Method for preparing butene through ethylene dimerization

Abstract

The invention relates to a method for preparing butene through ethylene dimerization, in particular to a method for reducing byproduct polymers on the premise of not sacrificing product selectivity and polymerization activity, which comprises the following step: ethylene is subjected to dimerization reaction in a system containing a fluorine-containing compound, a titanium catalyst, an aluminum compound and an organic solvent to generate butene. According to the method disclosed by the invention, the fluorine-containing compound is added into the system as an additive, so that the alkyl metal compound is modified, the dimerization activity is stabilized, the proportion of a polymerization active center is reduced, and the purpose of reducing a byproduct polymer is achieved.

Description

Technical Field

[0001] The invention belongs to the field of olefin polymerization, and relates to a method for preparing butene by ethylene dimerization, and specifically to a method for reducing reaction by-product polyethylene without sacrificing the selectivity and activity of ethylene dimerization products. Background Art

[0002] 1-Butene is a chemically active α-olefin and an important chemical raw material. 1-Butene is used downstream in the comonomer of LLDPE, HDPE and POE, and in the polymerization production of poly-1-butene, sec-butyl alcohol and butanone, valeraldehyde and its derivatives, and advanced plasticizer alcohols.

[0003] At present, the mainstream methods for producing 1-butene are mixed C4 separation (C4 mainly comes from catalytic cracking, steam cracking and coal-to-olefins) and ethylene dimerization. The ethylene dimerization technology is represented by the Alphabutol process of French Petroleum Company. The principle is that under the action of a catalyst, two molecules of ethylene react to produce one molecule of 1-butene, and the side reaction is that one molecule of butene reacts with one molecule of ethylene to produce hexene-1. Catalysts that can catalyze the dimerization of ethylene to produce 1-butene mainly include but are not limited to vanadium, iron, cobalt, nickel and titanium, etc. Among these systems, the catalytic system based on titanium is the best, but a certain amount of polymers will inevitably be produced in this system, and these by-product polymers will block the reaction and transportation system, affect mass transfer and heat generation, and reduce separation efficiency.

[0004] In the report on reducing the by-product polymers of ethylene dimerization, IFP patent CN105233868B and Sinopec patent CN111408412B introduced Lewis base into the system, which improved the activity of ethylene dimerization and reduced the selectivity of by-product polymers. Saudi Arabian Oil Company patents CN 107810057B and CN111094219B introduced quaternary ammonium salts, quaternary phosphonium salts, sulfonates and various types of surfactants into the system, and controlled the specific mixing method, which also achieved the above effect. However, these existing methods need to control the specific mixing method of adding additives and consider their solubility issues.

[0005] Therefore, how to effectively reduce the concentration of by-product polymers without sacrificing the existing ethylene dimerization activity and selectivity is a topic worthy of in-depth exploration. Summary of the invention

[0006] In view of the above problems existing in the prior art, the purpose of the present invention is to provide a method for preparing butene by ethylene dimerization. The method adopts a fluorine-containing compound modifier to improve the solubility of the catalyst system and the activity of the ethylene dimerization reaction, and reduce the amount of by-product polymer generated without sacrificing product selectivity and polymerization activity.

[0007] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing butene by dimerization of ethylene, comprising:

[0009] Ethylene undergoes a dimerization reaction in a system containing a fluorine-containing compound, a titanium-based catalyst, an aluminum compound, and an organic solvent to produce butene.

[0010] In the present invention, the fluorine-containing compound is selected from one or more of fluorinated alkanes, fluorinated cycloalkanes, fluorinated aromatic hydrocarbons, etc.; the fluorinated compound may be a polyfluorinated compound or a perfluorinated compound;

[0011] In some specific examples, the fluorine-containing compound is selected from one or more of 1,2,4,5-tetrafluorobenzene, 1,3,5-trifluorobenzene, hexafluorobenzene, perfluorononane, 1H-perfluorononane, perfluorohexane, 1H-perfluorohexane, perfluoroheptane, 1H-perfluoroheptane, decafluorobiphenyl, perfluorocyclohexane, and perfluoromethylcyclohexane;

[0012] Preferably, the molar ratio of the fluorine-containing compound to the aluminum compound is 0.05-1.5, for example, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, etc., preferably 0.1-1.

