RU2525118C1 - Catalyst system for trimerisation of ethylene to alpha-olefins - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: catalyst system includes a complex of chromium with a diphosphine ligand of general formula [(Ph₂PXPPh₂)Cr(THF)Cl₃] or [(Ph₂P(1,2-C₆H₄)PPh(1,2-C₆H₄)CH₂OC₂H₅)]CrCl₃, where X is selected from: a hydrocarbon biradical or a substituted hydrocarbon biradical, and also includes methylaluminoxane (activator) and trimethylaluminium (coactivator). Components of the system are in the following molar ratio: chromium complex:activator:coactivator = 0.12-0.13% : 24.97-42.22% : 57.66-74.91%.

EFFECT: high selectivity of the catalyst with respect to 1-hexene while maintaining efficiency of the catalyst system and reducing the amount of ethylene polymerisation by-products.

2 cl, 3 tbl, 19 ex

Description

The invention relates to organic chemistry, and in particular to a technology for the selective production of ethylene by 1-hexene tri -merization.

1-Hexene is an important commercial intermediate, widely used as a comonomer in the production of linear low density polyethylene.

The known technology of ethylene oligomerization using a catalytic mixture consisting of diphosphine ligands, “precursors” (chromium complexes — tris (tetrahydrofuran) chromium (III) trichloride, chromium (III) tris (acetylacetonate), chromium (III) 2-ethylhexanoate and activator - methylalumoxane (US2010145724).

A disadvantage of the technology is a high percentage of secondary polymer (minimum - 2%, on average 2-4%). It should be noted that in the catalyst system as part of the “precursors” there are unbound ligands (tetrahydrofuran, acetylacetonate, 2-ethylhexanoate), which are able to interact with the activator and reduce the catalytic activity of the system.

Closest to the claimed technology is the two-stage activation of the “oligomerization catalyst” (US 2010240847) (rather, it is not a catalyst with a specific structure, but a catalytic system — a mixture of Cr complexes and ligands), where the system is first activated with methylaluminoxane and then trialkylaluminium is added. But the process is characterized by selectivity for 1-octene, and not for 1-hexene, and not a ready-made chromium complex is used, but a mixture of a ligand and a "precursor" (a complex of chromium — tris (tetrahydrofuran) chromium (III) trichloride, tris (acetylacetonate) chromium (III), chromium (III) 2-ethylhexanoate).

The described technology has the following disadvantages: the process is difficult to control, because the activity of the catalyst is greatest in the first minutes of the process, then it drops sharply and the formation of polymer is observed and the actual activity of the catalyst is much less than claimed; unbound ligands (tetrahydrofuran), acetylacetonate or 2-ethylhexanoate are present in the reaction mixture, which interact with the activator and the addition of a coactivator, worsening the performance of the process.

The objective of the invention is to develop a productive catalytic system for the trimerization of ethylene in 1-hexene.

The technical result consists in achieving a selectivity of the catalyst for 1-hexene from 50 wt.% To 90 wt.% And higher with high productivity of the catalytic system and at the same time reducing the amount of by-products of ethylene polymerization.

The technical result is achieved by using a complex of chromium with a diphosphine ligand of the general formula [(Ph ₂ PXPh ₂ ) Cr (TNF) Cl ₃ ], where X is selected from the group: hydrocarbon diradical or substituted hydrocarbon diradical, and an activator is used, which is used as methylaluminoxane, and coactivator, which is used trimethylaluminum, while the system components are in the following ratio: chromium complex: activator: coactivator = 0.12-0.13%: 24.97-42.22%: 57.66-74.91 % According to the second option, in contrast to the first, a complex of chromium with a diphosphine ligand of the formula [(Ph ₂ P (1,2-C ₆ H ₄ ) PPh (1,2-С ₆ Н ₄ ) СН ₂ ОС ₂ Н ₅ )] CrCl _{3 is used} .

