Catalytic system for preparing ultra-pure isotactic polypropylene and application thereof

Abstract

The present application relates to the field of olefin catalytic polymerization, and aims to provide a catalytic system for preparing ultra-pure isotactic polypropylene and application thereof.The catalytic system comprises three components of a main catalyst, a cocatalyst and an external electron donor; wherein the main catalyst is a TiCl4 / MgCl2.ID supported high-efficiency spherical Ziegler-Natta catalyst, ID refers to diisobutyl phthalate or 2,2-diisobutyl-1,3-dimethoxypropane as an internal electron donor; the cocatalyst is a mixture of triethyl aluminum and triisobutyl aluminum; and the external electron donor is diisopropyl dimethoxysilane; or the cocatalyst is triethyl aluminum; and the external electron donor is a mixture of cyclohexyl methyl dimethoxysilane and dicyclopentyl dimethoxysilane.The catalytic system provided by the present application is simple to operate, does not need to synthesize complex-structure alkyl aluminum or siloxane, has controllable cost, and is easy to industrialize; and the product meets the requirements of low ash content, high polymerization activity and high isotacticity at the same time.

Description

Technical Field

[0001] This invention relates to the field of olefin catalytic polymerization, specifically to a catalytic system for preparing ultrapure isotactic polypropylene and its application. Background Technology

[0002] As the world's largest producer and consumer of polymers, and with the widest range of applications, polyolefins hold an irreplaceable position in industry. Due to their excellent performance, diverse varieties, readily available raw materials, and low price, polypropylene has a wide range of applications, including the food industry, building materials, electronics, medical equipment, and defense industries. Ultra-pure polypropylene with low ash content (especially below 20 ppm) is a crucial polymer material for capacitor films due to its excellent electrical properties and good processing and molding performance. Furthermore, ultra-pure polypropylene possesses extremely low high-frequency loss, high dielectric strength, high insulation resistance, and a small negative temperature coefficient, making it widely used in new energy, power grid construction, hybrid vehicles, consumer electronics, railway electrification, green lighting, and industries such as high-power pulsed lasers, electromagnetic railguns, and aircraft carrier electromagnetic catapults.

[0003] In 1954, Natta successfully synthesized isotactic polypropylene using TiCl3 / AlEt2Cl and proposed the theory of directional polymerization. In the subsequent development of polypropylene production technology, the catalytic system and polymerization process have played a decisive role in the performance of polypropylene. In actual production, to obtain polypropylene with low ash content, the catalytic system must have outstanding polymerization activity. However, a highly active catalytic system may not guarantee that the prepared polypropylene has a sufficiently high isotacticity. Therefore, it is often necessary to introduce external electron donors into the polymerization system. The presence of external electron donors usually reduces the polymerization activity of the catalytic system, resulting in increased ash content in the polypropylene product.

[0004] Therefore, how to reduce the ash content in the product while ensuring high polymerization activity and high isotacticity is a real problem that researchers need to face. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a catalytic system for preparing ultrapure isotactic polypropylene and its application.

[0006] To solve the technical problem, the solution of the present invention is:

[0007] A catalytic system for preparing ultrapure isotactic polypropylene is provided, comprising three components: a main catalyst, a co-catalyst, and an external electron donor; wherein the main catalyst is a TiCl4 / MgCl2·ID supported high-efficiency spherical Ziegler-Natta catalyst, and ID refers to diisobutyl phthalate or 2,2-diisobutyl-1,3-dimethoxypropane as an internal electron donor.

[0008] The compatibility between the co-catalyst and the external electron donor is any one of the following:

[0009] (1) The co-catalyst is a mixture of triethylaluminum / triisobutylaluminum; the external electron donor is diisopropyldimethoxysilane (P-donor); or,

[0010] (2) The co-catalyst is triethylaluminum; the external electron donor is a mixture of cyclohexylmethyldimethoxysilane (C-donor) / dicyclopentyldimethoxysilane (D-donor);

[0011] The molar ratio of Al in the co-catalyst to Ti in the main catalyst is 20–60:1; the molar ratio of Si in the external electron donor to Ti in the main catalyst is 2–5:1.

[0012] As a preferred embodiment of the present invention, the triethylaluminum / triisobutylaluminum mixture is a mixture obtained by mixing triethylaluminum and triisobutylaluminum in a molar ratio of 1:3 to 3:1.

