CN109679010B - Preparation method of high impact polypropylene - Google Patents
Preparation method of high impact polypropylene Download PDFInfo
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- CN109679010B CN109679010B CN201710976921.5A CN201710976921A CN109679010B CN 109679010 B CN109679010 B CN 109679010B CN 201710976921 A CN201710976921 A CN 201710976921A CN 109679010 B CN109679010 B CN 109679010B
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F210/00—Copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F210/04—Monomers containing three or four carbon atoms
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- C—CHEMISTRY; METALLURGY
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- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F110/00—Homopolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F110/04—Monomers containing three or four carbon atoms
- C08F110/06—Propene
Abstract
The invention provides a polymerization method of high impact polypropylene. The method specifically comprises the following steps: (1) adding a first external electron donor with excellent hydrogen regulation sensitivity into a loop propylene homopolymerization reactor in the first stage, so that a propylene homopolymer with high melt flow rate can be obtained under a lower hydrogen concentration; (2) adding a second external electron donor which is helpful for improving the isotacticity of the polypropylene into the loop reactor at the second stage, so that the high-crystalline polypropylene is prepared at the section to endow the material with excellent rigidity; (3) and spraying a third external electron donor on the surface of the polymer generated in the second stage, and enabling the polymer to enter a gas phase reactor in the third stage along with the polymer, thereby obtaining the propylene impact copolymer with uniform sequence distribution and high content in the section.
Description
Technical Field
The invention relates to a preparation method of high impact polypropylene, in particular to a preparation method of high impact polypropylene with high melt flow rate.
Background
High impact polypropylene resins having a high melt flow rate (high flow) have wide applications in the field of injection molding due to higher process molding efficiency than ordinary impact copolymers, and also have significantly higher market profits than ordinary impact copolymers. At present, the methods for preparing high-flow high-impact polypropylene resin are mainly divided into two main categories of post-processing modification and direct in-kettle polymerization. The post-processing modification means that the prepared impact-resistant polypropylene resin is subjected to chain scission treatment during melt processing, so that the molecular weight of the resin is reduced or the molecular weight distribution of the resin is widened, and the aim of improving the melt flow rate of the resin is fulfilled. Although the method has simple implementation steps, the chain scission process has no selectivity to the components of the homo-polypropylene and the co-polypropylene in the resin, so that the molecular weights of the components cannot be respectively regulated and controlled, and the performance of the resin cannot be optimized; in addition, product performance fluctuates widely when processing conditions vary. The in-kettle direct polymerization method directly realizes the design of resin molecular weight by adjusting polymerization process parameters in a reaction kettle, and generally achieves the purposes of regulating and controlling melt flow rate and producing high-flow polypropylene resin by using a catalyst system with special functions or adding a large amount of hydrogen (chain transfer agent) into the reaction kettle by adopting a supercritical method.
The method of using a special function catalyst is reported in patent CN1321178A of Basell company, and the core technology is to use a Ziegler-Natta catalyst which takes an ether compound as an internal electron donor to prepare an impact-resistant polyolefin resin with wide molecular weight distribution. For another example, patent CN1156999A invented a catalyst system containing two internal electron donors (tetraethoxysilane and dicyclopentyldimethoxysilane), which can effectively prepare polymers with high melt flow rate and medium and broad molecular weight distribution. However, the balance among high fluidity, rigidity and impact resistance of the resin is difficult to achieve due to the function singleness of the catalyst.
