GB2024832A

GB2024832A - Polymerisation of Ethylene

Info

Publication number: GB2024832A
Application number: GB7922906A
Authority: GB
Original assignee: Nippon Oil Corp
Current assignee: Eneos Corp
Priority date: 1978-07-05
Filing date: 1979-07-02
Publication date: 1980-01-16
Also published as: GB2024832B; DE2927259C2; FR2430429B1; DE2927259A1; FR2430429A1; IT7924129A0; IT1122026B; CA1118946A

Abstract

A process for preparing polymers and copolymers of ethylene by first contacting a catalyst consisting of an organometallic, compound and a solid substance containing magnesium and titanium and/or vanadium, with an alpha - olefin, preferably in the presence of a liquid hydrocarbon, and thereafter contacting ethylene or a mixture of ethylene and an alpha -olefin in gaseous phase with the treated catalyst whereby the homopolymerization of ethylene or the copolymerization of ethylene and alpha -olefin is effected.

Description

SPECIFICATION Process for Preparing Polyolefins This invention relates to a vapor phase polymerization of ethylene using a Ziegler-type catalyst of high activity. More particularly, it is concerned with a process for preparing polyolefins, which process comprises contacting a catalyst consisting of a solid substance and an organometallic compound, said solid substance containing magnesium and titanium and/or vanadium, with an sr-olefin in the absence or presence of a liquid hydrocarbon and thereafter contacting ethylene or a mixture of ethylene and an (t-olefin in gaseous phase with the treated catalyst whereby the homopolymerization of ethylene or the copolymerization of ethylene and r-olefin is effected.

It has heretofore been known that a catalyst system obtained by first supporting a transition metal on a magnesium-containing solid carrier such as MgO, Mg(OH)2, MgCI2, MgCO3, or Mg(OH)CI and then combining it with an organometallic compound can serve as a catalyst of remarkably high activity for the polymerization of olefins. It is also known that an organometallic compound and the reaction product of an organomagnesium compound such as RMgX, R2Mg, or RMg(OR) and a transition metal compound can be an excellent high polymerization catalyst for olefins see for example Japanese Patent Publication No.12105/64, Belgian Patent No. 742,112, Japanese Patent Publications Nos. 13050/68 and 9548/70).

The olefin polymerization using such highactivity Ziegler-type catalysts is in many cases carried out in liquid phase in the presence of an inert hydrocarbon as solvent such as butane, pentane, hexane and heptane. But the steps of separation, recovery, purification and re-use of the solvent used are so troublesome that, for the simplification of process to a large extent, there has also been tried a vapor phase polymerization in which olefin is polymerized in a condition substantially free from liquid phase, namely in vapor phase; more particularly, a catalyst is fed into a bed consisting of polymer particles which have been introduced in advance or of granular polymer particles which have been produced as the polymerization proceeded, and it contacts the starting gaseous olefin to produce a polymer.

Such vapor phase polymerization is advantageous in that the use of a high-activity catalyst can eliminate the recovery step for polymerization solvent and can omit the catalyst separation and inactivation step, so that the process as a whole can be simplified to a large extent. Because of the following technical problems, however, it is still difficult to practice such vapor phase polymerization industrially advantageously.

Although there is the possibility of such vapor phase polymerization becoming a very simplified process as mentioned above, its execution in an industrially advantageous manner is required to solve many technical problems. For example, the following are important technical problems to be solved: the catalyst to be used should be sufficiently high in activity to the extent that the residual catalyst removing step is not required; there should be no adhesion of the resulting polymer particles to the reactor walls, stirrer, etc.; there should occur no abnormal phenomenon which would cause blocking of the polymer discharge port from the reactor, transport line, etc. effected by the production of coarse or aggregated polymer particles; the production of ultra-fine particles which scatter easily during polymerization should be minimized; the particle properties, e.g. bulk density, should be satisfactory.

