CN112745440A - Impact-resistant polypropylene and preparation method thereof - Google Patents
Impact-resistant polypropylene and preparation method thereof Download PDFInfo
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Abstract
The invention relates to the field of propylene polymerization, and discloses impact-resistant polypropylene and a preparation method thereof. The process for preparing impact polypropylene comprises: (1) prepolymerizing propylene in the presence of a catalyst system; (2) then, the material after the prepolymerization reaction, hydrogen and propylene are contacted for homopolymerization reaction to obtain polymer powder; (3) introducing polymer powder and liquid-phase propylene into a gas-solid separator provided with a gas-phase outlet, wherein the liquid-phase propylene is vaporized in the gas-solid separator so as to carry and discharge light components from the gas-phase outlet of the gas-solid separator; (4) and (4) carrying out copolymerization reaction of propylene and alpha-olefin on the basis of removing the polymer powder carrying the light components in the step (3) to obtain the impact-resistant polypropylene powder. The invention also discloses impact polypropylene prepared by the method. The method of the invention can obtain the polymer product with high impact strength by effectively reducing the light components carried by the polymer powder at the upstream to enter the downstream reaction.
Description
Technical Field
The invention relates to the field of propylene polymerization, in particular to impact-resistant polypropylene and a preparation method thereof.
Background
The polypropylene is mainly classified into homo-polypropylene, random polypropylene and impact polypropylene, and the homo-polypropylene has poor impact resistance due to the characteristics of molecular structures. The impact-resistant polypropylene has good rigidity-toughness balance due to the rigidity of the homopolymerized polypropylene and the impact resistance of the ethylene propylene rubber component, and is widely applied to the fields of automobiles, household appliances, injection molding containers and the like.
The current polypropylene industry has two major categories of methods for improving the impact resistance of polypropylene. The first type is a blending modification method, in which polypropylene and an elastomer are physically blended to obtain a polypropylene product with good impact resistance, and common elastomers include ethylene propylene diene monomer (EPR), Ethylene Propylene Diene Monomer (EPDM), polyolefin elastomer (POE), powdered rubber and the like. The second way is a multistage reactor preparation method, generally, propylene homopolymerization is carried out in a first-stage reactor(s) to obtain a propylene polymer, then polymer powder is conveyed to a second-stage reactor to carry out copolymerization of propylene and alpha-olefin, and a propylene-alpha-olefin rubber phase is generated in pores of particles of the homopolymerized propylene polymer, thereby realizing the respective formation of a polypropylene matrix phase and a rubber phase. The second way is also the currently mainstream way of preparing impact polypropylene.
The preparation of impact-resistant polypropylene by adopting a multistage reactor usually enters a subsequent reactor along with the entrained gas of polymer powder obtained by a previous stage reactor, and the entrained gas (light component, mainly hydrogen) of the polypropylene powder participates in the subsequent polymerization reaction, so that the molecular weight of the polymer obtained in a gas-phase copolymerization stage is smaller, and the final impact resistance of the polymer is influenced. Therefore, the research on the method for removing the entrained gas in the polymer powder is of great significance.
Disclosure of Invention
The object of the present invention is to overcome the problems of the prior art and to provide a new impact polypropylene and a method for preparing the same.
In order to achieve the above object, the present invention provides, in one aspect, a method for preparing impact polypropylene, the method comprising:
(1) subjecting propylene to a prepolymerization reaction in the presence of a catalyst system comprising a catalyst, a cocatalyst and optionally an external electron donor;
(2) then, the material after the prepolymerization reaction, hydrogen and propylene are contacted for homopolymerization reaction to obtain polymer powder;
(3) introducing polymer powder and liquid-phase propylene into a gas-solid separator provided with a gas-phase outlet, wherein the liquid-phase propylene is vaporized in the gas-solid separator so as to carry and discharge light components from the gas-phase outlet of the gas-solid separator;
(4) and (3) carrying out copolymerization reaction of propylene and alpha-olefin on the basis of removing the polymer powder carrying light components in the step (3) to obtain the impact-resistant polypropylene powder, wherein the alpha-olefin is ethylene and/or alpha-olefin with 4-10 carbon atoms.