[0013] In the present invention, the titanium catalyst is a composition of alkoxy titanium and an ether solvent; preferably, the molar ratio of the ether solvent to the alkoxy titanium is 1-10, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., preferably 2-8.

[0014] In some specific examples, the alkoxy titanium structure is Ti(OR) 4 , wherein R is a straight or branched alkyl group containing 2 to 30 carbon atoms, such as a straight or branched alkyl group containing 2, 5, 10, 15, 20, 25, 30 carbon atoms, etc.;

[0015] Preferably, the alkoxytitanium is selected from one or more of tetraethyl titanate (tetraethoxytitanium), tetrapropyl titanate (tetraisopropoxytitanium), tetrabutyl titanate (tetra-n-butoxytitanium) and tetra-2-ethyloxytitanium.

[0016] In some specific examples, the ether solvent is an ether solvent commonly used in the titanium catalyst industry, selected from one or more of 2,5-dihydrofuran, tetrahydrofuran, 2-methoxytetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 2,3-dihydrofuran, benzofuran and 1,3-dioxolane.

[0017] In the present invention, the aluminum compound is selected from one or more of alkyl aluminum and alkyl aluminum chloride, preferably one or more of ethyl aluminum dichloride, triethyl aluminum trichloride, diethyl aluminum chloride, diisobutyl aluminum chloride, trimethyl aluminum, triethyl aluminum, tripropyl aluminum and triisobutyl aluminum;

[0018] Preferably, the molar ratio of the aluminum compound to the titanium element in the titanium-based catalyst is 1-10, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., preferably 1-6.

[0019] The present invention has no special requirements on the method of adding the fluorine-containing compound, the titanium-based catalyst, and the aluminum compound. For example, they can be directly added to the system in pure form, or they can be mixed with an organic solvent to form a solution and then added to the system. When the solution is prepared for use, conventional operations can be used to dissolve the raw materials to form a solution. There is no specific requirement for the amount of organic solvent used, and the type of organic solvent is preferably the same as the organic solvent used in the aforementioned dimerization reaction.

[0020] In the present invention, the organic solvent is selected conventionally in the field, for example, it can be one or more of alkanes, cycloalkanes or aromatic hydrocarbons;

[0021] In some specific examples, the organic solvent is selected from one or more of n-hexane, n-heptane, cyclohexane, methylcyclohexane, toluene, xylene or butene;

[0022] Preferably, the molar concentration of the titanium element in the titanium-based catalyst relative to the organic solvent is 0.01-10mmol / L, for example, 0.01mmol / L, 0.05mmol / L, 1mmol / L, 1.5mmol / L, 2mmol / L, 3mmol / L, 4mmol / L, 5mmol / L, 6mmol / L, 7mmol / L, 8mmol / L, 9mmol / L, 10mmol / L, etc., preferably 0.05-2mmol / L, wherein the amount of the organic solvent includes an organic solvent for dissolving fluorine-containing compounds, an organic solvent for dissolving the titanium-based catalyst, and an organic solvent for dissolving aluminum compounds.

[0023] In the present invention, the dimerization reaction is carried out at a temperature of 40-60°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, etc., and the reaction time is 0.5-5h, for example, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, etc.

[0024] In the present invention, the reaction pressure of the dimerization reaction is controlled at 2.0-3.0 MPaG, such as 2.0 MPaG, 2.2 MPaG, 2.4 MPaG, 2.6 MPaG, 2.8 MPaG, 3.0 MPaG, etc.;

[0025] Specifically, during the dimerization reaction, the amount of ethylene added satisfies the reaction pressure (ie, ethylene is added to the reactor and the ethylene pressure is increased to a preset ethylene pressure). In specific implementation, ethylene can be fed continuously.