Having made an intensive study of the aforesaid technical problems, we completed the present invention, that is, a vapor phase polymerization process for ethylene which as a whole is very simplified because a vapor phase polymerization reaction can be carried out extremely stably and because the catalyst removal step can be omitted.In more particular terms, this invention is concerned with a process for preparing polyolefins, which process comprises contacting a catalyst consisting of a solid substance and an organometallic compound said solid substance containing magnesium and titanium and/or vandadium with an cr-olefin in the absence or presence of a liquid hydrocarbon and thereafter contacting ethylene or a mixture of ethylene and an cr-olefin in gaseous phase with the treated catalyst whereby the homopolymerization of ethylene or the copolymerization of ethylene and cr-olefin is effected.According to the process of this invention, that is, by contacting a catalyst consisting of a solid substance and an organometallic compound, said solid substance containing magnesium and titanium and/or vanadium, with cr-olefin in the absence or presence of a liquid hydrocarbon and thereafter carrying out a vapor phase polymerization of ethylene, it has become clear that, as compared with the case where the said catalyst is not contacted with an a-olefin, the catalyst becomes extremely high in activity, the production of coarse and ultra-fine particles is decreased, the particle properties are satisfactory, the adhesion of polymer particles to the reactor and the aggregation thereof are minimized, and a vapor phase polymerization can be carried out extremely stably.It is quite unexpected and surprising that according to the process of this invention it has become possible to carry out a vapour phase polymerization extremely smoothly even with respect to those systems whose stable operation has heretofore been difficult.

We have firstly found that if a catalyst is contacted with a gaseous ct-olefin and then a vapor phase polymerization is carried out using the so-treated catalyst, improvements are attained in activity and in the properties of the resulting polymer particles. Secondly we have found further advantages such that if a catalyst is contacted with an (Z-olefin in the presence of a liquid hydrocarbon and then a vapor phase polymerization is carried out using the so-treated catalyst in addition to the above-mentioned advantage, it becomes possible to introduce the catalyst treated with the cr-olefin in the state of slurry into the reaction vessel so the operation is made easier, and the latent heat of vaporization caused by the introduction of a liquid hydrocarbon into the reaction vessel facilitates the removal of the reaction heat.

The catalyst system used in this invention is the combination of a solid substance and an organometallic compound, said solid substance containing magnesium and titanium and/or vanadium. The said solid substance is obtained by supporting a titanium compound and/or a vanadium compound on an inorganic solid carrier in known manner. Examples of such inorganic solid carrier are magnesium metal, magnesium hydroxide, magnesium carbonate, magnesium oxide and magnesium chloride; double salts, double oxides, carbonates, chlorides and hydroxides containing magnesium atom and a metal selected from the group consisting of magnesium, silicon, aluminium and calcium; furthermore, these inorganic solid carriers after treatment or reaction with an oxygen-containing compound, a sulfur-containing compound, a hydrocarbon or a halogen-containing substance.

As the titanium compound and/or vanadium compound referred to herein, mention may be made of halides, alkoxy halides, oxides and halide oxides of titanium and/or vanadium. Examples are tetravalent titanium compounds such as titanium tetrachloride, titanium tetrabromide, titanium tetraiodide, monoethoxytrichlorotitanium, diethoxydichiorotitanium, triethoxymonochlorotitanium, tetraethoxytitanium, monoisopropoxytrichlorotitanium, diisopropoxydichlorotitanium, and tetraisopropoxytitanium; various titanium trihalides obtained by reducing titanium tetrahalides with hydrogen, aluminium, titanium or an organometallic compound; trivalent titanium compounds such as compounds obtained by reducing tetravalent alkoxytitanium halides with an organometallic compound; tetravalent vanadium compounds such as vanadium tetrachloride; pentavalent vanadium compounds such as vanadium oxytrichloride and orthoalkyl vanadate; and trivalent vanadium compounds such as vanadium trichloride and vanadium triethoxide.

In this invention there is used as catalyst the combination of a solid substance, which is obtained by supporting a titanium compound and/or a vanadium compound on a solid carrier which has previously been exemplified, and an organometallic compound.

