DE1520532C - Process for the preparation of solid ethylene polymers and polymerization catalyst for use in this process - Google Patents

Description

It is known to produce normally solid, thermoplastic polymers by polymerizing ethylene and / or other 1-olefins in the presence of a catalyst which contains chromium oxide and at least one of the oxides silicon dioxide, aluminum oxide, zirconium oxide and thorium oxide, at least some of the chromium in the catalyst is in the hexavalent state upon initial contact with the hydrocarbon. Usually, the catalytic polymerization is conducted at a temperature in the range of 38 to 260 ° C, preferably in the range 66-190 ⁰ C is performed. The polymers obtained are useful in the manufacture of shaped articles, threads and films. Details of this process can be found in U.S. Patent 2,825,721. In this process, however, the productivity of the catalyst leaves something to be desired; the melt index of the polymer obtained is also somewhat too high. -

It is also known in the polymerization of olefins with the said chromium oxide supported catalysts Add aluminum trialkyls as activators. This increases productivity of the catalyst increased, but the polymer density drops sharply, which is very disadvantageous, and the melt index is only slightly reduced.

The invention now relates to a process for the production of solid ethylene polymers by polymerizing ethylene, alone or together with smaller proportions of higher olefins, in hydrocarbons as the reaction medium and in the presence of catalysts made from chromium oxide and at least one of the oxides silicon dioxide, aluminum oxide, zirconium dioxide and thorium dioxide as Carrier and organometallic compounds, which is characterized in that the organometallic compound is an organozinc compound of the general formula ZnR ₂ , in which R is a hydrogen atom or an alkyl, cycloalkyl or aryl radical or a combination of these radicals with 1 to 20 carbon atoms and where at least one of the radicals R represents one of the hydrocarbon radicals mentioned, is used in an amount of 0.1 to 15 percent by weight, based on the total weight of chromium oxide and silicon dioxide, aluminum oxide, zirconium dioxide and / or thorium dioxide.

As the comparative tests below show, when using the mentioned Organozinc compounds instead of aluminum trialkyls with high productivity with polymers higher density and lower melt index. · '. ·

It has been found that the amount of the zinc compound added must be carefully controlled within the aforesaid range, since if a larger amount of this compound is added, the activity and productivity of the chromium oxide polymerization catalyst are decreased rather than increased . According to the process of the invention, the amount of zinc compound is in the range from 0.1 to 15 percent by weight, based on the total weight of the oxides mentioned. The optimum amount to be used within this range depends to a certain extent in a particular polymerization system on the reaction conditions used, the specific properties of the catalyst and on the composition of the monomer starting material which is used for the polymerization. The optimum can easily be determined only by routine examinations according to the present teaching.

. Reference is also made to US Pat. No. 2,944,099, in which the use of certain Metal alkyls, metal aryls and the like for activating a chromium oxide catalyst in one of one halogenated hydrocarbon existing polymerization medium is described. It was, however completely unexpected that in a hydrocarbon medium, in which the chromium oxide catalyst is already highly active, the high activity is still considerable can be increased. Furthermore, it was not to be expected that in order to obtain such an increase, a regulated small amount of an organozinc compound would be required.

The term "hydrocarbon medium" means a polymerization system in which the reactants and optionally the diluent consist almost exclusively of hydrocarbons and all other types of compounds with the exception of the oxide catalyst and the zinc compound only as insignificant Impurities are present.

Zinc compounds which can be used according to the method of the invention are dimethyl zinc, diethyl zinc, Di-n-propyl zinc, diisopropyl zinc, di-n-butyl zinc, din-amyl zinc, the Diisoamy! zinc compounds, Din-hexylzinc, Di-n-octyl zinc and di-n-dodecyl zinc. Also usable according to the method of Invention are dicyclopentylzinc, dicyclohexylzinc, dimethylcyclopentylzinc, dimethylcyclohexylzinc, Diphenyl zinc, the ditoluyl zinc compounds, the dixylyl zinc compounds, Di- (2-hexyltetradecyl) -zinc, di- (4-cyclohexyloctyl) -zinc, di- (2-butylcyclohexyl) -zinc, Di (2,4,8-trimethylhexadecyl) zinc, di (phenyltetradecyl) zinc, di (2- [2,3,5-tributylphenyl] ethyl) zinc, Dibenzyl zinc or di (4,6-dicyclopentyldecyl) zinc. Generally because of their lighter weight Availability which uses dialkyl zinc compounds. However, it is also possible according to the invention Methyl zinc hydride, ethyl zinc hydride, n-butyl zinc hydride, phenyl zinc hydride, cyclohexyl zinc hydride, 2-methylcyclopentyl zinc hydride, 3-butylphenyl zinc hydride, 8-phenoctyl zinc hydride or 10-phenyltetradecyl zinc hydride to use.