[0013] As a preferred embodiment of the present invention, the cyclohexylmethyldimethoxysilane (C-donor) / dicyclopentyldimethoxysilane (D-donor) mixture is a mixture obtained by mixing C-donor and D-donor in a molar ratio of 1:3 to 3:1.

[0014] This invention further provides a method for applying the aforementioned catalytic system in the catalytic polymerization of propylene to prepare ultrapure isotactic polypropylene, comprising the following steps:

[0015] (1) Add hexane to the first polymerization reactor in an amount equal to half the reactor volume;

[0016] (2) Add the co-catalyst, external electron donor, and main catalyst in sequence, controlling the amount added so that the mass ratio of Ti to hexane in the main catalyst is 1.3 × 10⁻⁶. -7 ~4×10 -7 ;

[0017] (3) Propylene was introduced to make the pressure in the reactor 0.1 MPa, and the prepolymerization reaction was carried out at 30°C for 15 minutes to obtain the prepolymer;

[0018] (4) Transfer the material in the first polymerization reactor to the second polymerization reactor, control the temperature inside the reactor to 70-75°C; introduce a mixture of propylene and hydrogen until the pressure inside the reactor is 2.5-3.5 MPa, and carry out the polymerization reaction for 2-6 hours.

[0019] (5) Transfer the polymerization product to a washing vessel with a filter plate, release and recover propylene gas; after the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane; add isopropanol to the vessel to wash the polypropylene, and dry to obtain ultrapure isotactic polypropylene.

[0020] In a preferred embodiment of the present invention, the molar ratio of propylene to hydrogen in the mixed gas in step (2) is 3:1.

[0021] In a preferred embodiment of the present invention, in step (5), the washing is repeated 1 to 5 times, each time for 5 minutes; the amount of isopropanol added each time is twice the volume of the discharged hexane.

[0022] Description of the invention principle:

[0023] During the research process, the applicant discovered that when different alkylaluminum compounds are mixed together, group exchange occurs between the alkylaluminum compounds; similarly, when alkylaluminum compounds and siloxanes are mixed together, group exchange also occurs between the alkylaluminum compounds and the siloxanes. Therefore, when two different alkylaluminum compounds and one siloxane are mixed together, or two different siloxanes and one alkylaluminum compound are mixed together, group exchange occurs between the three substances, generating new substances and forming complex mixtures.

[0024] These new substances and their mixtures differ from commonly used alkylaluminum compounds (such as TEA and TIBA) in their role in reducing the main catalyst and alkylating TiCl4, and their effects on regulating the directed polymerization of propylene also differ from commonly used siloxanes (such as C-donor, D-donor, and P-donor). These new substances and their mixtures have lower reducing power than triethylaluminum and triisobutylaluminum, allowing more Ti to remain in the +3 valence state without being over-reduced to +2. +3 valence Ti exhibits polymerization activity towards propylene, while +2 valence Ti does not. Therefore, these new substances and their mixtures are beneficial for improving the polymerization activity of propylene and reducing the ash content in polypropylene products.

[0025] In addition, these new substances and their mixtures contain organoaluminum compounds with substituents larger than those in TEA and TIBA. After alkylating TiCl4, these organoaluminum compounds attach a large substituent to the Ti metal center. This substituent forms a better steric hindrance around the Ti metal center, which can better induce propylene to undergo directional polymerization and prepare polypropylene with higher isotacticity.

[0026] As can be seen from the above reaction mechanism, the establishment of the new catalytic system plays a positive role in reducing product ash content and preparing ultrapure isotactic polypropylene.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. Compared with the prior art, the catalytic system provided by the present invention is simple to operate, does not require the synthesis of complex alkylaluminum or siloxanes, and has controllable cost;

[0029] 2. In terms of catalytic propylene polymerization, this catalytic system has the characteristics of high catalytic activity, high isotacticity of the prepared polypropylene, and is easy to industrialize compared with existing catalytic systems.

[0030] 3. Extensive and repeated experimental results show that the catalytic system provided by this invention achieves a catalytic activity of no less than 80 kg PP / g Cat for propylene polymerization, with a product ash content of no more than 20 ppm and an isotacticity of no less than 98%. This effectively solves the problem that existing production processes cannot simultaneously achieve low ash content, high polymerization activity, and high isotacticity. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments and comparative examples, but the present invention is not limited to the following embodiments.