In a second aspect, the present invention provides an impact polypropylene produced by the process as described above.
Through the technical scheme, the method provided by the invention effectively reduces the influence of light components (including hydrogen and ethylene) carried by upstream polymer powder on the control of downstream reaction composition by effectively reducing the light components carried by the upstream polymer powder to enter the downstream reaction, thereby being beneficial to improving the performance of a polymer product and being capable of obtaining the polymer product with high impact strength. The invention has low requirement on equipment, and particularly can realize the removal of the entrained light components without additionally introducing equipment in the loop polypropylene production process of liquid-phase bulk polymerization and gas-phase polymerization.
Drawings
For the purpose of illustrating the invention more clearly, the drawings are illustrative of particular embodiments of the invention and are not to be construed as limiting the invention.
FIG. 1 is a schematic flow diagram according to one embodiment of the present invention.
Description of the reference numerals
1 Pre-complexing reactor
2 prepolymerization reactor
3 first stage polymerization reactor
4 gas-solid separator
5 second stage polymerization reactor
100 feed inlet of first stage polymerization reactor
101 discharge port of first-stage polymerization reactor
102 liquid phase propylene inlet
Gas phase outlet of 103 gas-solid separator
104 gas-solid separator
105 discharge port of second stage polymerization reactor
106 gas phase outlet of the second stage polymerization reactor
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
In the present invention, the term "removal" is used, without going to the contrary, to mean a reduction of the content of entrained light components by at least 80%; the unit "ppmV" refers to parts per million by volume.
The invention provides a method for preparing impact-resistant polypropylene, which is characterized by comprising the following steps:
(1) propylene is subjected to a prepolymerization reaction in the presence of a catalyst system comprising a (main) catalyst, a cocatalyst and optionally an external electron donor;
(2) then, the material after the prepolymerization reaction, hydrogen and propylene are contacted for homopolymerization reaction to obtain polymer powder;
(3) introducing polymer powder and liquid-phase propylene into a gas-solid separator provided with a gas-phase outlet, wherein the liquid-phase propylene is vaporized in the gas-solid separator so as to carry and discharge light components from the gas-phase outlet of the gas-solid separator;
(4) and (3) carrying out copolymerization reaction of propylene and alpha-olefin on the basis of removing the polymer powder carrying light components in the step (3) to obtain the impact-resistant polypropylene powder, wherein the alpha-olefin is ethylene and/or alpha-olefin with 4-10 carbon atoms.
According to the present invention, in the step (1), there is no particular requirement for the prepolymerization, and the conditions for the prepolymerization may include: the temperature is from-10 ℃ to 50 ℃, preferably from 0 ℃ to 40 ℃, more preferably from 5 ℃ to 20 ℃. The prepolymerization conditions may further comprise: the pressure is 1 to 8MPa, preferably 1.2 to 5.5MPa, more preferably 3 to 4.5 MPa. The prepolymerization conditions may further comprise: the prepolymerization ratio is 0.5 to 1000 times, preferably 5 to 500 times, more preferably 20 to 300 times, particularly 100 to 150 times. The "multiple prepolymerization" means the weight ratio of the polymer produced to the catalyst in the prepolymerization stage.
According to the present invention, in step (1), the weight ratio of the catalyst to the propylene is 1 (500-.
According to the present invention, in the step (1), the catalyst is not particularly limited, and may be any of various existing catalysts suitable for preparing propylene polymers, including single site catalysts such as Ziegler-Natta catalysts or metallocenes.
According to the present invention, in step (1), the prepolymerization reaction can be carried out in the presence of a cocatalyst such as organoaluminum and optionally an external electron donor. According to the method of the present invention, the catalyst, the cocatalyst and the optional external electron donor may or may not be subjected to a pre-complexation reaction before the prepolymerization reaction. The selection of the conditions for the pre-complexation reaction is within the ability of one skilled in the art and will not be described further herein.
