GB2033911A - Preparation of ethylene-propylene copolymers - Google Patents

Abstract

Ethylene-propylene copolymers having a melt index of 0.01 to 1 and a density of 0.910 to 0.945 are produced by vapor-phase polymerisation by copolymerising ethylene with 6 to 100 mol% thereof of propylene and optionally a diene in a substantially solvent-free vapor phase condition and in the presence of a catalyst consisting of an organoaluminium compound and a solid substance containing a magnesium-containing inorganic solid compound and a titanium compound and/or a vanadium compound.

Description

SPECIFICATION Process for preparing a copolymer This invention relates to a new process for preparing a medium or low density ethylene copolymer by a vapor phase polymerization using a Ziegler catalyst of high activity.

More particularly, this invention is concerned with a process for preparing an ethylene-propylene copolymer having a melt index ranging from 0.01 to 10 and a density ranging from 0.910 to 0.945, characterized in that ethylene and 6 to 100 molo/o thereof of propylene are copolymerized in a substantially solvent-free vapor phase condition and in the presence of a catalyst consisting of a solid substance and an organoaluminium compound, said solid substance containing a magnesium-containing inorganic solid compound and a titanium compound and/or a vanadium compound.

Polyethylenes prepared by polymerization using a catalyst consisting of a transition metal compound and an organometallic compound are generally prepared by the slurry polymerization process, and usually produced are only those having a density not lower than 0.945 which value is considered to be the limit of preventing polymer deposition or fouling on the inner wall or stirrer in the interior of a reactor at the time of polymerization.

Medium or low density polyethylenes having a density below 0.945 g/cma are usually prepared by the so-called high pressure process using a radical catalyst. Quite recently, however, there has also been tried a high-temperature solution polymerization process using a Ziegler catalyst.

Low density polyethylenes prepared by the high pressure process are advantageous in that they are superior in transparency and flexibility to high density polyethylenes; but at the same time they are disadvantageous in that the melting point is low and films formed therefrom are low in stiffness.

Also, polyethylenes prepared by the hightemperature solution polymerization process have a poor transparency and films formed therefrom give a sticky impression.

Regarding the production method, the high pressure process requires a very high pressure, thus causing the investment in production facilities to become increased, and also requires high power consumption and other operation costs. The hightemperature solution polymerization process is also disadvantageous in that the resulting polyethylene must be handled as solution, thus requiring operation at a relatively low concentration, resulting in the productivity becoming inferior and the production of polyethylenes of a high grade in molecular weight becoming impossible. Furthermore, the polymers prepared according to the high-temperature solution polymerization process contain a large amount of wax because of a high temperature polymerization, so itis necessaryto providemeansfortheseparation thereof.In the solution polymerization at a high temperature, moreover, there briskly occur side reactions such as the hydrogenation and dimerization of ethylene, thus requiring an increased unit of ethylene and that of hydrogen.

In the production of polyolefins, copolymerizing ethylene with other monomer has heretofore been known as the method of lowering the density of polyethylene. However, where a medium or low density polyethylene is to be prepared by the copolymerization of ethylene and other comonomer according to a known method, usually the other comonomer is required in an extremely excess amount, and this fact itself is very disadvantageous when viewed from the standpoint of process.The copolymerization according to the slurry polymerization process involves additional disadvantages such that the by-production of a low grade polymer or a solvent-soluble polymer becomes noticeable and the polymerization product takes in solvent and becomes milky or mushy, which not only makes the reactor operation and slurry transport difficult, but also results in the separation of solvent from the polymer being no longer easy. Furthermore, there occurs adhesion of copolymer to the reactor inside due to its fouling and the resulting deterioration in heat transfer characteristic causes the polymerization temperature to become uncontrollable.

In recent years it has been found that if a transition metal is attached to a magnesium-containing solid carrier, e.g. MgO, Mg(OH)2, MgCl2, MgCO3 and Mg(OH)CI, and then combined with an organometallic compound, the resulting catalyst system can serve as a catalyst of extremely high activity in olefin polymerization. It is also known that the reaction product of an organomagnesium compound, e.g. RMgX, R2Mg and RMg(OR), and a transition metal compound, can serve as a high activity catalyst for olefin polymerization (see, for example, Japanese Patent Publication No. 12105/64, Belgian Patent No.742,112, Japanese Patent Publications Nos. 13050/68 and 9548,70).

