DK141101B - Process for Continuous Polymerization of Ethylene. - Google Patents

Description

U1101

The present invention relates to a process for the continuous polymerization of ethylene, in which a gas mixture of ethylene and the hydrogen at a total pressure of not more than 40 kg / cm in a polymerization reactor is contacted with a catalyst material which is the reaction product of a transition metal complex with the general formula MRI with finely divided alumina or silicon oxide which is free of adsorbed water / where M is a transition metal from the groups IVA of the periodic table, vanadium or chromium, R is a hydrocarbon group or substituted hydrocarbon group, and m is a integer with a value equal to the valence of the metal M.

British Patent Specification No. 1,314,828 discloses a process for polymerization or copolymerization of olefinically unsaturated monomers in which the monomer is contacted with an initiator comprising one. transition metal material, which is the reaction product of reacting a transition metal complex with the general fomel R MX mp with a substantially inert matrix material with a hydroxyl-containing surface free of adsorbed water, wherein M is a transition metal of the groups IVA - VIA of the periodic system, preferably group IVA, R is a hydrocarbon group or substituted hydrocarbon group, X is a monovalent ligand, and m and p are integers, m having a value of 2 to the metal's largest valence, and p has a value di from 0 to 2 less than the valence of the metal M. New transient metal compounds used in this process are also disclosed in said British patent. In this connection, the term "hydroxyl-containing surface" is used to denote a large number of -OH groups attached to the surface of the matrix material, the hydrogen atom of the OH group being able to act as a proton source, i.e., having an acidic feature.

Such a material will be "substantially inert," in that the bulk of the matrix material, although said -OH groups are capable of reacting,

Ut101 tools with e.g. the transition metal hydrocarbyl complex is chemically inert. Particularly good examples of such materials are silica and alumina or mixtures thereof. These comprise a matrix of silicon or aluminum and oxygen atoms to which the surface -OH groups are attached, the hydrogen atoms of said groups having an acidic function.

However, apart from the presence of these -OH groups, silicon = dioxide and alumina are generally considered chemically inert. When the above method is used to polymerize ethylene, the product is generally a very high molecular weight polyethylene which requires the use of chain transfer agents to produce polymers with cranercially attractive melt flow indices (MFIs), i.e. from 0.005 to 10. A preferred chain transfer agent is hydrogen, as described and exemplified in the aforementioned British Patent Specification No. 1,314,828.

When hydrogen modification is used in such polymerizations, the MFI of the polyethylene produced for a given polymerization rate will depend on the hydrogen / ethylene ratio in the reactor. So far, it has been common practice to operate under conditions of maximum possible catalyst activity (to minimize catalyst residues) and to regulate the MFI of the product by continuously adjusting the ethylene / hydrogen ratio to a value appropriate to the currently prevailing polymerization rate. However, this method can cause complicated process control.

It has now been found that the combination of high catalyst activity and high tolerance of resulting catalyst residues using certain of these catalysts in hydrogen-modified ethylene polymerization methods allows the ethylene / hydrogen ratio to be kept constant at a predetermined value and to adjust the catalyst feed rate to controlling the rate of polymerization. Under these conditions, the MFI of the product is predominantly a function of the hydrogen / ethylene ratio and thus is kept at a constant value. This results in a simplification of the control of the method, either manually or automatically.

3 U1101

According to the present invention there is disclosed a process for continuous polymerization of ethylene in which a gas mixture of 2 ethylene and hydrogen is contacted with a catalyst material at a total pressure of not more than 40 kg / cm, which is the reaction product from reaction of a transition metal complex with the general formula MRI with finely divided alumina or silica free of adsorbed water, where M is a transition metal from Group IVA of the Periodic Table, vanadium or chromium, R is a hydrocarbon group or substituted hydrocarbon group, and m is an integer having a value equal to the valence of the metal M, characterized in that the hydrogen / ethylene ratio in the gas * 1 phase of the reactor is continuously measured and maintained at "a predetermined value 4 * di in the range 10/1 to 0.1A, preferably 5A to 0.5 / 1 and that the feed rate of the catalyst material to the polymerization reactor is controlled so that the polymerization rate one is held constant.

(All references to the Periodic Table refer to the version of the Periodic Table which is printed on the inside cover of "Advanced Inorganic Chemistry" by F A Cotton and G Wilkinson, 2nd Edition, Interscience Publishers, 1966).