The preparation of high flow polymers can also be achieved by the adjustment of the external electron donor, and many patents employ mixed (more than two) external electron donors. For example, patent CN102532380A reports a method for preparing high-fluidity impact polypropylene, in which two external electron donors with different hydrogen-adjusting sensitivities are respectively added in two-stage propylene homopolymerization reaction, so as to broaden the molecular weight distribution of the polymer, and prepare high-fluidity impact polypropylene with a melt index of 25-100g/10 min. However, the disadvantages of this method are also quite significant: because the copolymerization reaction effect of the third stage cannot be controlled, the product cannot well give consideration to high fluidity and impact resistance, and the improvement of fluidity causes the remarkable reduction of impact property (the highest impact strength of the polymer is 28 kJ/m)2When it is used, the melt index is only 7.8g/10 min). For example, patent CN102532381A reports a method for preparing an impact resistant propylene copolymer with high melt flowability, in which only one external electron donor is used in the homopolymerization of propylene, and a second external electron donor is added in the copolymerization of propylene and α -olefin, so as to respectively improve the flowability of the propylene homopolymer component and the copolymer component in the product, but the method has the disadvantages that the composition and performance of the copolymer cannot be controlled, the impact property cannot be improved while the flowability of the product is optimized, and the impact strength is only 11.3kJ/m2. As yet another example of this, the first,patent CN103788256A also mentions the preparation of high-flow impact polypropylene by using different external electron donors, which is characterized in that the copolymerization stage is the copolymerization of propylene monomer and alpha-olefin (ethylene and alpha-olefin are usually used in the process), and the resin thus prepared has high fluidity and high rigidity, but the impact resistance is poor (only 15 kJ/m)2)。
From the above technical analysis, it can be seen that the key factor (or difficulty) for preparing a resin product with high flow, good rigidity and excellent impact resistance is how to achieve the balance between the three properties, rather than considering the difference. High flow is achieved, requiring the polymer to contain a polypropylene component of relatively low molecular weight or of very broad molecular weight distribution; realizing high rigidity, and requiring a polypropylene component with high isotacticity (or high crystallinity) in the polymer; achieving high impact requires the polymer to contain a substantial amount of ethylene/alpha-olefin random copolymer, one of which is not preferred. However, none of the above three properties can be considered in the prior art.
The Spheripol propylene polymerization process is a mainstream process for preparing the impact-resistant copolymerized polypropylene and has wide application. The technical characteristics are that three-stage continuous polymerization process flow is adopted: comprises two-stage propylene bulk homopolymerization and one-stage gas-phase copolymerization. The three-stage process arrangement provides possibility for preparing the high-flow, high-rigidity and high-impact polypropylene provided by the invention.
Disclosure of Invention
The invention provides a polymerization process method for directly preparing a copolymer polypropylene resin with high fluidity, high rigidity and high impact resistance on a Spheripol polymerization process. Specifically, the preparation method of the polypropylene copolymer is to perform first-stage bulk polymerization, second-stage bulk polymerization and third-stage copolymerization of propylene and a comonomer in three reactors connected in series aiming at the Spheripol double-ring pipe gas-filled phase reactor technology.
The method specifically comprises the following steps:
1) the first stage is as follows: the liquid phase bulk polymerization of propylene is carried out in a first loop reactor in the presence of hydrogen and a Ziegler-Natta catalyst system comprising a first external electron donor.
The first external electron donor is selected from compounds of the general formula R1xR2ySi (OR3) z, wherein R1 and R2 are respectively identical OR different C1-C3 straight-chain alkyl groups, R3 is C1-C2 straight-chain alkyl groups, 0 ≦ x <2, 0 ≦ y <2, and 0< z ≦ 4, and is specifically selected from at least one of tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, and dimethyldiethoxysilane, preferably tetraethoxysilane.
The first-stage propylene polymerization pressure is preferably 4000-4500KPa, and the high-flow propylene homopolymer is obtained at the polymerization temperature of 70-80 ℃.
The Ziegler-Natta catalyst system mainly comprises: the component (1) is a solid catalyst component which takes magnesium, titanium, halogen and internal electron donor as main components, and the component (2) is an organic aluminum component; a first external electron donor of component (3); wherein the ratio of the component (1) to the component (2) of the organoaluminum compound is 1:10 to 1:500 in terms of titanium/aluminum; preferably 1:25 to 1: 100. Wherein the mass ratio of the organic aluminum component to the first external electron donor component is 1-50, preferably 2-20.
