CN109160963B - Magnesium modified chromium catalyst for ethylene polymerization and preparation method thereof - Google Patents
Magnesium modified chromium catalyst for ethylene polymerization and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a magnesium modified chromium catalyst for ethylene polymerization and a preparation method thereof, wherein the catalyst comprises a chromium compound, and the content of chromium in the total mass of the catalyst is 0.01-5.0 wt%; the content of the magnesium modified silica gel carrier in the total mass of the catalyst is 70.0-99.9 wt%, and the mass ratio of silica gel to a magnesium compound in the carrier is 100-20: 1; the content of aluminum in the total mass of the catalyst is 0.05-25.0 wt%, the catalyst is used in the industrial production of polyethylene, and the produced polyethylene has good particle shape, high bulk density and wide molecular weight distribution; the preparation method comprises the following steps: the preparation method comprises the steps of taking a magnesium salt solution of tetrahydrofuran as a dispersion medium, taking silica gel as a carrier, taking a chromium compound as an active component and taking an organic aluminum compound as a cocatalyst, modifying the carrier silica gel and loading the active component in a spray drying mode, and obtaining a catalyst product through drying, high-temperature activation, reduction, reactivation and re-reduction.
Description
Technical Field
The invention relates to the technical field of supported catalysts for ethylene polymerization, in particular to a magnesium modified chromium catalyst for ethylene polymerization and a preparation method thereof.
Background
The gas-phase fluidized bed polyethylene process is an advanced polyethylene production process, and a plurality of devices are used for producing polyethylene by using the gas-phase process in the world. Typical processes include Uniopl process by Univation, Innovene process by BP Amoco, Spherilene process by Basell, Lupotech G process, and Evolue process by Mitsui chemical, among others. The product can be from linear low density polyethylene to high density polyethylene, the used comonomers comprise propylene, 1-butene, 1-hexene, 1-octene and the like, wherein the 1-hexene and 1-octene are used as the comonomers, so that the transparency, the tensile resistance, the impact resistance and the flexibility of the product polyethylene can be obviously improved.
There are three main types of catalysts currently used industrially in gas phase processes for the production of polyethylene: one is chromium catalyst, which is prepared through soaking chromium containing compound, including chromium oxide catalyst and organic chromium catalyst, in silica gel or silica-alumina gel carrier; titanium series Ziegler-Natta catalyst, titanium halide catalyst combined on magnesium chloride carrier by chemical bond; and the third is single-site catalyst of metallocene, non-metallocene and post-transition metal. Among them, chromium catalysts are still the mainstream catalysts for gas-phase polyethylene processes at present due to the advantages of simple preparation process, low production cost, high catalytic activity and the like.
The chromium-based catalyst mainly comprises two main types of inorganic chromium-based catalysts and organic chromium-based catalysts. Both J.P Hogan and R.L. Bank reported in the last fifties of the century a silica gel supported chromium oxide catalyst, the later well known Phillips inorganic chromium catalyst. Leonard m. baker and Wayne l. carrick disclose an organochromium polyethylene catalyst, i.e., an S-2 organochromium catalyst from Union Carbide, in US3324101, US3324095 and CA 759121. Although the two catalysts are very similar in structure, there is a large difference in the catalytic and polymerization behavior. Because of the low activity of the organic chromium catalyst, the source of the catalyst precursor bis-triphenyl silane chromate is limited, the preparation cost is high, and the catalyst precursor bis-triphenyl silane chromate is gradually replaced by inorganic chromium at present.
Compared with other catalysts, the inorganic chromium catalyst can produce polyethylene with wide molecular weight distribution, high molecular weight and less long chain branch in the polymer. However, because of the disadvantages of high toxicity, long induction period, and difficult control of molecular weight of inorganic chromium catalysts, titanium and aluminum are generally used for modification. The titanium in the titanium modified chromium catalyst can shorten the initiation induction period of the catalyst, improve the melt flow rate of the polyethylene, prevent the comonomer from being inserted into the low relative molecular mass part of the polyethylene and effectively reduce the content of the branched low relative molecular mass polyethylene. With the addition of titanium, the copolymerized branches of the low relative molecular mass fraction are reduced, and the branching distribution of the polyethylene can be altered. The aluminum modified chromium-based catalyst is mainly embodied by using alumina and aluminum phosphate as a carrier, or using aluminum alkyl as a modifier. The polymerization activity and hydrogen regulation sensitivity of the modified chromium catalyst are obviously improved, the relative molecular mass distribution of the polymer generated by the modified chromium catalyst is widened, the environmental stress cracking resistance is improved, and the processability is excellent. The article "progress of titanium-modified chromium-based catalysts for ethylene polymerization", the "synthetic resins and plastics" in the 1 st stage of 2015 and "research on aluminum-modified chromium-based catalysts for ethylene polymerization" and the "industrial catalysts" in the 2016 stage 1 are described in detail.