Suitable hydrocarbon groups R, which may be the same or different, include alkyl, alkenyl groups (comprising ττ-alkenyl groups such as ττ-allyl) and cyclopentadienyl groups or substituted derivatives thereof. However, a preferred class of hydrocarbon groups is substituted methyl of the general formula -CHL / Y, where Y may be an aromatic or polyaromatic group such as phenyl or naphthyl or a ring-substituted derivative such as p-methylphenyl. Y may further comprise a group of the general formula ZfR1, where Z denotes silicon, germanium, tin or lead, and R denotes a hydrocarbon group or hydrogen. Z is preferably silicon.

Although suitable transition metals include titanium, zircon, hafnium, chromium and vanadium, the compounds of the Group IVA metals are preferred. This is especially true for zirconium tetrabenzyl, which has a very high catalytic activity, the residue which the compound forms is colorless 4 U1101 and has an extremely low toxicity. It will be appreciated that all the transition metal complexes defined above are halide free and that the catalyst residues they form are thus non-corrosive.

Examples of suitable transition metal complexes are zircon tetra (benzyl), zircon tetrakis (trimethylsilylmethylene), titanium tetra (benzyl), zircon and titanium tetrakis (1-methylene-1-naphthyl) and chromis (tri = methylsilylmethylene).

German Patent Publication No. 2,040,353 discloses a process for continuous polymerization of ethylene of the type mentioned in the preamble, wherein the process is such that regardless of the ethylene / hydrogen ratio being constant under stationary conditions, it would not be possible to control the magnitude of said ratio under the non-stationary conditions that occur in practice. The known process does not presuppose that the hydrogen / ethylene ratio is to be predetermined and, in the absence of such predetermination, it is not possible to control the catalyst feed in order to keep the rate of polymerization constant at that hydrogen / ethylene ratio.

From usa. U.S. Patent No. 3,551,403 discloses a method for controlling the polymerization of olefins, wherein the hydrogen / ethylene ratio and reaction temperature affecting the polymer melt flow index are mainly controlled by regulating the olefin flow, intermittently determining the hydrogen / ethylene ratio in the liquid phase of the reactor. and the olefin stream is adjusted accordingly, whereupon the catalyst stream is slowly adjusted to restore the reaction conditions. However, such a method is problematic according to the patent, in addition to the fact that the use of catalyst feed as a primary control agent is not considered to be suitable. It is believed that the reason for this is that the measurements of the hydrogen / ethylene ratio in the liquid phase are made intermittently, so that the ratio at the time of any change is noticeable is driven so far from the target that significant corrections must be made.

In the process of the invention, the hydrogen / ethylene ratio is measured by continuous analysis of the gas phase of the reactor. Hereby, answers or information are obtained much more quickly and only small corrections of the hydrogen / ethylene ratio have to be made, which corrections in contrast to the corrections of the method of said U.S.A. Patent writing can be performed almost exclusively by regulating the hydrogen flow and therefore decreases the extent of accompanying settings of the catalyst stream.

The catalyst materials for troughing in the practice of the present invention can be readily prepared by reacting the appropriate complex with comminuted alumina or silica by one of the methods set forth in detail in the aforementioned British patent. The alumina is preferably a γ-alumina having a particle size in the range of 20-150 µm, more preferably in the range 50-100 µm, and having substantially spherical particles, as disclosed in British Patent Specification No. 1,430,073.

Polymerizations of the present invention can be carried out using a variety of conditions as mentioned in British Patent Specification No. 1,314,828. However, they are most conveniently carried out by introducing the catalyst material as a slurry into a suitable hydrocarbon diluent, in a stirred reaction vessel to which ethylene and hydrogen are continuously supplied. It will be appreciated that the container, gases and diluent must be carefully cleaned and freed of oxygen, water, carbon monoxide, carbon dioxide, acetylene and oxygen-containing impurities which can react with and destroy the organometallic component of the catalyst.

Although reaction pressures up to 40 kg / cm can be used, it is preferred

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working with a total pressure in the range 1-30 kg / cm, preferably 2 2 4-15 kg / cm and an ethylene partial pressure in the range 1-20 kg / cm, preferably 1-10 kg / cm. The polymerization temperature will depend on many factors, e.g. the choice of catalyst and diluent, but is generally in the range of 70 to 100 ° C. However, since the polymerization reaction is exothermic, it is generally necessary to remove heat from the reaction vessel, e.g. using air or water cooling to control the temperature.

The choice of hydrogen / ethylene ratio in the described range will depend on the desired MFI of the polyethylene formed and can be readily ascertained by a suitable test series. The envisaged catalyst material may e.g. are used to polymerize a variety of hydrogen / ethylene mixtures with different hydrogen / ethylene ratios and link the MFI of the formed polyethylenes to said ratio. It will be seen that other experimental conditions, e.g. catalyst temperature, pressure and concentration and activity must be kept constant in the test series.