However, even if such high activity catalysts with carrier are used in the slurry polymerization or the high-temperature solution polymerization with a view to preparing medium or low density polyethylenes, the foregoing drawbacks heretofore have not been eliminated at all.

This invention provides a new process which remedies all the foregoing drawbacks.

Having made comprehensive studies about the foregoing technical problems, we completed this invention, according to which a vapor phase polymerization reaction can be carried out in an extremely stable manner and the catalyst removing step can be eliminated, so it is made possible to provide a vapor phase polymerization process for ethylene which process as a whole is very simple.

Surprisingly, moreover, we found that the process of this invention can afford very easily a medium or low density ethylene polymer which has excellent transparency and melts higher and is stronger than conventional low density polyethylenes prepared according to the high pressure process. Thus we accomplished this invention.

In more particularterms,this invention relates to a process for preparing an ethylene-propylene copolymer having a melt index ranging from 0.01 to 10 and a density ranging from 0.910 to 0.945, charac terized in that a mixture of ethylene and 6 to 100 mol% thereof of propylene is contacted in vapor phase condition with a catalyst consisting of a solid substance and an organoaluminium compound, said solid substance containing a magnesium-containing inorganic solid compound and a titanium compound and/or a vanadium compound, whereby ethylene and propylene are allowed to copolymerize.It has now become clearthat if a vapor phase polymerization reaction is carried out according to the process of this invention using ethylene and propylene in a quantitative ratio within the range specified herein and also using a catalyst consisting of a solid substance and an organoaluminium compound, said solid substance containing a magnesium-containing inorganic solid compound and a titanium compound and/or a vanadium compound, such polymerization reaction can be performed in extremely high activity and extremely stably with reduced production of coarse or ultra-fine particles and improved particle properties, and also with minimized adhesion to the reactor and conglomeration of polymer particles.It cannot help being considered quite unexpected and surprising that according to the process of this invention, not only a vapor phase polymerization reaction can be carried out extremely smoothly, but also medium or low density ethylene copolymers can be obtained easily.

The copolymerization reaction of this invention can be performed in a relatively low temperature to easily afford medium or low density ethylene copolymers, so that the adhesion to reactor or conglomeration of product is little observed. This point is another advantage of the invention.

The process of this invention is also characteristic in that a medium or low density ethylene copolymer having a high melt index can be obtained easily. And this point is a further advantage of the invention.

Thanks to these advantages, the copolymer asset forth herein can be obtained efficiently by vapor phase polymerization.

The propylene polymerized with ethylene in the process of this invention adjusts the density and molecular weight of the resulting copolymer, and the copolymer obtained is superior in transparency and elasticity, it also exhibits a very high resistance to impact and to environmental stress cracking.

Consequently, the copolymer according to the process of this invention can be formed into films, sheets, hollow containers, electric wires and various other products by means of known methods such as extrusion molding, blow molding, injection molding, press forming and vacuum forming, and thus can be used in various applications. Particularly in the field of films the copolymer in question exhibits its features because of excellent transparency, antiblocking property, heat sealing property and flexibility. That is, it is possible to attain an equal or even superiortransparencytothatofa high pressure process film, and the strength which is a specially important physical property required of a film is much higher than that of a high pressure process polyethylene. Besides, a large elongation permits forming of an extremely thin film.

Although the density of the copolymer according to the process of this invention is medium or low, the crystallinity is relatively high and the heat resistance is good, affording an unsticky film of high transparency, for which reason the copolymer in question is especially suitable for use as a film for packing or agricultural use. It is also suited to a blow molding because of high transparency, stiffness and resistance to environmental stress cracking.

