FIELD OF TI 11/ INVENTION

The invention relates to the field of olefin oligomerization to prepare alpha- olefins, in particular, hexene- 1 used in the production of linear low-density and high- density polyethylenes, polyhexene, etc.

BACKGROUND

The invention relates to the field of production of chromium-containing catalytic systems and their use for the production of hydrocarbons, in particular, olefin oligomers.

Conventional catalytic systems for olefin oligomerization processes, in particular for selective trimerization of ethylene to hexene-1 , are widely described in the literature. They usually contain a chromium source, a ligand, and an activator, which are mixed together in a hydrocarbon solvent before being used in olefin oligomerization.

Various methods for modifying such catalytic systems and methods for their preparation, known in the art, are directed to improving the activity and selectivity of these systems in oligomerization processes, in particular, to minimizing the formation of oligomeric and polymeric by-products.

For example, it is known that oligomerization can be accelerated and the activity of a corresponding catalytic system can be increased by feeding hydrogen into an oligomerization reactor, thus the process of oligomerization can be controlled by the addition of hydrogen, thereby reducing the amount of the resulting by-product polymer (see WO2016105227).

The performance characteristics of a catalytic system can be changed, for example, by varying the ratio of its components or by minimizing the content of water in the starting materials, including both in the starting materials for the catalytic system and in the feedstock for the oligomerization process as such.

Thus, document US7157612 discloses that almost five-fold increase in the activity of catalytic system can be achieved by varying the chrom i um : triet hy 1 al um i n um rat io .

Documents WO2016105227 and WO2013089963 teach that the reactivity of a catalytic system for olefin oligomerization decreases in the presence of water; therefore, it is preferable to use non-hydroly/.ed compounds as components of the catalytic system, for example, alkylaluminum compounds or their derivatives. In this case, the reactivity of the catalytic system and/or its end-product capacity increases. The use of hydrolyzed alkylmetals leads to a decrease in the yield of desired olefins.

The present inventors have previously shown that a significant improvement in the characteristics of a catalytic system for olefin oligomerization could be achieved by the use of a microwave-irradiated activator, in particular, alkylaluminum compounds or a mixture thereof (see WO2011093748 document). The present inventors have also shown that the use of zinc compounds in a catalytic system containing a microwave- irradiated activator could improve its catalytic performance (see document WO2016105227).

The closest analogue of the present invention known from the prior art is a method for improving catalyst performance in trimerization of ethylene to hexene- 1, as described in WO2015101959 document, the method comprising: pre-mixing a ligand and a chromium source in a hydrocarbon solvent to form a pre-mixed composition; activating a pre-mixed composition with an activator to form a pre-activated composition, followed by mixing (stirring) the pre-activated composition for a time of from 1 minute to 18 hours. Document W02015101959 discloses that such mixing of the pre-activated composition for said period of time provides a two-fold increase in the activity of the catalytic system. It should be noted that the achievement of the claimed effect, which is an increase in the catalytic activity, is confirmed only for systems in which the ligand is (phenyl)2PN(isopropyl)P(phenyl)NH(isopropyl) (so- called PIIPNH group).

The present inventors, when studying methods for preparing various catalytic systems for olefin oligomerization, in particular, ethylene trimerization, previously observed the formation of precipitate, the quantity of which was different in individual experiments.

When studying the use of the production method described in WO2015101959 directly for catalytic systems based on a pyrrole ligand, as well as for the catalytic system developed earlier by the inventors, which was a composition of a chromium source, a ligand and an activator previously subjected to microwave irradiation (UIIF- irradiation) in a hydrocarbon solvent, the inventors found that the above-mentioned mixing over a period of time of from 1 minute to 18 hours leads to the formation of a significant amount of precipitate. At that, a more detailed study has showed the amount of precipitate to increase significantly with increasing time and/or intensity of mixing. Thus, a disadvantage of the method known from WO2015101959 is a significant decrease in the concentration of the catalytically active compound in the resulting catalyst solution, which leads to an increase in the consumption standards for the resulting catalyst solution necessary for oligomerization and, as a consequence, an increase in the consumption standards of the starting components of the catalytic system.

The present inventors found that minimization and even complete elimination of the above-mentioned precipitation can be achieved with use of an effective method of mixing the components of a catalytic system for olefin oligomerization. The proposed method provides minimization and, in some cases, even complete elimination of the formation of undesirable precipitate.

