DE2335536A1 - PROCESS FOR CONTINUOUS POLYMERIZATION OF AETHYLENE - Google Patents

Description

PATENT ANWALTSBÜRO TlEDTKE - BüHLING "KlNNE

TEL. (089) 53 9653-56 TELEX: 524845 tlpat CABLE ADDRESS: Germaniapatent Munich

8000 Munich Bavariaring 4

P.O. Box 202403 November 30, 1973 Patent application P 23 35 536.4 B 5507 / Case. Q / E.25245

Imperial Chemical Industries Limited London (Great Britain)

Process for the continuous polymerization of ethylene

The invention relates to the continuous polymerization of ethylene to high density polyethylene.

In the patent application P 20 40 353.6-42 has already been proposed for polymerization or copolymerization olefinically unsaturated Elonerer the monomer in question to bring into contact with an initiator, consisting of a transition metal compound, which is obtained by reaction

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a transition metal complex of the general formula

with a substantially inert base material with a Hydroxy surface which is free of adsorbed water and in which M is a transition metal of groups IVa to VIa of the Periodic Table of the Elements, preferably group IVa, R is a hydrocarbon group or a substituted one Represents a hydrocarbon group, X is a monovalent ligand and m and ρ are integers, where m is a value from 2 to the highest valence of the metal M and ρ is a Value from 0 to 2 less than the valence of the metal M.

As used herein, the term "hydroxy surface" is used to illustrate a variety of -OH groups bonded to the surface of the base material, the hydrogen atom of the -OH group being suitable is to act as a proton source, i.e. it has an acidic effect Function. Such a material is "essentially inert" in that the bulk of the base material is chemical Is inert, even if the named -OH groups are capable, rait, for example, the transition metal hydrocarbon complex to react. Particularly good examples of such base materials are silicon dioxide and aluminum oxide or their mixtures. These consist of a basic material made of silicon or aluminum and oxygen atoms, on the top of which

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surface -OH groups are bonded and the hydrogen atoms of these groups have an acidic function. However, apart from the presence of these -OH groups, silicon dioxide becomes and alumina are generally considered to be chemically inert.

When the above process is used to polymerize ethylene, the product is usually a very high molecular weight polyethylene, which requires the use of a chain terminator, provided that polymers with technical Interesting melt flow indices (MFI), i.e. from 0.005 to 10, are to be produced. A preferred chain terminator is hydrogen, as described in the cited patent application P 20 40 353.6-42 and based on examples explained.

When a hydrogen-induced modification is applied to such polymerizations, it depends for one Given the rate of polymerization, the value of MFI of the polyethylene produced on the hydrogen / ethylene ratio inside the reaction vessel. Up to now it has been common practice to use the greatest possible catalytic conditions Activity. To work (to keep catalyst residues to a minimum) and the MFI value of the product continuous adjustment of the ethylene / hydrogen ratio to a value that corresponds to the

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prevailing polymerization rate is turned off. However, this procedure can lead to a complicated process control To give reason.

It has been found that using certain catalysts of the type mentioned in the case of hydrogen-modified Ethylene polymerization processes as described in general in German patent application P 20 40 353 6-42, the combination of high catalytic activity and extensive tolerance with regard to the resulting catalyst residues it enables the ethylene / hydrogen ratio to be kept constant at a predetermined value and the To vary the catalyst feed rate to control the rate of polymerization. Under these conditions is the The MFI value of the product is mainly a function of the hydrogen / ethylene ratio and is therefore at a kept constant value. This leads to a simplification of the control of the process both manual and with automatic procedure.

