JP5803774B2 - Method for producing chromium catalyst for ethylene polymerization - Google Patents

Description

The present invention relates to a method for producing a chromium catalyst for ethylene polymerization for producing polyethylene, and more particularly relates to a method for producing a chromium catalyst with improved flowability and melt tension of polyethylene and a method for producing polyethylene using the catalyst. .

In recent years, plastic pipes, films, injection molded articles, and hollow molded articles have been actively used in various industrial fields. Among them, when looking at the hollow molded body, plastic is also used for containers such as fuel cans and plastic bottles. In automobile parts, hollow plastic molded products made of polyethylene are used as fuel tanks, which are changing from conventional fuel tanks made of metal materials. Compared to metal materials, plastic containers and fuel tanks are advantageous in terms of weight reduction because of their small weight / volume ratio, and are less susceptible to corrosion such as rust and have good impact resistance. Because of this feature, it is gaining wider use.
In plastic fuel tanks obtained from polyethylene, a particularly high level is required in order to make it an important safety part for ensuring the safety of automobiles. Material development is underway.

In general, polyethylene is produced by homopolymerization of ethylene or copolymerization of ethylene and a comonomer such as an α-olefin using a polymerization catalyst. Various polymerization catalysts have been developed in order to produce polyethylene with suitable properties depending on the application. Currently, as a main polymerization catalyst, a Philips catalyst is used alongside a radical polymerization catalyst, a Ziegler catalyst, and a metallocene catalyst.
The Phillips catalyst supports a chromium compound on an inorganic oxide carrier such as silica, silica-alumina, silica-titania, etc., and activates it in a non-reducing atmosphere. Chromium catalyst with a valence. The Philips catalyst can produce polyethylene having excellent melt processing characteristics (moldability) resulting from a relatively wide molecular weight distribution and a long-chain branched structure. It has become.

Various studies have been made on the Philips catalyst for producing blow-molding polyethylene having excellent performance as described below.
For example, Patent Document 1 discloses that by carrying out ethylene polymerization using a catalyst obtained by supporting a zinc compound and a chromium compound on an inorganic carrier and calcining, high destruction resistance, high parison stability, and high environmental resistance. It is disclosed that polyethylene with stress cracking properties can be obtained.
Patent Document 2 discloses that environmental stress crack resistance (ESCR) and impact tensile strength are excellent by carrying out ethylene polymerization using a catalyst obtained by supporting a zirconium compound and a chromium compound on an inorganic carrier and firing them. Is obtained.
Furthermore, Patent Document 3 includes a chromium compound, Mg, Ca, Sr, B, Al, Si, P, Bi, Sc, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru. Using a chromium catalyst obtained by calcining a solid catalyst precursor obtained by preparing a homogeneous solution of a metal compound selected from Rh, Pd, Hf, Ta and W and then contacting with an inorganic carrier Performing ethylene polymerization is disclosed. Further, in Patent Document 3, a low emission of fine polymer dust is obtained by the above-described method, and a polymer product having improved characteristics, for example, a film quality improved in a polymer film and a film in which spots occur only less frequently. Is disclosed.
Although these patent documents 1-3 are the disclosure of the catalyst formed by baking the inorganic support | carrier containing a chromium compound and another metal compound, the detailed disclosure about these baking methods is not made | formed.
Conventionally, when the furnace temperature is raised in the presence of oxygen, heat is generated due to carbon and hydrogen in the chromium compound contained in the inorganic carrier, so that the furnace temperature rises rapidly, making it difficult to control the furnace temperature. It was. This increase in the furnace temperature due to the combustion of hydrocarbons becomes even more pronounced when the inorganic carrier contains a metal-containing hydrocarbon compound other than the chromium compound. However, Patent Documents 1 to 3 do not disclose an improvement method related to the firing method.

  In Patent Document 4, (a) a catalyst precursor is heated at 370 ° C. to 540 ° C. in an inert atmosphere, (b) oxygen is introduced at a furnace temperature not exceeding 510 ° C., and (c) a catalyst. A method for calcining a carrier carrying a titanium compound and a chromium compound, which completes calcining and obtains (d) a catalyst is disclosed. However, Patent Document 4 does not describe a method for producing a catalyst in which a catalyst precursor and oxygen are brought into contact at a low activation temperature of 300 ° C. to 500 ° C., and does not disclose an example. Further, Patent Document 4 discloses that when a catalyst precursor is calcined, temperature spikes are prevented from occurring when oxygen is introduced, but it does not disclose what kind of effect this has.

  Conventionally, it has been known that polyethylene obtained by polymerization using a Philips catalyst obtained by low-temperature activation has a broad molecular weight distribution, and a polyethylene having an excellent balance between rigidity and durability can be obtained. However, this polyethylene has been required to be further improved in terms of fluidity and melt tension.

  Under these circumstances, there is a need for a Phillips catalyst that can produce blow-molding polyethylene with better performance.

Special table 2008-502757 Special table 2008-502760 Special table 2008-502759 gazette WO2004 / 096434 International pamphlet

  The subject of this invention is providing the manufacturing method of the catalyst for manufacturing the polyethylene which was excellent in fluidity | liquidity and melt tension with high polymerization activity in spite of being low-temperature activation.

  As a result of intensive studies to achieve the above-mentioned problems, the inventors of the present invention have a specific contact temperature, especially a relatively low temperature, when firing a catalyst precursor supporting a chromium compound and a metal-containing hydrocarbon compound other than chromium. Chromium catalyst obtained through a process of introducing oxygen so as to be in a specific temperature range after heating in an inert atmosphere at a temperature is excellent in fluidity and melt tension. Based on these findings, the inventors have found that polyethylene can be obtained and have completed the present invention.

That is, according to the first invention of the present invention, the catalyst precursor (d) obtained by supporting the chromium compound (b) and the metal-containing hydrocarbon compound (c) other than chromium on the inorganic oxide support (a), respectively. ) In a non-reducing atmosphere, wherein the catalyst precursor (d) is calcined in a temperature range of 100 to 360 ° C. while introducing an inert gas. A first step of holding for 5 minutes to 48 hours, and after the first step, the concentration of oxygen introduced is continuously increased or staged so as to keep the contact temperature in the range of 200-500 ° C. And a second step of firing for 5 minutes to 72 hours while adjusting the final oxygen concentration to 15 to 30% by volume . A manufacturing method is provided.

According to the second invention of the present invention, in the first invention, the concentration of oxygen introduced when starting the introduction of oxygen in the second step is 2% by volume or less. A method for producing a chromium catalyst for ethylene polymerization is provided.

  Furthermore, according to the third invention of the present invention, in the first or second invention, the contact temperature when starting the introduction of oxygen in the second step is 200 to 450 ° C. A method for producing a chromium catalyst for ethylene polymerization is provided.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the ratio of the hexavalent chromium content to the total chromium content is 70 to 100% by weight. A method for producing a chromium catalyst is provided.

  Furthermore, according to a fifth invention of the present invention, in any one of the first to fourth inventions, the inorganic oxide support (a) is silica, and the method for producing a chromium catalyst for ethylene polymerization Is provided.

  Furthermore, according to the sixth invention of the present invention, in any one of the first to fifth inventions, the catalyst precursor (d) contains 0.5 to 5.0 wt% of the chromium compound (b). A method for producing a chromium catalyst for ethylene polymerization is provided.

  According to the seventh invention of the present invention, in any one of the first to sixth inventions, the metal-containing hydrocarbon compound (c) is selected from groups 1, 2, 3, and 13 of the periodic table. Provided is a method for producing a chromium catalyst for ethylene polymerization, which contains a selected metal element.