SUMMARY OF THE INVENTION

An objective of the present invention is to develop the effective method for preparing a catalytic system for olefin oligomerization, providing minimization of undesirable precipitation.

A technical result (technical effect) of the invention resides in minimization of precipitation, and as a result, an increase in the concentration of a catalytically active compound in a catalyst solution obtained, a reduction in the consumption standards of the obtained catalyst solution necessary for oligomerization and, accordingly, a reduction in the consumption standards of the starting components for the catalytic system.

An additional technical result (technical effect) of the invention resides in a significant increase in the stability of a catalytic system, which is expressed as the absence of precipitation for a long time, for example, for at least 180 days.

Another additional technical result is reduction in the load on filtering equipment and minimization of the risk of reducing the throughput capacity of flow meters and pumps that pump a catalyst solution, including to an oligomerization reactor. The technical problem is solved and the technical result is achieved by performing a method for preparing a catalytic system for olefin oligomerization, comprising the following steps:

A) pre-mixing at least one chromium source and at least one nitrogen- containing ligand in at least one hydrocarbon solvent to form a pre-mixed composition; and

B) mixing the pre-mixed composition with at least one activator, characterized in that the mixing process in step B) is performed under laminar flow conditions or under conditions that are conditions of a flow which is transitional between laminar and turbulent flow.

DESCRIPTION OF FIGURES

The technical solutions disclosing the essence of the present invention is explained with reference to Figs 1 to 6.

FIG. 1 is a block diagram showing the sequence of the method of Example 1 .

FIG. 2 is a block diagram showing the sequence of the method of Example 2.

FIG. 3 is a block diagram showing the sequence of the method of Example 3.

FIG. 4 is a block diagram showing the sequence of the method of Example 5.

FIG. 5 shows a photography demonstrating equipment plugged with precipitate.

FIG. 6 shows a photography demonstrating equipment plugged with precipitate. DETAILED DESCRIPTION OF THE INVENTION

The description of various embodiments of the present invention is given below.

According to the present invention, the olefin oligomerization process comprises interacting, under oligomerization conditions, a feedstock containing an initial olefin with a catalytic system that contains at least: 1) a chromium source, 2) a nitrogen-containing ligand, and 3) an activator.

According to the present invention, the catalytic system is prepared by mixing the chromium source and the nitrogen-containing ligand in a hydrocarbon solvent to form a pre-mixed composition (step A), followed by mixing the pre-mixed composition with the activator (step B).

It is necessary that the mixing process at step B be performed under conditions of a laminar flow or a flow transitional between laminar and turbulent one. The term "laminar flow" as used herein means an ordered fluid motion where the fluid moves in the form of layers parallel to the direetion of the flow and which is characterized by a Reynolds number, Re _kr , of not more than 2300 (see, for example, A.G. Kasatkin: The main processes and apparatuses of chemical technology. - M: Alliance, 2004. - pp. 40-42, “Modes of Fluid Movement”).

The term “turbulent flow” as used herein means a disordered fluid motion in which individual fluid particles move along entangled, chaotic trajectories, while the entire mass of the fluid moves in one direction. This flow is characterized by a Reynolds number, Re _kr , of at least 10000 (ibid.).

The flow at a Reynolds number, Rekr, of from 2300 to 10000 is transitional between laminar flow and turbulent flow.

The mixing process at step A can be performed in any mode, including turbulent; however, the mixing at step A under conditions of a laminar flow or a flow transitional between laminar and turbulent is preferred, although at this step said condition is optional.

The present inventors have found that the mixing of an activator with other components of a catalytic system should be conducted in a tranquil mode (without active agitation), i.e. without pressure and velocity surges. This provides a highly active and selective catalytic system without loss of the active component that could be precipitated in significant amounts. Without being bound by any theory, the inventors believe that the mode of mixing should be selected depending on the activity of the used activator. In particular, it is assumed that the higher activity of the used activator is, the less active mode should be applied for mixing the catalytic system components.

In this aspect, the activity of an activator should be understood as the ability of the activator to increase the activity of a catalytic system and provide an effect on the catalytic process selectivity.