The invention relates to a process for the continuous polymerization of ethylene, with a gaseous Mixture of ethylene and hydrogen at a total pressure

of not higher than 40 kg / cm in a polymerization reaction vessel is brought into contact with a catalytic compound which is the product of the conversion of a transition metal complex the general formula MR with finely divided

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ligem aluminum oxide or silicon dioxide which is free from adsorbed water and where M is a transition metal Group IVa of the periodic table denotes vanadium or chromium and R denotes a hydrocarbon group or a substituted one Is a hydrocarbon group and m is an integer with one Value equal to the valence of the metal M, characterized in that the hydrogen / ethylene ratio of gaseous phase in the reaction vessel at a predetermined value within the range of 10/1 to 0.1 / 1, preferably 5/1 to 0.5 / 1 »is maintained and the rate of supply of the catalytic compound to the polymerization vessel is so is regulated so that the polymerization rate is kept constant.

(All references to the periodic table refer to the version of the periodic table of the elements, which is on the inside cover of the book "Advanced Inorganic Chemistry" by F.A. Cotton and G. Wilkinson, 2nd edition, Interscience Publishers (1966).)

Suitable hydrocarbon groups R, which can be the same or different, include alkyl, alkenyl groups (including 'JT allyl groups such as TT allyl) and Glyclopentadienyl groups or their substituted derivatives. However, preferred hydrocarbon groups are the substituted ones AIk ^ Lu of the general formula -CH ^ Y, where Y is a a-Jise;: e oaer polyaromatic group, such as phenyl or

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Kaphthy, or a ring-substituted derivative such as p-methylphenyl, can be. Y can also be a group of general

SK

Formula Z (R), where Z is silicon, germanium, tin or is lead and R. is a hydrocarbon group or hydrogen and Z is preferably silicon.

Although suitable transition metals include titanium, zirconium, chromium and vanadium, the metals of Group IVa, especially zirconium, preferred because they generally have the highest catalytic activity and the residues, which they form are usually colorless and exceedingly little toxic. It should be noted that all of the above defined transition metal complexes are halide-free and thus the catalytic residues which they generate are not are corrosive.

For examples of suitable transition metal complexes include Zirkonte.trabenzyl, Zirknntetrakis (trimethylsilylmethylene), Titanium tetra (benzyl), zirconium and titanium tetrakis (i-methylen-1-naphthyl) and Chromtris (triraethylsilylmethylene)

The catalytic compounds for use in Practical implementation of the invention can easily be achieved by implementation of the complex in question with finely divided aluminum oxide or silicon dioxide by one of the above mentioned German patent application P 20 40 353-6-42 im Working methods described in detail can be produced. That

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Aluminum oxide is preferably a K-aluminum oxide with a Particle size in the range from 20 to 150 µm and especially ranging from 50 to 100 µm with substantially spherical Particles as described in British Patent Application 32811/72.

Polymerizations according to the invention can be used a wide range of conditions, as mentioned in German patent application P 20 40 353 * 6-42 will. However, they are most conveniently made by introducing the catalytic compound as a slurry in a suitable hydrocarbon diluent into one Reaction vessel with stirring, to which ethylene and hydrogen are continuously supplied, are carried out. It care must be taken to ensure that the vessel, gases and diluent have been carefully cleaned and removed from oxygen, water, carbon monoxide, Carbon dioxide, acetylene and oxygen-containing impurities must be freed, which could react with the organometallic component of the catalyst and destroy it.

Although reaction pressures up to 40 kg / cm ^"1 " can be used, ee. Is preferred, with a total pressure in the range

2 2

from 1 to 30 kg / cm ", preferably 4 to 15 kg / cm, and one Ethylene partial pressure in the range of 1 to 20 kg / cm, preferably 1 to 10 kg / cm to work. The polymerization temperature depends on various factors, for example the

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Choice of catalyst and diluent depends on, however generally in the range from 70 ° to 100 ° C. However, since the polymerization reaction is exothermic, it generally is required to remove heat from the reaction vessel, for example by air or water cooling, to maintain the temperature to regulate.

The choice of the hydrogen / ethylene ratio within the range described above depends on the desired MFI value of the polyethylene produced and can easily with; With the help of a suitable test series can be determined. For example, the catalytic compound to be used can be used to polymerize a number of hydrogen / ethylene mixtures with different hydrogen / ethylene ratios are used, and the value 11FI of the polyethylene produced be related to these relationships. It should be noted that other test conditions, e.g. temperature, Pressure and concentration and catalyst activity must be kept constant during the entire series of experiments.