  Furthermore, according to an eighth invention of the present invention, in any one of the first to seventh inventions, the metal contained in the metal-containing hydrocarbon compound (c) is aluminum, and the chromium for ethylene polymerization A method for producing a catalyst is provided.

  According to the ninth invention of the present invention, in any one of the first to eighth inventions, the metal-containing hydrocarbon compound (c) is 0.5 to 5.0% by weight of each metal portion in the catalyst. A method for producing a chromium catalyst for ethylene polymerization is provided, characterized in that the total amount of carbon and hydrogen is 0.5 to 20.0 wt% in the catalyst.

  According to a tenth aspect of the present invention, in any one of the first to ninth aspects, the metal-containing hydrocarbon compound (c) has 2 to 30 carbon atoms and 5 hydrogen atoms in one molecule. There is provided a method for producing a chromium catalyst for ethylene polymerization, characterized in that the number is ˜100.

  Furthermore, according to an eleventh aspect of the present invention, there is provided the method for producing a chromium catalyst for ethylene polymerization according to any one of the first to tenth aspects, wherein the inert gas is nitrogen.

  According to a twelfth aspect of the present invention, in any one of the first to eleventh aspects, the concentration of oxygen to be introduced is increased continuously or stepwise in the second step. A method for producing a chromium catalyst for ethylene polymerization is provided.

  According to a thirteenth aspect of the present invention, in any one of the first to twelfth aspects, the second step includes temporarily interrupting the introduction of oxygen. A method for producing a chromium catalyst is provided.

  According to the fourteenth invention of the present invention, in any one of the first to thirteenth inventions, the contact temperature is in the range of 250 to 550 ° C. A method for producing a chromium catalyst for ethylene polymerization is provided, which comprises a third step of introducing over 72 hours.

  According to a fifteenth aspect of the present invention, there is provided the method for producing a chromium catalyst for ethylene polymerization according to the fourteenth aspect, wherein the contact temperature is 350 ° C. to 420 ° C. in the third step. Provided.

On the other hand, according to the sixteenth invention of the present invention, it is obtained by performing ethylene homopolymerization or copolymerization of ethylene and α-olefin using the ethylene polymerization catalyst according to any one of the first to fifteenth inventions. A method for producing polyethylene is provided.

According to the seventeenth aspect of the present invention, in the sixteenth aspect, the melt flow rate (HLMFR) at a temperature of 190 ° C. and a load of 21.6 kg is 1 to 100 g / 10 minutes, and the density is 0.935 to 0.00. A process for producing polyethylene is provided, characterized in that it is 965 g / cm ³ .

Furthermore, according to an eighteenth aspect of the present invention, in the sixteenth or seventeenth aspect, the polyethylene has a HLMFR of 1 to 15/10 minutes and a density of 0.940 to 0.960 g / cm ^3. A manufacturing method is provided.

  By using the method for producing an ethylene polymerization catalyst of the present invention, it is possible to produce polyethylene having an excellent balance between rigidity and durability, high fluidity and high melt tension with high activity. The polyethylene is suitable for a hollow plastic product because of its fluidity and moldability, and the hollow plastic product has an excellent balance between rigidity and durability and can be suitably used for a fuel tank, particularly a fuel tank for automobiles. .

It is a pattern diagram which shows one embodiment which carries out baking activation of the chromium catalyst precursor by this invention.

The process for producing an ethylene polymerization catalyst according to the present invention comprises an inert atmosphere at a specific contact temperature, particularly at a relatively low temperature, when a catalyst precursor supporting a chromium compound and another metal-containing hydrocarbon compound chromium compound is calcined. After heating at, firing is performed while adjusting the introduced oxygen concentration so as to keep within a specific temperature range.
In addition, by using the ethylene polymerization catalyst produced by the method of the present invention, polyethylene having excellent fluidity and melt tension can be obtained with high activity, and particularly suitable for hollow plastic molded products. It can be produced with activity.
Hereinafter, the present invention will be specifically described for each item.

[I] Catalyst for ethylene polymerization The catalyst used in the present invention comprises at least a part of chromium by supporting a chromium compound (b) on a specific inorganic oxide carrier (a) and activating it by firing in a non-reducing atmosphere. It is a chromium catalyst whose atoms are hexavalent. The catalyst of the present invention is classified as a Philips catalyst.
General Philips catalysts are described in, for example, the following documents, and the present invention relates to improvements of these catalysts.
(I) M.M. P. McDaniel, Advances in Catalysis, Volume 33, 47, 1985, Academic Press Inc.
(Ii) M.M. P. McDaniel, Handbook of Heterogeneous Catalysis, 2400, 1997, VCH
(Iii) M.M. B. Welch et al., Handbook of Polyolefins: Synthesis and Properties, p. 21, 1993, Marcel Dekker.

1. Inorganic oxide support (a)
In the present invention, as the inorganic oxide carrier (a), a metal oxide of Group 2, 4, 13 or 14 of the periodic table can be used. Specific examples include magnesia, titania, zirconia, alumina, silica, tria, silica-titania, silica-zirconia, silica-alumina, or mixtures thereof.
For automotive fuel tank applications, silica alone is preferred as the inorganic oxide support. When a material other than silica is used as the carrier, the polymerization activity is lowered, and it is thought that the cause is an increase in the low molecular weight component of polyethylene, but the impact resistance tends to be lowered.
The production method, physical properties and characteristics of the support suitable for these chromium catalysts are described, for example, in the following documents.
(I) C.I. E. Marsden, Preparation of Catalysts, Volume V, 215, 1991, Elsevier Science Publishers.
(Ii) C.I. E. Marsden, Plastics, Rubber and Composites Processing and Applications, Volume 21, 193, 1994.

The ethylene-based polymerization catalyst in the present invention has a high specific surface area and a high pore volume as catalyst particles, and has a characteristic property and structure. This characteristic property and structure can be achieved by highly controlling the particle structure and intraparticle pore structure of the inorganic oxide support used.
In the present invention, the inorganic oxide support (a) has a specific surface area of 200~1000m ² / g, preferably 350~950m ² / g, more preferably may be selected those which are 625~900m ² / g. When the specific surface area is less than 200 m ² / g, the polymerization activity of the activated catalyst decreases. Moreover, when the specific surface area exceeds 1000 m ² / g, it is difficult to produce the carrier.

The pore volume of the inorganic oxide support (a) of the present invention is 1.0 to 5.0 cm ³ / g, preferably 1.0 to 3.0 cm ³ / g, more preferably 1.2 to 2. The range is 5 cm ³ / g. When the pore volume is less than 1.0 cm ³ / g, the pores become small due to the polymer during polymerization, and the monomer cannot be diffused, resulting in a decrease in activity. When the pore volume exceeds 5.0 cm ³ / g, it is difficult to produce the carrier.
The average particle size of the inorganic oxide carrier (a) of the present invention is 10 to 200 μm, preferably 25 to 180 μm, more preferably 35 to 170 μm. Outside the above range, it becomes difficult to balance the durability and impact resistance of polyethylene.