Examples of preferred catalyst systems are the combination of an organometallic compound with solid substances of the following systems (in which R represents an organic radical): MgO-RX TiCI4 (see Japanese Patent Publication No.

3514/76), Mg-SiCl4-ROH-TiCl4 (see Japanese Patent Publication No. 23864/75), MgCI2 Al(OR)3-TiCl4 (see Japanese Patent Publications Nos. 152/76 and 15111/77), MgCI2-SiCI4-ROH TiCI4 (see Japanese Patent Public Disclosure No.

106581/74), Mg(OOCR)2Al(OR)3-TiCI4 (see Japanese Patent Publication No. 11 710/77), Mg POCI3-TiC14 (see Japanese Patent Publication No.

153/76), MgCl2-AlOCl-TiCl4 (see Japanese Patent Public Disclosure No. 133386/76).

Another example of a catalyst system which may be suitably used in this invention is the combination of, as the solid substance, the reaction product of an organomagnesium compound such as a Grignard compound and a transition metal compound, and an organometallic compound. As an organomagnesium compound there may be used, for example, those represented by the general formulae RMgX, R2Mg, and RMg(OR) wherein R is an organic radical and X is halogen, ether complex thereof, and further these organomagnesium compounds after modification by adding other organometallic compounds, e.g. organosodium, organolithium, organopotassium, organoboron, organocalcium and organozinc.

Examples of these catalyst systems are the combination of solid substances of for example the following systems, RMgX-TiCI4 (see Japanese Patent Publication No. 39470/75),

(see Japanese Patent Public Disclosure No.

119977/74) and

(see Japanese Patent Public Disclosure No.

119982/74), and an organometallic compound.

In this invention, the catalyst systems exemplified above are first contacted with an a- olefin in the presence or absence of liquid hydrocarbon and then used in a vapor phase polymerization. In this case there may be used various a-olefins, but preferably those having 3 to 12 carbon atoms and more preferably those having 3 to 8 carbon atoms; for example, propylene, butene-1, pentene-1, 4- methylpentene- 1, heptene-1, hexene- 1, octene-1, and mixtures thereof. The contact temperature and time of catalyst and a-olefin may be selected in wide range, for example, 1 minute to 24 hours at 0 to 2000C, preferably 0 to 11 00C.

A liquid hydrocarbon which may be used in a preferred embodiment of this invention is a hydrocarbon which is liquid under the contacttreatment conditions, for example, C3 to C12 and preferably C3 to C8 n- and iso-paraffins and aromatic hydrocarbons, such as propane, n butane, iso-butane, n-pentane, iso-pentane, n- hexane, n-heptane, n-octane, iso-octane, benzene, toluene and xylene.

The (x-olefins previously exemplified are also employable as a liquid hydrocarbon in this invention.

Regarding the amount of a liquid hydrocarbon used in this invention, too great an amount would make it difficult to carry out a stable vapor-phase reaction in the reaction vessel, while too little an amount would make it difficult to introduce the catalyst after contact with an a-olefin into the reaction vessel. Usually it is desirable to use a liquid hydrocarbon in an amount ranging from 1 g.

to 1000 g., preferably 5 g. to 500 g. and more preferably 10 g. to 300 g., per gram of the solid substance.

The amount of an a-olefin to be contacted may also be selected in wide range, but usually it is 1 g. to 50,000 g. and preferably 5 g. to 30,000 g.

per gram of the solid substance, and it is desirable that 1 g. to 500 g. per gram of the solid substance of an a-olefin be reacted. The contact pressure may be selected optionally, but it is desired to be in the range of from -1 to 100 kg/cm2G.

In this invention, an organometallic compound to be used may be combined in its total amount with the solid substance and then contacted with an a-olefin; or alternatively, a part of the organometallic compound may be combined with the solid substance, then contacted with an aolefin and thereafter the remaining organometallic compound may be separately added in the vapor phase polymerization of ethylene. In the contact of catalyst with a-olefin, moreover, there may be present a gaseous hydrogen, or other inert gases such as nitrogen, argon and helium.

