JPS6247448B2 - - Google Patents

Description

[Detailed description of the invention]

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 resistance to environmental stress cracking. Prior Art Conventionally, a method for producing high-density polyethylene with a relatively high molecular weight using a chromium oxide catalyst supported on a carrier has been carried out, but when ethylene is polymerized using the chromium oxide catalyst alone, the resulting polymer The environmental stress cracking resistance (ESCR) of this product is not necessarily satisfactory. Methods for improving ESCR include a method in which ethylene is polymerized in the presence of hydrogen using an organoaluminum compound (Japanese Patent Publication No. 49-34759), and a method in which ethylene is polymerized using a catalyst treated with hydrocarbyl aluminum hydrocarbyl oxide (Japanese Patent Publication No. 49-34759). 1978-
17993) etc. are known. The polymers obtained by these methods all have a melt index (MI) of 0.2 or more,
ESCR is considerably improved, but catalyst activity decreases,
There are problems such as deterioration of product color and 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 MI of 0.1 or less, which has good ESCR 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 specific pore volume and specific surface area. Summary of the Invention The present invention provides (a) a chromium oxide catalyst supported on a carrier, which has a pore volume of 1.3 ml/g or less and a specific surface area of 330 m ² /g;
g or less and (b) the general formula R _o MX _3-o (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 halogen atom, an alkoxy group, or a hydrogen atom) Melt index 0.1 characterized by polymerizing ethylene or ethylene and α-olefin in the absence of hydrogen in the presence of an organometallic compound represented by (n is an arbitrary number in the range of 1n3) The gist of the method for producing polyethylene is as follows. Chromium Oxide Catalyst In the present invention, examples of the carrier supporting chromium oxide include silica, silica-alumina, silica-titania, alumina, zirconia, and thoria. Among these, silica and silica-alumina are particularly desirable. The chromium oxide catalyst used in the present invention has a pore volume of 1.3 ml/g or less, preferably 1.10 to 1.30 ml/g, and a specific surface area of 330 m ² /g.
It is essential that it is desirably 250 to 330 m ² /g, but it requires a pore volume of 1.55 ml / g or less,
It is desirable to use a carrier having a specific surface area of 350 m ² /g or less. The catalyst used in the present invention can be obtained by supporting a chromium compound on a carrier and then firing it. As a chromium compound, inorganic compounds such as chromium oxides, halides, oxyhalides, and salts of inorganic acids can be used. and organic compounds such as oxalate, acetate, tertiary butyl chromate, and chromium acetylacetonate. Examples of inorganic compounds of chromium include chromium trioxide, chromium chloride, chromium bromide, chromium chlorate, chromium phosphate, chromium sulfate, and chromium nitrate. In order to support these chromium compounds on a carrier,
The chromium compound is supported as it is or by using a solution dissolved in a suitable solvent by an impregnation method, a coprecipitation method, or the like. Then, usually in the presence of oxygen, 300-1100
°C, preferably 500 to 900 °C, more preferably 500 °C
The chromium oxide catalyst is prepared by firing at a temperature range of ~700°C for 5 minutes to 50 hours, preferably 10 minutes to 10 hours. The supported amount of the chromium oxide catalyst is usually 0.05 to 20% by weight, preferably 0.5 to 10% by weight as chromium oxide (CrO ₃ +Cr ₂ O ₃ ). The chromium oxide catalyst thus obtained has a pore volume of 1.3 ml/g or less as measured by the mercury intrusion method and the BET method at the adsorption temperature of liquid nitrogen.
It is important that the specific surface area is 330 m ² /g or less, and if a catalyst exceeding these values is used, the object of the present invention cannot be achieved. Organometallic Compounds Organometallic compounds used in conjunction with chromium oxide catalysts are
It is represented by the general formula RnMX _3-o . In the formula, M
is an aluminum atom or a boron atom. R is a hydrocarbon group such as alkyl, cycloalkyl, aryl, and aralkyl having 1 to 20 carbon atoms;
In the case of a compound having two or more R's, R may be the same or different. X is a halogen atom, an alkoxy group represented by OR' (wherein R' has the same meaning as R above), or a hydrogen atom. Also, n is 1
It is an arbitrary number within the range of n3. Examples of these organometallic compounds include trialkyl aluminum such as trimethylaluminum, triethylaluminum, tripropylaluminum, triisobutylaluminum, and trihexylaluminum, dimethylaluminum chloride, diethylaluminum chloride, diethylaluminum bromide, diethylaluminium iodide, and diisobutylaluminum. Dialkylaluminum monohalides such as chloride, methylaluminum dichloride, ethylaluminum dichloride, ethylaluminum dibromide, ethylaluminum diiodide, monoalkylaluminum dihalides such as isobutylaluminum dichloride, alkylaluminum sesquihalides such as ethylaluminum sesquichloride, dimethyl Aluminum methoxide, diethyl aluminum ethoxide,
Dialkyl aluminum monoalkoxides, dimethyl aluminum hydride, such as diethylaluminium phenoxide, dipropyl aluminum ethoxide, diisobutyl aluminum ethoxide, diisobutyl aluminum phenoxide,
Examples include dialkyl aluminum hydrides such as diethyl aluminum hydride, dipropyl aluminum hydride, and diisobutyl aluminum hydride, trialkyl boron such as trimethyl boron, triethyl boron, and triisobutyl boron, and dialkyl boron chlorides such as dimethyl boron chloride and 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 usually 0.1 to 100% by weight, preferably 0.5%.
~20%. Polymerization of ethylene The present invention is directed to homopolymerization of ethylene or ethylene and α-olefin, such as propylene, 1-butene, 1-pentene, 4-methyl-1-pentene,
It can be copolymerized with 1-hexene and the like. The polymerization reaction is preferably carried out by dispersing the chromium oxide catalyst and organometallic compound in an inert hydrocarbon, supplying ethylene or ethylene and α-olefin, and maintaining the mixture at a predetermined temperature and pressure. achieved. 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, isopentane, hexane, heptane, and octane, alicyclic hydrocarbons such as cyclopentane and cyclohexane, and aromatic hydrocarbons such as benzene, toluene, and xylene. Hydrogen is preferred. The reaction temperature is usually 50-120℃, preferably
70~110℃, reaction pressure is normal pressure~80 atm,
The reaction time is usually 0.1 to 10 hours. Slurry (catalyst,
The concentration of polymers, etc.) is preferably 50% by weight or less, but is not limited to this. 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 recovered as polyethylene by separating and purifying it by a conventional method. Effects of the Invention The polyethylene or the copolymer of ethylene and α-olefin obtained by the method of the present invention is colorless and odorless, has an excellent ESCR, and has an MI of 0.1 or less, and is suitable for, for example, large-scale 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 stated. The melt index (MI) of a polymer is
According to ASTM-D1238, temperature 190℃, load 2.16Kg
It was measured with HLMI measures the above MI,
This is a value measured with a load of 21.6Kg. ESCR is
Measured by ASTM-D1693 (Bell Tel method).
Regarding odor, the results of a sensory test are shown on a scale of 1 for no odor and 5 for particularly strong odor. The color was measured by whiteness (WBY) according to ASTM-E313. Moreover, productivity is the amount of polymer produced (g) per gram of chromium oxide catalyst. Examples 1, 2, 3, Comparative Example 1 Commercially available silica (W, R, grade 56 manufactured by Grace & Company) with a pore volume of 1.15 ml/g and a specific surface area of 313 m ² /g was impregnated with an aqueous chromium acetate solution. After drying at 150°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,
Its pore volume is 1.14ml/g, and its specific surface area is 278m ² /
It was hot at g. An autoclave with an internal volume of 2 and equipped with a stirrer was heated, and under a dry nitrogen gas atmosphere, the above catalyst (a) and then a predetermined amount of triisobutylaluminum as component (b) were charged. Then purified isobutane
700 ml was charged, ethylene was supplied at 100°C, the total pressure was maintained at 35 Kg/cm ² G while stirring, and the reaction was allowed to proceed for 1 hour. After the reaction was completed, unreacted ethylene and isobutane were removed to recover the polymer. These results are shown in Table 1 in comparison with the case where component (b) was not present (Comparative Example 1).

