DE2809337C2 - Process for the production of low-pressure polymers of ethylene with a broad molecular weight distribution - Google Patents

Description

A. a reaction product of one mole of dialkylaluminum hydride with alkyl groups of one chain length of 2 to 8 carbon atoms and 0.8 to 2 moles of hydrogen polysiloxane having a viscosity of 5 to 100 mnvVs (25 ° C) with units of the general formula

—Si - O -

wherein R can be an alkyl radical having 1 to 6 carbon atoms, an aryl or a cycloalkyl radical and the Silicon atoms at the ends of the siloxane chain through R, hydrogen or at most through a hydroxyl group per silicon atom are saturated, with

B. titanium tetrachloride and

C. one or more compounds of the general formula

Ti (OR ') 4.

where R 'denotes an aliphatic radical having 1 to 8 carbon atoms,

wherein the molar ratio of components B: C is between 10 and 100 and the degree of reduction of the reaction product D is at least 90, preferably 94 to 100%, characterized in that a calcium analyzer system is used which consists of the catalyst solid component D and an additional component F., where it is one or more compounds of the general formula W.

TiCI) (OR ') I.

U

in amounts of 0.01 to 0.8 mol per mol of compounds B + C used. ||

2. The method according to claim I, characterized in that the additional component E is used in amounts of 0.04 Fe to 0.4 mol per mole of compounds B + C used. m

3. The method according to claim 1 or 2, characterized in that for the preparation of the catalyst solid if fes D 1 to 2 moles of B were used per mole of A and the molar ratio B: C is between 10 and 50. | j

4. The method according to any one of claims 1 to 3, characterized in that the catalyst solids preparation jj, j was carried out at 20 to 45 ° C. / '

5. The method according to any one of claims 1 to 4, characterized in that for the preparation of the catalyst i'j peat solids D as component A a reaction product of 1 to 1.2 mol of methyl hydrogen polysiloxane i * '*

and 1 mole of diisobutylaluminum hydride and, as component C, titanium tetra-n-propylate have been used.

6. The method according to any one of claims 1 to 5, characterized in that the additional component E et ' titanium trichloro-n-propylate is used. *

7. The method according to any one of claims 1 to 6, characterized in that the additional component E of the \ solid catalyst component D is added before the polymerization. iL

8. The method according to any one of claims 1 to 5, characterized in that the polymerization of the 'ß

Ethylene is carried out continuously and the catalyst solid D and the additional component E dem The reactor can be metered in separately.

9. The method according to any one of claims 1 to 8, characterized in that for regulating the molecular weight distribution of the polymer, the amount of additional component E changed during the polymerization will.

10. The method according to any one of claims 1 to 9, characterized in that the polymerization of the Ethylene takes place in the presence of hydrogen.

For the production of low-pressure polyethylene (density range 0.94 to 0.97 g / cm ^J ) z. B. Catalysts are used, which are made from titanium compounds, such as titanium tetrachloride, on the one hand, and on the other

t> 5 a) from organic aluminum compounds, such as triethylaluminum or diethylaluminum chloride (Ziegler catalysts) or

b) from polymeric organic silicon compounds with silicon hydrogen bonds, such as methyl hydrogen polysiloxane and inorganic aluminum compounds such as aluminum chloride (Wacker catalyst

ren) or

from reaction products of one mole of trialkylaluminum, such as triethylaluminum, and 1 to 2 moles Can produce methyl hydrogen polysiloxane (DE-OS 21 26 250).

There are also known catalysts made from titanium compounds, organic aluminum compounds and methyl hydrogen polysiloxane are formed at the start of the polymerization (GB-PS 10 16 512). In the DE-OS 24 14 784 are catalysts made from dialkyl aluminum hydrides, hydrogen and polysiloxanes preferably Titanium compounds described.

The disadvantages of the known processes for the production of low-pressure polymers of ethylene exist i.a. in that the specific catalyst consumption is high and the polyethylene obtained is purified must become. In addition, the above-mentioned processes cause polymerization in a continuous manner more or less thick wall deposits. This makes it necessary, at intervals of 2 months, but usually earlier to clean the reactors. The regulation of the molecular weight distribution during the polymerization has not yet occurred.

A broad molecular weight distribution of the polymers is characterized by the flow factor F ₂ Lb of 15 to 35. This corresponds to a molecular weight range with a melt index / 5 of approx. 3 to 0.1. The F2L6 and / 5 values of polyethylene are explained below.