[0032] I. Compatibility Methods of Catalytic Systems

[0033] 1. In the catalytic system of this invention, the main catalyst is a TiCl4 / MgCl2·ID supported high-efficiency spherical Ziegler-Natta catalyst. This catalyst consists of titanium supported on active magnesium chloride and an internal electron donor compound. It is a widely used and mature product, with many commercially available models available. In this catalyst, the titanium is derived from titanium compounds (such as titanium halide, titanium alkoxy, or haloalcohols), and the internal electron donor can be an ether, lipid, or diether compound. The catalyst preparation method is a mature process, and specific details can be found in publications such as USP4,298,718, USP4,495,388, and CN 1199056A.

[0034] The core innovation of this invention lies in studying the influence of group exchange between different cocatalysts (alkylaluminum) and external electron donors (siloxanes) on the polymerization reaction. The main catalyst used and its preparation technology are not substantially different from existing publicly available technologies, and therefore will not be elaborated upon further.

[0035] 2. In the main catalysts used in the various embodiments and comparative examples of the present invention: when 2,2-diisobutyl-1,3-dimethoxypropane is used as the internal electron donor, the main catalyst contains 3.4% by weight of titanium, 14.4% by weight of magnesium, and 14.5% by weight of the internal electron donor (2,2-diisobutyl-1,3-dimethoxypropane); when diisobutyl phthalate is used as the internal electron donor, the prepared main catalyst contains 3.0% by weight of titanium, 15.6% by weight of magnesium, and 10.2% by weight of the internal electron donor (diisobutyl phthalate).

[0036] 3. In a catalytic system, there are two ways to pair the co-catalyst and the external electron donor:

[0037] (1) The co-catalyst is a mixture of triethylaluminum / triisobutylaluminum, which is a mixture obtained by mixing triethylaluminum and triisobutylaluminum in a molar ratio of 1:3 to 3:1; the external electron donor is diisopropyldimethoxysilane (P-donor);

[0038] (2) The co-catalyst is triethylaluminum; the external electron donor is a mixture of cyclohexylmethyldimethoxysilane (C-donor) / dicyclopentyldimethoxysilane (D-donor), which is a mixture obtained by mixing C-donor and D-donor in a molar ratio of 1:3 to 3:1.

[0039] 4. When using three components to construct a catalytic system, the dosage relationship needs to be controlled; the molar ratio of Al in the co-catalyst to Ti in the main catalyst should be 20-60:1, and the molar ratio of Si in the external electron donor to Ti in the main catalyst should be 2-5:1.

[0040] II. Application Methods of Catalytic Systems

[0041] Example 1

[0042] 1) Add hexane at 30°C to the first polymerization reactor, filling half the reactor volume. Then, sequentially add a triethylaluminum / triisobutylaluminum mixture (molar ratio of triethylaluminum to triisobutylaluminum is 3:1, molar ratio of Al in the co-catalyst to Ti in the main catalyst is 60:1), a P-donor (molar ratio of Si in the P-donor to Ti in the main catalyst is 5:1), and the main catalyst (ID in the main catalyst is 2,2-diisobutyl-1,3-dimethoxypropane, mass ratio of Ti to hexane is 1.3 × 10⁻⁶). -7 Propylene at 0.1 MPa is introduced to carry out a prepolymerization reaction for 15 minutes to obtain the prepolymer;

[0043] 2) Transfer the material in the first polymerization reactor to the second polymerization reactor. Set the temperature of the reactor to 70°C, introduce a mixture of propylene and hydrogen (molar ratio of propylene to hydrogen is 3:1), and set the pressure of the reactor to 3.5 MPa. The polymerization reaction is carried out for 2 hours.

[0044] 3) Transfer the polymerization product to a washing vessel with a filter plate, release and recover the propylene. After the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane, then add isopropanol at a volume of 2 times that of hexane. Wash the polypropylene once with isopropanol for 5 minutes each time, and then dry it to obtain ultrapure isotactic polypropylene.

[0045] Calculations show that the catalytic activity during the polymerization process is 94 kg PP / g Cat, the product ash content is 15 ppm, and the isotacticity is 99.2%.

