Process for the preparation of solutions of oligomeric methylaluminoxanes.

The invention relates to the preparation of solutions of oligomeric methylaluminoxanes, optionally containing higher alkyl groups, which contain trimethylaluminum in free and / or complexed form; aliphatic, cycloaliphatic or aromatic hydrocarbons serve as solvents.

Longer chain oligomeric and / or polymeric alkylaluminoxanes of the simplified structures<chemistry id="chem0001" num="0001"><img file="EP0442300A2_D0001.tif" /></chemistry> are known compounds that are used as catalyst components in the production of highly active polyolefin catalysts, some of which are oligomeric methylaluminoxanes (MAO) with R = CH₃ as preferred (DE-A-30 07 725, EP-B-0 069 951, DE-A-32 40 382, EP-A-0 170 059, DE-A-34 43 087, EP-B-0 128 046, US-A-4 665 046, EP-A-0 232 595, US-A-4 668 838, US-A-4 665 047, EP-A-0 241 560, WO 87/03887, EP-A-0 237 294).

The reaction of aluminum trialkyls with water in inert hydrocarbons is mentioned as a known production process for alkylaluminoxanes. Mainly for the production of oligomeric methylaluminoxanes (MAO) from trimethylaluminum (TMA) but other methods are mentioned as preferred, since it is known from the literature that after the z. B. in US-A-3 242 099 production method described in more detail by slow addition of water to trimethyl aluminum (TMA) MAO can be produced only with difficulty and in very poor yield (EP-A-0 108 339); In addition, products are obtained which, together with the transition metal component, do not result in highly active catalyst systems (EP-B-0 069 951).

In J. Polymer Science, <u style="single">23</u>, No. 8 (p. 2120) is explicitly stated: "Simple synthetic routes to the methyl aluminoxane [-O-Al (CH₃) -]_n are not available owing to the extremely high reactivity of the parent trimethylalane. This notwithstanding, the synthesis through direct reaction between Al (CH₃) ₃ and H₂O in a 1: 1 molar ratio in toluene solution has been reported. We found this method not very reliable. The degree of oligomerization of the resulting aluminoxane was scarcely reproducible and the reaction rather uncontrollable. "

These deficiencies should be remedied by reacting trimethyl aluminum (TMA) with salts containing water of crystallization, such as aluminum sulfate hydrate (EP-A-0 108 339) or generally hydrates of such salts which are not reduced under the reaction conditions (EP-A-0 0 208 561), or in another procedure by reacting TMA with inorganic substances which contain water bound by absorption or adsorption, such as finely divided silicon dioxide (WO-A-89/02453), Aluminum oxide (WO-A-89/02453), aluminum hydroxide (EP-A-0 315 234) or molecular sieves (Diss. I. Herwig, University of Hamburg, 1979).

The latter production methods naturally require additional technical and cost expenditure; They have the considerable disadvantage that the solids used generally have to be comminuted and sieved for good meterability (in particular salts containing water of crystallization) and, moreover, their water content has to be precisely adjusted and controlled for targeted and reproducible implementation. In addition, long reaction times and, at least at the beginning of the reaction, often low temperatures are required (EP-A-0 315 234, WO-A-89/02453), which not only results in correspondingly lower space / time yields, but also an increased technical level or energy expenditure result.

There was therefore a need for a simple process for the preparation of oligomeric MAO which, in good yield, gives a product which is soluble in inert hydrocarbons and, using special transition metal compounds, gives highly active catalyst systems for the polymerization of olefins.

Such a method is provided by the invention. According to the process according to the invention, solutions of oligomeric, optionally higher alkyl group-containing methylaluminoxanes (MAO) which contain trimethylaluminum (TMA) in free and / or complexed form are prepared by adding a solution of TMA and optionally further aluminum alkyls in inert aliphatic, cycloaliphatic or aromatic Hydrocarbons, preferably toluene, with water in a molar ratio of H₂O / TMA from 0.55 to 0.75 and subsequently separating the insoluble by-products formed in the reaction. The clear solutions of oligomeric MAO obtained can be used directly without further purification steps for the preparation of polymerization catalysts.