The object of the invention was to provide a process for the production of low-pressure polymers of ethylene find which has a / 5 range from 0.1 to 3 and a sufficiently broad molecular weight distribution of the Polymerisate allows. A low specific catalyst consumption should be aimed for and the 2υ Polymer properties are given that allow further processing without laborious work-up. In addition, the problem of the wall system in the polymerization facilities should be reduced and the possibility of regulating the molecular weight distribution during the polymerization.

This object is achieved by the subject matter of the invention characterized by the claims.

The molar data for hydrogen polysiloxanes relate to the stated unit of general formula

Si - O - H

30th

with the meanings given in claim 1 of R.

In addition to ethylene homopolymer, low-pressure polymers of ethylene also include Λ-Olfine Modified low-pressure polyethylene understood, which by polymerizing a mixture of ethylene and up to 10 mol% of Λ-olefins having 3 to 8 carbon atoms can be obtained.

It was impossible to foresee, dal? the combination of the specified 4 compounds or compound classes A + B + C in the solid and E as an additional component leads to a catalyst system which it allows a polymer with a broad and controllable molecular weight distribution among relatively simple and produce mild conditions. A continuous way of working with a high polymer concentration in the reactor, high space-time yield and low catalyst and solvent consumption long periods of time are guaranteed with the method according to the invention. However, this requires the special molar ratios of components B: C and B + C: E and the high degree of reduction of the Implementation product D to meet. If the molar ratios B: C are below 10 and B + C: E below 1.25, then polymers with a narrow molecular weight distribution are obtained. If the degree of reduction of D falls below 90%, then must in a continuous polymerization after z. B. expected 1 to 2 months with wall covering in the reactor will.

It was also surprising that the catalyst components C and E, the polymerization activity of the Influence the catalyst system used according to the invention decisively: Catalysts off

a) Solids A + B and the additional component E or systems

b) A + B + C without component E result in a greatly reduced catalyst activity and in case a) also low density and low notched tensile strength of the products. Furthermore, a catalyst must which from

c) A and B are formed, are designated as unusable due to insufficient activity. aside from that are obtained after c) very high molecular weights, which a normal extrusion processing of the Do not allow polyethylene.

The catalyst consumption, which is expressed in g of components used, is a measure of the catalyst activity A + B + C is expressed per kg of polyethylene produced. Comparative data from a continuously operated Test facility for the polymerization of ethylene, using an autoclave with a pot volume of 100 l are illustrated by the above-mentioned findings with regard to the chewing analyzer activity of the individual systems.

60

Catalyst system

A + B + CE

(according to the invention)

Catalyst consumption
g / kg polyethylene
0.6 to 1.1

Melt index A *) 0.30 to 036

a) A + B.E

b) A + B + C

c) a + B

028 0.32 0.09

*) Melt index is in g / 10 min. According to Dl N 53 735 at 5 kp (49 N) load and 190 ° C.

Further details are given in the following examples and comparative experiments.

An increase in the activity of the polymer batch by adding compounds of the type E TiCl ₃ (OR ') to solid suspensions of A + B + C was not to be expected because such solids with a high Ti ³⁺ content usually have to be activated with alkylaluminum compounds . However, if the solid D used according to the invention is activated with such organoaluminum compounds instead of E, fibrous polymers are obtained after a short polymerization time, usually after a few minutes, and deposits in the reactor after 1 hour at the latest. Continuous polymerization is practically impossible.

The process according to the invention makes it possible to determine the molecular weight distribution of polyethylene to regulate during a continuous polymerization phase. This is particularly necessary when the Degree of purity of the raw materials and auxiliary materials used, such as ethylene, hydrogen or solvents, Is subject to fluctuations, or if the flow behavior or the toughness of the polyethylene changes should be without having to discard existing catalyst batches. The higher the proportion of added component E, the narrower the molecular weight distribution of the polymer becomes. The same The dependency also applies to the amount of component C required to form the catalyst solid D is used. The broadest molecular weight distribution is accordingly obtained with molar ratios from B: C from z. B. 30 to 40 and an amount of component E of z. B. 0.04 moles per mole of B + C.

1 to 2 moles of component B are used per mole of component A to form the catalyst. The moles for A refer to the following general formula

R R '

H-Si-O-Al

R '

where R can be an alkyl radical with 1 to 6 carbon atoms, an aryl or a cycloalkyl radical, R 'different or the same alkyl groups with a chain length of 2 to 8 carbon atoms, which are straight-chain but also branched could be. Diethyl, di-n-butyl or diisobutyl derivatives are preferably used as R '.