In a variety of polymerizations in which ethylene was polymerized using a catalyst comprising zirconetetrabenzyl reacted with alumina in the presence of hydrogen, e.g. established the following relationship between the hydrogen / ethylene ratio and the MFI of the polyethylene formed.

Hydrogen / Ethylene Ratio MFI of Polyethylene 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 selecting an appropriate hydrogen / ethylene ratio for a given set of working conditions, the desired MFI of the product polyethylene can be obtained within reasonably precise limits. The desired MFI can then be maintained by controlling the catalyst feed rate to the polymerization vessel so that the polymerization rate is kept at a predetermined value by compensating for changes in catalyst activity.

The hydrogen / ethylene ratio can be investigated by any convenient method, e.g. by measuring the hydrogen concentration using a catharometer. However, it is most convenient to continuously analyze the gas mixture using an on-line gas-liquid chromatograph (GLC). Such an instrument can be easily connected to a printer or the like to produce a curve in which hydrogen and ethylene concentrations can be linked to peaks of varying heights. These peak heights can then be maintained at predetermined values, either by controlling the respective gas streams or preferably by keeping the ethylene stream constant and varying the hydrogen stream. The flow of gas can be controlled manually or by using automatic control valves coupled with the output of the GLC apparatus.

As previously mentioned, the feed of catalyst to the reactor is regulated so that the rate of polymerization is kept at a constant value. The rate of polymerization can most conveniently be investigated by observing the total pressure in the reactor as a decrease in reaction rate causes a reduction in the amount of polymerized ethylene and a corresponding increase in total pressure and counting versa. An alternative parameter that can be used in this way is the temperature of the effluent material from the reactor cooling system. However, the reactor pressure gives a faster reaction to changes in the reaction rate than the coolant temperature.

The catalyst slurry can be pumped to the reactor in a continuous stream, controlling the flow rate, or alternatively discrete standard amounts of catalyst may be released into the reactor at intervals, varying the interval between successive additions.

The invention will now be illustrated by the following examples.

In general.

Nitrogen and ethylene were deoxygenated and dried by passing them through two 2 m columns packed with freshly prepared, alumina (B.T.S catalyst) comminuted copper and a Type 5A molecular sieve.

Hydrogen was passed through a molecular sieve dryer.

Solvents and diluents were deoxygenated and dried by passing them through two 1.5 m columns packed with B.T.S. catalyst and 5A molecular sieve.

-. 8 141101

Preparation of zirconetetrabenzyl / alumina catalyst

Benzyl magnesium chloride (2.78 kg) as a solution in 25 L of diethyl ether was transferred under nitrogen to a reaction vessel at 0 ° C. Zirconium tetrachloride (1.2 kg) was added against a nitrogen purge stream in 300 g portions over a 45 minute period. The mixture was stirred for 2 hours during which time the temperature was allowed to rise to room temperature. Decalin (65 L) was added and the mixture was stirred for an additional 1 hour.

The resulting slurry was allowed to settle, and the above liquid was recirculated to a stainless steel filter and filtered under a slight positive nitrogen pressure.

Ether was removed from the decalin solution by passing it over heat exchange tubes at a temperature of ca. 50 ° C at the same time as nitrogen was passed through the liquid in a countercurrent.

The decalin solution from the heat exchanger was filtered under nitrogen. The average yield of zircon tetrabenzyl was 6%.

Ketjen grade B alumina was sieved to 53-99 µm and dried in a rotary tube oven at 500 ° C for 2 hours. Nitrogen was passed past the openings of the tubes once the furnace had been brought to operating temperature.

The alumina was cooled under nitrogen and portions (10 kg) were slurried with hexane (50 L), a zirconium tetrabenzylo solution (prepared as described above) was added and the mixture was stirred. The Ορε paralysis was allowed to settle and the above fluid was circumscribed. Additional zircon tetrabenzylo solution was added until the amount of the zircon on the alumina was approx. 0.5 m atoms / g alu = minium oxide.

The coated alumina was washed repeatedly with hexane and finalized as a 10-20% (w / v) slurry in hexane.

9 U1101

polymerization

A stirred reaction vessel (4.0 no. 5) was charged with hexane (2.0 m 2) and pressurized with ethylene and hydrogen. The gases were supplied through an opening below the liquid height. The reaction was started by injecting J the catalyst slurry. The temperature of the reactor was adjusted to the specified value by water cooling.

Ethylene, hydrogen and hexane were fed to the reactor at appropriate rates and the catalyst slurry was injected at discrete intervals. The gas composition in addition to the diluent was analyzed by on-line gas-liquid chromatography and the hydrogen flow was controlled automatically to maintain the required hydrogen / ethylene ratio. Polyethylene was formed as a slurry of particles. This slurry was taken continuously or at intervals through a dipping tube, fed to a strainer and then centrifuged.