Chromium complexes containing tetrahydrofuran molecules as a ligand or monomeric chromium diphosphine complexes having an additional heteroatom in the ligand structure capable of coordination with a metal atom can serve as chromophosphine complexes in the catalyst system. Examples of the complexes used are the following compounds:

Activators may include commercially available aluminoxanes methylaluminoxane, modified methylaluminoxane, ethylaluminoxane, isobutylaluminoxane. Of these, methylaluminoxane and modified methylaluminoxane are preferred.

Co-activators may be commercially available trimethylaluminum, triethylaluminum, tri-n-butylaluminum, tri-isobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. The most preferred coactivator is trimethylaluminum.

The task and technical result are achieved with the following methods for obtaining complexes and conditions for the oligomerization process:

1,2-bis (diphenylphosphine) benzene used for the synthesis of chromium complex 1 is a commercial product, diphosphines for the preparation of complexes 2-4 were synthesized using methods similar to those described in the examples of US2008058486.

Examples of the preparation of diphosphine complexes of chromium.

Example 1 (synthesis of complex 1)

To 0.4 mmol of tris (tetrahydrofuran) chromium (III) chloride, a solution of 0.44 mmol of 1,2-bis (diphenylphosphine) benzene in 6 ml of dry toluene was added, the mixture was stirred for 16-20 hours at room temperature, then heated under argon flow to 90 ° C, stirred for 60 minutes, then cooled again to room temperature. The precipitate was filtered off, washed with toluene, dried in vacuo.

Example 2 (synthesis of complex 2)

The example is similar to example 1, but instead of 1,2-bis (diphenylphosphino) benzene was taken 1,2-bis (diphenylphosphino) -4,5-dimethoxybenzene.

Example 3 (synthesis of complex 3)

The example is similar to example 1, but instead of 1,2-bis (diphenylphosphino) benzene was taken 1,2-bis (diphenylphosphino) -4,5-dimethylbenzene.

Example 4 (synthesis of complex 4)

The example is similar to example 1, but instead of 1,2-bis (diphenylphosphino) benzene was taken [2- (diphenylphosphino) phenyl] [2-ethoxymethyl) phenyl] phenylphosphine.

The output and data of elemental analysis of complexes 1-4 are presented in table 1.

Table 1 Data of elemental analysis of complexes 1-4 Complex (yield,%) C, wt.%, Practical. (C wt.%, Theory.) H, wt.%, Practical. (H wt.%, Theory.) P%, practical. (P wt.%, Theor.) 1 (97) 59.65 (60.33) 4.52 (4.76) 8.80 (9.15) 2 (92) 58.57 (58.67) 4.67 (4.92) 8.66 (8.41) 3 (96) 61.45 (61.33) 4.95 (5.15) 8.19 (8.79) 4 (96) 59.85 (59.79) 4.45 (4.56) 9.23 (9.35)

Example 5

Methodology for oligomerization using a diphosphine complex of chromium (III) 1.

A catalytic mixture was used with the following molar ratio of active components [chromium diphosphine complex]: [MAO] = 0.12%: 99.88%.

The preparation of catalytic solutions was carried out in a Schlenk vessel in an inert atmosphere of argon. A portion of complex 1 (0.61 mg) was loaded in a stream of argon, 5 ml of absolute methylcyclohexane was added. The catalytic solution was stirred for 15 minutes at room temperature. Then 0.6 ml of a 10% solution of methylaluminoxane in toluene was added, after which it was stirred for another 5 minutes and introduced into an autoclave in a stream of argon. After loading the obtained catalyst system into the autoclave, the ethylene supply was turned on and it was not interrupted during the entire experiment. The temperature and pressure in the autoclave were kept constant during the experiment (temperature 85 ° C, pressure 20 bar). After the reaction time (30 minutes), the ethylene supply was shut off, heating and stirring were turned off. After cooling and depressurization, methanol was introduced into the autoclave to decompose the catalyst system and an internal standard (n-decane; 0.2-0.8 g) was stirred for 10 minutes. After autoclaving, 10 ml of a 20% aqueous solution of HCl and 5 ml of toluene were added to the reaction mass.