2. Chromium compound (b)
In the present invention, the chromium compound (b) is supported on the inorganic oxide support (a). As a chromium compound (b), what is necessary is just a compound in which at least one chromium atom becomes hexavalent by carrying out baking activation in non-reducing atmosphere after carrying | supporting. Examples of the chromium compound (b) include chromium oxide, chromium halide, oxyhalide, chromate, dichromate, nitrate, carboxylate, sulfate, chromium-1,3-diketo compound, chromium. Acid ester etc. are mentioned.
Specifically, chromium trioxide, chromium trichloride, chromyl chloride, potassium chromate, ammonium chromate, potassium dichromate, chromium nitrate, chromium sulfate, chromium acetate, tris (2-ethylhexanoate) chromium, chromium Examples thereof include acetylacetonate and bis (tert-butyl) chromate. Of these, chromium trioxide, chromium acetate, and chromium acetylacetonate are preferable. Even when a chromium compound having an organic group such as chromium acetate or chromium acetylacetonate is used, the organic group part burns by firing activation in a non-reducing atmosphere described later, and finally chromium trioxide is used. As in the case of the above, it reacts with the hydroxyl group on the surface of the inorganic oxide carrier, and at least some of the chromium atoms become hexavalent and are fixed in a chromate ester structure. This is described, for example, in the following document.
(I) V. J. et al. Ruddick et al. Phys. Chem. , Volume 100, 11062, 1996 (ii) S. et al. M.M. Augustine et al. Catal. , Volume 161, 641, 1996. The support of the chromium compound (b) on the inorganic oxide support (a) can be carried out by a known method such as impregnation, solvent distillation, sublimation, etc. An appropriate method may be used depending on the type. At that time, the amount of the chromium compound (b) to be supported is preferably 0.5 to 5.0% by weight, more preferably 0.6 to 4.0% by weight, further preferably chromium atom as a chromium atom with respect to the carrier. 0.7 to 3.0% by weight.

3. Metal-containing hydrocarbon compounds other than chromium (c)
In the production of the polyethylene according to the present invention, in order to adjust the ethylene polymerization activity, the copolymerization with α-olefin, the molecular weight of the obtained polyethylene, and the molecular weight distribution, the chromium compound is loaded before or after the chromium compound is loaded. Simultaneously with the compound, a metal-containing hydrocarbon compound (c) other than chromium is supported. As the metal element, those belonging to Group 1, 2, 3, or 13 of the periodic table are selected. Of these metal elements, aluminum is most preferred. The number of carbons contained in one molecule of the metal-containing hydrocarbon compound is 2 to 30, and the number of hydrogen is 5 to 100.
Specific examples of the metal-containing hydrocarbon compound (c) other than chromium include, for example, an aluminum compound such as aluminum trisec-butoxide, a titanium compound such as titanium tetraisopropoxide, and a zirconium compound such as zirconium tetrabutoxide, A magnesium compound such as dialkylmagnesium may be mentioned, but aluminum trisec-butoxide is preferably used to adjust the copolymerizability with an α-olefin and the molecular weight and molecular weight distribution of the obtained polyethylene.
These methods are described in the following documents, for example.
(I) C.I. E. Marsden, Plastics, Rubber and Composites Processing and Applications, Volume 21, 193, 1994 (ii) T. et al. Pulukat et al. Polym. Sci. , Polym. Chem. Ed. , Volume 18, 2857, 1980 (iii) M .; P. McDaniel et al. Catal. , Volume 82, p. 118, 1983. Each metal in the metal-containing hydrocarbon compound other than chromium contained in the catalyst is preferably 0.5 to 5.0% by weight, more preferably 0.7 to 4.5. % By weight, more preferably 0.9 to 4.0% by weight. The total amount of carbon and hydrogen contained in the catalyst is preferably 0.5 to 20.0% by weight, more preferably 0.5 to 15.0% by weight.

  In the present invention, fluorine-containing salts such as ammonium silicofluoride may be added before the chromium compound is loaded, in order to adjust the ethylene polymerization activity, the copolymerization with α-olefin, the molecular weight of the resulting polyethylene, and the molecular weight distribution. It may be supported after the compound is loaded or simultaneously with the chromium compound.

4). Firing activation (activation) method In the present invention, after supporting the chromium compound / metal-containing hydrocarbon compound other than chromium, the firing activation is performed in a non-reducing atmosphere substantially free of moisture, for example, oxygen or air. Can be done below. At this time, an inert gas may coexist. Preferably, it is carried out in a fluidized state using a gas that is sufficiently dried by circulating molecular sieves or the like.
The firing activation is preferably performed in a fluidized state using sufficiently dried air in which molecular sieves or the like are circulated. In the literature (MP McDaniel, Advances in Catalysis, Volume 33, 47, 1985, Academic Press Inc.). 9. It is generally known that catalytic activity is exhibited at an activation temperature of 500 ° C. or higher as shown in FIG. In particular, in this figure, it is shown that it becomes highly active at an activation temperature of 800 to 900 ° C., and such activation conditions are technical common sense for those skilled in the art.

  For reactors that carry out calcination activation, US 2005/0255987 discloses an example method for the activation of a chromium catalyst on a bench / plant scale. H. Schonfelder et al., Reaction Kinetics and the Development of Catalytic Processes, Volume 122, page 255, disclose examples of the shape and size of plant scale activation reactors.

  Conventionally, firing activation of an inorganic oxide support containing a chromium compound is performed by raising the temperature in the furnace from room temperature in a non-reducing atmosphere or in an inert gas atmosphere. In order to remove the physically adsorbed water contained in the inorganic oxide support, there is a method of raising the contact temperature from room temperature by inert gasification and switching to a non-reducing atmosphere at a temperature in the middle of reaching the target contact temperature. Liked. When oxygen is present in a state where the contact temperature is increased, heat is generated by combustion of carbon and hydrogen in the chromium compound, so that the contact temperature rises rapidly and it becomes difficult to control the contact temperature. The effect of increasing the contact temperature due to hydrocarbon combustion becomes more remarkable when a metal-containing compound other than the chromium compound is included.

  The “contact temperature” described here is a temperature obtained by measuring the catalyst fluidized bed, and indicates that the catalyst is in contact with the gas at this temperature. Since the temperature distribution of the catalyst fluidized bed is constant, any point in the catalyst fluidized bed may be measured, but it is preferable to adopt the temperature at the center of the catalyst fluidized bed.

  In this invention, the process of performing baking of the catalyst precursor (d) which carry | supported the chromium compound is performed, adjusting the density | concentration of the oxygen introduce | transduced so that a contact temperature may be maintained at 200-500 degreeC. By adjusting the oxygen concentration, an increase in contact temperature due to combustion of the hydrocarbon portion contained in the catalyst can be suppressed, and the contact temperature is maintained in the above range. By polymerizing the catalyst obtained by this method with ethylene, polyethylene having fluidity and melt tension which may be at a low calcination temperature can be produced.

Next, the production method (activation method) of the ethylene polymerization chromium catalyst will be specifically described. (1) 1st process: The baking process in inert atmosphere The 1st process is a process of baking in inert atmosphere. Start heating at room temperature in an inert atmosphere. The contact temperature is raised to any temperature between 100 and 360 ° C. This contact temperature is preferably 120 to 320 ° C, more preferably 140 to 250 ° C. At this time, the contact temperature may be continuously increased, held at a certain temperature and gradually increased, or the contact temperature may be temporarily decreased. There is no particular limitation on the method for increasing the contact temperature. The time for continuously holding at 100 to 360 ° C. in an inert atmosphere is 5 minutes to 48 hours, preferably 30 minutes to 36 hours, and particularly preferably 1 hour to 24 hours. In addition, the heating rate at the time of raising the contact temperature is not particularly limited, but is 1 to 200 ° C./h, preferably 5 to 150 ° C./h, more preferably 10 to 100 ° C./h. desirable.

(2) Second step: A step of firing while adjusting the oxygen concentration.