CN 105566521A discloses a chromium-based polyethylene catalyst and a preparation method thereof, wherein the chromium-loaded content in the catalyst is 0.1-5 wt%, and the silica gel carrier is 95-99.9 wt%. The preparation steps are as follows: a water-organic solvent composite system is used as a dispersion medium, silica gel is used as a carrier, a chromium compound is used as an active component, an organic aluminum compound is used as a cocatalyst, the active component is loaded on the carrier silica gel in an impregnation mode, and then the catalyst product is obtained through drying, high-temperature activation and reduction processes.
CN 106317267A discloses a preparation method of a titanium-magnesium modified organic chromium catalyst for ethylene polymerization. The preparation steps are as follows: dissolving a titanium magnesium compound and a chromium compound in an organic solvent, and adding a carrier to obtain a mixture; and then adding alkyl alkoxy aluminum into the mixture, stirring and mixing, and removing the solvent to obtain the catalyst finished product. However, the catalyst prepared by the method is an organic chromium catalyst, the catalyst activity is low, the active component silane chromate ester of the catalyst is imported, and the production and popularization of the catalyst are limited by foreign manufacturers.
In addition, the above patents use compounds such as aluminum and magnesium to modify the chromium-based catalyst. The introduction of aluminum and magnesium has a remarkable influence on the chromium-based catalyst. However, at present, aluminum, magnesium and the like are introduced by modification by an immersion method, and water is generally selected as a solvent. In the preparation process of the catalyst, a large amount of chromium-containing wastewater is generated, which brings great environmental protection pressure to catalyst manufacturers. In addition, the impregnation time of the catalyst is long, the drying process is easy to cause silica gel carrier flaking, and the particle shape of the catalyst is irregular, thereby bringing difficulty to the application of the catalyst.
Disclosure of Invention
The invention aims to provide a magnesium modified chromium catalyst for ethylene polymerization, which solves the technical problems of low polymerization activity, long initiation induction period, and poor hydrogen regulation sensitivity and copolymerization performance of the conventional chromium catalyst.
In order to realize the purpose, the invention is realized by adopting the following technical scheme:
a magnesium modified chromium catalyst for ethylene polymerization comprises a main active catalyst, an inorganic oxide carrier and a cocatalyst; wherein the main active catalyst is a chromium compound, and the content of chromium in the total mass of the catalyst is 0.01-5.0 wt%; the inorganic oxide carrier is a magnesium modified silica gel carrier, the content of the inorganic oxide carrier in the total mass of the catalyst is 70.0-99.9 wt%, and the mass ratio of silica gel to a magnesium compound in the carrier is 100-20: 1; the cocatalyst is an alkyl aluminum compound, and the content of aluminum in the total mass of the catalyst is 0.05-25.0 wt%.
Preferably, the chromium compound is an organic chromium compound or/and an inorganic chromium compound, and can be one or a mixture of more of bistriphenylsilane chromate, chromocene, chromium oxide, chromium acetylacetonate, chromium acetate, basic chromium acetate, chromium nitrate and chromium chloride.
Preferably, the specific surface area of silica gel in the magnesium modified silica gel carrier is 100-500 cm2A pore diameter of 10 to 50nm and a pore volume of 1.2 to 2.0cm3The particle size is 20-200 nm.
Preferably, the magnesium compound is a magnesium halide compound, and the magnesium halide compound is one or a mixture of more of a magnesium dihalide compound, an alkyl magnesium halide compound, an alkoxy magnesium halide compound and aryloxy magnesium halide.
Preferably, the general formula of the alkyl aluminum compound is AlR'nX3-nRA 1R' or RaAlORbWherein R or R' is hydrogen or alkyl of 1-20 carbon atoms, which may be the same or different, X is halogen, n is 1<n is a number not more than 3, and a or b is an integer of 1 to 2, and they may be the same or different.
