A method for preparing propylene-based polymer

Abstract

The present invention provides a method for preparing a propylene-based polymer. The method comprises polymerizing propylene and a comonomer in a multistage reactor in the presence of a catalyst, wherein the multistage reactor comprises at least one reactor for polymerizing propylene and a comonomer to generate a first polymer product. The first polymer product is transferred to a second reaction zone comprising at least one gas phase reactor, where propylene and a comonomer are polymerized in the gas phase reactor to generate a second polymer product. The second polymer product is transferred to a third reaction zone comprising at least one gas phase reactor, where propylene and a comonomer are polymerized in the gas phase reactor to generate a third polymer product, wherein part of the third polymer product is transferred to the second reaction zone, and relates to a propylene-based polymer obtainable by this method. The propylene-based polymer can be used to prepare a film, blow mold or injection mold a sample, and can also be used for waterproofing rolls.

Description

Technical Field

[0001] The present invention relates to a method for preparing a propylene-based polymer, in particular to a method for preparing a heterophasic polypropylene with high fluidity, high activity and balanced rigidity and toughness. Background Art

[0002] Heterogeneous polypropylene generally has two phases (island structure), consisting of a polypropylene matrix and a distributed elastomeric phase, or there may be a three-phase structure (core-shell-matrix structure), consisting of a polypropylene matrix and a distributed elastomeric phase, but the elastomeric phase is encapsulated with other semi-crystalline polymers. In the existing polymerization process of heterogeneous copolymerized polypropylene, the typical method is to produce in series in two reaction stages. First, isotactic polypropylene (iPP) particles are produced in gaseous or liquid propylene. These polypropylene particles are then transferred to a gas phase fluidized bed reactor and copolymerized in an isotactic polypropylene matrix to produce an elastomeric rubber phase. The elastomeric phase contains propylene copolymer rubber, such as ethylene-propylene rubber (EPR). Therefore, the rubber component is a copolymer of propylene and another α-olefin (such as ethylene), and is mainly in amorphous (xylene soluble at room temperature) form.

[0003] Heterophasic propylene copolymers have good impact toughness and flowability, so they are used in many fields, such as molding applications (such as blow molding and injection molding), film extrusion, wire and cable or pipe. Heterophasic polymers are used to produce automotive exterior and interior, especially instrument panels, door cladding, consoles, trims, etc., and in the packaging field such as food packaging, medical packaging and consumer goods.

[0004] The polymer products obtained when producing multiphase propylene copolymers in the prior art are all sticky, and the particle fluidity is poor, which is easy to block the transportation pipeline and adhere to the wall of the reactor, so that the production cannot proceed normally. Therefore, when producing copolymerized polypropylene in the prior art, a sticking inhibitor, low-purity nitrogen (LPN), is often added to prevent the formation of undesirable sticky copolymers on the surface of polymer particles to improve the particle fluidity. However, adding a large amount of LPN also brings a series of problems. For example, the explosion limit of oxygen in LPN and molecular weight regulator hydrogen is very wide, and the effect of static electricity on the surface of the polymer has the potential danger of hydrogen-oxygen explosion. For safety reasons, hydrogen cannot be added when the device produces copolymers, which limits the optimization of product performance and the production of products of different grades.

[0005] In addition, the activity of ethylene-propylene gas phase copolymerization decays quickly after the previous stage produces isotactic polypropylene. The existing technology mainly improves the copolymerization activity of the catalyst or reduces the residence time of homopolypropylene production to achieve higher copolymerization activity, but such operation leads to a decrease in the production capacity of the catalyst. Therefore, it is of great significance to improve the polymerization method to improve the copolymerization activity.

[0006] Since the heat capacity of the reaction medium of ethylene and propylene is relatively small, the heat removal capacity of the gas phase copolymerization reactor is limited. Although the polymerization heat of ethylene-propylene copolymerization is about 33% lower than that of ethylene polymerization, the amorphous rubber of ethylene-propylene is more easily melted when heated, and poor heat transfer control will cause the products to stick together, which will damage the fluidity of the particles, and even cause the kettle to stick and the reactor to stop in severe cases. Therefore, good control of the temperature of the gas phase copolymerization reaction and effective enhancement of the heat transfer capacity are very important. The process disclosed in U.S. Patents US4543399 and US 4588790 cools the circulating gas to below the dew point to realize the liquid-carrying operation of the fluidized bed. This process is called "condensation mode polyolefin process", referred to as "condensation mode" or "condensation process". Since the gasification of liquid logistics can absorb a large amount of heat, the heat transfer capacity of the fluidized bed reaction is improved, thereby improving the space-time yield of the reactor.