The second step is a step of performing baking while adjusting the oxygen concentration. The period from the start of oxygen introduction to the end of oxygen concentration adjustment is the second step. When oxygen is introduced into the pre-activated catalyst heated in an inert atmosphere, the catalyst is burned with oxygen and the contact temperature rises, but the contact temperature is 200 to 500 ° C, preferably 250 to 480 ° C, more preferably 280 to 430 ° C. Oxygen is introduced so that As will be described later, when the contact temperature exceeds 500 ° C., the hexavalent chromium content decreases, and the desired effect is not obtained in the present invention. The oxygen concentration at the start of oxygen introduction is preferably 2% or less, and more preferably 1% or less. The contact temperature at the start of oxygen introduction is 200 to 450 ° C., preferably 250 to 420 ° C., more preferably 300 to 400 ° C.
Oxygen is raised, and at the end of this step, the oxygen concentration is desirably 5 to 50%, preferably 10 to 40%, and more preferably 15 to 30%. Specifically, it is most preferable that air is introduced at the end of this step.
This step of firing while adjusting the oxygen concentration is preferably 5 to 72 hours. When increasing the introduced oxygen concentration, the oxygen concentration may be continuously increased, may be increased stepwise, or the oxygen concentration may be temporarily decreased. The gas flow may be interrupted and started repeatedly (intermittently). Further, the contact temperature may always be held at a certain temperature or may be raised in multiple steps. In addition, the heating rate at the time of raising the contact temperature is not particularly limited, but is 1 to 200 ° C./h, preferably 5 to 150 ° C./h, more preferably 10 to 100 ° C./h. desirable. There is no particular restriction between the oxygen concentration of the oxygen and inert gas mixture and the contact temperature.

Specific methods for adjusting the contact temperature and the introduced oxygen concentration in the second step include the following.
1. Gradually increase the oxygen concentration in low temperature hold. For example, the oxygen concentration is increased stepwise (for example, by 1%) while being held at a desired contact temperature of 250 ° C. to 370 ° C.
2. Increase the oxygen concentration gradually and continuously with the low temperature hold. For example, the oxygen concentration is continuously increased (for example, at a rate of temperature increase of 1% / h) while being held at a desired contact temperature of 250 ° C. to 370 ° C.
3. The low temperature hold is divided into two stages, and the oxygen concentration is gradually increased at each stage. For example, the oxygen concentration is increased stepwise (for example, by 1%) while being held at a desired contact temperature of 250 ° C. to 320 ° C. Thereafter, the temperature is raised to a desired contact temperature of 320 ° C. to 370 ° C. and held at that temperature, and the oxygen concentration is further increased stepwise (for example, by 1%).
4). Divide the low temperature hold into multiple stages and gradually raise the temperature with low oxygen concentration. For example, the oxygen concentration is increased stepwise (for example, by 0.5%) while being held at a desired contact temperature of 250 ° C. to 300 ° C. Thereafter, the temperature is raised to a desired contact temperature of 300 ° C. to 350 ° C. and held at that temperature, and the oxygen concentration is further increased stepwise (for example, by 0.5%). Thereafter, the temperature is raised to a desired contact temperature of 350 ° C. to 375 ° C. and held at that temperature, and the oxygen concentration is further increased stepwise (for example, by 0.5%). Thereafter, the temperature is raised to a desired contact temperature of 375 ° C. to 400 ° C. and held at that temperature, and the oxygen concentration is further increased stepwise (for example, by 0.5%).

  The reaction performed by the activation operation when chromium trioxide is used as the chromium compound is shown below.

Silanol groups on the silica surface and chromium trioxide react to form a chromic ester structure, and dehydration of the silanol groups is caused by activation at high temperatures. Even when a chromium compound such as chromium acetate or tris (acetylacetonate) chromium is used as the chromium compound, organic groups such as carboxyl groups and acetylacetonate groups are burned by activation in the presence of oxygen, The end result is a chromium ester structure similar to that of chromium trioxide. This chromium ester structure is considered as an active precursor in conducting ethylene polymerization. However, this ester structure reacts with water to hydrolyze to become CrO ₃ , and a reaction of CrO ₃ → Cr ₂ O ₃ + 3 / 2O ₂ occurs to become inactive chromium (III) Cr ₂ O ₃ . . Therefore, when performing activation, sufficient attention must be paid to the moisture management of the circulation gas (the dew point of the circulation gas is desirably -80 ° C. or lower).

  In the present invention, when the activation of the chromium catalyst is performed at a low temperature of 250 ° C. to 550 ° C., the oxygen concentration is adjusted so that an excessive spike in contact temperature does not occur due to combustion of the hydrocarbon portion contained in the catalyst. It has been found that polyethylene having improved fluidity and moldability can be obtained. Analysis of the chromium valence of the chromium catalyst obtained after activation shows that the catalyst with spiked contact temperature has a smaller proportion of hexavalent chromium than the catalyst without temperature spike. It was. This is considered as follows. At the time of activation, the dehydration reaction of silanol groups has occurred as described above, but the dehydration reaction proceeds rapidly due to the contact temperature rise, and the amount of water exceeding the water removal capability by the flow gas remains in the catalyst system. End up. As a result, a dehydration reaction of the chromate structure is caused. This difference in the properties of the catalyst is thought to produce a difference in the properties of polyethylene obtained when polymerized. In the present invention, the content of hexavalent chromium is preferably 70% to 100%, more preferably 75% to 100%.

(3) Third step: calcination activation under a constant oxygen concentration After the second step, at a contact temperature of 250 to 550 ° C. for 5 minutes to 72 hours with the introduced oxygen concentration kept constant. It is preferably performed for 30 minutes to 54 hours, more preferably for 1 hour to 36 hours. The contact temperature in this step is preferably 300 to 500 ° C, more preferably 320 to 450 ° C, and further preferably 350 to 420 ° C. By this firing activation, at least a part of the chromium atoms of the chromium compound supported on the inorganic oxide support is oxidized to be hexavalent and chemically fixed on the support. When activation is performed at a temperature exceeding 550 ° C., the fluidity improvement and melt tension improvement effects of the present invention do not appear. Below 250 ° C, the catalytic activity is not sufficient. In addition, the heating rate at the time of raising the contact temperature is not particularly limited, but is 1 to 200 ° C./h, preferably 5 to 150 ° C./h, more preferably 10 to 100 ° C./h. desirable.

  As described above, in the chromium-supported catalyst obtained in the present invention, the ratio of hexavalent chromium to the total chromium content is 70% to 100% with respect to the chromium valence after the completion of calcination. The chromium content at this time is obtained by ICP measurement.

[II] Production method of polyethylene In the present invention, as described above, the oxygen concentration is adjusted so as to keep within a specific temperature range after heating in an inert atmosphere at a specific contact temperature, particularly at a relatively low temperature. However, the chromium catalyst obtained by firing is used to carry out ethylene homopolymerization or copolymerization of ethylene and α-olefin to produce polyethylene.

In producing polyethylene, any method such as a liquid phase polymerization method such as slurry polymerization or solution polymerization, or a gas phase polymerization method can be employed.
The liquid phase polymerization method is usually performed in a hydrocarbon solvent. As the hydrocarbon solvent, for example, an inert hydrocarbon such as propane, n-butane, isobutane, n-pentane, isopentane, hexane, heptane, octane, decane, cyclohexane, benzene, toluene, xylene or the like is used alone or as a mixture. .
In addition, the vapor phase polymerization method can adopt a commonly known polymerization method such as a fluidized bed and a stirring bed in the presence of an inert gas, and in some cases, a so-called condensing mode in which a medium for removing the heat of polymerization coexists. You can also.