In order to achieving the claimed technical result, the Reynolds number, Re _kr , in the mixing process in step B, should be not more than 8000, preferably not more than 4000, more preferably not more than 3500, more preferably not more than 2500, in particular, not more than 2300, and it is most preferably when the Reynolds number, Re _kr, ranges between 1500 and 3000.

The most effective range of the Reynolds number for the mixing process in step B (within the above ranges) in order to minimize or completely eliminate precipitation can be selected depending on the activity of a used activator and the time for mixing the components. Thus, the inventors believe that the higher the activity of the used activator is, the more preferable the mixing at lower values of the Reynolds number is. In this case, it is desirable to reduce the time of mixing the components when increasing the Reynolds number (within the specified ranges).

The time of mixing the catalytic system components in step A can have any duration.

The mixing of the catalytic system components in step B is conducted for not more than 30 minutes, preferably for not more than 10 minutes, more preferably for not more than 8 minutes. When the used activator is microwave-irradiated, it is preferable that the mixing in step B be conducted for not more than 6 minutes, more preferably for not more than 1 minute, and even more preferably for less than 30 seconds.

In addition, the inventors has found that the technical result expressed as minimization and even complete elimination of precipitation of by-products can be achieved by controlling delivery rates of the catalytic system components to step B of mixing.

It has been found that at the same (low rates of the catalytic system components to be mixed or at higher feed rate of the activator compared to the feed rate of the pre mixed composition, it is possible to minimize precipitation of the by-products to a large extent.

Wherein, it is preferred that the feed rates of all the components of the catalytic system be the same or that the feed rate ratio between the activator and the pre-mixed composition prepared in step A be from 1 :1 to 17:1 , more preferably from 3:1 to 15:1, and most preferably from 4:1 to 10:1.

According to the present invention, the chromium source may be an organic and/or inorganic chromium compound(s). The chromium oxidation degree in the compounds can vary and can be +1 , +2, +3, +4, +5 or +6. In general, the chromium source is a compound of the general formula CrX _n , wherein X groups may be the same or different, and n is an integer from 1 to 6. The X groups may be organic or inorganic substituents. Organic substituents X can have from 1 to 20 carbon atoms and be an alkyl group, alkoxy group, carboxy group, acetylacetonate group, amino group, amido group, etc.

Suitable inorganic substituents X are halides, sulfates, etc.

Examples of chromium sources include chromium(III) chloride, chromium(III) acetate, chromium(III) 2-ethylhexanoate, chromium(III) acetylacetonate, chromium(III) pyrrolide, chromium(II) acetate, chromium(VI) dichloridc dioxide (CrO2Cl2), etc.

The nitrogen-containing ligand forming a part of the catalytic system is an organic compound that includes a pyrrole ring moiety, i.e. a five-membered aromatic ring having one nitrogen atom. Suitable nitrogen-containing ligands are, but are not limited to, pyrrole, 2,5-dimethylpyrrole, lithium pyrrolide (C ₄ H ₄ NL1), 2-ethylpyrrole, 2-allylpyrrole, indole, 2-methylindole, 4,5,6,7-tetrahydroindolc. Pyrrole or 2,5- dimethylpyrrole is most preferred.

Alkylaluminum can be an alkylaluminum compound, as well as a halogenated alkylaluminum compound, an alkoxyalkylaluminum compound, and mixtures thereof In order to increase the selectivity of the catalytic system it is preferable to use the above-mentioned compounds that have not been in contact with water (not hydrolyzed), presented by the general formulas: AlR ₃ , AlR ₂ Hal, AIRHal ₂ , AIR ₂ OR, AIRHalOR and/or Al ₂ R ₃ Hal ₃ , wherein R is an alkyl group and Hal is a halogen atom. Suitable alkylaluminum compounds include, but are not limited to, triethylaluminum, dicthylaluminum chloride, tripropylaluminum, triisobutylaluminum, diethylaluminum ethoxidc and/or ethylaluminum sesquichloride, or mixtures thereof. Triethylaluminum or a mixture of triethylaluminum and diethylaluminum chloride is most preferred.

The greatest technical effect, which is expressed as minimization and even complete elimination of precipitation of by-products, is observed when the catalytic system is prepared by the claimed method using an activator subjected to microwave irradiation. As the activator it is preferred to use an alkylaluminum compound or a mixture of alkylaluminum compounds, which are microwave-irradiated; the use of microwave-irradiated triethylaluminum aluminum is more preferred, and the use of a microwave-irradiated mixture of triethylaluminum and diethylaluminum chloride is even more preferred. Lh alkylaluminum compound can be subjected to microwave irradiation in the form of a compound as such, preferably in the liquid aggregate state, or as a solution in a hydrocarbon solvent, for example, in hexane, cyclohexane, C10-C12 hydrocarbon fractions.