To prepare the reaction product A, 1 mole of dialkylaluminum hydride with 2 to 8 carbon atoms containing alkyl groups with 0.8 to 2 moles of hydrogen polysiloxane and a viscosity of 5 to 100 mm ² / s (25 ° C) with units of the general formula

- Si — O -

where R can be an alkyl radical with 1 to 6 carbon atoms, an aryl or cycloalkyl radical and the silicon atoms at the ends of the siloxane chain are saturated by R, hydrogen or at most one hydroxyl group per silicon atom, preferably 1 mol of dialkylaluminum hydride with alkyl chains of 2 to 4 chain length Carbon atoms and 1 to 1.2 mol of methyl hydrogen polysiloxane with a viscosity of 20 to 40 mm ² / s (25 ° C) reacted. Suitable dialkyl aluminum hydrides with alkyl groups with a chain length of 2 to 8 carbon atoms are, for. B. those with R '= ethyl, propyl, isopropyl, butyl, isobutyl, 2-ethylhexyl or n-octyl. The industrially readily available diisobutylaluminum hydride is preferably used.

Titanium tetrachloride is used as component B and titanium tetra-n-propoxide is preferably used as component C. In principle, other compounds of the general formula Ti (OR ') ₄ can also be reacted with substances A and B as component C. R 'represents an aliphatic radical with 1 to 8 carbon atoms. Further examples of C are titanium tetra-i-propoxide, titanium tetra-n-butoxide, titanium tetra-i-butoxide and titanium tetra-2-ethylhexoxide. The molar ratio of components B: C should be between 10 and 100, preferably between 10 and 50. Ratios below 10 result in catalysts which, under certain circumstances, lead to types of polyethylene which are no longer suitable for free-flowing blow molding.

The reaction to form the catalyst solid D is carried out with stirring in an inert hydrocarbon, such as B. heptane or isookiane, carried out under nitrogen protection and moisture exclusion. Before adding of component A, components B and C are left in the inert hydrocarbon solvent at 50 react up to 60 ° C for 1j to 30 minutes. This creates an equivalent amount of C used Amount of TiCh (OR '). Then component A is added and the actual reduction

tion reaction with formation of the catalyst solid D. Temperature, stirring speed. Time and dilution should be chosen so that the Ti ³⁺ content of the solid suspension is at least 90, preferably 94 to 100%. The reaction is easy to control at temperatures between 20 and 45 ° C. Catalysts which are produced in this way result in advantageous particle size, bulk density and low dust content (particle size below 100 μm) of the polyethylene in the polymerization step. In order to achieve the required degree of reduction, longer times are necessary for the preparation of D as the amount of C increases.

The catalyst solids D used according to the invention are dark brown solid suspensions which can be easily metered and which can be kept for any length of time when suitably diluted with an inert solvent with the exclusion of air and moisture. The one with z. B. dry heptane washed out and dried solid does not turn purple when heated to 150 to 200 ° C, but retains its brown color. It is therefore not a / 9-TiCh which can be produced according to Ziegler from titanium tetrachloride and aluminum alkyls or aluminum alkyl chlorine compounds such as alkyl aluminum sesquichloride, which, as is known, changes its color or its modification when heated.

The catalyst solid D is mixed with the additional component E of the general formula TiCb (OR ') for the polymerization of the ethylene. As in the case of component Ci, R 'denotes an aliphatic radical having 1 to 8 carbon atoms. Examples are titanium trichloro-i-propylate, titanium trichloro-n-butylate or titanium trichloro-2-ethyihexylate, preferably titanium trichloro-n-propylate. 0.01 to 0.8, preferably 0.04 to 0.4 mol of component E are used per mole of the compounds B + C used. The preparation of component E is performed by equilibrating 3 moles of titanium tetrachloride and 1 mole of titanium tetraalcoholate at 40 to 6O ⁰ C. The compound e may approach the catalyst is added after the solid catalyst preparation. It is then fed to the polymerization batch together with the solid or component E, preferably in equimolar mixing with solvent, is metered in separately in the polymerization room and thus has the ability to vary the amount of E and thus the molecular weight distribution of the given catalyst batch To fix polyethylene. As already mentioned, this is a particular advantage of the method.

The polymerization of ethylene or a mixture of ethylene and up to 10 mol% Λ-olefins with 3 to 8 carbon atoms can be carried out batchwise or, preferably, continuously. As «-olefins with 3 to 8 carbon atoms can be used together with ethylene e.g. propylene, butene-1, 3-methylbutene-1, Pentene-1,4-methylpentene-1, hexene-1 and octene-1 or mixtures thereof are used. You then get a Polyethylene, which has a reduced density.