As set forth hereinbefore, the polymerization of ethylene is carried out using the foregoing catalyst after contact with an a-olefin, but the copolymerization of ethylene and other a-olefin than ethylene may also be conducted in this invention; that is, ethylene or a mixture of ethylene and other a-olefin is polymerized in vapor phase. Known reactors such as a fluidized bed and an agitation vessel may be used.

The polymerization reaction is carried out at a temperature usually in the range of from 200 to 11 00C, preferably from 50 to 1000C, and at a pressure in the range of from atmospheric to 70 kg/cm2G, preferably from 2 to 60 kg/cm2G.

Adjustment of the molecular weight can be made by changing the polymerization temperature, the molar ratio of catalyst, the amount of comonomer, etc. But the addition of hydrogen into the polymerization system is more effective for this purpose. Of course, two or more stage polymerization reactions with different polymerization conditions, such as different hydrogen and co-monomer concentrations and different polymerization temperatures, can be carried out witout any trouble using the process of this invention.

As an organometallic compound used in this invention there may be employed organometallic compounds of Groups l-lV of the Periodic Table which are known to be one component of Ziegler catalyst, among which organoaluminium compounds and organozinc compounds are specially preferred; for example, organoaluminium compounds of the general formulae R3AI, R2AIX, RAIX2, R2AIOR, RAI(OR)X, and R3AI2X3 wherein R is C, to C20 alkyl or aryl and may be same or different, and X is halogen, and organozinc compounds of the general formula R2Zn wherein R is C1 to C20 alkyl and both Rs may be same or different, such as triethylaluminium, triisobutylaluminium, trihexylaluminium, trioctylaluminium, diethylaluminium chloride, ethylaluminium sesquichloride, diethylzinc, and mixtures thereof.

The amount of an organometallic compound to be used in this invention is not specially limited, but usually it is 0.1 to 1000 mols per mol of a transition metal compound.

The process of this invention is applicable to the homopolymerization of ethylene and also to the copolymerization of ethylene and other a olefin than ethylene, but the a-olefins used herein may be the same as or different from the cr-olefins which have been contacted with the foregoing catalyst system. Examples of these a-olefins are propylene, butene-1, pentene-1, hexene-1, 4- methylpentene-1, octene-1, decene-1, dodecene 1, and mixtures thereof. Various dienes as co monomer such as butadiene, 1,4-hexadiene and ethylidenenorbornene may be further added to ethylene or mixtures of ethylene and the above aolefins to carry out polymerization.

The following are working examples of this invention, but it is to be understood that these examples are for purpose of illustration to work the invention and that this invention is not limited thereto.

Example 1 A 2 liter stainless steel autoclave equipped with an induction stirrer was purged with nitrogen, and in it were then placed 50 g. of a dried polyethylene powder and 500 ml of hexane.

Further added were 10 mg of a solid substance (titanium content 67 mg/g. solid substance), which was obtained by subjecting 10 g.

anhydrous magnesium chloride, 0.5 g.

dichloroethane and 3.3 g. titaniurn trichloride- aluminiumchloride eutectic mixture to a ball milling for 1 6 hours at room temperature under a nitrogen atmosphere, and 5 millimols of triisobutylaluminium. The hexane was distilled off under reduced pressure with stirring to give a catalyst. The reaction temperature was raised to 700C, then propylene gas was introduced up to 7 kg/cm2G and the catalyst was treated with propylene for 10 minutes, during which period 3 g. of propylene was consumed. Then, propylene within the autoclave was purged and the purging was further repeated several times with nitrogen gas.After the reaction temperature had been raised to 800C, hydrogen was introduced up to 5 kg/cm2 G, then was introduced ethylene up to a total pressure of 10 kg/cm2,G and a polymerization was started, which was continued for 2 hours at 850C while ethylene was continuously introduced so as to maintain the total pressure at 10 kg/cm2G, to yield 1 85 g. of a white polyethylene, from which the weight of the polyethylene powder initially fed to the autoclave was deducted to find that the amount of polyethylene newly produced by the vapor phase polymerization was 135 g.