The solid catalyst component in the Zigler-Natta catalyst system adopted by the invention is a polypropylene main catalyst commonly used in the prior art, and the component (1) can be obtained by catalysts disclosed in CN85100997, CN98126385.2, CN00109216.2, CN99125567.4, CN201210077908.3 and CN201310552108.7 or preparation methods disclosed by the patent documents. The invention provides a preparation method of a preferable component (1), which comprises the following steps:
a) adding a spherical magnesium halide carrier into a liquid titanium compound at a temperature of between 15 ℃ below zero and 20 ℃ below zero, wherein the molar ratio of Ti to Mg is 20 to 40, preferably 25 to 30, and reacting at a low temperature for 1 to 2 hours;
b) the temperature is raised to 60-80 ℃, and an internal electron donor compound is added, wherein the internal electron donor compound is commonly used phthalic acid ester compounds, succinic acid ester compounds, diether compounds and the like, and the phthalic acid ester compounds are preferred. The molar ratio of the internal electron donor to the magnesium halide is 0.01-0.20, and the temperature is continuously increased to 120 ℃ for reaction for 2 hours;
c) filtering out liquid substances, adding fresh liquid titanium compound again, wherein the molar ratio of Ti to Mg is 20-40, preferably 25-30, and reacting for 2 hours at 120 ℃;
e) filtering out liquid substances, washing by normal hexane, and drying in vacuum to obtain the component (1).
The cocatalyst component (2) according to the present invention is an organoaluminium compound, preferably an alkylaluminium compound, more preferably a trialkylaluminium.
2) And a second stage: the first-stage polymerization product enters a second loop reactor, and propylene liquid-phase bulk polymerization is carried out in the presence of hydrogen and a second external electron donor;
the second external electron donor is selected from compounds with a general formula of R1xR2ySi (OR3)2, wherein R1 is C4-C10 branched OR cyclic alkyl, R2 is C1-C10 branched OR cyclic alkyl, R3 is C1-C2 straight-chain alkyl, wherein x is more than OR equal to 1 and less than OR equal to 2, and y is more than OR equal to 0 and less than 2, and the second external electron donor is specifically selected from at least one of Dicyclopentyldimethoxysilane (DCPMS), cyclohexylmethyldimethoxysilane, diisobutyldimethoxysilane and di-tert-butyldimethoxysilane, and dicyclopentyldimethoxysilane is preferred.
The polymerization temperature of propylene in the second stage is 70-80 ℃, the polymerization pressure is 4000-4500KPa, and the second stage reaction generates a macromolecular skeleton with higher isotacticity.
Wherein the mass ratio of the organic aluminum component to the second external electron donor is 1-100, preferably 5-30.
3) And a third stage: removing unreacted propylene monomers and hydrogen from the second-stage polymer product through a high-pressure flash evaporator, feeding the second-stage polymer product into a gas-phase reactor, arranging a branch port on a connecting pipeline between the high-pressure flash evaporator and the gas-phase reactor, adding a third external electron donor into the connecting pipeline through the branch port, mounting an atomizing nozzle on the branch port, uniformly spraying the third external electron donor on the surface of the second-stage polymer product flowing through the connecting pipeline through the atomizing nozzle, and feeding the third external electron donor into the gas-phase reactor along with the second-stage polymer product to perform copolymerization reaction.
The third external electron donor is selected from diether compounds. The diether compound has a structural formula shown as a general formula (I).
Formula (III) R, RI、RII、RIII、RIVAnd RVIdentical or different, is hydrogen or a linear or branched alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl radical having from 1 to 18 carbon atoms, and R, RINot both being H or CH3；RVIAnd RVIIIdentical or different, are linear or branched alkyl radicals having 1 to 18 carbon atoms, preferably methyl.
The diether compound is specifically selected from 2, 2-diphenyl-1, 3-dimethoxypropane, 2-di-tert-butyl-1, 3-diethoxypropane, 2-methyl-2-ethyl-1, 3-dimethoxypropane, 2-methyl-2-tert-butyl-1, 3-dimethoxypropane, 2-di-tert-butyl-1, 3-dimethoxypropane, 2-methyl-2-cyclohexyl-1, 3-dimethoxypropane and the like. 2, 2-di-tert-butyl-1, 3-dimethoxypropane is preferred.