As a further preferred of the present invention, the magnesium dihalide compound includes: magnesium chloride, magnesium iodide, magnesium fluoride and magnesium bromide; the alkyl magnesium halide compound includes: methyl magnesium halide, ethyl magnesium halide, propyl magnesium halide, butyl magnesium halide, isobutyl magnesium halide, hexyl magnesium halide and amyl magnesium halide; the alkoxy magnesium halide compound includes: methoxy magnesium halide, ethoxy magnesium halide, isopropoxy magnesium halide, butoxy magnesium halide and octoxy magnesium halide; the aryloxy magnesium halide comprises: phenoxy magnesium halides and methyl phenoxy magnesium halides.
In a further preferred embodiment of the present invention, the alkyl aluminum compound is one or more of methylaluminoxane, diethyl aluminum ethoxide, trimethylaluminum, triethylaluminum, triisobutyl aluminum and diethyl aluminum monochloride, and the alkyl aluminum compound is added in an amount of 0.5 to 10 mol% based on aluminum and chromium.
The second purpose of the invention is to provide a preparation method of a magnesium modified chromium catalyst for ethylene polymerization, which solves the technical problems of long catalyst impregnation time, irregular particle shape, difficult application, large amount of chromium-containing wastewater generated during preparation and serious environmental pollution in the existing chromium catalyst preparation process.
In order to achieve the purpose, the preparation method of the magnesium modified chromium catalyst for ethylene polymerization provided by the invention takes a magnesium salt solution of tetrahydrofuran as a dispersion medium, silica gel as a carrier, a chromium compound as an active component, and an alkyl aluminum compound as a cocatalyst, realizes the modification of the carrier silica gel and the loading of the active component by a spray drying mode, and obtains a catalyst product through the processes of drying, high-temperature activation, reduction, reactivation and re-reduction.
The preparation method of the magnesium modified chromium catalyst for ethylene polymerization comprises the following steps:
step S1, preparation of modified carrier: dissolving a magnesium compound and a chromium compound in tetrahydrofuran at room temperature according to the proportion requirement, adding a silica gel carrier for pulping, and performing spray drying after 1-10 hours to obtain a granular composite carrier;
step S2, activation: activating the modified carrier by introducing dry air at 400-1000 ℃ for 1-24 hours, cooling to 300 ℃, and introducing dry nitrogen for later use;
step S3, reduction: introducing carbon monoxide into the activated system at 300-400 ℃ for reduction for 1-10 hours, and introducing nitrogen for replacement;
step S4, reactivation: introducing air into the reduced product at 400-1000 ℃, roasting for 1-6 hours, cooling to room temperature, and introducing dry nitrogen for later use;
step S5, re-reduction: adding a cocatalyst into the system for reduction, and drying to obtain a final catalyst product.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) the chromium catalyst provided by the invention has high polymerization activity, short initiation induction period, good hydrogen regulation sensitivity and copolymerization performance and low cost; the catalyst is used in the industrial production of polyethylene, and the produced polyethylene has good particle shape, high bulk density and wide molecular weight distribution, and can be used for producing high-performance polyethylene pipes, membranes and the like.
(2) The preparation method of the chromium-based catalyst provided by the invention adopts a spray drying mode to ensure that the active centers of the catalyst are uniformly distributed, multiple times of impregnation is not needed, the process flow is simple and convenient, the industrial implementation is easy, and the energy consumption and the material consumption in the production process of the catalyst can be reduced; in addition, the magnesium compound is adopted to modify the silica gel carrier, so that the materials can be completely recovered, the generation of chromium-containing wastewater is avoided, and the pollution to the environment is reduced; meanwhile, the introduction of magnesium and the reduction-reactivation-reduciton process can effectively improve the catalytic efficiency and activity of the chromium active component in the catalyst, shorten the initiation induction period of the catalyst and improve the hydrogen regulation sensitivity and copolymerization performance of the catalyst.
(3) According to the invention, polyethylene products with different properties can be obtained by adjusting the preparation process conditions of the catalyst; the catalyst is used for the production of polyethylene resin, and can produce polyethylene resin with wide range of melt flow rate and density.
Detailed Description
In order to make the technical solutions and advantages of the present invention clear to those skilled in the art, the technical solutions of the present invention are described in detail below by examples and comparative examples, but are not intended to limit the scope of the present invention.