For example, in a series of polymerization experiments in which ethylene using a catalyst

citt
tors, enthsitendrAluminiumoxid in the presence of hydrogen-converted zirconium tetrabenzyl ^ was polymerized, the following relationship between the hydrogen / ethylene ratio and the MFI value of the polyethylene produced was established:

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23.35536 Hydrogen / ethylene WFI of polyethylene relationship 0.9 / 1 0.005 1.1 / 1 0.01 1.8 / 1 0.05 2.7 / 1 0.20 4.1 / 1 1.00

Thus, by choosing an appropriate hydrogen / ethylene ratio for a given set of process conditions the desired MFI value of the polyethylene produced is obtained within fairly precise limits will. The desired fourth MFI can then be regulated the catalyst feed rate can be maintained so that the polymerization rate at a predetermined value by compensating for changes in catalytic activity is retained.

The hydrogen / ethylene ratio can be any conventional technology can be monitored, for example by measuring the hydrogen concentration with the aid of a Catharometer. It however, it is extremely useful to continuously measure the gas mixture using a gas-liquid chromatograph (GLC) to analyze. Such an instrument can easily be connected to a recorder or the like .to create a trace showing the hydrogen and ethylene concentrations can be related to peaks of varying heights.

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These peak heights can then be set at predetermined values either by controlling the gas flow in question or preferably by keeping the flow of ethylene constant and varying the flow of hydrogen. The control of the Gas flow can be msnuell or by using automatic Control valves connected to the outlet from the GLC apparatus are coupled.

As mentioned above, the catalyst feed to the The reactor is regulated so that the rate of polymerization is kept at a constant value. The rate of polymerization can be most appropriately determined by observing the The total pressure in the reaction vessel must be monitored, since a drop in the reaction rate decreases the Amount of polymerized ethylene and a corresponding increase in the total pressure and vice versa. Another Parameter that can be used in this way is the temperature of the effluent from the reactor cooling system. However, the pressure of the reaction vessel results in a faster response to changes in the rate of the reaction than the coolant temperature.

The catalyst slurry can be added to the reaction vessel in pumping in a continuous stream with the flow rate being regulated; alternatively, individual standard amounts of catalyst can be used be fed intermittently to the reaction vessel, the interval between successive

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Additions vary.

The invention is illustrated in more detail below by the following examples.

General way of working

Nitrogen and ethylene were deoxygenated and dried by passing them through two 2 m columns, which with Freshly made, finely divided copper (BT.S catalyst) applied to aluminum oxide and a molecular sieve des Type 5A.

Hydrogen was passed through a molecular sieve dryer.

Solvent and diluent were deoxygenated and dried by passing through two 1.5 m columns, which are packed with B.T.S. catalyst and passed through a molecular sieve (5A).

Manufacture of zirconium tetrabenzyl / aluminum oxide catalyst

2.78 kg of benzyl magnesium chloride as a solution in 25 l of diethyl ether were transferred into a reaction vessel at ⁰ ° C. under nitrogen. 1.2 kg of zirconium tetrachloride were added in 300 g batches over a period of 45 minutes against a nitrogen flush. The mixture was for 2 hours

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stirred, during which the temperature to ambient temperature was allowed to rise. 65 liters of decalin were added and the mixture was stirred for a further hour.

The resulting slurry was allowed to settle, and the supernatant liquid was sucked into a stainless steel filter and under a slightly positive nitrogen pressure filtered.

Ether was removed from the decalin solution by passing through heat exchange screws at a temperature of about 50 ° C. While nitrogen flowed through the liquid in countercurrent operation.