The reaction temperature in the third stage gas phase reactor is 80-90 ℃, and the reaction pressure is 1200-1300 KPa.
The mass ratio of the organic aluminum component to the third external electron donor component is 1-100, preferably 5-30.
In the third stage, the comonomer is ethylene or butylene, and during copolymerization, the proportion of each monomer during gas phase polymerization is adjusted according to product performance requirements, and when the comonomer is ethylene, the ethylene/(ethylene + propylene) is usually controlled to be 0.25-0.41 (molar ratio), preferably 0.32-0.38 (molar ratio), and simultaneously the hydrogen content is controlled, so as to obtain the target product.
The invention utilizes the Spheripol polymerization process to realize the balance among high flow, high rigidity and high impact resistance of the propylene copolymer resin, and the specific method can be summarized as follows: aiming at the three performances, three different external electron donors are respectively adopted and are respectively used in three different sections of the Spheripol process, namely (1) a first external electron donor with excellent hydrogen regulation sensitivity is added into a loop propylene homopolymerization reactor at the first stage, so that a propylene homopolymer with high melt flow rate can be obtained under lower hydrogen concentration; (2) adding a second external electron donor which is helpful for improving the isotacticity of the polypropylene into the loop reactor at the second stage, so that the high-crystalline polypropylene is prepared at the section to endow the material with excellent rigidity; (3) and spraying a third external electron donor on the surface of the polymer generated in the second stage, and enabling the polymer to enter a gas phase reactor in the third stage along with the polymer, thereby obtaining the propylene impact copolymer with uniform sequence distribution and high content in the section. The inventors have found through trial and error that the Lewis basic order of the three external electron donors must be: and the third kind is the second kind, the first kind is the external electron donor, so that the final prepared polypropylene copolymer has high melt flow rate, high impact resistance and excellent rigidity.
On the basis of generating a propylene homopolymer with high melt flow rate in the first stage, propylene homopolymerization in the second stage is carried out, a second external electron donor with Lewis alkalinity stronger than that of the first external electron donor is additionally required to be added in the second stage, and a small amount of hydrogen can be added to generate a macromolecular polypropylene skeleton with high isotacticity. Before the homopolymerized polypropylene from the second reactor enters the gas phase reactor, a third external electron donor is additionally added to carry out copolymerization of propylene and alpha-olefin, the addition amount of the comonomer composition is adjusted, the composition and the content of a rubber phase are controlled, and the melt flow rate of a final product is controlled by adjusting the amount of hydrogen.
Wherein the yield ratio of the first reactor, the second reactor and the third reactor is controlled to be 10:50: 40-20: 60:20, preferably 15:55: 30-12: 53: 35.
The invention mainly aims at the Spheripol double-ring pipe gas-filled phase reactor technology, three-step polymerization reactions are respectively carried out in three reactors, and in the first-stage polymerization reaction, the three catalyst components can be directly added into the first reactor, or can be added into the first reactor after pre-complexing and/or pre-polymerizing known in the industry. The pre-complexing reaction aims to fully and effectively mix the components of the catalyst and can be used as a continuous stirred tank reactor, a loop reactor and the like. The temperature of the pre-complexing can be controlled between-10 ℃ and 60 ℃, and preferably 10 ℃ to 30 ℃. The pre-complexing time is controlled within 30-100 min, preferably 5-30 min.
The catalyst, with or without pre-complexing, can also be subjected to a propylene bulk or slurry prepolymerization. The prepolymerization can be carried out in a continuous stirrer or a loop reactor, and the temperature of the prepolymerization is controlled between-10 and 60 ℃, preferably between 10 and 30 ℃. The prepolymerization time is controlled to be 30-300 times, preferably 50-150 times.
The first-stage bulk polymerization of propylene is carried out in a first loop reactor of a Spheripol process, the polymerization temperature is 70-80 ℃, and the polymerization pressure is 4000-4500 KPa.
The second-stage bulk polymerization of propylene is carried out in a second loop reactor of a Spheripol process, the polymerization temperature is 70-80 ℃, and the polymerization pressure is 4000-4500 KPa.