  The polymerization temperature in the liquid phase or gas phase polymerization method is generally 0 to 300 ° C, practically 20 to 200 ° C, preferably 50 to 180 ° C, and more preferably 70 to 150 ° C. The catalyst concentration and ethylene concentration in the reactor may be any concentration sufficient to allow the polymerization to proceed. For example, the catalyst concentration can range from about 0.0001 to about 5% by weight based on the weight of the reactor contents in the case of liquid phase polymerization. Similarly, in the case of gas phase polymerization, the ethylene concentration can be in the range of 0.1 to 10 MPa as the total pressure.

  The concentration ratio or partial pressure ratio of hydrogen and ethylene coexisting with ethylene can be easily adjusted by changing the concentration or partial pressure of hydrogen and ethylene. Since hydrogen also acts as a chain transfer agent, when Hc / ETc or Hp / ETp is changed, the polymerization temperature must also be changed in order to obtain the same HLMFR product. That is, when Hc / ETc or Hp / ETp is raised, the polymerization temperature must be lowered, and when Hc / ETc or Hp / ETp is lowered, the polymerization temperature must be raised. However, since it depends on the absolute value of the hydrogen concentration or partial pressure, it is not always necessary to change the polymerization temperature in order to obtain the same HLMFR product.

  When ethylene is polymerized by the method of the present invention, it is preferable to copolymerize an α-olefin as a comonomer. As the α-olefin, for example, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene or the like is introduced alone or in two or more kinds into a reactor to carry out copolymerization. Preferably 1-butene, 1-hexene, more preferably 1-hexene is suitably used as a comonomer. The α-olefin content in the obtained polyethylene is 15 mol% or less, preferably 10 mol% or less.

[III] Polyethylene and its use Polyethylene obtained by the production method of the present invention is produced by the production method described above.
The polyethylene may be an ethylene homopolymer, or ethylene / α containing at least one α-olefin such as propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene as a comonomer. In some cases, it may be an olefin copolymer, and the α-olefin content in the ethylene / α-olefin copolymer obtained at this time is 15 mol% or less, preferably 10 mol% or less. As the α-olefin, 1-butene, 1-hexene, more preferably 1-hexene is preferably used. Further, as described above, a small amount of a modifying monomer such as dienes or styrenes may be contained.

The polyethylene of the present invention has a high load melt flow rate (hereinafter abbreviated as “HLMFR”) measured at a temperature of 190 ° C. and a load of 21.6 kg of 1 to 100 g / 10 minutes, and a density of 0.935 to 0.965 g. / Cm ³ . Since the polyethylene has both high impact resistance and durability and is excellent in balance, it is particularly effective in blow molded products, especially large blow molded products. The HLMFR of polyethylene for blow molded products is 1 to 100 g / 10 min, and particularly the polyethylene for large blow molded products is 1 to 15 g / 10 min. The density of polyethylene for blow molded products is 0.935 to 0.965 g / cm ³ , especially for polyethylene for large blow molded products is 0.940 to 0.960 g / cm ³ . It is also preferable to knead the obtained polyethylene. Kneading can be performed using a single or twin screw extruder or a continuous kneader. Moreover, the obtained polyethylene can be blow-molded by a conventional method.

  When polyethylene has an HLMFR of less than 1 g / 10 min, during extrusion of a parison (in blow molding, a pipe-shaped molten polymer extruded from the die of the molding machine; the state before being expanded by air pressure in the mold) The extrusion amount is insufficient and the molding becomes unstable, which is impractical, and even if it exceeds 100 g / 10 minutes, the formation of the parison becomes unstable due to insufficient melt viscosity and melt tension, which is not practical. Here, HLMFR is measured under conditions of a temperature of 190 ° C. and a load of 21.6 kg in accordance with JIS K-7210.

When the density of polyethylene is less than 0.935 g / cm ³ , the rigidity of the hollow plastic molded product is insufficient, and when it exceeds 0.965 g / cm ³ , the durability of the hollow plastic molded product is insufficient. The density can be adjusted by a method such as control of the type and content of α-olefin. For example, the density is increased by reducing the α-olefin content in polyethylene (lowering the α-olefin addition amount during polymerization) or by using an α-olefin having a small carbon number if the content is the same. can do. The density is in accordance with JIS K-7112. After the pellets are melted by a hot compression molding machine having a temperature of 160 ° C., the temperature is lowered at a rate of 25 ° C./minute to form a sheet having a thickness of 2 mmt. After conditioned for 48 hours, it was measured in a density gradient tube.

  The present invention is characterized in that oxygen is gradually introduced so as not to cause a temperature rise spike when the catalyst is activated by firing at a low temperature of 300 ° C. to 500 ° C. when oxygen is brought into contact with the catalyst precursor. By carrying out ethylene polymerization using the obtained catalyst, polyethylene having a good melt tension (MT) can be obtained. Here, it is known that the melt tension greatly depends on the number of long chain branches contained in polyethylene, which is related to the properties of the chromium catalyst. Therefore, it is shown that the properties of the catalyst change depending on the catalyst firing method related to the oxygen introduction method. Since it is known that polyethylene having a low melt tension can be obtained from a chromium catalyst obtained by low temperature activation, the present invention is useful in that the melt tension is improved by the low temperature activation catalyst.

  The resulting polyethylene can then be kneaded. It is carried out using a single or twin screw extruder or a continuous kneader. The polyethylene produced by the above method may be used alone or in combination of a plurality of types, and after being pelletized by mechanical melt mixing with a pelletizer or homogenizer, etc. according to a conventional method, it is molded by various molding machines. However, the polyethylene particles produced in the present invention can be directly applied to various molding machines without being pelletized by taking advantage of their very good powder particle properties. It is possible to supply and form a desired molded product, and since the step of pelletizing can be omitted, it is very preferable from the viewpoint of energy saving.

The polyethylene particles obtained by the method of the present invention refer to the state in which the shape of the polymer particles is maintained just after the production of polyethylene in the polymerization reaction tank using the above-mentioned catalyst for ethylene polymerization. Polyethylene particles that are not treated at a temperature of about 150 ° C., preferably about 130 ° C., and more preferably higher than about 110 ° C., which is necessary to dry out the solvent after completion. Say.
The polyethylene particles of the present invention have a bulk density of 0.20 to 0.60 g / cm ³ , preferably 0.22 to 0.55 g / cm ³ , more preferably 0.25 to 0.50 g / cm ³ . . The particles passing through the sieve having a mesh opening of 177 μm are 0.8% by weight or less, preferably 0.5% by weight or less, and more preferably 0.3% by weight or less. Needless to say, the lower limit is 0% by weight. When the amount of particles passing through a sieve having a mesh opening of 40 μm exceeds 0.8% by weight, contamination due to fine powder diffusion during air flow transportation becomes a problem, and adhesion to a vessel wall due to static electricity becomes unfavorable.

  In the polyethylene and polyethylene particles obtained by the method of the present invention, if necessary, in addition to other polyethylene and rubber, etc., an antioxidant, an ultraviolet absorber, a light stabilizer, a lubricant, an antistatic agent, Anti-fogging agent, anti-blocking agent, processing aid, coloring pigment, pearl pigment, polarizing pearl pigment, crosslinking agent, foaming agent, neutralizing agent, heat stabilizer, crystal nucleating agent, inorganic or organic filler, flame retardant, etc. Known additives can be blended.

  According to the polymerization method according to the present invention, polymerization is performed with high activity, and a molded product of the same standard can be stably and continuously produced. Therefore, the polyethylene polymerization method of the present invention is an excellent method suitable for continuously producing polyethylene of a certain quality.