The decalin solution from the heat exchangers was filtered under nitrogen. The average yield of zirconium tetrabenzyl was 61 %,

Alumina (Ketjen grade B) was screened to a particle size of 53-99 pm and dried in a rotary tube furnace at 50O ⁰ C for 2 hours. Nitrogen was passed through the "mouth" (openings) of the tubes after the furnace was brought up to operating temperature.

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The alumina was cooled under nitrogen, and batches (10 kg) were slurried with hexane (50 l). A zirconium tetrabenzyl solution (prepared as described above) was added and the mixture was stirred. The slurry was allowed to settle and the supernatant was aspirated. More zirconium tetrabenzyl solution was added until the concentration of zirconium on the aluminum oxide was about 0.5 m atoms / g aluminum oxide fraud.

The coated aluminum oxide was repeated with Washed hexane and worked up to a 10-20% (w / v) slurry in hexane.

Polymerization technology

A stirred polymerization kettle (4.0 m) was charged with hexane (2.0 mr) and pressurized with ethylene and hydrogen. The gases were through an inlet led below the liquid level. The reaction was started by injecting the catalyst slurry. The temperature of the reaction vessel was regulated at the set value by water cooling.

Ethylene, hydrogen and hoxane were added to the reaction vessel introduced at appropriate rates and the catalyst slurry injected at discrete intervals. the

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Gas composition; above the diluent was through
running gas-liquid chromatography analyzed, and the
Hydrogen flow regulated sutoraatically to the required
Maintain a hydrogen / ethylene ratio. Polyethylene was formed as a particle slurry. This slurry was continuously or intermittently withdrawn through a dip tube and passed into an expansion vessel and then centrifuged.

The granular polymer product was passed through a fluid bed dryer.

example 1

Ethylene was fed into a reaction vessel at a rate of 140 kg / h and hydrogen was fed with a suitable rate to maintain the hydrogen / ethylene ratio headed by 1.03. The Gesarat

working pressure was 5 kg / cm.

Hexane was added at a rate of 0.6 nr / h
was added, and catalyst slurry was added intermittently at a rate approximately equivalent to 42 m-atom Zr / h,
the precise rate being adjusted so that the working pressure was maintained at 5 kg / cm and a temperature of 80 ° C
became. The MFI value of the product was 0.008. After operation
of the reactor under these conditions during the desired

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Time, the flow rate of substance was reduced so that gave a hydrogen / ethylene ratio of 0.90 with the catalyst feed rate at the same average Level was maintained. After Btetige state conditions discontinued, the product had an MFI of 0.005.

Example 2

The general procedure of Example 1 was followed with a hydrogen / ethylene ratio of 2.0 and an average Kata.ly sat or feed rate of 5 ^ m-atom Zr / h followed, the exact rate being adjusted so that one

Working pressure was kept at 7 kg / cm. The MFI value of the Product was 0.07.

The hydrogen flow rate was then decreased to give a hydrogen / ethylene ratio of 1.35 and the Catalyst feed rate was kept at the same average level. Having steady state conditions

had set, the new working pressure was 6 kg / cm. Of the The MFI value of the product was then 0.02.

Example 3

The general procedure of Example 1 was followed, the hydrogen / ethylene ratio being 2.84. Hexane was added at a rate of 0.62 nr / h, and

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Catalyst slurry was added intermittently at an average speed of 48 m-atom Zr / h, although the exact speed was controlled so that the reaction pressure at 5.7 kg / cm "was maintained at 80 ⁰ G. The value of the MFI was then Polyäthylenproduktes 0.18.

To put the Vert MPI in the range of 0.2 bib υ, 25 to bring, the catalyst addition rate was increased to 52 m-atom / h, with all other feed rates constant were held. An MFI value of 0.22 for the polymer was obtained under steady state conditions.

Example 4

The procedure of Example 1 was followed with the hydrogen / ethylene ratio 1.53 »the hexane addition rate 0.6 nr / h and the catalyst slurry added intermittently at an average rate of 60 m-atoms Zr / h. The exact catalyst addition rate was adjusted so that a reactor pressure at 4.1 kg / cm was obtained at 80 ⁰ C. The MFI of the product was 0.023.