Wherein, the cocatalyst is generally an organic aluminum, the organic aluminum is not limited to a certain organic aluminum commonly used in the polyolefin industry at present, and is preferably at least one selected from trialkyl aluminum (such as trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, tri-n-butyl aluminum, trihexyl aluminum, trioctyl aluminum, etc.), diethyl aluminum monochloride, diisobutyl aluminum monochloride, monoethyl aluminum dichloride and ethyl aluminum dichloride. The external electron donor is a substance to be selectively used, and generally, when a Ziegler-Natta catalyst is used, the external electron donor is required to be used, and when a single-site catalyst such as metallocene is used, the external electron donor may not be used. The external electron donor is preferably an organosilicon compound with a general formula of RnSi(OR')4-nWherein n is more than 0 and less than or equal to 3, R is selected from hydrogen atom, halogen, alkyl, cycloalkyl, aryl and halogenated alkyl, and R' is selected from alkyl, cycloalkyl, aryl and halogenated alkyl. Specifically, the method may include but is not limited to: diisopropyldimethoxysilane, cyclohexylmethyldimethoxysilane, tetramethoxysilane, tetraethoxysilane, trimethylmethoxysilane, trimethylethoxysilane, trimethylphenoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, methyl-tert-butyldimethoxysilane, methylisopropyldimethoxysilane, diphenoxydimethoxysilane, diphenyldiethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, vinyltrimethoxysilane, (1,1, 1-trifluoro-2-propyl) -2-ethylpiperidinyldimethoxysilane, and (1,1, 1-trifluoro-2-propyl) -methyldimethoxysilane, and the like. The amount of the catalyst, the cocatalyst and the external electron donor can be determined according to the requirement, and preferably, the weight ratio of the cocatalyst to the catalyst is 1:4-50:1, more preferably 2:1-20:1. The weight ratio of the cocatalyst to the external electron donor can be 0.1:1-150:1, preferably 2:1-150: 1.
According to the present invention, in the step (2), there is no particular requirement on the conditions of the homopolymerization, and the conditions of the homopolymerization may include: the temperature is 30 to 150 ℃, preferably 50 to 100 ℃. The conditions for the homopolymerization reaction may further include: the pressure is 1-8MPa, preferably 1.2-5.5 MPa. The conditions for the homopolymerization reaction may further include: the time is 10-180min, preferably 20-120 min.
According to the invention, in step (2), the weight ratio of the material after the prepolymerization, hydrogen and propylene may be (0.02-1): 9.5X 10-6-1.4×10-3) 1, preferably (0.05-0.6): (9.5X 10)-6-5×10-4):1. The amount of propylene used here is only the amount of propylene additionally introduced in step (2), and does not include the amount of propylene inevitably introduced from the preceding step.
According to the present invention, step (2) is preferably carried out in a loop reactor.
In the present invention, the polymer powder in the step (3) inevitably carries entrained light components. The entrained lights are typically materials having a boiling point lower than that of propylene, and may be hydrogen, and may also be nitrogen, methane, ethane, ethylene, etc., if present. The inventor of the invention also finds that the propylene has certain removal effect on heavy components such as 1-butene and the like carried in polymer powder along with the increase of the amount of the propylene in the external liquid phase. In the step (3), the liquid-phase propylene is additionally introduced (added) with the liquid-phase propylene, rather than the liquid-phase propylene entrained in the polymer powder or the liquid-phase propylene from the upstream process.
In the present invention, the content of the entrained volatilizable component in the polymer powder entering the gas-solid separator is usually 500-50000ppm by weight, and the content of the light component (i.e., entrained light component, mainly hydrogen) in the volatilizable component is 1000-50000ppmV, preferably 2000-10000 ppmV. The method of the invention is suitable for removing light components carried in polymer powder with various shapes, including particle shape, spherical shape or sphere-like shape.
According to a preferred embodiment of the present invention, in order to more effectively achieve the removal of the entrained light components in the polymer powder, the residence time of the polymer powder in the gas-solid separator is 0.5 to 20min, more preferably 2 to 10min, still more preferably 5 to 10min, such as 5min, 8min, 9min, 10min or any value therebetween.
