A method for preparing a polypropylene-based composition

Abstract

The present invention provides a method for preparing a polypropylene composition, which produces a composition containing homopolypropylene, block copolymer and ethylene / α-olefin copolymer in at least three polymerization zones. Among them, at least one polymerization zone produces homopolypropylene; at least one polymerization zone produces a block copolymer of propylene and a comonomer, and the comonomer is selected from ethylene and C4-C 10 α-olefins; and at least one polymerization zone produces polyethylene or an ethylene / C4-C 10 α-olefin copolymer. Among them, the block copolymer and the random copolymer are preferably produced in a single liquid-holding gas-solid reactor. The obtained polypropylene composition has a balanced comprehensive performance, and the rigidity, toughness and glossiness are well matched, and it is suitable for preparing pipes, household appliances and the automotive industry.

Description

Technical Field

[0001] The present invention relates to a polymerization process for preparing a polypropylene based composition. Background Art

[0002] Polypropylene has the advantages of light weight, low price and good processing performance. It is widely used in many fields such as automobiles, home appliances, building materials, agriculture, etc. The demand for polypropylene is increasing year by year, and the output is also increasing. However, the polypropylene market has the problem of surplus of low-end varieties and shortage of high-end varieties. In addition, polypropylene materials have the problem of light-toughness mismatch and rigid-toughness imbalance, which greatly limits the application and development of polypropylene materials.

[0003] Impact propylene polymer compositions are well known in the art. Typically, they comprise a relatively high crystalline propylene polymer fraction insoluble in room temperature xylene, and a relatively low crystallinity copolymer fraction soluble in room temperature xylene. The relatively high crystallinity fraction is typically a propylene homopolymer, or a propylene random copolymer with a relatively low content of olefin comonomers, characterized by high isotacticity. The relatively low crystallinity fraction is typically a propylene copolymer and in particular a propylene-ethylene copolymer with an ethylene content of 15-75 wt%. The composition can be prepared by several methods, including mechanical blending of the two components. However, a preferred method is to prepare the composition by carrying out sequential polymerization steps in one or two reactors in a reactor. Typically, in a first step, propylene is copolymerized or copolymerized with a small amount of other olefins to produce a high crystallinity component. And in a second step, particularly in a reaction mixture containing a relatively high content of olefin comonomers, it produces a xylene soluble fraction. This method is used in large quantities industrially and is preferably carried out in two different reactors, which can be the same or different polymerization techniques. In particular, the first step can be carried out in a liquid phase reactor or a gas phase reactor, while the second step is usually carried out in the gas phase to avoid dissolution of the low crystallinity polymer in the liquid hydrocarbon.

[0004] It is known in the art that propylene homopolymerization is carried out in two or more stages to obtain products for manufacturing pipes or other uses, such as the Spherizone process can prepare impact-resistant polypropylene copolymers. There are also many patents disclosed for the production of polypropylene compositions by propylene polymerization in three or more stages, such as European Patent EP-A-2415831, Chinese Patent CN201910189051.6B and Patent WO2014 / 173532, etc. However, most of them stay in the sequential synthesis of propylene and ethylene or propylene and α-olefin copolymerization in different stages, and no disclosure of patents for the production of propylene block copolymers and propylene random copolymers in a single gas-phase liquid-holding reactor in one stage. It should be understood that the present invention is not a simple series combination between multiple polymerization zones, which is different from the multi-stage sequential polymerization method of the disclosed patent without causing a great improvement in product performance.

[0005] The impact-resistant propylene polymer compositions disclosed in the prior art have improved toughness, but the properties such as rigidity and toughness are not matched. Based on this consideration, the present invention has been studied to solve the problems exposed by the prior art in the relevant field, and to provide a high modulus, high impact / stress whitening resistance, high gloss, and low-cost polypropylene copolymer mixture. Summary of the invention

[0006] A method for preparing a polypropylene composition in the presence of a catalyst system, the method being characterized by comprising any combination of the following steps:

[0007] a. producing a polypropylene matrix in at least one polymerization zone (also referred to as the first polymerization zone in the present invention) in the presence of a catalyst system;

[0008] b. transferring the polypropylene matrix to a gas-phase liquid-holding reactor, wherein the gas-phase liquid-holding reactor comprises at least one gas-liquid-solid zone (the second polymerization zone) and one gas-solid zone (the third polymerization zone).