[0046] Example 2

[0047] 1) Add hexane at 30°C to the first polymerization reactor, filling half the reactor volume. Then, sequentially add a triethylaluminum / triisobutylaluminum mixture (molar ratio of triethylaluminum to triisobutylaluminum is 3:1, molar ratio of Al in the co-catalyst to Ti in the main catalyst is 30:1), a P-donor (molar ratio of Si in the P-donor to Ti in the main catalyst is 3:1), and the main catalyst (ID in the main catalyst is 2,2-diisobutyl-1,3-dimethoxypropane, and the mass ratio of Ti to hexane is 2.5 × 10⁻⁶). -7 Propylene at 0.1 MPa is introduced to carry out a prepolymerization reaction for 15 minutes to obtain the prepolymer;

[0048] 2) Transfer the material in the first polymerization reactor to the second polymerization reactor. Set the temperature of the reactor to 72°C and introduce a mixture of propylene and hydrogen (molar ratio of propylene to hydrogen is 3:1). The pressure of the reactor is 3.0 MPa, and the polymerization reaction is carried out for 4 hours.

[0049] 3) Transfer the polymerization product to a washing vessel with a filter plate, release and recover the propylene. After the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane, then add isopropanol at a volume of 2 times that of hexane. Wash the polypropylene with isopropanol 3 times, 5 minutes each time, and then dry to obtain ultrapure isotactic polypropylene.

[0050] Calculations show that the catalytic activity during the polymerization process is 88 kg PP / g Cat, the product ash content is 18 ppm, and the isotacticity is 98.5%.

[0051] Example 3

[0052] 1) Add hexane at 30°C to the first polymerization reactor, filling half the reactor volume. Then, sequentially add a triethylaluminum / triisobutylaluminum mixture (molar ratio of triethylaluminum to triisobutylaluminum is 3:1, molar ratio of Al in the co-catalyst to Ti in the main catalyst is 20:1), a P-donor (molar ratio of Si in the P-donor to Ti in the main catalyst is 2:1), and the main catalyst (TiID in the main catalyst is 2,2-diisobutyl-1,3-dimethoxypropane, with a mass ratio of 4 × 10⁻⁶ to hexane). -7 Propylene at 0.1 MPa is introduced to carry out a prepolymerization reaction for 15 minutes to obtain the prepolymer;

[0053] 2) Transfer the material in the first polymerization reactor to the second polymerization reactor. Set the temperature of the reactor to 75°C, introduce a mixture of propylene and hydrogen (molar ratio of propylene to hydrogen is 3:1), and set the pressure of the reactor to 2.5 MPa. The polymerization reaction is carried out for 6 hours.

[0054] 3) Transfer the polymerization product to a washing vessel with a filter plate, release and recover the propylene. After the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane, then add isopropanol at a volume of 2 times that of hexane. Wash the polypropylene with isopropanol 5 times, 5 minutes each time, and then dry to obtain ultrapure isotactic polypropylene.

[0055] Calculations show that the catalytic activity during the polymerization process is 90 kg PP / g Cat, the product ash content is 20 ppm, and the isotacticity is 98.2%.

[0056] Example 4

[0057] 1) Add hexane at 30°C to the first polymerization reactor, filling half the reactor volume. Then, add triethylaluminum (the molar ratio of Al to Ti in the main catalyst is 30:1), a mixture of C-donor and D-donor (the molar ratio of C-donor to D-donor is 1:1, and the molar ratio of Si to Ti in the external electron donor is 2:1), and the main catalyst (the ID in the main catalyst is 2,2-diisobutyl-1,3-dimethoxypropane, and the mass ratio of Ti to hexane is 2×10⁻⁶). -7 Propylene at 0.1 MPa is introduced to carry out a prepolymerization reaction for 15 minutes to obtain the prepolymer;

[0058] 2) Transfer the material in the first polymerization reactor to the second polymerization reactor. Set the temperature of the reactor to 70°C, introduce a mixture of propylene and hydrogen (molar ratio of propylene to hydrogen is 3:1), and set the pressure of the reactor to 3.5 MPa. The polymerization reaction is carried out for 4 hours.

[0059] 3) Transfer the polymerization product to a washing vessel with a filter plate, release and recover the propylene. After the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane, then add isopropanol at a volume of 2 times that of hexane. Wash the polypropylene with isopropanol 5 times, 5 minutes each time, and then dry to obtain ultrapure isotactic polypropylene.