During irradiation, it is necessary that the catalytic system components, which are subjected to activation, be in a vessel that is transparent to microwave radiation, for example, in a vessel made of glass, fluoroplastic, or polypropylene.

The frequency of the used microwave radiation can be in the range of from 0.3 to 20 GHz. It is particularly preferable to use microwave radiation with a frequency of 2.45 GHz, which does not cause radio interference and is widely used in household and industrial sources of microwave radiation.

The nominal power of the microwave radiation ranges from 1 W to 5000 W per 1 g of the used alkylaluminum in terms of elemental aluminum.

The power of microwave radiation as used herein means the total energy of electromagnetic waves transferred across a given surface per unit of time (Great Soviet Encyclopedia, 3rd ed., Volume 20. - M: Sovetskaya Entsyklopediya, 1975. - p. 435, col. 1293, lines 18-34, “Radiation flux”), and the microwave radiation frequency means the number of oscillations of the electric and magnetic fields of electromagnetic waves per unit of time (Great Soviet Encyclopedia, 3rd ed., volume 30. - M.: Sovetskaya Entsyklopediya, 1978. - p. 67, col. 189 - p. 68, col. 192, "Electromagnetic waves").

For the best results, it is preferable that the time of microwave treatment be from 20 seconds to 20 minutes, preferably 15 minutes. L time longer than 20 minutes usually does not provide additional advantageous properties of the resulting catalytic system. Irradiation for less than 20 seconds is not sufficient to significantly change the properties of the components subjected to activation, which in turn will lead to an insufficient increase in the activity and/or selectivity of the resulting catalytic system.

It is preferable that the mixing of alkylaluminum activated by microwave irradiation with the chromium source and the nitrogen-containing ligand be conducted not more than 5 minutes after the end of irradiation, preferably not more than 3 minutes more preferably not more than 1 minute after the end of irradiation.

According to the present invention, said catalytic system may further comprise a zinc compound.

The zinc compound can be used either as an individual compound or as a mixture with other compounds, for example, as a solution in hydrocarbons.

The zinc compound or a mixture of such compounds can be added directly to the catalytic system in the step of its preparation or separately into an oligomerization reactor.

The zinc compound is used as an additional activator for the catalytic center, in particular, chromium. It is preferable to use the zinc compound in the absence of visible and LJV radiation in order to increase its stability.

The zinc compound may be zinc metal, a zinc-copper pair, activated zinc, alkylzinc compounds, in particular dimethyl-, diethyl- and dibutylzinc, arylzinc compounds, such as diphenyl- and ditolylzinc, zinc amides, in particular zinc pyrrolides and zinc-porphyrin complexes, zinc oxygenates (including formate, acetate, basic acetate, 2-ethylhexanoate and other zinc carboxylates), zinc halides, in particular, anhydrous zinc chloride, or combinations thereof. It is preferable to use zinc compounds that are soluble in the solvents used in the oligomerization process.

The zinexhromium ratio can vary and is in the range of from 2:1 to 100:1, preferably from 5: 1 to 50:1.

Alternatively, alkylaluminum subjected to activation by microwave irradiation can be gradually fed to step B of mixing along with the other components of the catalytic system directly from the tank exposed to microwave irradiation, so that the mixing time can be any convenient time during which the irradiated component does not lose special properties acquired under microwave irradiation. The mixing in step B is performed preferably for not more than 6 minutes, more preferably for less than 1 minute, even more preferably for less than 30 seconds.

Herein, the mixing time should be understood as a time, which is sufficient for all the catalytic system components, originally located separately from each other, to form a homogeneous mixture.

The components arc mixed in a pipeline or any suitable mixing device known from the prior art, for example, in a bubbling apparatus, a static mixer, a tank with a mixing device. In this aspect, the mixing device means a construction for forcibly mixing Hows of various substances under the action of a pulse that is transmitted to the mixed medium from any mixing device known from the prior art, for example, a mechanical stirrer.