[0009] c. Producing block copolymers of propylene and comonomers in the gas-liquid-solid zone, producing ethylene and C3-C 10 The alpha-olefin random copolymer, the polymer particles quickly shuttle between the gas-liquid-solid zone and the gas-solid zone, and finally a polypropylene composition is obtained.

[0010] Although the present invention relates to a multi-zone polymerization process for producing a propylene polymer composition, it should be understood that the process may contain additional polymerization zones in addition to the three zones described above. As long as the polymer produced in the additional zones does not substantially affect the various properties of the polymer, the above process may include such additional polymerization zones. In addition, any of the multiple polymerization zones disclosed above may be performed as two or more zones, but the prerequisite is that the polymer produced by each such zone and its mixture are consistent with the polymer property description of the corresponding zones.

[0011] However, it is preferred to carry out each of the first, second and third polymerisation zones as a single polymerisation zone to prevent the process from becoming unnecessarily complex. Thus, in the most preferred embodiment, the process consists of three polymerisation zones, which may be followed by further polymerisation zones.

[0012] As known in the art, the propylene homopolymerization process in the first polymerization zone plays a role in breaking catalyst particles and releasing active centers. The polymerization site in the second polymerization zone is the active center exposed in the polypropylene matrix pores, and the second polymerization zone product has almost no breaking effect on the catalyst. The block copolymer produced in the second polymerization zone can be used as a compatibilizer for propylene homopolymer and the third polymerization zone random copolymer. The third polymerization zone will react on the original active center in the second polymerization zone, thereby forming a polypropylene composition with improved compatibility with the second polymerization zone product.

[0013] A continuously operating process refers to a process or a process stage into which raw materials are introduced continuously or intermittently, and from which products are removed continuously or intermittently. Continuous addition or removal refers to a continuous flow into or out of a process or process stage. Intermittent addition or removal refers to the uninterrupted addition of small batches of raw materials to a process or process stage, or the uninterrupted removal of products from a process or process stage, during the operation of the process.

[0014] According to the most preferred embodiment, the polymerization process of the present invention is carried out in a bulk polymerization-gas-liquid cloud polymerization (ie, polymerization in a gas-phase liquid-holding reactor) series process.

[0015] The polymerization process is carried out in the presence of an olefin polymerization catalyst. The catalyst system of the present invention comprises a solid catalyst component, an alkyl aluminum or an alkyl aluminoxane, and at least one external electron donor. The catalyst can be any catalyst capable of producing polypropylene and its copolymers. Suitable catalysts include chromium-based catalysts, Ziegler-Natta catalysts, metallocene catalysts, late transition metal catalysts or mixtures thereof. Among them, Ziegler-Natta catalysts are preferred because they have multiple active centers and a wide molecular weight distribution, which is what we expect to obtain.

[0016] Suitable Ziegler-Natta catalysts preferably contain a magnesium compound, an aluminum compound and a titanium compound, optionally supported on support particles.

[0017] The particle carrier can be an inorganic oxide carrier, such as silicon dioxide, aluminum oxide and silica gel. Preferably, the carrier is silicon dioxide. The average particle size of the silicon dioxide carrier can usually be 10 to 100 microns. Preferably, the average particle size is 6 to 30 microns, in which case the catalyst exhibits good catalytic performance.

[0018] The titanium compound is a halogen-containing titanium compound, preferably a chlorine-containing titanium compound. A particularly preferred titanium compound is titanium tetrachloride.