It is possible with the catalyst system used according to the invention at pressures of 1 to 50 bar, preferably at 5 to 20 bar, and at polymerization temperatures of 50 to 120 ° C in suspension or in the To polymerize gas phase. As a liquid distribution z. B. Isooctane or heptane in question. In general, the suspension process is carried out at polymerization temperatures between 60 and 90.degree.

With the help of a suitable fluidized bed reactor can be polymerized in the gas phase, with only very small amounts of solvent, namely those used for metering the catalyst solid suspension or the Component E is required and the catalyst solid D is preferably in the presence is prepared from slightly ventilated and dried polyethylene powder.

Aliphatic alcohols, in particular, are used to dissolve or to decompose the catalyst in the polymer Isopropyl alcohol, in amounts of 1 to 10% by volume, based on the total amount of solvent used, used.

To regulate the molecular weight of the polyethylene is primarily used for the polymerization of added Hydrogen. The polymerization temperature and the amounts of components C and E also affect the molecular weight of the polyethylene, as can be seen from the examples.

The polymers produced by the process according to the invention are suitable because of their broad spectrum Molecular weight distribution especially for the production of impact-resistant hollow bodies and thin, paper-like bodies Films, whereby also a cost-saving direct processing of the polymer powder to the finished article is possible.

Finally, the advantages of the method according to the invention are summarized:

a) Simple and cheap catalyst preparation with little use of solvents. The catalyst solid D is not washed out before polymerization.

b) No spontaneously flammable or dangerous substances such as B. aluminum trialkyls or aluminum dialkyi compounds are used

c) Low catalyst consumption and low use of solvents, 2.5 to 3.5 l / kg polyethylene.

d) Very good polyethylene powder properties. The bulk densities are usually between 430 and 480 g / l. This makes it possible, at high polymer concentrations, e.g. B. 35 to 45 wt .-%, continuously polymerize.

e) A continuous polymerization process produces polymers with a broad molecular weight distribution obtained, which have a high degree of homogeneity and are therefore used directly as a powder Further processing can be used.

f) The regulation of the molecular weight distribution of the polyethylene is during a continuous polymerization phase possible.

g) Even after prolonged continuous polymerization times, there are no noteworthy wall systems in the reactor ascertain.

The flow factor F ₂ Lh, which is the quotient of the melt index values / 21 * and / ■; calculated. The higher the flow factor, the wider the molecular weight ratio

division. The measurement of the melt index values / 21b and k in g / 10 minutes is carried out according to DIN 53 735 at 21.6 kp (211.8 N) or 5 kp (49 N) load and 190 ° C.

^{The density is measured in g / cm 3} using the buoyancy method on strips of 1 mm thick pressed plates (DIN 53 479, butyl acetate solvent, determination at 23 ° C., based on the density of water at 4 ° C. = 1 g / cm ³ ).

The powder bulk density is measured according to DIN 53 468 and stated in g / l. The tensile impact strength is determined in kj / m ² according to C 3.02 / D1N 53 448 on press plates.

The temperature difference At between the cooling jacket and the internal temperature is used as a measure for wall deposits in the reactor. In the given reactor unit of a small pilot plant with 100 l of a pot volume At 5-8 ⁰ C is normal. At an At of over 8 ^° C., this value rises relatively rapidly in the course of the polymerization. The reactor must be cleaned at an at of approx. 15 ° C.

Examples 1 to 4, comparative experiment A.
Catalyst preparation

Reaction product A is prepared in the following manner: 0.416 mol of diethylaluminum hydride are placed in a 250 ml three-necked flask with an addition funnel, thermometer and stirrer under nitrogen protection and with exclusion of moisture. At 25 ⁰ C with the dropwise addition of 26 g (0.433 mol) of methyl hydrogen polysiloxane started with a viscosity of 31 cSt (25 ° C). An exothermic reaction sets in immediately. The reaction temperature is kept constant by cooling and regulating the dropping rate. The reaction is generally complete after 90 minutes, and the reaction mixture is then stirred at 58 ° C. for a further 30 minutes. A colorless, slightly viscous reaction product (A) is obtained in 97.6% yield.
From the reaction product A, titanium tetrachloride B, and various amounts of titanium tetra-n-propylate C, 4 catalyst solids are prepared in isooctane. The molar ratio A: (B + C) is constant at 1: 1.63; according to Examples 1 to 4, the molar ratios A: B are set at 1: 1.58 to 1: 1.5 and the molar ratios B: C are set increasing from 1: 0.033 to 1: 0.081. The total amount of A + B + C is 320 g and the amount of solvent for preparing the solids of the catalyst is 260 ml. First, substances B and C are allowed to react at 55 ° in the specified amount of solvent for 15 minutes. After cooling to 37 ° C. and adding component A, the catalyst solids D are prepared at this temperature for increasing times, namely 7.8V4.9 and 10 "/ 2 hours for Examples 1 to 4. This gives the required degrees of reduction of over 90% Ti ³⁺ .