[0026] In some examples, the process can be carried out in a high-pressure stainless steel reactor equipped with a magnetic stirring paddle. Before use, the reactor is heated and evacuated, during which nitrogen is replaced at least three times, and then evacuated and replaced with ethylene at least three times;

[0027] At the same time, the fluorine-containing compound is mixed with part of the organic solvent to form solution 1, the titanium-based catalyst is mixed with part of the organic solvent to form solution 2, and the aluminum compound is mixed with part of the organic solvent to form solution 3 for later use;

[0028] After the temperature of the reactor is cooled to room temperature, solution 1, solution 2, solution 3, and the remaining organic solvent are added to the reactor to form a reaction liquid system; then ethylene is introduced and pressurized to a preset reaction pressure, the reactor is turned on for heating, and heated to the reaction temperature to carry out a dimerization reaction. During the reaction, ethylene is introduced to maintain a preset pressure. After the reaction is completed, the temperature is lowered. The reaction liquid in the reactor can be further separated and purified as needed to obtain a butene product.

[0029] Due to in the existing olefin polymerization reaction system, a certain amount of by-product polymer (including polyethylene wax, high-density polyethylene, etc.) will inevitably be produced, blocking the reaction and delivery system, affecting mass transfer heat generation and reducing separation efficiency. The inventors found through experiments that in the reaction system based on titanium catalysis and containing aluminum auxiliary agent, fluorine-containing compounds are added as modifiers, compared with halogenated hydrocarbons such as chlorine and bromine, wherein fluorine compounds can participate in the coordination of titanium catalysts as electron donors on the one hand, occupy the spatial environment of coordination, prevent ethylene molecules from continuing to insert, thereby reducing the possibility of polymer generation. On the other hand, it is also found that fluorine compounds can modify aluminum-containing co-catalysts, change their aggregation state and the type of active ingredients, improve the solubility of the catalyst system and the activity of ethylene dimerization, further reduce the selectivity of by-product polymers, and make the selectivity of by-product polymers in the product reduced to ppm level.

[0030] In the above method of the present invention, the reaction activity of the ethylene dimerization reaction is not less than 6000g butene / gTi, the selectivity of the product butene (1-butene) is not less than 92%, and the selectivity of the by-product polymer in the butene product is higher than 100ppm (i.e. 0.01%).

[0031] Compared with the prior art, the addition of fluorine-containing compounds as modifiers in the reaction system provided by the present invention can improve the solubility of the catalyst system and the activity of the ethylene dimerization reaction, reduce the selectivity of by-product polymers, and has potential industrial application prospects and economic benefits. DETAILED DESCRIPTION

[0032] 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.

[0033] 1. In each embodiment and comparative example of the present invention, the sources of the main raw materials used are shown in Table 1 below. Other raw materials and reagents, unless otherwise specified, were purchased from commercial sources:

[0034] Table 1 Sources and specifications of raw materials

[0035]

[0036]

[0037] Second, the test method of the sample in the present invention is as follows:

[0038] The liquid products are characterized by gas chromatography to obtain the mass of each liquid product, and the solid products are measured by filtering the reaction solution, drying it, and then weighing it.

[0039] Gas chromatography analysis conditions: sample inlet temperature: 250°C; column box temperature: 35°C;

[0040] Heating program: first keep at 35℃ for 10 minutes, then increase to 250℃ at a rate of 10℃ / min, then keep at 250℃ for 10min, and then start cooling to room temperature;

[0041] Detector temperature: 250℃; Carrier: 1.0Mpa; Air: 0.03Mpa; Hydrogen: 0.03Mpa;

[0042] The product was characterized using n-nonane as an internal standard, and the calculation method was as follows:

[0043]

[0044] In the formula, m1 represents the mass of a substance, m is the mass of nonane, a1 is the peak area of ​​the substance measured in GC, a is the peak area of ​​n-nonane measured in GC, and k is the correction factor.

[0045] (1) Calculation method of catalyst activity (unit: g / gTi·h):

[0046]

[0047] (Note: The molar mass of titanium is 48g / mol)

[0048] (2) Calculation method of C4 content (%) and 1-butene selectivity (%):

[0049]

[0050] Example 1

[0051] The high-pressure stainless steel reactor was replaced with nitrogen and ethylene in turn, and then 91 mL of methylcyclohexane containing 13.34 mg (0.04 mmol) of perfluorobiphenyl was added, 5 mL of a 0.02 mol / L titanium catalyst (a mixed solution of tetrabutyl titanate and tetrahydrofuran, a molar ratio of 1:6) of methylcyclohexane solution, and 4 mL of a 0.1 mol / L triethylaluminum methylcyclohexane solution were added, and ethylene was introduced to maintain a pressure of 2.5 MPaG, and ethylene dimerization was carried out at a temperature of 50 ° C to synthesize 1-butene. After 60 minutes of reaction, the ethylene feed was stopped and the reaction temperature was lowered to below 10 ° C, and the gas was sampled and analyzed by gas chromatography. Then the liquid phase in the reactor was weighed, the polymer was filtered, dried and weighed, and the specific reaction conditions and the results obtained are shown in Table 2.