[0007] The latest technology cited in the condensing mode operation uses nitrogen as the non-volatile component of the circulating gas stream, while allowing the presence of small amounts of ethane and methane to increase the heat capacity of the circulating gas stream. Inert condensing media such as isopentane and n-hexane usually act as medium-volatile components, evaporating away most of the polymerization heat and significantly increasing the heat capacity of the circulating gas stream. U.S. Patents US5405922, US5352749, US4588790, and US5436304 disclose a method for polymerizing alpha olefins in a gas phase reactor having a fluidized bed and a fluidizing medium, and the heat removal capacity of the reactor is increased by adding an inert condensing liquid. WO2011147539 discloses a method for gas phase polymerization of one or more olefin monomers in a fluidized bed reactor in a dry mode or (super) condensing mode with a gas stream containing an inert gas, preferably a gas phase polymerization method for ethylene.

[0008] These methods are characterized in that the circulating gas stream in the gas phase reactor contains an inert condensed liquid in an amount of up to 50%, thereby increasing the heat capacity of the circulating gas stream and removing a large amount of polymerization heat by vaporization absorption of the condensed liquid, thereby improving the space-time yield of the reactor. Summary of the invention

[0009] The purpose of the present invention is to solve the deficiencies in the prior art and provide a method for preparing a propylene-based polymer, wherein the polymerization activity of the reactor is increased by 20 to 50% overall, and the method is suitable for producing high-ethylene-content impact-resistant polypropylene. No anti-sticking agent is required, the particles have high fluidity and high copolymerization activity, and the device can operate stably for a long period of time.

[0010] The present invention relates to a method for preparing a propylene-based polymer, wherein propylene and a comonomer are polymerized in a multi-stage reactor in the presence of a catalyst system, the method comprising providing at least one reactor to polymerize propylene and a comonomer to generate a first polymerization product, transferring the first polymerization product to a second reaction zone comprising at least one gas phase reactor, polymerizing propylene and a comonomer in the gas phase reactor in the presence of the first polymerization product and a condensing medium to generate a second polymerization product, transferring the second polymerization product to a third reaction zone comprising at least one gas phase reactor, polymerizing propylene and a comonomer in the gas phase reactor in the presence of the second polymerization product to generate a third polymerization product, wherein part of the third polymerization product is transferred to the second reaction zone.

[0011] The present invention finds that in the presence of the first polymerization product and the condensation medium, propylene and comonomer are polymerized in a gas phase reactor to generate a second polymerization product, the copolymerization activity is improved, and the lower comonomer / (propylene+comonomer) molar ratio is conducive to enhancing the fluidity of the particles, and avoiding the problem of sticky blocks between particles of the polypropylene composition during the polymerization process. The high comonomer / (propylene+comonomer) molar ratio of the third reaction zone is conducive to improving the copolymerization activity and inhibiting the formation of rubber on the particle surface, and because part of the condensation medium is adsorbed inside the particles of the second polymerization product transported to the third reaction zone, the presence of the condensation medium will cause the ethylene / propylene molar ratio at the active center to decrease, so that the amorphous ethylene-propylene copolymer is more inclined to grow inside the polypropylene particles and will not flow out of the surface. The third polymerization product is partially transmitted to the second reaction zone to achieve molecular-level polymerization, which is beneficial to the fluidity and rigid-toughness balance performance of the propylene-based polymer.

[0012] According to a preferred embodiment of the present invention, the comonomers used in the second reaction zone and the third reaction zone may be the same or different, and are selected from one or more of ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, and 1-decene, preferably one or more of ethylene, butene, and hexene.