Suitable hydrocarbon solvents include, but are not limited to, hexene- 1 , benzene, toluene, ethylbenzene, xylene, or mixtures thereof. It is preferable to use those aromatic hydrocarbons as a solvent, which promote an increase in stability of the catalytic system and producing a highly active and selective catalytic system,. The aromatic hydrocarbon solvent is preferably selected from the group consisting of toluene, ethylbenzene, or mixtures thereof. The most preferred aromatic hydrocarbon is ethylbenzene.

After the mixing step is finished and the catalytic system is prepared, the hydrocarbon solvent can be removed from the mixture. As it is known in the art (see, for example, RU2104088 document), the presence of an aromatic hydrocarbon in the reaction mixture during oligomerization can reduce the activity of the catalytic system and increase the amount of by-products, such as polymers. The solvent can be removed by any known method, for example, by creating vacuum (vacuum treatment). However, it should be noted that when olefins oligomerization process is performed at an elevated temperature, the presence of an unsaturated hydrocarbon solvent (for example, such as ethylbenzene) could be preferable because such a solvent increases stability of the catalytic system.

The ratios of the components of the catalytic system may vary. The aluminum: chromium molar ratio can be from 5:1 to 500: 1, preferably from 10:1 to 100:1, most preferably from 20: 1 to 50:1. The ligandxhromium molar ratio can vary from 2: 1 to 50: 1 , preferably from 2.5:1 to 5: 1 .

The olefin oligomerization process in the presence of a catalytic system prepared by the method according to the present invention can be performed by reacting a feedstock containing an initial olefin in the presence of the catalytic system and optionally a zinc compound under oligomerization conditions.

The catalytic system prepared according to the present invention is characterized by a high stability expressed as the absence of precipitation for at least 180 days. Due to this technical effect, the catalytic system can be fed into a reactor both all at once or in parts from a tank for preparing the catalytic system to the oligomerization reactor. The catalytic system prepared according to the present invention is fed into the oligomerization reactor by any method known in the art in diluted or undiluted form. Preferably, the catalytic system is diluted with a hydrocarbon solvent. Dilution with a saturated hydrocarbon solvent or a mixture thereof is especially preferred. However, it is preferable that the content of aromatic compounds should not exceed 2 wt.%.

The hydrocarbon solvent used as a solvent in the oligomerization process can be, for example, alkane, cycloalkane, or a mixture of various alkanes and/or cycloalkanes. The composition of the hydrocarbon solvent may also include unsaturated hydrocarbons, such as olefins or aromatic compounds. Suitable hydrocarbon solvents or solvent components are, in particular, heptane, cyclohexane, decane, undccane, isodccane fraction, and hexene- 1. Heptane, cyclohexane, and undecane are preferably used as a solvent, and cyclohexane or heptane is most preferable.

Olefins used as an initial olefin in olefin oligomerization include ethylene (ethene), propylene (propene) and butylene (butene). Ethylene (ethene) is preferred as the initial olefin.

The olefin oligomerization process is aimed at obtaining oligomerization products, i.c. higher olefins. Industrially important processes arc processes for preparing a-olefin oligomerization products from ethylene. a-Olefins are compounds with a carbon-carbon double bond (C=C) in a-position. a-Olefins obtained in the oligomerization process may include various C4-C40 olefins and their mixtures. For example, a-olefins prepared by the process of ethylene oligomerization may be butene- 1, hexene- 1, octene-1, decene-1, dodccene-1 , higher a- olefins, or mixtures thereof. Preferably, the oligomerization process is the process of ethylene trimerization to prepare a desired a-olefin, hexene- 1.

The oligomerization process can be performed in any reactor known in the prior art. Suitable reactors are a continuous stirred-tank reactor, a batch reactor, a plug flow reactor, and a tubular reactor. The reactor may be a gas-liquid reactor, for example, an autoclave with a stirrer, a bubbling column (bubbling reactor) with co current or countercurrent gas-liquid flow, and a bubbling gas-lift reactor.

In a preferred embodiment of the method, when the oligomerization process is a process for trimerization of ethylene to produce hexene- 1 , the pressure of ethylene ranges from 1 to 200 atm, preferably from 10 to 60 atm, most preferably from 15 to 40 atm. To increase the rate of oligomerization, it is preferable to perform the process at elevated ethylene pressure.