The third stage of copolymerization of propylene and comonomer alpha-olefin is carried out in a gas phase reactor of Spheripol process, the reaction temperature is 75-80 ℃, and the reaction pressure is 1200-1300 KPa. The comonomer alpha-olefin is ethylene or butene, preferably ethylene. When the comonomer is ethylene, ethylene/(ethylene + propylene) is generally controlled to be 0.25 to 0.41 (molar ratio), preferably 0.32 to 0.38 (molar ratio).
The polymer obtained by the preparation method can be extruded and granulated by using common polyolefin equipment, and auxiliary agents commonly added in the field, such as an antioxidant, a light stabilizer, a nucleating agent and the like, are added during granulation.
The polymerization method is particularly suitable for preparing the copolymerized polypropylene product with high melt flow rate and high impact strength in the Spheripol process, and is particularly suitable for preparing the copolymerized polypropylene product with the melt flow rate of more than 30g/10min and the notch impact strength of more than 40kJ/m2The impact co-polypropylene product of (1). Only by adjusting the external electron donor species, the amount and the hydrogen concentration in each reaction stage.
The high-performance impact copolymer polypropylene product can be directly polymerized under the condition of a Ziegler-Natta catalyst with general performance, and the copolymer product with the performance can be prepared by a gas-phase polymerization process. The invention does not need special high-cost catalyst active components and does not need controllable degradation of products. The cost is relatively low, the existing large device is easy to operate and implement, and the technical bottleneck of developing a high-flow, high-impact and high-rigidity copolymerized polypropylene product by the Spheripol process can be effectively solved.
The method is suitable for producing the polypropylene resin with high melt index, good rigidity and excellent impact resistance on the Spheripol process in which a double loop reactor and a single gas phase kettle (or double gas phase kettles) are connected in series.
Detailed Description
Examples
The present invention will now be described in detail by way of specific examples, which are set forth herein for the purpose of illustration and explanation only and are not intended to be limiting of the present invention.
The polymer related data in the examples were obtained according to the following test methods:
melt Flow Rate (MFR): measured according to ISO1133, 230 ℃ under a load of 2.16 kg.
Bending modulus: measured according to ASTM D790-97.
③ Izod impact strength: measured according to ASTM D256-00.
Fourthly, measuring the content of the polymer ethylene: infrared (IR) method.
Measuring the content of polymer xylene solubles: according to ASTM D5492.
Example 1
The main catalyst (titanium-containing solid catalyst active component) is obtained by adopting the method described in example 1 of Chinese patent 201310552108.7, and the titanium content: 2.76%, magnesium content: 18.0%, diisobutyl phthalate content: 7.54 percent. The polymerized monomers are propylene and ethylene.
The polymerization was carried out in a Spheripol double loop plus single gas phase reactor apparatus.
Pre-polymerization: after a main catalyst, a cocatalyst (triethylaluminum) and a first external electron Donor (tetraethoxysilane) are precontacted for 20min at 10 ℃, the main catalyst, the cocatalyst (triethylaluminum) and the first external electron Donor (tetraethoxysilane) are continuously added into a prepolymerization reactor to carry out a prepolymerization reactor, the flow of Triethylaluminum (TEA) entering the prepolymerization reactor is 6.33g/hr, the flow of tetraethoxysilane (first external electron Donor, Donor-A) is 0.63g/hr, and the flow of the main catalyst is 0.01 g/hr. Wherein the TEA/Donor-A mass ratio is 10. The prepolymerization is carried out in a propylene liquid phase bulk environment, the temperature is 15 ℃, the residence time is 4min, and the prepolymerization multiple of the catalyst under the condition is about 120-150 times.
And continuously feeding the slurry after prepolymerization into a first loop reactor, finishing the preparation of the high melt flow rate homopolymerized polypropylene in the first loop reactor, wherein the polymerization temperature is 70 ℃, the reaction pressure is 4.0MPa, and 7000ppm hydrogen is added into the first loop reactor (gas chromatography detection). Since the main catalyst, the cocatalyst and the first external electron Donor (Donor-A) are pre-contacted and pre-polymerized into the first loop reactor, no additional components are added into the first loop reactor except for the propylene and hydrogen feeds.