[0013] According to a preferred embodiment of the present invention, the catalyst system comprises a solid catalyst component, an alkyl aluminum or an alkyl aluminoxane, and at least one external electron donor. The solid catalyst component is selected from Ziegler-Natta catalysts, chromium catalysts, metallocene catalysts, late transition metal catalysts or mixtures thereof.

[0014] According to a preferred embodiment of the present invention, the molecular weight of the condensing medium is 28 g / mol to 140 g / mol, and the condensing medium is selected from at least one hydrocarbon of C3 to C10. Preferably, the hydrocarbon is selected from alkanes, alkenes, halogenated alkanes, and more preferably one or more of propane, n-butane, isobutane, n-pentane, isopentane, cyclohexane, n-hexane or n-heptane. The condensing medium content accounts for 0.4 to 15.5 wt% of the total mass of the polymer particles, and the molar percentage of the condensing medium gas phase accounts for 0.2 to 6.9 mol% of the gas phase component (usually referred to as circulating gas) in the reactor.

[0015] According to a preferred embodiment of the present invention, the comonomer / (propylene+comonomer) molar ratio in the second reaction zone is 0.001-0.30, more preferably 0.04-0.25; the comonomer / (propylene+comonomer) molar ratio in the third reaction zone is 0.5-1, more preferably 0.50-0.80.

[0016] According to a preferred embodiment of the present invention, the third polymerization product transferred to the second reaction zone accounts for 0.1% to 45% of the total mass of the third polymerization product, more preferably 10% to 35%.

[0017] According to a preferred embodiment of the present invention, the second polymerization product is not subjected to flash evaporation or other processes to remove solvent or condensate the medium during the process of being transferred to the third reaction zone.

[0018] In a preferred embodiment of the present invention, in the presence of a condensing medium, the temperature of the reaction gas mixture in the second reaction zone gas phase reactor is close to (slightly higher than) the dew point, and the copolymerization activity is increased by 41.99% compared with the comparative example. With more precise temperature control, the copolymerization activity can be significantly improved, solving the problem of rapid decay of ethylene propylene gas phase copolymerization activity and long copolymerization residence time. In addition, the addition of an inert condensing medium improves the heat removal capacity of the reactor, and is therefore also beneficial to increasing the space-time yield of the reactor.

[0019] Compared with the existing multiphase polypropylene production process, the beneficial effects of the present invention include: the present invention does not need to add the anti-sticking agent -LPN, and the copolymerization activity is improved by adding the condensing medium and the lower comonomer / (propylene + comonomer) molar ratio in the gas phase reactor of the second reaction zone, and the lower comonomer / (propylene + comonomer) molar ratio is conducive to the enhancement of the fluidity of the particles. The high comonomer / (propylene + comonomer) molar ratio in the third reaction zone is conducive to the improvement of the copolymerization activity and the inhibition of the formation of rubber on the surface of the particles, and because part of the condensing medium is adsorbed inside the second polymerization product particles transported to the third reaction zone, the presence of the condensing medium will cause the ethylene / propylene molar ratio at the active center to decrease, so that the amorphous ethylene propylene copolymer is more inclined to grow inside the polypropylene particles and will not flow out of the surface. The third polymerization product is partially transmitted to the second reaction zone to achieve molecular-level polymerization, which is conducive to the balance of fluidity and toughness of the propylene-based polymer.

[0020] The prior art does not involve carrying out a copolymerization reaction in polypropylene particles in the presence of a condensing medium, which changes the copolymer monomer composition and concentration at the active site, improves the copolymerization activity of the olefin monomer in the gas phase reactor and the fluidity of the particles, and solves the problem that the copolymerized polypropylene is easy to become sticky.

[0021] In addition, the method of the present invention has high heat transfer efficiency and can achieve precise control of gas phase copolymerization temperature. The present invention also improves the dispersion of rubber in polypropylene particles and is suitable for preparing multiphase polypropylene with high fluidity, high activity and balanced rigidity and toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention is a schematic flow diagram of a method for preparing a propylene-based polymer in one embodiment of the present invention. DETAILED DESCRIPTION

[0023] The present invention is described in detail below in conjunction with the examples and drawings. The examples and drawings are only used to exemplify the present invention and do not constitute any limitation on the protection scope of the present invention. All reasonable changes and combinations within the scope of the inventive concept of the present invention fall within the protection scope of the present invention. In each embodiment and comparative example, the parts not further described are exactly the same. For example, in each embodiment and comparative example, the multistage reactor used is exactly the same, and the types and addition amounts of the catalysts and external electron donors used are the same; the method for testing the obtained multiphase polypropylene is exactly the same.