The catalyst activity was 225,000 g.

polyethylene/g.Ti, which is much higher than in Comparative Example 1 where the catalyst was not treated with propylene. There was neither aggregation nor adhesion of polymer within the autoclave and the results obtained were very satisfactory as compared with Comparative Example 1 in which the catalyst used was not treated with propylene. Besides, the bulk density of the resulting polyethylene particles was high with only a small production of coarse and ultra fine particles, and the particle properties were very good.

Comparative Example 1 Polymerization was carried out in the same manner as in Example 1 except that 30mg of the solid substance was used and the catalyst was not treated with propylene gas, to yield 1 32 g. of a white polyethylene as the product of the vapor phase polymerization. The catalyst activity was 73,000 g.polyethylene/g.Ti and thus it was lower than in Example 1. On the autoclave flange surface and the upper portion of the reactor wall was adhered 1 30 g. of polyethylene and thus the adhesion of polymer was conspicuous.

Example 2 10 mg of the catalyst obtained in Example 1 was treated with propylene for 1 minute at 700C and at a propylene pressure of 7 kg/cmZG, which treatment consumed 0.5 g. of propylene. Then propylene was purged and the purging was further repeated several times with nitrogen gas, thereafter the polymerization of ethylene was conducted for 2 hours at 10 kg/cm2G in the same manner as in Example 1 to yield 130 g. of a white polyethylene as the product of the vapor phase polymerization. The catalyst activity, 217,000 g.polyethylene/g.Ti, was much higher than in Comparative Example 1, and there was found no adhesion of polymer within the autoclave.

Example 3 10 mg of the catalyst obtained in Example 1 was treated with butene-1 for 30 minutes at 70"C and at 2 kg/cm2G, which treatment consumed 1.5 g. of butene-1. Then butene-1 was purged and the purging was further repeated several times with nitrogen gas, thereafter the polymerization of ethylene was conducted for 2 hours at 10 kg/cm2G in the same manner as in Example 1 to yield 128 g. of a white polyethylene as the product of the vapor phase polymerization.

The catalyst activity, 213,000 g.polyethylene/g.Ti, was much higher than in Comparative Example 1, and within the autoaclave there was only a small amount, about 3 grams, of polymer adhesion on the upper portion of the flange, which was much smaller than in Comparative Example 1.

Example 4 A 2 liter stainless steel autoclave equipped with an induction stirrer was purged with nitrogen, and in it were then placed 50 g. of a dried polyethylene powder and 500 ml of hexane.

Further added were 20 mg of a solid substance (titanium content 40 mg/g.solid substance), which was obtained by subjecting 10 g.

anhydrous magnesium chloride, 0.5 g.

dichloroethane and 1.7 g. titanium tetrachloride to a bail milling for 16 hours at room temperature under a nitrogen atmosphere, and 5 millimols of triisobutylaluminium. The hexane was distilled off under reduced pressure with stirring to give a catalyst. The reaction temperature was raised to 800 C, then 2 g. of hexene-1 was added and the catalyst was treated with hexene-1 for 10 hours at 80 C. After the interior of the autoclave was purged several times with nitrogen gas, the reaction temperature was raised to 850C, then hydrogen was introduced up to 5 kg/cm2G, and then ethylene up to a total pressure of 10 kg/cm2G and a polymerization was started, which was continued for 2 hours at 850C while ethylene was continuously introduced so as to maintain the total pressure at 10 kg/cm2G, to yield 91 g. of a white polyethylene. The catalyst activity, 114,000 g. polyethylene/g.Ti, was much higher than in Comparative Example 2, and within the autoclave there was only about 1 gram of polymer adhesion on the flange surface, which was much less than in Comparative Example 2.