The temperature of the oligomerization process can vary in the range of from 0 to 160°C, preferably from 40 to 130°C. It is most preferable to maintain the temperature in the reactor in the range of from 80 to 120°C. At this temperature, by product polymer, in particular polyethylene, will not precipitate from the solution and will be removed from the reactor as a solution, and the catalytic system will be most active and selective. The oligomerization process at higher temperatures (above 120°C) may lead to deactivation of the catalytic system.

According to the proposed method, the oligomerization reaction time can vary. The reaction time can be defined as the residence time of a feedstock and a solvent in an oligomerization reaction zone. When using continuous flow reactors, the reaction time can be defined as an average residence time. The reaction time can vary depending on an olefin used as feedstock, reaction temperature, pressure and other process parameters. In embodiments of the method, the reaction time usually does not exceed 24 hours. The reaction time can be less than 12 hours, less than 6 hours, less than 3 hours, less than 2 hours, less than 1 hour, less than 30 minutes, less than 15 minutes, and less than 10 min. The most preferred reaction time is from 30 minutes to 90 minutes.

According to the proposed method, the olefin and the catalytic system can be contacted with hydrogen fed into the oligomerization reactor and used as a diluent. Hydrogen can increase the activity of the organometallic catalyst, thereby accelerating the oligomerization reaction. In addition, hydrogen can reduce the amount of polymer produced as a by-product and limit the deposition of the polymer on the equipment walls.

The olefin oligomerization process is performed in the absence of water and oxygen.

An initial olefin, a solvent, and a catalytic system can be introduced into the oligomerization reactor in any order. Preferably, the components are introduced in the following order: a solvent, then a catalytic system, followed by dosing of an initial olefin. PREFERRED EMBODIMENTS OF THE INVENTION

For the examples below, the preparation of the catalytic system and the ethylene trimeri/ation process are performed as follows:

General description of techniques for preparing the catalytic system

In step A, chromium(III) 2-ethylhexanoate is mixed with 2,5-dimethylpyrrole in ethylbenzene at a chromium(III) 2-ethylhexanoate:2,5-dimethylpyrrole molar ratio of 1 :4.

In step B, the mixture prepared in step A is mixed with an activator, which is a mixture of triethylaluminum and diethylaluminum chloride, at a molar ratio of 32:15 (per 1 mol of chromium), wherein the activator is preliminarily subjected to microwave irradiation.

Microwave irradiation parameters are as follows:

- irradiation time, 6 min;

- radiation frequency, 2.45 GHz,

- radiation power, 1400 W.

General description of the ethylene trimerization process

A prepared ethylene oligomerization reactor is filled with a solvent and heated to a working temperature of 90-100°C. The catalyst is introduced at a calculated amount, and ethylene is fed.

Feed stream rates are as follows:

- catalyst, 2.0-3.5 kg/h;

- solvent, 100-200 kg/h;

- ethylene, 40-80 kg/h.

Process parameters are as follows:

Temperature, 90-110°C;

Pressure, 20-30 atmospheres;

Residence time in the reactor, 1-2 hours.

At the reactor outlet, the output stream passes the neutralization step. Then it is fed into a distillation unit to isolate the target product, recycled solvent and bottoms.

Example 1

The catalytic system is prepared according to the general description of techniques for preparing the catalytic system in a pilot plant having a unit for preparing the catalytic system configured according to scheme 1.

A solution of chromium(lll) 2-ethylhexanoate in ethylbenzene is mixed with

2,5-dimethylpyrrolc in a pipeline with a diameter of 15 mm. Then a stream of the activator previously subjected to microwave irradiation is fed into said pipeline. With that, the total flow rate of the components is approximately 1000 ml/min, which corresponds to a Reynolds number, Re _kr, of approximately 1500.

The results of the evaluation of the amount of precipitate formed and the catalytic characteristics of the system prepared in the ethylene trimerization process according to Example 1 arc given in Tabic 1 .

Example la

The catalytic system is prepared according to the general description of techniques for preparing the catalytic system in a pilot plant having a unit for preparing the catalytic system configured according to scheme 1.