  As a polymerization method according to the present invention, not only single-stage polymerization in which polyethylene is produced using one reactor, but also multistage polymerization can be performed by connecting at least two reactors in order to widen the molecular weight distribution. In the case of multi-stage polymerization, two-stage polymerization is preferred in which two reactors are connected and the reaction mixture obtained by polymerization in the first-stage reactor is continuously fed to the second-stage reactor.

  Any method for producing a high molecular weight component in the first stage reactor, a low molecular weight component in the second stage reactor, a low molecular weight component in the first stage reactor, and a high molecular weight component in the second stage reactor, respectively. Although it is better to produce a high molecular weight component in the first stage reactor and a low molecular weight component in the second stage reactor, it does not require an intermediate hydrogen flash tank for the transition from the first stage to the second stage. More preferable in terms of productivity.

  In the first stage, copolymerization of ethylene alone or optionally with α-olefin is carried out by adjusting the molecular weight by mass ratio or partial pressure ratio of hydrogen concentration to ethylene concentration (Hc / ETc or Hp / ETp), polymerization temperature or both. While adjusting, the polymerization reaction is carried out while adjusting the density by the mass ratio or partial pressure ratio of the α-olefin concentration to the ethylene concentration.

  In the second stage, there are hydrogen in the reaction mixture that flows from the first stage and α-olefin that also flows in, but if necessary, new hydrogen and α-olefin can be added respectively. Therefore, in the second stage, the mass ratio of the hydrogen concentration to the ethylene concentration or the partial pressure ratio (Hc / ETc or Hp / ETp), the polymerization temperature or the molecular weight is adjusted by both, and the mass of the α-olefin concentration to the ethylene concentration. The polymerization reaction can be carried out while adjusting the density by the ratio or the partial pressure ratio.

The polyethylene obtained by the present invention is useful in the following points.
In order to reduce the load on the extruder during molding, it is necessary to make the polyethylene highly fluidized, but in order to increase the fluidity (high load melt flow) of the polyethylene obtained with the chromium catalyst, it is usually during polymerization. The operation of raising the polymerization temperature and hydrogen concentration is performed. However, when the polymerization temperature is raised, the molecular weight distribution of the obtained polyethylene becomes narrow, and the balance between rigidity and durability is deteriorated. In addition, the control of the high load melt flow by the hydrogen concentration during polymerization is less effective than the polymerization temperature, and the moldability of polyethylene deteriorates due to a decrease in the high molecular weight component by introducing hydrogen. The polyethylene disclosed in the present invention has improved fluidity only by the method of calcining the catalyst regardless of the polymerization temperature and the hydrogen concentration.
Therefore, the polyethylene obtained by the present invention not only improves flowability (high load melt flow) and moldability (melt tension), but also improves the balance between rigidity and durability.

  The polyethylene produced by the present invention is excellent in fluidity, moldability, and balance between rigidity and durability, and is particularly suitable for hollow plastic molded products. Examples of the use include hollow plastic molded articles such as automobile fuel tanks, kerosene cans, drum cans, chemical containers, agricultural chemical containers, solvent containers, and plastic bottles.

  In the following, the present invention will be described in more detail with reference to examples and comparative examples, and the superiority of the present invention and the superiority in the structure of the present invention will be demonstrated, but the present invention is limited by these examples. It is not a thing.

(1) Hexavalent chromium content measurement 0.2 g of a catalyst sample was weighed and placed in a 100 ml beaker, and hot water extraction was performed with 50 ml of ultrapure water for 30 minutes. After cooling, a filtration operation was performed, the filtrate was made up to a constant volume of 100 ml, and the liquid was used as a sample for quantification with an ICP apparatus.
(2) High load melt flow rate (HLMFR)
As a polymer pretreatment for measuring physical properties, 0.2% by weight of B225 manufactured by Ciba Geigy Co. was added to the sample as an additive, kneaded with a single screw extruder and pelletized. According to JIS K-7210 (2004 edition), Annex A, Table 1-Condition G, the measured value at a test temperature of 190 ° C. and a nominal load of 21.60 kg was shown as HLMFR.
(3) Density As a polymer pretreatment for measuring physical properties, 0.2% by weight of B225 manufactured by Ciba Geigy Co. was added to the sample as an additive, kneaded with a single screw extruder, and pelletized. It measured according to JIS K-7112 (2004 edition).
(4) Melt tension (MT)
Using a Capillograph 1B manufactured by Toyo Seiki Seisakusho, extruding the molten resin under the conditions of a temperature of 190 ° C. (Example 2 also measures 230 ° C.), an orifice diameter of 2.095 mm, an orifice length of 8.0 mm, and an extrusion speed of 15 mm / min. It is a load when winding at a speed of 6.5 m / min with a winder, and the unit is mN.

[Example 1]
(1) Preparation of chromium catalyst precursor A carrier (silica gel) was prepared in accordance with US Pat. No. 5,232,883. This support had a specific surface area of 800 m ² / g, a pore volume of 2.0 cm ³ / g, and an average particle size of 100 μm.
Further, EXAMPLES I.I. of U.S. Pat. No. 4,119,773. By a method in accordance with the Catalyst Preparation Procedure, chromium (III) acetate and a solution of aluminum sec-butoxide in dichloromethane and silica gel were dried so that the Cr and Al contents would be 1% by weight and 2% by weight, respectively. Thus, chromium catalyst precursor particles exhibiting greenish white color and good fluidity were obtained.

(2) Calcination activation of chromium catalyst Using 180 kg of the chromium catalyst precursor particles obtained in (1) above, activation was performed in a cylindrical activation furnace having an inner diameter of 75 cm and a height of 8 m. Table 3 shows the activation method. FIG. 1 shows a time-series pattern of target contact temperature and introduced oxygen concentration.
In the furnace containing the chromium catalyst precursor particles, the catalyst was fluidized with dry nitrogen at a linear speed of 6 cm / s, and the temperature was increased to 150 ° C. at a temperature increase rate of 60 ° C./h. While maintaining the contact temperature at 150 ° C., the flow was continued with dry nitrogen for 3 hours. Again, the temperature was raised to 300 ° C. at a heating rate of 60 ° C./h, and held for 1 hour. While maintaining at 300 ° C., introduction of dry nitrogen containing 1% oxygen at a linear velocity of 6 cm / s was started and maintained for 30 minutes, and then dry nitrogen containing 2% oxygen was introduced for 30 minutes. Thereafter, dry nitrogen having an oxygen concentration stepwise increased from 3% → 4% → 5% was introduced for 2 hours and then switched to dry air. At the same time, heating was started at a heating rate of 60 ° C./h. Thereafter, baking was continued for 12 hours while maintaining the contact temperature at 400 ° C. After the calcination, the contact temperature was lowered to return to dry nitrogen containing no oxygen. When the contact temperature dropped to room temperature, the chromium catalyst was extracted in dry nitrogen. The hexavalent chromium content was measured and found to be 80%.

(3) Bench polymerization A 2.0 L autoclave sufficiently purged with nitrogen was charged with 100 mg of the chromium catalyst obtained in (2) above and 0.8 L of isobutane, and the internal temperature was raised to 98 ° C. 7.0 g of 1-hexene was introduced under pressure with ethylene, and polymerization was carried out so that the catalyst productivity was 3000 g-polymer / g-catalyst while maintaining the ethylene partial pressure at 1.4 MPa. Subsequently, the polymerization was terminated by releasing the content gas out of the system. Table 1 shows the polymerization results, the measurement results of physical properties (HLMFR, density), and the like.