Comparative Example 2 Polymerization was carried out in the same manner as in Example 4 except that 30 mg of the solid substance was used and the catalyst was not treated with hexene-1, to yield 96 g. of a white polyethylene as the product of the vapor phase polymerization. The catalyst activity, 80,000 g.polyethylene/g.Ti, was lower than in Example 4. On the autoclave flange surface and the upper portion of the inside wall was adhered 50 g. of polyethylene and thus the adhesion of polymer was conspicious.

Example 5 Polymerization was carried out in the same manner as in Example 4 except that as the solid substance there was used 20 mg of a solid substance (titanium content 40 mg/g.solid substance) obtained by subjecting 8.3 g.

anhydrous magnesium chloride, 1.2 g. anthracene and 1.7 g. titanium tetrachloride to a ball milling for 16 hours at room temperature under a nitrogen atmosphere, and there was used 4methylpentene-1 in place of hexene-1, to yield 88 g. of a white polyethylene as the product of the vapor phase polymerization. The catalyst activity, 110,000 g. polyethylene/g.Ti, was much higher than in Comparative Example 3 where the catalyst was not treated with 4-methylpentene-1.

Within the autoclave there was found no adhesion of polymer.

Comparative Example 3 Polymerization was carried out in the same manner as in Example 5 except that 30 mg of the solid substance was used and the catalyst was not treated with 4-methylpentene-1, to yield 92 g. of a white polyethylene as the product of the vapor phase polymerization. The catalyst activity was low, 77,000 g.polyethylene/g.Ti. The adhesion of polymer was conspicuous; there was found 30 g. of polymer adhesion on the autoclave flange surface and inside wall.

Example 6 Example 1 was repeated except that there was used 10 mg of a solid substance (titanium content 39 mg/g. solid substance) obtained by subjecting 9.5 g. of the product resulting from heat reaction for 4 hours at 3000C of 40 g. magnesium oxide and 133 g. aluminiumchloride, and 1.7 g. of titanium tetrachloride, to a ball milling for 1 6 hours at room temperature under a nitrogen atmosphere, the catalyst was treated with propylene at 50"C and at a propylene pressure of 7 kg/cm2G. In 30 minutes, 1.5 g. of propylene was consumed. Then propylene was purged and the purging was further repeated several times with nitrogen gas.Hydrogen was then introduced up to 5 kg/cm2.G, and then ethylene containing 2 mol% of butene-1 up to a total pressure of 10 kg/cm2G and a polymerization was conducted for 2 hours at 850C to yield 85 g. of a white polyethylene as the product of the vapor phase polymerization. The catalyst activity was very high, 21 8,000 g. polyethylene/g.Ti, and there was found no polymer adhesion within the autoclave.

Example 7 (1) Pre-treatment with Propylene In a 200 ml stainless steel autoclave equipped with an induction stirrer were placed 200 mg of a solid substance obtained by subjecting 10 g.

anhydrous magnesium chloride, 0.5 g.

dichloroethane and 3.3 g. titanium trichloridealuminiumtrichloride eutetic mixture to a ball milling for 1 6 hours at room temperature under a nitrogen atmosphere, 20 millimols of triisobutylaluminium and 100 ml of hexane, and a reaction was allowed to take place for 10 minutes at 700C. Then 3 g. of propylene was added and reacted for 10 minutes, then the temperature was brought down to room temperature to give a catalyst slurry pre-treated with propylene.

(2) Vapor Phase Polymerization A 2 liter stainless steel autoclave equipped with an induction stirrer was purged with nitrogen, and in it were placed 50 g. of a dried polyethylene powder and then 5 ml of the catalyst slurry pre-treated with propylene obtained in step (1) above. After the temperature had been raised to 800 C, hydrogen was introduced up to 5 kg/cm2G, then ethylene up to a total pressure of 10 kg/cm2G and a polymerization was started, which was continued for 2 hours at 85"C while ethylene was continuously introduced so as to maintain the total pressure at 10 kg/cm2G, to yield 193 g. of a white polyethylene, from which the weight of the polyethylene powder initially fed to the autoclave was deducted to find that the amount of polyethylene newly produced by the vapor phase polymerization was 143 g. The catalyst activity was 255,400 g.polyethylene/g.Ti, which is much higher than in Comparative Example 4 where the catalyst was not pre-treated with propylene. There was neither aggregation nor adhesion of polymer within the autoclave and the results obtained were very satisfactory as compared with Comparative Example 4 in which the catalyst used was not treated with propylene.