The starting materials are used in amounts such that the concentration of the MAO in the solvent used is in the range from 1 to 20% by weight, preferably 1 to 10% by weight. The concentrations can then be increased by condensing the solvent under mild conditions, preferably to 10 to 50% by weight of MAO. Even solid methylaluminoxane (MAO) can be obtained in this way by completely removing the solvent. Unreacted TMA, the z. T. passes over, can advantageously be used again for the production of MAO.

Aromatic hydrocarbons, especially alkylbenzenes, e.g. As toluene or xylene, and saturated aliphatic and cycloaliphatic hydrocarbons, such as heptane, into consideration.

The reaction is preferably carried out by slowly adding water to a solution of TMA in one of the hydrocarbons mentioned above, keeping the reaction temperature in a range from -50 ° C to 100 ° C. However, it is usually sufficient to work at a temperature of 0 to 50 ° C.

In order to avoid uncontrolled reactions in view of the relatively high exothermic nature of the reaction of TMA with water, the addition of the water to the solution of TMA should take place slowly and, at the same time, adequate heat dissipation should be ensured. Any insoluble by-products obtained are separated from the solution by customary measures, such as filtration, centrifugation or decanting.

Because of the reactivity of TMA and MAO towards atmospheric oxygen, the production of MAO has to be carried out under an inert gas atmosphere.

The reaction product obtained is a solution of an oligomeric methylaluminoxane (MAO) which contains unreacted TMA in free and / or complexed form. Such a solution is particularly suitable as a catalyst component for the production of highly active polyolefin catalysts. The MAO can also be isolated in solid form as described in Example 1. The solid is an oligomer with an average molecular weight of about 800 to 3000 g / mol.

The process according to the invention can also be used to prepare methylaluminoxanes which additionally contain higher alkyl groups (for example ethyl, butyl, isobutyl, hexyl, octyl) in the range from 5 to 20 mol%. on methyl, preferably 10-15 mol%. The incorporation of the higher alkyl groups results in better solubility in hydrocarbons, which is particularly advantageous in the case of aliphatic hydrocarbons, for example heptane (example 7), since pure MAO is poorly soluble in such solvents (example 6).

Contrary to the prevailing view in the professional world up to now that an H₂O / TMA molar ratio of about 1 must be observed for the production of an active MAO (US Pat. No. 3,242,099, EP-A-0 241 560, EP-A-0 208 561) and then by adding water to TMA - see e.g. B. US-A-3 242 099 or J. Polymer Science,<u style="single">23</u>, No. 8 p. 2120) - no catalytically active MAO is to be obtained, it was surprising that by the inventive simple and inexpensive process by reaction of TMA and water with a molar ratio of H₂O / TMA from 0.65 to 0.75, solutions from MAO can be obtained are, which are characterized in connection with special transition metal complexes by a high catalytic activity in the polymerization of olefins. A very active MAO is obtained in this area, which has a sufficiently high average molecular weight and good solubility in alkylbenzenes, e.g. B. toluene. In the procedure described in Examples 1 to 3, MAO is thus obtained in yields of 46-48%, based on the isolated solid. The proportion of insoluble by-products is relatively low and can be easily separated.

It was found that above a molar ratio of H₂O / TMA of 0.75, in particular close to a molar ratio of 1, the yield of soluble MAO drops drastically. The reaction also proceeds with strong foaming and a very strong precipitation of white solid appears (Comparative Example 1).

On the other hand, if the molar ratio of H₂O / TMA is below the range from 0.65 to 0.75 according to the invention, the yield of MAO decreases rapidly, making the process uneconomical (Comparative Examples 2 and 3).