[0060] Calculations show that the catalytic activity during the polymerization process is 100 kg PP / g Cat, the product ash content is 19 ppm, and the isotacticity is 98.1%.

[0061] Example 5

[0062] 1) Add hexane at 30°C to the first polymerization reactor, filling half the reactor volume. Then, sequentially add a triethylaluminum / triisobutylaluminum mixture (molar ratio of triethylaluminum to triisobutylaluminum is 1:3, molar ratio of Al in the co-catalyst to Ti in the main catalyst is 30:1), a P-donor (molar ratio of Si in the P-donor to Ti in the main catalyst is 5:1), and the main catalyst (ID in the main catalyst is diisobutyl phthalate, and the mass ratio of Ti to hexane is 1.3 × 10⁻⁶). -7 Propylene at 0.1 MPa is introduced to carry out a prepolymerization reaction for 15 minutes to obtain the prepolymer;

[0063] 2) Transfer the material in the first polymerization reactor to the second polymerization reactor. Set the temperature of the reactor to 70°C, introduce a mixture of propylene and hydrogen (molar ratio of propylene to hydrogen is 3:1), and set the pressure of the reactor to 3.5 MPa. The polymerization reaction is carried out for 2 hours.

[0064] 3) Transfer the polymerization product to a washing vessel with a filter plate, release and recover the propylene. After the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane, then add isopropanol at a volume of 2 times that of hexane. Wash the polypropylene once with isopropanol for 5 minutes each time, and then dry it to obtain ultrapure isotactic polypropylene.

[0065] Calculations show that the catalytic activity during the polymerization process is 87 kg PP / g Cat, the product ash content is 20 ppm, and the isotacticity is 98.3%.

[0066] Example 6

[0067] 1) Add hexane at 30°C to the first polymerization reactor, filling half the reactor volume. Then, sequentially add a triethylaluminum / triisobutylaluminum mixture (molar ratio of triethylaluminum to triisobutylaluminum is 1:1, molar ratio of Al in the co-catalyst to Ti in the main catalyst is 60:1), a P-donor (molar ratio of Si in the P-donor to Ti in the main catalyst is 5:1), and the main catalyst (ID in the main catalyst is 2,2-diisobutyl-1,3-dimethoxypropane, mass ratio of Ti to hexane is 1.3 × 10⁻⁶). -7 Propylene at 0.1 MPa is introduced to carry out a prepolymerization reaction for 15 minutes to obtain the prepolymer;

[0068] 2) Transfer the material in the first polymerization reactor to the second polymerization reactor. Set the temperature of the reactor to 70°C, introduce a mixture of propylene and hydrogen (molar ratio of propylene to hydrogen is 3:1), and set the pressure of the reactor to 3.5 MPa. The polymerization reaction is carried out for 2 hours.

[0069] 3) Transfer the polymerization product to a washing vessel with a filter plate, release and recover the propylene. After the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane, then add isopropanol at a volume of 2 times that of hexane. Wash the polypropylene with isopropanol 3 times, 5 minutes each time, and then dry to obtain ultrapure isotactic polypropylene.

[0070] Calculations show that the catalytic activity during the polymerization process is 88 kg PP / g Cat, the product ash content is 18 ppm, and the isotacticity is 98.4%.

[0071] Example 7

[0072] 1) Add hexane at 30°C to the first polymerization reactor, filling half the reactor volume. Then, add triethylaluminum (the molar ratio of Al to Ti in the main catalyst is 30:1), a mixture of C-donor and D-donor (the molar ratio of C-donor to D-donor is 3:1, and the molar ratio of Si to Ti in the external electron donor is 2:1), and the main catalyst (ID in the main catalyst is diisobutyl phthalate, and the mass ratio of Ti to hexane is 2 × 10⁻⁶). -7 Propylene at 0.1 MPa is introduced to carry out a prepolymerization reaction for 15 minutes to obtain the prepolymer;

[0073] 2) Transfer the material in the first polymerization reactor to the second polymerization reactor. Set the temperature of the reactor to 70°C, introduce a mixture of propylene and hydrogen (molar ratio of propylene to hydrogen is 3:1), and set the pressure of the reactor to 3.5 MPa. The polymerization reaction is carried out for 4 hours.