[Example 2]
(1) Activation of calcination of chromium catalyst Using 180 kg of the chromium catalyst obtained in (1) of Example 1 above, activation was performed in a cylindrical activation furnace having an inner diameter of 75 cm and a height of 8 m. Table 4 shows the activation method.
In the furnace in which the chromium catalyst precursor particles were charged, the catalyst was fluidized with dry nitrogen having a linear speed of 6 cm / s, and the temperature was increased to 150 ° C. at a temperature increase rate of 60 ° C./h. While maintaining the contact temperature at 150 ° C., the flow was continued with dry nitrogen for 3 hours. Again, the temperature was raised to 300 ° C. at a heating rate of 60 ° C./h, and held for 1 hour. Dry nitrogen in which the oxygen concentration was continuously changed from 0 to 10% at a concentration increasing rate of 1% / h was introduced while maintaining the contact temperature at 300 ° C. Thereafter, the contact temperature was raised to 400 ° C., and the firing was continued for 12 hours while maintaining the contact temperature at 400 ° C. After the calcination, the contact temperature was lowered to return to dry nitrogen containing no oxygen. When the contact temperature dropped to room temperature, the chromium catalyst was extracted in dry nitrogen. The hexavalent chromium content was measured and found to be 85%.

(2) Bench polymerization Polyethylene was obtained by performing the same polymerization operation as in Example 1 (3) using the chromium catalyst obtained in (1) above. Table 1 shows the polymerization results, the measurement results of physical properties (HLMFR, density), and the like.

[Example 3]
(1) Activation of calcination of chromium catalyst Using 180 kg of the chromium catalyst obtained in (1) of Example 1 above, activation was performed in a cylindrical activation furnace having an inner diameter of 75 cm and a height of 8 m. Table 5 shows the activation method.
In the furnace in which the chromium catalyst precursor particles were charged, the catalyst was fluidized with dry nitrogen having a linear speed of 6 cm / s, and the temperature was increased to 150 ° C. at a temperature increase rate of 60 ° C./h. While maintaining the contact temperature at 150 ° C., the flow was continued with dry nitrogen for 3 hours. Again, the temperature was raised to 300 ° C. at a heating rate of 60 ° C./h, and held for 1 hour. While maintaining the temperature at 300 ° C., a mixture of oxygen and nitrogen in which the oxygen concentration was continuously changed from 0% to 5% at a concentration increasing rate of 2% / h was introduced. While maintaining the oxygen concentration of the introduced mixture at 5%, the temperature was increased to 350 ° C. at a temperature increase rate of 60 ° C./h. Dry nitrogen was introduced in which the contact temperature was maintained at 350 ° C. and the oxygen concentration was continuously changed from 5 to 21% at a concentration increase rate of 2% / h. Thereafter, the temperature was raised to 400 ° C. at a temperature raising rate of 60 ° C./h, and baking was continued for 12 hours while maintaining the contact temperature at 400 ° C. After the calcination, the contact temperature was lowered to return to dry nitrogen containing no oxygen. When the contact temperature dropped to room temperature, the chromium catalyst was extracted in dry nitrogen. The hexavalent chromium content was measured and found to be 85%.

(2) Bench polymerization Polyethylene was obtained by performing the same polymerization operation as in Example 1 (3) using the chromium catalyst obtained in (1) above. Table 1 shows the polymerization results, the measurement results of physical properties (HLMFR, density), and the like.

[Example 4]
(Plant polymerization)
Isobutane is supplied to a pipe loop reactor having an internal volume of 200 L at a rate of 120 L / h and the chromium catalyst obtained in Example 1 (2) is continuously supplied at a rate of 5 g / h, and the reactor contents are discharged at a required rate. However, at 100.5 ° C., ethylene and 1-hexene were supplied so that the mass ratio of the 1-hexene concentration in the liquid phase to the ethylene concentration was maintained at 0.10, the total pressure was 4.0 MPa, and the average residence time was 1. Polymerization was continuously performed in a liquid-filled state under the condition of 5 h. The catalyst productivity was 3000 g-polymer / g-catalyst, and the average polymerization activity was 2000 g-polymer / g-catalyst / h. The measurement results of physical properties (HLMFR, density, MT) are shown in Table 2.

[Comparative Example 1]
(1) Activation of calcination of chromium catalyst Using 180 kg of the chromium catalyst precursor obtained in (1) of Example 1, activation was performed in a cylindrical activation furnace having an inner diameter of 75 cm and a height of 8 m. Table 6 shows the activation method.
In the furnace in which the chromium catalyst precursor particles were charged, the catalyst was fluidized with dry nitrogen having a linear speed of 6 cm / s, and the temperature was increased to 150 ° C. at a temperature increase rate of 60 ° C./h. While maintaining the contact temperature at 150 ° C., the flow was continued with dry nitrogen for 3 hours. Thereafter, the introduced gas was switched from dry nitrogen to dry air, and the temperature was increased to 400 ° C. at a temperature increase rate of 60 ° C./h. However, when the introduction of dry air was started, the catalyst was burned with oxygen and the contact temperature increased, and the contact temperature temporarily increased to 530 ° C. When the contact temperature reached 400 ° C., baking was continued for 12 hours while maintaining the temperature. After completion of the calcination, the contact temperature was reduced, and the furnace was returned to dry nitrogen containing no oxygen. When the contact temperature decreased to room temperature, the chromium catalyst was extracted in dry nitrogen. The hexavalent chromium content was measured and found to be 55%.
(2) Bench polymerization Polyethylene was obtained by performing the same polymerization operation as (3) of Example 1 using the chromium catalyst obtained in (1) above. Table 1 shows the polymerization results, the measurement results of physical properties (HLMFR, density), and the like.

[Comparative Example 2]
(1) Activation of calcination of chromium catalyst Using 180 kg of the chromium catalyst precursor particles obtained in (1) of Example 1, activation was performed in a cylindrical activation furnace having an inner diameter of 75 cm and a height of 8 m. Table 7 shows the activation method.
In the furnace in which the chromium catalyst precursor was charged, the catalyst was fluidized with dry air having a linear velocity of 6 cm / s, and the temperature was increased to 150 ° C. at a temperature increase rate of 60 ° C./h. While maintaining the contact temperature at 150 ° C., the flow was continued with dry air for 3 hours. Thereafter, the temperature was raised to 200 ° C. at a heating rate of 60 ° C./h, and the flow was continued with dry air for another 3 hours. Temperature increase was started at 60 ° C./h, and introduction of dry air was started at a linear speed of 6 cm / s. When the contact temperature was 340 ° C., the catalyst was burned with oxygen, the contact temperature rose rapidly, and the contact temperature temporarily increased to 520 ° C. When the contact temperature reached 400 ° C., baking was continued for 12 hours while maintaining the temperature. After the calcination, the contact temperature was lowered, the inside of the furnace was returned to dry nitrogen containing no oxygen, and the chromium catalyst was extracted in dry nitrogen when the contact temperature decreased to room temperature. The content of hexavalent chromium was measured and found to be 60%.
(2) Bench polymerization Polyethylene was obtained by performing the same polymerization operation as (3) of Example 1 using the chromium catalyst obtained in (1) above. Table 1 shows the polymerization results, the measurement results of physical properties (HLMFR, density), and the like.