Example 6

Similar to example 5, but instead of complex 1, complex 2 was used in an amount of 0.63 mg.

Example 7

Similar to example 5, but instead of complex 1, complex 3 was used in an amount of 0.60 mg.

Example 8

Similar to example 5, but instead of complex 1, complex 4 was used in an amount of 0.56 mg.

For comparison, experiments were also carried out, including the preparation of a chromium complex in situ (a mixture of a chromium "precursor" and diphosphine ligand is present in the catalytic system). The procedure is similar to that described in examples 5-8, except that a non-ready complex 1-4 was taken, but a mixture of the chromium “precursor” was prepared — tris (tetrahydrofuran) chromium (III) chloride or chromium acetylacetone and the corresponding diphosphine ligand. A catalytic mixture was used with the following molar ratio of active components, [chromium complex "precursor"]: [diphosphine]: [MAO] = 0.16%: 0.16%: 99.68%.

Example 9. Similar to example 5, but instead of a sample of the chromium diphosphine complex, a sample of tris (tetrahydrofuran) chromium (III) chloride (0.71 mg) and 1,2-bis (diphenylphosphino) benzene (0.86 mg) was taken.

Example 10

Similar to example 5, but instead of a sample of the chromium diphosphine complex, a sample of chromium (III) acetylacetonate (0.66 mg) and 1,2-bis (diphenylphosphino) -4,5-dimethoxybenzene (0.98 mg) was taken.

Example 11

Similar to example 5, but instead of a portion of the chromium diphosphine complex, a portion of chromium (III) acetylacetonate (0.65 mg) and 1,2-bis (diphenylphosphino) -4,5-dimethyl benzene (0.90 mg) were taken.

Example 12

Similar to example 5, but instead of a portion of the chromium diphosphine complex, a portion of chromium (III) acetylacetonate (0.67 mg) and [2- (diphenylphosphino) phenyl] [2-ethoxymethyl) phenyl] phenylphosphine (0.90 mg) were taken.

Table 2 shows the results of ethylene oligomerization on diphosphine chromium catalysts with methylaluminoxane as an activator (examples 5-8). Comparison with ethylene oligomerization data using mixtures of the chromium "precursor" and diphosphine ligand (examples 9-12). Numbers of relevant examples are given in parentheses.

table 2 Comparison of the performance of ethylene trimerization catalytic systems based on diphosphine chromium complexes with the performance of systems based on mixtures of chromium "precursors" and diphosphine ligands Complex Productivity, kg / g Cr * h (example number) 1-hexene selectivity, wt.% (Example number) Polymer selectivity, wt.% (Example number) ready complex with ligand L precursor + ligand L ready complex ligand L precursor + ligand L ready complex ligand L precursor + ligand L one 253.8 (5) 2.4 (9) 50.3 (5) 30.4 (9) 0.43 (5) 5.5 (9) 2 255.5 (6) 83.5 (10) 55.8 (6) 57.6 (10) 1.52 (6) 2.9 (10) 3 218.3 (7) 7.5 (11) 54.3 (7) 30.3 (11) 0.77 (7) 3.9 (11) four 33.3 (8) 29.7 (12) 90.0 (8) 89 (12) 1.52 (8) 0.6 (12)

As can be seen from table 2, the use of the finished complex significantly increases the performance of the catalytic system, and in examples 5 and 7, the selectivity for 1-hexene. In example 6, the selectivity of the catalytic system for 1-hexene is slightly reduced, but remains above 50%, which exceeds the same indicator for the catalytic systems presented in the prototype.

Next, a coactivator was introduced into the catalytic system while maintaining the total sum of activator and coactivator concentrations in the system.