[0024] Embodiment 1:

[0025] exist Figure 1A method for preparing propylene-based polymers shown in the figure produces heterophasic polypropylene. Propylene, comonomer 1-butene, catalyst, triethylaluminum, external electron donor and hydrogen are added to the vertical stirred reactor R1 for reaction. The temperature of the vertical stirred reactor R1 is controlled at 75°C, and the reactor pressure is controlled at about 2.8MPaG by adjusting the fresh propylene feed amount. The hydrogen / propylene molar ratio in the reactor is 0.08mol / mol, the butene / propylene molar ratio is 0.035mol / mol, and the propylene concentration is 86mol%. The vertical stirred reactor R1 is intermittently sent to the fluidized bed reactor R2 after the air lock is pressurized by the circulating gas of the vertical stirred reactor R1 through the switch valve on the discharge plug bottom pipe 1. Propylene, ethylene and hydrogen from the raw material refining unit are sent to the fluidized bed reactor R2, and the fluidizing gas has part of nitrogen. The temperature is controlled at 70°C, and the pressure of the fluidized bed reactor is controlled at about 2.5MPaG. The hydrogen / propylene molar ratio in the fluidized bed reactor is 0.02 mol / mol, the ethylene / (ethylene+propylene) molar ratio is 0.04 mol / mol, and the propylene concentration is 86 mol%. In this reactor, the ethylene-propylene rubber phase is mainly generated, and its circulating gas condensing medium content is 15.4 wt% of the total mass of the particles. After the gas lock is pressurized with the circulating gas of the gas phase fluidized bed reactor R3, the second polymerization product is intermittently sent to the fluidized bed reactor R3 through pipeline 4.

[0026] Propylene, ethylene and hydrogen from the raw material refining unit are fed into the gas phase fluidized bed reactor R3, the comonomer is ethylene, the fluidizing gas contains some nitrogen, the temperature is controlled at 75°C, and the pressure of the gas phase fluidized bed reactor is controlled at about 2.5MPaG. The ethylene / (ethylene+propylene) molar ratio in the gas phase fluidized bed reactor is 0.60mol / mol, the nitrogen concentration is 8.6mol%, and the high ethylene content rubber phase is mainly generated in this reactor. Among them, part of the third polymerization product is transmitted to the second reaction zone, and the material mass circulation ratio is 29%.

[0027] The activity of the obtained multiphase polypropylene was 12254 g polymer / g cat. , flow time is 38s, flexural modulus is 0.82Gpa, and simple supported beam notched impact strength is 36.4kJ / m 2 , the xylene room temperature soluble matter content is 32.2wt%. It can be used as a high rubber content polypropylene grade and applied in automotive soft parts.

[0028] Embodiment 2:

[0029] exist Figure 1A method for preparing propylene-based polymers shown in the figure produces heterophasic polypropylene. Propylene, comonomer ethylene, catalyst, triethylaluminum, external electron donor and hydrogen are added to the vertical stirred reactor R1 for reaction. The temperature of the vertical stirred reactor R1 is controlled at 75°C, and the reactor pressure is controlled at about 2.8MPaG by adjusting the fresh propylene feed amount. The hydrogen / propylene molar ratio in the reactor is 0.08mol / mol, the ethylene / propylene molar ratio is 0.01mol / mol, and the propylene concentration is 86mol%. The vertical stirred reactor R1 is intermittently sent to the fluidized bed reactor R2 after the air lock is pressurized by the circulating gas of the vertical stirred reactor R1 through the switch valve on the discharge plug bottom pipe 1. Propylene, ethylene and hydrogen from the raw material refining unit are sent to the fluidized bed reactor R2, and the fluidizing gas has part of nitrogen. The temperature is controlled at 70°C and the reactor pressure is controlled at about 2.5MPaG. The hydrogen / propylene molar ratio in the reactor is 0.02 mol / mol, the ethylene / (ethylene+propylene) molar ratio is 0.08 mol / mol, and the propylene concentration is 84 mol%. In this reactor, the ethylene-propylene rubber phase is mainly generated, and its circulating gas condensing medium content is 10.2 wt% of the total mass of the particles. After the gas lock is pressurized with the circulating gas of the gas phase fluidized bed reactor R3, the second polymerization product is intermittently sent to the fluidized bed reactor R3 through pipeline 4.