[0074] 3) Transfer the polymerization product to a washing vessel with a filter plate, release and recover the propylene. After the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane, then add isopropanol at a volume of 2 times that of hexane. Wash the polypropylene with isopropanol 5 times, 5 minutes each time, and then dry to obtain ultrapure isotactic polypropylene.

[0075] Calculations show that the catalytic activity during the polymerization process is 103 kg PP / g Cat, the product ash content is 12 ppm, and the isotacticity is 98.1%.

[0076] Example 8

[0077] 1) Add hexane at 30°C to the first polymerization reactor, filling half the reactor volume. Then, add triethylaluminum (the molar ratio of Al to Ti in the main catalyst is 60:1), a mixture of C-donor and D-donor (the molar ratio of C-donor to D-donor is 1:3, and the molar ratio of Si to Ti in the external electron donor is 5:1), and the main catalyst (the ID in the main catalyst is 2,2-diisobutyl-1,3-dimethoxypropane, and the mass ratio of Ti to hexane is 2×10⁻⁶). -7 Propylene at 0.1 MPa is introduced to carry out a prepolymerization reaction for 15 minutes to obtain the prepolymer;

[0078] 2) Transfer the material in the first polymerization reactor to the second polymerization reactor. Set the temperature of the reactor to 70°C, introduce a mixture of propylene and hydrogen (molar ratio of propylene to hydrogen is 3:1), and set the pressure of the reactor to 3.5 MPa. The polymerization reaction is carried out for 4 hours.

[0079] 3) Transfer the polymerization product to a washing vessel with a filter plate, release and recover the propylene. After the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane, then add isopropanol at a volume of 2 times that of hexane. Wash the polypropylene with isopropanol 5 times, 5 minutes each time, and then dry to obtain ultrapure isotactic polypropylene.

[0080] Calculations show that the catalytic activity during the polymerization process is 98 kg PP / g Cat, the product ash content is 15 ppm, and the isotacticity is 98.2%.

[0081] Compare with Example 1

[0082] 1) Add hexane at 30°C to the first polymerization reactor, filling half the reactor volume. Then, add triethylaluminum (in which the molar ratio of Al to ID in the main catalyst is 2,2-diisobutyl-1,3-dimethoxypropane, and the molar ratio of Ti is 60:1) and the main catalyst (in which the mass ratio of Ti to hexane in the main catalyst is 1.3 × 10⁻⁶). -7 Propylene at 0.1 MPa is introduced to carry out a prepolymerization reaction for 15 minutes to obtain the prepolymer;

[0083] 2) Transfer the material in the first polymerization reactor to the second polymerization reactor. Set the temperature of the reactor to 70°C and introduce a mixture of propylene and hydrogen (molar ratio of propylene to hydrogen is 3:1). The pressure of the reactor is 3.5 MPa, and the polymerization reaction lasts for 6 hours.

[0084] 3) Transfer the polymerization product to a washing vessel with a filter plate, release and recover the propylene. After the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane, then add isopropanol at a volume of 2 times that of hexane. Wash the polypropylene with isopropanol 5 times, 5 minutes each time, and then dry to obtain ultrapure isotactic polypropylene.

[0085] Calculations show that the catalytic activity during the polymerization process is 87 kg PP / g Cat, the product ash content is 25 ppm, and the isotacticity is 91.9%.

[0086] Compare with Example 2

[0087] 1) Add hexane at 30°C to the first polymerization reactor, filling half the reactor volume. Then, add triethylaluminum (the molar ratio of Al to Ti in the main catalyst is 60:1), P-donor (the molar ratio of Si to Ti in the main catalyst is 5:1), and the main catalyst (ID in the main catalyst is diisobutyl phthalate, and the mass ratio of Ti to hexane is 1.3 × 10⁻⁶). -7 Propylene at 0.1 MPa is introduced to carry out a prepolymerization reaction for 15 minutes to obtain the prepolymer;

[0088] 2) Transfer the material in the first polymerization reactor to the second polymerization reactor. Set the temperature of the reactor to 70°C and introduce a mixture of propylene and hydrogen (molar ratio of propylene to hydrogen is 3:1). The pressure of the reactor is 3.5 MPa, and the polymerization reaction lasts for 6 hours.