Example 13

A catalytic mixture was used with the following molar ratio of active components [chromium diphosphine complex]: [MAO]: [TMA] = 0.13%: 42.21%: 57.66%. The experiment is similar to that shown in example 5, but to a solution of the chromium (III) diphosphine complex (1) taken in the same amount as in example 5, instead of 0.6 ml, 0.25 ml of a 10% solution of methylaluminoxane in toluene was added, after which was stirred for 5 minutes, was introduced into the autoclave in a stream of argon. Then, 0.3 ml of a 1.36 M trimethylaluminum solution was additionally introduced into the autoclave. Further, the experiment was conducted as described in example 5.

Example 14

A catalytic mixture was used with the following molar ratio of active components [chromium diphosphine complex]: [MAO]: [TMA] = 0.13%: 42.18%: 57.70%. The experiment is similar to example 13, but instead of complex 1, complex 2 was used.

Example 15

A catalytic mixture was used with the following molar ratio of active components [chromium diphosphine complex]: [MAO]: [TMA] = 0.12%: 42.22%: 57.66%. The experiment is similar to example 13, but instead of complex 1, complex 3 was used.

Example 16

A catalytic mixture was used with the following molar ratio of active components [chromium diphosphine complex]: [MAO]: [TMA] = 0.12%: 24.97%: 74.91%. The experiment is similar to that described in example 5, but to a solution of the chromium (III) diphosphine complex (1) taken in the same amount as in example 5, instead of 0.6 ml, 0.15 ml of a 10% solution of methylaluminoxane in toluene was added, after which was stirred for 5 minutes, was introduced into the autoclave in a stream of argon. Then, 0.4 ml of a 1.36 M solution of trimethylaluminum in toluene was additionally introduced into the autoclave. Further, the experiment was conducted as described in example 5.

Example 17

A catalytic mixture was used with the following molar ratio of active components [chromium diphosphine complex]: [MAO]: [TMA] = 0.12%: 25.00%: 74.88%. The experiment is similar to example 16, but instead of complex 1, complex 2 was used.

Example 18

A catalytic mixture was used with the following molar ratio of active components [chromium diphosphine complex]: [MAO]: [TMA] = 0.12%: 25.00%: 74.88%. The experiment is similar to example 16, but instead of complex 1, complex 3 was used.

Example 19

A catalytic mixture was used with the following molar ratio of active components [chromium diphosphine complex]: [MAO]: [TMA] = 0.12%: 42.17%: 57.71%. The experiment is similar to that in Example 8, but to a solution of the chromium (III) diphosphine complex (4) taken in the same amount as in Example 8, instead of 0.6 ml, 0.15 ml of a 10% solution of methylaluminoxane in toluene was added, after which was stirred for 5 minutes, was introduced into the autoclave in a stream of argon. Then, 0.4 ml of a 1.36 M solution of trimethylaluminum in toluene was additionally introduced into the autoclave. Further, the experiment was conducted as described in example 8.

Table 3 shows the effect of replacing a portion of methylaluminoxane with trimethylaluminum on ethylene oligomerization indices on diphosphine chromium catalysts (a ready-made complex of chromium with a ligand) with methylaluminoxane and trimethylaluminium as activators (for comparison, indicators of processes without the addition of a coactivator under the same experimental conditions are also shown). It can be seen from the experiments that, at a molar ratio of Cr: MAO: TMA of 0.13: 42.21: 57.66, the productivity of the catalyst system increases by 15-29% with a significant decrease in the amount of polymer formed. In all three examples (examples 13-15), the process remains selective for 1-hexene, although the selectivity does not exceed 57.6%.