In comparative experiment A, a catalyst solid without component C is used for 5 1/2 hours, otherwise but prepared under the same conditions as above.

After preparation, all catalyst solids D are adjusted to 1.41 suspension with isooctane and with 0.12 mol of titanium trichloro-n-propylate E per mol of B + C, that is 80 mg of trichloro compound E / g of A + B + C, offset.

Polymerization of ethylene

An autoclave with a pot volume of 100 liters is used for the continuous polymerization of the ethylene. The polymerization is carried out at 85 ° C. and 9.8 bar. The H _r content in the gas space of the reactor is adjusted so that comparable melt index values / 5 are obtained. That amount of catalyst suspension is metered in per hour which corresponds to 5 g of substances A + B + C used for preparing the catalyst solids. Polymerization is carried out at concentrations of 37 to 40% by weight and residence times of 4.6 to 4.8 hours; in Comparative Experiment A, polymerization is carried out at 30% by weight for 6.2 hours of residence time.

After working up the polymer suspension, 5.2 to 5.5 kg of polyethylene per hour are obtained in the form of a very Free-flowing polymer powder with high bulk densities of 433 to 476 g / l. After the comparative experiment A With an hourly use A + B of 5 g, only 3.5 kg of polyethylene with a bulk density of 404 g / l.

After continuous polymerization according to the invention for 4/2 months, an at of 6 to 7 ° C. is found

The catalyst and polymerization data and the properties of the polymers obtained are summarized in Table I below. The polyethylene has a high molecular weight and is widely distributed and has high notched impact strengths. By changing the molar quotient B: C from 303 to 123, the flow factor F21.6 drops from 24.7 to 17.5 and is therefore adjustable; at the same time, the tensile impact strength increases from 160 to 181 kj / m ² . It can also be seen that increased amounts of C lead to catalysts which require smaller amounts of H2 if a polyethylene with the same melt index is to be obtained.

If a catalyst system is used without using component C for the polymerization of ethylene (Comparative experiment A) so are the polymerization results or the properties of the polymer obtained to be classified as negative compared to the catalyst systems used according to the invention.

Table I.

0.12 moles of E per mole of B + C, polymerization temperature 85 ° C

example Mole ratio Mole ratio : B. Ti ³ + H ₂ % Kai, - 11th 0.28 29.3 density Ki? *) B: C A. % Gabiaum consumption gA + B + C 0.32 24.7 : 1.63 per kg pole. 0.31 21.6 Comparison 1-0 1 94 28 1.4 0.32 18.5 0.948 99 attempt A : 1.58 0.33 17.5 1 1: 0.033 1 : 1.54 97 13th 0.95 0.951 160 2 1: 0.056 1 : 1.52 100 12.5 0.94 B, 0.952 168 3 1: 0.068 1 : 1.5 97 11.5 0.93 0.952 170 4th 1: 0.081 1 ink I / m ² 99 10.6 0.91 0.953 181 K zz *) = notched impact tensile strength Examples 5 to 11, comparative experiment Tabel

Catalyst preparation

A catalyst solid D is prepared from components A, B and C analogously to Examples 1 to 4. It will the amount of titanium tetra-n-propylate C selected so that a molar ratio of B: C = 1: 0.068 = 14.7 results; the molar ratio A: B is 1: 1.52. These molar ratios correspond to Example 3.

The catalyst solid D is after preparation with various amounts of titanium trichloro-n-propylate E. added, namely 0.06 to 0.24 moles E / mole B + C. In comparative experiment B, no component E admitted.

Polymerization of ethylene

The polymerization is generally carried out analogously to Examples 1 to 4. Two different polymerization temperatures, 80 and 85 ° C, are selected. The concentrations of the polyethylene in the reactor are 36 to 39% by weight and the residence times are 4 to 6 hours. In comparative experiment B 32.6% by weight and residence time 8 ¹ ₂ hours.

4.54 to 5.4 kg of polyethylene with a very high bulk density of 470 to 480 g / l are obtained per hour. After this Comparative experiment B only 2.5 kg of polyethylene / hour are obtained.

Even after a continuous polymerization time of 5 months, none are noteworthy in the reactor Deposits found.