The preferred oxide catalyst is a chromium oxide - silicon dioxide - aluminum oxide catalyst or a chromium oxide-silicon dioxide catalyst because of the very high activity that these special catalysts develop. The preparation of these catalysts ^l is described in detail in the USA.-. U.S. Patent 2,825,721. In general, the chromium content of these catalysts is 0.5 to 10 percent by weight.

It is also possible according to the invention to use a chromium oxide catalyst, its support (Silicon dioxide, silicon dioxide-aluminum oxide or aluminum oxide) with fluorides, such as hydrogen fluoride, hydrated aluminum fluoride or an ammonium fluorosilicate, to increase the polymerization activity has been heated. .

According to the process according to the invention is not only the production of homopolymers of ethylene possible, but also the copolymerization of

Ethylene with smaller proportions of higher olefins, such as. B. propylene, 1-butene, 2-butene, isobutylene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene and 1-dodecene. Generally, the comonomer can be any aliphatic monoolefin having from 3 to 12 carbon atoms be per molecule. In general, the amount of higher olefin comonomer employed will be range in the range from 1 to 25 percent by weight, based on comonomer plus ethylene. Preferably the amount of comonomer is between 2 and 15 percent by weight, based on the total olefins. usually the preferred olefinic comonomer is from a 1-olefin because of the higher reactivity of these olefins.

The reaction is carried out according to the method of Invention in general in a manner known per se in the temperature range from 38 to 260 ° C and on best - since the polymer yields are highest in this range - between 66 and 180 ° C accomplished.

As stated earlier, in the presence of a hydrocarbon diluent, usually one which is liquid and inert under the reaction conditions and that towards the catalyst shows no harmful effects, polymerizes. Suitable diluents are hydrocarbons with 3 to 12 carbon atoms. Because of their inertness, paraffins and cycloparaffins are generally used or aromatics selected. The aromatics are less preferred than the other two Hydrocarbon series, since they or the impurities that often accompany them appear to reduce the activity of the catalytic converter. Preferred diluents are propane, η-butane, isobutane, n-pentane, isopentane, η-hexane, n-heptane, 2,2,4-trimethylpentane, Cyclopentane, cyclohexane, methylcyclohexane, n-dodecane, and mixtures thereof. Through the Liquid diluents listed above also facilitate removal of the heat of reaction. The pressure is generally in the range between 0 and 1.41 atmospheres and only has to be sufficient be to keep the diluent in the liquid phase, d. H. is preferably from 3.5 to 53 atm.

If the reaction temperature is less than about 106 ° C, the polymer can form as a suspension form in the reaction mixture. In most cases, the polymer forms at higher temperatures as a solution in the diluent in the reaction zone.

Contacting the monomers with the catalyst can be carried out by any known technique the solid catalysis are effected. A very convenient working method is to use the Suspending oxide catalyst in the liquid diluent and stirring the reaction mixture, whereby the catalyst is held as a solid suspension in the "liquid diluent. Others known catalytic contacting methods can also be used, for example the fixed bed process, the fluidized bed process, the gravitational bed process and the like.

The organozinc compound used according to the method of the invention is preferred added to the reaction zone in the form of a separate stream from the oxide catalyst. she can are previously mixed with the chromium oxide catalyst, but in this case it is preferred that the zinc compound in the absence of the monomer in contact with the for no more than a few minutes Chromium catalyst remains. Contact of the zinc compound with the chromium oxide catalyst during prolonged periods in the absence of the monomer to be reacted there appears to be a decrease in the To give activity of the catalyst, ι. . .