[0019] Ziegler-Natta catalysts are used together with cocatalysts, suitable cocatalysts being alkyl metal compounds, in particular alkyl aluminum compounds. These compounds include alkyl aluminum halides, such as ethyl aluminum dichloride, dimethyl aluminum chloride, and the like. They may also include trialkyl aluminum compounds, such as trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, and the like. Particularly preferred cocatalysts are trialkyl aluminums, of which triethyl aluminum and trimethyl aluminum are particularly commonly used.

[0020] In a preferred embodiment of the present invention, in the first polymerization zone, the catalyst system, the polymerization monomer and the hydrogen are contacted at a temperature of 0-80°C for a period of 0-120 minutes, the polymerization monomer comprises at least propylene, and in addition to propylene, may also comprise a comonomer selected from ethylene and C4-C 10 The first polymerization zone is used to produce propylene homopolymer or random copolymer.

[0021] In addition, there may be other areas for prepolymerization before the first polymerization area. The purpose of prepolymerization is to polymerize a small amount of polymer onto the catalyst at a low temperature and / or a low monomer concentration. By prepolymerization, the performance of the catalyst in the slurry or the performance of the final polymer can be improved. The prepolymerization can be carried out in a slurry or gas phase state. The prepolymerization temperature is generally 0 to 80°C, preferably 5 to 50°C, and more preferably 10 to 40°C. The pressure is generally 0.1-3.0MPa, preferably 0.1-1.5MPa. The prepolymerization time is generally 0 to 100min, preferably 0 to 60min.

[0022] As known to those skilled in the art, the catalyst particles recovered from the continuous prepolymerization reactor do not all contain the same amount of prepolymer. On the contrary, each particle has its own characteristic amount, which depends on the residence time of the particles in the prepolymerization reactor. Due to the difference in the residence time of the reaction mass in the reactor, the particles with different residence times have different prepolymer contents and some individual particles may contain the amount of prepolymer exceeding the above-mentioned restriction. However, the average amount of prepolymer on the catalyst is still within the scope of the above limitation.

[0023] As is known in the art, the molecular weight of the prepolymer can be adjusted by adding hydrogen, and antistatic additives can be used to prevent the particles from sticking to each other or to the reactor walls.

[0024] The temperature in the first polymerization zone is usually 0-90°C, preferably 60-90°C. The pressure is usually 0.2-3.6MPa, preferably 1.0-3.0MPa. The first polymerization zone can be carried out in a slurry, liquid phase or gas phase state. It is preferred to polymerize in a gas phase in a vertical stirred reactor. This is because the initial activity of the propylene polymerization catalyst is high, and there is a peak of activity and heat release in the early stage of the reaction; excessive temperature should be avoided to cause the polymer to stick to the wall and cause parking for cleaning. In the vertical stirred reactor, the liquid propylene sprayed from the bottom and the top is vaporized, so that the polymer powder forms a subfluidized state; the single-ribbon stirrer drives the powder to circulate on the wall and the center area. Therefore, the powder reaches an almost completely mixed state in the reactor, and the flow pattern is close to full mixed flow, so the catalyst is well dispersed, the bed temperature gradient is small, and it is not easy to generate hot spots. At the same time, the propylene gasification takes away a large amount of reaction heat, so that the reactor can meet the heat removal requirements without a jacket and internal components, effectively improving the space-time yield of a single reactor. Therefore, a vertical stirred reactor is preferably used as the first reactor of the process of the present invention.

[0025] After using this reactor, the catalyst particles will be fully dispersed in the bed and then completely wrapped by the propylene homopolymer generated by polymerization, which increases the mass transfer resistance between propylene and the active sites of the catalyst, which is conducive to the smooth release of the reaction activity. At the same time, the catalyst particles are in a low concentration state in the full mixed flow, which can avoid the explosion and hot spot caused by excessive local concentration.