In order to more effectively achieve separation of entrained volatile components and propylene from solids after vaporization, the gas-solid separator is preferably a device (e.g., a fluidized bed device) provided with an expansion section at the upper part, which can be designed by calculation methods known in the art, wherein the expansion section is a region free of solid materials, and the ratio of the maximum cross-sectional diameter of the expansion section to the holding section (i.e., the stripping section mentioned below) is generally 1.5-3 (e.g., 1.5, 1.8, 1.9, 2, 2.1, 2.2, 2.5, 3 or any value therebetween), and the height is also set to meet the requirements of solid settlement and avoiding stacking along the wall. Furthermore, the gas-solid separator may be a cyclone separator. The lower part of the gas-solid separator is a stripping section, namely a region where solid materials exist. Maintaining a certain material level of the polypropylene powder in the stripping section, adding the added liquid-phase propylene into a polypropylene powder bed layer below the bubble point temperature, vaporizing under the action of polymerization reaction heat, and stripping out light components carried in the polymer powder. The residence time of the polymer powder in the stripping section is from 0.5 to 20min, preferably from 2 to 10 min.
According to the invention, the liquid phase propylene is preferably added in a proportion to the polymer powder, the weight ratio of liquid phase propylene to polymer powder being 0.05-1, more preferably 0.1-0.5, even more preferably 0.2-0.5, such as 0.2, 0.3, 0.4, 0.5 or any value between the above values.
According to the invention, in order to realize the uniform distribution of the liquid-phase propylene in the solid-phase polymer powder, the structures of a spray head, a dispersion pipe, a distribution disc and the like which are common in the field can be adopted. When the scheme of the gas-solid separator with the expansion section arranged at the upper part is adopted, the upper part can be also configured into a power separator, a filter and the like which are increased by realizing good gas-solid separation effect.
According to a preferred embodiment of the invention, the temperature in the gas-solid separator is between 50 ℃ and 100 ℃, more preferably between 60 ℃ and 80 ℃ (such as 60 ℃, 62 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃ or any value in between). The temperature is the temperature in the zone in which the polymer powder is located, for example the stripping section.
According to a preferred embodiment of the invention, the pressure in the gas-solid separator may be controlled between the pressure in the reactor upstream of the gas-solid separator and the pressure in the equipment downstream of the gas-solid separator, so that the material may be transported and transferred by means of a pressure difference, which may be in the range of 0.1-3MPa, preferably the pressure in the gas-solid separator is in the range of 1-2.5MPa, more preferably 1.5-2MPa (such as 1.5MPa, 1.6MPa, 1.7MPa, 1.8MPa, 1.9MPa, 2MPa or any value in between the above mentioned values).
According to the present invention, in the step (4), there is no particular requirement for the conditions of the copolymerization reaction, which may include: the temperature is 50 to 150 ℃ and preferably 60 to 95 ℃. The copolymerization conditions may further include: the pressure is 0.5-4MPa, preferably 1.2-3.5 MPa. The copolymerization conditions may further include: the time is 10-180min, preferably 20-90 min.
According to a preferred embodiment of the present invention, in the step (4), the α -olefin is used in an amount such that the volume of the α -olefin is 5 to 70% based on the total volume of the α -olefin and propylene in the copolymerization reaction system.
According to the present invention, in the step (4), the α -olefin may be any conventional olefin capable of being polymerized with propylene, for example, the α -olefin is ethylene and/or an α -olefin having 4 to 10 carbon atoms, and is preferably at least one of ethylene, 1-butene, 1-pentene, 1-hexene, 4-methylisoalene, 1-octene and 1-decene.
According to the present invention, step (4) is preferably carried out in a gas phase reactor.
The invention also provides impact polypropylene prepared by the method. The present invention achieves an impact polypropylene product with improved properties by reducing the amount of light components (including hydrogen) entrained with the upstream polymer powder entering downstream reactions during the manufacturing process.