Increasing the rate of hydrogen addition for generation a hydrogen / ethylene ratio of 3.3 with the The same average catalyst flow made it possible to maintain a reactor pressure of 6.7 kg / cm "at 80 ° C. and resulted

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a product with an MFI of 0.24.

The hydrogen / ethylene ratios were increased to 4.1 and the average rate of catalyst addition was increased to 70 m-atom Zr / h, the exact rate so

2 was regulated so that a reactor pressure of 7.4 kg / cm at 80 C was obtained. Under steady state conditions obtained a product with a melt flow index of 1.0.

Example 5

The general procedure of Example 1 was followed at a reaction temperature of 90 ° C with the same feed rate of ethylene and hexane. Hydrogen was introduced at a rate to give a hydrogen / ethylene ratio of 2.2 and the catalyst slurry was added at an average rate of 72 m-atoms Zr / hr, the addition being controlled so that a reactor pressure of 6.3 kg / cm was kept at 90 ^° C. A polymer with an MFI * 0.20 value was produced under steady state conditions.

Increasing the hydrogen addition rate to produce a hydrogen / ethylene ratio of 3 ^ O with the same average catalyst flow makes it possible ^{to obtain a reactor pressure of 7 »24 kg / cm at 90 °} C., with a polymer with a value MFI = 0.90 under steady state conditions.

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Maintaining the same rate of addition of Ethylene and hydrogen and the increase in the average catalyst feed rate slightly to 74.8 m-atom Zr / h causes an increase in the rate of polymerization and an increase in the hydrogen / ethylene ratio in the Reactor to 3> 16 · The pressure can then under steady state conditions at 7 »19 kg / cm, 90 ° C., resulting in a polymer product with a value of MFI» 1.0.

Example 6

The general procedure of Example 1 was followed at 75 ° C with the same feed rate of ethylene and hexane. Hydrogen was introduced at a rate that a hydrogen / ethylene ratio of 3 »2 was maintained, and catalyst slurry was added at an average rate of 4-2 m-atoms Zr / h, the addition being controlled so that a steady state pressure of 9.8 kg / cm was kept at 75 ^° C. A polymer with a value of MFI = 0.2 was produced.

Reduction of the hydrogen supply to a hydrogen / ethylene ratio of 1.8 while maintaining the same average catalyst flux to a steady state pressure of 7.4 kg / cm at 75 ° C and to a product with a value MFI * 0.02.

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Maintaining the same ethylene and hydrogen addition rates and increasing the average Catalyst feed rate to 48 m-Atoni Zr / h caused an increase in the hydrogen / ethylene ratio to 1.9 « The reactor pressure could be maintained at 7.2 kg / cm at 75 ° C by controlling the rate of catalyst addition, and the product then had an MFI »0.03.

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Claims (3)

- 20 - 2 3 3 b b 3 6 patent drifts 1. Process for the continuous polymerization of ethylene, in your a gaseous mixture of ethylene and Hydrogen at a total pressure not higher than 40 kg / cm in a polymerization reactor with a catalyst composition is brought into contact, which is the product of the conversion of a transition metal complex of the general Formula MR with finely divided aluminum oxide or silicon dioxide free of adsorbed water, in which M is a transition metal from group IYa of the periodic table, vanadium, or chromium and R is a hydrocarbon group or a substituted hydrocarbon group and m is an integer having a value equal to the valence of the metal M represents - - ' characterized in that the hydrogen / ethylene ratio of the gas phase in the reactor at a predetermined value within the range of 10/1 to 0.1 / 1, preferably 5/1 to 0 »5/1 * and the feed rate of the catalyst composition is regulated in the polymerization vessel so as to keep the rate of polymerization constant. 2. The method according to claim 1, characterized in that the transition metal complex is zirconium tetrabenzyl. 3. Polyethylene, characterized in that it was obtained by the method according to one of claims 1 or 2. 409816/1039