The magnesium modified chromium catalyst for ethylene polymerization provided by the invention comprises a main active catalyst, an inorganic oxide carrier and a cocatalyst; wherein the main active catalyst is a chromium compound, and the content of chromium in the total mass of the catalyst is 0.01-5.0 wt%; the inorganic oxide carrier is a magnesium modified silica gel carrier, the content of the inorganic oxide carrier in the total mass of the catalyst is 70.0-99.9 wt%, and the mass ratio of silica gel to a magnesium compound in the carrier is 100-20: 1; the cocatalyst is an alkyl aluminum compound, and the content of aluminum in the total mass of the catalyst is 0.05-25.0 wt%; wherein the chromium compound is an organic chromium compound or/and an inorganic chromium compound and is one or a mixture of more of bistriphenylsilane chromate, chromocene, chromium oxide, chromium acetylacetonate, chromium acetate, chromium subacetate, chromium nitrate and chromium chloride;
the specific surface area of silica gel in the magnesium modified silica gel carrier is 100-500 cm2A pore diameter of 10 to 50nm and a pore volume of 1.2 to 2.0cm3The particle size is 20-200 nm;
the magnesium compound is a magnesium halide compound, and the magnesium halide compound is one or a mixture of more of a magnesium dihalide compound, an alkyl magnesium halide compound, an alkoxy magnesium halide compound and aryloxy magnesium halide; the magnesium dihalide compound includes: magnesium chloride, magnesium iodide, magnesium fluoride and magnesium bromide; the alkyl magnesium halide compound includes: methyl magnesium halide, ethyl magnesium halide, propyl magnesium halide, butyl magnesium halide, isobutyl magnesium halide, hexyl magnesium halide and amyl magnesium halide; the alkoxy magnesium halide compound includes: methoxy magnesium halide, ethoxy magnesium halide, isopropoxy magnesium halide, butoxy magnesium halide and octoxy magnesium halide; the aryloxy magnesium halide comprises: phenoxy magnesium halides and methyl phenoxy magnesium halides.
The general formula of the alkyl aluminum compound is AlR'nX3-nRA 1R' or RaAlORbWherein R or R' is hydrogen or alkyl of 1-20 carbon atoms, which may be the same or different, X is halogen, n is 1<n is not more than 3, a or b is an integer of 1 to 2, the two can be the same or different, preferably one or a mixture of more of methylaluminoxane, diethyl aluminum ethoxide, trimethyl aluminum, triethyl aluminum, triisobutyl aluminum and diethyl aluminum monochloride, and the adding amount of the alkyl aluminum compound is 0.5 to 10 of the molar ratio of aluminum to chromium.
The invention also provides a preparation method of the magnesium modified chromium catalyst for ethylene polymerization, which takes the magnesium salt solution of tetrahydrofuran as a dispersion medium, silica gel as a carrier, a chromium compound as an active component and an alkyl aluminum compound as a cocatalyst, realizes the modification of the carrier silica gel and the loading of the active component by a spray drying mode, and obtains a catalyst product by the processes of drying, high-temperature activation, reduction, reactivation and re-reduction.
In order to make the preparation method of the magnesium modified chromium-based catalyst of the present invention more clear to those skilled in the art, the present invention will be further described with reference to the following examples:
example 1
A preparation method of a magnesium modified chromium catalyst for ethylene polymerization comprises the following specific preparation steps:
step S1, preparation of modified carrier: a250 mL three-necked flask sufficiently substituted with N2 was charged with 5.0g of magnesium chloride (MgCl2), 0.5g of chromium nitrate and 150mL of tetrahydrofuran, and after stirring and reacting at room temperature for 2 hours, 10.0g of silica gel (WR Grace 955 having a specific surface area of 240 to 375 cm)2A pore diameter of 20 to 35nm and a pore volume of 1.2 to 1.8cm3(g), the particle size is 20-50 nm), continuously stirring for 6 hours, and pulping for later use; and (3) carrying out spray drying on the stirred mixture by using a spray dryer, wherein the spray conditions are as follows: an inletThe temperature is 150 ℃, and the outlet temperature is 98 ℃, so that the granular composite carrier is obtained;
step S2, activation: activating the modified carrier by introducing dry air at 600 ℃ for 10 hours, cooling to 300 ℃, and introducing dry nitrogen for later use;
step S3, reduction: introducing carbon monoxide into the activated system at 350 ℃ for reduction for 4 hours, and introducing nitrogen for replacement;
step S4, reactivation: introducing air into the reduced product at 600 ℃, roasting for 4 hours, cooling to room temperature, and introducing dry nitrogen for later use;
step S5, re-reduction: 1.5ml (1mol/l, abbreviated as 1M) of triethylaluminum is added into the system for reduction, and the final catalyst product is obtained after drying.