[Table] 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.

[Table] Example 6, Comparative Example 2 Commercially available silica with a pore volume of 1.28 ml/g and a specific surface area of 303 m ² /g was impregnated with an aqueous solution of chromium oxide.
After drying at 150°C, firing activation was performed at 650°C for 8 hours in dry air. The chromium oxide catalyst (a) thus obtained contained 2% chromium oxide, had a pore volume of 1.25 ml/g, and a specific surface area of 261 m ² /g. 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 triisobutylaluminum was also conducted. These results are shown in Table 3.

[Table] Comparative Examples 3 to 6 Commercially available silica (Fuji Tevison Chemical grade 952) with a pore volume of 1.62 ml/g and a specific surface area of 368 m ² /g was impregnated with an aqueous solution of chromium oxide (), and after drying at 150°C, Calcination activation was performed at 650° C. for 8 hours in dry air. The chromium oxide catalyst (a) thus obtained contained 2% chromium oxide, had a pore volume of 1.56 ml/g, and a specific surface area of 341 m ² /g.
Ethylene polymerization was carried out in the same manner as in Example 1, except that this catalyst (a) was used and the polymerization times were changed as shown in Table 4. In addition, experiments were also conducted without using triisobutylaluminum. The results are shown in Table 4.

[Table] Examples 7, 8, 9, Comparative Example 7 In Example 1, the polymerization temperature and polymerization time were set as shown in Table 5, and 1-butene was supplied at a constant rate in the amount shown in Table 5 over the entire polymerization time. A copolymerization reaction of ethylene and 1-butene was carried out in the same manner as in Example 1 except for the following. These results are shown in Table 5 in comparison with the case where triisobutylaluminum was not present.

【table】 [Brief explanation of the drawing]

FIG. 1 is a flowchart showing the steps for preparing a catalyst according to the present invention.

Claims (1)

[Claims] 1 (a) A chromium oxide catalyst supported on a carrier, with a pore volume of 1.3 ml/g or less and a specific surface area of 330
m ² /g or less, and (b) the general formula R _o MX _3-o (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 halogen atom or an alkoxy group) or a hydrogen atom, and n is an arbitrary number within the range of 1n3. A method for producing polyethylene with an index of 0.1 or less.