[0052] Example 2

[0053] The high-pressure stainless steel reactor was replaced with nitrogen and ethylene in turn, and then 196 mL of methylcyclohexane containing 66.82 mg (0.2 mmol) of perfluorobiphenyl was added, 2 mL of methylcyclohexane solution of a titanium catalyst (a mixed solution of tetrabutyl titanate and tetrahydrofuran, molar ratio 1:6) with a concentration of 0.1 mol / L, and 2 mL of methylcyclohexane solution of triethylaluminum with a concentration of 0.2 mol / L, and ethylene was introduced to maintain a pressure of 2.7 MPaG, and ethylene dimerization was carried out at a temperature of 52 ° C to synthesize 1-butene. After 90 minutes of reaction, the ethylene feed was stopped and the reaction temperature was lowered to below 10 ° C, and the gas was sampled and analyzed by gas chromatography. Then the liquid phase in the reactor was weighed, the polymer was filtered, dried and weighed, and the specific reaction conditions and the results obtained are shown in Table 2.

[0054] Example 3

[0055] The high-pressure stainless steel reactor was replaced with nitrogen and ethylene in turn, and then 117 mL of methylcyclohexane containing 133.4 mg (0.4 mmol) of perfluorobiphenyl was added, 1 mL of a 0.1 mol / L titanium catalyst (a mixed solution of tetrabutyl titanate and tetrahydrofuran, molar ratio 1:6) of methylcyclohexane solution, and 2 mL of a 0.2 mol / L triisobutyl aluminum methylcyclohexane solution were added, and ethylene was introduced to maintain a pressure of 3.0 MPaG, and ethylene dimerization was carried out at a temperature of 55 ° C to synthesize 1-butene. After 120 min of reaction, the ethylene feed was stopped and the reaction temperature was lowered to below 10 ° C, and the gas was sampled and analyzed by gas chromatography. Then the liquid phase in the reactor was weighed, the polymer was filtered, dried and weighed, and the specific reaction conditions and the results obtained are shown in Table 2.

[0056] Example 4

[0057] The method of Example 1 was referred to, except that the amount of perfluorobiphenyl added was adjusted, and the molar ratio of the aluminum compound to the titanium element in the titanium catalyst, and the molar ratio of tetrahydrofuran to alkoxytitanium in the titanium catalyst were both adjusted to 5. Other operations and conditions remained unchanged. The results are shown in Table 2.

[0058] Example 5

[0059] The method of Example 1 was followed, except that perfluorobiphenyl was replaced by 1H-perfluorohexane, and other operations and conditions remained unchanged. The results are shown in Table 2.

[0060] Example 6

[0061] The method of Example 1 was followed, except that perfluorobiphenyl was replaced by perfluoromethylcyclohexane, and other operations and conditions remained unchanged. The results are shown in Table 2.

[0062] Comparative Example 1

[0063] The method of Example 1 was used with the exception that no perfluorobiphenyl was added to the system and other operations and conditions remained unchanged. The results are shown in Table 2.

[0064] Comparative Example 2

[0065] The method is the same as that in Example 1, except that perfluorobiphenyl is replaced by perbromobiphenyl, and other operations and conditions remain unchanged. The results are shown in Table 2.

[0066] Comparative Example 3

[0067] The method is the same as that in Example 1, except that perfluorobiphenyl is replaced by hexachloroethane, and other operations and conditions remain unchanged. The results are shown in Table 2.

[0068] Comparative Example 4

[0069] The method is the same as that in Example 1, except that perfluorobiphenyl is replaced by benzyl chloride, and other operations and conditions remain unchanged. The results are shown in Table 2.