A solution of chromium(lll) 2-ethylhexanoate in ethylbenzene is mixed with

2,5-dimethylpyrrolc in a pipeline with a diameter of 15 mm. Then, a stream of the activator previously subjected to microwave irradiation is fed into said pipeline through a 6-mm-diamcter pipeline, wwith that the feed rate ratio between the activator and the pre-mixed composition containing chromium(IIl) 2-ethylhexanoate in ethylbenzene and 2,5-dimethylpyrrole is 6: 1. With that, the total flow rate of the components is approximately 1000 ml/min, which corresponds to a Reynolds number, Rekr, of approximately 1500.

The results of the evaluation of the amount of precipitate formed and the catalytic characteristics of the system prepared in the ethylene trimerization process according to Example la are given in Table 1.

Example 2

The catalytic system is prepared according to the general description of techniques for preparing the catalytic system in a pilot plant having a unit for preparing the catalytic system configured according to scheme 2.

A solution of chromium(III) 2-cthylhexanoate in ethylbenzene is mixed with

2,5-dimethylpyrrolc in a pipeline with a diameter of 15 mm. The resulting mixture enters a static mixer (with a diameter of 15 mm and a length of 500 mm) equipped with plate elements. A stream of the activator previously subjected to microwave irradiation is fed into the second half of the mixer. The flow rate of the components at the mixer outlet is approximately 1000 ml/min, which corresponds to a Reynolds number, Re _kr , of approximately 1500.

The results of the evaluation of the amount of precipitate formed and the catalytic characteristics of the system prepared in the ethylene trimerization process according to Kxample 2 are given in Table 1 .

Example 3

The catalytic system is prepared according to the general description of techniques for preparing the catalytic system in a pilot plant having a unit for preparing the catalytic system configured according to scheme 2.

A solution of chromium(III) 2-cthylhexanoate in ethylbenzene is mixed with 2,5-dimethylpyrrole in a pipeline with a diameter of 15 mm. The resulting mixture enters a static mixer (with a diameter of 15 mm and a length of 500 mm) equipped with plate elements. A stream of the activator previously subjected to microwave irradiation is fed into the second half of the mixer. The flow rate of the components at the mixer outlet is approximately 1580 ml/min, which corresponds to a Reynolds number, Re _kr , of approximately 2300.

The results of the evaluation of the amount of precipitate formed and the catalytic characteristics of the system prepared in the ethylene trimerization process according to Example 3 are given in Table 1.

Example 4

The catalytic system is prepared according to the general description of techniques for preparing the catalytic system in a pilot plant having a unit for preparing the catalytic system configured according to scheme 1.

A solution of chromium(III) 2-ethylhexanoate in ethylbenzene is mixed with 2,5-dimethylpyrrole in a pipeline with a diameter of 15 mm. Then, a stream of the activator previously subjected to microwave irradiation is fed into said pipeline through a 6-mm-diameter pipeline, wwith that the feed rate ratio between the activator and the pre-mixed composition containing chromium(lll) 2-ethylhexanoate in ethylbenzene and 2,5-dimethylpyrrole is 6: 1. With that, the total flow rate of the components is approximately 1580 ml/min, which corresponds to a Reynolds number, Rekr, of approximately 2300. The results of the evaluation of the amount of precipitate formed and the catalytic characteristics of the system prepared in the ethylene trimerization process according to Example 4 are given in Table l.

Example 5

The catalytic system is prepared according to the general description of techniques for preparing the catalytic system in a pilot plant having a unit for preparing the catalytic system configured according to scheme 3.

A solution of chromium(lll) 2-cthylhexanoate in ethylbenzene is mixed with 2,5-dimethylpyrrole in a pipeline with a diameter of 15 mm. The resulting mixture enters static mixer 1 (with a diameter of 15 mm and a length of 500 mm), equipped with plate elements. A stream of the activator previously subjected to microwave irradiation is fed into the pipeline at the outlet of mixer 1. The mixture prepared as a result of mixing with the activator enters a static mixer 2 (with a diameter of 15 mm and a length of 500 mm) equipped with plate elements. The flow rate of the components at the outlet of mixer 2 is approximately 1800 ml/min, which corresponds to a Reynolds number, Re _kr , of approximately 2700.

The results of the evaluation of the amount of precipitate formed and the catalytic characteristics of the system prepared in the ethylene trimerization process according to Example 5 are given in ^' fable 1.

Example 5a

The catalytic system is prepared similarly to example 5. However, for performing the ethylene trimerization process, the solution flow rate of the resulting catalytic system is increased, taking into account the loss of the active component of the catalytic system in the form of precipitate.

