JPS5884806A - Preparation of polyethylene - Google Patents

Abstract

PURPOSE:To obtain the titled polymer of high quality having a low melt index and good environmental stress cracking resistance, by polymerizing ethylene, etc. in the presence of a catalyst containing chromium oxide supported on a carrier having a specific pore volume and specific surface area and a specific organometallic compound in combination. CONSTITUTION:Ehylene is polymerized or ethylene is copolymerized with an alpha-olefin, e.g. propylene, in the presence of (A) chromium oxide catalyst supported on a carrier, e.g. silica, having <=1.3ml/g pore volume and <=330m<2>/g specific surface area and (B) an organometallic compound expressed by the formula RnMX3-n[M is aluminum or boron; R is 1-20C hydrocarbon; X is halogen, alkoxyl or H; 1<=(n)<=3], e.g. triisobutylaluminum, to give the aimed polymer.

Description

TECHNICAL FIELD The present invention relates to a method for producing polyethylene, and more particularly to a method for producing polyethylene having a melt index of 0.1 or less and improved environmental stress cracking resistance.

PRIOR ART Conventionally, a method has been used to produce high-density polyethylene with a relatively high molecular weight using a chromium oxide catalyst supported on a carrier. Environmental stress racking of polymers (
ESCR) was not necessarily satisfactory.

ESC! Methods for improving Ri include a method in which ethylene is polymerized in the presence of hydrogen using an organoaluminum compound (Japanese Patent Publication No. 154759/1983), a method in which ethylene is polymerized using a catalyst treated with hydrocarbyl aluminum hydrocarbyl oxide ( % Kokai No. 51-17993) and the like are known.

The polymers obtained by these methods all have a melt index (MI) of 0.2 or more and an ESC
Although R is considerably improved, there is a decrease in catalyst activity, product color,
There are problems such as worsening odor and rough skin of molded products.

DISCLOSURE OF THE INVENTION The purpose of the present invention is to provide a polyethylene suitable for large-scale blow molding grade with an MIQ of 1 or less, which has good ESOF+ and improved color and odor. The present invention was completed by discovering that the above object can be achieved by polymerizing ethylene using a supported chromium oxide catalyst having a pore volume and a specific surface area.

Summary of the invention The present invention is.

(a) A chromium oxide catalyst supported on a carrier, with a pore size of 1.3-/f or less and a specific surface area of 350 m2.
7f or less, and (b) those with the general formula RnMX3-n (where M is an aluminum atom or a boron atom, R is a hydrocarbon group having 1 to 20 carbon atoms, and X is), a rogen atom, an alkoxy group, or a hydrogen atom. where n is any number in the range of 1 x n x 3. ]
The gist of the present invention is a method for producing polyethylene, which is characterized by polymerizing ethylene or an ethylene monoolefin in the presence of an organometallic compound represented by the following formula.

Chromium Oxide Catalyst In the present invention, materials that support chromium oxide include silica-di-silica-alumina, silica-titania, alumina, and zirconia-di-thoria. Among these, silica and silica-alumina are particularly desirable. The chromium oxide catalyst used in the present invention has a pore volume of 1.5
ml/? Below, preferably 1.10 to 1.50 w/
f? , the specific surface area is 311Om2/? It is essential that the area is desirably 250 to 530 m2/2;
27f? It is desirable to use a carrier having the following specific surface area: The catalyst used in the present invention is obtained by supporting a chromium compound on a carrier and then calcining it. .

Examples include inorganic compounds such as halides, oxyhalides, and salts of inorganic acids, and organic compounds such as oxalate, acetate, tertiary butyl chromate, and chromium acetylacetonate. Inorganic compounds of chromium include chromium trioxide, chromium chloride, chromium bromide, chromium chlorate, and chromium phosphate.

Examples include chromium sulfate and chromium nitrate.

In order to support these chromium compounds on a carrier, the chromium compounds are supported as they are or by using a solution dissolved in an appropriate solvent by an impregnation method, a coprecipitation method, or the like. Next, the temperature is usually 300 to 1100°C, preferably 500°C in the presence of oxygen.
A chromium oxide catalyst is prepared by calcining at a temperature range of ~900°C, more preferably 500~700°C for 5 minutes to 50 hours, preferably 10 minutes to 10 hours.

The amount of chromium oxide supported is usually chromium oxide (cro3+
cr2o3) and -(o, c+5 to 2o weight ratio, preferably 0.5 to 10 weight ratio).