[Comparative Example 3]
(1) Activation of calcination of chromium catalyst Using 180 kg of the chromium catalyst precursor obtained in (1) of Example 1, activation was performed in a cylindrical activation furnace having an inner diameter of 75 cm and a height of 8 m. Table 8 shows the activation method.
The inside of the furnace containing the chromium catalyst precursor was fluidized with dry nitrogen at a linear speed of 6 cm / s, and the temperature was raised to 150 ° C. at a temperature rising rate of 60 ° C./h. While maintaining the contact temperature at 150 ° C., the flow was continued with dry nitrogen for 3 hours. Again, the temperature was raised to 400 ° C. at a heating rate of 60 ° C./h, and held for 1 hour. After introducing dry nitrogen containing 1% oxygen at a linear velocity of 6 cm / s and maintaining for 30 minutes, dry nitrogen containing 2% oxygen was introduced for 30 minutes. Thereafter, dry nitrogen whose oxygen concentration was gradually increased from 3% → 4% → 5% was introduced every 2 hours. Further, dry nitrogen was introduced in which the oxygen concentration was continuously changed from 5 to 21% at a concentration increase rate of 2% / h. The catalyst was burned with oxygen, the contact temperature rose the highest, and the contact temperature rose temporarily to 550 ° C. Thereafter, the calcination was continued for 12 hours while maintaining the contact temperature at 400 ° C. After completion of the calcination, the contact temperature was reduced, and the furnace was returned to dry nitrogen containing no oxygen. When the contact temperature decreased to room temperature, the chromium catalyst was extracted in dry nitrogen. The content of hexavalent chromium was measured and found to be 60%.
(2) Bench polymerization Polyethylene was obtained by performing the same polymerization operation as (3) of Example 1 using the chromium catalyst obtained in (1) above. Table 1 shows the polymerization results, the measurement results of physical properties (HLMFR, density), and the like.

[Comparative Example 4]
(Plant polymerization)
To the pipe loop reactor having the same internal volume of 200 L as in Example 3, isobutane was continuously supplied at 120 L / h, and the chromium catalyst obtained in Comparative Example 2 (1) was continuously supplied at a rate of 5 g / h. At 102.5 ° C., ethylene and 1-hexene were supplied so that the mass ratio of the 1-hexene concentration in the liquid phase to the ethylene concentration was maintained at 0.10, and the total pressure was 4.0 MPa. Polymerization was continuously performed in a liquid-filled state under the condition of an average residence time of 1.5 h. The catalyst productivity was 2900 g-polymer / g-catalyst, and the average polymerization activity was 1900 g-polymer / g-catalyst / h. The measurement results of physical properties (HLMFR, density, MT) are shown in Table 2.

  As can be seen from the above results, when bench polymerization was performed under the same conditions (Example 1 and Comparative Example 1), the polymer obtained in Example 1 and polyethylene having high fluidity (HLMFR) were obtained. Further, it can be seen that, when polymerization was carried out at the plant scale, the polymerization temperature in Comparative Example 4 had to be 2 ° C. higher than that in Example 4 in order to obtain the same HLMFR polyethylene. Further, the polyethylene obtained in Example 4 had a higher melt tension than the polyethylene obtained in Comparative Example 4.

  By using the method for producing an ethylene polymerization catalyst provided by the present invention, polyethylene having excellent moldability and impact resistance and excellent balance between durability and rigidity can be obtained with high activity, particularly hollow plastic molding. Polyethylene that is suitable for products, and particularly has high fluidity and melt tension, can be produced efficiently and with high activity. The polyethylene is suitable for hollow plastic products, and the hollow plastic products have excellent moldability, durability, barrier properties, and excellent balance of impact resistance and rigidity, and are suitable for fuel tanks, particularly automobile fuel tanks. It can be used suitably.

Claims (18)

Chromium for ethylene polymerization in which a catalyst precursor (d) obtained by supporting a chromium compound (b) and a metal-containing hydrocarbon compound (c) other than chromium on the inorganic oxide support (a) is calcined in a non-reducing atmosphere. A method for producing a catalyst, comprising:
The catalyst precursor (d) firing step includes a first step of maintaining a contact temperature in the range of 100 to 360 ° C. for 5 minutes to 48 hours while introducing an inert gas, and the first step. Thereafter, the concentration of introduced oxygen is continuously increased or increased stepwise so as to keep the contact temperature at 200 to 500 ° C., and the final oxygen concentration is adjusted to 15 to 30% by volume. The manufacturing method of the chromium catalyst for ethylene polymerization including the 2nd process of baking for 5 minutes-72 hours, doing it. 2. The method for producing a chromium catalyst for ethylene polymerization according to claim 1, wherein in the second step, the concentration of oxygen introduced when starting the introduction of oxygen is 2% by volume or less.   3. The method for producing a chromium catalyst for ethylene polymerization according to claim 1, wherein in the second step, the contact temperature when starting the introduction of oxygen is 200 to 450 ° C. 4.   The method for producing a chromium catalyst for ethylene polymerization according to any one of claims 1 to 3, wherein a ratio of the hexavalent chromium content to the total chromium content of the ethylene polymerization chromium catalyst is 70 to 100 wt%.   The said inorganic oxide support | carrier (a) is a silica, The manufacturing method of the chromium catalyst for ethylene polymerization in any one of Claims 1-4.   The said catalyst precursor (d) is a manufacturing method of the chromium catalyst for ethylene polymerization in any one of Claims 1-5 in which 0.5-5.0 weight% of chromium compounds (b) are contained.   The chromium catalyst for ethylene polymerization according to any one of claims 1 to 6, wherein the metal-containing hydrocarbon compound (c) contains a metal element selected from Group 1, Group 2, Group 3, and Group 13 of the periodic table of elements. Manufacturing method. The method for producing a chromium catalyst for ethylene polymerization according to any one of claims 1 to 7 , wherein the metal contained in the metal-containing hydrocarbon compound (c) is aluminum.   The metal-containing hydrocarbon compound (c) is contained so that the metal content is 0.5 to 5.0% by weight and the carbon and hydrogen content is 0.5 to 20.0% by weight. Item 9. A method for producing a chromium catalyst for ethylene polymerization according to any one of Items 1 to 8.   The metal-containing hydrocarbon compound (c) has 2 to 30 carbon atoms in one molecule and 5 to 100 hydrogen atoms in one molecule, for ethylene polymerization according to any one of claims 1 to 9. A method for producing a chromium catalyst.   The method for producing a chromium catalyst for ethylene polymerization according to any one of claims 1 to 10, wherein the inert gas is nitrogen.   The method for producing a chromium catalyst for ethylene polymerization according to any one of claims 1 to 11, wherein in the second step, the concentration of the introduced oxygen is increased continuously or stepwise.   The method for producing a chromium catalyst for ethylene polymerization according to any one of claims 1 to 12, comprising temporarily interrupting the introduction of oxygen in the second step.   After the second step, the method includes a third step of introducing an oxygen and inert gas mixture having a constant oxygen concentration over a period of 5 minutes to 72 hours at a contact temperature in the range of 250 to 550 ° C. 14. A method for producing a chromium catalyst for ethylene polymerization according to any one of 13 above.   The method for producing a chromium catalyst for ethylene polymerization according to claim 14, wherein the contact temperature is 350 ° C to 420 ° C in the third step. The manufacturing method of the polyethylene obtained by performing ethylene homopolymerization or the copolymerization of ethylene and an alpha olefin using the chromium catalyst for ethylene polymerization obtained by the method in any one of Claims 1-15. The melt flow rate (HLMFR) at a temperature of 190 ° C and a load of 21.6 kg is 1 to 100 g / 10 min, and the density is 0.935 to 0.965 g / cm ³ . Manufacturing method . The method for producing polyethylene according to claim 16 or 17, wherein the HLMFR is 1 to 15/10 minutes and the density is 0.940 to 0.960 g / cm ³ .

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