The catalyst system used in the invention consists of the combination of a solid substance and an organoaluminium compound, said solid substance containing a magnesium-containing inorganic solid compound and a titanium compound and/or a vanadium compound. The solid substance just referred to above is obtained by attaching a titanium compound and/or a vanadium compound to an inorganic solid carrier typical of which are metallic magnesium, magnesium hydroxide, magnesium carbonate, magnesium oxide and magnesium chloride; double salt, double oxide, carbonate, chloride and hydroxide containing a metal selected from silicon, aluminium and calcium, and magnesium atom; further, these inorganic solid carriers treated or reacted 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 there may be used halides, alkoxyhalides, oxides and halogenated oxides of titanium and/or vanadium. Examples are tetravalent titanium compounds such as titanium tetrachloride, titanium tetrabromide, titanium tetraiodide, monoethoxytrichlorotitanium, diethoxydichlorotitanium, triethoxymonochlorotitanium, tetraethoxytitanium, monoisoprnpoxytnchlorntitanium, 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 various tetravalent alkxoytitanium halides with an organometallic compound; tetraval entvanadium compounds, e.g. vanadium tetrach bride; pentavalent vanadium compounds such as vanadium oxytrichloride and orthoalkylvanadate; and trivalent vanadium compounds such as vanadium trichloride and vanadium triethoxide.

Among the above-exemplified titanium compounds and vanadium compounds, tetravalent titanium compounds are specially preferred.

The catalyst used in this invention consists of the combination of a solid substance, which is obtained by attaching a titanium compound and/or a vanadium compound to the foregoing solid carrier, and an organoaluminium compound.

By way of illustrating preferred catalyst systems, mention may be made of the following solid substance (the R in the following formulae represents an organic radical and X represents halogen) combined with an organoaluminium compound: MgO - RX - Ti Cl4 system (see Japanese Patent Publication No.

3514/76), MG - SiCI4 - ROH - TiCI4 system (see Japanese Patent Publication No. 23864/75), MgCl2 - Al(OR)3 - TiCI4 system (see Japanese Patent Publication Nos.

15256 and 15111,77), MgCI2 - SiCI4 - ROH - TiCI4 sys tem (see Japanese Patent Laying Open Print No.

106581,74), Mg(OOCR)2 - Al(OR)3 - TiCI4 system (see Japanese Patent Publication No. 11710/77), Mg POCI3-TiCI4 system (see Japanese Patent Publication No. 153,76), MgCl2 - AIOCI - TiCI4 system (see Japanese Patent Laying Open Print No. 133386/76).

In these catalyst systems, a titanium compound and/or a vanadium compound may be used as the addition product with an organocarboxylic acid ester. The foregoing magnesium-containing inorganic compound carriers may be contacted with an organocarboxylic acid ester before use. Also, an organoaluminium compound may be used as the addition product with an organocarboxylic acid ester, which would cause no trouble. Furthermore, in every case in this invention there may be used, without any trouble, a catalyst system which has been prepared in the presence of an organocarboxylic acid ester.

Various aliphatic, alicyclic and aromatic carboxylic acid esters may be used as organocarboxylic acid esters, among which aromatic carboxylic acids having 7 to 12 carbon atoms are specially preferred. Examples are alkylesters such as methyl and ethyl of benzoic acid, anisic acid and toluic acid.

To illustrate organoaluminium compounds which may be used in this invention, mention may be made of those represented by the general formulae R3AI, R2AIX, RAIX2, R2AIOR, RAI(OR)X and R3AL2X3 wherein R, which may be same or different, is C, to C20 alkyl or aryl and X is halogen, for example, triethylaluminium, triisobutylaluminium, trihexylaluminium, trioctylaluminium, diethylaluminium chloride, ethylaluminiumsesquichloride, and mixtures thereof.

The amount of an organoaluminium compound used in this invention is not specially restricted, but usually it is in the range of from 0.1 to 1000 mols per mol of a transition metal compound.

In the polymerization reaction, a mixture of ethylene and propylene is polymerized in vapor phase in a reactor, which may be a known type such as a fluidized bed or an agitation vessel.

The polymerization reaction conditions involve temperatures usually in the range of from 20 to 1 10"C, preferably from 50'to 1000C, and pressures in the range of from atmospheric pressure to 70 kg/cm2 G, preferably from 2 to 60 kg/cm2 G. The molecular weight can be adjusted by changing the polymerization temperature, the molar ratio of catalyst or the amount of comonomer, but the addition of hydrogen into the polymerization system is more effective for this purpose. Of course, using the process of this invention there may be carried out, without any trouble, two or more stage polymerization reactions involving different polymerization conditions such as different hydrogen and comonomer concentrations and different polymerization temperatures.