Since it is advantageous to ensure thorough mixing of the reactants, various technical measures have been proposed for the production of MAO, such as, for example, ultrasound (EP-A-0 257 695) or stirrers with very high rotational speeds ("high shear-inducing") impeller "- EP-A 0 258 924). However, no further improvement of the method according to the invention by using these techniques could be found. There were only yields of MAO of 42% and 44% of theory. Th., Based on isolated solid (Comparative Examples 4 and 5). If one works with the above-mentioned mixing techniques according to EP-A-0 257 695 and EP-A-0 258 924 according to the regulations and operating conditions given there, MAO solutions of very low concentration (1-2% by weight) are obtained. ). Particularly good implementation results are now surprisingly obtained, even outside the preferred range for the H₂O / TMA molar ratio of 0.65 to 0.75, if the circulated solution of TMA in a hydrocarbon used the water required for the reaction in the range a turbulence field, which is generated in the external circuit by a liquid feeder. A rotor / stator reaction machine is particularly suitable for generating such a turbulence field. Such a rotor / stator reaction machine is described in structure and function, for example in DE-A-2 363 888.

As can be seen from FIG. 2, a stator (2.2) and a rotor tool set (2.3) are located in a housing (2.1). Both tool sets consist of concentrically arranged, ring-shaped individual tools that are provided with radially milled slots or bores. They are designed so that they work with a small gap distance from each other.

The stator tool set is fixed in the machine, while the rotor tool set is driven at high speed. The rotor tool set rotates in the annular gaps between the individual stator tool rings in such a way that one tool ring works in the space between two other tool rings.

When passing through the machine, the reaction components are alternately accelerated centrifugally in the rotor tools and set at high circumferential speeds in order to be braked again in the next stationary stator tool and to be steered in the radial direction. This creates high shear forces. This process is so frequent due to the speed and the tool configuration that product swirling is particularly good and a reactant, which is introduced into the system through a metering hole (4) at a suitable point in the housing, in a fraction of a second into the one flowing through the machine Reaction mixture can be incorporated homogeneously and reacted spontaneously. It does not matter whether the machine is installed inside a conventional stirred tank or externally.

The method according to the invention is explained in more detail below with reference to FIG. 1.

The TMA solution is expediently placed in a conventional stirred tank (1) which works in conjunction with the rotor / stator reaction machine (2), the contents of the stirred tank being fed to the rotor / stator reaction machine by a free inlet or by a pump ( 3) and is returned to the stirred tank after leaving the reaction machine.

The reaction of TMA with water takes place in the externally installed reaction machine (2), into which the water in the region of the turbulence field is metered in using a metering pump (6). The homogeneous incorporation of the water described above is supported and reinforced by the development of the gas methane that takes place during the implementation with TMA. The stirred tank content (4) flowing through the reaction machine then flows back into the stirred tank (1), where the heat of reaction and the additional heat generated by the drive power are dissipated through appropriate heat exchange surfaces (5) and any waste gas quantities are separated from the liquid and via the exhaust gas outlet (7) can be removed.

As can be seen from Examples 4 and 5, this process using a rotor / stator reaction machine represents a surprisingly simple variant for the economical production of MAO from TMA and water on an industrial scale. It is particularly characterized by high yields and high space-time - Yields to MAO. Solid by-products only arise to a minor extent. The technically very simple structure and, at the same time, easily controllable reaction procedure allows the production of MAO in reproducible quality with very short reaction times. In this way, the yield of soluble MAO can be increased by more than 20%. Furthermore, the reaction can be carried out conveniently at room temperature, which results in a significant saving in cooling energy.

example 1

1047 g of a solution of 92.3 g (1.28 mol) of trimethylaluminum (TMA) in were placed in a 2 liter three-necked flask equipped with a stirrer, a cooler, a 10 ml three-ring syringe and a nitrogen buffer system 954.7 g of toluene added. The solution was cooled to 2 ° C. With stirring, 15.8 g (0.88 mol) of distilled water were then added dropwise through the triple ring syringe at an internal temperature of 2 to 6 ° C. over the course of about 2 hours. The methane formed in the reaction was passed into a fume cupboard. The molar ratio H₂O / TMA was 0.7.

