalyst has a higher activity. In industrialization, the ethylene trimerization reaction can be carried out by in-situ polymerization without the need for prepolymerization.

[0024] (2) In the present invention, by connecting different groups to the pyridine ring, the pyridine ring can work together with metal chromium, triethylaluminum and chlorine-containing electron donors to flexibly adjust its electron donation performance and spatial structure, and efficiently catalyze the ethylene molecule to form a seven-membered ring with the metal, and release a 1-hexene molecule after β-dehydrogenation. Compared with pyrrole, the pyridine compound containing different groups has a larger spatial configuration, so it has suitable steric hindrance after coordination with the metal in the ethylene trimerization catalyst, which can effectively reduce the formation of polymers. DETAILED DESCRIPTION

[0025] The present invention is further described below with reference to specific embodiments, but the present invention is not limited thereto.

[0026] Example 1

[0027] The ethylene polymerization reaction was carried out in a high-pressure stainless steel reactor. The autoclave was heated to 100 °C for 1 h under vacuum to remove residual water, oxygen and oxygen-containing impurities. Then the temperature was set to 90 °C, and it was allowed to cool naturally, while being replaced with nitrogen several times. Then it was replaced with ethylene several times to ensure that the autoclave was full of ethylene. Then the solvent cyclohexane and the catalyst were added in sequence, and the catalyst contained chromium acetylacetonate: pyridine compound: triethylaluminum: hexachloroethane = 1: 1:100: 10), where R1=R3=R5=Cl, R2=R4=H in pyridine compound 1. The reaction pressure was controlled to 3MPa, and the reaction was stopped after 1h of reaction. The air inlet valve was closed and the temperature was rapidly cooled to below 10 °C. After the tail gas valve was opened to release the pressure, 5 mL of 10% HCl / ethanol solution was injected under stirring to quench the alkyl aluminum, and then the weight was weighed and recorded. A small amount of liquid product was taken and the product was analyzed using GC-MS. The remaining sample was filtered, and the filter paper was weighed in advance to record the mass. Then the polymer on the stirring paddle was scraped off with a spoon, washed with solvent into a beaker, and the obtained polymer was placed in a vacuum oven at 60°C for overnight drying, and weighed separately to calculate the mass of the polymer. According to the MS, the component types can be calibrated, and the selectivity of each product and the catalyst activity can be calculated based on the GC results combined with the mass of the liquid phase product and the mass of the polymer. The data results are shown in Table 1.

[0028] Example 2

[0029] Same as Example 1, except that the reaction temperature is 120°C. The data results are shown in Table 1.

[0030] Example 3

[0031] Same as Example 1, except that the reaction pressure is 6 MPa. The data results are shown in Table 1.

[0032] Example 4

[0033] The same as Example 1, except that the ratio of chromium acetylacetonate to pyridine compound is changed to 1:5. The data results are shown in Table 1.

[0034] Example 5

[0035] Same as Example 1, except that in pyridine compound 2, R1=R5=CH3, R2=R3=R4=H. The data results are shown in Table 1.

[0036] Comparative Example 1

[0037] Same as Example 1, except that pyridine compound 1 is replaced by pyrrole. The data results are shown in Table 1.

[0038] Table 1 Summary of reaction conditions and reaction performance of the embodiments and comparative examples of the present invention

[0039]

[0040] The above embodiments are only for the purpose of clearly illustrating the content of the present invention, and the implementation mode of the present invention is not limited thereto. Any modification, replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An ethylene trimerization catalyst composition, characterized in that: It is composed of chromium acetylacetonate, pyridine compound, triethylaluminum, and hexachloroethane in a molar ratio of 1:1:100:10; The structural formula of the pyridine compound is as follows: , where R1=R3=R5=Cl, R2=R4=H.

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