The catalyst and polymerization data as well as the properties of the polymers are shown below Table II summarized. The flow factor F21A is reduced by the increasing addition of E and can be managed. The values of the notched tensile impact strength increase accordingly. At a polymerization temperature from 80 ° C to 85 ° C higher flow factors and slightly higher densities are found.

If a catalyst system is used for the polymerization of ethylene without using the activation component E, the catalyst consumption g A + B + C / kg polyethylene increases by approx. 100%. The F ₂ i.6 value of this polymer of 29 is too high for the production of impact-resistant moldings.

Table II

B: C = 1: 0.068. A: B = 1: 1.52. Polymerization temperature 80 and 85 ° C.

example MoIcE H ₂ % K.at.-Ver / 5 29 density Kzz temperature per mole Gas compartment need B + C Comparison 20th 2 032 25th 0.951 135 attempt B 20.5 8O ⁰ C 19th 5/80 ⁰ C 0.06 16.5 1.1 0.30 17th 0.951 160 6 / 8O ⁰ C 0.12 15th 1.05 0.30 20th 0.952 166 7/80 ⁰ C 0.18 12th 0.92 0.34 18.5 0.953 174 8 / 8O ⁰ C 0.24 10.5 0.9 0.33 15.5 0.953 179 9/85 ° C 0.06 12.5 1.1 0.35 0.951 158 10/85 ° C 0.12 11.5 0.93 0.32 0.952 170 11/85 ° C 0.18 10 0.82 0.34 0.951 191

50 55

65

Example 12
Analyzer preparation

A catalyst solid is prepared from components A, B and C at 37.degree _{. C. for 9V for 4 hours.} The total amount of the starting materials A + B + C used is 320 g and the amount of isooctane used for solids preparation D is 650 ml. Molar ratio A: B and B: C as in Example 1. The degree of reduction of D is 99%. After dilution with isooctane, 0.12 mole of titanium trichloro-n-propylate E / mole of B + C is added to D.

in the polymerization of ethylene

The continuous polymerization of ethylene is analogous to the examples described above, which in the Table 1 listed, performed. In addition, 30 g of butene-1 per hour are put into the polymerization reactor dosed. The H2 content in the gas space is 8%, the residence time 4.5 hours and the polymer concentration 38.4 wt%.

5.55 kg of polyethylene are obtained per hour; this result corresponds to a quay analyzer consumption of 0.9 g Substances used A + B + C per kg of polyethylene.

The polymer product modified with butene-1 shows the following properties:

Melt index k 1.2 g / 10 minutes

Flow factor F ₂ ,. ,, 15.5

Density 0.949 g / cm ³

Kzz 121 k) / m ²

Titanium content 3.9 mg / kg polymer

This type of polyethylene has a very high resistance to stress corrosion cracking. From the Hollow bodies produced by the product show high toughness and high drop values. Blown foam can with high Throughputs are established.

B e i s ρ i e 1 13

Catalyst preparation

The catalyst is prepared analogously to Example 1. The amount of component E added is 0.12 mol per mole of B + C. A degree of reduction of 97.4% is obtained.

Ethylene polymerization

The continuous polymerization of ethylene is generally analogous to the examples described above 80 ° C carried out. Only 4.4 g of substances A + B + C are used for preparing the solids of the catalyst Hour metered into the reactor. In addition, 5 g of 1-butene are added every hour.

With an H2 content in the gas space of the reactor of 8%, with a dwell time of 3.8 hours and one Polymer concentration of 39.6% by weight is obtained after working up 6.8 kg of polyethylene per hour; This matches with a catalyst consumption of 0.65 g A + B + C / kg polyethylene. The polyethylene modified by a little butene-1 is of high molecular weight and has the following properties:

Melt index / 5 0.33 g / 10 minutes

Flow factor F21.6 18.2

Density 0.949 g / cm ³

Titanium content 3 mg / kg polymer

Chlorine content 2.6 mg / kg polymer

Only 2.6 liters of solvent per unit of dry product are required for the polymerization and for working up the polymer needed. The degree of purity of this type of polyethylene is extremely high.

Example 14 to 16

Catalyst preparation

The catalyst preparation takes place analogously to Example 12. Component E, as in the previous examples Titanium trichloro-n-propylate, however, is not the catalyst solid D after its preparation, but metered in during the polymerization.

Polymerization of ethylene

The continuous polymerization of ethylene is generally carried out according to the examples described above. It is polymerized at 85 ° C and 9 bar and a! - ^ - concentration in the gas space of 10%. Within of 3 continuous polymerisation phases, corresponding to Examples 14, 15 and 16, are different Quantities of component E entered into the reactor.