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

Example 1.

Ethylene was fed to the reactor at a rate of 140 kg / hour, and hydrogen was supplied at a rate suitable to maintain hydroxide.

ISLAND

the gene / ethylene ratio of 1.03. The total working pressure was 5 kg / cm.

Hexane was added at a rate of 0.6 m 2 / hr, and the catalyst slurry was fed at intervals at a rate of approx. equal to 42 m atoms Zr / hour, the precise speed being controlled so as to maintain the working pressure of 5 kg / cm -1 and the temperature at 80 ° C.

The MFI of the product was 0.008. After working with the reactor under these conditions for the desired time period, the hydrogen flow was reduced to give a hydrogen / ethylene ratio of 0.90, keeping the catalyst feed rate at the same average value. When constant state conditions were reached, the product had an MFI of 0.005.

1 * 11 * 1 10

Example 2.

The general procedure of Example 1 was followed with a hydrogen / ethylene ratio of 2.0 and an average catalyst feed rate of 54 m atoms Zr / hr, with the exact

'Q

value was controlled so that the working pressure was kept at 7 kg / cm. The MFI of the product was 0.07.

The hydrocarbon flow rate was then reduced to give a hydrogen / ethylene ratio of 1.55 and the catalyst feed rate was kept at the same average value. When constant state conditions were reached, the working pressure was 6 kg / cm.

The MFI of the product was then 0.02.

Example 5

The general procedure of Example 1 was followed, with the hydrogen / ethylene ratio being 2.84. Hexane was added at a rate of 0.62 m 2 / hr, and the catalyst slurry was added at intervals at an average rate of 48 m atoms Zr / hr, maintaining the exact value so that the reactor pressure was maintained at 5.7 kg / cm 2 at 80 ° C. The MFI of the product polyethylene was 0.18.

To bring the MFI to the range 0.2 - 0.25, the catalyst feed rate was increased to 52 m atoms / hour, with all other feed rates remaining constant. A polymer with MFI 0.22 was obtained under constant state conditions.

Example 4

The procedure of Example 1 was followed, with hydrogen / ethylene feed

--- 'Z

the holdings were 1.53, the hexane feed rate was 0.6 no / h, and the catalyst atorop the slurry was added at intervals with an average velocity of 60 m atoms Zr / hr. The exact catalyst feed rate was controlled such that the reactor pressure was maintained at 4.1 kg / cm 2. at 80 ° G. The MFI of the product was 0.023.

Increasing the hydrogen supply rate to give a hydrogen / ethylene ratio of 3.3 with the same average catalyst stream allowed the reactor pressure of 6.7 kg / cm H1101 to be maintained at 80 ° C to give a product with MFI 0 , 24th

The hydrogen / ethylene ratios were increased to 4.1, and the average catalyst feed rate was increased to 70 m atoms Zr / hr, the precise rate being regulated so that the reactor pressure was maintained at 7.4 kg / cm @ 80 ° C. Under constant state conditions, a melt flow index 1.0 was obtained.

Example 5

The general procedure of Example 1 was followed at a reaction temperature of 90 ° C with the same feed rate for ethylene and for hexane. Hydrogen was supplied at a rate maintaining a hydrogen / ethylene ratio of 2.2, and the catalyst slurry was fed at an average velocity of 72 m atoms Zr / hr, the addition being controlled so that the reactor pressure was maintained at 6.3 kg / cm 90 ° C. A polymer with MFI = 0.20 was prepared under constant state conditions.

By increasing the hydrogen addition rate to a hydrogen / ethylene = ratio of 3.10 with the same average catalyst flow, it became possible to maintain a reactor pressure of 7.24 kg / cm 2 at 90 ° C, giving a polymer with MFI = 0.90 under constant state conditions.

Keeping the same ethylene and hydrogen feed rates and increasing the average catalyst feed rate slightly to 74.8 m atoms Zr / hr caused the polymerization rate to increase and the hydrogen / ethylene ratio in the reactor to be increased to 3.16. The pressure could then be maintained under constant state conditions of 7.19 kg / cm 2, 90 ° C, giving a polymer product with MFI = 1.0.

Example 6

The general procedure of Example 1 was followed at 75 ° C with the same feed rate for ethylene and for hexane. Hydrogen was supplied at a rate such that the hydrogen / ethylene ratio was maintained at 3.2 and the catalyst slurry was added at an average rate of 42 m atoms Zr / hr, with the feed being refluxed.