At the beginning of the reaction, fog formation in the gas space and turbidity in the reaction solution were observed. With the progressive addition of water, the formation of a white solid which was insoluble in the reaction mixture began.

After the addition of water had ended, the reaction mixture was heated to 50 ° C. and boiled under reduced pressure (approx. 100 mbar) under reflux in order to remove dissolved methane. Insoluble by-products were then removed by filtration under nitrogen. The amount of insoluble by-product after drying in vacuo was 25 g or 27% (based on the TMA used).

925.5 g of a clear and colorless solution which contained MAO in soluble form and unconverted TMA were obtained as the filtrate. The Al content of the solution was 2.5% by weight. Thereafter, this solution contained 23.1 g (0.86 g atom) of Al. The yield of Al in solution, based on Al in the TMA used, was thus 67%. The proportion of Al which could be determined by titration with isoquinoline was 1.0% by weight, corresponding to an amount of 9.24 g (0.34 g atom) of Al. 104 g of the solution thus obtained were subjected to vacuum distillation under mild conditions. In this way, 4.8 g of MAO were isolated as a white solid, corresponding to a yield of 46%, based on Al in the TMA used. The Al content of the isolated solid was 39.6% by weight. 8.3% by weight of Al was determined by titration with isoquinoline. During the hydrolysis of the solid, 533 Nml / g methane was formed. The average molecular weight was determined to be 1500 g / mol (cryoscopy in benzene).

Example 2

Analogously to Example 1, water and TMA were reacted in a molar ratio of 0.65.

The filtrate obtained was 912 g of a clear and colorless solution which contained soluble MAO and unreacted TMA. The Al content of the solution was 2.7% by weight.

The filtrate was then concentrated in a distillation apparatus by distilling off 501 g of toluene under reduced pressure (approx. 100 mbar). The distilled toluene contained 8 g TMA or 8.7% of the TMA used.

400 g of a clear and colorless solution which contained soluble MAO and residual TMA were obtained as a concentrate. The Al content of the concentrate was 5.1% by weight. Accordingly, the concentrate contained 20.4 g (0.76 g atom) of Al, corresponding to a yield of 59% based on Al in the TMA used. The proportion of Al which could be determined by titration with isoquinoline was 1.5% by weight, corresponding to an amount of 6.0 g (0.22 g atom) of Al.

60 g of the 400 g concentrate were subjected to vacuum distillation under gentle conditions. In this way, 6.7 g of MAO was isolated as a white solid. Accordingly, the yield of isolable, oligomeric MAO is 48%, based on Al in the TMA used.

The Al content of the isolated solid was 42.4% by weight. 7% by weight of Al were determined by titration with isoquinoline. During the hydrolysis of the solid, 515 g Nml / g methane were formed. The average molecular weight was determined to be 1200 g / mol (cryoscopy in benzene).

Example 3

Analogously to Example 1, water and TMA were reacted in a molar ratio of 0.75.

The yield of isolated, oligomeric MAO was 48%, based on Al in the TMA used. The average molecular weight was approx. 2500 g / mol (cryoscopy in benzene.

Example 4

A solution of 7.6 kg (105.5 mol) of TMA in 40.0 kg of toluene with 1.211 kg (67.5 mm) was placed in a 100 1 stainless steel reactor coupled with a rotor-stator machine (type Supraton, from Krupp). 3 mol) dist. Water reacted. The water was metered in using a piston metering pump (Lewa type, 3 mm cap. Diameter, metering time: 3.5 h, 30 min post-reaction time). After filtration, 41.5 kg of MAO solution containing 5.5% by weight of Al were obtained (82% of theory or Al). The content of solid oligomeric MAO was determined to be 11.1% by weight (68% of theory relative to Al) by gentle vacuum distillation of an aliquot of the solution.