The thus obtained chromium oxide catalyst has a pore volume of 1.3 ml/? measured by the BET method at the mercury porosimetry method and the adsorption temperature of liquid nitrogen. Hereinafter, it is important that the specific surface area is 350 m279 or less, and if a catalyst exceeding these values is used, the object of the present invention cannot be achieved.

The organometallic compound used in combination with the organometallic compound chromium oxide catalyst has the general formula R
It is represented by nMX3-n. In the formula, M is an aluminum atom or a boron atom. R has 1 to 20 carbon atoms
--= in a hydrocarbon group such as alkyl, cycloalkyl, aryl, aralkyl, etc., and in the case of a compound having two or more R's, R's may be the same or different. X is a halogen atom, an alkoxy group represented by OR' (however,
' has the same meaning as R above. ) or a hydrogen atom〇Also, n is any number in the range of 1<'n<, 3゜3゜These organometallic compounds are exemplified by trimethylaluminum and triethylaluminum.

Dialkyl aluminum monohalides, methyl aluminum dichloride, such as triglobyl aluminum, triimbutyl aluminum, trihexyl aluminum natono-alkyl aluminum, dimethyl aluminum chloride, diethylaluminum chloride, diethylaluminum bromide, diethylaluminium hydride, diisobutyl aluminum chloride,
Ethylaluminum dichloride.

Monoalkylaluminum cibarides such as ethylaluminum cyfuromide, ethylaluminum diiodide, isobutylaluminum dichloride, alkylaluminum sesquihalides such as ethylaluminum sesquichloride, dimethylaluminum methoxide,
diethylaluminum ethoxide, diethylaluminum phenoxide, dipropylaluminum ethoxide,
Dialkyl aluminum monoalkoxides such as diisobutyl aluminum ethoxide and diisobutyl aluminum phenoxide; dialkyl aluminum hydrides such as dimethyl aluminum hydride, diethyl aluminum hydride, dipropyl aluminum hydride, and diisobutyl aluminum perhydride; trimethy/l boron, triethyl boron, triino Trialkyl boron such as butyl boron, dimethyl boron chloride.

Examples include dialkyl boron chloride such as diethyl boron chloride. Among these, trialkyl aluminum is preferred. Two or more kinds of these organometallic compounds can also be used.

The ratio of the organometallic compound to the chromium oxide catalyst is as follows:
Usually 0.1 to iD, 0% by weight, preferably 085 to 2
It is related to 0'.

The present invention is directed to an O polymerization reaction in which ethylene can be homopolymerized or copolymerized with ethylene and α-olefins such as propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, etc. This is preferably achieved by dispersing the chromium oxide catalyst and organometallic compound in an inert hydrocarbon, supplying ethylene or ethylene and α-olefin thereto, and maintaining it at a predetermined temperature and pressure. be done. Of course, the reaction can also be carried out in the absence of an inert hydrocarbon.

In the present invention, it is desirable to carry out the reaction in a state where hydrogen is not substantially present.

Examples of inert hydrocarbons include aliphatic hydrocarbons such as butane, isobutane, pentane, impentane, hexane, heptane, and octane, and alicyclic hydrocarbons such as cyclopentane and cyclohexane.

Aromatic hydrocarbons such as benzene, toluene and xylene are preferred. The reaction temperature is usually 50 to 120°C, preferably 7
0 to 110°C, reaction pressure is usually normal pressure to 80 atm,
Further, the reaction time is usually between 0.1 and 10 mm. When the reaction is carried out in an inert hydrocarbon, the concentration of the slurry (catalyst, polymer, etc.) is preferably 50% by weight or less, but is not limited thereto.

The polymerization reaction may be carried out either batchwise or continuously, and both homopolymerization and copolymerization may be carried out in one stage, or in multiple stages of two or more stages. The polymer obtained by the polymerization reaction is separated using the usual method.

It is recovered as polyethylene through purification.

Effects of the invention Polyethylene or ethylene obtained by the method of the invention and α
-Copolymers with olefins are colorless.

It is odorless, has an excellent B5OR, and has an MI of 01 or less.
For example, it is suitable for large-sized blow molding.

EXAMPLES AND COMPARATIVE EXAMPLES Next, the present invention will be specifically explained using examples and comparative examples. Percentages (%) given in the examples are by weight unless otherwise specified.