The slurry after passing through the first loop reactor continuously enters a second loop reactor, the polymerization temperature is 70 ℃, the reaction pressure is 4.0MPa, and 1000ppm of hydrogen is added into the second loop reactor (gas chromatography detection). And a second external electron Donor dicyclopentyl dimethoxy silane (Donor-B) is additionally added into the second loop reactor to complete the preparation of the macromolecular framework polypropylene with high isotacticity. Wherein the TEA/Donor-B mass ratio is 11.
And continuously feeding the slurry passing through the second loop reactor into a fluidized bed gas phase reactor with an expansion section to carry out copolymerization reaction of ethylene and propylene, wherein the reaction temperature is 75 ℃, the reaction pressure is 1.2MPa, the ethylene/(ethylene + propylene) is usually controlled to be 0.375 (molar ratio), a proper amount of hydrogen is additionally added into the gas phase reactor, the hydrogen/(ethylene + propylene) in the gas phase reactor is detected to be 1.1% by online chromatography, and a third external electron Donor, namely 2, 2-di-tert-butyl-1, 3-dimethoxypropane (Donor-C), which is additionally added is added at an outlet section of the second loop reactor, wherein the mass ratio of TEA/Donor-C is 12.
Specific process conditions are shown in table 1.
And treating a final product obtained after the gas phase reactor in a deactivation tank, and then passing through a dryer to obtain polymer powder.
Adding 1010.05 percent of polymer powder, 168 percent of polymer powder and 0.05 percent of calcium stearate into the polymer powder, uniformly mixing, extruding and granulating, and testing the performance of the granules according to the current relevant ASTM standard. The results of the performance tests are shown in Table 2.
Example 2
Examples 2 to 6 were the same as in example 1 except that the amounts of the respective components added were different, as shown in Table 1, and the performance test was shown in Table 2.
Example 7
Examples 7 to 8 are the same as example 1, wherein the main catalyst is a commercial CS-II spherical magnesium chloride supported catalyst, the addition amounts of the components in the polymerization process are different, specifically shown in Table 1, and the performance test is shown in Table 2.
Comparative example 1
In comparative example 1, only one external electron donor dicyclopentyldimethoxysilane was added to the first loop reactor, and no external electron donor was added to the second loop reactor or the gas phase reactor, except for the same conditions as in example 1. The specific process conditions are shown in Table 1, and the performance test results are shown in Table 2.
Comparative example 2
Comparative example 2 the first external electron donor tetraethoxysilane was fed into the first loop reactor, the second external electron donor dicyclopentyldimethoxysilane was fed into the second loop reactor, no additional external electron donor was added into the gas phase reactor, and the other conditions were the same as in example 2. The specific process conditions are shown in Table 1, and the performance test results are shown in Table 2.
Comparative example 3
In comparative example 3, dicyclopentyldimethoxysilane as an external electron donor was added to the first loop reactor, no additional external electron donor was added to the second loop reactor, and 2, 2-di-tert-butyl-1, 3-dimethoxypropane as an external electron donor was added to the gas phase reactor under the same conditions as in example 3. The specific process conditions are shown in Table 1, and the performance test results are shown in Table 2.
Comparative example 4
In comparative example 4, tetraethoxysilane as an external electron donor was added to the first loop reactor, and no additional external electron donor was added to the second loop reactor and the gas phase reactor, and the other conditions were the same as in example 4. The specific process conditions are shown in Table 1, and the performance test results are shown in Table 2.
Comparative example 5
Comparative example 5 the same conditions as in example 5 were used except that dicyclopentyldimethoxysilane was added to the first loop reactor, no additional external electron donor was added to the second loop reactor, and an external electron donor of 2, 2-di-t-butyl-1, 3-dimethoxypropane was added to the gas phase reactor. The specific process conditions are shown in Table 1, and the performance test results are shown in Table 2.