[0026] Hydrogen is introduced into the first polymerization zone for controlling the melt index of the polypropylene. The amount of hydrogen required to achieve the desired melt index depends on the catalyst used and the polymerization conditions. The desired polymer properties have been obtained in gas phase polymerizations in vertical stirred reactors, wherein the hydrogen / propylene molar ratio is from 0 to 0.125, preferably from 0.02 to 0.10. The average residence time in the first polymerization zone is generally from 20 to 120 minutes, preferably from 30 to 80 minutes.

[0027] The second polymerization zone and the third polymerization zone are located in the gas-liquid-solid zone and the gas-solid zone of the gas-phase liquid-holding reactor, respectively. The second polymerization zone is located in the gas-liquid-solid zone of the gas-phase liquid-holding reactor, and a block copolymer of propylene and a comonomer is formed in the second polymerization zone, which includes the production of a block copolymer of propylene and a comonomer on a polypropylene matrix. This is achieved by introducing a polypropylene matrix containing an active catalyst dispersed therein and additional ethylene or a second α-olefin comonomer into the second polymerization zone. Hydrogen can be introduced at the same time to control the molecular weight. It is worth noting that when the material enters the second polymerization zone from the first polymerization zone, the catalyst particles have been completely wrapped by the homopolymer, and the activity release is more stable. At this time, the copolymerization reaction also tends to be mild, and it is not easy to have local hot spots, temperature fluctuations, melting agglomeration and other faults, which is conducive to the stable operation of the device.

[0028] The gas-phase liquid-holding reactor comprises at least one gas-solid zone (third polymerization zone) and one gas-liquid-solid zone (second polymerization zone), wherein the gas-liquid-solid zone is created by spraying a condensing medium with at least one feed into the side wall or bottom of the reactor; polymer particles shuttle and react in the two types of zones to produce ethylene and C3-C 10 α-olefin random copolymers and block copolymers of propylene and comonomers having long blocks.

[0029] The condensing medium in the gas-liquid-solid zone is selected from one or more of propane, n-butane, isobutane, n-pentane, isopentane, cyclohexane, n-hexane or n-heptane; the molar percentage of the condensing medium in the gas phase component (usually called circulating gas) in the reactor is 3.2-8.0 mol%.

[0030] The second polymerization zone, i.e., the gas-liquid-solid zone of the gas phase liquid-holding reactor, operates at a reaction temperature in the range of 50 to 95° C., preferably 55 to 85° C. The pressure is usually 0.2 to 4.0 MPa, preferably 0.5 to 3.6 MPa. The average residence time in the second polymerization zone is usually 20 to 120 minutes, preferably 30 to 80 minutes.

[0031] The second copolymer mixture produced in the second zone typically comprises 30 to 85% by weight of the polypropylene matrix and 10 to 40% by weight of the second zone copolymer.

[0032] In order to produce high value-added polypropylene products with balanced rigidity, toughness and lightness, the method of the present invention produces propylene homopolymer, block copolymer and ethylene and C3-C 10 Alpha-olefin copolymers.

[0033] The second copolymer mixture obtained in the second polymerization zone is separated and enters the third polymerization zone. In the presence of the propylene block copolymer produced in the second polymerization zone, ethylene and C3-C10 Production of α-olefin copolymers. As is known in the art, the propylene homopolymerization process in the first zone plays a role in breaking up the catalyst particles and releasing the active centers. However, the polymerization site in the second zone is the active center exposed in the pores of the polypropylene matrix, and the block polymer in the second polymerization zone has almost no effect on breaking up the catalyst. The third polymerization zone will react on the original active center in the second polymerization zone, thereby forming a core-shell structure with the product of the second zone or playing a "synergistic role" in toughening polypropylene.