The melt index (Ml) of the polymer is determined by ASTM-
According to D 123 B, temperature 190°C, load 2, 56
Measured in kg. HLMI is the value measured as load i 21.6 B9 in the measurement of MI above. ESOR is ASTM-D 1695 (Be1
The 0 odor measured by Tel method (1Tel method) shows the results of a sensory test using a scale of 1 for no odor and 5 for particularly strong odor. Color was measured by whiteness (WBY) according to ASTM-E 315. Moreover, productivity is the amount of polymer produced per gram of chromium oxide catalyst (f).

Examples 1, 2, 5, Comparative Example 1 Pore volume t 15 at/l, specific surface area 513 m2/
? Commercially available silica (W, R, grade 56 manufactured by Brace & Company) was impregnated with an aqueous solution of chromium acetate.
After drying at 50°C, firing activation was performed at 650°C for 8 hours in dry air. The chromium oxide catalyst (a) thus obtained contains 2% chromium oxide, has a pore volume of 1.14-/f, and a specific surface area of 2781H27f.

An autoclave with an internal volume of 2 tons equipped with a stirrer was heated, and the above catalyst (a) was heated, followed by component (b) under an atmosphere of dry nitrogen gas.
) was charged with a predetermined amount of triisobutylaluminum. Next, it was charged with 700 d' of purified isobutane,
Feeding ethylene at 100 °C, total pressure f 5 with stirring
5 kg/cn? G and allowed to react for 1 hour. After the reaction was completed, unreacted ethylene and isotane were removed to recover the polymer. These results are shown in Table 1 in comparison with the case where component (b) k was not present (Comparative Example 1).

Examples 4 and 5 Ethylene polymerization was carried out in the same manner as in Example 1, except that predetermined amounts of diethyl aluminum ethoxide or triethyl boron were used as component (b). These results are shown in Table 2.
It was shown to.

Example 6. Comparative Example 2 Pore volume 1.28 mg/Si', specific surface area 505 m'
/'? Commercially available silica was impregnated with an aqueous solution of chromium oxide (Vl), dried at 150°C, and activated by firing at 650°C at 8 o'clock in dry air. The chromium oxide catalyst (a) thus obtained contains 20% of chromium oxide, has a pore volume of 1.25 tnl, and a specific surface area of 261 m2/
It was S'. Ethylene polymerization was carried out in the same manner as in Example 1 except that this catalyst (a) was used. In addition, an experiment (Comparative Example 2) without using triimbutylaluminum was also conducted. Table 5 shows the percentage of these results.

/ 7・″ // Comparative Examples 3 to 6 Pore volume t 6 '2 ym/f/, specific surface area 568
? 712/f commercially available silica (grade 952, manufactured by Fuji Tevison Chemical Co., Ltd.) was impregnated with an aqueous chromium oxide (Vl) solution, dried at 150°C, and activated by firing in dry air at 650°C for 8 hours. The chromium oxide catalyst (a) thus obtained contains 2 chromium oxides, has a pore volume of 1.56 m//r, and a specific surface area of 541 m/l.
Met. Using this catalyst (a), polymerization time is shown in Table 4.
Ethylene polymerization was carried out in the same manner as in Example 1, except that the procedure was as follows. In addition, we also conducted experiments without using triisobutylaluminum.The results are shown in Table 4.
Examples 7, 8, 9, Comparative Example 7 In Example 1, except that the polymerization temperature and polymerization time were as shown in Table 5, and the amount of 1-butene shown in Table 5 was fed at a constant rate over the entire polymerization time. A copolymerization reaction of ethylene and 1-butene was carried out in the same manner as in Example 1. The results are shown in Table 5 in comparison with the case where no triisobutylaluminum was present.

Claims (1)

[Claims] (1) (a) A chromium oxide catalyst supported on a carrier with a pore volume of 1.31 nl/f or less and a specific surface area of 3
S Om"/l The following and (1)) General formula RnMXB-r, - (where M is an aluminum atom or a boron atom, R is a carbon number of 1 to 20
hydrocarbon group, X is )・rogen atom. Indicates an alkoxy group or four hydrogen atoms, where n is 1 and n<:
A method for producing polyethylene, characterized by polymerizing ethylene or ethylene and α-olefin in the presence of an organometallic compound represented by 0, which is an arbitrary number within the range of 3.