[0070] Table 2 Ethylene dimerization test results in Examples and Comparative Examples

[0071]

[0072] It can be seen from the examples that the present invention uses fluorine-containing compounds as additives, which have a certain effect on the alkyl aluminum compounds, can stabilize the existing dimerization active centers and suppress the proportion of other active centers, can improve the reaction activity of ethylene dimerization and the selectivity of product C4, and can greatly reduce the selectivity of by-product polymers. However, in comparative examples 1-3, there is no external fluorine-containing compound, which does not play a corresponding modification role, resulting in low activity and high polymer selectivity; the bromine or chlorine-containing solvents used in comparative examples 2-4 will also greatly sacrifice the activity of ethylene reaction and the selectivity of polymers compared with the examples. The above proves the special role of the fluorine-containing additives of the present invention.

[0073] In short, the above is only a representative operation example of the present invention and is only used to illustrate the present invention, but not to limit the present invention. Any improvement of the present invention, including equivalent replacement and addition of each raw material, conversion of continuous or intermittent process, etc., belongs to the scope of the present invention, and relevant personnel in the technical field should be aware of this. The scope of patent protection of the present invention shall be defined by the claims.

Claims

1. A method for preparing butene by dimerization of ethylene, characterized in that: include: Ethylene undergoes a dimerization reaction in a system containing a fluorine-containing compound, a titanium-based catalyst, an aluminum compound, and an organic solvent to produce butene.

2. The method according to claim 1, characterized in that The fluorine-containing compound is selected from one or more of fluorinated alkanes, fluorinated cycloalkanes, and fluorinated aromatic hydrocarbons; and / or The molar ratio of the fluorine-containing compound to the aluminum compound is 0.05-1.5, preferably 0.1-1.

3. The method according to claim 1 or 2, characterized in that: The fluorine-containing compound is selected from one or more of 1,2,4,5-tetrafluorobenzene, 1,3,5-trifluorobenzene, hexafluorobenzene, perfluorononane, 1H-perfluorononane, perfluorohexane, 1H-perfluorohexane, perfluoroheptane, 1H-perfluoroheptane, decafluorobiphenyl, perfluorocyclohexane, and perfluoromethylcyclohexane.

4. The method according to claim 1, characterized in that: The titanium-based catalyst is a composition of alkoxy titanium and an ether solvent; preferably, the molar ratio of the ether solvent to the alkoxy titanium is 1-10, preferably 2-8.

5. The method according to claim 1 or 4, characterized in that: The alkoxytitanium structure is Ti(OR)4, wherein R is a straight or branched alkyl group containing 2 to 30 carbon atoms; preferably, the alkoxytitanium is selected from one or more of tetraethyl titanate, tetrapropyl titanate, tetrabutyl titanate and tetra-2-ethyloxytitanium; and / or The ether solvent is selected from one or more of 2,5-dihydrofuran, tetrahydrofuran, 2-methoxytetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 2,3-dihydrofuran, benzofuran and 1,3-dioxolane.

6. The method according to claim 1, characterized in that The aluminum compound is selected from one or more of alkyl aluminum and chloroalkyl aluminum, preferably one or more of ethyl aluminum dichloride, triethyl aluminum trichloride, diethyl aluminum chloride, diisobutyl aluminum chloride, trimethyl aluminum, triethyl aluminum, tripropyl aluminum and triisobutyl aluminum; and / or The molar ratio of the aluminum compound to the titanium element in the titanium-based catalyst is 1-10, preferably 1-6.

7. The method according to claim 1, characterized in that The organic solvent is one or more of alkanes, cycloalkanes or aromatic hydrocarbons, preferably one or more of n-hexane, n-heptane, cyclohexane, methylcyclohexane, toluene, xylene or butene; and / or The molar concentration of the titanium element in the titanium-based catalyst relative to the organic solvent is 0.01-10 mmol / L, preferably 0.05-2 mmol / L.

8. The method according to claim 1, characterized in that The dimerization reaction is carried out at a temperature of 40-60° C. and a time of 0.5-5 h.

9. The method according to claim 1, characterized in that: The reaction pressure of the dimerization reaction is controlled at 2.0-3.0 MPaG.

10. The method according to claim 9, characterized in that During the dimerization reaction, the amount of ethylene added meets the reaction pressure.

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