Besides, the bulk density of the resulting polyethylene particles was high with only a small production of coarse and ultra-fine particles, and the particle properties were very gooa.

Comparative Example 4 Polymerization was carried out in the same manner as in Example 7 except that the hexane slurry of catalyst was not treated with propylene, to yield 45 g. of a white polyethylene as the product of the vapor phase polymerization. The catalyst activity was 80,400 g.polyethylene/g.Ti and thus it was lower than in Example 7. On the autoclave flange surface and the upper portion of the reactor wall was adhered 41 g. of polyethylene and thus the adhesion of polymer was conspicious.

Example 8 Pre-treatment and vapor phase polymerization were conducted in the same manner as in Example 7 except that there was used 1 g., in place of 3 g., of propylene in the stage of pretreatment with propylene, to yield 1 31 g. of a white polyethylene as the product of the vapor phase polymerization. The catalyst activity, 234,000 g. polyethylene/g.Ti, was much higher than in Comparative Example 4, and there was found no adhesion of polymer within the autoclave.

Example 9 Pre-treatment with a-olefin and vapor phase polymerization were conducted in the same manner as in Example 7 except that the pretreatment applied was with butene-1 in place of propylene and the amount of butene-1 added was 2 grams, to yield 125 g. of a white polyethylene as the product of the vapor phase polymerization.

The catalyst activity, 223,200 g.polyethylene/g.Ti, was much higher than in Comparative Example 4, and there was found no adhesion of polymer within the autoclave.

Example 10 Pre-treatment with propylene and vapor phase polymerization were conducted in the same manner as in Example 7 except that there was used 100 ml of n-butane in place of hexane in the stage of pre-treatment with propylene, to yield 151 g. of a white polyethylene as the product of the vapor phase polymerization. The catalyst activity, 269,600 g.polyethylene/g.Ti, was much higher than in Comparative Example 5. There was found no adhesion of polymer within the autoclave, and the particle properties were satisfactory.

Comparative Example 5 Polymerization was carried out in the same manner as in Example 7 except that there was used 100 ml of n-butane in place of hexane and the pre-treatment with propylene was not applied, to yield 50 g. of a white polyethylene as the product of the vapor phase polymerization.

The catalyst activity, 89,300 g. polyethylene/g.Ti, was lower than in Example 1 0. On the autoclave flange surface and the upper portion of the reactor wall there was found a large amount of adhered polyethylene, and the polymer particles were irregular.

Example 11 (1) Pre-treatment with Hexene-1 In a 200 ml stainless steel autoclave equipped with an induction stirrer were placed 200 mg of a solid substance obtained by subjecting 10 g.

anhydrous magnesium chloride, 0.5 g.

dichloroethane and 1.7 g. titanium tetrachloride to a ball milling for 1 6 hours at room temperature under a nitrogen atmosphere, 20 millimols of triisobutylaluminium and 100 ml of hexane, and a reaction was allowed to take place for 10 minutes at 80at. Then 5 g. of hexene-1 was added and reacted for 5 hours, then the temperature was brought down to room temperature to give a catalyst slurry pre-treated with hexene 1.