In the following table 111 the catalyst and polymerization data as well as the properties of the Polymers obtained summarized The data given are after a respective polymerization time determined from 16 hours

Table III

Example Mol E / Mol B + C kg PolVhour chewing consumption / _s F ₂ Lb

gA + B + C
per kg pole.

! 0

14th Cl 2 5.74 0.87 0.40 23 15th 0.18 6.07 0.82 0.58 21 16 0.24 63 0.8 0.65 18.5

It is therefore easily possible to monitor the molecular weight distribution during the continuous polymerization to regulate.

Comparative experiment C

The catalyst solids are prepared according to Example 4 of DE-OS 24 14 784 in two stages. The molar ratio of catalyst component A to component B titanium tetrachloride is 1: 1.5, the molar ratio of B to C titanium tetra-n-propoxide is 1: 0.069. With the catalyst preparation conditions used, a degree of reduction of only 83% Ti ^{3+ is obtained} .

This catalyst suspension is used without component E, as described in Example 4 of DE-OS 24 14 784, for continuous ethylene polymerization. After only 3 weeks of polymerization, an at of 9.5 ° C is observed; After opening the reactor, solid wall deposits are found, which make it necessary to clean the reactor.

Comparative experiment D

In this comparative experiment, a catalyst solid is used which, analogously to comparative experiment A, is produced only from catalyst components A and B, molar ratio 1: 1.61. 192 g of A + B are used per catalyst charge. With a dilution of 5 parts by volume of isooctane per part by volume of component A, a degree of reduction of 93.2% Ti ^{3+ is} achieved _{after 3–2} hours at 50 ^{° C.}

For continuous ethylene polymerization, 6 g of catalyst starting materials A + B are metered into the reactor every hour. It is polymerized without component E. At a polymerization temperature of 8O ⁰ C, a H2 content in the gas space of 40%, a polymerization pressure of 9.8 bar is obtained and only 2 kg of polyethylene / hour with a residence time of IOV2 hours; this corresponds to a catalyst consumption A + B of 3 g / kg polyethylene.

The melt index 1? of the polymer is 0.09 g / 10 minutes, the flow factor F2ib is 51.1 and the bulk density 392 g / l.

It can be seen that a catalyst system composed of components A and B and without components C and E relatively much hydrogen is required to obtain a polyethylene with useful melt index values. Through this the catalyst consumption rises sharply. In addition, the polymer shows a relatively low bulk density. Of the The flow factor is extremely high, which indicates a high content of low molecular weight polymer fractions leaves.

Example 17
Catalyst preparation

^{A catalyst solid D is produced at 37 °} C. from components A, B and C analogously to Example 2. Instead of 260 ml of isooctane, however, 641 ml are used as a diluent for preparing the catalyst. This increases the preparation time to 11 1/2 hours. A Ti ³⁺ -WeN of 96.8% is obtained.

Polymerization of ethylene
The following data are given for continuous ethylene polymerization:

Polymerization temperature 85 ° C Polymerization pressure 9 bar Dwell time (in the middle!) 4.7 hours Hydrogen concentration in the gas space 10.5% Dosing of solid catalyst suspension per hour: 5 g starting materials A + B + C Dosage of component E per hour: 80 mg / g Starting materials A + B + C = 0.1.2 mol K / mol B +

45 50 55

60

b5

As in the previous examples, an autoclave with a pot volume of 100 l is used as the polymerization reactor used

After a continuous polymerization phase of 64 hours, with 6.7 kg of polyethylene per hour a catalyst consumption of 0.75 g / kg polymer product can be obtained, shows a sample of the polyethylene following properties:

Melt index i% 033 g / 10 minutes Flow factor F ₂ i. _b 22.4 Bulk density 443 g / l Dust content below 100 μΐη 0.4% Average grain size 520 μm

10 15th 20th 25th 30th 35

The following relationships can be recognized:

a) With a longer residence time compared to Example 3, somewhat higher yields and somewhat obtained higher F2i.e values of the polyethylene.

b) At higher catalyst preparation temperature of 60 ° C is compared to generally 37 ⁰ C - decreased the bulk density of the polymer - previous examples. Furthermore, the dust content of the polyethylene powder increases significantly and the grain size distribution becomes very broad; Comparison to example 17.

The polyethylene powder is very uniform and easy to pour.