In this invention, moreover, the foregoing catalyst systems may be contacted with an a - olefin before they use in vapor phase polymerization reaction whereby their polymerization activities can be largely improved and a more stable operation is assured than in untreated condition. In this case, various a - olefins are employable, 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, hexene - 1, heptene- 1, octene- land mixtures thereof.The temperature and time of the contact between the catalyst used in the invention and an a - olefin can be selected in a wide range, for example, the contact treatment may be applied for 1 minute to 24 hours at a temperature ranging from 0" to 200"C, preferably from 0'to 110"C.

The amount of an a - olefin to be brought into contact can also be selected in a wide range, but usually it is desired that the contact treatment in question be conducted with an a - olefin in an amount ranging from 1 g. to 50,000 g., preferably from 5 g. to 30,000 g., per gram of the aforesaid solid substance and that 1 g. to 500 g. of the a - olefin be reacted with the solid substance. The contact pressure may be selected optionally, but usually it is desired to be in the range of from -1 to 100 kg/cm2 G.

In the treatment with an a - olefin, the total amount of an organoaluminium compound to be used may be combined with the foregoing solid substance and thereafter the resulting mixture may be contacted with the xx - olefin, or part of the organoaluminium compound may be combined with the solid substance and thereafter the resulting mixture may be contacted with the a - olefin, while the remaining portion of the organoaluminium compound may be separately added in the vapor phase polymerization of ethylene. Furthermore, even in the simultaneous presence of hydrogen gas or other inert gas such as nitrogen, argon or helium, the catalyst used in the invention may be brought into contact with an a olefin without causing any trouble.

The amount of propylene should be in the range of from 6 to 100 mol%, preferably from 6 to 60 mol% based on the amount of ethylene. Outside this range, it is impossible to obtain the object product of this invention, namely an ethylene-propylene copolymer having a melt index ranging from 0.01 to 10 and a density ranging from 0.910 to 0.945. The amount of propylene to be used can be easily adjusted according to the composition ratio of the vapor phase in the polymerization vessel.

In the copolymerization according to the process of this invention, moreover, there may be added various dienes as termonomers, such as butadiene, 1,4 hexadiene, 1,5 - hexadiene, vinylnorbornene, ethylidenenorbornene and dicyclopentadiene.

Working examples of this invention are given below, but it is to be understood that these examples are for illustration only for working the invention and are not intended to place limitation thereon.

Example 1 1 kg. of anhydrous magnesium chloride, 50 g. of 1,2 - dichloroethane and 170 g. of titanium tetrach chloride were subjected to ball milling for 16 hours at room temperature in a nitrogen atmosphere to allow the titanium compound to be attached to the carrier.

The resulting solid substance contained 35 mg. of titanium per gram thereof.

There were used a stainless steel autoclave as a vapor phase polymerization apparatus, a blower, a flow ratio adjuster and a dry cyclone to form a loop, and the temperature of the autoclave was adjusted by passing warm water th rough jacket.

Into the autoclave adjusted to 80"C were intro duced the solid substance prepared above and triethylaluminium at the rates of 250 mg/hr and 50 mmol/hr, respectively, and also introduced were propylene, ethylene and hydrogen so that the propylene/ethylene ratio (molar ratio) was 0.35 and the hydrogen gas pressure was 10% of the total pressure, while the gases in the system were circulated by the blower, under which condition there was conducted polymerization. The resulting ethylene copolymer had a bulk density of 0.380, a melt index (Ml) of 1.6 and a density of 0.928. It was powdered with most particle sizes falling under the range of 250 to 5004. The polymerization activity was very high, 209,300 g. copolymer/g.Ti.

After a continuous operation for 10 hours, the autoclave was opened and its interior was checked to find that the inner wall and the stirrer were clean with no polymer adhesion observed. Thus, it is apparent that an extremely stable operation is made possible according to the process of this invention, though it is impossible according to the slurry polymerization shown in Comparative Example 1 below.