[0030] Propylene, ethylene and hydrogen from the raw material refining unit are fed into the reactor R3, the comonomer is ethylene, the fluidizing gas contains some nitrogen, the temperature is controlled at 75°C, and the reactor pressure is controlled at about 2.5MPaG. The ethylene / (ethylene+propylene) molar ratio in the reactor is 0.50 mol / mol, the nitrogen concentration is 9 mol%, and the high ethylene content rubber phase is mainly generated in this reactor. Among them, part of the third polymerization product is transmitted to the second reaction zone, and the material mass circulation ratio is 16%.

[0031] The activity of the obtained multiphase polypropylene was 11392 g polymer / g cat. , flow time is 34s, flexural modulus is 0.86Gpa, and simple supported beam notched impact strength is 29.7kJ / m 2 , the xylene room temperature soluble matter content is 28.4wt%. It can be used as a high rubber content polypropylene grade and applied in the field of injection molding.

[0032] Embodiment 3:

[0033] exist Figure 1A method for preparing propylene-based polymers shown in the figure produces heterophasic polypropylene. Propylene, comonomer 1-pentene, catalyst, triethylaluminum, external electron donor and hydrogen are added to the vertical stirred reactor R1 for reaction. The temperature of the vertical stirred reactor R1 is controlled at 75°C, and the reactor pressure is controlled at about 2.8MPaG by adjusting the fresh propylene feed amount. The hydrogen / propylene molar ratio in the reactor is 0.08mol / mol, the 1-pentene / propylene molar ratio is 0.006mol / mol, and the propylene concentration is 86mol%. The vertical stirred reactor R1 is intermittently sent to the fluidized bed reactor R2 after the air lock is pressurized by the circulating gas of the vertical stirred reactor R1 through the switch valve on the discharge bottom pipe 1. Propylene, ethylene and hydrogen from the raw material refining unit are sent to the fluidized bed reactor R2, and the fluidizing gas has part of nitrogen. The temperature is controlled at 70°C and the reactor pressure is controlled at about 2.5MPaG. The hydrogen / propylene molar ratio in the reactor is 0.02 mol / mol, the ethylene / (ethylene+propylene) molar ratio is 0.12 mol / mol, and the propylene concentration is 80.2 mol%. In this reactor, the ethylene-propylene rubber phase is mainly generated, and its circulating gas condensing medium content is 6.2 wt% of the total mass of the particles. After the gas lock is pressurized with the circulating gas of the gas phase fluidized bed reactor R3, the second polymerization product is intermittently sent to the fluidized bed reactor R3 through pipeline 4.

[0034] Propylene, ethylene and hydrogen from the raw material refining unit are fed into the reactor R3, the comonomer is ethylene, the fluidizing gas contains some nitrogen, the temperature is controlled at 75°C, and the reactor pressure is controlled at about 2.5MPaG. The ethylene / (ethylene+propylene) molar ratio in the reactor is 0.65mol / mol, the nitrogen concentration is 9.1mol%, and the high ethylene content rubber phase is mainly generated in this reactor. Among them, part of the third polymerization product is transmitted to the second reaction zone, and the material mass circulation ratio is 25%.

[0035] The activity of the obtained multiphase polypropylene was 11738 g polymer / g cat. , flow time is 31s, flexural modulus is 0.87Gpa, and simple supported beam notched impact strength is 27.5kJ / m 2 , the content of xylene soluble matter at room temperature is 26.5wt%.