The contents of chromium, magnesium and aluminum in the catalyst components are shown in Table 1, and the polymerization evaluation results of the catalysts are shown in Table 1.
Example 2
The catalyst component was prepared in the same manner as in example 1 except that the amount of chromium nitrate added was changed from 0.5g to 1.0 g.
Example 3
The catalyst component was prepared in the same manner as in example 1 except that the amount of chromium nitrate added was changed from 0.5g to 2.0 g.
Example 4
Except for MgCl2Except for changing the amount of the catalyst component (2) from 5.0g to 2.5g, the catalyst component was prepared in the same manner as in example 1.
Example 5
Except for MgCl2The catalyst component was prepared in the same manner as in example 1 except that the amount of the catalyst component (D) was changed from 5.0g to 1.0 g.
Example 6
The preparation method of the rest catalyst components was the same as example 1, with the addition of materials such as chromium nitrate and magnesium chloride being kept constant, and the activation temperatures of step S2 and step S4 being changed to 700 ℃.
Example 7
The preparation method of the rest catalyst components was the same as example 1, with the addition of materials such as chromium nitrate and magnesium chloride being maintained, and the activation temperatures of step S2 and step S4 being changed to 800 ℃.
Example 8
The preparation method of the rest catalyst components was the same as example 1, with the addition of materials such as chromium nitrate and magnesium chloride being kept constant, and the activation temperatures of step S2 and step S4 being changed to 900 ℃.
Example 9
The preparation method of the rest catalyst components was the same as example 1, with the addition of materials such as chromium nitrate and magnesium chloride being kept constant, and the activation temperatures of step S2 and step S4 being changed to 1000 ℃.
Example 10
The catalyst component was prepared as in example 1 except that the chromium nitrate was replaced with bistriphenylsilanyl chromate.
Example 11
The catalyst component was prepared in the same manner as in example 1 except that chromium nitrate was replaced with chromocene.
Example 12
The catalyst component was prepared in the same manner as in example 1 except that chromium nitrate was replaced with chromium acetylacetonate.
Example 13
The catalyst component was prepared in the same manner as in example 1 except that chromium nitrate was replaced with chromium acetate.
Example 14
The catalyst component was prepared in the same manner as in example 1 except that chromium nitrate was replaced with chromium chloride.
Example 15
The catalyst component was prepared in the same manner as in example 1 except that magnesium chloride was replaced with methyl magnesium chloride.
Example 16
The catalyst component was prepared in the same manner as in example 1 except that magnesium chloride was replaced with phenylmagnesium chloride.
Example 17
The catalyst component was prepared in the same manner as in example 1 except that magnesium chloride was replaced with 4-methoxyphenylmagnesium bromide.
Example 18
The catalyst component was prepared in the same manner as in example 1 except that triethylaluminum was replaced with triisobutylaluminum.
Example 19
The catalyst component was prepared in the same manner as in example 1 except that triethylaluminum was replaced with ethoxydiethylaluminum.
Example 20
The catalyst component was prepared in the same manner as in example 1 except that triethylaluminum was replaced with diethylaluminum monochloride.
Example 21
The catalyst component was prepared in the same manner as in example 1 except that the amount of triethylaluminum was increased to 3.0 ml.
Example 22
The catalyst component was prepared in the same manner as in example 1 except that the amount of triethylaluminum was increased to 6.0 ml.
Example 23
The catalyst component was prepared in the same manner as in example 1, except that the amount of triethylaluminum was increased to 10.0 ml.
Comparative example 1
The preparation method of the current industrial chromium catalyst comprises the following steps:
step S1, preparation of the vector: 0.5g of chromium nitrate and 150mL of water were added to a 250mL three-necked flask fully substituted with N2, and after stirring and reacting at room temperature for 2 hours, 10.0g of silica gel (WR Grace 955 with a specific surface area of 240 to 375 cm) was added2A pore diameter of 20 to 35nm and a pore volume of 1.2 to 1.8cm3The particle size is 20-50 nm), continuously stirring for 6 hours, and drying to obtain a granular carrier;
step S2, activation: and (3) activating the carrier at 600 ℃ by introducing dry air for 10 hours, cooling to room temperature, and introducing dry nitrogen for later use to obtain a final catalyst product.