[0089] 3) Transfer the polymerization product to a washing vessel with a filter plate, release and recover the propylene. After the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane, then add isopropanol at a volume of 2 times that of hexane. Wash the polypropylene with isopropanol 5 times, 5 minutes each time, and then dry to obtain ultrapure isotactic polypropylene.

[0090] Calculations show that the catalytic activity during the polymerization process is 62 kg PP / g Cat, the product ash content is 40 ppm, and the isotacticity is 97.6%.

[0091] Compare with Example 3

[0092] 1) Add hexane at 30°C to the first polymerization reactor, filling half the reactor volume. Then, add triisobutylaluminum (the molar ratio of Al to Ti in the main catalyst is 60:1), P-donor (the molar ratio of Si to Ti in the main catalyst is 5:1), and the main catalyst (the ID in the main catalyst is 2,2-diisobutyl-1,3-dimethoxypropane, and the mass ratio of Ti to hexane is 1.3 × 10⁻⁶). -7 Propylene at 0.1 MPa is introduced to carry out a prepolymerization reaction for 15 minutes to obtain the prepolymer;

[0093] 2) Transfer the material in the first polymerization reactor to the second polymerization reactor. Set the temperature of the reactor to 70°C and introduce a mixture of propylene and hydrogen (molar ratio of propylene to hydrogen is 3:1). The pressure of the reactor is 3.5 MPa, and the polymerization reaction lasts for 6 hours.

[0094] 3) Transfer the polymerization product to a washing vessel with a filter plate, release and recover the propylene. After the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane, then add isopropanol at a volume of 2 times that of hexane. Wash the polypropylene with isopropanol 5 times, 5 minutes each time, and then dry to obtain ultrapure isotactic polypropylene.

[0095] Calculations show that the catalytic activity during the polymerization process is 60 kg PP / g Cat, the product ash content is 42 ppm, and the isotacticity is 96.1%.

[0096] Compare with Example 4

[0097] 1) Add hexane at 30°C to the first polymerization reactor, filling half the reactor volume. Then, add triethylaluminum (the molar ratio of Al to Ti in the main catalyst is 60:1), C-donor (the molar ratio of Si to Ti in the main catalyst is 5:1), and the main catalyst (ID in the main catalyst is diisobutyl phthalate, and the mass ratio of Ti to hexane is 2×10⁻⁶). -7 Propylene at 0.1 MPa is introduced to carry out a prepolymerization reaction for 15 minutes to obtain the prepolymer;

[0098] 2) Transfer the material in the first polymerization reactor to the second polymerization reactor. Set the temperature of the reactor to 70°C and introduce a mixture of propylene and hydrogen (molar ratio of propylene to hydrogen is 3:1). The pressure of the reactor is 3.5 MPa, and the polymerization reaction lasts for 6 hours.

[0099] 3) Transfer the polymerization product to a washing vessel with a filter plate, release and recover the propylene. After the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane, then add isopropanol at a volume of 2 times that of hexane. Wash the polypropylene with isopropanol 5 times, 5 minutes each time, and then dry to obtain ultrapure isotactic polypropylene.

[0100] Calculations show that the catalytic activity during the polymerization process is 60 kg PP / g Cat, the product ash content is 41 ppm, and the isotacticity is 97.0%.

[0101] Compare with Example 5

[0102] 1) Add hexane at 30°C to the first polymerization reactor, filling half the reactor volume. Then, add triethylaluminum (in which the molar ratio of Al to Ti in the main catalyst is 60:1), a mixture of D-donors (in which the molar ratio of Si to Ti in the main catalyst is 5:1), and the main catalyst (where ID is 2,2-diisobutyl-1,3-dimethoxypropane, and the mass ratio of Ti to hexane is 2 × 10⁻⁶). -7 Propylene at 0.1 MPa is introduced to carry out a prepolymerization reaction for 15 minutes to obtain the prepolymer;

[0103] 2) Transfer the material in the first polymerization reactor to the second polymerization reactor. Set the temperature of the reactor to 70°C, introduce a mixture of propylene and hydrogen (molar ratio of propylene to hydrogen is 3:1), and set the pressure of the reactor to 3.5 MPa. The polymerization reaction is carried out for 4 hours.

[0104] 3) Transfer the polymerization product to a washing vessel with a filter plate, release and recover the propylene. After the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane, then add isopropanol at a volume of 2 times that of hexane. Wash the polypropylene with isopropanol 5 times, 5 minutes each time, and then dry to obtain ultrapure isotactic polypropylene.