Comparative example 6
Comparative example 6 the addition type and content conditions of each component are the same as those of example 6, except that the addition mode of the third external electron donor is changed from spraying on the surface of the homopolymer powder through an atomizing nozzle to directly introducing into the polymer powder through a metering pipeline, the specific process conditions are shown in table 1, and the performance test results are shown in table 2.
Comparative example 7
Comparative example 7 is the same as example 7, except that the third external electron donor is added into the gas phase kettle in a manner that the third external electron donor is sprayed on the surface of the homopolymer powder through an atomizing nozzle, and is directly introduced into the polymer powder through a metering pipeline, wherein the specific process conditions are shown in table 1, and the performance test results are shown in table 2.
Comparative example 8
Comparative example 8 is the same as example 8, except that the third external electron donor is added into the gas phase kettle in a manner that the third external electron donor is sprayed on the surface of the homopolymer powder through an atomizing nozzle, and is directly introduced into the polymer powder through a metering pipeline, wherein the specific process conditions are shown in table 1, and the performance test results are shown in table 2.
TABLE 1 specific process conditions for the examples and comparative examples
As can be seen from the analysis of the data in tables 1 and 2, in comparison with comparative example 2 and 1, the melt flow rate and impact property of the product are much higher than those of the product prepared by adding different external electron donors through the three-step method and adding a single external electron donor through the one-step method. Comparing example 2 with comparative example 2, the impact performance of the former is much higher than that of the latter and the combination property of the former is better than that of the latter by adding different external electron donors through a three-step method and adding different external electron donors into a double-ring pipe but not adding specific external electron donors into a gas phase kettle. Comparing example 2 with comparative example 3, the bending modulus (rigidity) of the former product is better than that of the latter product by adding different external electron donors through a three-step method and adding different external electron donors into the first loop reactor and the gas phase reactor, and the second loop reactor does not additionally add external electron donors. Comparing example 2 with comparative example 4, the three-step method of adding different external electron donors is compared with the whole reaction process of adding only one external electron donor tetraethoxysilane, the former has comprehensive performance of flexural modulus and impact performance far superior to the latter. Comparing example 2 with comparative example 5, the melt flow rate of the former is much better than that of the latter by adding different external electron donors through a three-step method compared with the case of adding different external electron donors to the first loop reactor and the gas phase reactor, and adding no external electron donor to the second loop reactor. Comparing example 2 with comparative example 6, the impact performance of the product prepared by spraying the third external electron donor (strong copolymerization ability) on the surface of the homopolymer powder through the atomizing nozzle is much better than that of the product in which the third external electron donor is directly introduced into the polymer powder through the metering line, because the third external electron donor can be more uniformly dispersed and diffused in the polymer powder by means of spraying through the atomizing nozzle.
The present invention is capable of other embodiments, and various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (16)
1. A polymerization method of high impact polypropylene is characterized by comprising the following steps:
1) the first stage is as follows: performing a liquid phase bulk polymerization of propylene in a first loop reactor in the presence of hydrogen and a Ziegler-Natta catalyst system comprising a first external electron donor; the first external electron donor is selected from compounds of the general formula R1xR2ySi (OR3) z, wherein R1 and R2 are respectively identical OR different C1-C3 straight-chain alkyl, R3 is C1-C2 straight-chain alkyl, x is more than OR equal to 0 and less than 2, y is more than OR equal to 0 and less than 2, and z is more than OR equal to 0 and less than OR equal to 4;
2) and a second stage: the first-stage polymerization product enters a second loop reactor, and propylene liquid-phase bulk polymerization is carried out in the presence of hydrogen and a second external electron donor; the second external electron donor is selected from compounds with a general formula of R1xR2ySi (OR3)2, wherein R1 is C4-C10 branched OR cyclic alkyl, R2 is C1-C10 branched OR cyclic alkyl, R3 is C1-C2 straight-chain alkyl, wherein x is more than OR equal to 1 and less than OR equal to 2, and y is more than OR equal to 0 and less than 2;
3) and a third stage: removing unreacted propylene monomers and hydrogen from the polymer product at the second stage by a high-pressure flash evaporator, feeding the polymer product into a gas phase reactor, and adding a third external electron donor into a connecting pipeline between the high-pressure flash evaporator and the gas phase reactor, wherein the third external electron donor is selected from diether compounds; arranging a branch port on a connecting pipeline of the high-pressure flash evaporator and the gas phase reactor, and adding a third external electron donor into the connecting pipeline through the branch port; the branch opening is provided with an atomizing nozzle, and the third external electron donor is sprayed on the surface of the second-stage polymer product flowing through the connecting pipeline through the atomizing nozzle;
the diether compound has a structural formula shown as a general formula (I):
formula (III) R, RI、RII、RIII、RIVAnd RVIdentical or different, is hydrogen or a linear or branched alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl radical having from 1 to 18 carbon atoms, and R, RINot both being H or CH3；RVIAnd RVIIThe same or different, is a linear or branched alkyl group having 1 to 18 carbon atoms;
the Lewis basic sequence of the three external electron donors satisfies the following relationship: the third external electron donor > the second external electron donor > the first external electron donor.