The contents of chromium, magnesium and aluminum in the catalyst components are shown in Table 1, and the polymerization evaluation results of the catalysts are shown in Table 1.
Comparative example 2
The preparation method of the magnesium modified industrial chromium catalyst comprises the following steps:
step S1, preparation of the vector: to a 250mL three-necked flask fully replaced with N2 was added 5.0g of magnesium chloride (MgCl)2) And 0.5g of chromium nitrate and 150mL of water,after stirring and reacting for 2 hours at room temperature, 10.0g of silica gel (WR Grace 955 with a specific surface area of 240-375 cm) is added2A pore diameter of 20 to 35nm and a pore volume of 1.2 to 1.8cm3The particle size is 20-50 nm), continuously stirring for 6 hours, and drying to obtain a granular carrier;
step S2, activation: and (3) activating the carrier at 600 ℃ by introducing dry air for 10 hours, cooling to room temperature, and introducing dry nitrogen for later use to obtain a final catalyst product.
The contents of chromium, magnesium and aluminum in the catalyst components are shown in Table 1, and the polymerization evaluation results of the catalysts are shown in Table 1.
Comparative example 3
The preparation method of the aluminum reduction modified industrial chromium catalyst comprises the following steps:
step S1, preparation of the vector: 0.5g of chromium nitrate and 150mL of water were added to a 250mL three-necked flask fully substituted with N2, and after stirring and reacting at room temperature for 2 hours, 10.0g of silica gel (WR Grace 955 with a specific surface area of 240 to 375 cm) was added2A pore diameter of 20 to 35nm and a pore volume of 1.2 to 1.8cm3The particle size is 20-50 nm), continuously stirring for 6 hours, and drying to obtain a granular carrier;
step S2, activation: the carrier was activated with dry air at 600 ℃ for 10 hours, cooled to room temperature and then charged with dry nitrogen for further use.
Step S3, aluminum reduction: 1.5ml (1M) of triethylaluminium is added to the system for reduction and the final catalyst product is obtained after drying.
Comparative example 4
The preparation method of the industrial chromium catalyst for CO reduction comprises the following steps:
step S1, preparation of the vector: 0.5g of chromium nitrate and 150mL of water were added to a 250mL three-necked flask fully substituted with N2, and after stirring and reacting at room temperature for 2 hours, 10.0g of silica gel (WR Grace 955 with a specific surface area of 240 to 375 cm) was added2A pore diameter of 20 to 35nm and a pore volume of 1.2 to 1.8cm3The particle size is 20-50 nm), continuously stirring for 6 hours, and drying to obtain a granular carrier;
step S2, activation: the carrier was activated with dry air at 600 ℃ for 10 hours, cooled to room temperature and then charged with dry nitrogen for further use.
Step S3, reduction: and introducing carbon monoxide into the system at 350 ℃ for reduction for 4 hours, introducing nitrogen for replacement, and cooling to obtain the final catalyst product.
Evaluation of slurry polymerization
Heating a 2L reaction kettle to about 80 ℃, vacuumizing for 1h, replacing with dry nitrogen, and then blowing out with hydrogen; 1L of hexane and 10ml of hexene-1 are sequentially added into a polymerization kettle, 2ml (1M) of triethyl aluminum and 500mg of the catalyst are added simultaneously, then the temperature is raised to 75 ℃, 0.1MPa of hydrogen is added, ethylene is added after hydrogenation is finished to enable the pressure in the kettle to reach 1.03MPa, after the temperature is raised to 85 ℃, reaction is carried out for 2 hours, and then cooling and discharging are carried out, wherein the contents of chromium, magnesium and aluminum in the catalyst components prepared in the above examples and comparative examples and the polymerization evaluation result of the catalyst are shown in Table 1.
The composition of the catalyst prepared in each example was determined as follows:
the contents of Mg, Cr and Al in the catalyst are measured by an ICP method;
the polymerization activity was calculated according to the following formula:
wpoly ═ Q/wcat, gPolyg-1 Cat, where Wpoly is the catalyst polymerization activity, Q is the yield (g) of the polymer in 2 hours of polymerization, and wcat is the catalyst amount.