Example 18
Catalyst preparation

Of the components A, reaction product of methylhydrogenpolysiloxane and diisobutylaluminum hydride, B of titanium tetrachloride and C titanium-n-propyl titanate, a solid catalyst D prepared mole ratios A at 60 ⁰ C and during 3V _{for 4} hours in 160 g batches to B and B to C analogously to Example 3. FIG. To prepare the catalyst, 5 parts by volume of isooctane are initially used per part by volume of component A; After a preparation time of 2 hours, further dilution to 7 parts by volume of solvent per part A by volume is necessary. The degree of reduction of the catalyst solids suspension is 100%.

After the catalyst has been prepared, 0.12 mol of component E titanium trichloropropoxide per mol of B + C is added as in Example 3 added to the catalyst solid.

Polymerization of ethylene

The continuous ethylene polymerization is generally, as described in the previous examples, carried out: 5 g of components A + B + C, which are used for catalyst preparation, are added every hour were used, metered into the reactor. At 85 "C, 11.5% H2 in the gas space and a residence time of 6 hours an average of 5.85 kg of polyethylene per hour is obtained with the following properties:

Melt index / 5 1C0 at 0.30 g / 10 minutes Flow factor F ₂ \ b 22.5 Bulk density 400 g / l Dust content below 5.8%

For these reasons, namely temperatures between 20 and 45 ° C are preferred preparation lower temperatures than 6O ⁰ C to the catalyst solid, is selected.

Examples 19-22, Table IV
Catalyst preparation

The catalyst solids preparation takes place according to Example 5, but at 30 ⁰ C; the sum of the substances A + B + C used is 33.77 g. After 11 hours of ^{preparation of the catalyst, a Ti 3+} content of 100% is found. Component E is only added before the polymerization.

Polymerization of ethylene

Ethylene is polymerized in a small laboratory unit with a volume of 1 liter at 80 ° C. for 2 hours. After 600 ml of isooctane have been poured into the polymerization vessel, 0.5 g of catalyst solids D, based on the components A + B used for preparing the catalyst solids + C is added as a suspension; 0.09 mmol of component E ₁ TiCh (OR '), molar ratio 0.06 mol of E per mol of B + C, is then added. In the series of Examples 19 to 22, R' denotes n-propyl , η-butyl, i-propyl and n-octyl. After pressing with hydrogen to 3 bar of ethylene and at 11 is polymerized at this pressure and at 8O ⁰ C for 2 hours at running subsequent addition of ethylene bar.

The results of the polymerization are summarized in Table IV below.

The use of titanium trichloro-n-propylate as component E is under the chosen test conditions from the point of view of the catalyst activity and the properties of the polymer, such as A, F ₂ ]. _b and density, particularly advantageous

Table IV R '
Comp. E G
Polyethylene Λ 22.6
15.5
19.9
25.8 density
(g / cm ^J ) Schütt
density
(g / i) example n-propyl
n-butyl
i-propyl
n-octyl 164
160
131
164 1.8
2.8
1.4
0.62 0.955
0.954
0.955
0.953 441
472
450
443 19th
20th
21
22nd

No deposit build-up was found on the glass wall of the polymer vessel. The autoclave can after emptying the polymer suspension can be used for further experiments without purification.

Comparative experiment E

The catalyst solids preparation and the ethylene polymerization are carried out under conditions as described in Examples 19 to 22 above. Instead of component E, however, 0.09 mmol of titanium tetrachloride are added to the polymer mixture. After a polymerization time of 2 hours, 210 g of polyethylene are obtained, which, similar to Example 22, has a high molecular weight and broadly distributed, melt index / 's = 0.48 and flow factor F2i, _b = 29. However, deposits and polymer fibers appear on the glass wall of the polymerization vessel and on the stirrer determined which make cleaning of the vessel necessary.

Comparative experiment F

Catalyst and polymerization conditions as in Examples 19 to 22. Instead of component E are however 0.1 mmol of triisobutylaluminum was added to the polymerization batch. The polymerization of ethylene must be stopped after 15 minutes because thick polymer strands and deposits have formed. Similar approaches with smaller amounts of catalyst solid D are also primarily difficult stirrable polymer bodies and no discrete polymer grains as when using the catalyst systems according to the invention from D + E.

Claims (1)

Patent claims: 1. Process for the production of low-pressure polyethylene with a melt index k (DIN 53 735) of 0.1 up to 3 and broad molecular weight distribution by polymerization of ethylene and possibly 10 Moi-%, based on the total olefin mixture, Λ-olefins with a maximum of 8 carbon atoms at pressures between 1 and 50 bar and temperatures between 50 and 120 ° C using catalysts based on a Catalyst solid D obtained by reacting