[0036] Embodiment 4:

[0037] exist Figure 1A method for preparing propylene-based polymers shown in the figure produces heterophasic polypropylene. Propylene, catalyst, triethylaluminum, external electron donor and hydrogen are added to a vertical stirred reactor R1 for reaction. The temperature of the vertical stirred reactor R1 is controlled at 75°C, and the reactor pressure is controlled at about 2.8MPaG by adjusting the fresh propylene feed amount. The hydrogen / propylene molar ratio in the reactor is 0.08mol / mol, and the propylene concentration is 86mol%. The vertical stirred reactor R1 is intermittently sent to the fluidized bed reactor R2 after the air lock is pressurized with the circulating gas of the vertical stirred reactor R1 through the switch valve on the discharge plug bottom pipe 1. Propylene, ethylene and hydrogen from the raw material refining unit are sent to the fluidized bed reactor R2, and the fluidizing gas has part of nitrogen. The temperature is controlled at 70°C and the reactor pressure is controlled at about 2.5MPaG. The hydrogen / propylene molar ratio in the reactor is 0.02mol / mol, the ethylene / (ethylene+propylene) molar ratio is 0.18mol / mol, and the propylene concentration is 78mol%. In this reactor, ethylene-propylene rubber phase is mainly produced, and the circulating gas condensing medium content is 8.6wt% of the total mass of the particles. After the gas lock is pressurized with the circulating gas of the gas phase fluidized bed reactor R3, the second polymerization product is intermittently sent to the fluidized bed reactor R3 through pipeline 4.

[0038] Propylene, ethylene and hydrogen from the raw material refining unit are fed into the reactor R3, the comonomer is ethylene, the fluidizing gas contains some nitrogen, the temperature is controlled at 75°C, and the reactor pressure is controlled at about 2.5MPaG. The ethylene / (ethylene+propylene) molar ratio in the reactor is 0.68 mol / mol, the nitrogen concentration is 8.4 mol%, and the high ethylene content rubber phase is mainly generated in this reactor. Among them, part of the third polymerization product is transmitted to the second reaction zone, and the material mass circulation ratio is 32%.

[0039] The activity of the obtained multiphase polypropylene is 12096 g polymer / g cat. , flow time is 40s, flexural modulus is 0.82Gpa, and simple supported beam notched impact strength is 38.3kJ / m 2 , the xylene room temperature soluble matter content is 31.4wt%. It can be used as a high rubber content polypropylene grade and applied in automotive soft parts.

[0040] Embodiment 5:

[0041] exist Figure 1A method for preparing propylene-based polymers is shown to produce heterophasic polypropylene. Propylene, catalyst, triethylaluminum, external electron donor and hydrogen are added to a vertical stirred reactor R1 for reaction. The temperature of the vertical stirred reactor R1 is controlled to 75°C, and the reactor pressure is controlled to about 2.8MPaG by adjusting the fresh propylene feed amount. The hydrogen / propylene molar ratio in the reactor is 0.08mol / mol, and the propylene concentration is 86mol%. The vertical stirred reactor R1 is intermittently sent to the fluidized bed reactor R2 after the air lock is pressurized with the circulating gas of the vertical stirred reactor R1 through the switch valve on the discharge plug bottom pipe 1. Propylene, ethylene and hydrogen from the raw material refining unit are sent to the fluidized bed reactor R2, and the fluidizing gas has part of nitrogen. The temperature is controlled to 70°C and the reactor pressure is controlled to about 2.5MPaG. The hydrogen / propylene molar ratio in the reactor is 0.02mol / mol, the ethylene / (ethylene+propylene) molar ratio is 0.25mol / mol, and the propylene concentration is 68mol%. In this reactor, ethylene-propylene rubber phase is mainly produced, and the circulating gas condensing medium content is 4.4wt% of the total mass of the particles. After the gas lock is pressurized with the circulating gas of the gas phase fluidized bed reactor R3, the second polymerization product is intermittently sent to the fluidized bed reactor R3 through pipeline 4.

[0042] Propylene, ethylene and hydrogen from the raw material refining unit are fed into the reactor R3, the comonomer is ethylene, the fluidizing gas contains some nitrogen, the temperature is controlled at 75°C, and the reactor pressure is controlled at about 2.5MPaG. The ethylene / (ethylene+propylene) molar ratio in the reactor is 0.71 mol / mol, the nitrogen concentration is 9 mol%, and the high ethylene content rubber phase is mainly generated in this reactor. Among them, part of the third polymerization product is transmitted to the second reaction zone, and the material mass circulation ratio is 35%.