The copolymer prepared above was formed into a film 400 mm in fold diameter by 30,a thick by an inflation film forming 75mama die in a 50 mma extruder. The film was superior in strength and had a high transparency with a haze value of 5.8% measured according to JIS K6714.

Comparative Example 1 A continuous slurry polymerization was carried out at 85"C using the same catalyst as that used in Example 1 and in the presence of hexane as solvent.

Hexane as a polymerization solvent containing 5 mg/l of the solid substance and 1 mmol/l of triethylaluminium was fed at the rate of 40 I/hr, and further introduced were ethylene, propylene (80 mol% of ethylene) and hydrogen at the rates of 8 kg/hr, 9.6 kg/hr and 3Nm3/hr, respectively, while a continuous polymerization was conducted on condition that the residence time was 1 hour. The resulting copolymerwas continuously withdrawn as slurry In 2 hours after initiation of the polymerization, the polymer slurry withdrawing pipe was obturated, so the polymerization was compelled to be discontinued.

A check was made for the interior of the reactor to find that the hexane layer was emulsified and a large amount of a rubbery polymer adhered to the gasliquid interface and to the withdrawing pipe.

The copolymer prepared above had a bulk density of 0.253, MI of 1.4 and a density of 0.930.

Example 2 830 g. of anhydrous magnesium chloride, 50 g. of aluminium oxychloride and 170 g. of titanium tet rachloride were subjected to ball milling for 16 hours at room temperature in a nitrogen atmosphere. The resulting solid substance contained 41 mg. of titanium per gram thereof.

The solid substance just prepared above and triethylaluminium were fed at the rates of 200 mg/hr and 50 mmol/hr, respectively, and the same polymerization as in Example 1 was carried out at 80 C with the proviso that the propylene/ethylene ratio in the vapor phase was 0.20 and the hydrogen gas pressure was 14% of the total pressure.

After 10 hours of continuous operation, the interior of the autoclave was checked, but there was no polymer adhesion.

The resulting copolymer had a bulk density of 0.406, Ml of 1.4 and a density of 0.938. The polymerization activity was very high, 300,500 g.ethylene copotymer/g.Ti.

In the same manner as in Example 1,the copolymer was formed in a thin film 400 mm in fold diameter by 304 thick, which was superior in transparencyand in strength.

Comparative Example 2 A solution polymerization was carried out using the same catalyst as that used in Example 2 and in the presence of n - paraffin as solvent n - Paraffin containing 25 mg/l of the solid substance prepared in Example 2 and 5 mmol/l of triethylaluminium was fed at the rate of 401/hr, and further introduced were ethylene, propylene (117 mol% of ethylene) and hydrogen at the rates of 8 kg/hr, 14 kg/hr and 0.1 Nm3/hr, respectively, and a continuous polymerization was carried out at 160"C on condition thatthe residence time was 1 hour.

The resulting ethylene copolymer had Ml of 1.5 and a density of 0.931, and the polymerization activity was 97,000 g. copolymer/g.Ti. Thus, it is apparent that in such a solution polymerization, despite of a large excess of propylene used with respect to ethylene, the density was not lowered so much, and the polymerization activity and efficiency were low.

Example 3 830 g. of anhydrous magnesium chloride, 120 g. of anthracene and 170 g. oftitanium tetrachloride were subjected to ball milling in the same manner as in Example 1 to give a solid substance which contained 40 mg. of titanium per gram thereof.

Using the same apparatus as that used in Example 1, the solid substance and triisobutylaluminium were fed at 80"C at the rates of 500 mg/hr and 150 mmol/hr, respectively, and a polymerization was conducted while making adjustment so that the prop ylene/ethytene ratio in the vapor phase was 0.82 and the hydrogen gas pressure was 15% of the total pressure.

The polymerization was continued stably for 10 hours,, then the autoclave was opened to find that there was no polymer adhesion inside the reactor.

The polymerization activity was 187,000 g.copolymer/g.Ti, and the resulting polymer had a bulk density of 0.375, Ml of 4.4 and a density of 0.915.