The present invention will be described in detail below by way of examples. In the following examples:
the double-screw extruder is a GLS-30B plastic granulator of Suzhou Congrale rubber and plastic machinery Limited company;
the method for detecting hydrogen is online chromatography, and TGC-2000 type online chromatograph of ABB company is adopted;
ethylene content in the impact polypropylene product: measuring the ethylene content by using a ThermoNicolet200 type infrared analyzer;
rubber phase content
1-homopolymeric polymers
Wherein the content of the first and second substances,
weight of homopolypropylene/weight of total polypropylene product x 100%;
izod impact strength: measured according to the method described in GB/T1843-2008;
melt mass flow rate (melt index, MFR): measured according to the method described in GB/T3682-2000, using a melt index apparatus model 7026 from CEAST, at 230 ℃ under a load of 2.16 kg; melt Flow Rate (MFR) of rubber phase Polymer2By
Is calculated to obtain wherein
MFR1、
MFR2MFR is the homopolymeric specific gravity, the homopolymeric melt index, the rubber phase polymeric specific gravity, the rubber phase polymeric melt index, the final polymeric melt index, respectively.
The following examples were carried out on a 25kg/h loop polypropylene pilot plant, as shown in FIG. 1, comprising:
the pre-complexing reactor 1 is used for pre-complexing,
the pre-polymerization reactor (2) is provided with a pre-polymerization reactor,
a first-stage polymerization reactor 3 (loop reactor) provided with a first-stage polymerization reactor inlet 100 and a first-stage polymerization reactor outlet 101;
the gas-solid separator 4 comprises an expansion section arranged at the upper part and a stripping section arranged at the lower part, the ratio of the maximum cross section diameter of the expansion section to the maximum cross section diameter of the stripping section is 2, the expansion section is provided with a feed inlet of the gas-solid separator and a gas phase outlet 103 of the gas-solid separator, and the stripping section is provided with a liquid phase propylene inlet 102 and a material outlet 104 of the gas-solid separator;
a second-stage polymerization reactor 5 (gas-phase reactor) provided with a feed port of the second-stage polymerization reactor, a discharge port 105 of the second-stage polymerization reactor, and a gas-phase outlet 106 of the second-stage polymerization reactor;
wherein the discharge port 101 of the first-stage polymerization reactor is connected to the feed port of a gas-solid separator, the material outlet 104 of the gas-solid separator is connected to the feed port of the second-stage polymerization reactor, and the second-stage polymerization reactor 5 is further provided with a circulation line for circulating the gas discharged from the gas-phase outlet 106 of the second-stage polymerization reactor in the second-stage polymerization reactor.
Example 1
(1) Pre-complexation and pre-polymerization
The flow rate of the main catalyst (DQC401 catalyst, Beijing Ondah company of China petrochemical catalyst division) is 0.8g/h, the flow rate of the cocatalyst (triethylaluminum, TEA) is 6.33g/h, the flow rate of the external electron donor (diisopropyldimethoxysilane, DIPDMS) is 0.8g/h, and the pre-complexing reaction is carried out in a pre-complexing reactor 1 at 6 ℃ for 8 min.
Continuously adding the catalyst system after pre-complexing into a continuous stirred tank type prepolymerization reactor 2, and carrying out prepolymerization reaction in a propylene liquid-phase body environment, wherein the dosage of propylene is such that the weight ratio of a main catalyst (DQC401 catalyst) to propylene is 5.33 multiplied by 10-5:1, the temperature is 12 ℃, the pressure is 4MPa, the reaction residence time is about 10min, and the prepolymerization multiple of the catalyst under the condition is about 120 times.