In general, it is desirable that the reactants and the diluent practically anhydrous and free from catalyst poisons such as sulfur compounds, Carbon monoxide and oxygen, are. Many halogen compounds are catalyst poisons. If small amounts of moisture or other catalyst poisons not before the polymerization reaction. removed, the amount of the applied organozinc compound should be increased, whereby the Amount of this compound decomposed by impurities such as water into consideration is to be drawn so that there is a sufficient amount within the above range to increase the activity of the chromium oxide catalyst after all moisture or other existing Has completely reacted impurities with the added amount of the organozinc compound. Apart from the increase in the polymer yield and the increase in the productivity of the catalyst the method of the invention brings with it considerable further advantages, as has already been indicated and is shown by comparative tests. So in many cases the addition of the zinc compound results

jo a decrease in the melt index, what the implementation allowed the polymerization reaction to take place at a slightly higher temperature, around a given polymer melt index than it would be without the zinc compound. Because of this improvement results in a drain from the reaction vessel with a reduced viscosity, whereby heat transfer, centrifugation and filtration are facilitated. In addition, the Melt index lowered and productivity increased without a decrease in the density of the polymer accompanies this phenomenon. A corresponding drop in the melt index will also occur in many cases achieved when ethylene is copolymerized with higher olefins.

Under the term "yield" or "productivity" as used herein is the total amount on solid. Polymer or copolymer to understand which by a given weight of the oxide catalyst during the reaction period is produced. This productivity or yield is expressed in kilograms of polymer per Kg of composite oxide catalyst, excluding the zinc compound.

example 1

In a number of approaches, ethylene has been polymerized into solid homopolymer by using it with a chromium oxide-silicon dioxide-aluminum oxide catalyst with 2.5 percent by weight chromium

was tacted. The basis of the catalyst consisted of a silica-alumina gel with about 12 weight percent aluminum oxide. The chromium oxide-containing catalyst was obtained by heating activated in a stream of dry air at 538 ° C for 5 hours. One with a motor-driven Stainless steel reaction vessel fitted with a stirrer was first heated and with purged with dry nitrogen, and then were

0.02 to 0.04 parts by weight of the chromium oxide catalyst introduced into the reaction vessel in suspension in 340 parts by weight of cyclohexane. then Zinc diethyl was added in the amounts given in the table below. The reaction vessel was then immediately capped and ethylene was added to the reaction vessel for a Reaction period of one hour supplied, with a pressure within the reaction vessel of 31.6 atm was maintained. At the end of the reaction time, the diluent was used Cyclohexane volatilized from the reaction mixture and the polymer isolated. The achieved Results are listed in the table below together with those of a comparative experiment, in which no diethyl zinc was present, while the other conditions were practically the same were.

Diethyl zinc, percent by weight, based on chromium

Oxide-Silica-Aluminum Oxide

Reaction temperature ^{, 0 C}

Productivity, kilograms of polymer per kilogram

catalyst

Density *), g / cm ³

Melt index **)

0 ***)
140

1480
0.963
1.03

6th
140

2510
• 0.962
0.36

12 140

1730 0.963 0.27

*) ASTM method D 1505-57T with the exception that the sample was preconditioned as follows: The samples were produced by compression molding tablets of the ethylene polymer into a strip of about 36.7 cm ² and 0.79 to 12.7 mm Thickness. A "Pasadena" press (Model P 325, Pasadena Hydraulics, Inc.) was used. The strips were molded at a pressure of 1410 kg / cm ² and 166 ° C. The heat was then turned off and tap water was passed through the mold cooling system. The strip was cooled to 93 ° C. at a rate of 13 ° C./minute and then to 66 "C. as quickly as possible by increasing the flow rate of the cooling water. The strip was then removed from the mold and allowed to stand at room temperature for 24 hours Small pieces of the strip, e.g., cubes about 6.3 mm, were cut to determine density, and these pieces were checked to be sure they did not contain surface defects or voids in which air could become trapped if they were The density was then determined as prescribed by the ASTM method, using ethanol and water as suspending liquids.
**) ASTM method D-1238-57 T, condition E..

***) Comparison test. .

The above values show that 6% diethyl zinc, based on the oxide catalyst, give an increase in the productivity of the catalyst of 65 to 70%, while a smaller increase when 12% diethyl zinc was added.

Furthermore, it follows from the values that a drop in the melt index is achieved without a cause a significant change in the density of the polymer.

B e i s ρ i e 1 .2

Ethylene was polymerized to solid homopolymer according to the general procedure of Example 1. In this case, however, was the chromium content of Oxydkatalysators Q, 70 weight percent, and the catalyst was activated for 5 hours at 704 ⁰ C. The chromium oxide was carried on microspheroidal silica in place of silica-alumina. The following results were obtained:

Diethyl zinc, percent by weight based on

• Chromium oxide-silicon dioxide

Reaction ^{temperature, 0} C ...