[0043] The activity of the obtained multiphase polypropylene was 13158 g polymer / g cat. , flow time is 43s, flexural modulus is 0.79Gpa, and simple supported beam notched impact strength is 45.2kJ / m 2 , the xylene room temperature soluble matter content is 38.3wt%. It can be used as a high impact polypropylene grade and applied in automotive soft parts.

[0044] Comparative Example 1:

[0045] exist Figure 1A method for preparing propylene-based polymers is shown to produce heterophasic polypropylene. Propylene, catalyst, triethylaluminum, external electron donor and hydrogen are added to a vertical stirred reactor R1 for reaction. The temperature of the vertical stirred reactor R1 is controlled to 75°C, and the reactor pressure is controlled to about 2.8MPaG by adjusting the fresh propylene feed amount. The hydrogen / propylene molar ratio in the reactor is 0.08mol / mol, and the propylene concentration is 86mol%. The vertical stirred reactor R1 is intermittently sent to the fluidized bed reactor R2 after the air lock is pressurized with the circulating gas of the vertical stirred reactor R1 through the switch valve on the discharge plug bottom pipe 1. Propylene, ethylene and hydrogen from the raw material refining unit are sent to the fluidized bed reactor R2, and the fluidizing gas has part of nitrogen. The temperature is controlled to 70°C and the reactor pressure is controlled to about 2.5MPaG. The hydrogen / propylene molar ratio in the reactor is 0.02mol / mol, the ethylene / (ethylene+propylene) molar ratio is 0.08mol / mol, and the propylene concentration is 84mol%. In this reactor, ethylene-propylene rubber phase is mainly produced, and the circulating gas condensing medium content is 0wt% of the total mass of particles. After the gas lock is pressurized with the circulating gas of the gas phase fluidized bed reactor R3, the second polymerization product is intermittently sent to the fluidized bed reactor R3 through pipeline 4.

[0046] Propylene, ethylene and hydrogen from the raw material refining unit are fed into the reactor R3, the comonomer is ethylene, the fluidizing gas contains some nitrogen, the temperature is controlled at 75°C, and the reactor pressure is controlled at about 2.5MPaG. The ethylene / (ethylene+propylene) molar ratio in the reactor is 0.50mol / mol, the nitrogen concentration is 9.2mol%, and the high ethylene content rubber phase is mainly generated in this reactor. Among them, part of the third polymerization product is transmitted to the second reaction zone, and the material mass circulation ratio is 0.

[0047] The activity of the obtained multiphase polypropylene is 8630 g polymer / g cat. , flow time is 46s, flexural modulus is 0.89Gpa, and simple supported beam notched impact strength is 6.8kJ / m 2 , the content of xylene soluble matter at room temperature is 17.5wt%.

[0048] Comparative Example 2

[0049] exist Figure 1A method for preparing propylene-based polymers shown in the figure produces heterophasic polypropylene. Propylene, catalyst, triethylaluminum, external electron donor and hydrogen are added to a vertical stirred reactor R1 for reaction. The temperature of the vertical stirred reactor R1 is controlled at 75°C, and the reactor pressure is controlled at about 2.8MPaG by adjusting the fresh propylene feed amount. The hydrogen / propylene molar ratio in the reactor is 0.08mol / mol, and the propylene concentration is 86mol%. The vertical stirred reactor R1 is intermittently sent to the fluidized bed reactor R2 after the air lock is pressurized with the circulating gas of the vertical stirred reactor R1 through the switch valve on the discharge bottom pipe 1. Propylene, ethylene and hydrogen from the raw material refining unit are sent to the fluidized bed reactor R2, and the fluidizing gas has part of nitrogen. The temperature is controlled at 70°C and the reactor pressure is controlled at about 2.5MPaG. The hydrogen / propylene molar ratio in the reactor is 0.02mol / mol, the ethylene / (ethylene+propylene) molar ratio is 0.04mol / mol, and the propylene concentration is 85mol%. In this reactor, ethylene-propylene rubber phase is mainly produced, and the circulating gas condensing medium content is 0wt% of the total mass of particles. After the gas lock is pressurized with the circulating gas of the gas phase fluidized bed reactor R3, the second polymerization product is intermittently sent to the fluidized bed reactor R3 through pipeline 4.