[0105] Calculations show that the catalytic activity during the polymerization process is 65 kg PP / g Cat, the product ash content is 37 ppm, and the isotacticity is 97.7%.

[0106] The aggregation results of all embodiments and comparative examples are summarized in Table 1 below.

[0107] Table 1 Summary of Aggregation Results

[0108]

[0109] Table 1 provides a clearer picture: comparing Comparative Examples 2, 3, 4, and 5 with Comparative Example 1, it can be seen that using commonly used triethylaluminum or triisobutylaluminum as a cocatalyst alone, and adding commonly used C-donor, D-donor, or P-donor as an external electron donor alone, can significantly improve the isotacticity of polypropylene products, but the polymerization activity is greatly reduced, resulting in higher ash content in the polypropylene products. Looking at Examples 1-8, it can be seen that using a triethylaluminum / triisobutylaluminum mixture as a cocatalyst and P-donor as an external electron donor; or using a C-donor / D-donor mixture as an external electron donor and triethylaluminum as a cocatalyst, can not only further improve the isotacticity of polypropylene products, ensuring that the isotacticity is not less than 98%, but also that the polymerization activity of this catalytic system for propylene polymerization is higher than that of Comparative Example 1, thereby significantly reducing the ash content in the product. Ultimately, ultrapure isotactic polypropylene with an ash content of no more than 20 ppm and an isotacticity of not less than 98% can be obtained, enabling polypropylene products to have wider applications.

Claims

1. A catalytic system for preparing ultrapure isotactic polypropylene, characterized in that, The catalytic system comprises three components: a main catalyst, a co-catalyst, and an external electron donor. The main catalyst is a TiCl4 / MgCl2·ID supported high-efficiency spherical Ziegler-Natta catalyst, where ID refers to 2,2-diisobutyl-1,3-dimethoxypropane as the internal electron donor. The co-catalyst is triethylaluminum. The external electron donor is a mixture of cyclohexylmethyldimethoxysilane and dicyclopentyldimethoxysilane. When this catalytic system is applied to the catalytic polymerization of propylene to prepare ultrapure isotactic polypropylene, the co-catalyst and the external electron donor exchange groups to maintain more Ti in the main catalyst at the +3 valence, which is active for propylene polymerization. Furthermore, the group exchange creates steric hindrance to induce directional polymerization of propylene. In the external electron donor, the molar ratio of cyclohexylmethyldimethoxysilane to dicyclopentyldimethoxysilane is 1:3 to 3:1; the molar ratio of Al in the co-catalyst to Ti in the main catalyst is 20 to 60:1; and the molar ratio of Si in the external electron donor to Ti in the main catalyst is 2 to 5:

1.

2. The method for applying the catalytic system of claim 1 in the catalytic polymerization of propylene to prepare ultrapure isotactic polypropylene, characterized in that, Includes the following steps: (1) Add hexane to the first polymerization reactor in an amount equal to half the reactor volume; (2) Add the co-catalyst, external electron donor, and main catalyst in sequence, controlling the amount added so that the mass ratio of Ti to hexane in the main catalyst is 1.3 × 10⁻⁶. -7 ~ 4×10 -7 ; (3) Propylene was introduced to make the pressure in the reactor 0.1 MPa, and the prepolymerization reaction was carried out at 30°C for 15 minutes to obtain the prepolymer; (4) Transfer the material in the first polymerization reactor to the second polymerization reactor, control the temperature inside the reactor to 70~75℃; introduce a mixture of propylene and hydrogen until the pressure inside the reactor is 2.5~3.5MPa, and carry out the polymerization reaction for 2~6 hours; (5) Transfer the polymerization product to a washing vessel with a filter plate, release and recover propylene gas; after the pressure drops to atmospheric pressure, open the bottom discharge valve to discharge hexane; add isopropanol to the vessel to wash the polypropylene, and dry to obtain ultrapure isotactic polypropylene.

3. The method according to claim 2, characterized in that, In the mixed gas of step (2), the molar ratio of propylene to hydrogen is 3:

1.

4. The method according to claim 2, characterized in that, In step (5), the washing is repeated 1 to 5 times, each time for 5 minutes; the amount of isopropanol added each time is twice the volume of the discharged hexane.

Images