The results of the evaluation of the amount of precipitate formed and the catalytic characteristics of the system prepared in the ethylene trimerization process according to Example 5a arc given in Table 1.

Example 6

The catalytic system was prepared similarly to example 5, but with a flow rate at the outlet of mixer 2 equal to 5000 ml/min, which corresponds to a Reynolds number, Re _kr , of approximately 7550.

The results of the evaluation of the amount of precipitate formed and the catalytic characteristics of the system prepared in the ethylene trimerization process according to Example 6 are given in Table 1.

Example 6a

The catalytic system was prepared similarly to example 6, but for performing the ethylene trimerization process, the solution flow rate of the resulting catalytic system is increased, taking into account the loss of the active component of the catalytic system in the form of precipitate.

The results of the evaluation of the amount of precipitate formed and the catalytic characteristics of the system prepared in the ethylene trimerization process according to Example 6a are given in Table 1.

Example 6b

The catalytic system was prepared similarly to example 5, but with a flow rate at the outlet of mixer 2 equal to 6000 ml/min, which corresponds to a Reynolds number, Re _kr, of approximately 9000.

The results of the evaluation of the amount of precipitate formed and the catalytic characteristics of the system prepared in the ethylene trimerization process according to Example 6b are given in Table 1.

Example 7

The catalytic system is prepared according to the general description of techniques for preparing the catalytic system in a pilot plant having a unit for preparing the catalytic system configured according to scheme 4.

A solution of chromium(III) 2-ethylhexanoate in ethylbenzene is mixed in a pipe with 2,5-dimethylpyrrole and delivered to a paddle mixer having an H/D aspect ratio of 3 (11 is the mixer height, D is the mixer diameter). Then a stream of the activator previously subjected to microwave irradiation is fed into said mixer, wherein the rotational speed of the paddle mixer is 48 rpm, which corresponds to a Reynolds number, Rci,,, of 1500.

The results of the evaluation of the amount of precipitate formed and the catalytic characteristics of the system prepared in the ethylene trimerization process according to Example 7 are given in ^' fable 1.

Example 7a

The catalytic system is prepared according to the general description of techniques for preparing the catalytic system in a pilot plant having a unit for preparing the catalytic system configured according to scheme 4.

A solution of chromium(IIl) 2-ethylhexanoatc in ethylbenzene is mixed in a pipe with 2,5-dimethylpyrrole and delivered to a paddle mixer having an H/D aspect ratio of 3 (H is the mixer height, D is the mixer diameter). Then a stream of the activator previously subjected to microwave irradiation is fed into said mixer, wherein the rotational speed of the paddle mixer is 240 rpm, which corresponds to a Reynolds number, Re _kr , of 7500.

The results of the evaluation of the amount of precipitate formed and the catalytic characteristics of the system prepared in the ethylene trimerization process according to Example 7a are given in fable 1.

Table 1. Comparative table of experiment data for preparing a catalytic system for ethylene trimerization

According to the data presented in fable 1, one can conclude that the rate of the combined stream containing the pre-mixed composition and the activator, expressed as the Reynolds number, has a significant effect on the amount of precipitate formed in the trimerization reactor. Thus, for instance, in Example 1, when the Reynolds number is 1500, the amount of precipitate formed is 0.03 wt.% based on the total, and in Example 6b where the Reynolds number is 9000 the amount of precipitate is 0.28 wt.%. Therefore, an increase in the Reynolds number leads to an increase in the amount of unwanted precipitate.

In addition, it was noted that a large amount of precipitate adversely affected the process equipment due to deposits formed on the component parts of the equipment (for clarity, see Fig. 5 and Fig. 6).

In addition, a relationship was found between the amount of undesirable precipitate and the activity and selectivity of the catalytic system. Thus, the greater the amount of precipitate, the lower the activity and the selectivity of the catalytic system were. Presumably, the reason for decreased activity and selectivity of the catalytic system is a decrease in the number of active centers in the catalytic system, capable of interacting with ethylene in the trimerization reaction, which is associated with changes in the composition of the catalytic system due to precipitation.

It was also found that the supply of the activator for mixing with a pre-mixed composition through a pipeline with diameter smaller than the diameter of the pipeline for supplying a pre-mixed composition provided an insignificant reduction in the amount of precipitate (examples 1 and la).