(2) Vapor Phase Polymerization A 2 liter stainless steel autoclave equipped with an induction stirrer was purged with nitrogen, and in it were placed 50 g. of a dried polyethylene powder and then 5 ml of the catalyst slurry pre-treated with hexene-1 obtained in step (1) above. After the temperature had been raised to 850C, hydrogen was introduced up to 5 kg/cm2G, then introduced ethylene up to a total pressure of 10 kg/cm2G and a polymerization was started, which was continued for 2 hours at 850C while ethylene was continuously introduced so as to maintain the total pressure at 10 kg/cm2G, to yield 62 g. of a white polyethylene as the product of the vapor phase polymerization. The catalyst activity was 155,000 g.polyethylene/g.Ti, which is much higher than in Comparative Example 6 where the catalyst was not treated with hexene 1.There was neither aggregation nor adhesion of polymer within the autoclave and the results obtained were very satisfactory as compared with Comparative Example 6 in which the catalyst was not treated with hexene-1. Besides, the bulk density of the resulting polyethylene particles was high with only a small production of coarse and ultra-fine particles, and the particle properties were very good.

Comparative Example 6 Vapor phase polymerization was carried out in the same manner as in Example 11 except that the catalyst was not treated with hexene-1, to yield 37 g. of a white polyethylene as the product of the vapor phase polymerization. The catalyst activity, 92,500 g. polyethylene/g.Ti, was lower than in Example 5. On the autoclave flange surface and the upper portion of the inside wall there was found a large amount of adhered polyethylene, and the polymer particles were irregular.

Example 12 Pre-treatment with propylene was conducted in the same manner as in Example 7 except that as the solid substance there was used a solid substance obtained by subjecting 9.5 g. of the product resulting from heat reaction for 4 hours at 3000C of 40 g. magnesium oxide and 133 g.

aluminiumchloride, and 1.7 g. of titanium tetrachloride, to a ball milling for 16 hours at room temperature under a nitrogen atmosphere.

Thereafter, a vapor phase polymerization was carried out in the same way as in Example 7 with the proviso that there was used ethylene containing 2 mol% of butene-1, to newly afford 93 g. of a white polyethylene. The catalyst activity was very high, 238,500 g.polyethylene/g.Ti, and there was found no adhesion of polymer within the autoclave.

Claims

1. A process for preparing polyolefins, which process comprises contacting a catalyst consisting of a solid substance and an organometallic compound, said solid substance containing magnesium and titanium and/or vanadium, with an a-olefin in the absence or presence of a liquid hydrocarbon and thereafter contacting ethylene or a mixture of ethylene and an a-olefin in gaseous phase with the so-treated catalyst whereby the homopolymerization of ethylene or the copolymerization of ethylene and a-olefin is effected.

2. A process according to claim 1, in which said catalyst is contacted with a gaseous a-olefin and then the homopolymerization of ethylene or the copolymerization of ethylene and a-olefin is effected.

3. A process according to claim 1, in which said catalyst is contacted with an ct-olefin in the presence of a liquid hydrocarbon and then the homopolymerization of ethylene or the copolymerization of ethylene and a-olefin is effected.

4. A process according to any one of the preceding claims in which said catalyst is contacted with 1 g. to 50,000 g., per gram of said solid substance, of an a-olefin at a pressure in the range of from -1 to 100 kg/cm2G and then the homopolymerization of ethylene or the copolymerization of ethylene and a-olefin is effected.

5. A process according to any one of the preceding claims in which said liquid hydrocarbon is selected from C3 to C12 n-paraffins, isoparaffins, aromatic hydrocarbons and a-olefins.

6. A process according to any one of the preceding claims in which said liquid hydrocarbon is used in an amount of 1 g. to 100 g. per gram of said solid substance.

7. A process according to any one of the preceding claims in which the homopolymerization of ethylene or the copolymerization of ethylene and a-olefin is carried out in the presence of hydrogen at a temperature in the range of from 20C to 11 00C and at a pressure in the range of from atmospheric to 70 kg/cm2G.

8. A process as claimed in claim 1, substantially as hereinbefore described with particular reference to the Examples.

9. A process as claimed in claim 1, substantially as illustrated in any one of the Examples.

10. A polymer or copolymer of ethylene when prepared by the process claimed in any one of the preceding claims.