The ethylene polymer thus prepared was formed into an inflation film 400 mm in fold diameter by 304 thick in the same manner as in Example 1. The film was superior in strength and in transparency with a haze value of 4.95/o measured according to JIS K6714.

Example 4 400 g. of magnesium oxide and 1300 g. of anhydrous aluminiumchloride were reacted together at 300"C for 4 hours, then 950 g. of the reaction product and 170 g. of titanium tetrachloride were treated in the same way as in Example 1 to give a solid substance which contained 39 mg of titanium per gram thereof.

Using the same apparatus as that used in Example 1, the solid substance just prepared above and triethylaluminium were fed as catalyst at the rates of 500 mg/hr and 250 mmol/hr, respectively, and a polymerization was conducted at 70"C while circulating a mixed ethylene-propylene gas containing 72% of propylene based on the amount of ethylene and also hydrogen gas adjusted to 10% of the total pressure.

After 18 hours of continuous operation, the interior of the reactor was checked to find that there was no polymer adhesion.

The resulting copolymer was composed of oval particles with a narrow particle size distribution, having an average particle diameter of 800, b, a bulk density of 0.368, Ml of 0.60 and a density of 0.920, and the polymerization activity was 223,000 g.copolymer/g.Ti.

The copolymer, without pelletizing, was formed into a hollow bottle having a capacity of 600 c.c. by means of a high-speed blow molding machine. The bottle had a clean surface without draw-down.

Claims (17)

1. A process for preparing an ethylene - propylene copolymer having a melt index ranging from 0.01 to 10 and a density ranging from 0.910 to 0.945, characterized in that ethylene and 6 to 100 mol% thereof of propylene are copolymerized in a substantially solvent-free vapor phase condition and in the presence of a catalyst consisting of a solid substance and an organoaluminium compound, said solid substance containing a magnesium-containing inorganic solid compound and a titanium compound and/or a vanadium compound.

2. A process according to claim 1, in which said titanium compound and/or vanadium compound is a halide, alkoxyhalide, oxide or halogenated oxide of titanium and/or vanadium.

3. A process according to claim 1 or claim 2 in which said magnesium-containing inorganic solid compound is selected from metallic magnesium, magnesium hydroxide, magnesium carbonate, magnesium oxide and magnesium chloride.

4. A process according to claim 1 or claim 2 in which said magnesium containing inorganic solid compound is selected from double salt, double oxide, carbonate, chloride and hydroxide containing magnesium atom and a metal selected from silicon, aluminium and calcium.

5. A process according to claim 1 or claim 2 in which said magnesium-containing inorganic solid compound is further treated or reacted with an oxygen-containing compound, a sulfur-containing compound, a hydrocarbon and halogen-containing substance.

6. A process according to any one of claims 1 to 5 in which said titanium compound and/or vanadium compound is used as the addition product with an organocarboxylic acid ester.

7. A process according to any one of claims 1 to 6 in which said magnesium-containing inorganic solid compound is contacted with an organocarboxylic acid ester before use.

8. A process according to any one of claims 1 to 7 in which said organolaluminium compound is used as the addition product with an organocarboxylic acid ester.

9. A process according to any one of claims 1 to 8 in which said catalyst is prepared in the presence of an organocarboxylic acid ester.

10. A process according to claim 6,7,8 or 9 in which said organocarboxylic acid ester is selected from alkylesters of benzoic acid, anisic acid and toluic acid.

11. A process according to any one of claims 1 to 10 in which said copolymerization is carried out at a temperature in the range of from 20 to 1 10"C and at a pressure in the range of from atmospheric to 70 kg/cm2 G.

12. A process according to any one of claims 1 to 11 in which said copolymerization is carried out in the presence of hydrogen.

13. A process according to any one of claims 1 to 12 in which, before initiating the copolymerization, the catalyst system is contacted with an a - olefin having 3 to 12 carbon atoms for 1 minute to 24 hours at a temperature in the range of from 0" to 200 C and at a pressure in the range of from -1 to 100 kg/cm2 G.

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

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

16. A copolymer of ethylene and propylene, when prepared by the process claimed in any one of the preceding claims.

17. An article fabricated from the copolymer claimed in claim 16.