(2) Homopolymerization of propylene
Continuously introducing the prepolymerized material (15kg/H) into the first-stage polymerization reactor 3 from the feed inlet 100 of the first-stage polymerization reactor for homopolymerization, wherein the temperature of the loop polymerization reaction is 70 ℃, the reaction pressure is 4MPa, the reaction residence time is about 1H, hydrogen (5.5g/H) is added into propylene (25kg/H), the obtained polymer powder is discharged from the discharge outlet 101 of the first-stage polymerization reactor, and the concentration of the hydrogen (marked as H) in the discharged material is detected2(101) ) and sampling to determine the MFR of the product1。
(3) Gas-solid separation stage
The polymer powder is continuously fed into a stripping section in the gas-solid separator 4 from a feed inlet of the gas-solid separator, and the operating temperature and the pressure of the gas-solid separator 4 are respectively 70 ℃ and 1.8 MPa. Continuously introducing liquid propylene from a liquid-phase propylene inlet 102 of a gas-solid separator, wherein the feeding amounts of polymer powder and the liquid-phase propylene are respectively 15kg/H and 7.5kg/H, the liquid-phase propylene is vaporized in the gas-solid separator so as to carry light components carried by the liquid-phase propylene to be discharged from a gas-phase outlet 103 of the gas-solid separator for recycling, the retention time of the polymer powder in the gas-solid separator is 10min, the polymer powder without the light components carried by the liquid-phase propylene is discharged from a material outlet 104 of the gas-solid separator, and the concentration (marked as H) of hydrogen in the discharged material is detected2(104))。
(4) Ethylene/propylene copolymerization
The polymer powder without the entrained light components enters a second-stage polymerization reactor 5 from a feed port of the second-stage polymerization reactor, copolymerization reaction of propylene and ethylene (ethylene/(ethylene + propylene) ═ 0.4(v/v)) is carried out on the basis of the polymer powder without the entrained light components, the temperature of the copolymerization reaction is 70 ℃, the pressure is 1.4MPa, the retention time is 30min, and the impact polypropylene product is continuously discharged from a discharge port 105 of the second-stage polymerization reactor. The resulting impact polypropylene product was tested for parameters such as MFR, ethylene content and impact strength.
Some experimental parameters and the results of the performance tests of the pellets obtained are shown in Table 1.
Example 2
(1) Pre-complexing and pre-polymerizing
The flow rate of the main catalyst (DQC401 catalyst, Beijing Ondah company of China petrochemical catalyst division) is 0.8g/h, the flow rate of the cocatalyst (triethylaluminum, TEA) is 6.33g/h, the flow rate of the external electron donor (cyclohexylmethyldimethoxysilane, CHMMS) is 0.8g/h, and the pre-complexing reaction is carried out in a pre-complexing reactor 1 at 6 ℃ for 8 min.
Continuously adding the catalyst system after pre-complexing into a continuous stirred tank type prepolymerization reactor 2, and carrying out prepolymerization reaction in a propylene liquid-phase body environment, wherein the dosage of propylene is such that the weight ratio of a main catalyst (DQC401 catalyst) to propylene is 6.15 multiplied by 10-5:1, the temperature is 8 ℃, the pressure is 3.5MPa, the reaction time is about 12min, and the prepolymerization multiple of the catalyst under the condition is about 100 times.
(2) Homopolymerization of propylene
Continuously (13kg/H) introducing the prepolymerized material into the first-stage polymerization reactor 3 from the feed inlet 100 of the first-stage polymerization reactor for homopolymerization, wherein the temperature of the loop polymerization reaction is 65 ℃, the reaction pressure is 3.5MPa, the reaction residence time is about 1.1H, hydrogen (5.5g/H) is added into propylene (23kg/H), the obtained polymer powder is discharged from the discharge outlet 101 of the first-stage polymerization reactor, and the concentration of the hydrogen (marked as H) in the discharged material is detected2(101) ) and sampling to determine the MFR of the product1。
(3) Gas-solid separation stage
The polymer powder is continuously fed into a stripping section in the gas-solid separator 4 from a feed inlet of the gas-solid separator, and the operating temperature and the pressure of the gas-solid separator 4 are respectively 75 ℃ and 1.9 MPa. Continuously introducing liquid propylene from a liquid-phase propylene inlet 102 of a gas-solid separator, wherein the feeding amounts of polymer powder and the liquid-phase propylene are respectively 15kg/H and 6kg/H, the liquid-phase propylene is vaporized in the gas-solid separator so as to carry light components carried by the liquid-phase propylene to be discharged from a gas-phase outlet 103 of the gas-solid separator for recycling, the retention time of the polymer powder in the gas-solid separator is 8min, the polymer powder without the light components carried by the liquid-phase propylene is discharged from a material outlet 104 of the gas-solid separator, and the concentration (marked as H) of hydrogen in the discharged material is detected2(104))。
(4) Ethylene/propylene copolymerization
The polymer powder without the entrained light components enters a second-stage polymerization reactor 5 from a feed port of the second-stage polymerization reactor, copolymerization reaction of propylene and ethylene (ethylene/(ethylene + propylene) ═ 0.4(v/v)) is carried out on the basis of the polymer powder without the entrained light components, the temperature of the copolymerization reaction is 70 ℃, the pressure is 1.4MPa, the residence time is 30min, and the impact polypropylene product is continuously discharged from a discharge port 105 of the second-stage polymerization reactor. The resulting impact polypropylene product was tested for parameters such as MFR, ethylene content and impact strength.