[0034] The third polymerization zone preferably uses the gas-solid zone of the gas phase liquid-holding reactor, and preferably has an ethylene / α-olefin comonomer concentration that is significantly different from the concentration atmosphere in the second polymerization zone. The ratio of ethylene to comonomer content depends on the type of comonomer and the type of catalyst. Hydrogen can also be added to adjust the molecular weight and melt index, and the amount of hydrogen added is adjusted according to product requirements. The ethylene generated in the third zone is mixed with C3-C 10 The α-olefin copolymer, due to the presence of the block copolymer produced in the second polymerization zone, will greatly improve the compatibility between the phases. The third polymerization zone uses the gas-solid zone of the gas-phase liquid-holding reactor. By changing the type and content of the comonomer in the gas-solid zone, the gloss of the product can also be regulated.

[0035] Extrusion

[0036] When the polymer product is removed from the polymerization reactor, it is necessary to remove the residual hydrocarbons. Such a process is well known in the art and may include a decompression step, a purification step, a desorption step, an extraction step, etc. It is also possible to combine different steps with each other.

[0037] According to a preferred procedure, part of the hydrocarbons in the polymer particles or powder are removed by decompression, and then the particles are contacted with steam at a temperature of 90-110° C. for a period of 10 minutes to 3 hours. Thereafter, the particles are purged with an inert gas (such as nitrogen) at a temperature of 20-90° C. for 5-60 minutes.

[0038] As is known in the art, after the residual hydrocarbons are removed, the polymer is preferably mixed with additives. Such additives include antioxidants, process stabilizers, neutralizers, lubricants, nucleating agents, etc. As is known in the art, the polymer particles are mixed with the additives and extruded into pellets, preferably using a counter-rotating twin-screw extruder for the extrusion step.

[0039] In addition, the polypropylene composition can be blended with other polymers known in the art to improve certain product properties. Such polymers include LDPE made by free radical polymerization in a high pressure process, other linear low density polyethylene, high density polyethylene, polystyrene, etc.

[0040] The copolymer particles obtained by the invention have good morphology, are not easy to adhere to the kettle wall, and are suitable for preparing pipes, automobile bumpers and interior decoration parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The present invention is a schematic flow diagram of a method for producing a polypropylene composition in one embodiment of the present invention;

[0042] In the figure, 1-homopolymerization reactor, 2-fluidized bed reactor, 3-gas phase polymerization zone, 4-gas-liquid cloud polymerization zone, 5-heat exchanger, 6-discharge pipe. DETAILED DESCRIPTION

[0043] 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 reactor type 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 the same.

[0044] Example 1

[0045] exist Figure 1A method for preparing a polypropylene composition is shown to produce a polypropylene composition. Propylene, catalyst, triethylaluminum, external electron donor and hydrogen are added to the first polymerization zone 1 (i.e., the first reactor, a vertical stirring reactor is used in this embodiment) to react. The temperature of the first reactor is controlled to 75.3°C, and the reactor pressure is controlled to about 3.0MPaG by adjusting the fresh propylene feed amount. The hydrogen / propylene molar ratio in the reactor is 0.08mol / mol, and the propylene concentration is 85mol%. The first reactor intermittently sends the polymer powder to the settler through the switch valve on the discharge plug bottom pipe. After settling, the polymer powder is sent to the air lock, and after the air lock is pressurized with the circulating gas of the second reaction system, the powder is pressed to the second reactor. The second reactor is a gas-phase liquid-holding reactor, having a typical gas-liquid-solid zone 2 and a gas-solid zone 3, wherein the gas-liquid-solid is created by spraying an inert refrigerant into the side wall of the reactor, and in this embodiment, the inert refrigerant is preferably n-hexane. Propylene, ethylene and hydrogen from the raw material refining unit are fed into the second reactor, 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 / propylene molar ratio is 0.21mol / mol, and the propylene concentration is 71mol%. The n-hexane concentration in the gas-liquid-solid zone 2 is about 6.9mol%, and ethylene-propylene block copolymers are mainly generated in this reaction zone. The third reaction zone 3, i.e., the gas-solid zone, has a reaction temperature of about 80°C, and no liquid n-hexane exists in this reaction zone. The ethylene / propylene molar ratio in the polymer is much higher than the polymerization atmosphere in the polymerization particles in the gas-liquid-solid zone, and ethylene-propylene random copolymers are mainly generated in this gas-solid zone. Since the polymer particles shuttle back and forth between the gas-liquid-solid zone and the gas-solid zone in the reactor, the components in the polymer particles can achieve uniform mixing at the molecular chain level.