2. The polymerization process of claim 1, wherein the first stage propylene polymerization pressure is 4000 to 4500KPa and the polymerization temperature is 70 to 80 ℃.
3. The polymerization process of claim 1, wherein said Ziegler-Natta catalyst system comprises: the component (1) is a solid catalyst component which takes magnesium, titanium, halogen and internal electron donor as main components, and the component (2) is an organic aluminum component; a first external electron donor of component (3); wherein the ratio of the component (1) to the component (2) of the organoaluminum compound is 1:10 to 1:500 in terms of titanium/aluminum; wherein the mass ratio of the organic aluminum component to the first external electron donor component is 1-50.
4. The polymerization process according to claim 3, wherein the ratio of the component (1) to the organoaluminum compound of the component (2) is 1:25 to 1: 100.
5. The polymerization method of claim 3, wherein the mass ratio of the organic aluminum component to the first external electron donor component is 2 to 20.
6. The polymerization process of claim 3, wherein the organoaluminum component is an alkylaluminum compound.
7. The polymerization process according to claim 1, wherein the second-stage propylene polymerization temperature is 70 to 80 ℃ and the polymerization pressure is 4000 to 4500 KPa.
8. The polymerization process according to claim 3, wherein the mass ratio of the organic aluminum component to the second external electron donor is 1 to 100.
9. The polymerization process of claim 3, wherein the mass ratio of the organoaluminum component to the second external electron donor is 5 to 30.
10. The polymerization process of claim 1, wherein the diether compound is selected from the group consisting of 2, 2-diphenyl-1, 3-dimethoxypropane, 2-di-tert-butyl-1, 3-diethoxypropane, 2-methyl-2-ethyl-1, 3-dimethoxypropane, 2-methyl-2-tert-butyl-1, 3-dimethoxypropane, 2-di-tert-butyl-1, 3-dimethoxypropane, 2-methyl-2-cyclohexyl-1, 3-dimethoxypropane.
11. The polymerization process of claim 1, wherein the diether compound is selected from the group consisting of 2, 2-di-tert-butyl-1, 3-dimethoxypropane.
12. The polymerization process according to claim 1, wherein the reaction temperature in the third-stage gas phase reactor is 80 to 90 ℃ and the reaction pressure is 1200 to 1300 KPa.
13. The polymerization method according to claim 3, wherein the mass ratio of the organic aluminum component to the third external electron donor component is 1 to 100.
14. The polymerization method of claim 3, wherein the mass ratio of the organic aluminum component to the third external electron donor component is 5-30.
15. The polymerization process of claim 1, wherein the first external electron donor is at least one selected from tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, and dimethyldiethoxysilane.
16. The polymerization process of claim 1, wherein the second external electron donor is at least one member selected from the group consisting of dicyclopentyldimethoxysilane, cyclohexylmethyldimethoxysilane, diisobutyldimethoxysilane, and di-t-butyldimethoxysilane.
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