Productivity, kilograms
Polymer per kilogram
catalyst

density

Melt index

*) Comparison test.

0 *) 3 2 138.9 144.4 145.5 1890 2130 2400 0.961 0.962 0.963 0.31 0.28 0.45

1.5
137.7

2490

0.17

1 1 139.4 145.5 2880 2950 0.962 0.963 0.25 0.67

0.5 140.5

2710 0.962 0.37

From the above values, there is a significant improvement in terms of productivity a chromium oxide catalyst based on silicon dioxide, which practically does not contain aluminum oxide contains, is achievable.

at

sp

ι el. 3

Solid copolymers of ethylene and 1-butene were prepared according to those generally described in Example 2 Procedure. The results are in the following Table summarized in which the: l'rozciHaiipabcn des 1-butene are based on the total weight of ethylene plus 1-butene. The catalyst activation temperature was 538 ° C for 5 hours.

<> 5

Diethyl zinc,% based on () *) 5 Chromium oxide silicon 140 142 dioxide Reaction ^{temperature, 1} C ... 1-butene in the Olcfin 4.7 5.0 loading weight percent

continuation

Productivity, kilograms
Polymer per kilogram
catalyst

density

Melt index '.

1180 0.949 0.27

1550 0.950 0.15.

booty of 1-butene-ethylene copolymers with a chromium oxide catalyst is achievable, improved.

Example 4

An additional Copolymerisationsansätze as described in Example 5, carried out using the stop, that the catalyst activation temperature was io the foregoing values ergibt'sich 704 ⁹ C. In the presence of small amounts of diethyl zinc, the following results were obtained:

Diethyl zinc,% based
from chromium oxide-silicon dioxide

Reaction temperature, ° C

1-butene in the olefin feed, weight percent

Productivity, kilograms
Polymer per kilogram
Catalyst ...........

Density ....... ■.: ...

Melt index

*). Comparative experiments.

■ ο ·)
138.9 0 *)
140.0 10
137.7 5
139.4 3 '
139.4 3
140.0 1
136.1 4.2 3.7 4.1 4.2 3.9 3.8 ' 3.4 3200
0.948
0.69 3050
0.948
0.79 1125.
0.956
0.13 1600
0.950
0.24 2890
0.949
0.44 2490
0.950
0.40 3790
0.949
0.39

Γ 141.6

4.0

4150 0.947 0.90

The above values again show the influence of adding different amounts of Diethyl zinc in a special polymerisation system. So 10% lower diethyl zinc, based on that Oxide catalyst, productivity as was the case with 5 and 3%. In contrast, 1% increased Diethyl zinc yields up to about 4000 kg per kilogram of catalyst. With yields in this The polymer can be of the order of magnitude out of the reaction process without any filtration or centrifugation step to remove the catalyst, since only 1 part by weight of catalyst is used here is present in about 4000 parts by weight of polymer. For many purposes for which the poly mere can be used, this amount of inorganic material or ash is portable, so 'that the catalyst can remain in the polymer, which leads to a reduction in production costs by avoiding a catalyst removal step.

B e i s ρ i e 1 5

In this example is the use of Din-butylzinc described. The copolymerization of ethylene and 1-butene was carried out as in Example 4 with the exception that the activation temperature was 593 ° C. The results are in the summarized in the following table:

Dibutyl zinc,%, based on chromium oxide-silicon dioxide

Reaction temperature, ° C ... '.

1-butene in the olefin feed,% ...

Productivity, kilograms of polymer per kilogram of catalyst

Density.

Melt index

*) Comparison test.

From the above values, it can be seen that DL-ri-butylzinc increases the productivity of the chromium oxide catalyst improved. It can be seen that the productivity after the addition of 0.78 percent by weight Di-n-butyizinc goes up and goes through a maximum at about 3 weight percent. With another Increasing the amount of dibutyl zinc resulted in a decrease in productivity. .

Those prepared according to the process of the invention Polymers can be isolated from the reaction mixture by methods such as are familiar to the person skilled in the art.

0 *) 0.78 1.0 1.5 . 3.0 140.5 143.9 141.6 141.1 140.5 3.5 3.8 3.6 3.6 3.6 2130 2270 2380 2280 2400 0.949 0.950 0.949 ■ 0.949 0.950 0.33 0.47 0.41 0.38 0.29

5.0

140.0

3.6

1640 0.949 0.18

Comparative experiments

The technical progress achieved by the method of the invention over that from the USA patent specification 3 037 008 known method is shown in the following table, in which the results are summarized by comparative experiments.