[0046] The melt index I of the obtained polypropylene composition is 2.16 The yield strength is 9.0g / 10min, the tensile yield strength is 23Mpa, the flexural modulus is 0.95Gpa, the cantilever beam impact strength is 75J / m, the heat deformation temperature is 88℃, the Rockwell hardness is 75R, and the gloss is 68Gu. It can be used as a rigid-tough-light-impact balanced copolymer grade for use in household appliances and automobile bumpers.

[0047] Example 2

[0048] exist Figure 1A method for preparing a polypropylene composition is shown to produce a polypropylene composition. Propylene, catalyst, triethylaluminum, external electron donor and hydrogen are added to the first reaction zone 1 (i.e., the first reactor, a vertical stirring reactor is used in this embodiment) to react. The temperature of the first reactor is controlled to 76°C, and the reactor pressure is controlled to about 3.0MPaG by adjusting the fresh propylene feed amount. The hydrogen / propylene molar ratio in the reactor is 0.10mol / mol, and the propylene concentration is 85mol%. The first reactor intermittently sends the polymer powder to the settler through the switch valve on the discharge plug bottom pipe. After settling, the polymer powder is sent to the air lock, and after the air lock is pressurized with the circulating gas of the second reaction system, the powder is pressed to the second reactor. The second reactor is a gas-phase liquid-holding reactor, having a typical gas-liquid-solid zone 2 and a gas-solid zone 3, wherein the gas-liquid-solid is created by spraying an inert refrigerant into the side wall of the reactor, and in this embodiment, the inert refrigerant is preferably n-hexane. Propylene, ethylene and hydrogen from the raw material refining unit are fed into the reactor, 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 0.03mol / mol, the ethylene / propylene molar ratio is 0.18mol / mol, and the propylene concentration is 79mol%. The n-hexane concentration in the gas-liquid-solid zone 2 is about 3.2mol%, and ethylene-propylene block copolymers are mainly produced in this reaction zone. The third reaction zone 3, i.e., the gas-solid zone, has a reaction temperature of about 84.3°C, and no liquid n-hexane exists in this reaction zone. The ethylene / propylene molar ratio in the polymer is much higher than the polymerization atmosphere in the polymerization particles in the gas-liquid-solid zone, and ethylene-propylene random copolymers are mainly produced in this gas-solid zone. Since the polymer particles shuttle back and forth between the gas-liquid-solid zone and the gas-solid zone in the reactor, the components in the polymer particles can achieve uniform mixing at the molecular chain level.

[0049] The melt index I of the obtained polypropylene composition is 2.16 The tensile yield strength is 30.0g / 10min, the flexural modulus is 1.1Gpa, the cantilever beam impact strength is 68J / m, the heat deformation temperature is 90℃, the Rockwell hardness is 75R, and the glossiness is 65Gu. It can be used as a general injection molding polymer grade.