Some experimental parameters and the results of the performance tests of the pellets obtained are shown in Table 1.
Example 3
(1) Pre-complexing and pre-polymerizing
The flow rate of the main catalyst (DQC401 catalyst, Luoyang division of China petrochemical Co., Ltd.) was 0.8g/h, the flow rate of the cocatalyst (triethylaluminum, TEA) was 5g/h, the flow rate of the external electron donor (diisopropyldimethoxysilane, DIPDMS) was 0.6g/h, and the pre-complexation reaction was carried out in the pre-complexation reactor 1 at 6 ℃ for 8 min.
Continuously adding the catalyst system after pre-complexing into a continuous stirred tank type prepolymerization reactor 2, and carrying out prepolymerization reaction in a propylene liquid-phase body environment, wherein the dosage of propylene is such that the weight ratio of a main catalyst (DQC401 catalyst) to propylene is 6.15 multiplied by 10-5:1, the temperature is 20 ℃, the pressure is 4.5MPa, the reaction residence time is about 12min, and the prepolymerization multiple of the catalyst under the condition is about 150 times.
(2) Homopolymerization of propylene
Continuously (13kg/H) introducing the prepolymerized material into the first-stage polymerization reactor 3 from the feed inlet 100 of the first-stage polymerization reactor for homopolymerization, wherein the temperature of the loop polymerization reaction is 70 ℃, the reaction pressure is 4.5MPa, the reaction residence time is about 1H, hydrogen (5.5g/H) is added into the propylene (27kg/H), the obtained polymer powder is discharged from the discharge outlet 101 of the first-stage polymerization reactor, and the concentration (marked as H) of the hydrogen in the discharged material is detected2(101) And sampling and measuringMFR of the product1。
(3) Gas-solid separation stage
The polymer powder is continuously fed into a stripping section in the gas-solid separator 4 from a feed inlet of the gas-solid separator, and the operating temperature and the pressure of the gas-solid separator 4 are 65 ℃ and 1.7MPa respectively. Continuously introducing liquid propylene from a liquid-phase propylene inlet 102 of a gas-solid separator, wherein the feeding amounts of polymer powder and the liquid-phase propylene are respectively 15kg/H and 5kg/H, the liquid-phase propylene is vaporized in the gas-solid separator so as to carry light components carried by the liquid-phase propylene to be discharged from a gas-phase outlet 103 of the gas-solid separator for recycling, the retention time of the polymer powder in the gas-solid separator is 5min, the polymer powder without the light components carried by the liquid-phase propylene is discharged from a material outlet 104 of the gas-solid separator, and the concentration (marked as H) of hydrogen in the discharged material is detected2(104))。
(4) Ethylene/propylene copolymerization
The polymer powder without the entrained light components enters a second-stage polymerization reactor 5 from a feed port of the second-stage polymerization reactor, copolymerization reaction of propylene and ethylene (ethylene/(ethylene + propylene) ═ 0.4(v/v)) is carried out on the basis of the polymer powder without the entrained light components, the temperature of the copolymerization reaction is 70 ℃, the pressure is 1.4MPa, the residence time is 30min, and the impact polypropylene product is continuously discharged from a discharge port 105 of the second-stage polymerization reactor. The resulting impact polypropylene product was tested for parameters such as MFR, ethylene content and impact strength.
Some experimental parameters and the results of the performance tests of the pellets obtained are shown in Table 1.
Example 4
(1) The same as example 1;
(2) the same as example 1, except that the amount of hydrogen fed was 10 g/h;
(3) the same as example 1;
(4) same as example 1
Some experimental parameters and the results of the performance tests of the pellets obtained are shown in Table 1.