The test conditions for the polymers are as follows:
melt index MI- -ASTM D1238-99.
Claims (7)
1. The magnesium modified chromium catalyst for ethylene polymerization is characterized by comprising a main active catalyst, an inorganic oxide carrier and a cocatalyst; wherein the main active catalyst is a chromium compound, and the content of chromium in the total mass of the catalyst is 0.01-5.0 wt%; the inorganic oxide carrier is a magnesium modified silica gel carrier, the content of the inorganic oxide carrier in the total mass of the catalyst is 70.0-99.9 wt%, and the mass ratio of silica gel to a magnesium compound in the carrier is 100-20: 1; the cocatalyst is an alkyl aluminum compound, and the content of aluminum in the total mass of the catalyst is 0.05-25.0 wt%;
the preparation method of the catalyst comprises the following steps:
step S1, preparation of modified carrier: dissolving a magnesium compound and a chromium compound in tetrahydrofuran at room temperature according to the proportion requirement, adding a silica gel carrier for pulping, and performing spray drying after 1-10 hours to obtain a granular composite carrier;
step S2, activation: activating the modified carrier by introducing dry air at 400-1000 ℃ for 1-24 hours, cooling to 300 ℃, and introducing dry nitrogen for later use;
step S3, reduction: introducing carbon monoxide into the activated system at 300-400 ℃ for reduction for 1-10 hours, and introducing nitrogen for replacement;
step S4, reactivation: introducing air into the reduced product at 400-1000 ℃, roasting for 1-6 hours, cooling to room temperature, and introducing dry nitrogen for later use;
step S5, re-reduction: adding a cocatalyst into the system for reduction, and drying to obtain a final catalyst product.
2. The magnesium-modified chromium-based catalyst for ethylene polymerization according to claim 1, wherein the chromium compound is an organic chromium compound or/and an inorganic chromium compound.
3. The magnesium-modified chromium-based catalyst according to claim 1, wherein the silica gel in the magnesium-modified silica gel carrier has a specific surface area of 100 to 500cm2A pore diameter of 10 to 50nm and a pore volume of1.2～2.0cm3The particle size is 20-200 nm.
4. The magnesium-modified chromium-based catalyst according to claim 1, wherein the magnesium compound is a magnesium halide compound, and the magnesium halide compound is one or more of a magnesium dihalide compound, an alkyl magnesium halide compound, an alkoxy magnesium halide compound, and an aryloxy magnesium halide compound.
5. The magnesium modified chromium-based catalyst for ethylene polymerization according to claim 2, wherein the chromium compound is one or more of bistriphenylsilane chromate, chromocene, chromium oxide, chromium acetylacetonate, chromium acetate, basic chromium acetate, chromium nitrate and chromium chloride.
6. The magnesium-modified chromium-based catalyst for ethylene polymerization according to claim 4, wherein said magnesium dihalide compound comprises: magnesium chloride, magnesium iodide, magnesium fluoride and magnesium bromide; the alkyl magnesium halide compound includes: methyl magnesium halide, ethyl magnesium halide, propyl magnesium halide, butyl magnesium halide, isobutyl magnesium halide, hexyl magnesium halide and amyl magnesium halide; the alkoxy magnesium halide compound includes: methoxy magnesium halide, ethoxy magnesium halide, isopropoxy magnesium halide, butoxy magnesium halide and octoxy magnesium halide; the aryloxy magnesium halide comprises: phenoxy magnesium halides and methyl phenoxy magnesium halides.
7. The magnesium-modified chromium-based catalyst according to claim 1, wherein the alkyl aluminum compound is one or more of methylaluminoxane, diethyl aluminum ethoxide, trimethylaluminum, triethylaluminum, triisobutylaluminum, and diethyl aluminum monochloride, and the molar ratio of aluminum to chromium is 0.5 to 10.
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| CN112679636B (en) * | 2019-10-18 | 2022-12-27 | 中国石油化工股份有限公司 | Method for preparing catalyst for ethylene polymerization |
| CN113583160A (en) * | 2021-09-14 | 2021-11-02 | 无锡玖汇科技有限公司 | Preparation method of composite carrier |
| CN113583159A (en) * | 2021-09-14 | 2021-11-02 | 无锡玖汇科技有限公司 | Supported polyolefin catalyst and preparation method thereof |
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