[0050] Propylene, ethylene and hydrogen from the raw material refining unit are fed into the reactor R3, the comonomer is ethylene, the fluidizing gas contains some nitrogen, the temperature is controlled at 75°C, and the reactor pressure is controlled at about 2.5MPaG. The ethylene / (ethylene+propylene) molar ratio in the reactor is 0.34 mol / mol, the nitrogen concentration is 9.1 mol%, and the high ethylene content rubber phase is mainly generated in this reactor. Among them, part of the third polymerization product is transmitted to the second reaction zone, and the material mass circulation ratio is 0.

[0051] The activity of the obtained multiphase polypropylene was 9184 g polymer / g cat. , flow time is 53s, flexural modulus is 0.84Gpa, and simple supported beam notched impact strength is 8.46kJ / m 2 , the content of xylene soluble matter at room temperature is 23.8wt%.

[0052] Although the specific implementations of the present invention have been described in detail above in conjunction with the embodiments, it should be pointed out that the protection scope of the present invention is not limited by these specific implementations, but is determined by the claims. Those skilled in the art may make appropriate changes to these implementations without departing from the technical ideas and purport of the present invention, and these changed implementations are obviously also included in the protection scope of the present invention.

Claims

1. A method for preparing a propylene-based polymer, characterized in that: It includes polymerizing propylene and comonomers in the presence of a catalyst system in a multi-stage reactor; The method comprises: providing at least one reaction zone to polymerize propylene and a comonomer to generate a first polymerization product; transmitting the first polymerization product to a second reaction zone comprising at least one gas phase reactor, and polymerizing propylene and a comonomer in the gas phase reactor in the presence of the first polymerization product and a condensing medium to generate a second polymerization product; transmitting the second polymerization product to a third reaction zone comprising at least one gas phase reactor, and polymerizing propylene and a comonomer in the gas phase reactor in the presence of the second polymerization product to generate a third polymerization product, wherein part of the third polymerization product is transmitted to the gas phase reactor of the second reaction zone, and the third polymerization product transmitted to the second reaction zone accounts for 0.1% to 45% of the total mass of the third polymerization product; The molecular weight of the condensing medium is 28 g / mol to 140 g / mol, and the condensing medium is selected from at least one hydrocarbon of C3 to C10, the content of the condensing medium accounts for 0.4 to 15.5 wt% of the total mass of the polymer particles, and the molar percentage of the gas phase of the condensing medium accounts for 0.2 to 6.9 mol% of the gas phase components in the reactor; The molar ratio of comonomer / (propylene+comonomer) in the second reaction zone is 0.001-0.30, and the molar ratio of comonomer / (propylene+comonomer) in the third reaction zone is 0.5-1; The solvent and the condensation medium are not removed during the transfer of the second polymer product to the third reaction zone.

2. The method according to claim 1, characterized in that The comonomers used in the first reaction zone, the second reaction zone and the third reaction zone may be the same or different, and are selected from one or more of ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene and 1-decene.

3. The method according to claim 1, characterized in that: The catalyst system comprises a solid catalyst component, alkyl aluminum or alkyl aluminoxane, and at least one external electron donor; the solid catalyst component is selected from Ziegler-Natta catalysts, chromium catalysts, metallocene catalysts, late transition metal catalysts or mixtures thereof.

4. The method according to claim 1, characterized in that The hydrocarbons are selected from alkanes, olefins, and halogenated alkanes.

5. The method according to claim 4, characterized in that The hydrocarbon is selected from one or more of propane, n-butane, isobutane, n-pentane, isopentane, cyclohexane, n-hexane or n-heptane.

6. The method according to claim 1, characterized in that The first reaction zone mainly carries out propylene homopolymerization or copolymerization of propylene and a small amount of comonomers, wherein the comonomers are ethylene, 1-butene and 1-pentene.

7. The method according to claim 1, characterized in that The polymerized product of the first reaction zone accounts for 30-80 wt% of the total product mass.

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