Table 3

Example [Cr], × 10 ⁵ mmol / ml [MAO], × 10 ² mmol / ml [TMA], × 10 ² mmol / ml The molar% ratio of Cr: MAO: TMA in the catalytic mixture Produce, kg / g _Cr * H Selectivity, wt.% poly measures C ₄ C ₆ C ₈ C ₁₀ 1-C ₆ to C ₆ Complex 1 5 3,59 2.81 - 0.12: 99.88: 0 253.8 0.43 6.3 50.3 29.7 13.3 86.9 13 3.52 1.17 1,60 0.13: 42.21: 57.66 294.6 0.02 0.5 56.3 32.9 10.3 87.7 16 3.40 0.70 2.11 0.12: 24.97: 74.91 212.7 0.04 0.5 57.4 33,2 9.0 88.0 Complex 2 6 3.32 2.81 - 0.12: 99.88: 0 255.5 1,52 0.5 55.8 27,2 14.9 88.6 fourteen 3.37 1.17 1,60 0.12: 42.18: 57.70 330.1 0.13 0.6 57.6 29.4 12.1 87.6 17 3.33 0.70 2.11 0.12: 25.00: 74.88 142.7 0.16 0.5 63.8 26.8 7.7 89.2 Complex 3 7 3.32 2.81 - 0.12: 99.88: 0 218.3 0.77 0.5 54.3 29.6 14.8 86.8 fifteen 3.33 1.17 1,60 0.12: 42.22: 57.66 278.8 0.19 0.4 56.8 31.5 10.0 87.5 eighteen 3.33 0.70 2.11 0.12: 25.00: 74.88 173.9 0,07 0.4 56.8 33.8 9.0 87.3 Complex 4 8 3.32 2.81 - 0.12: 99.88: 0 33.3 1,52 0.7 90.0 4.0 3,7 97.3 19 3.25 1.17 1,60 0.12: 42.17: 57.71 33.5 0.54 1,1 92.0 4.9 1.4 97.8

With a further increase in the coactivator fraction for catalytic systems based on complexes 1–3, the productivity decreases by 27–56%, but the systems remain selective for 1-hexene. In the case of using a catalyst system based on a complex of chromium 4, the process is highly selective for 1-hexene (selectivity of more than 90%), the introduction of a coactivator in this case practically does not affect the performance of the system, but the polymer selectivity decreases by 65% (a similar effect is observed in all examples of using the activator / coactivator system (examples 13-19)).

As can be seen from the results, the use of the claimed catalytic systems for the trimerization of ethylene in 1-hexene, activated by a mixture of the claimed activator and co-activator, leads to the combined effect of obtaining 1-hexene with high productivity and selectivity above 50%, while at the same time significantly reducing side-forming polymers. The use of the complex [(Ph ₂ P (1,2-C ₆ H ₄ ) PPh (1,2-С ₆ Н ₄ ) СН ₂ ОС ₂ Н ₅ )] CrCl ₃ promotes a highly selective process of formation of 1-hexene (selectivity higher than 90 %) also with minimal polymer formation.

Claims (2)

1. The catalytic system of the process of trimerization of ethylene into α-olefins, including a complex of chromium with a diphosphine ligand of the general formula [(Ph ₂ PXPPh ₂ ) Cr (THF) Cl ₃ ], where X is selected from the group: hydrocarbon diradical or substituted hydrocarbon diradical, and includes an activator, which is used methylaluminoxane and a coactivator, which is used trimethylaluminum, while the system components are in the following molar ratio: chromium complex: activator: coactivator = 0.12-0.13%: 24.97-42.22 %: 57.66-74.91%. 2. The catalytic system of the process of trimerization of ethylene into α-olefins, including a complex of chromium with a diphosphine ligand of the formula [(Ph ₂ P (1,2-C ₆ H ₄ ) PPh (1,2-C ₆ H ₄ ) CH ₂ OC ₂ H ₅ )] CrCl ₃ , an activator, which is used methylaluminoxane, and a coactivator, which is used trimethylaluminium, while the system components are in the following molar ratio: chromium complex: activator: coactivator = 0.12-0.13%: 24 97-42.22%: 57.66-74.91%.