[0050] Example 3

[0051] exist Figure 1A method for preparing a polypropylene composition is shown to produce a polypropylene composition. Propylene, catalyst, triethylaluminum, external electron donor and hydrogen are added to the first reaction zone 1 (i.e., the first reactor, a vertical stirring reactor is used in this embodiment) to react. The temperature of the first reactor is controlled to 75.1°C, and the reactor pressure is controlled to about 3.0MPaG by adjusting the fresh propylene feed amount. The hydrogen / propylene molar ratio in the reactor is 0.06mol / mol, and the propylene concentration is 87mol%. The first reactor intermittently sends the polymer powder to the settler through the switch valve on the discharge plug bottom pipe. After settling, the polymer powder is sent to the air lock, and after the air lock is pressurized with the circulating gas of the second reaction system, the powder is pressed to the second reactor. The second reactor is a gas-phase liquid-holding reactor, having a typical gas-liquid-solid zone 2 and a gas-solid zone 3, wherein the gas-liquid-solid is created by spraying an inert refrigerant into the side wall of the reactor, and in this embodiment, the inert refrigerant is preferably n-hexane. Propylene, ethylene and hydrogen from the raw material refining unit are fed into the reactor, 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 / propylene molar ratio is 0.24mol / mol, and the propylene concentration is 65mol%. The n-hexane concentration in the gas-liquid-solid zone 2 is about 7.9mol%, and ethylene-propylene block copolymers are mainly produced in this reaction zone. The third reaction zone 3, i.e., the gas-solid zone, has a reaction temperature of about 79.1°C, and no liquid n-hexane exists in this reaction zone. The ethylene / propylene molar ratio in the polymer is much higher than the polymerization atmosphere in the polymerization particles in the gas-liquid-solid zone, and ethylene-propylene random copolymers are mainly produced in this gas-solid zone. Since the polymer particles shuttle back and forth between the gas-liquid-solid zone and the gas-solid zone in the reactor, the components in the polymer particles can achieve uniform mixing at the molecular chain level.

[0052] The melt index I of the obtained polypropylene composition is 2.16 The tensile yield strength is 2.5g / 10min, the flexural modulus is 1.3Gpa, the cantilever beam impact strength is 64J / m, the heat deformation temperature is 92℃, the Rockwell hardness is 76R, and the glossiness is 72Gu. It can be used as a general injection molding polymer grade and applied in the field of automotive parts.

[0053] The above are only preferred embodiments of the present invention. It can be seen that a balance of comprehensive properties such as rigidity, toughness, glossiness, etc. has been achieved compared with the comparative examples, but it is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes.

[0054] Comparative Examples 1-2

[0055] Comparative Example 1

[0056] exist Figure 1A method for preparing a polypropylene composition is shown to produce a polypropylene composition. Propylene, catalyst, triethylaluminum, external electron donor and hydrogen are added to the first reaction zone 1 (i.e., the first reactor, in this case, a vertical stirring reactor is used) to react. The temperature of the first reactor is controlled to 75°C, and the reactor pressure is controlled to about 3.0MPaG by adjusting the fresh propylene feed amount. The hydrogen / propylene molar ratio in the reactor is 0.03mol / mol, and the propylene concentration is 81mol%. The first reactor intermittently sends polymer powder to the settler through the switch valve on the discharge bottom pipe. After settling, the polymer powder is sent to the air lock, and after the air lock is pressurized with the circulating gas of the second reaction system, the powder is pressed to the second reactor. Propylene, ethylene and hydrogen from the raw material refining unit are sent to the reactor, the temperature is controlled to 75°C, and the reactor pressure is controlled to about 2.3MPaG. The hydrogen / propylene molar ratio in the reactor is 0.015mol / mol, the ethylene / propylene molar ratio is 0.24mol / mol, and the propylene concentration is 77mol%. In the comparative example, since no condensing medium n-hexane was added, only a gas-solid zone existed in the second reactor, which was the same as or similar to a conventional gas phase reactor.

[0057] The melt index I of the obtained polypropylene composition is 2.16 The tensile yield strength is 0.5g / 10min, the flexural modulus is 1.3Gpa, the cantilever beam impact strength is 46J / m, the heat deformation temperature is 89℃, the Rockwell hardness is 76R, and the glossiness is 54Gu. It can be used as a pipe (it is not tough enough to meet the requirements of thin-wall injection molding and cannot be used as a general injection molding polymer grade) and is used in the field of pipes.