Comparative example 1
Impact polypropylene was prepared according to the method of example 1 except that in step (3), no liquid phase propylene was introduced. Some experimental parameters and the results of the performance tests of the pellets obtained are shown in Table 1.
Comparative example 2
Impact polypropylene was prepared as in example 1 except that in step (3), liquid phase propylene was replaced with vapor phase propylene. Some experimental parameters and the results of the performance tests of the pellets obtained are shown in Table 1.
TABLE 1
As can be seen from Table 1, the continuous feeding of liquid phase propylene to the stripping section of the gas-solid separator significantly reduced the concentration of hydrogen entrained to the gas phase reactor with the polymer powder, and thus the MFR of the rubber phase formed in the gas phase reactor2A significant decrease, i.e. an increase in the molecular weight of the rubber phase polymer. The impact strength of the polymer obtained by the method is obviously improved.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (10)
1. A process for preparing an impact polypropylene, comprising:
(1) subjecting propylene to a prepolymerization reaction in the presence of a catalyst system comprising a catalyst, a cocatalyst and optionally an external electron donor;
(2) then, the material after the prepolymerization reaction, hydrogen and propylene are contacted for homopolymerization reaction to obtain polymer powder;
(3) introducing polymer powder and liquid-phase propylene into a gas-solid separator provided with a gas-phase outlet, wherein the liquid-phase propylene is vaporized in the gas-solid separator so as to carry and discharge light components from the gas-phase outlet of the gas-solid separator;
(4) and (3) carrying out copolymerization reaction of propylene and alpha-olefin on the basis of removing the polymer powder carrying light components in the step (3) to obtain the impact-resistant polypropylene powder, wherein the alpha-olefin is ethylene and/or alpha-olefin with 4-10 carbon atoms.
2. The process according to claim 1, wherein in step (1), the conditions of the prepolymerization comprise: the temperature is-10 ℃ to 50 ℃, preferably 0-40 ℃; the pressure is 1-8MPa, preferably 1.2-5.5 MPa; the pre-polymerization multiple is 0.5 to 1000 times, preferably 5 to 500 times, and more preferably 20 to 300 times; the weight ratio of catalyst to propylene is 1: 500-: 800-80000.
3. The method according to claim 1, wherein in step (2), the conditions of the homopolymerization reaction include: the temperature is 30-150 ℃, preferably 50-100 ℃; the pressure is 1-8MPa, preferably 1.2-5.5 MPa; the time is 10-180min, preferably 20-120 min; the weight ratio of the materials after the prepolymerization reaction, hydrogen and propylene is 0.02-1: 9.5X 10-6-1.4×10-3:1, preferably 0.05 to 0.6: 9.5X 10-6-5×10-4：1。
4. The process according to any one of claims 1 to 4, wherein in step (3) the residence time of the polymer powder in the gas-solid separator is between 0.5 and 20min, preferably between 2 and 10 min.
5. The process according to any one of claims 1 to 4, wherein in step (3), the gas-solid separator is provided with an expanded section at an upper portion thereof and a stripping section at a lower portion thereof, and the ratio of the maximum cross-sectional diameter of the expanded section to the stripping section is 1.5 to 3.
6. The process according to any one of claims 1 to 4, wherein in step (3), the weight ratio of liquid phase propylene to polymer powder is from 0.05 to 1, preferably from 0.1 to 0.5.
7. The process according to any one of claims 1 to 4, wherein in the step (3), the temperature in the gas-solid separator is 50 to 100 ℃ and the pressure is 0.1 to 3 MPa.
8. The process according to any one of claims 1 to 4, wherein in step (4), the copolymerization reaction conditions comprise: the temperature is 50-150 ℃, preferably 60-95 ℃; the pressure is 0.5-4MPa, preferably 1.2-3.5 MPa; the time is 10-180min, preferably 20-90 min.
9. The process according to any one of claims 1 to 4, wherein the α -olefin is used in an amount such that the volume of the α -olefin is 5 to 70% based on the total volume of the α -olefin and propylene in the copolymerization reaction system in step (4).
10. An impact polypropylene produced by the process of any one of claims 1 to 9.
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