Example 5

The procedure was analogous to that in Example 4, only with the difference that the H₂O / TMA molar ratio was 0.5. After working up, a solution was obtained which contained 5.4% by weight of Al (87% of theory or Al). Removal of the solvent from 155 g of filtrate gave 12.5 g of MAO solid (51% of theory or Al).

Example 6

Analogously to Example 1, 150.0 g (2.083 mol) of trimethyl aluminum in 850 g of heptane were introduced and 23.8 g (1.322 mol) of water were metered in at 0 ° C. (molar ratio H₂O: TMA = 0.64) the suspension obtained was stirred for about 2 hours at room temperature and then filtered. 958 g of filtrate were obtained, the Al content of which was determined to be 4.04% by weight (yield: 65% of theory or Al). Removal of the solvent by evaporation in vacuo gave 25.4 g of solid (20% of theory or Al).

Example 7

Analogously to Example 1, 46.0 g (0.634 mol) of trimethyl aluminum and 18.5 g (0.091 mol) of triisobutyl aluminum in 196 g of heptane were introduced and 8.48 g (0.471 mol) were metered in so that the temperature did not exceed 20 ° C. Working up analogously to Example 4 gave 213 g of filtrate with an Al content of 5.8% by weight (63% of theory or Al). From 180 g of the filtrate, 21.0 g of solid were obtained by removing the solvent in vacuo (36% of theory or Al).

Comparative Example 1

A solution of 39.6 g (0.55 mol) of TMA in 409.4 g of toluene was placed in a 1 liter three-necked flask equipped as in Example 1. 9.9 g (0.55 mol) of water were then added dropwise under analogous conditions as in Example 1 (molar ratio H 2 O / TMA = 1.0). After adding about 8 g of water (molar ratio H₂O / TMA about 0.8) a very strong foam formation, which hindered thorough mixing of the entire reaction mixture and necessitated a slow addition of the water. After working up, based on TMA used, 28% oligomeric MAO was isolated. The proportion of the by-product insoluble in toluene was 54%, based on Al in the TMA used.

Comparative Example 2

Analogously to Example 1, water and TMA were reacted in a molar ratio of 0.4.

The yield of isolable, oligomeric MAO was 29%, based on Al in the TMA used.

Comparative Example 3

Analogously to Example 1, water and TMA were reacted in a molar ratio of 0.5.

The yield of isolable, oligomeric MAO was 26%. Al in the TMA used.

Comparative Example 4

Analogously to Example 1, 39 g (0.54 mol) of TMA, dissolved in 156 g of toluene, were distilled with 6.3 g (0.35 mol). Water reacted according to a molar ratio H₂O: TMA of 0.65. An ultrasonic probe (20 KHz, 150 W) was used instead of the KPG stirrer. 160 g of a colorless, water-clear filtrate were obtained, the Al content of which was determined to be 5.22% by weight (58% of theory or Al in the TMA). 110 g of the filtrate were freed from the solvent by evaporation in vacuo. The result was 11.0 g of solid (= 42% of theory or Al in the TMA).

Comparative Example 5

Analogously to Example 1, 61 g (0.83 mol) of TMA, dissolved in 244 g of toluene, were distilled with 9.7 g (0.54 mol). Water reacted according to a molar ratio H₂O: TMA of 0.65. An Ultraturrax stirrer was used instead of the KPG stirrer. After filtration, 258 g of a colorless, water-clear filtrate was obtained, which had an Al content of 5.6% by weight (65% of theory or Al in the TMA. 177 g of the filtrate was removed from the solvent by evaporation in vacuo exempted. 18.0 g of solid (= 44% of theory or Al in the TMA) resulted.