[0058] Comparative Example 2

[0059] exist Figure 1A method for preparing a polypropylene composition is shown to produce a polypropylene composition. Propylene, catalyst, triethylaluminum, external electron donor and hydrogen are added to the first reaction zone 1 (i.e., the first reactor, in this case, a vertical stirring reactor is used) to react. The temperature of the first reactor is controlled to 75°C, and the reactor pressure is controlled to about 2.5MPaG by adjusting the fresh propylene feed amount. The hydrogen / propylene molar ratio in the reactor is 0.02mol / mol, the ethylene / propylene molar ratio is 0.02mol / mol, and the propylene concentration is 85mol%. The first reactor intermittently sends the polymer powder to the settler through the switch valve on the unloading bottom pipe. After settling, the polymer powder is sent to the air lock, and after the air lock is pressurized with the circulating gas of the second reaction system, the powder is pressed to the second reactor. Propylene, ethylene and hydrogen from the raw material refining unit are sent to the reactor, the temperature is controlled to 72°C, and the reactor pressure is controlled to about 2.3MPaG. The hydrogen / propylene molar ratio in the reactor is 0.03 mol / mol, the ethylene / propylene molar ratio is 0.18 mol / mol, and the propylene concentration is 81 mol%. In the comparative example, since no condensing medium n-hexane is added, only a gas-solid zone exists in the second reactor, which is the same or similar to a conventional gas phase reactor.

[0060] The melt index I of the obtained polypropylene composition is 2.16 The tensile yield strength is 2.0g / 10min, the bending modulus is 19Mpa, the cantilever beam impact strength is 48.3J / m, the heat deformation temperature is 86℃, the Rockwell hardness is 76R, and the glossiness is 48Gu. It can be used as a pipe in the field of pipes.

[0061] 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 polypropylene composition in the presence of a catalyst system, characterized in that The following steps are involved: a. In the presence of a catalyst system, in at least one polymerization zone for the production of a polypropylene matrix; said polypropylene matrix is ​​a propylene homopolymer; b. transferring the polypropylene matrix to a gas-phase liquid-supported reactor, wherein the gas-phase liquid-supported reactor comprises at least one gas-liquid-solid zone and one gas-solid zone; wherein the gas-liquid-solid zone is formed by spraying a condensing medium into the side wall or the bottom of the reactor with at least one feed; and the condensing medium in the gas-liquid-solid zone is selected from one or more of propane, n-butane, isobutane, n-pentane, isopentane, cyclohexane, n-hexane or n-heptane; c. In the gas-liquid-solid zone, propylene and comonomer block copolymers are produced, and ethylene and C3-C are produced in the gas-solid zone. 10 The alpha-olefin random copolymer, the polymer particles quickly shuttle between the gas-liquid-solid zone and the gas-solid zone, and finally a polypropylene composition is obtained.

2. 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.

3. The method according to claim 1, characterized in that The molar percentage of the condensing medium to the gas phase components in the reactor is 3.2-8.0 mol%.

4. The method according to claim 1, characterized in that The comonomer is selected from ethylene and C4-C 10 α-Olefins.

5. The method according to claim 1, characterized in that In the gas-solid reaction zone of step c, C3-C 10 The molar ratio of the α-olefin comonomer to ethylene is 0 to 0.

95.

6. The method according to claim 1, characterized in that: The operating temperature of the polypropylene matrix production stage is 0~90 o C, pressure is 0.2-3.6 MPa, hydrogen to propylene molar ratio is 0-0.125; propylene and comonomer block copolymer production area operating temperature is 50-95 o C, pressure is 0.5-3.6 MPa; ethylene and C3-C 10 The operating temperature of the α-olefin random copolymer production area is 60~95℃ and the pressure is 0.2-4.0 MPa.

7. A polypropylene composition prepared by the method according to any one of claims 1 to 6, characterized in that The polypropylene composition at least comprises a polypropylene matrix, a block copolymer composed of polymer blocks with vinyl alkane monomer units as the main body, and ethylene and C4-C 10 Alpha-olefin copolymers.

8. The polypropylene composition according to claim 7, characterized in that The vinyl alkane monomer unit is ethylene, propylene, butene, hexene or octene.

Images