In the test group t) EF the results, -die can be obtained with diethylzinc as cocatalyst (F), compared with the results obtained in the blind test (D) or with triethylaluminum (E). .

109637/123

In., The table are comparative tests with others Tetrabutyltin and triethylboron, with added.

10

organometallic compounds, namely

Homopolymerization of ethylene

Polymerization time: 1 hour solid catalyst: chromium oxide on support. Pressure: 31.6 at. Diluent: cyclohexane

Ver Metallalky! and% by weight reaction
temperature productivity 140 147 153 1480 Polymer density 538 ° C 0.963 Polymer search on solid catalyst 139. 153 . 152 882 0.965 Melt index ⁰ C 140 154. 153 1730 g / ccm 0.963; : activated at 538 ° C. A. kg / kg . 760 1.03 B. 2.5% Cr on silica-alumina: activated at 1910 0.83 C. none 0.7% Cr on silica (0.6% aluminum oxide) 0.7% Cr on silica (0.1% aluminum oxide) 830 0.27 Tetrabutyl tin, 16% none none : activated .0.963 D. Diethyl zinc, 12% Triethyl aluminum, 10% Triethyl boron, 4% 960 0.959 0.48 E. Diethyl zinc, 10% Diethyl zinc, 4% 1230 0.965 0.42 F. 1190 at 538 ° C 0.38 G 0.38 H 0.42 I. 0.963 0.32 0.964 (0.963)

The results indicate that the use of diethyl zinc leads to better results than the use of triethylaluminum or the other organometallic compounds mentioned.

In order to be able to assess the effect of these cocatalysts, all results of an experimental approach must be taken into account.

The table above shows that when using diethyl zinc (F) the productivity, based on the comparative experiment (D), in which no metal alkyl is used, is increased; the polymer density is clearly increased compared to tests D and E; compared with comparative test D, the melt index is from 0.48 to 0.38 degraded.

The combination of these test results shows that diethyl zinc is clearly superior to triethylaluminum and also to the two other organometallic compounds. It must be emphasized that an increase in the polymer density is of great importance, since it shows that a more linear and less branched polymer is present, which in turn has a greater tensile strength and a higher softening point. A decrease in the melt index is also an essential and important feature, since the flow properties are then reduced, which leads to a stiffer polymer . · ^:

Thus it can be stated that only experiment F, in which diethyl zinc was used, influenced all three desired effects in a desired manner. This is not the case with triethylaluminum, since in this case productivity is increased, but the polymer density drops sharply and the melt index is only slightly reduced to 0.42. It follows that the process according to the invention leads to surprising technical advantages.

Claims (3)

Patent claims: 1. Process for the production of solid ethylene polymers by polymerizing ethylene, alone or together with smaller proportions of higher olefins, in hydrocarbons as a reaction medium and in the presence of catalysts made of chromium oxide, at least one of the oxides silicon dioxide, aluminum oxide, zirconium dioxide and thorium dioxide as a carrier and organometallic compounds , characterized in that the organometallic compound is an organozinc compound of the general formula ZnR ₂ , in which R is a hydrogen atom or an alkyl, cycloalkyl or aryl radical or a combination of these radicals with 1 to 20 carbon atoms and where at least one of the radicals R is one of the is used in an amount of 0.1 to 15 percent by weight, based on the total weight of, chromium oxide and silicon dioxide, aluminum oxide, zirconium dioxide and / or thorium dioxide. 2. The method according to claim 1, characterized in that that a catalyst is used which is composed of chromium oxide, silicon dioxide and a zinc dialkyl consists of the general formula mentioned in claim 1. 3. Polymerization catalyst for use in the method according to claim 1, arisen by mixing chromium oxide, at least one of the oxides silicon dioxide, aluminum oxide, zirconium dioxide and thorium dioxide as well as one organometallic compound, characterized by shows that the organometallic compound is an organozinc compound of the general formula ZnR ^, in which R is a hydrogen atom or an alkyl, cycloalkyl or aryl radical or a combination of these radicals having 1 to 20 carbon atoms, where at least one of the radicals R is a represents the hydrocarbon radicals mentioned, in an amount of 0.1 to 15 percent by weight, based on the total weight of chromium oxide and silicon dioxide, aluminum oxide, zirconium dioxide and / or thorium dioxide has been used.